Study On Rheological Characteristics And Physical Properties Of Chromium Bearing BOF Slag

In order to reduce costs, part of iron and steel enterprises increased the ore proportioning ratio of chromium bearing low grade ore in ironmaking process. And the rise of chromium content in molten iron, causing great quantities of Cr₂O₃ generated in slag, then resulting series of converting problems. At present, the researches of chromium bearing slag are mostly concentrated in the EAF slag and BF slag, while the research on chromium bearing BOF slag is relatively few.This paper focuses on the CaO-SiO₂-FeO-MgO-MnO-Cr₂O₃ system which include major component of chromium bearing BOF slag. The phase-containing, structure, physical properties, rheological characteristics and viscous flow activation energy of chromium bearing BOF slag were studied in this paper. The researches in this paper is hoped to provide certain theoretical basis for melting high chromium content hot metal. The main work and the corresponding results got in this paper are listed follows:The phase-containing, morphology and structure of chromium bearing BOF slag were tested by XRD, SEM/EDS and Raman spectra respectively. The results indicated that, the chromium in BOF slag is mainly existed as FeO?Cr₂O₃, MgO?Cr₂O₃ and a small amount of MnO?Cr₂O₃. The primarily microscopic phase of this slag: dark gray strip shaped merwinite, light gray piece shaped RO phase and gray irregular granular shaped chromium-enrichment phase. The chromium-enrichment phase is mainly composed of the solid solution of FeO?Cr₂O₃ and MgO?Cr₂O₃. With the increasing of Cr₂O₃ content in slag, the amount of merwinite in slag showed a trend of increasing first and decreasing soon, while the amount and size of chromium-enrichment phase has always been greater. With the increasing of Fe O content in slag, the Fe content in chromium-enrichment phase increases obviously. With the increasing of binary basicity of slag, the amount of merwinite increased, and the size of merwinite and chromium-rich phase increased. When the binary basicity of slag is increased to 2.0, a large number of light gray particulate phase appears.The melting temperature, density and surface tension were measured by hemispherical method, Archimedes method and pull-tube method, and each experimental results were compared with the model calculated results. Then, the value of ‘C' in foam index formula of chromium bearing BOF slag is obtained by the physical properties results. The results clarified the effect of Cr₂O₃, FeO and binary basicity on the melting temperature, surface tension and density of chromium bearing BOF slag. And the value of ‘C' in foam index formula is calculated as 800-900.The apparent viscosity of slag at 4r/min?8r/min?12r/min?16r/min?20r/min under 1500°C were measured by Brookfield, and then the speed was fixed at 12r/min,the apparent viscosity of slag under 1480°C, 1490°C, 1500°C, 1510°C, 1520°C were measured by Brookfield. The rheological property of chromium bearing BOF slag was discussed by the constitutive equations, and the viscous flow activation energy of chromium bearing BOF slag was discussed by the curve fitting of Arrhenius equation. The result of rheological property showed that the CaO-SiO₂-FeO-MgO-MnO system presented as Newtonian behavior before the adding of Cr₂O₃. And with the increasing of Cr₂O₃ content in slag, the performance of non-newtonian fluid property become more obvious. By the analysis of the effect of each component on the rheological property, it shows that the Cr₂O₃ content and binary basicity have greater impact on the rheological property, and the impact of FeO content on the rheological property of the slag is minimal. The experimental results of viscous flow activation energy indicated that the impact of Cr₂O₃ content and binary basicity on the viscous flow activation energy is greater than the impact of FeO content, which is consistent with the impact of rheological properties.