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 was developed based on which the pit growth automatically stops any time after the pit initiation under a chloride solution droplet. The atmospheric pitting corrosion of austenitic stainless steels with various sulfur (S) concentrations was investigated using this system. The results confirm that the initiation sites of pitting corrosion are manganese sulfide inclusions under the droplets regardless of the S concentration. In addition, the growth behavior of the active dissolution area is independent of the S concentration. When these specimens are subjected to wetdry cycle tests, the probability of pitting corrosion increases with increasing S concentration due to the increase in initiation sites. The onset of pitting corrosion is independent of the chloride concentration. On the other hand, repassivation strongly depends on the S concentration.

Review—Understanding and Controlling the Electrochemical Properties of Sulfide Inclusions for Improving the Pitting Corrosion Resistance of Stainless Steels

“…Among these, sulfide inclusions such as manganese sulfide (MnS) are known to initiate pitting corrosion. [2][3][4][5] Reducing sulfide inclusions can effectively improve the pitting corrosion resistance; however, complete removal of the inclusions is unfeasible. The prospect of reducing impurities to achieve resource conservation and improve pitting corrosion resistance is questionable.…”