A rolling brazing connection method for thermonuclear fusion reactor composite tube with high brazing rate

Abstract

The invention belongs to the technical field of high-performance composite pipe manufacturing under fusion reactor working conditions, and specifically relates to a rolling and brazing connection method for composite pipes with high brazing rate for thermonuclear fusion reactors, comprising the following steps: step one: surface treatment of copper pipe components; step two: surface treatment of steel pipe components; step three: selection of brazing material and assembly of bimetallic pipes; step four: cold rolling and assembling composite pipes; step five: inspection of brazing gap and cleanliness of cold rolling and assembling composite pipes; and step six: vacuum brazing of the composite pipe after rolling.

Description

Technical Field

[0001] The invention belongs to the technical field of high-performance composite pipe manufacturing under fusion reactor working conditions, and specifically relates to a rolling brazing connection method for composite pipes with high brazing rate for thermonuclear fusion reactors. Background Art

[0002] At present, one of the key issues restricting the research of nuclear fusion reactors is the connection problem between various functional materials such as plasma-facing materials, heat sink materials and structural materials. Stainless steels such as austenitic stainless steels and low-activated ferritic steels are considered to be ideal materials for structural materials because of their good resistance to radiation expansion, oxidation resistance and high-temperature mechanical properties. Copper alloys have good electrical and thermal conductivity and are widely used as heat sink materials in the cooling systems of key components such as superconducting magnets and the first wall of the divertor. There are a large number of steel pipe copper component connection structures in fusion reactors. Among them, the steel pipe is a current-carrying component, and high-temperature or low-temperature fluid is passed inside. Copper is used as a heat sink material to transfer heat. In order to obtain better heat transport performance, the copper-steel joint must have a high-performance defect-free metallurgical bonding interface.

[0003] Therefore, it is of great significance to connect the copper parts of steel pipes with high quality and ensure the performance at high and low temperatures. At present, the main methods for connecting steel and copper are diffusion welding and brazing. Among them, vacuum brazing is widely used as a manufacturing method for steel and copper composite pipes because different filling materials can be selected according to needs.

[0004] At present, there are still several key problems in the vacuum brazing of steel-copper composite pipes:

[0005] 1) Due to processing errors, differences in thermal expansion coefficients between copper and steel, and assembly errors, it is difficult to ensure that the radial brazing gap of the composite pipe is within 0-0.1mm, and the brazing rate of the brazing joint cannot be guaranteed.

[0006] 2) Due to the capillary action of solder at high temperature, it is difficult to ensure high-quality connection of composite pipes over 200 mm in length using traditional filler methods.

[0007] Therefore, it is necessary to design a high brazing rate composite pipe rolling brazing connection method to solve the above technical problems. Summary of the invention

[0008] The purpose of the present invention is to design a rolling brazing connection method for a thermonuclear fusion reactor composite tube with a high brazing rate, so as to solve the technical problems in the prior art that the brazing rate of the brazing joint cannot be guaranteed and the connection quality of composite tubes with a length of more than 200 mm is low.

[0009] The technical solution of the present invention:

[0010] A method for rolling and brazing a composite tube with a high brazing rate for a thermonuclear fusion reactor includes wrapping a stainless steel tube with a foil-like brazing material and inserting it into a copper tube, and inserting a supporting mandrel into the stainless steel tube. Then, a tube-binding machine is used to roll the assembly, and the deformation of the copper tube is controlled each time to prevent cracks. After rolling, the ends are cut off, and then vacuum brazing is performed.

[0011] The specific steps include:

[0012] Step 1: Surface treatment of copper tube parts;

[0013] Step 2: Surface treatment of steel pipe components;

[0014] Step 3: Selection of brazing material and assembly of bimetallic tube;

[0015] Step 4: cold rolling and assembling the composite pipe;

[0016] Step 5: Check the brazing gap and cleanliness of the cold-rolled assembled composite pipe;

[0017] Step 6: Vacuum brazing of the composite pipe after rolling.

[0018] The step 1, surface treatment of the copper tube component, includes: the double-layer composite tube to be brazed is a double-layer coaxial assembly tube structure, wherein the inner tube is a steel tube; the outer tube is a copper tube, and the brazing material is thin; and the inner and outer tubes are inspected for size using inner and outer diameter micrometers to ensure that they meet the basic requirements of rolling.

