Preparation of vanadium nitride
Vanadium has been used in the iron and steel industry for nearly a hundred years, and has been used in the form of ferrovanadium. In the 1960s and 1970s, people began to study vanadium nitride. However, due to technical problems, the prepared vanadium nitride carbon has high oxygen content
(10-12%), low nitrogen content (6-10%), unable to meet the use requirements. Until the 20th century
In the late 1980s, the strategic minerals company of the United States publicly issued vanadium nitride with low carbon oxygen and high nitrogen content, which really commercialized the production of vanadium nitride.
Before 2000, only vameteo Minerals Corporation, a subsidiary of the US strategic minerals company in Brits, South Africa, was able to produce vanadium nitride on a large scale in an industrialized manner, using high-temperature vacuum carbon reduction to produce vanadium nitride alloys. In 1990, the strategic minerals company of the United States sold about 350t of vanadium nitride, which reached 1050t in 2000, and the output reached 3000 tons in 2003. Due to the shortage of products, the capacity was expanded to 4500t in 2004, which has increased 10 times in the past 10 years, especially in recent years. In 1995, Panzhihua Iron and Steel Co., Ltd. of China began to independently develop the V2O3 continuous nitriding process with pusher kiln method to produce vanadium nitride, and achieved success. At present, its production capacity has exceeded 2000t/a.
In the past two years (2007), the sales volume of vanadium nitride in China is about 1000-1500t, which is far from the actual demand for the production of grade III building reinforcement. In 2004, China produced 45million tons of building reinforcement. If all vanadium nitride is used, 22500t vanadium nitride is required based on the minimum addition of 0.5kg vanadium nitride /t steel. Due to insufficient supply, most of them use ferrovanadium to realize alloying. The Ministry of construction requires that the use of grade III building steel bars in the construction industry should reach 80% by the end of the tenth five year plan. If grade III building steel with vanadium nitride is used
About 10000t vanadium nitride is required for 50% of the steel, which means that the output of vanadium nitride at home and abroad is seriously insufficient.
Vanadium nitride, also known as vanadium nitrogen alloy, is a new type of alloy additive, which can replace ferrovanadium in the production of microalloyed steel. It has two crystal structures: one is v3n, hexagonal crystal structure, with extremely high hardness, the microhardness is about 1900hv, and the melting point can not be measured; Second, VN, face centered cubic crystal structure, with a microhardness of about 1520hv and a melting point of 2360 degrees. They all have high wear resistance, and vanadium steel can be greatly improved after nitriding treatment
The strength, toughness, ductility, thermal fatigue resistance and other comprehensive mechanical properties of high steel make the steel have good weldability. At the same strength, the addition of vanadium nitride can save 20-40% of vanadium, thus reducing the cost. Vanadium nitrogen alloy can be used in structural steel, tool steel, pipe steel, reinforcement and cast iron. The application of V-N alloy in high strength low alloy steel can effectively microalloy V and N at the same time, promote the precipitation of carbon, V and N compounds in the steel, and play a more effective role in precipitation strengthening and grain refinement.
