THE WORKING OF STEEL ANNEALING, HEAT TREATING AND HARDENING OF CARBON AND ALLOY STEEL BY FRED H. COLVIN Member American Society of Mechanical Engineers and Franklin Institute;Editor of the _American Machinist_, Author of "_Machine ShopArithmetic_, " "_Machine Shop Calculations_, " "_American Machinists'Hand Book_. " AND K. A. JUTHE, M. E. Chief Engineer, American Metallurgical Corp. Member American SocietyMechanical Engineers, American Society Testing Materials, HeatTreatment Association, Etc. SECOND EDITION THIRD IMPRESSION McGRAW-HILL BOOK COMPANY, Inc. NEW YORK: 370 SEVENTH AVENUE LONDON: 6 & 8 BOUVERIE ST. , E. C. 4 PREFACE TO SECOND EDITION Advantage has been taken of a reprinting to revise, extensively, the portions of the book relating to the modern science ofmetallography. Considerable of the matter relating to the influenceof chemical composition upon the properties of alloy steels hasbeen rewritten. Furthermore, opportunity has been taken to includesome brief notes on methods of physical testing--whereby themetallurgist judges of the excellence of his metal in advance ofits actual performance in service. NEW YORK, N. Y. , _August, 1922. _ PREFACE TO FIRST EDITION The ever increasing uses of steel in all industries and the necessityof securing the best results with the material used, make a knowledgeof the proper working of steel more important than ever before. For it is not alone the quality of the steel itself or the alloysused in its composition, but the proper working or treatment ofthe steel which determines whether or not the best possible usehas been made of it. With this in mind, the authors have drawn, not only from theirown experience but from the best sources available, informationas to the most approved methods of working the various kinds ofsteel now in commercial use. These include low carbon, high carbonand alloy steels of various kinds, and from a variety of industries. The automotive field has done much to develop not only new alloys butefficient methods of working them and has been drawn on liberallyso as to show the best practice. The practice in government arsenalson steels used in fire arms is also given. While not intended as a treatise on steel making or metallurgy inany sense, it has seemed best to include a little information asto the making of different steels and to give considerable generalinformation which it is believed will be helpful to those who desireto become familiar with the most modern methods of working steel. It is with the hope that this volume, which has endeavored to givedue credit to all sources of information, may prove of value toits readers and through them to the industry at large. _July_, 1921. THE AUTHORS. CONTENTS PREFACE INTRODUCTION CHAPTER I. STEEL MAKING II. COMPOSITION AND PROPERTIES OF STEELS III. ALLOYS AND THEIR EFFECT UPON STEEL IV. APPLICATION OF LIBERTY ENGINE MATERIALS TO THE AUTOMOTIVE INDUSTRY V. THE FORGING OF STEEL VI. ANNEALING VII. CASE-HARDENING OR SURFACE-CARBURIZING VIII. HEAT TREATMENT OF STEEL IX. HARDENING CARBON STEEL FOR TOOLS X. HIGH SPEED STEEL XI. FURNACES XII. PYROMETRY AND PYROMETERS APPENDIX INDEX INTRODUCTION THE ABC OF IRON AND STEEL In spite of all that has been written about iron and steel thereare many hazy notions in the minds of many mechanics regardingthem. It is not always clear as to just what makes the differencebetween iron and steel. We know that high-carbon steel makes abetter cutting tool than low-carbon steel. And yet carbon alonedoes not make all the difference because we know that cast ironhas more carbon than tool steel and yet it does not make a goodcutting tool. Pig iron or cast iron has from 3 to 5 per cent carbon, while goodtool steel rarely has more than 1-1/4 per cent of carbon, yet oneis soft and has a coarse grain, while the other has a fine grainand can be hardened by heating and dipping in water. Most of thecarbon in cast iron is in a form like graphite, which is almost purecarbon, and is therefore called graphitic carbon. The resemblancecan be seen by noting how cast-iron borings blacken the hands justas does graphite, while steel turnings do not have the same effect. The difference is due to the fact that the carbon in steel is notin a graphitic form as well as because it is present in smallerquantities. In making steel in the old way the cast iron was melted and thecarbon and other impurities burned out of it, the melted iron beingstirred or "puddled, " meanwhile. The resulting puddled iron, alsoknown as wrought iron, is very low in carbon; it is tough, and onbeing broken appears to be made up of a bundle of long fibers. Then the iron was heated to redness for several days in materialcontaining carbon (charcoal) until it absorbed the desired amount, which made it steel, just as case-hardening iron or steel addscarbon to the outer surface of the metal. The carbon absorbed bythe iron does not take on a graphitic form, however, as in thecase of cast iron, but enters into a chemical compound with theiron, a hard brittle substance called "cementite" by metallurgists. In fact, the difference between the hard, brittle cementite andthe soft, greasy graphite, accounts for many of the differencesbetween steel and gray cast iron. Wrought iron, which has verylittle carbon of any sort in it, is fairly soft and tough. Theproperties of wrought iron are the properties of pure iron. Asmore and more carbon is introduced into the iron, it combines withthe iron and distributes itself throughout the metal in extremelysmall crystals of cementite, and this brittle, hard substance lendsmore and more hardness and strength to the steel, at the expenseof the original toughness of the iron. As more and more carbon iscontained in the alloy--for steel is a true alloy--it begins toappear as graphite, and its properties counteract the remainingbrittle cementite. Eventually, in gray cast iron, we have propertieswhich would be expected of wrought iron, whose tough metallic texturewas shot through with flakes of slippery, weak graphite. But to return to the methods of making steel tools in use 100 yearsago. The iron bars, after heating in charcoal, were broken and the carboncontent judged by the fracture. Those which had been in the hottestpart of the furnace would have the deepest "case" and highest carbon. So when the steel was graded, and separated into different piles, a few bars of like kind were broken into short lengths, meltedin fire-clay crucibles at an intense white heat, cast carefullyinto iron molds, and the resulting ingot forged into bars undera crude trip hammer. This melting practice is still in use forcrucible steel, and will be described further on page 4. THE WORKING OF STEEL ANNEALING, HEAT TREATING AND HARDENING OF CARBON AND ALLOY STEEL CHAPTER I STEEL MAKING There are four processes now used for the manufacture of steel. These are: The Bessemer, Open Hearth, Crucible and Electric FurnaceMethods. BESSEMER PROCESS The bessemer process consists of charging molten pig iron intoa huge, brick-lined pot called the bessemer converter, and thenin blowing a current of air through holes in the bottom of thevessel into the liquid metal. The air blast burns the white hot metal, and the temperature increases. The action is exactly similar to what happens in a fire box underforced draft. And in both cases some parts of the material burneasier and more quickly than others. Thus it is that some of theimpurities in the pig iron--including the carbon--burn first, andif the blast is shut off when they are gone but little of the ironis destroyed. Unfortunately sulphur, one of the most dangerousimpurities, is not expelled in the process. A bessemer converter is shown in Fig. 1, while Fig. 2 shows thedetails of its construction. This shows how the air blast is forcedin from one side, through the trunnion, and up through the metal. Where the steel is finished the converter is tilted, or swung onits trunnions, the blast turned off, and the steel poured out ofthe top. OPEN HEARTH PROCESS The open hearth furnace consists of a big brick room with a lowarched roof. It is charged with pig iron and scrap through doorsin the side walls. [Illustration: FIG. 1. --A typical Bessemer converter. ] Through openings at one end of the furnace come hot air and gas, which burn in the furnace, producing sufficient heat to melt thecharge and refine it of its impurities. Lime and other nonmetallicsubstances are put in the furnace. These melt, forming a "slag"which floats on the metal and aids materially in the refiningoperations. In the bessemer process air is forced _through_ the metal. In theopen-hearth furnace the metal is protected from the flaming gasesby a slag covering. Therefore it is reasonable to suppose thatthe final product will not contain so much gas. [Illustration: FIG. 2. --Action of Bessemer converter. ] [Illustration: FIG. 3. --Regenerative open hearth furnace. ] A diagram of a modern regenerative furnace is shown in Fig. 3. Air and gas enter the hearth through chambers loosely packed withhot fire brick, burn, and exit to the chimney through another pairof chambers, giving to them some of the heat which would otherwisewaste. The direction is reversed about every twenty minutes bychanging the position of the dampers. CRUCIBLE STEEL Crucible steel is still made by melting material in a clay or graphitecrucible. Each crucible contains about 40 lb. Of best puddled iron, 40 lb. Of clean "mill scrap"--ends trimmed from tool steel bars--andsufficient rich alloys and charcoal to make the mixture conform tothe desired chemical analysis. The crucible is covered, loweredinto a melting hole (Fig. 4) and entirely surrounded by burningcoke. In about four hours the metal is converted into a quiet whitehot liquid. Several crucibles are then pulled out of the hole, andtheir contents carefully poured into a metal mold, forming an ingot. [Illustration: FIG. 4. --Typical crucible furnace. ] If modern high-speed steel is being made, the ingots are takenout of the molds while still red hot and placed in a furnace whichkeeps them at this temperature for some hours, an operation knownas annealing. After slow cooling any surface defects are groundout. Ingots are then reheated to forging temperature, hammereddown into "billets" of about one-quarter size, and 10 to 20 percent of the length cut from the top. After reheating the billetsare hammered or rolled into bars of desired size. Finished bars arepacked with a little charcoal into large pipes, the ends sealed, and annealed for two or three days. After careful inspection andtesting the steel is ready for market. THE ELECTRIC PROCESS The fourth method of manufacturing steel is by the electric furnace. These furnaces are of various sizes and designs; their size may besufficient for only 100 lb. Of metal--on the other hand electricfurnaces for making armor-plate steel will hold 40 tons of steel. Designs vary widely according to the electrical principles used. A popular furnace is the 6-ton Heroult furnace illustrated in Fig. 5. It is seen to be a squat kettle, made of heavy sheet steel, witha dished bottom and mounted so it can be tilted forward slightlyand completely drained. This kettle is lined with special firebrick which will withstand most intense heat and resist the cuttingaction of hot metal and slag. For a roof, a low dome of fire brickis provided. The shell and lining is pierced in front for a pouringspout, and on either side by doors, through which the raw materialis charged. Two or three carbon "electrodes"--18-in. Cylinders of speciallyprepared coke or graphite--extend through holes in the roof. Electricalconnections are made to the upper ends, and a very high currentsent through them. This causes tremendous arcs to form betweenthe lower ends of the electrodes and the metal below, and theseelectric arcs are the only source of heat in this style of furnace. Electric furnaces can be used to do the same work as is done incrucible furnaces--that is to say, merely melt a charge of carefullyselected pure raw materials. On the other hand it can be used toproduce very high-grade steel from cheap and impure metal, whenit acts more like an open-hearth furnace. It can push the refiningeven further than the latter furnace does, for two reasons: firstthe bath is not swept continuously by a flaming mass of gases;second, the temperature can be run up higher, enabling the operatorto make up slags which are difficult to melt but very useful toremove small traces of impurities from the metal. Electric furnaces are widely used, not only in the iron industry, but in brass, copper and aluminum works. It is a useful melter ofcold metal for making castings. It can be used to convert ironinto steel or vice versa. Its most useful sphere, however, is as arefiner of metal, wherein it takes either cold steel or molten steelfrom open hearth or bessemer furnaces, and gives it the finishingtouches. [Illustration: FIG. 5. --"Slagging off" an electric furnace. ] [Illustration: FIG. 6. --Pouring the ingots. ] As an illustration of the furnace reactions that take place thefollowing schedule is given, showing the various stages in themaking of a heat of electric steel. The steel to be made was ahigh-carbon chrome steel used for balls for ball bearings: 6-TON HEROULT FURNACE 11:50 A. M. --Material charged: Boiler plate 5, 980 lb. Stampings 5, 991 lb. ----------- 11, 971 lb. Limestone 700 lb. 12:29 P. M. --Completed charging (current switched on). 3:20 P. M. --Charge melted down. Preliminary analysis under black slag. Analysis: Carbon Silicon Sulphur Phosphorus Manganese 0. 06 0. 014 0. 032 0. 009 0. 08 Note the practical elimination of phosphorus. 3:40 P. M. --The oxidizing (black) slag is now poured and skimmed off as clean as possible to prevent rephosphorizing and to permit of adding carburizing materials. For this purpose carbon is added in the form of powdered coke, ground electrodes or other forms of pure carbon. The deoxidizing slag is now formed by additions of lime, coke andfluorspar (and for some analyses ferrosilicon). The slag changesfrom black to white as the metallic oxides are reduced by thesedeoxidizing additions and the reduced metals return to the bath. A good finishing slag is creamy white, porous and viscous. Afterthe slag becomes white, some time is necessary for the absorptionof the sulphur in the bath by the slag. The white slag disintegrates to a powder when exposed to the atmosphereand has a pronounced odor of acetylene when wet. Further additions of recarburizing material are added as needed tomeet the analysis. The further reactions are shown by the following: 3:40 P. M. --Recarburizing material added: 130 lb. Ground electrodes. 25 lb. Ferromanganese. Analysis: Carbon Silicon Sulphur Phosphorus Manganese 0. 76 0. 011 0. 030 0. 008 0. 26 To form white slag there was added: 225 lb. Lime. 75 lb. Powdered coke. 55 lb. Fluorspar. 4:50 P. M. -- Analysis: Carbon Silicon Sulphur Phosphorus Manganese 0. 75 0. 014 0. 012 0. 008 0. 28 Note reduction of the sulphur content. During the white-slag period the following alloying additions weremade: 500 lb. Pig iron. 80 lb. Ferrosilicon. 9 lb. Ferromanganese. 146 lb. 6 per cent carbon ferrochrome. The furnace was rotated forward to an inclined position and thecharge poured into the ladle, from which in turn it was pouredinto molds. 5:40 P. M. --Heat poured. Analysis: Carbon Silicon Sulphur Phosphorus Manganese Chromium 0. 97 0. 25 0. 014 0. 013 0. 33 0. 70 Ingot weight poured 94. 0 per centScull 2. 7 per centLoss 3. 3 per cent Total current consumption for the heat, 4, 700 kW. -hr. Or 710 kw. -hr. Per ton. Electric steel, in fact, all fine steel, should be cast in big-end-upmolds with refractory hot tops to prevent any possibility of pipagein the body of the ingot. In the further processing of the ingot, whether in the rolling mill or forge, special precautions shouldbe taken in the heating, in the reduction of the metal and in thecooling. No attempt is made to compare the relative merits of open hearthand electric steel; results in service, day in and day out, have, however, thoroughly established the desirability of electric steel. Ten years of experience indicate that electric steel is equal tocrucible steel and superior to open hearth. The rare purity of the heat derived from the electric are, combinedwith definite control of the slag in a neutral atmosphere, explainsin part the superiority of electric steel. Commenting on this recentlyDr. H. M. Howe stated that "in the open hearth process you have suchatmosphere and slag conditions as you can get, and in the electricyou have such atmosphere and slag conditions as you desire. " Another type of electric furnace is shown in Figs. 7 and 8. Thisis the Ludlum furnace, the illustrations showing a 10-ton size. Figure 7 shows it in normal, or melting position, while in Fig. 8 it is tilted for pouring. In melting, the electrodes first reston the charge of material in the furnace. After the current isturned on they eat their way through, nearly to the bottom. Bythis time there is a pool of molten metal beneath the electrodeand the charge is melted from the bottom up so that the roof isnot exposed to the high temperature radiating from the open arc. The electrodes in this furnace are of graphite, 9 in. In diameterand the current consumed is about 500 kw. -hr. Per ton. [Illustration: FIG. 7. --Ludlum electric furnace. ] [Illustration: FIG. S. --The furnace tilted for pouring. ] One of the things which sometimes confuse regarding the contentsof steel is the fact that the percentage of carbon and the otheralloys are usually designated in different ways. Carbon is usuallydesignated by "points" and the other alloys by percentages. Thepoint is one ten-thousandth while 1 per cent is one one-hundredthof the whole. In other words, "one hundred point carbon" is steelcontaining 1 per cent carbon. Twenty point carbon, such as is usedfor carbonizing purposes is 0. 20 per cent. Tool steel varies fromone hundred to one hundred and fifty points carbon, or from 1. 00to 1. 50 per cent. Nickel, chromium, etc. , are always given in per cent, as a 3. 5per cent nickel, which means exactly what it says--3-1/2 parts in100. Bearing this difference in mind all confusion will be avoided. CLASSIFICATIONS OF STEEL Among makers and sellers, carbon tool-steels are classed by "grade"and "temper. " The word grade is qualified by many adjectives ofmore or less cryptic meaning, but in general they aim to denotethe process and care with which the steel is made. _Temper_ of a steel refers to the carbon content. This should preferablybe noted by "points, " as just explained; but unfortunately, a 53-pointsteel (containing 0. 53 per cent carbon) may locally be called somethinglike "No. 3 temper. " A widely used method of classifying steels was originated by theSociety of Automotive Engineers. Each specification is representedby a number of 4 digits, the first figure indicating the class, thesecond figure the approximate percentage of predominant alloyingelement, and the last two the average carbon content in points. Plain carbon steels are class 1, nickel steels are class 2, nickel-chromium steels are class 3, chromium steels are class 5, chromium-vanadium steels are class 6, and silico-manganese steelsare class 9. Thus by this system, steel 2340 would be a 3 per centnickel steel with 0. 40 per cent carbon; or steel 1025 would be a0. 25 plain carbon steel. Steel makers have no uniform classification for the various kindsof steel or steels used for different purposes. The following listshows the names used by some of the well-known makers: Air-hardening steel Chrome-vanadium steelAlloy steel Circular saw platesAutomobile steel Coal auger steelAwl steel Coal mining pick or cutter steelAxe and hatchet steel Coal wedge steelBand knife steel Cone steelBand saw steel Crucible cast steelButcher saw steel Crucible machinery steelChisel steel Cutlery steelChrome-nickel steel Drawing die steel (Wortle) Drill rod steel Patent, bush or hammer steelFacing and welding steel Pick steelFork steel Pivot steelGin saw steel Plane bit steelGranite wedge steel Quarry steelGun barrel steel Razor steelHack saw steel Roll turning steelHigh-speed tool steel Saw steelHot-rolled sheet steel Scythe steelLathe spindle steel Shear knife steelLawn mower knife steel Silico-manganese steelMachine knife steel Spindle steelMagnet steel Spring steelMining drill steel Tool holder steelNail die shapes Vanadium tool steelNickel-chrome steel Vanadium-chrome steelPaper knife steel Wortle steel Passing to the tonnage specifications, the following table fromTiemann's excellent pocket book on "Iron and Steel, " will givean approximate idea of the ordinary designations now in use: Approximate Grades carbon range Common uses Extra soft 0. 08-0. 18 Pipe, chain and other welding purposes;(dead soft) case-hardening purposes; rivets; pressing and stamping purposes. Structural (soft) 0. 15-0. 25 Structural plates, shapes and bars for(medium) bridges, buildings, cars, locomotives; boiler (flange) steel; drop forgings; bolts. Medium 0. 20-0. 35 Structural purposes (ships); shafting; automobile parts; drop forgings. Medium hard 0. 35-0. 60 Locomotive and similar large forgings; car axles; rails. Hard 0. 60-0. 85 Wrought steel wheels for steam and electric railway service; locomotive tires; rails; tools, such as sledges, hammers, pick points, crowbars, etc. Spring 0. 85-1. 05 Automobile and other vehicle springs; tools, such as hot and cold chisels, rock drills and shear blades. Spring 0. 90-1. 15 Railway springs; general machine shop tools. CHAPTER II COMPOSITION AND PROPERTIES OF STEEL It is a remarkable fact that one can look through a dozen textbooks on metallurgy and not find a definition of the word "steel. "Some of them describe the properties of many other irons and thenallow you to guess that everything else is steel. If it was difficulta hundred years ago to give a good definition of the term when themetal was made by only one or two processes, it is doubly difficultnow, since the introduction of so many new operations and furnaces. We are in better shape to know what steel is than our forefathers. They went through certain operations and they got a soft malleable, weldable metal which would not harden; this they called iron. Certainother operations gave them something which looked very much likeiron, but which would harden after quenching from a red heat. Thiswas steel. Not knowing the essential difference between the two, they must distinguish by the process of manufacture. To-day wecan make either variety by several methods, and can convert eitherinto the other at will, back and forth as often as we wish; sowe are able to distinguish between the two more logically. We know that iron is a chemical element--the chemists write itFe for short, after the Latin word "ferrum, " meaning iron--it isone of those substances which cannot be separated into anythingelse but itself. It can be made to join with other elements; forinstance, it joins with the oxygen in the air and forms scale orrust, substances known to the chemist as iron oxide. But the samemetal iron can be recovered from that rust by abstracting the oxygen;having recovered the iron nothing else can be extracted but iron;_iron is elemental_. We can get relatively pure iron from various minerals and artificialsubstances, and when we get it we always have a magnetic metal, almost infusible, ductile, fairly strong, tough, something whichcan be hardened slightly by hammering but which cannot be hardenedby quenching. It has certain chemical properties, which need not bedescribed, which allow a skilled chemist to distinguish it withoutdifficulty and unerringly from the other known elements--nearly100 of them. Carbon is another chemical element, written C for short, which iswidely distributed through nature. Carbon also readily combineswith oxygen and other chemical elements, so that it is rarely foundpure; its most familiar form is soot, although the rarer graphite andmost rare diamond are also forms of quite pure carbon. It can alsobe readily separated from its multitude of compounds (vegetation, coal, limestone, petroleum) by the chemist. With the rise of knowledge of scientific chemistry, it was quicklyfound that the essential difference between iron and steel was thatthe latter was _iron plus carbon_. Consequently it is an alloy, and the definition which modern metallurgists accept is this: "Steel is an iron-carbon alloy containing less than about 2 percent carbon. " Of course there are other elements contained in commercial steel, and these elements are especially important in modern "alloy steels, "but carbon is the element which changes a soft metal into one whichmay be hardened, and strengthened by quenching. In fact, carbon, of itself, without heat treatment, strengthens iron at the expenseof ductility (as noted by the percentage elongation an 8-in. Barwill stretch before breaking). This is shown by the following table: -------------------------------------------------------------------------- | | |Elastic |Ultimate|Percentage. Class by use. | Class by | Per cent | limit |strength|elongation | hardness. | carbon. |lb. Per |lb. Per |in 8 inches. | | |sq. In. |sq. In. |------------------|-----------|------------|--------|--------|------------Boiler rivet steel|Dead soft |0. 08 to 0. 15| 25, 000 | 50, 000 | 30Struc. Rivet steel|Soft |0. 15 to 0. 22| 30, 000 | 55, 000 | 30Boiler plate steel|Soft |0. 08 to 0. 10| 30, 000 | 60, 000 | 25Structural steel |Medium |0. 18 to 0. 30| 35, 000 | 65, 000 | 25Machinery steel |Hard |0. 35 to 0. 60| 40, 000 | 75, 000 | 20Rail steel |Hard |0. 35 to 0. 55| 40, 000 | 75, 000 | 15Spring steel |High carbon|1. 00 to 1. 50| 60, 000 |125, 000 | 10Tool steel |High carbon|0. 90 to 1. 50| 80, 000 |150, 000 | 5-------------------------------------------------------------------------- Just why a soft material like carbon (graphite), when added toanother soft material like iron, should make the iron harder, hasbeen quite a mystery, and one which has caused a tremendous amountof study. The mutual interactions of these two elements in variousproportions and at various temperatures will be discussed at greaterlength later, especially in Chap. VIII, p. 105. But we may anticipateby saying that some of the iron unites with all the carbon to form anew substance, very hard, a carbide which has been called "cementite. "The compound always contains iron and carbon in the proportionsof three atoms of iron to one atom of carbon; chemists note thisfact in shorthand by the symbol Fe3C (a definite chemical compoundof three atoms of iron to one of carbon). Many of the propertiesof steel, as they vary with carbon content, can be linked up withthe increasing amount of this hard carbide cementite, distributedin very fine particles through the softer iron. SULPHUR is another element (symbol S) which is always found insteel in small quantities. Some sulphur is contained in the orefrom which the iron is smelted; more sulphur is introduced by thecoke and fuel used. Sulphur is very difficult to get rid of insteel making; in fact the resulting metal usually contains a littlemore than the raw materials used. Only the electric furnace isable to produce the necessary heat and slags required to eliminatesulphur, and as a matter of fact the sulphur does not go untilseveral other impurities have been eliminated. Consequently, anelectric steel with extremely low sulphur (0. 02 per cent) is bythat same token a well-made metal. Sulphur is of most trouble to rolling and forging operations whenconducted at a red heat. It makes steel tender and brittle at thattemperature--a condition known to the workmen as "red-short. " Itseems to have little or no effect upon the physical propertiesof cold steel--at least as revealed by the ordinary testingmachines--consequently many specifications do not set any limiton sulphur, resting on the idea that if sulphur is low enough notto cause trouble to the manufacturer during rolling, it will notcause the user any trouble. Tool steel and other fine steels should be very low in sulphur, preferably not higher than 0. 03 per cent. Higher sulphur steels(0. 06 per cent, and even up to 0. 10 per cent) have given very goodservice for machine parts, but in general a high sulphur steelis a suspicious steel. Screw stock is purposely made with up to0. 12 per cent sulphur and a like amount of phosphorus so it willcut freely. Manganese counteracts the detrimental effect of sulphur when presentin the steel to an amount at least five times the sulphur content. PHOSPHORUS is an element (symbol P) which enters the metal fromthe ore. It remains in the steel when made by the so-called acidprocess, but it can be easily eliminated down to 0. 06 per centin the basic process. In fact the discovery of the basic processwas necessary before the huge iron deposits of Belgium and theFranco-German border could be used. These ores contain severalper cent phosphorus, and made a very brittle steel ("cold short")until basic furnaces were used. Basic furnaces allow the formationof a slag high in lime, which takes practically all the phosphorusout of the metal. Not only is the resulting metal usable, but theslag makes a very excellent fertilizer, and is in good demand. SILICON is a very widespread element (symbol Si), being an essentialconstituent of nearly all the rocks of the earth. It is similar tocarbon in many of its chemical properties; for instance it burnsvery readily in oxygen, and consequently native silicon is unknown--itis always found in combination with one or more other elements. When it bums, each atom of silicon unites with two atoms of oxygento form a compound known to chemists as silica (SiO2), and to thesmall boy as "sand" and "agate. " Iron ore (an oxide of iron) contains more or less sand and dirtmixed in it when it is mined, and not only the iron oxide but alsosome of the silicon oxide is robbed of its oxygen by the smeltingprocess. Pig iron--the product of the blast furnace--thereforecontains from 1 to 3 per cent of silicon, and some silicon remainsin the metal after it has been purified and converted into steel. However, silicon, as noted above, burns very readily in oxygen, and this property is of good use in steel making. At the end ofthe steel-making process the metal contains more or less oxygen, which must be removed. This is sometimes done (especially in theso-called acid process) by adding a small amount of silicon tothe hot metal just before it leaves the furnace, and stirring itin. It thereupon abstracts oxygen from the metal wherever it findsit, changing to silica (SiO2) which rises and floats on the surfaceof the cleaned metal. Most of the silicon remaining in the metalis an excess over that which is required to remove the dangerousoxygen, and the final analysis of many steels show enough silicon(from 0. 20 to 0. 40) to make sure that this step in the manufacturehas been properly done. MANGANESE is a metal much like iron. Its chemical symbol is Mn. Itis somewhat more active than iron in many chemical changes--notablyit has what is apparently a stronger attraction for oxygen andsulphur than has iron. Therefore the metal is used (especially inthe so-called basic process) to free the molten steel of oxygen, acting in a manner similar to silicon, as explained above. Thecompound of manganese and oxygen is readily eliminated from themetal. Sufficient excess of elemental manganese should remain sothat the purchaser may be sure that the iron has been properly"deoxidized, " and to render harmless the traces of sulphur present. No damage is done by the presence of a little manganese in steel, quite the reverse. Consequently it is common to find steels containingfrom 0. 3 to 1. 5 per cent. ALLOYING ELEMENTS. --Commercial steels of even the simplest typesare therefore primarily alloys of iron and carbon. Impurities andtheir "remedies" are always present: sulphur, phosphorus, siliconand manganese--to say nothing of oxygen, nitrogen and carbon oxidegases, about which we know very little. It has been found that othermetals, if added to well-made steel, produce definite improvementsin certain directions, and these "alloy steels" have found muchuse in the last ten years. Alloy steels, in addition to theabove-mentioned elements, may commonly contain one or more of thefollowing, in varying amounts: Nickel (Ni), Chromium (Cr), Vanadium(Va), Tungsten (W), Molybdenum (Mo). These steels will be discussedat more length in Chapters III and IV. PROPERTIES OF STEEL Steels are known by certain tests. Early tests were more or lesscrude, and depended upon the ability of the workman to judge the"grain" exhibited by a freshly broken piece of steel. The cold-bendtest was also very useful--a small bar was bent flat upon itself, and the stretched fibers examined for any sign of break. Harderstiff steels were supported at the ends and the amount of centralload they would support before fracture, or the amount of permanentset they would acquire at a given load noted. Files were also usedto test the hardness of very hard steel. These tests are still used to a considerable extent, especially inworks where the progress of an operation can be kept under closewatch in this way, the product being periodically examined by moreprecise methods. The chief furnace-man, or "melter, " in a steelplant, judges the course of the refining process by casting smalltest ingots from time to time, breaking them and examining thefracture. Cutlery manufacturers use the bend test to judge thetemper of blades. File testing of case-hardened parts is very common. However there is need of standardized methods which depend lessupon the individual skill of the operator, and which will yieldresults comparable to others made by different men at differentplaces and on different steels. Hence has grown up the art of testingmaterials. TENSILE PROPERTIES Strength of a metal is usually expressed in the number of poundsa 1-in. Bar will support just before breaking, a term called the"ultimate strength. " It has been found that the shape of the testbar and its method of loading has some effect upon the results, so it is now usual to turn a rod 5-1/2 in. Long down to 0. 505 in. In diameter for a central length of 2-3/8 in. , ending the turnwith 1/2-in. Fillets. The area of the bar equals 0. 2 sq. In. , sothe load it bears at rupture multiplied by 5 will represent the"ultimate strength" in pounds per square inch. Such a test bar is stretched apart in a machine like that shownin Fig. 9. The upper end of the bar is held in wedged jaws by thetop cross-head, and the lower end grasped by the movable head. The latter is moved up and down by three long screws, driven atthe same speed, which pass through threads cut in the corners ofthe cross-head. When the test piece is fixed in position the motorwhich drives the machine is given a few turns, which by propergearing pulls the cross-head down with a certain pull. This pullis transmitted to the upper cross-head by the test bar, and canbe weighed on the scale arm, acting through a system of links andlevers. Thus the load may be increased as rapidly as desirable, alwayskept balanced by the weighing mechanism, and the load at fracturemay be read directly from the scale beam. This same test piece may give other information. If light punchmarks are made, 2 in. Apart, before the test is begun, the brokenends may be clamped together, and the distance between punch marksmeasured. If it now measures 3 in. The stretch has been 1 in. In 2, or 50 per cent. This figure is known as the elongation at fracture, or briefly, the "elongation, " and is generally taken to be a measureof ductility. When steel shows any elongation, it also contracts in area at thesame time. Often this contraction is sharply localized at the fracture;the piece is said to "neck. " A figure for contraction in area isalso of much interest as an indication of toughness; the diameterat fracture is measured, a corresponding area taken out from atable of circles, subtracted from the original area (0. 200 sq. In. ) and the difference divided by 0. 2 to get the percentagecontraction. [Illustration: FIG. 9. --Olsen testing machine. ] Quite often it is desired to discover the elastic limit of thesteel, in fact this is of more use to the designer than the ultimatestrength. The elastic limit is usually very close to the load wherethe metal takes on a permanent set. That is to say, if a delicatecaliper ("extensometer, " so called) be fixed to the side of thetest specimen, it would show the piece to be somewhat longer underload than when free. Furthermore, if the load had not yet reached theyield point, and were released at any time, the piece would returnto its original length. However, if the load had been excessive, andthen relieved, the extensometer would no longer read exactly 2. 0in. , but something more. Soft steels "give" very quickly at the yield point. In fact, ifthe testing machine is running slowly, it takes some time for thelower head to catch up with the stretching steel. Consequently atthe yield point, the top head is suddenly but only temporarilyrelieved of load, and the scale beam drops. In commercial practice, the yield point is therefore determined by the "drop of the beam. "For more precise work the calipers are read at intervals of 500 or1, 000 lb. Load, and a curve plotted from these results, a curvewhich runs straight up to the elastic limit, but there bends off. A tensile test therefore gives four properties of great usefulness:The yield point, the ultimate strength, the elongation and thecontraction. Compression tests are seldom made, since the actionof metal in compression and in tension is closely allied, and thedesigner is usually satisfied with the latter. IMPACT TESTS Impact tests are of considerable importance as an indication ofhow a metal will perform under shock. Some engineers think thatthe tensile test, which is one made under slow loading, shouldtherefore be supplemented by another showing what will happen ifthe load is applied almost instantaneously. This test, however, hasnot been standardized, and depends to a considerable extent uponthe type of machine, but more especially the size of the specimenand the way it is "nicked. " The machine is generally a swingingheavy pendulum. It falls a certain height, strikes the sample atthe lowest point, and swings on past. The difference between thedownward and upward swing is a measure of the energy it took tobreak the test piece. FATIGUE TESTS It has been known for fifty years that a beam or rod would failat a relatively low stress if only repeated often enough. It hasbeen found, however, that each material possesses a limiting stress, or endurance limit, within which it is safe, no matter how oftenthe loading occurs. That limiting stress for all steels so farinvestigated causes fracture below 10 million reversals. In otherwords, a steel which will not break before 10, 000, 000 reversalscan confidently be expected to endure 100, 000, 000, and doubtlessinto the billions. About the only way to test one piece such a large number of timesis to fashion it into a beam, load it, and then turn the beam inits supports. Thus the stress in the outer fibers of the bar variesfrom a maximum stretch through zero to a maximum compression, andback again. A simple machine of this sort is shown in Fig. 10, where _B_ and _E_ are bearings, _A_ the test piece, turned slightlydown in the center, _C_ and _D_ ball bearings supporting a load_W_. _K_ is a pulley for driving the machine and _N_ is a counter. [Illustration: FIG. 10. --Sketch of rotating beam machine for measuringendurance of metal. ] HARDNESS TESTING The word "hardness" is used to express various properties of metals, and is measured in as many different ways. "Scratch hardness" is used by the geologist, who has constructed"Moh's scale" as follows: Talc has a hardness of 1 Rock Salt has a hardness of 2 Calcite has a hardness of 3 Fluorite has a hardness of 4 Apatite has a hardness of 5 Feldspar has a hardness of 6 Quartz has a hardness of 7 Topaz has a hardness of 8 Corundum has a hardness of 9 Diamond has a hardness of 10 A mineral will scratch all those above it in the series, and willbe scratched by those below. A weighted diamond cone drawn slowlyover a surface will leave a path the width of which (measured bya microscope) varies inversely as the scratch hardness. "Cutting hardness" is measured by a standardized drilling machine, and has a limited application in machine-shop practice. "Rebounding hardness" is commonly measured by the Shore scleroscope, illustrated in Fig. 11. A small steel hammer, 1/4 in. In diameter, 3/4 in. In length, and weighing about 1/12 oz. Is dropped a distanceof 10 in. Upon the test piece. The height of rebound in arbitraryunits represents the hardness numeral. [Illustration: FIG. 11. --Shore scleroscope. ] Should the hammer have a hard flat surface and drop on steel so hardthat no impression were made, it would rebound about 90 per centof the fall. The point, however, consists of a slightly spherical, blunt diamond nose 0. 02 in. In diameter, which will indent the steelto a certain extent. The work required to make the indentationis taken from the energy of the falling body; the rebound willabsorb the balance, and the hammer will now rise from the samesteel a distance equal to about 75 per cent of the fall. A permanentimpression is left upon the test piece because the impact willdevelop a force of several hundred thousand pounds per square inchunder the tiny diamond-pointed hammer head, stressing the testpiece at this point of contact much beyond its ultimate strength. The rebound is thus dependent upon the indentation hardness, forthe reason that the less the indentation, the more energy willreappear in the rebound; also, the less the indentation, the harderthe material. Consequently, the harder the material, the more therebound. "Indentation hardness" is a measure of a material's resistanceto penetration and deformation. The standard testing machine isthe Brinell, Fig. 12. A hardened steel ball, 10 mm. In diameter, is forced into the test piece with a pressure of 3, 000 kg. (3-1/3tons). The resulting indentation is then measured. [Illustration: FIG. 12. --Hydraulic testing machine. (Brinellprinciple. )] While under load, the steel ball in a Brinell machine naturallyflattens somewhat. The indentation left behind in the test piece isa duplicate of the surface which made it, and is usually regardedas being the segment of a sphere of somewhat larger radius thanthe ball. The radius of curvature of this spherical indentationwill vary slightly with the load and the depth of indentation. The Brinell hardness numeral is the quotient found by dividing thetest pressure in kilograms by the spherical area of the indentation. The denominator, as before, will vary according to the size of thesphere, the hardness of the sphere and the load. These items havebeen standardized, and the following table has been constructedso that if the diameter of the identation produced by a load of3, 000 kg. Be measured the hardness numeral is found directly. TABLE FOR BRINELL BALL TEST------------------------------------------------------------------------Diameter of Ball | Hardness Number | Diameter of Ball | Hardness NumberImpression, mm. | for a Load of | Impression, mm. | for a Load of | 3, 000 kg. | | 3, 000 kg. -----------------|-----------------|------------------|----------------- 2. 0 | 946 | 4. 5 | 179 2. 1 | 857 | 4. 6 | 170 2. 2 | 782 | 4 7 | 163 2. 3 | 713 | 4. 8 | 156 2. 4 | 652 | 4. 9 | 149 2. 5 | 600 | 5. 0 | 143 | | | 2. 6 | 555 | 5. 1 | 137 2. 7 | 512 | 5. 2 | 131 2. 8 | 477 | 5. 3 | 126 2. 9 | 444 | 5. 4 | 121 3. 0 | 418 | 5. 5 | 116 | | | 3. 1 | 387 | 5. 6 | 112 3. 2 | 364 | 5. 7 | 107 3. 3 | 340 | 5. 8 | 103 3. 4 | 321 | 5. 9 | 99 3. 5 | 302 | 6. 0 | 95 | | | 3. 6 | 286 | 6. 1 | 92 3. 7 | 269 | 6. 2 | 89 3. 8 | 255 | 6. 3 | 86 3. 9 | 241 | 6. 4 | 83 4. 0 | 228 | 6. 5 | 80 | | | 4. 1 | 217 | 6. 6 | 77 4. 2 | 207 | 6. 7 | 74 4. 3 | 196 | 6. 8 | 71. 5 4. 4 | 187 | 6. 9 | 69------------------------------------------------------------------------ CHAPTER III ALLOYS AND THEIR EFFECT UPON STEEL In view of the fact that alloy steels are coming into a great dealof prominence, it would be well for the users of these steels tofully appreciate the effects of the alloys upon the various gradesof steel. We have endeavored to summarize the effect of these alloysso that the users can appreciate their effect, without having tostudy a metallurgical treatise and then, perhaps, not get the cruxof the matter. NICKEL Nickel may be considered as the toughest among the non-rare alloysnow used in steel manufacture. Originally nickel was added to giveincreased strength and toughness over that obtained with the ordinaryrolled structural steel and little attempt was made to utilize itsgreat possibilities so far as heat treatment was concerned. The difficulties experienced have been a tendency towards laminatedstructure during manufacture and great liability to seam, botharising from improper melting practice. When extra care is exercisedin the manufacture, particularly in the melting and rolling, manyof these difficulties can be overcome. The electric steel furnace, of modern construction, is a very importantstep forward in the melting of nickel steel; neither the crucibleprocess nor basic or acid open-hearth furnaces give such good results. Great care must be exercised in reheating the billet for rollingso that the steel is correctly soaked. The rolling must not beforced; too big reduction per pass should not be indulged in, asthis sets up a tendency towards seams. Nickel steel has remarkably good mechanical qualities when suitablyheat-treated, and it is preeminently adapted for case-hardening. Itis not difficult to machine low-nickel steel, consequently it isin great favor where easy machining properties are of importance. Nickel influences the strength and ductility of steel by beingdissolved directly in the iron or ferrite; in this respect differingfrom chromium, tungsten and vanadium. The addition of each 1 percent nickel up to 5 per cent will cause an approximate increase offrom 4, 000 to 6, 000 lb. Per square inch in the tensile strength andelastic limit over the corresponding steel and without any decreasein ductility. The static strength of nickel steel is affected tosome degree by the percentage of carbon; for instance, steel with0. 25 per cent carbon and 3. 5 per cent nickel has a tensile strength, in its normal state, equal to a straight carbon steel of 0. 5 percent with a proportionately greater elastic limit and retainingall the advantages of the ductility of the lower carbon. To bring out the full qualities of nickel it must be heat-treated, otherwise there is no object in using nickel as an alloy with carbonsteel as the additional cost is not justified by increased strength. Nickel has a peculiar effect upon the critical ranges of steel, the critical range being lowered by the percentage of nickel; inthis respect it is similar to manganese. Nickel can be alloyed with steel in various percentages, each percentagehaving a very definite effect on the microstructure. For instance, asteel with 0. 2 per cent carbon and 2 per cent nickel has a pearliticstructure but the grain is much finer than if the straight carbonwere used. With the same carbon content and say 5 per cent nickel, the structure would still be pearlitic, but much finer and denser, therefore capable of withstanding shock, and having greater dynamicstrength. With about 0. 2 per cent carbon and 8 per cent nickel, thesteel is nearing the stage between pearlite and martensite, andthe structure is extremely fine, the ferrite and pearlite havinga very pronounced tendency to mimic a purely martensite structure. Steel with 0. 2 per cent carbon and 15 per cent nickel is entirelymartensite. Higher percentages of nickel change the martensiticstructure to austenite, the steel then being non-magnetic. Thehigher percentages, that is 30 to 35 per cent nickel, are usedfor valve seats, valve heads, and valve stems, as the alloy is apoor conductor of heat and is particularly free from any tendencytowards corrosion or pitting from the action of waste gases ofthe internal-combustion engine. Nickel steels having 3-1/2 per cent nickel and 0. 15 to 0. 20 percent carbon are excellent for case-hardening purposes, giving hardsurfaces and tough interiors. To obtain the full effect of nickel as an alloy, it is essentialthat the correct percentage of carbon be used. High nickel andlow carbon will not be more efficient than lower nickel and highercarbon, but the cost will be much greater. Generally speaking, heat-treated nickel alloy steels are about two to three times strongerthan the same steel annealed. This point is very important as manyinstances have been found where nickel steel is incorrectly used, being employed when in the annealed or normal state. CHROMIUM Chromium when alloyed with steel, has the characteristic functionof opposing the disintegration and reconstruction of cementite. This is demonstrated by the changes in the critical ranges of thisalloy steel taking place slowly; in other words, it has a tendencyto raise the _Ac_ range (decalescent points) and lower the _Ar_range (recalescent points). Chromium steels are therefore capableof great hardness, due to the rapid cooling being able to retardthe decomposition of the austenite. The great hardness of chromium steels is also due to the formationof double carbides of chromium and iron. This condition is notremoved when the steel is slightly tempered or drawn. This additionalhardness is also obtained without causing undue brittleness such aswould be obtained by any increase of carbon. The degree of hardnessof the lower-chrome steels is dependent upon the carbon content, as chromium alone will not harden iron. The toughness so noticeable in this steel is the result of thefineness of structure; in this instance, the action is similarto that of nickel, and the tensile strength and elastic limit istherefore increased without any loss of ductility. We then havethe desirable condition of tough hardness, making chrome steelsextremely valuable for all purposes requiring great resistanceto wear, and in higher-chrome contents resistance to corrosion. All chromium-alloy steels offer great resistance to corrosion anderosion. In view of this, it is surprising that chromium steelsare not more largely used for structural steel work and for allpurposes where the steel has to withstand the corroding actionof air and liquids. Bridges, ships, steel building, etc. , wouldoffer greater resistance to deterioration through rust if thechromium-alloy steels were employed. Prolonged heating and high temperatures have a very bad effect uponchromium steels. In this respect they differ from nickel steels, which are not so affected by prolonged heating, but chromium steelswill stand higher temperatures than nickel steels when the periodis short. Chromium steels, due to their admirable property of increased hardness, without the loss of ductility, make very excellent chisels andimpact tools of all types, although for die blocks they do not givesuch good results as can be obtained from other alloy combinations. For ball bearing steels, where intense hardness with great toughnessand ready recovery from temporary deflection is required, chromiumas an alloy offers the best solution. Two per cent chromium steels; due to their very hard tough surface, are largely used for armor-piercing projectiles, cold rolls, crushers, drawing dies, etc. The normal structure of chromium steels, with a very low carboncontent is roughly pearlitic up to 7 per cent, and martensiticfrom 8 to 20 per cent; therefore, the greatest application is inthe pearlitic zone or the lower percentages. NICKEL-CHROMIUM A combination of the characteristics of nickel and the characteristicsof chromium, as described, should obviously give a very excellentsteel as the nickel particularly affects the ferrite of the steeland the chromium the carbon. From this combination, we are able toget a very strong ferrite matrix and a very hard tough cementite. The strength of a strictly pearlitic steel over a pure iron is dueto the pearlitic being a layer arrangement of cementite runningparallel to that of a pure iron layer in each individual grain. Theferrite _i. E. _, the iron is increased in strength by the resistanceoffered by the cementite which is the simple iron-carbon combinationknown to metallurgists as Fe3C. The cementite, although addingto the tensile strength, is very brittle and the strength of thepearlite is the combination of the ferrite and cementite. In theevent of the cementite being strengthened, as in the case of strictlychromium steels, an increased tensile strength is readily obtainedwithout loss of ductility and if the ferrite is strengthened thenthe tensile strength and ductility of the metal is still furtherimproved. Nickel-chromium alloy represents one of the best combinations availableat the present time. The nickel intensifies the physical characteristicsof the chromium and the chromium has a similar effect on the nickel. For case-hardening, nickel-chromium steels seem to give very excellentresults. The carbon is very rapidly taken up in this combination, and for that reason is rather preferable to the straight nickel steel. With the mutually intensifying action of chromium and nickel thereis a most suitable ratio for these two alloys, and it has been foundthat roughly 2-1/2 parts of nickel to about 1 part of chromiumgives the best results. Therefore, we have the standard types of3. 5 per cent nickel with 1. 5 per cent chromium to 1. 5 per centnickel with 0. 