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The basic principles of spray control during casting speed changes in the continuous casting of steel have been studied. The normal spray control practice in which water flow in the sprays is made proportional to the casting speed has been found to be completely inadequate from the standpoint of controlling the surface temperature of the strand. A computer model based upon the principle of controlling the sprays as a function of the age of the metal passing through the machine has been developed. The model predicts both the average local residence time and water flux in a spray zone for any casting speed change. An accompanying heat flow model has also been developed for characterization of cooling rates and simulation of the effects of spray control practices on the surface temperature of the strand. The control model has been used for the development of a new spray control practice in an industrial slab caster. Tests have been performed both using the new practice and the normal spray control practice. Although, a complete verification has not been possible at this time, the model appears to realistically predict the thermal requirements of the strand during casting speed change. The necessity for automatic control of the sprays has become evident during the development of the present work. The principles of automatic control of the sprays have been studied and the control model adapted for this purpose. It has been shown that a true automatic control of spray cooling can be attained using the mathematical model for spray control. / Applied Science, Faculty of / Materials Engineering, Department of / Unknown

The heat-transfer phenomena in the quenching process have been studied using stainless steel and mild steel specimens in brine (3% by wt. NaCl), water, oil and air, under controlled conditions. The experimental data were analysed using a simple mathematical model of the quenching process to study the relationship between the surface temperature of the specimen and the surface heat-transfer coefficient. The influence on this relationship, of important variables such as initial specimen temperature, quenchant temperature, surface oxidation, etc. has been studied. The results from the experimental data are in good agreement with the results of previous workers. The results obtained in this work, together with Jominy-test data and the mathematical model, were used to determine the necessary quenching conditions required to obtain a desired thermal history or mechanical property at a given position in a 4 inch diameter steel grinding-ball. A steel ball was then quenched under the above determined conditions and an examination of the ball section showed that the desired property was indeed present at the given location. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Orientador: Itamar Ferreira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-12T16:02:28Z (GMT). No. of bitstreams: 1 Marcomini_JoseBenedito_M.pdf: 10388005 bytes, checksum: e970602f47c86edad59a5fdbb89fd097 (MD5) Previous issue date: 2008 / Resumo: Este trabalho tem como objetivo caracterizar e analisar o fenômeno da fragilização da martensita revenida no aço SAE 5160H, por meio de ensaios metalográficos, mecânicos, microscopia eletrônica de varredura e difratometria de raios-x. Corpos-de-prova do aço supracitado, laminado, foram austenitizados em duas temperaturas: 800ºC e 1050ºC, temperados em óleo a 80ºC, para obtenção de austenita retida e posteriormente, revenidos em 280ºC, 350ºC e 420ºC. Foram caracterizadas a microestrutura, as propriedades mecânicas e o micromecanismo de fratura em amostras nas condições laminado, temperado e temperado e revenido. Foi detectada a fragilização a 350ºC, temperatura na qual foi observada menor energia no ensaio de impacto, para ambas as temperaturas de austenitização, 800ºC e 1050ºC, em concordância com a literatura, porém com um micromecanismo de fratura misto: intergranular e alveolar, para a temperatura de austenitização de 1050ºC e micromecanismo intergranular para a temperatura de austenitização de 800ºC, como mostram as análises de microscopia eletrônica de varredura (MEV). Foi estudada, também a decomposição da austenita retida por análise de difração de raios-x nas amostras, nas varias condições cujos resultados mostram concordância com o previsto na literatura. Foi feita a análise por espectro de energia dispersiva (EDS acoplado ao MEV), com o intuito de verificar a influência de elementos como S e P neste fenômeno, porém, não foi detectada a presença destes elementos na superfície de fratura, por este método. Foi observado que existe uma concorrência de mecanismos para a fragilização da martensita revenida no aço SAE 5160H e que o fenômeno apresenta-se com maior intensidade para temperatura de austenitização mais alta. / Abstract: The purpose of this work is the characterization and analysis of tempered martensite embrittlement phenomena in SAE 5160 steel using metallographic and mechanical tests, scanning electron microscopy and X-Ray diffraction. The rolled SAE 5160 H steel samples were austenitized in two temperatures: 800ºC and 1050ºC, quenched in oil at 80ºC, to obtain retained austenite and tempered in three different temperatures: 280ºC, 350ºC and 420ºC. Mechanical properties, microstructure and fracture mechanism were analyzed in samples in the conditions: as rolled, quenched and quenched and tempered. The 350ºC tempered martensite embrittlement was detected by impact tests according to the references with an intergranular and dimples fracture mechanism for surface fracture of samples austenitized at 1050ºC and intergranular fracture mechanism for fracture surface of samples austenitized at 800ºC, as showed by scanning electron microscopy (SEM) analysis. The retained austenite decomposition was studied by X-Ray diffraction in all conditions samples and the behavior is in accordance with references. The X-Ray energy dispersive spectrum (EDS) was performed to study the influence of impurities like S and P in this phenomenon but no impurities were detected in fracture surface, by this method. It was observed that some mechanisms contribute to tempered martensite embrittlement in 5160H steel and the effects of this phenomenon are enhanced for higher austenitizing temperature. / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica