Preparation method of aircraft-grade low-oxygen low-nitrogen vanadium-aluminum alloy

Abstract

The invention provides a preparation method of an aircraft-grade low-oxygen low-nitrogen vanadium-aluminum alloy, which comprises the following steps: (1) mixing a vanadium pentoxide raw material, an aluminum raw material, a slag former and a coolant, and carrying out a vacuum aluminothermic reaction; (2) after the vacuum aluminothermic reaction starts, sequentially blowing vanadium pentoxide powder and aluminum powder into the molten pool by taking inert gas as a carrier, and carrying out primary cooling to obtain a vanadium-aluminum primary alloy; and (3) crushing the vanadium-aluminum primary alloy, carrying out vacuum medium-frequency induction melting, and carrying out secondary cooling to obtain the aviation-grade low-oxygen low-nitrogen vanadium-aluminum alloy. The aircraft-grade low-oxygen low-nitrogen vanadium-aluminum alloy prepared through the method is good in uniformity and low in gas phase impurity content, the content of impurity oxygen and the content of impurity nitrogen can reach 0.015% or below and 0.008% or below respectively, and the product can meet the use standard of aircraft-grade titanium alloy raw materials at a time.

Description

Technical Field

[0001] The invention relates to the technical field of alloy smelting, and in particular to a method for preparing an aviation-grade low-oxygen and low-nitrogen vanadium aluminum alloy. Background Art

[0002] With the rapid development of aviation, military industry and other fields, the demand for high-strength and high-toughness aviation-grade titanium alloys has increased sharply. As an important intermediate alloy for titanium alloys, the quality and supply requirements of vanadium aluminum alloys are also particularly urgent.

[0003] At present, vanadium aluminum alloy is basically prepared based on the aluminothermic reduction method, that is, vanadium pentoxide and aluminum are reduced at high temperature to form vanadium aluminum alloy. However, the traditional aluminothermic reduction reaction is carried out in the atmosphere, and the oxygen and nitrogen content in the alloy is relatively high. The oxygen and nitrogen elements in the vanadium aluminum alloy are difficult to remove in the subsequent production of titanium alloys, so the vanadium aluminum alloy products prepared by conventional methods cannot meet the requirements for the use of aviation-grade titanium alloys.

[0004] There are limited reports on the preparation methods of aviation-grade vanadium aluminum alloys in the prior art, and all of them have obvious advantages and disadvantages. For example, CN116770072A discloses a method for preparing an aerospace-grade vanadium aluminum alloy with low oxygen content, in which V55Al alloy is covered with V65Al during the aluminothermic reaction to isolate gas impurities from entering during the cooling process, thereby preparing a method for preparing a low-oxygen vanadium aluminum alloy. The preparation method is simple and easy to operate, but the low-oxygen vanadium aluminum alloy is obtained at the expense of wasting the surface V65Al alloy, and the preparation cost is relatively high. CN117604256A discloses a method for controlling oxygen and nitrogen in vanadium aluminum alloys, in which a layer of aluminum hydroxide is covered on the surface of a vanadium aluminum alloy reactant prepared by a conventional aluminothermic reduction method to isolate impurity gases from entering during the cooling process, thereby preparing a method for preparing a low-oxygen and nitrogen vanadium aluminum alloy. However, the flame retardant aluminum hydroxide used in this method decomposes at around 200°C, and the decomposition product contains H2O, which may increase oxygen and explode. CN117660790A discloses a metallurgical furnace and a method for preparing an aerospace-grade vanadium-aluminum alloy with low oxygen content, but the device is too complex in structure and has high single production cost, which is not suitable for industrial-scale production. CN118064751A discloses a method for preparing a vanadium-aluminum alloy by vacuum treatment aluminothermic reduction, and CN118516574A discloses a method for preparing a molybdenum-vanadium-aluminum alloy with low gas impurities. Both are prepared based on vacuum aluminothermic method, but the alloy prepared by this method has the disadvantages of too high impurity content and uneven composition.

[0005] Therefore, developing a vanadium-aluminum alloy with mature preparation equipment, low alloy impurity content and high uniformity to meet the demand for intermediate alloys for high-performance titanium alloys in the aerospace field is an urgent problem to be solved in the intermediate alloy industry. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a method for preparing an aviation-grade low-oxygen and low-nitrogen vanadium aluminum alloy, in which the raw materials are subjected to vacuum thermite reaction, powder blowing refining and vacuum medium-frequency induction melting in sequence to obtain an aviation-grade low-oxygen and low-nitrogen vanadium aluminum alloy with low oxygen and nitrogen contents and good uniformity, thereby solving the problems of complex preparation equipment, high preparation cost and difficulty in balancing impurity content and uniformity in the current method for preparing low-oxygen and low-nitrogen vanadium aluminum alloy.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for preparing an aviation-grade low-oxygen and low-nitrogen vanadium aluminum alloy, the preparation method comprising the following steps:

[0009] (1) mixing a vanadium pentoxide raw material, an aluminum raw material, a slag-making agent and a coolant to perform a vacuum thermite reaction;

[0010] (2) after the vacuum aluminothermic reaction begins, vanadium pentoxide powder and aluminum powder are blown into the molten pool in sequence using an inert gas as a carrier, and a vanadium-aluminum primary alloy is obtained after a first cooling process;

[0011] (3) crushing the primary vanadium-aluminum alloy, performing vacuum medium-frequency induction melting, and obtaining the aviation-grade low-oxygen and low-nitrogen vanadium-aluminum alloy after a second cooling;

[0012] The aviation-grade low-oxygen and low-nitrogen vanadium aluminum alloy has an oxygen content of less than 0.015% and a nitrogen content of less than 0.008%.

