Martensite Formation in Partially and Fully Austenitic Plain Carbon Steels
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INTRODUCTION
IN steels, the transformation from austenite to martensite usually takes place due to a decreasing temperature rather than as a function of time, which is referred to as an athermal transformation.[1–6] It is well known that the mechanism of growth is displacive, but how the phase nucleates and which material properties determine the amount of martensite formed is even today not completely understood despite all the efforts to study this transformation in various systems. Besides the fundamental interest in the nature of the transformation, a better understanding of the material properties that influence the progress of the martensitic transformation can also be important in the development of new advanced high-strength steels (e.g., dualphase steels), because the mechanical properties are, to a large degree, dictated by both the volume fraction and distribution of martensite in the microstructure. In the present study, dilatometry measurements have been conducted on three plain carbon steels with different carbon content to determine the progress of the austenite to martensite transformation. The primary aim of this investigation is to get a better understanding of the differences in the kinetics of martensite formation in lean-Si steels with a bainitic/austenitic or ferritic/austenitic microstructure as compared to a fully S.M.C. VAN BOHEMEN, Researcher, formerly with the Department of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands, is with Corus Research Development & Technology, 1970 CA IJmuiden, The Netherlands. Contact e-mail: [email protected] J. SIETSMA, Associate Professor, is with the Department of Materials Science and Engineering, Delft University of Technology. Manuscript submitted July 15, 2008. Article published online February 21, 2009 METALLURGICAL AND MATERIALS TRANSACTIONS A
austenitic microstructure. Due to the low Si content (
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