Steel with high cleanliness requirements require an accurate control of the non-metallic inclusions, such as its quantity, morphology, chemical composition and size distribution. The continuous casting tundish has a fundamental role in steel cleanliness, avoiding its reoxidation by air and ladle slag that retain inclusions, as well as aiding the removal of those same inclusions along the continuous casting (Sahai, 2008). To perform the study, IF steel samples were collected in RH at the start, in the middle and at the end of the continuous casting of the tundish's first heat in three different conditions of tundish processing, alternating between heating and purging. These samples had their inclusions characterized by MEV/ EDS using the ASCAT (Automated Steel Cleanliness Analysis Tool) technology. The results showed that more than 90% of the oxide inclusions generated in that type of steel are Al 2 O 3 and AlTi. It was also observed that there is an increase of steel inclusions originating from RH in the tundish and that area fraction and average inclusionary density decreases along the continuous casting in two of the processing conditions.
ResumoO fluxante é composto por uma mistura de materiais não metálicos que, em contato com o aço líquido, funde formando escória que age principalmente como lubrificante e controla a transferência de calor na interface placa/molde durante o lingotamento contínuo de aços. O fluxante sem flúor, quando comparado ao fluxante convencional, apresenta como vantagens a redução tanto do desgaste da máquina, quanto da válvula submersa. A sua aplicação no lingotamento contínuo de placas tem sido um grande desafio no que se refere à sua viabilidade operacional aliado à qualidade interna e superficial das placas. Outro diferencial do fluxante sem flúor é a redução de problemas ambientais, devido à contaminação da água do resfriamento secundário por fluoretos. Considera-se que as propriedades dos fluxantes, como composição química, viscosidade, temperaturas de amolecimento, fusão e fluidez, velocidade de fusão etc., devem estar adequadas à composição química e às propriedades mecânicas a quente do aço, bem como aos parâmetros operacionais de temperatura, velocidade de lingotamento, frequência de oscilação do molde, entre outros. Este trabalho mostra uma análise preliminar do uso do fluxante sem flúor no que se refere à viabilidade operacional, qualidade das placas produzidas e contaminação da água de refrigeração secundária da máquina. Também são analisados fatores operacionais como desgaste de SEN, consumo do fluxante, nível de escória no molde e o comportamento dos termopares do sistema de detecção de rompimento (MSD). Palavras-chave: Fluxantes sem flúor; Propriedades físico-químicas; Lingotamento contínuo de placas. DEVELOPMENT OF FLUORINE-FREE MOULD FLUX APPLIED IN LOW CARBON STEEL AbstractThe mould flux is a mixture of non-metallic oxides that, in contact with liquid steel melts, becomes a liquid slag which the mainly function is to lubricate and control heat transfer between mould and strand during the continuous casting process. The mould flux without fluoride has the advantage of decreasing the wear of machine and the SEN in comparison to common mould flux. The application in Continuous Casting of Slabs has been a great challenge in relation to the operational viability together with internal and surface quality of slabs. Another differential is the decrease of environmental issues on account of the contamination of secondary cooling water by the fluorides. It is considered that properties of mould flux as chemical composition, viscosity, softening, melting flowing temperatures, fusion rate, etc, should be suitable to the chemical composition and the mechanical properties at elevated temperatures of steel and also the operational parameters such as casting temperature, casting speed, mould frequency, among others. This work presents a preliminary analysis in relation to operational viability, analysis of surface quality of slabs, measurements of fluorides content in the water of secondary cooling of machine. In addition to that, the analyses of operational features as measurements of wear of SEN, mould flux consumptio...
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