Cyclic deformation behaviour of superduplex stainless steels

The cyclic hardening–softening response, the cyclic stress–strain curve (CSSC) and the substructure evolution within the constitutive phases of a high nitrogen superduplex stainless steel SAF 2507 have been studied and the results compared with reference to low and medium nitrogen duplex stainless steels (DSSs), particularly AISI 329 and SAF 2205 grades, respectively. All three materials were manufactured in the form of hot rolled and solution annealed cylindrical bars with the same diameter. It is shown that the previously reported description of the CSSC of a DSS in terms of three regimes, each associated to distinct controlling cyclic deformation mechanisms, applies well in the case of the superduplex steel too. The main differences between the cyclic deformation behaviour of the DSSs studied are: (i) the CSSC of the SAF 2507 steel is placed at higher stress levels, mainly as a consequence of nitrogen alloying; (ii) the initial hardening period is shorter whereas the softening stage is more prolonged; and (iii) increasing nitrogen content promotes a more planar glide deformation character in austenite.