1 1, Si GAO2, Tensile Properties and Deformation Behavior at Low Temperatures in Ferrite and Austenite Duplex Stainless Steel with Various Grain Sizes N. Koga 1, M. Noguchi 2 and C. Watanabe1 Faculty of Mechanical Engineering, Institute of Science and Engineering, Kanazawa University 2 Division of Mechanical Science and Engineering, Graduate School of Natural Science and Technology, Kanazawa University Ferrite and austenite duplex stainless steels exhibit an excellent strength-ductility balance at low temperatures. On the other hand, it is well known that grain refinement improves not only the strength but also the toughness of metallic materials. In this study, the effects of grain size on the low-temperature tensile properties of ferrite and austenite duplex stainless steel having different grain sizes were revealed, and then, the improvement mechanisms of the properties by grain refinement were discussed based on the obtained deformation behavior. Three specimens of duplex stainless steel with identical chemical compositions in each phase and phase ratio but different grain sizes ranging from 2.0 to 7.4 μm were prepared. At room temperature, the strength increased, but the elongation decreased with refining the grain size. Whereas at 77 K, both strength and elongation were increased by grain refinement. The formation of deformation-induced martensites was detected in the fractured specimens at 77 K, and its volume fraction increased with the grain size refinement. Therefore, the transformation-induced plasticity effect should provide high elongation at 77 K in the fine-grained specimen. The increase in strength by grain refinement strengthening at 77 K was significantly larger than that at room temperature. These results strongly suggest that grain refinement effectively improves the low-temperature tensile properties of ferrite and austenite duplex stainless steel. Excellent Combination of Strength and Ductility of an Ultrafine-grained Stainless Steel at Cryogenic Temperatures Studied by in Situ Neutron Diffraction Wenqi MAO1 J-PARC Center, Japan Atomic Energy Agency 2 Department of Materials Science and Engineering, Kyoto University The yield strengths of traditional austenitic stainless steels (ASSs), such as 304 ASS, remain relatively low at cryogenic temperatures, due to the face-centered cubic crystal structure. Recent studies reveal that ultrafine-grain (UFG) refinement of 304 ASS can be easily achieved by heavy cold-rolling and subsequent annealing. Compared to conventional 304 ASS with coarse grains, at room temperature, the UFG 304 ASS has significantly higher yield strength owing to the grain refinement strengthening, while it still maintains good ductility. However, the low-temperature mechanical properties of UFG 304 ASS are still unclear. In this study, we systematically investigated the tensile deformation behavior of an UFG 304 ASS at different temperatures ranging from 77 to 295 K. The results showed that the optimal mechanical properties were achieved at 77 K, with extremely high yield strength and ultimate tensile strength as well as a relatively good elongation. The low-temperature deformation mechanism of UFG 304 ASS was discussed in light of in situ neutron diffraction and microstructure observation. The details will be presented in the poster. This study got partially support from MEXT with No. JPMXP1122684766. Wu GONG1, Takuro KAWASAKI1, Tatsuya ITO1 and Stefanus HARJO1 Poster Presentation ｜NIMS Award Symposium 2023 P2 ｜ CharacterizationPP22--1111 PP22--1122 49
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