Large-specification high-purity molybdenum-rhenium alloy pipe and preparation method thereof

Abstract

The invention belongs to the technical field of metal pipe machining, and particularly relates to a preparation method of a large-size high-purity molybdenum-rhenium alloy pipe. According to the method, the large-size high-purity molybdenum-rhenium alloy pipe is prepared through the steps of (1) molybdenum-rhenium alloy ingot blank high-purity preparation, (2) surface turning, (3) molybdenum-rhenium alloy pipe blank high-speed near-isothermal extrusion, (4) high-temperature spinning forming, (5) recrystallization annealing treatment, (6) surface finish machining treatment and the like. According to the large-size molybdenum-rhenium alloy pipe prepared through the method, the mode of controlling the electron beam scanning track is adopted, the electron beam power during raw material melting and refining is reasonably distributed, the ingot casting specification of molybdenum-rhenium alloy is improved, a high-purity ingot blank is obtained, the mode of combining high-speed near-isothermal extrusion and high-temperature spinning is adopted, and the large-size molybdenum-rhenium alloy pipe is obtained. And the deformation uniformity of the molybdenum-rhenium alloy pipe is improved, the comprehensive performance of the molybdenum-rhenium alloy pipe is improved, and good application prospects and economic benefits are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of metal pipe processing, and in particular relates to a method for preparing a large-size high-purity molybdenum-rhenium alloy pipe. Background Art

[0002] Molybdenum-rhenium alloy (Mo-Re) is an alloy with 2% to 50% rhenium (Re) added to molybdenum (Mo) as the matrix. It has excellent high-temperature strength, good thermophysical properties and radiation resistance, and good compatibility with nuclear fuel and alkali metals Li, Na, K, which makes molybdenum-rhenium alloy the best reactor core structural material in high-temperature nuclear reactors. The core container, cladding tube and other structural components in the core structure of the new generation of nuclear reactors require large-sized molybdenum-rhenium alloy tubes with excellent mechanical and welding properties and a diameter greater than 60mm.

[0003] Molybdenum-rhenium alloy is mainly prepared by powder metallurgy and vacuum melting. However, the content of impurity elements and gas elements in molybdenum-rhenium alloy prepared by powder metallurgy is relatively high (generally, the sum of C, N, and O contents is greater than 100ppm), which makes the molybdenum-rhenium alloy pipe obtained by subsequent processing have low mechanical properties and poor welding performance and cannot meet the use requirements. Vacuum melting can obtain relatively pure molybdenum-rhenium alloy ingots, reduce the total content of gas elements to below 100ppm, and improve welding performance, but the grain size of the ingot is large. For example, the grain size of molybdenum alloy ingots melted by vacuum electron beam is generally greater than 5mm, or even greater than 20mm. Molybdenum alloy ingots need to be processed with large deformation and refined organization to obtain satisfactory mechanical properties. Therefore, large-scale high-purity ingot preparation and large deformation processing are the key to obtaining large-scale molybdenum-rhenium alloy pipes.

[0004] There are very few patents for large-scale, high-purity molybdenum-rhenium alloy pipes disclosed in the prior art. Chinese patent CN108213440A adopts a powder metallurgy method to load molybdenum-rhenium alloy powder into a specific mold, and then hot isostatic pressing to obtain a molybdenum-rhenium tube blank, and then shaping and heat treating the molybdenum-rhenium tube blank to obtain a pipe. Although the size specifications are diverse, due to the limitations of traditional powder metallurgy, the impurity and gas content of the molybdenum-rhenium alloy tube blank is inevitably high, which cannot meet the requirements of mechanical properties and welding performance. Chinese patent CN117443937A adopts vacuum electron beam melting billet preparation, tube blank preparation, tube rolling, heat treatment and other steps to achieve the preparation of large aspect ratio molybdenum-rhenium alloy seamless thin-walled pipes, but the outer diameter of the pipe is small and cannot be applied to large-size structures such as new generation nuclear reactor core containers and cladding tubes. Chinese patent CN116809682A continuously uses extrusion, forging, and rotary forging processes to improve the quality of molybdenum-rhenium alloy rods and tubes, and obtains molybdenum-rhenium alloy tubes with a diameter of Φ25.4mm. However, there is also the problem of small tube specifications. At present, only small-sized molybdenum-rhenium alloy tubes purified by vacuum melting can be prepared, and large-sized molybdenum-rhenium alloy tubes have the problem of difficulty in preparing high-purity ingots and deformation processing. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a method for preparing a large-scale high-purity molybdenum-rhenium alloy pipe, which can realize the preparation of large-scale molybdenum-rhenium alloy pipes, and specifically includes the following contents:

