Strain-Hardening Behavior of Dual-Phase Steel under Multistress States

The complexity and nonuniformity of microdeformation in high-strength dual-phase (DP) steels make it difficult to accurately predict the deformation processes in stamping. Here, in situ experiments under three kinds of stress states and a crystal plasticity finite element (CPFE) model were used to predict the strain-hardening behavior of DP steel. The microdeformation in various deformation stages was extracted from metallographs captured during in situ experiments to calculate the strain partitioning functions of each phase. Then, the multistress state mechanical behavior of DP steel was calculated based on the CPFE model combined with the strain partitioning functions of ferrite and martensite. The calculation results showed that (1) the CPFE model could accurately describe the load-stroke curves of the three experiments and that (2) the stress state had a significant effect on the strain partition ratio and the initial critical resolved shear stress of the material. In addition, the stress-strain curves of DP800 steel were predicted under six stress states; these curves did not coincide and had obvious deviations. Finally, the activity of the grain slip systems and the dislocation evolution were analyzed and discussed to predict the microdeformation and stress state effects on strain-hardening behavior.