Effect of Sigma Phase Precipitated at 850 °C on Corrosion Behaviour of UNS S82441 Duplex Stainless Steel

Abstract

Duplex stainless steels (DSS) are alloys with binary microstructure consisting of ferrite (δ) and austenite (γ),
combining high mechanical properties and corrosion resistance by pitting and stress corrosion, due to the two
phases austenite/ferrite. However, the formation of secondary and intermetallic phases, during solidification
processes, heat treatment or welding in duplex steels tend to cause the degradation of its main properties. The
present study aim to investigate the corrosion behaviour of UNS S82441 aged at 850°C for 30, 300 and 3000
minutes, due to the formation of sigma phase. Corrosion resistance evaluation was performed by means of
stress corrosion testing, potenciodinamic polarization and mass loss. The microstructural characterization and
morphology confirmed the presence of sigma phase in the UNS S82441 duplex stainless steel, and that the
amount of this phase increases with the time of heat treatment of aging. The aging time influences negatively
the corrosion resistance of this steel, with a gradual drop of up to 50% on passivation regime for the condition
of aging at 850°C for 3000 minutes.
Keywords: Duplex Stainless Steel. Corrosion. Sigma Phase. Heat Treatment of Aging.