Niobium alloy precision capillary tube and preparation method thereof

Abstract

According to the niobium alloy precise capillary tube and the preparation method thereof, the Nb521 alloy precise capillary tube with the diameter phi of 2.0-3.0 * 0.2-0.7 * L mm is prepared by adding inner wall reaming, two-roller and multi-roller cold rolling process parameter control, core rod drawing instead of all hollow drawing and other processes to a rolled intermediate tube blank; the niobium alloy precise capillary tube is a key material for a closed circulation system of a hypersonic engine, has the advantages of high dimensional precision, good surface quality, stable mechanical property and the like, and can completely meet the requirements of the closed circulation system of the hypersonic engine on high quality and high precision of a high-temperature heat transfer tube. The invention provides a method for manufacturing an Nb521 alloy precise capillary tube. The method comprises the steps of niobium alloy tube blank preparation, scaling and boring, two-roller rolling, acid pickling and oil removal, vacuum annealing, reaming, two-roller or multi-roller rolling, acid pickling and oil removal, vacuum annealing, drawing, acid pickling, finished product heat treatment, finishing and finished product obtaining.

Description

Technical Field

[0001] The invention provides a niobium alloy precision capillary and a preparation method thereof, belonging to the technical field of aerospace. Background Art

[0002] One of the uses of niobium alloy capillaries (generally, capillaries are tubes with an outer diameter of no more than 3mm) is as heat transfer tubes in high-temperature environments or flow guide tubes in high-temperature corrosive environments, which require high high-temperature mechanical properties, good surface quality and high dimensional accuracy. Currently, the alloy tubes of this specification produced on the market have problems such as low inner hole dimensional accuracy control, wrinkles and microcracks on the inner surface, etc.

[0003] Nb521 (Nb-5W-2Mo-1Zr) niobium alloy is a medium-strength plastic niobium alloy that adds W, Mo, Zr alloying elements and a small amount of C element to the niobium matrix. The room temperature and high temperature mechanical properties of the niobium alloy are further improved by combining solid solution strengthening and precipitation strengthening. Nb521 niobium alloy has high melting point, good corrosion resistance, high high temperature (600-1600℃) specific strength and good hot and cold processing performance. It can be used to make parts with complex shapes and is one of the important candidate materials for aerospace structural parts. The alloy can be used to manufacture rocket engines, space-to-earth shuttles, hypersonic aircraft, satellites, missiles and key components of nuclear reactors, including protective covers of combustion chambers of large-thrust aerospace engines, combustion chambers, small vector or attitude control nozzles and extended protective covers of orbital control engines.

[0004] Nb521 niobium alloy products are mostly supplied in the form of bars, plates and forgings, and pipes are rarely used. Usually most nozzles are obtained by machining bars, while plates are mostly used for spinning to prepare nozzle extensions with uniform transitions. However, with the development of a new generation of hypersonic propulsion technology, the use of strong precooling technology to alleviate the high temperature protection problem of the engine body has become one of the key issues that need to be addressed. In order to meet the requirements of "super-high pressure resistance, ultra-high heat resistance, ultra-high precision and ultra-high reliability" for the manufacture of heat exchangers, high temperature and high pressure resistant Nb521 alloy capillaries have become the key material and top priority for the realization of the entire hypersonic engine closed circulation system.

[0005] There are no patents or papers related to Nb521 alloy capillaries. Most patents and papers are about the preparation methods, organization and properties of niobium alloy ingots, bars, plates and coatings. In particular, there are many documents on the development, mechanical properties, bars and plates of low-density niobium alloys in recent years. The existing niobium alloy capillaries in China have problems such as low precision control of the inner hole size of the alloy tube, wrinkles and microcracks on the inner surface, etc., which makes it difficult to meet the high quality and high precision requirements of the closed circulation system of hypersonic engines for high-temperature heat transfer tubes. Related and similar documents are as follows:

[0006] Chinese patent CN 113560824 A discloses a method for preparing a long thin-walled tube of Nb521 niobium alloy. The method controls the surface quality, rolling parameters and complete recrystallization annealing temperature of the niobium alloy tube blank to obtain a long thin-walled tube of niobium alloy with short processing cycle, good surface quality and good plasticity. The outer diameter of the thin-walled tube is 10 mm to 20 mm, the wall thickness is 0.5 mm to 1 mm, the length is 3000 mm to 6000 mm, and the surface roughness is not greater than 1.6 μm, which meets the market demand for long thin-walled tubes of niobium alloy.

