In a considerable number of published articles dealing with the process of pit nucleation, it has been shown that pits predominantly develop close to non-metallic inhomogeneities within the metal surface.1-18 In 1933 Tronstad and Sejersted,12 using a chemical test method, were the first to show that among all inhomogeneities, those containing sulfur were the most effective to cause pit formation. More recently, this result has been confirmed many times by electron microprobe analysis. A review of theseinvestigations has been published by Szklarska-Smialowska.17 Inclusions which cause pitting consist of iron or manganese sulfides. Very often, mixed sulfides of the type (Mn, Fe)S have been detected. In many cases the sulfides were located close to oxide inclusions such as chromium oxide or aluminum oxide.
To explain the effectiveness of sulfide inclusions relative to other chemical inhomogeneities in initiating pittings, several interpretations are given in the literature. According to Szklarska-Smialowska,...
