Vacuum melting system and method for high-purity molybdenum and fiber-structured molybdenum material

Abstract

The application relates to the technical field of refractory metal material processing, in particular to a vacuum smelting system and method for high-purity molybdenum and a fiber-structure molybdenum material, the vacuum smelting system for high-purity molybdenum comprises a three-layer composite crucible, the vacuum smelting method for high-purity molybdenum comprises the following steps: step S1): under the condition of a vacuum degree of less than or equal to 5*10 ‑3 Pa, a three-layer composite crucible is used to perform consumable smelting on molybdenum raw materials; step S2): a directional solidification rate is controlled to be 8-12 mm / min, and a longitudinal temperature gradient is formed to be greater than or equal to 100 DEG C / cm; step S3): multi-stage plastic deformation is implemented on a solidified ingot, and a total deformation amount is greater than or equal to 90%; the fiber-structure molybdenum material is formed with a longitudinal continuous fiber structure in the material, a grain length-diameter ratio is greater than or equal to 10:1, a fiber diameter is less than or equal to 5 microns, hydrogen content is less than or equal to 5 ppm, oxygen content is less than or equal to 50 ppm, and a room-temperature tensile strength is greater than or equal to 780 MPa; the application can prepare high-purity fiber-structure molybdenum material, and improves the problem of insufficient axial performance caused by the isotropy of a traditional equiaxed crystal structure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of refractory metal material processing, in particular to a vacuum melting system for high-purity molybdenum, a vacuum melting method and a fiber structure molybdenum material. BACKGROUND

[0002] As a key refractory metal, molybdenum has a melting point of 2620°C. Due to its excellent high-temperature strength, low thermal expansion coefficient and good thermal conductivity, it has become a core material for high-end equipment such as semiconductor ion implantation machine components, rocket engine nozzles and nuclear reactor cladding. Especially in the field of military high-speed aircraft, the material is required to maintain a tensile strength of more than 700 MPa at 1600°C.

[0003] The current mainstream production process is powder metallurgy, which includes molybdenum powder pressing, sintering and hot forging / rolling. However, this technology has the following fatal defects:

[0004] (1) Purity problem: In the semiconductor field, the content of hydrogen and oxygen in molybdenum materials is extremely strict. However, the purity of molybdenum materials produced by existing technologies is difficult to meet the requirements, especially the gas content exceeds the standard. The purity of domestic molybdenum materials can only reach 99.97%, and the hydrogen and oxygen content cannot meet the high requirements of high-end manufacturing and military industries on purity. The main reason is that the traditional melting process and equipment cannot effectively control the mixing and removal of gases.

[0005] (2) Material internal structure problem: The existing process cannot produce a specific fiber structure, making it difficult to achieve the required grain change. In the semiconductor and military fields, special parts have strict requirements on material structure. If the specified structure requirements are not met, qualified parts cannot be processed. This is because the principles and operating methods of traditional processes limit the precise control of the internal structure of the material.

[0006] The existing vacuum melting process cannot stably produce molybdenum materials that meet the requirements of high purity and specific fiber structure. SUMMARY

[0007] The present application provides a vacuum melting system for high-purity molybdenum, a vacuum melting method and a fiber structure molybdenum material, which can effectively solve the problems in the background art.

[0008] To achieve the above-mentioned purposes, the present application provides the following technical solutions:

[0009] The vacuum melting system of high-purity molybdenum comprises an electrode feeding transmission device, an electrode rod, a vacuum furnace body, a consumable molybdenum rod, a three-layer composite crucible, a water cooling cycle and a vacuum pumping system, the electrode feeding transmission device is connected with the electrode rod for controlling the lifting of the electrode rod, the lower end of the electrode rod is connected with the consumable molybdenum rod used as a cathode, the consumable molybdenum rod is suspended in the interior of the vacuum furnace body, the three-layer composite crucible used as an anode is arranged in the interior of the vacuum furnace body, the vacuum furnace body is connected with the vacuum pumping system, and the water cooling cycle is connected with the three-layer composite crucible.

[0010] The three-layer composite crucible comprises an inner layer, an intermediate layer and an outer layer, the inner layer is a W-Re alloy layer, the intermediate layer is a graphite-potassium carbide composite layer, and the outer layer is a copper-based water cooling jacket.

[0011] The vacuum melting method of high-purity molybdenum comprises the following steps.

[0012] Step S1: the consumable molybdenum rod is melted by using the three-layer composite crucible under the environment with a vacuum degree of ≤5*10 -3 Pa.