[0007] Chinese patent CN 108213109 A discloses a method for preparing a large-diameter, ultra-long, thin-walled NbZr10 niobium alloy tube. The large-diameter, ultra-long, thin-walled niobium and niobium alloy tube prepared by the present invention has an outer diameter of Φ60 to 200 mm, a wall thickness of 0.5 mm to 3 mm, and a length of 3500 mm to 12000 mm. The product has uniform structure, high comprehensive performance, high added value, and has good application and promotion prospects and certain economic and social benefits.

[0008] Chinese patents CN 104561575 A and CN 108213109 A disclose methods for preparing niobium-zirconium alloy tubes, which are prepared by static pressing and sintering or extruding powder into tubes, respectively, and the preparation cycle is relatively long.

[0009] Chinese patent CN 116423167 A discloses a method for improving the plasticity of low-density niobium alloy rods. The method adopts the processing technology of "jacket extrusion + forging + water bath cooling" to make the grain refinement and homogenization degree in the low-density niobium alloy structure obvious, and the carbide reinforcement phase is more dispersed, so as to achieve a significant improvement in the room temperature plasticity of the low-density niobium alloy rods. At the same time, the tensile strength is improved, which is conducive to its application in the aerospace field.

[0010] Chinese patent CN 115287515 A discloses a lightweight niobium alloy material for cryogenic environments and its preparation method and application. The plastic-brittle transition temperature of the lightweight niobium alloy is greatly reduced by multi-element alloying and appropriate proportioning of tungsten, molybdenum, rhenium, hafnium, titanium, aluminum, vanadium, chromium, zirconium and other elements, and the high-temperature strength of the alloy is improved by solid solution strengthening of the niobium alloy; low-density elements are added to reduce the density of the alloy. The alloy can be widely used in deep space exploration, Antarctic and Arctic exploration and other fields. .

[0011] Chinese patent CN 114855107 A discloses a method for preparing a low-density Nb-Ti-Al-VZC niobium alloy rod. The low-density niobium alloy rod is prepared by a process of "double extrusion + quenching + forging". By adding quenching treatment and secondary extrusion process, the carbide reinforcement phase TiC is dissolved back and precipitated again to nucleate and dispersed in the matrix, which effectively reduces the size of the carbide reinforcement phase and improves its dispersion, thereby achieving an increase in the elongation after fracture of the low-density niobium alloy rod, so that it exhibits high-strength and high-plasticity mechanical properties at room temperature.

[0012] Niobium alloy capillaries are generally made by repeatedly processing tube billets through rolling, pickling, vacuum annealing, rolling and other processes until the diameter is smaller (for example, the outer diameter is less than 6mm), and then prepared into capillaries with a diameter of less than 3mm through hollow drawing + vacuum annealing and other methods. The niobium alloy capillaries prepared by this method have problems such as low control of inner hole size accuracy, wrinkles and microcracks on the inner surface, and it is difficult to meet the requirements of high quality and high precision of tubes in high temperature, complex and harsh environments. Summary of the invention

[0013] The present invention prepares a φ2.0-3.0×0.2-0.7×L mm Nb521 alloy precision capillary by adding inner wall reaming to the rolled intermediate tube blank, controlling the process parameters of two-roll and multi-roll cold rolling, and replacing all hollow drawing with core rod drawing. The niobium alloy precision capillary is a key material for a closed circulation system of a hypersonic engine, and has the advantages of high dimensional accuracy (outer diameter and inner diameter dimensional deviation ≤±0.02mm), good surface quality (inner and outer surface roughness ≤0.8μm), stable mechanical properties (tensile strength ≥420MPa, specified non-proportional elongation strength ≥280MPa, elongation ≥20%), etc., and can fully meet the high quality and high precision requirements of the closed circulation system of a hypersonic engine for high-temperature heat transfer tubes.

