Закономірності змін складу шлаку і вмісту сірки в чавуні у технологічному ланцюзі "доменна піч - комплекс десульфурації чавуну - конвертер"

Abstract

This paper analyzes the change in the sulfur content of cast iron and the composition of slag in the technological chain of BF - CIDC - OCS. Based on the results of the conducted research, technical solutions and technological techniques aimed at eliminating cast iron resulfurization have been developed and recommended. The analysis of the structure of the slag "beads" by the methods of optical microscopy and scanning electron microscopy was performed, which showed that they have a ferrite-graphite structure of the pre-eutectic or eutectic type with non-metallic inclusions in the form of manganese and iron sulfides. Spot probe scanning of bucket slag samples showed that in the slag phase, along with CaO∙SiO2∙Al2O3 type systems with different ratios of components containing 0.2–3.5% sulfur, CaxSiyAlz type systems containing up to 1% sulfur were found; in "beads" the sulfur content varies no more than 0.1- 0.85% and is in the form of sulfides of the (Fe, Mn)S type, mainly MnS, and in the non-metallic inclusions of "beads" the sulfur content is no more than 15- 30%. The conducted studies of the composition of dry, friable and liquid glassy ladle slags after desulfurization showed that they do not change the phase composition, but unlike the initial ladle slags, in the slag phase of such slags there are mainly CaO∙SiO2∙Al2O3∙MgO systems enriched with magnesium oxides, with a variable ratio of components. At the same time, sulfur in the slag phase of dry slags is mainly in the form of complexes (Ca, Mn, Mg, Al, Si)S, and in the slag phase of liquid slags it is mainly in the form of MnS and less often in the form of complexes (Ca, Mn,)S. According to the results of industrial experiments carried out at a number of enterprises in Ukraine and China, it was established that in order to limit the introduction of sulfur to converter steel with slag at the level of ≤0.002%, the remaining ladle slag after desulfurization should not exceed 0.5- 0.7 kg/t of cast iron. The analysis of the results obtained in the series of experimental melting in 300-ton converters with the use of scraps showed that the arrival of sulfur in the steel in all five treatments was lower than the calculated (according to the balance) by 0.00002 - 0.00165%.