Abstract
Tailoring thermal stability of austenite through a Q&P thermal cycle is essential for obtaining a beneficial strength-ductility balance. In this study, factors affecting the thermal stability of austenite during the Q&P process applied for thermomechanically processed medium-Mn steel were analyzed. Q&P thermal cycles in which the partitioning steps were carried out in a temperature range from 350°C to 450°C for times from 90s to 900s were investigated. An influence of time-temperature parameters of the partitioning step on the microstructure evolution of 0.17C-4.2Mn-0.98Al-0.87Si-Nb alloy was quantitative and qualitative investigated using techniques with different resolution. The thermal stability of austenite was tailored by optimizing its fraction during a quenching step and by minimizing the undesirable carbides and bainite formation occurred during the partitioning step. As a consequence, the formation of undesired secondary martensite was significantly reduced. Obtained results showed that the thermal stability of austenite was mainly controlled by its carbon content, morphology and lath/grain size.