Molybdenum-rhenium alloy thin-wall pipe introduced with multiple times of extrusion and preparation method

Abstract

The invention relates to a molybdenum-rhenium alloy thin-wall pipe introduced with multiple times of extrusion and a preparation method, and aims to solve the problems of small extrusion ratio, non-uniform grain size and mixed crystal phenomenon in the existing molybdenum-rhenium alloy pipe preparation process. The preparation method comprises the following steps: S1, uniformly mixing molybdenum powder and rhenium powder, pressing and sintering to obtain a molybdenum-rhenium alloy electrode; s2, vacuum electron beam melting is conducted on the molybdenum-rhenium alloy electrode, and a molybdenum-rhenium alloy melting ingot blank is obtained; s3, the molybdenum-rhenium alloy smelting ingot blank is extruded and annealed at least twice, and an extruded bar blank is obtained; s4, processing the extruded bar blank to obtain a pipe blank; s5, the pipe blank is subjected to multi-pass warm rolling, and a rolled pipe blank is obtained; and S6, the rolled pipe blank is subjected to aftertreatment, and the molybdenum-rhenium alloy thin-wall pipe is obtained. According to the method, through the innovative process of replacing forging with extrusion, multiple times of extrusion are introduced to replace traditional forging, crystal grains are fully refined, the large extrusion ratio is achieved, and meanwhile the molybdenum-rhenium alloy thin-wall pipe with uniform and clear crystal grains and excellent mechanical performance is prepared.

Description

Technical Field

[0001] This invention relates to the field of deformation processing technology for refractory metal molybdenum-rhenium alloys, and particularly to a thin-walled molybdenum-rhenium alloy tube produced by multiple extrusion processes and its preparation method. Background Technology

[0002] With the development of fourth-generation nuclear energy systems (such as ultra-high temperature gas-cooled reactors and molten salt reactors), the working environment of reactor cores is becoming increasingly extreme, with core temperatures generally exceeding 1000°C. This is accompanied by complex conditions such as high-dose neutron radiation and intense corrosion from liquid metals or molten salts, placing near-stringent demands on the key structural materials within the reactor core. Against this backdrop, traditional zirconium alloys, austenitic stainless steels, and even nickel-based high-temperature alloys are no longer sufficient to meet long-term service requirements. Therefore, refractory metals with extremely high melting points, excellent high-temperature strength, good resistance to radiation swelling, and high thermal conductivity, such as tungsten (W) and molybdenum (Mo) and their alloys, have become the preferred materials for next-generation nuclear reactors, especially for core components such as core cladding tubes and fuel assemblies.

[0003] Preparing reactor core cladding requires not only mastering the preparation technology of refractory metal alloys but also possessing the ability to form thin-walled tubes. Among many refractory metals, molybdenum alloys have attracted much attention due to their relatively good processing performance and low cost. However, pure molybdenum itself exhibits significant intrinsic brittleness, limiting its forming, processing, and application reliability in engineering. The "rhenium (Re) effect" offers a direction for improving this problem: adding a certain proportion of rhenium to molybdenum can significantly increase the recrystallization temperature of the alloy, enhance its strength and plasticity at room temperature and high temperatures, effectively reduce the ductile-brittle transition temperature, and improve its weldability. Therefore, molybdenum-rhenium (Mo-Re) alloys are considered highly promising core cladding materials for certain reactor types with special requirements.

[0004] Currently, commonly used methods for preparing molybdenum-rhenium alloys include traditional powder metallurgy and vacuum electron beam melting. However, molybdenum-rhenium alloys prepared by traditional powder metallurgy may have porosity defects, leading to low billet density and reduced weldability of the reactor core cladding. In contrast, molybdenum-rhenium alloys prepared by vacuum electron beam melting have lower content of gaseous and other impurity elements and higher billet density, but the ingots have coarse grains and are prone to cracking due to deformation, making billet preparation and tube rolling extremely difficult.

