Continuous cooling deformation testing of steels
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I.
INTRODUCTION
T O obtain the desired mechanical properties, i.e., microstructure, in a given steel by heat treatment or thermomechanical processing (TMP), the critical transformation temperatures must be identified, tl] One of these temperatures is the start of the austenite-to-ferrite transformation (Ar3). The Ar3 has been measured by thermal analysis, dilatometry, microstructural changes, and texture intensity measurements, t21 With respect to thermomechanical processing, the drawback of all of these tests is that the microstructure whose transformation characteristics are being determined bears little relation to the microstructure of interest, i.e., the microstructure immediately exiting the final deformation pass. Typical changes in the microstructure that can occur in a roiling schedule include the austenite grain size, degree of recrystallization, and level of strain accumulation. These will all affect the transformation behavior significantly. A torsional physical simulation technique to generate the three critical rolling temperatures, i.e., the Tnr, Ar3, and Arl, was developed by Boratto et al. t31 to examine the transformation characteristics of an austenite microstructure produced during industrial hot rolling. However, the measured Ar3 and Ar~ temperatures are only valid for a schedule involving deformation stages through the austenite transformation temperature into the two-phase region. The majority of industrial schedules finish hot deformation above the Ar3. To address this problem, a A. ZAREI HANZAKI, Ph.D. Student, and S. YUE, Assistant Professor, are with the Department of Mining and Metallurgical Engineering, McGill University, Montreal, PQ, H3A-2A7 Canada. R. PANDI, Ph.D. Student, formerly with the Department of Mining and Metallurgical Engineering, McGill University, is with the Department of Metals and Materials Engineering, The University of British Columbia, Vancouver, BC V6T-124. P.D. HODGSON, Principal Research Engineer, is with Secondary Steel Processing, BHP Research, Victoria, Australia 3170. Manuscript submitted February 22, 1993. METALLURGICAL TRANSACTIONS A
continuous cooling, continuous deformation test was developed and is the subject of this article. It should be noted that the continuous cooling deformation test is intended to be used immediately after executing a physical simulation of the desired rolling schedule so that the relevant microstructure can then be evaluated. Thus, in the ideal case, torsion testing, for example, would be used to generate the specific as-hotrolled austenite microstructure, and the transformation behavior of this structure would then be evaluated by continuous cooling torsion testing. In the present work, in order to clearly illustrate the principles of the test and to highlight the effects of chemical composition rather than microstructural condition, the steels were simply reheated. These microstructures were then subjected to continuous cooling compression testing in order to examine their transformation behavior.
II.
EXPERIMENTAL
PROCED
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