Electrochemical Extraction Technique and SEM Study of Precipitated Carbides at Grain Boundaries in Austenitic Stainless Steel

Abstract

Losses from corrosion are a damage which is difficult to quantify at world level, and a large variety of service failure problems of materials is due mainly to corrosion-related problems. One of the localized types of corrosion is originated by exposure to stainless steel at work temperatures where the sensitization phenomenon occurs. This phenomenon occurs due to second stage precipitation at grain boundaries, whether by thermal treatment or by welding. In this study, a thermally treated steel AISI 304 was used, and it shows the results of various chemical and electrochemical attacks to reveal the presence of carbides at grain boundaries, chromium carbides are precursors of localized corrosion. Linear polarization was performed in the sensitized samples to estimate the repercussion of this phenomenon on the overall corrosion resistance of the stainless steel. Surface evaluation was carried out using a Scanning Electron Microscope and an EDS X-ray detector, through which it was possible to do an in situ chemical analysis of the particles and the extracted carbides, after having dissolved the steel matrix electrochemically.