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 . This is important . It does away with the chief cause of

r r dation of the heated steel . Fur ther , the tempe ature of the elect i c furnaces can be easily and accurately regulated to , and maintained i uniform at , any desired point . When electric power s g enerated for

other purposes , the increased cost of this form of energy for operating furnaces is not sufficient to argue against it . E ven when the current

is purchased , the superior quality of work performed by this kind of furnace frequently more than offsets the slightly hi gher cost of opera

tion .

e In the actual heating of a piece of steel , several requirements ar essential to good hardening : first , that small projections or cutting t edges are not heated more rapidly than is the body of the piec e , hat

are is , that all parts heated at the same rate , and second , that all parts are heated to the same temperature . T hese conditions are facilitated A by slow heating, especially when the heated piece is large . uni

form heat , as low in temperature as will give the required hardness , L p r oduces the best product . ack of uniformity in heating causes ir regular gr ain and internal strains , and may even produce sur face “ ” A c racks . ny temperature above the critical point of steel tend s to — open its gragI to make it coarse and to diminish its str ength though such a temperature may not be sufficient to lessen apprecia bly its hardness . C r i t i c a l Te m p e r a t u r e s

The temperatures at whi ch take place the previously mentioned i n ternal changes in the structure of a steel are frequently spoken of as th e “ T critical points . hese are different in steels of different carbon con — The c tents . higher the per entage of carbon present, the lower the

temperature required to produce the internal change . In other words , the critical points of a hi gh carbon steel are lower than those of a low

e s carbon ste l . In teels of the commonly used carbon contents , there are two of these critical temperatures , called the d e cal es ce n ce point e and the re cal es c n ce point , respectively . " D e c a l e s c e n c e a n d I t s R e l a t i o n t o H a r d e n ing E veryone interested in the hardening of steel will have noticed the increasing frequency with which reference is made to the decalescence s c and recale ence points of steel , in articles appearing in the technical “ r press f om time to time . It is only during the past few years that this

c r pe ulia ity in steel has come to the front , and there are still very

many who do not p ossess even a rudimentary knowledge of the subject . The somewhat obscur e references one usually sees in the treatises on hardening will not help the man in the hardening shop very much to a

better understanding of the matter , and ther efore an elementary ex

planation of the phenomenon will be welcome to many . It may be quoted that, as a matter of history , hardening has been done with m ore or less success , from the days of the famous D amascus swords u p 6 ~ H E A T E A N o . 63 TR TM E N T OF S TE E L

to only a comparatively short time ago , without anyone having dis

t s covered that s eel pos essed such a peculiarity as decalescen ce , but t nevertheless its rela ion to hardening has always existed , and its dis co ve ry paved the way for much scientific investigation into a subject

that had been previously controlled by rule of thumb . “ ” “ “ The decalescence and recalescence or critical points ( also

A A r . 1 sometimes desi gnated c . 1 and ) that bear relation t o the hard

e n i ng of steel , are simply evolut ions that occur in the chemical com position of steel at certain temperat ures during both heating and cool t ing . Steel at normal tempera ures carries its carbon , which is i ts — c hief hardening compon ent , in a certain form pearlite carbon to be more explici t— and if heated to a certain temperature a change occurs an d the p earlite carbon becomes cementite or hardening

carbon . L ikewise , if allowed to

cool slowly , the hardening car bon changes back again to pearlite . The points at which these s vo l u t ions occur are the decalescence ' and recalescence or critical points , and the effect of these molecular changes is to cause an i ncreased abso rption of heat on a rising temperature and an evo l ution of heat on a falling temperature . T hat is to say , during the heating of a piece of steel a halt occurs , and it continues to a bsorb heat without appreciably rising in tem

ra u re pe t , at the decalescence point, although its i m m e i d ate surround

ings may be hotter than the steel . F i g L ikewise , steel cooling slowly , will ,

“ 0 6 19 80 9 3 0 9 9 0 mm at a certain temperature , actually

T s increase in temperature al though its surroundings may be colde r . hi t akes place at the recalescence point .

c In Fig . 1 is shown a curve , taken on a recording pyrometer , in whi h

the decalescence and recalescence points are well developed . From this it will be seen that the absorp tion of heat occ u rr ed at a point

r t marked 73 3 degrees C . on the rising temperat u e , and the evolu ion of The t heat at 72 4 degrees C . on the falling temperature . rela ion of these critical points to hardening is in the fact tha t unless a tempe ra t ture sufficient t o produce the first action is reached , so that the pearli e

r s i s car bon will be chan ged t o hardening ca bon , and unles it cooled

with sufficient rapidity to practically eliminate the second action , no

The t t ao hardening can take place . ra e of cooling is ma erial and counts for the fact that large articles require t o be quenched at higher

temperat ures than small ones . H A R D E NI N G CA R B ON S TE E L S

A very important feature is that steel containing hardening carbon ,

- 6 steel above the temperature of decalescence, is non magnetic . A nyone may demonstrate this for himself by heating a p iece of steel to a bright red and testing it with an ordinary magnet . While bright red it will be found to have no attraction for the magnet , but at about

- T a cherry red it regains its magnetic properties . his feature has been taken ad vantage of as a means of determining the cor rect hardening “ temperature , and appliances for its application are on the market . Its use is certainly to be recommended where no installation of pyromet ers exists ; the only point requiring judgment is the length of time an article should remain in the furnace after it has become

- non magnetic . This varies with the weight and cooling surface , but

may be tabulated according to weight , leaving very little to personal j udgment . . It is difficult to quote reliable temperatures at whi ch decalescen c e occurs . The temperatures vary with the amount of the carbon con t a i ne d hi - in the steel , and are much gher for high speed than for ordi nary crucible steel . Special electric furnaces are generally used for

d u r obtaining ecalescence curves , b t with ca e it can be done in an ordi l l nary gas furnace , with a suitable pyrometer . A that is necessary is to bore a blind hole in a piece of the steel to be treated , to form a

pocket to receive the end of the pyrometer . This must be of sufficient

length to cover the resistance c oil in the end of the pyrometer . The t specimen should hen be put in the furnace , wi t h the pyrometer in , t he r ' gas applied , and , if the fu nace is allowed to heat up very slowly o f t ward a temperat ure o say 1 3 80 degrees F . ( 750 degrees the

decalescence curve will be developed , if the pyrometer is a recording one . h In t e same way, if the furnace is allowed to cool slowly it will be

t the ff seen tha at recalescence point , the specimen gives o heat and even

increases in temperature for a time . E xperiments of this kind are

r scarcely p acti cable for the average hardening shop , but when it i s h desired to find t e lowest hard e ning temperature for a piece of steel ,

‘ the magnet can be used t o advantage .

R e c a p it u l a t i o n

To s sum up , the decalescence point of any steel mark the correct hard

h r t I e ing tempe a ure of that part icular steel . t occ urs while the tempe ra T ture of the st eel is rising . he piece is ready to be removed from the source of heat directly after it has been heated uniformly to this

temperature , for then the structural c hange necessary to produce hard

ness has been completed . H eating the piece slightly more may be de

w r sirable for either or both of the t o following reasons . Fi st, in case h t e piece has been heated too quickly, that is , not uniformly, this excess temperat ure will assure the structural change being complete throughout the piece . Second , any slight loss of heat which may take place in transferring the piece from the furnace to the quenching h bath may thus be allowed for , leaving the piece at t e proper tempera

r t u e when quenched . If a piece of s teel which has been heated above its decalescence 8 — A N o . 63 H E T TR E A TM E N T OF S TE E L

he point allowed to cool slowly , it will pass through a structural t change , the reverse of hat which takes place on a rising temperature . The point at which this takes place is the recalescence point and is i lower than the r sing critical temperature by some 85 to 2 1 5 degrees . The location of these points is made evident by the fact t hat while passing through them the temperature of the steel remains stationary

for an appreciable length of time . It is well to observe that the lower of these points does not manifest itself unless the hi gher one has been

fi r A st fully passed . s these critical points are diff e rent for different

steels , they cannot be definitely known for any particular steel with

an out actual determination . While heating a piece of steel to its cor rect hardening temperature produces a c hange in its structure which

makes possible an increase in its hardness , this condition is only tem

r r po a y unless the piece is quenched .

Q u e n c h in g

The quenching consists in plunging the heated steel into a bath ,

cooling it quickly . B y this operation the structur al change seems to “ ” be trapped and permanently set . Were it possible to make this cool i n g instantaneous and uniform throughout t he piece , it would be per

f e l ct y and symmetrically hardened . This condition cannot, however ,

be realized , as the rate of cooling is affected both by the size and

shape of the treated piece ; the bulkier the pi ece , the larger the amount of heat - t hat must be transferred to the surface and there dissi

thro u h the the pated g . cooling bath ; smaller the exposed surface in

comparison with the bulk, the longer will be the time re quired for m cooli ng. R emembering that the cooling hould be as quickly acco 4 s l i h p s e d as possible , the bath should be amply large to dissipate the heat T rapidly and uniformly . oo small a quenching bath will cause much T w . o loss , due to the resulting irregular and slo cooling insure uni

formly quenched products , the temperature of the bath should be kept

constant, so that successive pieces immersed in it will be acted upon by

the same quenching temperature . R unning water is a satisfactory

means of producing this condition . The composition of the quenching bath may vary for different pur

poses , water , oil or brine being used . Greater hardness is obtained t a from q u enching , at the same emperature , in s lt brine and less in oil , T than is obtained by quenching in water . his is due to a differ

- e ncc in the heat dissipating power possessed by these substances . Quenching thin and compli c ated pieces in salt brine is unsafe as t here ‘ is danger of the piece cracking , due to the extreme suddenness of ccc .

ing thus produced . I n actual shop work the steel to be hardened is generally of a I To t variety of sizes , shapes and compositions . obtain uniformity bo h

of heating and of cooling, as well as the correct limiting temperature , the peculiarities of each piece must be given consideration in accord

r ance with the points outlined above . In other wo ds , to harden all pieces in a manner best adapted to but one piece would result in i n

f e ri o r quality and possible loss of all except this one . E ach diff erent H AR D E N I N G CA R B ON S TE E L S 9

e t piec mus be treated individually in a way calculated to bring o u t.

the best results from it .

Th e o ry o f C ri t i c a l P o in t s ~ The rese n ce the c he hea ti n , p of ritical g and cooling of a

' " “ n m e n n Th o - piece of p e o o . e m s t reasona ble explanation is

While heating, the steel uniformly absorbs heat . U p to the de cales cence point all of the energy of this heat is exert ed in raising the A temperature of the piece . t this point , the heat taken on by the s te el

is expended , not in raising the temperature of the piece , but in work whi c h produces the internal changes here taking place between the

. H , u carbon and the iron , ence when the heat added is sed in this man '

ner , the temperature of the piece , having nothing to increase it , re l mains stationary , or , owing to surface radiation , may even fall slight y .

A fter the change is complete , the added heat is again expended in rais

i ng the temperature of the piece , which increases proportionally . When the pi ece has been heated above the decalescence point an d allowed to cool slowly , the process is reversed . H eat is then radiated

r . U s f om the piece ntil the recalescence point j reached , the tempera ture falls uniformly . H ere the internal relation of the carbon and

iron is transformed to its ori ginal condition , the energy p r eviou s ly ab

Thi s h e at sorbed being converted into heat . , set free in the steel , sup

plies , for the moment, the equivalent of that being radiated from the surface , and the temperature of the piece ceases falling and remains stationary . Should the heat resulting from the internal changes be

greater than that of surface radiation , the resulting temperature of the piece will not only cease falling but will obviously rise slightly at; this point . In either event the condition exists only momentarily, but when the carbon and iron constituents have resumed their original

r elation , the internal heating ceases , and the temperatu r e of the piece

falls steadily , due to surface radiation .

