Microstructure and Toughness in Weld Heat-Affected Zone of Duplex Stainless Steel(Materials, Metallurgy & Weldability)

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Relation between microstructure and toughness in weld heat affected zones of SUS329J1 duplex stainless steel has been investigated by means of fractography. Base metal of SUS329J1 has duplex microstructure consisting of a phase and elongated γ phase. The upper shelf energy in the Charpy impact value versus temperature curve was affected by the location of V notch of Charpy impact specimen. For the specimen occuring crack propagation to the short transverse direction, the energy was highest, because of the presence of the platelet and elongated γ phase. The presence of γ phase extremely causes the increase of the toughness for the ductile fracture. But the brittle fracture was hardly affected by the γ phase. For the microstructure of weld heat affected zones, the specimen heated up to 1373K has α+γ duplex microstructure and was similar to that of the base metal. The Charpy impact value was also similar to that of the base metal. For the specimen heated at 1473K and 1573K such as weld bond region, the toughness considerably decreased, because of the large grain size, the decrease of the volume fraction of γ phase and the precipitation of Cr_2N in the α phase.