THS HEAT TREATMENT AND HARDENING 0F GREY IRON CASTiNOé THESIS FOR DEGREE OF M. B. ZENAS EUGENE COLBY 1928 "(H 5.835" _ _ *A'._._-_‘_-— HEAT TREATMENT AND HARDENING OF GREY IRON CASTINGS Thesis for Degree of M E Z nas Eugene Colby w m“_o- ‘awr- *4. THngg __ ofiir_~‘m. p...” -v-_ ..v. . .— .. HEAT TREATMENT AICD HARDENING OF GREY IRON CASTIKGS The object of this thesis is not intended to be a metallurgical research, but has for its sole object the advancement of the mechanical phase of and results which may be obtained through the heat treatment of grey iron castings. The accompanying chemical and metallurgical date being used only as a means to this end. At the time the writer started this research, but very little data seemed to be available, in fact, I was unable to obtain any outside info mation, but of late a considerable amount of metallurgical research work has been done but still leaving the subject far from a thorough survey. In fact, present foundry practice has not as yet reached the stage where grey iron foundries producing a variety of work can maintain absolute control and which is absolutely essential for uniform results. Late in 1923, the writer was confronted with the problem of producing a grade of cast iron rollers which would be much higher in hardness than would be possible to machine with the result that a large number of tests were run to determine a prOper analysis and method to be pursued to properly harden yet toughen these rollers. Various methods were tried for quenching and drawirg. These rollers were quenched in a salt orine solution also in oil and in water with a final result that the production method adopted was that of partially quenchir g in oil and finishing in water. The oil was kept at a constant temperature by mea:.s of a circulating system which circulated the oil through coolir g vats and back to the tan’n again holding the oil at between 70 and 90 degrees F. our reason for finish quenching in water was not because of any definite reaction to the work beirg heat treated but because the one minute in the oil bath was sufficient to cool the work below the critical temperature and thus making it easier to maintain a satisfactorily low oil temperature without a too elaborate oil cooling system. These rollers were heated in an electric furnace to a temperature of lbOO degrees F. and left in the furnace a sufficient length of time to produce a uniform temperature throughout the entire structure. These rollers were then with— ”2'. In drawing, care mus be taken to see that the work is not left at this tezn perature a length of time sufficient to bring the work up to 1300 degrees as by so doing, the work will be, not only softened, but actually weakened. The result desired is simply to remove the internal stress produced by quenching. A better method to strengthen the work after treating is to heat the work slowly but thoroughly to a much lower temperature, preferably between 700 degrees and 800 degrees F. and allowed to cool slowly. We adopted the first method after considerable trials to determine the exact time to be left in the annealing furnace, simply as an aid to production and would not recommend this as a safe method where the work is not of a uniform size or character. To show the effect of drawing at 1300 degrees, seven samples of exactly the same analysis were heat treated and drawn and curves plotted as shown on sheet marked Sample M~ll~H. It will be noted from sheets 2~l6~H and 2-20-0, also the microphotographic views of 2-1'0-3, 2-l5~H, 2~l6~H and 2—i7—H that the physical change resulting from heat treatment is the raising of the combined carbon and the lowering of the graphitic carbon, also that the best hardening or quenching temperature for all analysis seems to be around 1600 degrees F. Also that the degree of hardness is also influenced by the amount of silicon. The higher degrees of hardness are obtained with low silicon. It was found that the degree of hardness as well as toughness varied with the manganese and with the silico on, our best result was obtained by running our silicon about 1.657 to 1.70: with the manganese about .607 to .707. This after hardening and drawing with this analysis produced a roller which was stronger against shock than was the original casting. However, before drawing, the roller would be quite brittle and would not stand the shock that the original roller before heat treatment would stand. It was also found that we could not manna so hwfih 9 Andrea of hardness with the silicon about 2%- -3- The result obtained from these eXperiments convinced the writer that if the analysis of our metal could be held absolutely uniform and our quenching and drawing conditions absolutely uniform that we could produce a very uniform and satisfactory product and to