[0006] A method for preparing a large-scale high-purity molybdenum-rhenium alloy pipe is characterized by comprising the following steps:

[0007] (1) High purity preparation of molybdenum-rhenium alloy ingots:

[0008] The sintered molybdenum-rhenium alloy strip is purified and melted by a vacuum high-energy electron beam to obtain a molybdenum-rhenium alloy ingot;

[0009] The molybdenum-rhenium alloy ingot in step (1) has a size of Φ160-240 mm and an electron beam power of 500-700 kW;

[0010] The molybdenum-rhenium alloy billet is melted by electron beam center focusing. After the molybdenum-rhenium alloy billet is melted and flows into a water-cooled crystallizer, an electron beam scanning power supply is turned on to make the electron beam tracks equidistantly distributed at 3 / 4 to 1 / 4 of the radius of the molten pool, and the energy of the outermost electron beam track gradually decreases inward, and the refining time is maintained for 2 to 5 minutes; the molybdenum-rhenium alloy molten pool is fully decomposed, degassed, and impurities are removed, and ingots are pulled after refining. The ingot is pulled once every time the molybdenum-rhenium alloy molten pool increases by 10 to 20 mm, and after the ingot is pulled, the material is continuously fed to maintain the center focusing melting, and this process is repeated until a molybdenum-rhenium alloy ingot of a desired size is obtained;

[0011] (2) Surface turning:

[0012] Turning the molybdenum-rhenium alloy ingot obtained in step (1) to remove surface defects and obtain a bright molybdenum-rhenium alloy ingot;

[0013] (3) High-speed near-isothermal extrusion of molybdenum-rhenium alloy tube billet:

[0014] The molybdenum-rhenium alloy ingot after turning in step (2) is subjected to high-temperature and high-speed near-isothermal extrusion to prepare a molybdenum-rhenium alloy tube blank;

[0015] The extrusion temperature is 1520-1620℃, the extrusion speed is 100-140mm / s, the extrusion die preheating temperature is 850-950℃, the extrusion mandrel preheating temperature is 600-700℃, and the extrusion pad preheating temperature is 950-1050℃; the high extrusion temperature can significantly reduce the deformation resistance of the material, increase the extrusion speed, reduce heat loss during the extrusion process, and achieve near-isothermal extrusion forming. The extrusion outlet temperature of the molybdenum-rhenium alloy pipe is basically constant, and the temperature fluctuation range is controlled within ±20℃;

[0016] (4) High temperature spinning:

[0017] The molybdenum-rhenium alloy tube blank obtained in step (3) is prepared into a semi-finished tube by high-temperature spinning. Furthermore, the spinning temperature is 800-900° C., the pass thinning rate is 25%-38%, the spinning passes are 3-6 passes, and intermediate annealing is performed after every 2 spinning passes. The annealing temperature is 1300-1350° C., the holding time is 0.5-1h, the total thinning rate of high-temperature spinning is 60% or more, and the feed ratio is 0.5-1.5 mm / r;

[0018] (5) Recrystallization annealing treatment:

[0019] Recrystallization annealing, annealing temperature is 1150~1250℃, holding time is 0.5~1h;

[0020] (6) Surface finishing

[0021] The recrystallized annealed tube is surface processed to obtain a finished molybdenum-rhenium alloy tube;

[0022] The present invention provides the application of the above preparation method in the preparation of large-scale high-purity molybdenum-rhenium alloy pipes. The diameter of the molybdenum-rhenium alloy pipe is not less than 60 mm, the wall thickness is 2 to 6 mm, the C, N, and O contents are all less than 10 ppm, the tensile strength of the pipe is greater than 650 MPa, and the elongation is greater than 15%.

