Flow Stress Behavior, Constitutive Modeling, and Microstructural Characteristics of DP 590 Steel at Elevated Temperatures

In the present study, the flow stress behavior and material properties of dual-phase (DP) 590 steel have been investigated for different process parameters such as temperature (room temperature (RT) to 400 °C), strain rate (0.0001-0.01 s⁻¹), and three different sheet orientations, viz., rolling direction (RD), transverse direction (TD), and normal direction (ND). The flow stress increases with an increase in temperature and strain rate. The yield and ultimate stress also decreased by approximately 13.85 and 13.45%, respectively, with an increase in temperature from RT to 400 °C; but no particular trend was observed for elongation. Subsequently, microstructural and fractographic studies were conducted using a scanning electron microscope. The volume fraction of the martensitic phase seems to decrease with an increase in temperature. In addition, from the electron backscattering diffraction studies, an increase in the ratio of high-angle grain boundaries was observed with an increase in the grain size of the material. The ductile type of failure was observed at all testing conditions. Furthermore, an investigation of strain hardening behavior using Swift and Voce modeling was carried out for DP590 steel. Three stages of hardening were observed in the case of both the applied strain hardening models. Predicted flow stress with the Voce model displayed a good agreement with the experimental data. The combined effect of temperature and strain rate was considered by formulating an Arrhenius-based Sellar model for the flow stress prediction.