In-situ Studies of Precursor Sites for Pit Initiation on Corrosion Resistant Alloys in Chloride Containing Solutions

摘要

The present work has as an objective to show a new technique to study in-situ the determination of precursor sites for pitting corrosion on a 25 Cr Duplex Stainless Steels (DSS) using a conventional optical microscope coupled to a potentiostat and additional hardware that allows the real time imaging on the surface of the steels above room temperature inside an electrochemical cell. The results shows that the precursor sites for pitting on 25 Cr DSS are very complex in nature. The larger inclusions within several areas analyzed and tested did not undergo pitting corrosion, in some cases at much higher temperatures than the Critical Pitting Temperature (CPT). However, small inclusions adjacent to the larger ones could nucleate pits and develop stable pitting in chloride containing environments. The inclusions were analyzed and found to be inhomogeneous in nature and consisting of a mixture of various elements (Si, Al, Mg, Ca, Ti, Mn and S). After analysis of the particles, in-situ microscopy and simultaneous anodic polarization studies in chloride containing environments showed that the pits started at small inclusions with further dissolution of the ferrite matrix.