Electrochemical Impedance Spectroscopy Study of the Corrosion Behavior of Some Niobium Bearing Stainless Steels in 3.5% NaCl

Electrochemical Impedance Spectroscopy (EIS) is a powerful, rapid and accurate non-destructive method for the evaluation of wide range of materials. In this work, the corrosion behavior of some austenitic stainless steels was studied in 3.5%NaCl. The effect of Nb content and cold deformation on the corrosion resistance was investigated. The occurrence of localized corrosion due to chloride ion attack was examined by visual inspection and SEM-EDS. XRD analysis was used to identify the chemical composition of the outer oxide layer. According to EIS, the corrosion resistance increased by increasing the Nb content. Cold deformation (CD) has a critical effect on the corrosion resistance. The specimens prepared at 23% CD showed the best corrosion resistance. The surface resistance increased double compared with that without CD. Increasing the deformation to 40% and 50% affects negatively the corrosion resistance. XRD reveled presence of Cr-rich film in the specimen bearing the highest Nbcontent. It is argued that increasing the Nb-content enhancing formation of surface film enriched with Cr and Ni which has a high corrosion resistance.