A p p a r a t u s f o r D e t e rm ining t h e C r it i c a l P o in t s

From the foregoing sections it is evident, first, that there is a d efi

an d nite temperature at which any carbon steel should be hardened , , c c se ond that a great loss o curs , both of labor and material , unles s the

r ha den i ng is carried out at this temperature . The actual shop p rob ' lem thu s pre s ente d is to determine readily and accurately the co r

rect hardening temperature for any carbon steel that may be in use . This can be done by the use of various types of pyrometers ; the ap

. 2 H M f paratus illustrated in Fig , which is made by the oskins g. Co . ,

D M . of etroit , ich , is well adapted for the purpose . This apparatus consists of a small electric furnace in which to heat a specimen of the

r - steel to be tested , and a special the mo couple pyrometer for indicating the r temperature of this specimen th oughout its range of heating . The specimen itself should be properly shaped for clamping to the the rmo couple . The furnace may be operated on either alternating or direct current Th circuits . e furnace chamber is inches in diameter and 1 6 N 0 6 —H E A T TR E A M E p . 3 T N T o S TE E L

e inches deep . H at is produced by means of the resistance offered to “ ” the passage of an electric current through the resistor or heating element whi c h in the form of wire is wound in close contact with the Th chamber lining . e furnace is designed so that it can be used on standard lighting circuits to which ready connection is made with a twin conductor cord and lamp plug . In operation , it consumes amperes at 1 1 0 volts , and is capable of producing a chamber tempera ture of 1 83 0 degrees F . , which is considerably higher than required for a carbon steel . — The pyrometer consists of a thermo couple , connecting leads and i h

Th - d i cati ng meter . e thermo couple is of small wire so as to respond

2 n F i g . . H o s ki s E l e c tri c F u rn a c e a n d P y ro m e te r u s e d f o r a s c e rt ai ni n g the D e c a l e s c e n c e a n d R e c a l e s c e n c e P o i n t s o f S t e e l

quickly to any slight variation in temp erature . The welded end of this couple is slightly flattened to enable a good contact between it and the Th steel specimen . e meter is portable and indicates temperatures up to 2 552 degrees F .

The specimen of the steel to be te sted should be small , so as t o heat

- quickly and uniformly . A well formed specimen is made with two 1 duplicate parts , each inch long by inch wide by 4 inch thick .

1 - The pieces are clamped by means of two inch bolts , one on each side 743

- of the welded part of the extreme end of the thermo couple . Care is taken to form a tight conta ct though not to cause an undue strain on ,

h Th e f r t e couple . e dimensions here giv n o the test specimen are not H A RD E N I N G CA RB ON S TE E L S 1 1 essential thou h convenient any pieces which will permit of tight , g ;

- contact with the thermo couple and of heating in the furnace chamber ,

may be used .

With the specimen fastened to the couple as just described , the fur nace is connected in circuit and the cover placed over the chamber W opening. The temperature within the chamber rises steadily . hen at it becomes 1 700 degrees F . , the end of the couple with specimen The i t ache d , is inserted in the chamber . steel spec men rapidly heats , its temper ature being constantly the same as that of the welded junc

- tion of the thermo couple , due to the intimate contact between them .

This temperature , indicated by the meter , will rise uniformly until A the decalescence point of the steel tested is reached . t this tempera ture t he indicating needle of the meter becomes s tationary, the added T heat being consumed by internal changes . hese changes completed , the temperature again rises , the length of the elapsed period of time depending upon the speed of heating . With the furnace temperature 1 00 kept nearly constant at the initial point , here given as 7 degrees

F . this speed of heating will be such as to allow of readily observing , the pause in motion of the needle . The temperature at which this occurs should be carefully noted . h To obtain t e lower critical point , the temperature of the piece i s

first raised above the decalescence point by about 1 05 degrees F . In this condition it is removed from the furnace and reste d on top to

- cool . The decrease of temperature is at once noticeable by the fall A l of the meter needle . t a temperature somewhat below the d eca es cence point, varying with the composition of the steel , as previously mentioned , there is again a noticeable lag in the movement of the needle . The temperature at which the movement ceases entirely is the l recalescence point . Immediately fo lowing there may occur a slight rising movement of the needle , as previously explained . D uring these intervals of temperature lag, both during the heating and cooling of the steel , there may occur a small fluctuation in the tem pe ratu re . In order to get results that are comparable a definite point , in each of these intervals should be considered each time a test is made . H ence , both the decalescence and recalescence temperatures

are taken as the points at which the needle first becomes stationary . A s all operations of heat treatment of a steel center around its critical

r points , the importance of knowing these exactly is ealized ; to m ake

certain , each test should be checked by a second reading . The time required for this is small . A close agreement of two succeeding read ings will give assurance of the correctness of the determination .

R e s u l t s O b t a in e d f r o m S a m p l e S p e c im e n s

In order to show graphically the necessity of wor king carbon steels at the proper temperature points , a series of specimen p iec es of the

same steel were treated at different temperatures . The steel used contained exactly 1 per cent carbon . A number of test specimens were

made of this from adjacent parts of the same bar .

First the critical points of this steel were determined . Tempera 12 o 6 —H E A T TR E A TM E N . 3 N T OF S TE E L

tures were recorded throughout both the heating and cooling . In the

F i . diagram , g 3 , these values have been plott ed . The curve shows th graphically the location of e critical points , and also the slight fall

or rise of temperature as the case may be .

With this data obtained , seven specimens of the same steel were

heated , in the electric furnace , each to a different temperature . A s these pieces were removed from the furnace they were immediately

The quenched in water . temperature of the quenching bath was held

The r constant at 45 degrees F . ha dened pieces were then broken at ri ght angles and the fract ured surfac e of each was photographed under A n a. mi croscope . inspection of the photographs at once showed the

3 4 5 6 7 9 10 TIME (MI NU TES)

F h n T m wh e n h e a ti n i g . 8. Di a gra m sh o wi n g t e R e l a ti o n b e tw e e n Ti m e a d e p e ra tu re g T e m e u r e o f n e e r c e n t a rb o n S te e l S t e e l , a n d th e C ri ti c a l p ra t s O p C s erious effects of overheating on the structure of the steel and hence on its strength . One specimen was hardened just as the temperature reached the decalescence point . This showed clearly the direction in which the hardening moves , namely, from the exterior toward the interior .

This would naturally be expected as the temperature of the surface , which is exposed directly to the source of heat, reaches the critical : he po int first . This condition indicates t necessity of heating the piece uniformly .

C o n c l u s i o n s I

The hardening of carbo n steels for highest quality and grea test t saving entails , then , three t hings . First, a defini e knowledge of what The consti tutes the correct temperature at which to harden the steel . second point necessitates a positive means of accurately determining The this hardening temperature for any carbon steel . third considera CA R B ON A N D L O W - TU N GS TE N S TE E L S 1 3

t ion is that the correct hardening temperature , once determined , is a ct ually carried out in the hardening work . A simple and effective way of doing this is by checking the temperature of the hardening

furnace by means of a pyrometer . When there is a large quantity of work to be hardened, economy dict ates a permanent installation of A pyrometers . The convenience of such installations is manifest .

- A thermo couple is placed in each furnace . number of these , from thr ee to sixteen depending upon individual conditions , are connected , by wire leads through a selective switch to one meter . B y a turn of , h t e switch , the temperature of any furnace may be read at once from T w the meter . his makes it possible for the foreman to kno definitely,

at a single point , the temperatures of all of the hardening furnaces in use .

CHAPTE R I I

H A R D E NI N G C A R B ON A N D L OW " TU N GSTE N STE E L S

The hardening of steel has always been considered an operation for which definite rules could not be laid down , but in which the ex pe ri e n ce and judgment of the hardener would almost exclusively have

to be relied upon . P ractically the only definite rules that have been laid down are that steel should be hardened at as low a heat as pos sible , and that there is a definite t em perat u re _ f or each kind of steel , above which i t must be heated to harden at all .

A r pa t from this meager information , a few generalities only have

been furni s hed for the guidance of men doing this work , including directions for cooling, so as to minimize the risk of cracking ; but

d efinite information on the process of hardening is singularly lacking, a n d many have considered it impos s ible to shape rules for this opera

e h e tion , ven as t e res ult of careful experim nts .

F o r this reason the experiments conducted by M r . Shipley N . B ray M E shaw of anchester , ngland , the results of which were reported in a paper read before the Institution OF M echanical E ngineers at the

A 5 1 9 1 0 r pril 1 , , meeting, and which a e recorded in detail in this chap ter , are all the more remarkable and of great interest to everyone e u a ' g ge d i n mechani cal work . These experiments appear to have been t made wi h extraordinary care , and two of the points brought out i n

One his investi gations deserve to be particularly mentioned, of them relates to the shortening or lengthening of steel in hardening . It has o ften been stated that steel is unreliable and not uniform in this res pect , and that the same kind of steel has sometimes been known to shorten i n hardening, and sometimes to lengthen . This phenomenon has been

M A C N E Y u n e 1 9 1 0. HI R J , , N o —H E A T TR E A TM E N T r S TE E L . 63 o

attributed to defects , or , at least, to special conditions in the steel , ’ ha r r h over which the hardener s no cont rol . M . B ays aw s experiments , however, show that the shortening and lengthening of steel in harden i ng follows a uniform law, and that steel hardened below a given tem

u re - pe rat , which he calls the change point , will shorten when

- quenched ; whereas the same steel , if heated above this change point H before quenching, will lengthen . e also shows that by heating the steel in two furnaces , first bringing it up to a certain temperature in one , and then soaking it for a given time at a definite temperature in h i t t e other, it is possible to harden steel so that will neither lengthen nor shorten when quenched . This is , without doubt , the first d e fi nite information that has been published on the change in the length of steel in hardening, the uncertainty of which has caused considerable ffi di culty in making accurate taps , dies , etc . ’ Another interesting point brought forth by M r . B rayshaw s experi ments relates to the proper hardening temperature . While it is pos

sible to harden steel within a temperature range of about 2 00 degrees , and obtain what to the ordinary observer would seem to be good re

u l w s t s , the bes t results are always obtained within a very narro range

of temperatures , approaching closely the decalescence point , or the temperature at which steel changes into a condition when it can be hardened by q uenching . It is interesting to note that this result agrees with the old theory that steel should be hardened at as low a tem pe ratu re as possible . In a number of cases certain tools are found to last exceptionally well , while other tools in the same lot show only ordinary durability , although no difference can be detected in the grain of the hardened steel . Such differences can now be accounted for by the slight variations in the temperature at which the various tools have been hardened . These experiments open up an entirely new field for investigation T and new possibilities in the hardening of tool steel . hey indicate that ‘ i ii cases where it is important to prevent the cracking of tools in hard e h ing and the deformation of tools due to internal stresses , they should be hardened at a temperature higher than that which gives the T best results as regards hardness only . hus we find that certain of r the desirable qualities in a hardened tool a e antagonistic ; that is , we are unlikely to obtain a tool having extreme hardness and elastic limit and which at the same is not likely to crack or lose i ts .time shape . U nder these conditions one of the necessary qualities must be " fi partly sacri e d to another, and a tool must be hardened so as to obtain good general results rather than the best specific one . The influence of previous annealing on hardening is also of interest ; and many of the points brought out in the abstract of the original paper are well worth considering .

R e s ul t s o f t h e B ra y s h a w E x p e r im e n t s

The experiments mentioned deal exclusively with the results o h ‘ f r t ta i ne d from two kinds of carbon tool steel that , excep t o minu e variations differed only in the fact that one of them contained about , CA R B ON AN D L O W - TU N GS TE N S TE E L S 1 5

Th per cent of tungsten . e steel c ontained on an average of

pe r cent carbon , per cent silicon , per cent manganese , Th . e of pe r cent sulphur , and per cent phosphorus whole work investigation was devoted to questions directly conne cted with machine shop har dening with the aim in view of throwing light on the many ,

problems met with in daily practice .

