DISLOCATION STRUCTURE DEVELOPED IN AGED DUPLEX STAINLESS STEEL DURING LOW CYCLE FATIGUE

S. HEREÑÚ; I. ALVAREZ-ARMAS; A. EL BARTALI; A. ARMAS; S. DEGALLAIX

Rosario, Argentina

Congreso; 10th Inter-American Congress of Electron Microscopy 2009,CIASEM 2009/1st Congress of the Argentine Society of Microscopy,SAMIC 2009; 2009

CIASEM

Previous studies of the low cycle fatigue behaviour at different temperatures of aged (100 hours at 475ºC) SAF 2507 duplex stainless steel (DSS) have reported cyclic softening at all temperatures during most of the fatigue life. Transmission electron microscopy (TEM) observations of these cyclic tested samples show localized dislocation bands in the hardened ferritic phase with channels of low dislocation density. These channels still exhibit the strikingly mottled surface characteristic of the initial spinodal decomposition. In this aged condition the austenite phase shows a planar arrangement of dislocations similar to that observed in unaged samples. In this respect, this paper focus on the substructure dislocation evolution during fatigue in both phases in order to rationalize the cyclic softening observed. Special attention is placed on analysing the dislocation evolution towards the formation of the localized dislocation bands. To achieve this objective TEM studies were performed in interrupted cyclic tests.