Large-diameter heat-resistant alloy pipe for nuclear power equipment and preparation method of large-diameter heat-resistant alloy pipe

Abstract

The invention relates to a large-diameter heat-resistant alloy pipe for nuclear power equipment and a preparation method of the large-diameter heat-resistant alloy pipe, and belongs to the technical field of nickel-based heat-resistant alloy pipes. The preparation method comprises the following steps: preparing an electrode by adopting vacuum induction melting, refining and solidifying in a crystallizer through vacuum consumable remelting, and finally obtaining an alloy ingot; the obtained alloy cast ingot is subjected to homogenization treatment and forging, and then a bar is obtained; the obtained bar is heated and then subjected to hot piercing, then machining is conducted, a blank is obtained, the blank is of a hollow cylinder structure, and an inclined face is formed at one end of the blank; respectively heating the obtained material blank and the mold, and extruding by adopting a follow-up core rod to obtain an extruded blank; carrying out solution treatment and processing on the obtained extruded blank, and then carrying out primary cold rolling to obtain an intermediate cold-rolled tube; and finally, carrying out secondary cold rolling on the obtained intermediate cold-rolled tube to obtain the heat-resistant alloy tube.

Description

Technical Field

[0001] This invention relates to the field of nickel-based heat-resistant alloy pipe technology, and in particular to a large-diameter heat-resistant alloy pipe for nuclear power equipment and its preparation method. Background Technology

[0002] Currently, nuclear power equipment is mainly manufactured using high-temperature nickel-based heat-resistant alloys, which possess excellent high-temperature performance, superior creep resistance, and fatigue resistance. However, due to the high alloy content in nickel-based heat-resistant alloys, there is a significant tendency for alloy segregation and high deformation resistance. This makes them highly susceptible to cracking during the fabrication of tubing (a common component in nuclear power equipment), especially when manufacturing large-sized tubing, leading to the scrapping of the entire tubing. Summary of the Invention

[0003] Based on the above analysis, the present invention aims to provide a large-diameter heat-resistant alloy pipe for nuclear power equipment and its preparation method, which ensures the performance of the pipe while preventing crack formation.

[0004] On one hand, the present invention provides a method for preparing large-diameter heat-resistant alloy pipes for nuclear power equipment, comprising the following steps:

[0005] S1: The electrode is prepared by vacuum induction melting, then refined and solidified in a crystallizer by vacuum self-consumable remelting, and finally the alloy ingot is obtained.

[0006] S2: After homogenization and forging of the obtained alloy ingot, a bar is obtained;

[0007] S3: The obtained bar is heated and then hot-pierced, and then processed to obtain a blank. The blank is a hollow cylindrical structure with an inclined surface at one end.

[0008] S4: Heat the obtained blank and the mold separately, and then use a follower mandrel to extrude the blank to obtain the extruded blank;

[0009] S5: After solution treatment and processing of the obtained extruded billet, perform a cold rolling to obtain an intermediate cold-rolled tube;

[0010] S6: Finally, the intermediate cold-rolled tube is subjected to a second cold rolling process to obtain heat-resistant alloy tube.

[0011] Further, the chemical composition of the pipe, by weight percentage, includes: C: 0.05-0.15%, Cr: 20.0-24.0%, Co: 10.0-15.0%, Mo: 8.0-10.0%, Al: 0.8-1.5%, Ti: ≤0.6%, B: ≤0.006%, Cu: ≤0.5%, Si: ≤1.0%, Fe: ≤3.0%, Mn≤1.0%, with the balance being nickel and unavoidable impurity elements.

[0012] Furthermore, in step S2, the homogenization treatment temperature is 1190–1230°C, and the holding time is more than 48 hours.

[0013] Furthermore, in step S3, the heating temperature of the bar is 1180–1230°C, and the holding time is 8–16 hours.

[0014] Further, in step S4, the heating temperature of the blank is 1180-1220℃, and the holding time is 8-12h; the heating temperature of the mold is 350-450℃.

[0015] During the extrusion process, the initial extrusion temperature is 1160–1200℃.