[0013] The preparation method of the aviation-grade low-oxygen and low-nitrogen vanadium aluminum alloy of the present invention comprises vacuum thermite reaction, powder blowing refining reaction and induction refining reaction performed in sequence.

[0014] The preparation method of the present invention includes three reactions, which are used to remove impurities and reduce oxygen, and control the oxygen content in the vanadium-aluminum primary alloy to be below 0.02%. First, the preparation method mixes vanadium pentoxide raw material, aluminum raw material, slag-making agent and coolant, and performs vacuum aluminum thermal reaction, i.e., primary reaction. At this time, the oxygen content in the alloy liquid is relatively high, and the oxygen in the alloy liquid exists in the form of low-valent oxides and slag particles (i.e., Al2O3). Secondly, the blown-in vanadium pentoxide powder reacts with aluminum in the alloy liquid for a secondary reaction to release high heat, so that the high-temperature maintenance time of the alloy liquid is prolonged, the floating time of the slag particles is prolonged, and the floating efficiency of the slag formed by the primary reaction and the secondary reaction is improved. Thirdly, the blown-in aluminum powder reacts with the low-valent oxides for a third time, i.e., oxidation-reduction reaction, and the low-valent oxides are reduced to metallic vanadium and aluminum oxide particles. At the same time, the heat released by the third reaction is used to realize the re-floating and discharge of the generated aluminum oxide particles. The induction refining reaction of the present invention is embodied in two aspects: impurity removal and improving alloy uniformity. In terms of impurity removal: the partial pressure characteristics are used in the process of vacuum medium frequency induction melting to further reduce the oxygen and nitrogen content of the alloy, so that the quality of the alloy is continuously improved. The partial pressure of free gas impurities (mainly oxygen and nitrogen) in the induction-melted alloy liquid is reduced under a high vacuum environment, which promotes the removal of the impurities. At the same time, due to the difference in density between the slag in the alloy liquid and the alloy liquid, under the action of the thermal eddy current generated by electromagnetic induction, the two are separated due to different centrifugal forces, and the slag adheres to the crucible wall to achieve the separation of the slag. Under the combined influence, the oxygen and nitrogen impurity content of the alloy is reduced. In terms of improving the uniformity of the alloy: since the vanadium-aluminum primary alloy is separated by self-weight and cooled at room temperature, and the difference between high and low density elements in the alloy system is large, the degree of element segregation in the vanadium-aluminum primary alloy is large. In the process of vacuum medium frequency induction melting, the alloy liquid continuously realizes self-stirring of the molten pool under the action of electromagnetic eddy currents, and is cooled at high speed with the water-cooled copper ingot mold, and the uniformity of the alloy is significantly improved.

[0015] The vanadium aluminum alloy prepared by the method of the present invention has good uniformity and low gas phase impurity content, wherein the impurity oxygen and nitrogen contents can reach below 0.015% and 0.008% respectively, and the product can meet the use standard of aviation-grade titanium alloy raw materials at one time.

[0016] The oxygen content of the aviation-grade low-oxygen and low-nitrogen vanadium aluminum alloy of the present invention is less than 0.015%, for example, it can be 0.015%, 0.014%, 0.012%, 0.01%, 0.009%, 0.005% or 0.003%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0017] The nitrogen content is below 0.008%, for example, it can be 0.008%, 0.007%, 0.005%, 0.003%, 0.002% or 0.001%, but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0018] Preferably, the purity of the vanadium pentoxide raw material in step (1) is not less than 98%, for example, it can be 98%, 98.3%, 98.5%, 98.8%, 99%, 99.3% or 99.5%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0019] The weight proportion of particles below 100 μm is not less than 20%, for example, it can be 20%, 20.5%, 21%, 22%, 23%, 25% or 30%, etc., but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] The present invention preferably adopts the method that the weight proportion of the vanadium pentoxide raw material with a particle size of less than 100 μm is not less than 20%, because if the large-particle vanadium pentoxide accounts for too much, on the one hand, it will reduce the probability of triggering the vacuum reduction reaction; on the other hand, there are too many high-heat reaction points during the reaction, resulting in heat imbalance at the same interface in the molten pool, causing serious splashing in the later stage of the reaction, resulting in alloy loss and reducing the alloy yield.

[0021] Preferably, the purity of the aluminum raw material is not less than 99.7%, for example, it can be 99.7%, 99.75%, 99.78%, 99.8%, 99.85% or 99.9%, etc., but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable;

[0022] The particle size is not greater than 1 mm, for example, it can be 1 mm, 0.9 mm, 0.8 mm, 0.7 mm, 0.5 mm or 0.3 mm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] The present invention preferably has a particle size of no more than 1 mm, in order to increase the contact area between the oxidant and the reductant as much as possible, ensure the full progress of the reaction, maximize the full reduction of the oxide, and avoid the waste of the rare metal vanadium.

[0024] Preferably, the slag former comprises calcium fluoride and / or calcium oxide.

[0025] Preferably, the coolant comprises any one of V40Al, V55Al, V65Al, V70Al or V80Al, or a combination of at least two of them, wherein typical but non-limiting combinations include a combination of V40Al and V55Al, a combination of V65Al and V70Al, or a combination of V80Al and V40Al.

[0026] The vanadium pentoxide raw material, aluminum raw material, slag-forming agent and coolant of the present invention are dried before mixing. During the drying process, the oxides and the reduced products are placed separately. After drying, they are taken out and aired to below 60° C. and then loaded into a V-type mixer for mixing.