6 per cent chromium and the various intermediatetypes. This ratio, however, does not give the whole story ofnickel-chromium combinations, and many surprising results havebeen obtained with these alloys when other percentage combinationshave been employed. VANADIUM Vanadium has a very marked effect upon alloy steels rich in chromium, carbon, or manganese. Vanadium itself, when combined with steel verylow in carbon, is not so noticeably beneficial as in the same carbonsteel higher in manganese, but if a small quantity of chromiumis added, then the vanadium has a very marked effect in increasingthe impact strength of the alloy. It would seem that vanadium hasthe effect of intensifying the action of chromium and manganese, orthat vanadium is intensified by the action of chromium or manganese. Vanadium has the peculiar property of readily entering into solutionwith ferrite. If vanadium contained is considerable it also combineswith the carbon, forming carbides. The ductility of carbon-vanadiumsteels is therefore increased, likewise the ductility of chrome-vanadiumsteels. The full effect of vanadium is not felt unless the temperatures towhich the steel is heated for hardening are raised considerably. It is therefore necessary that a certain amount of "soaking" takesplace, so as to get the necessary equalization. This is true of allalloys which contain complex carbides, i. E. , compounds of carbon, iron and one or more elements. Chrome-vanadium steels also are highly favored for case hardening. When used under alternating stresses it appears to have superiorendurance. It would appear that the intensification of the propertiesdue to chromium and manganese in the alloy steel accounts for thispeculiar phenomenon. Vanadium is also a very excellent scavenger for either removingthe harmful gases, or causing them to enter into solution with themetal in such a way as to largely obviate their harmful effects. Chrome-vanadium steels have been claimed, by many steel manufacturersand users, to be preferable to nickel-chrome steels. While notwishing to pass judgment on this, it should be borne in mind thatthe chrome-vanadium steel, which is tested, is generally comparedwith a very low nickel-chromium alloy steel (the price factor enteringinto the situation), but equally good results can be obtained bynickel-chromium steels of suitable analysis. Where price is the leading factor, there are many cases where astronger steel can be obtained from the chrome and vanadium thanthe nickel-chrome. It will be safe to say that each of these twosystems of alloys have their own particular fields and chrome-vanadiumsteel should not be regarded as the sole solution for all problems, neither should nickel-chromium. MANGANESE Manganese adds considerably to the tensile strength of steel, butthis is dependent on the carbon content. High carbon materially addsto the brittleness, whereas low-carbon, pearlitic-manganese steelsare very tough and ductile and are not at all brittle, providing theheat-treating is correct. Manganese steel is very susceptible tohigh temperatures and prolonged heating. In low-carbon pearlitic steels, manganese is more effective inincreasing ultimate strength than is nickel; that is to say, a0. 45 carbon steel with 1. 25 per cent manganese is as strong as a0. 45 carbon steel with 1. 5 per cent nickel. The former steel ismuch used for rifle barrels, and in the heat-treated condition willgive 80, 000 to 90, 000 lb. Per square inch elastic limit, 115, 000 to125, 000 lb. Per square inch tensile strength, 23 per cent elongation, and 55 per cent reduction in area. Manganese when added to steel has the effect of lowering the criticalrange; 1 per cent manganese will lower the upper critical point60°F. The action of manganese is very similar to that of nickelin this respect, only twice as powerful. As an instance, 1 percent nickel would have the effect of lowering the upper criticalrange from 25 to 30°F. Low-carbon pearlitic-manganese steel, heat-treated, will give dynamicstrength which cannot be equaled by low-priced and necessarilylow-content nickel steels. In many instances, it is preferable to usehigh-grade manganese steel, rather than low-content nickel steel. High-manganese steels or austenite manganese steels are used for avariety of purposes where great resistance to abrasion is required, the percentage of manganese being from 11 to 14 per cent, and carbon1 to 1. 5 per cent. This steel is practically valueless unlessheat-treated; that is, heated to about yellow red and quenchedin ice water. The structure is then austenite and the air-cooledstructure of this steel is martensite. Therefore this steel has tobe heated and very rapidly cooled to obtain the ductile austenitestructure. Manganese between 2 and 7 per cent is a very brittle material whenthe carbon is about 1 per cent or higher and is, therefore, quitevalueless. Below 2 per cent manganese steel low in carbon is veryductile and tough steel. The high-content manganese steels are known as the "Hadfield manganesesteels, " having been developed by Sir Robert Hadfield. Small additionsof chrome up to 1 per cent increase the elastic limit of low-carbonpearlitic-manganese steels without affecting the steel in its resistanceto shock, but materially decrease the percentage of elongation. Vanadium added to low-carbon pearlitic manganese steel has a verymarked effect, increasing greatly the dynamic strength and changingslightly the susceptibility of this steel to heat treatments, givinga greater margin for the hardening temperature. Manganese steelwith added vanadium is most efficient when heat-treated. TUNGSTEN Tungsten, as an alloy in steel, has been known and used for a longtime. The celebrated and ancient damascus steel being a form oftungsten-alloy steel. Tungsten and its effects, however, did notbecome generally realized until Robert Mushet experimented anddeveloped his famous mushet steel and the many improvement madesince that date go to prove how little Mushet himself understoodthe peculiar effects of tungsten as an alloy. Tungsten acts on steel in a similar manner to carbon, that is, it increases its hardness, but is much less effective than carbonin this respect. If the percentage of tungsten and manganese ishigh, the steel will be hard after cooling in the air. This isimpossible in a carbon steel. It was this combination that Mushetused in his well-known "air-hardening" steel. The principal use of tungsten is in high-speed tool steel, buthere a high percentage of manganese is distinctly detrimental, making the steel liable to fire crack, very brittle and weak inthe body, less easily forged and annealed. Manganese should bekept low and a high percentage of chromium used instead. Tools of tungsten-chromium steels, when hardened, retain theirhardness, even when heated to a dark cherry red by the friction ofthe cutting or the heat arising from the chips. This characteristicled to the term "red-hardness, " and it is this property that hasmade possible the use of very high cutting speeds in tools madeof the tungsten-chromium alloy, that is, "high-speed" steel. Tungsten steels containing up to 6 per cent do not have the propertyof red hardness any more than does carbon tool steel, providingthe manganese or chromium is low. When chromium is alloyed with tungsten, a very definite red-hardnessis noticed with a great increase of cutting efficiency. The maximumred-hardness seems to be had with steels containing 18 per centtungsten, 5. 5 per cent chromium and 0. 70 per cent carbon. Very little is known of the actual function of tungsten, althougha vast amount of experimental work has been done. It is possiblethat when the effect of tungsten with iron-carbon alloys is betterknown, a greater improvement can be expected from these steels. Tungsten has been tried and is still used by some steel manufacturersfor making punches, chisels, and other impact tools. It has alsobeen used for springs, and has given very good results, althoughother less expensive alloys give equally good results, and arein some instances, better. Tungsten is largely used in permanent magnets. In this, its actionis not well understood. In fact, the reason why steel becomes apermanent magnet is not at all understood. Theories have been evolved, but all are open to serious questioning. The principal effect oftungsten, as conceded by leading authorities, is that it distinctlyretards separation of the iron-carbon solution, removing the lowestrecalescent point down to atmospheric temperature. A peculiar property of tungsten steels is that if a heating temperatureof 1, 750°F. Is not exceeded, the cooling curves indicate but onecritical point at about 1, 350°F. But when the heating temperatureis raised above 1, 850°F. , this critical point is nearly if notquite suppressed, while a lower critical point appears and growsenormously in intensity at a temperature between 660 and 750°F. The change in the critical ranges, which is produced by heatingtungsten steels to over 1, 850°F. , is the real cause of the red-hardproperties of these alloys. Its real nature is not understood, and there is no direct evidence to show what actually happens atthese high temperatures. It may readily be understood that an alloy containing four essentialelements, namely: iron, carbon, tungsten and chromium, is one whosestudy presents problems of extreme complexity. It is possible thatcomplex carbides may be formed, as in chromium steels, and thatcompounds between iron and tungsten exist. Behavior of thesecombinations on heating and cooling must be better known beforewe are able to explain many peculiarities of tungsten steels. MOLYBDENUM Molybdenum steels have been made commercially for twenty-five years, but they have not been widely exploited until since the war. Verylarge resources of molybdenum have been developed in America, andthe mining companies who are equipped to produce the metal arevery active in advertising the advantages of molybdenum steels. It was early found that 1 part molybdenum was the equivalent of from2 to 2-1/2 parts of tungsten in tool steels, and magnet steels. Itfell into disrepute as an alloy for high-speed tool steel, however, because it was found that the molybdenum was driven out of thesurface of the tool during forging and heat treating. Within the last few years it has been found that the presence ofless than 1 per cent of molybdenum greatly enhances certain propertiesof heat-treated carbon and alloy steels used for automobiles andhigh-grade machinery. In general, molybdenum when added to an alloy steel, increases thefigure for reduction of area, which is considered a good measureof "toughness. " Molybdenum steels are also relatively insensibleto variations in heat treatment; that is to say, achromium-nickel-molybdenum steel after quenching in oil from 1, 450°F. May be drawn at any temperature between 900 and 1, 100°F. Withsubstantially the same result (static tensile properties and hardness). SILICON Silicon prevents, to a large extent, defects such as gas bubblesor blow holes forming while steel is solidifying. In fact, steelafter it has been melted and before it has been refined, is "wild"and "gassy. " That is to say, if it would be cast into molds itwould froth up, and boil all over the floor. A judicious amountof silicon added to the metal just before pouring, prevents thisaction--in the words of the steel maker, silicon "kills" the steel. If about 1. 75 per cent metallic silicon remains in a 0. 65 carbonsteel, it makes excellent springs. PHOSPHORUS Phosphorus is one of the impurities in steel, and it has been theobject of steel makers for years to eliminate it. On cheap gradesof steel, not subject to any abnormal strain or stress, 0. 1 percent phosphorus is not objectionable. High phosphorus makes steel"cold short, " i. E. , brittle when cold or moderately warm. SULPHUR Sulphur is another impurity and high sulphur is even a greaterdetriment to steel than phosphorus. High sulphur up to 0. 09 percent helps machining properties, but has a tendency to make thesteel "hot short, " i. E. , subject to opening up cracks and seamsat forging or rolling heats. Sulphur should never exceed 0. 06 percent nor phosphorus 0. 08 per cent. Steel used for tool purposes should have as low phosphorus and sulphurcontents as possible, not over 0. 02 per cent. We can sum up the various factors something as follows for readyreference. The ingredient Its effect Iron The basis of steel Carbon The determinative Sulphur A strength sapper Phosphorus The weak link Oxygen A strength destroyer Manganese For strength Nickel For strength and toughness Tungsten Hardener and heat resister Chromium For resisting shocks Vanadium Purifier and fatigue resister Silicon Impurity and hardener Titanium Removes nitrogen and oxygen Molybdenum Hardener and heat resister Aluminum Kills or deoxidizes steel PROPERTIES OF ALLOY STEELS The following table shows the percentages of carbon, manganese, nickel, chromium and vanadium in typical steel alloys for engineeringpurposes. It also gives the elastic limit, tensile strength, elongationand reduction of area of the various alloys, all being given the sameheat treatment with a drawing temperature of 1, 100°F. (600°C. ). Thespecimens were one inch rounds machined after heat treatment. Tungsten is not shown in the table because it is seldom used inengineering construction steels and then usually in combinationwith chromium. Tungsten is used principally for the magnets ofmagnetos, to some extent in the manufacture of hacksaws, and forspecial tool steels. TABLE I. --PROPERTIES OF ALLOY STEELS------------------------------------------------------------------------------ \Manganese, / \Chromium, / |Elastic|Tensile |Elongation|ReductionCarbon, \ per /Nickel, \ per /Vanadium, |limit, |Strength, |in 2 in. , | of area, per | cent | per | cent |per cent |lb. Per|lb. Per |per cent | per cent cent | | cent | | |sq. In. |sq. In. | |-------|------|-------|------|---------|-------|---------|----------|--------- 0. 27 | 0. 55 | | | | 49, 000| 80, 000 | 30 | 65 0. 27 | 0. 47 | | | 0. 26 | 66, 000| 98, 000 | 25 | 52 0. 36 | 0. 42 | | | | 58, 000| 90, 000 | 27 | 60 0. 34 | 0. 87 | | | 0. 13 | 82, 500| 103, 000 | 22 | 57 0. 45 | 0. 50 | | | | 65, 000| 96, 000 | 22 | 52 0. 43 | 0. 60 | | | 0. 32 | 96, 000| 122, 000 | 21 | 52 0. 47 | 0. 90 | | | 0. 15 |102, 000| 127, 500 | 23 | 58 0. 30 | 0. 60 | 3. 40 | | | 75, 000| 105, 000 | 25 | 67 0. 33 | 0. 63 | 3. 60 | | 0. 25 |118, 000| 142, 000 | 17 | 57 0. 30 | 0. 49 | 3. 60 | 1. 70 | |119, 000| 149, 500 | 21 | 60 0. 25 | 0. 47 | 3. 47 | 1. 60 | 0. 15 |139, 000| 170, 000 | 18 | 53 0. 25 | 0. 50 | 2. 00 | 1. 00 | |102, 000| 124, 000 | 25 | 70 0. 38 | 0. 30 | 2. 08 | 1. 16 | |120, 000| 134, 000 | 20 | 57 0. 42 | 0. 22 | 2. 14 | 1. 27 | 0. 26 |145, 000| 161, 500 | 16 | 53 0. 36 | 0. 61 | 1. 46 | 0. 64 | |117, 600| 132, 500 | 16 | 58 0. 36 | 0. 50 | 1. 30 | 0. 75 | 0. 16 |140, 000| 157, 500 | 17 | 54 0. 30 | 0. 50 | | 0. 80 | | 90, 000| 105, 000 | 20 | 50 0. 23 | 0. 58 | | 0. 82 | 0. 17 |106, 000| 124, 000 | 21 | 66 0. 26 | 0. 48 | | 0. 92 | 0. 20 |112, 000| 137, 000 | 20 | 61 0. 35 | 0. 64 | | 1. 03 | 0. 22 |132, 500| 149, 500 | 16 | 54 0. 50 | 0. 92 | | 1. 02 | 0. 20 |170, 000| 186, 000 | 15 | 45------------------------------------------------------------------------------ NON-SHRINKING, OIL-HARDENING STEELS Certain steels have a very low rate of expansion and contractionin hardening and are very desirable for test plugs, gages, punchesand dies, for milling cutters, taps, reamers, hard steel bushingsand similar work. It is recommended that for forging these steels it be heated slowlyand uniformly to a bright red, but not in a direct flame or blast. Harden at a dull red heat, about 1, 300°F. A clean coal or cokefire, or a good muffle-gas furnace will give best results. Fishoil is good for quenching although in some cases warm water willgive excellent results. The steel should be kept moving in the bathuntil perfectly cold. Heated and cooled in this way the steel isvery tough, takes a good cutting edge and has very little expansionor contraction which makes it desirable for long taps where theaccuracy of lead is important. The composition of these steels is as follows: Per cent Manganese 1. 40 to 1. 60 Carbon 0. 80 to 0. 90 Vanadium 0. 20 to 0. 25 [Illustration: FIG. 13. --Effect of copper in steel. ] EFFECT OF A SMALL AMOUNT OF COPPER IN MEDIUM-CARBON STEEL This shows the result of tests by C. R. Hayward and A. B. Johnstonon two types of steel: one containing 0. 30 per cent carbon, 0. 012per cent phosphorus, and 0. 860 per cent copper, and the other 0. 365per cent carbon, 0. 053 per cent phosphorus, and 0. 030 per centcopper. The accompanying chart in Fig. 13 shows that high-coppersteel has decided superiority in tensile strength, yield point andultimate strength, while the ductility is practically the same. Hardness tests by both methods show high-copper steel to be harderthan low-copper, and the Charpy shock tests show high-copper steelalso superior to low-copper. The tests confirm those made by Stead, showing that the behavior of copper steel resembles that of nickelsteel. The high-copper steels show finer grain than the low-copper. The quenched and drawn specimens of high-copper steel were foundto be slightly more martensitic. HIGH-CHROMIUM OR RUST-PROOF STEEL High-chromium, or what is called stainless steel containing from11 to 14 per cent chromium, was originally developed for cutlerypurposes, but has in the past few years been used to a considerableextent for exhaust valves in airplane engines because of its resistanceto scaling at high temperatures. Percentage Carbon 0. 20 to 0. 40 Manganese, not to exceed 0. 50 Phosphorus, not to exceed 0. 035 Sulphur, not to exceed 0. 035 Chromium 11. 50 to 14. 00 Silicon, not to exceed 0. 30 The steel should be heated slowly and forged at a temperature above1, 750°F. Preferably between 1, 800 and 2, 200°F. If forged at temperaturesbetween 1, 650 and 1, 750°F. There is considerable danger of rupturingthe steel because of its hardness at red heat. Owing to theair-hardening property of the steel, the drop-forgings should betrimmed while hot. Thin forgings should be reheated to rednessbefore trimming, as otherwise they are liable to crack. The forgings will be hard if they are allowed to cool in air. Thishardness varies over a range of from 250 to 500 Brinell, dependingon the original forging temperature. ANNEALING can be done by heating to temperatures ranging from 1, 290to 1, 380°F. And cooling in air or quenching in water or oil. Afterthis treatment the forgings will have a hardness of about 200 Brinelland a tensile strength of 100, 000 to 112, 000 lb. Per square inch. If softer forgings are desired they can be heated to a temperatureof from 1, 560 to 1, 650°F. And cooled very slowly. Although softerthe forgings will not machine as smoothly as when annealed at thelower temperature. HARDENING. --The forgings can be hardened by cooling in still airor quenching in oil or water from a temperature between 1, 650 and1, 750°F. The physical properties do not vary greatly when the carbon iswithin the range of composition given, or when the steel is hardenedand tempered in air, oil, or water. When used for valves the following specification of physical propertieshave been used: Yield point, pounds per square inch 70, 000 Tensile strength, pounds per square inch 90, 000 Elongation in 2 in. , per cent 18 Reduction of area, per cent 50 The usual heat treatment is to quench in oil from 1, 650°F. Andtemper or draw at 1, 100 to 1, 200°F. One valve manufacturer statedthat valves of this steel are hardened by heating the previouslyannealed valves to 1, 650°F. And cooling in still air. This treatmentgives a scleroscope hardness of about 50. In addition to use in valves this steel should prove very satisfactoryfor shafting for water-pumps and other automobile parts subject toobjectionable corrosion. TABLE 2. --COMPARISON OF PHYSICAL PROPERTIES FOR HIGH-CHROMIUM STEELS OF DIFFERENT CARBON CONTENT -------------------------------------------------------------------------- | C 0. 20 | C 0. 27 | C 0. 50 | Mn 0. 45 | Mn 0. 50 | | Cr 12. 56 | Cr 12. 24 | Cr 14. 84-----------------------------------------|----------|----------|----------Quenched in oil from degrees Fahrenheit | 1, 600 | 1, 600 | 1, 650Tempered at degrees Fahrenheit | 1, 160 | 1, 080 | 1, 100Yield point, pounds per square inch | 78, 300 | 75, 000 | 91, 616Tensile strength, pounds per square inch | 104, 600 | 104, 250 | 123, 648Elongation in 2 in. , per cent | 25. 0 | 23. 5 | 14. 5Reduction of area, per cent | 52. 5 | 51. 4 | 33. 5-------------------------------------------------------------------------- TABLE 3. --COMPARISON OF PHYSICAL PROPERTIES BETWEEN AIR, OIL AND WATER-HARDENED STEEL HAVING CHEMICAL ANALYSIS IN PERCENTAGE OF------------------------------------------------------------------------- Carbon 0. 24 Manganese 0. 30 Phosphorus 0. 035 Sulphur 0. 035 Chromium 12. 85 Silicon 0. 20 ------------------------------------------------------------------------- | Hardened | | Elastic | Tensile | |Hardening| from, | Tempered | limit, |strength, |Elongation|Reductionmedium | degrees |at, degrees| per lb. |lb. Per | in 2 in. |of area, |Fahrenheit|Fahrenheit | sq. In. | sq. In. | per cent |per cent---------|----------|-----------|---------|---------|----------|--------- | | 930 | 158, 815 | 192, 415 | 13. 0 | 40. 5 | | 1, 100 | 99, 680 | 120, 065 | 21. 0 | 59. 2 Air | 1, 650 | 1, 300 | 70, 785 | 101, 250 | 26. 0 | 64. 6 | | 1, 380 | 66, 080 | 98, 335 | 28. 0 | 63. 6 | | 1, 470 | 70, 785 | 96, 990 | 27. 0 | 64. 7---------|----------|-----------|---------|---------|----------|--------- | | 930 | 163, 070 | 202, 720 | 8. 0 | 18. 2 Oil | 1, 650 | 1, 100 | 88, 255 | 116, 480 | 20. 0 | 56. 9 | | 1, 300 | 77, 950 | 105, 505 | 25. 5 | 63. 8 | | 1, 380 | 88, 255 | 98, 785 | 27. 0 | 66. 3---------|----------|-----------|---------|---------|----------|--------- | | 930 | 158, 815 | 202, 050 | 12. 0 | 34. 2 Water | 1, 650 | 1, 100 | 90, 270 | 120, 735 | 22. 0 | 59. 8 | | 1, 300 | 66, 080 | 102, 590 | 25. 8 | 64. 8 | | 1, 380 | 67, 200 | 97, 890 | 27. 0 | 65. 2------------------------------------------------------------------------- This steel can be drawn into wire, rolled into sheets and stripsand drawn into seamless tubes. CORROSION. --This steel like any other steel when distorted by coldworking is more sensitive to corrosion and will rust. Rough cutsurfaces will rust. Surfaces finished with a fine cut are lessliable to rust. Ground and polished surfaces are practically immuneto rust. When chromium content is increased to 16 to 18 per cent and siliconis added, from 2 to 4 per cent, this steel becomes rust proof inits raw state, as soon as the outside surface is removed. It doesnot need to be heat-treated in any way. These compositions areboth patented. S. A. E. STANDARD STEELS The following steel specifications are considered standard by theSociety of Automotive Engineers and represents automobile practice inthis country. These tables give the S. A. E. Number, the compositionof the steel and the heat treatment. These are referred to byletter--the heat treatments being given in detail on pages 134to 137 in Chap. 8. It should be noted that the percentage of thedifferent ingredients desired is the mean, or halfway between theminimum and maximum. TABLE 4. --CARBON STEELS------------------------------------------------------------------------------ S. A. E. | Carbon | Manganese | | |Specification|(minimum and |(minimum and |Phosphorus| Sulphur | Heat no. | maximum) | maximum) |(maximum) |(maximum)| treatment-------------|-------------|-------------|----------|---------|--------------- 1, 010 | 0. 05 to 0. 15| 0. 30 to 0. 60| 0. 045 | 0. 05 |Quench at 1, 500 1, 020 | 0. 15 to 0. 25| 0. 30 to 0. 60| 0. 045 | 0. 05 | A or B 1, 025 | 0. 20 to 0. 30| 0. 50 to 0. 80| 0. 045 | 0. 05 | H | | | | | 1, 035 | 0. 30 to 0. 40| 0. 50 to 0. 80| 0. 045 | 0. 05 | H, D or E 1, 045 | 0. 40 to 0. 50| 0. 50 to 0. 80| 0. 045 | 0. 05 | H, D or E 1, 095 | 0. 90 to 1. 05| 0. 25 to 0. 50| 0. 040 | 0. 05 | F------------------------------------------------------------------------------ TABLE 5. --SCREW STOCK--------------------------------------------------------------------------- S. A. E. | Carbon | Manganese | Phosphorus | SulphurSpecification no. | | | (maximum) |-----------------|--------------|--------------|------------|-------------- 1, 114 | 0. 08 to 0. 20 | 0. 30 to 0. 80 | 0. 12 | 0. 06 to 0. 12--------------------------------------------------------------------------- TABLE 6. --NICKEL STEELS----------------------------------------------------------------------------- S. A. E. | | | Phosphorus| | |Specification | | | (maximum) | | | no. ---- | \ / | | | Carbon | Manganese | | Sulphur | Nickel | Heat |(minimum and|(minimum and| |(maximum)|(minimum and|treatment | maximum) | maximum) | | | maximum) |---------|------------|------------|-------|---------|------------|---------- 2, 315 |0. 10 to 0. 20|0. 50 to 0. 80| 0. 04 | 0. 045 |3. 25 to 3. 75|G, H or K 2, 320 |0. 15 to 0. 25|0. 50 to 0. 80| 0. 04 | 0. 045 |3. 25 to 3. 75|G, H or K 2, 330 |0. 25 to 0. 35|0. 50 to 0. 80| 0. 04 | 0. 045 |3. 25 to 3. 75| H or K | | | | | | 2, 335 |0. 30 to 0. 40|0. 50 to 0. 80| 0. 04 | 0. 045 |3. 25 to 3. 75| H or K 2, 340 |0. 35 to 0. 45|0. 50 to 0. 80| 0. 04 | 0. 045 |3. 25 to 3. 75| H or K 2, 345 |0. 40 to 0. 50|0. 50 to 0. 80| 0. 04 | 0. 045 |3. 25 to 3. 75| H or K----------------------------------------------------------------------------- TABLE 7. --NICKEL-CHROMIUM STEELS------------------------------------------------------------------------------- S. A. E. | | | Phosphorus| Sulphur | | |Specification| | | (maximum)|(maximum) | | | Heat no. ------ | ------ | ---- | |treatment | Carbon | Manganese | | | Nickel | Chromium \ |(minimum and|(minimum and| | |(minimum and|(minimum and | | maximum) | maximum) | | | maximum) | maximum) |------|------------|------------|----|-----|------------|-------------|-------- 3, 120|0. 15 to 0. 25|0. 50 to 0. 80|0. 04|0. 045|1. 00 to 1. 50|0. 45 to 0. 75*|G, H or D 3, 125|0. 20 to 0. 30|0. 50 to 0. 80|0. 04|0. 045|1. 00 to 1. 50|0. 45 to 0. 75*|H, D or E 3, 130|0. 25 to 0. 35|0. 50 to 0. 80|0. 04|0. 045|1. 00 to 1. 50|0. 45 to 0. 75*|H, D or E | | | | | | | 3, 135|0. 30 to 0. 40|0. 50 to 0 80|0. 04|0. 045|1. 00 to 1. 50|0. 45 to 0 75*|H, D or E 3, 140|0. 35 to 0. 45|0. 50 to 0. 80|0. 04|0. 045|1. 00 to 1. 50|0. 45 to 0. 75*|H, D or E 3, 220|0. 15 to 0. 25|0. 30 to 0. 60|0. 04|0. 040|1. 50 to 2. 00|0. 90 to 1. 25 |G, H or D | | | | | | | 3, 230|0. 25 to 0. 35|0. 30 to 0. 60|0. 04|0. 040|1. 50 to 2. 00|0. 90 to 1. 25 | H or D 3, 240|0. 35 to 0. 45|0. 30 to 0. 60|0. 04|0. 040|1. 50 to 2. 00|0. 90 to 1. 25 | H or D 3, 250|0. 45 to 0. 55|0. 30 to 0. 60|0. 04|0. 040|1. 50 to 2. 00|0. 90 to 1. 25 | M or Q | | | | | | |X3, 315|0. 10 to 0. 20|0. 45 to 0. 75|0. 04|0. 040|2. 75 to 3. 25|0. 60 to 0. 95 | GX3, 335|0. 30 to 0. 40|0. 45 to 0. 75|0. 04|0. 040|2. 75 to 3. 25|0. 60 to 0. 95 | P or RX3, 350|0. 45 to 0. 55|0. 45 to 0. 75|0. 04|0. 040|2. 75 to 3. 25|0. 60 to 0. 95 | P or R | | | | | | | 3, 320|0. 15 to 0. 25|0. 30 to 0. 60|0. 04|0. 040|3. 25 to 3. 75|1. 25 to 1. 75 | L 3, 330|0. 25 to 0. 35|0. 30 to 0. 60|0. 04|0. 040|3. 25 to 3. 75|1. 25 to 1. 75 | P or R 3, 340|0. 35 to 0. 45|0. 30 to 0. 60|0. 04|0. 040|3. 25 to 3. 75|1. 25 to 1. 75 | P or R-------------------------------------------------------------------------------* Another grade of this type of steel is available with chromium contentof 0. 15 per cent to 45 per cent. It has somewhat lower physical properties. TABLE 8. --CHROMIUM STEELS------------------------------------------------------------------------------- S. A. E. | | | | | |Specification| | | | | | no. --- Carbon | Manganese | | | Chromium | |(minimum and|(minimum and|Phosphorus|Sulphur |(minimum and| Heat | maximum) | maximum) |(maximum) |(maximum)| maximum) |treatment---------|------------|------------|----------|---------|------------|--------- 5, 120 |0. 15 to 0. 25| * | 0. 04 | 0. 045 |0. 65 to 0. 85| B 5, 140 |0. 35 to 0. 45| * | 0. 04 | 0. 045 |0. 65 to 0. 85| H or D 5, 165 |0. 60 to 0. 70| * | 0. 04 | 0. 045 |0. 65 to 0. 85| H or D | | | | | | 5, 195 |0. 90 to 1. 05|0. 20 to 0. 45| 0. 03 | 0. 03 |0. 90 to 1. 10|M, P or R 51, 120 |1. 10 to 1. 30|0. 20 to 0. 45| 0. 03 | 0. 03 |0. 90 to 1. 10|M, P or R 5, 295 |0. 90 to 1. 05|0. 20 to 0. 45| 0. 03 | 0. 03 |1. 10 to 1. 30|M, P or R 52, 120 |1. 10 to 1. 30|0. 20 to 0. 45| 0. 03 | 0. 03 |1. 10 to 1. 30|M, P or R---------------------------------------------------------------------------------Two types of steel are available in this class, one with manganese 0. 25to 0. 50 per cent (0. 35 per cent desired), and silicon not over 0. 20 percent; the other with manganese 0. 60 to 0. 80 per cent (0. 70 per centdesired), and silicon 0. 15 to 0. 50 per cent. TABLE 9. --CHROMIUM-VANADIUM STEELS------------------------------------------------------------------------------- S. A. E. | | |Phosphorus| Sulphur | |Vanadium |Specification| | | (maximum)|(maximum)| |(minimum)| no. ------ | -- | / - | | Carbon | Manganese | | | Chromium | | Heat |(minimum and|(minimum and| | |(minimum and| |treatment | maximum) | maximum) | | | maximum) | |------|------------|------------|-------|-------|------------|-------|---------6, 120 |0. 15 to 0. 25|0. 50 to 0. 80| 0. 04 | 0. 04 |0. 80 to 1. 10| 0. 15 | S6, 125 |0. 20 to 0. 30|0. 50 to 0. 80| 0. 04 | 0. 04 |0. 80 to 1. 10| 0. 15 | S or T6, 130 |0. 25 to 0. 35|0. 50 to 0. 80| 0. 04 | 0. 04 |0. 80 to 1. 10| 0. 15 | T or U6, 135 |0. 30 to 0. 40|0. 50 to 0. 80| 0. 04 | 0. 04 |0. 80 to 1. 10| 0. 15 | T or U6, 140 |0. 35 to 0. 45|0. 50 to 0. 80| 0. 04 | 0. 04 |0. 80 to 1. 10| 0. 15 | T or U6, 145 |0. 40 to 0. 50|0. 50 to 0. 80| 0. 04 | 0. 04 |0. 80 to 1. 10| 0. 15 | U6, 150 |0. 45 to 0. 55|0. 50 to 0. 80| 0. 04 | 0. 04 |0. 80 to 1. 10| 0. 15 | U6, 195 |0. 90 to 1. 05|0. 20 to 0. 45| 0. 03 | 0. 03 |0. 80 to 1. 10| 0. 15 U------------------------------------------------------------------------------- TABLE 10. --SILICO-MANGANESE STEELS----------------------------------------------------------------------------- S. A. E. | | | | | |Specification| | | | | | no. ----- Carbon| Manganese | | | Silicon | |(minimum and|(minimum and|Phosphorus|Sulphur |(minimum and| Heat | maximum) | maximum) |(maximum) |(maximum)| maximum) |treatment-------|------------|------------|----------|---------|------------|--------- 9, 250 |0. 45 to 0. 55|0. 60 to 0. 80| 0. 045* | 0. 045 |1. 80 to 2. 10| V 9, 260 |0. 55 to 0. 65|0. 50 to 0. 70| 0. 045* | 0. 045 |1. 50 to 1. 80| V-----------------------------------------------------------------------------* Steel made by the acid process may contain maximum 0. 05 phosphorus. LIBERTY MOTOR CONNECTING RODS The requirements for materials for the Liberty motor connecting rodsare so severe that the methods of securing the desired qualitieswill be of value in other lines. The original specifications calledfor chrome-nickel but the losses due to the difficulty of handlingcaused the Lincoln Motor Company to suggest the substitution ofchrome-vanadium steel, and this was accepted by the Signal Corps. Therods were accordingly made from chromium-vanadium steel, containingcarbon, 0. 30 to 0. 40 per cent; manganese, 0. 50 to 0. 80 per cent;phosphorus, not over 0. 04 per cent; sulphur, not over 0. 04 percent; chromium, 0. 80 to 1. 10 per cent; vanadium, not less than 0. 15per cent. This steel is ordinarily known in the trade as 0. 35 carbonsteel, S. A. E. , specification 6, 135, which provides a first-ratequality steel for structural parts that are to be heat-treated. The fatigue resisting or endurance qualities of this material areexcellent. It has a tensile strength of 150, 000 lb. Minimum persquare inch; elastic limit, 115, 000 lb. Minimum per square inch;elongation, 5 per cent minimum in 2 in. ; and minimum reductionin area, 25 per cent. The original production system as outlined for the manufacturershad called for a heat treatment in the rough-forged state for theconnecting rods, and then semi-machining the rod forgings beforegiving them the final treatment. The Lincoln Motor Company insistedfrom the first that the proper method would be a complete heattreatment of the forging in the rough state, and machining therod after the heat treatment. After a number of trial lots, theSignal Corps acceded to the request and production was immediatelyincreased and quality benefited by the change. This method waslater included in a revised specification issued to all producers. The original system was one that required a great deal of laborper unit output. The Lincoln organization developed a method ofhandling connecting rods whereby five workmen accomplished thesame result that would have required about 30 or 32 by the originalmethod. Even after revising the specification so as to allow completeheat treatments in the rough-forged state, the ordinary methodsemployed in heat-treating would have required 12 to 15 men. Withthe fixtures employed, five men could handle 1, 300 connecting rods, half of which are plain and half, forked, in a working period oflittle over 7 hr. [Illustration: Fig. 14. --Rack for holding rods. ] [Illustration: Fig. 15. --Sliding rods into tank. ] The increase in production was gained by devising fixtures whichenabled fewer men to handle a greater quantity of parts with lesseffort and in less time. In heat-treating the forgings were laid on a rack or loop _A_, Fig. 14, made of 1-1/4-in. Double extra-heavy pipe, bent up withparallel sides about 9 in. Apart, one end being bent straight acrossand the other end being bent upward so as to afford an easy graspfor the hook. Fifteen rods were laid on each loop, there beingfour loops of rods charged into a furnace with a hearth area of 36by 66 in. The rods were charged at a temperature of approximately900°F. They were heated for refining over a period of 3 hr. To1, 625°F. , soaked 15 min, at this degree of heat and quenched insoluble quenching oil. In pulling the heat to quench the rods, the furnace door was raisedand the operator pulls one of the loops _A_, Fig. 15 forward tothe shelf of the furnace, supporting the straight end of the loopby means of the porter bar _B_. They swung the loop of rods aroundfrom the furnace shelf and set the straight end of the loop onthe edge of the quenching tank, then raise the curved end _C_, by means of their hook _D_ so that all the rods on the loop slideinto the oil bath. Before the rods cooled entirely, the baskets in the quenching tankwere raised and the oil allowed to partly drain off the forgings, and they were stacked on curved-end loops or racks and charged intothe furnace for the second or hardening heat. The temperature ofthe furnace was raised in 1-1/2 hr. To 1, 550°F. , the rods soakedfor 15 min. At this degree of heat and quenched in the same manneras above. They were again drained while yet warm, placed on loops and chargedinto the furnace for the third or tempering heat. The temperature ofthe furnace was brought to 1, 100°F. In 1 hr. , and the rods soaked atthis degree of heat for 1 hr. They were then removed from the furnacethe same as for quenching, but were dumped onto steel platformsinstead of into the quenching oil, and allowed to cool on thesesteel platforms down to the room temperature. PICKLING THE FORGINGS The forgings were then pickled in a hot solution of either nitercake or sulphuric acid and water at a temperature of 170°F. , andusing a solution of about 25 per cent. The solution was maintainedat a constant point by taking hydrometer readings two or threetimes a day, maintaining a reading of about 1. 175. Sixty forked orone hundred single rods were placed in wooden racks and immersedin a lead-lined vat 30 by 30 by 5 ft. Long. The rack was loweredor lifted by means of an air hoist and the rods were allowed tostay in solution from 1/2 to 1 hr. , depending on the amount ofscale. The rods were then swung and lowered in the rack into runninghot water until all trace of the acid was removed. The rod was finally subjected to Brinell test. This shows whetheror not the rod has been heat-treated to the proper hardness. Ifthe rods did not read between 241 and 277, they were re-treateduntil the proper hardness is obtained. CHAPTER IV APPLICATION OF LIBERTY ENGINE MATERIALS TO THE AUTOMOTIVE INDUSTRY[1] [Footnote 1: Paper presented at the summer meeting of the S. A. E. At Ottawa Beach in June, 1919. ] The success of the Liberty engine program was an engineering achievementin which the science of metallurgy played an important part. Thereasons for the use of certain materials and certain treatmentsfor each part are given with recommendations for their applicationto the problems of automotive industry. The most important items to be taken into consideration in theselection of material for parts of this type are uniformity andmachineability. It has been demonstrated many times that the ordinarygrades of bessemer screw stock are unsatisfactory for aviationpurposes, due to the presence of excessive amounts of unevenlydistributed phosphorus and sulphide segregations. For this reason, material finished by the basic open hearth process was selected, in accordance with the following specifications: Carbon, 0. 150 to0. 250 per cent; manganese, 0. 500 to 0. 800 per cent; phosphorus, 0. 045 maximum per cent; sulphur, 0. 060 to 0. 090 per cent. This material in the cold-drawn condition will show: Elastic limit, 50, 000 lb. Per square inch, elongation in 2 in. , 10 per cent, reductionof area, 35 per cent. This material gave as uniform physical properties as S. A. E. No. 1020 steel and at the same time was sufficiently free cutting toproduce a smooth thread and enable the screw-machine manufacturersto produce, to the same thread limits, approximately 75 per centas many parts as from bessemer screw stock. There are but seven carbon-steel carbonized parts on the Libertyengine. The most important are the camshaft, the camshaft rockerlever roller and the tappet. The material used for parts of thistype was S. A. E. No. 1, 020 steel, which is of the following chemicalanalysis: Carbon 0. 150 to 0. 250 per cent; manganese, 0. 300 to 0. 600per cent; phosphorus, 0. 045 maximum per cent; sulphur, 0. 050 maximumper cent. The heat treatment consisted in carbonizing at a temperature offrom 1, 650 to 1, 700°F. For a sufficient length of time to securethe proper depth of case, cool slowly or quench; then reheat to atemperature of 1, 380 to 1, 430°F. To refine the grain of the case, and quench in water. The only thing that should limit the rate ofcooling from the carbonizing heat is distortion. Camshaft rockerlever rollers and tappets, as well as gear pins, were quencheddirectly from the carbonizing heat in water and then case-refinedand rehardened by quenching in water from a temperature of from1, 380 to 1, 430°F. The advantage of direct quenching from the carbonizing heat isdoubtless one of economy, and in many cases will save the costof a reheating. Specifications for case hardening, issued by theSociety of Automotive Engineers, have lately been revised; whereasthey formerly called for a slow cooling, they now permit a quenchingfrom the pot. Doubtless this is a step in advance. Warpage causedby quenching can be reduced to a minimum by thoroughly annealingthe stock before any machine work is done on it. Another advantage obtained from rapid cooling from the carbonizingheat is the retaining of the majority of the excess cementite insolution which produces a less brittle case and by so doing reducesthe liability of grinding checks and chipping of the case in actualservice. In the case of the camshaft, it is not possible to quench directlyfrom the carbonizing heat because of distortion and therefore excessivebreakage during straightening operations. All Liberty camshaftswere cooled slowly from carbonizing heat and hardened by a singlereheating to a temperature of from 1, 380 to 1, 430°F. And quenchingin water. Considerable trouble has always been experienced in obtaining uniformhardness on finished camshafts. This is caused by insufficientwater circulation in the quenching tank, which allows the formationof steam pockets to take place, or by decarbonization of the caseduring heating by the use of an overoxidizing flame. Another cause, which is very often overlooked, is due to the case being ground offone side of cam more than the other and is caused by the roughingmaster cam being slightly different from the finishing master cam. Great care should be taken to see that this condition does not occur, especially when the depth of case is between 1/32 and 3/64 in. CARBON-STEEL FORGINGS Low-stressed, carbon-steel forgings include such parts as carburetercontrol levers, etc. The important criterion for parts of this typeis ease of fabrication and freedom from over-heated and burnedforgings. The material used for such parts was S. A. E. No. 1, 030steel, which is of the following chemical composition: Carbon, 0. 250to 0. 350 per cent; manganese, 0. 500 to 0. 800 per cent; phosphorus, 0. 045 maximum per cent; sulphur, 0. 050 maximum per cent. To obtain good machineability, all forgings produced from thissteel were heated to a temperature of from 1, 575 to 1, 625°F. Torefine the grain of the steel thoroughly and quenched in waterand then tempered to obtain proper machineability by heating to atemperature of from 1, 000 to 1, 100°F. And cooled slowly or quenched. Forgings subjected to this heat treatment are free from hard spotsand will show a Brinell hardness of 177 to 217, which is proper forall ordinary machining operations. Great care should be taken notto use steel for parts of this type containing less than 0. 25 percent carbon, because the lower the carbon the greater the liabilityof hard spots, and the more difficult it becomes to eliminate them. The only satisfactory method so far in commercial use for theelimination of hard spots is to give forgings a very severe quenchfrom a high temperature followed by a proper tempering heat tosecure good machine ability as outlined above. The important carbon-steel forgings consisted of the cylinders, the propeller-hubs, the propeller-hub flange, etc. The materialused for parts of this type was S. A. E. No. 1, 045 steel, whichis of the following chemical composition: Carbon, 0. 400 to 0. 500per cent; manganese, 0. 500 to 0. 800 per cent; phosphorus, 0. 045maximum per cent; sulphur, 0. 050 maximum per cent. All forgings made from this material must show, after heat treatment, the following minimum physical properties: Elastic limit, 70, 000;lb. Per square inch, elongation in 2 in. , 18 per cent, reductionof area, 45; per cent, Brinell hardness, 217 to 255. To obtain these physical properties, the forgings were quenched inwater from a temperature of 1, 500 to 1, 550°F. , followed by temperingto meet proper Brinell requirements by heating to a temperatureof 1, 150 to 1, 200°F. And cooled slowly or quenched. No troubleof any kind was ever experienced with parts of this type. The principal carbon-steel pressed parts used on the Liberty enginewere the water jackets and the exhaust manifolds. The materialused for parts of this type was S. A. E. No. 1, 010 steel, whichis of the following chemical composition: Carbon, 0. 05 to 0. 15 percent; manganese, 0. 30 to 0. 60 per cent; phosphorus, 0. 045 maximumper cent; sulphur, 0. 045 maximum per cent. No trouble was experienced in the production of any parts fromthis material with the exception of the water jacket. Due to theparticular design of the Liberty cylinder assembly, many failuresoccurred in the early days, due to the top of the jacket crackingwith a brittle fracture. It was found that these failures werecaused primarily from the use of jackets which showed small scratchesor die marks at this joint and secondarily by improper annealing ofthe jackets themselves between the different forming operations. By a careful inspection for die marks and by giving the jackets1, 400°F. Annealing before the last forming operation, it was possibleto completely eliminate the trouble encountered. HIGHLY STRESSED PARTS The highly stressed parts on the Liberty engine consisted of theconnecting-rod bolt, the main-bearing bolt, the propeller-hub key, etc. The material used for parts of this type was selected at theoption of the manufacturer from standard S. A. E. Steels, thecomposition of which are given in Table 11. TABLE 11. --COMPOSITION OF S. A. E. STEELS Nos. 2, 330, 3, 135 AND 6, 130 Steel No 2, 330 3, 135 6, 130 Carbon, minimum 0. 250 0. 300 0. 250 Carbon, maximum 0. 350 0. 400 0. 450 Manganese, minimum 0. 500 0. 500 0. 500 Manganese, maximum 0. 800 0. 800 0. 800 Phosphorus, maximum 0. 045 0. 040 0. 040 Sulphur, maximum 0. 045 0. 045 0. 045 Nickel, minimum 3. 250 1. 000 Nickel, maximum 3. 750 1. 500 Chromium, minimum 0. 450 0. 800 Chromium, maximum 0. 750 1. 100 Vanadium, minimum 0. 150 All highly stressed parts on the Liberty engine must show, afterheat treatment, the following minimum physical properties: Elasticlimit, 100, 000 lb. Per square inch; elongation in 2 in. , 16 percent; reduction of area, 45 per cent; scleroscope hardness, 40to 50. The heat treatment employed to obtain these physical propertiesconsisted in quenching from a temperature of 1, 525 to 1, 575°F. , inoil, followed by tempering at a temperature of from 925 to 975°F. Due to the extremely fine limits used on all threaded parts forthe Liberty engine, a large percentage of rejection was due towarpage and scaling of parts. To eliminate this objection, manyof the Liberty engine builders adopted the use of heat-treatedand cold-drawn alloy steel for their highly stressed parts. Onall sizes up to and including 3/8 in. In diameter, the physicalproperties were secured by merely normalizing the hot-rolled barsby heating to a temperature of from 1, 525 to 1, 575°F. , and coolingin air, followed by the usual cold-drawing reductions. For partsrequiring stock over 3/8 in. In diameter, the physical propertiesdesired were obtained by quenching and tempering the hot-rolled barsbefore cold-drawing. It is the opinion that the use of heat-treatedand cold-drawn bars is very good practice, provided proper inspectionis made to guarantee the uniformity of heat treatment and, therefore, the uniformity of the physical properties of the finished parts. The question has been asked many times by different manufacturers, asto which alloy steel offers the best machineability when heat-treatedto a given Brinell hardness. The general consensus of opinion amongthe screw-machine manufacturers is that S. A. E. No. 6, 130 steelgives the best machineability and that S. A. E. No. 2, 330 steelwould receive second choice of the three specified. In the finishing of highly stressed parts for aviation engines, extreme care must be taken to see that all tool marks are eliminated, unless they are parallel to the axis of strain, and that properradii are maintained at all changes of section. This is of theutmost importance to give proper fatigue resistance to the partin question. GEARS The material used for all gears on the Liberty engine was selectedat the option of the manufacturer from the following standard S. A. E. Steels, the composition of which are given in Table 12, TABLE 12. --COMPOSITION OF STEELS NOS. X-3, 340 AND 6, 140 Steel No X-3, 340 6, 140 Carbon, minimum 0. 350 0. 350 Carbon, maximum 0. 450 0. 450 Manganese, minimum 0. 450 0. 500 Manganese, maximum 0. 750 0. 800 Phosphorus, maximum 0. 040 0. 040 Sulphur, maximum 0. 045 0. 045 Nickel, minimum 2. 750 Nickel, maximum 3. 250 Chromium, minimum 0. 700 0. 800 Chromium, maximum 0. 950 1. 100 Vanadium, minimum 0. 150 All gears were heat-treated to a scleroscope hardness of from 55to 55. The heat treatment used to secure this hardness consistedin quenching the forgings from a temperature of 1, 550 to 1, 600°F. In oil and annealing for good machineability at a temperature offrom 1, 300 to 1, 350°F. Forgings treated in this manner showed aBrinell hardness of from 177 to 217. RATE OF COOLING At the option of the manufacturer, the above treatment of gearforgings could be substituted by normalizing the forgings at atemperature of from 1, 550 to 1, 600°F. The most important criterionfor proper normalizing, consisted in allowing the forgings to coolthrough the critical temperature of the steel, at a rate not to exceed50°F. Per hour. For the two standard steels used, this consisted incooling from the normalizing temperature down to a temperatureof 1, 100°F. , at the rate indicated. Forgings normalized in thismanner will show a Brinell hardness of from 177 to 217. The questionhas been repeatedly asked as to which treatment will produce thehigher quality finished part. In answer to this I will state thaton simple forgings of comparatively small section, the normalizingtreatment will produce a finished part which is of equal quality tothat of the quenched and annealed forgings. However, in the case ofcomplex forgings, or those of large section, more uniform physicalproperties of the finished part will be obtained by quenching andannealing the forgings in the place of normalizing. The heat treatment of the finished gears consisted of quenchingin oil from a temperature of from 1, 420 to 1, 440°F. For the No. X-3, 340 steel, or from a temperature of from 1, 500 to 1, 540°F. For No. 6, 140 steel, followed by tempering in saltpeter or in anelectric furnace at a temperature of from 650 to 700°F. The question has been asked by many engineers, why is the comparativelylow scleroscope hardness specified for gears? The reason for this isthat at best the life of an aviation engine is short, as compared withthat of an automobile, truck or tractor, and that shock resistanceis of vital importance. A sclerescope hardness of from 55 to 65will give sufficient resistance to wear to prevent replacementsduring the life of an aviation engine, while at the same time thishardness produces approximately 50 per cent greater shock-resistingproperties to the gear. In the case of the automobile, truck ortractor, resistance to wear is the main criterion and for thatreason the higher hardness is specified. Great care should be taken in the design of an aviation enginegear to eliminate sharp corners at the bottom of teeth as wellas in keyways. Any change of section in any stressed part of anaviation engine must have a radius of at least 1/32 in. To giveproper shock and fatigue resistance. This fact has been demonstratedmany times during the Liberty engine program. CONNECTING RODS The material used for all connecting rods on the Liberty enginewas selected at the option of the manufacturer from one of twostandard S. A. E. Steels, the composition of which are given inTable 13. TABLE 13. --COMPOSITION OF STEELS NOS. X-3, 335 AND 6, 135 Steel No. X-3, 335 6, 135 Carbon, minimum 0. 300 0. 300 Carbon, maximum 0. 400 0. 400 Manganese, minimum 0. 450 0. 500 Manganese, maximum 0. 750 0. 800 Phosphorus, maximum 0. 040 0. 040 Sulphur, maximum 0. 045 0. 045 Nickel, minimum 2. 750 Nickel, maximum 3. 250 Chromium, minimum 0. 700 0. 800 Chromium, maximum 0. 950 1. 100 Vanadium minimum 0. 150 All connecting rods were heat-treated to show the following minimumphysical properties; Elastic limit, 105, 000 lb. Per square inch:elongation in 2 in. , 17. 5; per cent, reduction of area 50. 0; percent. , Brinell hardness, 241 to 277. The heat treatment used to secure these physical properties consistedin normalizing the forgings at a temperature of from 1, 550 to 1, 600°F. , followed by cooling in the furnace or in air. The forgings were thenquenched in oil from a temperature of from 1, 420 to 1, 440°F. For theNo. X-3, 335 steel, or from a temperature of from 1, 500 to 1, 525°F. For No. 6, 135 steel, followed by tempering at a temperature of from1, 075 to 1, 150°F. At the option of the manufacturer, the normalizingtreatment could be substituted by quenching the forgings from atemperature of from 1, 550 to 1, 600°F. , in oil, and annealing forthe best machineability at a temperature of from 1, 300 to 1, 350°F. The double quench, however, did not prove satisfactory on No. X-3, 335steel, due to the fact that it was necessary to remove forgingsfrom the quenching bath while still at a temperature of from 300to 500°F. To eliminate any possibility of cracking. In view of thefact that this practice is difficult to carry out in the averageheat-treating plant, considerable trouble was experienced. The most important criterion in the production of aviation engineconnecting rods is the elimination of burned or severely overheatedforgings. Due to the particular design of the forked rod, considerabletrouble was experienced in this respect because of the necessityof reheating the forgings before they are completely forged. Asa means of elimination of burned forgings, test lugs were forgedon the channel section as well as on the top end of fork. Afterthe finish heat treatment, these test lugs were nicked and brokenand the fracture of the steel carefully examined. This precautionmade it possible to eliminate burned forgings as the test lugs wereplaced on sections which would be most likely to become burned. There is a great difference of opinion among engineers as to whatphysical properties an aviation engine connecting rod should have. Many of the most prominent engineers contend that a connecting rodshould be as stiff as possible. To produce rods in this manner inany quantity, it is necessary for the final heat treatment to be madeon the semi-machined rod. This practice would make it necessary for alarger percentage of the semi-machined rods to be cold-straightenedafter the finish heat treatment. The cold-straightening operationon a part having important functions to perform as a connectingrod is extremely dangerous. In view of the fact that a connecting rod functions as a strut, it is considered that this part should be only stiff enough toprevent any whipping action during the running of the engine. Thegreater the fatigue-resisting property that one can put into therod after this stiffness is reached, the longer the life of therod will be. This is the reason for the Brinell limits mentionedbeing specified. In connection with the connecting rod, emphasis must be laid on theimportance of proper radii at all changes of section. The connectingrods for the first few Liberty engines were machined with sharpcorners at the point where the connecting-rod bolt-head fits onassembly. On the first long endurance test of a Liberty engineequipped with rods of this type, failure resulted from fatiguestarting at this point. It is interesting to note that every rod onthe engine which did not completely fail at this point had startedto crack. The adoption of a 1/32-in. Radius at this point completelyeliminated fatigue failures on Liberty rods. CRANKSHAFT The crankshaft was the most highly stressed part of the entireLiberty engine, and, therefore, every metallurgical precautionwas taken to guarantee the quality of this part. The material usedfor the greater portion of the Liberty crankshafts produced wasnickel-chromium steel of the following chemical composition: Carbon, 0. 350 to 0. 450 per cent; manganese, 0. 300 to 0. 600 per cent; phosphorus, 0. 040 maximum per cent; sulphur, 0. 045 maximum per cent; nickel, 1. 750 to 2. 250 per cent; chromium, 0. 700 to 0. 