Effect of cold reduction on corrosion of carbon steel in aerated 3% sodium chloride

The influence of various degrees of plastic deformation by cold reduction on the corrosion behavior of a carbon steel sheet in 396 sodium chloride (NaCl) solution was investigated. Microstructural, diffraction, and hardness studies were also conducted. The material was evaluated after 0%, 2796, and 5096 thickness reductions. Electrochemical impedance spectroscopy (EIS) and polarization tests were used for corrosion characterization of each reduced condition, white scanning electron microscopy (SEM), x-ray diffraction (XRD), and hardness measurements gave complementary information. SEM observations manifested an appreciable reduction of pearlitic interlamellar spacing and grain alignment in the rolling direction whereas image analysis illustrated a linear grain length increment with cold reduction. Hardness also increased linearly with cold reduction. XRD patterns showed that the initial sheet exhibited a random grain orientation and was characterized by the main crystallographic (110) plane, while the cold-reduced sheet at various percentages showed a preferential crystalline orientation in (211), (100), and (111) planes. Corrosion studies in aerated 396 NaCl solution based on polarization tests, EIS, and electrode surface appearance revealed that cold reduction led to significant improvements in corrosion resistance when compared with the unrolled material. However, in deaerated solution, the difference among these conditions was quite small. The resultant properties in aerated solution were attributed to removal of blowholes, fissures, and microstructural defects by the compressive stress associated with the cold reduction process. They were also associated with differential dissolution of the different atomic arrangements exposed at the surface as a result of the texture components developed as the steel sheet was deformed.