Initiation and propagation of localized corrosion induced by (Zr, Ti, Al)-O_x inclusions in low-alloy steels in marine environment

The effects of inclusions on localized corrosion of Zr–Ti deoxidized low-alloy steels in marine environment were investigated by various analytical techniques including scanning electron microscopy with X-ray microanalysis (SEM/EDS), confocal Raman microscopy (CRM), and in situ scanning vibrating electrode technique (SVET). It was found that complex (Zr, Ti, Al)-O_x inclusions were responsible for the initiation of localized corrosion. Localized corrosion preferentially occurred at Fe matrix adjacent to these inclusions and formed micro-gaps. In the early stage of corrosion, catalytic-occluded cells and the diffusion of chloride ions played a major role in the propagation of corrosion, further accelerating the dissolution of Fe matrix and (Zr, Ti, Al)-O_x inclusions. Combining SVET and CRM results, it revealed that the maximum anodic current density in local area gradually decreased with prolonged exposure time, indicating that corrosion products covered the steel surface and lowered the propagation rate of corrosion. In the later stage of corrosion, the barrier effect of corrosion products played an important role in inhibiting localized corrosion.