Tensile deformation behavior of cold-rolled TRIP-aided steels over large range of strain rates

Abstract

Multi-phase transformation-induced plasticity (TRIP) steels exhibit a combination of good ductility and high strength, and can be good candidates for automotive applications in improving crashworthiness of car bodies. Understanding of the mechanical properties of the TRIP steels under high strain rate is essential. In this paper, the tensile deformation behavior of cold-rolled TRIP-aided DP steels over the large range of the strain rates (400–1600 s −1) was studied using a pneumatic indirect bar–bar tensile impact tester based on one-dimensional elastic stress wave principle. The volume fraction of transformed retained austenite was analyzed by XRD. The strain rate effect on the amount of transformed retained austenite was also analyzed and discussed. The void initialization and morphology of fracture surfaces at different strain rates were observed by SEM. The results indicate that with increasing strain rates, both the yield strength and tensile strength of TRIP-aided steels increase, but the elongations decrease. The stability of retained austenite is strain rate dependent because the adiabatic temperature rises under high deformation rate. Increased strain rate results in the decrease of the amount of transformed retained austenite. The site of initialized void is located in the ferrite matrix resulting from TRIP effect. Furthermore, the morphology of fracture surface at high strain rate is different from that at the static or quasi-static tensile conditions.