Experimental Study On Preparation Of Nitrided Ferrovanadium Using Vanadium Oxide By Short Process

Vanadium is an important alloy additive of micro-alloyed steel because it plays a part in refining grain size and precipitation strengthening.Its addition form includes such vanadium-based alloys as ferrovanadium,vanadium nitride and nitrided ferrovanadium etc.Comparatively speaking,because of containing iron and high specific gravity,nitrided ferrovanadium can pass through the slag layer more effectively and owns better micro-alloying effect.The traditional preparation method of nitrided ferrovanadium is liquid or solid nitriding into ferrovanadium.However,the preparation of ferrovanadium needs high energy consumption and high cost with large quantities of vanadium residues,causing vanadium loss.In this paper,short-process preparation of nitrided ferrovanadium under flowing nitrogen in the tube furnace was studied by selecting industrial leafy vanadium（V₂O₅）as raw material,iron power as iron source and carbon powder as reducing agent.The method has the advantages of simple process and high utilization of vanadium without vanadium residues.It not only saves resources and protects environment,but also reduces production cost.The thermodynamic analysis shows that V₂O₅ can be reduced to low valence vanadium oxides with high melting point under the melting point of V₂O₅,and the reduction process is step by step.Vanadium carbide can be nitrided to vanadium nitride,and increasing the pressure of N2 is favorable to the reaction.But when the temperature is higher than 1544.81K（1271.03℃）under the atmospheric pressure,vanadium nitride can be translated into vanadium carbide.Fe was oxidized preferentially to Fe3O4 and then reduced to iron element.The kinetics results show that it is reasonable to use first-order reaction kinetic mechanism function to analyze the preparation of nitrided ferrovanadium from vanadium oxide.The linear correlation coefficients are all above 0.94.The nitrogen gas only plays a protection role in the initial stage.The reduction and nitriding reaction take place at the same time under high temperature,and nitriding reaction may promote the carbonation reaction.XRD measurements of the products at different temperatures exhibit the existence of vanadium carbide at 1000℃ and the beginning of nitriding reaction at 1200℃.The results of pre-reduction test show that the best pre-reduction condition is holding at 650℃ for 4h.Based on thermodynamic and kinetic analyses,single factor test and orthogonal test were carried out for preparing nitrided ferrovanadium using vanadium oxide.It suggests in single factor experiments that nitrogen content of the product reaches the maximum with reaction parameters as following: mixed carbon coefficient: 0.35;nitrided temperature: 1400℃;reaction time: 120min;nitrogen flow: 150L/h;reactant particle size: 200 mesh;sample forming pressure: 8MPa.The orthogonal experiment results indicate that the main to secondary order of factors effecting nitrogen content in the nitrided ferrovanadium is: reaction time> reactant particle size> nitrided temperature > mixed carbon coefficient > nitrogen flow.The nitrogen content of the product obtained by stability test is 12.04%.The semi-industrial experiment by adopting double-pusher kiln was further carried out.The four test results show that vanadium content >43%,nitrogen content >9% and V:N>0.2 in the product,conforming to the requirement of FeV45N10-B grade in the national standard of People’s Republic of China GB/T30896-2014.