The main advantages of VN alloys are:
(1) V-N alloy has more effective strengthening and grain refining effect than FEV
(2) The addition of vanadium can be saved by using vanadium nitrogen alloy. Compared with ferrovanadium, vanadium nitrogen alloy can save 20-40% vanadium under the same strength
(3) The vanadium nitrogen alloy is used to stabilize the vanadium and nitrogen yield and reduce the performance fluctuation of the steel. (4) It is very convenient to use vanadium nitrogen alloy with less loss. Adopt high-strength moisture-proof packaging,
Can be directly put into the furnace
With the deepening of research on vanadium nitride at home and abroad, people have fully realized the beneficial role of vanadium nitride in the iron and steel industry. According to the research findings of modern materials science,
When some steels contain a certain amount of alloying elements and a certain amount of nitrogen, the properties of steels can be greatly improved after heat treatment. For example, nitrogen can stabilize austenitic stainless steel and improve its corrosion resistance; If the steel containing V or v+c contains a certain amount of nitrogen, nitride precipitation can be produced after heat treatment, which can promote the hardening of the steel and improve the strength of the steel. The usual methods for increasing nitrogen in steel are: ① adding nitrogen rich ferromanganese ② adding calcium cyanamide ③ blowing nitrogen. However, the shortcomings of the above methods are obvious. Method ① is expensive, method ② has low and unstable yield, and method ③ requires special devices during nitrogen blowing. Nitrogen rich vanadium nitride can provide a convenient way to add vanadium and nitrogen at the same time. The physical metallurgical principle of vanadium nitrogen microalloying has the following key points: first, after nitrogen addition in steel, vanadium in the original solid solution state will be transformed into vanadium in the precipitated state, giving full play to the precipitation strengthening effect of vanadium; second, nitrogen also has an obvious role in grain refinement in steel. Thirdly, V-N microalloying gives full play to the role of refinement and precipitation strengthening by optimizing vanadium precipitation and refining ferrite grains, greatly improves the toughness coordination of steel, and fully reflects the advantages of Microalloying in technology and economy. Fourth, vanadium nitrogen microalloying does not need to add other valuable alloy elements. High strength steel with yield strength of 550 to 600MPa can be obtained under hot rolling conditions. Therefore, vanadium nitride is widely used in iron and steel industry.
In the production of microalloyed steel, vanadium nitride alloy has the characteristics of saving vanadium addition, reducing cost, stable vanadium and nitrogen yield, reducing steel performance fluctuation, more effective precipitation strengthening and grain refinement than FEV, and saving 20-40% vanadium. Therefore, as an economic and effective additive for high-strength low-alloy steel, vanadium nitride has positive application value.
Market prospect of vanadium nitride
With the rapid development of China's economy, the product structure adjustment of the iron and steel industry is the primary task at present. The use of vanadium nitrogen microalloying can promote the upgrading of iron and steel products under the most economic conditions. The development and application of high light low alloy steel (HSLA) in China is far from reaching the development scale of developed countries, but it has made some progress in recent years. Among them, the steel consumed by the construction industry accounts for 30-50% of the total steel consumption. If the grade III steel bar of 400MPa is used to replace the grade II steel bar of 335mpa, the strength of concrete structures can be effectively improved, which is important for the safety of high-rise buildings and large bridges, In particular, earthquake resistance is very necessary.
At present, 95% of the annual consumption of building steel bars in China are grade II steel bars. The main drawback of grade II steel bars is the low strength. Industrial developed countries, such as the United States, Britain, Germany and other countries, have eliminated the grade II reinforcement in the national standards for building steel, and all use the building reinforcement above grade III. In order to connect with the world as soon as possible and save steel, China is accelerating the upgrading of construction steel, vigorously promoting the application of 400MPa grade III steel bars and making them the leading steel bars. Grade III steel bar uses the precipitation strengthening effect of vanadium nitride in vanadium to improve the strength of steel and meet the performance requirements of grade III steel bar. However, the cost of steel is increased due to the addition of vanadium. In order to further reduce the cost of grade steel bars, it is urgent to develop economical grade steel bars for construction. And using vanadium nitride to produce 400MPa steel bar
(0.5-0.7kgvn is added per ton), 20-40% vanadium can be saved under the same strength conditions. At the same time, 400MPa steel bars meeting the standard can also be produced for rolling mills with poor controlled rolling and cooling capacity. Therefore, the application of vanadium nitride can reduce the production cost of 400MPa steel bar and provide reliable technical guarantee for accelerating its popularization and application.