900 per cent. Each crankshaft was heat-treated to show the following minimumphysical properties: Elastic limit, 116, 000 lb. Per square inch;elongation in 2 in. , 16 per cent, reduction of area, 50 per cent, Izod impact, 34 ft. -lb. ; Brinell hardness, 266 to 321. For every increase of 4, 000 lb. Per square inch in the elasticlimit above 116, 000 lb. Per square inch, the minimum Izod impactrequired was reduced 1 ft. -lb. The heat treatment used to produce these physical properties consistedin normalizing the forgings at a temperature of from 1, 550 to 1, 600°F. , followed by quenching in water at a temperature of from 1, 475 to1, 525°F. And tempering at a temperature of from 1, 000 to 1, 100°F. It is absolutely necessary that the crankshafts be removed from thequenching tank before being allowed to cool below a temperature of500°F. , and immediately placed in the tempering furnace to eliminatethe possibility of quenching cracks. A prolongation of not less than the diameter of the forging bearingwas forged on one end of each crankshaft. This was removed fromthe shaft after the finish heat treatment, and physical tests weremade on test specimens which were cut from it at a point half waybetween the center and the surface. One tensile test and one impacttest were made on each crankshaft, and the results obtained wererecorded against the serial number of the shaft in question. Thisserial number was carried through all machining operations andstamped on the cheek of the finished shaft. In addition to theabove tensile and impact tests, at least two Brinell hardnessdeterminations were made on each shaft. All straightening operations on the Liberty crankshaft which wereperformed below a temperature of 500°F. Were followed by retemperingat a temperature of approximately 200°F. Below the original temperingtemperature. Another illustration of the importance of proper radii at all changesof section is given in the case of the Liberty crankshaft. The presenceof tool marks or under cuts must be completely eliminated from anaviation engine crankshaft to secure proper service. During theduration of the Liberty program, four crankshafts failed from fatigue, failures starting from sharp corners at bottom of propeller-hubkeyway. Two of the shafts that failed showed torsional spiralsrunning more than completely around the shaft. As soon as thisdifficulty was removed no further trouble was experienced. One of the most important difficulties encountered in connectionwith the production of Liberty crankshafts was hair-line seams. Thequestion of hair-line seams has been discussed to greater lengthby engineers and metallurgists during the war than any other singlequestion. Hair-line seams are caused by small non-metallic inclusionsin the steel. There is every reason to believe that these inclusionsare in the greater majority of cases manganese sulphide. There isa great difference of opinion as to the exact effect of hair-lineseams on the service of an aviation engine crankshaft. It is theopinion of many that hair-line seams do not in any way affect theendurance of a crankshaft in service, provided they are parallel tothe grain of the steel and do not occur on a fillet. Of the 20, 000Liberty engines produced, fully 50 per cent of the crankshaftsused contain hair-line seams but not at the locations mentioned. There has never been a failure of a Liberty crankshaft which couldin any way be traced to hair-line seams. It was found that hair-line seams occur generally on highnickel-chromium steels. One of the main reasons why the comparativelymild analysis nickel-chromium steel was used was due to the veryfew hair-line seams present in it. It was also determined thatthe hair lines will in general be found near the surface of theforgings. For that reason, as much finish as possible was allowedfor machining. A number of tests have been made on forging barsto determine the depths at which hair-line seams are found, andmany cases came up in which hair-line seams were found 3/8 in. From the surface of the bar. This means that in case a crankshaftdoes not show hair-line seams on the ground surface this is noindication that it is free from such a defect. One important peculiarity of nickel-chromium steel was broughtout from the results obtained on impact tests. This peculiarityis known as "blue brittleness. " Just what the effect of this ison the service of a finished part depends entirely upon the designof the particular part in question. There have been no failures ofany nickel-chromium steel parts in the automotive industry whichcould in any way be traced to this phenomena. Whether or not nickel-chromium-steel forgings will show "bluebrittleness" depends entirely upon the temperature at which theyare tempered and their rate of cooling from this temperature. Thedanger range for tempering nickel-chromium steels is between atemperature of from 400 to 1, 100°F. From the data so far gatheredon this phenomena, it is necessary that the nickel-chromium steelto show "blue brittleness" be made by the acid process. There hasnever come to my attention a single instance in which basic openhearth steel has shown this phenomena. Just why the acid open hearthsteel should be sensitive to "blue brittleness" is not known. All that is necessary to eliminate the presence of "blue brittleness"is to quench all nickel-chromium-steel forgings in water from theirtempering temperature. The last 20, 000 Liberty crankshafts thatwere made were quenched in this manner. PISTON PIN The piston pin on an aviation engine must possess maximum resistanceto wear and to fatigue. For this reason, the piston pin is considered, from a metallurgical standpoint, the most important part on theengine to produce in quantities and still possess the abovecharacteristics. The material used for the Liberty engine pistonpin was S. A. E. No. 2315 steel, which is of the following chemicalcomposition: Carbon, 0. 100 to 0. 200 per cent; manganese, 0. 500to 0. 800 per cent; phosphorus, 0. 040 maximum per cent; sulphur, 0. 045 maximum per cent; nickel, 3. 250 to 3. 750 per cent. Each finished piston pin, after heat treatment, must show a minimumscleroscope hardness of the case of 70, a scleroscope hardness ofthe core of from 35 to 55 and a minimum crushing strength whensupported as a beam and the load applied at the center of 35, 000lb. The heat treatment used to obtain the above physical propertiesconsisted in carburizing at a temperature not to exceed 1, 675°F. , for a sufficient length of time to secure a case of from 0. 02 to0. 04 in. Deep. The pins are then allowed to cool slowly from thecarbonizing heat, after which the hole is finish-machined and thepin cut to length. The finish heat treatment of the piston pinconsisted in quenching in oil from a temperature of from 1, 525 to1, 575°F. To refine the grain of core properly and then quenching inoil at a temperature of from 1, 340 to 1, 380°F. To refine and hardenthe grain of the case properly, as well as to secure proper hardnessof core. After this quenching, all piston pins are tempered in oilat a temperature of from 375 to 400°F. A 100 per cent inspectionfor scleroscope hardness of the case and the core was made, andno failures were ever recorded when the above material and heattreatment was used. APPLICATION TO THE AUTOMOTIVE INDUSTRY The information given on the various parts of the Liberty engineapplies with equal force to the corresponding parts in the constructionof an automobile, truck or tractor. We recommend as first choice forcarbon-steel screw-machine parts material produced by the basicopen hearth process and having the following chemical composition;Carbon, 0. 150 to 0. 250 per cent; manganese, 0. 500 to 0. 800 percent; phosphorus, 0. 045 maximum per cent; sulphur, 0. 075 to 0. 150per cent. This material is very uniform and is nearly as free cutting asbessemer screw stock. It is sufficiently uniform to be used forunimportant carburized parts, as well as for non-heat-treatedscrew-machine parts. A number of the large automobile manufacturersare now specifying this material in preference to the regular bessemergrades. As second choice for carbon-steel screw-machine parts we recommendordinary bessemer screw stock, purchased in accordance with S. A. E. Specification No. 1114. The advantage of using No. 1114 steellies in the fact that the majority of warehouses carry standardsizes of this material in stock at all times. The disadvantageof using this material is due to its lack of uniformity. The important criterion for transmission gears is resistance towear. To secure proper resistance to wear a Brinell hardness offrom 512 to 560 must be obtained. The material selected to obtainthis hardness should be one which can be made most nearly uniform, will undergo forging operations the easiest, will be the hardestto overheat or burn, will machine best and will respond to a goodcommercial range of heat treatment. It is a well-known fact that the element chromium, when in the formof chromium carbide in alloy steel, offers the greatest resistance towear of any combination yet developed. It is also a well-known fact thatthe element nickel in steel gives excellent shock-resisting propertiesas well as resistance to wear but not nearly as great a resistanceto wear as chromium. It has been standard practice for a number ofyears for many manufacturers to use a high nickel-chromium steelfor transmission gears. A typical nickel-chromium gear specificationis as follows: Carbon, 0. 470 to 0. 520 per cent; manganese, 0. 500to 0. 800 per cent; phosphorus, 0. 040 maximum per cent; sulphur, 0. 045 maximum per cent; chromium, 0. 700 to 0. 950 per cent. There is no question but that a gear made from material of such ananalysis will give excellent service. However, it is possible toobtain the same quality of service and at the same time appreciablyreduce the cost of the finished part. The gear steel specified isof the air-hardening type. It is extremely sensitive to secondarypipe, as well as seams, and is extremely difficult to forge andvery easy to overheat. The heat-treatment range is very wide, butthe danger from quenching cracks is very great. In regard to themachineability, this material is the hardest to machine of anyalloy steel known. COMPOSITION OF TRANSMISSION-GEAR STEEL If the nickel content of this steel is eliminated, and the percentageof chromium raised slightly, an ideal transmission-gear material isobtained. This would, therefore, be of the following composition:Carbon, 0. 470 to 0. 520 per cent; manganese, 0. 500 to 0. 800 percent; phosphorus, 0. 040 maximum per cent; sulphur, 0. 045 maximumper cent; chromium, 0. 800 to 1. 100 per cent. The important criterion in connection with the use of this materialis that the steel be properly deoxidized, either through the useof ferrovanadium or its equivalent. Approximately 2, 500 sets oftransmission gears are being made daily from material of this analysisand are giving entirely satisfactory results in service. The heattreatment of the above material for transmission gears is as follows:"Normalize forgings at a temperature of from 1, 5. 50 to 1, 600°F. Cool from this temperature to a temperature of 1, 100°F. At therate of 50° per hour. Cool from 1, 100°F. , either in air or quenchin water. " Forgings so treated will show a Brinell hardness of from 177 to217, which is the proper range for the best machineability. Theheat treatment of the finished gears consists of quenching in oilfrom a temperature of 1, 500 to 1, 540°F. , followed by temperingin oil at a temperature of from 375 to 425°F. Gears so treatedwill show a Brinell hardness of from 512 to 560, or a scleroscopehardness of from 72 to 80. One tractor builder has placed in service20, 000 sets of gears of this type of material and has never had toreplace a gear. Taking into consideration the fact that a tractortransmission is subjected to the worst possible service conditions, and that it is under high stress 90 per cent of the time, it seemsinconceivable that any appreciable transmission trouble would beexperienced when material of this type is used on an automobile, where the full load is applied not over 1 per cent of the time, or on trucks where the full load is applied not over 50 per centof the time. The gear hardness specified is necessary to reduce to a minimumthe pitting or surface fatigue of the teeth. If gears having aBrinell hardness of over 560 are used, danger is encountered, dueto low shock-resisting properties. If the Brinell hardness is under512, trouble is experienced due to wear and surface fatigue ofthe teeth. For ring gears and pinions material of the following chemicalcomposition is recommended: Carbon, 0. 100 to 0. 200 per cent; manganese, 0. 350 to 0. 650 per cent; phosphorus, 0. 040 maximum per cent; sulphur, 0. 045 maximum per cent; chromium, 0. 550 to 0. 750 per cent; nickel, 0. 400 to 0. 600 per cent. Care should be taken to see that this material is properly deoxidizedeither by the use of ferrovanadium or its equivalent. The advantageof using a material of the above type lies in the fact that it willproduce a satisfactory finished part with a very simple treatment. The heat treatment of ring gears and pinions is as follows: "Carburizeat a temperature of from 1, 650 to 1, 700°F. For a sufficient lengthof time to secure a depth of case of from 1/32 to 3/64 in. , andquench directly from carburizing heat in oil. Reheat to a temperatureof from 1, 430 to 1, 460°F. And quench in oil. Temper in oil at atemperature of from 375 to 425°F. The final quenching operationon a ring gear should be made on a fixture similar to the Gleasonpress to reduce distortion to a minimum. " One of the largest producers of ring gears and pinions in the automotiveindustry has been using this material and treatment for the last 2years, and is of the opinion that he is now producing the highestquality product ever turned out by that plant. On some designs of automobiles a large amount of trouble is experiencedwith the driving pinion. If the material and heat treatment specifiedwill not give satisfaction, rather than to change the design it ispossible to use the following analysis material, which will raisethe cost of the finished part but will give excellent service:Carbon, 0. 100 to 0. 200 per cent; manganese, 0. 350 to 0. 650 percent; phosphorus, 0. 040 maximum per cent; sulphur, 0. 045 maximumper cent; nickel, 4. 750 to 5. 250 per cent. The heat treatment of pinions produced from this material consistsin carburizing at a temperature of from 1, 600 to 1, 650°F. For asufficient length of time to secure a depth of case from 1/32 to3/64 in. The pinions are then quenched in oil from a temperatureof 1, 500 to 1, 525°F. To refine the grain of the core and quenchedin oil from a temperature of from 1, 340 to 1, 360°F. To refine andharden the case. The use of this material however, is recommendedonly in an emergency, as high-nickel steel is very susceptibleto seams, secondary pipe and laminations. The main criterion on rear-axle and pinion shafts, steering knucklesand arms and parts of this general type is resistance to fatigue andtorsion. The material recommended for parts of this character iseither S. A. E. No. 6135 or No. 3135 steel, which have the chemicalcomposition given in Tables 9 and 7. HEAT TREATMENT OF AXLES Parts of this general type should be heat-treated to show the followingminimum physical properties: Elastic limit, 115, 000 lb. Per squareinch; elongation in 2 in. , 16 per cent; reduction of area, 50 percent; Brinell hardness, 277 to 321. The heat treatment used to secure these physical properties consistsin quenching from a temperature of from 1, 520 to 1, 540°F. In waterand tempering at a temperature of from 975 to 1, 025°F. Where theaxle shaft is a forging, and in the case of steering knuckles andarms, this heat treatment should be preceded by normalizing theforgings at a temperature of from 1, 550 to 1, 600°F. It will benoted that these physical properties correspond to those workedout for an ideal aviation engine crankshaft. If parts of this typeare designed with proper sections, so that this range of physicalproperties can be used, the part in question will give maximumservice. One of the most important developments during the Liberty engineprogram was the fact that it is not necessary to use a high-analysisalloy steel to secure a finished part which will give proper service. This fact should save the automotive industry millions of dollarson future production. If the proper authority be given the metallurgical engineer togovern the handling of the steel from the time it is purchaseduntil it is assembled into finished product, mild-analysis steelscan be used and the quality of the finished product guaranteed. It was only through the careful adherence to these fundamentalprinciples that it was possible to produce 20, 000 Liberty engines, which are considered to be the most highly stressed mechanism everproduced, without the failure of a single engine from defectivematerial or heat treatment. MAKING STEEL BALLS Steel balls are made from rods or coils according to size, stockless than 9/16-in. Comes in coils. Stock 5/8-in. And larger comesin rods. Ball stock is designated in thousandths so that 5/8-in. Rods are known as 0. 625-in. Stock. Steel for making balls of average size is made up of: Carbon 0. 95 to 1. 05 per cent Silicon 0. 20 to 0. 35 per cent Manganese 0. 30 to 0. 45 per cent Chromium 0. 35 to 0. 45 per cent Sulphur and phosphorus not to exceed 0. 025 per cent For the larger sizes a typical analysis is: Carbon 1. 02 per cent Silicon 0. 21 per cent Manganese 0. 40 per cent Chromium 0. 65 per cent Sulphur 0. 026 per cent Phosphorus 0. 014 per cent Balls 5/8 in. And below are formed cold on upsetting or headingmachines, the stock use is as follows: TABLE 14. --SIZES OF STOCK FOR FORMING BALLS ON HEADER ------------------------------------------------------- Diameter of | Diameter of | Diameter of | Diameter of ball, inch | stock inch | ball, inch | stock, inch -------------|-------------|-------------|------------- 1/8 | 0. 100 | 5/16 | 0. 235 5/32 | 0. 120 | 3/8 | 0. 275 3/16 | 0. 145 | 7/16 | 0. 320 7/32 | 0. 170 | 1/2 | 0. 365 1/4 | 0. 190 | 9/16 | 0. 395 9/32 | 0. 220 | 5/8 | 0. 440 ------------------------------------------------------- For larger balls the blanks are hot-forged from straight bars. They are usually forged in multiples of four under a spring hammerand then separated by a suitable punching or shearing die in apress adjoining the hammer. The dimensions are: ----------------------------------------------------------- Diameter of ball, | Diameter of die, | Diameter of stock, inch | inch | inch -------------------|------------------|-------------------- 3/4 | 0. 775 | 0. 625 7/8 | 0. 905 | 0. 729 1 | 1. 035 | 0. 823 ----------------------------------------------------------- Before hardening, the balls are annealed to relieve the stressesof forging and grinding, this being done by passing them through arevolving retort made of nichrome or other heat-resisting substance. The annealing temperature is 1, 300°F. The hardening temperature is from 1, 425 to 1, 475°F. According tosize and composition of steel. Small balls, 5/16 and under, arequenched in oil, the larger sizes in water. In some special casesbrine is used. Quenching small balls in water is too great a shockas the small volume is cooled clear through almost instantly. Thelarger balls have metal enough to cool more slowly. Balls which are cooled in either water or brine are boiled in waterfor 2 hr. To relieve internal stresses, after which the balls arefinished by dry-grinding and oil-grinding. The ball makers have an interesting method of testing stock forseams which do not show in the rod or wire. The Hoover Steel BallCompany cut off pieces of rod or wire 7/16 in. Long and subjectthem to an end pressure of from 20, 000 to 50, 000 lb. A pressureof 20, 000 lb. Compresses the piece to 3/16 in. And the 50, 000 lb. Pressure to 3/32 in. This opens any seam which may exist but asolid bar shows no seam. Another method which has proved very successful is to pass thebar or rod to be tested through a solenoid electro-magnet. Withsuitable instruments it is claimed that this is an almost infallibletest as the instruments show at once when a seam or flaw is presentin the bar. CHAPTER V THE FORGING OF STEEL So much depends upon the forging of steel that this operation mustbe carefully supervised. This is especially true because of thetendency to place unskilled and ignorant men as furnace-tendersand hammer men. The main points to be supervised are the slow andcareful heating to the proper temperature; forging must be continuedat a proper rate to the correct temperature. The bar of stock fromwhich a forging was made may have had a fairly good structure, butif the details of the working are not carefully watched, a seamy, split article of no value may easily result. HEATING. --Although it is possible to work steels cold, to an extentdepending upon their ductility, and although such operations arecommonly performed, "forging" usually means working _heated_ steel. _Heating_ is therefore a vital part of the process. Heating should be done slowly in a soaking heat. A soft "lazy"flame with excess carbon is necessary to avoid burning the cornersof the bar or billet, and heavily scaling the surface. If thetemperature is not raised slowly, the outer part of the metal maybe at welding heat while the inner part is several hundred degreescolder and comparatively hard and brittle. The above refers to muffle furnaces. If the heating is done ina small blacksmith's forge, the fire should be kept clean, andremade at intervals of about two hours. Ashes and cinders shouldbe cleaned from the center down to the tuyere and oily waste andwood used to start a new fire. As this kindles a layer of cokefrom the old fire is put on top, and another layer of green coal(screened and dampened blacksmiths' coal) as a cover. When thegreen coal on top has been coked the fire is ready for use. Asthe fuel burns out in the center, the coke forming around the edgeis pushed inward, and its place taken by more green coal. Thus thefire is made up of three parts; the center where coke is burningand the iron heating; a zone where coke is forming, and the outsidebank of green coal. STEEL WORKED IN AUSTENITIC STATE. --As a general rule steel shouldbe worked when it is in the austenitic state. (See page 108. ) Itis then soft and ductile. As the steel is heated above the critical temperature the size ofthe austenite crystals tends to grow rapidly. When forging starts, however, these grains are broken up. The growth is continuallydestroyed by the hammering, which should consequently be continueddown to the upper critical temperature when the austenite crystalsbreak up into ferrite and cementite. The size of the final grainswill be much smaller and hence a more uniform structure will resultif the "mother" austenite was also fine grained. A final steelwill be composed of pearlite; ferrite and pearlite; or cementiteand pearlite, according to the carbon content. The ultimate object is to secure a fine, uniform grain throughoutthe piece and this can be secured by uniform heating and by thoroughlyrolling it or working it at a temperature just down to its criticalpoint. If this is correctly done the fracture will be fine andsilky. Steel which has been overheated slightly and the forgingstopped at too high a temperature will show a "granular" fracture. A badly overheated or "burned" steel will have iridescent colorson a fresh fracture, it will be brittle both hot and cold, andabsolutely ruined. STEEL CAN BE WORKED COLD. --As noted above, steel can be worked cold, as in the case of cold-rolled steel. Heat treatment of cold-workedsteel is a very delicate operation. Cold working hardens and strengthenssteel. It also introduces internal stresses. Heat-treatments aredesigned to eliminate the stresses without losing the hardnessand strength. This is done by tempering at a low heat. Avoid the"blue" range (350 to 750°C. ). Tempering for a considerable time justunder the critical is liable to cause great brittleness. Annealing(reheating through the critical) destroys the effect of cold work. FORGING HIGH-SPEED STEEL. --Heat very slowly and carefully to from 1, 800to 2, 000°F. And forge thoroughly and uniformly. If the forgingoperation is prolonged do not continue forging the tool when thesteel begins to stiffen under the hammer. Do not forge below 1, 700°F. (a dark lemon or orange color). Reheat frequently rather than prolongthe hammering at the low heats. After finishing the forging allow the tool to cool as slowly aspossible in lime or dry ashes; avoid placing the tool on the dampground or in a draught of air. Use a good clean fire for heating. Do not allow the tool to soak at the forging heat. Do not heat anymore of the tool than is necessary in order to forge it to thedesired shape. CARBON TOOL STEEL. --Heat to a bright red, about 1, 500 to 1, 550°F. Do not hammer steel when it cools down to a dark cherry red, orjust below its hardening point, as this creates surface cracks. OIL-HARDENING STEEL. --Heat slowly and uniformly to 1, 450°F. Andforge thoroughly. Do not under any circumstances attempt to hardenat the forging heat. After cooling from forging reheat to about1, 450°F. And cool slowly so as to remove forging strains. CHROME-NICKEL STEEL. --Forging heat of chrome-nickel steel dependsvery largely on the percentage of each element contained in thesteel. Steel containing from 1/2 to 1 per cent chromium and from1-1/2 to 3-1/2 per cent nickel, with a carbon content equal tothe chromium, should be heated very slowly and uniformly toapproximately 1, 600° F. , or salmon color. After forging, reheatthe steel to about 1, 450° and cool slowly so as to remove forgingstrains. Do not attempt to harden the steel before such annealing. A great deal of steel is constantly being spoiled by carelessnessin the forging operation. The billets may be perfectly sound, buteven if the steel is heated to a good forging heat, and is hammeredtoo lightly, a poor forging results. A proper blow will cause theedges and ends to bulge slightly outwards--the inner-most partsof the steel seem to flow faster than the surface. Light blowswill work the surface out faster; the edges and ends will curveinwards. This condition in extreme cases leaves a seam in the axisof the forging. Steel which is heated quickly and forging begun before uniformheat has penetrated to its center will open up seams because thecooler central portion is not able to flow with the hot metalsurrounding it. Uniform heating is absolutely necessary for thebest results. Figure 16 shows a sound forging. The bars in Fig. 17 were burstby improper forging, while the die, Fig. 18, burst from a pipedcenter. Figure 19 shows a piece forged with a hammer too light for the sizeof the work. This gives an appearance similar to case-hardening, the refining effect of the blows reaching but a short distancefrom the surface. While it is impossible to accurately rate the capacity of steamhammers with respect to the size of work they should handle, onaccount of the greatly varying conditions, a few notes from theexperience of the Bement works of the Niles-Bement-Pond Companywill be of service. [Illustration: FIG. 16. --A sound forging. ] [Illustration: FIG. 17. --Burst from improper forging. ] For making an occasional forging of a given size, a smaller hammermay be used than if we are manufacturing this same piece in largequantities. If we have a 6-in. Piece to forge, such as a pinion ora short shaft, a hammer of about 1, 100-lb. Capacity would answervery nicely. But should the general work be as large as this, itwould be very much better to use a 1, 500-lb. Hammer. If, on theother hand, we wish to forge 6-in. Axles economically, it wouldbe necessary to use a 7, 000- or 8, 000-lb. Hammer. The followingtable will be found convenient for reference for the proper sizeof hammer to be used on different classes of general blacksmithwork, although it will be understood that it is necessary to modifythese to suit conditions, as has already been indicated. [Illustration: FIG. 18. --Burst from a piped center. ] [Illustration: FIG. 19. --Result of using too light a hammer. ] Diameter of stock Size of hammer 3-1/2 in. 250 to 350 lb. 4 in. 350 to 600 lb. 4-1/2 in. 600 to 800 lb. 5 in. 800 to 1, 000 lb. 6 in. 1, 100 to 1, 500 lb. Steam hammers are always rated by the weight of the ram, and theattached parts, which include the piston and rod, nothing beingadded on account of the steam pressure behind the piston. This makesit a little difficult to compare them with plain drop or tiltinghammers, which are also rated in the same way. [Illustration: FIG. 20. --Good and bad ingots. ] Steam hammers are usually operated at pressures varying from 75to 100 lb. Of steam per square inch, and may also be operated bycompressed air at about the same pressures. It is cheaper, however, in the case of compressed air to use pressures from 60 to 80 lb. Instead of going higher. Forgings must, however, be made from sound billets if satisfactoryresults are to be secured. Figure 20 shows three cross-sectionsof which _A_ is sound, _B_ is badly piped and _C_ is worthless. PLANT FOR FORGING RIFLE BARRELS The forging of rifle barrels in large quantities and heat-treatingthem to meet the specifications demanded by some of the foreigngovernments led Wheelock, Lovejoy & Company to establish a completeplant for this purpose in connection with their warehouse in Cambridge, Mass. This plant, designed and constructed by their chief engineer, K. A. Juthe, had many interesting features. Many features of thisplant can be modified for other classes of work. [Illustration: FIG 21. --Cutting up barrels. ] [Illustration: FIG. 22. --Upsetting the ends. ] The stock, which came in bars of mill length, was cut off so as tomake a barrel with the proper allowances for trimming (Fig. 21). They then pass to the forging or upsetting press in the adjoiningroom. This press, which is shown in more detail in Fig. 22, handledthe barrels from all the heating furnaces shown. The men changedwork at frequent intervals, to avoid excessive fatigue. [Illustration: FIG. 23. --Continuous heating furnace. ] Then the barrels were reheated in the continuous furnace, shownin Fig. 23, and straightened before being tested. The barrels were next tested for straightness. After the heat-treating, the ends are ground, a spot ground on the enlarged end and eachbarrel tested on a Brinell machine. The pressure used is 3, 000 kg. , or 6, 614 lb. , on a 10-millimeter ball, which is standard. Hardnessof 240 was desired. The heat-treating of the rifle blanks covered four separate operations:(1) Heating and soaking the steel above the critical temperatureand quenching in oil to harden the steel through to the center;(2) reheating for drawing of temper for the purpose of meeting thephysical specifications; (3) reheating to meet the machine abilitytest for production purposes; and (4) reheating to straighten theblanks while hot. A short explanation of the necessity for the many heats may beinteresting. For the first heat, the blanks were slowly broughtto the required heat, which is about 150°F. Above the criticaltemperature. They are then soaked at a high heat for about 1 hr. Before quenching. The purpose of this treatment is to eliminateany rolling or heat stresses that might be in the bars from milloperations; also to insure a thorough even heat through a cross-sectionof the steel. This heat also causes blanks with seams or slightflaws to open up in quenching, making detection of defective blanksvery easy. The quenching oil was kept at a constant temperature of 100°F. , to avoid subjecting the steel to shocks, thereby causing surfacecracks. The drawing of temper was the most critical operation andwas kept within a 10° fluctuation. The degree of heat necessarydepends entirely on the analysis of the steel, there being a certainvariation in the different heats of steel as received from the mill. MACHINEABILITY Reheating for machine ability was done at 100° less than the drawingtemperature, but the time of soaking is more than double. Afterboth drawing and reheating, the blanks were buried in lime wherethey remain, out of contact with the air, until their temperaturehad dropped to that of the workroom. For straightening, the barrels were heated to from 900 to 1, 000°F. In an automatic furnace 25 ft. Long, this operation taking about 2hr. The purpose of hot straightening was to prevent any stressesbeing put into the blanks, so that after rough-turning, drillingor rifling operations they would not have a tendency to springback to shape as left by the quenching bath. A method that produces an even better machining rifle blank, whichpractically stays straight through the different machining operations, was to rough-turn the blanks, then subject them to a heat of practically1, 0000 for 4 hr. Production throughout the different operations ismaterially increased, with practically no straightening requiredafter drilling, reaming, finish-turning or rifling operations. [Illustration: FIG. 24. FIG. 25. FIGS. 24 and 25. --Roof system of cooling quenching oil. ] This method was tested out by one of the largest manufacturers andproved to be the best way to eliminate a very expensive finishedgun-barrel straightening process. [Illustration: FIG. 26. --Details of the cooler. ] The heat-treating required a large amount of cooling oil, and theproblem of keeping this at the proper temperature required considerablestudy. The result was the cooling plant on the roof, as shown inFigs. 24, 25 and 26. The first two illustrations show the plant asit appeared complete. Figure 26 shows how the oil was handled inwhat is sometimes called the ebulator system. The oil was pumpedup from the cooling tanks through the pipe _A_ to the tank _B_. From here it ran down onto the breakers or separators _C_, whichbreak the oil up into fine particles that are caught by the fans_D_. The spray is blown up into the cooling tower _E_, which containsbanks of cooling pipes, as can be seen, as well as baffies _F_. Thespray collects on the cool pipes and forms drops, which fall onthe curved plates _G_ and run back to the oil-storage tank belowground. The water for this cooling was pumped from 10 artesian wells at therate of 60 gal. Per minute and cooled 90 gal. Of oil per minute, lowering the temperature from 130 or 140 to 100°F. The water asit came from the wells averaged around 52°F. The motor was of a7-1/2-hp. Variable-speed type with a range of from 700 to 1, 200r. P. M. , which could be varied to suit the amount of oil to be cooled. The plant handled 300 gal. Of oil per minute. CHAPTER VI ANNEALING There is no mystery or secret about the proper annealing of differentsteels, but in order to secure the best results it is absolutelynecessary for the operator to know the kind of steel which is tobe annealed. The annealing of steel is primarily done for one ofthree specific purposes: To soften for machining purposes; to changethe physical properties, largely to increase ductility; or to releasestrains caused by rolling or forging. Proper annealing means the heating of the steel slowly and uniformlyto the right temperature, the holding of the temperature for a givenperiod and the gradual cooling to normal temperature. The propertemperature depends on the kind of steel, and the suggestions of themaker of the special steel being used should be carefully followed. For carbon steel the temperatures recommended for annealing varyfrom 1, 450 to 1, 600°F. This temperature need not be long continued. The steel should be cooled in hot sand, lime or ashes. If heated inthe open forge the steel should be buried in the cooling materialas quickly as possible, not allowing it to remain in the open airany longer than absolutely necessary. Best results, however, aresecured when the fire does not come in direct contact with thesteel. Good results are obtained by packing the steel in iron boxes ortubes, much as for case-hardening or carbonizing, using the samematerials. Pieces do not require to be entirely surrounded by carbonfor annealing, however. Do not remove from boxes until cold. Steel to be annealed may be classified into four different groups, each of which must be treated according to the elements contained inits particular analysis. Different methods are therefore necessaryto bring about the desired result. The classifications are as follows:High-speed steel, alloy steel, tool or crucible steel, and high-carbonmachinery steel. ANNEALING OF HIGH-SPEED STEEL For annealing high-speed steel, some makers recommend using groundmica, charcoal, lime, fine dry ashes or lake sand as a packingin the annealing boxes. Mixtures of one part charcoal, one partlime and three parts of sand are also suggested, or two parts ofashes may be substituted for the one part of lime. To bring about the softest structure or machine ability of high-speedsteel, it should be packed in charcoal in boxes or pipes, carefullysealed at all points, so that no gases will escape or air be admitted. It should be heated slowly to not less than 1, 450°F. And the steelmust not be removed from its packing until it is cool. Slow heatingmeans that the high heat must have penetrated to the very core ofthe steel. When the steel is heated clear through it has been in the furnacelong enough. If the steel can remain in the furnace and cool downwith it, there will be no danger of air blasts or sudden or unevencooling. If not, remove the box and cover quickly with dry ashes, sand or lime until it becomes cold. Too high a heat or maintaining the heat for too long a period, produces a harsh, coarse grain and greatly increases the liabilityto crack in hardening. It also reduces the strength and toughnessof the steel. Steel which is to be used for making tools with teeth, such astaps, reamers and milling cutters, should not be annealed too much. When the steel is too soft it is more apt to tear in cutting andmakes it more difficult to cut a smooth thread or other surface. Moderate annealing is found best for tools of this kind. TOOL OR CRUCIBLE STEEL Crucible steel can be annealed either in muffled furnace or bybeing packed. Packing is by far the most satisfactory method as itprevents scaling, local hard spots, uneven annealing, or violentchanges in shape. It should be brought up slowly to just aboveits calescent or hardening temperature. The operator must knowbefore setting his heats the temperature at which the differentcarbon content steels are hardened. The higher the carbon contentsthe lower is the hardening heat, but this should in no case beless than 1, 450°F. ANNEALING ALLOY STEEL The term alloy steel, from the steel maker's point of view, referslargely to nickel and chromium steel or a combination of both. Thesesteels are manufactured very largely by the open-hearth process, although chromium steels are also a crucible product. It is nextto impossible to give proper directions for the proper annealingof alloy steel unless the composition is known to the operator. Nickel steels may be annealed at lower temperatures than carbonsteels, depending upon their alloy content. For instance, if apearlitic carbon steel may be annealed at 1, 450°C. , the same analysiscontaining 2-1/2 per cent nickel may be annealed at 1, 360°C. Anda 5 per cent nickel steel at 1, 270°. In order that high chromium steels may be readily machined, theymust be heated at or slightly above the critical for a very longtime, and cooled through the critical at an extremely slow rate. For a steel containing 0. 9 to 1. 1 per cent carbon, under 0. 50 percent manganese, and about 1. 0 per cent chromium, Bullens recommendsthe following anneal: 1. Heat to 1, 700 or 1, 750°F. 2. Air cool to about 800°F. 3. Soak at 1, 425 to 1, 450°F. 4. Cool slowly in furnace. HIGH-CARBON MACHINERY STEEL The carbon content of this steel is above 30 points and is hardlyever above 60 points or 0. 60 per cent. Annealing such steel isgenerally in quantity production and does not require the care thatthe other steels need because it is very largely a much cheaperproduct and a great deal of material is generally removed fromthe outside surface. The purpose for which this steel is annealed is a deciding factoras to what heat to give it. If it is for machineability only, thesteel requires to be brought up slowly to just below the critical andthen slowly cooled in the furnace or ash pit. It must be thoroughlycovered so that there will be no access of cool air. If the annealingis to increase ductility to the maximum extent it should be slowlyheated to slightly over the upper critical temperature and kept atthis heat for a length of time necessary for a thorough penetrationto the core, after which it can be cooled to about 1, 200°F. , thenreheated to about 1, 360°F. , when it can be removed and put in anash pit or covered with lime. If the annealing is just to relievestrains, slow heating is not necessary, but the steel must be broughtup to a temperature not much less than a forging or rolling heatand gradually cooled. Covering in this case is only necessary insteel of a carbon content of more than 40 points. ANNEALING IN BONE Steel and cast iron may both be annealed in granulated bone. Pack thework the same as for case-hardening except that it is not necessaryto keep the pieces away from each other. Pack with bone that hasbeen used until it is nearly white. Heat as hot as necessary forthe steel and let the furnace cool down. If the boxes are removedfrom furnace while still warm, cover boxes and all in warm ashesor sand, air slaked lime or old, burned bone to retain heat aslong as possible. Do not remove work from boxes until cold. ANNEALING OF RIFLE COMPONENTS AT SPRINGFIELD ARMORY In general, all forgings of the components of the arms manufacturedat the Armory and all forgings for other ordnance establishmentsare packed in charcoal, lime or suitable material and annealedbefore being transferred from the forge shop. Except in special cases, all annealing will be done in annealingpots of appropriate size. One fire end of a thermo-couple is insertedin the center of the annealing pot nearest the middle of the furnaceand another in the furnace outside of but near the annealing pots. The temperatures used in annealing carbon steel components of thevarious classes used at the Armory vary from 800°C. To 880°C. Or1, 475 to 1, 615°F. The fuel is shut off from the annealing furnace gradually as thetemperature of the pot approaches the prescribed annealing temperatureso as to prevent heating beyond that temperature. The forgings of the rifle barrel and the pistol barrel are exceptionsto the above general rule. These forgings will be packed in limeand allowed to cool slowly from the residual heat after forging. CHAPTER VII CASE-HARDENING OR SURFACE-CARBURIZING Carburizing, commonly called case-hardening, is the art of producinga high-carbon surface, or case, upon a low carbon steel article. Wrenches, locomotive link motions, gun mechanisms, balls and ballraces, automobile gears and many other devices are thereby givena high-carbon _case_ capable of assuming extreme hardness, whilethe interior body of metal, the _core_, remains soft and tough. The simplest method is to heat the piece to be hardened to a brightred, dip it in cyanide of potassium (or cover it by sprinklingthe cyanide over it), keep it hot until the melted cyanide coversit thoroughly, and quench in water. Carbon and nitrogen enter theouter skin of the steel and harden this skin but leave the centersoft. The hard surface or "case" varies in thickness according tothe size of the piece, the materials used and the length of timewhich the piece remains at the carburizing temperature. Cyanidecase-hardening is used only where a light or thin skin is sufficient. It gives a thickness of about 0. 002 in. In some cases of cyanide carburizing, the piece is heated in cyanideto the desired temperature and then quenched. For a thicker casethe steel is packed in carbon materials of various kinds such asburnt leather scraps, charcoal, granulated bone or some of themany carbonizing compounds. Machined or forged steel parts are packed with case-hardening materialin metal boxes and subjected to a red heat. Under such conditions, carbon is absorbed by the steel surfaces, and a carburized case isproduced capable of responding to ordinary hardening and temperingoperations, the core meanwhile retaining its original softness andtoughness. Such case-hardened parts are stronger, cheaper, and more serviceablethan similar parts made of tool steel. The tough core resists breakageby shock. The hardened case resists wear from friction. The low costof material, the ease of manufacture, and the lessened breakagein quenching all serve to promote cheap production. For successful carburizing, the following points should be carefullyobserved: The utmost care should be used in the selection of pots for carburizing;they should be as free as possible from both scaling and warping. These two requirements eliminate the cast iron pot, although manyare used, thus leaving us to select from malleable castings, wroughtiron, cast steel, and special alloys, such as nichrome or silchrome. If first cost is not important, it will prove cheaper in the endto use pots of some special alloy. [Illustrations: FIGS. 27 to 30. --Case-hardening or carburizing boxes. ] [Illustration: FIG. 31. --A lid that is easily luted. ] The pots should be standardized to suit the product. Pots should bemade as small as possible in width, and space gained by increasingthe height; for it takes about 1-1/2 hr. To heat the average smallpot of 4 in. In width, between 3 and 4 hr. To heat to the centerof an 8-in. Box, and 5 to 6 hr. To heat to the center of a 12-in. Box; and the longer the time required to heat to the center, themore uneven the carburizing. The work is packed in the box surrounded by materials which willgive up carbon when heated. It must be packed so that each pieceis separate from the others and does not touch the box, with asufficient amount of carburizing material surrounding each. Figures27 to 31 show the kind of boxes used and the way the work should bepacked. Figure 31 shows a later type of box in which the edges canbe easily luted. Figure 30 shows test wires broken periodically todetermine the depth of case. Figure 28 shows the minimum clearancewhich should be used in packing and Fig. 29 the way in which theouter pieces receive the heat first and likewise take up the carbonbefore those in the center. This is why a slow, soaking heat isnecessary in handling large quantities of work, so as to allowthe heat and carbon to soak in equally. While it has been claimed that iron below its critical temperaturewill absorb some carbon, Giolitti has shown that this absorptionis very slow. In order to produce quick and intense carburizationthe iron should preferably be above its upper critical temperatureor 1, 600°F. , --therefore the carbon absorbed immediately goes intoaustenite, or solid solution. It is also certain that the higherthe temperature the quicker will carbon be absorbed, and the deeperit will penetrate into the steel, that is, the deeper the "case. "At Sheffield, England, where wrought iron is packed in charcoal andheated for days to convert it into "blister steel, " the temperaturesare from 1, 750 to 1, 830°F. Charcoal by itself carburizes slowly, consequently commercial compounds also contain certain "energizers"which give rapid penetration at lower temperatures. The most important thing in carburizing is the human element. Mostcareful vigilance should be kept when packing and unpacking, and theoperator should be instructed in the necessity for clean compoundfree from scale, moisture, fire clay, sand, floor sweepings, etc. From just such causes, many a good carburizer has been unjustlycondemned. It is essential with most carburizers to use about 25 to50 per cent of used material, in order to prevent undue shrinkingduring heating; therefore the necessity of properly screening usedmaterial and carefully inspecting it for foreign substances beforeit is used again. It is right here that the greatest carelessnessis generally encountered. Don't pack the work to be carburized too closely; leave at least1 in. From the bottom, 3/4 in. From the sides, and 1 in. From thetop of pots, and for a 6-hr. Run, have the pieces at least 1/2in. Apart. This gives the heat a chance to thoroughly permeatethe pot, and the carburizing material a chance to shrink withoutallowing carburized pieces to touch and cause soft spots. Good case-hardening pots and annealing tubes can be made from thedesired size of wrought iron pipe. The ends are capped or welded, and a slot is cut in the side of the pot, equal to one quarter ofits circumference, and about 7/8 of its length. Another piece ofthe same diameter pipe cut lengthwise into thirds forms a coverfor this pot. We then have a cheap, substantial pot, non-warping, with a minimum tendency to scale, but the pot is difficult to sealtightly. This idea is especially adaptable when long, narrow potsare desired. When pots are packed and the carburizer thoroughly tamped down, the covers of the pot are put on and sealed with fire clay whichhas a little salt mixed into it. The more perfect the seal themore we can get out of the carburizer. The rates of penetrationdepend on temperature and the presence of proper gas in the requiredvolume. Any pressure we can cause will, of course, have a tendencyto increase the rate of penetration. If you have a wide furnace, do not load it full at one time. Putone-half your load in first, in the center of the furnace, andheat until pots show a low red, about 1, 325 to 1, 350°F. Then fillthe furnace by putting the cold pots on the outside or, the sectionnearest the source of heat. This will give the work in the slowestportion of the furnace a chance to come to heat at the same timeas the pots that are nearest the sources of heat. To obtain an even heating of the pots and lessen their tendencyto warp and scale, and to cause the contents of the furnace toheat up evenly, we should use a reducing fire and fill the heatingchamber with flame. This can be accomplished by partially closingthe waste gas vents and reducing slightly the amount of air usedby the burners. A short flame will then be noticed issuing fromthe partially closed vents. Thus, while maintaining the temperatureof the heating chamber, we will have a lower temperature in thecombustion chamber, which will naturally increase its longevity. Sometimes it is advisable to cool the work in the pots. This savescompound, and causes a more gradual diffusion of the carbon betweenthe case and the core, and is very desirable condition, inasmuchas abrupt cases are inclined to chip out. The most satisfactory steel to carburize contains between 0. 10and 0. 20 per cent carbon, less than 0. 35 per cent manganese, lessthan 0. 04 per cent phosphorus and sulphur, and low silicon. Butsteel of this composition does not seem to satisfy our progressiveengineers, and many alloy steels are now on the market, these, although more or less difficult to machine, give when carburizedthe various qualities demanded, such as a very hard case, very toughcore, or very hard case and tough core. However, the additionalelements also have a great effect both on the rate of penetrationduring the carburizing operation, and on the final treatment, consequently such alloy steels require very careful supervisionduring the entire heat treating operations. RATE OF ABSORPTION According to Guillet, the absorption of carbon is favored by thosespecial elements which exist as double carbides in steel. For example, manganese exists as manganese carbide in combination with the ironcarbide. The elements that favor the absorption of carbon are:manganese, tungsten, chromium and molybdenum those opposing it, nickel, silicon, and aluminum. Guillet has worked out the effectof the different elements on the rate of penetration in comparisonwith steel that absorbed carbon at a given temperature, at an averagerate of 0. 035 in. Per hour. His tables show that the following elements require an increasedtime of exposure to the carburizing material in order to obtainthe same depth of penetration as with simple steel: When steel contains Increased time of exposure 2. 0 per cent nickel 28 per cent 7. 0 per cent nickel 30 per cent 1. 0 per cent titanium 12 per cent 2. 0 per cent titanium 28 per cent 0. 5 per cent silicon 50 per cent 1. 0 per cent silicon 80 per cent 2. 0 per cent silicon 122 per cent 5. 0 per cent silicon No penetration 1. 0 per cent aluminum 122 per cent 2. 0 per cent aluminum 350 per cent The following elements seem to assist the rate of penetration ofcarbon, and the carburizing time may therefore be reduced as follows: When steel contains Decreased time of exposure 0. 5 per cent manganese 18 per cent 1. 0 per cent manganese 25 per cent 1. 0 per cent chromium 10 per cent 2. 0 per cent chromium 18 per cent 0. 5 per cent tungsten 0 1. 0 per cent tungsten 0 2. 0 per cent tungsten 25 per cent 1. 0 per cent molybdenum 0 2. 0 per cent molybdenum 18 per cent The temperature at which carburization is accomplished is a veryimportant factor. Hence the necessity for a reliable pyrometer, located so as to give the temperature just below the tops of thepots. It must be remembered, however, that the pyrometer givesthe temperature of only one spot, and is therefore only an aid tothe operator, who must use his eyes for successful results. The carbon content of the case generally is governed by the temperatureof the carburization. It generally proves advisable to have thecase contain between 0. 90 per cent and 1. 10 carbon; more carbonthan this gives rise to excess free cementite or carbide of iron, which is detrimental, causing the case to be brittle and apt to chip. T. G. Selleck gives a very useful table of temperatures and therelative carbon contents of the case of steels carburized between4 and 6 hrs. Using a good charcoal carburizer. This data is asfollows: TABLE 15. --CARBON CONTENT OBTAINED AT VARIOUS TEMPERATURES At 1, 500°F. , the surface carbon content will be 0. 90 per cent At 1, 600°F. , the surface carbon content will be 1. 00 per cent At 1, 650°F. , the surface carbon content will be 1. 10 per cent At 1, 700°F. , the surface carbon content will be 1. 25 per cent At 1, 750°F. , the surface carbon content will be 1. 40 per cent At 1, 800°F. , the surface carbon content will be 1. 75 per cent To this very valuable table, it seems best to add the followingdata, which we have used for a number of years. We do not knowthe name of its author, but it has proved very valuable, and seemsto complete the above information. The table is self-explanatory, giving depth of penetration of the carbon of the case at differenttemperatures for different lengths of time: --------------------------------------------------------- | Temperature Penetration |----------------------------- | 1, 550 | 1, 650 | 1, 800 ---------------------------|---------|---------|--------- Penetration after 1/2 hr. | 0. 008 | 0. 012 | 0. 030 Penetration after 1 hr. | 0. 018 | 0. 026 | 0. 045 Penetration after 2 hr. | 0. 035 | 0. 048 | 0. 060 Penetration after 3 hr. | 0. 045 | 0. 055 | 0. 075 Penetration after 4 hr. | 0. 052 | 0. 061 | 0. 092 Penetration after 6 hr. | 0. 056 | 0. 075 | 0. 110 Penetration after 8 hr. | 0. 062 | 0. 083 | 0. 