[0027] Preferably, the mass content of V in the alloy composition after the vacuum thermite reaction in step (1) is 50% to 60%, for example, it can be 50%, 52%, 55%, 57%, 58%, 59% or 60%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0028] Al is the balance, and the mass content of impurity elements is Fe≤0.15%, for example, it can be 0.15%, 0.14%, 0.13%, 0.1%, 0.09% or 0.05%, etc., but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable; Si≤0.15%, for example, it can be 0.15%, 0.14%, 0.13%, 0.1%, 0.09% or 0.05%, etc., but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable;

[0029] The mass content of other single impurity elements is ≤ 0.1%, for example, it can be 0.1%, 0.09%, 0.08%, 0.07%, 0.05%, 0.03% or 0.01%, etc., but it is not limited to the listed values. Other values ​​not listed in the numerical range are also applicable;

[0030] The total mass content of other impurities is ≤0.3%, for example, it can be 0.3%, 0.25%, 0.22%, 0.2%, 0.18%, 0.15% or 0.1%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] Preferably, the vacuum thermite reaction in step (1) is carried out in a vacuum thermite furnace.

[0032] Preferably, before ignition of the vacuum thermite reaction, a vacuum pump is turned on to evacuate the vacuum to 15-50Pa, for example, 15Pa, 20Pa, 25Pa, 30Pa, 40Pa or 50Pa, etc., but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] The present invention preferably turns on the vacuum pump to evacuate to 15-50Pa before ignition of the vacuum thermite reaction, because one of the important sources of oxygen in the alloy prepared by the thermite reaction is the introduction of the reaction atmosphere. Therefore, the environmental vacuum before the vacuum thermite reaction needs to be strictly controlled. If the vacuum before the reaction is too low, the content of gas impurities (mainly oxygen and nitrogen) in the reaction environment is high, which will cause the content of gas impurities in the alloy to exceed the standard; if the vacuum before the reaction is too high, the combustion-supporting gas generated during ignition will diffuse too quickly, making the ignition process difficult and the reaction cannot be triggered.

[0034] Preferably, the blowing of vanadium pentoxide powder in step (2) is carried out within 15 to 25 seconds after the start of the vacuum thermite reaction, for example, it can be 15 seconds, 18 seconds, 20 seconds, 21 seconds, 23 seconds or 25 seconds, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] Preferably, after the vanadium pentoxide powder is blown in, the aluminum powder is blown in after standing for 10 to 15 seconds, for example, 10 seconds, 12 seconds, 12.5 seconds, 13 seconds, 14 seconds or 15 seconds, etc., but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0036] The present invention fully considers that the aluminothermic reaction under vacuum is faster than the conventional out-of-furnace method. Under vacuum, the time from the start of the reaction to the complete end of the reaction of the charge is about 10 to 15 seconds. The time for blowing in vanadium pentoxide powder is controlled within 15 to 25 seconds after the start of the vacuum aluminothermic reaction. The purpose is to use the secondary reaction of vanadium pentoxide powder and aluminum in the alloy liquid to accelerate the discharge of the remaining slag with weak buoyancy after most of the slag in the alloy liquid has floated up under the heat of the primary reaction itself, so as to play a reinforcing and speeding role. The purpose of standing for 10 to 15 seconds after blowing in vanadium pentoxide powder is to leave enough time for the slag to float up due to the heat released by the secondary reaction. When the slag discharge power caused by the heat released by the secondary reaction becomes weak, aluminum powder is blown in again. The heat released by the tertiary reaction between aluminum powder and residual low-valent oxides provides power reinforcement for the slag to float up again.

[0037] Preferably, the purity of the vanadium pentoxide powder in step (2) is not less than 99.5%, for example, it can be 99.5%, 99.6%, 99.7%, 99.8%, 99.85% or 99.9%, etc., but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0038] The particle size is not greater than 50 μm, for example, it can be 50%, 49%, 45%, 40%, 38%, 35% or 30%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] Preferably, the purity of the aluminum powder is not less than 99.9%, for example, it can be 99.9%, 99.91%, 99.93%, 99.94%, 99.95% or 99.98%, etc., but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable;

[0040] The particle size is below 150 μm, for example, it can be 150 μm, 148 μm, 145 μm, 140 μm, 135 μm or 130 μm, etc., but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] Preferably, the mass flow rate of the vanadium pentoxide powder is 15.8-25.8 kg / min, for example, 15.8 kg / min, 16 kg / min, 17 kg / min, 20 kg / min, 22 kg / min or 25.8 kg / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] Preferably, the mass flow rate of the aluminum powder is 3.0 to 8.0 kg / min, for example, 3.0 kg / min, 3.5 kg / min, 4 kg / min, 5 kg / min, 7 kg / min or 8.0 kg / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] The present invention preferably has a mass flow rate of 15.8-25.8 kg / min for the vanadium pentoxide powder and a mass flow rate of 3.0-8.0 kg / min for the aluminum powder. If the mass flow rate is too fast, the secondary and tertiary reaction times are too short, the slag floating time is not fully extended, and the slag floating effect is poor. If a large amount of reactants are blown in quickly, the alloy liquid reacts violently in a short time. Under the action of thermal convection, the slag in the floating process is re-involved in the alloy liquid, which has the opposite effect. If the mass flow rate is too slow, the heat released by the secondary and tertiary reactions is lower than the heat dissipation rate of the molten pool, the alloy tends to solidify gradually, and the slag is not completely separated, which does not have the effect of reducing oxygen.

[0044] Preferably, different paths are used for blowing in vanadium pentoxide powder and aluminum powder. This is because some vanadium pentoxide powder will inevitably adhere to the inner wall of the pipeline during the blowing of vanadium pentoxide powder. If the pipeline is used to continue blowing aluminum powder in the next step, the aluminum powder and vanadium pentoxide powder will react inside the pipeline under the high temperature environment at that time. The heat released by the reaction will damage the powder blowing channel on the one hand, and will also make the powder blowing refining effect worse on the other hand.

