Region-resolved study of hydrogen embrittlement mitigation in CrMoV welds through post-weld heat treatment

Hydrogen embrittlement compromises the integrity of welded components, limiting the safe implementation of hydrogen-based energy infrastructure. This study examines the effect of a post-weld heat treatment on hydrogen trapping and hydrogen embrittlement susceptibility in the base metal, coarse-grain heat-affected zone, and weld metal of a 2.25Cr1Mo0.25V weld. Electrochemical permeation tests were combined with in-situ small punch tests, allowing the independent evaluation of the narrow weld regions with minimal material requirements. Conducting small punch test on the same specimens used for permeation enabled a direct correlation between hydrogen transport and mechanical behaviour. Post-weld heat treatment was found to markedly reduce the density of hydrogen traps in the heat-affected zone and weld metal, enhancing their resistance to hydrogen embrittlement. Microstructural and fractographic analyses confirmed that this improvement results from microstructural homogenization and lattice relaxation induced by the heat treatment.