The Effect of the Heating Process on the Warm Deformation Behavior and Microstructure of Medium Mn Steel

This study investigates the effects of heating processes on the microstructure and deformation behavior of medium Mn steel during warm deformation. The samples treated by austenitization maintain an austenitic microstructure during deformation, which transforms into martensite upon cooling to room temperature. In contrast, the room‐temperature microstructure of samples deformed by direct heating to the deformation temperature is dependent on the deformation temperature: deformation above Ac 3 results in a martensitic microstructure; deformation within the intercritical range (Ac 1 –Ac 3 ) produces a mixture of ferrite, martensite, and austenite; and deformation below Ac 1 yields a microstructure of ferrite and carbides at room temperature. When the microstructure only contains austenite during deformation, medium Mn steel exhibits excellent work‐hardening capability, characterized by a gradual increase in work hardening with strain until a dynamic balance between hardening and softening. Conversely, when ferrite is present in the microstructure during deformation, the flow behavior is dominated by ferrite, resulting in poor work‐hardening capability, with peak stress reached at low strain, followed by dynamic softening. Microstructure and stress–strain curve analyses reveal that, below 640 °C, ferrite exhibits higher strength than austenite. At 640 °C, the strengths of ferrite and austenite are approximately equal; above this temperature, austenite surpasses ferrite in strength.