[0013] Step S2: the directional solidification rate is controlled to be 8-12 mm / min, and a longitudinal temperature gradient of ≥100℃ / cm is formed.

[0014] Step S3: multi-stage plastic deformation is implemented on the solidified ingot, and the total deformation amount is ≥90%.

[0015] Preferably, the consumable molybdenum rod is subjected to acid pickling pretreatment before melting in step S1: the consumable molybdenum rod is soaked in mixed acid liquid with a volume ratio of HF:HNO3=1:3 for 30 seconds, and the purity of the molybdenum ingot in the consumable molybdenum rod is ≥99.98%.

[0016] Preferably, the melting parameters in step S1 comprise: a melting current of 25-28 kA; a voltage fluctuation of ≤±0.5 V; a melting temperature of 2550-2600℃, and a constant temperature time of 10-20 min.

[0017] Preferably, the multi-stage plastic deformation in step S3 is three-time multi-directional forging, and the single deformation amount is 30-35%, and the final forging temperature is 800-850℃.

[0018] Preferably, gradient annealing is implemented after forging: first stage: 1200℃*2h; second stage: 800℃*4h.

[0019] A fiber structure molybdenum material is prepared by using the above-mentioned vacuum melting method of high-purity molybdenum, the hydrogen content of the molybdenum material is ≤5ppm, the oxygen content is ≤50ppm, the grain length-diameter ratio is ≥10:1, a longitudinal continuous fiber structure is formed in the interior of the material, the fiber diameter is ≤5μm, the room temperature tensile strength is ≥780MPa, and the high-temperature creep life at 1200℃ is ≥300 hours.

[0020] Compared with the prior art, the beneficial effects of this application are:

[0021] 1. The molybdenum material of this fiber structure has a hydrogen content of ≤5ppm, an oxygen content of ≤50ppm, and a purity of over 99.99%, meeting the limit requirements of the target material gas impurities for the 3nm semiconductor process; it forms a longitudinal continuous fiber structure, which improves the problem of insufficient axial performance caused by the isotropy of the traditional equiaxed crystal structure.

[0022] 2. The fiber network of this fiber structure molybdenum material is oriented axially, which significantly extends the crack propagation path when the material is subjected to axial loads in military components; the room temperature tensile strength is ≥780MPa, which is significantly higher than that of traditional processes, breaking through the 700MPa strength threshold of hot-end components of hypersonic aircraft; the high-temperature creep life at 1200℃ is ≥300 hours, which is 3-5 times that of traditional materials, significantly improving the service reliability of rocket engine nozzles;

[0023] 3. The composite crucible design reduces the contamination rate and extends the crucible life; the gradient annealing process avoids abnormal grain growth, significantly improving product yield. Attached Figure Description

[0024] Figure 1 Metal structure of transverse (a) and longitudinal (b) sections of fiber-structured molybdenum rods.

[0025] Figure 2 This is a schematic diagram of the structure of a three-layer composite crucible.

[0026] Figure 3 This is a schematic diagram of the working principle of a vacuum melting system for high-purity molybdenum.

[0027] In the diagram: 1 Electrode feed transmission device, 2 Electrode rod, 3 Vacuum furnace body, 4 Consumable molybdenum rod, 5 Three-layer composite crucible, 51 Inner layer, 52 Middle layer, 53 Outer layer, 6 Water cooling circulation, 7 Vacuum system. Detailed Implementation

[0028] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] Please see Figures 1-3 This application provides the following technical solutions:

[0030] A vacuum melting system for high-purity molybdenum includes an electrode feeding transmission device 1, an electrode rod 2, a vacuum furnace body 3, a consumable molybdenum rod 4, a three-layer composite crucible 5, a water cooling circulation system 6, and a vacuum pumping system 7.

[0031] The electrode feeding transmission device 1 is connected with the electrode rod 2, and is used for controlling the lifting of the electrode rod 2.

[0032] The lower end of the electrode rod 2 is connected with a consumable molybdenum rod 4 used as a cathode, and the consumable molybdenum rod 4 is suspended in the vacuum furnace body 3.

[0033] The three-layer composite crucible 5 is arranged in the vacuum furnace body 3 as an anode, and is connected with a water cooling circulation 6 outside the vacuum furnace body 3.

[0034] The vacuum system 7 is connected with the vacuum furnace body 3, and is used for maintaining the vacuum degree in the furnace to be less than or equal to 5*10 -3 Pa.

