Microstructural evolution and localized corrosion behavior of friction stir welded super duplex UNS S32760 in chloride-containing environments

Abstract

This study investigates the microstructural evolution and localized corrosion behavior of friction stir welded (FSWed) super duplex stainless steel 2507 (UNS S32760) sheets. The distinct regions on the top surface of the welded joint were examined by microscopy analysis, hardness measurements, and electrochemical polarization techniques in various environments. Discussion of the results focused on microstructure-property relationships, emphasizing these relationships in understanding changes in local corrosion behavior. Our main findings indicating a Cr₂N precipitation, attributed to rapid cooling during the FSW process, at the ferrite/ferrite boundaries in the stir zone in the retreatment side (SZ/RS), stir zone (SZ), and thermomechanical affected zone in the advancing side (TMAZ/AS). This increases the degree of sensitization, resulting in reduced localized corrosion behavior at high potentials in a NaCl solution and diminished passivity in an HCl solution for the RS, SZ, and AS regions. In addition, a grain refinement was observed in the TMAZ/RS, SZ/RS, SZ, SZ/AS and TMAZ/AS regions. These findings unravel the relationship between microstructural evolution and localized corrosion behavior and underscore the critical importance of considering the exposure of FSWed SDSS UNS S32760 to oxidizing environments with chlorides. This consideration has significant implications, including potential challenges related to pitting, intergranular corrosion, and stress corrosion cracking, which should be carefully addressed in practical applications and future research.