Relationships Between the Phase Transformation Kinetics, Texture Evolution, and Microstructure Development in a 304L Sta
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METASTABLE austenitic steels exhibit martensitic phase transformation, which involves the transformation of the parent austenite (c) phase to bcc/bct (a¢) and hcp (e) martensite phases under applied strains, cooling, or both.[1–4] The in situ formation of the harder a¢ martensite phase during deformation increases ductility while maintaining the high strength of the material by not only forming effective barriers to dislocation motions stronger than dislocation tangles, but also deforming with the austenite matrix,[5] thus bringing forth the transformation-induced plasticity (TRIP) effect. Due to their exceptional mechanical properties, TRIP and TRIP-assisted steels have garnered significant interest. Consequently, TRIP behavior has been studied extensively and is fairly well understood under monotonic uniaxial deformation conditions (tension or compression) at a wide range of temperature;[6–11] strain rates;[8,12,13]; and grain sizes.[14–17] Furthermore, fundamental studies of texture-transformation relationERCAN CAKMAK, Postdoctoral Research Associate, is with the Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6064. HAHN CHOO, Associate Professor, is with the Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996. Contact e-mail: [email protected] JUN-YUN KANG, Research Scientist, is with the Ferrous Alloys Group, Korea Institute of Materials Science, 797 Changwondaero, Changwon 642-831, South Korea. YANG REN, Instrument Scientist, is with the X-ray Science Division, Argonne National Laboratory, Argonne, IL 60439. Manuscript submitted August 26, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
ship[3,6,18] and distribution of lattice strains between the constituent phases[19–22] have been conducted for a better understanding of the micro-mechanics of the TRIP phenomenon. During cold-forming operations, conventional steels may require additional processes such as inter-pass annealing to achieve the final desired form without premature failure. However, the TRIP phenomenon can help achieve higher cold deformation levels without the need of additional treatments and hence plays an important role in determining material formability. Therefore, understanding the factors affecting transformation kinetics in more realistic forming operations is of significant technical importance. Specifically, the loading-path dependency of phase transformations is one of the most important fundamental issues and requires further investigation. According to Patel and Cohen,[4] martensitic transformation can be enhanced or suppressed by the stress imposed in relation to the nature of the work done by the stress during the transformation. In this context, shear and normal tensile components were reported to favor the transformation, whereas the normal compressive stress would act against it. Kulin et al.[23] have also pointed out the importance of the sign of normal stresses on the phase transformation behavior. In their research using bent steel allo
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