Effects of Cu on Corrosion Resistance of Low Alloyed Steels in Acid Chloride Media

The corrosion resistance of two kinds of low alloyed steels was studied according to the test procedures for qualification of corrosion resistant steel for cargo oil tanks issued by International Maritime Organization. The results indicated that the addition of Cu improved the corrosion resistance of the NS-D36 steel to more than three times that of the conventional D36 steel in the strong acid solution containing chloride (10% NaC1, pH =0. 85). The anodic polarization behavior of the copper-bearing steel was studied by polarization curves and electrochemical impedance spectroscopy (EIS), and alloying element Cu showed beneficial effects including an active potential range, low current density and high transfer resistance of electric charge. The rust layer was analyzed by scanning electron microscopy (SEM) and Auger electron spectroscopy (AES), and the results pointed out that the mechanism of copper's beneficial effects was based on the suppression of anodic dissolution by metallic copper re-deposition on the steel surface immersed in the strong acid chloride media.