130 --------------------------------------------------------- From the tables given, we may calculate with a fair degree of certaintythe amount of carbon in the case, and its penetration. These figuresvary widely with different carburizers, and as pointed out immediatelyabove, with different alloy steels. CARBURIZING MATERIAL The simplest carburizing substance is charcoal. It is also theslowest, but is often used mixed with something that will evolvelarge volumes of carbon monoxide or hydrocarbon gas on being heated. A great variety of materials is used, a few of them being charcoal(both wood and bone), charred leather, crushed bone, horn, mixturesof charcoal and barium carbonate, coke and heavy oils, coke treatedwith alkaline carbonates, peat, charcoal mixed with common salt, saltpeter, resin, flour, potassium bichromate, vegetable fibre, limestone, various seed husks, etc. In general, it is well to avoidcomplex mixtures. H. L. Heathcote, on analyzing seventeen different carburizers, foundthat they contained the following ingredients: Per cent Moisture 2. 68 to 26. 17 Oil 0. 17 to 20. 76 Carbon (organic) 6. 70 to 54. 19 Calcium phosphate 0. 32 to 74. 75 Calcium carbonate 1. 20 to 11. 57 Barium carbonate nil to 42. 00 Zinc oxide nil to 14. 50 Silica nil to 8. 14 Sulphates (SO3) trace to 3. 45 Sodium chloride nil to 7. 88 Sodium carbonate nil to 40. 00 Sulphides (S) nil to 2. 80 Carburizing mixtures, though bought by weight, are used by volume, and the weight per cubic foot is a big factor in making a selection. A good mixture should be porous, so that the evolved gases, whichshould be generated at the proper temperature, may move freelyaround the steel objects being carburized; should be a good conductorof heat; should possess minimum shrinkage when used; and shouldbe capable of being tamped down. Many "secret mixtures" are sold, falsely claimed to be able toconvert inferior metal into crucible tool steel grade. They aregenerally nothing more than mixtures of carbonaceous and cyanogencompounds possessing the well-known carburizing properties of thosesubstances. QUENCHING It is considered good practice to quench alloy steels from the pot, especially if the case is of any appreciable depth. The textureof carbon steel will be weakened by the prolonged high heat ofcarburizing, so that if we need a tough core, we must reheat itabove its critical range, which is about 1, 600°F. For soft steel, but lower for manganese and nickel steels. Quenching is done ineither water, oil, or air, depending upon the results desired. The steel is then very carefully reheated to refine the case, thetemperature varying from 1, 350 to 1, 450°F. , depending on whetherthe material is an alloy or a simple steel, and quenched in eitherwater or oil. [Illustration: FIG. 32. --Case-hardening depths. ] There are many possibilities yet to be developed with the carburizingof alloy steels, which can produce a very tough, tenacious austeniticcase which becomes hard on cooling in air, and still retains asoft, pearlitic core. An austenitic case is not necessarily filehard, but has a very great resistance to abrasive wear. The more carbon a steel has to begin with the more slowly will itabsorb carbon and the lower the temperature required. Low-carbonsteel of from 15 to 20 points is generally used and the carbonbrought up to 80 or 85 points. Tool steels may be carbonized ashigh as 250 points. In addition to the carburizing materials given, a mixture of 40per cent of barium carbonate and 60 per cent charcoal gives muchfaster penetration than charcoal, bone or leather. The penetrationof this mixture on ordinary low-carbon steel is shown in Fig. 32, over a range of from 2 to 12 hr. EFFECT OF DIFFERENT CARBURIZING MATERIAL [Illustrations: FIGS. 33 to 37. ] Each of these different packing materials has a different effectupon the work in which it is heated. Charcoal by itself will givea rather light case. Mixed with raw bone it will carburize morerapidly, and still more so if mixed with burnt bone. Raw bone andburnt bone, as may be inferred, are both quicker carbonizers thancharcoal, but raw bone must never be used where the breakage ofhardened edges is to be avoided, as it contains phosphorus andtends to make the piece brittle. Charred leather mixed with charcoalis a still faster material, and horns and hoofs exceed even thisin speed; but these two compounds are restricted by their costto use with high-grade articles, usually of tool or high-carbonsteel, that are to be hardened locally--that is, "pack-hardened. "Cyanide of potassium or prussiate of potash are also included inthe list of carbonizing materials; but outside of carburizing bydipping into melted baths of this material, their use is largelyconfined to local hardening of small surfaces, such as holes indies and the like. Dr. Federico Giolitti has proven that when carbonizing with charcoal, or charcoal plus barium carbonate, the active agent which introducescarbon into the steel is a gas, carbon monoxide (CO), derived bycombustion of the charcoal in the air trapped in the box, or bydecomposition of the carbonate. This gas diffuses in and out ofthe hot steel, transporting carbon from the charcoal to the outerportions of the metal: If energizers like tar, peat, and vegetable fiber are used, theyproduce hydrocarbon gases on being heated--gases principally composedof hydrogen and carbon. These gases are unstable in the presence ofhot iron: it seems to decompose them and sooty carbon is depositedon the surface of the metal. This diffuses into the metal a little, but it acts principally by being a ready source of carbon, highlyactive and waiting to be carried into the metal by the carbonmonoxide--which as before, is the principal transfer agent. Animal refuse when used to speed up the action of clean charcoalacts somewhat in the same manner, but in addition the gases givenoff by the hot substance contain nitrogen compounds. Nitrogen andcyanides (compounds of carbon and nitrogen) have long been knownto give a very hard thin case very rapidly. It has been discoveredonly recently that this is due to the steel absorbing nitrogenas well as carbon, and that nitrogen hardens steel and makes itbrittle just like carbon does. In fact it is very difficult todistinguish between these two hardening agents when examining acarburized steel under the microscope. One of the advantages of hardening by carburizing is the fact thatyou can arrange to leave part of the work soft and thus retainthe toughness and strength of the original material. Figures 33to 37 show ways of doing this. The inside of the cup in Fig. 34is locally hardened, as illustrated in Fig. 34, "spent" or usedbone being packed around the surfaces that are to be left soft, while cyanide of potassium is put around those which are desiredhard. The threads of the nut in Fig. 35 are kept soft by carburizingthe nut while upon a stud. The profile gage, Fig. 36, is made ofhigh-carbon steel and is hardened on the inside by packing withcharred leather, but kept soft on the outside by surrounding itwith fireclay. The rivet stud shown in Fig. 37 is carburized whileof its full diameter and then turned down to the size of the rivetend, thus cutting away the carburized surface. After packing the work carefully in the boxes the lids are sealedor luted with fireclay to keep out any gases from the fire. Thesize of box should be proportioned to the work. The box shouldnot be too large especially for light work that is run on a shortheat. If it can be just large enough to allow the proper amountof material around it, the work is apt to be more satisfactoryin every way. Pieces of this kind are of course not quenched and hardened inthe carburizing heat, but are left in the box to cool, just as inbox annealing, being reheated and quenched as a second operation. In fact, this is a good scheme to use for the majority of carburizingwork of small and moderate size. Material is on the market with whichone side of the steel can be treated; or copper-plating one sideof it will answer the same purpose and prevent that side becomingcarburized. QUENCHING THE WORK In some operations case-hardened work is quenched from the box bydumping the whole contents into the quenching tank. It is commonpractice to leave a sieve or wire basket to catch the work, allowingthe carburizing material to fall to the bottom of the tank where itcan be recovered later and used again as a part of a new mixture. For best results, however, the steel is allowed to cool down slowlyin the box after which it is removed and hardened by heating andquenching the same as carbon steel of the same grade. It has absorbedsufficient carbon so that, in the outer portions at least, it isa high-carbon steel. THE QUENCHING TANK The quenching tank is an important feature of apparatus incase-hardening--possibly more so than in ordinary tempering. Onereason for this is because of the large quantities of pieces usuallydumped into the tank at a time. One cannot take time to separatethe articles themselves from the case-hardening mixture, and thewhole content of the box is droped into the bath in short order, as exposure to air of the heated work is fatal to results. Unlessit is split up, it is likely to go to the bottom as a solid mass, in which case very few of the pieces are properly hardened. [Illustration: FIG. 38. --Combination cooling tank for case-hardening. ] A combination cooling tank is shown in Fig. 38. Water inlet andoutlet pipes are shown and also a drain plug that enables the tankto be emptied when it is desired to clean out the spent carburizingmaterial from the bottom. A wire-bottomed tray, framed with angleiron, is arranged to slide into this tank from the top and restsupon angle irons screwed to the tank sides. Its function is tocatch the pieces and prevent them from settling to the tank bottom, and it also makes it easy to remove a batch of work. A bottomlessbox of sheet steel is shown at _C_. This fits into the wire-bottomedtray and has a number of rods or wires running across it, theirpurpose being to break up the mass of material as it comes fromthe carbonizing box. Below the wire-bottomed tray is a perforated cross-pipe that isconnected with a compressed-air line. This is used when case-hardeningfor colors. The shop that has no air compressor may rig up asatisfactory equivalent in the shape of a low-pressure hand-operatedair pump and a receiver tank, for it is not necessary to usehigh-pressure air for this purpose. When colors are desired oncase-hardened work, the treatment in quenching is exactly the sameas that previously described except that air is pumped throughthis pipe and keeps the water agitated. The addition of a slightamount of powdered cyanide of potassium to the packing materialused for carburizing will produce stronger colors, and where this isthe sole object, it is best to maintain the box at a dull-red heat. [Illustration: FIG. 39. --Why heat treatment of case-hardened workis necessary. ] The old way of case-hardening was to dump the contents of the boxat the end of the carburizing heat. Later study in the structureof steel thus treated has caused a change in this procedure, theuse of automobiles and alloy steels probably hastening this result. The diagrams reproduced in Fig. 39 show why the heat treatment ofcase-hardened work is necessary. Starting at _A_ with a close-grainedand tough stock, such as ordinary machinery steel containing from 15to 20 points of carbon, if such work is quenched on a carbonizingheat the result will be as shown at _B_. This gives a core that iscoarse-grained and brittle and an outer case that is fine-grainedand hard, but is likely to flake off, owing to the great differencein structure between it and the core. Reheating this work beyondthe critical temperature of the core refines this core, closesthe grain and makes it tough, but leaves the case very brittle;in fact, more so than it was before. REFINING THE GRAIN This is remedied by reheating the piece to a temperature slightlyabove the critical temperature of the case, this temperaturecorresponding ordinarily to that of steel having a carbon contentof 85 points, When this is again quenched, the temperature, whichhas not been high enough to disturb the refined core, will haveclosed the grain of the case and toughened it. So, instead of butone heat and one quenching for this class of work, we have threeof each, although it is quite possible and often profitable toomit the quenching after carburizing and allow the piece or piecesand the case-carburizing box to cool together, as in annealing. Sometimes another heat treatment is added to the foregoing, forthe purpose of letting down the hardness of the case and givingit additional toughness by heating to a temperature between 300°and 500°. Usually this is done in an oil bath. After this the pieceis allowed to cool. It is possible to harden the surface of tool steel extremely hardand yet leave its inner core soft and tough for strength, by aprocess similar to case-hardening and known as "pack-hardening. "It consists in using tool steel of carbon contents ranging from60 to 80 points, packing this in a box with charred leather mixedwith wood charcoal and heating at a low-red heat for 2 or 3 hr. , thus raising the carbon content of the exterior of the piece. Thearticle when quenched in an oil bath will have an extremely hardexterior and tough core. It is a good scheme for tools that mustbe hard and yet strong enough to stand abuse. Raw bone is neverused as a packing for this class of work, as it makes the cuttingedges brittle. CASE-HARDENING TREATMENTS FOR VARIOUS STEELS Plain water, salt water and linseed oil are the three most commonquenching materials for case-hardening. Water is used for ordinarywork, salt water for work which must be extremely hard on the surface, and oil for work in which toughness is the main consideration. Thehigher the carbon of the case, the less sudden need the quenchingaction take hold of the piece; in fact, experience in case-hardeningwork gives a great many combinations of quenching baths of thesethree materials, depending on their temperatures. Thin work, highlycarbonized, which would fly to pieces under the slightest blow ifquenched in water or brine, is made strong and tough by properlyquenching in slightly heated oil. It is impossible to give anyrules for the temperature of this work, so much depending on thesize and design of the piece; but it is not a difficult matter totry three or four pieces by different methods and determine whatis needed for best results. The alloy steels are all susceptible of case-hardening treatment;in fact, this is one of the most important heat treatments for suchsteels in the automobile industry. Nickel steel carburizes moreslowly than common steel, the nickel seeming to have the effectof slowing down the rate of penetration. There is no cloud withoutits silver lining, however, and to offset this retardation, a singletreatment is often sufficient for nickel steel; for the core is notcoarsened as much as low-carbon machinery steel and thus ordinarywork may be quenched on the carburizing heat. Steel containingfrom 3 to 3. 5 per cent of nickel is carburized between 1, 650 and1, 750°F. Nickel steel containing less than 25 points of carbon, with this same percentage of nickel, may be slightly hardened bycooling in air instead of quenching. Chrome-nickel steel may be case-hardened similarly to the method justdescribed for nickel steel, but double treatment gives better resultsand is used for high-grade work. The carburizing temperature is thesame, between 1, 650 and 1, 750°F. , the second treatment consistingof reheating to 1, 400° and then quenching in boiling salt water, which gives a hard surface and at the same time prevents distortionof the piece. The core of chrome-nickel case-hardened steel, likethat of nickel steel, is not coarsened excessively by the firstheat treatment, and therefore a single heating and quenching willsuffice. CARBURIZING BY GAS The process of carburizing by gas, briefly mentioned on page 88, consists of having a slowly revolving, properly heated, cylindricalretort into which illuminating gas (a mixture of various hydrocarbons)is continuously injected under pressure. The spent gases are ventedto insure the greatest speed in carbonizing. The work is constantlyand uniformly exposed to a clean carbonizing atmosphere insteadof partially spent carbonaceous solids which may give off verycomplex compounds of phosphorus, sulphur, carbon and nitrogen. Originally this process was thought to require a gas generator butit has been discovered that city gas works all right. The gas consistsof vapors derived from petroleum or bituminous coal. Sometimes thegas supply is diluted by air, to reduce the speed of carburizationand increase the depth. PREVENTING CARBURIZING BY COPPER-PLATING Copper-plating has been found effective and must have a thicknessof 0. 0005 in. Less than this does not give a continuous coating. The plating bath used has a temperature of 170°F. A voltage of4. 1 is to be maintained across the terminals. Regions which areto be hardened can be kept free from copper by coating them withparaffin before they enter the plating tank. The operation is asfollows: Operation No. Contents of bath Purpose 1 Gasoline To remove grease 2 Sawdust To dry 3 Warm potassium hydroxide solution To remove grease and dirt 4 Warm water To wash 5 Warm sulphuric acid solution To acid clean 6 Warm water To wash 7 Cold water Additional wash 8 Cold potassium cyanide solution Cleanser 9 Cold water To wash 10 Electric cleaner, warm sodium Cleanser to give good hydroxide case-iron anode plating surface 11 Copper plating bath of copper Plating bath sulphate and potassium cyanide solution warm There are also other methods of preventing case-hardening, onebeing to paint the surface with a special compound prepared forthis purpose. In some cases a coating of plastic asbestos is usedwhile in others thin sheet asbestos is wired around the part tobe kept soft. PREPARING PARTS FOR LOCAL CASE-HARDENING At the works of the Dayton Engineering Laboratories Company, Dayton, Ohio, they have a large quantity of small shafts, Fig. 40, thatare to be case-hardened at _A_ while the ends _B_ and _C_ are tobe left soft. Formerly, the part _A_ was brush-coated with meltedparaffin but, as there were many shafts, this was tedious and greatcare was necessary to avoid getting paraffin where it was not wanted. [Illustration: FIG. 40. --Shaft to be coated with paraffin. ] To insure uniform coating the device shown in Fig. 41 was made. Melted paraffin is poured in the well _A_ and kept liquid by settingthe device on a hot plate, the paraffin being kept high enoughto touch the bottoms of the rollers. The shaft to be coated islaid between the rollers with one end against the gage _B_, whena turn or two of the crank _C_ will cause it to be evenly coated. [Illustration: FIG. 41. --Device for coating the shaft. ] THE PENETRATION OF CARBON Carburized mild steel is used to a great extent in the manufactureof automobile and other parts which are likely to be subjected torough usage. The strength and ability to withstand hard knocksdepend to a very considerable degree on the thoroughness with whichthe carburizing process is conducted. Many automobile manufacturers have at one time or another passedthrough a period of unfortunate breakages, or have found that fora certain period the parts turned out of their hardening shopswere not sufficiently hard to enable the rubbing surfaces to standup against the pressure to which they were subjected. So many factors govern the success of hardening that often thissuccession of bad work has been actually overcome without thoseinterested realizing what was the weak point in their system oftreatment. As the question is one that can create a bad reputationfor the product of any firm it is well to study the influentialfactors minutely. INTRODUCTION OF CARBON The matter to which these notes are primarily directed is theintroduction of carbon into the case of the article to be hardened. In the first place the chances of success are increased by selectingas few brands of steel as practicable to cover the requirements ofeach component of the mechanism. The hardener is then able to becomeaccustomed to the characteristics of that particular material, andafter determining the most suitable treatment for it no furtherexperimenting beyond the usual check-test pieces is necessary. Although a certain make of material may vary in composition fromtime to time the products of a manufacturer of good steel can begenerally relied upon, and it is better to deal directly with himthan with others. In most cases the case-hardening steels can be chosen from thefollowing: (1) Case-hardening mild steel of 0. 20 per cent carbon;(2) case-hardening 3-1/2 per cent nickel steel; (3) case-hardeningnickel-chromium steel; (4) case-hardening chromium vanadium. Afterhaving chosen a suitable steel it is best to have the sample analyzedby reliable chemists and also to have test pieces machined and pulled. To prepare samples for analysis place a sheet of paper on the tableof a drilling machine, and with a 3/8-in. Diameter drill, machinea few holes about 3/8 in. Deep in various parts of the sample bar, collecting about 3 oz. Of fine drillings free from dust. This can beplaced in a bottle and dispatched to the laboratory with instructionsto search for carbon, silicon, manganese, sulphur, phosphorus andalloys. The results of the different tests should be carefullytabulated, and as there would most probably be some variation anaverage should be made as a fair basis of each element present, and the following tables may be used with confidence when decidingif the material is reliable enough to be used. TABLE 16. --CASE-HARDENING MILD STEEL OF 0. 20 PER CENT CARBON Carbon 0. 15 to 0. 25 per cent Silicon Not over 0. 20 per cent Manganese 0. 30 to 0. 60 per cent Sulphur Not over 0. 04 per cent Phosphorus Not over 0. 04 per cent A tension test should register at least 60, 000 lb. Per square inch. TABLE 17. --CASE-HARDENING 3-1/2 PER CENT NICKEL STEEL Carbon 0. 12 to 0. 20 per cent Manganese 0. 65 per cent Sulphur Not over 0. 045 per cent Phosphorus Not over 0. 04 per cent Nickel 3. 25 to 3. 75 per cent TABLE 18. --CASE-HARDENING NICKEL CHROMIUM STEEL Carbon 0. 15 to 0. 25 per cent Manganese 0. 50 to 0. 80 per cent Sulphur Not over 0. 045 per cent Phosphorus Not over 0. 04 per cent Nickel 1 to 1. 5 per cent Chromium 0. 45 to 0. 75 per cent TABLE 19. --CASE-HARDENING CHROMIUM VANADIUM STEEL Carbon Not over 0. 25 per cent Manganese 0. 50 to 0. 85 per cent Sulphur Not over 0. 04 per cent Phosphorus Not over 0. 04 per cent Chromium 0. 80 to 1. 10 per cent Vanadium Not less than 0. 15 per cent Having determined what is required we now proceed to inquire intothe question of carburizing, which is of vital importance. USING ILLUMINATING GAS The choice of a carburizing furnace depends greatly on the facilitiesavailable in the locality where the shop is situated and the natureand quantity of the work to be done. The furnaces can be heated withproducer gas in most cases, but when space is of value illuminatinggas from a separate source of supply has some compensations. Whenthe latter is used it is well to install a governor if the pressureis likely to fluctuate, particularly where the shop is at a highaltitude or at a long distance from the gas supply. Many furnaces are coal-fired, and although greater care is requiredin maintaining a uniform temperature good results have been obtained. The use of electricity as a means of reaching the requisite temperatureis receiving some attention, and no doubt it would make the controlof temperature comparatively simple. However, the cost when appliedto large quantities of work will, for the present at least, preventthis method from becoming popular. It is believed that the resultsobtainable \with the electric furnace would surpass any others; butthe apparatus is expensive, and unless handled with intelligencewould not last long. The most elementary medium of carburization is pure carbon, butthe rate of carburization induced by this material is very low, and other components are necessary to accelerate the process. Manymixtures have been marketed, each possessing its individual merits, and as the prices vary considerably it is difficult to decide whichis the most advantageous. Absorption from actual contact with solid carbon is decidedly slow, and it is necessary to employ a compound from which gases are liberated, and the steel will absorb the carbon from the gases much more readily. Both bone and leather charcoal give off more carburizing gasesthan wood charcoal, and although the high sulphur content of theleather is objectionable as being injurious to the steel, as alsois the high phosphorus content of the bone charcoal, they are bothpreferable to the wood charcoal. By mixing bone charcoal with barium carbonate in the proportionsof 60 per cent of the former to 40 per cent of the latter a veryreliable compound is obtained. The temperature to which this compound is subjected causes theliberation of carbon monoxide when in contact with hot charcoal. Many more elaborate explanations may be given of the actions andreactions taking place, but the above is a satisfactory guide toindicate that it is not the actual compound which causes carburization, but the gases released from the compound. Until the temperature of the muffle reaches about 1, 300°F. Carburizationdoes not take place to any useful extent, and consequently it isadvisable to avoid the use of any compound from which the carburizinggases are liberated much before that temperature is reached. Inthe case of steel containing nickel slightly higher temperaturesmay be used and are really necessary if the same rate of carbonpenetration is to be obtained, as the presence of nickel resiststhe penetration. At higher temperatures the rate of penetration is higher, but notexactly in proportion to the temperature, and the rate is alsoinfluenced by the nature of the material and the efficiency of thecompound employed. The so-called saturation point of mild steel is reached when thecase contains 0. 90 per cent of carbon, but this amount is frequentlyexceeded. Should it be required to ascertain the amount of carbonin a sample at varying depths below the skin this can be done byturning off a small amount after carburizing and analyzing theturnings. This can be repeated several times, and it will probablybe found that the proportion of carbon decreases as the test pieceis reduced in diameter unless decarburization has taken place. [Illustration: FIG. 42. --Chart showing penetration of carbon. ] The chart, Fig. 42, is also a good guide. In order to use the chart it is necessary to harden the samplewe desire to test as we would harden a piece of tool steel, andthen test by scleroscope. By locating on the chart the point onthe horizontal axis which represents the hardness of the samplethe curve enables one to determine the approximate amount of carbonpresent in the case. Should the hardness lack uniformity the soft places can be identifiedby etching. To accomplish this the sample should be polished afterquenching and then washed with a weak solution of nitric acid inalcohol, whereupon the harder points will show up darker than thesofter areas. The selection of suitable boxes for carburizing is worthy of alittle consideration, and there can be no doubt that in certaincases results are spoiled and considerable expense caused by usingunsuitable containers. As far as initial expense goes cast-iron boxes are probably themost expedient, but although they will withstand the necessarytemperatures they are liable to split and crack, and when theyget out of shape there is much difficulty in straightening them. The most suitable material in most cases is steel boiler plate 3/8or 1/2 in. Thick, which can be made with welded joints and willlast well. The sizes of the boxes employed depend to a great extent on thenature of the work being done, but care should be exercised toavoid putting too much in one box, as smaller ones permit the heatto penetrate more quickly, and one test piece is sufficient togive a good indication of what has taken place. If it should benecessary to use larger boxes it is advisable to put in three or fourtest pieces in different positions to ascertain if the penetrationof carbon has been satisfactory in all parts of the box, as itis quite possible that the temperature of the muffle is not thesame at all points, and a record shown by one test piece wouldnot then be applicable to all the parts contained in the box. Ithas been found that the rate of carbon penetration increases withthe gas pressure around the articles being carburized, and it istherefore necessary to be careful in sealing up the boxes afterpacking. When the articles are placed within and each entirelysurrounded by compound so that the compound reaches to within 1in. Of the top of the box a layer of clay should be run around theinside of the box on top of the compound. The lid, which shouldbe a good fit in the box, is then to be pressed on top of this, and another layer of clay run just below the rim of the box ontop of the cover. A SATISFACTORY LUTING MIXTURE A mixture of fireclay and sand will be found very satisfactoryfor closing up the boxes, and by observing the appearance of thework when taken out we can gage the suitability of the methodsemployed, for unless the boxes are carefully sealed the work isgenerally covered with dark scales, while if properly done thearticles will be of a light gray. By observing the above recommendations reliable results can be obtained, and we can expect uniform results after quenching. GAS CONSUMPTION FOR CARBURIZING Although the advantages offered by the gas-fired furnace for carburizinghave been generally recognized in the past from points of view asclose temperature regulation, decreased attendance, and greaterconvenience, very little information has been published regardingthe consumption of gas for this process. It has therefore been amatter of great difficulty to obtain authentic information uponthis point, either from makers or users of such furnaces. In view of this, the details of actual consumption of gas on aregular customer's order job will be of interest. The "Revergen"furnace, manufactured by the Davis Furnace Company, Luton, Bedford, England, was used on this job, and is provided with regeneratorsand fired with illuminating gas at ordinary pressure, the air beingintroduced to the furnace at a slight pressure of 3 to 4 in. Watergage. The material was charged into a cold furnace, raised to 1, 652°F. , and maintained at that temperature for 8 hr. To give the necessarydepth of case. The work consisted of automobile gears packed insix boxes, the total weight being 713 lb. The required temperatureof 1, 652°F. Was obtained in 70 min. From lighting up, and a summaryof the data is shown in the following table: Cubic Foot Total Per Pound Number of of Load Cubic Foot Gas to raise furnace and charge from cold to 1, 652°F. , 70 min. 1. 29 925 Gas to maintain 1, 652°F. For 1st hour 0. 38 275 Gas to maintain 1, 652°F. For 2nd hour 0. 42 300 Gas to maintain 1, 652°F. For 3rd hour 0. 38 275 Gas to maintain 1, 652°F. For 4th hour 0. 42 300 Gas to maintain 1, 652°F. For 5th hour 0. 49 350 Gas to maintain 1, 652°F. For 6th hour 0. 49 350 Gas to maintain 1, 652°F. For 7th hour 0. 45 325 Gas to maintain 1, 652°F. For 8th hour 0. 45 325 The overall gas consumption for this run of 9 hr. 10 min. Was only4. 8 cu. Ft. Per pound of load. THE CARE OF CARBURIZING COMPOUNDS Of all the opportunities for practicing economy in the heat-treatmentdepartment, there is none that offers greater possibilities forprofitable returns than the systematic cleaning, blending and reworkingof artificial carburizers, or compounds. The question of whether or not it is practical to take up the workdepends upon the nature of the output. If the sole product of thehardening department consists of a 1. 10 carbon case or harder, requiring a strong highly energized material of deep penetrativepower such as that used in the carburizing of ball races, hub-bearingsand the like, it would be best to dispose of the used material tosome concern whose product requires a case with from 0. 70 to 0. 90carbon, but where there is a large variety of work the compoundmay be so handled that there will be practically no waste. This is accomplished with one of the most widely known artificialcarburizers by giving all the compound in the plant three distinctclassifications: "New, " being direct from the maker; "half andhalf, " being one part of new and one part first run; and "2 to 1, "which consists of two parts of old and one part new. SEPARATING THE WORK FROM THE COMPOUND During the pulling of the heat, the pots are dumped upon a cast-ironscreen which forms a table or apron for the furnace. Directly beneaththis table is located one of the steel conveyor carts, shown in Fig. 43, which is provided with two wheels at the rear and a dolly clevisat the front, which allows it to be hauled away from beneath thefurnace apron while filled with red-hot compound. A steel cover isprovided for each box, and the material is allowed to cool withoutlosing much of the evolved gases which are still being thrown offby the compound. [Illustration: FIG. 43. --The cooling carts. ] [Illustration: FIG. 44. --Machine for blending the mixture. ] As this compound comes from the carburizing pots it contains bitsof fireclay which represent a part of the luting used for sealing, and there may be small parts of work or bits of fused materialin it as well. After cooling, the compound is very dusty anddisagreeable to handle, and, before it can be used again, must besifted, cleaned and blended. Some time ago the writer was confronted with this proposition forone of the largest consumers of carburizing compound in the world, and the problem was handled in the following manner: The cooledcompound was dumped from the cooling cars and sprinkled with alow-grade oil which served the dual purposes of settling the dustand adding a certain percentage of valuable hydrocarbon to thecompound. In Fig. 44 is shown the machine that was designed to dothe cleaning and blending. BLENDING THE COMPOUND Essentially, this consists of the sturdy, power-driven separatorand fanning mill which separates the foreign matter from the compoundand elevates it into a large settling basin which is formed bythe top of the steel housing that incloses the apparatus. Afterreaching the settling basin, the compound falls by gravity intoa power-driven rotary mixing tub which is directly beneath thesettling basin. Here the blending is done by mixing the properamount of various grades of material together. After blending thecompound, it is ready to be stored in labeled containers and deliveredto the packing room. It will be seen that by this simple system there is the least possibleloss of energy from the compound. The saving commences the momentthe cooling cart is covered and preserves the valuable dust which issaved by the oiling and the settling basin of the blending machine. Then, too, there is the added convenience of the packers who havea thoroughly cleaned, dustless, and standardized product to workwith. Of course, this also tends to insure uniformity in thecase-hardening operation. With this outfit, one man cleans and blends as much compound inone hour as he formerly did in ten. CHAPTER VII HEAT TREATMENT OF STEEL Heat treatment consists in heating and cooling metal at definiterates in order to change its physical condition. Many objects maybe attained by correct heat treatment, but nothing much can beexpected unless the man who directs the operations knows what isthe essential difference in a piece of steel at room temperatureand at a red heat, other than the obvious fact that it is hot. Thescience of metallography has been developed in the past 25 years, and aided by precise methods of measuring temperature, has donemuch to systematize the information which we possess on metallicalloys, and steel in particular. CRITICAL POINTS One of the most important means of investigating the properties ofpure metals and their alloys is by an examination of their heatingand cooling curves. Such curves are constructed by taking a smallpiece and observing and recording the temperature of the mass atuniform intervals of time during a _uniform_ heating or cooling. These observations, when plotted in the form of a curve will showwhether the temperature of the mass rises or falls uniformly. The heat which a body absorbs serves either to raise the temperatureof the mass or change its physical condition. That portion of theheat which results in an increase in temperature of the body iscalled "sensible heat, " inasmuch as such a gain in heat is apparentto the physical senses of the observer. If heat were supplied to thebody at a uniform rate, the temperature would rise continuously, and if the temperature were plotted against time, a smooth risingcurve would result. Or, if sensible heat were abstracted from thebody at a uniform rate, a time-temperature curve would again be asmooth falling curve. Such a curve is called a "cooling curve. " However, we find that when a body is melting, vaporizing, or otherwisesuffering an abrupt change in physical properties, a quantity ofheat is absorbed which disappears without changing the temperatureof the body. This heat absorbed during a change of state is called"latent heat, " because it is transformed into the work necessary tochange the configuration and disposition of the molecules in thebody; but it is again liberated in equal amount when the reversechange takes place. From these considerations it would seem that should the coolingcurve be continuous and smooth, following closely a regular course, all the heat abstracted during cooling is furnished at the expenseof a fall in temperature of the body; that is to say, it disappearsas "sensible heat. " These curves, however, frequently show horizontalportions or "arrests" which denote that at that temperature allof the heat constantly radiating is being supplied by internalchanges in the alloy itself; that is, it is being supplied by theevolution of a certain amount of "latent heat. " In addition to the large amount of heat liberated when a metalsolidifies, there are other changes indicated by the thermal analysisof many alloys which occur _after_ the body has become entirelysolidified. These so-called transformation points or ranges maybe caused by chemical reactions taking place within the solid, substances being precipitated from a "solid solution, " or a suddenchange in some physical property of the components, such as inmagnetism, hardness, or specific gravity. It may be difficult to comprehend that such changes can occur ina body after it has become entirely solidified, owing to the usualconception that the particles are then rigidly fixed. However, thisrigidity is only comparative. The molecules in the solid statehave not the large mobility they possess as a liquid, but even so, they are still moving in circumscribed orbits, and have the power, under proper conditions, to rearrange their position or internalconfiguration. In general, such rearrangement is accompanied by asudden change in some physical property and in the total energyof the molecule, which is evidenced by a spontaneous evolution orabsorption of latent heat. Cooling curves of the purest iron show at least two well-defineddiscontinuities at temperatures more than 1, 000°F. , below itsfreezing-point. It seems that the soft, magnetic metal so familiaras wrought iron, and called "alpha iron" or "ferrite" by themetallurgist, becomes unstable at about 1, 400°F. And changes intothe so-called "beta" modification, becoming suddenly harder, andlosing its magnetism. This state in turn persists no higher than1, 706°C. , when a softer, non-magnetic "gamma" iron is the stablemodification up to the actual melting-point of the metal. Thesevarious changes occur in electrolytic iron, and therefore cannot beattributed to any chemical reaction or solution; they are entirelydue to the existence of "allotropic modifications" of the iron inits solid state. [Illustration: FIG. 45. --Inverse Rate Cooling Curve of 0. 38 C Steel. ] Steels, or iron containing a certain amount of carbon, developsomewhat different cooling curves from those produced by pure iron. Figure 45 shows, for instance, some data observed on a coolingpiece of 0. 38 per cent carbon steel, and the curve constructedtherefrom. It will be noted that the time was noted when the needleon the pyrometer passed each dial marking. If the metal were notchanging in its physical condition, the time between each readingwould be nearly constant; in fact for a time it required about 50sec. To cool each unit. When the dial read about 32. 5 (correspondingin this instrument to a temperature of 775°C. Or 1, 427°F. ) thecooling rate shortened materially, 55 sec. Then 65, then 100, then100; showing that some change inside the metal was furnishing someof the steadily radiating heat. This temperature is the so-called"upper critical" for this steel. Further down, the "lower critical"is shown by a large heat evolution at 695°C. Or 1, 283°F. Just the reverse effects take place upon heating, except that thetemperatures shown are somewhat higher--there seems to be a lagin the reactions taking place in the steel. This is an importantpoint to remember, because if it was desired to anneal a piece of0. 38 carbon steel, it is necessary to heat it up to and beyond1, 476° F. (1, 427°F. _plus_ this lag, which may be as much as 50°). It may be said immediately that above the upper critical the carbonexists in the iron as a "solid solution, " called "austenite" bymetallographers. That is to say, it is uniformly distributed as atomsthroughout the iron; the atoms of carbon are not present in any fixedcombination, in fact any amount of carbon from zero to 1. 7 per centcan enter into solid solution above the upper critical. However, upon cooling this steel, the carbon again enters into combinationwith a definite proportion of iron (the carbide "cementite, " Fe3C), and accumulates into small crystals which can be seen under a goodmicroscope. Formation of all the cementite has been completed bythe time the temperature has fallen to the lower critical, andbelow that temperature the steel exists as a complex substanceof pure iron and the iron carbide. It is important to note that the critical points or critical rangeof a plain steel varies with its carbon content. The followingtable gives some average figures: Carbon Content. Upper Critical. Lower Critical. 0. 00 1, 706°F. 1, 330°F. 0. 20 1, 600°F. 1, 330°F. 0. 40 1, 480°F. 1, 330°F. 0. 60 1, 400°F. 1, 330°F. 0. 80 1, 350°F. 1, 330°F. 0. 90 1, 330°F. 1, 330°F. 1. 00 1, 470°F. 1, 330°F. 1. 20 1, 650°F. 1, 330°F. 1. 40 1, 830°F. 1, 330°F. 1. 60 2, 000°F. 1, 330°F. It is immediately noted that the critical range narrows with increasingcarbon content until all the heat seems to be liberated at onetemperature in a steel of 0. 90 per cent carbon. Beyond that compositionthe critical range widens rapidly. Note also that the lower criticalis constant in plain carbon steels containing no alloying elements. [Illustration: FIG. 46. --Microphotograph of steel used in S. K. F. Bearings, polished and etched with nitric acid and magnified1, 000 times. Made by H. O. Walp. ] This steel of 0. 90 carbon content is an important one. It is called"eutectoid" steel. Under the microscope a properly polished andetched sample shows the structure to consist of thin sheets oftwo different substances (Fig. 46). One of these is pure iron, and the other is pure cementite. This structure of thin sheetshas received the name "pearlite, " because of its pearly appearanceunder sunlight. Pearlite is a constituent found in all annealedcarbon steels. Pure iron, having no carbon, naturally would show nopearlite when examined under a microscope; only abutting granulesof iron are delicately traced. The metallographist calls this pureiron "ferrite. " As soon as a little carbon enters the alloy and asoft steel is formed, small angular areas of pearlite appear at theboundaries of the ferrite crystals (Fig. 47). With increasing carbonin the steel the volume of iron crystals becomes less and less, andthe relative amount of pearlite increases, until arriving at 0. 90per cent carbon, the large ferrite crystals have been suppressed andthe structure is all pearlite. Higher carbon steels show films ofcementite outlining grains of pearlite (Fig. 48). This represents the structure of annealed, slowly cooled steels. It is possible to change the relative sizes of the ferrite andcementite crystals by heat treatment. Large grains are associatedwith brittleness. Consequently one must avoid heat treatments whichproduce coarse grains. [Illustration: FIG. 47. --Structure of low carbon steel, polished, etched and viewed under 100 magnifications. Tiny white granulesof pure iron (ferrite) have small accumulations of dark-etchingpearlite interspersed between them. Photograph by H. S. Rawdon. ] [Illustration: FIG. 48. --Slowly cooled high-carbon steel, polished, etched and viewed at 100 magnifications. The dark grains are pearlite, separated by white films of iron carbide (cementite). Photographby H. S. Rawdon. ] In general it may be said that the previous crystalline structureof a steel is entirely obliterated when it passes just through thecritical range. At that moment, in fact, the ferrite, cementite orpearlite which previously existed has lost its identity by everythinggoing into the solid solution called austenite. If sufficient timeis given, the chemical elements comprising a good steel distributethemselves uniformly through the mass. If the steel be then cooled, the austenite breaks up into new crystals of ferrite, cementiteand pearlite; and in general if the temperature has not gone farabove the critical, and cooling is not excessively slow, a veryfine texture will result. This is called "refining" the grain;or in shop parlance "closing" the grain. However, if the heatinghas gone above the critical very far, the austenite crystals startto grow; a very short time at an extreme temperature will causea large grain growth. Subsequent cooling gives a coarse texture, or an arrangement of ferrite, cementite and pearlite grains whichis greatly coarsened, reflecting the condition of the austenitecrystals from which they were born. It maybe noted in passing that the coarse crystals of cast metalcannot generally be refined by heat treatment unless some forgingor rolling has been done in the meantime. Heat treatment alone doesnot seem to be able to break up the crystals of an ingot structure. HARDENING Steel is hardened by quenching from above the upper critical. Apparentlythe quick cooling prevents the normal change back to definite andsizeable crystals of ferrite and cementite. Hardness is associatedwith this suppressed change. If the change is allowed to continueby a moderate reheating, like a tempering, the hardness decreases. If a piece of steel could be cooled instantly, doubtless austenitecould be preserved and examined. In the ordinary practice of hardeningsteels, the quenching is not so drastic, and the transformation ofaustenite back to ferrite and cementite is more or less completelyeffected, giving rise to certain transitory forms which are knownas "martensite, " "troostite, " "sorbite, " and finally, pearlite. Austenite has been defined as a solid solution of cementite (Fe3C)in gamma iron. It is stable at various temperatures dependent uponits carbon content, which may be any amount up to the saturatedsolution containing 1. 7 per cent. Austenite is not nearly as hardas martensite, owing to its content of the soft gamma iron. Fig. 49 shows austenite to possess the typical appearance of any pure, crystallized substance. In the most quickly quenched high carbon steels, austenite commonlyforms the ground mass which is interspersed with martensite, a largefield of which is illustrated in Fig. 50. Martensite is usuallyconsidered to be a solid solution of cementite in beta iron. Itrepresents an unstable condition in which the metal is caught duringrapid cooling. It is very hard, and is the chief constituent ofhardened high-carbon steels, and of medium-carbon nickel-steeland manganese-steel. Troostite is of doubtful composition, but possibly is an unstablemixture of untransformed martensite with sorbite. It contains moreor less untransformed material, as it is too hard to be composedentirely of the soft alpha modification, and it can also be temperedmore or less without changing in appearance. Its normal appearance asrounded grains is given in Fig. 51; larger patches show practicallyno relief in their structure, and a photograph merely shows a dark, structureless area. [Illustration: FIG. 49. --Coarse-grained martensite, polished andetched with nitric acid and magnified 50 times. Made by Prof. Chas. Y. Clayton. ] Sorbite is believed to be an early stage in the formation of pearlite, when the iron and iron carbide originally constituting the solidsolution (austenite) have had an opportunity to separate from eachother, and the iron has entirely passed into the alpha modification, but the particles are yet too small to be distinguishable underthe microscope. It also, possibly, contains some incompletelytransformed matter. Sorbite is softer and tougher than troostite, and is habitually associated with pearlite. Its components aretending to coagulate into pearlite, and will do so in a fairlyshort time at temperatures near the lower critical, which heat willfurnish the necessary molecular freedom. The normal appearance, however, is the cloudy mass shown in Fig. 52. Pearlite is a definite conglomerate of ferrite and cementite containingabout six parts of the former to one of the latter. When pure, ithas a carbon content of about 0. 95 per cent. It represents thecomplete transformation of the eutectoid austenite accomplished byslow-cooling of an iron-carbon alloy through the transformationrange. (See Fig. 46. ) [Illustration: FIG. 50. --Quenched high-carbon steel, polished, etched and viewed at 100 magnifications. This structure is calledmartensite and is desired when maximum hardness is essential. Photographby H. S. Rawdon. ] [Illustration: FIG. 51. --Martensite (light needles) passing intotroosite (dark patches). 130 X. From a piece of eutectoid steelelectrically welded. ] [Illustration: FIG. 52. --Sorbite (dark patches) passing into pearlite(wavy striations). Light Areas are Patches of Ferrite. 220 X. Froma piece of hypo-eutectoid steel electrically welded. ] These observations are competent to explain annealing and tougheningpractice. A quickly quenched carbon steel is mostly martensiticwhich, as noted, is a solid solution of beta iron and cementite, hard and brittle. Moderate reheating or annealing changes thisstructure largely into troostite, which is a partly transformedmartensite, possessing much of the hardness of martensite, but witha largely increased toughness and shock resistance. This toughness isthe chief characteristic of the next material in the transformationseries, sorbite, which is merely martensite wholly transformed intoa mixture of ultramicroscopic crystals of ferrite (alpha iron)and cementite (Fe3C). "Tempering" or "drawing" should be restricted to mean moderatereheating, up to about 350° C. , forming troostitic steel. "Toughening"represents the practice of reheating hardened carbon steels from350° C. Up to just below the lower critical, and forms sorbiticsteel; while "annealing" refers to a heating for grain size ator above the transformation ranges, followed by a slow cooling. Any of these operations not only allows the transformations fromaustenite to pearlite to proceed, but also relieves internal stressesin the steel. Normalizing is a heating like annealing, followed by a moderatelyrapid quench. JUDGING THE HEAT OF STEEL While the use of a pyrometer is of course the only way to haveaccurate knowledge as to the heat being used in either forging orhardening steels, a color chart will be of considerable assistanceif carefully studied. These have been prepared by several of thesteel companies as a guide, but it must be remembered that the colorsand temperatures given are only approximate, and can be nothingelse. [Illustration: FIG. 53. --Finding hardening heats with a magnet. ] _The Magnet Test_. --The critical point can also be determined byan ordinary horse-shoe magnet. Touch the steel with a magnet duringthe heating and when it reaches the temperature at which steel failsto attract the magnet, or in other words, loses its magnetism, the critical point has been reached. Figures 53 and 54 show how these are used in practice. The first (Fig. 53) shows the use of a permanent horse-shoe magnetand the second (Fig. 54) an electro-magnet consisting of an ironrod with a coil or spool magnet at the outer end. In either casethe magnet should not be allowed to become heated but should beapplied quickly. [Illustration: FIG. 54. --Using electro-magnet to determine heat. ] The work is heated up slowly in the furnace and the magnet appliedfrom time to time. The steel being heated will attract the magnetuntil the heat reaches the critical point. The magnet is appliedfrequently and when the magnet is no longer attracted, the pieceis at the lowest temperature at which it can be hardened properly. Quenching slightly above this point will give a tool of satisfactoryhardness. The method applies only to carbon steels and will notwork for modern high-speed steels. HEAT TREATMENT OF GEAR BLANKS This section is based on a paper read before the American GearManufacturers' Association at White Sulphur Springs, W. Va. , Apr. 18, 1918. Great advancement has been made in the heat treating and hardening ofgears. In this advancement the chemical and metallurgical laboratoryhave played no small part. During this time, however, the conditionof the blanks as they come to the machine shop to be machined hasnot received its share of attention. There are two distinct types of gears, both types having theirchampions, namely, carburized and heat-treated. The differencebetween the two in the matter of steel composition is entirely inthe carbon content, the carbon never running higher than 25-pointin the carburizing type, while in the heat-treated gears the carbonis seldom lower than 35-point. The difference in the final gearis the hardness. The carburized gear is file hard on the surface, with a soft, tough and ductile core to withstand shock, while theheat-treated gear has a surface that can be touched by a file witha core of the same hardness as the outer surface. ANNEALING WORK. --With the exception of several of the higher typesof alloy steels, where the percentages of special elements run quitehigh, which causes a slight air-hardening action, the carburizingsteels are soft enough for machining when air cooled from anytemperature, including the finishing temperature at the hammer. This condition has led many drop-forge and manufacturing concernsto consider annealing as an unnecessary operation and expense. In many cases the drop forging has only been heated to a lowtemperature, often just until the piece showed color, to relievethe so-called hammer strains. While this has been only a compromiseit has been better than no reheating at all, although it has notproperly refined the grain, which is necessary for good machiningconditions. Annealing is heating to a temperature slightly above the highestcritical point and cooling slowly either in the air or in the furnace. Annealing is done to accomplish two purposes: (1) to relieve mechanicalstrains and (2) to soften and produce a maximum refinement of grain. PROCESS OF CARBURIZING. --Carburizing imparts a shell of high-carboncontent to a low-carbon steel. This produces what might be termeda "dual" steel, allowing for an outer shell which when hardenedwould withstand wear, and a soft ductile core to produce ductilityand withstand shock. The operation is carried out by packing thework to be carburized in boxes with a material rich in carbon andmaintaining the box so charged at a temperature in excess of thehighest critical point for a length of time to produce the desireddepth of carburized zone. Generally maintaining the temperatureat 1, 650 to 1, 700° F. For 7 hr. Will produce a carburized zone1/32 in. Deep. Heating to a temperature slightly above the highest critical pointand cooling suddenly in some quenching medium, such as water or oilhardens the steel. This treatment produces a maximum refinementwith the maximum strength. Drawing to a temperature below the highest critical point (thetemperature being governed by the results required) relieves thehardening strains set up by quenching, as well as the reducingof the hardness and brittleness of hardened steel. EFFECTS OF PROPER ANNEALING. --Proper annealing of low-carbon steelscauses a complete solution or combination to take place betweenthe ferrite and pearlite, producing a homogeneous mass of smallgrains of each, the grains of the pearlite being surrounded bygrains of ferrite. A steel of this refinement will machine to goodadvantage, due to the fact that the cutting tool will at all timesbe in contact with metal of uniform composition. While the alternate bands of ferrite and pearlite are microscopicallysized, it has been found that with a Gleason or Fellows gear-cuttingmachine that rough cutting can be traced to poorly annealed steels, having either a pronounced banded structure or a coarse granularstructure. TEMPERATURE FOR ANNEALING. --Theoretically, annealing should beaccomplished at a temperature at just slightly above the criticalpoint. However, in practice the temperature is raised to a higherpoint in order to allow for the solution of the carbon and iron tobe produced more rapidly, as the time required to produce completesolution is reduced as the temperature increases past the criticalpoint. For annealing the simpler types of low-carbon steels the followingtemperatures have been found to produce uniform machining conditionson account of producing uniform fine-grain pearlite structure: 0. 