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.
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Resultados da Pesquisa
Item Microstructure and mechanical properties of a flash butt welded pearlitic rail.(2019) Porcaro, Rodrigo Rangel; Faria, Geraldo Lúcio de; Godefroid, Leonardo Barbosa; Apolonio, Gabriela Ribeiro; Cândido, Luiz Cláudio; Pinto, Elisângela SilvaThe structural changes resulting from the Flash Butt Welding (FBW) of pearlitic rails have been associated with wear/premature failures, despite this, there are no studies applying dilatometry to correlate the welding thermal cycles with the microstructural development of such material. The microstructural evolution of the heat affected zone is clarified with the aid of dilatometry. The increase in the steel hardenability associated with a larger austenitic grain size promotes the austenite-pearlite transformation at lower temperatures in the grain growth region. This explains why this region has larger pearlite colony size but smaller interlamellar pearlite spacing and higher hardness than the grain refined region. Partial cementite spheroidization in the heat affected zone is responsible for significant decrease in hardness and tensile strength and is correlated to localized dipping, rolling contact fatigue and failures. A dilatometry based methodology is proposed to define a process window and control the post-weld cooling rate at the rail head in order to improve the weld performance due to a better hardness profile, without increasing costs or welding time. For the steel evaluated, a 20% increase in the hardness of the softened area at the HAZ was obtained by dilatometric simulation of a safe accelerated cooling (5 °C/s).Item Evaluation of the influence of post welding heat treatments on microstructure and mechanical properties of API 5L X70Q weld joints.(2016) Araújo, Lívia Carla Silva de; Cândido, Luiz Cláudio; Trindade, Vicente Braz; Porcaro, Rodrigo RangelSteels that meet the API 5L standard are employed in pipeline construction, and there is considerable interest in those of higher strength, such as grade API 5L X70Q. There have nevertheless been few studies relating to seamless pipes. During installation, the pipes may be welded with covered electrodes (SMAW) and may optionally undergo inductive heating for adjustment to the topography of the terrain, processes that may alter the microstructure of the joints. In this work, welded joints were obtained by the SMAW process, from seamless pipe of grade API 5L X70Q. The joints were submitted to post-weld heat treatments at temperatures of 920 and 600 °C. Tensile, Charpy impact and microhardness tests were carried out, besides metallographic characterization in specimens of base metal and in the joints, as-welded and after the heat treatments. Heat treatment at 920 °C promoted formation of a ferrite/pearlite structure, with consequent reduction in the mechanical strength of the joints to values below those specified for grade X70Q. However, heat treatment at 600 °C proved to be beneficial owing to the reduction of the volume fraction of the martensite/austenite and martensite-austenitebainite constituents, without significantly reducing the mechanical strength and with a relative gain in impact toughness in the heat-affected zone and in the fusion zone (FZ).Item Avaliação da influência de tratamentos térmicos pós-soldagem sobre a microestrutura e propriedades mecânicas de juntas de um aço API 5L X70Q.(2015) Araújo, Lívia Carla Silva de; Cândido, Luiz Cláudio; Trindade, Vicente Braz; Porcaro, Rodrigo RangelAços que atendem à norma API 5L são aplicados na construção de dutos e há grande interesse naqueles de maior resistência, como o grau API 5L X70Q. Ainda são escassos os estudos relacionados a tubos sem costura. Durante a montagem, os tubos podem ser soldados por eletrodos revestidos (SMAW) e eventualmente sofrer aquecimento indutivo para adequação à topografia do terreno, processos que podem alterar a microestrutura das juntas. Neste trabalho foram obtidas juntas soldadas pelo processo SMAW, a partir de tubo sem costura grau API 5L X70Q. As juntas foram submetidas a tratamentos térmicos pós-soldagem nas temperaturas 920 °C e 600 °C. Foram realizados ensaios de tração, impacto Charpy e microdureza, além de caracterização metalográfica nas amostras de metal base e nas juntas como soldadas e após os tratamentos térmicos. O tratamento térmico a 920 °C promoveu a formação de estrutura ferrita/perlita, com consequente redução na resistência mecânica das juntas a valores inferiores aos especificados para o grau X70Q. Porém, o tratamento térmico a 600 °C mostrou-se benéfico devido à redução da fração volumétrica dos constituintes martensita/austenita e martensita-austenita-bainita, sem reduzir de forma significativa a resistência mecânica e com relativo ganho na tenacidade ao impacto na ZTA e na ZF.