Kinetics of the γ → ε Martensitic Transformation in Fine-Grained Fe-26Mn-0.14C Austenitic Steel

A high-Mn Fe-26Mn-0.14C austenitic steel was hot deformed at 900 °C, 1000 °C, and 1100 °C with the strain rate of 5 s−1 followed by air cooling (AC) or water quenching (WQ). Deformation at 1100 °C results in the occurrence of dynamic recrystallization (DRX) that produces a fine grain size (∼10 μm), which was found to prevent the γ fcc → ε hcp transformation upon cooling. The transformation in the fine-grained austenite is insensitive to the defect concentration. Isothermal holding of the dynamically recrystallized specimen at 1100 °C for 3 minutes results in grain growth (∼40 μm). The coarser grain size was observed to allow the transformation to proceed (17 pct martensite). The role of grain boundaries, twins, and faults in suppressing the phase transformation is discussed.