Commentary by: Transformation of austenite at constant subcritical temperatures
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Commentary by
HAROLD W. PAXTON* Professor, Carnegie-Mellon University
Series Associate Editor * Professor Pax,on holds the Bachelor of Science and Master of Science degrees from the University of Manchester and the Doctor of Philosophy in Metallurgy from the University of Birmingham. Since 1953 he has been associated with the metallurgical faculty of Carnegie-Mellon University. His research interest lies in the areas of phase transformation. plastic deformation, and corrosion of metals. He presently is collaborating with E. C. Bain in a revision of Bain's "Functions of Alloying Elements in Steel."
METALLURGICAL TRANSACTIONS
VOLUME 1,DECEMBER 1970-3479
Metallurgical Classics
Isothermal Transformation of Austenite and the Hardening of Steel
HE hardening of steel, and before that, iron, has fascinated men for millenia; and, with true scientific curiosity, they have sought .lithe reasons for the unusual changes in properties which can be obtained by proper heat treatment simultaneously with empirical developments in practice. Ingenious experiments contributed various pieces of the puzzle, and we shall shortly review these. However, it is fair to say that the transformations which occur in steel on continuous cooling of austenite were first clearly understood following the work of Davenport and Bain reported in this 1930 paper. All of the concepts were not absolutely correct, notably the time dependence of martensite formation, but this was not essential to the central theme. The value of the work is perhaps best illustrated by the fact that when sufficient data had been assembled using the concepts of the paper, it was then possible, following the teaching of Grossman ~1', to predict the transformations in almost any steel cooled in a variety of fashions by the simple manipulation of a few charts. Understanding the derivation of these charts is not even necessary.
T
History It is ahvays difficult in a review such as this to decide when "history begins!" Since an arbitrary choice is unavoidable, we shall select the paper of Tchernoff, read before the Imperial Russian Technical Society in 1868, and published in English in 1880 '2', in which he showed that steel cannot be hardened unless it is heated above a temperature a. As Mehl '~), quoting Benedicks '4) points out, this had been presaged a century before in Sweden by Angerstein, but unfortunately Angerstein published in a rather obscure journal and his work did not become widely known. The work of Roberts-Austen ''~) and Osmond '6' made it possible for Roozeboom '~' to publish an equilibrium diagram for the iron-carbon
3480-VOLUME
I,DECEMBER
1970
METALLURGICAL TRANSACTIONS
Metallurgical Classics Isothermal Transformation of Austenite and the Hardening of Steel
system in 1900. The effects of heating and cooling rates on transformation temperatures were recognized and the terminology A r and Ac was generally utilized. It should perhaps be mentioned that the heating and cooling rates which were accurately measurable at this poi
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