Corrosion behaviour and mechanism of acid-resistant steel in acidic solutions with different Cl− concentrations

This study aimed to enhance the corrosion resistance of low-alloy steel in acidic solutions with varying Cl− concentrations. A new acid-resistant steel incorporating Cu and Sb was developed. Various analyses, including immersion tests under different Cl− concentrations and pH values, corrosion weight loss tests, electrochemical tests, morphological observations, and X-ray diffraction (XRD) analysis, were conducted to investigate the corrosion behaviour and mechanism. The results show that in chlorine-containing acidic environments, acid-resistant steel undergoes chemical dissolution at the anode, with hydrogen gas precipitation at the cathode. The corrosion current density is influenced mainly by the pH and immersion time. The primary corrosion products include Fe2O3, Fe3O4, α-FeOOH, γ-FeOOH, Cu, and Sb oxides, and the intensities of the diffraction peaks of Sb2O3 and Sb2O5 increase as the pH decreases. Acid resistance primarily comes from the protective effects of Sb2O3 and Sb2O5. An increase in H+ concentration promotes uniform coverage of Sb2O3 and Sb2O5. A higher H+ concentration has a greater protective effect on the corrosion product layer than does an increased Cl− concentration, although the influence of Cu cannot be ignored.