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.

Temperature and time effect of thermal aging treatment on microstructure and corrosion resistance of UNS S31803 duplex stainless steel

“…The mechanism of nucleation and growth occurs when the chromium content in the ferrite phase is inferior to 23% (mass) and the thermal treatment of aging is performed above 500°C. For this mechanism, the diffusion occurs with a greater reduction in the Gibbs free energy and phase α' is more roughly formed than in the spinodal decomposition, because of the formation of coherent interfaces (Cavalcanti, Muterlle & Reinke, 2019, Haupt, Silva, Falcade, Santos & Reguly, 2019, Kisasoz, Gurel & Karaaslan, 2016, Mehta, Jadhav, Shaikh, Kumar & Kirwai, 2019, Nithin, Sekar & Joseph, 2019, Ogawa & Osuki, 2020, Powar, Gujar, Manthani, Pawar & Singh, 2017, Valeriano, Correa, Mariano, Robin & Machado, 2019.…”

Laves phase precipitation and sigma phase transformation in a duplex stainless steel microalloyed with niobium.

“…The 12 samples were first heated to 1050°C and held in an oven for 60 minutes to dissolve precipitates and intermetallic phases in the microstructure of the material. In the aging heat treatment, 9 samples were heated again to a temperature of 850ºC and held for 15, 30 and 60 minutes [3,11]. In this way, 12 different samples were prepared.…”

“…Stainless steels are materials used in a wide variety of applications, including the chemical and petrochemical industries, power generation, pumps, implants, and surgical instruments, as well as a variety of other consumer and commercial products [1][2][3][4][5][6].…”