Preparation method of large-diameter zirconium-niobium alloy pipe for nuclear industry

Abstract

The application relates to the technical field of zirconium-niobium alloy material processing, in particular to a preparation method of a large-diameter zirconium-niobium alloy pipe for nuclear industry, which comprises the following steps: S1, mixing nuclear-grade sponge zirconium and niobium scraps, or mixing zirconium-niobium alloy, zirconium dioxide and iron; melting the mixture and preparing a zirconium-niobium alloy ingot; S2, sequentially performing large deformation forging in a beta single-phase zone and an alpha+beta two-phase zone; S3, drilling a central hole in the axial direction of a round-forging blank; quenching in the beta single-phase zone; S4, coating an anti-galling agent on the surface of the central hole and heating to prepare a pipe blank in the mode of cross piercing; S5, performing periodic forging and rolling on the pipe blank; S6, annealing the hot-rolled pipe twice; and straightening the hot-rolled pipe after the second-stage annealing. The zirconium-niobium alloy pipe has uniform microstructure, good mechanical properties and corrosion resistance, the production direction of the brittle hydride is nearly parallel to the circumferential direction of the pipe, and brittle damage of the pipe wall thickness caused by the crack propagation of the hydride is avoided.

Description

Technical Field

[0001] This application relates to the technical field of zirconium-niobium alloy material processing, and in particular to a method for preparing large-diameter zirconium-niobium alloy pipes for nuclear industry. Background Technology

[0002] Nuclear-grade zirconium alloys possess low neutron absorption cross-sections and excellent corrosion resistance, making them widely used as core structural materials in water-cooled nuclear reactors. Zirconium-niobium alloys, in particular, are superior to other zirconium alloys such as zirconium-tin alloys in terms of dimensional stability, corrosion resistance, and mechanical properties, especially strength and creep resistance. They are mainly used as pressure-bearing structural materials such as reactor pressure tubes and component housings. These products are typically small in size and can be manufactured through tube extrusion, cold rolling, or cold drawing. With the development of nuclear technology, the applications of zirconium-niobium alloys are gradually expanding, leading to a growing demand for large-diameter zirconium-niobium alloy tubing for the nuclear industry.

[0003] Currently, the main methods for manufacturing large-diameter pipes include casting, forging, and hot extrusion. Cast zirconium alloys, due to their coarse microstructure and casting defects such as porosity and inclusions, as well as the potential for material contamination during casting, cannot be used in reactors. Forged pipes require advanced equipment and are inefficient; the forging process suffers from poor billet temperature uniformity, making process control difficult, and they cannot produce pipes with large lengths and thin walls. Hot extrusion of large-diameter pipes also requires advanced equipment, and suffers from uneven microstructure, low material utilization, and poor economic efficiency. None of these processes can produce large-diameter zirconium-niobium alloy pipes for the nuclear industry with uniform microstructure, good mechanical properties, corrosion resistance, and excellent resistance to hydrogen embrittlement. Summary of the Invention

[0004] The purpose of this application is to provide a method for preparing large-diameter zirconium-niobium alloy pipes for nuclear industry, so as to solve the problem that existing technologies are unable to prepare large-diameter zirconium-niobium alloy pipes with uniform microstructure, good mechanical properties and corrosion resistance, and excellent resistance to hydrogen embrittlement.

[0005] To address the aforementioned technical problems, according to some embodiments, this application provides a method for preparing large-diameter zirconium-niobium alloy pipes for nuclear industry, comprising:

[0006] S1. Mix nuclear-grade sponge zirconium and niobium scraps, or zirconium-niobium alloy, zirconium dioxide and iron; melt the mixture and prepare zirconium-niobium alloy ingots;

[0007] S2. The zirconium-niobium alloy ingot is subjected to large deformation forging in the β single-phase region and the α+β two-phase region in sequence to obtain a forging blank.

[0008] S3. Round the forging blank; drill a center hole in the axial direction of the rounded forging blank; quench in the β single-phase region to obtain a preform;

[0009] S4. After coating the surface of the central hole with an anti-galling agent, heat it and prepare the tube blank by skew rolling and piercing.

