Effect of PWHT and Electrical Parameters on Austenitic Phase, Sigma Phase and Corrosion in Duplex Steels S32205

Abstract

This study investigates the influence of post-weld heat treatments (PWHT) at 450, 850°C and 1020°C on phase evolution and corrosion behavior in UNS S32205 duplex stainless steel welded with GMAW. The ferrite content decreased progressively with an increase in the temperature of PWHT, accompanied by the formation of secondary austenite. Treatment at 850°C produced the highest phase fractions in sigma (σ), phase fractions—up to ∼5% in the fusion zone (FZ)—which corresponded to the greatest mass loss during ASTM G48 pitting corrosion testing (0.35%–0.40%). At 1020°C, σ-phase dissolution resulted in substantially lower mass loss (< 0.1%). A significant outcome of this work is the demonstration that a 1-h PWHT at 850°C applied to the base metal reproduces the microstructural characteristics of a welded heat-affected zone (HAZ), enabling its characterization on larger and more uniform specimens. These results confirm that σ-phase formation is governed exclusively by PWHT temperature.