[0016] Furthermore, in step S5, the solution treatment temperature is 1130–1180°C, the holding time is 1–2 hours, and then the product is removed from the furnace and cooled by water.

[0017] Furthermore, in step S5, the cold rolling speed is controlled at 20-50 times / minute, the cold rolling feed amount is 1-5mm, and the cold rolling deformation amount is ≥20%.

[0018] After one cold rolling, the furnace is held at 1130-1180℃ for 0.5-1 hour, and then the furnace is cooled by water.

[0019] Furthermore, in step S6, the deformation of the secondary cold rolling should be ≥40%. After the secondary cold rolling is completed, the temperature is kept at 1150~1180℃ for 1~2 hours, and then the product is removed from the furnace and water-cooled.

[0020] Furthermore, the heat-resistant alloy pipe has a grain size of 2 to 6, with a grade difference of ≤2, and a uniform structure without cracks.

[0021] On the other hand, the present invention provides a large-diameter heat-resistant alloy pipe for nuclear power equipment, which is obtained by the preparation method described in the present invention. The heat-resistant alloy pipe has an outer diameter ≥ Φ200mm and a wall thickness ≥ 10mm.

[0022] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0023] 1. In this invention, a large-diameter heat-resistant alloy pipe for nuclear power equipment is prepared by a combination of duplex smelting, ingot homogenization treatment, forging, hot piercing, extrusion, primary cold rolling and secondary cold rolling. It has high performance and no cracks are generated.

[0024] 2. A blank is obtained after hot piercing. The blank is a hollow cylindrical structure with an inclined surface at one end. This can optimize the metal flow during the hot extrusion filling stage, significantly reduce the risk of defect generation, and reduce the maximum extrusion pressure in the initial stage of extrusion.

[0025] 3. Optimize cold rolling process parameters. By controlling the feed amount (1-5mm) and rolling speed (20-50 times / minute), reduce the occurrence of rolling defects, and at the same time ensure the deformation amount of the second cold rolling pass (≥40%) to achieve grain refinement and uniform structure.

[0026] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0027] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0028] Figure 1 The pipe obtained in Example 1;

[0029] Figure 2 The pipe obtained in Comparative Example 3;

[0030] Figure 3 The pipe obtained for Comparative Example 4;

[0031] Figure 4 The metallographic structure inside the pipe obtained in Example 2;

[0032] Figure 5 The metallographic structure inside the pipe prepared in Comparative Example 5;

[0033] Figure 6 The metallographic structure inside the pipe prepared in Comparative Example 6;

[0034] Figure 7 This is a diagram of the blank processing in Example 1. Detailed Implementation

[0035] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0036] Currently, nuclear power equipment is mainly manufactured using high-temperature nickel-based heat-resistant alloys, which possess excellent high-temperature performance, superior creep resistance, and fatigue resistance. However, due to the high content of alloying elements in nickel-based heat-resistant alloys, there is a strong tendency for alloy segregation and high deformation resistance. This makes them highly susceptible to cracking during the fabrication of tubing (a common component in nuclear power equipment), especially when manufacturing large-sized tubing, leading to the scrapping of the entire tubing.

[0037] Therefore, the present invention provides a method for preparing large-diameter heat-resistant alloy pipes for nuclear power equipment, comprising the following steps:

[0038] S1: The electrode is prepared by vacuum induction melting, then refined and solidified in a crystallizer by vacuum self-consumable remelting, and finally the alloy ingot is obtained.

[0039] S2: After homogenization and forging of the obtained alloy ingot, a bar is obtained;

[0040] S3: The obtained bar is heated and then hot-pierced, and then processed to obtain a blank. The blank is a hollow cylindrical structure with an inclined surface at one end.

[0041] S4: Heat the obtained blank and the mold separately, and use a follower mandrel to extrude the blank to obtain the extruded blank;

[0042] S5: After solution treatment and processing of the obtained extruded billet, perform a cold rolling to obtain an intermediate cold-rolled tube;

[0043] S6: Finally, the intermediate cold-rolled tube is subjected to a second cold rolling process to obtain heat-resistant alloy tube.

