The corrosion behavior of niobium bearing cold deformed austenitic stainless steels in 3.5% NaCl solution

The corrosion behavior of some austenitic stainless steels was studied in 3.5% NaCl solution. The effects of Nb content and cold deformation on the corrosion resistance were investigated. Electrochemical impedance spectroscopy (EIS) technique was used to investigate the corrosion behavior after two weeks of immersion in NaCl solution. The occurrence of pitting corrosion due to chloride ion attack was also examined by visual inspection, cyclic potentiodynamic, Scanning Electron Microscope (SEM) and microprobe analysis using energy dispersive X-ray (EDS). According to EIS measurements, the corrosion resistance increased by increasing the Nb content. Cold deformation (CD) has a critical effect on the corrosion resistance. The specimens worked at 23% CD showed the best corrosion resistance. The surface corrosion resistance increased double compared with non-deformed specimens. Increasing the deformation to 40% and 50% affects negatively the corrosion resistance. It is argued that on cold working, strain-induced martensite and residual stresses are significantly introduced on the surface, which affects the localized corrosion resistance by increasing the number of active anodic sites on the surface. (C) 2006 Elsevier B.V. All rights reserved.