New insights into the influence mechanism of carbides on the localized corrosion of N80 carbon steel: Experiments and first-principles study

Carbides significantly influenced the corrosion behavior of N80 carbon steel. The specific types of carbides and their adsorption behavior at the interface with the steel matrix were particularly complex. This study comprehensively evaluated the impact of carbides on the localized corrosion of N80 steel using both computational and experimental techniques. The findings revealed that the predominant carbides in the steel were Fe₃C, with a potential difference of approximately 65.3 mV greater than that of the steel matrix, leading to preferential dissolution of the steel matrix. The corrosion film that formed on the steel surface was loose and porous, enriched with Cl-, and insufficient to effectively prevent the penetration of corrosive media. The work function relationship between Fe₃C and the steel matrix was Fe < Fe₃C, and O exhibited a higher adsorption energy on the Fe surface than on the Fe₃C surface. This resulted in a strong galvanic coupling corrosion effect between Fe₃C and the steel matrix. Fe₃C, acting as the cathodic phase in the galvanic corrosion process, accelerated the adsorption of O₂ on the steel surface, which in turn led to significant dissolution of the steel matrix. This process facilitated the nucleation of pits, ultimately resulting in the formation of stable pits on the surface.