H a r d e n i n g Te m p e r a t u r e s

Th e hardening point of both low -tun gsten and carbon steel may be

located with great accuracy, and the complete change from soft to hard is accomplished within a range of about 1 0 degrees F . or less . A fter / f the temperature has been raised mor e than from 3 5 to 55 degrees F .

above the hardening point, the hardness of the steel is lessened by

further increases in the temperature , p rovided the heating is s u ffi ci en tl y prolonged for the steel to acquire thoroughly the condition ” m T - pertaining to the te perature . here is a change point at about

- 1 61 5 degrees F . in low tungsten steel and at a somewhat higher tem

n r pe rat u re in carbon steel . O e of the seve al indications of this change -point is the shortening of bars hardened in water at tempera tures below that point, whereas the bar lengthens if this temperature is exceeded at the time of quenching . P ractically the same results are obtained by heat ing low -tungsten bars to any temperature from 1 400 to

1 72 5 degrees F . and quenchin g in oil , as by quenching in water .

L e n g t h o f Tim e o f H e a t in g

R egarding the effect of heating to various temperatures for variou s

e lengths of time b fore quenching for hardening, the following con e lusions are drawn : P rolonged soaking up to 1 2 0 minutes at tempera tures at which the hardening change is half accomp lished in 3 0 min

chan e “ P g utes , does not suffice to complete the g , rolon ed soaking for hardening at a temperature of 1 400 degrees F . has a slightly injurious

effect on the steel , but does not materially influence the har dness . A t 1 a temperature of about 490 degres F . a great degree of hardness is attained by quick heating, but the hardness is impaired with 3 0 min

P r utes soaking . olonged soaking for hardening at a temperature of

1 61 5 . e about degrees F has a seriously injurious ffect upon the steel . 4 A specially great degree of hardness may be obtained by means o f

1 61 5 f or soaking at a high temperature , such as a very short time , but even as long a time as minutes is long enough to seriously impair the hardness . The temperature of brine for quenching is of considerable import

- ance . B oth low tungsten and carbon steel bars quenched at 41 degr ees

r F . were decidedly ha der than bars quenched at 75 degrees , and quench

i . r ng at 1 2 4 degrees F rendered the ba s much s ofter .

E ff e c t s o f P r e vi o u s A n n e a l i n g

The method o f previ o u s annealing affects the hardn e s s of steel con

i d e ra l T - s b y . he elastic limit of low tungsten bars hardened at either 1 400 o r 1 5 80 degrees F . varies according to the annealing they have Th undergone . e elastic limit is high after annealing at about 1 470 1 6 N O 6 —H E A T TR E A TM E N T OF S TE E L . 3

1 2 9 2 0 degrees F . for 3 0 minutes , or 0 degrees F . for 1 minutes , but it is

r 1 4 0 seriously i mpai ed by annealing at 7 degrees F . for 1 2 0 minut e s .

- 1 2 If low tungsten steel is annealed at 7 5 degrees F . and hardened a t

F . 1 400 degrees , the elastic limit is inferior , and the adverse effect of the previous annealing is m uch more p ronounced if the hardenin g i s done at 1 580 degrees F . The elastic limit of carbon steel anneal e d 2 at any temperat ure between 1 90 and 1 72 5 degrees F . and hardened at either 1 400 or 1 580 degrees F . does not vary by nearly such great

- amounts as the elastic limit of the low tungsten bars , and the highest annealing temperature given above is not inj urious so far as the elas tic limit is concerned .

The o f - hardness low tungsten bars hardened at 1 400 degre es F . decreases from a high scleroscope figure to a low one a s the tempe ra ture of annealing increases from 1 2 90 to 1 72 5 degrees F . The hardness

s he r is increa ed by prolonging the annealing at t lower temperatu e . - The hardness of low tungsten steel hardened at 1 580 degrees F . is fairly

constant at a moderately high scleroscope figure , what ever the tem

u re perat of annealing.

E f f e c t o f H e a t in g i n Tw o F u r n a c e s

A n interesting part of t he experiments relates to the use of two furnac e heats for hardening, heating the steel first in one furnace to a

certain temperature for a given time , and then immediately , without

cooling , soaking in a second furnace at a known temperature and for

T - a definite time . hese experiments show that low tungsten and car bon steel bars heated for half an hour to temperatures between 1 545 and

1 0 fie 65 degrees F . are not much a cte d so far as their elastic limit and maximum strength are concerned by a fu rther immediate soaking for 1 400 half an hour at degrees F . If , however , the temperature in the

2 - m first furnace is 1 7 5 degrees F . , the low tungsten steel is much i proved by a further soaking at 1 400 degrees F . , but the carbon steel

r B - i s¢m u ch injured by the same t eatment . ars of low tungsten steel heated for 3 0 minutes at 1 61 6 degrees F . and then soaked at 1 3 3 2 de

grees F . for a further 3 0 minutes , give a high elastic limit and maxi

r mum strength , and are harder than if the second soaking we e at a ‘ T temperature of 1 400 degrees F . he carbon steel , again , is but littl e affected by th e se variations in the second furnace .

- The change of length in hardening, however , of both low tungsten and carbon steel is much affected by the above variat ions in the te m pe rat u re of the second furnace . Good results as regards elastic limit and maximum strength , and also as regards hardness , are obtained by

1 61 5 F . very short soaking, first at a high temperature , say degrees ,

and then at a l ow one , the results being best when the second tempera ture is near to or a l ittle below the hardening point . If the furnace be at a sufficiently hi gh temperature it is easy either by variations of

the t emperatures of the two furnaces , or by variations in the time of

t - soaking, to arrive at a treatment of the s eel , both low tungsten and

. U carbon , whereby they neither lengthen nor shorten nder the same treatment carbon steel has a greater tendency to short en than low

tungs ten steel .

1 8 — A N O. b e H E T TR E A TM E N T OF S TE E L y

time gave a much lower elastic limit . The maximum strength alone i s not necessarily any indi cation of the condition of the steel in ques tion , or of the treatment to which it has been subjected ; nor is the hardness alone necessarily an indication of the condition of the steel

or the treatment .

The u following conclusions refer both to t ngsten and c arbon steels .

T r empering up to a tempe ature of 570 degrees F . gradually increases the maximum strength and the elastic limit , although some i rre gu l ar i i e t s enter which have not been fully accounted for . Tempering to this temperature reduces for a given stress , the extension under load and the permanent extension .

C o n c l u s i o n

In conclusion it may be stated , that these experiments show that steel of the quality treated in these experiments may be hardened

r T within a tempe ature range of about 2 1 5 degrees F . he lower end

r of this range is ve y sharply defined , but the highest temper ature al ‘ lowable is difficult to determine , and as far as the appearance of the fracture is concerned there is little evidence of improper hardening until the temperature of the proper hardening point has been ex

r ce ed e d by 2 70 deg ees F . So wi de , in fact , is the margin of allowable variation for hardening that when the hardness is decided by the ap

e r p a ance of the fracture alone , any workman of average skill can

easily keep within the limits and judge the temperature by sight alone , and as a matter of fact this is being done all the time in the manu facture of such articles as pocket knives , small files , etc which are

B u r hardened by the thousands with practically no waste . t , of Cou se , it must not be understood that articles so hardened reach anything like their maximum efficiency because even small variations in the , heat treatment previous to the quenching have a pronounced effect

upon the condition of the steel , and even the previous treatment, such as the annealing to which the steel has been subjected , may influence

l r he na s . t Qfi e ult While it is thus easy to harden so as to obtain reasonably g ood re

s u l ts , the production of the bes t results nece s s itates a high degree of accuracy which can never be obtained by sight alone , and it is also impo rtant to notice that the diff erence between good hardening and A the best hardening is very great . s an example may be mentioned

the hardening of razors . It is sometimes said that whatever price one O pays for a razor , the buying is a game of chance . ccasionally one hears of a remarkable razor that holds its edge as if by magic , while others of the same make and type may not be anywhere near as good .

s r A l l of them , however , would show to the eye practically the ame f ac The ture , and apparently seem to have been treated in the same way .

r h v experiments refer ed to above , however , indicate that there may a e been a sli ght diffe r ence in the hardening temperature and co nse n u entl y d e in the subseq uent condition of the steel , and also that it woul b pos sible to harden every razor in a gross so that each one would be truly u m a duplicate of the best . The same , of course , holds true of a great n ber of other too ls . CA R B ON A ND L O W - TU N GSTE N S TE E L S 1 9

The author concludes by saying that there have , for some years , been

e fi o rts ma de by steel makers to discover new alloy steels , and splendid

success has been obtained in this direction , but there is still a wide

’ field for the steel u se rs f o r discove r ing the best use of the material

already known . It is of little avail that occasionally tools show h marvelous results , unless the hardener can at any time produce t e

same results with the same steel . The time is likely to come when all the factors in the hardening of tool steel will be controlled with accu

racy withi n predetermined limits , and any failure may be investigated and the cause located with as much certainty as if a mistake had

been made i nthe machine shop .

- C a rb o n St e e l v s . H i g h s p e e d St e e l

The idea that the proper hardening of carbon steel will make it pos sible to obtain better results by the use of this steel than has ordi n ari l y been the case in the past has been expressed in this country as

r well as in E ngland . A t least one la ge machine tool building and tool making firm has made extensive inquiries in the direction of d ete rm i n ing proper methods for hardening ordinary carbon steel so as to obtain

the best results , and several writers on mechanical subjects who have

investigated the subject concur in the opinion that carbon steel , p rop erly heat treated , can be made to produce better results than usually

A expected . One contributor to M C H I N E RY writes as follows : ae “ H - T igh speed steel is in fashion nowadays . his fact together with the high degree of skill required to get the best results from carbon

steel has caused this steel to be neglected . For some kinds of work , how

- ever , carbon steel is superior to any high speed steel on the market, if it

is dressed properly and receives the proper heat treatment . “ The carbon ih steel may be in one of two forms : A nnealed steel ,

- has the carbon in the non hardening or cementite form . H ardened

’ ‘ ’ steel has the carbon in the hardening or m art e n é i te form . That these are two distin ct forms may be seen by taking a small piece of an nealed steel and a small piece of hardened steel and dissolving each in Th hydrochloric a cid . e annealed steel will dissolve , leaving a black ' T residue , while the hardened piece dissolves , leaving no residue . his shows that in one c as e some of the carbon is in the free or graphitic form and does not dissolve in acid , while in the other case , the carbon is in the combined form and all dissolves . “ A nothe r point that is important to the steel wor ker is that the car bon changes form suddenly at the critical temperature . This is T shown in the sample reproduced in Fig . 4 . his sample was made in the following way : A piece of steel V2 inch by 1 inch was heated and nicked parallel with the axis as seen in the engraving ; then this piece was heated till it began to fuse on the end A the heat gradually B T e B decreasing toward . h end was not hot enough to harden . I n this condition the piece was cooled as quickly as possible and then Th broken along the nick . e characteristic burned grain is seen at A .

This gets finer as the part that is not so badly burned i s reached .

“ H l l M A C NE Y u n e 1 9 1 0 J . . Gi , HI R , J , . 2 0 0 6 —H E A T TR E A TM E N T 1: S E E N . 3 0 T L ' J ust before the point C is reached we find the maximum fineness and

h r o t e maximum ha dness ; as so n as the line 0 is crossed , we find the

The . T grain of the annealed steel sample is soft from B to C . his ' T shows that there is a sudden change , on the rising heat, at C . he

best condition for hardening is j ust after crossing this l ine . R egarding the use of the magnetic needle for indicating the correct

r hardening temperatu e , the same writer says e “ There are two hardening methods which depend on the fact that

r steel loses its magnetic properties when the ha dening point is reached . A piece of steel heated to a dull re d and brought into the plane of a " magnetic needle will attract the needle . If heated until the tempera

ture is above the hardening point , there will be no attraction and the

f the needle will not be a fected by the presence of steel . In using this

test, care must be taken that the presence of the tongs does not mis The lead the workman . comparatively cool tongs may attract the

needle even when the steel is above the critical point . A n ordinary

- horse shoe magnet may be used instead of the magnetic needle . It is less likely to mislead because of the tongs or cooler parts of the steel

F i g . 4 S a m pl e o f C a rb o n S t e e l b ro k e n t o s h o w D i ff e r e n c e i n ’ Gra i n a t D i fle r e n t H a r d e ni n g H e a t s

but is less sensit ive . A bar magnet hung on a pivot at the center and i n provided with a handle can be used very satisfactorily . It can be t rod u ce d into the furnace to test the steel during the process of heat

ing and is more convenient than either of the other methods . It i s

net necessary to test every piece of s teel , but a test should be made whenever the person takes another grade of steel or whenever the light T h changes . he intensity of the light makes a great difference in t e ” color of a piece of iron or steel at a given temperature .

