Study on the mixture strain hardening of multi-phase steels

During the forming process, the soft and hard microstructures of multi-phase steels have complex deformation state. So it is critical to describe the mechanical behaviour of composite material with an accurate stress–strain relationship considering the stress–strain response of each phase. In this study, a mixture strain hardening law is proposed based on the hypothesis that the strain energy density of material equals the sum of that in each phase. The stress–strain relationship of each phase is described by Swift law. The strain of each phase is a non-linear function of the overall strain of material. The slip activation coefficient and the grain boundaries hardening coefficient, controlled by the overall strain of material, are introduced to balance the distribution of the stress of each phase. TRIP590/DP590 (with/without phase transformation phenomenon) high strength steels are evaluated to verify the model and the calculated results are in a good agreement with experimental data.

► A phenomenological stress–strain model for the multi-phase is developed. ► The stress of individual phase is described by Swift laws. ► The strain of individual phase is a function of the overall strain of material. ► Coefficients are introduced to balance the distribution of the stress of phases.