[0044] Compared with the prior art, the present invention adopts

[0045] Specifically, the chemical composition of the pipe, by weight percentage, includes: C: 0.05-0.15%, Cr: 20.0-24.0%, Co: 10.0-15.0%, Mo: 8.0-10.0%, Al: 0.8-1.5%, Ti: ≤0.6%, B: ≤0.006%, Cu: ≤0.5%, Si: ≤1.0%, Fe: ≤3.0%, Mn≤1.0%, with the balance being nickel and unavoidable impurity elements.

[0046] It should be noted that the total content of Co and Mo elements in the alloy is 18-25%. Both Co and Mo are solid solution strengthening elements. Their high content gives the alloy good high-temperature performance, but it also causes a large tendency for element segregation and high deformation resistance. In the subsequent hot piercing, extrusion and cold rolling processes, cracks are very easy to be generated.

[0047] Specifically, in step S1, vacuum induction melting and vacuum consumable remelting are performed.

[0048] It should be noted that in step S1, the combined process of vacuum induction melting and vacuum arc remelting effectively reduces the segregation of alloying elements and ensures the uniformity of the alloy ingot. Existing smelting methods can be used for vacuum induction melting and vacuum arc remelting, and will not be elaborated further here.

[0049] Specifically, in step S2, the homogenization treatment temperature is 1190-1230℃, and the holding time is more than 48 hours.

[0050] It should be noted that the homogenization treatment aims to eliminate elemental segregation within the alloy ingot and dissolve large, harmful precipitates, increasing the chemical composition and microstructure uniformity of the material. Simultaneously, it effectively eliminates internal stresses caused by compositional inhomogeneity and cold / hot working, providing a homogeneous and stable microstructure foundation for subsequent processing and final performance. Therefore, the homogenization temperature in this invention can be 1190℃, 1195℃, 1200℃, 1205℃, 1210℃, 1215℃, 1220℃, 1225℃, or 1230℃.

[0051] Specifically, in step S3, the heating temperature of the bar is 1180-1230℃, and the holding time is 8-16h.

[0052] It should be noted that holding the nickel-based heat-resistant alloy bars at 1180–1230℃ for 8–16 hours provides good processing performance. Below 1180℃, the deformation temperature is low, the deformation resistance is high, the alloy is difficult to deform, causing significant damage to processing equipment and increasing the risk of cracking. Above 1230℃, the excessively high temperature can lead to melting of the alloy grain boundaries, resulting in hot cracking. After the bars are removed from the furnace, they are thoroughly lubricated using glass powder lubricant spraying, followed by hot piercing. After piercing, they are air-cooled to room temperature. Therefore, the heating temperature of the bars in this invention can be 1180℃, 1185℃, 1190℃, 1195℃, 1200℃, 1205℃, 1210℃, 1215℃, 1220℃, 1225℃, or 1230℃.

[0053] It should be noted that the billet is processed after piercing. To ensure the uniformity of the thickness of the thick-walled tube billet during hot extrusion, the billet has a hollow cylindrical structure with a bevel at one end, with an angle of 30-60°. This optimizes the uniformity of metal flow during the extrusion filling stage, significantly reduces the risk of defects, and lowers the maximum extrusion pressure during the breakthrough extrusion stage. After piercing, the billet needs to be fully processed, with both inner and outer surfaces polished to a smooth finish, free of deep tool marks, burrs, and cracks, to reduce friction and stress concentration between the workpiece and the extrusion cylinder wall.

[0054] Specifically, in step S4, the heating temperature of the blank is 1180-1220℃, and the holding time is 8-12h; the heating temperature of the mold is 350-450℃.

[0055] During the extrusion process, the initial extrusion temperature is 1160–1200℃.

[0056] It should be noted that after the billet is obtained through piercing, the alloy's deformation resistance decreases following the initial deformation. Therefore, the heating temperature of the billet can be reduced during the extrusion process. Lowering the billet heating temperature reduces the grain coarsening rate during the holding period, thereby decreasing the initial grain size of the extruded tube.

