M A CHINERY ’S REFERENCE SERIES EACH NU M BER IS ONE U NIT IN A COM PL ETE LIBRARY OF M ACHINE DESIGN A ND SHO P PR A CTIC E R EV ISED AND R EPU BLISH ED FROM M ACHINERY NUM BER 63 HEAT TREA TM ENT OF STEEL — — HARDENING TEM PERING C ASE-HARDENING SE COND E DITION CONTE NTS H arden i n arbon tee s AL g C S l b R P H B ADGER and J . , y STOREY H ardeni ng Carbon and L ow T u ngst en Stee ls ‘ The E lectri c Hardeni ng F urnace Heat Treatm ent of Spri ng Stee l Heat Treatm ent of A lloy Steels Case - Harden i ng ase - ar deni n F urn ace s an d h i r C H g T e U se b J . , y SALL OWS Co ri ht 1910 Th e I nd u st ri al e P l i py g , , P r s s . u b sher s of M A CHIN E RY . L f a ay et t e St r e e t , N e w Y ork Ci t y CHAPTE R I H A R D E N I N G C A R B ON S TE E L S " Ori ginally the name steel was applied to various combinations of - i ron and carbon , there being present, together with these , as impuri A ties , small proportions of silicon and manganese . t the pres ent time , however , the use of the name is extended to c over combinations r of i on with tungsten , vanadium , nickel , chromium , molybdenum , titan r ium and some of the ra er elements . These latter combinations are quite generally known as the a l l oy steels to distinguish them from the t r car bo n steels , in which la ter the characteristic p operties are de r T pendent upon the p esence of carbon alone . he alloy steels a re di - M u he r - i vi d e d into the hi gh speed steels and the s t or ai harden ng steels . The specific properties that distingui s h these different steels a re due in part to their respective compositions , that is , to the particular ele e ments they contain , and , in part , to their sub s quent working and heat t reatment . E ff e c t o f D iff e r e n c e i n C o m p o s it i o n o f St e e l In gener al , any change in the composition of a steel results in some change in its properties . For example , the addition of certain metallic e elements t o a carbon st el causes , in the alloy steel thus formed , a change in position of the p r oper hardening temperature point . T ungsten or manganese tend to lower this point , boron and vanadium to raise it ; the amount of the change is p r acti cally proportional to the amount of r r the element added . J ust as a small propo tion of ca bon added to - iron p roduces steel which has decidedly di ffe rent properties than those found in pure iron , so increasin g the proportion of carbon in the steel thus fo rmed , within certain limits , causes a variation in the degree in r whi ch these p operties manifest themselves . For example , consider “ ” - the p rope r ty of tensile strength . In a ten point carbon steel ( one in r r o f car bon s which the e is p esent but per cent , ) the tensile trength is very nearly 2 5 per cent greater than that of pure iron . A dding more carbon causes the tensile s trength to ri s e , approximately, at the rate of per cent for each per cent of carbon added . Car bon steels are divided into three classes according to the propor T tion of car bon which they contain . he first of these embr aces the “ ’ t unsaturated steels , in which the carbon con ent is lower than “ ” r r per cent ; the second , the saturated steel s , in whi ch the p opo tion r r of carbon is exactly per cent ; and , the thi d , the supers atu ated e ste els in which the carbon content i s hi gh r than per cent . , E ff e c t o f H e a t Tr e a t m e n t With a steel of a given compos it ion , p roper heat t r eat ments may be e applied which , of t h mselves , will fi rs t alter in form or degr ee s ome M A N Y o be r 1 9 09 a n a n r 1 C H I E R , Oct , , d J u a y , 1 9 0. 3 4 7 6 1 7 Q s T N b: 253 . H F A J TR E A TM E N T OF S TE E L e of its specific properties , or s cond , practically eliminate one or mor e of these , or third , add certain new ones . P hysical properties of si e z , shape and ductili ty a re examples of the first case ; an example of the second case is found in the heating of steel beyond i t s hardening t e m e r u r - p at e , which takes away its magnetism , making it non magnetic ; and an example of the third cas e is t he fact that a greater degree of hardness may be added to steel by the process of hardening . In this connection it must be understood that, strictly speaking, hardnes s is a r e lative te rm and all steel has some hardness . T r he e are three general heat treatment operations , so considered r r — — fo ging, ha dening with which this chapter will deal and tempering. In al l of these the obj e ct sought i s t o chan ge in some manner the exist th r ing properties of the steel ; in o e words , to produce in it certain permanent condi tions . The controlling factor in all heat treatment is temperature . r - Whether the operation is forging , ha dening or tempering there i s f o r any certain steel and particular use thereof a definite temperatur e r point that alone gives the best results in wo king i t . Insufficient tem E e r u r e . r p a t e s do not produce the r sults sought xcessive temperatu es, r either through i gnorance of what the co rect point is , or through i n “ ” ability to tell when it exists , cause burned steel ; this is a common failing, resulting in great loss . V ery slight variations from the proper temperature ma y do irreparable damage . D u e to temperature variation alone , carbon steel may be had in : a any of three conditions first , in the unh rdened or annealed s tate , 1 0 F when not heated to temperatures above 3 5 degrees . ; second , in the r hardened state , by heating to tempe atures between 1 3 50 and 1 500 de ’ r r grees F . thi d , in a state softer than the second though ha der than 0 the first when heated to temperatures which exceed 1 5 0 degrees F . , Th e H a r d e n i n g P r o c e s s Th e har dening of a c arbon steel is the result of a change of inte rnal structure which takes place in the steel when heated p r oper ly to a f r r correct temperature . In the di fe ent ca bon steels this change , for practical purposes , is effective only in those in which the proportion ’ of carbon is between per cent and per cent, th at is , between , “ - twenty point and two carbon steels , respectively . r 0 When heated , ordinary ca bon steels begin to soften at about 3 9 0 degrees F . and continue to soften throughout a range of 3 1 degrees F . i A t the point 700 degrees F . practically al l o f the hardness has d s ap “ ” r r s pe a re d . R e d ha dness in a steel is a prope ty which enable it to - remain hard at red heat . In a high speed steel this property is of the first importance , 1 02 0 degrees F . being a minimum temperature at T whi ch softening may begin . his is some 63 0 degrees F . above the r point at which softening commences in o dinary carbon steels . The process of hardening a steel is best carried out in a clos ed t c re furnace . Of he many sources of energy apable of producing the quired heat electrici ty offe rs the most attractiv e advantages . The elec , tri c res i s tance fu rnace , as now built in a variety of sizes of either H A RD E N I N G CA R B ON S TE E L S muffle or tube chamber types , has one fundamental point of superiority - over all coal , coke , gas , or oil heated furnaces . It is entirely free from re all products of combustion , the heat being produced by electrical oxi s i stance .