Based on thermodynamics on dephosphorizing oxidation reaction

the dephosphorizing equilibrium tempera ture of semi-steel by the C-P-Fe coupling action and the dephosphorizing equilibrium temperature of BOF end liquid by the P-Fe action are studied

and the temperature control model for "dephosphorization window" of double slag process is put forward. And the dephosphorizing test of 46 heats 45t top and bottom combined converter double slag process is carried out to obtain the effect of first turning-down temperature of liquid and BOF end temperature on dephosphorization rate and phosphorus distribution ratio. By theoretical calculation and process test analysis it is obtained that with present hot metal/% : 4.41C

0.41Si

0.19Mn

0.128P

0.034S

1250~1300℃

and end liquid/% : 0.08C

0.01Si

0.06Mn

0.0090P

0.017S

1600~1660°C and relative process conditions

by the first turning-down temperature of liquid being controlled between 1400℃ and 1440℃ and the BOF end temperature being controlled between 1610℃ and 1650℃ the dephosphorization rate in first turning-down period is up to 62.1%

the end dephosphorization rale of liquid is up to 93.9%

and the end phosphorus content in liquid decreases from original 0.0090% to 0.0078% .