At present, V-N microalloying technology is widely used in high-strength welded steel bars and non quenched and tempered steel
Type steel products have been mature application in the development. Through a lot of in-depth research in recent years, a series of thin slab continuous casting and rolling high strength steel products with yield strength have been successfully developed by using vanadium nitrogen microalloying alloy design. At the same time, the third generation tm-cp controlled rolling and cooling technology with VN induced intragranular ferrite as the core has strongly promoted the successful application of V-N microalloying technology in the development of high-strength thick plate and thick wall H-beam products. A typical example is the development and application of new grade III reinforcement: through the use of vanadium nitrogen microalloying technology, a low-cost hbr400 grade I seismic reinforcement has been developed. The product quality is excellent, and the alloying cost has been reduced by 40%. At present, it has been successfully applied in Shougang, Maanshan Iron and steel, Tangshan Iron and steel and other enterprises, with remarkable economic benefits.
It is difficult to research and develop vanadium nitrogen alloy, which is the top cutting-edge technology in the metallurgical industry. At present, only vametco and Pangang can produce in the world. Through scientific research, Panzhihua Iron and Steel Co., Ltd. pioneered a more advanced "non vacuum continuous production" technology than foreign countries, filling the gap in China's vanadium nitrogen alloy production field.
In 1998, the vanadium company of the United States came to China for the first time to promote vanadium nitride alloy. During the investigation in Panzhihua Iron and Steel Co., Ltd., it was emphasized that "over the past 20 years, Germany, Russia and Japan have studied vanadium nitride alloy and claimed to have developed their own vanadium nitride alloy production technology, but over the past 20 years, they have not been able to mass produce vanadium nitride alloy. There is a lot of knowledge in vanadium nitride alloy production, and only we can truly commercialize production." At the same time, Panzhihua Iron and Steel Co., Ltd. resolutely rejected and challenged "I will buy yours if you develop it". After years of research, in September, 1996, Panzhihua Iron and Steel Co., Ltd. initiated the project of "Research on Preparation of vanadium carbide and vanadium nitride with V2O3" and passed the review of national scientific and technological research project in the ninth five year plan. After several years of arduous exploration, it finally achieved the success of vanadium nitrogen alloy industrialization technology. This technology of Pangang
The success of the company not only breaks through the global exclusive monopoly of the United States, but also has more advanced technology, reaching the international leading level, forming a patented technology with independent intellectual property rights. The vanadium nitrogen alloy industrialization technology of Panzhihua Iron and Steel Co., Ltd. comprehensively exceeds the similar technologies of the American vametco company, which is mainly reflected in the following aspects: first, Panzhihua Iron and Steel Co., Ltd. can produce in a non vacuum environment rather than the high vacuum environment required by vametco company, with simple equipment, lower requirements, strong stability and less equipment investment; Second, Pangang process can produce continuously, reduce energy consumption and significantly improve labor productivity; Third, the carbonization and nitridation reactions are carried out simultaneously in the process of Panzhihua Iron and Steel Co., Ltd., with simple process flow and short operation cycle.
From 2002 to 2004, Pangang rapidly reached the production capacity of 2000 tons of vanadium nitrogen alloy per year in three years. In June2002, the 300t/a industrial trial pusher kiln was successfully built and put into operation at Pangang; In 2003, due to the breakthrough of key technologies of 300t/a industrial trial pusher kiln, Pangang decided to officially realize industrialized production. The industrialization project was supported by the state and was listed as a national high-tech industrialization project; In August, 2003, the second and third 300t/a industrialization equipment of Panzhihua Iron and steel group were successively completed and put into operation, expanding the production capacity to 1000t/a; In June and July of 2004, three new 300t/a industrialization equipment were put into operation in Panzhihua Iron and Steel Co., Ltd., making the total production capacity of vanadium nitrogen alloy of Panzhihua Iron and Steel Co., Ltd. reach the scale of 2000t/a.
one Preparation of vanadium nitride
The research and preparation of vanadium nitride are currently in the forefront in the United States, followed by Germany, Japan, Russia, etc. The research of vanadium nitride in China started late, but it has developed rapidly in recent years, and its output has ranked first in the world. At present, the domestic manufacturers that have industrialized the production of vanadium nitride include Panzhihua Iron and steel (pusher kiln method), Chenggang (Tangshan Iron and steel, microwave method), Jilin Ferroalloy Plant (vacuum carbon reduction method), among which Panzhihua Iron and Steel Group is in the forefront of similar enterprises in China, and took the lead in formulating the world's first national standard for vanadium nitrogen alloy (gb/t20567-2006) in February 2007.
