Effect of strain rate-induced microstructure on mechanical behavior of dual-phase steel

Abstract

In this work, the microstructure evolution characteristics after 3% pre-strained at different strain rates are elaborated to reveal the effect on the mechanical behavior of dual-phase steel. The results showed the strain field simulated by the representative volume element model shows obvious strain heterogeneity, and the degree of strain localization intensifies with the increase of the strain rate. There is sufficient time to complete the dynamic transition among geometrically necessary dislocations (GNDs)-low-angle grain boundaries (LAGBs)-middle angle grain boundaries (MAGBs)-high angle grain boundaries (HAGBs) at low strain rates (10−4 s−1∼10−3 s−1), thereby releasing strain distortion energy. As the strain rate increases, the transformation process from LAGBs to HAGBs is hindered due to the shortened strain response time. It can promote the accumulation of high-density GNDs and LAGBs inside the grains, which intensifies strain localization. The incomplete evolution of the microstructure caused by the pre-strain history becomes a resistance to dislocation motion during re-deformation, and more importantly, the higher the strain rate, the more severe the hardening rate loss. This leads to an increase in yield strength and a decrease in uniform elongation, which drastically deteriorates the mechanical stability of the steel.