Mechanism of (Mg, Al, Ca)-oxide inclusion-induced pitting corrosion in 316L stainless steel exposed to sulphur environments containing chloride ion

The mechanism of oxide inclusion-induced pitting corrosion in 316L stainless steel exposed to sulphur environments containing chloride ions was investigated by scanning electron microscope analysis, electrochemical measurements and scanning Kelvin probe force microscopy (SKPFM). Two inclusion types were observed. The (Mg, Al, Ca)-oxide inclusions play an important role in pitting formation. SKPFM measurement results show that the inclusion sites exhibited a lower surface potential than the matrix. Finally, the schematic representation of the initiation and propagation process of the (Mg, Al, Ca)-oxide inclusion-induced pitting corrosion in 316L stainless steel exposed to sulphur environments containing chloride ions was established.

► Two inclusion types are observed in 316L stainless steel.
► (Mg, Al, Ca)-oxide inclusions play an important role in pitting formation.
► The dissolved part was the Ca–Al–O impurity rather than the Mg–Al–O crystal.
► The inclusion sites exhibited a lower surface potential than the matrix.
► A possible mechanism of oxide inclusion-induced pitting corrosion is established.