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.