[0019] The outer diameter of the outer copper tube before rolling is 2-30 mm and the thickness is 2-10 mm. 1200 mesh sandpaper is used to remove the oil and oxide film on the inner and outer surfaces of the outer copper tube. The outer copper tube before rolling is then placed in anhydrous ethanol for ultrasonic cleaning for 30-60 minutes and then blown dry for use.

[0020] The second step is surface treatment of the steel pipe component, including: the outer diameter of the inner steel pipe before rolling is 2-30mm, the thickness is 2-10mm, and the inner and outer surfaces of the inner steel pipe before rolling are cleaned with 1200 mesh sandpaper to remove oil and oxide film, and then the inner steel pipe before rolling is placed in anhydrous ethanol for ultrasonic cleaning for 30-60 minutes, and then blown dry for use.

[0021] The step three: selection of solder and assembly of bimetallic tubes, including: selecting foil-shaped Ag-based or Ni-based solder with a thickness of 0.05 mm; evenly wrapping the foil-shaped solder on the inner steel tube before rolling, and then inserting the inner steel tube before rolling into the outer copper tube before rolling; controlling the gap between the outer copper tube before rolling and the inner steel tube before rolling to be within the range of 1-2 mm.

[0022] The fourth step, cold rolling and assembling the composite pipe, includes: selecting a matching roller according to the size of the steel-copper composite pipe to be rolled, and selecting a solid mandrel with a diameter smaller than the inner diameter of the inner steel pipe;

[0023] Insert a solid core rod into the inner steel pipe, and control the gap between the core rod and the inner steel pipe within 0.15mm; use a tube rolling machine to roll the brazing assembly, and after each rolling pass, measure the size of the outer copper tube online, and fine-tune the roller gap according to the target value until the size is qualified; control the deformation of the outer copper tube at each pass at 20%-30%. After rolling, a metal composite tube to be brazed is formed, remove the surface oil and dirt of the metal composite tube to be brazed, ultrasonically clean it in anhydrous ethanol for 30 minutes, and blow dry it for use.

[0024] The step 5 comprises: cutting off 50 mm at each end of the metal composite pipe to be brazed to prevent the oil stains during the rolling process from affecting the brazed joint;

[0025] At the same time, the cut material is used for macroscopic metallographic detection to determine that the gap between the copper tube and the stainless steel tube should be controlled within 0.00-0.05mm to ensure the effect of subsequent vacuum brazing.

[0026] The step six, vacuum brazing of the rolled composite pipe, comprises: placing the brazing assembly in a vacuum furnace, and performing vacuum brazing simultaneously according to the following steps

[0027] Step 6.1: Evacuate to 8×10-3Pa, heat from room temperature to 600℃ for 2 hours, and keep warm for 30 minutes;

[0028] Step 6.2: Heat to 600°C-760°C for 30 minutes, and keep warm for 30 minutes;

[0029] Step 6.3: Heat to 760°C-815°C for 30 minutes, and keep warm for 30 minutes;

[0030] Step 6.4: Cooling to 600°C in the furnace;

[0031] Step 6.5: Fill with nitrogen and use a fan to quickly cool to room temperature at a cooling rate of about 10℃ / min.

[0032] The method of the present invention can uniformly fill a predetermined amount of solder, and the present invention ensures that the controlled brazing gap at any point of the composite pipe is the same, thereby ensuring a brazing rate of more than 95%; the present invention enables the brazing gap between the components to be brazed to be 0-0.02mm, which is particularly suitable for high-strength connection with a small brazing gap.

[0033] The size of the composite pipe manufactured by the method of the present invention is not limited by length, and is particularly suitable for brazing connection of a metal pipe with a large thermal expansion coefficient on the outer layer and a metal composite pipe with a small thermal expansion coefficient on the inner layer.

[0034] Beneficial effects of the present invention:

[0035] The high brazing rate composite pipe rolling brazing connection method designed by the present invention mainly ensures the brazing gap between the steel and copper composite pipes by rolling to obtain a high-quality brazing joint. The specific effects are as follows:

[0036] 1) This method can avoid the influence of the processing error of the bimetallic pipe to be brazed on the quality of the brazed joint. At the same time, the brazing gap between the copper pipe and the stainless steel pipe can be accurately determined by performing macroscopic metallographic inspection on the ends of the brazed composite pipe.