[0035] The three-layer composite crucible 5 comprises, from inside to outside, the following layers:

[0036] The inner layer 51 is a W-Re alloy layer, wherein the content of Re is 3-8wt%, the thickness is 5mm, and the melting point is greater than 3200℃.

[0037] The intermediate layer 52 is a graphite-potassium carbide composite layer, and the thickness is 15mm, and the thermal conductivity is less than or equal to 50W / (m*K).

[0038] The outer layer 53 is a copper-based water cooling jacket, and cooling water is circulated in the copper-based water cooling jacket, and the flow rate is greater than or equal to 5m³ / h.

[0039] The water cooling circulation 6 is in communication with the copper-based water cooling jacket of the outer layer 53 of the three-layer composite crucible 5, and forms a closed cooling loop.

[0040] Specifically, the application discloses a three-layer composite crucible structure with specific material composition and functional layering, and the structure solves the core contradiction between high purity and specific fiber structure in high-purity molybdenum vacuum consumable smelting through the synergistic effect of the materials of the layers.

[0041] The single-layer water-cooled copper crucible is commonly used in the prior art, which is a conventional design for vacuum consumable melting (especially for active metals such as titanium and zirconium), and utilizes the high thermal conductivity of copper and water cooling for rapid cooling. However, the melting point of molybdenum (2620°C) is much higher than that of copper (1083°C). During the melting process, if a copper crucible is used, the high-temperature molybdenum liquid will corrode and react with the copper crucible, resulting in copper element contamination of the molybdenum melt, so that the purity of the final product is difficult to exceed 99.97%, and the content of gas impurities (O, H) is high, which is a bottleneck that cannot be overcome by powder metallurgy and traditional melting methods. At the same time, although copper has good thermal conductivity, its strength is relatively low, and when it bears a large radial thermal gradient, it is prone to thermal stress deformation, cracking and even melting through, so the service life of the crucible is extremely short, and stable and continuous industrial production cannot be carried out. Although the single-layer copper crucible has strong cooling capacity, it is difficult to form a controllable and stable longitudinal high-temperature gradient (≥100°C / cm), which is a key prerequisite for realizing directional solidification to obtain an axial fiber crystal structure.

[0042] The three-layer crucible of the present application includes an inner layer (W-Re alloy) that directly faces the high-temperature molybdenum liquid. The melting point (>3200°C) of the inner layer is much higher than that of molybdenum, which fundamentally solves the problem of crucible corrosion and contamination, and provides a source guarantee for obtaining ultra-high purity of 99.992% or more. The addition of Re element further enhances the high-temperature strength.

[0043] The middle layer (graphite-potassium carbide composite layer) is one of the most creative designs of the present application, and its low thermal conductivity coefficient (≤50 W / (m·K)) acts like a "thermal barrier layer", slowing down the intense heat transfer from the inner layer to the outer layer, greatly relieving the thermal stress caused by the large difference in thermal expansion coefficients between the inner and outer layers, thereby solving the problem of cracking of the copper crucible and increasing the service life of the crucible from dozens of times to more than 300 times. Chemical barrier: Potassium carbide (TaC) can effectively inhibit the reaction between molybdenum and carbon in the graphite layer, prevent the "carburization" of the molybdenum ingot, and further guarantee the purity and plasticity of the product.

[0044] The outer layer (copper-based water cooling jacket) is responsible for the final heat dissipation. Under the protection of the middle layer, the copper jacket can work stably, and by controlling the cooling water flow (≥5 m³ / h), it cooperates with the middle layer to build and accurately control the longitudinal temperature gradient necessary for directional solidification.

[0045] At the same time, compared with other multi-layer crucibles in the prior art, the present application solves the problem of service life that cannot be avoided by traditional multi-layer crucible structures, and realizes precise control of the solidification process, so as to prepare materials with a specific fiber structure.

[0046] The vacuum melting method of high-purity molybdenum includes the following steps:

[0047] Step S1: A vacuum degree of ≤5×10 -3The consumable molybdenum rod is smelted by using a three-layer composite crucible 5 under the environment of Pa.

[0048] Step S2: the directional solidification rate is controlled to be 8-12 mm / min, and a longitudinal temperature gradient is formed to be greater than or equal to 100 ℃ / cm.

