Influence of rare earth metals on mechanisms of localised corrosion induced by inclusions in Zr-Ti deoxidised low alloy steel

•Rare earth influence on pitting in Zr-Ti deoxidised steel in marine environment was studied.•No galvanic couple formed between inclusion and Zr-Ti deoxidized steel before/after adding rare earth.•Pitting initiated by microcrevices/lattice distortion surround ZrO2-Ti2O3-Al2O3 inclusion.•Chemical dissolution of ((RE)2O2S-(RE)xSy) in rare earth modified inclusion induced pits.•Oxygen-concentration gradients and catalytic-occluded cells may accelerate pit growth. The influence of rare earth addition on the mechanism of localised corrosion induced by inclusions in Zr-Ti deoxidised steel was investigated in a simulated marine environment. Inclusion size and composition changed after rare earth addition, profoundly affecting the localised corrosion. Current sensing atomic force microscopy results showed that no galvanic couple formed between inclusions and matrix owing to the insulating property of different inclusions. Matrix dissolution resulting from the microcrevices and lattice distortion surrounding ZrO2-Ti2O3-Al2O3 inclusions initiated localised corrosion in Zr-Ti deoxidised steel. After adding RE, localised corrosion was induced by dissolution of the (RE)2O2S-(RE)xSy part of the inclusion.