EM - Escola de Minas

Resultados da Pesquisa

Agora exibindo 1 - 3 de 3

Effect of thermal aging on the microstructure and mechanical properties of stainless steel UNS S31803.
(2020) Costa, Junia Maria Gândara; Lacerda, José Carlos de; Godefroid, Leonardo Barbosa; Cândido, Luiz Cláudio
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 prime - α'). 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.
Effect of PWHT on laser-welded duplex stainless steel : the effects of postweld heat treatments on the microstructure, tensile behavior, and corrosion resistance of laser-welded duplex stainless steel were investigated.
(2020) Magalhaes, Aparecida Silva; Magalhães, Charles Henrique Xavier Morais; Lima, Milton Sérgio Fernandes de; Alves, Juliane Ribeiro da Cruz; Godefroid, Leonardo Barbosa; Bertazzoli, Rodnei; Faria, Geraldo Lúcio de
The welded joints of duplex stainless steels (DSSs) have been widely used in petrochemical, nuclear, pulp, and paper industries. Welds require a good, superficial finishing and a combination of mechanical and corrosion properties in these types of high-quality, demanding applications. Even though laser welding promotes narrow weld beads and a small heataffected zone, when it is applied to DSSs, it can produce dangerous microstructural discontinuities. In this context, the effects of subsequent heat treatments on the microstructure, corrosion resistance, microhardness, and tensile properties of DSS laser-welded joints are investigated. In this study, samples of UNS S32304 DSS were submitted to two different conditions of laser welding. Subsequently, the plates submitted to the best welding condition were subjected to isothermal heat treatments at different temperatures (850°, 950°, 1050°, and 1150°C) for 10 min. Then they were microstructurally characterized. Phase fraction measurements and microhardness tests were performed. Based on the obtained results, postweld heat-treated samples at 1150°C, which is the best condition, were subjected to corrosion and tensile tests. It was possible to conclude the corrosion properties of the welded joint were significantly improved after the heat treatment. However, the mechanical behavior was strongly influenced by the presence of volumetric discontinuities and intermetallic compounds, which considerably deteriorated the mechanical strength of the material.
Effect of volume fraction of phases and precipitates on the mechanical behavior of UNS S31803 duplex stainless steel.
(2015) Lacerda, José Carlos de; Cândido, Luiz Cláudio; Godefroid, Leonardo Barbosa
Mechanical properties of a grade UNS S31803 duplex stainless steel were studied. Samples were annealed at three different temperatures, 1060 C, 1200 C, and 1300 C, to change the a/c proportion, to precipitate undesirable phases (for example, a0 , r and chromium nitrides), and to study the effect of the microstructure on the mechanical behavior. Specimens with a thickness of 1.8 mm were prepared according to ASTM standards and tested at room temperature. Tensile tests were conducted using displacement control at a rate of 5 mm/min. Force-controlled constant amplitude axial fatigue tests were conducted at a frequency of 30 Hz and an R stress ratio of 0.1. Microstructural analyses, performed by optical microscopy and scanning electron microscopy, showed the following modifications to the microstructure: changes in the phase volume fractions, the phase grain growths, and the morphology of the c-phase and the precipitation of chromium nitrides in the a-phase. The mechanical properties of the steel were significantly changed due to the changed microstructure. The results demonstrate the sensitivity of the steel to the annealing temperature.

EM - Escola de Minas

Notícias

Navegar

Filtros

Configurações

Ordenar por

Resultados por página

Resultados da Pesquisa