15 to 0. 25 per cent carbon, straight carbon steel. --Heat to 1, 650°F. Hold at this temperature until the work is uniformly heated; pullfrom the furnace and cool in air. 0. 15 to 0. 25 per cent carbon, 1-1/2 per cent nickel, 1/2 per centchromium steel. --Heat to 1, 600°F. Hold at this temperature untilthe work is uniformly heated; pull from the furnace and cool in air. 0. 15 to 0. 25 per cent carbon, 3-1/2 per cent nickel steel. --Heatto 1, 575°F. Hold at this temperature until the work is uniformlyheated; pull from the furnace and cool in air. CARE IN ANNEALING. --Not only will benefits in machining be foundby careful annealing of forgings but the subsequent troubles inthe hardening plant will be greatly reduced. The advantages inthe hardening start with the carburizing operation, as a steel ofuniform and fine grain size will carburize more uniformly, producinga more even hardness and less chances for soft spots. The holes inthe gears will also "close in more uniformly, " not causing somegears to require excessive grinding and others with just enoughstock. Also all strains will have been removed from the forging, eliminating to a great extent distortion and the noisy gears whichare the result. With the steels used, for the heat-treated gears, always of a highercarbon content, treatment after forging is necessary for machining, asit would be impossible to get the required production from untreatedforgings, especially in the alloy steels. The treatment is moredelicate, due to the higher percentage of carbon and the naturalincrease in cementite together with complex carbides which arepresent in some of the higher types of alloys. Where poor machining conditions in heat-treated steels are presentthey are generally due to incomplete solution of cementite ratherthan bands of free ferrite, as in the case of case-hardening steels. This segregation of carbon, as it is sometimes referred to, causeshard spots which, in the forming of the tooth, cause the cutterto ride over the hard metal, producing high spots on the face ofthe tooth, which are as detrimental to satisfactory gear cuttingas the drops or low spots produced on the face of the teeth whenthe pearlite is coarse-grained or in a banded condition. In the simpler carburized steels it is not necessary to test theforgings for hardness after annealing, but with the high percentagesof alloys in the carburizing steels and the heat-treated steelsa hardness test is essential. To obtain the best results in machining, the microstructure of themetal should be determined and a hardness range set that coversthe variations in structure that produce good machining results. By careful control of the heat-treating operation and with the aidof the Brinell hardness tester and the microscope it is possibleto continually give forgings that will machine uniformly and besoft enough to give desired production. The following gives a fewof the hardness numerals on steel used in gear manufacture thatproduce good machining qualities: 0. 20 per cent carbon, 3 per cent nickel, 1-1/4; per centchromium--Brinell 156 to 170. 0. 50 per cent carbon, 3 per cent nickel, 1 per cent chromium--Brinell179 to 187. 0. 50 per cent carbon chrome-vanadium--Brinell 170 to 179. THE INFLUENCE OF SIZE The size of the piece influences the physical properties obtained insteel by heat treatment. This has been worked out by E. J. Janitzky, metallurgical engineer of the Illinois Steel Company, as follows: [Illustration: FIG. 55. --Effect of size on heating. ] "With an increase in the mass of steel there is a correspondingdecrease in both the minimum surface hardness and depth hardness, when quenched from the same temperature, under identical conditionsof the quenching medium. In other words, the physical propertiesobtained are a function of the surface of the metal quenched fora given mass of steel. Keeping this primary assumption in mind, itis possible to predict what physical properties may be developed inheat treating by calculating the surface per unit mass for differentshapes and sizes. It may be pointed out that the figures and chartthat follow are not results of actual tests, but are derived bycalculation. They indicate the mathematical relation, which, basedon the fact that the physical properties of steel are determinednot alone by the rate which heat is lost per unit of surface, butby the rate which heat is lost per unit of weight in relation tothe surface exposed for that unit. The unit of weight has for thedifferent shaped bodies and their sizes a certain surface whichdetermines their physical properties. "For example, the surface corresponding to 1 lb. Of steel has beencomputed for spheres, rounds and flats. For the sphere with a unitweight of 1 lb. The portion is a cone with the apex at the centerof the sphere and the base the curved surface of the sphere (surfaceexposed to quenching). For rounds, a unit weight of 1 lb. May betaken as a disk or cylinder, the base and top surfaces naturally donot enter into calculation. For a flat, a prismatic or cylindricalvolume may be taken to represent the unit weight. The surfacesthat are considered in this instance are the top and base of thesection, as these surfaces are the ones exposed to cooling. " The results of the calculations are as follows: TABLE 20. --SPHERE Diameter Surface per of sphere pound of steel _X_ _Y_ 8 in. 2. 648 sq. In. 6 in. 3. 531 sq. In. 4 in. 5. 294 sq. In. 3 in. 7. 062 sq. In. 2 in. 10. 61 sq. In. _XY_ = 21. 185. TABLE 21. --ROUND Diameter Surface per of round pound of steel _X_ _Y_ 8. 0 in. 1. 765 sq. In. 6. 0 in. 2. 354 sq. In. 5. 0 in. 2. 829 sq. In. 4. 0 in. 3. 531 sq. In. 3. 0 in. 4. 708 sq. In. 2. 0 in. 7. 062 sq. In. 1. 0 in. 14. 125 sq. In. 0. 5 in. 28. 25 sq. In. 0. 25 in. 56. 5 sq. In. _XY_ = 14. 124. TABLE 22. --FLAT Thickness Surface per of flat pound of steel _X_ _Y_ 8. 0 in. 0. 8828 sq. In. 6. 0 in. 1. 177 sq. In. 5. 0 in. 1. 412 sq. In. 4. 0 in. 1. 765 sq. In. 3. 0 in. 2. 345 sq. In. 2. 0 in. 3. 531 sq. In. 1. 0 in. 7. 062 sq. In. 0. 5 in. 14. 124 sq. In. 0. 25 in. 28. 248 sq. In. _XY_ = 7. 062. Having once determined the physical qualities of a certain specimen, and found its position on the curve we have the means to predict thedecrease of physical qualities on larger specimens which receivethe same heat treatment. When the surfaces of the unit weight as outlined in the foregoingtables are plotted as ordinates and the corresponding diameters asabscissæ, the resulting curve is a hyperbola and follows the law_XY = C_. In making these calculations the radii or one-half ofthe thickness need only to be taken into consideration as the heatis conducted from the center of the body to the surface, followingthe shortest path. The equations for the different shapes are as follows: For flats _XY_ = 7. 062 For rounds _XY_ = 14. 124 For spheres _XY_ = 21. 185 It will be noted that the constants increase in a ratio of 1, 2, and 3, and the three bodies in question will increase in hardnesson being quenched in the same ratio, it being understood that thediameter of the sphere and round and thickness of the flat areequal. Relative to shape, it is interesting to note that rounds, squares, octagons and other three axial bodies, with two of their axes equal, have the same surface for the unit weight. For example: Size Length Surface Weight Surface for 1 lb. 2 in. Sq. 12 in. 96. 0 sq. In. 13. 60 lb. 7. 06 sq. In. 2 in. Round 12 in. 75. 4 sq. In. 10. 68 lb. 7. 06 sq. In. Although this discussion is at present based upon mathematicalanalysis, it is hoped that it will open up a new field of investigationin which but little work has been done, and may assist in settlingthe as yet unsolved question of the effect of size and shape inthe heat treatment of steel. HEAT-TREATING EQUIPMENT AND METHODS FOR MASS PRODUCTION The heat-treating department of the Brown-Lipe-Chapin Company, Syracuse, N. Y. , runs day and night, and besides handling all thehardening of tools, parts of jigs, fixtures, special machines andappliances, carburizes and heat-treats every month between 150, 000and 200, 000 gears, pinions, crosses and other components enteringinto the construction of differentials for automobiles. The treatment of the steel really begins in the mill, where thesteel is made to conform to a specific formula. On the arrivalof the rough forgings at the Brown-Lipe-Chapin factory, the firstof a long series of inspections begins. ANNEALING METHOD. --Forgings which are too hard to machine are putin pots with a little charcoal to cause a reducing atmosphere andto prevent scale. The covers are then luted on and the pots placedin the furnace. Carbon steel from 15 to 25 points is annealed at1, 600°F. Nickel steel of the same carbon and containing in addition3-1/2 per cent nickel is annealed at 1, 450°F. When the pots areheated through, they are rolled to the yard and allowed to cool. This method of annealing gives the best hardness for quick machining. The requirements in the machine operations are very rigid and, inspite of great care and probably the finest equipment of specialmachines in the world, a small percentage of the product failsto pass inspection during or at the completion of the machineoperations. These pieces, however, are not a loss, for they playan important part in the hardening process, indicating as they dothe exact depth of penetration of the carburizing material andthe condition of both case and core. HEAT-TREATING DEPARTMENT. --The heat-treating department occupies anL-shaped building. The design is very practical, with the furnaceand the floor on the same level so that there is no lifting ofheavy pots. Fuel oil is used in all the furnaces and gives highlysatisfactory results. The consumption of fuel oil is about 2 gal. Per hour per furnace. The work is packed in the pots in a room at the entrance to theheat-treatment building. Before packing, each gear is stamped witha number which is a key to the records of the analysis and completeheat treatment of that particular gear. Should a question at any timearise regarding the treatment of a certain gear, all the necessaryinformation is available if the number on the gear is legible. Forinstance, date of treatment, furnace, carburizing material, positionof the pot in the furnace, position of gear in pot, temperature offurnace and duration of treatment are all tabulated and filed forreference. After marking, all holes and parts which are to remain uncarburizedare plugged or luted with a mixture of kaolin and Mellville gravelclay, and the gear is packed in the carburizing material. Bohnite, a commercial carburizing compound is used exclusively at this plant. This does excellent work and is economical. Broadly speaking, theeconomy of a carburizing compound depends on its lightness. Thespace not occupied by work must be filled with compound; therefore)other things being equal, a compound weighing 25 lb. Would be worthmore than twice as much as one weighing 60 lb. Per cubic foot. Ithas been claimed that certain compounds can be used over and overagain, but this is only true in a limited way, if good work isrequired. There is, of course, some carbon in the compound afterthe first use, but for first-class work, new compound must be usedeach time. THE PACKING DEPARTMENT. --In Fig. 56 is shown the packing pots wherethe work is packed. These are of malleable cast iron, with an internalvertical flange around the hole _A_. This fits in a bell on theend of the cast-iron pipe _B_, which is luted in position withfireclay before the packing begins. At _C_ is shown a pot readyfor packing. The crown gears average 10 to 12 in. In diameter andweigh about 11 lb. Each. When placed in the pots, they surroundthe central tube, which allows the heat to circulate. Each potcontains five gears. Two complete scrap gears are in each furnace(_i. E. _, gears which fail to pass machining inspection), and atthe top of front pot are two or more short segments of scrap gear, used as test pieces to gage depth of case. [Illustration: FIG. 56. --Packing department and special pots. ] After filling to the top with compound, the lid _D_ is luted on. Ten pots are then placed in a furnace. It will be noted that thepots to the right are numbered 1, 2, 3, 4, indicating the positionthey are to occupy in the furnace. The cast-iron ball shown at _E_ is small enough to drop throughthe pipe _B_, but will not pass through the hole _A_ in the bottomof the pot. It is used as a valve to plug the bottom of the potto prevent the carburizing compound from dropping through whenremoving the carburized gears to the quenching bath. Without detracting from the high quality of the work, the metallurgistin this plant has succeeded in cutting out one entire operationand reducing the time in the hardening room by about 24 hr. Formerly, the work was carburized at about 1, 700°F. For 9 hr. Thepots were then run out into the yard and allowed to cool slowly. When cool, the work was taken out of the pots, reheated and quenchedat 1, 600°F. To refine the core. It was again reheated to 1, 425°F. And quenched to refine the case. Finally, it was drawn to the propertemper. SHORT METHOD OF TREATMENT. --In the new method, the packed pots arerun into the case-hardening furnaces, which are heated to 1, 600°F. On the insertion of the cold pots, the temperature naturally falls. The amount of this fall is dependent upon a number of variables, but it averages nearly 500°F. As shown in the pyrometer chart, Fig. 61. The work and furnace must be brought to 1, 600°F. Within2-1/2 hr. ; otherwise, a longer time will be necessary to obtainthe desired depth of case. On this work, the depth of case requiredis designated in thousandths, and on crown gears, the depth in0. 028 in. Having brought the work to a temperature of 1, 600°F. The depth of case mentioned can be obtained in about 5-1/2 hr. Bymaintaining this temperature. As stated before, at the top of each pot are several test piecesconsisting of a whole scrap gear and several sections. After thepots have been heated at 1, 600°F. For about 5-1/4 hr. , they areremoved, and a scrap-section test-piece is quenched direct fromthe pot in mineral oil at _not more than_ 100°F. The end of a toothof this is then ground and etched to ascertain the depth of case. As these test pieces are of exactly the same cross-section as thegears themselves, the carburizing action is similar. When the depthof case has been found from the etched test pieces to be satisfactory, the pots are removed. The iron ball then is dropped into the tubeto seal the hole in the bottom of the pot; the cover and the tubeare removed, and the gears quenched direct from the pot in mineraloil, which is kept at a temperature not higher than 100°F. THE EFFECT. --The heating at 1, 600°F. Gives the first heat treatmentwhich refines the core, which under the former high heat (1, 700°F. )was rendered coarsely crystalline. All the gears, including thescrap gears, are quenched direct from the pot in this manner. The gears then go to the reheating furnaces, situated in front ofa battery of Gleason quenching machines. These furnaces accommodatefrom 12 to 16 crown gears. The carbon-steel gears are heated in areducing atmosphere to about 1, 425°F. (depending on the carboncontent) placed in the dies in the Gleason quenching machine, andquenched between dies in mineral oil at less than 100°F. The testgear receives exactly the same treatment as the others and is thenbroken, giving a record of the condition of both case and core. AFFINITY OF NICKEL STEEL FOR CARBON. --The carbon- and nickel-steelgears are carburized separately owing to the difference in timenecessary for their carburization. Practically all printed informationon the subject is to the effect that nickel steel takes longer tocarburize than plain carbon steel. This is directly opposed tothe conditions found at this plant. For the same depth of case, other conditions being equal, a nickel-steel gear would requirefrom 20 to 30 min. Less than a low carbon-steel gear. From the quenching machines, the gears go to the sand-blastingmachines, situated in the wing of the heat-treating building, wherethey are cleaned. From here they are taken to the testing department. The tests are simple and at the same time most thorough. TESTING AND INSPECTION OF HEAT TREATMENT. --The hard parts of thegear must be so hard that a new mill file does not bite in theleast. Having passed this file test at several points, the gears goto the center-punch test. The inspector is equipped with a woodentrough secured to the top of the bench to support the gear, a numberof center punches (made of 3/4-in. Hex-steel having points sharpenedto an angle of 120 deg. ) and a hammer weighing about 4 oz. Withthese simple tools, supplemented by his skill, the inspector can_feel_ the depth and quality of the case and the condition of thecore. The gears are each tested in this way at several points onthe teeth and elsewhere, the scrap gear being also subjected tothe test. Finally, the scrap gear is securely clamped in thestraightening press shown in Fig. 57. With a 3-1/2-lb. Hammer anda suitable hollow-ended drift manipulated by one of Sandow'sunderstudies, teeth are broken out of the scrap gear at variouspoints. These give a record confirming the center-punch tests, which, if the angle of the center punch is kept at 120 deg. Andthe weight of the hammer and blow are uniform, is very accurate. After passing the center-punch test the ends of the teeth are peenedlightly with a hammer. If they are too hard, small particles flyoff. Such gears are drawn in oil at a temperature of from 300 to350°F. , depending on their hardness. Some builders prefer to havethe extreme outer ends of the teeth drawn somewhat lower than therest. This drawing is done on gas-heated red-hot plates, as shownat _A_ in Fig. 58. [Illustration: FIG. 57. --Press for holding test gears for breaking. ] Nickel steel, in addition to all the tests given to carbon steel, is subjected to a Brinell test. For each steel, the temperatureand the period of treatment are specific. For some unknown reason, apparently like material with like treatment will, in isolatedcases, not produce like results. It then remains for the treatmentto be repeated or modified, but the results obtained during inspectionform a valuable aid to the metallurgist in determining furthertreatment. TEMPERATURE RECORDING AND REGULATION. --Each furnace is equippedwith pyrometers, but the reading and recording of all temperaturesare in the hands of one man, who occupies a room with an openinginto the end of the hardening department. The opening is about 15ft. Above the floor level. On each side of it, easily legible fromall of the furnaces, is a board with the numbers of the variousfurnaces, as shown in Figs. 59 and 60. Opposite each furnace numberis a series of hooks whereon are hung metal numbers representing thepyrometer readings of the temperature in that particular furnace. Within the room, as shown in Fig. 60, the indicating instrumentis to the right, and to the left is a switchboard to connect itwith the thermo-couples in the various furnaces. The boards shownto the right and the left swing into the room, which enables theattendant easily to change the numbers to conform to the pyrometerreadings. Readings of the temperatures of the carburizing furnacesare taken and tabulated every ten minutes. These, numbered 1 to10, are shown on the board to the right in Fig. 59. The card shownin Fig. 61 gives such a record. These records are filed away forpossible future reference. [Illustration: FIG. 58. --Gas heated drawing plate for tooth ends. ] The temperatures of the reheating furnaces, numbered from 1 to26 and shown on the board to the left in Fig. 59, are taken every5 min. Each furnace has a large metal sign on which is marked the temperatureat which the furnace regulator is required to keep his heat. Assoon as any variation from this is posted on the board outsidethe pyrometer room, the attendant sees it and adjusts the burnersto compensate. [Illustration: FIG. 59. --Pyrometer recording room. ] [Illustration: FIG. 60. --Inside of Pyrometer switch room. ] DIES FOR GLEASON TEMPERING MACHINES. --In Fig. 62 is shown a setof dies for the Gleason tempering machine. These accurately madedies fit and hold the gear true during quenching, thus preventingdistortion. [Illustration: FIG. 61. --Carburizing furnace record. ] Referring to Fig. 62, the die _A_ has a surface _B_ which fits theface of the teeth of the gear _C_. This surface is perforated bya large number of holes which permit the quenching oil to circulatefreely. The die _A_ is set in the upper end of the plunger _A_of the tempering machine, shown in Fig. 63, a few inches abovethe surface of the quenching oil in the tank _N_. Inside the die_A_ are the centering jaws _D_, Fig. 62, which are an easy fitfor the bore of the gear _C_. The inner surface of the centeringjaws is in the shape of a female cone. The upper die is shown at_E_. In the center (separate from it, but a snug sliding fit init) is the expander _G_, which, during quenching, enters the taperin the centering jaws _D_, expanding them against the bore of thegear _C_. The faces _F_ of the upper die _E_ fit two angles at theback of the gear and are grooved for the passage of the quenchingoil. The upper die _E_ is secured to the die carrier _B_, shown inFig. 9, and inside the die is the expander _G_, which is backedup by compression springs. [Illustration: FIG. 62. --Dies for Gleason gear-hardening machine. ] HARDENING OPERATION. --Hardening a gear is accomplished as follows:The gear is taken from the furnace by the furnaceman and placed inthe lower die, surrounding the centering jaws, as shown at _H_ inFig. 62 and _C_ in Fig. 63. Air is then turned into the cylinder_D_, and the piston rod _E_, the die carrier _B_, the top die _F_and the expander _G_ descend. The pilot _H_ enters a hole in thecenter of the lower die, and the expander _G_ enters the centeringjaws _I_, causing them to expand and center the gear _C_ in thelower die. On further advance of the piston rod _E_, the expander_G_ is forced upward against the pressure of the springs _J_ andthe upper die _F_ comes in contact with the upper surface of thegear. Further downward movement of the dies, which now clamp thework securely, overcomes the resistance of the pressure weight_K_ (which normally keeps up the plunger _A_), and the gear issubmerged in the oil. The quenching oil is circulated through acooling system outside the building and enters the tempering machinethrough the inlet pipe _L_. When the machine is in the positionshown, the oil passes out through the ports _M_ in the lower plungerto the outer reservoir _N_, passing to the cooling system by way ofthe overflow _O_. When the lower plunger _A_ is forced downward, the ports _M_ are automatically closed and the cool quenching oilfrom the inlet pipe _L_, having no other means of escape, passesthrough the holes in the lower die and the grooves in the upper, circulating in contact with the surfaces of the gear and passes tothe overflow. When the air pressure is released, the counterweightsreturn the parts to the positions shown in Fig. 63, and the operatorremoves the gear. [Illustration: FIG. 63. --Gleason tempering machine. ] The gear comes out uniformly hard all over and of the same degree ofhardness as when tempered in an open tank. The output of the machinedepends on the amount of metal to be cooled, but will average from8 to 16 per hour. Each machine is served by one man, two furnacesbeing required to heat the work. A slight excess of oil is usedin the firing of the furnaces to give a reducing atmosphere andto avoid scale. [Illustration: FIG. 64. --Hardening and shrinking sleeves. ] CARBURIZING LOW-CARBON SLEEVES. --Low-carbon sleeves are carburizedand pushed on malleable-iron differential-case hubs. Formerly, these sleeves were given two treatments after carburization inorder to refine the case and the core, and then sent to the grindingdepartment, where they were ground to a push fit for the hubs. Afterthis they were pushed on the hubs. By the method now employed, the first treatment refines the core, and on the second treatment, the sleeves are pushed on the hub and at the same time hardened. This method cuts out the internal grinding time, pressing on hubs, and haulage from one department to another. Also, less work islost through splitting of the sleeves. The machine for pushing the sleeves on is shown in Fig. 64. At_A_ is the stem on which the hot sleeve _B_ is to be pushed. Thecarburized sleeves are heated in an automatic furnace, which takesthem cold at the back and feeds them through to the front, by whichtime they are at the correct temperature. The loose mandrel _C_is provided with a spigot on the lower end, which fits the holein the differential-case hub. The upper end is tapered as shownand acts as a pilot for the ram _D_. The action of pushing on andquenching is similar to the action of the Gleason tempering machine, with the exception that water instead of oil is used as a quenchingmedium. The speed of operation depends on a number of variables, but from 350 to 500 can be heated and pressed on in 11 hr. CYANIDE BATH FOR TOOL STEELS. --All high-carbon tool steels areheated in a cyanide bath. With this bath, the heat can be controlledwithin 3 deg. The steel is evenly heated without exposure to theair, resulting in work which is not warped and on which there is noscale. The cyanide bath is, of course, not available for high-speedsteel because of the very high temperatures necessary. DROP FORGING DIES The kind of steel used in the die of course influences the heattreatment it is to receive, but this also depends on the kind ofwork the die is to perform. If the die is for a forging which ismachined all over and does not have to be especially close to size, where a variation of 1/16 in. Is not considered excessive, a lowgrade steel will be perfectly satisfactory. In cases of fine work, however, where the variation cannot be over0. 005 to 0. 01 in. We must use a fine steel and prevent its goingout of shape in the heating and quenching. A high quality cruciblesteel is suggested with about the following analysis: Carbon 0. 75per cent, manganese 0. 25 per cent, silicon 0. 15 per cent, sulphur0. 015 per cent, and phosphorus 0. 015 per cent. Such a steel willhave a decalescent point in the neighborhood of 1, 355°F. And forthe size used, probably in a die of approximately 8 in. , it willharden around 1, 450°F. To secure best results care must be taken at every step. The blockshould be heated slowly to about 1, 400°F. , the furnace closed tightand allowed to cool slowly in the furnace itself. It should notsoak at the high temperature. After machining, and before it is put in the furnace for hardening, it should be slowly preheated to 800 or 900°F. This can be done inseveral ways, some putting the die block in front of the open doorof a hardening furnace and keeping the furnace at about 1, 000°F. The main thing is to heat the die block very slowly and evenly. The hardening heat should be very slow, 7 hr. Being none too longfor such a block, bringing the die up gradually to the quenchingtemperature of 1, 450°. This should be held for 1/2 hr. Or even alittle more, when the die can be taken out and quenched. Thereshould be no guess work about the heating, a good pyrometer beingthe only safe way of knowing the correct temperature. The quenching tank should be of good size and have a spray or streamof water coming up near the surface. Dip the die block about 3 in. Deep and let the stream of water get at the face so as to playon the forms. By leaving the rest of the die out of the water, moving the die up and down a trifle to prevent a crack at the lineof immersion, the back of the block is left tough while the faceis very hard. To overcome the tendency to warp the face it is agood plan to pour a little water on the back of the die as thistends to even up the cooling. The depth to which the die is dippedcan be easily regulated by placing bars across the tank at theproper depth. After the scleroscope shows the die to be properly hardened, whichmeans from 98 to 101, the temper should be drawn as soon as convenient. A lead pot in which the back of the die can be suspended so asto heat the back side, makes a good method. Or the die block canbe placed back to the open door of a furnace. On a die of thissize it may take several hours to draw it to the desired temper. This can be tested while warm by the scleroscope method, bearingin mind that the reading will not be the same as when cold. Ifthe test shows from 76 to 78 while warm, the hardness when coldwill be about 83, which is about right for this work. S. A. E. HEAT TREATMENTS The Society of Automotive Engineers have adopted certain heat treatmentsto suit different steels and varying conditions. These have alreadybeen referred to on pages 39 to 41 in connection with the differentsteels used in automobile practice. These treatments are designatedby letter and correspond with the designations in the table. HEAT TREATMENTS _Heat Treatment A_ After forging or machining: 1. Carbonize at a temperature between 1, 600°F. And 1, 750°F. (1, 650-1, 700°F. Desired. ) 2. Cool slowly or quench. 3. Reheat to 1, 450-1, 500°F. And quench. _Heat Treatment B_ After forging or machining: 1. Carbonize between 1, 600°F. And 1, 750°F. (1, 650-1, 700°F. Desired. ) 2. Cool slowly in the carbonizing mixture. 3. Reheat to 1, 550-1, 625°F. 4. Quench. 5. Reheat to 1, 400-1, 450°F. 6. Quench. 7. Draw in hot oil at 300 to 450°F. , depending upon the degree of hardness desired. _Heat Treatment D_ After forging or machining: 1. Heat to 1, 500-1, 600°F. 2. Quench. 3. Reheat to 1, 450-1, 500°F. 4. Quench. 5. Reheat to 600-1, 200°F. And cool slowly. _Heat Treatment E_ After forging or machining: 1. Heat to 1, 500-1, 550°F. 2. Cool slowly. 3. Reheat to 1, 450-1, 500°F. 4. Quench. 5. Reheat to 600-1, 200°F. And cool slowly. _Heat Treatment F_ After shaping or coiling: 1. Heat to 1, 425-1, 475°F. 2. Quench in oil. 3. Reheat to 400-900°F. , in accordance with temper desired and cool slowly. _Heat Treatment G_ After forging or machining: 1. Carbonize at a temperature between 1, 600°F. And 1, 750°F. (1, 650-1, 700°F. Desired). 2. Cool slowly in the carbonizing mixture. 3. Reheat to 1, 500-1, 550°F. 4. Quench. 5. Reheat to 1, 300-1, 400°F. 6. Quench. 7. Reheat to 250-500°F. (in accordance with the necessities of the case) and cool slowly. _Heat Treatment H_ After forging or machining: 1. Heat to 1, 500-1, 600°F. 2. Quench. 3. Reheat to 600-1, 200°F. And cool slowly. _Heat Treatment K_ After forging or machining: 1. Heat to 1, 500-1, 550°F. 2. Quench. 3. Reheat to 1, 300-1, 400°F. 4. Quench. 5. Reheat to 600-1, 200°F. And cool slowly. _Heat Treatment L_ After forging or machining: 1. Carbonize between 1, 600°F. And 1, 750°F. (1, 650-1, 700°F. Desired). 2. Cool slowly in the carbonizing mixture. 3. Reheat to 1, 400-1, 500°F. 4. Quench. 5. Reheat to 1, 300-1, 400°F. 6. Quench. 7. Reheat to 250-500°F. And cool slowly. _Heat Treatment M_ After forging or machining: 1. Heat to 1, 450-1, 500°F. 2. Quench. 3. Reheat to 500-1. 250°F. And cool slowly. _Heat Treatment P_ After forging or machining: 1. Heat to 1, 450-1, 500°F. 2. Quench. 3. Reheat to 1, 375-1, 450°F. Slowly. 4. Quench. 5. Reheat to 500-1, 250°F. And cool slowly. _Heat Treatment Q_ After forging: 1. Heat to 1, 475-1, 525°F. (Hold at this temperature one-half hour, to insure thorough heating. ) 2. Cool slowly. 3. Machine. 4. Reheat to 1, 375-1, 425°F. 5. Quench. 6. Reheat to 250-550°F. And cool slowly. _Heat Treatment R_ After forging: 1. Heat to 1, 500-1, 550°F. 2. Quench in oil. 3. Reheat to 1, 200-1, 300°F. (Hold at this temperature three hours. ) 4. Cool slowly. 5. Machine. 6. Reheat to 1, 350-1, 450°F. 7. Quench in oil. 8. Reheat to 250-500°F. And cool slowly. _Heat Treatment S_ After forging or machining: 1. Carbonize at a temperature between 1, 600 and 1, 750°F. (1, 650-1, 700°F. Desired. ) 2. Cool slowly in the carbonizing mixture. 3. Reheat to 1, 650-1, 750°F. 4. Quench. 5. Reheat to 1, 475-1, 550°F. 6. Quench. 7. Reheat to 250-550°F. And cool slowly. _Heat Treatment T_ After forging or machining: 1. Heat to 1, 650-1, 750°F. 2. Quench. 3. Reheat to 500-1, 300°F. And cool slowly. _Heat Treatment U_ After forging: 1. Heat to 1, 525-1, 600°F. (Hold for about one-half hour. ) 2. Cool slowly. 3. Machine. 4. Reheat to 1, 650-1, 700°F. 5. Quench. 6. Reheat to 350-550°F. And cool slowly. _Heat Treatment V_ After forging or machining: 1. Heat to 1, 650-1, 750°F. 2. Quench. 3. Reheat to 400-1, 200°F. And cool slowly. RESTORING OVERHEATED STEEL The effect of heat treatment on overheated steel is shown graphicallyin Fig. 65 to the series of illustrations on pages 137 to 144. Thiswas prepared by Thos. Firth & Sons, Ltd. , Sheffield, England. [Illustration: FIG. 65. --Chart of changes due to heating and cooling. ] The center piece Fig. 65 represents a block of steel weighing about25 lb. The central hole accommodated a thermo-couple which was attachedto an autographic recorder. The curve is a copy of the temperaturerecord during heating and cooling. Into the holes in the side ofthe block small pegs of overheated mild steel were inserted. Onepeg was withdrawn and quenched at each of the temperatures indicatedby the numbered arrows, and after suitable preparation these pegswere photographed in order to show the changes in structure takingplace during heating and cooling operations. The illustrations herereproduced are selected from those photographs with the objectof presenting pictorially the changes involved in the refining ofoverheated steel or steel castings. Figures 66 to 79 with theircaptions show much that is of value to steel users. [Illustration: FIG. 66. --The structure of overheated mild steelfrom which all the pegs were made (magnified 25 diameters). Thepegs withdrawn at 720°C. , or earlier, had this structure and werequite soft. ] [Illustration: FIG. 67. --Peg withdrawn at 750°C. (magnified 25diameters). The structure is apparently unaltered, but the peg washard and, unlike the earlier ones, would not bend double. ] [Illustration: FIG. 68. --A portion of 66 magnified 200 diametersto show that the dark (pearlite) areas are laminated. ] [Illustration: FIG. 69. --A portion of 67 magnified 200 diameters, showing that pearlite areas are no longer laminated and providingreason for observed hardness. ] [Illustration FIG. 70. --Peg withdrawn at 780°C. (magnified 25diameters), showing inter-diffusion of transformed pearlite andferrite areas. ] [Illustration: FIG. 71. --Peg withdrawn at 800°C. (magnified 25diameters), showing inter-diffusion so far advanced that the originaloutline of the crystals is now only faintly suggested. ] [Illustration: FIG. 72. --Peg withdrawn at 850°C. (magnified 100diameters) after inter-diffusion was completed. Note the regularoutlines and the small size of the crystals as compared with 67. ] [Illustration: FIG. 73. --To facilitate comparison 67 was enlargedto the same magnification as 62, and the one superimposed on theother. The single large crystal occupied as much space as 8, 000of the smaller ones. ] [Illustration: FIG. 74. --The peg withdrawn on cooling at 800°C. (magnified 100 diameters) shows the first reappearance of freeferrite. All pegs withdrawn at higher temperatures were like Fig. 72. ] [Illustration: FIG. 75. --Peg withdrawn after cooling to 760°C. Theincreased amount of free ferrite arranges itself about the crystalsas envelopes. ] [Illustration: FIG. 76. -Peg withdrawn after cooling to 740°C. ] [Illustration: FIG. 77. --Peg withdrawn after cooling to 670°C. (magnified 800 diameters). Just at this moment the lamination ofpearlite, which now occupied its original area, was taking place. In some parts the lamination was perfect, in other parts the ironand iron-carbide were still dissolved in each other. ] [Illustration: FIG. 78. --Any peg withdrawn after 670°C. On cooling(magnified 100 diameters). ] [Illustration: FIG. 79. --Structure of overheated steel before (left)and after refining (right). ] CHAPTER IX HARDENING CARBON STEEL FOR TOOLS For years the toolmaker had full sway in regard to make of steelwanted for shop tools, he generally made his own designs, hardened, tempered, ground and usually set up the machine where it was tobe used and tested it. Most of us remember the toolmaker during the sewing machine periodwhen interchangeable tools were beginning to find their way; rathercautiously at first. The bicycle era was the real beginning oftool making from a manufacturing standpoint, when interchangeabletools for rapid production were called for and toolmakers were ingreat demand. Even then, jigs, and fixtures were of the toolmaker'sown design, who practically built every part of it from start tofinish. The old way, however, had to be changed. Instead of the toolmakerstarting his work from cutting off the stock in the old hack saw, a place for cutting off stock was provided. If, for instance, aforming tool was wanted, the toolmaker was given the master toolto make while an apprentice roughed out the cutter. The toolmaker, however, reserved the hardening process for himself. That was oneof the particular operations that the old toolmaker refused togive up. It seemed preposterous to think for a minute that anyone else could possibly do that particular job without spoilingthe tools, or at least warp it out of shape (most of us did notgrind holes in cutters 15 to 20 years ago); or a hundred or morethings might happen unless the toolmaker did his own hardeningand tempering. That so many remarkably good tools were made at that time is stilla wonder to many, when we consider that the large shop had from 30to 40 different men, all using their own secret compounds, heatingto suit eyesight, no matter if the day was bright or dark, and thentempering to color. But the day of the old toolmaker has changed. Now a tool is designed by a tool designer, O. K. 'd, and then a printgoes to the foreman of the tool department, who specifies the sizeand gets the steel from the cutting-off department. After finishingthe machine work it goes to the hardening room, and this is theproblem we shall now take up in detail. THE MODERN HARDENING ROOM. --A hardening room of today means a verydifferent place from the dirty, dark smithshop in the corner withthe open coal forge. There, when we wanted to be somewhat particular, we sometimes shoveled the coal cinders to one side and piled a greatpile of charcoal on the forge. We now have a complete equipment;a gas- or oil-heating furnace, good running water, several sizesof lead pots, and an oil tank large enough to hold a barrel ofoil. By running water, we mean a large tank with overflow pipesgiving a constant supply. The ordinary hardening room equipmentshould consist of: Gas or oil muffle furnace for hardening. Gas or oil forge furnace. A good size gas or oil furnace for annealing and case-hardening. A gas or oil furnace to hold lead pots. Oil tempering tank, gas- or oil-heated. Pressure blower. Large oil tank to hold at least a barrel of oil. Big water tank with screen trays connected with large pipe from bottom with overflow. Straightening press. The furnace should be connected with pyrometers and tempering tank with a thermometer. Beside all this you need a good man. It does not make much differencehow completely the hardening department is fitted up, if you expectgood work, a small percentage of loss and to be able to tackle anythingthat comes along, you must have a good man, one who understandsthe difference between low- and high-carbon steel, who knows whenparticular care must be exercised on particular work. In otherwords, a man who knows how his work should be done, and has theintelligence to follow directions on treatments of steel on whichhe has had no experience. Jewelers' tools, especially for silversmith's work, probably haveto stand the greatest punishment of any all-steel tools and tomake a spoon die so hard that it will not sink under a blow froman 1, 800-lb. Hammer with a 4-ft. Drop, and still not crack, demandscareful treatment. To harden such dies, first cover the impression on the die withpaste made from bone dust or lampblack and oil. Place face downin an iron box partly filled with crushed charcoal, leaving backof die uncovered so that the heat can be seen at all times. Heatslowly in furnace to a good cherry red. The heat depends on thequality and the analysis of steel and the recommended actions ofthe steel maker should be carefully followed. When withdrawn fromthe fire the die should be quenched as shown in Fig. 80 with theface of die down and the back a short distance out of the water. When the back is black, immerse all over. [Illustration: FIG. 80. --Quenching a die, face down. ] If such a tank is not at hand, it would pay to rig one up at once, although a barrel of brine may be used, or the back of the diemay be first immersed to a depth of about 1/2 in. When the pieceis immersed, hold die on an angle as in Fig. 81. [Illustration: FIG. 81. --Hold die at angle to quench. ] This is for the purpose of expelling all steam bubbles as theyform in contact with hot steel. We are aware of the fact that agreat many toolmakers in jewelry shops still cling to the overheadbath, as in Fig. 82, but more broken pieces and more dies withsoft spots are due to this method than to all the others combined, as the water strikes one spot in force, contracting the surfaceso much faster than the rest of the die that the results are thesame as if an uneven heating had been given the steel. TAKE TIME FOR HARDENING. --Uneven heating and poor quenching hascaused loss of many very valuable dies, and it certainly seemsthat when a firm spends from $75 to $450 in cutting a die thata few hours could be spared for proper hardening. But the usualfeeling is that a tool must be hurried as soon as the hardenergets it, and if a burst die is the result from either uneven oroverheated steel and quenching same without judgment, the steelgets the blame. [Illustration: FIG. 82. --An obsolete method. ] Give the steel a chance to heat properly, mix a little common sensewith "your 30 years experience on the other fellows steel. " Rememberthat high-carbon steel hardens at a lower heat than low-carbonsteel, and quench when at the right heat in the two above ways, and 99 per cent of the trouble will vanish. When a die flies to pieces in quenching, don't rush to thesuperintendent with a "poor-steel" story, but find out first why itbroke so that the salesman who sold it will not be able to hardenpiece after piece from the same bar satisfactorily. If you finda "cold short, " commonly called "a pipe, " you can lay the blameon the steelmaker. If it is a case of overheating and quenchingwhen too hot, you will find a coarse grain with many bright spotslike crystals to the hardening depth. If uneven heating is thecause, you will find a wider margin of hardening depth on one sidethan on the other, or find the coarse grain from over-heating onone side while on the other you will find a close grain, whichmay be just right. If you find any other faults than a "pipe, "or are not able to harden deep enough, then take the blame likea man and send for information. The different steel salesmen aregood fellows and most of them know a thing or two about their ownbusiness. For much work a cooling bath at from 50 to 75°F. Is very good bothfor small hobs, dies, cutter plates or plungers. Some work willharden best in a barrel of brine, but in running cold water, splendidresults will be obtained. Cutter plates should always be dippedcorner first and if any have stripper holes, they should firstbe plugged with asbestos or fire clay cement. In general it may be said that the best hardening temperature forcarbon steel is the lowest temperature at which it will hardenproperly. CARBON IN TOOL STEEL Carbon tool steel, or "tool steel" as it is commonly called, usuallycontains from 80 to 125 points (or from 0. 80 to 1. 25 per cent)of carbon, and none of the alloys which go to make up the highspeed steels. This was formerly known also as crucible or "cast"steel, or crucible cast steel, from the way in which it was made. This was before the days of steel castings. The advent of thesecaused so much confusion that the term was soon dropped. When wesay "tool steel, " we nearly always refer to carbon-tool steel, high-speed steel being usually designated by that name. For many purposes carbon-steel cutters are still found best, althoughwhere a large amount of material is to be removed at a rapid rate, it has given way to high-speed steels. CARBON STEELS FOR DIFFERENT TOOLS All users of tool steels should carefully study the different qualitiesof the steels they handle. Different uses requires different kinds ofsteel for best results, and for the purpose of designating differentsteels some makers have adopted the two terms "temper, " and "quality, "to distinguish between them. In this case temper refers to the amount of carbon which is combinedwith the iron to make the metal into a steel. The quality meansthe absence of phosphorous, sulphur and other impurities, thesedepending on the ores and the methods of treatment. Steel makers have various ways of designating carbon steels fordifferent purposes. Some of these systems involve the use of numbers, that of the Latrobe Steel Company being given herewith. It willbe noted that the numbers are based on 20 points of carbon perunit. The names given the different tempers are also of interest. Other makers use different numbers. The temper list follows: LATROBE TEMPER LIST OF CARBON TOOL STEELS No. 3 temper 0. 60 to 0. 69 per cent carbon No. 3-1/2 temper 0. 70 to 0. 79 per cent carbon No. 4 temper 0. 80 to 0. 89 per cent carbon No. 4-1/2 temper 0. 90 to 0. 99 pet cent carbon No. 5 temper 1. 00 to 1. 09 per cent carbon No. 5-1/2 temper 1. 10 to 1. 19 per cent carbon No. 6 temper 1. 20 to 1. 29 per cent carbon No. 6-1/2 temper 1. 30 to 1. 39 per cent carbon No. 7 temper 1. 40 to 1. 49 per cent carbon USES OF THE VARIOUS TEMPERS OF CARBON TOOL STEEL DIE TEMPER. --No. 3: All kinds of dies for deep stamping, pressingand drop forgings. Mining drills to harden only. Easily weldable. SMITHS' TOOL TEMPER. --No. 3-1/2: Large punches, minting and rivetdies, nailmakers' tools, hammers, hot and cold sets, snaps andboilermakers' tools, various smiths' tools, large shear blades, double-handed chisels, caulking tools, heading dies, masons' toolsand tools for general welding purposes. SHEAR BLADE TEMPER. --No. 4: Punches, large taps, screwing dies, shear blades, table cutlery, circular and long saws, heading dies. Weldable. GENERAL PURPOSE TEMPER. --No. 4-1/2: Taps, small punches, screwingdies, sawwebs, needles, etc. , and for all general purposes. Weldable. AXE TEMPER. --No. 5: Axes, chisels, small taps, miners' drills andjumpers to harden and temper, plane irons. Weldable with care. CUTLERY TEMPER. --No. 5-1/2: Large milling cutters, reamers, pocketcutlery, wood tools, short saws, granite drills, paper and tobaccoknives. Weldable with very great care. TOOL TEMPER. --No. 6: Turning, planing, slotting, and shaping tools, twist drills, mill picks, scythes, circular cutters, engravers'tools, surgical cutlery, circular saws for cutting metals, beveland other sections for turret lathes. Not weldable. HARD TOOL TEMPER. --No. 6-1/2: Small twist drills, razors, smalland intricate engravers' tools, surgical instruments, knives. Notweldable. RAZOR TEMPER. --No. 7: Razors, barrel boring bits, special lathetools for turning chilled rolls. Not weldable. STEEL FOR CHISELS AND PUNCHES The highest grades of carbon or tempering steels are to be recommendedfor tools which have to withstand shocks, such as for cold chiselsor punches. These steels are, however, particularly useful whereit is necessary to cut tempered or heat-treated steel which ismore than ordinarily hard, for cutting chilled iron, etc. They areuseful for boring, for rifle-barrel drilling, for fine finishingcuts, for drawing dies for brass and copper, for blanking dies forhard materials, for formed cutters on automatic screw machinesand for roll-turning tools. Steel of this kind, being very dense in structure, should be givenmore time in heating for forging and for hardening, than carbonsteels of a lower grade. For forging it should be heated slowlyand uniformly to a bright red and only light blows used as theheat dies out. Do not hammer at all at a black heat. Reheat slowlyto a dark red for hardening and quench in warm water. Grind on awet grindstone. Where tools have to withstand shocks and vibration, as in pneumatichammer work, in severe punching duty, hot or cold upsetting orsimilar work, tool steels containing vanadium or chrome-vanadiumgive excellent results. These are made particularly for work ofthis kind. CHISELS-SHAPES AND HEAT TREATMENT[1] [Footnote 1: Abstract of paper by HENRY FOWLER, chief mechanicalengineer of the Midland Ry. , England, before the Institution ofMechanical Engineers. ] In the chief mechanical engineer's department of the Midland Ry. , after considerable experimenting, it was decided to order chiselsteel to the following specifications: carbon, 0. 75 to 0. 85 percent, the other constituents being normal. This gives a completeanalysis as follows: carbon, 0. 75 to 0. 85; manganese, 0. 30; silicon, 0. 10; sulphur, 0. 025; phosphorus, 0. 025. The analysis of a chisel which had given excellent service was asfollows: carbon, 0. 75; manganese, 0. 38; silicon, 0. 16; sulphur, 0. 028; phosphorus, 0. 