Modelling the evolution of microstructural bands in a martensite/austenite Q&P-processed stainless steel

This work discusses the microstructure evolution observed in a quenching and partitioning (Q&P)-processed martensite/austenite stainless steel during the partitioning step at 400 °C for 300 s, where distinct microstructural bands rich in austenite due to elemental segregation, evolve into a uniform distribution of austenite grains. This phenomenon is characterised and investigated using a model for the carbon partitioning from martensite to austenite coupled with the movement of the martensite-austenite interface. The observed elimination of microstructural bands is found to be related to the topological distribution of austenite grains and the heterogeneity of the thermodynamic equilibrium regime at the various interfaces governing the partitioning process. Furthermore, the concurrence of banding elimination (local equilibrium) and phase growth towards the global equilibrium phase fractions is investigated in the simulations in terms of the role of Mn. It is found that the local equilibrium-negligible partitioning (LENP) conditions lead to the most realistic outcome.