Modelling the effect of microstructural banding on the flow curve behaviour of dual-phase (DP) steels

Dual-phase steels (DP) are well suited for automotive application due to their attractive mechanical properties, such as high strength and good formability. These properties are achieved by the dispersion of hard martensite particles in the soft and ductile ferrite matrix. The current work aims to predict the mechanical properties of dual-phase steels. A microstructure based approach by means of representative volume element (RVE) was employed for this purpose. Available and novel routines were used to create the 2D RVEs from the real microstructures. Periodic and homogeneous boundary conditions were imposed. Dislocation based model was implemented to predict the flow behaviour of the single phases. Computational first order homogenization strategy was employed to obtain the true stress–true strain curves from the RVE calculations. The implementation of the periodic boundary condition results in a better agreement with the converged effective value compared to the displacement boundary condition. Equiaxed microstructures show higher strength and work hardening compared to that of the banded microstructures. In the same fraction of martensite, the yield stress of DP steels decreases by increasing the aspect ratio of martensite bands.

The microstructural in-homogeneities in DP steels were quantified. The RVE size was estimated for the first time based on real microstructure using homogeneous and periodic boundary conditions. The effect of martensite banding was studied on the mechanical behavior of DP steels.