Oxygen distribution between phases during ladle processing of aluminum killed bof steels

Abstract

The modern state of secondary metallurgy is characterized by the sustainable development of technologies that ensure high metal quality by reducing the number of non-metallic inclusions, the which is closely related to the oxygen content in steel after smelting. Therefore, the issues of regularities of oxygen distribution between phases at the stage, BOF - CCM. Purpose. The aim of the research was to determine the conditions of redistribution of oxygen dissolved in the metal depending on the stages of steel processing, to determine the degree of approach of deoxidation processes to thermodynamic equilibrium. Methodology. Research was carried out in industrial scale. Steel grades 34Cr and 36CrB were smelted in BOF of 170-t capacity. Processing of crude steel was carried out in a LF unit with further vacuum degassing and wi thout it and transfer of steel to CCM. At each stage of steel treatment, metal and slag samples were taken using an automatic sampler to determine the chemical composition, and the temperature. Oxygen content were monitored using a "Celox" analyzer. Findings. The carried-out studies showed that before the end of metal processing in the ladle, it is possible to detect individual reoxidation processes caused by unwanted ingress of oxygen from the air and from ladle slag oxides. Accor ding to calculations, in the second half of processing in the ladle and during casting, there is a slight deoxidation of steel with aluminum due to a decrease in temperature. Even if during this time due to the exchange reaction between steel and slag, a small amount of Mn and Si is recovered from the ladle slag, while its composition is practically constant throughout the period of steel processing in the ladle, while the metallurgical reactions proceed in the region of thermodynamic equilibrium. Originality. It has been determined that oxygen activity in steel varies unevenly over time and decreases to 3 ppm by the end of treatment in the ladle. While in each case it is in the Fe – a[O] – Al system near the calculated values of thermodynamic equilibrium. Practical value. The use of the obtained regularities makes it possible to obtain the specified content of aluminum in steel for the studied assortment and to predict the burning of deoxidizers and alloying elements, ensuring the reliability of obtaining the required chemical composition of steel with a high degree of purity. Key words: reoxidation, deoxidation, oxygen activity, slag, metal, non-metallic inclusion After blowing end in the converter, the oxygen activity in steel is in the range of 1000-1500 ppm [1-3]. After tapping from the vessel to a teeming ladle, the oxygen content in the metal is reduced by secondary metallurgy processes in order to provide high-quality of continuously cast billets and high purity of steel. At this stage steel reaches necessary temperature and chemical composition. Important for theory and practice are patterns of oxygen distribution between phases at each stage of secondary metallurgy, studied directly under production conditions. This distribution determines the removal efficiency of harmful impurities, non-metallic inclusions and gases from the steel. It is advisable to compare the measured oxygen contents with equilibrium states, which can be easily achievable in practice, and their calculation can be carried by metallurgical scientists.