Investigation on the second anodic current maximum on the polarization curves of commercial stainless steels in sulphuric acid

Abstract It is known that the utilization of electrochemical methods to measure the corrosion resistance of metallic materials requires an adequate study of the influence of the various experimental factors in the system under consideration on the course of the polarization curves. The behaviour of AISI 430, 302, 304, 304L, 316 and Durimet 20 in 5 and 1N H 2 SO 4 saturated with N 2 was studied at 23 ± 1°C. The quantities of Fe, Cr and Ni in the corroding solution were determined by atomic absorption spectrophotometry for samples in free corrosion and polarized at a given potential to point out cases of preferential dissolution of the components in alloy. This paper discusses the influence on the second maximum of anodic current in the polarization curve by the following factors: (1) time of immersion before polarization, (2) cathodic pre-polarization, (3) rate of free corrosion, (4) preferential dissolution and (5) the presence of phases. For the alloys and the environment under consideration, evidence is given to demonstrate that factors (1), (2), (3) and (5) are of prime importance. Microscopic observations of the corrosion type of the samples were made and the application of electrochemical methods for the evaluation of the corrosion current is analysed.