Abstract:Two different slags, A ((mass% CaO)/(mass% SiO2)=5, Al2O3=25 mass%) and B ((mass% CaO)/(mass% SiO2)=8, Al2O3=46 mass%), were investigated to show the relation between slag composition and molten steel cleanliness based on laboratory experiments. The results show that, cleanliness of molten steel refined by slag B was obviously better than that of molten steel refined by slag A after 90 minutes’ reaction at 1600 ℃:the average total oxygen content were 9.25×10-6 vs 12.25×10-6,the average sulphur contents were 8.63×10-6 vs 19×10-6,the sulphur partifion coefficients in the range of 120260 and 717 respectively; most of the inclusions in molten steels reacted by slag A or slag B were calciummagnesiumaluminium silicate inclusion and the melting point of the inclusions in molten steel refined by slag B was obviously lower than that of the inclusions in molten steel refined by slag A.