[0057] It should be noted that when the initial extrusion temperature is controlled at 1160–1200℃, the alloy has low deformation resistance and the recrystallization process during extrusion is more complete.

[0058] By employing a follower mandrel, the relative movement between the inner surface of the tube blank and the outer surface of the mandrel during extrusion, which would otherwise lead to poor inner wall quality and uneven wall thickness, is avoided. The follower mandrel moves along with the tube blank during extrusion, minimizing the relative movement between the inner surface of the tube blank and the mandrel. This prevents the formation of V-shaped cracks inside the tube and improves the inner surface quality of the extruded tube blank.

[0059] Specifically, in step S5, the solution treatment temperature is 1130-1180℃, the holding time is 1-2 hours, and then the product is removed from the furnace and cooled by water.

[0060] It should be noted that in this invention, a solution treatment is required before cold rolling, with the treatment temperature controlled between 1130 and 1180°C. If the solution treatment temperature is below 1130°C, the precipitation re-dissolution rate is slow, resulting in poor solution treatment effect; if the solution treatment temperature is above 1180°C, the grain size coarsens significantly, easily leading to excessively large grain size in the subsequent finished product. The solution treatment time is controlled between 1 and 2 hours. Since the wall thickness of the S5 production billet is greater than that of the intermediate and finished tubes, a longer solution treatment time is required, set at 1 to 2 hours. Recrystallization through solution treatment eliminates work hardening, restores the plasticity of the material for subsequent deformation; simultaneously, by allowing the precipitated phase to dissolve back, the risk of cracking caused by coarse phases is eliminated, and the compositional uniformity is improved. Therefore, the solution treatment temperature in this invention can be 1130°C, 1140°C, 1150°C, 1160°C, 1170°C, or 1180°C.

[0061] Specifically, in step S5, the cold rolling speed is controlled at 20-50 times / minute, the cold rolling feed amount is 1-5mm, and the cold rolling deformation is ≥20%.

[0062] After one cold rolling, the furnace is held at 1130-1180℃ for 0.5-1 hour, and then the furnace is cooled by water.

[0063] It should be noted that after one cold rolling, it is necessary to hold the product at 1130-1180℃. If the holding temperature is lower than 1130℃, the precipitation and re-dissolution rate will be slow and the solid solution effect will be poor. If the holding temperature is higher than 1180℃, the grain size will be significantly coarsened, which will easily lead to excessively large grain size in the subsequent finished product. The solid solution time is 0.5-1h. The intermediate product has a thin wall and the solid solution time is shorter than that of the S5 billet.

[0064] Specifically, in step S6, the deformation of the second cold rolling is ≥40%. After the second cold rolling is completed, it is kept at 1150~1180℃ for 1~2 hours, and then it is taken out of the furnace and water-cooled.

[0065] It should be noted that in order to ensure that the precipitated phase is dissolved as much as possible, the solution temperature should be ≥1150℃, and this temperature should meet the ASME standard. Temperatures exceeding 1180℃ are likely to cause excessive coarsening of the pipe grains.

[0066] It should be noted that the second cold rolling process is crucial for refining the grain size, ensuring sufficient deformation in the final pass. After the second cold rolling, the finished pipe undergoes a performance heat treatment at 1150–1180℃ to allow the precipitated phases to dissolve back as much as possible, fully utilizing the solid solution strengthening elements to improve the high-temperature performance of the pipe.

[0067] The present invention also provides a large-diameter heat-resistant alloy pipe for nuclear power equipment, which is prepared by the method described in the present invention. The heat-resistant alloy pipe has an outer diameter ≥ Φ200mm, a wall thickness ≥ 10mm, a grain size of 2 to 6 grades with a grade difference ≤ 2 grades, and a uniform structure without cracks.

[0068] To more clearly describe the present invention, the following embodiments and comparative examples are provided for further illustration.