[0010] S5. Perform cyclic forging and rolling on the tube blank to obtain hot-rolled tube;

[0011] S6. The hot-rolled pipe is annealed twice; after the second stage of annealing, the hot-rolled pipe is straightened.

[0012] Furthermore, in step S1,

[0013] The zirconium-niobium alloy ingot is a nuclear industry grade Zr-2.5Nb-0.10O-0.01Ge, with a mass ratio of 2.4wt%–2.8wt% Nb, 0.10wt%–0.14wt% O, 0.005wt%–0.015wt% Ge, and the balance being Zr; or,

[0014] The zirconium-niobium alloy ingot is nuclear industry grade Zr-2.5Nb-0.05Fe-0.01Ge, with a mass ratio of 2.4wt% to 2.8wt% Nb, 0.03wt% to 0.10wt% Fe, 0.005wt% to 0.015wt% Ge, and the balance being Zr.

[0015] Further, in step S1, the melting of the mixture includes:

[0016] The mixture is smelted repeatedly four or more times in a vacuum consumable arc furnace;

[0017] The specifications of the zirconium-niobium alloy ingot are Φ720mm~Φ820mm.

[0018] Furthermore, in step S2, before forging the zirconium-niobium alloy ingot in the β single-phase region, the zirconium-niobium alloy ingot is heated to a temperature of 1000℃~1040℃; the forging adopts a deformation method combining upsetting and drawing, and the total forging ratio is greater than or equal to 8.

[0019] Before forging the zirconium-niobium alloy ingot in the β single-phase region: the zirconium-niobium alloy ingot is heated to a temperature of 820℃~880℃; the forging adopts a deformation method combining upsetting and drawing, and the total forging ratio is greater than or equal to 10.

[0020] Furthermore, in step S2, water cooling is performed immediately after each forging.

[0021] Furthermore, in step S3, the quenching temperature is 930℃~980℃, and the diameter of the center hole of the preform is Φ55mm~Φ75mm;

[0022] After quenching, the blank is machined to remove oxide scale and defects from the inner and outer surfaces and to flatten the end faces.

[0023] Furthermore, in step S4, the anti-biting agent is a nickel-based anti-biting agent containing copper powder and graphite flakes;

[0024] The heating temperature is 780℃~840℃;

[0025] The outer diameter of the tube blank is Φ400mm~Φ570mm, and the inner diameter is Φ230mm~Φ420mm.

[0026] Furthermore, in step S5, during forging and rolling, the inner surface of the tube blank is coated with a silica-based protective lubricant containing boron nitride and aluminum oxide;

[0027] The heating temperature is 720℃~800℃, the forging deformation is ≥50%, the ratio of the tube wall deformation to the diameter deformation of the tube blank is greater than or equal to 5, and the outer diameter of the obtained hot-rolled tube is Φ280mm~Φ460mm and the inner diameter is Φ250mm~Φ410mm.

[0028] Furthermore, in step S6, the first-stage annealing temperature is 640℃~720℃;

[0029] The second-stage annealing temperature is 500℃~590℃;

[0030] The hot-rolled pipe is straightened using the residual heat after the second-stage annealing, with the temperature of the hot-rolled pipe before straightening between 100℃ and 250℃.

[0031] Furthermore, the preparation method also includes:

[0032] S7. The straightened hot-rolled tube is subjected to surface machining treatment to obtain a zirconium-niobium alloy tube; the zirconium-niobium alloy tube has an outer diameter of Φ270mm~Φ450mm, an inner diameter of Φ260mm~Φ420mm, and a length of 2000mm~6000mm.

[0033] The above-described technical solution of the present invention has at least the following beneficial technical effects:

[0034] (1) Vacuum self-consuming electric arc furnace melting with four or more times ensures the uniform distribution of niobium element with small diffusion coefficient, reduces the content of impurity gas elements, and at the same time prepares large-size zirconium-niobium alloy ingots, improving material utilization.

[0035] (2) By forging with large deformation in the β single-phase region, the as-cast structure of the zirconium-niobium alloy ingot is fully broken. Forging with large deformation in the α+β two-phase region further refines the microstructure. At the same time, water cooling is performed immediately after forging to retain more deformation distortion energy. Combined with the lower quenching heating temperature in the subsequent steps, it ensures that the preform can obtain a smaller β grain size. Drilling before quenching is conducive to uniform cooling of the billet as a whole.

