Analysis of Nonmetallic Inclusions in Steel When Cerium Oxide Is Used in Ladle Metallurgy Slags

The development of effective technological methods for controlling the formation of nonmetallic inclusions (NMIs) is a promising direction for improving the properties and quality characteristics of steels. The sulfur content is one of the factors controlling the quantity, morphology, and distribution (over the metal volume) of sulfide inclusions is. To organize the production of steel with a low (down to 0.003%) sulfur content, desulfurization is carried out at ladle furnace units with the formation of basic Ca–SiO2–Al2O3 slags and deep aluminum deoxidation of steel. Here, one of the main oxide inclusions in aluminum-killed steel is corundum (Al2O3), which impairs the properties of steel and leads to “clogging” of the inner surface of a submerged entry nozzle during continuous casting. The negative effect of corundum in steel can be neutralized by its removal into the basic fluid slag formed in a ladle furnace unit by decreasing the activity of Al2O3. However, in practice, an excessive increase in the basicity of a refining slag to decrease the activity of Al2O3 is usually accompanied by slag heterogenization, an increase in the melting temperature of slag, and a decrease in its refining properties. The use of rare earth metal (REM) oxide additives can be a promising direction for decreasing the activity coefficient of Al2O3 in basic refining slags. The application of REM oxides ensures a decrease in their melting temperature, an increase in the fluidity, an increase in the sulfur distribution ratio, and a decrease in the REM distribution ratio. In this wok, we study the influence of cerium oxide in Ca–SiO2–Al2O3–MgO–Ce2O3 slags on NMIs. Experimental samples of clean steel held under a slag containing 15.0% cerium oxide exhibit the presence of up to 10 ppm cerium in the metal, a decrease in the total oxygen concentration to 13 ppm, a decrease in sulfur in the metal from 20 to 5 ppm, and the absence of manganese sulfide and corundum (Al2O3) NMIs. The Ce2O2S oxysulfide phase, magnesium and cerium oxide inclusions, and the MgO–Al2O3 oxide phase are also detected.