Vanadium nitride is prepared by using vanadium oxides V2O3 and V2O5 and vanadium compounds ammonium metavanadate (NH4VO3) and ammonium polyvanadate as raw materials, using carbon, hydrogen, ammonia, Co, etc. as reducing agents, reducing under high temperature or vacuum, and then nitriding with nitrogen or ammonia. The methods for preparing vanadium nitride can be divided into two categories: high temperature vacuum method and high temperature non vacuum method according to the different preparation systems and conditions. In each category, the methods for preparing vanadium nitride with C and V2O3, C and V2O5, and C and NH4 VO3 as solid reactants can be divided according to the different raw materials used. The present situation and development trend of these methods are briefly introduced and commented.
one point one High temperature vacuum method
High temperature vacuum method refers to that vanadium oxide is reduced to vanadium carbide by carbonaceous reductant under high temperature (1373 ~ 1873K) and vacuum conditions, and then in the furnace at atmospheric pressure or slightly lower than atmospheric pressure, N2 or NH3 is introduced under reduction or protective atmosphere, nitriding, and finally the vanadium nitride product is produced under protective atmosphere. The main reactions are as follows:
V2O3+5C = 2VC+3CO(g) (1)
V+1/2N2(g) = VN (2)
It can be seen that reducing the partial pressure of CO is beneficial to the reduction reaction, and increasing the partial pressure of nitrogen is beneficial to the formation of vanadium nitride. Therefore, the so-called high temperature vacuum method is only for the reaction
In terms of the original process, i.e. reducing the pressure at the initial stage of the reaction to promote the reduction reaction, this is the same as the principle of vacuum method in vanadium carbide production.
1.1.1 Preparation of vanadium nitride by high temperature vacuum method with V2O3 as solid reactant
U.S. patent us3334992 introduces a method for preparing vanadium nitride by vacuum method. After mixing 181 kg V2O3, 62 kg carbon powder, 41 kg resin glue and 3 kg iron powder, the
Press forming under the pressure of 21.1 MPa, and the sample size is 51 mm × 51 mm × 38 mm, put the sample into the furnace with a size of 2800 mm × 1680 mm × In a 686 mm vacuum furnace, vacuumize to a pressure of 26 PA. When the temperature rises to 1658 K, the pressure rises to 2666 Pa. after holding for 60H at this temperature, the pressure drops to 22.7 PA to obtain vanadium carbide. Reduce the temperature to 1373 K, connect N2, keep the partial pressure of N2 at pn2=700 ~ 1000Pa, conduct constant temperature nitriding for 2 h, then reduce the furnace temperature to 1273K, stop heating the electric furnace after nitriding for 6 h, cool it to room temperature in N2 atmosphere and discharge it. In this process, 106.6 kg of nitrogen is used, and the recovery rate of nitrogen is about 75%. A (w%) 914 kg vanadium nitride containing 78.7%v, 10.5%c, 7.3%n was obtained.
R. F.merkert et al. Reacted V2O3 and C by vacuum method:
V2O3+3C=2V+3CO(g) (3)
Mix according to the stoichiometric number of formula (3), add water and binder, press and dry them, and put them into a general vacuum furnace for reduction under the vacuum of 1373 ~ 1773 K and 13 ~ 40 Pa. when the vacuum degree remains stable at 13 ~ 40Pa, it can be considered that the reduction process has reached equilibrium. Then, N2 is introduced into the furnace, and nitridation treatment is carried out under the condition of pn2=101325 PA in the furnace to accelerate the nitridation process, The method of repeatedly treating pN2 in the furnace from 101325 PA to vacuum 13 ~ 40 PA can be adopted. The times of vacuumizing and nitriding depend on the operating temperature and pressure, as well as the amount of mixture added into the furnace and the