Corrosion of Low Carbon Steel in Chloride Containing Environment

Abstract

This research aims to investigate the corrosion of low-carbon steel in a chloride-containing environment. The investigation started by preparing and studying the surface condition of the specimens. The mechanical properties, microstructures and chemical compositions were also comparatively investigated between standard and corroded specimens. The results showed that the surface of the corroded samples was rough and peeling, different from the standard specimens, which were relatively smooth and non-corrosive. The average ultimate tensile strength and average yield strength of normal specimens were higher than those of corroded specimens at 5.39% and 2.32%, respectively. The corrosion products developed on the surface of corroded specimens caused a high-stress concentration area. The specimen is more prone to cracks and breaks when subjected to tensile stress. The surface of the normal specimen was composed of iron, oxygen, carbon, and silicon. In contrast, the surface of the corroded specimen contained the same elements as the normal specimen except chlorine which was detected. The film layer of the corroded specimen was cracked in contrast with the normal specimen, where the film still covered the metal substrate. The chemical composition analysis found that the corroded specimen's film layer contained chlorine, which is not detected in the film layer of the normal specimen. This is because the film layer of hot-rolled steel remains porous even passing the hot-rolling process. These pores allow chloride ions to diffuse and react with the film layer and the metal substrate. This makes the film layer of the corroded specimen thicker and initiates cracks. When stable alpha-iron-oxyhydroxide is formed on the steel surface, it can help to suppress corrosion.