Study On Direct Smelting Of Vanadium-bearing Semi-steels By Vanadium-bearing Hot Metal In Blast Furnace

Vanadium is considered to a modern industrial monosodium glutamate,85%of its output is used in the field of alloy steel.Nowadays,there are mainly three ways to produce vanadium steel.However,vanadium ferroalloy alloy the alloying of molten steel,or taking vanadium slags or V2O5 in place of vanadium-iron alloy and alloying directly,both are in the technical process of blowing the vanadium in molten iron into slags,forming vanadium slags that separate from semi-steel.The problem that long technical process,lower usage rate of vanadium,high energy consumption can’t be solved fundamentally.The author’s research group put forward a new method called "a new method for decarburization by CO2 to directly smelt vanadium-containing steel in blast furnace".In other words,vanadium-bearing molten iron in the blast furnace is blown by CO2 gas,without being blown by O2 gas.This procedure make use of the low oxidation of CO2 to get rid of carbon in molten iron,and won’t react with vanadium in molten iron so that achieves the goal of lowering carbon and remaining vanadium,and realize the aim that use V-containing molten iron in the blast furnace smelt vanadium steel directly.This solves the limits of traditional smelting of vanadium steel,including complex procedures,long processing period,high V loss and lower usage rate of energy.In the basis of former research,this paper mainly calculates the thermodynamics of decarbonization,dephosphorization and vanadium protection process through FactSage software.Conclusions can be drawed by investigating the influence of smelting temperature,slag system composition,gas flow and composition on the three smelting stages of pre-dephosphorization,decarbonization and dephosphorization.Under the standard condition,the Gibbs free energy of reaction between carbon,silicon,manganese,phosphorus,vanadium in hot metal and CO2 becomes less than 0 in the temperature range of 1400-2000 k,which means all those elements could react with CO2.The transformation temperature of C and V is 1630 K,and the transformation temperature of C and P is 1712 K.When the smelting temperature is higher than 1630 K,the targets of decarburization,dephosphorization and vanadium preservation can be achieved.The results of FactSage calculation show that when the temperature of vanadium-bearing hot metal 1500℃,the amount of CO2 8.15L/100g iron,and the basicity of slag more than 3,the oxidation product of vanadium is V2O3 and the dephosphorization products are Ca3(PO4)2 and FePO4.The oxygen potential of slag first increases and then decreases with the basicity,and then remains unchanged.The CaO will not react with V2O3 to promote the oxidation of vanadium.Under the same oxygen potential,the decrease of phosphorus content in the system may lead to the oxidation of vanadium.Under the same phosphorus content,the decrease of oxygen content in the system will promote the oxidation of vanadium.The suitable conditions of dephosphorization pretreatment are as follows:smelting temperature 1400℃,Fe2O3 content of initial slag 10%,slag basicity 4,BaO content of initial slag 5%,gas flows 350 mL·min-1,CO2 ratio 100%.The content of carbon,phosphorus and vanadium in vanadium-bearing hot metal at the end of smelting is 3.94%,0.0767%,0.28%respectively,and dephosphorization rate 36.67%.The suitable decarburization conditions are smelting 1500℃,gas flow 1200 mL·min-1,gas composition 20%O2 and 80%CO2,and blowing time 20 min.Under this condition,the final carbon content is 0.60%,and the final vanadium content is 0.299%.The suitable conditions of dephosphorization are as follows:smelting temperature 1500℃,Fe2O3 content of initial slag 0%,basicity 4,BaO content of initial slag 5%,gas flows 250 mL·min-1,CO2 ratio 100%,and blowing time 9 min.The results of thermodynamics and experiment show that it is feasible to directly smelt vanadium bearing semi steel by decarburization,dephosphorization of vanadium bearing hot metal in blast furnace.The yielding rate of vanadium from vanadium-bearing hot metal to vanadium-bearing semi-steel is 90.53%,and the end-point vanadium content of V,C,P,Si,Mn,S is 0.291%,0.329%,0.0176%,less than 0.01%,less than 0.01%,0.01%,respectively.The target steel can be obtained by modulating it species.