Stainless-steel corrosion and MnS inclusions

The pitting corrosion of stainless steels that occurs in environments containing chloride usually initiates at manganese sulphide particles in the steel. Ryan et al.1 describe the presence of a wide chromium-depleted zone around MnS inclusions in a stainless steel (316F grade), suggesting that pitting could be triggered by an attack on these chromium-depleted zones instead of at the MnS inclusions themselves2,3,4. Here we investigate several different stainless steels, including the same 316F sample used by Ryan et al.1, and find no evidence of chromium-depleted zones in any of them. Further analysis is evidently needed to clarify the mechanism of pitting in these materials.