Caracterização de inclusões não-metálicas de aços peritéticos produzidos com diferentes técnicas de desoxidação

• Ano de defesa: 2018
• Autor(a) principal: Leão, Pablo Bruno Paiva
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Palavras-chave em Português: Ciência dos materiais; Termodinâmica; Aço - Produção; Computational thermodynamics; Clogging; Nonmetallic inclusions
• Link de acesso: http://www.repositorio.ufc.br/handle/riufc/31879

The present work is based on the characterization of non-metallic inclusions of peritectic steel produced in a large steel mill. Due to a high incidence of clogging in submerged valve, changes were made in the steelmaking process in order to reduce or stop this problem. Based on this change the work was important to validate the improvement of the process and to know the characteristics of the inclusions before and after the change and throughout the process. Samples of peritectic steel were obtained from the following steps of the steelmaking: Before the arrival to the ladle furnace, after final adjustment of chemical composition in the ladle furnace, in the tundish and in the plate. One heat was used to analyze the evolution of inclusions during the process and ten heats to validate the improvement. The samples of steels were prepared metallographically without the need of surface attack for later analysis in manual, via Scanning Electron Microscope (SEM) coupled with an EDS detector. Then the sizes, amounts and chemical compositions of the inclusions were obtained, the latter provided plots in ternary diagrams, allowing to know the influence of the inclusions under the process castability. It was also applied the computational thermodynamics using Software Factsage to calculate the castability windows, thus obtaining the optimal ratios of Al and Ca in ppm, to obtain liquid inclusions during the treatment with calcium. In addition, with the objective of generating a new alternative to the manual method, which presents a long time of analysis, a new methodology was developed to make feasible the analysis of non-metallic inclusions. Finally, the results showed that the inclusion profile after the improvement of the process presented itself more appropriately, the behavior of the characteristics of the inclusions during a run in the steelmaking and through the new methodology of exploration of inclusions, the analysis time was reduced in up to 2/3 in relation to the manual method.