[0023] Beneficial effects of the present invention:

[0024] (1) The method for preparing large-scale high-purity molybdenum-rhenium alloy pipes disclosed in the present invention adopts a method of controlling the electron beam scanning trajectory to reasonably distribute the electron beam power during melting the raw material billet and refining, thereby improving the ingot specifications of the molybdenum-rhenium alloy and obtaining high-purity ingots. The contents of gas elements C, N, and O are all less than 10 ppm, ensuring the preparation of large-scale molybdenum-rhenium alloy pipes and the mechanical properties of the pipes.

[0025] (2) Isothermal extrusion refers to the extrusion of alloys at a constant outlet temperature (difference of ±20°C, preferably ±10°C). Its characteristics are that the temperature of the metal in the deformation zone of the die hole is always kept constant during the extrusion process, and the deformation resistance and fluidity of the metal are kept uniform. Isothermal extrusion can achieve the best geometric dimensions, surface quality, internal structure and physical properties of the entire product head and tail. When using traditional extrusion technology, the preheating temperature of the tool and die is low (only about 400°C), and the extrusion speed is below 45mm / s. Since the extrusion temperature of the molybdenum-rhenium alloy is as high as 1500°C, the billet temperature drops greatly during the extrusion process, and the extrusion temperature fluctuates greatly, resulting in poor consistency in the structure and performance of the extruded pipe, making the subsequent forming and processing of the pipe difficult. In view of this, the present invention adopts high-speed near-isothermal extrusion, which minimizes the die contact cooling, significantly reduces the fluctuation range of the extrusion outlet temperature, realizes near-isothermal extrusion, improves the deformation consistency of the molybdenum-rhenium alloy tube billet, and obtains high-quality extruded pipes with good consistency in structure and performance.

[0026] (3) The method for preparing large-scale high-purity molybdenum-rhenium alloy pipes disclosed in the present invention adopts a combination of high-speed extrusion and high-temperature spinning to improve the uniformity of deformation of the molybdenum-rhenium alloy pipes and improve the mechanical properties of the molybdenum-rhenium alloy pipes. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The figure is a flow chart of the preparation method of large-size high-purity molybdenum-rhenium alloy pipes. DETAILED DESCRIPTION

[0028] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments shown below do not limit the invention content recorded in the claims. In addition, the entire content of the composition represented by the following embodiments is not limited to the necessary solutions of the invention recorded in the claims.

[0029] Example 1

[0030] The flow chart of the preparation method of large-size high-purity molybdenum-rhenium alloy pipe is shown in Figure 1 , the specific steps are as follows:

[0031] (1) Purify and melt the sintered Mo-5Re alloy billet using a vacuum high-energy electron beam. The size of the Mo-5Re alloy ingot is Φ210 mm, the electron beam power is 510 kW, and the Mo-5Re alloy billet is melted by focusing the electron beam center. After the Mo-5Re alloy billet melts and flows into the water-cooled crystallizer, the electron beam scanning power supply is turned on to make the electron beam trajectory equidistantly distributed at 3 / 4 to 1 / 4 of the radius of the molten pool. The energy of the outermost electron beam trajectory gradually decreases toward the inside, and the refining time is maintained for 3 minutes. After refining, the ingot is pulled again. The ingot is pulled once every time the molten pool increases by about 10 to 20 mm, until the Mo-5Re alloy ingot length is 600 mm.

