Observation of Pit Initiation and Growth of Stainless Steel under a Chloride Solution Droplet―Effect of S Content on Pit Initiation, Growth and Repassivation―

Abstract

A system that can stop pit growth automatically at any time after the pit initiation under a chloride solution droplet was developed. Using this system, atmospheric pitting corrosion of austenitic stainless steels with various sulfur （S） concentrations was investigated. It was confirmed that initiation site of pitting corrosion was manganese sulfide （MnS） inclusions under the droplets regardless of S concentrations. In addition, the growth behavior of the active dissolution area doesn't also depend on S concentrations. When these specimens were subjected to wet-dry cycle tests, probability of pitting corrosion increases with S concentrations due to increasing initiation site, and there is no clear difference in chloride concentrations for onset of the pitting corrosion. On the other hand, repassivation behavior is strongly depends on S concentrations.