026. The heat treatment is unknown. [Illustration: FIG. 83. --Forms of chisels standardized for thelocomotive shops of the Midland Ry. , England. ] At the same time that chisel steel was standardized, the form ofthe chisels themselves was revised, and a standard chart of theseas used in the locomotive shops was drawn up. Figure 83 shows themost important forms, which are made to stock orders in the smithyand forwarded to the heat-treatment room where the hardening andtempering is carried out on batches of fifty. A standard systemof treatment is employed, which to a very large extent does awaywith the personal element. Since the chemical composition is moreor less constant, the chief variant is the section which causesthe temperatures to be varied slightly. The chisels are carefullyheated in a gas-fired furnace to a temperature of from 730 to 740°C. (1, 340 to 1, 364°F. ) according to section. In practice, the firstchisel, is heated to 730°C. ; and the second to 735°C. (1, 355°F. );and a 1 in. Half round chisel to 740°C. , because of their varyingincreasing thickness of section at the points. Upon attaining thissteady temperature, the chisels are quenched to a depth of 3/8to 1/2 in. From the point in water, and then the whole chisel isimmersed and cooled off in a tank containing linseed oil. The oil-tank is cooled by being immersed in a cold-water tank throughwhich water is constantly circulated. After this treatment, thechisels have a dead hard point and a tough or sorbitic shaft. Theyare then tempered or the point "let down. " This is done by immersingthem in another oil-bath which has been raised to about 215°C. (419°F). The first result is, of course, to drop the temperatureof the oil, which is gradually raised to its initial point. Onapproaching this temperature the chisels are taken out about every2°C. Rise and tested with a file, and at a point between 215 and220°C. (428°F. ), when it is found that the desired temper has beenreached, the chisels are removed, cleaned in sawdust, and allowedto cool in an iron tray. No comparative tests of these chisels with those bought and treatedby the old rule-of-thumb methods have been made, as no exact method ofcarrying out such tests mechanically, other than trying the hardnessby the Brinell or scleroscope method, are known; any ordinary testdepends so largely upon the dexterity of the operator. The universalopinion of foremen and those using the chisels as to the advantagesof the ones receiving the standard treatment described is thata substantial improvement has been made. The chisels were not"normalized. " Tests of chisels normalized at about 900°C. (1, 652°F. )showed that they possessed no advantage. Tools or pieces which have holes or deep depressions should befilled before heating unless it is necessary to have the holeshard on the inside. In that case the filling would keep the wateraway from the surface and no hardening would take place. Wherefilling is to be done, various materials are used by differenthardeners. Fireclay and common putty seem to be favored by many. Every mechanic who has had anything to do with the hardening oftools knows how necessary it is to take a cut from the surface ofthe bar that is to be hardened. The reason is that in the processof making the steel its outer surface has become decarbonized. This change makes it low-carbon steel, which will of course notharden. It is necessary to remove from 1/16 to 1/4 in. Of diameteron bars ranging from 1/2 to 4 in. This same decarbonization occurs if the steel is placed in theforge in such a way that unburned oxygen from the blast can get atit. The carbon is oxidized, or burned out, converting the outsideof the steel into low-carbon steel. The way to avoid this is to usea deep fire. Lack of this precaution is the cause of much spoiledwork, not only because of decarbonization of the outer surfaceof the metal, but because the cold blast striking the hot steelacts like boiling hot water poured into an ice-cold glass tumbler. The contraction sets up stresses that result in cracks when thepiece is quenched. PREVENTING DECARBONIZATION OF TOOL STEEL It is especially important to prevent decarbonization in such toolsas taps and form cutters, which must keep their shape after hardeningand which cannot be ground away on the profile. For this reasonit is well to put taps, reamers and the like into pieces of pipein heating them. The pipe need be closed on one end only, as theair will not circulate readily unless there is an opening at bothends. Even if used in connection with a blacksmith's forge the lead bathhas an advantage for heating tools of complicated shapes, sinceit is easier to heat them uniformly and they are submerged andaway from the air. The lead must be stirred frequently or the heatis not uniform in all parts of the lead bath. Covering the leadwith powdered charcoal will largely prevent oxidization and wasteof lead. Such a bath is good for temperatures between 620 and 1, 150°F. Athigher temperatures there is much waste of lead. ANNEALING TO RELIEVE INTERNAL STRESSES Work quenched from a high temperature and not afterward temperedwill, if complex in shape, contain many internal stresses which maylater cause it to break. They may be eased off by slight heatingwithout materially lessening the hardness of the piece. One wayto do this is to hold the piece over a fire and test it with amoistened finger. Another way is to dip the piece in boiling waterafter it has first been quenched in a cold bath. Such steps arenot necessary with articles which will afterward be tempered andin which the strains are thus reduced. In annealing steels the operation is similar to hardening, as faras heating is concerned. The critical temperatures are the properones for annealing as well as hardening. From this point on thereis a difference, for annealing consists in cooling as slowly aspossible. The slower the cooling the softer will be the steel. Annealing may be done in the open air, in furnaces, in hot ashesor lime, in powdered charcoal, in burnt bone, in charred leatherand in water. Open-air annealing will do as a crude measure incases where it is desired to take the internal stresses out ofa piece. Care must be taken in using this method that the pieceis not exposed to drafts or placed on some cold substance thatwill chill it. Furnace annealing is much better and consists inheating the piece in a furnace to the critical temperature andthen allowing the work and the furnace to cool together. When lime or ashes are used as materials to keep air away fromthe steel and retain the heat, they should be first heated to makesure that they are dry. Powdered charcoal is used for high-gradeannealing, the piece being packed in this substance in an iron boxand both the work and the box raised to the critical temperatureand then allowed to cool slowly. Machinery steel may be annealed inspent ground-bone that has been used in casehardening; _but toolsteel must never be annealed in this way_, as it will be injuredby the phosphorus contained in the bone. Charred leather is thebest annealing material for high-carbon steel, because it preventsdecarbonizing taking place. DOUBLE ANNEALING Water annealing consists in heating the piece, allowing it to coolin air until it loses its red heat and becomes black and thenimmediately quenching it in water. This plan works well for verylow-carbon steel; but for high-carbon steel what is known as the"double annealing treatment" must be given, provided results arewanted quickly. The process consists in heating the steel quickly to200° or more above the upper critical, cooling in air down throughthe recalescence point, then reheating it to just above the criticalpoint and again cooling slowly through the recalescence, then quenchingin oil. This process retains in the steel a fine-grained structurecombined with softness. QUENCHING TOOL STEEL To secure proper hardness, the cooling of quenching of steel isas important as its heating. Quenching baths vary in nature, therebeing a large number of ways to cool a piece of steel in contrastto the comparatively few ways of heating it. Plain water, brine and oil are the three most common quenchingmaterials. Of these three the brine will give the most hardness, and plain water and oil come next. The colder that any of thesebaths is when the piece is put into it the harder will be the steel;but this does not mean that it is a good plan to dip the heatedsteel into a tank of ice water, for the shock would be so greatthat the bar would probably fly to pieces. In fact, the quenchingbath must be sometimes heated a bit to take off the edge of theshock. Brine solutions will work uniformly, or give the same degree ofhardness, until they reach a temperature of 150°F. Above whichtheir grip relaxes and the metals quenched in them become softer. Plain water holds its grip up to a temperature of approximately100°F. ; but oil baths, which are used to secure a slower rate ofcooling, may be used up to 500° or more. A compromise is sometimeseffected by using a bath consisting of an inch or two of oil floatingon the surface of water. As the hot steel passes through the oil, the shock is not as severe as if it were to be thrust directlyinto the water; and in addition, oil adheres to the tool and keepsthe water from direct contact with the metal. The old idea that mercury will harden steel more than any otherquenching material has been exploded. A bath consisting of meltedcyanide of potassium is useful for heating fine engraved dies andother articles that are required to come out free from scale. Onemust always be careful to provide a hood or exhaust system to getrid of the deadly fumes coming from the cyanide pot. The one main thing to remember in hardening tool steel is to quenchon a rising heat. This does not mean a rapid heating as a slowincrease in temperature is much better in every way. THE THEORY OF TEMPERING. --Steel that has been hardened is generallyharder and more brittle than is necessary, and in order to bringit to the condition that meets our requirements a treatment calledtempering is used. This increases the toughness of the steel, _i. E. _, decrease the brittleness at the expense of a slight decrease inhardness. There are several theories to explain this reaction, but generallyit is only necessary to remember that in hardening we quench steelfrom the austenite phase, and, due to this rapid cooling, the normalchange from austenite to the eutectoid composition does not havetime to take place, and as a consequence the steel exists in apartially transformed, unstable and very hard condition at atmospherictemperatures. But owing to the internal rigidity which exists incold metal the steel is unable to change into its more stable phaseuntil atoms can rearrange themselves by the application of heat. The higher the heat, the greater the transformation into the softerphases. As the transformation takes place, a certain amount of heatof reaction, which under slow cooling would have been released inthe critical range, is now released and helps to cause a furtherslight reaction. If a piece of steel is heated to a certain temperature and heldthere, the tempering color, instead of remaining unchanged at thistemperature, will advance in the tempering-color scale as it wouldwith increasing temperature. This means that the tempering colorsdo not absolutely correspond to the temperatures of steels, but thevariations are so slight that we can use them in actual practice. (See Table 23, page 158. ) TEMPERATURES TO USE. --As soon as the temperature of the steel reaches100°C. (212°F. ) the transformation begins, increasing in intensityas the temperature is raised, until finally when the lower criticalrange is reached, the steel has been all changed into the ordinaryconstituents of unhardened steels. If a piece of polished steel is heated in an ordinary furnace, athin film of oxides will form on its surface. The colors of thisfilm change with temperature, and so, in tempering, they are generallyused as an indication of the temperature of the steel. The steelshould have at least one polished face so that this film of oxidesmay be seen. An alternative method to the determination of temper by color isto temper by heating in an oil or salt bath. Oil baths can be usedup to temperatures of 500°F. ; above this, fused-salt baths arerequired. The article to be tempered is put into the bath, broughtup to and held at the required temperature for a certain lengthof time, and then cooled, either rapidly or slowly. This takeslonger than the color method, but with low temperatures the resultsare more satisfactory, because the temperature of the bath canbe controlled with a pyrometer. The tempering temperatures givenin the following table are taken from a handbook issued by theMidvale Steel Company. TABLE 23. --TEMPERING TEMPERATURES FOR STEELS---------------------------------------------------------------------------- Temperature | | Temperature | for 1 hr. | | for 8 min. |---------------| Color |---------------| UsesDeg. F. |Deg. C. | |Deg. F. |Deg. C. |-------|-------|------------|-------|-------|------------------------------- 370 | 188 |Faint yellow| 460 | 238 |Scrapers, brass-turning tools, | | | | |reamers, taps, milling cutters, | | | | |saw teeth. 390 | 199 |Light straw | 510 | 265 |Twist drills, lathe tools, | | | | |planer tools, finishing tools 410 | 210 |Dark straw | 560 | 293 |Stone tools, hammer faces, | | | | |chisels for hard work, boring | | | | |cutters. 430 | 221 |Brown | 610 | 321 |Trephining tools, stamps. 450 | 232 |Purple | 640 | 337 |Cold chisels for ordinary work, | | | | |carpenters' tools, picks, cold | | | | |punches, shear blades, slicing | | | | |tools, slotter tools. 490 | 254 |Dark blue | 660 | 343 |Hot chisels, tools for hot | | | | |work, springs. 510 | 265 |Light blue | 710 | 376 |Springs, screw drivers. ---------------------------------------------------------------------------- It will be noted that two sets of temperatures are shown, one beingspecified for a time interval of 8 min. And the other for 1 hr. Forthe finest work the longer time is preferable, while for ordinaryrough work 8 min. Is sufficient, after the steel has reached thespecified temperature. The rate of cooling after tempering seems to be immaterial, andthe piece can be cooled at any rate, providing that in large piecesit is sufficiently slow to prevent strains. KNOWING WHAT TAKES PLACE. --How are we to know if we have given apiece of steel the very best possible treatment? The best method is by microscopic examination of polished and etchedsections, but this requires a certain expense for laboratory equipmentand upkeep, which may prevent an ordinary commercial plant fromattempting such a refinement. It is highly recommended that anyfirm that has any large amount of heat treatment to do, installsuch an equipment, which can be purchased for from $250 to $500. Its intelligent use will save its cost in a very short time. The other method is by examination of fractures of small test bars. Steel heated to its correct temperatures will show the finest possiblegrain, whereas underheated steel has not had its grain structurerefined sufficiently, and so will not be at its best. On the otherhand, overheated steel will have a coarser structure, dependingon the extent of overheating. To determine the proper quenching temperature of any particulargrade of steel it is only necessary to heat pieces to varioustemperatures not more than 20°C. (36°F. ) apart, quench in water, break them, and examine the fractures. The temperature producingthe finest grain should be used for annealing and hardening. Similarly, to determine tempering temperatures, several piecesshould be hardened, then tempered to various degrees, and cooledin air. Samples, say six, reheated to temperatures varying by 100°from 300 to 800°C. Will show a considerable range of properties, and the drawing temperature of the piece giving the desired resultscan be used. For drawing tempers up to 500°F. Oil baths of fresh cotton seedoil can be safely and satisfactorily used. For higher temperaturea bath of some kind of fused salt is recommended. HINTS FOR TOOL STEEL USERS Do not hesitate to ask for information from the maker as to thebest steel to use for a given purpose, mentioning in as much detailas possible the use for which it is intended. Do not heat the steel to a higher degree than that fixed in thedescription of each class. Never heat the steel to more than acherry red without forging it or giving it a definite heat treatment. Heating steel at even moderate temperature is liable to coarsen thegrain which can only be restored by forging or by heat treating. Let the forging begin as soon as the steel is hot enough and neverlet tool steel soak in the fire. Continue the hammering vigorouslyand constantly, using lighter blows as it cools off, and stoppingwhen the heat becomes a very dull red or a faint brown. Should welding be necessary care should be taken not to overheatin order to make an easy weld. Keep it below the sparkling pointas this indicates that the steel is burnt. Begin to forge as soon as the welds are put together, taking careto use gentle strokes at first increasing them as the higher heatfalls, but not overdoing the hammering when the steel cools. Thehammering should be extended beyond the welding point and shouldcontinue until the dull red or brown heat is reached. PREVENTING CRACKS IN HARDENING The blacksmith in the small shop, where equipment is usually verylimited, often consisting of a forge, a small open hard-coal furnace, a barrel of water and a can of oil must have skill and experience. With this equipment the smith is expected to, and usually can, produce good results if proper care is taken. In hardening carbon tool steel in water, too much cannot be said infavor of slow, careful heating, nor against overheating if cracksare to be avoided. It is not wise to take the work from the hardening bath and leaveit exposed to the air if there is any heat left in it, becauseit is more liable to crack than if left in the bath until cold. In heating, plenty of time is taken for the work to heat evenlyclear through, thus avoiding strains caused by quick and improperheating, In quenching in water, contraction is much more rapidthan was the expansion while heating, and strains begin the momentthe work touches the water. If the piece has any considerable sizeand is taken from the bath before it is cold and allowed to come tothe air, expansion starts again from the inside so rapidly that thechilled hardened surface cracks before the strains can be relieved. Many are most successful with the hardening bath about blood warm. When the work that is being hardened is nearly cold, it is takenfrom the water and instantly put into a can of oil, where it isallowed to finish cooling. The heat in the body of the tool willcome to the surface more slowly, thus relieving the strain andovercoming much of the danger of cracking. Some contend that the temper should be drawn as soon as possibleafter hardening: but that if this cannot be done for some hours, thework should be left in the oil until the tempering can be done. Itis claimed that forming dies and punch-press dies that are difficultto harden will seldom crack if treated in this way. Small tools or pieces that are very troublesome because of peculiarshape should be made of steel which has been thoroughly annealed. It is often well to mill or turn off the outer skin of the bar, to remove metal which has been cold-worked. Then heat slowly justthrough the critical range and cool in the furnace, in order toproduce a very fine grain. Tools machined from such stock, andhardened with the utmost care, will have the best chance to survivewithout warping, growth or cracking. SHRINKING AND ENLARGING WORK Steel can be shrunk or enlarged by proper heating and cooling. Pins for forced fits can be enlarged several thousandths of aninch by rapid heating to a dull red and quenching in water. Thetheory is that the metal is expanded in heating and that the suddencooling sets the outer portion before the core can contract. Indipping the piece is not held under water till cold but is dipped, held a moment and removed. Then dipped again and again until cold. Rings and drawing dies are also shrunk in a similar way. The ringsare slowly heated to a cherry red, slipped on a rod and rolledin a shallow pan of water which cools only the outer edge. Thisholds the outside while the inner heated portion is forced inward, reducing the hole. This operation can be repeated a number of timeswith considerable success. TEMPERING ROUND DIES A number of circular dies of carbon tool steel for use in toolholders of turret lathes were required. No proper tempering ovenwas available, so the following method was adopted and proved quitesuccessful. After the dies had been hardened dead hard in water, they werecleaned up bright. A pair of ordinary smiths' tongs was made withjaws of heavy material and to fit nicely all around the outside ofthe die, leaving a 3/32-in. Space when the jaws were closed aroundthe die. The dies being all ready, the tongs were heated red hot, andthe dies were picked up and held by the tongs. This tempered themfrom the outside in, left the teeth the temper required and theoutside slightly softer. The dies held up the work successfullyand were better than when tempered in the same bath. THE EFFECT OF TEMPERING ON WATER-QUENCHED GAGES The following information has been supplied by Automatic and ElectricFurnaces, Ltd. , 6, Queenstreet, London, S. W. : Two gages of 3/4 in. Diameter, 12 threads per inch, were heatedin a Wild-Barfield furnace, using the pyroscopic detector, andwere quenched in cold water. They were subsequently tempered in asalt bath at various increasing temperatures, the effective diameterof each thread and the scleroscope hardness being measured at eachstage. The figures are in 10, 000ths of an inch, and indicate thechange + or - with reference to the original effective diameterof the gages. The results for the two gages have been averaged. TABLE 24. --CHANGES DUE TO QUENCHING---------------------------------------------------------------- | After |Tempering temperature, degrees Centigrade Thread |quenching|----------------------------------------- | | 220 | 260 | 300 | 340 | 380 | 420------------|---------|------|------|------|------|------|------ 1 | +25 | +19 | +17 | +15 | +13 | +11 | +11 2 | +18 | +12 | +11 | + 9 | + 6 | + 5 | + 5 3 | +12 | + 6 | + 5 | + 3 | 0 | 0 | 0 4 | +10 | + 4 | + 4 | + 2 | . .. | 0 | - 1 5 | + 9 | + 4 | + 4 | + 2 | 0 | 0 | 0 6 | + 9 | + 4 | + 3 | + 2 | 0 | 0 | 0 7 | +10 | + 5 | + 5 | + 3 | + 2 | + 1 | + 2 8 | + 8 | + 4 | + 3 | + 2 | 0 | 0 | + 1 9 | + 9 | + 4 | + 3 | + 2 | + 1 | + 1 | + 1 10 | + 9 | + 5 | + 5 | + 3 | + 2 | + 2 | + 2 11 | + 7 | + 4 | + 4 | + 2 | + 1 | + 1 | + 1 12 | + 9 | + 5 | + 5 | + 5 | + 4 | + 4 | + 3 | | | | | | |Scleroscope | 80 | 70 | 70 | 62 | 56 | 53 | 52---------------------------------------------------------------- Had these gages been formed with a plain cylindrical end projectingin front of the screw, the first two threads would have been preventedfrom increasing more than the rest. The gages would then have beenfairly easily corrected by lapping after tempering at 220°C. Practicallyno lapping would be required if they were tempered at 340°C. Thereseems to be no advantage in going to a higher temperature thanthis. The same degree of hardness could have been obtained withconsiderably less distortion by quenching directly in fused salt. Itis interesting to note that when the swelling after water quenchingdoes not exceed 0. 0012 in. , practically the whole of it may berecovered by tempering at a sufficiently high temperature, but whenthe swelling exceeds this amount the steel assumes a permanentlystrained condition, and at the most only 0. 0014 in. Can be recoveredby tempering. TEMPERING COLORS ON CARBON STEELS Opinions differ as to the temperature which is indicated by thevarious colors, or oxides, which appear on steel in tempering. The figures shown are from five different sources and while thevariations are not great, it is safer to take the average temperatureshown in the last column. TABLE 25. --COLORS, TEMPERATURES, DEGREES FAHRENHEIT---------------------------------------------------------- | _A_ | _B_ | _C_ | _D_ | _E_ | Average------------------|-----|-----|-----|-----|-----|--------- Faint yellow | 430 | 430 | 430 | 430 | 430 | 430 Light straw | 475 | 460 | 450 | . .. | 450 | 458 Dark straw | 500 | 500 | 470 | 450 | 470 | 478 Purple (reddish) | 525 | 530 | 520 | 530 | 510 | 523 Purple (bluish) | . .. | 555 | 550 | 550 | 550 | 551 Blue | 575 | 585 | 560 | 580 | 560 | 572 Gray blue | . .. | 600 | . .. | 600 | 610 | 603 Greenish blue | . .. | 625 | . .. | . .. | 630 | 627---------------------------------------------------------- TABLE 26. --ANOTHER COLOR TABLE---------------------------------------------------------- Degrees | Fahrenheit | High temperatures judged by color------------|--------------------------------------------- 430 | Very pale yellow \ 460 | Straw-yellow | 480 | Dark yellow | 500 | Brown-yellow > Visible in full daylight 520 | Brown-purple | 540 | Full purple | 560 | Full blue | 600 | Very dark blue / 752 | Red heat, visible in the dark 885 | Red heat, visible in the twilight 975 | Red heat, visible in the daylight 1, 292 | Dark red 1, 652 | Cherry-red 1, 832 | Bright cherry-red 2, 012 | Orange-red 2, 192 | Orange-yellow 2, 372 | Yellow-white 2, 552 | White welding heat 2, 732 | Brilliant white 2, 912 | Dazzling white (bluish-white)---------------------------------------------------------- These differences might easily be due to the difference in the lightat the time the colors were observed. It must also be rememberedthat even a thin coating of oil will make quite a difference andcause confusion. It is these possible sources of error, coupledwith the ever present chance of human error, that makes it advisableto draw the temper of tools in an oil bath heated to the propertemperature as shown by an accurate high-temperature thermometer. Another table, by Gilbert and Barker, runs to much higher temperatures. Beyond 2, 200°, however, the eye is very uncertain. TABLE 26. --COLORS FOR TEMPERING TOOLS----------------------------------------------------------------------- Approximate | color and | Kind of tool temperature |--------------|-------------------------------------------------------- Yellow | Thread chasers, hollow mills (solid type) twist drills 430 to 450°F. | centering tools, forming tools, cut-off tools, profile | cutters, milling cutters, reamers, dies, etc. --------------|-------------------------------------------------------- Straw-yellow | Thread rolling dies, counterbores, countersinks. Shear 460°F. | blades, boring tools, engraving tools, etc. --------------|-------------------------------------------------------- Brown-yellow | Taps, Thread dies, cutters, reamers, etc. 500°F. |--------------|-------------------------------------------------------- Light purple | Taps, dies, rock drills, knives, punches, gages, etc. 530°F. |--------------|-------------------------------------------------------- Dark purple | Circular saws for metal, augers, dental and surgical 550°F. | instruments, cold chisels, axes. --------------|-------------------------------------------------------- Pale blue | Bone saws, chisels, needles, cutters, etc. 580°F. |--------------|-------------------------------------------------------- Blue | Hack saws, wood saws, springs, etc. 600°F. |----------------------------------------------------------------------- CHAPTER X HIGH-SPEED STEEL For centuries the secret art of making tool steel was handed downfrom father to son. The manufacture of tool steel is still an artwhich, by the aid of science, has lost much of its secrecy; yettool steel is today made by practical men skilled as melters, hammer-men, and rollers, each knowing his art. These practicalmen willingly accept guidance from the chemist and metallurgists. A knowledge of conditions existing today in the manufacture ofhigh-speed steel is essential to steel treaters. It is well forthe manufacturer to have steel treaters understand some of histroubles and difficulties, so that they will better comprehend thenecessity of certain trade customs and practices, and, realizingthe manufacturer's desire to cooperate with them, will reciprocate. The manufacturer of high-speed steel knows and appreciates thetroubles and difficulties that may sometimes arise in the heat-treatingof his product. His aim is to make a uniform steel that will bestmeet the requirements of the average machine shop on general work, and at the same time allow the widest variation in heat treatmentto give desired results. High speed steel is one of the most complex alloys known. Arepresentative steel contains approximately 24 per cent of alloyingmetals, namely, tungsten, chromium, vanadium, silicon, manganese, and in addition there is often found cobalt, molybdenum, uranium, nickel, tin, copper and arsenic. STANDARD ANALYSIS The selection of a standard analysis by the manufacturer is theresult of a series of compromises between various properties impartedto the steel by the addition of different elements and there is awide range of chemical analyses of various brands. The steel, tobe within the range of generally accepted analysis, should containover 16 per cent and under 20 per cent tungsten; if of lower tungstencontent it should carry proportionately more chromium and vanadium. The combined action of tungsten and chromium in steel gives to it theremarkable property of maintaining its cutting edge at relatively hightemperature. This property is commonly spoken of as "red-hardness. "The percentages of tungsten and chromium present should bear adefinite relationship to each other. Chromium imparts to steela hardening property similar to that given by carbon, althoughto a less degree. The hardness imparted to steel by chromium isaccompanied by brittleness. The chromium content should be between3. 5 and 5 per cent. Vanadium was first introduced in high-speed steel as a "scavenger, "thereby producing a more homogeneous product, of greater densityand physical strength. It soon became evident that vanadium usedin larger quantities than necessary as a scavenger imparted tothe steel a much greater cutting efficiency. Recently, no less anauthority than Prof. J. O. Arnold, of the University of Sheffield, England, stated that "high-speed steels containing vanadium havea mean efficiency of 108. 9, as against a mean efficiency of 61. 9obtained from those without vanadium content. " A wide range ofvanadium content in steel, from 0. 5 to 1. 5 per cent, is permissible. An ideal analysis for high-speed steel containing 18 per cent tungstenis a chromium content of approximately 3. 85 per cent; vanadium, 0. 85to 1. 10 per cent, and carbon, between 0. 62 and 0. 77 per cent. DETRIMENTAL ELEMENTS. --Sulphur and phosphorus are two elements knownto be detrimental to all steels. Sulphur causes "red-shortness"and phosphorus causes "cold-shortness. " The detrimental effectsof these two elements counteract each other to some extent butthe content should be not over 0. 02 sulphur and 0. 025 phosphorus. The serious detrimental effect of small quantities of sulphur andphosphorus is due to their not being uniformly distributed, owingto their tendency to segregate. The manganese and silicon contents are relatively unimportant inthe percentages usually found in high-speed steel. The detrimental effects of tin, copper and arsenic are not generallyrealized by the trade. Small quantities of these impurities areexceedingly harmful. These elements are very seldom determinedin customers' chemical laboratories and it is somewhat difficultfor public chemists to analyze for them. In justice to the manufacturer, attention should be called to thevariations in chemical analyses among the best of laboratories. Generally speaking, a steel works' laboratory will obtain resultsmore nearly true and accurate than is possible with a customer'slaboratory, or by a public chemist. This can reasonably be expected, for the steel works' chemist is a specialist, analyzing the samematerial for the same elements day in and day out. The importance of the chemical laboratory to a tool-steel plantcannot be over-estimated. Every heat of steel is analyzed for eachelement, and check analyses obtained; also, every substance usedin the mix is analyzed for all impurities. The importance of usingpure base materials is known to all manufacturers despite chemicalevidence that certain detrimental elements are removed in the processof manufacture. The manufacture of high-speed steel represents the highest artin the making of steel by tool-steel practice. Some may say, onaccount of our increased knowledge of chemistry and metallurgy, that the making of such steel has ceased to be an art, but hasbecome a science. It is, in fact an art; aided by science. Thehuman element in its manufacture is a decided factor, as will bebrought in the following remarks: The heat treatment of steel in its broad aspect may be said tocommence with the melting furnace and end with the hardening andtempering of the finished product. High-speed steel is melted bytwo general types of furnace, known as crucible and electric. Steeltreaters, however, are more vitally interested in the changes thattake place in the steel during the various processes of manufacturerather than a detailed description of those processes, which aremore or less familiar to all. In order that good high-speed steel may be furnished in finishedbars, it must be of correct chemical analysis, properly melted andcast into solid ingots, free from blow-holes and surface defects. Sudden changes of temperature are to be guarded against at everystage of its manufacture and subsequent treatment. The ingots arerelatively weak, and the tendency to crack due to cooling strainsis great. For this reason the hot ingots are not allowed to coolquickly, but are placed in furnaces which are of about the sametemperature and are allowed to cool gradually before being placedin stock. Good steel can be made only from good ingots. Steel treaters should be more vitally interested in the importantchanges which take place in high-speed steel during the hammeringoperations than that of any other working the steel receives inthe course of its manufacture. QUALITY AND STRUCTURE The quality of high-speed steel is dependent to a very great extentupon its structure. The making of the structure begins under thehammer, and the beneficial effects produced in this stage persistthrough the subsequent operations, provided they are properly carriedout. The massive carbides and tungstides present in the ingot arebroken down and uniformly distributed throughout the billet. To accomplish this the reduction in area must be sufficient and thehammer blows should be heavy, so as to carry the compression intothe center of the billet; otherwise, undesirable characteristicssuch as coarse structure and carbide envelopes will exist and causethe steel treater much trouble. Surface defects invisible in theingot may be opened up under the hammering operation, in whichevent they are chipped from the hot billet. Ingots are first hammered into billets. These billets are carefullyinspected and all surface defects ground or chipped. The hammeredbillets are again slowly heated and receive a second hammering, known as "cogging. " The billet resulting therefrom is known asa "cogged" billet and is of the proper size for the rolling millor for the finishing hammer. Although it is not considered good mill practice, some manufacturerswho have a large rolling mill perform the very important coggingoperation in the rolling mill instead of under the hammer. Coggingin a rolling mill does not break up and distribute the carbides andtungstides as efficiently as cogging under the hammer; another objectionto cogging in the rolling mill is that there is no opportunity tochip surface defects developed as they can be under the trained eyeof a hammer-man, thereby eliminating such defects in the finishedbillet. The rolling of high-speed steel is an art known to very few. Thevarious factors governing the proper rolling are so numerous thatit is necessary for each individual rolling mill to work out apractice that gives the best results upon the particular analysisof steel it makes. Important elements entering into the rollingare the heating and finishing temperatures, draft, and speed ofthe mill. In all of these the element of time must be considered. High-speed steel should be delivered from the rolling mill to theannealing department free from scale, for scale promotes the formationof a decarbonized surface. In preparation of bars for annealing, they are packed in tubes with a mixture of charcoal, lime, andother material. The tubes are sealed and placed in the annealingfurnace and the temperature is gradually raised to about 1, 650°F. , and held there for a sufficient length of time, depending upon thesize of the bars. After very slow cooling the bars are removedfrom the tubes. They should then show a Brinnell number of between235 and 275. The inspection department ranks with the chemical and metallurgicaldepartments in safeguarding the quality of the product. It inspectsall finished material from the standpoint of surface defects, hardness, size and fracture. It rejects such steel as is judged not to meetthe manufacturer's standard. The inspection and metallurgicaldepartments work hand in hand, and if any department is not functioningproperly it will soon become evident to the inspectors, enablingthe management to remedy the trouble. The successful manufacture of high-speed steel can only be obtainedby those companies who have become specialists. The art and skillnecessary in the successful working of such steel can be attainedonly by a man of natural ability in his chosen trade, and trainedunder the supervision of experts. To become an expert operatorin any department of its manufacture, it is necessary that theoperator work almost exclusively in the production of such steel. As to the heat treatment, it is customary for the manufacturerto recommend to the user a procedure that will give to his steela high degree of cutting efficiency. The recommendations of themanufacturer should be conservative, embracing fairly wide limits, as the tendency of the user is to adhere very closely to themanufacturer's recommendations. Unless one of the manufacturer'sexpert service men has made a detailed study of the customer'sproblem, the manufacturer is not justified in laying down set rules, for if the customer does a little experimenting he can probablymodify the practice so as to produce results that are particularlywell adapted to his line of work. The purpose of heat-treating is to produce a tool that will cut soas to give maximum productive efficiency. This cutting efficiencydepends upon the thermal stability of the complex hardenites existingin the hardened and tempered steel. The writer finds it extremelydifficult to convey the meaning of the word "hardenite" to those thatdo not have a clear conception of the term. The complex hardenitesin high-speed steel may be described as that form of solid solutionwhich gives to it its cutting efficiency. The complex hardenites areproduced by heating the steel to a very high temperature, near themelting point, which throws into solution carbides and tungstides, provided they have been properly broken up in the hammering processand uniformly distributed throughout the steel. By quenching thesteel at correct temperature this solid solution is retained atatmospheric temperature. It is not the intention to make any definite recommendations as toheat-treating of high-speed steel by the users. It is recognizedthat such steel can be heat-treated to give satisfactory resultsby different methods. It is, however, believed that the Americanpractice of hardening and tempering is becoming more uniform. Thisis due largely to the exchange of opinions in meetings and elsewhere. The trend of American practice for hardening is toward the following: _First_, slowly and carefully preheat the tool to a temperatureof approximately 1, 500°F. , taking care to prevent the formationof excessive scale. _Second_, transfer to a furnace, the temperature of which isapproximately 2, 250 to 2, 400°F. , and allow to remain in the furnaceuntil the tool is heated uniformly to the above temperature. _Third_, cool rapidly _in oil_, dry air blast, or lead bath. _Fourth_, draw back to a temperature to meet the physical requirementsof the tool, and allow to cool in air. It was not very long ago that the desirability of drawing hardenedhigh-speed steel to a temperature of 1, 100° was pointed out, and itis indeed encouraging to learn that comparatively few treaters havefailed to make use of this fact. Many treaters at first contendedthat the steel would be soft after drawing to this temperature andit is only recently, since numerous actual tests have demonstratedits value, that the old prejudice has been eliminated. High-speed steel should be delivered only in the annealed conditionbecause annealing relieves the internal strains inevitable in themanufacture and puts it in vastly improved physical condition. Themanufacturer's inspection after annealing also discloses defectsnot visible in the unannealed state. The only true test for a brand of high-speed steel is the service thatit gives by continued performance month in and month out under actualshop conditions. The average buyer is not justified in conducting atest, but can well continue to purchase his requirements from areputable manufacturer of a brand that is nationally known. Themanufacturer is always willing to cooperate with the trade in theconducting of a test and is much interested in the informationreceived from a well conducted test. A test, to be valuable, should beconducted in a manner as nearly approaching actual working conditionsin the plant in which the test is made as is practical. In conductinga test a few reputable brands should be allowed to enter. All toolsentered should be of exactly the same size and shape. There is muchdifference of opinion as to the best practical method of conductinga test, and the decision as to how the test should be conductedshould be left to the customer, who should cooperate with themanufacturers in devising a test which would give the best basisfor conclusions as to how the particular brands would perform underactual shop conditions. The value of the file test depends upon the quality of the file andthe intelligence and experience of the person using it. The filetest is not reliable, but in the hands of an experienced operator, gives some valuable information. Almost every steel treater knowsof numerous instances where a lathe tool which could be touchedwith a file has shown wonderful results as to cutting efficiency. Modern tool-steel practice has changed from that of the past, notby the use of labor-saving machinery, but by the use of scientificdevices which aid and guide the skilled craftsman in producing asteel of higher quality and greater uniformity. It is upon theintelligence, experience, and skill of the individual that qualityof tool steel depends. HARDENING HIGH-SPEED STEELS We will now take up the matter of hardening high-speed steels. Themost ordinary tools used are for lathes and planers. The forgingshould be done at carbon-steel heat. Rough-grind while still hotand preheat to about carbon-steel hardening heat, then heat quicklyin high-speed furnace to white heat, and quench in oil. If a veryhard substance is to be cut, the point of tool may be quenched inkerosene or water and when nearly black, finish cooling in oil. Tempering must be done to suit the material to be cut. For cuttingcast iron, brass castings, or hard steel, tempering should be donemerely to take strains out of steel. On ordinary machinery steel or nickel steel the temper can be drawnto a dark blue or up to 900°F. If the tool is of a special formor character, the risk of melting or scaling the point cannot betaken. In these cases the tool should be packed, but if there isno packing equipment, a tool can be heated to as high heat as issafe without risk to cutting edges, and cyanide or prussiate ofpotash can be sprinkled over the face and then quenched in oil. Some very adverse criticism may be heard on this point, but experiencehas proved that such tools will stand up very nicely and be perfectlyfree from scales or pipes. Where packing cannot be done, millingcutters, and tools to be hardened all over, can be placed in muffledfurnace, brought to 2, 220° and quenched in oil. All such tools, however, must be preheated slowly to 1, 400 to 1, 500° then placed ina high-speed furnace and brought up quickly. Do not soak high-speedsteel at high heats. Quench in oil. We must bear in mind that the heating furnace is likely to expandtools, therefore provision must be made to leave extra stock totake care of such expansion. Tools with shanks such as counterbores, taps, reamers, drills, etc. , should be heated no furtherthan they are wanted hard, and quench in oil. If a forge is notat hand and heating must be done, use a muffle furnace and coversmall shanks with a paste from fire clay or ground asbestos. Hollowmills, spring threading dies, and large cutting tools with smallshanks should have the holes thoroughly packed or covered withasbestos cement as far as they are wanted soft. CUTTING-OFF STEEL FROM BAR To cut a piece from an annealed bar, cut off with a hack saw, millingcutter or circular saw. Cut clear through the bar; do not nick orbreak. To cut a piece from an unannealed bar, cut right off withan abrasive saw; do not nick or break. If of large cross-section, cut off hot with a chisel by first slowly and uniformly heatingthe bar, at the point to be cut, to a good lemon heat, 1, 800 to1, 850°F. And cut right off while hot; do not nick or break. Allowthe tool length and bar to cool before reheating for forging. LATHE AND PLANER TOOLS FORGING. --Gently warm the steel to remove any chill, is particularlydesirable in the winter, then heat slowly and carefully to a scalingheat, that is a lemon heat (1, 800 to 2, 000°F. ), and forge uniformly. Reheat the tool for further forging directly the steel begins tostiffen under the hammer. Under no circumstances forge the steelwhen the temperature falls below a dark lemon to an orange colorabout 1, 700°F. Reheat as often as is necessary to finish forgingthe tool to shape. Allow the tool to cool after forging by buryingthe tool in dry ashes or lime. Do not place on the damp groundor in a draught of air. The heating for forging should be done preferably in a pipe ormuffle furnace but if this is not convenient use a good clean firewith plenty of fuel between the blast pipe and the tool. Neverallow the tool to soak after the desired forging heat has beenreached. Do not heat the tool further back than is necessary toshape the tool, but give the tool sufficient heat. See that theback of the tool is flatly dressed to provide proper support underthe nose of the tool. HARDENING HIGH-SPEED STEEL. --Slowly reheat the cutting edge ofthe tool to a cherry red, 1, 400°F. , then force the blast so asto raise the temperature quickly to a full white heat, 2, 200 to2, 250°F. , that is, until the tool starts to sweat at the cuttingface. Cool the point of the tool in a dry air blast or preferablyin oil, further cool in oil keeping the tool moving until the toolhas become black hot. To remove hardening strains reheat the tool to from 500 to 1, 100°F. Cool in oil or atmosphere. This second heat treatment adds to thetoughness of the tool and therefore to its life. GRINDING TOOLS. --Grind tools to remove all scale. Use a quick-cutting, dry, abrasive wheel. If using a wet wheel, be sure to use plentyof water. Do not under any circumstances force the tool againstthe wheel so as to draw the color, as this is likely to set upchecks on the surface of the tool to its detriment. FOR MILLING CUTTERS AND FORMED TOOLS FORGING. --Forge as before. --ANNEALING. --Place the steel in a pipe, box or muffle. Arrange the steel so as to allow at least 1 in. Of packing, consisting of dry powder ashes, powdered charcoal, mica, etc. , between the pieces and the walls of the box or pipe. If using a pipe close the ends. Heat slowly and uniformly to acherry red, 1, 375 to 1, 450°F. According to size. Hold the steel atthis temperature until the heat has thoroughly saturated throughthe metal, then allow the muffle box and tools to cool very slowlyin a dying furnace or remove the muffle with its charge and buryin hot ashes or lime. The slower the cooling the softer the steel. The heating requires from 2 to 10 hr. Depending upon the size ofthe piece. HARDENING AND TEMPERING. --It is preferable to use two furnaceswhen hardening milling cutters and special shape tools. One furnaceshould be maintained at a uniform temperature from 1, 375 to 1, 450°F. While the other should be maintained at about 2, 250°F. Keep thetool to be hardened in the low temperature furnace until the toolhas attained the full heat of this furnace. A short time should beallowed so as to be assured that the center of the tool is as hotas the outside. Then quickly remove the tool from this preheatingfurnace to the full heat furnace. Keep the tool in this furnace onlyas long as is necessary for the tool to attain the full temperatureof this furnace. Then quickly remove and quench in oil or in adry air blast. Remove before the tool is entirely cold and drawthe temper in an oil bath by raising the temperature of the oilto from 500 to 750°F. And allow this tool to remain, at thistemperature, in the bath for at least 30 min. , insuring uniformityof temper; then cool in the bath, atmosphere or oil. If higher drawing temperatures are desired than those possiblewith oil, a salt bath can be used. A very excellent bath is madeby mixing two parts by weight of crude potassium nitrate and threeparts crude sodium nitrate. These will melt at about 450°F. Andcan be used up to 1, 000°F. Before heating the steel in the saltbath, slowly preheat, preferably in oil. Reheating the hardenedhigh-speed steel to 1, 000°F. Will materially increase the lifeof lathe tools, but milling and form cutters, taps, dies, etc. , should not be reheated higher than 500 to 650°F. , unless extremehardness is required, when 1, 100 to 1, 000°F. , will give the hardestedge. INSTRUCTIONS FOR WORKING HIGH-SPEED STEEL Owing to the wide variations in the composition of high-speed steelsby various makers, it is always advisable to follow the directionsof each when using his brand of steel. In the absence of specificdirections the following general suggestions from several makerswill be found helpful. The Ludlum Steel Company recommend the following: CUTTING-OFF. --To cut a piece from an annealed bar, cut off witha hack saw, milling cutter or circular saw. Cut clear through thebar; do not nick or break. To cut a piece from an unannealed bar, cut right off with an abrasive saw; do not nick or break. If oflarge cross-section, cut off hot with a chisel by first slowlyand uniformly heating the bar, at the point to be cut, to a goodlemon heat, 1, 800°-1, 850°F. And cut right off while hot; do not nickor break. Allow the tool length and bar to cool before reheatingfor forging. LATHE AND PLANER TOOLS TO FORGE. --Gently warm the steel to remove any chill is particularlydesirable in the winter. Then heat slowly and carefully to a scalingheat, that is a lemon heat (1, 800°-2, 000°F. ), and forge uniformly. Reheat the tool for further forging directly the steel begins tostiffen under the hammer. Under no circumstances forge the steelwhen the temperature falls below a dark lemon to an orange color:about 1, 700°F. Reheat as often as is necessary to finish forgingthe tool to shape. Allow the tool to cool after forging by buryingthe tool in dry ashes or lime. Do not place on the damp groundor in a draught of air. The heating for forging should be done preferably in a pipe ormuffle furnace, but if this is not convenient use a good cleanfire with plenty of fuel between the blast pipe and the tool. Neverallow the tool to soak after the desired forging heat has beenreached. Do not heat the tool further back than is necessary toshape the tool, but give the tool sufficient heat. See that theback of the tool is flatly dressed to provide proper support underthe nose of the tool. HARDENING. --Slowly reheat the cutting edge of the tool to a cherryred, 1, 400°F. , then force the blast so as to raise the temperaturequickly to a full white heat, 2, 200°-2, 250°F. , that is, until thetool starts to sweat at the cutting face. Cool the point of thetool in a dry air blast or preferably in oil; further cool in oil, keeping the tool moving until the tool has become black hot. To remove hardening strains reheat the tool to from 500° to 1, 100°F. Cool in oil or atmosphere. This second heat treatment adds to thetoughness of the tool and therefore to its life. GRINDING. --Grind tools to remove all scale. Use a quick cutting, dry, abrasive wheel. If using a wet wheel, be sure to use plentyof water. Do not under any circumstances force the tool againstthe wheel so as to draw the color, as this is likely to set upchecks on the surface of the tool to its detriment. The Firth-Sterling Steel Company say: INSTEAD OF PRINTING ANY RULES ON THE HARDENING AND TEMPERING OFFIRTH-STERLING STEELS WE WISH TO SAY TO OUR CUSTOMERS: TRUST THESTEEL TO THE SKILL AND THE JUDGEMENT OF YOUR TOOLSMITH AND TOOLTEMPERER. The steel workers of today know by personal experience and byinheritance all the standard rules and theories on forging, hardeningand tempering of all fine tool steels. They know the importance ofslow, uniform heating, and the danger of overheating some steels, and underheating others. The tempering of tools and dies is a science taught by heat, muscleand brains. The tool temperer is the man to hold responsible for results. Thetempering of tools has been his life work. He may find suggestionson the following pages interesting, but we are always ready totrust the treatment of our steels to the experienced man at thefire. HEAT TREATMENT OF LATHE, PLANER AND SIMILAR TOOLS FIRE. --For these tools a good fire is one made of hard foundrycoke, broken in small pieces, in an ordinary blacksmith forge witha few bricks laid over the top to form a hollow fire. The bricksshould be thoroughly heated before tools are heated. Hard coalmay be used very successfully in place of hard coke and will givea higher heat. It is very easy to give Blue Chip the proper heatif care is used in making up the fire. FORGING. --Heat slowly and uniformly to a good forging heat. Donot hammer the steel after it cools below a bright red. Avoid asmuch as possible heating the body of the tool, so as to retainthe natural toughness in the neck of the tool. HARDENING. --Heat the point of the tool to an extreme white heat(about 2, 200°F. ) until the flux runs. This heat should be the highestpossible short of melting the point. Care should be taken to confinethe heat as near to the point as possible so as to leave the annealingand consequent toughness in the neck of the tool and where the toolis held in the tool post. COOL in an air blast, the open air or in oil, depending upon thetools or the work they are to do. For roughing tools temper need not be drawn except for work wherethe edge tends to crumble on account of being too hard. For finishing tools draw the temper to suit the purpose for whichthey are to be used. GRIND thoroughly on dry wheel (or wet wheel if care is used to preventchecking). HEAT TREATMENT OF MILLING CUTTERS, DRILLS, REAMERS, ETC. THE FIRE. --Gas and electric furnaces designed for high heats arenow made for treating high-speed steels. We recommend them fortreating all kinds of Blue Chip tools and particularly the aboveclass. After tools reach a yellow heat in the forge fire they mustnot be allowed to touch the fuel or come in contact with the blastor surrounding air. HEATING. --Tools of this kind should be heated to a mellow whiteheat, or as hot as possible without injuring the cutting edges(2, 000 to 2, 200°F. ). For most work the higher the heat the betterthe tool. Where furnaces are used, we recommend preheating thetools to a red heat in one furnace before putting them in a whitehot furnace. COOLING. --We recommend quenching all of the above tools in oilwhen taken from the fire. We have found fish oil, cottonseed oil, Houghton's No. 2 soluble oil and linseed oil satisfactory. Thehigh heat is the important thing in hardening Blue Chip tools. If a white hot tool is allowed to cool in the open air it will behard, but the air scales the tool. DRAWING THE TEMPER. --Tools of this class should be drawn considerablymore than water-hardening steel for the same purpose. HEAT TREATMENT OF PUNCHES AND DIES, SHEARS, TAPS, ETC. HEATING. --The degree to which tools of the above classes shouldbe heated depends upon the shape, size and use for which they areintended. Generally, they should not be heated to quite as high aheat as lathe tools or milling cutters. They should have a highheat, but not enough to make the flux run on the steel (by pyrometer1, 900 to 2, 100°F. ). COOLING. --Depending on the tools, some should be dipped in oilall over, some only part way, and others allowed to cool down inthe air naturally, or under air blast. In