[0032] (2) removing surface defects by turning to obtain a bright Mo-5Re alloy ingot with an ingot size of Φ200×600 mm;

[0033] (3) The ingot of step (2) is subjected to high temperature and high speed near isothermal extrusion to prepare a tube billet, wherein the extrusion temperature is 1520° C., the extrusion speed is 120 mm / s, the extrusion die preheating temperature is 850° C., the extrusion mandrel preheating temperature is 600° C., the extrusion pad preheating temperature is 950° C., the temperature difference during the tube billet extrusion process is ±15° C., and the Mo-5Re alloy tube billet size after extrusion is Φ100×20 mm;

[0034] (4) the extruded tube in step (3) is subjected to inner and outer surface turning to obtain a Mo-5Re alloy spinning tube of Φ94×14 mm, and then subjected to high-temperature spinning forming, the spinning temperature is 800° C., the multi-pass spinning thinning rate is 25% to 38%, the spinning pass number is 4, and intermediate annealing is performed after every 2 spinning passes, the annealing temperature is 1300° C., the holding time is 1 h, the feed ratio is 1 mm / r, the total thinning rate of high-temperature spinning is 71.4%, and the spinning is formed into a Mo-5Re alloy tube of Φ74×4 mm;

[0035] (5) subjecting the Mo-5Re alloy tube in step (4) to recrystallization annealing at a temperature of 1150° C. and a holding time of 1 h;

[0036] (6) After recrystallization annealing, the Mo-5Re alloy tube is turned and cut on the inner and outer surfaces to obtain a high-purity Mo-5Re alloy tube with a tube specification of Φ72×2×600mm. The test analysis shows that the C, N, and O contents are all less than 10ppm (the lower limit of the existing test method), the tensile strength of the tube is 655MPa, and the elongation is 16%.

[0037] Example 2

[0038] (1) A vacuum high-energy electron beam is used to purify and melt the sintered Mo-14Re alloy billet. The size of the Mo-14Re alloy ingot is Φ210mm, the electron beam power is 540kW, and the Mo-14Re alloy billet is melted by focusing the electron beam center. After the Mo-14Re alloy billet melts and flows into the water-cooled crystallizer, the electron beam scanning power supply is turned on to make the electron beam trajectory equidistantly distributed at 3 / 4 to 1 / 4 of the radius of the molten pool. The energy of the outermost electron beam trajectory gradually decreases toward the inside, and the refining time is maintained for 3 minutes. After refining, the ingot is pulled again. The ingot is pulled once every 10 to 20 mm increase in the molten pool until the Mo-14Re alloy ingot length is 600 mm.

[0039] (2) removing surface defects by turning to obtain a bright Mo-14Re alloy ingot with an ingot size of Φ200×600 mm;

[0040] (3) The ingot of step (2) is subjected to high temperature and high speed near isothermal extrusion to prepare a tube billet, wherein the extrusion temperature is 1550°C, the extrusion speed is 120 mm / s, the extrusion die preheating temperature is 900°C, the extrusion mandrel preheating temperature is 650°C, the extrusion pad preheating temperature is 980°C, the temperature difference during the tube billet extrusion process is ±16°C, and the Mo-14Re alloy tube billet size after extrusion is Φ100×20 mm;

[0041] (4) the extruded tube in step (3) is subjected to inner and outer surface turning to obtain a Mo-14Re alloy spinning tube of Φ94×14 mm, and then subjected to high-temperature spinning forming, the spinning temperature is 850° C., the multi-pass spinning thinning rate is 25% to 38%, the spinning pass number is 4, and intermediate annealing is performed after every 2 spinning passes, the annealing temperature is 1320° C., the holding time is 1 h, the feed ratio is 1.2 mm / r, the total thinning rate of high-temperature spinning is 71.4%, and the spinning is formed into a Mo-14Re alloy tube of Φ74×4 mm;

[0042] (5) subjecting the Mo-14Re alloy tube in step (4) to recrystallization annealing at a temperature of 1200° C. and a holding time of 1 h;

[0043] (6) After recrystallization annealing, the Mo-14Re alloy tube is turned and cut on the inner and outer surfaces to obtain a high-purity Mo-14Re alloy tube with a tube specification of Φ72×2×600mm. The test analysis shows that the C, N, and O contents are all less than 10ppm (the lower limit of the existing test method), the tensile strength of the tube is 755MPa, and the elongation is 21%.