[0045] Preferably, the dosage of the vanadium pentoxide powder in step (2) is to increase the grade of V in the alloy liquid to 75.0% to 85.0%, for example, it can be 75.0%, 76%, 78%, 80%, 82%, 84% or 85.0%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0046] Preferably, the dosage of the aluminum powder is to reduce the V grade in the alloy liquid to 60.0% to 70.0%, for example, it can be 60.0%, 63%, 65%, 67%, 69% or 70.0%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] Preferably, the inert gas in step (2) comprises any one of helium, neon, argon or krypton, or a combination of at least two of them, wherein typical but non-limiting combinations include a combination of helium and neon, a combination of argon and krypton, or a combination of helium and argon. Considering the convenience and economy, argon is preferred.

[0048] Preferably, the vacuum degree during the first cooling process is not higher than 100Pa, for example, it can be 100Pa, 98Pa, 95Pa, 90Pa, 85Pa or 80Pa, etc., but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable;

[0049] Preferably, the first cooling time is not less than 8 hours, for example, it can be 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours or 12 hours, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0050] Preferably, the first cooling temperature is 20-30°C, for example, 20°C, 22°C, 25°C, 27°C, 29°C or 30°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0051] Preferably, in step (3), the vanadium-aluminum primary alloy is crushed to a particle size of 5 to 50 mm, for example, 5 mm, 10 mm, 15 mm, 20 mm, 30 mm or 50 mm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0052] The present invention preferably crushes the primary vanadium-aluminum alloy to a particle size of 5 to 50 mm, and during the crushing process, the same alloy block is crushed by a jaw crusher no more than 5 times to prevent the alloy from being oxygenated during the processing and crushing process.

[0053] Preferably, the vacuum medium frequency induction melting is carried out in a vacuum medium frequency induction melting furnace.

[0054] Preferably, argon is filled during the vacuum medium frequency induction melting process, and the argon filling time is 4 hours from the completion of vacuum evacuation of the vacuum medium frequency induction melting furnace to the start of cooling, so as to prevent nitrogen addition to the alloy during the vacuum medium frequency induction melting process.

[0055] Preferably, the vacuum degree of the vacuum medium frequency induction melting is below 20Pa, for example, it can be 20Pa, 19Pa, 17Pa, 15Pa, 10Pa or 8Pa, etc., but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0056] Preferably, the temperature of the vacuum medium frequency induction melting is 1700-1880°C, for example, it can be 1700°C, 1730°C, 1750°C, 1770°C, 1800°C or 1880°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0057] The frequency of the vacuum medium frequency induction melting of the present invention is between high frequency (higher than 20KHz) and low frequency (lower than 50Hz).

[0058] Preferably, the second cooling is performed using a water-cooled copper ingot mold.

[0059] As a preferred technical solution of the present invention, the preparation method comprises the following steps:

[0060] (1) mixing vanadium pentoxide raw material, aluminum raw material, slag-making agent and coolant, and performing vacuum aluminothermic reaction in a vacuum aluminothermic furnace; before igniting the vacuum aluminothermic reaction, turning on a vacuum pump to evacuate to 15-50 Pa;

[0061] The purity of the vanadium pentoxide raw material is not less than 98%, and the weight proportion of particles less than 100 μm is not less than 20%;

[0062] The purity of the aluminum raw material is not less than 99.7% and the particle size is not greater than 1 mm;

[0063] The slag-forming agent includes calcium fluoride and / or calcium oxide;

[0064] The coolant includes any one of V40Al, V55Al, V65Al, V70Al or V80Al or a combination of at least two thereof;

[0065] The mass content of V in the alloy composition after the vacuum aluminothermic reaction is 50% to 60%, Al is the balance, the mass content of impurity elements is Fe≤0.15%, Si≤0.15%, the mass content of other single impurity elements is ≤0.1%, and the total mass content of other impurities is ≤0.3%;

[0066] (2) 15 to 25 seconds after the vacuum aluminothermic reaction begins, vanadium pentoxide powder is blown into the molten pool using an inert gas as a carrier, and after the vanadium pentoxide powder is blown into the molten pool, the vanadium pentoxide powder is allowed to stand for 10 to 15 seconds, and then aluminum powder is blown into the molten pool to obtain a vanadium-aluminum primary alloy after a first cooling process;

[0067] The purity of the vanadium pentoxide powder is not less than 99.5%, and the particle size is not greater than 50 μm; the purity of the aluminum powder is not less than 99.9%, and the particle size is less than 150 μm; the mass flow rate of the vanadium pentoxide powder is 15.8-25.8 kg / min; the mass flow rate of the aluminum powder is 3.0-8.0 kg / min; the blowing of the vanadium pentoxide powder and the blowing of the aluminum powder use different paths; the dosage of the vanadium pentoxide powder is to increase the grade of V in the alloy liquid to 75.0%-85.0%; the dosage of the aluminum powder is to reduce the grade of V in the alloy liquid to 60.0%-70.0%;

[0068] The inert gas includes any one of helium, neon, argon or krypton, or a combination of at least two of them;

[0069] During the cooling process, the vacuum degree is not higher than 100 Pa, the time is not less than 8 hours, and the temperature is 20-30°C;

[0070] (3) crushing the vanadium-aluminum primary alloy to a particle size of 5 to 50 mm, performing vacuum medium-frequency induction melting in a vacuum medium-frequency induction melting furnace at a vacuum degree of less than 20 Pa and a temperature of 1700 to 1880° C., and cooling the alloy in a water-cooled copper ingot mold to obtain the aviation-grade low-oxygen and low-nitrogen vanadium-aluminum alloy;

[0071] The aviation-grade low-oxygen and low-nitrogen vanadium aluminum alloy has an oxygen content of less than 0.015% and a nitrogen content of less than 0.008%;

[0072] Argon is filled during the vacuum medium frequency induction melting process, and the argon filling time is 4 hours from the completion of vacuum evacuation of the vacuum medium frequency induction melting furnace to the start of cooling.