[0036] (3) A specific type of coating was applied to the inner hole of the preform and the inner surface of the tube blank to obtain a better surface quality; the selected heating temperature ensured that the primary α phase of the tube had an appropriate proportion, the tube forging deformation was ≥50%, the ratio of tube wall deformation to diameter deformation was not less than 5, and a texture orientation with excellent texture was obtained, so that the direction of hydride production after hydrogen absorption was perpendicular to the radial direction of the tube, thus ensuring the mechanical properties and hydrogen embrittlement resistance of the tube.

[0037] (4) The use of a special annealing rack improves the stress on the pipe during annealing, avoids creep deformation during annealing, and obtains a more uniform microstructure through two annealing processes, while improving the corrosion resistance of the pipe. The use of residual heat from annealing for straightening reduces the internal stress of the pipe after straightening and ensures the straightness of the pipe. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this application or in the conventional technology, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a flowchart illustrating a method for preparing large-diameter zirconium-niobium alloy pipes for nuclear industry, as described in one embodiment of this application.

[0040] Figure 2 This is a microstructure diagram of a typical large-diameter zirconium-niobium alloy pipe for nuclear industry, as shown in one embodiment of this application.

[0041] Figure 3 This is a hydride orientation diagram of a typical large-diameter zirconium-niobium alloy pipe for nuclear industry in one embodiment of this application. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the various embodiments of this application will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details are presented in the various embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments. The division of the various embodiments below is for ease of description and should not constitute any limitation on the specific implementation of this application. The various embodiments can be combined with and referenced by each other without contradiction.

[0043] Currently, existing technologies struggle to produce large-diameter zirconium-niobium alloy pipes for the nuclear industry that exhibit uniform microstructure, good mechanical and corrosion resistance, and excellent resistance to hydrogen embrittlement.

[0044] To address the aforementioned problems, one embodiment of this application provides a method for preparing large-diameter zirconium-niobium alloy tubing for nuclear industry, comprising:

[0045] S1. Mix nuclear-grade sponge zirconium and niobium scraps, or zirconium-niobium alloy, zirconium dioxide and iron; melt the mixture and prepare zirconium-niobium alloy ingots;

[0046] Alloy mixtures were obtained in two different ways.

[0047] The first mixing method: Before mixing, nuclear-grade sponge zirconium is sorted and magnetically separated to remove inclusions. High-purity niobium shavings are then selected and uniformly mixed. The mass ratio of niobium (Nb) is 2.4wt% to 2.8wt%, oxygen (O) is 0.10wt% to 0.14wt%, germanium (Ge) is 0.005wt% to 0.015wt%, and the balance is zirconium (Zr). In actual production, a small amount of unavoidable impurity elements are also included, resulting in a nuclear-grade Zr-2.5Nb-0.10O-0.01Ge composition.

[0048] The second mixing method involves uniformly mixing zirconium-niobium alloy, zirconium dioxide, and iron; the mass percentages are: 2.4wt%–2.8wt% niobium (Nb), 0.03wt%–0.10wt% iron (Fe), 0.005wt%–0.015wt% germanium (Ge), with the balance being Zr. In actual production, a small amount of unavoidable impurity elements are also included, resulting in a nuclear industry grade Zr-2.5Nb-0.05Fe-0.01Ge.

[0049] After obtaining the alloy mixture, it is repeatedly melted in a vacuum arc remelting furnace four or more times; the melted mixture is then used to produce zirconium-niobium alloy ingots with dimensions of Φ720~Φ820mm. The use of four or more vacuum arc remelting processes ensures a uniform distribution of niobium, which has a low diffusion coefficient, reduces the content of impurity gaseous elements, and simultaneously produces large-sized zirconium-niobium alloy ingots, thus improving material utilization.

[0050] S2. Two forms of forging are performed on zirconium-niobium alloy ingots.

[0051] First, the zirconium-niobium alloy ingot is heated to a temperature of 1000℃~1040℃; then, the zirconium-niobium alloy ingot is subjected to large deformation forging in the β single-phase region. The forging adopts a deformation method combining upsetting and drawing, with a total forging ratio greater than or equal to 8; after the β single-phase region forging is completed, water cooling treatment is performed immediately to retain deformation distortion energy.

