Original: Zou Jianxin, Cui Xumei, Professor Li Junhan, etc





1 Product performance and use


Vanadium carbide and vanadium nitride are two important vanadium alloy additives, which can be used in structural steel, tool steel, pipeline steel, reinforcement, ordinary engineering steel and cast iron. 80% - 90% of vanadium output is used in the steel industry. The main reason is that vanadium reacts with carbon and chlorine to form fusion-resistant carbon and nitride. According to the composition of steel and the temperature of steel treatment process, these compounds can play the role of precipitation hardening and grain refinement in steel. Therefore, vanadium carbide and vanadium nitride alloys play an increasingly important role in vanadium steel production. The existing research shows that the addition of vanadium carbide and vanadium chloride to steel can improve the comprehensive mechanical properties of steel, such as wear resistance, corrosion resistance, toughness, strength, ductility, hardness and thermal fatigue resistance, and make the steel have good weldability, and can also play a role in eliminating the extension of inclusions. Especially in high-strength low-alloy steel, vanadium nitride contains carbon, which is more conducive to promote the precipitation of nitrogen-rich carbon and vanadium chloride than vanadium carbide, thus strengthening and refining the grain more effectively, saving vanadium containing raw materials and reducing production costs. In addition, vanadium carbide can also be used as raw material for the preparation of vanadium metal. Due to the difficulties in manufacturing vanadium nitride and vanadium carbide, they are still in the development stage. At present, only the United States, South Africa, China and other countries can produce them, and China is still in the further research and development stage.



Vanadium nitride, also known as "NITROVAN", is a composite alloy containing both vanadium, nitrogen and carbon, and is an excellent steelmaking additive. FeV nitride can greatly improve the strength and toughness of steel through grain refinement and precipitation strengthening; The steel bar added with ferrovanadium nitride has the characteristics of low cost, stable performance, small strength fluctuation, cold bending, excellent welding performance and basically no aging; The addition of ferrovanadium nitride does not need to change the current production process of Grade II deformed steel bars in domestic steel enterprises, and has no special requirements for temperature control and rolling control. It is especially suitable for Chinese steel enterprises to rapidly realize the upgrading of deformed steel products from Grade II to Grade III, Grade IV and even Grade V deformed steel bars under the existing production equipment and process conditions. Ferrovanadium nitride is also widely used in thin slab continuous casting and rolling high strength strip steel, non-quenched and tempered steel, high strength H-beam steel, high-speed tool steel, high strength pipeline steel and other products. It is an economic and effective way to improve the strength and toughness of steel through microalloying.



Vanadium carbide has high melting point and good chemical stability. It is mainly used to manufacture cermets, heat-resistant alloys and hard alloys. Adding 6%~30% titanium carbide into WC-Co cemented carbide can form Ti-WC solid solution with WC, which can significantly improve the red heat resistance, wear resistance, oxidation resistance, corrosion resistance and other properties of the alloy, making WC-Co cemented carbide more suitable for processing steel. Tungsten free cemented carbide can also be made with Ni-Mo and other alloys as binders, which can improve the turning speed and the precision and finish of the machined parts.



Vanadium and nitrogen can be directly added to low alloy and high strength steel to reduce costs. The reliable method is to add vanadium nitride. In the presence of nitrogen, vanadium forms nitrogen-rich vanadium carbonitride. Compared with ferrovanadium, the use of vanadium carbonitride has the following advantages: a. It can strengthen and refine the grain more effectively than ferrovanadium; B. Reducing the amount of vanadium can reduce the cost; C. Favorable utilization of vanadium and nitrogen; C. High purity; D. The particle size is uniform and convenient for packaging.

Therefore, because of its low price, it is suitable to be used as an additive for many carbon-containing high-strength steels. The industrial vanadium nitride and vanadium carbide products are shown in Figure 5.7.1.

(a) Coal spherical vanadium nitride (b) vanadium carbide

Figure 5.7.1 Visual diagram of vanadium nitride and vanadium carbide products

2 Introduction to preparation methods of vanadium nitride

The main methods of industrial production of vanadium nitride at home and abroad are as follows:

(1) The raw material is V2O3 or ammonium metavanadate, and the reduction gas is the mixture of H2, N2 and natural gas or the mixture of N2 and natural gas, NH3 and natural gas, pure NH3 gas or the mixture of 20% (volume) CO, etc. The vanadium nitride is prepared by high-temperature reduction in the flowing bed or rotary tube, and the materials can be continuously in and out.