Ge n e r a l R u l e s f o r H a r d e ning If steel workers would observe the following in all cases when

H ar e ar on e e l hardening steel , they would have better results : d n c b s t

The M a t the l owes t pos s i bl e hea t a nd a l ways o n the ri si ng hea t . S]:

part of this rule is the one more often overlooked . Steel may be forged at a higher heat than the hardening heat but should in all cases be ah T t nealed before being heated for hardening . he grain of the s eel cor

responds to the highest heat it has r eceived since it was black . If a 1 6 piece of steel is forged at 00 degrees F . and allowed to cool down to 1 600 1 400 degrees F . to harden , it will have a grain corresponding to d egrees .

’ “ ” Se e M A C N E Y S R e f e nce Seri es No. 46 H a r eni n and Tem eri n HI R g , d g p g. ha e r C pt V I I . CHAPTE R I I I

" TH E E L E C TR I C H A R D E N I N G F U R N A C E

This chapter consists of an abstract of a paper by M essrs . E . Saber

sky and E . A dler read before the Faraday Society . A great many factors must be considered in the development of the design of an electrical hardening furnace . The practical requirements which ‘ should be fulfilled by an ideal hardening furnace may be summarized in a general way as follows

1 . The furnace should make it possible to obtain all hardening tem pe rat u re s required in industrial practice , thus having a range of from

1 400 to 2 450 degrees F .

2 . The steel should be heated to the required temperature easily and rapidly .

The 3 . temperature of the steel should be easily ascertained , and it should be possible to keep it well under control within a ma rgin of,

say , 50 degrees F . above or below the exact temperature required .

4 . The steel must be equally heated all over , notwithstanding dif

- - f e re nt cross sections of the object, thus preventing the over heating and burning of edges and points .

5. D uring the heating process foreign matter must not come in contact with the steel so as to change its carbon content, or affect it in

other respects .

6 . It should be possible to place the cooling tank c lo s e to the f u r

he r nace in order to minimize t los s of heat during the t an s fer , and avoid the oxidizing influence of the air .

‘ o bno x i ofi r r 7 . The furnace should not give off s o poisonous vapo s of lead , potassium , cyanide , etc .

e 8. The total operating cost incident to the hardening proc s s should be low . In the following will be described an electric ha rdening furnace

which fulfills to a considerable extent all of the previous requirement s , ' and a general review of the advantages of electric hardening will be given . D e s c r ipt i o n o f H a r d e nin g F u r n a c e

c In Fig . 5 are shown vertical and horizontal se tions of the hardening

fire - furnace . A bath of metal salts is contained in a clay crucible . C u t rent is transmitted to the bath by two electrodes made of Swedi s h

r ingot iron , which is cha acterized by a particularly low percentage of

carbon , and therefore has a melting point of as high as 2 700 to 2 900

- degrees F . A s shown in the horizontal cross section , the electrod e s end in iron terminals sweated in turn to copper conductors . The

e fir - crucible is surrounded by an asb stos lining, a e clay r eceiver , and a

- layer of insulatin g material , the whole being c ontained in a cast iron

" i l a E i i n A ri l 1 Y a w . M AC HI N E R , R y d t o . p , 9 1 0 2 2 N o —H E A T TR E A TM E N T OF STE EL . og

case . This construction greatly reduces the radiation losses , and ’ 4 after ten hours o peration of the furnace at about 2 50 degree s F . , the 85 cast iron case has a temperature of only from to 1 05 degrees F . Over the bath a sheet iron hood is placed fitted with chimney and d i fie re n damper . These furnaces are made in several t sizes . In the smallest size the inside dimensions of the crucible are about 5 inches

r 1 2 square by 5 inches deep , and in the la gest size inches square by 1 5 Th inches deep . e approximate consumption of current in kilowatts at various temperatures for the large and small furnaces are given in

Table I . The best c omposition of the bath depends mainly on the tempe rature T required for the hardening . able I I gives the composition of various sa lts to be used for different proc e sses . The conductivity of the salts at normal temperature is very small while at hi gh temperatures ( when in a melted c ondition ) they offer to the electr ic cu rrent a comparatively W l o w resistance . hen the mixture is sufficiently hot, the bath , there fore , forms an electric conductor , and each par t of the bath produces

its own heat . This featur e dis t i ngu i s he s this class of electric fur

naces from other types . The heating of the salts prior to their becoming highly conductive i sr d o ne by means of an auxiliary electrode and a p iece of arc lamp carbon . The carbon is first pressed against one of the main electrodes

and soon reaches a white glow , melting the salts immediately about

. The N Y it auxiliary electrode , which M a chi n e r y, . .

e c ti o n o f El e c tri c a l consists of an iron stick fitted into a F i g . 5 . S H a r d e n i n g F u r n a c e wooden handle , is then drawn to

r r wa ds the othe main electrode , the molten salt trailing behind it until Th a bridge is establi s he d between the t wo main electrodes . e current which now passes through the molten salt continues to raise the tem T pe rat ure of the bath until the required heat is attained . he articles

to be heated are dipped into the bath , suspended by thin iron wires or held by tongs , and are allowed to remain in the bath until uniformly heated th roughout . The most striking feature of this furnace is the possibility of se cu r C ing uniformity in temperature throughout the whole bath . areful E L E C TR I C H A RD E NI N G F U R N A CE S 2 3 measurements with a pyrometer of the thermo -couple type at various parts of the bath have shown that the temperature varies only 5 or 6 F degrees . , except in an upper layer about inch thick , where , owing

2 0 . . A to radiation , the temperature is from to 3 5 degrees F lower lter ' nating and not continuous current s hould be used ; all frequencies be tween 2 5 and 60 cycle s may be applied ; with less than 2 5 cycles elec t rol yti c phenomena appear . The furnace , having only two electrodes ,

E R E NT C O N S U PT O N O F E E C TR C F U R N A C E S TA B L I . C U R M I L I I N K ILO W A TTS

r l rn a h Si z e o f C u c i b e o f F u c e , I n c e s

5 x 5 x 5 6 x 6 x 7 8 x 8 x 1 1 12 x 12 x 15

- - it suitable for single phase currents only . If a single phase supply i s

not available , a c onverter mu s t be in s talled . A n important pa r t of the hardening installation for electric fur naces is the pyrometer . The most reliable results for the tempera tures in question are obtained by instruments of the thermo -coupl e

type , but the instruments must be such that the te r minals are kept

r - outside of the dest uctive influence of the heat . The thermo couple — used is platinum platinum rhodium , protected by M arquardt compo

A B E TE P E R A TU E N D P O T O N O F A D E T L II . M R A C O M S I I H R N IN G B A TH

T a t t e ’ P ro c e s s Sa l t s figggzgé fi

S r T i S l 400 1 0 o d i u m nit ate and empe r ng tee . t o 75 potassiu m nit r ate Sod iu m chl or ide or so A 3 1 nnealing copper , 1200 t o 1 650 d i u m chl oride a n d al loys , e tc potassium c hl orid e H arden ing r e g u l a r P otassium chl oride and carbon st e e l bar ium chl oride B m hl H a r d e n i n hi h ariu c oride g g C l s eed steel s a c i u m fluoride or p magnesium fl uoride

i i on A e c s t and steel . ste l ylinder protects the parts projecting from t he T r bath . his cylinde gets white hot and deter iorates unless pro t ect e d t agains the oxidizing influence of the air . t When the sal s are melted , the voltage necessary for maintaining

5 3 0 - the temperature is from to volts , while the heating u p voltage is 0 about 7 volts . Su ch low voltages are not av ailable from ordinary

r supply systems , and consequently a t ansformer must be used . The heat developed , and consequently the temperature of the bath depends , 24 N o 6 — H E A T TR E A TM E . 3 N T OF S TE E L

f on the volta ge . i it is desired t o alter the temperature this can , h therefore be done by a variation of t e voltage . The use of the trans

former makes the voltage control comparatively simple .

Th e H a r d e n i n g P r o c e s s

t When heating carbon s eel for hardening, i t is advisable to heat it as rapidly as possib l e because t he prolonged influen ce of the heat f seems to a fect the chemical constitution and mechanical structure . In most cases it is advisa ble to pre -heat the steel to a certain tem

e rat u re t he p before final heating in the bat h takes place . This pre heating should be d one thoroughly in order to make sure that all por~

- tions are well heated . U nless this is done during the p re heating period the heat during the main heating p eriod must be directed to

t n o t he at e d whi ch l e n the ns the the par s properly , , g process and may c t t t he ause damage to the ex ernal por ions of tool , such as edges , pro

e ct i o n . j s , etc E ach brand of steel requires a certain temperature t o which i t ‘ - should be heated for hardening . For high speed steels this tempera ’ ture is about from 1 800 to 2 3 75 degrees F and for carbon steels about

from 1 3 00 to 1 650 degrees F . Generally speaki n g, t he cooling pro

be . f cess for alloy steels need not so abrupt as o r carbon st eels . I n h f stead o f quenching the o t t ool in water or oil , it is s u ficient to ex pose it to a current of air or t o dip i t into molten tallow .

A d v a n t a g e s o f E l e c t r i c F u r n a c e s

A great advantage of t he electric furnace is t hat it is possible to cover a wide range o f t emperatures wi t h one equipment by only changing the composit ion of the bat h . The tool can thus stay in t he

bath until it has acquired the temperature of the bath , and does n ot need to be removed before it has assumed the temperature of i t s sur h r o u d i ngs , which i s quite commonly t e case in other heat ing pro

t e c ess es . With the electric hardening ba h , having a pred termined m te perature , less dependence is placed upon the skill of the operator , a nd no account need be taken of t he fact that smaller c r os s -sec tion s heat up quicker than larger ones .

When dipping cold steel into the heating chamber , the temperature

-fire of the latter mu s t drop . In fact, with gas d furnaces and salt

baths it falls rapidly , unless the uncertain procedure of increasing the gas supply is resorted to . In the electric furnace , when the tool is

dipped into the salt, the level of the salt bath rises , and the current of

heat produced increase s automatically . B esides , when it is neces s ary i n to immerse large solid masses , the current supply can be easily creased by the regulator , thus preventing a drop in temperature .

