Improvement of sulfide stress corrosion cracking resistance of the Inconel 625/X80 weld overlay by post-weld heat treatment

The effect of post-weld heat treatment (PWHT) on the microstructure, penetration and distribution of hydrogen, and sulfide stress corrosion cracking (SSCC) behavior was investigated to improve the cracking resistance of Inconel 625/X80 dissimilar weld overlay. Among nine candidate PWHT procedures, only the PWHT at 620 °C/20 h could improve the SSCC resistance of the overlay as no crack but only shallow pits were observed in the fusion boundary (FB) region. This PWHT procedure decreased the microhardness, increased the fraction of low-angle grain boundaries, eliminated the susceptible microstructure to hydrogen embrittlement, and therefore enhanced the SSCC resistance of the heat-affected zone. Further, in addition to the decrease of misorientation at the FB, the enhanced SSCC resistance of the FB after PWHT was mainly owing to precipitation of dispersed M₂₃C₆ carbides, which may reduce the amount of diffusible hydrogen within the martensite layer and prevent localized hydrogen concentration from reaching the cracking threshold.