Avaliação dos fatores que afetam a taxa de desnitrogenação no Desgaseificador a Vácuo RH para aços destinados a aplicação em Chapas Grossas

Abstract

The steel industry has faced an increase in the demand for steels with increasingly quality requirements, mainly regarding surface quality and mechanical properties of products, requiring steels with chemical composition in ever narrower ranges, this has happened with steels for Heavy Plates in Usiminas Ipatinga. Nitrogen is an important factor that influences the quality of products. Not only does it affect the mechanical properties of steels, but it is also the main cause of cracking. Using a vacuum treatment equipment it is possible to reduce the nitrogen content in order to improve the quality of the steel. In this work the nitrogen content and the denitrogenation rate were evaluated during the treatment in the Vacuum Degasser RH for Heavy Plates steels. In addition, we analyzed the factors that affect these variables through statistical analysis using software. A kinetic model was also developed using macro processing in the FactSage computational tool capable of predicting the evolution of nitrogen in the bath during treatment. Through the analysis, the influence of the initial nitrogen content on the denitrogenation rate and on the final nitrogen content was identified. For the nitrogen group higher than 0.0046% we had an average rate of 28% denitrogenation and an average final nitrogen of 0.0040%. For initial values lower than 0.0046%, the rate was 18% and the final nitrogen was 0.032%. Statistical analyzes confirmed the influence of the initial nitrogen on the rate of denitrogenation and the final nitrogen. The higher the initial nitrogen, the higher the denitrogenation rate and the higher the final nitrogen. For the final nitrogen, the vacuum time less than 2 torr also had a statistically significant influence. The longer the time, the lower the final nitrogen. The kinetic model, while maintaining the parameters, was able to predict denitrogenation in steels for any initial nitrogen value.