[0049] Specifically, step S2 is directional solidification, and a longitudinal temperature gradient greater than or equal to 100 ℃ / cm is superimposed on a solidification rate of 8-12 mm / min: the axial growth of the crystal grains can be promoted, a longitudinal continuous fiber structure is formed, and the traditional isometric crystal anisotropy defect is solved. The fiber diameter is less than or equal to 5 μm: the grain refinement improves the strength, and the room temperature tensile strength reaches 825 MPa. The longitudinal direction refers to the axial direction of the three-layer composite crucible.

[0050] Step S3: multi-stage plastic deformation is performed on the solidified ingot, and the total deformation amount is greater than or equal to 90%.

[0051] Specifically, the total deformation amount of multi-directional forging is greater than or equal to 90%, which can crush coarse grains and promote the densification of the fiber structure.

[0052] Preferably, before step S1 of smelting, the consumable molybdenum rod 4 is subjected to pickling pretreatment: the consumable molybdenum rod 4 is immersed in a mixed acid solution of HF:HNO3=1:3 for 30 seconds, and the purity of the molybdenum ingot is greater than or equal to 99.98%.

[0053] Specifically, the mixed acid solution can quickly dissolve the oxide layer on the surface of the molybdenum ingot, so that the gaseous impurities can be controlled from the source.

[0054] Preferably, the smelting parameters of step S1 include: a smelting current of 25-28 kA; a voltage fluctuation of less than or equal to ±0.5 V; a smelting temperature of 2550-2600 ℃, and a constant temperature time of 10-20 min.

[0055] Preferably, the multi-stage plastic deformation in step S3 is three times of multi-directional forging, and the single deformation amount is 30-35%, and the final forging temperature is 800-850 ℃.

[0056] Preferably, gradient annealing is performed after forging: the first stage is 1200 ℃×2 h; the second stage is 800 ℃×4 h.

[0057] Specifically, the first stage is 1200 ℃×2 h: the forging stress is eliminated, and the grain boundary oxidation is avoided.

[0058] The second stage is 800 ℃×4 h: the recrystallization is accurately controlled, the abnormal grain growth is prevented, and the yield is improved by 20%.

[0059] A fiber structure molybdenum material is prepared by the above-mentioned vacuum melting method of high-purity molybdenum, and has a hydrogen content of ≤5 ppm, an oxygen content of ≤50 ppm, a grain length-diameter ratio of ≥10:1, a longitudinal continuous fiber structure formed in the material, a fiber diameter of ≤5 μm, a tensile strength at room temperature of ≥780 MPa, and a high-temperature creep life at 1200℃ of ≥300 hours.

[0060] A preparation operation method of the fiber structure molybdenum material is provided in the following specific embodiments.

[0061] Embodiment 1:

[0062] 1. Raw material pretreatment: a molybdenum ingot with a purity of ≥99.98% (hydrogen content ≤0.0003%, oxygen content ≤0.004%) is used as a consumable electrode.

[0063] Acid pickling treatment: a mixed acid solution with a volume ratio of HF:HNO3=1:3 is used for soaking for 30 seconds, and then deionized water is used for rinsing and vacuum drying.

[0064] 2. Melting system and crucible structure:

[0065] A three-layer composite crucible is used, and the structure is as follows:

[0066] Inner layer: W-5%Re alloy, thickness 5 mm;

[0067] Middle layer: graphite-20% tantalum carbide composite layer, thickness 15 mm, thermal conductivity coefficient ≤50 W / (m·K);

[0068] Outer layer: copper-based water cooling jacket, cooling water flow rate ≥5 m³ / h.

[0069] Vacuum system limit vacuum degree: ≤5×10 -3 Pa, leakage rate <1×10 -4 Pa·m³ / s.

[0070] 3. Melting process parameter control: melting current: 26 kA; melting voltage: 21 V, voltage fluctuation ≤±0.5 V; melting temperature: 2575℃; constant temperature time: 15 min; vacuum degree maintenance: ≤5×10 -3 Pa.

[0071] 4. Directional solidification control:

[0072] Solidification rate: 10 mm / min;

[0073] Longitudinal temperature gradient: ≥100℃ / cm.

[0074] 5. Multidirectional forging process: 3 times of forging, single deformation amount: 32%; total deformation amount: 90%; final forging temperature: 825℃.

[0075] 6. Gradient annealing process:

[0076] First stage: 1200℃ x 2h, argon protection;

[0077] Second stage: 800℃ x 4h, vacuum degree ≤1 x 10 -2 Pa.

[0078] 7. The final product performance is as follows: purity: 99.992%, hydrogen content: 4.2ppm, oxygen content: 42ppm, grain aspect ratio: 18:1, room temperature tensile strength: 825MPa.

