Fatigue-resistant internal thread copper pipe and preparation method thereof

Abstract

The application discloses a preparation method of fatigue-resistant inner thread copper pipe, which comprises the following steps: horizontally continuous casting copper liquid into ingot; milling, rolling and two-union drawing the ingot into hard-state union drawing pipe blank; the rolling process is as follows: the deformation temperature is 700-800 DEG C, the elongation coefficient is 5-8, the water flow of one-time rolling is 5-10 m 3 / h, and the water temperature is 35-55 DEG C; drawing the hard-state union drawing pipe blank through multiple passes to obtain inner thread mother pipe; on-line induction annealing the inner thread mother pipe to obtain soft-state inner thread mother pipe; sequentially performing inner thread forming and product annealing on the soft-state inner thread mother pipe to obtain the fatigue-resistant inner thread copper pipe; the product annealing process is as follows: the product annealing temperature is 330-380 DEG C, and the annealing time is 45-60 min. The application further discloses the inner thread copper pipe prepared through the preparation method, and the inner thread copper pipe can meet the fatigue-resistant test requirements when the environment-friendly CO2 is used.

Description

Technical Field

[0001] This invention belongs to the field of copper alloy processing, specifically relating to a high-fatigue internally threaded copper tube and its preparation method. Background Technology

[0002] Internally threaded copper tubes, also known as non-smooth tubes, refer to copper tubes with a smooth outer surface and a certain number of regularly spaced internal threads on the inner surface. Due to the increased inner surface area, the thermal conductivity of internally threaded copper tubes is 20% to 30% higher than that of smooth tubes. Internally threaded copper tubes are high-performance, high-value-added products that emerged after the national promotion of energy conservation and emission reduction. They retain the excellent thermal conductivity and high-temperature resistance of copper itself, and the tightly threaded structure expands the heat exchange surface, resulting in very high heat exchange efficiency. This allows for a significant reduction in the amount of copper material used while achieving the same heat exchange capacity. With the implementation of the energy efficiency ratio air conditioning access system in China, internally threaded copper tubes will be widely used in the air conditioning and refrigeration industry.

[0003] The inner surface of the internally threaded copper tube has a certain number of teeth of equal height. Compared with conventional smooth copper tubes, its inner surface heat exchange area increases by more than 20%. In addition, the internal teeth of the internal thread have a certain angle with the axis of the copper tube, which can promote the turbulent flow of refrigerant in the tube and effectively improve the heat exchange efficiency of the heat exchanger. It is widely used in air conditioning heat exchangers.

[0004] After the internally threaded copper tubing is processed into heat exchangers, a pulse fatigue test is used to evaluate the durability of the heat exchangers made of copper tubing material after long-term use. This involves repeatedly pressurizing and depressurizing the copper tubing under a set pressure until fatigue fracture and leakage occur, thus determining its lifespan and reliability. Currently, conventional refrigerants use R22 or R410A, requiring air conditioning heat exchangers to withstand 200,000 fatigue cycles at 3-4 MPa pressure without leakage.

[0005] Chinese patent CN109175283A discloses a heat pipe material tube processing technology, including: furnace cleaning and phosphorus reduction, horizontal continuous casting, milling, three-planetary rolling, three-stage stretching, coil stretching, online annealing, internal thread forming, rewinding, intermediate annealing, packaging, air stretching, straightening and sawing + flaw detection and packaging for warehousing. The furnace cleaning and phosphorus reduction, horizontal continuous casting, internal thread forming, intermediate annealing, air stretching, and straightening and sawing processes are special processes for producing TU2 copper tubes, which are different from TP2 air conditioning tubes.