(2) V2O3, iron powder and carbon powder are used to obtain vanadium carbide in a vacuum furnace, and then nitrogen is introduced to nitride and cooled in nitrogen to obtain vanadium nitride.

(3) Vanadium nitride is prepared by mixing V2O3 and carbon, heating in the pusher kiln, and nitrogen nitriding.

(4) The raw material is ammonium vanadate or vanadium oxide, which is mixed with carbon black, and then heated in a microwave oven with nitrogen or ammonia atmosphere for high temperature treatment to produce vanadium nitride.

(5) In China, the University of Science and Technology of Beijing uses vanadium pentoxide and activated carbon to produce vanadium carbide in a high-temperature vacuum molybdenum wire furnace and then nitrogen nitriding to obtain vanadium nitride.

The overall situation of vanadium nitride production in industry is as follows:

(1) Raw material for production of vanadium nitride: V2O3 or ammonium polyvanadate.

(2) Auxiliary materials for production of vanadium nitride: reducing agent (mixture of H2, N2 and natural gas, or mixture of NH3 and natural gas).

(3) Final product: vanadium alloy additive --- coal ball vanadium nitride.

(4) Main equipment for production of vanadium nitride: vacuum furnace, flowing bed, etc.

(5) Production process of vanadium nitride: vacuum reduction method.



3 Preparation principle of vanadium nitride



(1) Preparation of VN with V2O3



V2O3+N2=2VN+1.5O2 = 773620-72.67T



=At 0, the starting reaction temperature T=10646K=10373 ℃



V2O3+3C+N2=2VN+3CO = 430420-329.98T



=At 0, the starting reaction temperature T=1304K=1031 ℃



=430420+(19.143lgp3CO/pN2-329.98)T



(2) Making VN from metal V



V+0.5N2=VN = -214640+82.43T



=At 0, cut-off reaction temperature T=2604K=2331 ℃



=-214640+ (82.43-9.5715lgpN2)T



The higher the temperature, the more difficult the reaction is. The relationship between pN2 and the cut-off reaction temperature calculated according to the above formula is shown in Table 5.7.1.



Table 5.7.1 Relationship between the cut-off reaction temperature and pN2 for preparing VN from metal V

(3) Use V2C to obtain VN



V2C+0.5N2=VN+VC = -170340+88.663T



=At 0, cut-off reaction temperature T=1921K=1648 ℃



=-170340+88.663T+19.143T lg（1/p0.5N2)= -170340+(88.66-9.5715lgpN2) T



The higher the temperature, the more difficult the reaction is. The relationship between pN2 and the cut-off reaction temperature calculated according to the above formula is shown in Table 5.7.2.



Table 5.7.2 Relation between cut-off reaction temperature and pN2 for preparing VN with V2C

4 Industrial production of vanadium nitride



4.1 Vanadium-nitrogen alloy produced by Pangang Group



After years of production practice, the vanadium-nitrogen alloy production line of Vanadium Products Plant of Panzhihua Iron and Steel Group Co., Ltd. has gradually improved its vanadium-nitrogen alloy smelting technology, advanced technology, low product cost and stable technical and economic indicators. The vanadium-nitrogen alloy of Panzhihua Iron and Steel Co., Ltd. has basically the same performance as that of the advanced countries in the world. Its chemical composition and apparent density are stable, and its products have already possessed international competitiveness. The vanadium-nitrogen alloy smelting plant of Pangang adopts the traditional single-pass TBY kiln independently developed by Pangang, and at the same time adopts a double-pass nitrogen protection pusher kiln with high production capacity and low cost, with an annual capacity of more than 5000 t/a. With technological progress and capacity expansion and transformation, the following technical indicators also change, and various parameters are only of relative reference value.



(1) Consumption and source of main raw and auxiliary materials



① Vanadium trioxide. The main raw material is V2O3, which is produced by the vanadium product factory.



② Reductant powder. The reductant powder is purchased and supplied and transported into the plant by truck.



(2) Process flow



① Workshop composition



Vanadium-nitrogen alloy production line is mainly composed of raw material grinding room, raw material preparation room (including batching, dry and wet mixing), raw material drying room (including pressure ball drying), and TBY kiln room.



