Stress-strain relationship between ferrite and martensite in a dual-phase steel studied by in situ neutron diffraction and crystal plasticity theories

The stress-strain relationship between ferrite and martensite phases in the commercial dual-phase DP980 steel was studied using in situ neutron diffraction and the crystal plasticity finite element method (CPFEM). The phase identification method based on the image quality of electron backscatter diffraction and a filtering process was used to obtain information concerning individual crystallographic orientations for ferrite and martensite phases in DP980 steel. The (2 0 0) and (2 1 1) lattice strains of ferrite and martensite phases were measured along the loading and transverse directions as a function of macroscopic stress using in situ neutron diffraction. A CPFEM based on representative volume elements (RVE) was applied to determine the microscopic hardening parameters for each phase by fitting the measured macroscopic stress and measured (2 0 0) and (2 1 1) lattice strains. The microscopic hardening parameters for each phase successfully captured the influence of the crystallographic orientation of the ferrite phase on the localization of shear strain and the behavior of ductile failure in RVE of the unit cell during uniaxial tension. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.