Abstract: Interstitialfree(IF) steel was produced by KR→BOF→RH→CC process. Different amounts modifier were added to ladle slag after tapping. The effect of top slag conditioning was compared. The composition of molten steel and the morphology, composition, size, number of inclusions during RH refining were studied. In addition, total oxygen and the characteristic of inclusions in the surface layer of continuously-cast slab were analyzed. The results show that enough lime must be added to top slag to ensure the Al₂O₃ absorption capacity by using Al-based modifier. The loss rate of soluble aluminum in steel declines 30 %－40 % and the total oxygen at the end of RH refining is below 20×10^-6 when the mass fraction of FeO in slag decreases from 13 %－16 % to 0.77%, then the change of inclusion number in slab is significant from 5.66 cm^-2 to 2.96 cm^-2.

Key words: Interstitial-Free steel, oxidizing slag, inclusion, cleanliness