[0014] The present invention provides a method for manufacturing a Nb521 alloy precision capillary, and the process flow is: niobium alloy tube blank→skinning and boring→two-roll rolling→pickling and degreasing→vacuum annealing (two-roll rolling+vacuum annealing cycle multiple times)→reaming→two-roll or multi-roll rolling→pickling and degreasing→vacuum annealing→drawing (drawing+vacuum annealing cycle multiple times)→pickling→finished product heat treatment→finishing→finished product.

[0015] The technical solution of the present invention is described in detail below:

[0016] The present invention provides a method for preparing a niobium alloy precision capillary, comprising the following steps:

[0017] Step 1: Tube preparation:

[0018] There are two methods for preparing extruded tube billets and drilled tube billets. The method for preparing extruded tube billets is to use extruded or forged rod billets to drill holes to prepare hollow ingot billets for secondary hot extrusion to produce an extruded tube billet with a diameter-to-thickness ratio (i.e., the ratio of the outer diameter of the tube to the wall thickness) of 6 to 10, i.e., a tube billet of φ32 to 52 × 3 to 8 × L mm; the method for preparing drilled tube billets is to use a method for drilling holes in completely recrystallized annealed φ30 to 50 mm rod billets to prepare hollow tube billets, and the diameter-to-thickness ratio (i.e., the ratio of the outer diameter of the tube to the wall thickness) of the tube billet is controlled at 6 to 10, i.e., a tube billet of φ30 to 50 × 3 to 8 × L mm.

[0019] Step 2: Surface treatment of tube blank:

[0020] The tube blank prepared in step 1 is surface treated, the inner wall is bored by a boring machine, the single-side boring amount is 0.3-0.8mm, and the inner wall is polished with sandpaper to ensure that there are no defects visible to the naked eye on the inner wall; the outer surface is peeled by a peeling machine (if the outer surface of the rod blank has been machined, there is no need to continue peeling the outer surface), the single-side peeling amount is 0.5-1mm, if there are still local defects after peeling, a grinding machine or a scraper can be used to grind or scrape it thoroughly, and the grinding marks left by the grinder after grinding must be eliminated with a polishing wheel or a flap wheel.

[0021] Step 3: Cold rolling of tube billet:

[0022] The blank is made by a two-roller cold rolling mill, with a processing rate of ≤45% and a feed amount of 2 to 4 mm.

[0023] Step 4: Pickling and washing of intermediate products:

[0024] First, soak the intermediate product pipe in hot water (the hot water can be added with some detergent or ultrasonic cleaning facilities) to remove most of the oil stains, and then soak it in pickling solution (H 2 SO 4 , HF, HNO 3 and water in a certain proportion) for pickling, and finally for water washing and drying.

[0025] Step 5: Intermediate annealing:

[0026] The annealing is carried out in a vacuum annealing furnace at a temperature of 1300-1450°C, a holding time of 60-120 min, and a vacuum degree of no less than 5×10 -2 Pa.

[0027] Step 6: Intermediate product tube rolling:

[0028] After 3-4 cold rolling passes on a two-roller rolling mill, the feed amount is 2-3mm, and the processing rate is controlled at 50%-60%; then after 2-3 cold rolling passes on a multi-roller rolling mill, the pass processing rate is 28%-36%, the total processing rate is 50%-60%, and the feed amount is 2-3mm.

[0029] Step 7: Ream the inner wall of the intermediate product:

[0030] The inner wall is reamed with a reamer, with a single-side cutting amount of 0.2 to 0.3 mm and an inner surface roughness of ≤1.6 μm, ensuring that there are no defects visible to the naked eye on the inner wall.

[0031] Step 8: Surface oxidation treatment:

[0032] The tube to be drawn is heated in a box-type resistance furnace at a temperature of 650-750°C for a holding time of 20-40 minutes, and the surface color changes to blue-gray or gray.

[0033] Step 9: Hollow and Cored Rod Pulling:

[0034] Firstly, the hollow steel is drawn through 2-3 cold rolling passes, and then through 3-5 core rod drawing passes, with a pass processing rate of 5%-16% and a total processing rate of 29%-40%.

