Effects of spinodal decomposition induced by thermal aging on the hydrogen embrittlement response of Fe-20Cr-5Al alloy

To understand the hydrogen embrittlement mechanism in the Fe-20Cr-5Al alloy for high-temperature hydrogen applications, the effects of thermal aging on hydrogen embrittlement were investigated. Thermal aging was simulated at 475 °C for 300 hours, and its effects were evaluated by examining the changes in hydrogen embrittlement sensitivity and mechanism. This was done using slow strain rate testing (SSRT) combined with cathodic hydrogen precharging. After thermal aging, hydrogen embrittlement sensitivity increased dramatically from 19.5% to 89.9%. Before aging, the influence of hydrogen on fracture behavior was negligible, indicating no significant signs of embrittlement. However, after thermal aging, the fracture mode shifted to a combination of intergranular and enhanced transgranular fracture, suggesting that hydrogen-enhanced decohesion (HEDE) became the dominant embrittlement mechanism. The observed increase in hydrogen sensitivity arises from the spatial correlation between stress concentration caused by thermal aging and hydrogen trapping associated with precharging.