二相ステンレス鋼の溶接金属における水素割れ発生特性に及ぼす微視組織の影響に関する数値解析

抄録

Duplex stainless steels and their deposited weld metal have ferrite and austenite microstructure, which have material properties that are different. In addition, the microstructure of the base metal and weld metal are clearly different; therefore, it affects the hydrogen diffusion and accumulation, and hydrogen-induced cracking behavior at the microstructural scale. In this study, the influence of the microstructure on hydrogen-induced cracking behavior of duplex stainless steel weld metal was investigated. Specimens of duplex stainless steel weld metal were prepared and slow strain rate tensile test was performed after hydrogen charging. Cracks were observed at boundaries of ferrite and austenite phases. In order to clarify the stress and hydrogen concentration distribution at the microstructural scale, a microstructure-based finite element simulation was performed. A finite element model based on a cross sectional observation of the microstructure was designed to calculate the stress and hydrogen concentration distribution. The simulation result showed that the hydrogen accumulation occurs at ferrite/austenite boundaries, which corresponded to the locations where cracks were observed in the experiment. On the other hand, the hydrogen concentration at the accumulation site in the weld metal was low compared to that in the base metal. Therefore, the influence of the phase fraction and the stress-strain curves of the ferrite and austenite phases on the hydrogen concentration was investigated by the proposed numerical simulation. It was demonstrated that both the phase fraction and stress-strain curves have significant influence on the microscopic distribution of hydrogen concentration.