Study of the Constitutive Equations of Austenitic Stainless Steels under High Strain Rate Loading Considering Phase Transformation Effects

Interrupted tensile tests were used to investigate the phase transformation and deformation behavior of SUS304 stainless steel under quasi-static to high strain rates. In tensile experiments at high strain rates, a single loading test was realized by a modified Hopkinson bar technique. The results show that there is a significant strain rate effect on the strain-induced martensitic transformation (SIMT). A modified Olson–Cohen model with a wide strain rate has been developed for the strain rate effect and the adiabatic temperature increase effect in the quasi-static to dynamic range. A constitutive equation was constructed from a combination of macroscopic and microscopic aspects, which mainly includes austenite volume content, SIMT content, strain rate, and adiabatic temperature increase. The constitutive model realizes the description of the flow stresses in the specimen at wide strain rates and strains and predicts the phenomenon that the quasi-static to dynamic strain-hardening rate transitions from s-type to parabolic. This phenomenon can be attributed to lower SIMT at higher strain rates caused by an adiabatic temperature increase. The validity of this constitutive model was verified by means of finite element simulations.