Effects of Temperature and Strain Rate on TRIP Effect in SUS301L Metastable Austenitic Stainless Steel

Effects of temperature and strain rate on tensile properties in metastable austenitic stainless steel SUS301L were studied in order to clarify the conditions of stress-induced martensitic transformation behavior for the maximum uniform elongation through the TRIP effect. The experimental results of the previously studied SUS304 steel were used to compare the conditions of metastable austenitic steels with different austenite stability. In the static tensile tests for the SUS301L steel at temperatures between 123 K and 373 K, the tensile strength increased with decreasing temperature, and uniform elongation reached a maximum at 323 K. The volume fraction of stress-induced martensite (Vα) at the same true strain increased with a decrease in temperature. For the strain-rate dependence on transformation kinetics, Vα decreased at strain rates higher than about 10–2 s–1 due to the temperature rise caused by adiabatic deformation. The equation for stress-induced transformation behavior proposed by Matsumura et al. was modified to consider the saturation value of stress-induced martensite, and the modified equation could describe the transformation kinetics precisely. The conditions of stress-induced transformation for the maximum uniform elongation through the TRIP effect were coincident between the SUS301L and the SUS304 with different austenite stability: the volume fraction of martensite at a true strain of 0.3 is approximately 5% and the maximum transformation rate is almost 2 at a higher true strain near uniform elongation.