Effect of high anodic polarization on the passive layer properties of superduplex stainless steel friction stir welds at different chloride electrolyte pH values and temperatures

The conditions used for friction stir welding of duplex stainless steels determine the resulting mechanical and corrosion performance of the material. This study investigates the corrosion resistance of UNS S32750 and S32760 superduplex stainless steels (SDSSs) joined by friction stir welding, employing cyclic polarization, Mott-Schottky, and microscopy techniques for analysis. The microscopy images indicated the presence of a deleterious intermetallic phase after electrolytic etching of S32760, as well as decreased corrosion resistance. The presence of molybdenum in the steels promoted better passive behavior at low pH. The Mott-Schottky curves revealed p-n heterojunction behavior of the passive oxide. Images acquired after the polarization test by scanning electron microscopy showed higher passivation propensity with increases of temperature and pH.