Regulation of Composition Distribution in Austenite of Medium Manganese Steel and Formation Mechanism of Dual-Phase Heterostructure

This study focused on low-carbon medium-manganese steel and utilized short-time austenitization treatment to prepare a nanosheeted FCC/BCC dual-phase structure in its pearlite matrix. However, the Mn element distribution mechanism, interface behavior, and the organization regulation mechanism of this structure still require further exploration. To this end, by combining carburizing, pearlite phase transformation, and austenitization as a coordinated regulation strategy, a controllable construction of nanoscale FCC/BCC dual-phase structure was successfully achieved in the Fe-0.2C-5Mn-1Al-0.5Si medium-manganese steel. Experimental results demonstrate that the pearlite-to-duplex phase transition is governed by austenitizing temperature and duration, with optimal parameters identified as 790°C for 25 s, yielding 31.8% retained austenite. Notably, the Mn content in the FCC phase peaks at 15 wt%, while the BCC phase exhibits a gradient decrease (2-5 wt%). Elemental redistribution is dominated by interface-mediated short-circuit diffusion (diffusion distance ∼12.5 nm). The duplex microstructure achieves a hardness of 6.63 ± 0.65 GPa through synergistic interfacial strengthening and TRIP/RICT effects, providing theoretical insights for designing high-performance medium manganese steels.