Enhanced high-temperature deformation compatibility of an austenite-ferrite duplex microstructure in medium-Mn steel

This study systematically elucidates the underlying mechanisms for the enhanced deformation compatibility of austenite-ferrite duplex microstructure compared to single-phase austenitic microstructure in Fe-0.18C-8.4Mn-3.1Al medium-Mn steel during hot tensile deformation. Single-phase (SP) specimens exhibited higher peak stresses than dual-phase (DP) specimens at identical strain rates, with the difference decreasing as the strain rate increased. At the low strain rate of 0.01 s −1 , the duplex microstructure achieved the lowest peak stress, superior necking resistance, and maximum elongation, accompanied by predominantly equiaxed grains and minimal deformation texture, demonstrating optimal hot workability. Ferrite underwent continuous dynamic recrystallization (CDRX) via progressive subgrain misorientation accumulation, while austenite was dominated by discontinuous dynamic recrystallization (DDRX). Insufficient stored deformation energy and high-energy phase boundary barriers substantially suppressed DDRX in austenite, resulting in lower DRX fraction than in ferrite. Strain preferentially localized in the softer ferrite, where pronounced dynamic softening halted flow stress rise. Conversely, geometrically necessary dislocation (GND) density in austenite accumulated continuously, surpassing ferrite at high strain levels and result in dynamic strain partitioning reversal. Moreover, pronounced grain boundary sliding (GBS) in the duplex microstructure further reduced high-temperature deformation resistance.