Abstract: In this paper, the effect of oxygen transfer from RH ladle slag to molten steel on the purity of molten steel is analyzed. The reasonable dissolved oxygen level of RH ladle slag is determined by calculation to ensure that the balanced top slag FeO activity is in a lower range. In addition, the effect of top slag composition on activity coefficient of top slag FeO was analyzed, and reasonable slag composition was determined: from the end of tapping to decarburization of RH, the top slag w(SiO2)=4 %–5 %, w(MgO)=8 %–9 %, w(CaO)/w(Al2O3) of IF steel was controlled between 1.8–2.2, and after the end of RH deoxidation, the slag w(CaO)/w(Al2O3)=1.3–1.5 was ensured, which not only reduced oxygen transfer between slags, but also ensured the top slag adsorption. The ability of inclusion.

Key words: IF steeltop slag, modification, FeO activity, activity coefficient