Unraveling the Effect of Sulfide-Oxide Complex Inclusions on the Localized Corrosion Mechanism for Carbon Steel

The localized corrosion induced by (Ca, Mn)S-(Al, Mg)O complex inclusions was investigated. It revealed that MgO·Al2O3 served as cores and MnS·CaS as shells in the carbon steel. MnS and CaS acted as an anodic phase in the galvanic corrosion formed with steel matrix, while MgO and Al2O3 had no galvanic couple effect with MnS and CaS. MnS was the most preferentially dissolved and triggered localized corrosion, which expanded in the order of CaS-Fe-MgO·Al2O3. The driving force for sulfides and steel matrix dissolution was the effect of galvanic couple, and high local plastic deformation caused by oxides, respectively.