<p>A long-term in-situ marine study was carried out to evaluate the corrosion behavior of Q355B carbon steel across various ocean zones in the Dalian Sea. The results reveal significant variations in the rust layers formed in different regions, which in turn influence the progression of the corrosion process. In the atmospheric zone, the primary corrosion products include γ-FeOOH, α-Fe₂O₃, and Fe₃O₄, and the development of the rust layer contributes to a reduction in the corrosion rate. In the tidal zone, the main corrosion products were α-FeOOH, γ-FeOOH, α-Fe₂O₃, and Fe₃O₄. The irregular distribution of the rust layer in this area resulted in localized corrosion on the steel surface. In the immersion zone, in addition to the previously mentioned corrosion products, the rust layer also fosters an environment conducive to microbial growth. The metabolic activities of these microorganisms compromise the structural integrity of the rust layer, thereby exacerbating the corrosion process.</p>