[0037] 2) The uniformity of the brazing gap of the composite pipe to be brazed is ensured by rolling within the circumference, thereby obtaining a vacuum brazed joint with a brazing rate of 100%;

[0038] 3) The metal composite pipe prepared by this method has higher strength because the width of the brazed joint is smaller than that of the ordinary joint;

[0039] 4) Since the brazing material is filled into the composite pipe to be brazed in advance, the disadvantage of the traditional method of filling the composite pipe due to the brazing material flow distance is overcome;

[0040] 5) This method can achieve close fit of the bimetallic composite pipe to be brazed, avoiding the hot assembly process before brazing in the prior art where the upper outer layer is a metal pipe with a large thermal expansion coefficient and the inner layer is a metal composite pipe with a small thermal expansion coefficient;

[0041] 6) In the case of using the same or different brazing materials of the brazing method, the method is also applicable to the brazing connection of multi-layer metal composite pipes. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of the structure of the composite pipe before rolling described in the present invention;

[0043] Figure 2 It is a schematic diagram of the cross-sectional structure of the composite pipe before rolling described in the present invention;

[0044] Figure 3 A schematic diagram of the rolled composite tube designed in the present invention;

[0045] Figure 4 This is a schematic diagram of the cross-sectional structure of the rolled composite tube designed in the present invention.

[0046] Among them: 1-outer copper tube before rolling, 2-foil brazing filler metal, 3-inner steel tube before rolling, 4-roller, 5-inner steel tube after rolling, 6-outer copper tube after rolling DETAILED DESCRIPTION

[0047] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0048] A method for rolling and brazing a composite tube with a high brazing rate for a thermonuclear fusion reactor, comprising the following steps:

[0049] Step 1: Surface treatment of copper tube components; including: the double-layer composite tube to be brazed is a double-layer coaxial assembly tube structure, wherein the inner tube is a steel tube; the outer tube is a copper tube, and the brazing material is thin; the inner and outer tubes are inspected by using inner and outer diameter micrometers to ensure that they meet the basic requirements of rolling.

[0050] The outer diameter of the outer copper tube before rolling is 2-30 mm and the thickness is 2-10 mm. 1200 mesh sandpaper is used to remove the oil and oxide film on the inner and outer surfaces of the outer copper tube. The outer copper tube before rolling is then placed in anhydrous ethanol for ultrasonic cleaning for 30-60 minutes and then blown dry for use.

[0051] Step 2: Surface treatment of steel pipe components; including: the outer diameter of the inner steel pipe before rolling is 2-30mm, the thickness is 2-10mm, and the inner and outer surfaces of the inner steel pipe before rolling are cleaned with 1200 mesh sandpaper to remove oil and oxide film, and then the inner steel pipe before rolling is placed in anhydrous ethanol for ultrasonic cleaning for 30-60 minutes, and then blown dry for use.

[0052] Step 3: Selection of solder and assembly of bimetallic tubes; including: selecting foil-like Ag-based or Ni-based solder with a thickness of 0.05 mm; evenly wrapping the foil-like solder on the inner steel tube before rolling, and inserting the inner steel tube before rolling into the outer copper tube before rolling; controlling the gap between the outer copper tube before rolling and the inner steel tube before rolling to be within the range of 1-2 mm.

[0053] Step 4: cold rolling and assembling the composite pipe; including: selecting a matching roller according to the size of the steel-copper composite pipe to be rolled, and selecting a solid mandrel with a diameter smaller than the inner diameter of the inner steel pipe;

[0054] Insert a solid core rod into the inner steel pipe, and control the gap between the core rod and the inner steel pipe within 0.15mm; use a tube rolling machine to roll the brazing assembly, and after each rolling pass, measure the size of the outer copper tube online, and fine-tune the roller gap according to the target value until the size is qualified; control the deformation of the outer copper tube at each pass at 20%-30%. After rolling, a metal composite tube to be brazed is formed, remove the surface oil and dirt of the metal composite tube to be brazed, ultrasonically clean it in anhydrous ethanol for 30 minutes, and blow dry it for use.

[0055] Step 5: Check the brazing gap and cleanliness of the cold-rolled composite pipe assembly; including: cutting off 50mm at both ends of the metal composite pipe to be brazed to prevent the oil stains during the rolling process from affecting the brazing joint;

[0056] At the same time, the cut material is used for macroscopic metallographic detection to determine that the gap between the copper tube and the stainless steel tube should be controlled within 0.00-0.05mm to ensure the effect of subsequent vacuum brazing.