[0069] Example 1

[0070] A method for preparing a large-diameter heat-resistant alloy pipe for nuclear power equipment includes the following steps:

[0071] S1: The electrode is prepared by vacuum induction melting, then refined and solidified in a crystallizer by vacuum self-consumable remelting, and finally the alloy ingot is obtained.

[0072] The chemical composition of the alloy ingot is C: 0.08%, Cr: 22.0%, Co: 12.0%, Mo: 9.0%, Al: 1.2%, Ti: 0.4%, B: 0.004%, Cu: 0.3%, Si: 0.8%, Fe: 2.0%, Mn: 0.5%, with the balance being nickel and unavoidable impurity elements.

[0073] S2: The obtained alloy ingot is homogenized; the homogenization temperature is 1200℃ and the holding time is 50h, followed by forging to obtain a bar.

[0074] S3: The obtained bar is heated and then hot-pierced, and then processed to obtain a blank. The blank is a hollow cylindrical structure with an inclined surface at one end.

[0075] The bar stock is heated to 1220℃ and held for 12 hours. The cylindrical blank is obtained by hot piercing. The inner and outer surfaces of the workpiece are then machined. The blank surface is smooth and free of deep tool marks, burrs and cracks.

[0076] S4: The obtained billet and mold are heated separately, and then extruded using a follower mandrel to obtain an extruded billet; the billet is heated to 1200℃ and held for 10 hours, then heated to 1220℃ and held for 0.5 hours. During the transfer from the furnace, an insulating cover is added, the mold is preheated to 400℃, and extrusion is performed using a follower mandrel.

[0077] S5: After solution treatment and processing of the obtained extruded billet, it is subjected to one cold rolling to obtain intermediate cold-rolled tube; the solution treatment temperature is 1150℃, the holding time is 1.5h, and it is water-cooled and processed; one cold rolling (30 times / minute, 3mm feed) with a deformation of 25%; after the one cold rolling is completed, it is held at 1150℃ for 0.75h, and then removed from the furnace and water-cooled.

[0078] S6: Finally, the obtained intermediate cold-rolled tube is subjected to a second cold rolling (deformation amount of 50%). After the second cold rolling, it is held at 1160℃ for 1.5h, and then cooled by water. The heat-resistant alloy tube is obtained with an outer diameter of 438mm, a wall thickness of 16mm, and a length of 8m.

[0079] Example 2

[0080] The preparation process of Example 2 is largely the same as that of Example 1, except that in Example 2:

[0081] S2: Homogenization treatment at 1200℃ for 48 hours.

[0082] S3: The bar is heated to 1180℃ for 16 hours.

[0083] S4: The billet is heated to 1170℃ for 12 hours, then raised to 1190℃ and held for 0.5 hours. During the transfer process after unloading from the furnace, an insulated cover is used, and the mold is preheated to 350℃.

[0084] S5: Solution treatment is 1130℃ / 2h water cooling; one cold rolling (20 times / minute, 1mm feed); followed by 1130℃ / 1h water cooling, with a deformation of 20%.

[0085] S6: Secondary cold rolling (deformation amount of 40%); finally water-cooled at 1150℃ for 2 hours.

[0086] Example 3

[0087] The preparation process of Example 3 is largely the same as that of Example 1, except that in Example 3:

[0088] S2: Homogenization treatment at 1200℃ for 60 hours.

[0089] S3: The bar is heated to 1230℃ for 8 hours.

[0090] S4: The billet is heated to 1210℃ for 8 hours, then raised to 1230℃ and held for 0.5 hours. During the transfer process after unloading from the furnace, an insulated cover is used, and the mold is preheated to 450℃.

[0091] S5: Solution treatment is 1180℃ / 1h water cooling; one cold rolling (50 times / minute, 5mm feed) with a deformation of 25%; followed by 1180℃ / 0.5h water cooling.

[0092] S6: Secondary cold rolling (40% deformation); finally water-cooled at 1180℃ / 1h.

[0093] Example 4

[0094] The preparation process of Example 4 is largely the same as that of Example 1, except that in Example 4:

[0095] S2: Homogenization treatment at 1200℃ for 55 hours.