[0044] Example 3

[0045] (1) A vacuum high-energy electron beam is used to purify and melt the sintered Mo-14Re alloy billet. The size of the Mo-14Re alloy ingot is Φ190mm, the electron beam power is 510kW, and the Mo-14Re alloy billet is melted by focusing the electron beam center. After the Mo-14Re alloy billet melts and flows into the water-cooled crystallizer, the electron beam scanning power supply is turned on to make the electron beam trajectory equidistantly distributed at 3 / 4 to 1 / 4 of the radius of the molten pool. The energy of the outermost electron beam trajectory gradually decreases toward the inside, and the refining time is maintained for 3 minutes. After refining, the ingot is pulled again. The ingot is pulled once every 10 to 20 mm increase in the molten pool until the Mo-14Re alloy ingot length is 600 mm.

[0046] (2) removing surface defects by turning to obtain a bright Mo-14Re alloy ingot with an ingot size of Φ180×600 mm;

[0047] (3) The ingot of step (2) is subjected to high temperature and high speed near isothermal extrusion to prepare a tube billet, wherein the extrusion temperature is 1550°C, the extrusion speed is 110 mm / s, the extrusion die preheating temperature is 900°C, the extrusion mandrel preheating temperature is 650°C, the extrusion pad preheating temperature is 980°C, the temperature difference during the tube billet extrusion process is ±15°C, and the Mo-14Re alloy tube billet size after extrusion is Φ90×20 mm;

[0048] (4) the extruded tube in step (3) is subjected to inner and outer surface turning to obtain a Mo-14Re alloy spinning tube of Φ84×14 mm, and then subjected to high-temperature spinning forming, the spinning temperature is 850° C., the multi-pass spinning thinning rate is 25% to 38%, the spinning pass number is 4, and intermediate annealing is performed after every 2 spinning passes, the annealing temperature is 1320° C., the holding time is 1 h, the feed ratio is 1.2 mm / r, the total thinning rate of high-temperature spinning is 71.4%, and the spinning is formed into a Mo-14Re alloy tube of Φ64×4 mm;

[0049] (5) subjecting the Mo-14Re alloy tube in step (4) to recrystallization annealing at a temperature of 1200° C. and a holding time of 1 h;

[0050] (6) After recrystallization annealing, the Mo-14Re alloy tube is turned and cut on the inner and outer surfaces to obtain a high-purity Mo-14Re alloy tube with a tube specification of Φ62×2×600mm. The test analysis shows that the C, N, and O contents are all less than 10ppm (the lower limit of the existing test method), the tensile strength of the tube is 758MPa, and the elongation is 22%.

[0051] Example 4

[0052] (1) A vacuum high-energy electron beam is used to purify and melt the sintered Mo-47.5Re alloy billet. The size of the Mo-47.5Re alloy ingot is Φ210mm, the electron beam power is 580kW, and the Mo-47.5Re alloy billet is melted by focusing the electron beam center. After the Mo-47.5Re alloy billet melts and flows into the water-cooled crystallizer, the electron beam scanning power supply is turned on to make the electron beam trajectory equidistantly distributed at 3 / 4 to 1 / 4 of the radius of the molten pool. The energy of the outermost electron beam trajectory gradually decreases toward the inside, and the refining time is maintained for 4 minutes. After refining, the ingot is pulled again. The ingot is pulled once every 10 to 20 mm increase in the molten pool until the Mo-47.5Re alloy ingot length is 600 mm.