[0052] Secondly, the zirconium-niobium alloy ingot is heated again to a temperature of 820℃~880℃. Then, the ingot undergoes large deformation forging in the α+β two-phase region, employing a combination of upsetting and drawing deformation, with a total forging ratio greater than or equal to 10. Immediately after forging in the α+β two-phase region, it is water-cooled to retain deformation distortion energy, ultimately yielding a forged blank. Through large deformation forging in the β single-phase region, the as-cast microstructure of the zirconium-niobium alloy ingot is sufficiently fragmented. Large deformation forging in the α+β two-phase region further refines the microstructure. Simultaneously, immediate water cooling after forging retains a significant amount of deformation distortion energy. Combined with the relatively low quenching temperature in subsequent steps, this ensures that the preform can achieve a small β grain size. Drilling before quenching facilitates uniform cooling of the entire blank.

[0053] S3. The forging blank is rounded by machining, and a center hole is drilled in the axial direction of the rounded forging blank.

[0054] The forged blank is then quenched in the β single-phase region at a temperature of 930℃~980℃.

[0055] After quenching, the blank is machined to remove oxide scale and defects from the inner and outer surfaces and to flatten the end faces to obtain a preform.

[0056] S4. Pierce the preform.

[0057] First, an anti-seize agent is applied to the surface of the central hole. The anti-seize agent is a nickel-based anti-seize agent containing copper powder and graphite flakes, with a coating thickness of 0.10 mm to 0.25 mm. Then, the preform is heated to a temperature of 780℃ to 840℃ and a tube blank is prepared by skew rolling and piercing.

[0058] S5. Perform cyclic forging and rolling on the tube blank to obtain hot-rolled tube;

[0059] Before forging and rolling, the surface of the tube blank is ground to remove impurities. After grinding, a silica-based protective lubricant containing boron nitride and aluminum oxide is coated on the inner surface of the tube blank, with a coating thickness of 0.07–0.20 mm. Then, the tube blank is heated and periodically forged and rolled using a rolling mill to obtain hot-rolled tubes. The heating temperature is 720℃–800℃, the forging deformation is ≥50%, and the ratio of tube wall deformation to diameter deformation is greater than or equal to 5. The outer diameter of the obtained hot-rolled tube is Φ280 mm–Φ460 mm. Applying the protective lubricant to the inner hole of the preform and the inner surface of the tube blank respectively achieves good surface quality. The selected heating temperature ensures that the primary α phase of the tube has an appropriate proportion, the forging deformation is ≥50%, and the ratio of tube wall deformation to diameter deformation is not less than 5, resulting in excellent texture orientation. This ensures that the direction of hydride production after hydrogen absorption is perpendicular to the radial direction of the tube, guaranteeing the mechanical properties and resistance to hydrogen embrittlement of the tube.

[0060] S6. The hot-rolled pipe is annealed twice in succession.

[0061] This application uses a self-made annealing rack; the annealing rack has a semi-circular cross-section and is made of heat-resistant steel. The inner radius of the annealing rack is 5-10 mm larger than the outer radius of the hot-rolled pipe. The length of the rack is equivalent to the diameter of the hot-rolled pipe, and the interval between adjacent annealing racks is less than or equal to twice the diameter of the hot-rolled pipe. A first-stage annealing is performed at a temperature of 640℃-720℃; then a second-stage annealing is performed at a temperature of 500℃-590℃.

[0062] After the second-stage annealing, the residual heat from the second-stage annealing is used to straighten the hot-rolled tube using a multi-roll straightener. The temperature of the hot-rolled tube before and during straightening is between 100 and 250°C. A special annealing rack is used to improve the stress condition of the tube during annealing, avoiding creep deformation. Two annealing processes result in a more uniform microstructure and improve the corrosion resistance of the tube. Using the residual heat from annealing for straightening reduces the internal stress of the tube after straightening, ensuring the straightness of the tube.