[0096] S3: The bar is heated to 1210℃ for 10 hours.

[0097] S4: The billet is heated to 1180℃ for 11 hours, then raised to 1200℃ and held for 0.5 hours. During the transfer process after unloading from the furnace, an insulated cover is used, and the mold is preheated to 380℃.

[0098] S5: Solution treatment at 1160℃ for 1.2h followed by water cooling; one cold rolling (40 times / minute, 2mm feed) with a deformation of 25%; followed by water cooling at 1160℃ for 0.8h.

[0099] S6: Secondary cold rolling (50% deformation); finally water-cooled at 1160℃ for 1.2h.

[0100] Comparative Example 1

[0101] The preparation process of Comparative Example 1 is largely the same as that of Example 1, except that in Comparative Example 1, the homogenization treatment temperature of S2 is reduced to 1100℃ (far below 1200℃) and kept at that temperature for 50 hours.

[0102] Results: Dendritic segregation in the ingot was not completely eliminated, resulting in uneven microstructure, grain size difference > 3 grade, and local microcracks during subsequent processing.

[0103] Comparative Example 2

[0104] The preparation process of Comparative Example 2 is largely the same as that of Example 1, except that in Comparative Example 2, the heating temperature of the bar is reduced to 1100℃ (below the lower limit of 1180℃) and kept at that temperature for 12 hours.

[0105] If the heating temperature is too low, the material has poor plasticity, exceeding the equipment's processing capacity, and a complete tube blank cannot be obtained, resulting in process failure.

[0106] Comparative Example 3

[0107] The preparation process of Comparative Example 3 is largely the same as that of Example 1. The difference is that in Comparative Example 3, S3: after perforation, the inner and outer surfaces are roughly processed, and the inner surface has some residual cracks and deep tool marks.

[0108] During subsequent extrusion, the cracks expand further, increasing the amount of subsequent processing and resulting in a decrease in the yield of the pipe fittings.

[0109] Comparative Example 4

[0110] The preparation process of Comparative Example 4 is largely the same as that of Example 1, except that in Comparative Example 4, the billet temperature in S4 is reduced to 1150°C and an insulation cover is added.

[0111] During the billet transfer process, the surface temperature of the workpiece drops, especially at the end face where the surface is thinner and the cooling rate is faster, resulting in a more severe temperature drop. This leads to excessive stress during the extrusion process, causing transverse cracks.

[0112] Comparative Example 5

[0113] The preparation process of Comparative Example 5 is largely the same as that of Example 1, except that in Comparative Example 5: S5: the solution treatment temperature is increased to 1200℃ (higher than the upper limit of 1180℃), and the solution is kept at this temperature for 1.5h before water cooling.

[0114] The grains grow abnormally, and the grain size coarsens to grade 0-3, exhibiting obvious mixed crystal phenomenon. Although there are no cracks, the strength of the pipe is significantly reduced.

[0115] Comparative Example 6

[0116] The preparation process of Comparative Example 6 is largely the same as that of Example 1, except that in Comparative Example 6: S6: the amount of secondary cold rolling deformation is 20% (far lower than 40%).

[0117] Insufficient deformation and inadequate recrystallization driving force result in uneven microstructure, severe mixed crystals, and a significant decrease in pipe strength after final heat treatment.

[0118] Grain size detection

[0119] The above Examples 1-4 and Comparative Examples 1-6 were subjected to grain size testing and surface quality inspection. The main test results are shown in Table 1.

[0120] Table 1 Grain size detection and surface quality inspection

[0121]

[0122]

[0123] Performance testing

[0124] The above Examples 1-4 and Comparative Examples 1-6 were subjected to performance tests, mainly including tensile strength, yield strength and elongation after fracture at 750℃. The test results are shown in Table 2.