[0053] (2) removing surface defects by turning to obtain a bright Mo-47.5Re alloy ingot with an ingot size of Φ200×600 mm;

[0054] (3) The ingot of step (2) is subjected to high temperature and high speed near isothermal extrusion to prepare a tube billet, wherein the extrusion temperature is 1600° C., the extrusion speed is 100 mm / s, the extrusion die preheating temperature is 920° C., the extrusion mandrel preheating temperature is 700° C., the extrusion pad preheating temperature is 1000° C., the temperature difference during the tube billet extrusion process is ±18° C., and the Mo-47.5Re alloy tube billet size after extrusion is Φ100×20 mm;

[0055] (4) the extruded tube in step (3) is subjected to inner and outer surface turning to obtain a Mo-47.5Re alloy spinning tube of Φ94×14 mm, and then subjected to high-temperature spinning forming, the spinning temperature is 900° C., the multi-pass spinning thinning rate is 25% to 38%, the spinning passes are 4 passes, and intermediate annealing is performed after every 2 spinning passes, the annealing temperature is 1350° C., the holding time is 1 h, the feed ratio is 1.5 mm / r, the total thinning rate of high-temperature spinning is 71.4%, and the spinning is formed into a Mo-47.5Re alloy tube of Φ74×4 mm;

[0056] (5) subjecting the Mo-47.5Re alloy tube in step (4) to recrystallization annealing at a temperature of 1250° C. and a holding time of 1 h;

[0057] (6) After recrystallization annealing, the Mo-47.5Re alloy tube is turned and cut on the inner and outer surfaces to obtain a high-purity Mo-47.5Re alloy tube with a tube specification of Φ72×2×600mm. The test analysis shows that the C, N, and O contents are all less than 10ppm (the lower limit of the existing test method), the tensile strength of the tube is 810MPa, and the elongation is 26%.

[0058] Example 5

[0059] (1) A vacuum high-energy electron beam is used to purify and melt the sintered Mo-47.5Re alloy billet. The size of the Mo-47.5Re alloy ingot is Φ230mm, the electron beam power is 680kW, and the Mo-47.5Re alloy billet is melted by focusing the electron beam center. After the Mo-47.5Re alloy billet melts and flows into the water-cooled crystallizer, the electron beam scanning power supply is turned on to make the electron beam trajectory equidistantly distributed at 3 / 4 to 1 / 4 of the radius of the molten pool. The energy of the outermost electron beam trajectory gradually decreases toward the inside, and the refining time is maintained for 4 minutes. After refining, the ingot is pulled again. The ingot is pulled once every 10 to 20 mm increase in the molten pool until the Mo-47.5Re alloy ingot length is 600 mm.

[0060] (2) removing surface defects by turning to obtain a bright Mo-47.5Re alloy ingot with an ingot size of Φ220×600 mm;

[0061] (3) The ingot of step (2) is subjected to high temperature and high speed near isothermal extrusion to prepare a tube billet, wherein the extrusion temperature is 1600° C., the extrusion speed is 100 mm / s, the extrusion die preheating temperature is 920° C., the extrusion mandrel preheating temperature is 700° C., the extrusion pad preheating temperature is 1000° C., the temperature difference during the tube billet extrusion process is ±18° C., and the Mo-47.5Re alloy tube billet size after extrusion is Φ110×20 mm;

[0062] (4) the extruded tube in step (3) is subjected to inner and outer surface turning to obtain a Mo-47.5Re alloy spinning tube of Φ104×14 mm, and then subjected to high-temperature spinning forming, the spinning temperature is 900° C., the multi-pass spinning thinning rate is 25% to 38%, the spinning passes are 4 passes, and intermediate annealing is performed after every 2 spinning passes, the annealing temperature is 1350° C., the holding time is 1 h, the feed ratio is 1.5 mm / r, the total thinning rate of high-temperature spinning is 71.4%, and the spinning is formed into a Mo-47.5Re alloy tube of Φ84×4 mm;