[0035] Step 10: Pickling and washing of finished pipes:

[0036] The finished pipe can be soaked in kerosene, then cleaned with a cleaning agent, followed by pickling (the pickling time is 0.3 to 0.6 times the pickling time of the intermediate product), water washing and drying.

[0037] Step 11: Surface finishing and treatment of intermediate and finished pipes:

[0038] After annealing, the intermediate and finished pipes are straightened by a straightening machine. The straightness of the pipes after straightening is ≤3mm / m. After straightening, the pipes are cut and trimmed. Pipes with an outer diameter of more than 10mm can be cut and trimmed by a pipe cutter, and pipes with an outer diameter of ≤10mm can be cut and trimmed by wire cutting. Any defects visible to the naked eye on the surface of the pipe in each pass can be completely eliminated by a scraper or other means. The inner wall of the pipe before rolling must not have any hard particles, metal debris, etc.

[0039] Step 12: Finished product annealing:

[0040] The annealing temperature is 1350-1400℃, the holding time is 60-90min, and the vacuum degree of the annealing furnace is not less than 5×10 - 2 Pa.

[0041] The niobium alloy capillary prepared by the present invention has high inner and outer surface quality, high dimensional accuracy and stable performance, and can fully meet the application requirements of fine conduits in high-temperature, complex and harsh environments such as high-temperature heat transfer tubes and high-temperature corrosive environment guide tubes.

[0042] Compared with the prior art, the present invention has the following advantages:

[0043] (1) Small outer diameter and wide diameter-to-thickness ratio range: outer diameter is φ2.0-3.0 mm, and diameter-to-thickness ratio is 4-15;

[0044] (2) High dimensional accuracy: outer diameter and inner diameter deviation ≤ ±0.02mm;

[0045] (3) Good internal and external surface quality: internal and external surface roughness ≤ 0.8 μm;

[0046] (4) Good matching of strength and plasticity: tensile strength ≥420MPa, specified non-proportional elongation strength ≥280MPa, elongation ≥20%. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of the preparation process of the present invention. DETAILED DESCRIPTION

[0048] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings and examples. It should be understood that the examples are used to illustrate the present invention rather than to limit the present invention. The scope and core content of the present invention are determined according to the claims.

[0049] Example 1: Nb521 alloy φ3.0×0.7×L mm precision capillary:

[0050] Step 1: Preparation of tube billet: Nb521 alloy φ106mm extruded rod billet is machined, peeled and drilled to prepare φ97.5×φ35×L mm hollow ingot billet, and then subjected to secondary hot extrusion to obtain φ52×9.8×L mm extruded tube billet with a diameter-to-thickness ratio of 6.25.

[0051] Step 2: Surface treatment of tube blank: Surface treatment is performed on the extruded tube blank. The inner wall is bored by a boring machine with a single-side boring amount of 0.8 mm, and the inner wall is polished with sandpaper to ensure that there are no visible defects on the inner wall. The outer surface is peeled by a peeling machine with a single-side peeling amount of 1 mm. The size of the tube blank after treatment is φ50×8×L mm.

[0052] Step 3: Cold rolling of tube billets: The tube billets are rolled using a two-roller cold rolling mill with a processing rate of 44% and a feed amount of 3 to 4 mm. The size of the tube billets after cold rolling is φ40×5.5×L mm.

[0053] Step 4: Pickling and washing of intermediate products:

[0054] First, soak the intermediate product pipe in hot water (the hot water can be added with some detergent or ultrasonic cleaning facilities) to remove most of the oil stains, and then soak it in pickling solution (H 2 SO 4 , HF, HNO 3 and water in a certain proportion) for pickling, and finally for water washing and drying.

[0055] Step 5: Intermediate annealing: annealing is performed in a vacuum annealing furnace at a temperature of 1400-1450°C, a holding time of 90-120 min, and a vacuum degree of no less than 5×10 -2 Pa.

[0056] Step 6: intermediate product tube rolling: after 4 cold rolling passes on a two-roller mill, with a feed of 2-3 mm and a processing rate of 50%-60%, the tube is rolled to φ8×1.5×L mm; then after 3 cold rolling passes on a multi-roller mill, with a pass processing rate of 32%-35%, a total processing rate of 56%, a feed of 2-3 mm, the tube is rolled to φ5.4×0.9×L mm.