[0063] S7. The straightened hot-rolled tube is subjected to surface machining treatment to obtain a zirconium-niobium alloy tube; the zirconium-niobium alloy tube has an outer diameter of Φ270mm~Φ450mm, an inner diameter of Φ260mm~Φ420mm, and a length of 2000mm~6000mm.

[0064] Example 1

[0065] Step 1: Remove inclusions from nuclear industry-grade sponge zirconium using sorting and magnetic separation. Then, uniformly mix high-purity niobium shavings and zirconium dioxide powder according to the alloy composition requirements of Zr-2.5Nb-0.10O-0.01Ge, containing 2.4wt% Nb, 0.10wt% O, 0.10wt% Ge, with the balance being Zr. Finally, repeatedly melt the mixture five times in a vacuum arc remelting furnace to obtain a zirconium-niobium alloy ingot with a diameter of Φ720mm.

[0066] Step Two: First, the zirconium-niobium alloy ingot obtained in Step One is heated to 1020℃ in an electric resistance furnace and held for 3.5 hours. Two cycles of forging are then performed, involving large deformation forging in the β single-phase region. The forging process combines upsetting and drawing to obtain an intermediate billet with a diameter of Φ450mm. The total forging ratio is 9. Water cooling is performed immediately after forging. Second, after cooling, the intermediate billet undergoes surface grinding. It is then heated to 850℃ and held for 2.5 hours before three cycles of forging are performed, involving large deformation forging in the α+β two-phase region. The forging process combines upsetting and drawing to obtain a forged blank with a diameter of Φ400mm. The total forging ratio is 12.5. Water cooling is performed immediately after forging.

[0067] Step 3: The forging blank obtained in Step 2 is machined and rounded, and a center hole with a diameter of Φ55mm is drilled in the axial direction of the blank. Then, it is heated to 960℃, held for 2 hours and then quenched. After the forging blank is cooled, the oxide scale and defects on the inner and outer surfaces are removed by machining, and the end face is flattened to obtain a pre-formed blank with an outer diameter of Φ390mm and an inner diameter of Φ61mm.

[0068] Step 4: Coat the inner surface of the preform obtained in Step 3 with a nickel-based anti-galling agent, heat it in a resistance heating furnace at 780℃ for 2.5h, and then prepare a tube blank with an outer diameter of Φ400mm and an inner diameter of Φ260mm by skew rolling and piercing.

[0069] Step 5: The tube blank obtained in Step 4 is subjected to surface grinding to remove surface defects and coated with a silica-based protective lubricant on the inner surface. After heating in a resistance heating furnace at 740℃ for 2 hours, it is periodically forged and rolled using a rolling mill. The forging deformation is 82%, and the ratio of tube wall deformation to diameter deformation is 7, resulting in a hot-rolled tube with an outer diameter of Φ280mm and an inner diameter of Φ260mm.

[0070] Step Six: Place the hot-rolled pipe obtained in Step Five on a heat-resistant steel rack for annealing. The annealing rack has an inner radius of Φ285mm, a length of 300mm, and is evenly distributed at 500mm intervals. The first stage annealing regime is 640℃ / 1.5h, and the second stage annealing regime is 530℃ / 2h. After the second stage annealing, when the pipe temperature drops to about 200℃, perform multi-roll straightening.

[0071] Step 7: Perform surface machining on the pipe obtained in Step 6 to obtain a zirconium-niobium alloy pipe with an outer diameter of Φ270mm, an inner diameter of Φ260mm, and a length of 2000mm to 4000mm.

[0072] Example 2

[0073] Step 1: Remove inclusions by sorting and magnetic separation of nuclear-grade sponge zirconium. Mix zirconium dioxide powder, zirconium-niobium master alloy and pure iron particles evenly according to the Zr-2.5Nb-0.10O-0.01Ge alloy composition requirements. Then, repeatedly vacuum melt four times in a vacuum arc furnace to obtain a zirconium-niobium alloy ingot with a specification of Φ820mm.

