Effect of rare-earth modified inclusions on the initiation of marine localized corrosion in high-strength low-alloy steel

Pitting corrosion is a prevalent issue in marine engineering steels, primarily initiated by non-metallic inclusions. This study investigates the effects of rare-earth (Ce, La) deoxidation on the characteristics of inclusions and the initiation of marine localized corrosion in FH460 high-strength low-alloy steel through a combined approach of thermodynamic calculations, finite element simulations, and experimental validationsl. The results indicate that in the absence of rare-earth deoxidation, the steel contains a high number of large-sized inclusions with a clustered distribution. After rare-earth treatment, the inclusions are significantly refined: the average diameter decreases by 33.8%, the average area reduces by 70.8%, and the number density increases from 216/mm 2 to 615/mm 2 . In non-rare-earth deoxidized steels, the chemical dissolution of CaS inclusions not only generates micropores but also produces an acidic environment. In non-rare-earth deoxidized steel, the chemical dissolution of CaS inclusions not only generates micropores but also creates an acidic local environment. Although the inclusions themselves do not participate in the galvanic effect, significant potential inhomogeneity is observed in the matrix surrounding CaS. In contrast, the potential distribution around rare-earth inclusion is more uniform, with the maximum interfacial potential difference reduced by approximately 80%. Rare-earth inclusions exhibit higher thermodynamic stability than CaS, resulting in minimal dissolution and a weaker autocatalytic effect. Furthermore, these inclusions promote the formation of a dense Cr-rich protective film on the pit surface, thereby inhibiting the galvanic effect induced by inhomogeneous matrix potentials. This mechanism effectively suppresses the dissolution of the anodic matrix and slows the growth rate of corrosion pits.