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 degrees C, 1000 degrees C, and 1100 degrees C with the strain rate of 5 s(-1) followed by air cooling (AC) or water quenching (WQ). Deformation at 1100 degrees C results in the occurrence of dynamic recrystallization (DRX) that produces a fine grain size (similar to 10 mu m), which was found to prevent the gamma(fcc) -> epsilon(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 degrees C for 3 minutes results in grain growth (similar to 40 mu m). 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.