Microstructure and Toughness in Weld Heat-Affected Zone of Duplex Stainless Steel

Relation between microstructure and toughness in weld heat affected zones of SUS 329JI duplex stainless steel has been investigated by means of fractography. Base metal of SUS 329JI has duplex microstructure consisting of alpha phase and elongated gamma phase. The upper shelf energy in the Charpy impact value vs. temperature curve was affected by the location of V notch of Charpy impact specimen. For the specimen with crack propagation occurring in the short transverse direction, the energy was highest, because of the presence of the platelet and elongated gamma phase. The presence of gamma phase causes the increase of the toughness for the ductile fracture; but the brittle fracture was hardly affected by the gamma phase. For the microstructure of weld heat affected zones, the specimen heated up to 1373K has alpha + gamma duplex microstructure and was similar to that of the base metal. For the specimen heated at 1473 and 1573K, such as weld bond region, the toughness considerably decreased, because of the large grain size, the decrease of the volume fraction of gamma phase and the precipitation of Cr sub 2 N in the alpha phase. 11 ref.--AA