Evolution of Surface Changes and Corrosion Kinetics During Atmospheric Corrosion in Seacoast Environment, Part II: Low Carbon Steel

This study investigates the corrosion behavior of low carbon steel (LCS) during 1 y of exposure in a seacoast environment. Potentiodynamic polarization tests with a modified droplet cell method simulating the atmospheric exposure conditions were used to understand the corrosion kinetics under a thin electrolyte layer. Ion chromatography experiments were performed to track changes in the concentration of the soluble species on the surface of the samples. Optical microscopy, scanning electron microscopy, and Raman spectroscopy were used to analyze the corrosion morphology and chemical composition. During the first 4 d to 7 d, (LCS) exhibited active behavior, with anodic reactions driven by chloride deposition and minimal corrosion product formation. Only small pits filled with lepidocrocite and amorphous ferrihydrite were present. Between 14 d and 30 d, a thin lepidocrocite layer covered the entire surface, increasing surface passivity and reducing anodic reaction rates. By 90 d, the surface was fully covered with a yellow rust layer of lepidocrocite, but high chloride concentrations continued to drive anodic activity. A strong correlation between chloride concentration and corrosion rate was observed during the first 90 d. After 180 d, goethite, along with lepidocrocite and akageneite, formed a thicker protective layer, significantly reducing corrosion. Chloride remained as the dominant anion throughout the exposure period. Dissolution of sulfate ions from the surface required repeated ultrasonication, suggesting the formation of sulfate nests within the rust layer.