Temperature influence on the cyclic behaviour of aged and unaged super duplex stainless steels

A. F. ARMAS; S. HEREÑÚ; S. DEGALLAIX; A. CONDÓ; F. LOVEY

Grado, Italy

Conferencia; DUPLEX 2007 International Conference & Expo; 2007

Associazione Italiana di Metallurgia

The cyclic behavior of type UNS S32750 (super) duplex stainless steels (DSSs) in as received and aged conditions was investigated between room temperature and 500ºC. In spite of the spinodal decomposition (SD) that could take place in DSSs during aging in the temperature range 300-500ºC, which is considered to be the cause of embrittlement of these steels, no appreciable influence was found in the cycles to failure of aged and unaged samples cycled at intermediate temperatures. The observed shortening of the lifetime, also exhibited by other commercial steels, could be attributed to the influence of high temperature effects and not to the spinodal decomposition. By conventional and high resolution transmission electron microscopy it could be observed that SD, when present, was not dissolved as a consequence of cycling. Nevertheless, it did not cause the embrittlement of the samples. The cyclic behavior of unaged samples of the material showed a strong influence of the temperature with a clear evidence of the presence of dynamic strain aging (DSA) in the ferritic phase of the steel. On the contrary, aged samples showed only cyclic softening behavior from the beginning of the test up to the failure of the sample. Only at 475ºC a secondary hardening was present that could be attributed to DSA of the austenitic phase.