| In view of the acceleration of BOF production pace as well as the in-depth restructuring of ultra low carbon product mix, a steel plant, where slag used can’t meet the need of production, conducted necessary research on physics-chemistry and metallurgical property of ultra-low carbon steel, with aim to improve quality and productin capability of ultra-low carbon steel.The steel plant conducted site investigation of slag used for refining of ultra-low carbon steel, analysis on metallurgical property of slag as well as main contributors to metallurgical property of furnace slag. Also, it conducted research on protective powder used for ultra-low carbon steel, and comparisons of melting point of slag carry-over, de-S rate of liquid steel as well as Als/Alt at different compositions of refining slag, and defined range of the refining slag composition, based on data of continuous caster and characteristics of steel grades.Research shows that, refining slag of silicon killed steel shall be controlled at Ca O 50-60%(actual slag 45~54%), Al2O3 30-40%, Si O2 12-18%,so as to reduce Al consumption and improve de-S performance. Regarding steel grade which is demanding in cleanness, Al2O3 content shall be well controlled, with Ca O/Al2O3=1.5-2.0, R>5, MI=0.20-0.30.Research on top slag treatment for DC04 or higher ultra-low carbon steel shows that, after 120 kg Al40 and 240 kg Al40 are added during converter tapping, Ca O and Al2O3 when entry into RH will be 2.9 and 1.8 respectively; and after 240 kg Al40 is added at converter tapping, the RH top slag’s absorption of Al2O3 becomes strong.Research on protective powder for SPHE(IF steel) shows that, melting point of protective powder during casting of IF steel can be increased by 8℃, and basicity will increase then decrease, with fluctuation of 0.2, and viscosity will increase by 0.2Pa.s,Al2O3 will increase by 6.2%. Protective powder of IF steel has key function of lubrication, with prefered transition temperature 1160℃.
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