[0057] Step 7: Ream the inner wall of the intermediate product: Use a reamer to ream the inner wall of the φ12×2×L mm intermediate tube blank, with a single-side cutting amount of 0.25 mm and an inner surface roughness of ≤1.6μm to ensure that there are no defects visible to the naked eye on the inner wall.

[0058] Step 8: Surface oxidation treatment: The tube to be drawn is heated in a box-type resistance furnace at a temperature of 750°C for 20 to 30 minutes, and the surface color turns gray.

[0059] Step 9: Hollow and cored rod drawing: first, 1 pass of hollow drawing + 1 pass of cored rod drawing, then 1 pass of cored rod drawing + 1 pass of hollow drawing, with a pass processing rate of 10% to 15% and a total processing rate of 39%, drawing to φ3.9×0.8×L mm, acid water washing for degreasing and intermediate annealing; continue with two passes of cored rod drawing + 1 pass of hollow drawing, with a pass processing rate of 10% to 16% and a total processing rate of 35%, drawing to φ3.0×0.7×L mm.

[0060] Step 10: Pickling and washing of finished pipes:

[0061] The finished pipe can be soaked in kerosene, then cleaned with a cleaning agent, followed by pickling (the pickling time is 0.3 to 0.6 times the pickling time of the intermediate product), water washing and drying.

[0062] Step 11: Surface finishing and treatment of intermediate and finished pipes:

[0063] After annealing, the intermediate and finished pipes are straightened by a straightening machine. The straightness of the pipes after straightening is ≤3mm / m. After straightening, the pipes are cut and trimmed. Pipes with an outer diameter of more than 10mm can be cut and trimmed by a pipe cutter, and pipes with an outer diameter of ≤10mm can be cut and trimmed by wire cutting. Any defects visible to the naked eye on the surface of the pipe in each pass can be completely eliminated by a scraper or other means. The inner wall of the pipe before rolling must not have any hard particles, metal debris, etc.

[0064] Step 12: Finished product annealing: annealing temperature is 1350℃, holding time is 90min, and the vacuum degree of annealing furnace is not less than 5×10 -2 Pa.

[0065] The precision capillary material φ3.0×0.7×L mm has good tensile properties and plasticity after annealing, with a tensile strength of 452MPa, a specified non-proportional elongation strength of 301MPa, an elongation of 22.0%, high dimensional accuracy (outer diameter and inner diameter dimensional deviation ≤±0.02mm), and good surface quality (inner and outer surface roughness ≤0.8μm).

[0066] Example 2: Nb521 alloy φ2.0×0.20×L mm precision capillary:

[0067] Step 1: Preparation of tube blank: A φ3 mm rod blank that has been completely recrystallized and annealed by Nb521 alloy is drilled to prepare a φ30×3.3×L mm drilled tube blank with a diameter-to-thickness ratio of 9.1.

[0068] Step 2: Surface treatment of the tube: The inner wall of the drilled tube is bored by a boring machine, with a single-side boring amount of 0.3 mm, and the inner wall is polished with sandpaper to ensure that there are no visible defects on the inner wall. The size of the tube after treatment is φ30×3.0×L mm.

[0069] Step 3: Cold rolling of tube billets: The tube billets are rolled using a two-roller cold rolling mill with a processing rate of 44% and a feed amount of 3 to 4 mm. The size of the tube billets after cold rolling is φ22×2.3×L mm.

[0070] Step 4: Pickling and washing of intermediate products:

[0071] First, soak the intermediate product pipe in hot water (the hot water can be added with some detergent or ultrasonic cleaning facilities) to remove most of the oil stains, and then soak it in pickling solution (H 2 SO 4 , HF, HNO 3 and water in a certain proportion) for pickling, and finally for water washing and drying.

[0072] Step 5: Intermediate annealing: annealing is performed in a vacuum annealing furnace at a temperature of 1300-1400°C for 60-90 minutes. The vacuum degree of the annealing furnace is not less than 5×10 -2 Pa.

