Continuous Quenching and Partitioning of Medium-Mn Steels: Linking Martensite Topology with Retained Austenite Stability

Abstract The effect of interrupted quenching (Q) temperature on retained austenite (RA) stabilization during quenching and partitioning (Q&P) of a medium-Mn steel was investigated using complementary experimental and computational methods. Q temperatures from 140 °C to 350 °C, spanning from above martensite start ( M s ) to below martensite finish ( M f ), were examined under conditions compatible with industrial continuous processing. The results demonstrate that the topology of the primary martensite network, controlled by Q temperature, governs carbon partitioning, RA stability, and the resulting mechanical properties. RA stabilization was found to be spatially limited to approximately 0.3 to 0.7 μ m from the martensite/austenite interface. Consequently, decreasing the Q temperature increased the martensite/austenite interfacial area, subdivided the remaining austenite into smaller regions, and promoted more efficient carbon partitioning and RA stabilization. The highest RA fraction (~ 23 vol pct) and the optimum strength–ductility balance were obtained for Q temperatures of 220 °C to 240 °C. The results further show that RA stability governs the balance between uniform and post-necking deformation. Low-stability RA transforms at the early stages of deformation, whereas highly stabilized RA transforms predominantly after necking, while intermediate stability provides the most favorable mechanical response. The proposed mechanism establishes a comprehensive process–microstructure–property relationship linking Q temperature, martensite topology, carbon partitioning, RA stability, and mechanical performance, providing a framework for optimizing Q&P processing of medium-Mn steels.