[0079] Example 2:

[0080] 1. Raw material pretreatment: using molybdenum ingot with purity ≥99.98% (hydrogen content ≤0.0003%, oxygen content ≤0.004%) as consumable electrode.

[0081] Pickling treatment: using mixed acid solution with volume ratio of HF:HNO3=1:3 for soaking for 30 seconds, then rinsing with deionized water and vacuum drying.

[0082] 2. Melting system and crucible structure:

[0083] Using three-layer composite crucible, the structure is as follows:

[0084] Inner layer: W-5%Re alloy, thickness 5mm;

[0085] Middle layer: graphite-20% tantalum carbide composite layer, thickness 15mm, thermal conductivity coefficient ≤50W / (m·K);

[0086] Outer layer: copper-based water cooling jacket, cooling water flow ≥5m³ / h.

[0087] Vacuum system limit vacuum degree: ≤5 x 10 -3 Pa, leakage rate <1 x 10 -4 Pa·m³ / s.

[0088] 3. Melting process parameters: melting current: 27.5kA; melting voltage: 21.5V, voltage fluctuation ≤±0.5V; melting temperature: 2590℃; constant temperature time: 18min; vacuum degree maintenance: ≤5 x 10 -3 Pa.

[0089] 4. Directional solidification control: solidification rate: 11.5mm / min; longitudinal temperature gradient: ≥100℃ / cm.

[0090] 5. Multidirectional forging process: forging for 3 times, single deformation amount: 34%; total deformation amount: 92%; final forging temperature: 840℃.

[0091] 6. Gradient annealing process:

[0092] First stage: 1200°C x 2h, argon protection;

[0093] Second stage: 800°C x 4h, vacuum degree ≤ 1 x 10 -2 Pa.

[0094] 7. The final product performance is as follows: purity: 99.990%, hydrogen content: 4.8 ppm, oxygen content: 47 ppm, grain aspect ratio: 15:1, room temperature tensile strength: 795 MPa.

[0095] Example 3:

[0096] 1. Raw material pretreatment: using molybdenum ingot with purity ≥ 99.98% (hydrogen content ≤ 0.0003%, oxygen content ≤ 0.004%) as consumable electrode.

[0097] Pickling treatment: using mixed acid solution with volume ratio of HF:HNO3=1:3 for soaking for 30 seconds, then rinsing with deionized water and vacuum drying.

[0098] 2. Melting system and crucible structure:

[0099] Using three-layer composite crucible, the structure is as follows:

[0100] Inner layer: W-5%Re alloy, thickness 5mm;

[0101] Middle layer: graphite-20% tantalum carbide composite layer, thickness 15mm, thermal conductivity coefficient ≤ 50 W / (m·K);

[0102] Outer layer: copper-based water cooling jacket, cooling water flow ≥ 5m³ / h.

[0103] Vacuum system limit vacuum degree: ≤ 5 x 10 -3 Pa, leakage rate < 1 x 10 -4 Pa·m³ / s.

[0104] 3. Melting process parameters: melting current: 25kA; melting voltage: 20.5V, voltage fluctuation ≤ ±0.5V; melting temperature: 2550°C; constant temperature time: 12min; vacuum degree maintenance: ≤ 5 x 10 -3 Pa.

[0105] 4. Directional solidification control: solidification rate: 8.5mm / min; longitudinal temperature gradient: ≥ 100°C / cm.

[0106] 5. Multidirectional forging process: forging for 3 times, single deformation amount: 30%; total deformation amount: 90%; final forging temperature: 810°C.

[0107] 6. Gradient annealing process:

[0108] First stage: 1200℃ x 2h, argon protection;

[0109] Second stage: 800℃ x 4h, vacuum degree ≤ 1 x 10 -2 Pa.

[0110] 7. The final product performance is as follows: purity: 99.989%, hydrogen content: 5.1 ppm, oxygen content: 53 ppm, grain aspect ratio: 12:1, room temperature tensile strength: 780 MPa

[0111] The performance test results of the fiber structure molybdenum rods finally obtained in Examples 1-3 and those obtained by using traditional powder metallurgy (Comparative Example 1) and ordinary vacuum melting (Comparative Example 2) are shown in Table 1 below:

[0112] Table 1 is comparative data of Examples 1-3 and Comparative Examples 1-2:

