Multi-interface migration mechanism induced by carbide precipitation during the quenching-partitioning-tempering process in a high-carbon steel

Phase-field finite element (PFFE) modeling of the quenching-partitioning-tempering (Q-P-T) process is proposed, and the two-dimensional PFFE-QPT model considering carbide precipitation and the interface migration between martensite and austenite is used to investigate microstructural evolution and the elastic/plastic strain distribution at quenching, partitioning and tempering stages in a high-carbon steel, respectively. The simulation results of the high carbon Q-P-T steel indicate that the precipitation strengthening of carbides occurs not only because they can block the movement of dislocations, but also because they can produce high internal stress. Meanwhile, the volume fractions of different phases (including primary martensite, retained austenite, secondary martensite, and carbide) and the carbon content in retained austenite predicted by the PFFE-QPT model are slightly better than those predicted by the novel one-dimensional QPT-LE (local equilibrium) model and much closer to experimental values. The PFFE-QPT model is also used to successfully predict the volume fractions of different phases in low-carbon and medium-carbon Q-P-T steels. More importantly, the microstructural morphologies closely related to mechanical properties can be demonstrated by the PFFE-QPT model and are comparable with the experimental observation. Therefore, the PFFE-QPT model will be a more powerful tool for guiding the process and microstructure design of Q-P-T steels compared with the QPT-LE model.