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. The results revealed that MgO·Al2O3 served as cores and MnS·CaS as shells in the carbon steel. MnS and CaS could form the galvanic corrosion with steel matrix, while MgO and Al2O3 had no galvanic coupling effect with steel matrix and deserved high stability. As the immersion time prolonged, the average pit depth increased linearly, and the pit developed longitudinally. MnS with the lowest work function was the most preferentially dissolved as an anodic phase and triggered pitting corrosion, which expanded in the order of CaS-Fe-MgO·Al2O3.