Strain-Hardening Model of Dual-Phase Steel With Geometrically Necessary Dislocations

The strain-hardening behavior of metal during the uniaxial tension can be treated as the competing result of generation and annihilation of statistically stored dislocations (SSDs). Geometrically necessary dislocations (GNDs) are generated to accommodate a lattice mismatch and maintain deformation compatibility in dual-phase (DP) steels because of the heterogeneous deformation of the microstructure. In this study, a dislocation-based strain-hardening model that encompasses GNDs was developed to describe the mechanical properties of dual-phase steel. The GNDs were obtained based on a cell model of uniaxial deformation and the SSDs were calculated using a dynamic recovery model. The strain of each phase is a nonlinear function of the overall material strain obtained by the point-interpolation method (PIM). The proposed strain-hardening model was verified by using commercially produced DP600 steel. The calculated results obtained with GNDs are able to predict more precisely the experimental data than that without. The effects of martensite volume fraction and grain size on the strain-hardening behaviors of individual phases and material were studied.