Warm tensile properties of low-alloy TRIP steel warm-rolled just prior to isothermal holding treatment

Abstract

Abstract. Low-alloy TRIP steel sheets with ultra-high-strength that utilize transformation-induced plasticity of retained austenite have high strength and ductility. In this study, low-alloy TRIP steel sheets with thermo-mechanical treatment with warm rolling were prepared, and the effects of warm rolling on tensile properties were investigated. A hot-rolled sheet of the steel with Ms of 418.5°C was austenized and then quenched in a salt bath kept at 450°C. Two specimens of the sheet were warm-rolled by 40 and 60% and then isothermally held at 350℃ for 1ks. For comparison, a specimen was directly isothermally heat-treated at 350°C for 1ks. The three specimens were subjected to microstructural characterizations and tensile tests at temperatures ranging from 25 to 300°C. It was confirmed that the warm rolling increases the ductility/strength balance. The X-ray diffraction showed that the warm rolling causes an increase in volume fraction of the retained austenite, while its stability against the tensile deformation was somewhat complicated. The effect of the temperature and rolling reduction on the uniform elongation, which is the parameter mostly affected by TRIP, was successfully understood in terms of the volume fraction and the stability of the retained austenite.