Corrosion Resistance of Epoxy-Coated 3% Cr Steel in Saline Environment Measured Using EIS and SECM

Electrochemical impedance spectroscopic (EIS) and scanning electrochemical microscopic (SECM) techniques are used primarily to evaluate the corrosion protection performance of epoxy-coated 3% Cr steel. Wet/dry cyclic corrosion tests (EIS) were performed on epoxy-coated carbon and 3% Cr steel samples in a 3 % NaCl solution. The EIS results showed that corrosion resistance of 3% Cr steel sample is greater than carbon steel sample. In order to determine the tip potentials for dissolution of Fe2+ and Cr2+, cyclic voltammetry experiments were performed using the SECM tip at open circuit potential (OCP). The tip potential was set at -0.7, +0.04 and +0.60 V to determine the concentration of dissolved oxygen, and dissolution of Cr2+ and Fe2+ respectively. The dissolution of Fe2+ at the scratch defect was much lower in coated 3% Cr steel than in carbon steel. The consumption of oxygen was less for 3% Cr steel which is attributed to the fact that the dissolved oxygen reduction was decreased on the surface of 3% Cr steel compared to carbon steel. Thus, it was indicated that the weaker anodic and cathodic reactions were observed at the scratch of coated 3% Cr steel. In the case of dissolved oxygen, the tip current decreases for 3% Cr steel, which is ascribed to the reduction in the amount of dissolved oxygen over the sample surface. Corrosion resistance was much higher for the 3% Cr steel sample because the anodic and cathodic reactions at the scratch were weaker for coated 3% Cr steel than carbon steel.