Composition changes around sulphide inclusions in stainless steels, and implications for the initiation of pitting corrosion

• DOI: 10.1016/j.corsci.2010.07.021
• Publication Date: 2010-07-20T04:51:57Z
• Authors: David E. Williams; Matt R. Kilburn; John Cliff; Geoffrey I.N. Wat...
• Keywords: Pitting Corrosion; Non-metallic inclusions

We report high-resolution SIMS microscopy measurements, which show that many ‘MnS’ inclusions have surrounding them a narrow ‘halo’ of half-width typically 100 nm that is strongly enriched in Fe, forcing consideration of the electrochemistry of FeS as a determinant of the behaviour of the inclusion boundary. We suggest that on exposure to water a very thin and porous metal-deficient polysulphide skin forms between the bulk of the inclusion and the steel, within which a pit can be triggered. The results resolve a controversy concerning the composition of the boundary region around inclusions in stainless steel and re-emphasise its potential significance.