Investigation of martensite particles distribution on strain localization in dual phase steels using SEM examination as well as crystal plasticity simulation

The morphology of the dispersed martensite islands between ferrite phases has a key role in formation shear bands of dual phase steels. In this study, the relationship between strain localization regions and the formation of shear bands with martensite dispersion was investigated for fine-grained DP 780 steel by using experimental observation and numerical simulation. SEM studies of the deformed structure showed that voids nucleated at ferritemartensite interface within larger ferrite grains and lower local martensite fraction. This is believed to be mainly due to the higher shear deformation ability of the larger ferrite grains and the less uniform strain distribution within the larger ferrite grains compared to the smaller ones. These results were analyzed precisely with crystal plasticity finite element method and the correlation between shear bands and microstructure-level inhomogeneity was identified.