- Of course , the smaller cross sections of the tool will heat up quicker t han the larger ones in the electric furnace as well as in other heating furnaces bu t the delicate parts will not o ver -h ea t because they cannot ,

ass ume a higher tempe rature than that of the bath itself . The bath

equalizes all d i fiere nce s in temperature , and in a very short time

T he heats the whole mass uniformly . his explains t very small loss

CHAPTE R I V

H E A T TR E A TM E N T O F SP R I N G STE E L "

The p r es ent chapter is an abst ract of a paper by M r . L awfo rd h A H . Fry , read before t e Copenhagen Int ernational ssociation for Test

r 1 0 a i ng M aterials . A number of experiments we e undertaken in 9 7 t the B aldwin L ocomotive Works to determine the eff ect of different kinds of heat treatment s on the transverse elastic limit and t he l modulus of elasticity of steels commonly used for ocomot ive springs . Th e points inves tigated were the effect of annealing , the comparative l h ‘ ff h effect of quenching in water and o i , and t e e e ct of reheating t e steel to various temperatures after complet e cooling in wat er or oil . The steel experiment ed upon was basic open -heart h spring steel of the followin g composition

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

M e t h o d o f H e a t in g a n d C o o l i n g t h e Te s t P i e c e s

The tempe rat u r e at which t he specimens were quenched wa s no t

varied because , as is well known , t here is a d efini t e t emperat ure for any given steel at which that steel should be quenched in order to

t r obtain the best results . H aving once det ermined his p oper quench i ng temperature it should always be used , any variation in the final degree of hardness being produced by a change in the t emperat ure at which the temper is drawn . The temperature at which t he s teel T s lfd u l d be hardened is called i t s point of decalescence . his t empera

ture is conveniently ascertained by means of a magnet, due to the fact that steel becomes non -magnetic when i t reaches its decalescen ce Th or hardening temperature . e steel experimented upon was found to reach its decalescence point at 1 3 60 degrees F . P revious e xpe ri ments with the steel had shown that for annealing it should be heated

0 r to 4 or 50 deg ees above this temperature , and for hardenin g it ou ght to be brou ght about from 50 t o 1 00 degrees abov e t he point of dec al

e n The e s c ce . present investigations were carried on with t he follow i n g te mpe ratures :

D r e g e e s F . For annealing 1 400 For quenchin g in oil 1 450 For quenchin g in water 1 42 5

A l l the operations wer e carried on at these temperatures and t he heats at whi ch ° t he temper was drawn and the mode of qu e n ching

M A NE Y R a i l w E i n M a 1 1 0 CH I R a y d t io , y , 9 . , SP R I N G A N D A L L O Y S TE E L S 27

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a g n m o n n o o o a 2 a n n o o e o a n n o y n o e 8 n n n . o m g n a e n w m o m a » w s n o . y n n n o o E n 8 r n o n o o d o e R o o m n _ n o . m w o n P o fi w r . a £ n o s n a o a S m o e n n o o s 3 n n o n fi ? w s b . 5 o b i a fi o o m w 6 s o 8 n . n m n $ n ? n n a K . p fi o e m 3 n a 3 : n m mm h a m n o a » n E s n o m y c c c 0 0 c o n a n o o . n o H e o o o 0 o o n o w .e n z m o o c 8 0 n o 3 o o o o m w n e n n n a 9 s o n o n n . m 2 e e n n fi ‘ a o o o a e A o B O n 8 n a m w ? o n o . 8 8 n o o » S n y o n n e o n n w n E n . a m e o g 2 fi “ o w n s o n n 8 e o n a s n o n n n o o n n m n w s 5 n d z 3 n a o e n B B 0 o r e m n n 5 o s n m n n w ; E x fi w n S o a . . n n o o 3 o n o 6 S 6 m E m s e n o a m S S Rw m s 0 g s o o m o n n 8 5 fi S e e S o i s i o n o .e ; E E ; E fi ; fi fl n m S n o n fl E n e d .e m o a A E n a R a 2 n w a n t o h s 9 v 3 n / o s S : o a o s 8 d n o ? 5 s n 9 0 n ? g o w » m 6 R o o $ 9 v v o o 9 a 3 n o 9 0 9 a 0 n n 5 s 0 o w o 8 2 o 9 fi o f 2 o o n e o w o a a 0 v V w n o o o n 5 s v 9 3 b n ? v v e n o d n w e a e n s n n ? “ n n o n m o o o o w o fi n : o o n n n e fi n n n o n n 3 .e o n w n w “ n n ? v n v 9 v a o 8 z 9 s 3 o a o u 9 0 w B E a m o w z n s n n n n m ? o o o n e H e 2 n n E n n 9 o ? m : a 3 o a ? “ 5 w 2 8 N O —H E A T TR E A TM E N T F S TE E . 63 O L

Th of springs or tools . e theory of the har dening of steel tells us that there are two ways of modifying this hardnes s and brittl e T n ess of the steel . hey are , first, the a llowing of some of the fi carbon xed in the hardening state by quenching, to change back to

the annealing state , by reheating the steel above 400 degrees F . ( the

higher this reheating or drawing of the temper is carried , the softer the steel becomes ) , and second , the using of a quenching bath having T less heat conductivity . he slower the steel i s cooled from above the

critical point to about 400 degrees F . , the more carbon is allowed to

change to the annealing state , and the less the steel hardens . B y the f second method , steel can be obtained of di ferent degrees of hard ness without drawing the temper after hardening the steel . These two

methods of regulating the hardness of steel can also be used jointly . Th These points are illustrated in the tests . e higher the t emper is drawn after hardenin g, the lower the elastic limit falls ; also a lower elastic limit is obtained with the test pieces quenched in the bath ' Th vi a . e having less heat conductivity , , oil tests show that the elas tic limit of 1 per cent carbon steel can be made to vary from pounds per square inch to pounds per square inch by changes

in the heat treatment , and that very small changes in the drawing of fi f T the temper are suf cient to a fect the elastic limit of the steel . his proves once more that the heat treatment of steel is a delicate opera

tion and that to obtain good and uniform results , it is necessary to , have means of heating the steel uniformly to the proper temperatur e and cooling it at the desired rate in a cooling medium , the temperature and heat conductivity of which can be kept reasonably constant . CHAPTE R V

"" H E A T TR E A TM E N T O F A L L OY S TE E L

The rapid development of the automobile indust ry in A mer i ca has

e awakened a quick , keen appreciation of the great importanc of proper heat treatment of steel . Sc ientific heat treatment is quite as

essential as the quality of steel . Ordinar y steel may acquire good

e r phy s ical qualiti s wi t h proper heat t eatment , and the be s t of steel

an T r c be ruined by defe ct ive methods . he e mu s t b e thorou ghness in

the various operations of annealing, hardening and tempering, for

r o only treatment carried on with car e , makes uniformity of p oduct p s

T r r sible . his is particularly true in the produ ction of d op fo gings .

T h e r he diff erence between ordinary and t e b st st e el i s g eat . For

example , the elastic limit of ordinary steel is about pounds per

squar e inch , wit h a redu ct ion of area of , say , 50 per c ent . N ickel steel properly heat treated has an elas tic limit of to pounds

r pe square inch of section , wit h a reduction of area of 50 per c ent , or

more . B rittleness does not follow proper heat treatment, the enduring quality being increased in a gre ater ratio than the elastic limit . Con

sequently crystallization , fatigue , or whatever we name the cause of

r r - breakage , is less likely to develop in a p ope ly heat treated and temp ered material than in an annealed and s oft material . This fact , d i s

covered in the laborato r y and established in actual practice , is now

commonly accepted by metallurgical experts , notwithstanding that it completely overturns previous general belief . A nother commonly a ccepted belief disprove d i s that strength and

“ f i s r sti fness are coordinate , or the stronger a p ece of steel , the tiffe ” T f r it is . o illustrate , it was thought if one piece o steel we e twi ce as

- s trong as another , it would bend only one half as mu ch under a given weight ; but actual test has shown that a chrome -nickel steel having

r an elastic limit of pounds or more per squa e inch of section ,

r bends under a given load the same amount as a ca bon steel specimen , and this condition holds true as long as the load is within the elastic

T - limit of the weake r material . he elasti c limit of a well tempered

s teel spring is about pounds per square inch , but a spring can be made of soft steel . If it is not loaded beyond its elastic limit, the

r t sp ing will return to i s original shape after every deflection , but the

deflection would not be sufficient to make a good spring . In fact , it

an r . would be hardly noti ceable , d of cou se , would be of little value B etween these extremes lie the s teels used by th e spr ing makers in

the past . N o t only has the automobile industry forced the spring makers to

r t r n depa from their old mate ials and methods , but the cha ge extends all along the line . A ssume that a car bon steel has been used

M AC H i N E R Y A u u s a n Oc o b r 1 , g t d t e . 009 . 30 —H E A T TR E A TM E N T OF S TE E L N 0 . 63

- wi th advantage for a given design of crank shaft, neither bending nor t h e r c s breaking through long cont inued use , and that bearing su fa e

r a re as small in area as can be used without heating or excessive wea .

- - A crank shaft of properly treated chrome nickel steel , having an elastic limit four or five times as high as the carbon steel would be no

e Th stiffe r but would have greatly increased lif and reliability . e steel , makers must be prepared to meet these new conditions . Sound knowl edge of steel has spread fast among intelligent manufacturers ; from

r the knowled ge obtained in the labo atories established , where all ma t e ri al s are physically and chemically tested , they have learned to dis

criminate in selection . With known characteristics , heat treatment scientifically conducted is sure of results that make high -grade steels

KE S TE E S TA B LE I V . N I C L L

Tre a t m e nt

l 0 2 1 1550F . o 600F i .

0 25 1550F . o i l 600F .

0 2 7 1550F . o i l 600F i l 600 1550F . o F .

1 600F . bri ne .

0 60 1600F . brin e . 3 w 2 0 2 1550F . ater 12 F . w 2 12 1500F . at e r F. 200F 0 63 1400F . o i l 1 . , 9 0F 0 45 1500F . wate r 0 . 4 3 0F 1 500F . water . l l r d . Nat ural , as o e

a r com able with ordinary steel in about the ratio they in turn , bear p , to cast iron .

In a paper read by M r . J ohn A . M athews before the F ranklin Insti tute in 1 909 , a valuable contribution was made to the question of heat treatment of alloy steels , especially as employed in motor car con Th struction . e cost of the materials used in automobile construction

r amounts to about sixty per cent of the total cost of p oduction . In view of this fact, the kind of material best suited for the more vital h parts is highly important . In t e following the composition and treat ment of some of the most commonly used alloy steels are reviewed .

N i c k e l St e e l

N ickel steel is the most generally used of the alloy steels . The best

o quality contains t per cent carbon , per cent nickel , to per cent manganese , and not over per cent sulphur and r phospho us . With carbon and nickel as given above , the manganese A content ought never to exceed the limits mentioned . slightly lower

- carbon content is sometime s used for case hardening purposes , and a A L L O Y S TE E L S 3 1

- higher carbon percentage is much used for crank shafts . N ickel steel

- r is usually made in the basic open hea th furnace . It is an excellent

- steel for case hardening, and is easier to machine than other alloy

s teels . C h r o m e -V a n a d i u m St e e l

The chrome -vanadium alloy steels are preferably made in the cru

- r c ible or electric furnace , although the open hearth p ocess is also mu ch

T - used for the purpose . he open hearth product , however , is somewhat

uncertain , and while springs of steel made by this process may be bet

ter than those made from ordinary crucible steel , they cannot be com

- pared with springs made of crucible chrome vanadium steel . F or ex

TA B E KE - A D TE E S L V . N I C L V A N IU M S L

Tre at me nt

d N at ural as r ol l e .

Natural as r olled .

Nat ural as rolled .

5 oi l 1150 F . 1 00 F .

oi l 1 150 F . 1500F .

1500 F . oi 1 1 150 F .

600 . 1 500F . oi l F ' 1500 F . o i l 600F .

i l 600F . 1 500F . o Natural as rol led ;

i l . 1600F . o

r . 1 600F . wate

400 F . 1 600F . brine c e l l ent quality the latter product constitutes the highest attainment of ’ the steel makers art . Chrome -vanadium steel made with high carbon content is suitable

- for oil hardened gears and springs . When made with a low carbon

- content it is used for case hardened gears , and , when oil quenched and

annealed , for axles , shafts and steering knuckles . When a better ma t e ri al than the best nickel steel is needed , the various kinds of chrome T vanadium steel are to be recommended . hey can be easily forged and can be machined more readily than chrome -nickel steels of cor responding carbon percentages .

C hr om e -N i c k e l St e e l s

Chrome -nickel steels are made either with a high carbon content ,

- and used for oil hardened gears and springs , or with a low carbon con n tent, i which case the steel is used for axles” shafts forged parts and , , - Th case hardened gears . e high carbon steel carries about per

cent of carbon , while the low carbon alloy carries per cent . The 2 nickel content is from to per cent , while the chro m i u m v ari es N O — . 63 H E A T TR E A TM E N T OF S TE E L

A - - from 1 to per cent . special nickel chrome tungsten steel is

- sometimes used for sp r ings . N ickel chrome steels possess excellent ff sta tic qualities , but present di iculties in heat treatment , forging and machining. ‘ Silico-mangane s e and silico-chrome steels with medium and low carbon contents are u sed to a considerable extent abroad for sprin gs T and gears . heir relatively low cost favors their use , but they do n ot stand up well when subjected to shocks , and are too sensitive to heat

“ treatment . When handled with great care they give good results

where the temperatures for the heat treatment can be accurately gaged .

