Unraveling the anomalous work hardening behavior in a 10Mn steel under the warm temperature deformation

This study investigates the origin of anomalous fluctuations in the work hardening rate of a Fe-9.8Mn-2.0Al-0.33C-0.4V (wt.%) steel during tensile deformation at 200 °C. By utilizing interrupted tensile tests, the microstructural evolution and underlying deformation mechanisms were systematically elucidated. The initial microstructure, featuring over 80% austenite, undergoes a strain-dependent transformation sequence: planar slip and microband formation dominate at low strains, followed by the activation of deformation twinning for grain refinement at intermediate strains, and culminating in a sequential strain-induced martensite transformation that produces a fine, interwoven lath martensite network at high strains. The periodic oscillations in the work hardening rate are attributed to a dynamic competition between multiple hardening mechanisms (dislocation accumulation, deformation twinning, and sequentially formed martensite) and softening mechanisms (dynamic recovery and, crucially, adiabatic thermal softening). The significant adiabatic heating generated during deformation elevates the stacking fault energy, temporarily suppressing martensite nucleation and promoting recovery, thereby creating a self-regulating feedback loop. Concurrently, the dynamic precipitation of nano-sized V-carbides during deformation homogenizes dislocation glide and further stabilizes the plastic flow. This synergistic interplay of mechanisms effectively suppresses common plastic instabilities, resulting in smooth stress-strain curves and a balanced strength-ductility combination. The findings provide fundamental insights into the thermo-mechanically coupled deformation behavior of medium-Mn steels at warm temperatures.