Mechanism based mean-field modeling of the work-hardening behavior of dual-phase steels

Low-alloyed dual-phase (DP) steels exhibit good mechanical properties due to their composite-like microstructure of strong martensitic inclusions embedded in a ductile ferritic-matrix. This work presents an efficient two-scale approach to model the work-hardening of DP steels based on physically-motivated work-hardening contributions from geometrically necessary dislocations. The resulting mean-field model of Hashin-Shtrikman type comprises a minimal amount of free parameters and incorporates two main physical aspects motivated from presented experimental data: First, the constitutive equations for ferrite incorporate the averaged microstructural morphology (obtained by electronic backscatter diffraction) in terms of grain size and martensite coverage. Second, a direct interaction between ferrite and martensite phases is achieved via kinematic-hardening which models the long-range stresses experimentally observed in tensile tests of the bulk material. The presented approach is able to both reproduce the measured DP600 tensile curve and predict the distinctly different work-hardening rates observed for high-strength DP steels.