| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing a high cleanliness steel in which inclusion caused by the involution of slag into a steel ingot does not almost exist. SOLUTION: In the first secondary refining treatment, the flowing rate of blowing gas is adjusted so that the stirring power density becomes 5-60 W/ton and also, the adjustment of the slag is performed so that the slag composition after degassing treatment, becomes CaO/SiO<SB>2</SB>≥3.5, CaO/Al<SB>2</SB>O<SB>3</SB>=1.5-3.5 and Fe+MnO≤1.0 mass%. In the degassing treatment, the flowing rate of the blowing gas is adjusted till this middle period, so that the stirring power density becomes 50-200 W/ton, and the flowing rate of the blowing gas is adjusted after the middle period, so that the stirring power density becomes≤140 W/ton (except 0 w/ton). In the second secondary refining treatment, the flowing rate of the blowing gas is adjusted, so that the stirring power density becomes≤25 W/ton (except 0 W/ton). COPYRIGHT: (C)2007,JPO&INPIT
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