Influence of MC Carbides on Pitting Corrosion Resistance of Weld Metal in Austenitic Stainless Steels

The influence of MC-type carbide formation on pitting corrosion resistance in weld metal of austenitic stainless steel was investigated. The relationship between the microstructure such as carbides and element distribution, and pitting corrosion resistance of the simulated weld metal of austenitic stainless steel was studied. The addition of molybdenum improved the pitting corrosion resistance. The effect of niobium addition on the pitting resistance was negligible. However, the addition of titanium significantly reduced the pitting corrosion resistance. The addition of niobium or titanium induced the formation of MC-type carbides, such as TiC and NbC, at the cellular boundaries. The pits were mainly initiated near or at carbides. The chromium depletion zone was formed near M23C6 coexisting with TiC only in the specimen added titanium. Thus, TiC formed during solidification accelerated the chromium diffusion-associated M23C6 precipitation on TiC. The depletion zone deteriorated the pitting corrosion resistance of the titanium-containing specimen.