[0005] However, for the forming of molybdenum-rhenium alloy tubes, existing technologies mostly employ a "extrusion + forging" or "single extrusion + rolling" process. For example, patent CN111036893A uses steps such as powder metallurgy billet preparation, billet forging, tube extrusion, and heat treatment to prepare molybdenum-rhenium alloy tubes. However, due to limitations of traditional powder metallurgy methods, the impurity and gas content of the molybdenum-rhenium alloy billet is relatively high, and the extrusion ratio is small (approximately 2.4–9.4). Patent CN117443937A uses steps such as vacuum electron beam melting to prepare billets, billet extrusion, billet forging, and tube rolling to prepare molybdenum-rhenium alloy tubes with a large aspect ratio. However, due to the limitations of the extrusion process and equipment, there are still problems such as a small single-pass extrusion ratio (approximately 3.5–5) and obvious mixed crystal phenomena, which prevent sufficient recrystallization to refine the grains. Summary of the Invention

[0006] To address the aforementioned problems, this invention aims to provide a thin-walled molybdenum-rhenium alloy tube with multiple extrusion processes and its preparation method. Addressing the issues of low extrusion ratio and poor grain refinement in existing molybdenum-rhenium alloy tubes, this invention utilizes a synergistic method of multiple extrusion and warm rolling processes to achieve the preparation of thin-walled molybdenum-rhenium alloy tubes with a high extrusion ratio, fine grain structure, and high surface quality.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a method for preparing a thin-walled molybdenum-rhenium alloy tube, comprising the following steps: S1: Molybdenum powder and rhenium powder are mixed evenly, pressed and sintered to obtain a molybdenum-rhenium alloy electrode; S2: The molybdenum-rhenium alloy electrode is subjected to vacuum electron beam melting to obtain a molybdenum-rhenium alloy ingot. S3: The molybdenum-rhenium alloy smelting ingot is subjected to at least two extrusions and annealings to obtain an extruded bar billet; S4: Deep drilling, internal honing, and external diameter machining are performed on the extruded bar blank to obtain a tube blank; S5: The tube blank is cleaned and preheated, and then subjected to multi-pass diameter reduction finishing rolling and annealing to obtain the rolled tube blank; S6: Post-process the rolled tube blank to obtain a thin-walled molybdenum-rhenium alloy tube.

[0008] Furthermore, in step S1, the mass percentage of rhenium in the molybdenum-rhenium alloy powder is 5% to 25%, with the remainder being molybdenum.

[0009] Furthermore, in step S2, the vacuum electron beam melting is performed at least twice, the ingot pulling speed is 5~10mm / min, and the ingot puller adopts an up-and-down reciprocating spiral pulling motion.

[0010] Furthermore, step S3 includes a first extrusion and annealing, a second extrusion and annealing, and surface defect detection and high-temperature protective coating treatment are performed before each extrusion, and a glass lubricant is used.

[0011] Furthermore, before each extrusion, the extrusion die is preheated to 300℃~500℃.

[0012] Furthermore, the annealing process after the first extrusion is (1100℃~1600℃)×(0.5~1.5h), and the annealing process after the second extrusion is (1500℃~1700℃)×(0.5~2h).

[0013] Furthermore, in step S6, the multi-pass diameter reduction finishing rolling process uses induction coils for online heating or hydrogen ignition heating, with a heating temperature of 500~800℃, 2~4 rolling passes, and the cross-sectional deformation of each pass is 30%~80%.

[0014] Furthermore, during the rolling process, the feed amount of the tube in each stroke is 1~5mm, the tube rotation angle is 45~65°, and the rolling speed is 150~200mm / s.

[0015] On the other hand, the present invention also provides a molybdenum-rhenium alloy thin-walled tube prepared using the preparation method of the molybdenum-rhenium alloy thin-walled tube as described above.

[0016] Furthermore, this invention also provides the application of molybdenum-rhenium alloy thin-walled tubing in key equipment such as nuclear reactor core cladding materials, nuclear energy systems, and spacecraft propulsion systems.

[0017] The beneficial effects of this invention are: compared with the prior art, the improvement of this invention lies in that... 1. This invention replaces the traditional single deformation of the "extrusion + forging" process by introducing two or more hot extrusion and intermediate annealing processes, achieving a large extrusion ratio (approximately 13:1). The multiple large-deformation extrusions thoroughly break down the original coarse cast structure, and combined with a precisely controlled annealing process, promotes complete dynamic and static recrystallization, resulting in a fine, uniform, and distinct equiaxed grain structure, significantly improving the material's comprehensive mechanical properties. This preparation method can design different extrusion cycles according to different composition requirements and pipe size requirements. Combined with multi-pass warm rolling processes, the resulting molybdenum-rhenium alloy thin-walled pipes are suitable for various molybdenum-rhenium alloy compositions, with diverse product sizes and specifications, suitable for mass industrial production, and possess advantages such as good surface quality, fine and uniform grains, no mixed crystal phenomenon, and diverse size specifications.

