Abstract: The double slag process of BOF was optimized by balance calculation and research of dephosphorization law. Then the requirement of the tapping temperature was satisfied by raising the hot metal ratio from 84% to 88%. Moreover，results showed that w(MgO) of slag was best satisfy to 6%~8% with the basicity was 1.6~1.8 at the first deslagging and the final slag basicity was controlled at 3.5~ 4.0 , then the phosphorus mass fraction could be lower than 0.02% and the temperature of steel was higher than 1680℃ at BOF steelmaking end.

Key words: double slag, BOF, dephosphorization