Corrosion Protection Performance of Epoxy Coated High Tensile Strength Steel Measured by Scanning Electrochemical Microscope and Electrochemical Impedance Spectroscopy Techniques

The corrosion protection performance of epoxy coated High Tensile Strength (HT) steel was evaluated by using Electrochemical Impedance Spectroscopy (EIS) and Scanning Electrochemical Microscope (SECM) analysis. EIS was performed on coated HT steel with a scratch in a 0.1 M NaCl solution after a wet/dry cyclic corrosion test. The charge transfer resistance (R-ct) and film resistance (R-f) of coated HT steel displayed a higher value than coated carbon steel. SECM was conducted to estimate the corrosion performance of the epoxy coated HT steel immersed in a 0.1 M NaCl solution. It was measured that dissolution of Fe2+ was suppressed at the scratch on the coated HT steel due to the higher resistance for anodic dissolution of the substrate. SEM/EDX analysis showed that Cr and Mo were enriched in corrosion products at a scratched area of the coated steel after corrosion testing. FIB-TEM analysis confirmed the presence of the nanoscale oxide layers containing Cr, Ni and Mo in the rust of the steel, which had a beneficial effect on the corrosion resistance of coated steel by forming protective corrosion products in the wet/dry cyclic test.