determine, if possible, just what actually took place during these hardening and annealing processes, the writer ran a series of approximately 130 samples of standard test bars of 1/2 square inch cross section of area of which analysis was taken before hardening and analysis of the carbon contents taken after hardening also the tensile strength was determined as well as the degree of hardness and these results were plotted in a series of curves showing a hardness compared with the tensile strength. None of these samples, however, were annealed to show the effect on these test bars with the exception of sample h—ll—H, as our previous test in production had convinced the writer that the castings could be brought back to their original degree of hardness and that the strength could even be increased by a heat treatment process. However, from the laboratory eXperiments, it is very evident that unless all conditions are kept absolutely uniform that very erratic results will be obtained. No heat treating was recorded at a lower than 1300 degrees F. as it was found that there was very little effect on the cast iron below this temperature, at least, as far as its hardening qualities were concerned. The time for heating and quenching depends entirely upon the size and shape of the specimen, but in all cases the work should be left in the furnace sufficiently long to insure a uniform temperature throughout. MECHANICAL APPLICATION We have found through investigation, that it is frequently more economical when requiring large size drill bushings for jig work to use cast iron bushings cored nearly to size, machine nearly to size allowing grinding stock, heat to 1600 degrees F. quench in oil and finish grinding. Tool bits can also be made from low silicon hardened cast iron which will be slightly better than carbon steel but its use for this purpose is not economical or justifiable except in special cases of emergency. The writer has used hardened cast iron tool bits simply to determine what actually could be done. (I .. N T ~ ' i -- VA? :2, wii '2‘ a, - . ' _ . 1 n. A. In. 1 1-1 .5 1....-5‘, .L. final? ?:1...~.T.. air ":4 , L' a ., -Ar.o- - I'H'f — n " ' “AI-g l 7 .. -, . ‘. ,er - - . I ._ 4 - (.I.1 ‘_' ,AADZI‘ " ‘“ ‘V ‘ ‘ ' * L.-1w ;. ,1 a -— - - - - .I‘Jj" es execs s— - . — .rie .u-h V . I -v. ’ LIAJUAE‘T-{E “ ‘ ' " o t 3.5 'x‘: ~: ' T 7 7 7 + .I. I". ‘ 1 1 1 1 11 L 11 l ‘ — “ .r/ r 7 \1\‘ I “,11,__.7 ’ , .1 . 11,____.x.’__r‘7. ii‘ .,.——— “‘wh,_ Wicnnsow ANALYSIS Arranggrlr_rnsarunwr ,Treatmeqt , Oraphitic Combined, Carbon CarDOn I c? ,1 .1121e31 . 1.1 .52% g I I I I 7“.- --—-\ I ,1/ g iwmg” I shat .mfl F) ,.1 7,1eoo 1 I 1.99% 1.16; .1 . 13309 ‘ ”c‘“2.11t ” ”1.0u; (,3; I P, I 1 1 I f: I I ‘9‘? 7 1 7* 1 1 7 1 k 1 » *P—— v 1 r 1 1 1.;i '15 ‘ I i I I I a I , I : 1 _1 1.1 1 ~~ ~ — . —I~ 1;, -~—:— ,1; L 'I . - : . ,T' {N k i E I g I I ! E‘Eg a -— ~- *1~’»~*-—"»-~“r—~r-¢n~ t I l I a. .. .1 . __1f1111__111.11_u1 -1.__1I_1_.1_1_1_ '_ I eI : I I ‘ ‘ I I I I u+ ‘ g. I I T ' I ,4] 1 1 1 .1l ‘11 1_ -uL _ _H 1 1____L_L __-_ “iii I §I I I I . f ! I ’ Ail l , , 7J4 #§AMPLE~ z- 20 o amen-17H 2:000 .7 e 8 (o 113,, /4 /6_ 18 21121 aurora 10131134 HEnT ThEanlt r I ; ‘ I ‘1 CKilITnL AnALYSIs an smsmmscwmmnm . GhAiHITIC “—-; 3. TOTAL 21-1l 3. 2. "3' F’0 g‘ql :13 . n SILICON-» -~»~-~a I I ‘D SULrFUR ............ I . , - I ‘ IHJSFHURUS~-~—-—>- '.23% 7' "’ I ' ’ " 7" ' II“ , I ~ I Mnucnwrss_-1111-n H\NU7 H\~b¢ “1 (QUENOHED IN OIL AT 73 F.-NOT m A ‘2; ATM: ‘ . -1 HEAT TE LVN ) RA 3 NOT Ed Hi3 IN OIL A N U l 7,7“ I \~(, 4 NT REST TREATMJ a. dnfifiLE ~2z/0-C) STRENGTH Jar/a" _LDQO 4 (a e {oL/fl I6 /a 20 22 a 21. 23 .30 .32 341 I I l ! I Icaruicwu anLYs s T I 7* - conaiwso~enssow . cansHITic ‘ -—+---13. ‘ I l ,1ITOT‘ STRENGTH ~2'/5~H .g .4 SAXPL ., 1-31.711'132— z-/ 7—H STRENGTH #540 2000 4___ 6 SHEEIICAB JQIBINEU iRnPHITIC TOTAL ’7' SILICON; EHO \I \ v 14ml: dAfl Ln I If */ sanusiH ' " 7 l- 1‘ Lu I”? 15.0 4&1er AU 1 9 50 Jfii_J_AJ_ ..2Ep : "§:r'? 1' '5’.» '1‘ 't ‘ w . Unetched — 18000 Magnification - X100 Constituents - rs Etched — Untreated, Magnification — x400 Constituents - Graphite' Pearlite, Csmentite r? ,._V , H ” G ' a}? A.» isoo° agn ‘ication a7"' Oust ‘ehta -,§ velart” ‘iteyc-a Unetched-Untreated n o Magnification ~ ch0 Constit“ents — Graphite Unetohed - Untreated Magnification - X100 Constituents - Graphite V 7 "7' ‘f: ' ' V *‘T_"‘;_‘._-”— Unetc‘ned - 17oo°1~x Etched — Untreated Eton-d 41’] Magnification - X100 Magnification - X400 ' Magnifiaajt Constituents — Graphite Constituents - Graphite, Conqtit it Pearlite, Ferrite_ 7'33‘.»"" 7—-“ i,,LT z” t'm~‘-_~3 ‘ ' ‘ gm “-7“ -, _ ' ” Unetohed - 1700° F. T‘ 3.39 Ti 1 Magnification - XlOO;‘ T j. Constituents - Graphitefijxfi EOOf‘A U SE Of‘ii‘r’ \HIHIWIWHIMIIH 8 6 0 3 5 rm 0 3 o 3 9 2 4| 3 I “ Mll H S" .||||| “ll u