| Summary: | This study presents a combined electrochemical and X-ray photoelectron spectroscopy (XPS) surface analytical investigation on the natural passivation process and its effect on Cl− induced corrosion resistance of traditional carbon steel, ferritic and austenitic stainless steels (SSs) (i.e. HRB400 steel, 430 and 304 SSs) in simulated concrete pore solution (SPS). It was found that a complete and more compact passive film with a stratified structure could be naturally formed on the tested steel surfaces after different immersion time. The chemical composition of the passive film and its corrosion resistance strongly depended on the alloying element and natural passivation time. For HRB400 steel, the outer layer of natural passive film was mainly composed of Fe3+ species and the inner layer was predominated by Fe2+ ones, while the outer layer of natural passive film formed on SSs surface consisted of Fe and Cr oxides and hydroxides, enriched in Fe3+ species, and an inner layer was made of mixed Fe2+ and Cr3+ oxides (enriched in Fe2+ species). The natural pre-passivation could effectively improve the Cl− induced corrosion resistance of three steels. Compared with HRB400 steel, both austenitic and ferritic SSs exhibited the better corrosion resistance due to the formation of Cr-enriched passive film, of which, 304 SS had the highest pitting corrosion resistance.
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