Researches on X70 cleanliness in refine and continuous casting process

Using systematic sampling and comprehensive analysis, the variation of total oxygen content and amount, dimension and distribution of nonmetallic inclusions were studied systematically during the production process of hot metal pretreatment-LD-LF-VD-slab CC in Angang. The results show that:(1) The average total oxygen content of slab is 17.33×10^-6 and the number of micro inclusions is 2.40 mm^-2; (2) Before and after the LF process, micro nonmetallic inclusions in the steel are mainly strip or block Al₂O₃ and global or polyhedral silicate;after calcium treatment in VD, the pure brittle Al₂O₃ inclusions and harmful MnS inclusions along boundaries were not found; (3) The reappearance of Al₂O₃ inclusions in mold and slab indicates that secondary oxidation happens in the tundish or mold; (4) Oxide and sulfide inclusions are not modified fully.