Abstract
Equilibrium calculations on some sulflde systems actual in commercial stainless steel have shown that the sulfides cannot thermodynamically exist at the potential of the passive steel. The ions released by the dissolution of the sulfides give rise to an acid solution in microareas. A pitting corrosion mechanism based on the sulfides themselves is suggested. The sulfides are polarized to the potential of the passive steel surface and tend to dissolve. During the dissolution a virgin metal surface is exposed to the environment. When the solution in the microarea thus developed has reached a certain composition, the contacting metal can no longer passivate and the metal starts to dissolve.