Effect of Microstructure on Hydrogen Embrittlement in Weld Heat-Affected Zone of Duplex Stainless Steel

Effect of microstructure on hydrogen embrittlement in the weld heat-affected zone (HAZ) of SUS 329J1 duplex stainless steel has been investigated by means of fractography and transmission electron microscopy. The hydrogenation to the specimen was carried out using cathodic charging in 5% H2SO4 aqueous solution. The susceptibility to hydrogen embrittlement was evaluated by fracture strain. The base metal had duplex structure consisting of α phase and elongated γ phase. The microstructure in the HAZ depended on the peak heating temperature. The volume fraction of γ phase decreased and the precipitation amount of Cr2N in the α phase and at the α grain boundary increased with increasing heating temperature. When the specimens were sensitized at 923K, M23C6 precipitated at α/γ interface, and the growth of γ* phase to the α phase occurred. And then, σ phase precipitated in the α phase side at the α/γ* interface for any specimen. The hydrogen embrittlement occurred in the α phase at any heat-treated specimen. The susceptibility increased with increasing heating temperature in the HAZ. In the case of sensitization, the hydrogen embrittlement occurred not only in the α phase but also at the α/γ interface. The fracture morphology of hydrogen was characterized in the stripe pattern in the α phase. and the secondary cracks occurred at the α/γ interface.