A method by combination of soft-blow with oxygen bottom blowing (CS-OB method) which is suitable for decarburization of desiliconized, dephoshorized and desulphurrized (pre-refined) hot metal in BOF has been developed. Its blowing condition had to be decided to increase the Fe yield. The Fe yield in the decarburization of pre-refined hot metal was mainly affected by spitting and Fe oxidation since the decarburization was carried out with small amount of slag. The CS-OB method was characterized by the combination of extremely soft top blowing with bottom gas stirring to decrease both spitting and Fe oxidation at the same time.
The most suitable condition found in the 0.5t/ch lab. test and the 100t/ch BOF test was L/L0=0.10.2, the bottom gas flow rate=0.20.25 Nm3/t·min.
Oxygen used for the post combustion of CO gas in the furnace increased by soft blowing in the CS-OB method. Heat efficiency of the post combustion was estimated about 90% in the 100t/ch BOF test.
