MICROSTRUCTURAL CHANGES IN DUPLEX STAINLESS STEELS DURING LOW CYCLE FATIGUE

S. HEREÑÚ; I. ALVAREZ-ARMAS; A. F. ARMAS; S DEGALLAIX; A. CONDÓ; F. LOVEY

Berlin ,Alemania

Conferencia; Sixth International Conference on Low Cycle Fatigue; 2008

DVM

Low cycle fatigue (LCF) behaviour at different temperatures of duplex stainless steel (DSS) SAF 2507 samples with two thermal treatment conditions: as-received (unaged) and aged (100 hours at 475¨¬C) has been studied. In order to have a complete understanding of the cyclic response, the corresponding cyclic flow stress components, the effective, ¥òeff, and the internal stresses, ¥òint, have been analyzed in relation with the microstructure observed. ¥òeff attains higher levels at room temperature than at intermediate temperatures in both thermal conditions due to the lattice friction stress experienced by screw dislocations in the ferrite phase. The cyclic softening observed in aged samples at all temperatures is caused by the decrease of ¥òint .The demodulation of the initial spinodal decomposition is responsible for such behaviour. On the other hand, the increase of ¥òint in unaged samples at 300¡ÆC is consistent with the high dislocation density observed in the ferrite phase ascribed as a typical manifestation of DSA.