Research on the Dynamic Softening Mechanism of Dual-Phase Structure During Warm Forming of Fe–8.5Mn–1.5Al Medium-Manganese Steel

In this article, Fe–8.5Mn–1.5Al medium-manganese steel is taken as the research object, and Gleeble 3500 thermal simulation testing machine is used to conduct isothermal compression at different deformation temperatures, strain rates, and strains in its austenite ferrite two-phase zone. A constitutive model and a dynamic recrystallization volume fraction model for materials are established, and finite-element method is used to simulate the temperature, equivalent strain, and dynamic recrystallization volume fraction distribution in different regions of the workpiece under different deformation conditions. By comparing and analyzing the microstructure, finite-element simulation results, and hot working diagrams obtained from the experiment, the microscopic mechanism of dynamic softening of the material when ferrite and austenite coexist is explained; the transformation of the dynamic softening mechanism of the two phases with the hot deformation process is also explained. Early deformation mainly occurs in softer ferrite, which preferentially undergoes continuous dynamic recrystallization. Austenite has a lower stacking fault energy, and discontinuous dynamic recrystallization (DDRX) occurs when the dislocation density reaches a certain critical value. At the same time, when the strain reaches a certain level, the dynamic softening behavior of ferrite will also transform into DDRX. The optimal deformation conditions for Fe–8.5Mn–1.5Al medium-manganese steel during warm processing in the two-phase zone are a temperature of 720 °C, a strain rate of 0.01 s⁻¹, and a large deformation zone.