Corrosion behavior of alloy 52M and 52MSS weld surfacing

Abstract

High chromium nickel-based fillers are used in nuclear dissimilar joints or repairs. Due to the risks of ductility dip cracking of Alloy 52 M weld surfacing, a nickel-based filler with a high niobium and molybdenum content (Alloy 52MSS) is expected to enhance the stability of grain boundary and improve the resistance to stress corrosion cracking. In this study, Alloy 52 M and Alloy 52MSS were used in weld surfacing on A508 steel. The results showed that Nb concentrated in the interdendritic region, and Mo gathered around Nb-rich carbide grains. The hardness profile presented similar trends for both filler metals. In potentiodynamic testing, the corrosion potential was increased while the corrosion current density was lowered for 52MSS.Further cyclic polarization testing indicated that 52MSS had the capability to increase the protection potential and reduce the pitting phenomenon. The morphology of 52 M welding surfacing after testing showed a feature of interdendritic corrosion, while the characteristic of 52MSS′ showed a behavior in general corrosion. The Mo addition resulted in the formation of a metastable oxide scale that improved the alloy's corrosion resistance in the trans-passivity region. The 52MSS had a more remarkable ability to prevent the outer surface of weld surfacing from interdendritic corrosion.