[0018] 2. This invention effectively prevents oxidation of the material during heating by inspecting the surface defects of the billet and spraying it with a high-temperature resistant protective coating before extrusion. This reduces surface cracks during extrusion, reduces friction, alleviates thermal stress, and significantly improves the stability and yield of the extrusion process. Furthermore, by precisely controlling the extrusion temperature and effectively lubricating at high temperatures, near-isothermal extrusion is achieved, reducing friction and temperature gradient between the billet and the die, lowering deformation resistance, and thus improving the surface quality and internal structure uniformity of the extruded billet.

[0019] 3. This invention employs a combined heating method of "preheating + online induction heating" for multi-pass temperature rolling. Preheating ensures the uniformity of the initial temperature of the billet, while the in-situ follow-up induction heating during the rolling process effectively compensates for the rapid heat loss during the rolling of thin-walled tubes, ensuring that deformation always occurs within the optimal plastic temperature range, and avoiding cracking and abnormal structure caused by uneven or excessively low temperatures. Alternatively, hydrogen ignition heating can be used, utilizing the reducing atmosphere formed by hydrogen combustion to effectively inhibit oxidation on the tube surface and ensure the surface quality of the tube.

[0020] 4. This invention employs a "large deformation rolling + recrystallization annealing" process. Large deformation rolling introduces a large number of dislocations into the material and accumulates sufficient deformation energy, providing ample driving force for subsequent recrystallization. Combined with subsequent recrystallization annealing, it promotes the formation of new fine equiaxed crystals through recrystallization nucleation and grain growth, ultimately significantly refining the material's grain size and improving grain morphology uniformity. Through three-pass rolling and three-stage recrystallization annealing, the high deformation in the first two passes fully refines the grains, while the final pass moderately converges to stabilize the microstructure and improve surface quality. The process design is scientific and reasonable, resulting in a significant grain refinement effect. Attached Figure Description

[0021] Figure 1 This is a process flow diagram of the preparation method of the molybdenum-rhenium alloy thin-walled tube of the present invention.

[0022] Figure 2 This is the extruded billet obtained after one extrusion and annealing during the preparation of Mo-8Re alloy thin-walled tubes according to the present invention.

[0023] Figure 3 This invention relates to the extruded billet obtained after secondary extrusion and annealing during the preparation of Mo-8Re alloy thin-walled tubes.

[0024] Figure 4 The image shows the finished Mo-8Re alloy thin-walled tube prepared according to the present invention.

[0025] Figure 5 The ultrasonic test results are for the Mo-8Re alloy thin-walled tube prepared according to the present invention.

[0026] Figure 6 The image shows the metallographic structure of the cross-section of the Mo-8Re alloy thin-walled tube prepared according to the present invention at 200 μm.

[0027] Figure 7 The image shows the metallographic structure of the cross-section of the Mo-8Re alloy thin-walled tube prepared according to the present invention at 50 μm.

[0028] Figure 8 This is a grain size distribution diagram of the cross-section of the Mo-8Re alloy thin-walled tube prepared according to the present invention. Detailed Implementation

[0029] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0030] See attached document Figure 1 As shown, this invention provides a method for preparing a thin-walled molybdenum-rhenium alloy tube through multiple extrusion processes. This method utilizes the synergistic effect of multiple extrusion and warm rolling processes to ultimately produce a thin-walled molybdenum-rhenium alloy tube with a high extrusion ratio, fine grain structure, and high surface quality. Furthermore, the resulting thin-walled molybdenum-rhenium alloy tube can be used as a core cladding material in the nuclear field. The specific preparation method of the thin-walled molybdenum-rhenium alloy tube of this invention is as follows: S1: Preparation of molybdenum-rhenium alloy electrode: Molybdenum powder and rhenium powder are mixed, pressed, and sintered to obtain molybdenum-rhenium alloy electrode.

[0031] Specifically: the molybdenum powder and rhenium powder are selected from high-purity molybdenum-rhenium powders with a purity ≥99.99% and a Fisher particle size of 2.0~5.0μm (preferably 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm); the molybdenum powder and rhenium powder are mixed evenly in a three-dimensional mixer according to a predetermined ratio to obtain molybdenum-rhenium alloy powder. The composition of the molybdenum-rhenium alloy powder is: rhenium 5~25% (preferably 7%, 9%, 11%, 13%). The molybdenum-rhenium alloy powder is then loaded into a pressing mold and subjected to cold isostatic pressing at a pressure of 150-250 MPa (preferably 160 MPa, 170 MPa, 180 MPa, 190 MPa, 200 MPa, 210 MPa, 220 MPa, 230 MPa, or 240 MPa). The holding time is 5-30 min (preferably 10 min, 15 min, 20 min, 25 min); the molybdenum-rhenium alloy powder is pressed into a compact with a diameter of 40-80 mm (preferably 50 mm, 60 mm, 70 mm) and a length of 500-1000 mm (preferably 550 mm, 600 mm, 650 mm, 700 mm, 750 mm, 800 mm, 850 mm, 900 mm, 950 mm), which is a slender round bar; then the compact is placed in a hydrogen-protected high-temperature furnace and pressureless sintering is performed under hydrogen protection at a sintering temperature of 1900-2250℃ (preferably 1950℃, 2000℃, 2050℃, 2100℃, 2150℃, 2200℃) and a holding time of 3-8 h (preferably 4 h, 5 h, 6 h, 7 h) to obtain a molybdenum-rhenium alloy electrode.