[0073] Compared with the prior art, the present invention has at least the following beneficial effects:

[0074] The preparation method of an aviation-grade low-oxygen and low-nitrogen vanadium aluminum alloy provided by the present invention is simple to operate, and the preparation device is mature. The prepared vanadium aluminum alloy has good internal microscopic quality, high uniformity, and low impurity content, wherein the O content is less than 0.015%, and the N content is less than 0.008%. The product indicators meet the raw material standards for titanium alloys for aerospace use at one time. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 This is a graph showing changes in the contents of vanadium and oxygen during the preparation of the vanadium-aluminum primary alloy in Example 1 of the present invention.

[0076] Figure 2 It is a schematic diagram of the uniformity sampling sites of the vanadium aluminum alloy prepared in Example 1 of the present invention and Comparative Example 3.

[0077] Figure 3 This is a low-magnification microstructure metallographic photograph of the vanadium-aluminum alloy prepared in Example 1 of the present invention.

[0078] Figure 4 This is a low-magnification microstructure metallographic photograph of the vanadium-aluminum alloy prepared in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0079] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0080] The present invention is further described in detail below. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0081] Example 1

[0082] This embodiment provides a method for preparing an aviation-grade low-oxygen and low-nitrogen vanadium aluminum alloy, the preparation method comprising the following steps:

[0083] (1) Weigh 160.6 kg of vanadium pentoxide (of which 32.5 kg is powdered vanadium pentoxide with a particle size of less than 80 mesh, and the rest is flake vanadium pentoxide with a size between 5 mm and 30 mm), 138.1 kg of aluminum powder, 51.3 kg of coolant V55Al master alloy recovery material and 21.0 kg of calcium fluoride, dry them at 120° C. for 6 h, take them out and air them to below 60° C. after drying, and put them into a V-type mixer for mixing, the mixer speed is 30 r / min, and the mixing time is 20 min; after cleaning the crucible in the vacuum aluminothermic furnace, put the mixed raw materials into the crucible, flatten the upper layer of the raw materials, put in the ignition agent, connect the ignition line, cover the furnace, turn on the cooling water switch, turn on the vacuum pump to evacuate, when the vacuum degree drops to 20 Pa, turn off the vacuum pump, and ignite, when the vacuum degree and temperature indication change, it indicates that the vacuum aluminothermic reaction has begun;

[0084] (2) 15 seconds after the vacuum aluminothermic reaction begins, argon gas is used as a raw material delivery carrier to blow vanadium pentoxide powder into the alloy liquid molten pool, wherein the purity of the vanadium pentoxide powder is 99.5%, the particle size is 30 μm, the delivery weight is 80 kg, the mass flow rate is 16 kg / min, and after 5 minutes, all the vanadium pentoxide powder is blown in. After standing for 15 seconds, aluminum powder is blown in through other feeding paths, wherein the purity of the aluminum powder is 99.99%, the particle size is less than 125 μm, the delivery speed is 3.0 kg / min, and the delivery weight of the aluminum powder is 30 kg. After 10 minutes, the aluminum powder is blown in. After standing for 30 minutes, the vacuum pump is turned on to evacuate the furnace body. After the vacuum degree in the furnace is reduced to 80 Pa, the vacuum pump is stopped to perform the first cooling of the alloy. After cooling for 12 hours, the furnace cover is opened to obtain the vanadium-aluminum primary alloy;

[0085] (3) The vanadium-aluminum primary alloy was manually crushed into pieces less than 15 cm in size, and then put into a jaw crusher. After five times of crushing to a particle size range of 5 to 50 mm, it was loaded into a corundum crucible of a vacuum medium-frequency induction melting furnace, and the furnace cover was closed to start vacuuming. When the vacuum degree dropped to 10 Pa, the argon filling switch was turned on to fill the furnace with argon at a flow rate of 20 L / min. After five minutes, the argon flow rate was reduced to 10 L / min, and the heating switch was turned on to start power smelting. The smelting parameters were 60 kW × 5 min, 80 kW × 10 min, 100 kW × 20 min, 120 kW × 20 min, and 130 kW × 10 min (the melting temperature was 1770 ° C at this time), and the refining parameters were 140 kW × 5 min (the melting temperature was 1850 ° C at this time). Then, pouring and cooling processes were carried out. Argon was continuously introduced during the cooling process. The argon was turned off after cooling for 4 hours. The vanadium-aluminum finished alloy was taken out of the furnace after cooling for 6 hours.

[0086] The primary vanadium-aluminum alloy in step (2) of Example 1 and the finished vanadium-aluminum alloy in step (3) were sampled and analyzed. The analysis results are shown in Table 1.

[0087] Table 1

[0088]

[0089] As can be seen from Table 1, the O content in the vanadium-aluminum primary alloy prepared by the preparation method described in Example 1 is less than 0.02wt%, and the N content is less than 0.01wt%. The O content in the finished alloy obtained after induction refining of the primary alloy is 0.013wt%, and the N content is 0.007wt%, reaching the technical indicators of O less than 0.015wt% and N less than 0.008wt%.

