Correlation between individual phase constitutive properties and plastic heterogeneities in advanced-high strength dual-phase steels

Abstract

The present study comprehensively investigates the individual phase constitutive properties and plastic heterogeneities in advanced high-strength steels (AHSS), particularly DP590 and DP780 dual-phase (DP) steels. A machine learning-based model is implemented to identify the ferrite and martensite phases in the microstructures of DP590 and DP780. Then, the constitutive properties of ferrite and martensite phases are successfully obtained through a hybrid approach of in-situ neutron diffraction coupled with the crystal plasticity finite element method (CPFEM). The distinct microstructures between DP590 and DP780 result in different macroscopic and microscopic properties among the two materials. Owing to different martensite volume fractions (V_m) in DP590 (V_m = 8.3 %) and DP780 (V_m = 35.4 %), a noticeable dependency of plastic heterogeneities during deformation on martensite fraction and its spatial distribution is revealed. Compared to DP590, the deformed microstructure of DP780 exhibits a more heterogeneous distribution of stress and strain fields, along with significant formation of plastic strain localization leading to a remarkable increase in strain partitioning index. It shows that a lower fraction of martensite with its discrete distribution decreases martensite ability to hinder the ferrite deformation, thus strain localization is primarily concentrated within the ferrite phase as the predominant failure mode in DP590. In contrast, a higher martensite fraction in DP780 causes more pronounced strain localization which occurs in the ferrite and at the ferrite/martensite interface. In addition, interconnect distribution between martensite islands enhances the inhibition of martensite to ferrite deformation, thereby high strain gradient at their interface leads to prevalence of ferrite/martensite interface decohesion in DP780.