Effect of Al content on work hardening in austenitic Fe-Mn-Al-C alloys

The work hardening curves of austenitic Fe-25Mn-(0.57-5.02)Al-0.15C alloys were measured from tensile tests at room temperature. These curves are described according to a model sigma = sigma(0) + K epsilon(jt) at lower strains and by one or two parabolic functions at higher strains. With an increasing Al content, the work hardening and work hardening rate for these alloys decrease markedly at high strains since the contributions of strain induced epsilon-martensite and deformation twins to the flow stress are lower. The work hardening rate increases slightly at lower strains except for the alloy with 0.57% Al in which the strain induced epsilon-martensite formed at lower strains leads to the high work hardening rate at higher strains. The addition of aluminum increases the stacking fault energy and phase stability in Fe-Mn alloys. Specifically, it suppresses the strain induced gamma -> epsilon transformation and twinning which reduces much final strain hardening and enhances the dislocation cell structures which slightly improve the initial work hardening.