Failure Mode and Ductility of Dual Phase Steel with Edge Crack

Abstract

Dual phase steels having a microstructure consisting of a ferrite matrix, in which particles of martensite are dispersed, have received a great deal of attention due to their useful combination of high strength, high work hardening rate and ductility, all of which are favorable properties for forming processes. In the present work, various microstructure-level finite element models are generated based on the actual microstructure of DP590 steel, to capture the mechanical behavior and fracture mode. The failure mode of DP steels is predicted using the plastic strain localization theory, mainly resulting from the material microstructure-level inhomogeneity as well as the initial geometrical imperfection. Besides the simulation, tensile test specimens of dog bone type with different edge cracks were prepared on an internally designed blanking tool, and the corresponding deformation processes were recorded via digital image correlation system. It is found that the overall ductility of the DP590 steel strongly depends on the ductility of the ferrite matrix, and pre-existing edge cracks reduce the overall ductility of the steel and change the failure mode.