Incomplete carbon partitioning during quenching and partitioning of Fe–C–Mn–Si steels: Modeling and experimental validations

Abstract

Carbon trapping at dislocations and carbide precipitation in martensite could significantly reduce the amount of carbon partitioning into austenite, e.g. incomplete carbon partitioning phenomenon, which would alter austenite decomposition behavior and austenite stability during the Quenching and Partitioning (Q&P) process. In this study, an integrated model is developed to clarify the mechanism of incomplete carbon partitioning and quantify its effects on austenite stabilization in the low-alloy medium-carbon Fe–C–Mn–Si steels. The fraction of carbon consumed by Cottrell atmospheres around dislocations is described using a semi-empiric equation. Then, the kinetic competition among carbide precipitation, carbon partitioning and austenite decomposition during the partitioning step is simulated by coupling the Deschamps–Bréchet model and quenching and partitioning-local equilibrium (QP-LE) model. It is found that transition carbide precipitation in martensite and carbon partitioning into austenite are kinetically coupled at the very early stage of the partitioning step and subsequently promotes austenite decomposition. Taking the synergy effects of incomplete carbon partitioning and austenite decomposition into account, our model is capable of predicting the evolution of volume fraction of austenite and its carbon content during partitioning.