Modification of a martensitic transformation model and control of microstructure and properties in Q&P980 steel

Controlling the martensite content and retained austenite (RA) is crucial for optimizing the mechanical properties of quenching and partitioning (Q&P) steels. Accurate description of martensitic transformation kinetics is important for understanding the evolution of microstructure during the Q&P process. In this study, the classical Koistinen–Marburger (KM) model was modified by incorporating alloying effects and recalibrating transformation parameters through combined experimental and numerical analysis. The modified formulation was applied to analyze the martensitic transformation behavior during quenching in a Fe–0.20C–2.50Mn–1.73Si–0.02Ti–0.04Al(wt.%) steel, with subsequent partitioning at 400 °C for 300 s. The RA fraction first increases and then decreases with increasing quenching temperature, and the calculated optimal quenching temperature shifts from 221 °C in the conventional model to 292 °C in the modified formulation. Experimental results show that the RA fraction reaches approximately 7.9% when quenched at 300 °C. The product of strength and elongation (PSE) exhibits a similar trend with quenching temperature, reaching 20.7 GPa·% at 300 °C. Analysis of the work-hardening behavior using the Crussard–Jaoul (C–J) model suggests that the presence of RA may contribute to the transformation-induced plasticity (TRIP) effect, which could be responsible for the enhanced ductility.