The effect of weld chemistry on the oxidation of Alloy 82 dissimilar metal welds

•Dilution resulted in significantly altered chemical composition in Alloy 82 dissimilar metal welds.•Internal oxidation of Cr occurred in all areas of the weld, except the root.•An external Fe-rich oxide formed on the root, beneficially preventing inward oxygen diffusion.•Depletion of Cr and segregation of impurities possibly increases PWSCC susceptibility in the root.•Internal oxidation in the crown may result in intergranular embrittlement if exposed to primary water.

Alloy 82 dissimilar weld joints between carbon steel and Alloy 600 were exposed to a simulated primary water environment consisting of hydrogenated steam at 480 °C and 1 bar. Dilution due to mixing from the parent materials to the weld was significant, particularly in the root where there was Fe enrichment (35 at.%) and Cr depletion (10 at.%). The heterogeneous composition of the weld from root to crown resulted in differences with respect to surface versus internal oxidation. A Fe-rich surface oxide formed on the weld root which may help to prevent embrittlement and SCC by internal intergranular oxidation.