DAMAGE AND RUPTURE MECHANISMS IN AN AUSTENOFERRITIC DUPLEX STEEL

The influence of ageing on damage and rupture mechanisms in an austeno ferritic duplex stainless steel is studied using conventional strainin g and impact toughness testing at 20 degrees C and 320 degrees C, and in situ SEM straining at 20 degrees C. While the as-received alloy fai ls in a ductile mode, damage in the aged material starts with cleavage nucleation in ferrite. We show that, owing to the bipercolated topolo gy of the alloy, these cleavage cracks can propagate while passing rou nd austenite ligaments whose plastic stretching controls the crack ext ension. The variations with strain of both the crack size and the aver age crack separation are computed analytically and their comparison gi ves a good prediction of ductility. (C) 1997 Acta Metallurgica Inc.