Refining properties of magnesia slags by heat periods in EAF ДСП-135 with various degree of saturation by magnesium oxide

Abstract

To increase technological, technical and economical parameters in electric steelmaking, operation of modern EAFs under magnesia slags is a perspective way. Therefore, forming the magnesia slags, ensuring early formation of a stable refining slag foam, is an actuals task. The slag foam must have not only high refining properties, ensuring necessary degree of steel desulphurization, but also have low aggressive impact on refractory lining of EAF. The aim of the work was the study of influence of slags oxidation, basicity and saturation degree by magnesium oxide on their refining properties in EAF ДСП-135. In the process of the stud, industrial high-magnesia slags were used, formed in reducing and oxidizing periods of heat running in EAF ДСП-135. The refining properties of high-magnesia slags were evaluated by equilibrium phosphor concentration under slags of the investigated oxide system, completeness of phosphor oxidation reaction progress by periods of heat in the EAF and by variation of actual phosphor content in metal during oxidation period of heat. To calculate the equilibrium phosphor content under magnesia slags, the known calculation method was used with application of V.A. Kozheurov’ model, adapted to real oxide system. It was determined, that the forming of slags of oxidizing period with basicity of 1.9 and higher in the area, tending to their saturation by magnesium oxide, ensures the metal dephosphorization process development. At the basicity less 1.9, the development of metal dephosphorization process does not take place, and phosphor reduction process from slag in the metal is observed, resulting in an increase of its concentration, comparing with phosphor in the metal of melting period in average by 0.0005%. At the basicity of slags of oxidizing period 1.9 and higher, the process of the metal rephosphorization practically is not observed and phosphor content in the metal is at the level of its concentration in the metal of melting period. To keep high refining properties it was recommended to form the magnesia slags within the melting period and oxidizing period in the area tending to saturation by magnesium oxide with the basicity not lower 1.9.