Mechanical properties and deformation behaviour of Fe-(20/27)Mn-4Al-0.3C austenitic steels

The mechanical properties of the Fe-20Mn-4Al-0.3C (20Mn) and Fe-27Mn-4Al-0.3C (27Mn) austenitic steels are investigated, and the deformation behavior under uniaxial tension was analysed. The 20Mn steel displays superior tensile properties to steel 27Mn, but the latter has a higher work hardening rate at the onset of deformation. The medium stacking fault energy (SFE) of the two steels impedes the boom of deformation twinning and promotes the appearance of microbands in the late stage of straining, so that the work hardening rate is monotonously diminishing and fails to rise again. The maximum volume fraction of twin lamellae is less than 8 vol.%, and their mean spacing was also estimated. The distribution of grain orientation spread (GOS) indicates that twinning process contributes to relieving the locally high distortion generated by the dislocation cross-slip inside the grains, which improves the uniform plasticity. The 27Mn steel keeps a much higher toughness than 20Mn steel for each temperature. The Charpy impact energy of steel 27Mn after annealing reaches 310 J and 188 J at room temperature and -196 degrees C, respectively.