The estimation of desulphurization property of boron-containing slags of the reduction period of the AOD process

Now the main industrial method for producing stainless steel is smelting in an argon-oxygen decarburization (AOD) furnace, therefore the paper presents the results of thermodynamic modeling of the desulfurization process of low-carbon semi-finished stainless steel during the reduction period of AOD process by treating it with boron-containing slags. The use of boron oxide as a fluxing material instead of fluorspar reduces the environmental harm and decrease the viscosity of the formed slags. Using the simplex lattice method of experiment planning, a matrix was constructed containing 16 compositions of the oxide system СаО–SiO₂–(3-6%)В₂О₃–12%Cr₂O₃–3%Al₂O₃–8%MgO with variable basicity of 1.0–2.5. Based on the generalization of the thermodynamic modeling results, approximating mathematical models in the form of a reduced third-degree polynomial were constructed. The adequacy of the models is verified by three control points not included in the experimental design matrix using the t-criterion at a significance level of 0.01. The results of mathematical modeling are presented graphically in the form of diagrams of the dependence of the equilibrium sulfur distribution on the slag composition at temperatures of 1600 and 1700°C. The constructed diagrams made it possible to quantitatively estimate the effect of temperature, basicity and boron oxide content on the equilibrium interphase distribution coefficient of sulfur. It is found that an increase in slag basicity from 1.0 to 2.5 in the considered range of boron oxide content (3.0–6.0%) improves the metal desulfurization process, ensuring an increase in the equilibrium interphase distribution coefficient of sulfur from 0.1 to 5.0–7.0 at temperatures of 1700 and 1600°C. It’s shown that the process of metal desulfurization in slags with low basicity of 1.05–1.15 is accompanied by a slight decrease in the sulfur content in the metal. At the same time, the concentration of boron oxide has virtually no negative effect on the process of metal desulfurization. Slags with increased basicity up to 2.0–2.5 have more favorable refining properties. The sulfur concentration in the metal during their formation decreases from 0.015 to 0.007–0.008%.