[0032] S2: Vacuum electron beam melting: The molybdenum-rhenium alloy electrode is melted by vacuum electron beam to obtain a molybdenum-rhenium alloy ingot.

[0033] Specifically: The molybdenum-rhenium alloy electrode obtained in S1 is placed in a melting crucible and subjected to three vacuum electron beam melting processes. The ingot pulling speed during the melting process is 5~10 mm / min (preferably 6 mm / min, 7 mm / min, 8 mm / min, and 9 mm / min) to obtain a molybdenum-rhenium alloy molten ingot. The three vacuum electron beam melting processes make the purification of the molybdenum-rhenium alloy electrode more thorough. The first two low-speed melting processes enhance impurity volatilization by extending the residence time in the molten pool and lay a high-purity foundation based on stable thermodynamic conditions in the molten pool. The third speed-up process promotes composition homogenization by enhancing convection in the molten pool, while shortening the melting cycle to reduce alloy element volatilization loss and process energy consumption. During the vacuum electron beam melting process, the ingot puller adopts an up-and-down reciprocating spiral downward motion, which is conducive to the uniform distribution of alloy composition in the ingot and the removal of interstitial impurities, avoiding defects such as porosity and segregation in the ingot during the melting process.

[0034] S3: Extrusion and annealing: The molybdenum-rhenium alloy smelting ingot is subjected to at least two extrusions and annealings to obtain an extruded bar billet.

[0035] Specifically: the extrusion and annealing are performed twice, namely a first extrusion and annealing and a second extrusion and annealing. The molybdenum-rhenium alloy smelting billet obtained in S2 is subjected to the first extrusion and annealing and the second extrusion and annealing to obtain the extruded billet. Alternatively, more than two extrusions and annealings can be performed. The specific number of extrusions and annealings is selected according to the specific requirements of the molybdenum-rhenium alloy thin-walled tube to be prepared. Before each extrusion, the opening defects of the billet need to be tested by penetrant testing to accurately identify potential surface defects such as cracks and pinholes, so as to ensure the stable operation of the subsequent extrusion process. A high-temperature resistant protective coating is also sprayed to avoid material oxidation during the induction heating process.

[0036] The surface of the molybdenum-rhenium alloy smelted ingot is machined to remove surface defects. The extrusion die is then preheated to 300℃~500℃ (preferably 350℃, 400℃, or 450℃). The machined ingot is then placed on a horizontal extrusion press and extruded once using the die. During the first extrusion, a glass lubricating pad is used to lubricate the ingot, and a hydrogen furnace is used to heat it to 1200~1500℃ (preferably 1250℃, 1300℃, 1350℃, 1400℃, or 1450℃), holding it for 1~2 hours (preferably 1.5 hours). The extrusion speed is 40~70 mm / s (preferably 45 mm / s). The extrusion speeds are 50 mm / s, 55 mm / s, 60 mm / s, and 65 mm / s. After extrusion, the billet is straightened, machined, cut into sections, and annealed at 1200℃~1700℃ (preferably 1200℃, 1250℃, 1300℃, 1350℃, 1400℃, 1450℃, 1500℃, 1550℃, 1600℃, 1650℃, and 1700℃) for 30~90 min (preferably 45 min, 60 min, and 75 min). The annealing process after extrusion is (1100℃~1600℃)×(0.5~1.5h). After annealing, a single-extrusion billet is obtained.

