Improvement of high speed plastic deformation behavior of ultrafine grained high Mn steel

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Difference between the strength at high speed and that at low speed (quasi-static rate) (DSHQ) is desired to become larger value for industrial applications. The aim of this study was to obtain an appropriate DSHQ in high Mn TWIP (Twinning induced plasticity) steel. The samples with different microstructures were fabricated and then those plastic behaviors were measured by room temperature tensile test at a strain rate up to 10^3/sec. When the sample was fully recrystallized, the strength becomes larger but the DSHQ decreases with decreasing of the mean grain size ; whereas the higher strength with larger DSHQ can be achieved successfully by means of the mixture of fine grains and lamellar dislocation structure. The microstructural observations clarified that the improvement of DSHQ is corresponded with the appearance of twinning deformation.