Abstract: Ultra-low carbon IF steel sheet is mainly used in ultra-deep drawing parts such as automotive exposed panel, etc., which is faced with main surface quality problems caused by the steelmaking defects of inclusions, mold flux entrapment and bubbles. Therefore, the slag properties used in the whole steelmaking process play an important role in controlling inclusions in steel. In the present paper, the effects of slag on inclusion control were summarized from two aspects of the slag physicochemical properties and the slag characteristics in different steelmaking stages. It was found that the adsorption and dissolution of inclusions by slag was related to the physicochemical properties of slag and the sizes of inclusions. The main control objectives of RH refining slag were low oxidation and appropriate w(CaO)/w(Al₂O₃). The TFe mass fraction was generally controlled in 2.0 %–8.0 %, and the w(CaO)/w(Al₂O₃) was controlled in 1.2–1.8. In addition, the basicity of refining slag was generally controlled in 4–10. The tundish flux and mold flux should first prevent the carbon increase in the molten steel, and secondly prevent the secondary oxidation of the molten steel caused by SiO₂ in the slag. At the same time, they should also be capable of adsorbing inclusions. The high basicity tundish flux for ultra-low carbon IF steel generally had the basicity of 2.9–11.5, the w(CaO)/w(Al₂O₃) was controlled in 1.0–2.5, and the (FeO +MnO) mass fraction was controlled in 1.9 %–4.0%. The basicity of the mold flux for ultralow carbon IF steel was generally controlled in 0.85–1.0, the w(CaO)/w(Al₂O₃)  was controlled in 5.0–8.5, and the (FeO+MnO) mass fraction was less than 1 %.

Key words: ultra-low carbon IF steel, Al₂O₃ inclusions, refining slag, tundish flux, mold flux, secondary oxidation