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Thermal stabilization of austenite iron-carbon-nickel alloys
376
ACTA
METALLURGICA,
VOL.
1, 1953
lization effect that occurred during cooling within a certain temperature range above the M,. Thus, in a steel containing 1.0 per cent C and 5 per cent Ni, this temperature range was found to be between 310” and 405°C (590” and 760°F). They do not, however, explain the two exceptions where no such effect occurred. We found that varying the cooling rate from 1400’ to 2200” to 5000°F per second in the temperature range 1300” to 900°F had no significant effect on the temperature of M, in the two steels studied. Although not calculated, the three quenching media used had widely different cooling rates at lower temperatures. If the M, of all steels were indeed sensitive to a stabilization effect at some temperature above the M, it would seem that widely different cooling rates would have an effect upon the M,. That B. WELEER, R. WEBELER, and F. TRUMBORE the M, of some steels are not so affected is shown Lewis Flight Propulsion Laboratory by the data of Messrs. Morgan and Ko as well as National Advisory Committee for Aeronautics our own. Cleveland, Ohio The authors also comment on the fact that their References data show that the grain size had no effect upon the BOUDOUARD, 0. Comptes Rendus, 134 (1902) 1431. progress of the martensite transformation. This i: HUME-ROTHERY,W. and ROWELL, S. W. J, Inst. finding is contrary to ours as we find that not only Metals, 38 (1927) 137. 3. GRUBE, G. and SCHIEDT,E. Z. anorg. Chem., 194 do coarser austenite grains result in a decrease in the (1934) 190. rate of the austenite + martensite reaction in an K. G:, HOLLER,V. A., and TROSHKINA, V. A. 4. HOMIAKOV, Moscow University, Reports, 6 (1950) 55. appreciable temperature range below the M,, but 5. BUCK,T. M., JR., WALLACE,W. E., and RULON,R. M. that it also raises the M, itself. As an indication of J. Amer. Chem. Sot., 74 (1952) 136. F. A., WALLACE,W. E., and CRAIG, R. S. 6. TRUMBORE, the magnitude of these changes, the rate of formation J. Amer. Chem. Sot., 74 (1952) 132. of martensite in one of the steels was approximately WELBER,B. J. Appl. Phys., 23 (1952) 876. C. B. Ph.D. Thesis, University of Yi SATTERTHWAITE, 0.7 per cent per degree F drop in temperature Pittsburg (1950). below the M, when the austenite grain size was 9. See for example HILLEBRANDand LUNDELL,Applied Inorganic Analysis (John Wiley and Sons, 1929), p. 204. ASTM No. 5 and 0.2 per cent per degree F drop in 10. Specific heats of Mg and Cd taken from U.S. Bur. Mines temperature ,when the austenite grain size was Bulletin II 476 (U.S. Government Printing Office, 1949). ASTM No. 2. The M, corresponding to these two Thermal Stabilization of Austenite Irongrain sizes was 590” and 613”F, respectively. It was Carbon-Nickel Alloys* established that these differences were actually We have read, with considerable interest, the associated with the austenite grain size and the temperatures from which the various samples paper on thermal stabilization of austenite in ironwere quenched. carbonnickel alloys, by E. R. Morgan and T. Ko It must be emphasized that our findings are conthat appeared in the January issue of Acta Metallurcerned only with the steels noted. A formal paper gicu. It is interesting to compare some of their embodying the results of our studies is now in the conclusions with data obtained at the National process of preparation. In view of the many disaBureau of Standards in a study of the factors greements among various investigators as to the affecting the M, in two SAE 1050 steels. effects of certain variables on the martensite reMessrs. Morgan and Ko note that, except for action, it must be concluded that our understanding two steels (1.0% C, 10% Ni, and 1.3ye C, 5% Ni), of the natural laws governing this phenomenon is the M, was dependent upon the quenching medium far from complete. used, an indication that the rate of cooling through the austenitic range must have an effect upon the SAMUEL J. ROSENBERG martensitic transformation. They ascribe this deNational Bureau of Standards pression in M, with slower rates of cooling to a stabiU.S. Department of Commerce Washington, D.C. *Received February 23, 1953.
location of the smaller peak on the other hand varies with rate in very much the fashion one would expect if it were determined by a rate process. The total heat of transformation, represented by the area between the experimental curve and the curve to be expected in the absence of a transformation (indicated by the dashed line), is obtained as 6.5 cal/gm or 0.30 Kcal/gm atom, which is the average obtained from the separate determinations shown in Figures 1 and 2. This is to be compared with the value of 0.24 Kcal/gm atom for MgCdo obtained by Homiakov, Holler, and Troshkina for the case of MgCd3 which undergoes second order transformation at 78°C. We are indebted to Dr. G. Groetzinger and Dr. P. Schwed for helpful discussions.