[0057] Step 6: vacuum brazing of the rolled composite pipe, including: placing the brazing assembly in a vacuum furnace, and performing vacuum brazing simultaneously according to the following steps. The following is a detailed description of the vacuum brazing process using SCP1 brazing filler metal Ag68.4Cu26.6Pd5 brazing filler metal as an example.

[0058] Step 6.1: Evacuate to 8×10-3Pa, heat from room temperature to 600℃ for 2 hours, and keep warm for 30 minutes;

[0059] Step 6.2: Heat to 600°C-760°C for 30 minutes, and keep warm for 30 minutes;

[0060] Step 6.3: Heat to 760°C-815°C for 30 minutes, and keep warm for 30 minutes;

[0061] Step 6.4: Cooling to 600°C in the furnace;

[0062] Step 6.5: Fill with nitrogen and use a fan to quickly cool to room temperature at a cooling rate of about 10℃ / min.

[0063] The method of the present invention can uniformly fill a predetermined amount of solder, and the present invention ensures that the controlled brazing gap at any point of the composite pipe is the same, thereby ensuring a brazing rate of more than 95%; the present invention enables the brazing gap between the components to be brazed to be 0-0.02mm, which is particularly suitable for high-strength connection with a small brazing gap.

[0064] The size of the composite pipe manufactured by the method of the present invention is not limited by length, and is particularly suitable for brazing connection of a metal pipe with a large thermal expansion coefficient on the outer layer and a metal composite pipe with a small thermal expansion coefficient on the inner layer.

[0065] Embodiment 1:

[0066] Made of 1 meter long 316L stainless steel tube (inner layer) + T2 pure copper rod (outer layer) composite tube (served at extremely low temperature 4K, using SCP1 solder Ag68.4Cu26.6Pd5 solder)

[0067] Step 1. Select a T2 R-state pure copper tube with a specification of φ28mm*5mm and a length of 600mm. The straightness tolerance requirement of the copper tube is 0.2mm / 100mm.

[0068] Step 2. Select a 316L stainless steel pipe with a specification of φ17.15mm*2.31mm and a length of 1m. The straightness tolerance of the stainless steel pipe shall not exceed 0.2mm / 100mm.

[0069] Step 3. Use 1200-grit sandpaper to clean the oxides and impurities on the copper tube and stainless steel tube. Then put them into 10% nitric acid for pickling. Then put the copper tube and stainless steel tube into anhydrous ethanol for ultrasonic cleaning and blow dry for use. Select a foil-like AgCu272 solder with a thickness of 0.1mm, and evenly wrap the steel tube with a layer of solder. Then insert the steel tube wrapped with solder into the copper tube, and seal the gaps at both ends with glass glue; select a core rod with a diameter smaller than the inner diameter of the stainless steel tube, and control the gap between the core rod and the inner diameter of the stainless steel tube to 0.2-0.4mm.

[0070] Step 4. Use a pilger mill to roll the three-layer structure of copper tube, solder and stainless steel tube, and control the deformation of the copper tube in each pass within 15%-25%. After rolling, use petroleum ether to remove the surface oil and use ultrasonic cleaning in anhydrous ethanol for 30 minutes, remove the material heads at both ends of the composite tube and blow dry for use. Through macroscopic metallographic inspection of the material heads, it is confirmed that the gap between the copper tube and the stainless steel tube after rolling should be controlled within 0-0.05mm.

[0071] Step 5. Place the brazing assembly in a vacuum furnace and perform vacuum brazing simultaneously according to the following process: vacuumize to 5×10 -3 Pa, 0-600℃ (2h), keep warm for 1h, 600℃-760℃ (30min), keep warm for 30min, 760℃-815℃ (30min), keep warm at 815℃ for 30min, cool with the furnace to below 600℃, quickly cool to 80℃ with nitrogen and then take out the workpiece.

[0072] Embodiment 2:

[0073] Preparation of 1 meter long 316L stainless steel tube (inner layer) + T2 pure copper rod (outer layer) composite tube

[0074] (Ag72Cu28 solder used at extremely low temperatures)

[0075] Step 1. Select a T2 R-state pure copper tube with a specification of φ28mm*5mm and a length of 500mm. The straightness tolerance requirement of the copper tube is 0.2mm / 100mm.