② Main equipment selection



Pendulum mill: 2 sets of 2R2714 type mills with a capacity of about 10t/d · set. The main motor power of the equipment is 18.5 kW. The mill equipment load rate is 90%, and the operation rate is 82%.



Mixer: 2 rotary dry mixers with a capacity of 9 t/d. The equipment load rate is 78%, and the operation rate is 82%.



Wet mixer: one XLH-1000 planetary wheel mill mixer (with capacity of about 7 5 t/d), 1 XLH-1600 planetary wheel mill mixer (with a capacity of about 11 t/d), the total load rate of the equipment is 100%, and the operation rate is 82%.



Molding equipment: 6 powerful pressure balls are used, and the single molding capacity is 3.5 t/d. Equipment load rate 85 7%, operation rate 82%.



Drying equipment: drying equipment: 2 tunnel type two-hole drying kilns, with operating temperature of 150~180 ℃. Its structural characteristics are that the raw materials should not be turned and collided during drying, and the drying time is long, so the tunnel drying kiln is selected. Tunnel drying kiln has the advantages of continuous operation, easy control of furnace temperature, good product quality, large output, etc., simple structure and low labor intensity. According to production requirements, two-hole tunnel drying kiln is adopted. The kiln body is rectangular, the furnace wall is built with clay bricks (N-2a), and the outer layer is insulated with fire-resistant fiber. The furnace top is made of reinforced concrete cover plate with refractory fiber and red brick. The kiln is paved with tracks, and the trolley with material balls is pulled in from the kiln end by the winch, moves towards the kiln end, and is gradually dried in the kiln. The dried materials are finally pulled out from the kiln end. The drying kiln adopts resistance heating, and the heater adopts waveform resistance belt, which is installed in groups. Each kiln is equipped with 8 exhaust holes on the top of the furnace, and the water vapor generated is discharged by the exhaust fan on the top of the furnace. Each kiln is equipped with 12 temperature measuring points, and the furnace temperature is automatically adjusted and controlled by sections. Main dimensions of drying kiln: L × W × H = 30500 × one thousand two hundred and ninety × 1850 mm； The overall dimension of two-hole tunnel drying kiln masonry is: L × W × H = 30500 × three thousand six hundred and seventy-eight × 2190.5 mm。 Drying capacity 0.7 t/h; Heating mode: electric heating; Maximum power 2 × 412 kW； Drying temperature 150~180 ℃; Drying time 48h; The heat preservation and cooling time is about 36h. Production capacity: 16 t/d per set, which can meet the production requirements of 4000 t/a vanadium-nitrogen alloy.



TBY kiln: The main process equipment for vanadium nitrogen alloy production is 4 TBY kilns.



(3) Main process technical indicators



See Table 5.7.3 for technical indicators, Table 5.7.4 for technical performance of vanadium-nitrogen alloy products of Pangang, and Table 5.7.5 for comprehensive energy consumption per unit product.



Table 5.7.3 Main process technical indexes (calculated based on vanadium nitrogen alloy output of 2000t/a)

Table 5.7.4 Technical properties of vanadium-nitrogen alloy products of Pangang

Table 5.7.5 Comprehensive energy consumption per unit product

4.2 Vanadium nitride produced by Vametco Minerals, South Africa

The production method is as follows:

(1) Mixing V2O3 with carbon and binder to form a pellet;

(2) React in a vacuum furnace to generate VCx (X<1) from V2O3 and CO;

(3) Inject nitrogen and cool under vacuum or inert atmosphere to obtain "NITROVAN".

Its chemical formula can be expressed as V (CxNy), where x+y=1. Its chemical composition and physical properties are shown in Table 5.7.7 and Table 5.7.8 respectively.

Table 5.7.7 Vanadium nitride composition produced by Vametco Mining Company (%)

Table 5.7.8 Physical characteristics of Nitrovan12

4.3 CBC method for producing FeV nitride in Russia

(1) Basic principle

The formation of nitride is determined by the combustion of pure metal in nitrogen:

xR+(y/2){N2}RxNy

lg/()= -/(2.3RT)

When=1,=105Pa and=107Pa, the equilibrium constant calculated according to the change of Gibbs free energy. The calculated results are listed in Table 5.7.9.

