Strain-age cracking in vacuum electron beam welded IN738LC alloy during post-weld heat treatment

Abstract IN738LC joint by vacuum electron beam welding (VEBW) exhibited high strain-age cracking (SAC) susceptibility and SAC mainly propagated along grain boundaries (GBs) of fusion zone (FZ) after post-weld heat treatment (PWHT). SAC occurred in the temperature range of 700 °C ∼1000 °C when IN738LC joints were subjected to PWHT with air atmosphere. The time to crack initiation decreased rapidly as the holding temperature rose. The investigation of influence factors of SAC indicated that the precipitation of γʹ particles, age hardening, oxidation-induced embrittlement and residual stress had a significant impact on the formation of SAC in FZ. Age-contraction stress induced by the precipitation of γʹ particles and residual stress acting on FZ were the essential factors to induce SAC. In addition, age hardening originating from the precipitation of γʹ particles and surface oxidation of weld metal exacerbated the formation of SAC during PWHT.