The converter dephosphorization process takes the advantages of capacious furnace，which enables the rapid and efficient dephosphorization with low slag basicity in the early stage of converter steelmaking. The recycling of decarburization slag can also reduce the consumption of lime and other auxiliary materials and the amount of slag emission. Under the conditions of low basicity and low temperature，the low temperature is beneficial to dephosphorization in thermodynamics. But too low temperature will result in the high slag viscosity，which affect the kinetic conditions and make it difficult to pour the slag. The dephosphorization effect is better when the basicity is properly increased. With the increase of FeO content in slag，the dephosphorization ratio first increases and then decreases. The solid and liquid phase coexist in the dephosphorization slag，and the solid solution of Prich phase has good phosphorus enrichment ability. Owing to the complete separation of slag and hot metal after dephosphorization，the duplex process can effectively improve the dephosphorization ratio and is suitable for the production of ultralow phosphorus steel. However，because the process requires two converters，the utilization efficiency of converter is low and the heat loss of intermediate tapping is large. The double slag process only needs one converter，and the cleanliness of molten steel is high，which is an important development direction of converter dephosphorization.

Aiming at the characteristics of the 120 t converter and smelting process of a certain plant of Ma’anshan Iron and Steel Co．，Ltd.，the parameters of the original fourhole nozzle of the oxygen lance were optimized．The number of nozzle holes，nozzle angle，operating pressure，throat diameter，outlet diameter and expansion length had all been adjusted appropriately．Mach number of the optimized oxygen lance nozzle had been increased from 1.98% to 2.05%．Combined with the production practice of the plant，it shows that the optimized 5hole nozzle of oxygen lance can increase the oxygen supply intensity of converter，optimize the dynamic reaction conditions in converter，shorten the oxygen blowing time by 128 s，increase the dephosphorization rate by 4.65 %，decrease w(TFe) of final slag from 18.59 % to 15.84 %，and decrease molten hot metal consumption by 22 kg/t，which is not only conducive to improving the scrap steel ratio of converter，but also to improving the metal yield．

转炉；钒渣；改质；溅渣护炉