Abstract: This paper is based on a vanadium extraction converter to study the semi-steel dephosphorization process outside the furnace, in order to select a suitable dephosphorization agent for the semi-steel dephosphorization outside the furnace, so as to reduce the dephosphorization pressure of the converter and reduce the final phosphorus content to achieve ultra-low phosphorus steel production level. The vanadium-extracted semi-steel sample was tested in a laboratory tube furnace, and the most suitable amount of dephosphorizing agent for CaO-Fe2O3-CaF2 was 60 kg/t. Based on this, the proportion of the CaO-Fe2O3-CaF2 dephosphorizing agent was studied to obtain the optimal ratio: w(CaO)=30 %－45 %，w(Fe2O3)=40 %－55 %，w(CaF2)=10 %－15 %，and get the best dephosphorization rate of 79.1%. Finally, the dephosphorization process outside the semi-steel after field extraction of vanadium was designed and field tests were conducted to obtain an optimum dephosphorization rate of 61.4 %. Through the analysis of the optical basicity and phosphate capacity of dephosphorized slag, it is further verified that CaO-Fe2O3-CaF2 dephosphorization agent has a good dephosphorization effect, which provides a certain reference for production practice.

Key words: semi-steel, secondary dephosphorization, dephosphurization agent, phosphate capacity, optical basicity