Duplex stainless steel UNS S31803 exhibits high mechanical strength with high corrosion properties, due to its microstructure composed of ferrite and austenite phases, in equal proportion. When the UNS S31803 steel is submitted to high temperatures, some precipitations can occur, such as nitrites, carbides, and third phases (e.g. sigma phase -σ, and alpha primeα'). These phases are deleterious in relation to the mechanical properties and corrosion resistance, and their effects are analyzed regarding the properties of the steel. In order to evaluate the precipitation of this deleterious phase, isothermal treatment was done at 500°C for 144 hours (α' phase) and at 850ºC for 80 minutes (σ phase). The results were obtained through the microstructural analysis and tensile tests. The presence of sigma phase was verified in the grain boundary, an increase in the mechanical resistance with a loss of toughness. There was as well as an increase in mechanical resistance with the precipitation of α', with less loss of ductility than that observed in the experiments involving the presence of sigma phase.
Resumo O aço inoxidável duplex UNS S31803 apresenta alta resistência mecânica com alta resistência à corrosão, devido a sua microestrutura composta pelas fases ferrita e austenita, em igual proporção. Quando submetido a tratamentos isotérmicos em certas faixas de temperatura, podeocorrer precipitação de nitretos, carbonetos e fases como fase sigma e fase α'. Essas fases são deletérias às propriedades mecânicas e corrosivas do material. Neste trabalho é analisado a influência dessas fases nas propriedades do aço inoxidável duplex. Para isso foi realizado tratamento isotérmico à 500ºC por 144 horas e à 850ºC por 80 minutos. Para obtenção dos resultados foi realizado análise microestrutural, ensaio de tração. Os resultados foram comparados com a literatura a fim de estabelecer a influência das fases sigma e α' nas propriedades mecânicas do material. Palavras-chave:Aço inoxidável duplex; Fragilização à 500ºC; Fragilização por fase sigma.
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