[0037] The primary extruded billet is then heated in an induction heating furnace and transferred to a horizontal extruder for secondary extrusion. Simultaneously, a high-temperature glass lubricant is applied to the surface of the primary extruded billet using a rolling method for lubrication. The heating temperature during extrusion is 1350~1700℃ (preferably 1400℃, 1450℃, 1500℃, 1550℃, 1600℃, 1650℃), the heating time is 5~20min (preferably 10min, 15min), and the extrusion speed is 20~50mm / s (preferably 25mm / s, 30mm / s, 35mm / s, 40mm / s, 45mm / s). s); then the primary extruded billet after secondary extrusion is straightened, surface-machined and cut into sections, and then subjected to secondary annealing at a temperature of 1200℃~1700℃ (preferably 1200℃, 1250℃, 1300℃, 1350℃, 1400℃, 1450℃, 1500℃, 1550℃, 1600℃, 1650℃, 1700℃) for a time of 30~120min (preferably 45min, 60min, 75min, 90min, 105min). That is, the annealing regime after secondary extrusion is (1500℃~1700℃)×(0.5~2h) to obtain extruded bar billets.

[0038] In the above extrusion process, if the extrusion speed is too low, the temperature of the billet will drop too quickly during the extrusion process, which will cause the billet to crack. If the extrusion speed is too high, the requirements of the hydraulic system of the equipment will be too high, which will lead to extrusion difficulties. Therefore, controlling the extrusion speed within the above range can avoid the situation where the deformation resistance increases due to the excessive extrusion ratio, which in turn leads to extrusion difficulties or billet cracking.

[0039] S4: Tube blank processing: Deep drilling, internal honing and external diameter turning are performed on the extruded bar blank to obtain the tube blank.

[0040] Specifically: The extruded bar billet is pierced using machining equipment to obtain the required inner hole size. The outer diameter of the resulting tube billet is 15~35mm (preferably 18mm, 21mm, 24mm, 27mm, 30mm, 33mm), the wall thickness is 1~5mm (preferably 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm), and the length is 300~900mm (preferably 350mm, 400mm, 450mm, 500mm, 550mm, 600mm, 650mm, 700mm, 750mm, 800mm, 850mm).

[0041] By combining two extrusion processes (S3 and S4) with machining, the resulting billet has finer grains and lower deformation resistance. This innovative "extrusion-instead-of-forging" process allows the molybdenum-rhenium alloy to withstand a triaxial compressive stress field within the die cavity during extrusion, achieving a significant grain refinement effect. Simultaneously, the continuous plastic deformation of extrusion effectively breaks up dendritic structures and eliminates grain boundary segregation, greatly improving the uniformity of alloy composition and microstructure. In contrast, the periodic impact deformation of forging easily leads to uneven deformation and incomplete recrystallization in localized areas, resulting in inferior grain refinement and microstructure uniformity compared to extrusion.

[0042] The formation of a fine-grained structure and uniform flow lines through extrusion can reduce the deformation resistance of molybdenum-rhenium alloys, widen their hot working window, and make them more susceptible to plastic deformation in subsequent warm rolling processes. This also effectively avoids the risk of cracking due to excessive deformation resistance. In contrast, forged molybdenum-rhenium alloys, due to their coarser grains and greater deformation resistance, are more sensitive to temperature drops during hot working, resulting in a significantly increased tendency to crack.

[0043] Extrusion is a near-net-shape forming process that can directly produce billets with dimensions close to the finished product, with less machining allowance. In contrast, forging requires a larger machining allowance. For rare and difficult-to-deform metals such as molybdenum-rhenium alloys, extrusion can achieve a dual optimization of economy and processing efficiency while ensuring microstructure and properties.

[0044] S5: Multi-pass warm rolling: The tube blank is cleaned and preheated, and then subjected to multi-pass diameter reduction finishing rolling and annealing to obtain the rolled tube blank.

