Abstract: Non-metallic inclusions in steel have a great influence on the properties of steel. In the continuous casting process, as the temperature decreases, the molten steel cools and solidifies, and the thermodynamic equilibrium between the steel and the inclusions moves, resulting in a change in the average composition of the inclusions. Therefore, it is meaningful to study the transformation of inclusions during solidification and cooling of molten steel. In this paper, 20CrMnTiH sulfur-containing gear steel was studied, and the evolution of inclusions during solidification and cooling of molten steel was studied by thermodynamics and factory experiments. The results show that the inclusions in the tundish steel and the continuous casting billet are mainly Al2O3-Ti2O3-MgO-CaO-CaS inclusions, but the CaO in the inclusions in the continuous casting billet is significantly lower than the CaS content. This is consistent with the thermodynamic calculation of the solidification cooling process and the conversion law of CaO inclusions. However, due to the limit of thermodynamic and kinetic conditions, the calculated average composition of inclusions and the actual detection values still have some differences.

Key words: sulfur-containing gear steel, inclusion transformation, solidification cooling