[0074] Step 2: The zirconium-niobium alloy ingot obtained in Step 1 is heated to 1040℃ in a resistance heating furnace and held for 4 hours. Then, it undergoes two cycles of forging, including large deformation forging in the β single-phase region. The forging adopts a deformation method combining upsetting and drawing to obtain an intermediate billet with a specification of Φ520mm. The total forging ratio is 10. After forging, it is immediately water-cooled. After the intermediate billet cools, the surface is ground, and then it is heated to 875℃ and held for 3 hours. Then, it undergoes three cycles of forging, including large deformation forging in the α+β two-phase region. The forging adopts a deformation method combining upsetting and drawing to obtain a forged blank with a specification of Φ550mm. The total forging ratio is 12. After forging, it is immediately water-cooled.

[0075] Step 3: The forging blank obtained in Step 2 is machined and rounded, and a center hole with a diameter of Φ60mm is drilled in the axial direction of the blank. Then, it is heated to 980℃, held for 2.5h and then quenched. After the blank is cooled, the oxide scale and defects on the inner and outer surfaces are removed by machining, and the end face is flattened to obtain a pre-formed blank with an outer diameter of Φ540mm and an inner diameter of Φ65mm.

[0076] Step 4: Coat the inner surface of the preform obtained in Step 3 with a nickel-based anti-galling agent, heat it in a resistance heating furnace at 840℃ for 2.5h, and then prepare a tube blank with an outer diameter of Φ550mm and an inner diameter of Φ420mm by skew rolling and piercing.

[0077] Step 5: The tube blank obtained in Step 4 is subjected to surface grinding to remove surface defects and coated with a silica-based protective lubricant on the inner surface. After heating in a resistance heating furnace at 780℃ for 2.5h, it is periodically forged and rolled using a rolling mill. The forging deformation is 65%, and the ratio of tube wall deformation to diameter deformation is 8.5, to obtain a hot-rolled tube with an outer diameter of Φ460mm and an inner diameter of Φ410mm.

[0078] Step Six: Place the hot-rolled pipe obtained in Step Five on a heat-resistant steel rack for annealing. The annealing rack has an inner radius of Φ465mm, a length of 450mm, and is evenly distributed at 800mm intervals. The first stage annealing regime is 690℃ / 1.5h, and the second stage annealing regime is 550℃ / 2h. After the second stage annealing, when the pipe temperature drops to ~230℃, perform multi-roll straightening.

[0079] Step 7: Perform surface machining on the pipe obtained in Step 6 to obtain a zirconium-niobium alloy pipe with an outer diameter of Φ450mm, an inner diameter of Φ420mm, and a length of 2000mm to 6000mm.

[0080] The inventors tested the zirconium-niobium alloy tubes obtained in Examples 1 and 2, measuring their tensile strength, yield strength, elongation after fracture, etc., and observed their microstructure and hydride orientation.

[0081] Testing revealed that the large-diameter pipe obtained in this application possesses a uniform microstructure, excellent mechanical properties, and corrosion resistance. Furthermore, after hydrogen absorption, the direction of the precipitated brittle hydrides is nearly parallel to the circumferential direction of the pipe, preventing brittle fracture of the pipe wall caused by hydride crack propagation and thus giving the pipe excellent resistance to hydrogen embrittlement. The microstructure of the large-diameter zirconium-niobium alloy pipe for nuclear industry in this application is shown in [the attached image / image / description]. Figure 2 The hydride orientation of zirconium-niobium alloy tubing is shown in [reference needed]. Figure 3 The room temperature mechanical properties of zirconium-niobium alloy pipes are shown in Table 1. Table 1 contains the test data of zirconium-niobium alloy pipes obtained in Examples 1 and 2.

[0082] Table 1. Room temperature mechanical properties of zirconium-niobium alloy tubing

[0083]

[0084] This application provides a new approach for the preparation and processing of large-diameter zirconium-niobium alloy pipes for nuclear industry, resulting in large-diameter zirconium-niobium alloy pipes with uniform microstructure, good mechanical properties and corrosion resistance, and excellent resistance to hydrogen embrittlement. It is applicable to, but not limited to, the processing of pressure-bearing structural materials in the nuclear industry.

