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Grain Refinement and Mechanical Properties of a Metastable Austenitic Fe-Cr-Ni-Mn Alloy

A lot of works for developing the structural nano-materials have been performed all over the world in recent years. Severe deformation techniques like HPT, ECPA and ARB have been applied to different materials such as Al, Cu, Ti and several steels. Such techniques greatly reduced the grain size and improved the yield and tensile strengths. However, the elongation of the materials is greatly decreased due to the small amount of work hardening, and these techniques do not seem suitable for the mass production. Therefore, this study has been carried out as a fundamental research for developing austenitic steels with high strength and good elongation using a conventional rolling and annealing processes. Fe-0.1%C-10%Cr-5%Ni-8%Mn alloy was melted, homogenized, hot rolled, and cold rolled at room temperature to transform γ austenite to α ’ martensite. After that, the specimens were annealed just above its reverse transformation finish temperature (Af) to obtain the fine reversed austenite grains. The grain size of the metastable austenitic steel was successfully refined to less than 200nm by repeating rolling and annealing processes. The resultant nanocrystalline material shows not only high strength but also large elongation because the work hardening ability is enhanced by the strain-induced martensitic transformation during the tensile test.