TA B E - L V I . C H R O ME V A N A D IU M S TE E LS

T re a t m e nt

l l l d Na t ura as ro e .

1570F oi l 400 F .

A nneal e d 1475 F .

Oi l t em pe re d and d rawn t o vari ous

A nneal ed .

1650 F . oi l 840F . i 1025 F 1650 F . o l .

Natu ral as rol l ed .

1660 F . o i l 600 F .

1 660F . oi l 850F .

1500F . oi l 1 12 5F . w 1600F . a ter 600F . 5 F 0F i l 112 . 1 60 . o 0 1 0F o l 43 F . 60 . i

Nat ural as rol l ed .

00F i l 1 150 F . 15 . o

500F o i l 600F . 1 .

Chrome steels with high carbon content are used to a considerable ex T f or tent for balls and ball races . ungsten steels are uni versally used k ma ing magneto magnets .

H e a t Tr e a t m e n t o f A l l o y St e e l s While the best alloy steels are none too good for most of the parts i n automobile constr uction their qualities will not become pronounced , t o unless they receive proper heat treatment . It is waste of money buy good alloy steels without knowing how to proper l y treat them to ' ' a n the rom bring forth their e xce pti onal qu al i ti e s . F o r g gi g heat a py eter is necessary but it is too often supposed to take care of its elf . , The best pyrometer of the thermo -couple type should be regularly i n a i n re s pe cte d . The protecting tubes should be frequently ex m ed and l newed , and the electrica contacts looked over .

4 N o —H E A T TR E A TM E T F 3 . 63 N O S TE E L

In the column marked Treatment is given the temperature to which the steel is heated before quenching, followed by the liquid in which it is quenched ; where a second temperature is given it indi cates the temperature to which the steel is reheated to draw the tem “ T ° per or anneal . his will make clear such terms as 1 600 F . oil

° 600 F . For springs it seems that no material is better than crucible chrome

The vanadium steel . tempering of this steel is quite simple . The springs made from it should be heated to from 1 675 to 1 700 degrees

The F . and quenched in oil . temper is then drawn according to the Th nature of the spring, and the duty expected . e drawing range i s 1 0 very wide varying from 600 to about 0 0 degrees F . ,

- - C a s e h a r d e n e d v s . O i l h a r d e n e d Ge a r s

B oth case -hardened and oil -hardened gears are largely used in auto

- . A s mobile construction s previou ly mentioned , the chrome vanadium , chrome -nickel and silico -manganese alloys are made with both hi gh n The and low carbon conte ts . former contains about to per cent carbon and enough other hardening elements so that by merely quenching the steel in oil from a bright red heat, surface hardening is p roduced sufficient for ordinary wearing purposes , while the hardness

does not penetrate deeply into the gear , but leaves a tough and strong

core . The low carbon alloy steels , with about per cent carbon , require to be case -hardened in order to produce sufficiently hard sur ’ Th e f ace for wearing purposes . e author s observations lead him to m

- f er the case hardened gear , the following conclusions being based on the results of direct tests on thousands of gears .

- e 1 . The static strength of case hard ned gears is equal to that of

- oi l hardened gears , assuming that in both cases steel of the same class of appropriate composition has been used , and the respective heat treatments have been equally well and properly conduc ted .

C - 2 . D irect experiments prove that case hardened gears resist shocks

- better than oil hardened .

- a l 3 . The case hardened gear resists wear incomparably better , though i t is perhaps not as silent in action . ' The strong objection to the case -h ard e n i ng i s in nine cases out of t en doub tless due to the fact that the case -hardening operation is no t

r the properly understood . The depth of the hard case or cove ing, t ime and temperature required to produce certa in results , and the e xact control of the conditions , together with an accurate knowledge o f the material to be treated , are factors which enter into s uccessful

- c as e hardening .

- To obtain the best results in case hardening ordinary carbon steel , e the following rules should be observed . St el containing less than

and per cent of carbon , with a low percentage of manganese ( less than per cent ) s hould be used ; the case -hardening should be ao 0 complished by a chemically definite material , such as a mixture of 6 per cent charcoal and 400per cent barium carbonate , and at a tempera Th tu re between 1 560 to 1 92 0 degrees F . e higher the temperature , the A L L OY S TE E L S 35

- - more rapid will be the case hardening . A fter the case hardening o p 1 1 0 T 0 . e rati o n , allow the s teel to cool down to about degrees F hen

- - 6 re heat the work to be case hardened , and quench it at 1 50 degrees F .

This heating and quenching has the effect of toughening the center, but the outside will be coarse -grained and brittle ; therefor e heat the material a second time to 1 470 degrees F . to render the outside non

bri ttle .

This procedure is more elaborate than that most commonly used , in which pi e ces are dumped directly from the case -hardening boxes into

water . The process , however , can be somewhat modified if one uses

» a good grade of nickel steel, low in carbon , and aft er having case h hardened it at t e appropriate temperature , permits the material . to

h r - cool off in t e boxes before e heating and quenching . In this case , if

- the mate r ial is re heated but on ce to 1 470 degrees F . the result will be fully equal to or better than those obtained by the most careful an

nealing and double quenching of ordinary carbon steels . It is , how

r ever , better to give a double quenching, as then extraordina y toughness and wearing qualities are obtained . A n ideal way of making a nickel steel gear consists in first anneal i n g the blank , then rough machining it approximately to size , and then

- ' re annealing before taking the last finishing cut . The gears are the packed in a mixture as mentioned , heated to a temperature of about

1 62 5 to 1 650 degrees F . , carbonizing to a depth of about to Th inch . e gears are then permitted to cool in the boxes , are heated to 1 500 degrees F and quenched in a hot brine or calcium -chloride solu

- 1 1 40 r tion , and finally re heated to 3 75 or 0 deg ees F . and quenched in

Th . oil . e temper need not be drawn A nother important point is that of drop forging small parts which m can also be made from bars in automatic machines . N o steel is i

' ‘q proved by drop forging, although some ste e l s are less susceptible to

r inju y than others . In drop forging work , in order to give plasticity , the material must be heated very hot . A n investigation of drop f o rg n i g and bar cut gears , the former being the product of one of the fore most drop forging companies , showe d that under static test the bar cut gears were fully 2 5 per cent stronger and their resistance to shock was also greater . CHAPTER VI

“ C A SE - H A R D E NI N G

The present chapter contains an abstract of a pap er re ad by M r. l h E ’ D avid F at er before the Cycle ngineers Institute , B irmingham ,

E ngland . The term case -hardening naturally implies the hardening of the skin of an article , and in order to fully understand the process and its object we must briefly consider the facts and laws upon which it is founded . Carbon has a very great affinity for iron an d combines with it at all temperatures above faint red heat . A dvantage is taken of this — fact in the production of steel by cementation i n fact , the process of case -hardening is in reality incomplete cementation followed by water

- or oil hardening . F or many purposes in machine work we require articles to have a perfectly hard surface and yet be of such a nature that there is no chance of their breaking in use . In many instances this result can

- be obtained with high class crucible steel , but for axles , cups , cones , and many similar parts , it is extremely difficult to obtain perfect hard ness combined with great resistance to torsional , shearing, or bursti ng strains . For such purposes nothing can meet these requirements so

- fully as articles whi ch have been ase hardened . The greatest risks ‘ c in the employment of all steel often occur during its treatment by the producer, and whether it be the finest cast steel or only common

B e s se m e r i t , . is of first importance that it should be carefully and properly treated with a view to the work it has to do . B oth iron and mild steel have been employed as material f o r case “ hardening ; but this is the steel age , and iron has long passed its

day . The steel employed should be prepared , selected , and controlled from the beginning with the object of suiting it to its requirements . T here are , of course , many points relating to its composition and tr eatment by the producer which can only be gained by long e xpe ri ence and by study of the requirements . Suffice it to say that the steel used should be low in carbon and capable of absorbing more carbon with great u niformity when heated under proper conditions ; it should contain a minimum of deleterious impurities , and be perfectly sound and free from mechanical faults or weaknesses caused by overheating during the manufacturing processes .

Th e C a s e -h a r d e n ing F urn a c e a n d M u tfle s

The furnace should be so constructed as to be capable of being rais ed to a full orange heat ( 1 83 0 degrees and maintained at that

e heat with great regularity . It should be so constructed that neith r Th the fuel nor the direct fl ame can come in contact with the charge . e

M A NE Y A u u s 5. C HI R , g t , 1 90 ' CA SE -H A R D E N I N G 3 7

flames should uniformly impinge on the sides and roof of the m u t

fle in such a ma nner as to raise them to a high temperature , thus heat f ing the contents of the mu fle by radiated and not by direct heat . A furnace designed on this principle not only gives the best result but f is also most economical in the matter of fuel . The mu fle chamber and

fire bri ck u l flu e s must , of course , be constructed of , and the doors sho d

fi ri k fit closely and also be lined with reb c . It is important that there ,

- should be a small peep hole in the door , with a cover plate ; a hole T m inch in diameter is quite large enough . his latter is a most i portant detail as it provides against the need of opening the doors in , order to judge the heat, and is ind eed the most accurate means of T estimating the temperature by the eye . he furnace must be fitted with a reliable damper plate or other effectual means of controlling the draft . F i g . 6 shows a furnace which may be useful as a guide for the erection . The upper chamber in this furnace is not necessary for case

hardening, but it may be found useful to have such a chamber and emp loy it for annealing small articles while case -hardening is being T done . his will add only very slightly to the amount of fuel used .

n ' h H ardening pots are made in both cast a d wrou g t iron , the forme r being cheaper in first cost, but the latter bear reheating so many Th times that they are cheaper in the end . e pots should not be of too large dimensions , or there is great risk of articles in the middle

u fli i n of a charge not being carbonized to a s c e t depth . N o pot should 2 1 1 be above 1 8 by 1 by inches for such parts as cycle axles , pedal pins ,

and the like ; while for small articles like cups , cones , etc . , 1 2 by 1 0 by

- 8 inches is large enough . The pots should each have a plate lid fitting closely inside . The carbonizers in general use at the present day are animal char coal , bones , and one or two other compositions sold under various

r names , consisting of mixtu es of carbonaceous matter and certain cyan

" ides or nitrates . For very slight hardening, Ryani d es alone are still found very useful , but nc great depth of casing is ever attempted with T t . hese heoretically , the perfect carbonizer should be a simple and pure form of carbon , and good charred leather gives the most certain and satisfactory results . Care should be taken to avoid poorly charred leather or that made from old boots , belting, etc .

A s clay must be used for a luting around the pot lid and is also , frequently used for stopping ofi portions to be left soft it is important ,

r to see that a good clay is used , and that it is free f om grease . Clay c ontaminated with grease in any way will cause irregularity in the prod uct . R e h e a t in g M u ffi e s

A s all case -hardened articles have to be reheated before uenchi ng q , it is important that a suitable furnace should be employed for the pur pose . It is not advisable that the reheating should be done in the ,

- case hardening muffle , unless it is run specially for the purpose and 3 8 N o — . 63 H E A T TR E A TM E N T OF S TE E L

at a lower heat . If possible a small gas muffle should be used for

reheating, and indeed for all hardening work properly . A constructed gas muffle can be regulated with great exactness and this very , i s

important in all hardening .