cooling, the toughnessis retained by allowing some parts to cool slowly and quenchingparts that should be hard. DRAWING THE TEMPER. --As in cooling, some parts of these tools willrequire more drawing than others, but, on the whole, they mustbe drawn more than water hardening tools for the same purpose orto about 500°F. All over, so that a good file will just "touch"the cutting or working parts. BARIUM CHLORIDE PROCESS. --This is a process developed for treatingcertain classes of tools, such as taps, forming tools, etc. It isbeing successfully used in many large plants. Briefly the treatmentis as follows: In this treatment the tools are first preheated to a red heat, but small tools may be immersed without preheating. The bariumchloride bath is kept at a temperature of from 2, 000 to 2, 100°F. , and tools are held in it long enough to reach the same temperature. They are then dipped in oil. The barium chloride which adheresto the tools is brushed off, leaving the tools as dean as beforeheating. A CHROMIUM-COBALT STEEL The Latrobe Steel Company make a high-speed steel without tungsten, its red-hardness properties depending on chromium and cobalt insteadof tungsten. It is known as P. R. K-33 steel. It does not requirethe high temperature of the tungsten steels, hardening at 1, 830 to1, 850°F. Instead of 2, 200° or even higher, as with the tungsten. This steel is forged at 1, 900 to 2, 000°F. And must not be workedat a lower temperature than 1, 600°F. It requires soaking in thefire more than the tungsten steels. It can be normalized by heatingslowly and thoroughly to 1, 475°F. , holding this for from 10 to 20min. According to the size of the piece and cooling in the openair, protected from drafts. A peculiarity of this steel is that it becomes non-magnetic at orabove 1, 960°F. And the magnetic quality is not restored by cooling. Normalizing as above, however, restores the magnetic qualities. Thisenables the user to detect any tools which have been overheated, with a horseshoe magnet. It is sometimes advantageous to dip tools, before heating for hardening, in ordinary fuel or quenching oil. The oil leaves a thin film ofcarbon which tends to prevent decarbonization, giving a very hardsurface. For other makes of high-speed steel used in lathe and planer toolsthe makers recommend that the tools be cut from the bar with ahack saw or else heated and cut with a chisel. The heating shouldbe very slow until the steel reaches a red after which it can beheated more rapidly and should only be forged at a high heat. Itcan be forged at very high heats but care should be taken not toforge at a low heat. The heating should be uniform and penetrateclear to the center of the bar before forging is begun. Reheatas often as necessary to forge at the proper heat. After forging cool in lime before attempting to harden. Do notattempt to harden with the forging heat as was sometimes done withthe carbon tools. For hardening forged tools, heat slowly up to a bright red andthen rapidly until the point of the tool is almost at a meltingheat. Cool in a blast of cold, dry air. For large sizes of steel, cool in linseed oil or in fish oil as is most convenient. If thetools are to be used for finishing cuts heat to a bright yellowand quench in oil. Grind for use on a sand wheel or grindstonein preference to an emery or an artificial abrasive wheel. For hardening milling and similar cutters, preheat to a brightred, place the cutter on a round bar of suitable size, and revolveit quickly over a very hot fire. Heat as high as possible withoutmelting the points of the teeth and cool in a cold blast of dryair or in fish oil. Light fragile cutters, twist drills, taps and formed cutters maybe heated almost white and then dipped in fish oil for hardening. Where possible it is better to give an even higher heat and coolin the blast of cold, dry air as previously recommended. SUGGESTIONS FOR HANDLING HIGH-SPEED STEELS The following suggestions for handling high-speed steels are givenby a maker whose steel is probably typical of a number of differentmakes, so that they will be found useful in other cases as well. These include hints as to forging as well as hardening, togetherwith a list of "dont's" which are often very useful. This appliesto forging, hardening of lathe, slotting, planing and all similartools. [Illustration: FIG. 84. --All-steel, 5/8 in. Square, 1/2 X 1 in. , and larger is usually mild finished, and can be cut in a hack saw. If cut off hot, be sure to heat the butt end slowly and thoroughlyin a clean fire. Rapid and insufficient heating invariably cracksthe steel. If you want to stamp the end with the name of the steel, it is necessary that this is done at a good high orange color heat, as it is otherwise apt to split the steel. (Take your time, donot hurry. )] HARDENING HIGH-SPEED STEEL In forging use coke for fuel in the forge. Heat steel slowly andthoroughly to a lemon heat. Do not forge at a lower heat. Do notlet the steel cool below a bright cherry red while forging. Afterthe tool is dressed, reheat to forging heat to remove the forgingstrain, and lay on the floor until cold. Then have the tool roughground on a dry emery wheel. [Illustration: FIG. 85. --Be sure to have a full yellow heat at thedotted line. Remember this is a boring mill tool and will standout in the tool-post, and if you do not have a high thorough lemonheat, your tool will snap off at the dotted line. (Ninety-fiveper cent of all tools which break, have been forged at too low aheat or at a heat not thorough to the center. )] [Illustration: FIG. 86. --Keep your high lemon forging heat up. If you forge under a steam hammer, take light blows. Do not jamyour tool into shape. Put frequently back into the fire. Neverlet the high lemon color go down and beyond the dotted line. ] For built-up and bent tools special care should be taken that theforging heat does not go below a bright cherry. For tools 3/4 by1-1/2 or larger where there is a big strain in forging, such asbending at angles of about 45 deg. And building the tools up, theyshould be heated to at least 1, 700°F. Slowly and without much blast. For a 3/4 by 1-1/2 tool it should take about 10 min. With the correctblast in a coke fire. Larger tools in proportion. They can then bebent readily, but no attempt should be made to forge the steelfurther without reheating to maintain the bright cherry red. Thisis essential, as otherwise the tools crack in hardening or whilein use. [Illustration: FIG. 87. --Be sure that the tool is absolutely straightat the bottom, so as to lie flat in the tool-post. ] [Illustration: FIG. 88. --This is the finished forged tool, andlet this grow cold by itself, the slower the better. It is well tocool the tool slowly in hot ashes, to remove all forging strain. You can now grind the tool dry on a sharp emery wheel. The moreyou now finish the tool in grinding, the less there is to comeoff after hardening. ] In hardening place the tool in a coke fire (hollow fire if possible)with a slow blast and heat gradually up to a white welding heaton the nose of the tool. Then dip the white hot part only intothin oil or hold in a strong cold air blast. When hardening inoil do not hold the tool in one place but keep it moving so thatit cools as quickly as possible. It is not necessary to draw thetemper after hardening these tools. [Illustration: FIG. 89. --This tool is ground, ready for hardening. Never harden from the forging heat. ] [Illustration: FIG. 90. --Heat the nose of the tool only up to dottedline, very slowly and thoroughly to an absolutely white weldingheat, so that it shows a trifle fused around the edges, and bevery sure that this fusing has gone thoroughly through the nose, otherwise the fusing effect will be taken off after the secondgrinding. Note the difference of the nose between this and Fig. 86. ] [Illustration: FIG. 91. --Shows unnecessary roasting and drossing. Such hardening requires a great amount of grinding and is not good. After hardening grind carefully on a wet emery wheel, and be surethat the wheel is sharp with a plentiful supply of water. Do notforce the grinding, otherwise the cold water striking the steelheated up by friction, will crack the nose. Be sure that the grindingwheel is sharp. ] In grinding all tools should be ground as lightly as possible ona soft wet sandstone or on a wet emery wheel, and care should betaken not to create any surface cracks, which are invariably theresult of grinding too forcibly. The foregoing illustrations, Figs. 84 to 91, with their captions, will be found helpful. Special points of caution to be observed when hardening high-speedsteel. DON'T use a green coal fire; use coke, or build a hollow fire. DON'T have the bed of the fire free from coal. DON'T hurry the heating for forging. The heating has to be donevery slowly and the forging heat has to be kept very high (a fulllemon color) heat and the tool has to be continually brought backinto the fire to keep the high heat up. When customers complainabout seams and cracks, in 9 cases out of 10, this has been causedby too low a forging heat, and when the blacksmith complains abouttools cracking, it is necessary to read this paragraph to him. DON'T try to jam the tool into shape under a steam hammer with oneor two blows; take easy blows and keep the heat high. DON'T have the tool curved at the bottom; it must lie perfectlyflat in the tool post. DON'T harden from your forging heat; let the tool grow cold orfairly cold. After forging you can rough grind the tool dry, butnot too forcibly. DON'T, for hardening, get more than the nose white hot. DON'T get the white heat on the surface only. DON'T hurry your heating for hardening; let the heat soak thoroughlythrough the nose of the tool. DON'T melt the nose of the tool. DON'T, as a rule, dip the nose into water; this should be doneonly for extremely hard material. It is dangerous to put the noseinto water for fear of cracking and when you do put the nose intowater put just 1/2 in. Only of the extreme white hot part into thewater and don't keep it too long in the water; just a few seconds, and then harden in oil. We do not recommend water hardening. DON'T grind too forcibly. DON'T grind dry after hardening. DON'T discolor the steel in grinding. DON'T give too much clearance on tools for cutting cast iron. DON'T start on cast iron with a razor edge on the tool. Take anoil stone and wipe three or four times over the razor edge. DON'T use tool holder steel from bars without hardening the noseof each individual tool bit. AIR-HARDENING STEELS. --These steels are recommended for boring, turning and planing where the cost of high-speed seems excessive. They are also recommended for hard wood knives, for roughing andfinishing bronze and brass, and for hot bolt forging dies. Thissteel cannot be cut or punched cold but can be shaped and groundon abrasive wheels of various kinds. It should be heated slowly and evenly for forging and kept as evenlyheated at a bright red as possible. It should not be forged afterit cools to a dark red. After the tool is made, heat it again to a bright red and lay itdown to cool in a dry place or it can be cooled in a cold, dryair blast. Water must be kept away from it while it is hot. CHAPTER XI FURNACES There are so many standard furnaces now on the market that it isnot necessary to go into details of their design and constructionand only a few will be illustrated. Oil, gas and coal or coke aremost common but there is a steady growth of the use of electricfurnaces. [Illustration: FIG. 92. --Standard lead pot furnace. ] TYPICAL OIL-FIRED FURNACES. --Several types of standard oil-firedfurnaces are shown herewith. Figure 92 is a lead pot furnace, Fig. 93 is a vertical furnace with a center column. This column reducesthe cubical contents to be heated and also supports the cover. [Illustration: FIG. 93. --Furnace with center column. ] A small tool furnace is shown in Fig. 94, which gives the constructionand heat circulation. A larger furnace for high-speed steel isgiven in Fig. 95. The steel is supported above the heat, the lowerflame passing beneath the support. For hardening broaches and long reamers and taps, the furnace shownin Fig. 96 is used. Twelve jets are used, these coming in radiallyto produce a whirling motion. [Illustration: FIG. 94. --Furnace for cutting tools. ] [Illustration: FIG. 95. --High-speed steel furnace. ] Oil and gas furnaces may be divided into three types: the openheating chamber in which combustion takes place in the chamberand directly over the stock; the semimuffle heating chamber inwhich combustion takes place beneath the floor of the chamber fromwhich the hot gases pass into the chamber through suitable openings;and the muffle heating chamber in which the heat entirely surroundsthe chamber but does not enter it. The open furnace is used forforging, tool dressing and welding. The muffle furnace is used forhardening dies, taps, cutters and similar tools of either carbonor high-speed steel. The muffle furnace is for spring hardening, enameling, assaying and work where the gases of combustion mayhave an injurious effect on the material. [Illustration: FIG. 96. --Furnace for hardening broaches. ] [Illustration: FIG. 97. --Forging and welding furnace. ] [Illustration: FIG. 98. --Semi-muffle furnace. ] [Illustration: FIG. 99. --Muffle furnace. ] Furnaces of these types of oil-burning furnaces are shown in Figs. 97, 98, and 99; these being made by the Gilbert & Barker ManufacturingCompany. The first has an air curtain formed by jets from the largepipe just below the opening, to protect the operator from heat. [Illustration: FIG. 100. --Gas fired furnace. ] [Illustration: FIG. 101. --Car door type of annealing furnace. ] Oil furnaces are also made for both high- and low-pressure air, each having its advocates. The same people also make gas-firedfurnaces. Several types of furnaces for various purposes are illustratedin Fig. 100 and 101. The first is a gas-fired hardening furnaceof the surface-combustion type. A large gas-fired annealing furnace of the Maxon system is shownin Fig. 101. This is large enough for a flat car to be run intoas can be seen. It shows the arrangement of the burners, the trackfor the car and the way in which it fits into the furnace. Theseare from the designs of the Industrial Furnace Corporation. Before deciding upon the use of gas or oil, all sides of the problemshould be considered. Gas is perhaps the nearest ideal but is as arule more expensive. The tables compiled by the Gilbert & BarkerManufacturing Company and shown herewith, may help in decidingthe question. TABLE 27. --SHOWING COMPARISON OF OIL FUEL WITH VARIOUS GASEOUS FUELS Heat units per thousand cubic feet Natural gas 1, 000, 000 Air gas (gas machine) 20 cp 815, 500 Public illuminating gas, average 650, 000 Water gas (from bituminous coal) 377, 000 Water and producer gas, mixed 175, 000 Producer gas 150, 000 Since a gallon of fuel oil (7 lb. ) contains 133, 000 heat units, thefollowing comparisons may evidently be made. At 5 cts. A gallon, the equivalent heat units in oil would equal: Per thousand cubic feet Natural gas at $0. 375 Air gas, 20 cp at 0. 307 Public illuminating gas, average at 0. 244 Water gas (from bituminous coal) at 0. 142 Water and producer gas, mixed at 0. 065 Producer gas at 0. 057 Comparing oil and coal is not always simple as it depends on thework to be done and the construction of the furnaces. The variationrises from 75 to 200 gal. Of oil to a ton of coal. For forgingand similar work it is probably safe to consider 100 gal. Of oilas equivalent to a ton of coal. Then there is the saving of labor in handling both coal and ashes, the waiting for fires to come up, the banking of fires and the dirtand nuisance generally. The continuous operation possible withoil adds to the output. When comparing oil and gas it is generally considered that 4-1/2gal. Of fuel oil will give heat equivalent to 1, 000 cu. Ft. Ofcoal gas. The pressure of oil and air used varies with the system installed. The low-pressure system maintains a pressure of about 8 oz. On theoil and draws in free air for combustion. Others use a pressureof several pounds, while gas burners use an average of perhaps1-1/2 lb. Of air to give best results. The weights and volumes of solid fuels are: Anthracite coal, 55 to65 lb. Per cubic foot or 34 to 41 cubic feet per ton; bituminouscoal, 50 to 55 lb. Per cubic foot or 41 to 45 cubic feet per ton;coke, 28 lb. Per cubic foot or 80 cubic feet per ton--the ton beingcalculated as 2, 240 lb. In each case. A novel carburizing furnace that is being used by a number of people, is built after the plan of a fireless cooker. The walls of thefurnace are extra heavy, and the ports and flues are so arrangedthat when the load in the furnace and the furnace is thoroughlyheated, the burners are shut off and all openings are tightly sealed. The carburization then goes on for several hours before the furnaceis cooled below the effective carburizing range, securing an idealdiffusion of carbon between the case and the core of the steelbeing carburized. This is particularly adaptable where simple steelis used. PROTECTIVE SCREENS FOR FURNACES Workmen needlessly exposed to the flames, heat and glare from furnaceswhere high temperatures are maintained suffer in health as well asin bodily discomfort. This shows several types of shields designedfor the maximum protection of the furnace worker. Bad conditions are not necessary; in almost every case means of reliefcan be found by one earnestly seeking them. The larger forge shopshave adopted flame shields for the majority of their furnaces. Yearsago the industrial furnaces (particularly of the oil-burning variety)were without shields, but the later models are all shield-equipped. These shields are adapted to all of the more modern, heat-treatingfurnaces, as well as to those furnaces in use for working forges;and attention should be paid to their use on the former type sincethe heat-treating furnaces are constantly becoming more numerousas manufacturers find need of them in the many phases of munitionsmaking or similar work. The heat that the worker about these furnaces must face may bedivided in general into two classes: there is first that heat dueto the flame and hot gases that the blast in the furnaces forcesout onto a man's body and face. In the majority of furnaces thisis by far the most discomforting, and care must be taken to fendit and turn it behind a suitable shield. The second class is theradiant heat, discharged as light from the glowing interior ofthe furnace. This is the lesser of the two evils so far as generalforging furnaces are concerned, but it becomes the predominatingfeature in furnaces of large door area such as in the usualcase-hardening furnaces. Here the amount of heat discharged isoften almost unbearable even for a moment. This heat can be takencare of by interposing suitable, opaque shields that will temporarilyabsorb it without being destroyed by it, or becoming incandescent. Should such shields be so constructed as to close off all of theheat, it might be impossible to work around the furnace for theremoval of its contents, but they can be made movable, and in sucha manner as to shield the major portion of the worker's body. First taking up the question of flame shields, the illustration, Fig. 102, is a typical installation that shows the main featuresfor application to a forging machine or drop-hammer, oil-burningfurnace, or for an arched-over, coal furnace where the flame blowsout the front. This shield consists of a frame covered with sheetmetal and held by brackets about 6 in. In front of the furnace. It will be noted that slotted holes make this frame adjustablefor height, and it should be lowered as far as possible when inuse, so that the work may just pass under it and into the furnaceopenings. Immediately below the furnace openings, and close to the furnaceframe will be noted a blast pipe carrying air from the forge-shopfan. This has a row of small holes drilled in its upper side forthe entire length, and these direct a curtain of cold air verticallyacross the furnace openings, forcing all of the flame, or a greaterportion of it, to rise behind the shield. Since the shield extendsabove the furnace top there is no escape for this flame until it haspassed high enough to be of no further discomfort to the workman. In this case fan-blast air is used for cooling, and this is cheaperand more satisfactory because a great volume may be used. However, where high-pressure air is used for atomizing the oil at the burner, and nothing else is available, this may be employed--though naturallya comparatively small pipe will be needed, in which minute holesare drilled, else the volume of air used will be too great forthe compressor economically to supply. Steam may also be employedfor like service. [Illustration: FIGS. 102 to 108. --Protective devices for furnacefronts. ] The latest shields of this type are all made double, as illustrated, with an inner sheet of metal an inch or two inside of the front. In the illustration, _A_, Fig. 102, this inner sheet is smaller, but some are now built the same size as the front and bolted toit with pipe spacers between. The advantage of the double sheetis that the inner one bears the brunt of the flame, and, if needsbe, burns up before the outer; while, if due to a heavy fire itshould be heated red at any point, the outer sheet will still bemuch cooler and act as an additional shield to the furnace man. HEAVY FORGING PRACTICE. --In heavy forging practice where the metalis being worked at a welding heat, the amount of flame that willissue from an open-front furnace is so great that a plain, sheet-steelfront will neither afford sufficient protection nor stand up inservice. For such a place a water-cooled front is often used. Thegeneral type of this front is illustrated in Fig. 103, and appears tohave found considerable favor, for numbers of its kind are scatteredthroughout the country. In this case the shield is placed at a slight angle from the vertical, and along the top edge is a water pipe with a row of small holesthrough which sprays of water are thrown against it. This water runsdown in a thin sheet over the shield, cooling it, and is collectedin a trough connected with a run-off pipe at the bottom. The lowerblast-pipe arrangement is similar to the one first described. There are several serious objections to this form of shield thatshould lead to its replacement by a better type; the first is thatwith a very hot fire, portions in the center may become so rapidlyheated that the steam generated will part the sheet of water andcause it to flow from that point in an inverted V, and that sectionwill then quickly become red hot. Another feature is that afterthe water and fire are shut down for the night the heat of thefurnace can be great enough to cause serious warping of the surfaceof the shield so that the water will no longer cover it in a thin, uniform sheet. After rigging up a big furnace with a shield of this type severalyears ago, its most serious object was found in the increase ofthe water bill of the plant. This was already of large proportions, but it had suddenly jumped to the extent of several hundred dollars. Investigation soon disclosed the fact that this water shield was oneof the main causes of the added cost of water. A little estimatingof the amount of water that can flow through a 1/2-in. Pipe under30-lb. Pressure, in the course of a day, will show that this amountat 10 cts. Per 1, 000 gal. , can count up rather rapidly. Figure 103 is a section through a portion of the furnace front andshield showing all of the principal parts. This shield consistsessentially of a very thin tank, about 2-1/2 in. Between walls, and filled with water. Like other shields it is fitted with anadjustment, that it may be raised and lowered as the work demands. The tank having an open top, the water as it absorbs heat fromthe flame will simply boil away in steam; and only a small amountwill have to be added to make up for that which has evaporated. Thewater-feed pipe shown at _F_ ends a short distance above the topof the tank so that just how much water is running in may readilybe seen. An overflow pipe is provided at _O_ which aids in maintaining thewater at the proper height, as a sufficient quantity can always bepermitted to run in, to avoid any possibility of the shield everboiling dry; at the same time the small excess can run off withoutdanger of an overflow. The shield illustrated in Fig. 104 has beenin constant use for over two years, giving greater satisfactionthan any other of which the writer has known. It might also benoted that this shield was made with riveted joints, the shop nothaving a gas-welding outfit. To flange over the edges and thenweld them with an acetylene torch would be a far more economicalprocedure, and would also insure a tight and permanent joint. The water-cooled front shown in Fig. 105 is an absurd effort toaccomplish the design of a furnace that will provide cool workingconditions. This front was on a bolt-heating furnace using hardcoal for fuel; and it may be seen that it takes the place of allof the brickwork that should be on that side. Had this been nothingmore than a very narrow water-cooled frame, with brickwork belowand supporting bricks above, put in like the tuyeres in a foundrycupola, the case would have been somewhat different, for then itwould have absorbed a smaller proportion of the heat. A blacksmith who knows how a piece of cold iron laid in a smallwelding furnace momentarily lowers the temperature, will appreciatethe enormous amount of extra heat that must be maintained in thecentral portion of this furnace to make up for the constant chillingeffect of the cold wall. Moreover, since there would have beenserious trouble had steam generated in this front, a steady streamof water had to be run through it constantly to insure againstan approach to the boiling point. This is illustrated because ofits absurdity, and as a warning of something to avoid. Water-cooled, tuyere openings, as mentioned above, which supportbrick side-walls of the furnace, have proved successful for coalfurnaces used for forging machine and drop-hammer heating, sincethey permit a great amount of work to be handled through theiropenings without wearing away as would a brick arch. Great careshould be exercised properly to design them so that a minimum amountof the cold tuyere will be in contact with the interior of thefurnace, and all interior portions possible should be covered bythe bricks. However, a discussion of these points will hardly comein the flame-shield class, although they can be made to do a greatdeal toward relieving the excessive heat to be borne by the furnaceworker. FLANGE SHIELDS FOR FURNACES. --Such portable flame shields as theone illustrated in Fig. 106 may prove serviceable before furnacesrequired for plate work, where the doors are often only openedfor a moment at a time. This shield can be placed far enough infront of the furnace, that it will be possible to work under itor around it, in removing bulky work from the furnace, and yetit will afford the furnace tender some relief from the excessiveglare that will come out the wide-opened door. To have this shieldof light weight so that it may be readily pushed aside when notwanted, the frame may be made up of pipe and fittings, and a pieceof thin sheet steel fastened in the panel by rings about the frame. About the most disagreeable task in a heat-treating shop is theremoval of the pots from the case-hardening furnaces; these mustbe handled at a bright red heat in order that their contents may bedumped into the quenching tank with a minimum-time contact with theair, and before they have cooled sufficiently to require reheating. Facing the heat before the large open doors of the majority ofthese furnaces, in a man-killing task even when the weather ismoderately cool. The boxes soon become more or less distorted, and then even the best of lifting devices will not remove a hotpot without several minutes labor in front of the doors. In Fig. 107 is shown a method of arranging a shield on one type ofcharging and removing truck. This shield cannot afford more thana partial protection to the body of the furnace tender, becausehe must be able to see around it, and in some cases even push itpartly through the door of the furnace, but even small as it is itmay still afford some welcome protection. The great advantage inthis case of having the shield on the truck instead of stationaryin front of the furnace, is that it still affords protection aslong as the hot pot is being handled through the shop on its wayto the quenching tank. It might be interesting to many engaged in the heat-treating orcase hardening of steel parts, to make a special note of the designof the truck that is illustrated in connection with the shield;the general form is shown although the actual details for theconstruction of such a truck are lacking; these being simple, may bereadily worked out by anyone wishing to build one. This is consideredto be one of the quickest and easiest operated devices for theremoval of this class of work from the furnace. To be sure it mayonly be used where the floor of the furnace has been built levelwith the floor of the room, but many of the modern furnaces ofthis class are so designed. The pack-hardening pots are cast with legs, from two to three incheshigh, to permit the circulation of the hot gases, and so heat morequickly. Between these legs and under the body of the pot, the twoforward prongs of the truck are pushed, tilting the outer handleto make these prongs as low as possible. The handle is then loweredand, as it has a good leverage, the pot is easily raised from thefloor, and the truck and its load rolled out. HEATING OF MANGANESE STEEL. --Another form of heat-treating furnaceis that which is used for the heating of manganese and other alloysteels, which after having been brought to the proper heat are drawnfrom the furnace into an immediate quenching tank. With manganesesteel in particular, the parts are so fragile and easily damagedwhile hot that it is frequent practice to have a sloping platformimmediately in front of the furnace door down which the castingsmay slide into a tank below the floor level. Such a furnace witha quenching tank in front of its door is shown in Fig. 108. These tanks are covered with plates while charging the furnaceand the cold castings are placed in a moderately cool furnace. Since some of these steels must not be charged into a furnace wherethe heat is extreme but should be brought up to their final heatgradually, there is little discomfort during the charging process. When quenching, however, from a temperature of 1, 800° to 1, 900°, it is extremely unpleasant in front of the doors. The swingingshield is here adapted to give protection for this work. As willbe noted it is hung a sufficient distance in front of the doors, that it may not interfere with the castings as they come from thefurnace, and slide down into the tank. To facilitate the work, and avoid the necessity of working withthe bars outside the edges of the shield, the slot-like hole iscut in the center of the shield, and through this the bars or rakesfor dragging out the castings are easily inserted and manipulated. The advantage of such a swinging shield is that it may be readilymoved from side to side, or forward and back as occasion requires. FURNACE DATA In order to give definite information concerning furnaces, fuelsetc. , the following data is quoted from a paper by Seth A. Moultonand W. H. Lyman before the Steel Heat Treaters Society in September, 1920. This considers a factory producing 30, 000 lb. Of automobile gearsper 24 hr. The transmission gears will be of high-carbon steel andthe differential of low-carbon steel, carburized. The heat-treatingequipment required is: 1. Annealing furnaces 1, 400 to 1, 600°F. 2. Carburizing furnaces 1, 700 to 1, 800°F. 3. Hardening furnaces 1, 450 to 1, 550°F. 4. Drawing furnaces 350 to 950°F. All of the forging blanks are annealed before machining, aboutthree-quarters of the machined gears and parts are carburized, all the carburized gears are given a double treatment for core andcase, all gears and parts are hardened and all parts are drawn. The possible sources of heat supply and their values are as follows:-- 1. Oil 140, 000 B. T. U. Per gallon 2. Natural gas 1, 100 B. T. U. Per cubic foot 3. City gas 650 B. T. U. Per cubic foot 4. Water gas 300 B. T. U. Per cubic foot 5. Producer gas 170 B. T. U. Per cubic foot 6. Coal 12, 000 B. T. U. Per pound 7. Electric current 3, 412 B. T. U. Per kilowatt-hour For the heat treatment specified only comparatively low temperaturesare required. No difficulty will be experienced in attaining thedesired maximum temperature of 1, 800°F. With any of the heatingmedium above enumerated; but it should be noted that the producergas with a B. T. U. Content of 170 per cubic foot and the electriccurrent would require _specially_ designed furnaces to obtain highertemperatures than 1800°F. TABLE 28. --COMPARATTVE OPERATING COSTS Assuming Cost of oil- and gas-fired furnaces installed as $100. 00 per square foot of hearth Cost of coal-fired furnace installed as 150. 00 per square foot of hearth Cost of electric furnace 100 kw. Capacity installed as 90. 00 per kilowatt Cost of electric furnace 150 kw. Capacity installed as 70. 00 per kilowatt Output 3, 000 lb. Charge, 8 hr. Heat carburizing, 2 hr. Heatingonly. Annual service 7, 200 hr. Fixed charges including interest, depreciation, taxes, insurance and maintenance 15 per cent. Extraoperating labor for coal-fired furnace 60 cts. Per hour, one manfour furnaces. COST OF VARIOUS TYPES OF FURNACES------------------------------------------------------------------------------- | Class fuel | Fuel per | Unit fuel|Installation|Efficiency| Fixed |Cost per | | charge | cost | cost | per cent |charges| charge-|------------|------------|----------|------------|----------|-------|-------- | 1 | 2 | 3 | 4 | 5 | 6 | 7-|------------|------------|----------|------------|----------|-------|--------Carburizing-|------------|------------|----------|------------|----------|-------|--------1|Oil | 52. 0 gal. |$0. 15 gal. | $2, 400. 00 | 12. 6 | $. 40 | $8. 202|Natural gas | 4. 4 M | 0. 50 M | 2, 400. 00 | 18. 8 | 0. 40 | 2. 603|City gas | 8. 3 M | 0. 80 M | 2, 400. 00 | 17. 0 | 0. 40 | 7. 044|Water gas | 18. 7 M | 0. 40 | 2, 400. 00 | 16. 4 | 0. 40 | 7. 885|Producer gas| 37. 3 M | 0. 10 M | 2, 400. 00 | 14. 5 | 0. 40 | 4. 136|Coal |814. 0 lb. | 6. 00 ton | 3, 600. 00 | 9. 4 | 0. 60 | 3. 987|Electricity |500. 0 kw-hr. | 0. 015 kw. | 9, 000. 00 | 53. 0 | 1. 50 | 9. 00-|------------|------------|----------|------------|----------|-------|--------Heating-|------------|------------|----------|------------|----------|-------|--------1|Oil | 30. 8 gal. | 0. 15 gal. | 2, 400. 00 | 21. 4 | 0. 10 | 4. 722|Natural gas | 2. 61 M | 0. 50 M | 2, 400. 00 | 32. 0 | 0. 10 | 1. 403|City gas | 4. 9 M | 0. 80 M | 2, 400. 00 | 28. 8 | 0. 10 | 4. 024|Water gas | 11. 1 M | 0. 40 M | 2, 400. 00 | 27. 6 | 0. 10 | 4. 545|Producer gas| 22. 1 M | 0. 10 M | 2, 400. 00 | 24. 6 | 0. 10 | 2. 316|Coal |348. 0 lb. | 6. 00 ton | 3, 600. 00 | 22. 0 | 0. 15 | 1. 387|Electricity |329. 0 kw-hr. | 0. 015 kw. | 10, 500. 00 | 81. 75 | 0. 44 | 5. 38------------------------------------------------------------------------------- This shows but two of the operations and for a single furnace. The total costs for all operations on the 30, 000 lb. Of gears per24 hr. Is shown in Table 29. TABLE 29. --COMPARATIVE ANNUAL PRODUCTION COSTS FOR 30, 000 POUNDSOUTPUT IN 24 HOURS ---------------------------------------------------------- No. | Equipment | Installation | | cost -----|-------------------------------------|-------------- 1 | 2 | 3 | | I | Oil | $179, 000. 00 II | Oil and electric | 213, 000. 00 III | Natural gas | 117, 000. 00 IV | (A) Natural gas containing furnaces | 120, 000. 00 V | Natural gas and electric | 181, 000. 00 VI | City gas | 122, 000. 00 VII | City gas and electric | 182, 000. 00 VIII| Water gas | 214, 000. 00 IX | Water gas and electric | 238, 000. 00 X | Producer gas | 246, 000. 00 XI | Producer gas and electric | 255, 000. 00 XII | Coal and electric | 194, 000. 00 XIII| Electric | 257, 000. 00 ---------------------------------------------------------- --------------------------------------------------------------------- | Annual operating expenses | | Cost No. |----------------------------------------| Total | per lb. | Fixed | Heat | Labor | | metal, | charges | | | | cents -----|------------|-------------|-------------|-------------|-------- 1 | 4 | 5 | 6 | 7 | 8 | | | | | I | $26, 850. 00 | $156, 000. 00 | $105, 000. 00 | $287, 850. 00 | $3. 19 II | 31, 950. 00 | 142, 770. 00 | 97, 000. 00 | 271, 720. 00 | 3. 02 III | 17, 550. 00 | 44, 250. 00 | 97, 000. 00 | 158, 800. 00 | 1. 78 IV | 18, 000. 00 | 41, 000. 00 | 94, 000. 00 | 153, 000. 00 | 1. 70 V | 27, 150. 00 | 73, 820. 00 | 90, 000. 00 | 190, 970. 00 | 2. 13 VI | 18, 300. 00 | 123, 200. 00 | 94, 000. 00 | 235, 500. 00 | 2. 62 VII | 27, 300. 00 | 128, 820. 00 | 90, 000. 00 | 246, 020. 00 | 2. 74 VIII| 18, 600. 00 | 104, 000. 00 | 94, 000. 00 | 216, 600. 00 | 2. 41 IX | 27, 450. 00 | 117, 420. 00 | 90, 000. 00 | 234, 870. 00 | 2. 62 X | 18, 900. 00 | 69, 300. 00 | 90, 000. 00 | 178, 200. 00 | 1. 98 XI | 27, 750. 00 | 92, 520. 00 | 90, 000. 00 | 210, 270. 00 | 2. 34 XII | 29, 100. 00 | 87, 220. 00 | 90, 000. 00 | 206, 320. 00 | 2. 30 XIII| 38, 550. 00 | 135, 000. 00 | 84, 000. 00 | 257, 550. 00 | 2. 86 --------------------------------------------------------------------- NOTE. --Producer plant fixed charges are included in the cost ofgas and are charged as "heat" in column 5, so they are omittedfrom column 4. CHAPTER XII PYROMETRY AND PYROMETERS A knowledge of the fundamental principles of pyrometry, or themeasurement of temperatures, is quite necessary for one engagedin the heat treatment of steel. It is only by careful measurementand control of the heating of steel that the full benefit of aheat-treating operation is secured. Before the advent of the thermo-couple, methods of temperaturemeasurement were very crude. The blacksmith depended on his eyesto tell him when the proper temperature was reached, and of coursethe "color" appeared different on light or dark days. "Cherry"to one man was "orange" to another, and it was therefore almostimpossible to formulate any treatment which could be applied byseveral men to secure the same results. One of the early methods of measuring temperatures was the "ironball" method. In this method, an iron ball, to which a wire wasattached, was placed in the furnace and when it had reached thetemperature of the furnace, it was quickly removed by means ofthe wire, and suspended in a can containing a known quantity ofwater; the volume of water being such that the heat would not causeit to boil. The rise in temperature of the water was measured by athermometer, and, knowing the heat capacity of the iron ball andthat of the water, the temperature of the ball, and therefore thefurnace, could be calculated. Usually a set of tables was preparedto simplify the calculations. The iron ball, however, scaled, andchanged in weight with repeated use, making the determinationsless and less accurate. A copper ball was often used to decreasethis change, but even that was subject to error. This method isstill sometimes used, but for uniform results, a platinum ball, which will not scale or change in weight, is necessary, and thecost of this ball, together with the slowness of the method, haverendered the practice obsolete, especially in view of moderndevelopments in accurate pyrometry. PYROMETERS Armor plate makers sometimes use the copper ball or Siemens' waterpyrometer because they can place a number of the balls or weights onthe plate in locations where it is difficult to use other pyrometers. One of these pyrometers is shown in section in Fig. 109. SIEMENS' WATER PYROMETER. --It consists of a cylindrical copper vesselprovided with a handle and containing a second smaller copper vesselwith double walls. An air space _a_ separates the two vessels, anda layer of felt the two walls of the inner one, in order to retardthe exchange of temperature with the surroundings. The capacityof the inner vessel is a little more than one pint. A mercurythermometer _b_ is fixed close to the wall of the inner vessel, its lower part being protected by a perforated brass tube, whilstthe upper projects above the vessel and is divided as usual on thestem into degrees, Fahrenheit or Centigrade, as desired. At theside of the thermometer there is a small brass scale _c_, whichslides up and down, and on which the high temperatures are markedin the same degrees as those in which the mercury thermometer isdivided; on a level with the zero division of the brass scale asmall pointer is fixed, which traverses the scale of the thermometer. [Illustration: FIG. 109. --Siemens' copper-ball pyrometer. ] Short cylinders _d_, of either copper, iron or platinum, are suppliedwith the pyrometer, which are so adjusted that their heat capacity atordinary temperature is equal to one-fiftieth of that of the coppervessel filled with one pint of water. As, however, the specific heatof metals increases with the temperature, allowance is made on thebrass sliding scales, which are divided according to the metal usedfor the pyrometer cylinder _d_. It will therefore be understood thata different sliding scale is required for the particular kind ofmetal of which a cylinder is composed. In order to obtain accuratemeasurements, each sliding scale must be used only in conjunctionwith its own thermometer, and in case the latter breaks a new scalemust be made and graduated for the new thermometer. The water pyrometer is used as follows: Exactly one pint (0. 568 liter) of clean water, perfectly distilledor rain water, is poured into the copper vessel, and the pyrometeris left for a few minutes to allow the thermometer to attain thetemperature of the water. The brass scale _c_ is then set with its pointer opposite thetemperature of the water as shown by the thermometer. Meanwhileone of the metal cylinders has been exposed to the high temperaturewhich is to be measured, and after allowing sufficient time forit to acquire that temperature, it is rapidly removed and droppedinto the pyrometer vessel without splashing any of the water out. The temperature of the water will rise until, after a little while, the mercury of the thermometer has become stationary. When thisis observed the degrees of the thermometer are read off, as wellas those on the brass scale _c_ opposite the top of the mercury. The sum of these two values together gives the temperature of theflue, furnace or other heated space in which the metal cylinderhad been placed. With cylinders of copper and iron, temperatures upto 1, 800°F. (1, 000°C. ) can be measured, but with platinum cylindersthe limit is 2, 700°F. (1, 500°C. ). For ordinary furnace work either copper or wrought-iron cylindersmay be used. Iron cylinders possess a higher melting point and haveless tendency to scale than those of copper, but the latter aremuch less affected by the corrosive action of the furnace gases;platinum is, of course, not subject to any of these disadvantages. The weight to which the different metal cylinders are adjusted isas follows: Copper 137. 0 grams Wrought-iron 112. 0 grams Platinum 402. 6 grams In course of time the cylinders lose weight by scaling; but tablesare provided giving multipliers for the diminished weights, bywhich the reading on the brass scale should be multiplied. THE THERMO-COUPLE With the application of the thermo-couple, the measurement oftemperatures, between, say, 700 and 2, 500°F. , was made more simpleand precise. The theory of the thermo-couple is simple; it is thatif two bars, rods, or wires of different metals are joined togetherat their ends, when heated so that one junction is hotter than theother, an electromotive force is set up through the metals, whichwill increase with the increase of the _difference_ of temperaturebetween the two junctions. This electromotive force, or voltage, maybe measured, and, from a chart previously prepared, the temperaturedetermined. In most pyrometers, of course, the temperatures areinscribed directly on the voltmeter, but the fact remains thatit is the voltage of a small electric current, and not heat, thatis actually measured. There are two common types of thermo-couples, the first making useof common, inexpensive metals, such as iron wire and nichrome wire. This is the so-called "base metal" couple. The other is composed ofexpensive metals such as platinum wire, and a wire of an alloy ofplatinum with 10 per cent of rhodium or iridium. This is calledthe "rare metal" couple, and because its component metals are lessaffected by heat, it lasts longer, and varies less than the basemetal couple. The cold junction of a thermo-couple may be connected by meansof copper wires to the voltmeter, although in some installationsof base metal couples, the wires forming the couple are themselvesextended to the voltmeter, making copper connections unnecessary. From the foregoing, it may be seen that accurately to measure thetemperature of the hot end of a thermo-couple, we _must know thetemperature of the cold end_, as it is the _difference_ in thetemperatures that determines the voltmeter readings. This is absolutelyessential for precision, and its importance cannot be over-emphasized. When pyrometers are used in daily operation, they should be checkedor calibrated two or three times a month, or even every week. Wherethere are many in use, it is good practice to have a master pyrometerof a rare metal couple, which is used only for checking up theothers. The master pyrometer, after calibrating against the meltingpoints of various substances, will have a calibration chart whichshould be used in the checking operation. It is customary now to send a rare metal couple to the Bureau ofStandards at Washington, where it is very carefully calibratedfor a nominal charge, and returned with the voltmeter readingsof a series of temperatures covering practically the whole rangeof the couple. This couple is then used only for checking thosein daily use. Pyrometer couples are more or less expensive, and should be caredfar when in use. The wires of the couple should be insulated fromeach other by fireclay leads or tubes, and it is well to encase themin a fireclay, porcelain, or quartz tube to keep out the furnacegases, which in time destroy the hot junction. This tube of fireclay, or porcelain, etc. , should be protected against breakage by aniron or nichrome tube, plugged or welded at the hot end. Thesesimple precautions will prolong the life of a couple and maintainits precision longer. Sometimes erroneous temperatures are recorded because the "coldend" of the couple is too near the furnace and gets hot. This alwayscauses a temperature reading lower than the actual, and should beguarded against. It is well to keep the cold end cool with water, a wet cloth, or by placing it where coal air will circulate aroundit. Best of all, is to have the cold junction in a box, togetherwith a thermometer, so that its temperature may definitely be known. If this temperature should rise 20°F. On a hot day, a correction of20°F. Should be added to the pyrometer reading, and so on. In themost up-to-date installations, this cold junction compensation istaken care of automatically, a fact which indicates its importance. Optical pyrometers are often used where it is impracticable touse the thermo-couple, either because the temperature is so highthat it would destroy the couple, or the heat to be measured isinaccessible to the couple of ordinary length. The temperatures ofslag or metal in furnaces or running through tap-holes or troughsare often measured with optical pyrometers. In one type of optical pyrometer, the observer focuses it on themetal or slag and moves an adjustable dial or gage so as to getan exact comparison between the color of the heat measured withthe calor of a lamp or screen in the pyrometer itself. This, ofcourse, requires practice, and judgment, and brings in the personalequation. With care, however, very reliable temperature measurementsmay be made. The temperatures of rails, as they leave the finishingpass of a rolling mill, are measured in this way. Another type of optical pyrometer is focused on the body, thetemperature of which is to be measured. The rays converge in thetelescope on metal cells, heating them, and thereby generating asmall electric current, the voltage of which is read an a calibratedvoltmeter similar to that used with the thermo-couple. The bestprecision is obtained when an optical pyrometer is used each timeunder similar conditions of light and the same observer. Where it is impracticable to use either thermo-couples or opticalpyrometers, "sentinels" may be used. There are small cones or cylindersmade of salts or other substances of known melting points and coveringa wide range of temperatures. If six of these "sentinels, " melting respectively at 1, 300°, 1, 350°, 1, 400°, 1, 450°, 1, 500°, and 1, 550°F. , were placed in a row in afurnace, together with a piece of steel to be treated, and thewhole heated up uniformly, the sentinels would melt one by one andthe observer, by watching them through an opening in the furnace, could tell when his furnace is at say 1, 500° or between 1, 500° and1, 550°, and regulate the heat accordingly. A very accurate type of pyrometer, but one not so commonly used asthose previously described, is the resistance pyrometer. In thistype, the temperature is determined by measuring the resistance to anelectric current of a wire which is at the heat to be measured. Thiswire is usually of platinum, wound around a quartz tube, the wholebeing placed in the furnace. When the wire is at the temperature ofthe furnace, it is connected by wires with a Wheatstone Bridge, adelicate device for measuring electrical resistance, and an electriccurrent is passed through the wire. This current is balanced byswitching in resistances in the Wheatstone Bridge, until a delicateelectrical device shows that no current is flowing. The resistanceof the platinum wire at the heat to be measured is thus determinedon the "Bridge, " and the temperature read off on a calibrationchart, which shows the resistance at various temperatures. These are the common methods used to-day for measuring temperatures, but whatever method is used, the observer should bear in mind thatthe greatest precision is obtained, and hence the highest efficiency, by keeping the apparatus in good working order, making sure thatconditions are the same each time, and calibrating or checkingagainst a standard at regular intervals. THE PYROMETER AND ITS USE In the heat treatment of steel, it has become absolutely necessarythat a measuring instrument be used which will give the operator anexact reading of heat in furnace. There are a number of instrumentsand devices manufactured for this purpose but any instrument thatwill not give a direct reading without any guess work should haveno place in the heat-treating department. A pyrometer installation is very simple and any of the leadingmakers will furnish diagrams for the correct wiring and give detailedinformation as to the proper care of, and how best to use theirparticular instrument. There are certain general principles, however, that must be observed by the operators and it cannot be too stronglyimpressed upon them that the human factor involved is always thedeciding factor in the heat treatment of steel. A pyrometer is merely an aid in the performance of doing good work, and when carefully observed will help in giving a uniformity ofproduct and act as a check on careless operators. The operatormust bear in mind that although the reading on the pyrometer scalegives a measure of the temperature where the junction of the twometals is located, it will not give the temperature at the centerof work in the furnace, unless by previous tests, the heat forpenetrating a certain bulk of material has been decided on, andthe time necessary for such penetration is known. Each analysis of plain carbon or alloy steel is a problem in itself. Its critical temperatures will be located at slightly differentheats than for a steel which has a different proportion of alloyingelements. Furthermore, it takes time for metal to acquire the heatof the furnace. Even the outer surface lags behind the temperatureof the furnace somewhat, and the center of the piece of steel lagsstill further. It is apparent, therefore, that temperature, althoughimportant, does not tell the whole story in heat treatment. _Time_is also a factor. Time at temperature is also of great importance because it takestime, after the temperature has been reached, for the various internalchanges to take place. Hence the necessity for "soaking, " whenannealing or normalizing. Therefore, a clock is as necessary tothe proper pyrometer equipment as the pyrometer itself. For the purpose of general work where a wide range of steels ora variable treatment is called for, it becomes necessary to havethe pyrometer calibrated constantly, and when no master instrumentis kept for this purpose the following method can be used to givethe desired results: CALIBRATION OF PYROMETER WITH COMMON SALT An easy and convenient method for standardization and one whichdoes not necessitate the use of an expensive laboratory equipmentis that based upon determining the melting point of common tablesalt (sodium chloride). While theoretically salt that is chemicallypure should be used (and this is neither expensive nor difficultto procure), commercial accuracy may be obtained by using commontable salt such as is sold by every grocer. The salt is melted ina clean crucible of fireclay, iron or nickel, either in a furnaceor over a forge-fire, and then further heated until a temperatureof about 1, 600 to 1, 650°F. Is attained. It is essential that thiscrucible be clean because a slight admixture of a foreign substancemight noticeably change the melting point. The thermo-couple to be calibrated is then removed from its protectingtube and its hot end is immersed in the salt bath. When this endhas reached the temperature of the bath, the crucible is removedfrom the source of heat and allowed to cool, and cooling readingsare then taken every 10 sec. On the milli-voltmeter or pyrometer. Acurve is then plotted by using time and temperature as coördinates, and the temperature of the freezing point of salt, as indicatedby this particular thermocouple, is noted, _i. E. _, at the pointwhere the temperature of the bath remains temporarily constantwhile the salt is freezing. The length of time during which thetemperature is stationary depends on the size of the bath and therate of cooling, and is not a factor in