EVOLUTION AND MICROSTRUCUTRAL CHARACTERISTICS OF DEFORMATION BANDS IN FATIGUED DUPLEX STAINLESS STEEL.

MARINELLI MC, MALARRÍA JA, ALVAREZ I

Mendoza, Argentina

Jornada; Reunión Fundacional de la Sociedad Argentina de Microscopía; 2003

Sociedad Argentina de Microscopía SAMIC

Crack initiation, as well as the whole fatigue process, is controlled by cyclic plastic deformation. That is why fatigue cracks initiation at positions where the cyclic plastic deformation is higher than average. This work has investigated the dislocation arrangements, crystallographic characteristics and fatigue crack initiation of deformation bands in duplex stainless steels deformed during low cycle fatigue. The mechanical tests have been performed under strain controlled conditions with a total strain rate of =0.8% and strain rate 2x10-3s-1 . These tests have been carried out at different number of cycles and the surface damage has been monitored by optical microscopy using differential interference contrast technique. The surface morphology of the fatigued duplex was observed to display the following features. 1) Fine slips bands which seem to carry little plastic strain. 2) Intensive deformation bands and the formation of persistent slip bands (PSBs) which seems to establish the stage-I cracks. 3) The dislocation patterns just below the surface specimen to connect the cyclic slip localization and the crack initiation. 4) Formation of short cracks. 5) Propagation of stage-I cracks.