[0125] Table 2 Performance Test Results

[0126]

[0127]

[0128] Referring to Examples 1-4 and Comparative Examples 1-6, and referring to Tables 1 and 2, and referring to... Figure 1-6 As can be seen, the large-diameter heat-resistant alloy pipe prepared by the method provided in this invention has an outer diameter of 438 mm and a wall thickness of 16 mm. It possesses excellent surface quality, is defect-free, and has a surface roughness Ra ≤ 1.6 μm. The microstructure is uniform, with a grain size ranging from 2 to 6 grades, and a grade difference of less than 2 grades. It exhibits excellent high-temperature performance, with a tensile strength exceeding 470 MPa, a yield strength exceeding 170 MPa, and an elongation after fracture exceeding 82% at 750℃.

[0129] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing a large-diameter heat-resistant alloy pipe for nuclear power equipment, characterized by, The method comprises the following steps: S1: preparing an electrode by vacuum induction smelting, and then refining and solidifying in a crystallizer by vacuum consumable remelting to obtain an alloy ingot; S2: homogenizing and forging the obtained alloy ingot to obtain a rod; S3: heating the obtained rod, hot piercing, and then processing to obtain a blank, wherein the blank is a hollow cylindrical structure, and a bevel is formed at one end of the blank; S4: heating the obtained blank and a die, and then extruding by using a follow-up core rod to obtain an extruded blank; S5: solid solution treating and processing the obtained extruded blank, and then cold rolling once to obtain an intermediate product cold-rolled tube; S6: finally cold rolling the obtained intermediate product cold-rolled tube twice to obtain a heat-resistant alloy tube.

2. The method of claim 1, wherein the method is characterized by: The chemical composition of the tube comprises, in percentage by weight: C: 0.05-0.15%, Cr: 20.0-24.0%, Co: 10.0-15.0%, Mo: 8.0-10.0%, Al: 0.8-1.5%, Ti: ≤0.6%, B: ≤0.006%, Cu: ≤0.5%, Si: ≤1.0%, Fe: ≤3.0%, Mn: ≤1.0, and the balance being nickel and inevitable impurities.

3. The method of claim 1, wherein the method further comprises the steps of: In step S2, the homogenizing temperature is 1190-1230°C, and the holding time is more than 48 h. ​ 4. The method of claim 1, wherein the method further comprises the steps of: In step S3, the heating temperature of the rod is 1180-1230°C, and the holding time is 8-16 h. ​ 5. The method of claim 1, wherein the large diameter heat resistant alloy pipe for nuclear power equipment is prepared by the steps of: In step S4, the heating temperature of the blank is 1180-1220°C, and the holding time is 8-12 h; and the heating temperature of the die is 350-450°C. ​ In the extrusion process, the initial extrusion temperature is 1160-1200°C.

6. The method of claim 1, wherein the method further comprises the step of: In step S5, the solid solution treatment temperature is 1130-1180°C, and the holding time is 1-2 h, and then water cooling is performed after the furnace is discharged. ​ 7. The method of claim 1, wherein the large diameter heat resistant alloy pipe for nuclear power equipment is prepared by the steps of: In step S5, the first cold rolling speed is controlled to be 20-50 times per minute, the first cold rolling feed amount is 1-5 mm, and the first cold rolling deformation amount is ≥20%; ​ After the first cold rolling is completed, the holding temperature is 1130-1180°C, the holding time is 0.5-1 h, and then water cooling is performed after the furnace is discharged.

8. The method of claim 1, wherein the method is characterized by: In step S6, the second cold rolling deformation amount is ≥40%, and after the second cold rolling is completed, the holding temperature is 1150-1180°C, the holding time is 1-2 h, and then water cooling is performed after the furnace is discharged.

9. The method of claim 1, wherein the large diameter heat resistant alloy pipe for nuclear power equipment is prepared by the steps of: The heat-resistant alloy tube has a grain size of 2-6 levels, a level difference of ≤2 levels, a uniform structure, and no cracks. ​ 10. A large diameter heat resistant alloy pipe for nuclear power equipment, characterized by, The heat-resistant alloy tube obtained by the preparation method of any one of claims 1-9 has an outer diameter of ≥Φ200 mm and a wall thickness of ≥10 mm.

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