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The similar crystal structures of martensite (BCT) and ferrite (BCC) cause difficulty in distinguishing the grain orientations of individual phases in dual-phase (DP) steels. A dislocation-based multiphase mixed hardening model is presented, considering both ferrite and martensite strain partitioning, to describe the texture-dependent mechanical behavior of DP steels more precisely. This model is based on the ideals that (i) the volume fractions of the constituent phases and the corresponding strain partitioning function are obtained through in situ tensile experimentation, and (ii) the grain orientations of ferrite and martensite are assumed to be in accordance with the overall texture. We applied the model to calculate the macroscopic and microscopic mechanical behavior of DP800 steel using a crystal plasticity finite element (CPFE) code. The results show that the calculated stress-strain response and textural evolution are in good agreement with the experimental results. The dislocation evolution indicates that the rapid hardening of ferrite induces a high hardening rate for DP steels early in plastic deformation. In addition, for the grains corresponding to the texture center orientations of DP800, the activity and dislocation density evolutions of the slip systems are studied.

The complex strain hardening behaviors of dual phase (DP) steel are subjected to the heterogeneous microstructures. The current work aims to predict the strain hardening behaviors of ferrite-martensite DP steel, focusing on the effects of heterogeneous microstructure on mechanical properties. The flow stress of material was calculated based on the dislocation-based work-hardening model with considering the multi-boundaries hardening. The ferrite-martensite phase boundary percent and grain shape factor were selected as the heterogeneous feature parameters, which were introduced into the new proposed model. The theoretical calculated stress-strain responses were verified with experimental results using the tensile test. The model with the boundary strengthening consideration has more accurate results. The parameter effects of ferrite-ferrite boundary (FFB) spacing, ferrite-martensite boundary (FMB) percent, and grain shape factor on the flow stress-strain curve were researched.