On the cyclic softening behavior of SAF 2507 duplex stainless steel

The correlation between the low-cycle fatigue behavior and microstructure of SAY 2507 duplex stainless steel has been studied. The cyclic behavior has been analy2ed 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 Delta epsilon(p) = 1.5 x 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 Delta epsilon(p) >= 6.0 x 10(-3), dislocations on two {111} 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. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.