Abstract
The rare oxide, La2O3, was added to the refined slag as a tracer to evaluate the origin of large-size inclusions in the steel. The composition of CaO-Al2O3 was similar to that of the VD refining slag. Three different forms of inclusions came from the slag entrainment and the amount were large. The proportion of large-size inclusions caused by calcium treatment was stable and small. Besides, the formation mechanism of large-size inclusions was also discussed.