the calibration. The meltingpoint of salt is 1, 472°F. , and the needed correction for the instrumentunder observation can be readily applied. It should not be understood from the above, however, that the salt-bathcalibration cannot be made without plotting a curve; in actualpractice at least a hundred tests are made without plotting any curveto one in which it is done. The observer, if awake, may reasonablybe expected to have sufficient appreciation of the lapse of timedefinitely to observe the temperature at which the falling pointerof the instrument halts. The gradual dropping of the pointer beforefreezing, unless there is a large mass of salt, takes place rapidlyenough for one to be sure that the temperature is constantly falling, and the long period of rest during freezing is quite definite. The procedure of detecting the solidification point of the saltby the hesitation of the pointer without plotting any curve issuggested because of its simplicity. COMPLETE CALIBRATION OF PYROMETERS. --For the complete calibrationof a thermo-couple of unknown electromotive force, the new couplemay be checked against a standard instrument, placing the two barecouples side by side in a suitable tube and taking frequent readingsover the range of temperatures desired. If only one instrument, such as a millivoltmeter, is available, and there is no standard couple at hand, the new couple may becalibrated over a wide range of temperatures by the use of the followingstandards: Water, boiling point 212°F. Tin, under charcoal, freezing point 450°F. Lead, under charcoal, freezing point 621°F. Zinc, under charcoal, freezing point 786°F. Sulphur, boiling point 832°F. Aluminum, under charcoal, freezing point 1, 216°F. Sodium chloride (salt), freezing point 1, 474°F. Potassium sulphate, freezing point 1, 958°F. A good practice is to make one pyrometer a standard; calibrate itfrequently by the melting-point-of-salt method, and each morningcheck up every pyrometer in the works with the standard, making thenecessary corrections to be used for the day's work. By pursuingthis course systematically, the improved quality of the productwill much more than compensate for the extra work. The purity of the substance affects its freezing or melting point. The melting point of common salt is given in one widely used handbookat 1, 421°F. , although chemically pure sodium chloride melts at1, 474°F. As shown above. A sufficient quantity for an extendedperiod should be secured. Test the melting point with a pyrometerof known accuracy. Knowing this temperature it will be easy tocalibrate other pyrometers. PLACING OF PYROMETERS. --When installing a pyrometer, care should betaken that it reaches directly to the point desired to be measured, that the cold junction is kept cold, and that the wires leading tothe recording instrument are kept in good shape. The length ofthese lead wires have an effect; the longer they are, the lowerthe apparent temperature. When pyrometers placed in a number of furnaces are connected upin series, and a multiple switch is used for control, it becomesapparent that pyrometers could not be interchanged between furnacesnear and far from the instrument without affecting the uniformityof product from each furnace. Calibration can best be done without disturbing the working pyrometer, by inserting the master instrument into each furnace separately, placeit alongside the hot junction of the working pyrometer, and comparethe reading given on the indicator connected with the multipleswitch. Protection tubes should be replaced when cracked, as it is importantthat no foreign substance is allowed to freeze in the tube, sothat the enclosed junction becomes a part of a solid mass joinedin electrical contact with the outside protecting tube. Wires overthe furnaces must be carefully inspected from time to time, as notrue reading can be had on an instrument, if insulation is burnedoff and short circuits result. If the standard calibrating instrument used contains a dry battery, it should be examined from time to time to be sure it is in goodcondition. THE LEEDS AND NORTHRUP POTENTIOMETER SYSTEM The potentiometer pyrometer system is both flexible and substantialin that it is not affected by the jar and vibration of the factoryor the forge shop. Large or small couples, long or short leadscan be used without adjustment. The recording instrument may beplaced where it is most convenient, without regard to the distancefrom the furnace. ITS FUNDAMENTAL PRINCIPLE. --The potentiometer is the electricalequivalent of the chemical balance, or balance arm scales. Measurementsare made with balance scales by varying known weights until theyequal the unknown weight. When the two are equal the scales standat zero, that is, in the position which they occupy when there isno weight on either pan; the scales are then said to be balanced. Measurements are made with the potentiometer by varying a knownelectromotive force until it equals the unknown; when the two areequal the index of the potentiometer, the galvanometer needle, stands motionless as it is alternately connected and disconnected. The variable known weights are units separate from the scales, butthe potentiometer provides its own variable known electromotiveforce. The potentiometer provides, first, a means of securing a knownvariable electromotive force and, second, suitable electricalconnections for bringing that electromotive force to a point whereit may be balanced against the unknown electromotive force of thecouple. The two are connected with opposite polarity, or so thatthe two e. M. F. S oppose one another. So long as one is strongerthan the other a current will flow through the couple; when thetwo are equal no current will flow. Figure 107 shows the wiring of the potentiometer in its simplestform. The thermo-couple is at _H_, with its polarity as shown bythe symbols + and -. It is connected with the main circuit of thepotentiometer at the fixed point _D_ and the point _G_. [Illustration: FIG. 110. --Simple potentiometer. ] A current from the dry cell _Ba_ is constantly flowing through themain, or so-called potentiometer circuit, _ABCDGEF_. The section_DGE_ of this circuit is a slide wire, uniform in resistance throughoutits length. The scale is fixed on this slide wire. The currentfrom the cell _Ba_ as it flows through _DGE_, undergoes a fallin potential, setting up a difference in voltage, that is, anelectromotive force, between _D_ and _E_. There will also beelectromotive force between _D_ and all other points on the slidewire. The polarity of this is in opposition to the polarity of thethermo-couple which connects into the potentiometer at _D_ andat _G_. By moving _G_ along the slide wire a point is found wherethe voltage between _D_ and _G_ in the slide wire is just equal tothe voltage between _D_ and _G_ generated by the thermo-couple. Agalvanometer in the thermo-couple circuit indicates when the balancepoint is reached, since at this point the galvanometer needle willstand motionless when its circuit is opened and closed. [Illustration: FIG. 111. --Standard cell potentiometer. ] The voltage in the slide wire will vary with the current flowingthrough it from the cell _Ba_ and a means of standardizing this isprovided. _SC_, Fig. 111, is a cadmium cell whose voltage is constant. It is connected at two points _C_ and _D_ to the potentiometercircuit whenever the potentiometer current is to be standardized. At this time the galvanometer is thrown in series with _SC_. Thevariable rheostat _R_ is then adjusted until the current flowingis such that as it flows through the standard resistance _CD_, the fall in potential between _C_ and _D_ is just equal to thevoltage of the standard cell _SC_. At this time the galvanometerwill indicate a balance in the same way as when it was used witha thermo-couple. By this operation the current in the slide wire_DGE_ has been standardized. [Illustration: FIG. 112. --Hand adjusted cold-end compensator. ] DEVELOPMENT OF THE WIRING SCHEME OF THE COLD-END COMPENSATOR. --Thenet voltage generated by a thermo-couple depends upon the temperatureof the hot end and the temperature of the cold end. Therefore, anymethod adopted for reading temperature by means of thermo-couplesmust in some way provide a means of correcting for the temperature ofthe cold end. The potentiometer may have either of two very simpledevices for this purpose. In one form the operator is requiredto set a small index to a point on a scale corresponding to theknown cold junction temperature. In the other form an even moresimple automatic compensator is employed. The principle of each isdescribed in the succeeding paragraphs, in which the assumption ismade that the reader already understands the potentiometer principleas described above. As previously explained the voltage of the thermo-couple is measuredby balancing it against the voltage drop _DG_ in the potentiometer. As shown in Fig. 111, the magnitude of the balancing voltage iscontrolled by the position of _G_. Make _D_ movable as shown in Fig. 112 and the magnitude of the voltage _DG_ may be varied either fromthe point _D_ or the point _G_. This gives a means of compensatingfor cold end changes by setting the slider _D_. As the cold endtemperature rises the net voltage generated by the couple decreases, assuming the hot end temperature to be constant. To balance thisdecreased voltage the slider _D_ is moved along its scale to a newpoint nearer _G_. In other words, the slider _D_ is moved alongits scale until it corresponds to the known temperature of the coldend and then the potentiometer is balanced by moving the slider_G_. The readings of _G_ will then be direct. [Illustration: FIG. 113. --Another type of compensator. ] The same results will be obtained if a slide wire upon which _D_bears is in parallel with the slide wire of _G_, as shown in Fig. 113. AUTOMATIC COMPENSATOR. --It should be noted that the effect of movingthe contact _D_, Fig. 113, is to vary the ratio of the resistanceson the two sides of the point _D_ in the secondary slide wire. Inthe recording pyrometers, an automatic compensator is employed. This automatic compensator varies the ratio on the two sides ofthe point _D_ in the following manner: The point _D_, Fig. 114, is mechanically fixed; on one side of_D_ is the constant resistance coil _M_, on the other the nickelcoil _N_. _N_ is placed at or near the cold end of the thermo-couple(or couples). Nickel has a high temperature coefficient and theelectrical proportions of _M_ and _N_ are such that the resistancechange of _N_, as it varies with the temperature of the cold end, has the same effect upon the balancing voltage between _D_ and_G_ that the movement of the point _D_, Fig. 114, has in thehand-operated compensator. Instruments embodying these principles are shown in Figs. 115 to117. The captions making their uses clear. [Illustration: FIG. 114. --Automatic cold-end compensator. ] PLACING THE THERMO-COUPLES The following illustrations from the Taylor Instrument Companyshow different applications of the thermo-couples to furnaces ofvarious kinds. Figure 118 shows an oil-fired furnace with a simplevertical installation. Figure 119 shows a method of imbedding thethermo-couple in the floor of a furnace so as to require no spacein the heating chamber. [Illustration: FIG. 115. --Potentiometer ready for use. ] Various methods of applying a pyrometer to common heat-treatmentfurnaces are shown in Figs. 120 to 122. [Illustration: FIG. 116. --Eight-point recording pyrometer-CarpenterSteel Co. ] LEEDS AND NORTHRUP OPTICAL PYROMETER The principles of this very popular method of measuring temperatureare sketched in Fig. 123. [Illustration: FIG. 117. --Multiple-point thermocouplerecorder--Bethlehem Steel Co. ] [Illustration: FIG. 118. --Tycos pyrometer in oil-fired furnace. ] The instrument is light and portable, and can be sighted as easilyas an opera glass. The telescope, which is held in the hand, weighsonly 25 oz. ; and the case containing the battery, rheostat andmilliammeter, which is slung from the shoulder, only 10 lb. [Illustration: FIG. 119. --Thermocouple in floor of furnace. ] [Illustration: FIG. 120. --Pyrometer in gas furnace. ] A large surface to sight at is not required. So long as the imageformed by the objective is broader than the lamp filament, thetemperature can be measured accurately. [Illustration: FIG. 121. --Tycos multiple indicating pyrometer andrecorder. ] [Illustration: FIG. 122. --Pyrometer in galvanizing tank. ] Distance does not matter, as the brightness of the image formedby the lens is practically constant, regardless of the distanceof the instrument from the hot object. [Illustration: FIG. 123. --Leeds & Northrup optical pyrometer. ] The manipulation is simple and rapid, consisting merely in the turningof a knurled knob. The setting is made with great precision, due tothe rapid change in light intensity with change in temperature andto the sensitiveness of the eye to differences of light intensity. In the region of temperatures used for hardening steel, for example, different observers using the instrument will agree within 3°C. [Illustration: FIG. 124. --Too low. FIG. 125. --Too high. FIG. 126. --Correct. ] Only brightness, not color, of light is matched, as light of onlyone color reaches the eye. Color blindness, therefore, is no hindranceto the use of this method. The use of the instrument is shown inFig. 127. OPTICAL SYSTEM AND ELECTRICAL CIRCUIT OF THE LEEDS & NORTHRUP OPTICALPYROMETER. --For extremely high temperature, the optical pyrometer islargely used. This is a comparative method. By means of the rheostatthe current through the lamp is adjusted until the brightness ofthe filament is just equal to the brightness of the image producedby the lens _L_, Fig. 123, whereupon the filament blends with orbecomes indistinguishable in the background formed by the imageof the hot object. This adjustment can be made with great accuracyand certainty, as the effect of radiation upon the eye varies sometwenty times faster than does the temperature at 1, 600°F. , and somefourteen times faster at 3, 400°F. When a balance has been obtained, the observer notes the reading of the milliammeter. The temperaturecorresponding to the current is then read from a calibration curvesupplied with the instrument. [Illustration: FIG. 127. --Using the optical pyrometer. ] As the intensity of the light emitted at the higher temperaturesbecomes dazzling, it is found desirable to introduce a piece of redglass in the eye piece at _R_. This also eliminates any questionof matching colors, or of the observer's ability to distinguishcolors. It is further of value in dealing with bodies which donot radiate light of the same composition as that emitted by ablack body, since nevertheless the intensity of radiation of anyone color from such bodies increases progressively in a definitemanner as the temperature rises. The intensity of this one colorcan therefore be used as a measure of temperature for the bodyin question. Figures 124 to 126 show the way it is read. CORRECTION FOR COLD-JUNCTION ERRORS The voltage generated by a thermo-couple of an electric pyrometer isdependent on the difference in temperature between its hot junction, inside the furnace, and the cold junction, or opposite end of thethermo-couple to which the copper wires are connected. If thetemperature or this cold junction rises and falls, the indicationsof the instrument will vary, although the hot junction in the furnacemay be at a constant temperature. A cold-junction temperature of 75°F. , or 25°C. , is usually adoptedin commercial pyrometers, and the pointer on the pyrometer shouldstand at this point on the scale when the hot junction is not heated. If the cold-junction temperature rises about 75°F. , where base metalthermo-couples are used, the pyrometer will read approximately 1°low for every 1° rise in temperature above 75°F. For example, if theinstrument is adjusted for a cold-junction temperature of 75°, andthe actual cold-junction temperature is 90°F. , the pyrometer willread 15° low. If, however, the cold-junction temperature falls below75°F. , the pyrometer will read high instead of low, approximately1° for every 1° drop in temperature below 75°F. With platinum thermo-couples, the error is approximately 1/2° for1° change in temperature. CORRECTION BY ZERO ADJUSTMENT. --Many pyrometers are supplied witha zero adjuster, by means of which the pointer can be set to anyactual cold-junction temperature. If the cold junction of thethermo-couple is in a temperature of 100°F. , the pointer can beset to this point on the scale, and the readings of the instrumentwill be correct. COMPENSATING LEADS. --By the use of compensating leads, formed ofthe same material as the thermo-couple, the cold junction can beremoved from the head of the thermo-couple to a point 10, 20 or 50ft. Distant from the furnace, where the temperature is reasonablyconstant. Where greater accuracy is desired, a common method isto drive a 2-in. Pipe, with a pointed closed end, some 10 to 20ft. Into the ground, as shown in Fig. 128. The compensating leadsare joined to the copper leads, and the junction forced down tothe bottom of the pipe. The cold junction is now in the ground, beneath the building, at a depth at which the temperature is veryconstant, about 70°F. , throughout the year. This method will usuallycontrol the cold-junction temperature within 5°F. Where the greatest accuracy is desired a compensating box willovercome cold-junction errors entirely. It consists of a case enclosinga lamp and thermostat, which can be adjusted to maintain any desiredtemperature, from 50 to 150°F. The compensating leads enter the boxand copper leads run from the compensating box to the instrument, so that the cold junction is within the box. Figure 129 shows aBrown compensating box. [Illustration: FIG. 128. --Correcting cold-junction error. ] If it is desired to maintain the cold junction at 100°: the thermostatis set at this point, and the lamp, being wired to the 110- or220-volt lighting circuit, will light and heat the box until 100°is reached, when the thermostat will open the circuit and the lightis extinguished. The box will now cool down to 98°, when the circuitis again closed, the lamp lights, the box heats up, and the operationis repeated. [Illustration: FIG. 129. --Compensating box. ] BROWN AUTOMATIC SIGNALING PYROMETER In large heat-treating plants it has been customary to maintainan operator at a central pyrometer, and by colored electric lightsat the furnaces, signal whether the temperatures are correct ornot. It is common practice to locate three lights above eachfurnace-red, white and green. The red light burns when the temperatureis too low, the white light when the temperature is within certainlimits--for example, 20°F. Of the correct temperature--and thegreen light when the temperature is too high. [Illustration: FIG. 130. --Brown automatic signaling pyrometer. ] Instruments to operate the lights automatically have been devised andone made by Brown is shown in Fig. 130. The same form of instrument isused for this purpose to automatically control furnace temperatures, and the pointer is depressed at intervals of every 10 sec. On contactscorresponding to the red, white and green lights. [Illustration: FIG. 131. --Automatic temperature control. ] AN AUTOMATIC TEMPERATURE CONTROL PYROMETER Automatic temperature control instruments are similar to the Brownindicating high resistance pyrometer with the exception that thepointer is depressed at intervals of every 10 sec. Upon contact-makingdevices. No current passes through the pointer which simply depressesthe upper contact device tipped with platinum, which in turn comesin contact with the lower contact device, platinum-tipped, and thecircuit is completed through these two contacts. The current is verysmall, about 1/10 amp. , as it is only necessary to operate the relaywhich in turn operates the switch or valve. A small motor is used todepress the pointer at regular intervals. The contact-making deviceis adjustable throughout the scale range of the instrument, and anindex pointer indicates the point on the instrument at which thetemperature is being controlled. The space between the two contactson the high and low side, separated by insulating material, isequivalent to 1 per cent of the scale range. A control of temperatureis therefore possible within 1 per cent of the total scale range. Figure 131 shows this attached to a small furnace. [Illustration: FIG. 132. --Portable thermocouple testing molten brass. ] PYROMETERS FOR MOLTEN METAL Pyrometers for molten metal are connected to portable thermocouplesas in Fig. 132. Usually the pyrometer is portable, as shown inthis case, which is a Brown. Other methods of mounting for thiskind of work arc shown in Figs. 133 and 134. The bent mountingsare designed for molten metal, such as brass or copper and aresupplied with either clay, graphite or carborundum tubes. Fifteenfeet of connecting wire is usually supplied. The angle mountings, Fig. 134, are recommended for baths such aslead or cyanide. The horizontal arm is usually about 14 in. Long, and the whole mounting is easily taken apart making replacementsvery easy. Details of the thermo-couple shown in Fig. 132 are givenin Fig. 135. This is a straight rod with a protector for the handof the operator. The lag in such couples is less than one minute. These are Englehard mountings. PROTECTORS FOR THERMO-COUPLES Thermo-couples must be protected from the danger of mechanicalinjury. For this purpose tubes of various refractory materialsare made to act as protectors. These in turn are usually protectedby outside metal tubes. Pure wrought iron is largely used for thispurpose as it scales and oxidizes very slowly. These tubes areusually made from 2 to 4 in. Shorter than the inner tubes. In leadbaths the iron tubes often have one end welded closed and are usedin connection with an angle form of mounting. [Illustration: FIG. 133. --Bent handle thermocouple with protector. ] Where it is necessary for protecting tubes to project a considerabledistance into the furnace a tube made of nichrome is frequently used. This is a comparatively new alloy which stands high temperatureswithout bending. It is more costly than iron but also much moredurable. When used in portable work and for high temperatures, pure nickeltubes are sometimes used. There is also a special metal tube madefor use in cyanide. This metal withstands the intense penetratingcharacteristics of cyanide. It lasts from six to ten months asagainst a few days for the iron tube. The inner tubes of refractory materials, also vary according tothe purposes for which they are to be used. They are as follows: MARQUARDT MASS TUBES for temperatures up to 3, 000°F. , but they willnot stand sudden changes in temperature, such as in contact withintermittent flames, without an extra outer covering of chamotte, fireclay or carborundum. [Illustration: FIG. 134. --Other styles of bent mounting. ] FUSED SILICA TUBES for continuous temperatures up to 1, 800°F. Andintermittently up to 2, 400°F. The expansion at various temperaturesis very small, which makes them of value for portable work. Theyalso resist most acids. CHAMOTTE TUBES are useful up to 2, 800°F. And are mechanically strong. They have a small expansion and resist temperature changes well, which makes them good as outside protectors for more fragile tubes. They cannot be used in molten metals, or baths of any kind norin gases of an alkaline nature. They are used mainly to protecta Marquardt mass or silica tube. CARBORUNDUM TUBES are also used as outside protection to othertubes. They stand sudden changes of temperature well and resistall gases except chlorine, above 1, 750°F. Especially useful inprotecting other tubes against molten aluminum, brass, copper andsimilar metals. CLAY TUBES are sometimes used in large annealing furnaces where theyare cemented into place, forming a sort of well for the insertion ofthe thermo-couple. They are also used with portable thermo-couplesfor obtaining the temperatures of molten iron and steel in ladles. Used in this way they are naturally short-lived, but seem the bestfor this purpose. [Illustration: FIG. 135. --Straight thermocouple and guard. ] CORUNDITE TUBES are used as an outer protection for both the Marquardtmass and the silica tubes for kilns and for glass furnaces. Graphitetubes are also used in some cases for outer protections. CALORIZED TUBES are wrought-iron pipe treated with aluminum vaporwhich often doubles or even triples the life of the tube at hightemperature. These tubes come in different sizes and lengths depending on theuses for which they are intended. Heavy protecting outer tubesmay be only 1 in. In inside diameter and as much as 3 in. Outsidediameter, while the inner tubes, such as the Marquardt mass andsilica tubes are usually about 3/4 in. Outside and 3/8 in. Insidediameter. The length varies from 12 to 48 in. In most cases. Special terminal heads are provided, with brass binding posts forelectrical connections, and with provisions for water cooling whennecessary. APPENDIX TABLE 32. --Temperature Conversion Tables. TABLE 33. --Comparison Between Degrees Centigrade and Degrees Fahrenheit. TABLE 34. --Weight of Round, Octagon and Square Carbon Tool Steelper Foot. TABLE 35. --Weight of Round Carbon Tool Steel 12 In. In Diameterand Larger, per Foot. TABLE 36. --Decimal Equivalents of a foot. TEMPERATURE CONVERSION TABLES By ALBERT SAUVEUR -------------------------------------------------------------------------- -459. 4 to 0 | 0 to 100 | 100 to 1000 -----------------|------------------------------|------------------------- C. F. | C. F. | C. F. | C. F. | C. F. -----------------|---------------|--------------|-----------|------------- -273 -459. 4 |-17. 8 0 32 |10. 0 50 122. 0| 38 100 212|260 500 932 -268 -450 |-17. 2 1 33. 8|10. 6 51 123. 8| 43 110 230|266 510 950 -262 -440 |-16. 7 2 35. 6|11. 1 52 125. 6| 49 120 248|271 520 968 -257 -430 |-16. 1 3 37. 4|11. 7 53 127. 4| 54 130 266|277 530 986 -251 -420 |-15. 6 4 39. 2|12. 2 54 129. 2| 60 140 284|282 540 1004 -246 -410 |-15. 0 5 41. 0|12. 8 55 131. 0| 66 150 302|288 550 1022 -240 -400 |-14. 4 6 42. 8|13. 3 56 132. 8| 71 160 320|293 560 1040 -234 -390 |-13. 9 7 44. 6|13. 9 57 134. 6| 77 170 336|299 570 1058 -229 -380 |-13. 3 8 46. 4|14. 4 58 136. 4| 82 180 358|304 580 1076 -223 -370 |-12. 8 9 48. 2|15. 0 59 138. 2| 88 190 374|310 590 1094 -218 -360 |-12. 2 10 50. 0|15. 6 60 140. 0| 93 200 392|316 600 1112 -212 -350 |-11. 7 11 51. 8|16. 1 61 141. 8| 99 210 410|321 610 1130 -207 -340 |-11. 1 12 53. 6|16. 7 62 143. 6|100 212 413|327 620 1148 -201 -330 |-10. 6 13 55. 4|17. 2 63 145. 4|104 220 428|332 630 1166 -196 -320 |-10. 0 14 57. 2|17. 8 64 147. 2|110 230 446|338 640 1184 -190 -310 | -9. 44 15 59. 0|18. 3 65 149. 0|116 240 464|343 650 1202 -184 -300 | -8. 89 16 61. 8|18. 9 66 150. 8|121 250 482|349 660 1220 -179 -290 | -8. 33 17 63. 6|19. 4 67 152. 6|127 260 500|354 670 1238 -173 -280 | -7. 78 18 65. 4|20. 0 68 154. 4|132 270 518|360 680 1256 -169 -273 -459. 4| -7. 22 19 67. 2|20. 6 69 156. 2|138 280 536|366 690 1274 -168 -270 -454 | -6. 67 20 68. 0|21. 1 70 158. 0|143 290 554|371 700 1292 -162 -260 -436 | -6. 11 21 69. 8|21. 7 71 159. 8|149 300 572|377 710 1310 -157 -250 -418 | -5. 56 22 71. 6|22. 2 72 161. 6|154 310 590|382 720 1328 -151 -240 -400 | -5. 00 23 73. 4|22. 8 73 163. 4|160 320 608|388 730 1346 -146 -230 -382 | -4. 44 24 75. 2|23. 3 74 165. 2|166 330 626|393 740 1364 -140 -220 -364 | -3. 89 25 77. 0|23. 9 75 167. 0|171 340 644|399 750 1382 -134 -210 -346 | -3. 33 26 78. 8|24. 4 76 168. 8|177 350 662|404 760 1400 -129 -200 -328 | -2. 78 27 80. 6|25. 0 77 170. 6|182 360 680|410 770 1418 -123 -190 -310 | -2. 22 28 82. 4|25. 6 78 172. 4|188 370 698|416 780 1436 -118 -180 -292 | -1. 67 29 84. 2|26. 1 79 174. 2|193 380 716|421 790 1454 -112 -170 -274 | -1. 11 30 86. 0|26. 7 80 176. 0|199 390 734|427 800 1472 -107 -160 -256 | -0. 56 31 87. 8|27. 2 81 177. 8|204 400 752|432 810 1490 -101 -150 -238 | 0 32 89. 6|27. 8 82 179. 6|210 410 770|438 820 1508 -95. 6 -140 -220 | 0. 56 33 91. 4|28. 3 83 181. 4|216 420 788|443 830 1526 -90. 0 -130 -202 | 1. 11 34 93. 2|28. 9 84 183. 2|221 430 806|449 840 1544 -84. 4 -120 -184 | 1. 67 35 95. 0|29. 4 85 185. 0|227 440 824|454 850 1562 -78. 9 -110 -166 | 2. 22 36 96. 8|30. 0 86 186. 8|232 450 842|460 860 1580 -73. 3 -100 -148 | 2. 78 37 98. 6|30. 6 87 188. 6|238 460 860|466 870 1598 -67. 8 -90 -130 | 3. 33 38 100. 4|31. 1 88 190. 4|243 470 878|471 880 1616 -62. 2 -80 -112 | 3. 89 39 102. 2|31. 7 89 192. 2|249 480 896|477 890 1634 -56. 7 -70 -94 | 4. 44 40 104. 0|32. 2 90 194. 0|254 490 914|482 900 1652 -51. 1 -60 -76 | 5. 00 41 105. 8|32. 8 91 195. 8| |488 910 1670 -45. 6 -50 -58 | 5. 56 42 107. 6|33. 3 92 197. 6| |493 920 1688 -40. 0 -40 -40 | 6. 11 43 109. 4|33. 9 93 199. 4| |499 930 1706 -34. 4 -30 -22 | 6. 67 44 111. 2|34. 4 94 201. 2| |504 940 1724 -28. 9 -20 4 | 7. 22 45 113. 0|35. 0 95 203. 0| |510 950 1742 -23. 3 -10 14 | 7. 78 46 114. 8|35. 6 96 204. 8| |516 960 1760 -17. 8 0 32 | 8. 33 47 116. 6|36. 1 97 206. 6| |521 970 1778 | 8. 89 48 118. 4|36. 7 98 208. 4| |527 980 1796 | 9. 44 49 120. 2|37. 2 99 210. 2| |532 990 1814 | |37. 8 100 212. 0| |538 1000 1832 -------------------------------------------------------------------------- ---------------------------------------------------------------- 1000 to 2000 | 2000 to 3000 -------------------------------|-------------------------------- C. F. | C. F. | C. F. | C. F. --------------|----------------|----------------|--------------- 538 1000 1832 | 816 1500 2732 | 1093 2000 3632 | 1371 2500 4534 543 1010 1850 | 821 1510 2750 | 1099 2010 3650 | 1377 2510 4552 549 1020 1868 | 827 1520 2768 | 1104 2020 3668 | 1382 2520 4560 554 1030 1886 | 832 1530 2786 | 1110 2030 3686 | 1388 2530 4588 560 1040 1904 | 838 1540 2804 | 1116 2040 3704 | 1393 2540 4606 566 1050 1922 | 843 1550 2822 | 1121 2050 3722 | 1399 2550 4622 571 1060 1940 | 849 1560 2840 | 1127 2060 3740 | 1404 2560 4640 577 1070 1958 | 854 1570 2858 | 1132 2070 3758 | 1410 2570 4658 582 1080 1976 | 860 1580 2876 | 1138 2080 3776 | 1416 2580 4676 588 1090 1994 | 866 1590 2894 | 1143 2090 3794 | 1421 2590 4694 593 1100 2012 | 871 1600 2912 | 1149 2100 3812 | 1427 2600 4712 599 1110 2030 | 877 1610 2930 | 1154 2110 3830 | 1432 2610 4730 604 1120 2048 | 882 1620 2948 | 1160 2120 3848 | 1438 2620 4748 610 1130 2066 | 888 1630 2966 | 1166 2130 3866 | 1443 2630 4766 616 1140 2084 | 893 1640 2984 | 1171 2140 3884 | 1449 2640 4784 621 1150 2102 | 899 1650 3002 | 1777 2150 3902 | 1454 2650 4802 627 1160 2120 | 904 1660 3020 | 1182 2160 3920 | 1460 2660 4820 632 1170 2138 | 910 1670 3038 | 1188 2170 3938 | 1466 2670 4838 638 1180 2156 | 916 1680 3056 | 1193 2180 3956 | 1471 2680 4854 643 1190 2174 | 921 1690 3074 | 1199 2190 3974 | 1477 2690 4876 649 1200 2192 | 927 1700 3092 | 1204 2200 3992 | 1482 2700 4892 654 1210 2210 | 932 1710 3110 | 1210 2210 4010 | 1488 2710 4910 660 1220 2228 | 938 1720 3128 | 1216 2220 4028 | 1493 2720 4928 666 1230 2246 | 943 1730 3146 | 1221 2230 4046 | 1499 2730 4946 671 1240 2264 | 949 1740 3164 | 1227 2240 4064 | 1504 2740 4964 677 1250 2282 | 954 1750 3182 | 1232 2250 4082 | 1510 2750 4982 682 1260 2300 | 960 1760 3200 | 1238 2260 4100 | 1516 2760 5000 688 1270 2318 | 966 1770 3218 | 1243 2270 4118 | 1521 2770 5018 693 1280 2336 | 971 1780 3236 | 1249 2280 4136 | 1527 2780 5036 699 1290 2354 | 977 1790 3254 | 1254 2290 4154 | 1532 2790 5054 704 1300 2372 | 982 1800 3272 | 1260 2300 4172 | 1538 2800 5072 710 1310 2390 | 988 1810 3290 | 1266 2310 4190 | 1543 2810 5090 716 1320 2408 | 993 1820 3308 | 1271 2320 4208 | 1549 2820 5108 721 1330 2426 | 999 1830 3326 | 1277 2330 4226 | 1554 2830 5126 727 1340 2444 | 1004 1840 3344 | 1282 2340 4244 | 1560 2840 5144 732 1350 2462 | 1010 1850 3362 | 1288 2350 4262 | 1566 2850 5162 738 1360 2480 | 1016 1860 3380 | 1293 2360 4280 | 1571 2860 5180 743 1370 2498 | 1021 1870 3398 | 1299 2370 4298 | 1577 2870 5198 749 1380 2516 | 1027 1880 3416 | 1304 2380 4316 | 1582 2880 5216 754 1390 2534 | 1032 1890 3434 | 1310 2390 4334 | 1588 2890 5234 760 1400 2552 | 1038 1900 3452 | 1316 2400 4352 | 1593 2900 5252 766 1410 2570 | 1043 1910 3470 | 1321 2410 4370 | 1599 2910 5270 771 1420 2588 | 1049 1920 3488 | 1327 2420 4388 | 1604 2920 5288 777 1430 2606 | 1054 1930 3506 | 1332 2430 4406 | 1610 2930 5306 782 1440 2624 | 1060 1940 3524 | 1338 2440 4424 | 1616 2940 5324 788 1450 2642 | 1066 1950 3542 | 1343 2450 4442 | 1621 2950 5342 793 1460 2660 | 1071 1960 3560 | 1349 2460 4460 | 1627 2960 5360 799 1470 2678 | 1077 1970 3578 | 1354 2470 4478 | 1632 2970 5378 804 1480 2696 | 1082 1980 3596 | 1360 2480 4496 | 1638 2980 5396 810 1490 2714 | 1088 1990 3614 | 1366 2490 4514 | 1643 2990 5414 | 1093 2000 3632 | | 1649 3000 5432 --------------------------------------------------------------- NOTE. --The numbers in bold face type refer to the temperature eitherin degrees Centigrade or Fahrenheit which it is desired to convertinto the other scale. If converting from Fahrenheit degrees toCentigrade degrees the equivalent temperature will be found inthe left column, while if converting from degrees Centigrade todegrees Fahrenheit, the answer will be found in the column on theright. These tables are a revision of those by Sauveur & Boylston, metallurgical engineers, Cambridge, Mass. Copyright, 1920. INTERPOLATION FACTORS C. F. C. F. 0. 56 1 1. 8 | 3. 33 6 10. 8 1. 11 2 3. 6 | 3. 89 7 12. 6 1. 67 3 5. 4 | 4. 44 8 14. 4 2. 22 4 7. 2 | 5. 00 9 16. 2 2. 78 5 9. 0 | 5. 56 10 18. 0 Those using pyrometers will find this and the preceding conversiontable of great convenience: TABLE 33. --COMPARISON BETWEEN DEGREES CENTIGRADE AND DEGREES FAHRENHEIT ------------------------------------------------------------------------- Degrees | Degrees | Degrees | Degrees | Degrees | Degrees | Degrees ---------|---------|---------|---------|---------|---------|------------- F. | C. | F. | C. | F. | C. | F. | C. | F. | C. | F. | C. | F. | C. ---|-----|---|-----|---|-----|---|-----|---|-----|---|-----|-----|------- -40|-40. 0| 3|-16. 1| 46| 7. 7| 89| 31. 6|132| 55. 5|175| 79. 4| 275| 135. 0 -39|-39. 4| 4|-15. 5| 47| 8. 3| 90| 32. 2|133| 56. 1|176| 80. 0| 300| 148. 8 -38|-38. 8| 5|-15. 0| 48| 8. 8| 91| 32. 7|134| 56. 6|177| 80. 5| 325| 162. 7 -37|-38. 3| 6|-14. 4| 49| 9. 3| 92| 33. 3|135| 57. 2|178| 81. 1| 350| 176. 6 -36|-37. 7| 7|-13. 8| 50| 10. 0| 93| 33. 9|136| 57. 7|179| 81. 6| 375| 190. 5 -35|-37. 2| 8|-13. 3| 51| 10. 5| 94| 34. 4|137| 58. 3|180| 82. 2| 400| 204. 4 -34|-36. 6| 9|-12. 7| 52| 11. 1| 95| 35. 0|138| 58. 8|181| 82. 7| 425| 218. 3 -33|-36. 1| 10|-12. 2| 53| 11. 6| 96| 35. 5|139| 59. 4|182| 83. 3| 450| 232. 2 -32|-35. 5| 11|-11. 6| 54| 12. 2| 97| 36. 1|140| 60. 0|183| 83. 8| 475| 246. 1 -31|-35. 0| 12|-11. 1| 55| 12. 7| 98| 36. 6|141| 60. 5|184| 84. 4| 500| 260. 0 -30|-34. 4| 13|-10. 5| 56| 13. 3| 99| 37. 2|142| 61. 1|185| 85. 0| 525| 273. 8 -29|-33. 9| 14|-10. 0| 57| 13. 8|100| 37. 7|143| 61. 6|186| 85. 5| 550| 287. 7 -28|-33. 3| 15| -9. 3| 58| 14. 4|101| 38. 3|144| 62. 2|187| 86. 1| 575| 301. 6 -27|-32. 7| 16| -8. 8| 59| 15. 0|102| 38. 8|145| 62. 7|188| 86. 6| 600| 315. 5 -26|-32. 2| 17| -8. 3| 60| 15. 5|103| 39. 4|146| 63. 3|189| 87. 2| 625| 329. 4 -25|-31. 6| 18| -7. 7| 61| 16. 1|104| 40. 0|147| 63. 8|190| 87. 7| 650| 343. 3 -24|-31. 1| 19| -7. 2| 62| 16. 6|105| 40. 5|148| 64. 4|191| 88. 3| 675| 357. 2 -23|-30. 5| 20| -6. 6| 63| 17. 2|106| 41. 1|149| 65. 0|192| 88. 8| 700| 371. 1 -22|-30. 0| 21| -6. 1| 64| 17. 7|107| 41. 6|150| 65. 5|193| 89. 4| 725| 385. 0 -21|-29. 4| 22| -5. 5| 65| 18. 3|108| 42. 2|151| 66. 1|194| 90. 0| 750| 398. 8 -20|-28. 8| 23| -5. 0| 66| 18. 8|109| 42. 7|152| 66. 6|195| 90. 5| 775| 412. 7 -19|-28. 3| 24| -4. 4| 67| 19. 4|110| 43. 3|153| 67. 2|196| 91. 1| 800| 426. 6 -18|-27. 7| 25| -3. 8| 68| 20. 0|111| 43. 8|154| 67. 7|197| 91. 6| 825| 440. 5 -17|-27. 2| 26| -3. 3| 69| 20. 5|112| 44. 4|155| 68. 3|198| 92. 2| 850| 454. 4 -16|-26. 6| 27| -2. 7| 70| 21. 1|113| 45. 0|156| 68. 8|199| 92. 7| 875| 468. 3 -15|-26. 1| 28| -2. 2| 71| 21. 6|114| 45. 5|157| 69. 4|200| 93. 3| 900| 482. 2 -14|-25. 5| 29| -1. 6| 72| 22. 2|115| 46. 1|158| 70. 0|201| 93. 8| 925| 496. 1 -13|-25. 0| 30| -1. 1| 73| 22. 7|116| 46. 6|159| 70. 5|202| 94. 4| 950| 510. 0 -12|-24. 4| 31| -0. 5| 74| 23. 3|117| 47. 2|160| 71. 1|203| 95. 0| 975| 523. 8 -11|-23. 8| 32| -0. 0| 75| 23. 8|118| 47. 7|161| 71. 6|204| 95. 5|1, 000| 537. 7 -10|-23. 3| 33| +0. 5| 76| 24. 4|119| 48. 3|162| 72. 2|205| 96. 1|1, 100| 593. 3 -9|-22. 7| 34| 1. 1| 77| 25. 0|120| 48. 8|163| 72. 7|206| 96. 6|1, 200| 648. 8 -8|-22. 2| 35| 1. 6| 78| 25. 5|121| 49. 4|164| 73. 3|207| 97. 2|1, 300| 704. 4 -7|-21. 6| 36| 2. 2| 79| 26. 1|122| 50. 0|165| 73. 8|208| 97. 7|1, 400| 760. 0 -6|-21. 1| 37| 2. 7| 80| 26. 6|123| 50. 5|166| 74. 4|209| 98. 3|1, 500| 815. 5 -5|-20. 5| 38| 3. 3| 81| 27. 2|124| 51. 1|167| 75. 0|210| 98. 8|1, 600| 871. 1 -4|-20. 0| 39| 3. 8| 82| 27. 7|125| 51. 6|168| 75. 5|211| 99. 4|1, 700| 926. 6 -3|-19. 4| 40| 4. 4| 83| 28. 3|126| 52. 2|169| 76. 1|212|100. 0|1, 800| 982. 2 -2|-18. 8| 41| 5. 0| 84| 28. 8|127| 52. 7|170| 76. 6|213|100. 5|1, 900|1, 037. 7 -1|-18. 3| 42| 5. 5| 85| 29. 4|128| 53. 3|171| 77. 2|214|101. 1|2, 000|1, 093. 3 0|-17. 7| 43| 6. 1| 86| 30. 0|129| 53. 8|172| 77. 7|215|101. 6|2, 100|1, 148. 8 +1|-17. 2| 44| 6. 6| 87| 30. 5|130| 54. 4|173| 78. 3|225|107. 2|2, 200|1, 204. 4 2|-16. 6| 45| 7. 2| 88| 31. 1|131| 55. 0|174| 78. 8|250|121. 1|2, 300|1, 260. 0 ------------------------------------------------------------------------- 9 x degrees C. Degrees Fahrenheit = -------------- + 32 5 5 x (degrees F. - 32)Degrees Centigrade = --------------------- 9 Three other useful tables are also given on the following pages. TABLE 34. --WEIGHT OF ROUND, OCTAGON AND SQUARE CARBON TOOL STEEL PER FOOT ------------------------------------------------------------------------ Size | | | | Size | | | in | Round |Octagon | Square | in | Round | Octagon | Square inches | | | | inches | | | --------|--------|--------|--------|--------|--------|---------|-------- 1/16 | 0. 010 | 0. 011 | 0. 013 | 2-1/2 | 16. 79 | 17. 71 | 21. 37 1/8 | 0. 042 | 0. 044 | 0. 053 | 2-5/8 | 18. 51 | 19. 52 | 23. 56 3/16 | 0. 094 | 0. 099 | 0. 120 | 2-3/4 | 20. 31 | 21. 42 | 25. 86 1/4 | 0. 168 | 0. 177 | 0. 214 | 2-7/8 | 22. 20 | 23. 41 | 28. 27 5/16 | 0. 262 | 0. 277 | 0. 334 | 3 | 24. 17 | 25. 50 | 30. 78 3/8 | 0. 378 | 0. 398 | 0. 481 | 3-1/8 | 26. 23 | 27. 66 | 33. 40 7/16 | 0. 514 | 0. 542 | 0. 655 | 3-1/4 | 28. 37 | 29. 92 | 36. 12 1/2 | 0. 671 | 0. 708 | 0. 855 | 3-3/8 | 30. 59 | 32. 27 | 38. 95 9/16 | 0. 850 | 0. 896 | 1. 082 | 3-1/2 | 32. 90 | 34. 70 | 41. 89 5/8 | 1. 049 | 1. 107 | 1. 336 | 3-5/8 | 35. 29 | 37. 23 | 44. 94 11/16 | 1. 270 | 1. 339 | 1. 616 | 3-3/4 | 37. 77 | 39. 84 | 48. 09 3/4 | 1. 511 | 1. 594 | 1. 924 | 3-7/8 | 40. 33 | 42. 54 | 51. 35 13/16 | 1. 773 | 1. 870 | 2. 258 | 4 | 42. 97 | 45. 34 | 54. 72 7/8 | 2. 056 | 2. 169 | 2. 618 | 4-1/4 | 48. 51 | 51. 17 | 61. 77 15/16 | 2. 361 | 2. 490 | 3. 006 | 4-1/2 | 54. 39 | 57. 37 | 69. 25 1 | 2. 686 | 2. 833 | 3. 420 | 4-3/4 | 60. 60 | 63. 92 | 77. 16 1-1/8 | 3. 399 | 3. 585 | 4. 328 | 5 | 67. 15 | 70. 83 | 85. 50 1-1/4 | 4. 197 | 4. 427 | 5. 344 | 5-1/4 | 74. 03 | 78. 08 | 94. 26 1-3/8 | 5. 078 | 5. 356 | 6. 646 | 5-1/2 | 81. 25 | 85. 70 | 103. 45 1-1/2 | 6. 044 | 6. 374 | 7. 695 | 5-3/4 | 88. 80 | 93. 67 | 113. 07 1-5/8 | 7. 093 | 7. 481 | 9. 031 | 6 | 96. 69 | 101. 99 | 123. 12 1-3/4 | 8. 226 | 8. 674 | 10. 474 | 7 | 131. 61 | 138. 82 | 167. 58 1-7/8 | 9. 443 | 9. 960 | 12. 023 | 8 | 171. 90 | 181. 32 | 218. 88 2 | 10. 744 | 11. 332 | 13. 680 | 9 | 217. 57 | 229. 48 | 277. 02 2-1/8 | 12. 129 | 12. 793 | 15. 443 | 10 | 268. 60 | 283. 31 | 342. 00 2-1/4 | 13. 598 | 14. 343 | 17. 314 | 11 | 325. 01 | 342. 80 | 413. 82 2-3/8 | 15. 151 | 15. 981 | 19. 291 | 12 | 386. 79 | 407. 97 | 492. 48 ------------------------------------------------------------------------ High-speed steel, being more dense than carbon steel, weighs from10 to 11 per cent more than carbon steel. This should be addedto figures given in the table. TABLE 35. --WEIGHT OF ROUND, CARBON TOOL STEEL 12 IN. IN DIAMETER AND LARGER, PER FOOT -------------------------------------------------------------------- Diameter, | Weight | Diameter, | Weight | Diameter, | Weight inches | per foot | inches | per foot | inches | per foot -----------|----------|-----------|----------|-----------|---------- 12 | 386. 790 | 15-7/8 | 677. 527 | 19-3/4 | 1, 049. 010 12-1/8 | 395. 518 | 16 | 687. 600 | 19-7/8 | 1, 061. 705 12-1/4 | 404. 246 | 16-1/8 | 699. 017 | 20 | 1, 074. 400 12-3/8 | 412. 974 | 16-1/4 | 710. 435 | 20-1/8 | 1, 088. 502 12-1/2 | 421. 702 | 16-3/8 | 721. 852 | 20-1/4 | 1, 102. 605 12-5/8 | 430. 430 | 16-1/2 | 733. 270 | 20-3/8 | 1, 116. 707 12-3/4 | 439. 158 | 16-5/8 | 744. 687 | 20-1/2 | 1, 130. 810 12-7/8 | 447. 886 | 16-3/4 | 756. 105 | 20-5/8 | 1, 144. 912 13 | 456. 615 | 16-7/8 | 767. 522 | 20-3/4 | 1, 159. 015 13-1/8 | 465. 343 | 17 | 778. 940 | 20-7/8 | 1, 173. 118 13-1/4 | 474. 071 | 17-1/8 | 790. 358 | 21 | 1, 187. 220 13-3/8 | 482. 799 | 17-1/4 | 801. 777 | 21-1/8 | 1, 201. 322 13-1/2 | 491. 527 | 17-3/8 | 813. 195 | 21-1/4 | 1, 215. 425 13-5/8 | 500. 255 | 17-1/2 | 824. 614 | 21-3/8 | 1, 229. 527 13-3/4 | 508. 983 | 17-5/8 | 836. 030 | 21-1/2 | 1, 243. 630 13-7/8 | 517. 711 | 17-3/4 | 847. 447 | 21-5/8 | 1, 257. 732 14 | 526. 440 | 17-7/8 | 858. 863 | 21-3/4 | 1, 271. 835 14-1/8 | 536. 512 | 18 | 870. 280 | 21-7/8 | 1, 285. 937 14-1/4 | 546. 585 | 18-1/8 | 883. 105 | 22 | 1, 300. 040 14-3/8 | 556. 657 | 18-1/4 | 895. 920 | 22-1/8 | 1, 315. 485 14-1/2 | 566. 730 | 18-3/8 | 908. 740 | 22-1/4 | 1, 330. 930 14-5/8 | 576. 802 | 18-1/2 | 921. 560 | 22-3/8 | 1, 346. 375 14-3/4 | 586. 875 | 18-5/8 | 934. 380 | 22-1/2 | 1, 361. 820 14-7/8 | 596. 947 | 18-3/4 | 947. 200 | 22-5/8 | 1, 377. 265 15 | 607. 020 | 18-7/8 | 960. 020 | 22-3/4 | 1, 392. 710 15-1/8 | 617. 092 | 19 | 972. 840 | 22-7/8 | 1, 408. 155 15-1/4 | 627. 165 | 19-1/8 | 985. 035 | 23 | 1, 423. 600 15-3/8 | 637. 237 | 19-1/4 | 998. 230 | 23-1/8 | 1, 454. 490 15-1/2 | 647. 310 | 19-3/8 |1, 010. 925 | 23-1/4 | 1, 485. 380 15-5/8 | 657. 382 | 19-1/2 |1, 023. 620 | 23-3/8 | 1, 516. 270 15-3/4 | 667. 455 | 19-5/8 |1, 036. 315 | 24 | 1, 547. 160 -------------------------------------------------------------------- To find the weight of discs made of carbon steel, in diametersup to and including 12 in. , without any allowance for finishingmultiply the per foot weight of round bar steel, shown herewithby the decimal equivalent of a foot given in the following table: TABLE 36. --DECIMAL EQUIVALENTS OF A FOOT --------------------------------------------------------------------- In. | 0 | 1/8 | 1/4 | 3/8 | 1/2 | 5/8 | 3/4 | 7/8 -----|-------|-------|-------|-------|-------|-------|-------|------- 0 | 0. 000 | 0. 010 | 0. 021 | 0. 031 | 0. 042 | 0. 052 | 0. 063 | 0. 073 1 | 0. 083 | 0. 094 | 0. 104 | 0. 115 | 0. 125 | 0. 135 | 0. 146 | 0. 156 2 | 0. 167 | 0. 177 | 0. 188 | 0. 198 | 0. 208 | 0. 219 | 0. 229 | 0. 240 3 | 0. 250 | 0. 260 | 0. 270 | 0. 281 | 0. 292 | 0. 302 | 0. 313 | 0. 323 4 | 0. 333 | 0. 344 | 0. 354 | 0. 364 | 0. 375 | 0. 385 | 0. 396 | 0. 406 5 | 0. 416 | 0. 427 | 0. 437 | 0. 448 | 0. 458 | 0. 469 | 0. 479 | 0. 480 6 | 0. 500 | 0. 510 | 0. 520 | 0. 531 | 0. 542 | 0. 552 | 0. 563 | 0. 573 7 | 0. 583 | 0. 594 | 0. 604 | 0. 615 | 0. 625 | 0. 635 | 0. 646 | 0. 656 8 | 0. 666 | 0. 677 | 0. 687 | 0. 698 | 0. 708 | 0. 719 | 0. 729 | 0. 740 9 | 0. 750 | 0. 760 | 0. 770 | 0. 781 | 0. 792 | 0. 802 | 0. 813 | 0. 823 10 | 0. 833 | 0. 844 | 0. 854 | 0. 865 | 0. 875 | 0. 885 | 0. 896 | 0. 906 11 | 0. 916 | 0. 927 | 0. 937 | 0. 948 | 0. 953 | 0. 969 | 0. 979 | 0. 990 --------------------------------------------------------------------- EXAMPLE. --If the weight of a carbon steel disc 7 in. Diameter, 1-5/8 in. Thick is desired, turn to page 233, where the per footweight of 7 in. Round is given as 131. 6 lb. Multiply this by thedecimal equivalent of 1-5/8 in. , or 0. 135, as shown in the abovetable, and the product will be the net weight of the disc. 131. 61 lb. = the weight of 1 ft. Of 7 in. Round. 0. 135 = the per foot decimal equivalent of 1-5/8 in: ------------ 65805 39483 13161 ------------ 17. 76735 lb. = weight of disc 7 in. Diam. 1-5/8 in. Thick without anyallowance for finishing. AUTHORITES QUOTED A ADDIS, W H. AMERICAN MACHINISTS' HANDBOOKAMERICAN STEEL TREARERS' SOCIETYAMERICAN GEAR MFRS. ASSO. AUTOMATIC AND ELECTRIC FURNACES LTD. ARNOLD, PROF. J. O. B BURLEIGH, R. W. BORDEN, B. BOKER, HERMAN & Co. BROWN INSTRUMENT Co. BROWN-LIPE-CHAPLIN Co. C CAMPBELL, H. H. CARHART, H. A. CLAYTON, C. Y. CURTIS AIRPLANE Co. E ENGLEHARD, CHARLESENSAW, HOWARD F FIRTH-STERLING STEEL Co. FIRTH, THOMAS & SONSFOWLER, HENRY G GILBERT & BARKER H HAYWAHD, C. R. HOWE, DR. H. M. HOOVER STEEL BALL CO. HEATHCOTE, H. L. HARRIS, MATTHEWHUNTER, J. V. J JANITZKY, E. J. JOHNSTON, A. B. JUTHE, K. A. L LATROBE STEEL CO. LUDLUM STEEL CO. LEEDS & NORTHRUP CO. LYMAN, W. H. M MANSFIELD, C. A. MIDVALE STEEL Co. McKENNA, ROY C. MOULTON, SETH A. N NILES, BEMENT, POND P PARKER, S. W. POOLE, C. R. R RAWDON, H. S. S S. A. E. (SOCIETY AUTOMOTIVE ENGINEERS)SAUVEUR, ALBERTSPRINGFIELD ARMORYSELLACK, T. G. SMITH, A. J. SHIRLEY, ALFRED J. T TAYLOR INSTRUMENT Co. THUM, E. E. TIEMANN, H. P. U U. S. BALL BEARING Co. UNITED STEEL Co. UNDERWOOD, CHARLES N. V VAN DE VENTER, JOHN H. W WALP, H. O. WOOD, HAROLD F. WHEELOCK, LOVEJOY & Co. INDEX A ABC of iron and steelAbsorption of carbon, rate ofAir hardening steelsAnalysis of high speed steelAllotropic modificationsAlloy steel, annealing properties ofAlloys and their effect in high speed steel in steel, value of upon steelAlpha ironAnnealing care in furnace high-chromium steel high speed tools in bone methods proper rifle components rust-proof steel steels temperatureArrestsAustentiteAutomotive industry, application of Liberty engine materials to temperature controlAxles, heat treatment of B Balls, making steelBarium chloride processBaths for temperingBessemer converterBeta ironBlending compoundsBlister steelBlue brittlenessBone, annealing inBoxes for case hardening or carburizingBreaking test gearsBrinell hardnessBroach hardening furnaceBrown automatic pyrometerBurning C Calorized tubesCarbon content at various temperatures content of case hardened work in cast iron, ix in tool steel introduction of penetration of steel steel forgings, Liberty engine steel tools steels, S. A. E. Steels, temper colors strengthens iron tool steel, forgingCarbonizing, _see_ CarburizingCarborundum tubesCarburization, preventingCarburizing by gas boxes compounds gas consumption by local material nickel steel or case hardening pots forCarburizing, process of short method sleeves with charcoal _See_ Case hardeningCar door type of furnaceCase, depth ofCase hardening boxes cast iron local or surface carburizing treatments for various steels _see_ CarburizingCast iron, carbon in case hardeningCementiteCenter column furnaceCentigrade tableChamotte tubesChart of carbon penetration heat treatment shapeChrome steelChrome-nickel steel steel, forgingChrome-vanadium steelChromium steels, S. A. E. Chromium-cobalt steelChromium-vanadium steel, S. A. E. Classification of steelClay tubesCold end compensator junction errors shortness worked steelColor in temperingColors on carbon steelsCombination tankComparison of fuelsCompensating leadsCompensator for cold ends automaticComposition of steelCompound, blending separating from workCompounds for carburizingConnecting rods, Liberty motorContinuous heating furnaceConverter, BessemerCooling curvesCooling quenching oil, roof system rate of, for gear-forgingsCopper, effect of, in medium carbon steelCopper-plating to prevent carburizingCorrosion of high-chromium steel of rust-proof steelCorundite tubesCost of operating furnacesCracks in hardening, preventingCrankshaft, Liberty motorCritical pointCrucible or tool steelCutting off high speed steelCyanide bath for tool steel D Decarbonizing of outer surface preventingDepth of caseDetrimental elements in steelDies, drop forging quenching soft spots in tempering roundDrawing ends of gear teethDrop forging diesDuctility E Effect of alloys of different carburizing material of size of piece of copper in medium carbon steelElastic limitElectric process of steel makingElectrodeElements, chemicalElongationEndurance limitEnergizer, 81Enlarging steelEquipment for heat treatingEutectoid F Fahrenheit temperature tableFatigue testFerriteFile testFlame shieldsFlange shields for furnacesForging furnace high speed tools improper of steel practice, heavy rifle barrelsForgings, carbon steel Liberty engineFormed tools, high speedFractures, examining byFurnace, continuous heating crucible data electric Heroult open hearth recordsFurnaces annealing broach hardening car door type center column cost of operating data on forging, heavy fuels for gas fired high speed steel lead pot manganese steel muffle oil fired operating costs screens for toolFurnaces, water cooled frontsFuels, comparison of for furnaces G Gages, changes due to quenching temperingGamma ironGas, carburizing by consumption for carburizing fired furnace illuminating, for carburizingGear blanks, heat treatment of forgings, rate of cooling for Liberty engine hardening machine steel, transmission teeth, drawing ends ofGears, Liberty engineGleason tempering machineGrade of steelGrain, refining sizeGraphitic carbonGrinding high speed steel H Hair lines in forgingsHardening carbon steel for tools cracks, preventing dies gears high speed steel high speed tools of high-chromium steel of rust-proof steel room, modernHardness testsHeating, effect of size for forgingHeat, judging by color treating departments equipment forgings inspection of Liberty motorHeat treating, of axles of chisels of gears of high speed steel of steel S. A. E. Heat treatmentHeroult furnaceHigh-chromium steel annealing of corrosion of hardening ofHighly stressed parts of Liberty engineHigh speed steel, analysis of annealing cutting off forging furnace hardening heat treatment of instructions for manufacture pack hardening structure ofHints for steel users I Illuminating gas for carburizingImpact testImproper forgingInfluence of size on heatingInspection of heat treatmentInternal stresses, relievingIntroduction of carbon J Jewelers' toolsJudging heat of steel by color L Latent heatLathe and planer tools tools, high speedLatrobe temper listLead bath pot furnaceLeeds & Northrup potentiometer optical pyrometerLiberty engine, highly stressed parts ofLiberty engine materials, application to automotive industry motor connecting rods motor, crankshaft motor piston pinLocal case hardeningLuting mixture M Machineability of steelMachinery steel, annealingMagnet testMaking steel in electric furnaceManganese steel furnaceManufacture of high speed steelMarquardt mass tubesMartensiteMedium carbon steel, effect of copper onMetallographyMicrophotographsMicroscopic examinationMilling cutters, high speedMixture for lutingModern hardening roomMolten metal pyrometersMolybdenumMuffle furnace N NickelNickel-chromium steel steels, S. A. E. Nickel, influence of, on steel steel affinity for carbon steels, S. A. E. Non-homogeneous meltingNon-shrinking steelsNormalizing O Oil bath for tempering cooling on roof fired furnace hardening steel, forging steels temperature of quenchingOpen hearth furnaceOperating costs of furnacesOuter surface decarbonizerOver-heated steel, restoringOverheating dies P Pack-hardening high speed steelPacking work for carburizingPaste for hardening diesPearlitePenetration of carbon carbon, chart of in case hardeningPhosphorusPickling Liberty motor forgingsPig ironPiston pin, Liberty motorPlacing pyrometersPlaner tools, high speed"Points" of carbon in steelPotentiometer, Leeds & NorthrupPots for carburizingPress for testing gearsPreventing carburization cracks in hardeningProperties of alloy steels of alloy steels, table of steelProtective screens for furnacesPuddled ironPunches and chisels, steels forPyrometers calibration copper ball indicating inspection iron ball molten metal optical placing recording Siemens testing water Q Quality and structure of high speed steel of steelQuenching, after carburizing dies in tank obsolete method oil, temperature of tank tool steel R Rate of absorption of carbonRecording temperaturesRed shortnessRefining the grainRegenerative open hearth furnaceRestoring overheated steelRifle barrels, forging components, annealingRoof system of cooling oilRust-proof steel annealing of corrosion of hardening of S S. A. E. Carbon steels chromium steels chromium-vanadium heat treatments nickel-chromium steels nickel steels screw stock silico-manganese steel standard steelsSalt bath for temperingScleroscope testScratch hardnessScreens for furnacesScrew stock, S. A. E. Sensible heatSentinels, melting ofSeparating work from compoundShields for furnace doorsShore ScleroscopeShort method of carburizingShrinking steelSilica tubesSilico-manganese steels, S. A. E. SiliconSilversmiths' toolsSize of piece, effect ofSlagsSleeves, carburizing hardening and shrinking shrinkingSolid solutionSorbiteSpecimens, testStandard S. A. E. SteelsSteel, balls, stock for bolts, making composition of deoxidation for chisels and punches forging of give it a chance heat treatment of high speed making Bessemer process crucible process electric furnace process open hearth tools, carbon, in users' hintsStructure of high speed steelSulphur T Tables, air, oil and water hardened steel alloy steels, properties of carbon content carbon steels case hardening changes due to quenching chromium steels chromium-vanadium steels colors and temperature composition of steels cost of furnaces effect of size fuels, comparison of high-chromium steel nickel-chromium steels nickel steels operating cost of furnaces production cost of furnaces S. A. E. Steels screw stock silico-manganese steels stock for balls temperature conversion tempering temperatures weight of steelTank for quenching diesTaylor instrumentsTemper, colors of list, Latrobe of steelTemperature recorders tablesTemperatures for temperingTempering colors on carbon steels gages high speed tools machine, Gleason round dies temperatures theory ofTempers of carbon steelTensile testTesting heat treatmentTests of steelTest specimensTheory of temperingThermocouple base metal cold end placing protectors rare metalTime for hardeningTool furnace, smallTool or crucible steel, annealingTool steel, cyanide bath for quenchingTools, carbon in different carbon steel of high speed steel sulphur in tempers of various transformation pointsTransmission gear steelTreatments for various steelsTroositeTubes, calorized carborundum Chamotte clay Marquardt mass silicaTungsten steel U Ultimate strengthUsers of steel, hints for V Vanadium steel W Water annealing cooled furnace frontsWeight of steel barsWorking instructions for high speed steelWrought iron, ix Y Yield Point