[0090] Example 2

[0091] This embodiment provides a method for preparing an aviation-grade low-oxygen and low-nitrogen vanadium aluminum alloy, the preparation method comprising the following steps:

[0092] (1) Weigh 118.4 kg of vanadium pentoxide (of which 35.5 kg is powdered vanadium pentoxide with a particle size less than 100 mesh, and the rest is flake vanadium pentoxide with a size between 5 mm and 30 mm), 137 kg of aluminum powder, 51.3 kg of V85Al master alloy recovery material and 23.5 kg of calcium fluoride, dry them at 120° C. for 6 h, take them out and air them to below 53° C. after drying, and put them into a V-type mixer for mixing, the mixer speed is 30 r / min, and the mixing time is 25 min; after cleaning the crucible in the vacuum aluminothermic furnace, put the mixed raw materials into the crucible, flatten the upper layer of the raw materials, put in the ignition agent, connect the ignition line, cover the furnace, turn on the cooling water switch, start the vacuum pump to evacuate, when the vacuum degree drops to 15 Pa, turn off the vacuum pump, and ignite, when the vacuum degree and temperature indication change, it indicates that the vacuum aluminothermic reaction has begun;

[0093] (2) 17 seconds after the vacuum aluminothermic reaction begins, argon gas is used as a raw material delivery carrier to blow vanadium pentoxide powder into the alloy liquid molten pool, wherein the purity of the vanadium pentoxide powder is 99.5%, the particle size is 30 μm, the delivery weight is 114 kg, the mass flow rate is 23 kg / min, and after 5 minutes, all the vanadium pentoxide powder is blown in. After standing for 20 seconds, aluminum powder is blown in through other feeding paths, wherein the purity of the aluminum powder is 99.99%, the particle size is less than 125 μm, the delivery speed is 6.0 kg / min, and the delivery weight of the aluminum powder is 60 kg. After 10 minutes, the aluminum powder is blown in. After standing for 40 minutes, the vacuum pump is turned on to evacuate the furnace body. After the vacuum degree in the furnace is reduced to 70 Pa, the vacuum pump is stopped to perform the first cooling of the alloy. After cooling for 12 hours, the furnace cover is opened to obtain the vanadium-aluminum primary alloy;

[0094] (3) The vanadium-aluminum primary alloy is manually crushed into pieces less than 15 cm in size, and then put into a jaw crusher. After five crushings, the pieces are crushed into a particle size range of 5 to 50 mm. The pieces are then loaded into a corundum crucible of a vacuum medium-frequency induction melting furnace, the furnace cover is closed, and vacuuming is started. When the vacuum degree drops to 10 Pa, the argon filling switch is turned on, and argon is filled into the furnace at a flow rate of 20 L / min. After five minutes, the argon flow rate is reduced to 10 L / min, and the heating switch is turned on to start power smelting. The smelting parameters are 60 kW × 5 min, 80 kW × 10 min, 100 kW × 15 min, 120 kW × 30 min, and 130 kW × 8 min (at this time, the melting temperature is 1745° C.), and the refining parameters are 140 kW × 5 min (at this time, the melting temperature is 1831° C.). Then, pouring and cooling processes are carried out. Argon is continuously introduced during the cooling process. After cooling for 4 hours, the argon is turned off. After cooling for 6 hours, the low-oxygen and low-nitrogen vanadium-aluminum alloy ingot prepared by the method of the present invention is obtained.

[0095] The primary vanadium-aluminum alloy in step (2) of Example 2 and the finished vanadium-aluminum alloy in step (3) were sampled and analyzed. The analysis results are shown in Table 2.

[0096] Table 2

[0097]

[0098]

[0099] As can be seen from Table 2, the O content in the vanadium-aluminum primary alloy prepared by the preparation method described in Example 2 is less than 0.02wt%, and the N content is less than 0.01wt%. The O content in the finished alloy obtained after induction refining of the primary alloy is 0.014wt%, and the N content is 0.006wt%, reaching the technical indicators of O less than 0.015wt% and N less than 0.008wt%.

[0100] Embodiments 3 to 7

[0101] The differences between Examples 3 to 7 and Example 1 are shown in Table 3, and the remaining steps are the same as those of Example 1.

[0102] Table 3

[0103]

[0104] The primary vanadium-aluminum alloy in step (2) of Examples 3 to 7 and the finished vanadium-aluminum alloy in step (3) were sampled and analyzed. The analysis results are shown in Table 4.

[0105] Table 4

[0106]

[0107]

[0108] As can be seen from Table 4, the O content in the vanadium-aluminum primary alloys prepared by the preparation methods described in Examples 3 to 7 is lower than 0.02wt%, and the N content is lower than 0.01wt%. The O content in the finished alloys obtained after induction refining of the primary alloys is lower than 0.015wt%, and the N content is lower than 0.008wt%.

[0109] Comparative Example 1

[0110] This comparative example provides a method for preparing vanadium aluminum alloy, and the difference between the preparation method and Example 1 is reflected in that the vacuum degree before ignition of the vacuum thermite reaction in step (1) is 200Pa.

[0111] Comparative Example 2

[0112] This comparative example provides a method for preparing vanadium-aluminum alloy. The difference between the preparation method and Example 1 is that in step (2), the mass flow rates of vanadium pentoxide powder and aluminum powder blown in are 35 kg / min and 10.0 kg / min respectively.

[0113] The components of the primary vanadium-aluminum alloy in step (2) of comparative example 1 and comparative example 2 and the finished vanadium-aluminum alloy in step (3) were characterized. The results are shown in Table 5.

