EM - Escola de Minas

URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6

Notícias

A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.

Navegar

Filtros

2017 - 201912020 - 20223

Configurações

Autor: search.filters.author.Magalhães, Charles Henrique Xavier Morais

Resultados da Pesquisa

Agora exibindo 1 - 4 de 4
  • Nenhuma Miniatura Disponível
    Item
    Effect of step quenching heat treatments on the kinetics of ferrite formation and quenching & partitioning modeling for a commercial C-Mn-Si steel.
    (2022) Magalhães, Charles Henrique Xavier Morais; Campos, Pablo Henrique Kelly; Faria, Geraldo Lúcio de
    Aiming to meet current demands from the automotive industry, a third generation of advanced high strength steel (AHSS) has been developed as an alternative to previous generations. Different alloys and innovative processes have been deeply studied as, for example, quenching and partitioning (Q&P). The published papers highlight that the best heat treatment parameters for a satisfactory Q&P execution are strongly dependent on the austenite conditioning and they can be optimized if thermodynamic and kinetics calculations are performed. In this context, this work evaluated the effect of step quenching (SQ) heat treatments on the kinetics of ferrite formation and Q&P modeling for a commercial C-Mn-Si steel, predicting the microstructural evolution and the final phase fractions as a function of the heat treatment parameters. The JMAK model was optimally fitted to the ferrite fraction, as well as to the microhardness data. The kinetics characterization and the thermodynamic modeling showed that the combination of SQ and Q&P can provide a high retained austenite fraction in a multiphase microstructure. As a conclusion, it is possible to state that a well-planned SQ heat treatment followed by an optimized Q&P cycle has the potential to generate an advanced steel with a final microstructure assisted by the TRIP effect.
  • Nenhuma Miniatura Disponível
    Item
    Efeitos de tratamentos térmicos de têmpera com austenitização intercrítica na microestrutura, partição de elementos e temperatura Ms em um aço TRIP780.
    (2021) Pimenta, Natália Aparecida Barbosa; Magalhães, Charles Henrique Xavier Morais; Campos, Pablo Henrique Kelly; Faria, Geraldo Lúcio de
    Neste trabalho, o efeito de tratamentos térmicos de têmpera com austenitização intercrítica sobre a microestrutura, partição de elementos e temperatura Ms foi estudado para um aço TRIP780. Por meio de dados dilatométricos e caracterização microestrutural, diferentes ciclos térmicos de têmpera com austenitização intercrítica foram avaliados. Os resultados obtidos experimentalmente foram comparados com aqueles obtidos por meio de simulações computacionais no equilíbrio. Concluiu-se que, quanto menor a temperatura de austenitização intercrítica, menor é a fração de austenita formada tanto no equilíbrio quanto fora dele. Verificou-se ainda que, quanto menor a fração de austenita formada, maior é a concentração de C e Mn na referida fase, assim como menor é a concentração de Si. Esse cenário favorece a formação de bainita durante a têmpera e diminui significativamente a temperatura Ms . Os resultados obtidos apontam que o conhecimento dos efeitos da austenitização intercrítica em um aço C-Mn-Si tem grande potencial para ser aplicado com o objetivo de se definir ciclos térmicos que favoreçam a estabilidade da austenita e permitam o ajuste fino da temperatura Ms , possibilitando que tratamentos térmicos atuais, como têmpera e partição, possam ser empregados com significativas chances de sucesso.
  • Nenhuma Miniatura Disponível
    Item
    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.
  • Nenhuma Miniatura Disponível
    Item
    Characterization of the austenite reformation mechanisms as a function of the initial ferritic state in a UNS S32304 duplex stainless steel.
    (2017) Magalhães, Charles Henrique Xavier Morais; Faria, Geraldo Lúcio de; Lagoeiro, Leonardo Evangelista; Silva, Jéssica Dornelas
    Aiming to better understand the effects of heat treatment parameters on Ferrite-Austenite phase transformation in a 2304 duplex stainless steel different thermal cycles were applied to this steel in a quenching dilatometer. The obtained microstructures were characterized by optical microscopy, transmission electron microscopy and electron backscatter diffraction. It was noticed that the austenite formation mechanism is strongly dependent on initial ferritized state. If the initial structure is completely ferritized, the nitrogen supersaturated solid solution leads to chromium nitrides precipitation and the rate of austenite nucleation decreases. For higher cooling rates, the ferrite grain boundaries control the austenite nucleation rate. The higher the ferrite grain size, the lower the final austenite fraction. If the steel is cooled from a partial ferritized state, the ferrite-austenite phase boundaries work as austenite nucleation site and the austenite growth rate is favored due to the high interfacial energy and the austenitic structures becomes coarser.