Effect of the La2O3 Content in Slag on Inclusions in Al-Killed Steels

In order to explore the reaction between the molten steel and the slag containing rare earth oxides, the effect of the La2O3 in slag on inclusions in the molten steel was carried out through laboratory experiments and thermodynamic calculations. In the case of steel-slag ratio of 5:1, the chemical reaction between La2O3 in slag and the molten steel occurred so that the element La was transferred to the molten steel and reacted with the existing inclusions in the steel generating a large amount of inclusions containing La2O3. As the La2O3 content in the slag increased to 5 pct, the total La content in the steel and the La2O3 content in inclusions gradually increased to 1.9 ppm and 4.63 pct, respectively. Both of them changed slightly when the La2O3 in slag further increased to 10 pct. The number density of>5 lm inclusions decreased from 4.76 to 0.44 #/mm(2) when the La2O3 content in the slag increased from 0 to 10 pct. Moreover, it was found that the La2O3 in the slag was beneficial to remove Al2O3-MgO inclusions from the molten steel. An activity model of slag was established based on the ion and molecule coexistence theory, and it was proved that the activity of Al2O3 in the slag increased with the increase of La2O3 in the slag. In addition, the dissolved aluminum in the molten steel would promote the reduction of La2O3 in the slag, which was verified by both the experimental data and the thermodynamic calculation. The formation mechanism of inclusions during the steel-slag equilibrium reaction was discussed. (C) The Minerals, Metals & Materials Society and ASM International 2022