Electrochemical analysis of austenitic stainless steel of type 304L SS in nitric acid medium

Abstract

Austenitic stainless steels type 304L and 316L are largely used as structural materials for equipments handling nitric acid media in nuclear reprocessing plants. In almost all nitric media, these materials, protected by a chromium oxide rich layer, remain in their passive state. However, in some particular nitric media, their corrosion potential may be shifted towards their transpassive domain. The corrosion potential of the steel depends greatly on the cathodic reaction involved in the oxidoreduction process between the elements Fe, Cr, Ni of the steel and the oxidizing species of the medium. In this experiment, we have observed corrosion behavior of 304L SS by both electrochemical analysis and non-electrochemical analysis in different nitric acid concentrations such as 0.4M, 0.5M, 0.6M, 1M, 2M and concentrated solution. We measured corrosion rate and relation between corrosion current and corrosion rate by Tafel extrapolation method. Surface morphology of corroded surfaces were analysed by using AFM. The Micro hardness test was carried out to measure the hardness of both the non-corroded and corroded specimens. It is observed that the corrosion current density is inversely proportional to the corrosion potential and implies same pattern of corrosion tendency. The AFM results, we found that there is decreasing the density of pits on the surface by increasing concentration of nitric acid solution.