Analysis of interface migration and isothermal martensite formation for quenching and partitioning process in a low-carbon steel by phase field modeling

A modified two-dimensional phase field microelasticity model coupling the Cahn–Hillard equation is applied to investigate the microstructural evolution of interface migration and isothermal martensitic transformation accompanying carbon diffusion and redistribution during quenching and partitioning (Q and P) process in a low-carbon steel. In the modeling, the Kim–Kim–Suzuki model is adopted to depict interface conditions for carbon diffusion, while the transformation behavior during partitioning is assumed as a displacive manner. Simulations were done for one-step Q and P processes with various partitioning temperatures. Simulated results reveal that carbon enrichment within untransformed austenite varies significantly with the local microstructural features formed during Q and P process. With the proposed phase field model, the isothermal martensite formation and migration of existing austenite–martensite interfaces during partitioning are realized by simulation. It is also revealed that the interface migration behavior during partitioning is strongly correlated with the spatial distribution of the local elastic strain energy inherited from quenching process. Furthermore, temperature dependence of isothermal martensitic transformation kinetics is also studied, with the competition between martensitic transformation and reverse transformation during partitioning, a favorable partitioning temperature is found to have the maximum amount of isothermal martensite formed during partitioning. (paper)