[0073] Step 6: Rolling of intermediate product pipe: After 3 cold rolling passes of two-roller cold rolling, the feed amount is 2-3mm, the processing rate is controlled at 50%-59%, and the pipe is rolled to φ6.5×0.55×L mm; after 2 cold rolling passes of multi-roller cold rolling, the pass processing rate is 33%-35%, the total processing rate is 57%, the feed amount is 2-3mm, and the pipe is rolled to φ4.6×0.33×L mm; after acid water washing and degreasing and intermediate annealing, the pipe is rolled to φ3.9×0.26×L mm with a pass processing rate of 33%.

[0074] Step 7: Ream the inner wall of the intermediate product: Use a reamer to ream the inner wall of the φ10×1.0×L mm intermediate tube blank, with a single-side cutting amount of 0.2 mm and an inner surface roughness of ≤1.6μm to ensure that there are no defects visible to the naked eye on the inner wall.

[0075] Step 8: Surface oxidation treatment: The tube to be drawn is heated in a box-type resistance furnace at a temperature of 650-700°C for 30-40 minutes, and the surface color changes to blue-gray or gray.

[0076] Step 9: Hollow and cored rod drawing: first, after 1 pass of cored rod drawing + 1 pass of hollow drawing, the pass processing rate is 9% to 15%, the total processing rate is 48% (including φ4.6×0.33mm rolled to φ3.9×0.26mm, the pass processing rate is 33%), and the rod is drawn to φ3.3×0.24×L mm, and acid water washing and degreasing and intermediate annealing are performed; continue to perform two passes of cored rod drawing, the pass processing rate is 15% to 16%, the total processing rate is 29%, and the rod is drawn to φ2.6×0.22×L mm, and acid water washing and degreasing and intermediate annealing are performed; continue to perform two passes of cored rod drawing + 1 pass of hollow drawing, the pass processing rate is 5% to 16%, the total processing rate is 31%, and the rod is drawn to φ2.0×0.20×L mm.

[0077] Step 10: Pickling and washing of finished pipes:

[0078] The finished pipe can be soaked in kerosene, then cleaned with a cleaning agent, followed by pickling (the pickling time is 0.3 to 0.6 times the pickling time of the intermediate product), water washing and drying.

[0079] Step 11: Surface finishing and treatment of intermediate and finished pipes:

[0080] After annealing, the intermediate and finished pipes are straightened by a straightening machine. The straightness of the pipes after straightening is ≤3mm / m. After straightening, the pipes are cut and trimmed. Pipes with an outer diameter of more than 10mm can be cut and trimmed by a pipe cutter, and pipes with an outer diameter of ≤10mm can be cut and trimmed by wire cutting. Any defects visible to the naked eye on the surface of the pipe in each pass can be completely eliminated by a scraper or other means. The inner wall of the pipe before rolling must not have any hard particles, metal debris, etc.

[0081] Step 12: Finished product annealing: annealing temperature is 1400℃, holding time is 60min, and the vacuum degree of annealing furnace is not less than 5×10 -2 Pa.

[0082] The precision capillary material φ2.0×0.20×L mm has good tensile properties and plasticity after annealing, with a tensile strength of 437MPa, a specified non-proportional elongation strength of 289MPa, an elongation of 23.5%, high dimensional accuracy (outer diameter and inner diameter dimensional deviation ≤±0.015mm), and good surface quality (inner and outer surface roughness ≤0.8μm).

