Abstract: In order to make the requirement of phosphorus mass fraction is less than 0.010 % for low phosphorous steel, and according to the effect of temperature, slag basicity，w(FeO) of slag and mixing parameters on dephosphorization, the offgas analysis dynamic control steelmaking model was applied on 120 t BOF of Ma’anshan Iron & Steel Company Limited. “Slag-Remaining+Double-Slag” technology, suitable loading system, slagging system and oxygen supply system, optimizing dephosphorization parameter were used in steelmaking. Through the analysis and comparison of 500 experiments, dephosphorization rate 95.2 % can be achieved by taking measures such as the temperature and the carbon mass fraction of the first turning down 1 540~1 580 ℃ and 0.10 %~0.25 %, final slag basicity 3.0~3.5, w(FeO) =15 %~23 %, and suitable stirring intensity. And the phosphorus mass fraction of converter tapping is less than 0.070 % and the hit rates of carbon content and temperature both meet the requirement of 96.4 %.

Key words: converter, ultra-low phosphorous steel, the offgas analysis, dephosphorization technoiogy