[0045] Specifically: the rolls in the rolling mill are made of hot-work die steel, and the mandrel and mandrel rod are made of nickel-based high-temperature alloy to reduce the impact of temperature rise on the rolls. Before rolling, the billet is cleaned, then inserted into the mandrel and placed in a hydrogen furnace for preheating at a temperature of 300~500℃ (preferably 325℃, 350℃, 375℃, 400℃, 425℃, 450℃, 475℃). After preheating, the billet is transferred to the rolling mill for rolling. During the rolling process, online real-time heating or hydrogen ignition heating is implemented. Hydrogen ignition heating can effectively inhibit the oxidation of the pipe surface by utilizing the reducing atmosphere formed by hydrogen combustion, ensuring the surface quality of the pipe. Online real-time heating uses induction coil heating, which has less heat loss and more precise temperature control. The heating temperature during the rolling process is 500~800℃ (preferably 525℃, 550℃, 575℃, 600℃, 625℃, 650℃, 675℃, 700℃, 725℃, 750℃, 775℃); during the billet rolling process, the feed amount of the tube per stroke is 1~5mm (preferably 2mm, 3mm, 4mm), and the tube rotation angle is 45~65° (preferably 47°, 50°, 55°). The rolling angles are 2°, 55°, 57°, 60°, and 62°, with a rolling speed of 150~200 mm / s (preferably 160 mm / s, 170 mm / s, 180 mm / s, and 190 mm / s). The tube blank is rolled in 3 passes, and the intermediate tube blank is annealed after each pass at a temperature of 1200℃~1700℃ (preferably 1200℃, 1250℃, 1300℃, and 1350℃). The temperature is set at 1400℃, 1450℃, 1500℃, 1550℃, 1600℃, 1650℃, and 1700℃, with a holding time of 0.5~2h (preferably 0.75h, 1h, 1.25h, 1.5h, and 1.75h), and the cooling method is air cooling. After three passes of rolling, the cross-sectional deformation is 45%~60% (preferably 48%, 50%, 53%, 55%, and 58%) in the first pass, 45%~60% (preferably 48%, 50%, 53%, 55%, and 58%) in the second pass, and 40%~50% (preferably 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, and 49%) in the third pass. The cross-sectional deformation is calculated as (cross-sectional area before deformation - cross-sectional area after deformation) / cross-sectional area before deformation. Finally, the tube blank is straightened by heating to obtain the rolled tube blank.

[0046] In the above process, the molybdenum-rhenium tube, due to its thin wall, cools down quickly. Real-time online heating ensures smooth rolling deformation. Furthermore, the method of preheating followed by real-time online heating fully guarantees that the molybdenum-rhenium alloy deforms within the optimal deformation temperature range, avoiding problems such as abnormal grain structure and cracking caused by excessively low or high temperatures or uneven heating. Controlling the preheating temperature within the above range achieves the preheating purpose while preventing grain growth in the billet. Controlling the real-time online heating temperature within the above range ensures equipment precision and accurate temperature control while also preventing grain growth in the billet. Furthermore, the rolling process with large deformation can introduce a large number of dislocations into the material and accumulate deformation energy, providing sufficient driving force for recrystallization. Combined with subsequent recrystallization annealing, it can promote the formation of new fine equiaxed crystals through recrystallization nucleation and grain growth, achieving significant refinement of the material grain size and improving the uniformity of grain morphology. Moreover, the deformation of the billet in the three rolling passes adopts a decreasing scheme of high deformation at the beginning and low deformation at the end. The high deformation in the first two passes activates dislocation proliferation and dynamic recrystallization, laying the foundation for enhanced phase precipitation. The final pass moderately converges to protect the stability of the structure, while reducing equipment load and improving surface quality.

[0047] S6: Post-processing of rolled tube blank: The rolled tube blank obtained in S6 is post-processed to obtain molybdenum-rhenium alloy thin-walled tube.

[0048] Specifically: The rolled tube is straightened, alkaline washed, and then the inner hole is honed to obtain a molybdenum-rhenium alloy thin-walled tube with an outer diameter of 5~15mm (preferably 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm), a wall thickness of 0.5~1mm (preferably 0.6mm, 0.7mm, 0.8mm, 0.9mm), and a length ≤500mm (preferably 450mm, 400mm, 350mm, 300mm, 250mm, 200mm, 150mm, 100mm).

[0049] Example 1: This embodiment prepares Mo-8Re alloy using the above-described method for preparing thin-walled molybdenum-rhenium alloy tubing. The specific preparation process is as follows: 1. Preparation of Molybdenum-Rhenium Alloy Electrode: Molybdenum powder with a purity of 99.99% and a Fisher particle size of 2.5μm and rhenium powder were mixed evenly in a three-dimensional mixer at a mass ratio of 92:8 to obtain Mo-8Re alloy powder; the powder was then cold isostatically pressed into a Φ65×600mm blank under a pressure of 230MPa; the pressed blank was then placed in a hydrogen-protected high-temperature furnace for sintering at a temperature of 2000℃ for a holding time of 7h to obtain the Mo-8Re alloy electrode.

[0050] 2. Vacuum electron beam melting: The sintered Mo-8Re alloy electrode is subjected to three electron beam melting processes to obtain a molybdenum-rhenium alloy ingot. The first two melting processes use crucibles with a diameter of 120 mm and a pulling speed of 6.7 mm / min. The third melting process uses crucibles with a diameter of 160 mm and a pulling speed of 5.5 mm / min. During the melting process, the ingot puller adopts a reciprocating spiral downward motion to obtain the Mo-8Re alloy ingot.

