On the cyclic softening behavior of SAF 2507 duplex stainless steel

The correlation between the low-cycle fatigue behavior and microstructure of SAF 2507 duplex stainless steel has been studied. The cyclic behavior has been analyzed through the cyclic flow stress components, i.e. the effective and the internal ones, as well as the activation volume parameter. A change in the deformation mechanism occurs at Δεp = 1.5 × 10−3, where the accommodation of the plastic strain changes from the reversible to the irreversible bow-out of dislocations giving rise to a continuous increase of the internal stress. The analysis of the effective stress has shown that the interaction between nitrogen atoms and dislocations can be explained through a model for weak obstacles. Finally, above Δεp ⩾ 6.0 × 10−3, dislocations on two {1 1 1} planes in the austenite can interact and form a well-developed cell structure, which increases the hardening of the phase. Consequently, the typical softening process characteristic of duplex steels diminishes with an increase in plastic strain amplitude.