Abstract: In order to reduce the flocculating flow or clogging of continuous casting and the content of inclusions in steel, a new technology of ladle top slag denaturalization was introduced in the production of IF steel with the process of “BOF→Argon station→RH→CC” at one company. To examine the effect of the use of the ladle slag modification technology, trial research on slag denaturalization was also carried. Molten steel samples were taken from RH refining end-point and tundish by using the barrel sampler. The corresponding slab samples were also taken. Inclusions were tested by using ASPEX Explore automatic Scanning Electron Microscopy(SEM). Contrast analysis of the quantity, type and size of the inclusions of RH→tundish→slab were carried on under the condition of denaturalization and non-denaturalization process. The results show that slag denaturalization effectively reduce slag oxidizability, improving steel cleanliness; the main types of inclusions under both process conditions are Al2O3，TiOx-Al2O3 and Oxides. The proportion of Oxides inclusions with denaturalization process is significantly higher than non-modification process; clusters of inclusion types in slab with the process of modification are single and the quantity and size are smaller than non-modification process.

Key words: slag denaturalization, inclusion, IF steel, steel cleanliness