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.
Highlights
Duplex stainless steels (DSS) are system alloys Fe-Cr-Ni-Mo, 50% ferrite (δ) and 50% austenite (γ), with similar amounts of δ/δ and γ/γ grain boundaries, and δ/γ interfaces [1-3]
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
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
Summary
Duplex stainless steels (DSS) are system alloys Fe-Cr-Ni-Mo, 50% ferrite (δ) and 50% austenite (γ), with similar amounts of δ/δ and γ/γ grain boundaries, and δ/γ interfaces [1-3]. In industries of oil prospecting, oil refining, petrochemical and energy, there is a great attraction for the use of duplex steels due to the combination of corrosion resistance and high mechanical properties, mainly in aggressive environments for steels [2,3] These properties can be drastically reduced, if undesirable secondary phases formations occur, such as sigma phase (σ), chi phase (χ), austenite (γ2), chromium nitrides (Cr2N) and carbides (M23C6, M7C3). Recent developments in stainless steels led to the evolution of the subgroup of duplex stainless steels known as Lean Duplex Stainless Steels (LDX or LDSS) It has less content of alloying elements in relation to standard DSS, and lower cost plus greater corrosion resistance combined with mechanical properties about twice higher than the austenitic stainless steels [3,10]. The present study aims to investigate the effect of sigma phase in corrosion resistance of UNS S82441 LDSS after heat treatment of the aging at 850°C for different times (30, 300 and 3000 minutes)
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