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·Al 2 O 3 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 Al 2 O 3 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·Al 2 O 3. The driving force for sulfides and steel matrix dissolution was the effect of galvanic couple, and high local plastic deformation caused by oxides, respectively. • MnS and CaS could form the galvanic corrosion with steel matrix, while MgO and Al 2 O 3 had no galvanic couple effect. • MnS was the most preferentially dissolved as an anodic phase and triggered localized corrosion. • Pit nucleated at the MnS position, and expanded in the order of CaS-Fe-MgO·Al 2 O 3. • Driving force for carbon steel matrix dissolution was the effect of high local plastic deformation caused by MgO·Al 2 O 3. [ABSTRACT FROM AUTHOR]