Microstructure and stress corrosion cracking of the fusion boundary region in an alloy 182-A533B low alloy steel dissimilar weld joint

► High-angle misorientation at FB, type-II and type-I boundaries. ► Highest residual strain and hardness in the zone between FB and type-II boundary. ► Type-II and type-I boundaries had lower resistance to SCC growth than the FB. ► Crack growth blunted by pitting at the FB. ► Reactivation of crack growth from the pitting by oxidation along the grain boundary. Stress corrosion cracking (SCC) in the fusion boundary (FB) region of an Alloy 182-A533B low alloy steel (LAS) dissimilar weld joint in high temperature water doped with sulfate was studied following a microstructure characterization of the FB region. The microstructure characterization suggested the type-II and type-I boundaries in the dilution zone (DZ) adjacent to the FB had lower resistance to SCC growth than the FB. Crack propagating perpendicular to the FB in the DZ was observed to be blunted by pitting at the FB, followed by the reactivation from the pitting by localized oxidation along the grain boundary in LAS.