[0076] Step 2. Select a 316L stainless steel pipe with a specification of φ17.15mm*2.31mm and a length of 1m. The straightness tolerance of the stainless steel pipe shall not exceed 0.2mm / 100mm.

[0077] Step 3. Use 1200-grit sandpaper to clean the oxides and impurities on the copper and stainless steel tubes. Then put them in 10% nitric acid for pickling. Then put the copper and stainless steel tubes in anhydrous ethanol for ultrasonic cleaning and blow dry for later use. Use AgCu272 solder with a thickness of 0.1mm.

[0078] Step 4. Use the electroplating method to electroplate a 5 μm nickel layer on the 316L steel pipe to improve the wettability of the brazing material on the outer surface of the stainless steel.

[0079] Step 5. Evenly wrap the steel pipe with solder. Then insert the steel pipe wrapped with solder into the copper pipe and seal the gaps at both ends with glass glue; select a core rod with a diameter smaller than the inner diameter of the stainless steel pipe, and control the gap between the core rod and the inner diameter of the stainless steel pipe to be 0.2-0.4mm.

[0080] Step 6. Use a pilger mill to roll the three-layer structure of copper tube, solder and stainless steel tube, and control the deformation of the copper tube in each pass within 15%-25%. After rolling, use petroleum ether to remove the surface oil and use ultrasonic cleaning in anhydrous ethanol for 30 minutes, remove the material heads at both ends of the composite tube and blow dry for use. Through macroscopic metallographic inspection of the material heads, it is confirmed that the gap between the copper tube and the stainless steel tube after rolling should be controlled within 0-0.05mm.

[0081] Step 7. Place the brazing assembly in a vacuum furnace and perform vacuum brazing simultaneously according to the following process: vacuumize to 5×10 -3 Pa, 0-600℃ (2h), keep warm for 1h, 600℃-760℃ (30min), keep warm for 30min, 760℃-800℃ (30min), keep warm at 800℃ for 30min, cool with the furnace to below 600℃, quickly cool to 80℃ with nitrogen and then take out the workpiece.

[0082] Embodiment 3:

[0083] Preparation of 1 meter long alloy718 tube (inner layer) + CuZrCr (outer layer) composite tube

[0084] (Serving at high temperature, using BNi2 brazing filler metal)

[0085] Step 1. Select a CuZrCr copper tube with a size of φ20mm*5mm and a length of 500mm. The straightness tolerance of the copper tube is required to be 0.2mm / 100mm.

[0086] Step 2. Select alloy718 tube with specification of φ10mm*3mm and length of 1m. The straightness requirement of alloy718 tube is 0.2mm / 100mm.

[0087] Step 3. Use 1200-grit sandpaper to clean the oxides and impurities of the CuZrCr copper tube and alloy718 tube. Then put them into 10% nitric acid for pickling. Then put the CuZrCr copper tube and alloy718 tube into anhydrous ethanol for ultrasonic cleaning and blow dry for use. Use foil-shaped BNi2 solder with a thickness of 0.02mm.

[0088] Step 4. Use solder to evenly wrap three layers of alloy718. Then insert the alloy718 tube wrapped with solder into the copper tube, and seal the gaps at both ends with glass glue;

[0089] Step 5. Use a pilger mill to roll the three-layer structure of copper tube, solder, and alloy718 tube. The deformation of the copper tube in each pass is controlled within 10%-20%. After rolling, use petroleum ether to remove the surface oil and use ultrasonic cleaning in anhydrous ethanol for 30 minutes. Remove the material heads at both ends of the composite tube and blow dry for use. Through macroscopic metallographic inspection of the material heads, it is confirmed that the gap between the copper tube and the stainless steel tube after rolling should be controlled within 0-0.15mm.

[0090] Step 6. Place the brazing assembly in a vacuum furnace and perform vacuum brazing simultaneously according to the following process: vacuumize to 1×10 -2 Pa, 0-600℃ (2h), keep warm for 1h, 600℃-800℃ (1h), keep warm for 30min, 800℃-1020℃ (1h), keep warm at 1020℃ for 30min, cool with the furnace to below 600℃, quickly cool to 80℃ with nitrogen and then take out the workpiece.

[0091] The present invention is described in detail above with reference to the accompanying drawings and embodiments, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of ordinary technicians in the field without departing from the purpose of the present invention. Any content not described in detail in the present invention can adopt the existing technology.

