Corrosion Estimation of Epoxy Coated High Tensile Strength Steel Measured by Statistical Analysis and TEM–EELS

Abstract

Distribution of the corrosion depth around a surface scratch of epoxy-coated High Tensile (HT) Strength steel (0.7Ni-0.6Cr–0.3Mo–Fe) was measured by using a laser microscope after a wet and dry cyclic corrosion test and compared with that of epoxy-coated carbon (SM) steel. The Gumbel distribution analysis was applied to the corrosion depth profile as a function of distance far from the scratch. In the analysis, the mode (λ) and distribution parameter (α) of the coated HT steel displayed much smaller values than those of coated carbon (SM) steel. The smaller values indicate that the coated HT steel has higher corrosion resistance than that of the coated SM steel. The SEM (Scanning Electron Microscope)-EDS (Energy dispersive X-ray spectrometry) analysis showed that Cr and Mo were enriched in the inner rust layer and Ni distributed in all rust layer around the scratched area of the coated HT steel after the corrosion test. The TEM (Transmission Electron Microscope)-EELS (Electron Energy Loss Spectroscopy) analysis confirmed the presence of nanoscale Fe oxides containing Cr, Ni and Mo in the rust of the HT steel, and these nanostructures of the rust was assumed to enhance the corrosion resistance of the coated HT steel.