THE INFLUENCE OF AGING AT INTERMEDIATE TEMPERATURES ON THE MONOTONIC STRESS-STRAIN BEHAVIOR AND FRACTURE-TOUGHNESS OF A DUPLEX STAINLESS-STEEL

The mechanical behaviour of the duplex stainless steel AISI 329 has be en investigated for ageing times up to 15,000 h at 475, 425, 375, 325 and 275 degrees C. The study has concentrated on changes in the monoto nic stress-strain behaviour and fracture toughness as a function of ag eing temperature and time. It is shown that the tensile behaviour of t he steel changes strongly due to ageing. A large increase in yield str ength and reductions in ductility and fracture toughness are observed. The deformation hardening behaviour of the aged steel is explained by using a model based on a modified rule of mixtures. Finally it is sho wn that the higher toughness of aged duplex stainless steels, in compa rison with ferritic stainless steels aged under the same ageing condit ions, may be associated with the increase in crack growth resistance i nduced by ductile ligaments of austenite which bridge the crack faces.