Abstract: The first turndown temperature of BOF double slag melting process was discussed, from the point of the selective oxidation of phosphorus and carbon, the equilibrium of the dephosphorization reaction, the distribution ratio of phosphorus in BOF bath, and the melting point of the dephosphorization slag. The temperature region from 1 350 ℃ to 1 400 ℃ was proposed as the optimal choice in this article, and trial experiments were also taken into action, the results of the first turndown show that, the average dephosphorization ratio of 63.11 % and the average P2O5 mass fraction of the dephosphorization slag of 3.1 % were got, while the first turndown temperature were located in the region from 1 350 ℃ to 1 400 ℃. And further investigation about the influence made by the slag basicity and oxidbillity were also made under the circumstance of the first turndown temperature was controlled in the region from 1 350 ℃ to 1 400 ℃, which revealed that the basicity of 1.8to 2.0 and the oxidbillity of 14 % to 17 % make more contribution to the acquisition of the optimal dephosphorization results of the first turndown point.

Key words: double slag, dephosphorization, first turndown temperature, dephosphorization rate, distribution ratio of phosphorous