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Steels for several applications, such as steel cord for tires and heavy plates, present severe hydrogen restriction in their chemical composition. However, the hydrogen content of the liquid steel usually increases during tundish filling. This phenomenon, known as hydrogen pick-up, occurs due to direct steel contact with humidity present in the lining refractory, ladle sand and atmospheric air. The present work investigated by means of an analytical mathematical model the magnitude of hydrogen pick-up promoted by steel-air interaction. The relative importance of this mechanism was evaluated comparing the predictions with industrial data of hydrogen pick-up for a specific microalloyed steel grade. Results showed that air contamination can contribute to approximately 40% of the total hydrogen pick-up. An appropriate tundish inertization, which eliminates completely the air contamination, would be able to reduce approximately 1.5 ppm from the total hydrogen pick-up that happens during the beginning of the first heat of a sequence. As a consequence, it would be reduced more than 0.20 ppm of the total hydrogen pick-up in 36t of the steel cast.

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Resumo A prática de inertização de um distribuidor de 17,7 t para lingotamento contínuo de aços foi estudada numericamente através de um modelo matemático tridimensional não-isotérmico. O modelo considera uma única fase gasosa composta de dois componentes: argônio e ar. A turbulência foi levada em conta por meio do modelo k-ε padrão. Os cálculos foram executados utilizando o software de CFD comercial ANSYS CFX. Diferentes configurações do sistema de inertização foram simuladas. Os resultados indicaram que a configuração atual é ineficiente e novas configurações foram sugeridas. Algumas recomendações para a correta prática de inertização também são fornecidas. Palavras-chave: Inertização de distribuidor; Simulação matemática; Lingotamento contínuo; Inclusão não-metálica. A NUMERICAL STUDY OF THE TUNDISH INERTIZATION PRACTICE The inertization practice for a 17.7 tonne of steel continuous casting tundish has been studied numerically by means of a three-dimensional non-isothermal mathematical model. The model considers a single gaseous phase composed of two components: argon and air. Turbulence was accounted for with the standard k-ε model. The calculations were carried out using the commercial CFD software ANSYS CFX. Different configurations of the inertization system were simulated. The results indicated that the present configuration is ineffective and new ones were suggested. Some guidelines for the correct inertization practice are also provided.

ResumoO desgaseificador RH é um reator de refino secundário bem estabelecido. Nesse equipamento, gás inerte é usado para promover a circulação de aço entre a panela de aciaria e uma câmara de vácuo. A predição correta da dispersão de gás na perna de subida do RH é importante para a modelagem confiável do processo. O presente trabalho estudou a penetração de gás na perna de subida do RH por meio de modelos físico e matemático. No estudo, foram considerados apenas um ou dois bicos injetores e vazões de gás, por bico, entre 5l/min e 50l/min. Para as condições com um bico injetor, os resultados das duas abordagens mostraram boa concordância qualitativa. Já para as condições com dois bicos injetores, a concordância só foi satisfatória para vazões de até 30l/min por bico. Adicionalmente, os resultados obtidos indicaram que o problema de penetração de gás em modelos matemáticos de desgaseificador RH identificado na literatura está relacionado com erros numéricos e não com falhas na modelagem da física do problema. Palavras-chave: Desgaseificador RH; Modelo físico, Modelo matemático; penetração de gás. PHYSICAL AND MATHEMATICAL SIMULATION OF THE GAS PENETRATION IN THE UPPER LEG OF A PHYSICAL MODEL OF RH DEGASSER AbstractThe RH degasser is a well-established secondary refining reactor. In this equipment, inert gas is used to promote the circulation of steel between a steelmaking ladle and a vacuum chamber. The correct prediction of gas dispersion in the upper leg of RH is important to ensure a reliable modeling of the process. This work studied the gas penetration in the upper leg of RH by means of physical and mathematical models. Only one or two injectors were considered and gas flow rates, by injector, between 5l/min and 50l/min were employed. For cases with one injector, results from both approaches showed good qualitative agreement. On other hand, for cases with two injectors, the agreement was just satisfactory for gas flow rates up to 30l/min by injector. Additionally, the obtained results showed that the issue of gas penetration in mathematical models of RH degasser identified in the literature is related to numerical errors and does not stem from inadequate modeling of problem physics.