[0114] Table 5

[0115]

[0116] As can be seen from Table 5, in Comparative Example 1, since the vacuum degree of the vacuum aluminothermic reaction atmosphere does not meet the requirements, a large amount of oxygen and nitrogen exist in the furnace. Under this condition, the raw material absorbs a large amount of impurity gases during the entire reaction process, making the oxygen and nitrogen content inside the vanadium aluminum primary alloy higher than that in Example 1. Although the subsequent vacuum medium frequency induction melting process can remove part of the oxygen content, the oxygen content still cannot meet the index requirements, and the vacuum medium frequency induction process cannot reduce the nitrogen content in the alloy. This shows that it is of great significance to turn on the vacuum pump to evacuate to 15-50Pa before igniting the vacuum aluminothermic reaction.

[0117] In Comparative Example 2, the mass flow rates of vanadium pentoxide powder and aluminum powder are relatively large, resulting in excessive reaction in the molten pool during the powder blowing refining process. The violent stirring of the molten pool will re-introduce the upper layer of unsolidified alumina slag into the alloy liquid, which not only fails to achieve the expected refining effect, but also increases the oxygen of the alloy.

[0118] Comparative Example 3

[0119] This comparative example provides a method for preparing a vanadium aluminum alloy. The difference between the preparation method and Example 1 is that step (3) of vacuum medium frequency induction melting is not performed.

[0120] The vanadium aluminum finished alloy prepared in this comparative example and in Example 1 was Figure 2 Sampling was carried out at the sampling positions shown and component testing was performed. The results are shown in Table 6.

[0121] Table 6

[0122]

[0123] It can be seen from Table 6 that the oxygen content in the vanadium-aluminum finished alloy of Comparative Example 3 is slightly higher than that in Example 1, and the uniformity of each point inside the vanadium-aluminum finished alloy deteriorates, which proves the important role of vacuum medium-frequency induction melting process in reducing oxygen and homogenizing elements in primary vanadium-aluminum alloy.

[0124] At the same time, the macrostructures of the vanadium aluminum finished alloys prepared in Example 1 and Comparative Example 3 were analyzed. The macrostructure metallographic photographs of the vanadium aluminum alloy prepared in Example 1 are as follows: Figure 3 As shown, the low-magnification microstructure metallographic photograph of the vanadium aluminum alloy prepared in Comparative Example 3 is as follows Figure 4 It can be seen that the interior of the alloy of Example 1 is relatively pure, while there are more black-gray aluminum oxide inclusions in the macrostructure of the alloy in Comparative Example 3, which is also the reason why the oxygen content of Comparative Example 3 is slightly higher than that of Example 1.

[0125] Comparative Example 4

[0126] In this comparative example, a vanadium-aluminum alloy is prepared by a conventional vacuum aluminothermic reaction method, and the specific process is as follows: 196.3 kg of vanadium pentoxide, 152.9 kg of aluminum powder, 34.2 kg of V55Al master alloy recovery material and 21.0 kg of calcium fluoride are weighed, and dried at 120° C. for 6 h. After drying, the mixture is taken out and aired to below 60° C. and then loaded into a V-type mixer for mixing. The mixer speed is 30 r / min, and the mixing time is 20 min. After cleaning the crucible in the vacuum aluminothermic furnace, the mixed raw materials are loaded into the crucible, the upper layer of the raw materials is flattened, an ignition agent is put in, and after the ignition line is connected, the furnace cover is covered, the cooling water switch is turned on, and the vacuum pump is turned on for evacuation. When the vacuum degree drops to 20 Pa, the vacuum pump is turned off and ignition is performed. When the vacuum degree and the temperature indication change, it indicates that the reaction has begun. Vacuuming is started 60 min after the reaction, and the vacuuming duration is 4 h. The alloy is cooled for 24 h before being taken out of the furnace to obtain a vanadium-aluminum finished alloy.

[0127] The composition of the vanadium-aluminum finished alloy prepared in Comparative Example 4 was characterized, and the results are shown in Table 7.

[0128] Table 7

[0129]

[0130] It can be seen from Table 7 that the O and N contents in the vanadium aluminum finished alloy prepared by vacuum aluminothermic method in Comparative Example 4 are relatively high, and the difference in gas phase impurity content between the vanadium aluminum finished alloy prepared by Example 1 of the method of the present invention is large, and the requirements for the use of aviation-grade titanium alloy raw materials are not met.

[0131] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing aviation-grade low-oxygen and low-nitrogen vanadium aluminum alloy, characterized in that: The preparation method comprises the following steps: (1) mixing a vanadium pentoxide raw material, an aluminum raw material, a slag-making agent and a coolant to perform a vacuum thermite reaction; (2) after the vacuum aluminothermic reaction begins, vanadium pentoxide powder and aluminum powder are blown into the molten pool in sequence using an inert gas as a carrier, and a vanadium-aluminum primary alloy is obtained after a first cooling process; (3) crushing the primary vanadium-aluminum alloy, performing vacuum medium-frequency induction melting, and obtaining the aviation-grade low-oxygen and low-nitrogen vanadium-aluminum alloy after a second cooling; The aviation-grade low-oxygen and low-nitrogen vanadium aluminum alloy has an oxygen content of less than 0.015% and a nitrogen content of less than 0.008%.

2. The preparation method according to claim 1, characterized in that: The purity of the vanadium pentoxide raw material in step (1) is not less than 98%, and the weight proportion of the vanadium pentoxide raw material with a particle size of less than 100 μm is not less than 20%; Preferably, the purity of the aluminum raw material is not less than 99.7% and the particle size is not greater than 1 mm; Preferably, the slag-forming agent comprises calcium fluoride and / or calcium oxide; Preferably, the coolant includes any one of V40Al, V55Al, V65Al, V70Al or V80Al, or a combination of at least two of them.

