The Incomplete transformation phenomenon in Fe-C-Mo alloys
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I.
INTRODUCTION
IN the
preceding paper, Shiflet and Aaronson tll have shown, that the thickening kinetics of grain boundary allotriomorphs incorporating Mo2C carbides exhibit complex and variegated growth kinetics behavior in a number of Fe-C-Mo alloys reacted at temperatures from near that of the bay, Tb, tO approximately 50 ~ above this temperature. They also found no evidence for "incomplete transformation" or stasis in the bainite reaction during studies of the overall transformation kinetics performed simultaneously. During the present investigation, these studies were extended below To in many of these alloys. As our predecessors had found, Ill the extreme morphological degeneracy of the ferritic component of bainite below Tb severely restricted growth kinetics measurements in this temperature range. Emphasis was therefore placed upon quantitative optical metallographic studies of overall reaction kinetics, conducted for the
W.T. REYNOLDS, Jr., formerly Graduate Student, Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University, is Assistant Professor, Department of Materials Engineering, Virginia Polytechnic Institute, Blacksburg, VA 24061-0237. F.Z. LI, Visiting Professor, Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University, is Professor, Department of Mechanical Engineering, Shandong Polytechnical University, Jinan, Shandong, People's Republic of China. C.K. SHUI, Visiting Professor, Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University, is Professor, Department of Metallurgy and Materials Engineering, Chongqing University, Chongqing, Sichuan, People's Republic of China. H.I. AARONSON, R.F. Mehl Professor, is with the Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University, Pittsburgh, PA 15213-3890. This paper is based on a presentation made in the symposium "International Conference on Bainite" presented at the 1988 World Materials Congress in Chicago, IL, on September 26 and 27, 1988, under the auspices of the ASM INTERNATIONAL Phase Transformations Committee and the TMS Ferrous Metallurgy Committee. METALLURGICALTRANSACTIONSA
purpose of characterizing the incomplete transformation phenomenon as a function of temperature, percent C, and percent Mo. Although such characterizations have been previously conducted on other Fe-C-X systems using physical properties measurements, [2-nl this is the first such undertaking utilizing the more reliable tl21 technique of quantitative metallography. Complementary TEM studies were conducted of the ferrite and the carbide microstructures associated with critical aspects of stasis. Inasmuch as a historical survey of the stasis phenomenon was presented as an introduction to Reference 1, summarization of background will be confined here to recent work bearing directly upon the main objectives of the present investigation. The presence of stasis in a variety of alloy steels has led to the belief that it is a general feature of the
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