[0085] In the description of this invention, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this invention, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0086] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of this application and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of this application should be included within the protection scope of this application. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A method for preparing large-diameter zirconium-niobium alloy pipes for nuclear industry, characterized in that, include: S1. Mix nuclear-grade sponge zirconium and niobium shavings, or mix zirconium-niobium alloy, zirconium dioxide and iron; The mixture was smelted and zirconium-niobium alloy ingots were prepared. S2. The zirconium-niobium alloy ingot is forged in the β single-phase region using a deformation method that combines upsetting and drawing, with a total forging ratio greater than or equal to 8; water cooling treatment is performed immediately after the forging in the β single-phase region is completed. Large deformation forging is performed in the α+β two-phase region. The forging adopts a deformation method combining upsetting and drawing, and the total forging ratio is greater than or equal to 10. After the α+β two-phase region forging is completed, water cooling treatment is performed immediately to obtain a forging blank. S3. The forging blank is rounded. A center hole is drilled in the axial direction of the rounded forging blank. The blank is quenched in the β single-phase region to obtain a preform. S4. After coating the surface of the central hole with an anti-galling agent, heat it and prepare the tube blank by skew rolling and piercing. S5. Perform cyclic forging and rolling on the tube blank to obtain hot-rolled tube; S6. The hot-rolled pipe is annealed twice; after the second stage of annealing, the hot-rolled pipe is straightened.

2. The preparation method according to claim 1, characterized in that, In step S1, The zirconium-niobium alloy ingot is a nuclear industry grade Zr-2.5Nb-0.10O-0.01Ge, with a mass ratio of 2.4wt%~2.8wt% Nb, 0.10wt%~0.14wt% O, 0.005wt%~0.015wt% Ge, and the balance being Zr; or, The zirconium-niobium alloy ingot is nuclear industry grade Zr-2.5Nb-0.05Fe-0.01Ge, with a mass ratio of 2.4wt%~2.8wt% Nb, 0.03wt%~0.10wt% Fe, 0.005wt%~0.015wt% Ge, and the balance being Zr.

3. The preparation method according to claim 1, characterized in that, In step S1, the melting of the mixture includes: The mixture is smelted repeatedly four or more times in a vacuum consumable arc furnace; The specifications of the zirconium-niobium alloy ingot are Φ720~Φ820mm.

4. The preparation method according to claim 1, characterized in that, In step S2, before forging the zirconium-niobium alloy ingot in the β single-phase region, the zirconium-niobium alloy ingot is heated to a temperature of 1000℃~1040℃. Before forging the zirconium-niobium alloy ingot in the α+β two-phase region: the zirconium-niobium alloy ingot is heated to a temperature of 820℃~880℃.

5. The preparation method according to claim 4, characterized in that, In step S3, the quenching temperature is 930℃~980℃, and the diameter of the center hole of the preform is Φ55 mm~Φ75 mm. After quenching, the blank is machined to remove oxide scale and defects from the inner and outer surfaces and to flatten the end faces.

6. The preparation method according to claim 5, characterized in that, In step S4, the anti-biting agent is a nickel-based anti-biting agent containing copper powder and graphite flakes; The heating temperature is 780℃~840℃; The outer diameter of the tube blank is Φ400 mm ~ Φ570 mm, and the inner diameter is Φ230 mm ~ Φ420 mm.

7. The preparation method according to claim 6, characterized in that, In step S5, during forging and rolling, the inner surface of the tube blank is coated with a silica-based protective lubricant containing boron nitride and aluminum oxide; The heating temperature is 720℃~800℃, the forging deformation is ≥50%, the ratio of the tube wall deformation to the diameter deformation of the tube blank is greater than or equal to 5, and the outer diameter of the obtained hot-rolled tube is Φ280mm~Φ460mm and the inner diameter is Φ250mm~Φ410mm.

8. The preparation method according to claim 7, characterized in that, In step S6, the first stage annealing temperature is 640℃~720℃; The second-stage annealing temperature is 500℃~590℃; The hot-rolled pipe is straightened using the residual heat after the second-stage annealing, with the temperature of the hot-rolled pipe before straightening between 100℃ and 250℃.

9. The preparation method according to claim 8, characterized in that, Also includes: S7. The straightened hot-rolled tube is subjected to surface machining treatment to obtain zirconium-niobium alloy tube. The zirconium-niobium alloy tube has an outer diameter of Φ270mm~Φ450mm, an inner diameter of Φ260mm~Φ420mm, and a length of 2000mm~6000mm.

Images