Modeling retained austenite in Q&P steels accounting for the bainitic transformation and correction of its mismatch on optimal conditions

Modeling retained austenite in quenching and partitioning (Q&P) steels remains a challenge, and the conventional ‘constrained carbon equilibrium’ (CCE) model fails to predict the optimal condition for achieving the maximal amount of retained austenite in various systems, which impedes the optimization of the Q&P process. One of the main limitations is that the possible decomposition of austenite to bainite during partitioning is completely ignored by the essential assumptions of the Q&P process and hence the associated CCE model. In this study, a CCET model that combines the conventional CCE model with the T0 model for the bainitic transformation and incorporates the effect of the isothermal bainitic transformation to describe the austenite stability during the Q&P process has been proposed. A detailed comparison between the experimental observation and model predictions demonstrated that the retained austenite could be better described by the CCET model, including its carbon content. The current model therefore provides a more accurate approach for tailoring the amount and stability of retained austenite after the Q&P processing of Fe-C-Mn-Si steels.