Abstract: In order to improve the castability and cleanliness of ultra-low carbon IF steel in continuous casting, the optimization of converter bottom blowing process, carbon and oxygen contents control at the endpoint, top slag modification, efficient vacuum deeper decarburization technology and enhancing protection of casting process were carried out. The results showed that using the annular-tubes type bottom nozzle instead of the original capillary type gas permeable brick bottom blowing, the single tube bottom blowing intensity 0.086 m³/(t·min), and the stirring energy 0.40 W/t, which could significantly improve the stirring capacity in the later stage of blowing. The average carbon and oxygen product of the molten steel at the endpoint of the converter reached 0.002 09. The vacuum was rapidly pumped to the limit vacuum degree, and the vacuum decarburization efficiency was the highest at 3-5 min forced oxygen blowing stage and holding 8-12 min under limit vacuum degree. Reducing the residual oxygen content after vacuum decarburization and optimizing the top slag composition of ladle could significantly reduce the Al₂O₃ inclusion formation and promote the adsorption and dissolution of inclusions by top slag. With the protection of continuous casting,the control level of oxide inclusion and pouring ability of molten steel has been significantly improved.

Key words: ultra-low carbon IF steel, inclusion, casting ability, total oxygen content