Claims

1. A method for rolling and brazing composite pipes with high brazing rate for thermonuclear fusion reactors, characterized in that: The steps include: Step 1: Surface treatment of copper tube components; including: the double-layer composite tube to be brazed is a double-layer coaxial assembly tube structure, wherein the inner tube is a steel tube; the outer tube is a copper tube, the brazing material is thin, and the brazing material is wrapped on the outer surface of the inner tube; Step 2: Surface treatment of steel pipe components; Step 3: Selection of solder and assembly of bimetallic tube; including: selecting foil-shaped Ag-based or Ni-based solder with a thickness of 0.05 mm; evenly wrapping the foil-shaped solder on the inner steel tube before rolling, and inserting the inner steel tube before rolling into the outer copper tube before rolling; controlling the gap between the outer copper tube before rolling and the inner steel tube before rolling to be within the range of 1-2 mm; Step 4: cold rolling and assembling the composite pipe; including: selecting a matching roller according to the size of the steel-copper composite pipe to be rolled, and selecting a solid mandrel with a diameter smaller than the inner diameter of the inner steel pipe; Insert a solid mandrel into the inner steel pipe, and control the gap between the mandrel and the inner steel pipe within 0.15 mm; use a tube rolling machine to roll the brazing assembly, and after each rolling pass, measure the size of the outer copper pipe online, and fine-tune the roller gap according to the target value until the size is qualified; control the deformation of the outer copper pipe at each pass to be 20%-30%, and after rolling, form a metal composite pipe to be brazed, remove the surface oil of the metal composite pipe to be brazed, ultrasonically clean it in anhydrous ethanol for 30 minutes, and blow dry it for use; Step 5: Check the brazing gap and cleanliness of the cold-rolled assembled composite pipe; Step 6: Vacuum brazing of the composite pipe after rolling.

2. A method for rolling and brazing a composite tube with high brazing rate for a thermonuclear fusion reactor as claimed in claim 1, characterized in that: In the step 1, the surface treatment of the copper tube parts uses inner and outer diameter micrometers to check the dimensions of the inner and outer tubes to ensure that they meet the basic requirements of rolling; The outer diameter of the outer copper tube before rolling is 2-30 mm and the thickness is 2-10 mm. 1200 mesh sandpaper is used to remove the oil and oxide film on the inner and outer surfaces of the outer copper tube. The outer copper tube before rolling is then placed in anhydrous ethanol for ultrasonic cleaning for 30-60 minutes and then blown dry for use.

3. A method for rolling and brazing a composite tube with high brazing rate for a thermonuclear fusion reactor as claimed in claim 2, characterized in that: The second step is surface treatment of the steel pipe component, including: the outer diameter of the inner steel pipe before rolling is 2-30mm, the thickness is 2-10mm, and the inner and outer surfaces of the inner steel pipe before rolling are cleaned with 1200 mesh sandpaper to remove oil and oxide film, and then the inner steel pipe before rolling is placed in anhydrous ethanol for ultrasonic cleaning for 30-60 minutes, and then blown dry for use.

4. A method for rolling and brazing a composite tube with high brazing rate for a thermonuclear fusion reactor as claimed in claim 3, characterized in that: The step 5 comprises: cutting off 50 mm at each end of the metal composite pipe to be brazed to prevent the oil stains during the rolling process from affecting the brazed joint; At the same time, the cut material is used for macroscopic metallographic detection to determine that the gap between the copper tube and the stainless steel tube should be controlled within 0.00-0.05mm to ensure the effect of subsequent vacuum brazing.

5. A method for rolling and brazing a composite tube with a high brazing rate for a thermonuclear fusion reactor as claimed in claim 4, characterized in that: The step six, vacuum brazing of the rolled composite pipe, comprises: placing the brazing assembly in a vacuum furnace, and performing vacuum brazing simultaneously according to the following steps Step 6.1: Evacuate to 8×10-3Pa, heat from room temperature to 600℃ for 2 hours, and keep warm for 30 minutes; Step 6.2: Heat to 600°C-760°C for 30 minutes, and keep warm for 30 minutes; Step 6.3: Heat to 760°C-815°C for 30 minutes, and keep warm for 30 minutes; Step 6.4: Cooling to 600°C in the furnace; Step 6.5: Fill with nitrogen and use a fan to quickly cool to room temperature at a cooling rate of about 10℃ / min.

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