Corrosion Evaluation of Duplex and Superduplex Stainless Steel Friction Stir Welds Using Potentiodynamic Measurements and Immersion Tests in Chloride Environments

Austenitic–ferritic stainless steels submitted to friction stir welding show good mechanical properties, although there are concerns regarding their application in marine environments, related to their corrosion performance. Friction stir welds of UNS S32101, S32205, S32750, and S32760 steels were successfully produced at 200 rpm and 100 mm/min. The corrosion resistance of the FSW joint was evaluated by application of the ASTM A923 standard method, cyclic polarization measurements, and determination of weight loss during the FeCl₃ immersion test. The sodium hydroxide etch test was used to evaluate the presence of intermetallic phases. Cyclic polarization measurements of the S32205, S32750, and S32760 base metals showed good corrosion resistance, while poorer corrosion resistance was observed for S32101. Cyclic polarization tests at the friction stir welds indicated that for S32205 and S32750, the corrosion resistance was higher, compared to the respective base metals. The S32760 and S32101 welded joints showed lower noble potential and higher corrosion current density, compared to the base metals. NaOH etching indicated affected areas at the ferrite–ferrite grain boundaries for the S32760 FSW joint, which also showed a large loss of mass in ferric chloride solution, associated with the presence of deleterious intermetallic phases.