Microstructure-based finite element modeling of effect of metastable austenite on mechanical properties of quenching and partitioning (Q&P) 980 steel

The microstructure-based finite element modeling was conducted to study the mechanical properties of Q&P 980 steel at the microscopic level. The two-dimensional representative volume elements of real microstructure were obtained from electron backscattered diffraction mapping. Mecking–Kocks equation was used to predict the constitutive strain–stress relationships of individual phases. Mechanical-induced martensitic transformation takes place when the driving force exceeds the critical driving force according to a stress-invariant-based model. The macroscopic stress–strain curves and the work-hardening rate curves obtained from modeling fit well with the experimental results. The simulation results also indicate that the local distributions of stress and strain in constituent phases are dependent on their strength. Soft ferrite carries the highest strain, while hard mechanical-induced martensite carries the highest stress. By comparing the modeling results of the microstructures with and without austenite, it shows that the transformation of retained austenite to hard martensite can increase the work-hardening ability and hence improve the strength and ductility of the steel. The detailed finite element modeling methods and results are presented and discussed.