The CBC method for preparing FeV nitride is to inject high pressure (=105Pa) liquid nitrogen into a closed container and conduct nitridation reaction

The heat released causes FeV powder to form nitride. The degree of nitride formation decreases with the increase of temperature, so the CBC method does not need to reach a very high temperature. The necessary condition to reach this conclusion is that the gas permeability layer should be maintained in the automatic channel of the nitrogen front and the stoichiometric nitride composition should be obtained.

Table 5.7.9 Calculation results of starting temperature of nitrogen absorption during synthesis

(2) Production process and equipment

The principle of the new process for producing nitrogen-containing raw materials is based on the principle of self-diffusion high-temperature synthesis (CBC method) and the comprehensive equipment to realize it. The raw materials used for forming nitrogen-containing alloys by CBC method are mainly realized by combining or combining V, Cr, Ni, Mn and other metals that can generate nitride. They can be used to make structural steel, tool steel, stainless steel and other special purpose steel with new components and formulate corresponding production processes.

The process and equipment flow of producing nitrogen-containing materials by CBC method is as follows:

① Crusher: crushing ferrovanadium alloy to a certain size;

② Air flow crusher: continue to crush alloy;

③ Classifier and dust separator: select alloy powder with uniform particle size;

④ Storage and discharge hopper;

⑤ CBC reactor: conduct nitriding autothermal reaction to generate nitriding alloy powder;

⑥ Compression device: make nitrogen reach a certain pressure.

This technology includes the nitriding process. The entire initial material does not complete the nitrogen absorption at the same time, but carries out the nitriding process through the layering of self-diffusion combustion. The reason why the nitriding process is stratified in the combustion mode is that the initial raw material is specially treated from the chlorine atmosphere to increase the process pressure and temperature.

Nitriding is a process that does not use electricity. The process of nitrogen saturation is completed by the heat of exothermic reaction generated by nitrides.

Since there is no heating device for nitriding, the device is simple in structure and operation.

In production, neither the initial product nor the final product need to be pressed or extruded.

The high temperature process helps to melt some of the products and accelerate the densification of the materials. The product densification after nitrogen absorption directly occurs stratification without increasing the process time. By nitriding and densification in the stratified self-diffusion process, the material with uniform structure without nitrogen concentration gradient along the section can be obtained. The nitriding of initial products is a synchronous and instantaneous process. In the relatively small 0.2m3 capacity device, the nitriding speed is 0.5t/h, which can avoid the loss and pollution of raw materials, and one person can control and operate the nitriding device.

(3) Composition of nitriding alloy

Compared with similar products at home and abroad, the nitrogen-containing alloy prepared by the new CBC method has the following advantages: high density (6.2-7.0g/cm3), high nitrogen content (w (N)=10% - 11%) and low porosity (1% - 3%). Such high-strength alloying material can ensure a high nitrogen absorption rate in the steel and can stably produce the specified nitrogen concentration. The nitrogen absorption rate is 80% - 90%. The new nitriding alloy has special stability. The compressive strength of the new alloy is 10-100 times higher than that of known materials. Due to its high strength and high wear resistance, the cracking and dust generation of the new alloy during packaging, transportation and use can be completely avoided. In terms of environmental protection, the process can ensure the ecological environment.

With CBC nitriding, FeV with high nitrogen content and specified vanadium concentration can be obtained (the molar ratio of nitrogen to vanadium is 0.6-0.9).

In addition to the above three domestic and foreign representative production enterprises, there are also several other vanadium nitride production enterprises in China, such as Hunan Sanqi Metallurgical Materials Co., Ltd., which has achieved atmospheric pressure, stable, continuous and batch production with a supply capacity of more than 500 tons/month by adopting the solid nitriding continuous nitriding process with unique intellectual property rights; Sichuan Zhanxiang Special Alloy Technology Co., Ltd., which was completed and put into operation in early 2010, has adopted advanced production technology. Panzhihua High-tech Industrial Park built a vanadium nitride plant in 2009, using the patented technology of Kunming University of Technology.

The comparison of technical indicators of vanadium-nitrogen alloy products at home and abroad is shown in Table 5.7.10. Domestic representative product models include FeV45N10, FeV55N12, FeV68N14, etc.