[0113] Item Example 1 Example 2 Example 3 Comparative Example 1 (conventional powder metallurgy) Comparative Example 2 (ordinary vacuum melting) Purity (%) 99.992 99.990 99.989 99.97 99.96 Hydrogen content (ppm) 4.2 4.8 5.1 12.5 15.3 Oxygen content (ppm) 42 47 53 85 105 Grain aspect ratio 18:1 15:1 12:1 1 : 1 (equiaxed grains) 3:1 Tensile strength (MPa) 825 795 780 620 650

[0114] From Table 1, we can see that the high-purity molybdenum material prepared by using the present application has a hydrogen content reduced by more than 60% (compared with traditional processes) and an oxygen content reduced by more than 50% (compared with ordinary vacuum melting), which can meet the strict requirements of high-end manufacturing and military industries for high-purity molybdenum materials.

[0115] In combination with the drawings attached to the specification Figure 1 As can be seen, the high-purity molybdenum material prepared by using the present application has a structure deformed and with elongated fibers in the longitudinal section, in which the grains are elongated; in the transverse section, the grain size is small (i.e., there is no coarse grain structure), and this special structure makes it have good adaptability in the processing of special parts in the semiconductor and military fields, which can effectively improve the performance and quality of the parts.

[0116] The high-purity molybdenum material prepared by using the present application has a grain aspect ratio ≥ 10:1 and a fiber diameter ≤ 5 μm; the tensile strength is increased by 25-30%; and the high-temperature creep life is prolonged by 3-5 times (tested at 1200℃).

[0117] Although the embodiments of the present application have been shown and described, it can be understood by those of ordinary skill in the art that various changes, modifications, replacements and variations can be made to these embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A vacuum melting method of high purity molybdenum, characterized by, The method comprises the following steps: Step S1: The consumable molybdenum rod (4) is smelted in a three-layer composite crucible (5) under an environment with a vacuum degree ≤5×10 -3 Pa. Step S2: controlling the directional solidification rate to be 8-12 mm / min, and forming a longitudinal temperature gradient ≥100℃ / cm; Step S3: performing multi-stage plastic deformation on the solidified ingot, with a total deformation amount ≥90%; The molybdenum material prepared by the method has a hydrogen content ≤5ppm, an oxygen content ≤50ppm, a grain length-diameter ratio ≥10:1, and a longitudinal continuous fiber structure formed in the material, with a fiber diameter ≤5μm. The vacuum melting method for high-purity molybdenum adopts a melting system comprising an electrode feeding transmission device (1), an electrode rod (2), a vacuum furnace body (3), a consumable molybdenum rod (4), a three-layer composite crucible (5), a water cooling cycle (6), and a vacuum pumping system (7), wherein the electrode feeding transmission device (1) is connected with the electrode rod (2) to control the lifting of the electrode rod (2), the lower end of the electrode rod (2) is connected with the consumable molybdenum rod (4) used as a cathode, the consumable molybdenum rod (4) is suspended in the interior of the vacuum furnace body (3), the three-layer composite crucible (5) used as an anode is placed in the interior of the vacuum furnace body (3), the vacuum furnace body (3) is connected with the vacuum pumping system (7) outside, and the water cooling cycle (6) is connected with the three-layer composite crucible (5). The three-layer composite crucible (5) comprises an inner layer (51), an intermediate layer (52), and an outer layer (53), wherein the inner layer (51) is a W-Re alloy layer, the intermediate layer (52) is a graphite-tantalum carbide composite layer, and the outer layer (53) is a copper-based water cooling jacket.

2. The vacuum melting method of high purity molybdenum according to claim 1, characterized by: Before step S1, the consumable molybdenum rod (4) is pretreated by pickling: soaking in a mixed acid solution with a volume ratio of HF:HNO3=1:3 for 30 seconds, and the purity of the molybdenum ingot in the consumable molybdenum rod (4) is ≥99.98%; The melting parameters of step S1 include: a melting current of 25-28kA; a voltage fluctuation ≤±0.5V; a melting temperature of 2550-2600℃, and a constant temperature time of 10-20min; The multi-stage plastic deformation in step S3 is 3-time multi-directional forging, with a single deformation amount of 30-35%, and a final forging temperature of 800-850℃; and gradient annealing is performed after forging: first stage: 1200℃×2h; second stage: 800℃×4h.

3. A fibrous structural molybdenum material characterized by, The molybdenum material is prepared by the vacuum melting method for high-purity molybdenum according to any one of claims 1-2, has a room temperature tensile strength ≥780MPa, and a high-temperature creep life ≥300 hours at 1200℃.

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