[0063] (5) subjecting the Mo-47.5Re alloy tube in step (4) to recrystallization annealing at a temperature of 1250° C. and a holding time of 1 h;

[0064] (6) After recrystallization annealing, the Mo-47.5Re alloy tube is turned and cut on the inner and outer surfaces to obtain a high-purity Mo-47.5Re alloy tube with a tube specification of Φ82×2×600mm. The test analysis shows that the C, N, and O contents are all less than 10ppm (the lower limit of the existing test method), the tensile strength of the tube is 815MPa, and the elongation is 28%.

[0065] Comparative Example 1

[0066] The difference from Example 1 is that in step (1), the electron beam power is 400 kW, and the rest of the settings are the same as those in Example 1.

[0067] The comparative example obtained a Mo-5Re alloy pipe with a specification of Φ72×2×600mm. The test analysis showed that the C, N and O contents were 25ppm, 12ppm and 32ppm respectively. The tensile strength of the pipe was 640MPa and the elongation was only 8%.

[0068] Comparative Example 2

[0069] The difference from Example 1 is that in step (1), the electron beam trajectory is only located at the center of the molten pool, and the electron beam trajectory is not evenly distributed at 3 / 4 to 1 / 4 of the radius of the molten pool. The rest of the settings are the same as Example 1.

[0070] The comparative example obtained a Mo-5Re alloy pipe with a specification of Φ72×2×600mm. The test analysis showed that the C, N and O contents were 20ppm, 10ppm and 24ppm respectively. The tensile strength of the pipe was 610MPa and the elongation was only 9%.

[0071] Comparative Example 3

[0072] The difference from Example 1 is that in step (3), the extrusion speed is 30 mm / s, and the other settings are the same as those in Example 1.

[0073] In this comparative example, at an extrusion speed lower than that of the present invention, the temperature difference during the tube extrusion process is ±110° C., and the molybdenum-rhenium alloy tube billet is severely deformed and cracked during the non-isothermal extrusion process, and the next step of processing cannot be performed.

[0074] Comparative Example 4

[0075] The difference from Example 1 is that in step (4), the spinning temperature is 750° C., and the rest of the settings are the same as those in Example 1.

[0076] In this comparative example, at a spinning temperature lower than that of the present invention, the crude molybdenum-rhenium alloy tube cracked and could not be processed into shape.

[0077] Comparative Example 5

[0078] The difference from Example 1 is that in step (4), after turning the inner and outer surfaces, a Mo-5Re alloy spinning tube blank Φ94×14 mm is obtained, and high-temperature spinning is not used, but a rolling method is used to prepare the molybdenum-rhenium alloy semi-finished tube. The rest of the settings are the same as in Example 1.

[0079] In this comparative example, when the high-temperature spinning forming step is not used to prepare large-sized molybdenum-rhenium alloy pipes, the pipe wall thickness is large and the deformation resistance is large, and cracks occur during the rolling process. After turning the inner and outer surfaces, Mo-5Re alloy pipes with specifications of Φ72×2×600mm are obtained. After testing and analysis, the tensile strength of the pipe is only 582MPa and the elongation is only 3%.

