Anomalous Deformation Behavior and Strain Induced Martensitic Transformation in SUS304 Stainless Steel at Low Strain Rates

In our previous paper (J. Japan Inst. Metals 71(2007) 620-628), anomalous plastic deformation behavior accompanied by propagation of X-shaped strain localization was found in tensile test of SUS304 stainless steel at low strain rate less than 10(-4) s(-1). In this paper, the phenomenon was further investigated related to strain induced martensitic transformation (SIMT). Tensile tests for a plate specimen were conducted at room temperature at higher strain rates of 6.7 x 10(-4) s(-1) where no propagating strain localization was found and at lower strain rate of 6.1 x 10(-5) s(-1) where propagating strain localization was found. The volume fraction of martensite (VFM) that generated accompanied by propagation of plastic deformation was quantitatively estimated by X-ray diffraction. In the case of higher strain rate, the VFM was followeded as predicated by the kinetic model of Olson and Cohen. On the contrary, in the case of lower strain rate, the VFM increased almost linearly depending on the strain increase. It is clearly shown that the anomalous plastic deformation behavior found in the condition of low strain rate is caused by strengthening by SIMT.