Immersion Behavior of Carbon Steel, Phosphate Carbon Steel and Phosphate and Painted Carbon Steel in Saltwater

The carbon steel is used in many areas due to its good mechanical properties; however, its low corrosion resistance presents a very important problem, for example, when carbon steel carabiners are used in the petroleum industry or navy, the possibility of an accident is higher due to carabiner failure. This phenomenon could occur as a consequence of the corrosion process which negatively affects mechanical properties. This paper study the possibility to improve its corrosion resistance by depositing on its surface a phosphate layer and a paint layer, and also aims to analyze the immersion behavior in saltwater of carbon steel, phosphate carbon steel, and phosphate and painted carbon steel. According to this study, by coating the carbon steel with a phosphate or paint layer, a higher polarization resistance is obtained in saltwater. Moreover, by electrochemical impedance spectroscopy (EIS), it was observed that the corrosion rate decreases with the increase of the immersion time. Meanwhile scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) revealed that the main compounds which formed on the sample's surface were iron oxides or hydroxy-oxides, after immersion for a longer period. The overall results show that all types of deposited layers increase the corrosion resistance of C45 steel.