[0080] The above description of the disclosed embodiments and comparative examples enables professionals in the field to implement or use the present invention. Various modifications to these embodiments will be apparent to professionals in the field, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a large-scale high-purity molybdenum-rhenium alloy pipe, characterized in that: The following steps are involved: (1) High purity preparation of molybdenum-rhenium alloy ingots: The sintered molybdenum-rhenium alloy strip is purified and melted by a vacuum high-energy electron beam to obtain a molybdenum-rhenium alloy ingot; (2) Surface turning: Turning the molybdenum-rhenium alloy ingot obtained in step (1) to remove surface defects and obtain a bright molybdenum-rhenium alloy ingot; (3) High-speed near-isothermal extrusion of molybdenum-rhenium alloy tube billet: The molybdenum-rhenium alloy ingot after turning in step (2) is subjected to high-temperature and high-speed near-isothermal extrusion to prepare a molybdenum-rhenium alloy tube blank; The extrusion temperature is 1520-1620°C, and the extrusion speed is 100-140 mm / s; The extrusion die, extrusion mandrel and extrusion pad are all preheated, and the extrusion outlet temperature of the molybdenum-rhenium alloy tube is basically constant, and the temperature fluctuation range is controlled within ±20°C; (4) High temperature spinning: The molybdenum-rhenium alloy tube blank obtained in step (3) is prepared into a semi-finished tube by high-temperature spinning; (5) Recrystallization annealing: (6) Surface finishing The tube after recrystallization annealing is surface processed to obtain a finished product of molybdenum-rhenium alloy tube.

2. The method for preparing a large-scale high-purity molybdenum-rhenium alloy pipe according to claim 1 is characterized in that: The purification smelting in step (1) specifically includes decomposition, degassing, impurity removal, refining, and ingot pulling; Preferably, the purification smelting process of step (1) is repeated until a molybdenum-rhenium alloy ingot of a desired size is obtained; more preferably, the ingot is pulled once every time the molybdenum-rhenium alloy molten pool increases by 10 to 20 mm.

3. The method for preparing a large-scale high-purity molybdenum-rhenium alloy pipe according to claim 2 is characterized in that: In the step (1), the center of the electron beam is focused to melt the molybdenum-rhenium alloy billet. After the molybdenum-rhenium alloy billet is melted and flows into a water-cooled crystallizer, an electron beam scanning power supply is turned on to make the electron beam tracks equidistantly distributed at 3 / 4 to 1 / 4 of the radius of the molten pool, and the energy of the outermost electron beam track gradually decreases inward, and the refining time is maintained for 2 to 5 minutes.

4. A method for preparing a large-scale high-purity molybdenum-rhenium alloy pipe according to claim 1, 2 or 3, characterized in that: The power of the electron beam in step (1) is 500-700 kW.

5. The method for preparing a large-scale high-purity molybdenum-rhenium alloy pipe according to claim 1, characterized in that: The size of the molybdenum-rhenium alloy ingot in step (1) is Φ160-240 mm.

6. The method for preparing a large-scale high-purity molybdenum-rhenium alloy pipe according to claim 1, characterized in that: In the step (4), the temperature of high temperature spinning is 800-900° C., the total thinning rate of high temperature spinning is ≥60%, and the feed ratio is 0.5-1.5 mm / r.

7. The method for preparing a large-size high-purity molybdenum-rhenium alloy pipe according to claim 1 or 6, characterized in that: In the step (4), the number of high temperature spinning passes is 3 to 6; Perform intermediate annealing during high temperature spinning, preferably perform intermediate annealing after two passes of high temperature spinning; Preferably, the intermediate annealing temperature is 1300-1350° C., and the intermediate annealing holding time is 0.5-1 h.

8. The method for preparing a large-scale high-purity molybdenum-rhenium alloy pipe according to claim 1, characterized in that: In the step (3), the preheating temperature of the extrusion die is 850-950°C, the preheating temperature of the extrusion core rod is 600-700°C, and the preheating temperature of the extrusion pad is 950-1050°C.

9. The method for preparing a large-size high-purity molybdenum-rhenium alloy pipe according to claim 1 or 6, characterized in that: In the step (5), the temperature of the recrystallization annealing is 1150-1250° C., and the holding time of the recrystallization annealing is 0.5-1 h.

10. A large-size high-purity molybdenum-rhenium alloy pipe prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The diameter of the molybdenum-rhenium alloy tube is not less than Φ60mm, and the wall thickness is 2-6mm; preferably, the contents of C, N and O in the molybdenum-rhenium alloy tube are all less than 10ppm, the tensile strength of the tube is greater than 650MPa, and the elongation is greater than 15%.

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