Influence of Al on the temperature dependence of strain hardening behavior and glide planarity in Fe-Cr-Ni-Mn-C austenitic stainless steels

Two austenitic stainless steels of compositions Fe-17Cr-9Ni-6Mn-0.4C-(0 and 4)Al (mass-%) were tensile tested at temperatures between −196 °C and 200 °C. The influence of Al on the temperature dependence of the strain hardening behavior, tensile properties, and deformed microstructures was subsequently studied. For both alloys, the strain hardening at high deformation temperatures was characterized by near-linear hardening at low stresses and transition to a regime of non-linear hardening at higher stresses. Lower tensile temperatures resulted in the extension of the initial near-linear regime of hardening. Near-linear hardening until necking was established at a lower temperature for the Al-containing alloy than for the Al-free alloy (−100 °C vs −40 °C). This was correlated with a higher glide waviness in the Al-containing alloy. Deformation twinning was the most obvious feature of glide planarity in the deformed microstructures. Tensile elongation of both steels showed a maximum within the temperature range studied. The peak elongation temperature almost exactly coincided with the temperature at which near-linear hardening until necking occurred and was therefore lower for the Al-containing alloy. The loss of ductility at temperatures below the peak elongation temperature was attributed to the occurrence of a small fraction of deformation-induced α′ at intersections of deformation twins. In agreement with the reported stacking fault energy-raising effect of Al, results indicated an increased stability of austenite upon Al addition.