Table 5.7.10 Comparison of technical indexes of vanadium-nitrogen alloy at home and abroad (%)

5 New production technology of vanadium nitride alloy

(1) Wu'an Weirong Materials Co., Ltd. has invented a simple production method of vanadium nitride. The process steps are as follows: ① mix V2O5 powder and graphite powder on a dry mixer at a weight ratio of 4:1; ② Add 4% polyvinyl alcohol aqueous solution to the above mixture powder according to the weight ratio of 100:15, and mix it in the wet mixer for 10 minutes; ③ Press the wet mixed powder into balls; ④ Wet bulb drying of mixed powder; ⑤ Load the dried mixed powder ball into the hopper car, into the furnace, and seal the furnace door; ⑥ Vacuum to -0.02MPa; ⑦ Feed nitrogen pressure to 0.04MPa; ⑧ Heat to 800 ℃ and conduct pre-reduction at this temperature for about 5 hours; ⑨ Then continue to heat up to 1350 ℃ for at least 6 hours of deep reduction and carbonization, and constantly fill nitrogen with purity of 99.99% or more in the process; ⑩ Heat up to 1600 ℃ and conduct nitriding sintering for 6 to 10 hours. The pressure in this process is controlled at 0.02Mpa. Power off and cool down to 150 ℃.

(2) Sichuan University has invented a preparation method of vanadium nitride alloy. It is to mix vanadium oxide, carbonaceous powder and density intensifier evenly, press them into the reaction furnace, inject nitrogen or ammonia into the reaction furnace as reaction and protective gas before holding at 650 ℃, and heat the reaction furnace to 1000~1250 ℃. The material will carbonize and nitride within this temperature range, and the reaction time is less than 3 hours, Then it is cooled to below 100 ℃ and discharged to finally obtain vanadium nitride alloy. The vanadium nitride alloy contains V 73 ～ 80%, N 12 ～ 20%, C 3 ～ 8%, O 0.5 ～ 2.0%, and its apparent density reaches 3000 ～ 4000kg/m3. The invention has the characteristics of low reaction temperature, short reaction time, simple process, low production cost, etc., and is more suitable for mass production in industry. The vanadium nitride alloy prepared by the invention has high nitrogen content, and is more suitable for steelmaking requirements in steel industry.

(3) Sichuan University has invented a preparation method of nano-vanadium nitride powder. The process steps are as follows: (1) Preparation of precursor, using V2O5 and oxalic acid as raw materials, the weight ratio of V2O5 and oxalic acid is 1 ∶ 1~1 ∶ 3, put the V2O5 and oxalic acid in the reaction vessel and add water, then stir at atmospheric pressure, 40 ℃~70 ℃, until the reduction reaction of V2O5 and oxalic acid is completed, after the reduction reaction is completed, Evaporating the obtained solution to dryness to obtain the precursor vanadium oxalate; (2) For the ammonolysis of precursor, put the obtained precursor vanadium oxyoxalate into the heating furnace, heat it to 600 ℃~750 ℃ in the flowing ammonia atmosphere for ammonolysis, turn off the power supply of the heating furnace after holding for 10 minutes~3 hours, maintain the ammonia atmosphere in the furnace, and take out the decomposition product after it is cooled to below 100 ℃ to obtain nanometer vanadium nitride powder.

(4) Sichuan Chuanwei Group Co., Ltd. and Northeast University jointly invented a method for producing vanadium-nitrogen alloy. The steps are as follows: a. Mix the vanadium-containing raw materials, additives, C-reducing agent and binder, and press them to obtain the molding materials; Among them, according to the weight ratio, the vanadium containing raw material is 60-80 parts of vanadium, the additive is 1-2 parts of iron, the C-reducing agent is 20-40 parts, and the binder is 0-0.4 parts; B. The molding materials are dried, and then react with nitriding gas at 1300~1500 ℃ for 1.5~5h under oxygen-free conditions, and then cooled to obtain vanadium-nitrogen alloy; The nitriding gas comprises at least one of nitrogen and ammonia.




-Document: Production Process and Equipment of Vanadium and Titanium Products, Beijing: Chemical Industry Press, author: Zou Jianxin, etc., January 2014

Physical Chemistry of Vanadium and Titanium, Beijing: Chemical Press, author: Zou Jianxin, 2016

(Sichuan Key Laboratory for Comprehensive Utilization of Vanadium and Titanium Resources [Panzhihua University], cnzoujx@sina.com ）

Sichuan Vanadium and Titanium Materials Engineering Technology Center