ACTA
METALLURGICA,
VOL.
1, 1953
lization effect that occurred during cooling within a certain temperature range above the M,. Thus, in a steel containing 1.0 per cent C and 5 per cent Ni, this temperature range was found to be between 310” and 405°C (590” and 760°F). They do not, however, explain the two exceptions where no such effect occurred. We found that varying the cooling rate from 1400’ to 2200” to 5000°F per second in the temperature range 1300” to 900°F had no significant effect on the temperature of M, in the two steels studied. Although not calculated, the three quenching media used had widely different cooling rates at lower temperatures. If the M, of all steels were indeed sensitive to a stabilization effect at some temperature above the M, it would seem that widely different cooling rates would have an effect upon the M,. That B. WELEER, R. WEBELER, and F. TRUMBORE the M, of some steels are not so affected is shown Lewis Flight Propulsion Laboratory by the data of Messrs. Morgan and Ko as well as National Advisory Committee for Aeronautics our own. Cleveland, Ohio The authors also comment on the fact that their References data show that the grain size had no effect upon the BOUDOUARD, 0. Comptes Rendus, 134 (1902) 1431. progress of the martensite transformation. This i: HUME-ROTHERY,W. and ROWELL, S. W. J, Inst. finding is contrary to ours as we find that not only Metals, 38 (1927) 137. 3. GRUBE, G. and SCHIEDT,E. Z. anorg. Chem., 194 do coarser austenite grains result in a decrease in the (1934) 190. rate of the austenite + martensite reaction in an K. G:, HOLLER,V. A., and TROSHKINA, V. A. 4. HOMIAKOV, Moscow University, Reports, 6 (1950) 55. appreciable temperature range below the M,, but 5. BUCK,T. M., JR., WALLACE,W. E., and RULON,R. M. that it also raises the M, itself. As an indication of J. Amer. Chem. Sot., 74 (1952) 136. F. A., WALLACE,W. E., and CRAIG, R. S. 6. TRUMBORE, the magnitude of these changes, the rate of formation J. Amer. Chem. Sot., 74 (1952) 132. of martensite in one of the steels was approximately WELBER,B. J. Appl. Phys., 23 (1952) 876. C. B. Ph.D. Thesis, University of Yi SATTERTHWAITE, 0.7 per cent per degree F drop in temperature Pittsburg (1950). below the M, when the austenite grain size was 9. See for example HILLEBRANDand LUNDELL,Applied Inorganic Analysis (John Wiley and Sons, 1929), p. 204. ASTM No. 5 and 0.2 per cent per degree F drop in 10. Specific heats of Mg and Cd taken from U.S. Bur. Mines temperature ,when the austenite grain size was Bulletin II 476 (U.S. Government Printing Office, 1949). ASTM No. 2. The M, corresponding to these two Thermal Stabilization of Austenite Irongrain sizes was 590” and 613”F, respectively. It was Carbon-Nickel Alloys* established that these differences were actually We have read, with considerable interest, the associated with the austenite grain size and the temperatures from which the various samples paper on thermal stabilization of austenite in ironwere quenched. carbonnickel alloys, by E. R. Morgan and T. Ko It must be emphasized that our findings are conthat appeared in the January issue of Acta Metallurcerned only with the steels noted. A formal paper gicu. It is interesting to compare some of their embodying the results of our studies is now in the conclusions with data obtained at the National process of preparation. In view of the many disaBureau of Standards in a study of the factors greements among various investigators as to the affecting the M, in two SAE 1050 steels. effects of certain variables on the martensite reMessrs. Morgan and Ko note that, except for action, it must be concluded that our understanding two steels (1.0% C, 10% Ni, and 1.3ye C, 5% Ni), of the natural laws governing this phenomenon is the M, was dependent upon the quenching medium far from complete. used, an indication that the rate of cooling through the austenitic range must have an effect upon the SAMUEL J. ROSENBERG martensitic transformation. They ascribe this deNational Bureau of Standards pression in M, with slower rates of cooling to a stabiU.S. Department of Commerce Washington, D.C. *Received February 23, 1953.
location of the smaller peak on the other hand varies with rate in very much the fashion one would expect if it were determined by a rate process. The total heat of transformation, represented by the area between the experimental curve and the curve to be expected in the absence of a transformation (indicated by the dashed line), is obtained as 6.5 cal/gm or 0.30 Kcal/gm atom, which is the average obtained from the separate determinations shown in Figures 1 and 2. This is to be compared with the value of 0.24 Kcal/gm atom for MgCdo obtained by Homiakov, Holler, and Troshkina for the case of MgCd3 which undergoes second order transformation at 78°C. We are indebted to Dr. G. Groetzinger and Dr. P. Schwed for helpful discussions.