Effect of Artificial Aging in the Microstructure and Corrosion Performance of Superduplex UNS S32750 Stainless Steel

Abstract

Superduplex stainless steels have great mechanical and corrosion properties. However, its chemical composition makes it prone to intermetallic phase precipitation during thermal processing. Sigma (σ), chi (χ), and chromium nitrides (Cr2N) remove Cr and Mo from the matrix, reducing the corrosion and mechanical resistance. Understanding the effects of thermal processing on the secondary phase’s precipitation and depletion of the material’s performance is crucial to its applications. Thus, this work aims to analyze the behavior of the corrosion performance of the UNS S32750 after thermal treatment at 800°C, for 60, 180, 300, and 420 minutes, in comparison to the as-received material. Optical emission spectrometry, X-ray diffraction, and SEM with backscattered electrons (BSE) were used to evaluate the material. The corrosion performance was evaluated with the cyclic potentiodynamic polarization technique. The main results and conclusions obtained in the study were a decomposition of the ferrite phase into the χ and σ phases, with the formation of the χ phase being predominant in shorter times, while for longer aging times σ formed in greater quantities. It was also possible to verify a more aggressive corrosion trend for aged samples in the regions adjacent to the formation of the χ and σ phases. It was also possible to observe that the losses generated in corrosion resistance were greater for aging times longer than 60 minutes. The aging treatment significantly reduced the material’s corrosion resistance in conjunction with the formation of precipitates.