Microstructural evolution and pitting corrosion behavior of friction stir welded joint of high nitrogen stainless steel

Highlights: • Pitting corrosion behavior of high nitrogen steel joint was studied after friction stir welding. • No drastic decrease in breakdown potentials was observed in the heat affected zones. • Nugget zone showed good pitting corrosion resistance due to microstructural changes. • δ-ferrite and tool wear bands were detected in friction-stir weld zone of high nitrogen stainless steel. • Pitting corrosion resistance of the nugget zone was found to be unaffected by δ-ferrite and tool wear. With the achievement of sound joints of high nitrogen stainless steel via friction stir welding, significant microstructural changes take place in various regions of the joints. This would bring out the change in the corrosion properties of the joints. In this study, the corrosion behavior of friction stir welded joint of high nitrogen stainless steel was investigated using electrochemical and immersion tests. No drastic decrease in breakdown potentials was observed in the heat affected zones with number and size distribution densities of pits being similar to that in the base metal. The nugget zone exhibited a relatively good pitting corrosion resistance, mainly attributing to the breakup of coarse inclusions and grain refinement during welding. The δ-ferrite bands and tool wear exerted no obvious effects on the corrosion behavior of the welded joint due to the lack of Cr diffusion.