EVOLUTION OF MICROSTRUCTURE AND FATIGUE DAMAGE IN DUPLEX STAINLESS STEELS

MA. C. MARINELLI, J.A. MALARRÍA, I. ÁLVAREZ

San Nicolás, Argentina

Congreso; 2ª Conferencia sobre Usos del Acero del IAS; 2004

Instituto Argentino de Siderurgia IAS

The aim of the present work is to study the surface fatigue damage evolution on specimens of austenitic-ferritic superduplex stainless steels SAF 2507 and to correlate it  with the dislocation structures. The dislocation arrangement, crystallographic characteristics and fatigue crack initiation of deformation bands have been investigated using a technique whereby the surface of metal specimens can be examined by transmission electron microscopy. ie, the specimens are prepared by thinning from one side only, so that one original face is retained. In this way surface markings, such as slip lines can be seen at the same time as the dislocation and other defects just below the surface of the metal. The mechanical tests have been performed under strain controlled conditions with a total strain of Det = 0.8 % and strain rate de/dt = 3 x10 -3  s-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, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In this way the propagation of slip lines from austenitic to ferritic phase, intensive deformation bands and the formation of persistent slip bands (PSBs), formation of short cracks and propagation of stage-I cracks were observed.   Key words: Duplex stainless steels, fatigue, dislocations, short cracks