Microstructural banding and failure of a stainless steel

The presence of microstructural bands in AL-6XN stainless steel plate has been examined. The bands, which consist of a high density of second-phase particles, are located near the midthickness of the plate, range in thickness up to 300 mum, and are continuous over lengths up to 50 mm. Chemical analyses of the microstructural bands indicate elevated levels of chromium and molybdenum, while orientation imaging microscopy identified primarily sigma-phase particles within the bands; a small volume fraction of chi phase was also found. Tensile specimens oriented in the short transverse direction of the plate show low ductility and exhibit a large variation in failure strains, depending on the continuity of the bands as well as the presence of large precipitate particles within the bands. When oriented in either the longitudinal or the long transverse direction of the plate, circumferentially notched tensile specimens exhibit comparatively high ductility, although at high stress triaxialities, the material was susceptible to specimen splitting parallel to the tensile axis due to cracking along microstructural bands.