Claims

1. A method for preparing a niobium alloy precision capillary, characterized in that: The steps include: Step 1: Tube preparation: Adopting an extrusion tube blank preparation method or a drilling tube blank preparation method; Step 2: Surface treatment of tube blank: The tube blank prepared in step 1 is subjected to surface treatment. The inner wall is bored by a boring machine and polished with sandpaper to ensure that the inner wall is free of defects. The outer surface is peeled by a peeling machine. If there are still local defects after peeling, a grinding wheel machine or a scraper is used to grind or scrape them thoroughly. The grinding marks left by the grinding machine must be removed with a polishing wheel or a flap wheel. Step 3: Cold rolling of tube billet: The two-roller cold rolling mill is used to produce the blank; Step 4: Pickling and washing of intermediate products: First, soak the intermediate product pipe in hot water to remove the oil stains, then pickle it in pickling liquid, and finally wash it with water and dry it; Step 5: Intermediate annealing: The annealing is carried out in a vacuum annealing furnace at a temperature of 1300-1450°C, a holding time of 60-120 min, and a vacuum degree of no less than 5×10 -2 Pa; Step 6: Intermediate product tube rolling: After 3-4 cold rolling passes of two-roller cold rolling, the feed amount is 2-3mm, and the processing rate is controlled at 50%-60%; after 2-3 cold rolling passes of multi-roller cold rolling, the pass processing rate is 28%-36%, the total processing rate is 50%-60%, and the feed amount is 2-3mm; Step 7: Ream the inner wall of the intermediate product: The inner wall is reamed with a reamer, with a single-side cutting amount of 0.2-0.3 mm and an inner surface roughness of ≤1.6 μm to ensure that the inner wall is free of defects; Step 8: Surface oxidation treatment: The tube to be drawn is heated in a box-type resistance furnace at a temperature of 650-750°C for 20-40 minutes, and the surface color changes to blue-gray or gray; Step 9: Hollow and Cored Rod Pulling: Firstly, the hollow steel is drawn through cold rolling for 2-3 passes, and then through core rod drawing for 3-5 passes, with a pass processing rate of 5%-16% and a total processing rate of 29%-40%; Step 10: Pickling and washing of finished pipes: The finished pipes are soaked in kerosene, then cleaned with a detergent, followed by pickling, water washing and drying; Step 11: Surface finishing and treatment of intermediate and finished pipes: After annealing, the intermediate and finished pipes are straightened by a straightening machine. The straightness of the pipes after straightening is ≤3mm / m. After straightening, the pipes are cut and the ends are removed. The defects on the surface of the pipes in each pass are completely eliminated with a scraper. There must be no hard particles or metal debris on the inner wall of the pipe before rolling. Step 12: Finished product annealing: The annealing temperature is 1350~1400℃, the holding time is 60~90min, and the vacuum degree of the annealing furnace is not less than 5×10 -2 Pa.

2. The method for preparing a niobium alloy precision capillary according to claim 1, characterized in that: In step 1, the method for preparing the extruded tube is to use an extruded or forged rod to drill a hole to prepare a hollow ingot for secondary hot extrusion to obtain an extruded tube with a diameter-to-thickness ratio of 6 to 10, that is, a tube of φ32 to 52×3 to 8×L mm.

3. The method for preparing a niobium alloy precision capillary according to claim 1, characterized in that: In step 1, the method for preparing the drilled tube blank is to drill a completely recrystallized annealed φ30-50 mm rod blank to prepare a hollow tube blank. The diameter-to-thickness ratio of the tube blank, that is, the ratio of the outer diameter of the tube to the wall thickness, is controlled at 6-10, that is, a φ30-50×3-8×L mm tube blank.

4. The method for preparing a niobium alloy precision capillary according to claim 1, characterized in that: In step 2, if the outer surface of the rod blank or the tube blank has been machined, there is no need to continue with the outer surface peeling.

5. The method for preparing a niobium alloy precision capillary according to claim 1, characterized in that: In step 2, the peeling amount on one side is 0.5-1mm.

6. The method for preparing a niobium alloy precision capillary according to claim 1, characterized in that: In step 3, the processing rate is ≤45% and the feed amount is 2 to 4 mm.

7. The method for preparing a niobium alloy precision capillary according to claim 1, characterized in that: In step 4, a cleaning agent is added to the hot water or an ultrasonic cleaning device is added; the pickling solution is a mixture of H2SO4, HF, HNO3 and water in a certain proportion.

8. The method for preparing a niobium alloy precision capillary according to claim 1, characterized in that: In step 10, the pickling time is 0.3 to 0.6 times the pickling time in step 4.

9. The method for preparing a niobium alloy precision capillary according to claim 1, characterized in that: In step 11, the pipe with an outer diameter greater than 10 mm is cut and trimmed using a pipe cutting machine, and the pipe with an outer diameter less than 10 mm is cut and trimmed using a wire cutting machine.

10. A niobium alloy precision capillary, characterized in that: A Nb521 alloy precision capillary of φ2.0-3.0×0.2-0.7×L mm is prepared by any one of claims 1-9.

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