Investigation of the Deformation Heterogeneity of (Α+Γ) Dual Phase Steel in Micro-Scale by Coupled In-Situ Tensile Experiment and Crystal Plasticity Finite Element Method (Cpfem)

Abstract

The deformation heterogeneity in the grain scale of a ferrite (α) +austenite (γ) dual phase steel was investigated utilizing a microstructure-based crystal plasticity finite element method (CPFEM) and in-situ tensile deformation. The slip deformation characteristics of various grains and the corresponding orientation response for coordinating deformation between them were characterized in detail using in-situ observation. In the framework of Representative Volume Elements (RVEs) modeling, the activated slip system of grain in each phase was analyzed by CPFEM. Especially, two specific parameters, i.e., the deformation degree coordination parameter (kl) and the slip transfer parameter (ktf), were proposed to evaluate the deformation heterogeneity between the neighboring grains on the sides of phase boundaries (PBs) and/or grain boundaries (GBs). The results showed that the deformation heterogeneity strongly depended on the slipping rates of activated slip systems near the PB or/and GB, and in particular, the strain localization more easily tended to develop at the boundary with an approximate angle of 45° to the loading direction. Furthermore, when this boundary of 45° to the loading direction was nearly parallel to the activated slip system of the nearby grains, a large shear behavior was formed at this position, where the degree of deformation heterogeneity was the most prominent. Multi-variant slip systems are necessarily activated in austenite to coordinate further deformation, thereby the degree of deformation heterogeneity caused by a single slip of each grain at the early stage of process could be more rapidly reduced, that is, the rising rate of kl increases, and the ktf shows a jump rapid increase. The grains orientation on both sides of the boundary rotates towards a specific state where the activated slip system is parallel to coordinate heterogeneous deformation between interphase or intergranular.

Keywords: deformation heterogeneity, crystal plasticity finite element method, slipping rate, slip transfer, grain orientation