Aqueous Corrosion Behavior of Weathering Steel and Carbon Steel in Acid-Chloride Environments

Aqueous corrosion characteristics of carbon steel and weathering steel in aerated acid-chloride solutions were studied by using immersion weight loss tests, crevice corrosion tests, electrochemical measurements, and analytical techniques. Neither carbon steel nor weathering steel showed passive behavior in these acid-chloride solutions. Corrosion morphology was examined using scanning electron microscopy (SEM). Surface morphology showed uniform attack with some shallow pits. Weathering steel was not susceptible to crevice corrosion because of the small potential difference between the steel within the crevice and the steel outside the crevice. Weathering steel was more resistant to acid-chloride solutions than plain carbon steel. The better corrosion resistance of the weathering steel is attributed to protectiveness of the surface layer. X-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) analyses revealed that the rust layer formed in acid-chloride solution was composed of hematite (Fe₂O₃) and magnetite (Fe₃O₄). From XPS analyses, however, there were some Cr and Cu compounds in the rust layer of the weathering steel. These compounds act as a factor for corrosion resistance in aqueous solutions.