Short crack growth of an aged second generation duplex stainless steel fatigued at room temperatura

M BALBI; I ALVAREZ

Rosario, Argentina

Conferencia; 17ª Conferencia de Laminación / 4ª Conferencia Usos del Acero del IAS; 2008

Instituto Argentino de Siderurgia

In the present work, the kinetics of short crack growth during cycling has been studied in a second generation duplex stainless steel in the as-received and aged conditions. The heat treatment of aging was carried out in the following thermal conditions 100hr at 475ºC. Cylindrical specimens with shallow notch were subjected to constant plastic strain amplitude loading in both thermal conditions. The notch area has been mechanically and electrolytically polished to facilitate the observation of crack initiation and growth. The crack growth was studied by plastic replicas in an optical microscope. The characteristic features of the surface damage and crack growth at both thermal conditions have shown striking differences in micro-crack density, nucleation place and propagation rate even though the fatigue life was not very different. In the as-received specimens, microcracks density is very low and nucleates mainly at grain boundary or second phase particles. In the aged condition, the panorama is completely different. Slips lines firstly appear heterogeneously distributed in the ferritic phase and are the preferred site for microcracks nucleation. The propagation of them takes place along slip bands of adjacent grains.