Role of Al2O3 inclusions on the localized corrosion of Q460NH weathering steel in marine environment

•The role of Al2O3 inclusions in the pitting corrosion initiation stage in a marine environment was studied.•A high dislocation density region existed around Al2O3 inclusions in the cold rolling Q460NH steel.•A mechanism different from the galvanic coupling was used to explain the selective dissolution of matrix around inclusions.•Al2O3 clusters had a more negative effect on the corrosion behaviour of the Q460NH steel analysed than single inclusions. The influence of Al2O3 inclusions on the localized corrosion behaviour of Q460NH steel was investigated in a simulated marine environment. According to the current sensing atomic force microscopy (CS-AFM) result, there was no galvanic couple between Al2O3 inclusions and the adjacent steel. Therefore, a different mechanism from that traditionally used (considering the galvanic coupling between inclusions and matrix) to explain the selective dissolution of the matrix around inclusions, dominated the pit initiation and propagation process in this system. Electron backscattered diffraction (EBSD) analysis showed a region of high dislocation density around the inclusions. Both microcrevices and the high dislocation density region around inclusions can easily induce localized corrosion. The catalytic-occluded cells and oxygen-concentration cell could accelerate the propagation of the pits. Furthermore, inclusion clusters had a larger negative effect than single inclusions on the corrosion resistance of the steel. Scanning vibrating electrode technique (SVET) measurements confirmed that inclusions play a key role in the corrosion process.