Kyslík v oceli, způsoby dezoxidace a moderní prvky optimalizace výroby oceli

Abstract

The thesis focuses primarily on current metallurgical problems of the steel industry consisting in increasing the quality of steel, mainly its purity, which guarantees to achieve better mechanical properties such as ductility, toughness and fatigue properties of steel. The main aim of the thesis is to assess the potential application of the method of Single Spark Evaluation (SSE), with which an optical emission spectrometer SPECTRO LAB 10 at the Vítkovice. Vítkovice Testing Centrum a.s. is equipped. For the steelworks Vítkovice Heavy Machinery a.s., Vítkovice Testing Centrum a.s. ensures all chemical analyzes of produced melts. In the context of determining the chemical analysis of the sample, the SSE method allows to determine the qualitative and quantitative information about the analyzed inclusions sampled during the production of steel. Evaluation programs of the SSE method on the optical emission spectrometer Spectro Lab 10 are set by the manufacturer and were not put in doubt. The theoretical part of the thesis deals with deoxidation and reoxidation procedures, which primarily determine the type of an inclusion and its major part in steels and their classification. The experimental part of the thesis focuses primarily on the results of the measurements obtained using the SSE method. It assesses whether the obtained results are applicable in the steelmaking practice to determine the inclusions during the on-line process of steel production on the LF, VD and VOD secondary metallurgy equipment in Vítkovice Heavy Machinery a.s. The measurement results are compared at different production processes, which include deoxidation technology of precipitation VOD and deoxidation of diffusive VCD and half-diffusive LF-VD. On the basis of the experiments carried out on a statistically significant number of melts measured by the SSE method, it was concluded that there is necessary to optimize the factory settings in the main parameter of the method in the standard deviation sigma, which quantifies the number and defines the chemical composition of the inclusion. It is necessary to optimize the standard deviation for the individual process steps, for each method of steel production and chemical composition of the inclusions. The results obtained in the experimental part show that the experiments carried out with the standard deviation allow more precise interpretation of the measured values. Obtained results evaluating steel purity are compared with the results of X-ray spectral analysis. After adjusting the standard deviation sigma it can be said that their mutual correlation is possible particularly in the chemical composition of the inclusions.