Pit Propagation at the Boundary between Manganese Sulfide Inclusions and Austenitic Stainless Steel 303 and the Role of Copper

摘要

MnS inclusions have long been studied as key pit nucleation sites in austenitic stainless steels. Many different mechanisms have been proposed as to the manner in which these inclusions serve as initiation sites. Here, the behavior of MnS inclusions in a free machining stainless steel was studied via a combination of surface topographical and localized electrochemical techniques. A mechanism was proposed where preferential dissolution of the inclusion occurs until a preexisting trench at the inclusion/base metal interface is reached. As dissolution continues, a critical pitting solution is formed within the occluded geometry, resulting in enhanced dissolution of the base metal and the release of Cu(II).