3. The preparation method according to claim 1 or 2, characterized in that: The mass content of V in the alloy composition after the vacuum aluminothermic reaction in step (1) is 50% to 60%, Al is the balance, the mass content of impurity elements is Fe≤0.15%, Si≤0.15%, the mass content of other single impurity elements is ≤0.1%, and the total mass content of other impurities is ≤0.3%.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The vacuum aluminothermic reaction in step (1) is carried out in a vacuum aluminothermic furnace; Preferably, before ignition of the vacuum thermite reaction, a vacuum pump is turned on to evacuate the vacuum to 15-50 Pa.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The blowing of vanadium pentoxide powder in step (2) is carried out within 15 to 25 seconds after the start of the vacuum thermite reaction; Preferably, after the vanadium pentoxide powder is blown in, the mixture is left to stand for 10 to 15 seconds before the aluminum powder is blown in.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The purity of the vanadium pentoxide powder in step (2) is not less than 99.5%, and the particle size is not greater than 50 μm; Preferably, the purity of the aluminum powder is not less than 99.9% and the particle size is less than 150 μm; Preferably, the mass flow rate of the vanadium pentoxide powder is 15.8 to 25.8 kg / min; Preferably, the mass flow rate of the aluminum powder is 3.0 to 8.0 kg / min; Preferably, the blowing of vanadium pentoxide powder and the blowing of aluminum powder use different paths.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The amount of vanadium pentoxide powder added in step (2) is such that the grade of V in the alloy liquid is increased to 75.0% to 85.0%; Preferably, the dosage of the aluminum powder is such that the grade of V in the alloy liquid is reduced to 60.0% to 70.0%.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The inert gas in step (2) includes any one of helium, neon, argon or krypton, or a combination of at least two of them, preferably argon; Preferably, the vacuum degree during the first cooling process is not higher than 100 Pa; Preferably, the first cooling time is not less than 8 hours; Preferably, the first cooling temperature is 20-30°C.

9. The preparation method according to any one of claims 1 to 8, characterized in that: Step (3) crushing the primary vanadium-aluminum alloy into particles with a diameter of 5 to 50 mm; Preferably, the vacuum medium frequency induction melting is carried out in a vacuum medium frequency induction melting furnace; Preferably, argon is filled during the vacuum medium frequency induction melting process, and the argon filling time is 4 hours from the completion of vacuum evacuation of the vacuum medium frequency induction melting furnace to the start of cooling; Preferably, the vacuum degree of the vacuum medium frequency induction melting is below 20Pa; Preferably, the temperature of the vacuum medium frequency induction melting is 1700-1880°C; Preferably, the second cooling is performed using a water-cooled copper ingot mold.

10. The preparation method according to any one of claims 1 to 9, characterized in that: The preparation method comprises the following steps: (1) mixing vanadium pentoxide raw material, aluminum raw material, slag-making agent and coolant, and performing vacuum aluminothermic reaction in a vacuum aluminothermic furnace; before igniting the vacuum aluminothermic reaction, turning on a vacuum pump to evacuate to 15-50 Pa; The purity of the vanadium pentoxide raw material is not less than 98%, and the weight proportion of particles less than 100 μm is not less than 20%; The purity of the aluminum raw material is not less than 99.7% and the particle size is not greater than 1 mm; The slag-forming agent includes calcium fluoride and / or calcium oxide; The coolant includes any one of V40Al, V55Al, V65Al, V70Al or V80Al or a combination of at least two thereof; The mass content of V in the alloy composition after the vacuum aluminothermic reaction is 50% to 60%, Al is the balance, the mass content of impurity elements is Fe≤0.15%, Si≤0.15%, the mass content of other single impurity elements is ≤0.1%, and the total mass content of other impurities is ≤0.3%; (2) 15 to 25 seconds after the vacuum aluminothermic reaction begins, vanadium pentoxide powder is blown into the molten pool using an inert gas as a carrier, and after the vanadium pentoxide powder is blown into the molten pool, the vanadium pentoxide powder is allowed to stand for 10 to 15 seconds, and then aluminum powder is blown into the molten pool to obtain a vanadium-aluminum primary alloy after a first cooling process; The purity of the vanadium pentoxide powder is not less than 99.5%, and the particle size is not greater than 50 μm; the purity of the aluminum powder is not less than 99.9%, and the particle size is less than 150 μm; the mass flow rate of the vanadium pentoxide powder is 15.8-25.8 kg / min; the mass flow rate of the aluminum powder is 3.0-8.0 kg / min; the blowing of the vanadium pentoxide powder and the blowing of the aluminum powder use different paths; the dosage of the vanadium pentoxide powder is to increase the grade of V in the alloy liquid to 75.0%-85.0%; the dosage of the aluminum powder is to reduce the grade of V in the alloy liquid to 60.0%-70.0%; The inert gas includes any one of helium, neon, argon or krypton, or a combination of at least two of them; During the first cooling process, the vacuum degree is not higher than 100 Pa, the time is not less than 8 hours, and the temperature is 20-30° C.; (3) crushing the vanadium-aluminum primary alloy to a particle size of 5 to 50 mm, performing vacuum medium-frequency induction melting in a vacuum medium-frequency induction melting furnace at a vacuum degree of less than 20 Pa and a temperature of 1700 to 1880° C., and cooling the alloy in a water-cooled copper ingot mold to obtain the aviation-grade low-oxygen and low-nitrogen vanadium-aluminum alloy; The aviation-grade low-oxygen and low-nitrogen vanadium aluminum alloy has an oxygen content of less than 0.015% and a nitrogen content of less than 0.008%; Argon is filled during the vacuum medium frequency induction melting process, and the argon filling time is 4 hours from the completion of vacuum evacuation of the vacuum medium frequency induction melting furnace to the start of cooling.

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