Improvement of Corrosion Resistance of Low Carbon Steels by Surface Modification

Abstract

This research aims to investigate the corrosion resistance of surface layers of pack chromizing, titanizing, and chromtitanize low-carbon steel in a chloride-containing environment at room temperature. The parameters affecting the diffused coat, such as the coating time, coating temperature, and the effect of pack compositions, were also studied. Tests are performed to measure wet corrosion behavior using the Potentiodynamic polarization corrosion test. The microstructures and elemental analysis using a scanning electron microscope (SEM) attached to an EDX unit were obtained. Phase analysis is determined using EDX. X-ray diffraction examination indicated that in the chromizing, titanizing, and chromotitanizing processes at different coating times and temperatures of 900°C, 1000°C, and 1100°C. The outer layer is composed basically of Cr,Ti, Cr1.9Ti, FeTi, Al2O3, Cr2O3, TiO2, Cr1.36Fe0.52, (Ti0.86)3.58, and Ti0.86 phases in addition to the elemental iron. The thickness of the coating increases with the increase of the deposition time. The coating is composed of a thick outer layer and a thin inner layer. The formation of the coating depends on the inward diffusion of Cr and Ti atoms and the outward diffusion of Fe atoms. The linear polarization examination showed that the corrosion resistance of steel is enhanced by coating it in a 3.5% NaCl aqueous solution at room temperature. Potentiodynamic polarization examination showed a lower corrosion rate of the coated specimens than the uncoated ones, and the coated specimens exhibit nobler behavior than the uncoated ones in a 3.5% NaCl aqueous solution at room temperature. The corrosion resistance of the coating is proportional to the deposition time and temperature.