The effect of austenite grain size on deformation mechanism of Fe–17Mn steel

Abstract The transition of deformation mechanism from transformation-induced plasticity (TRIP) to twinning-induced plasticity (TWIP) was investigated in a viewpoint of γ-austenite grain size (AGS) using Fe-17Mn steel. When the AGS decreased from 51.72 μm to 0.75 μm, the apparent stacking fault energy (SFE) value increased from 10.8 mJ/m2 to 23.5 mJ/m2. The transition of deformation mechanism from TRIP to TWIP occurred at the late stage of tensile strain in ultrafine-grained specimens with high apparent SFE values (>23.2 mJ/m2). This result matches well with the fact that a critical AGS for the transition of deformation mechanism is ∼0.52 μm, which was calculated from the relationships between AGS and critical resolved shear stresses for mechanical twinning (τtwin) and e-martensitic transformation (τe-mart). UFG specimens with the AGSs below 1.12 μm exhibited a two-step rise at the stage II of strain hardening rate curves due to active mechanical twinning and possessed high tensile strength without a great loss of elongation.