E LEVATION OF FRONT LONGITU DINAL SECTION

t mcx M ETAL PLATES B

S EC TIONAL PLAN

N“M p"r cs oss SECTtON 8-8 M Y

F i . 6 P g . l a n a n d E l e v a ti - o n o f F l a th e r C a s e h a rd e n i n g F u rn a c e

hardening pot and well pressed down . U pon this are placed the arti ~ t o cles be hardened . Care must be taken to leave sufficient spac all e around each piece to prevent its touchin g the others or the walls of 1 the pot ; a space of 1 75 inch should be sufficient . A nother layer of car CA SE -H ARD E NI N G 39

. boni z er is then put in and well pressed down , taking care not to dis place any o f t he articles already packed , continuing until the po t is

ff . nearly full , and then finishing o with another layer of inch at

t he top . The object i n view must be to make the contents of the pot as compact as possible , consistent with a sufficiency of carbonizer in c ontact with the arti cles . The more solidly a pot is packed the more Th c omplete is the exclusion of air . e lid is then put on , and the joint all around well luted with pl ay . B y the time the proper number of pe ts have been filled , the furnace must have been raised steadily to the f ull working heat . "F u r na c e H e a t

The proper heat for case -hardening is about 1 800 degrees F or a full orange heat and this should be maintained with great regularity throughout the operation . The length of time occupied in carbonizing is regulated by the depth of casing required , - and indirectly by the ' d imensions of the article . At the close of the carbonizing pe ri od the . pot is withdrawn from the furnace and placed in a dry place , where it _ is allowed to become quite cold . It is then opened , the articles taken out and brushed over to remove all adhering matter . If the pot has been properly packed and luted up , the articles should be quite white , o r at least have only a slight film or bloom of a deep blue color ; the denser and more inclined to redness is the surface , the more imperfect has been the packing and sealing of the pot .

R e h e a t in g a n d H a rd e ning

The carbonized articles are now placed in a m u ffie furnace and s teadily raised to a good cherry red ( 1 470 degrees and then quenched in cold or tepid water or oil , according to the purpose of the a rticles required . They should remain in the cooling liquid until they a re quite cold right through the body of the metal , thus completing the p rocess . A lthough the proper temperature for case -hardening is about 1 83 0

F . d egrees , this temperature may be modified to suit the purpose in Th view . e absorption of the carbon commences when the steel reaches

- 1 00 a low cherry red heat ( 3 degrees it begins , of course , at the outer surface and grad u l l y spreads until the whole of the steel is carbonized . The length of time this requires depends upon the thick ness of the metal being treated . The percentage of carbon absorbed is g overned by the temperature , and although the increase of carbon is not in uniform proportion to the rising temperature throughout it is , perhaps sufficient for our present purpose to note that at 1 3 00 degrees

F iron , if completely saturated , can contain no more than about F 1 650 . per cent carbon ; at degrees , about per cent carbon ; and

2 000 . T at degrees F about per cent hese results , however are only , o btainable when the whole section of the iron has received all the car

bon it is capable of absorbing at the given temperature , and is there fore in a state of equilibrium . From this it will be seen t hat if the

process is stopped before the action is complete , the central parts of

the iron must contain less carbon than the outside , and upon this fact t he - process of cas e hardening is founded . 40 —H E A T TR E A TM E N ] OF S TE E N O. (fig L

If we take two pieces of inch diameter round mild steel , and

i - heat one of t hem with a carbon zer at a cherry red heat , and t he other at a bright orange heat, for six hours , the first will be cased t o a depth to of about inch , and the other a depth of nearly inch , while the amount of car bon taken up wil l be a bout and per cent re

e v l d t he h s p ct i e y ; so that, so far as regar s ardness of the skin , t he

t he piece carbonized at the higher tempera ure gives t best result . From t his we learn that a temperature of 1 83 0 degrees F . will give u s s u ffi cient hardness of case .

We have next to find which temperat ure has the least harmful e fi ect t t on t he mild steel core , and his can bes be found by heating pieces of the mild steel at varying t emperat ures at and above the selected one for the same length of time , using lime or other inert substance in the pot instead of a carbonizing material , and afterward reheating and S t quenching in water . uppose , for example , we take hree pieces , heat

2 2 0 r F . ing at 1 83 0, 3 70 and 73 deg ees , or full orange , white and bright white respectively . We shal l find that t hose at 2 3 70 and 2 73 0 degrees

break very short and have lost nearly all their original tenacity , while that a t 1 830 degrees appears t ougher and al together stronger than before . H aving arrived at a knowledge of the right temperature , it remains now to inquire as t o the length of time requisite to yi eld a sufficient A depth of case . t a full orange heat a bracket cup of ordinary d i m e n sions should in two hours he hardened inch deep , and a bracket 6 axle inch diameter in hours would have a case inch deep . F be t t he t t t rom this, it will seen hat speed of pene ra ion it not in exac proport ion to the time of heating .

R e s u l t s o f H a r d e n i ng w i t h o u t R e h e a t i ng

We no w arrive at that part of the process where a most important — i mprovement has been made i . e . the final hardening by quenching in , water . It formerly was cus tomary at the end of t he carbonizing period tn open the pot and fling t he cont ent s headlong into a t ank of cold water; H ere and t here some of the more careful workers t ook each

he article separately , but direct from t pot, and plunged it into water . T hese latter obtained better results , but even they had a great deal of trouble in the way of breakages and want of regular hardness . Find i ng that axles taken singly from t he pot and quenched were better

t o t than t hose quenched in bulk , and that if allowed cool down o

cherry red they were better still , an application of the old rule to harden on a rising heat led to the no w established principle of al low ing the pot and its contents to become quite cold , afterward reheating to cherry red and quenching with water . B y this means we obtain a — case of great hardness wit h a very tough core that is , of course , pro vi d ed a suitable steel is employed . To understand the r eason of this improved method of working we must remember that the exterior of the st eel is now of about per t t at cent carbon , and that s eel of all kinds raised to and main ained

- b the high temperature employed for case hardening will , unless su jected

CHAPTE R VI I

" C A SE - H A R D E NI N G F U R N A C E S A N D TH E I R U SE

No doubt the majority of tool -steel wor kers know that heating hi gh

a r carbon steel in a g s or any open fu nace without packing, oxidizes

r and deca bonizes the steel , making it impossible to obtain a uniform

L s re hardness . ead baths have their di advantages and , in general , a of

- ve ry little value . The method of pack hardening and dipping de

r s c ibed i n this chapter has given the mos t satisfactory results , but

fi r st we must have a furnace s uited to s u ch wor k .

Th e C a s e - h a r d e n i n g F u r n a c e

The e - r ca s hardening fu nac e shown in Fi gs . 7, 8, 9 and 1 0 is one of t he e r - b s t ha d coal furnaces for pack hardening, case hardening, mot

0

F i -h rd e n i n F u rn a c e g . 7 . F ro n t V i e w o f C a s e a g

fir - tling and coloring. It can be built from c ommon brick and e brick .

and is large enou gh for an ordinary shop . If a larger one is required , it will be necessary to use large tile in place of fire -brick f o r the bottom of the oven . A blast is used in connection with this furnac e when starting the fire , but very little is required after the boxes con

i - tain ng the work to be hardened are red hot, but this , of course , de pends upon the draft i n the chimney . A damper should be supplied Th in the pipe behind the furnace to regulate the heat . e following

r r : A - -s t B are the p incipal parts of the fu nace , cast iron buck ays ; ,

M A C E ne 1 9 0 . HI N R Y J u , 7 , CA SE - H AR D E N I N G 43

1 - 5 - - e r 0 4 x 1 % inc h from D , sh et i on 43 inch stay bolts ; , door frame , 5

1 - F d E 1 in ch gas pipe , slott ed ; dampe r ; caps for ues ; , blast pipe , 7é ,

- I J s t G dampe r support H cast iron ; , grate support ; , bla t shu , ; , K t ofi ; and , s ack . P a c k i n g St e e l f o r H a r d e n i n g

r In pac king tool st e el parts for ha dening, do not use raw bone or l e athe r unles s a low -carbon s t eel is t o be t reated and more carbon to

be supplied . The s teel generally used for such tools as reamers ,

- i n shears e tc i s high car bon , and by packing raw bone we shall get , t s rc the c utt ing part s too brit le . U e instead only fine wood cha oal

the s about the size of kernels of corn . Fig. 1 1 is not be t kind of box

- - F i . 8 . C a s e h a rd e ni n rn e e cti o n n B F i 9 g g F u a c . S i A , g .

to u s e for thi s kind of work, as the parts cannot be properly packed

in it , and if very long they cannot be gotten out without bending .

F . i g. 1 2 shows a better form Seal the cover on with asbestos cement

- and put a few inch rods down through holes d r illed in the cover .

A r fter the work has been in the oven a easonable length of time , take

he out one of the rods ; if hot enough , draw t box out , pick the work

out , and dip ; but , if the rod is not hot enough , replace the box , and

afte r half an hour d raw another rod , and rep e at , if nece s sary , until

one i s pulled that shows that the prop e r h e at has been reached .

D ip p i n g W o r k

r s When dipping wo k of thi kind use salt water , and never use clear

r water only, because the pa ts do not chill quickly enough . Whe n dip

a r ping tool in water , do not sta t off sidewise whe n immersing the object, the reason being that one side of the tool will be exposed to 44 N O —H E A T TR E A TM E N T OF S TE E L , 63 cold water and hot water and steam will be c oming up on the other , w side thus causin warped wo rk and uneven harde ning . We all kno , g v t hat hot water come s quickly t o t he top , so pro ide a deep tank of cold salt water and s tart the wor k in straight ; carry it clear down t o t the bottom of the t ank and then raise it slowly up again . Ins ead of leaving it in the water until entirely cold , remove while quite warm The to a tank of fish o i l to draw down and relieve the strain . ream 1 6 r i n as - e rs shown in the cut, Fig . , we e heated a large g pipe , the t same as that indicated in Fig . 1 3 , and were dipped in cold salt wa er T re j ust long e nough to harden the cutting parts . hey were then The moved to a tank of fish oil and left there until cold . illustration

- 9 S e c ti o n i n C D F i . 8 F i g . . , g

T shows them in a sieve as they were drawn from the oil . here are t r fourteen of the reamers ranging in size from 1 to 1 % inch diame e , , T and in length of cutting edges from 5 to 1 2 inches . hese reamers

The hav given remarkable satisfaction . method is much quicker e w than the old way of cooling completely in clear ater , then cleaning up and drawing down the temper , to say nothing of the danger of cracking before this time -consuming and edge -destroying practice is

completed .

The gas -pipe is a very convenient holder for packing work for hard To as it can be rolled over easily to get a uniform heat . make e ni ng, it rivet a thin plug of machine steel in one end , and after the work , T t . is packed plug the other end with asbe stos cemen ake , for exam , s ple some long thin bl des about 1 2 inches long or le s , inch wide , a CA SE - H A R D E NI N G 45

I and A, inch thi ck ; it is a difficult task to harden this class of work re t r and keep i t s t raight . The wri ter has pea edly ha dened such blades and kept them perfectly straight by arranging them as shown i n

4 t c C F i g. 1 . M ake hree small lamps like , long enough to take in from 1 2 to 1 6 blades ; then fasten one clamp on each end and one Th tt i n the c e nter of the blades . e blades should be a li le higher t han the clamp so as to allow the top part of the clamp B to bind

- o n the edges of blades B when tightened down Wi th cap screws A .

- Then pack in the pipe or open top box in wood charcoal , and heat and

- dip sam e as explained about reamers . H igh speed steel blades can be

F 0 e c - i . 1 S ti o n i n E F 8 g . , F i g .

r — t eated this way , but must be b rought to a much higher heat just a s hot as a hard Coal furnace will make them . They s hould be dipped

in hot salt water and removed to the oil bath while a lit tle warm , and let remain there until cold . This treatment will make them very hard

and at the same t ime keep them straight .

U s e o f F u r n a c e f o r C y a n i d e H a r d e nin g T his same furnace is invaluable for hardening wit h cyanide . P ut

e a box containing potassium cyanide in the . furnace and h at it to a r b ight cherry red . P u t the work to be hardened in an open furnace and heat to the same heat as the cyanide . Then place the work in

' - the cyanide and let it remai n for from five to twenty five minutes ,

r e r T k acco ding to the depth d si ed . hen ta e the work out of the box 46 N ~ H E A T TR E A TM E N T F S TE E o . 63 O L — and cool off in some light oil kerosene is the best . Keep a cover o n t he bo x while heating the cyanide ; j ust put it on l oosely and do not

- seal . Cyanide should always be kept in air tight cans , as it will air slake if exposed , and will not melt if it has been exposed for any considerable length of time .

