Tailoring Heterogeneous Austenite Stability via Rapid Heating in Medium‐Mn Steel: Enabling Discontinuous Sustained Transformation‐Induced Plasticity

This study systematically investigates the effects of heating rate on the microstructural evolution, mechanical properties, austenite stability, and deformation strengthening mechanisms of Fe‐6Mn‐3Al‐0.2C medium‐Mn steel under austenite reverse transformation (ART), moderate rapid heating (MRH), and rapid heating (RH) processes. The results reveal that RH significantly enhanced mechanical performance, with the RH‐750‐300 specimen exhibiting the highest austenite fraction (76.65%) and the most pronounced transformation‐induced plasticity (TRIP) effect. RH promotes a heterogeneous microstructure consisting of equiaxed austenite, ultrafine film‐like austenite (FA), and granular austenite (GA), contributing grain refinement strengthening and hetero‐deformation‐induced (HDI) strengthening. Heterogeneous austenite stability facilitates a discontinuous yet sustained TRIP effect. Specifically, equiaxed austenite exhibits complex crystallographic orientation and a pronounced Mn concentration gradient, which induced strain incompatibility and reduced stability. In contrast, FA demonstrates a more uniform Mn distribution, consistent crystallographic orientation, and high dislocation density, thereby enhancing austenite stability and promoting boundary‐localized strengthening via dislocation pile‐ups.