[0051] 3. Extrusion and annealing: 3.1 Primary Extrusion and Annealing: A high-temperature protective coating was applied to the surface of the obtained Mo-8Re alloy smelted ingot, followed by rapid application of a high-temperature resistant glass lubricant. The surface was then machined, and the ingot was cut into 320mm lengths and extruded on a 2800t horizontal extrusion press. The extrusion cylinder diameter was Φ155mm, the die inner diameter was 70mm, the die preheating temperature was 350℃, the extrusion heating temperature was 1350℃, and the holding time was 1h. The extrusion speed was 65mm / s. After straightening, the extruded Mo-8Re alloy smelted ingot was machined and cut into sections to obtain billets with a diameter of 65mm and a length of 250mm. These billets were then annealed at 1450℃ for 1h to obtain the primary extruded Mo-8Re alloy billet. For details of the primary extruded Mo-8Re alloy billet, please refer to the appendix. Figure 2 As shown.

[0052] 3.2 Secondary Extrusion and Annealing: The surface of the obtained Mo-8Re alloy primary extrusion billet was coated with a high-temperature protective coating, heated to 1600℃ in an induction heating furnace, and then rapidly rolled with a high-temperature resistant glass lubricant. It was then transferred to a 1000t horizontal extrusion press for extrusion. The extrusion die inner diameter was 40mm, the extrusion temperature was 1520℃, and the extrusion speed was 35mm / s. After secondary extrusion, the primary extrusion billet was straightened, its surface was machined, and it was cut into sections to obtain billets with a diameter of 35mm and a length of 450mm. A secondary annealing was then performed at 1650℃ for 1.5h to obtain Mo-8Re alloy extrusion bars. For details of the Mo-8Re alloy extrusion bars, please refer to the appendix. Figure 3 As shown.

[0053] 4. Tube blank processing: The obtained Mo-8Re alloy extruded bar blank is machined by hollowing, honing the inner hole and turning the outer diameter to obtain the tube blank required for rolling with an outer diameter of 22mm, a wall thickness of 3mm and a length of 560mm. 5. Multi-pass warm rolling: The tube blanks required for rolling are cleaned and preheated in a hydrogen furnace to 300℃. They are then transferred to the rolling mill, where they are heated in real-time by a main induction coil fixed to the mill stand at 800℃. During Pilger warm rolling, the feed rate for each stroke is planned to be 3mm, the tube rotation angle to be planned to be 55°, and the rolling speed to be 165mm / s. After each pass, the intermediate tube blanks are annealed at 1100℃ for 2 hours, and air-cooled. The cross-sectional deformation is 52.5% in the first pass, 50.8% in the second pass, and 47.6% in the third pass, ultimately yielding the rolled tube blank.

[0054] 6. Post-processing of rolled tube blank: The rolled tube blank obtained after multiple warm rolling passes is straightened, surface treated, and the inner hole is honed to finally obtain a finished Mo-8Re alloy thin-walled tube with an outer diameter of 9mm, a wall thickness of 0.7mm, and a length of 500mm. The finished Mo-8Re alloy thin-walled tube is shown in the attached figure. Figure 4 As shown.

[0055] Example 2: This embodiment conducts a series of performance tests on the Mo-8Re alloy thin-walled tube prepared in Example 1 to ensure that the various properties of the prepared Mo-8Re alloy thin-walled tube meet the required usage requirements. Specifically: See attached document Figure 5 As shown, the prepared Mo-8Re alloy thin-walled tube was subjected to ultrasonic performance testing (in accordance with GJB1580A-2019 "Ultrasonic Testing Method for Deformed Metals"). The ultrasonic test results showed that there were no flat-bottom hole equivalent defects with a diameter greater than or equal to 1.0 mm. This indicates that the molybdenum-rhenium alloy thin-walled tube prepared by the above method is of good quality, meets the requirements for use, and the performance of the finished product is stable and reliable, and it can be put into use.

[0056] The composition of the prepared Mo-8Re alloy thin-walled tubes was analyzed, and the impurity content was found to be: O ≤ 0.0034%, Ni ≤ 0.0005%, and Fe ≤ 0.0010%. This composition analysis indicates that the molybdenum-rhenium alloy thin-walled tubes prepared by the above method have high purity, ensuring good room temperature plasticity and a high recrystallization temperature, reducing grain boundary weakening, and improving the overall strength and reliability of the molybdenum-rhenium alloy thin-walled tubes.