H a r d e n i n g f o r C o l o r s

When hardening for colors , a furnace like the one described is nece s s ary . A very satisfactory method of coloring which at the same ti me

1 1 F o rm o f B o x n o u i t e d ki n F i g . . t S f o r P a c g hardens deep enough for the class of work which is to be colored such ,

as wrenches , crank levers for aut omobiles , nuts , etc . , is as follows : i x 6 M 1 0 parts charred bone , parts wood charcoal , 4 parts charred

The oh leather and 1 part powdered cyanide . charred bone may be

2 ui t a b l e F o rm o f B o x f o r P a c k i n W o rk f o r H a r d e ni n F i g . 1 . S g g tai ne d by placing a f e w boxes of raw bone in t he furnace on Satu r day night ( if the furnace is not run over Sunday ) . If much fire is

- in the fire bo x it should be drawn , as the heat in the furnace will be Th sufficient to char the bone to a dark brown . e charred leather m ay

i 1 3 F g . . Ga s Pi p e u s e d f o r P a c ki n g m Th be obtained in the sa e way . e leather should be black , cri s p and well pulverized , and the four ingr edients should be well mixed to Th gether . e object in charring the bone and leather is to remove all Th grease . e parts to be colored must be well polished and they should

s not be handled with grea y hands . Th ese rules must be observed if

r a nice class of work is d esi ed . CASE - H A R D E N I N G

If the colors obtained are too gaudy , the cyanide may be left out , and if there is still too much color , leave out the charcoal . When pack n d i ng part s to be colored and harde e , they should be be packed in a

1 4 l a m f r o n Thi n W o rk F i g . . C p o L g

F i H ni n Ta n k A rra n e d f o r o ttl i n n d C o l o ri n g . 15 . a rd e g g M g a g

common gas pipe , for the reason t hat when dumping into the water the par ts must not be exposed to the air , and a pipe is much easi e r to handle than any other shape . The open end can be brought down

F i . 16 . R g Hard e ne d e am e rs, ju s t R e m o ve d f ro m 011 B ath c t he t o lose to p of t he water before the parts are liable to come out , bu t n ot s o f t t he with a box , o r just as soon as a box is t ipped a lit le a n parts begin to fall out , d become e xposed to the ai r . —H E A T TR E A TM E T F S E N O. 63 N O T E L

In heating this class of work, heat to a dark cherry red and keep at that heat for about f ou r . o r five hours ; if heated too hot no colors T and will appear . o harden color the work when dumped a tank ,

A - must be arranged as shown in Fig . 1 5. compressed air pipe A must B be connected with the water pipe , and a large cap 0 should be

1 - - inch holes on top and around the sides . A n over drilled full of 74

be e . the flow D should also suppli d Fill tank with water , then turn

F i rk a s e -h a rd e n e d g . 17 . S a m pl e o f W o C fo r C o l o rs on air enough to fill the tank with lively bubbles and dump the work

t he u in center, as shown at B . When the work is all dumped , pull p k the sieve which should be in the tank for the work to fall on , pic . the work out and p l ace it in pails of boiling w ater drawn from the boiler ; let it remain for five minutes and then remove i t to a box o f dry sawdust for half an hour ; remove it from here and dust i t o ff and give it, finally , a coating of oil or lacquer .

C O N TE N TS O F D A TA S H E E T B O O K S 9 — ‘ 1 r e w Th re a . l i N o . . Sc d s w t c t e l o o l s a r T u r ni d S t a s , S t e e T ; T p e ng ; C ha nge Ge " i W l . i two rt h S h a V a n d B ri t i s h A s s o c i a i a r h L a t h e B o ri o . p n g f t e ; n g B a rs a n d T " ’ ’ 'e "l u l l S t a n d a rd . h r e d s B r i s l i e T a . g g p e t T h r e a d ; O i l “k i l C a s i n Ga e s ; F i re H o s e l xi l g g $0 . 1 1 . M i l i n g M a chi n e I n d e ‘' C o n ne c t i o n s ; u m e T h r e a d : W o r m C l a m pi n g D e v i c e s an d P l a ne r J ac k s ' 5 0 1 1 11 T h re a d s m h av “ki nd 1 : ; hi e . i n i n i e i , "T a b l e s f o r M g M a c h n l n l e x l L a S c i o I ' a nd g rew T h re a d s ; C a rr a g e B l t C h a n g e G e a rs i n M i l l i n g S pi ra l s ; A u g

T h re a s e t c . d . f o r s e t t i n g s i n g l i c a d whe n M i l l i r — N o . 2 . Sc ews B o l t s an d N u t s F i l c h i C l a m i n D e i e s S i , C l u t e s , J g p g v c ; n, l i s t e r- h e a d S a re - h e a d H e a d l e s s C o l , q u , , a n d C l a m s P l a n e r a c k s . ' p ; J - - e . i r h e a d a nd H e x a g o n h a d S c re ws ; S t a n d N o . 1 2 . P i e a n d P i e £1 ' p p l t s - n s - o s w d a : S p e C i a N u ; T u t T b l t a nd - { T h re a d s a n d Ga g e s ; C a s t i rpon i t t i ni

T h u m b S c re w s a r N t s A . L . W ". rs : d : e s u B ro nz e F i t t i n g s ; P i p e F l a n e s ; P ' ‘ g A . ll ? S t a n d a rd S c r e ws a n d N u rs ; M a c h i n e B e nd s ; P i p e ( l a m p s a n d H a n g e r s ; D i m S c r e w H e a d s : W o o d S c re ws : T a D ri l l s ; p s i o n s o f P i e f o r V a r o us Se r i ce s c “ p i v . e t o c s - l e L k N u t ; E y e b o t s , . ‘ o . 1 B i l e r — N 3 . o s mi d C hi m n ew i e n d M a c h i n e . N o . 3 . T a ps a n d D m H a . “ S pa c i n g a n d B ra c i n g f o r B o i l e r s ; S t ren g Ta r m a c h i n e S c re w T a p s ; T a e r g , p o f B o i l e r J o i n t s ; R i ve t i n g ; B o i l e r S e t t i s D i . y e s : H o b : S c re w M ac h i n e ' T a p s ; St ra i g h t a n d T a p e r R n l er T a p s ; ' - o - S t a y b o l t , Vva s h u t . a n d P a t c h b o l t T a p s ; n u s o b o l i r e T a p a n d H s ; S d S q u a . R o u n d s a l e i n d S pr i n g S c r e w T h re a d i n g C l a s s i fic a t i o n s : R a i l S c 3 S wi t c h e s a nd . i 1 0 . 4 . R ea m e rs , S ke t s . D r l l s a n d ‘ ‘ — F o rc e : I n c : i s o f T ra i s , i t r . a ri e J i l l ng C u t e s H u . R e a m r s : S he l l B ra k e R o d s . e t c . e a rn e r s an d A rb o rs ; P i p e R e d i r i e rs ; T ap e r

N o . 1 5. St e m a m m e e n . a nd C. . s i a i R e a r s ; B r ) S a i r pc , ' ‘ " ' “ » r n o T a e r S o c k e t s a n d i t ~u m u ra t e d S t e a m S l m l\ r e a zr p ‘ i e l e s E n g i n e D e s i g n ; o l u m s . D ri i V r Ga g. M l i n g C u t t r : ~ S n fli i n B o x e s S wi n g A l l ": s f o r M i l l i n g T e e t h i n E n d i g ; S e t t i n g ’ e ' ‘ ~ a ? V a l v i i e a i s : C o n d e n m t . l n A n g u C u t u r . e ' a l a fl s a w e i - i i : D H r e p e r o f ( 1 s pu r a r n g . i i m e t ra l an d l A n t . m a i l e E n i ne C ra l i f P i xe r Sp u r G e a rs : g

i i Tl i s d u n r . a m e r . i L f e t O t o g a p N o . - 1 f i l e : f l i n g M i l l Gea r i n g S t r e n g t h c f e r G e a r s : H o r s e p o n T ra n s m i t t e d h v ‘t l u l ‘ ‘ - t i r n t r i i o i L s : n a n d R a d e P m i n s , D e s g n o f e - Sp u a rs : W e i g h . o f C a s t i ro n Ge a r s ; '

r i Ge a r i n . E p u c g i n g B e g u l a r P o l y g o n “ l re s Sm n c e e e t . R 6 . B v , Spi ral an d W o rm Ge e g ‘ , “ i ng . z i u l e s a n F o rm u l a s f o r B e v e l 7 N o . 1 . M e c h an i c s an . e a r s S t r n t h o f cl o v e ] Ge a r s D e s i n ’ G ; e g : g t e ri ~ — a l s . VVo r k ; B u e rg v e u d o f B o l Ge a r s ; R bs ; a n f o r i ' ‘ F o rc e : C e n t e r f Gr m r p i ra l Ge a r i n ; T a b i c s I l a c i l i t a t i n : C a l c u i g t i o n ; P e n d u l u m : F a l l -i z; D i t o “ ‘ l a t i o n s ; a i nm f o r C u t e r s f r S pi ra l s g ‘ o f M a t e r i a l : S tr e n g ( Tl R u l e s a n d F o r m ul a s f o r Wo rm “ R a t i o Of (p u t s f a n ' I n ‘ I L d A 9 1 C . g , J ri i ck C y l n d e rs , e t c . i N o 7 . Su t i ng , K ey s an d K eyway s . ’ l i o rs e p o vée r o f S hm ti ng ; D i a g ra m s a n d ‘ f l a b l e s f o r t h e S t re e g t l . c S ha f t i n g ; “l F r c i n D i i S r i n k i n i d . . u n n i o g , r v n g . h g n g ’ F i t s EVo u l r i i ff K e s n i t L , : y

i l l S t a nd a rd K e y s ; Gr K e y s : ~ xs ; D u p l ex K i g 8. B ri n s o u l n s l u t ea g , C p , C c h e s , r a: 3 i - ' C . C h a n an d H o o k s . l . i l o w B l o c k s

’ l e u - b u b b z d B ea r i n g s ; B a l l a n d R o l l e r fl ( i r ' ‘m l g s ; C l a m C o u p l i n g s : P l a t m l m s ‘ p g ; a o l i s o h ' l l ng e C u p n g , T o t h C l u t c e s C ra b ‘ ‘ a - p e s L l i n g s ; C o n e C l u t c h U i z w rs a l C r a n e C ha i n ; F r i c t i o n ; o . s o n H e u k ; D r um Sc re s . i C h a n .

n o . 9 . Spri n e u Sl i d e s an d M a ch i n e p a r ka —F o r m a s a n d T a b l e s f o r S r i n ‘ p g ( m v i i z a t i o n s z M a c hi n e S l i d e s ; M a c hi n e H a n dl e s a nd. L e v e rs ; C o l l a r s ; H a n d ” ‘ 5 P i n s n d C o t t e rs T u r n - b u c kl e s ; a ; ,

N o . r ri M ot o D f . Sp e ed s an d F e e d s , h an ri — w e C g e Ge a n g , an d I J i g B ar s P o r

‘ ‘ ’ l H j u i f: f o r NI a c h i n e T 0 0 18 ; C u t t i n g “ ’ S e a e e s f u r p e d . n d l d r V e no n a n d H i g h m o ‘ - e s d S. e e l : S t i t w M a t hi r S e e d s a n d F e e d r - s ; i l e a t T e a t m e nt n. i g h s p e e d

‘ M ac smi m r t he m n h h i , o t ; mec an cal 0 9 S i es i s u b s he i n h er , p li d t ree ' the E rzgzm en ng Ed i

- “ 4 9 55 L fa v e t t e Str e e t .