Influence of nitrogen addition on the crevice corrosion resistance of nitrogen-bearing austenitic stainless steels

Crevice corrosion studies were carried out on nitrogen-bearing types 304, 316 and 317 austenitic stainless steels (SS) by a potentiodynamic anodic polarisation method in an acidic chloride medium. A special all-glass crevice assembly was used for providing reproducible crevice effects on the surface of the test specimen. The results indicated that the increase in nitrogen content improved the crevice corrosion resistance of the alloys by decreasing the active dissolution, and increasing both passive film stability and the potential at which crevice attack was stable. This was very significant for 304 and 316 SS alloys in comparison with 317 SS alloys. The combined influence of nitrogen and molybdenum was found to be very significant in providing high crevice corrosion resistance for 317 SS alloys. Optical microscopic observation revealed severe crevice attack on types 304 and 316 SS alloys compared to mild crevice attack on type 317 alloys. Based on the results of the present investigation a possible mechanism by which nitrogen addition improved the crevice corrosion resistance is discussed.