Double Slag Operation Dephosphorization in BOF for Producing Low Phosphorus Steel

A study on the production of low phosphorus steel by double slag operation in 210 t converter was carried out. A phosphorus content of less than 0.005% (mass percent) was obtained before tapping. About 80% phosphorus could be removed by the first slag after 5 min. High Fe³⁺ content and high basicity in the first slag were in favor of dephosphorization. On the other hand, Fe³⁺ content had less effect on dephosphorization during second slag treatment. In the second slag period, the fraction of dephosphorization increased with the increase of basicity up to a basicity of 6. Further increase of basicity of the second slag had very little effect on dephosphorization. The tapping temperature had great impact on dephosphorization. It was impossible to get phosphorus less that 0. 005% when the tapping temperature was higher than 1 943 K. The optimum operation conditions were suggested. On the basis of these conditions, the amount of the second slag and the effect of the remaining first slag were estimated.