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.

摘要：双相不锈钢（Duplex Stainless Steels, DSS）是由铁素体（δ相）与奥氏体（γ相）构成二元微观组织的合金，凭借奥氏体/铁素体双相结构兼具优异的力学性能与抗点蚀、抗应力腐蚀性能。然而，双相不锈钢在凝固过程、热处理或焊接过程中生成的第二相及金属间相，往往会导致其核心性能劣化。本研究旨在探究经850℃时效处理30、300及3000分钟的UNS S82441双相不锈钢的腐蚀行为，该时效过程会引发σ相（sigma phase）析出。本次研究通过应力腐蚀试验、动电位极化以及质量损失法开展耐腐蚀性能评估。微观组织表征与形貌分析证实，UNS S82441双相不锈钢中存在σ相，且该相的占比随时效热处理时长的增加而升高。时效时长对该钢的耐腐蚀性能存在负面影响，在850℃时效3000分钟的试样条件下，其钝化区的耐腐蚀性能最多可下降50%。