[0057] The prepared Mo-8Re alloy thin-walled tubes were subjected to room temperature tensile tests (according to GB / T228.1-2010 "Metallic materials - Tensile testing - Part 1 - Room temperature test method"). The test results showed that the tensile strength was greater than 700 MPa and the elongation was greater than 15%. The tensile test results indicate that the molybdenum-rhenium alloy thin-walled tubes prepared by the above method can withstand very high loads without breaking, and have strong load-bearing capacity and structural safety. At the same time, they can effectively alleviate stress concentration and avoid sudden brittle fracture.

[0058] See attached document Figure 6-8 As shown, metallographic analysis was performed on the finished Mo-8Re alloy thin-walled tubing. Figure 6 and Figure 7 It is evident that an equiaxed crystal structure with good uniformity was formed, by Figure 8 It is evident that the grain size distribution exhibits good consistency with the Gaussian fitting curve, with the main grain size concentrated between 40 and 60 μm. This indicates that the grain size of the molybdenum-rhenium alloy thin-walled tubing prepared using the above method is approximately equal in all directions. Figure 7 It can also be seen that the grain size, shape and distribution are highly consistent throughout the observation area, with no abnormally large grains or severe mixed crystal phenomenon, which improves the uniformity of the mechanical properties of the molybdenum-rhenium alloy thin-walled tube in all directions, and thus improves the reliability of the molybdenum-rhenium alloy thin-walled tube under complex stress.

[0059] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a thin-walled molybdenum-rhenium alloy tube, characterized in that: Includes the following steps: S1: Molybdenum powder and rhenium powder are mixed evenly, pressed, and sintered to obtain a molybdenum-rhenium alloy electrode; S2: The molybdenum-rhenium alloy electrode is subjected to vacuum electron beam melting to obtain a molybdenum-rhenium alloy ingot. S3: The molybdenum-rhenium alloy smelting ingot is subjected to at least two extrusions and annealings to obtain an extruded bar billet; S4: Deep drilling, internal honing, and external diameter machining are performed on the extruded bar blank to obtain a tube blank; S5: The tube blank is cleaned and preheated, and then subjected to multi-pass diameter reduction finishing rolling and annealing to obtain the rolled tube blank; S6: Post-process the rolled tube blank to obtain a thin-walled molybdenum-rhenium alloy tube.

2. The method for preparing the molybdenum-rhenium alloy thin-walled tube according to claim 1, characterized in that: In step S1, the mass percentage of rhenium in the molybdenum-rhenium alloy powder is 5% to 25%, with the remainder being molybdenum.

3. The method for preparing the molybdenum-rhenium alloy thin-walled tube according to claim 1, characterized in that: In step S2, the vacuum electron beam melting is performed no less than twice, the ingot pulling speed is 5~10mm / min, and the ingot puller adopts an up-and-down reciprocating spiral pulling motion.

4. The method for preparing the molybdenum-rhenium alloy thin-walled tube according to claim 1, characterized in that: Step S3 includes a first extrusion and annealing, a second extrusion and annealing, and surface defect detection and high-temperature protective coating treatment are performed before each extrusion, and glass lubricant is used.

5. The method for preparing the molybdenum-rhenium alloy thin-walled tube according to claim 4, characterized in that: Before each extrusion, the extrusion die is preheated to 300℃~500℃.

6. The method for preparing the molybdenum-rhenium alloy thin-walled tube according to claim 4, characterized in that: The annealing process after the first extrusion is (1100℃~1600℃)×(0.5~1.5h), and the annealing process after the second extrusion is (1500℃~1700℃)×(0.5~2h).

7. The method for preparing the molybdenum-rhenium alloy thin-walled tube according to claim 1, characterized in that: In step S6, the multi-pass diameter reduction finishing rolling process uses induction coils for online heating or hydrogen ignition heating, with a heating temperature of 500~800℃, 2~4 rolling passes, and cross-sectional deformation of 30%~80% for each pass.

8. The method for preparing the molybdenum-rhenium alloy thin-walled tube according to claim 7, characterized in that: During the rolling process, the feed amount of the tube in each stroke is 1~5mm, the tube rotation angle is 45~65°, and the rolling speed is 150~200mm / s.

9. A molybdenum-rhenium alloy thin-walled tube prepared by the method for preparing molybdenum-rhenium alloy thin-walled tubes according to any one of claims 1-8.

10. The application of the molybdenum-rhenium alloy thin-walled tube as described in claim 9 in key equipment such as nuclear reactor core cladding materials, nuclear energy systems, and spacecraft propulsion systems.

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