Effects of deformation induced phase transformation and twinning on the mechanical properties of austenitic Fe-Mn-Al alloys.

Structure and mechanical properties of austenitic Fe–(20 and 30)Mn–(0 to 7) Al alloys in the temperature range between 77 and 295 K have been investigated in relation to the occurrences of phase transformation and deformation twinning. Additions of aluminum to the 20 wt% Mn alloys significantly decreased the γ→ε transformation temperature. The yield stress of these alloys increased with increasing aluminum content, whereas the strain hardening of them decreased. This tendency is prominent at low temperatures. In the 30 wt% Mn alloys the yield stress and strain hardening were almost identical regardless of aluminum contents. Additions of aluminum strongly suppress the γ→ε transformation and give birth to the occurrence of deformation twinning. Calculated stacking fault energy based on a regular solution approach shows that the austenitic Fe–Mn–Al alloys which have the stacking fault energy approximately larger than 20 erg/cm2 favor the deformation twinning leading to the increase in low temperature ductility.