[0006] Because R22 or R410A refrigerants damage the atmospheric ozone layer, the refrigeration industry is gradually using environmentally friendly CO2 refrigerant. However, the new CO2 refrigerant has poor cooling performance, requiring a larger amount of CO2 refrigerant to be injected into the copper pipes and condensers to ensure cooling efficiency. Therefore, when CO2 refrigerant is used, the air conditioner's evaporator and condenser must withstand 200,000 cycles at 5-8 MPa without leakage. The fatigue resistance test of the internally threaded copper pipe disclosed in the aforementioned patent can meet the testing requirements of air conditioner condensers using conventional refrigerants R22 or R410A, but it cannot meet the fatigue resistance test requirements when using environmentally friendly CO2 refrigerant. During repeated pressing and depressurization, the copper pipe is prone to cracking at the grain boundaries where the microstructure is coarse, leading to leakage in the condenser and condenser. Summary of the Invention

[0007] This invention discloses a method for preparing fatigue-resistant internally threaded copper tubes. The internally threaded copper tubes prepared by this method can meet the fatigue resistance test requirements when using environmentally friendly CO2.

[0008] This invention provides a method for preparing a fatigue-resistant internally threaded copper tube, comprising:

[0009] (1) Continuously cast the molten copper into ingots horizontally;

[0010] (2) The ingot is successively milled, rolled, and double-stretched into a hardened tube blank. The rolling process is as follows: deformation temperature is 700-800℃, elongation coefficient is 5-8, and water flow rate for one rolling pass is 5-10 m³. 3 / h, water temperature is 35-55℃;

[0011] (3) The internally threaded mother tube is obtained by multi-pass coil drawing of the hardened tube blank, wherein the drawing coefficient of the first and second passes is 1.6-1.8;

[0012] (4) The internally threaded mother tube is subjected to online induction annealing to obtain a soft internally threaded mother tube;

[0013] (5) The soft internal thread mother tube is subjected to internal thread forming, horizontal rewinding and finished product annealing in sequence to obtain fatigue-resistant internal thread copper tube. The finished product annealing process is as follows: the finished product annealing temperature is 330-380℃ and the annealing cycle time is 45-60min.

[0014] This invention achieves dynamic recrystallization of the tube blank by providing a suitable deformation temperature, further refining and homogenizing the grains. By providing a suitable rolling elongation coefficient, coarse grains in the microstructure are fully broken and refined, promoting uniform grain size and resulting in smaller grains. Controlling the water flow rate and temperature allows the grains to grow to a suitable size; that is, the average grain size of the rolled tube blank is 0.025-0.05 mm, with a grain size deviation not exceeding 0.02 mm. This invention uses multi-pass coiling and a suitable stretching coefficient to stretch the hardened tube blank to the target size of the internally threaded mother tube, controlling the average grain size of the internally threaded mother tube to be 0.003-0.006 mm, with a grain size deviation not exceeding 0.003 mm. Online induction annealing softens the internally threaded mother tube to facilitate internal thread forming. Through a suitable finished product annealing process, a fatigue-resistant internally threaded copper tube with an average grain size of 0.010-0.015 mm and a grain size deviation within 0.005 mm is finally obtained. This invention controls the average grain size and grain size deviation of the tube blanks produced in each process, so that the final process, namely the finished product annealing process, can produce finished internal threaded copper tubes with suitable average grain size and grain size deviation, which meet the fatigue resistance test requirements when using environmentally friendly CO2.

[0015] When the elongation coefficient provided by this invention is less than 1.6, the degree of grain deformation is small, dislocations accumulate near the grain boundaries, there is no interaction between grains, and grain breakage is not obvious. As the elongation coefficient increases, entanglement occurs between grains, causing the grains to break into subgrains. The greater the deformation, the more fragmented the grains, the more subgrains there are, and the more obvious the grain refinement is, with the edges being refined and the center being larger. When the elongation coefficient exceeds 1.8, the tensile stress exceeds the ultimate tensile strength of the copper tube, and tube breakage is likely to occur.

[0016] If the average grain size of the copper tube after online annealing provided by this invention is less than 0.010 mm, the internal stress of the copper tube is not fully released, the copper tube performance is too hard, which will increase the total resistance of subsequent internal thread forming and drawing, and affect the filling of the tooth shape; if the grain size of the copper tube after online annealing is greater than 0.020 mm, the copper tube performance is too soft, the grain is coarse, which will indirectly affect the grain size of the finished product, making the finished product grain larger.

[0017] The average grain size of the finished copper tube provided by this invention needs to be controlled between 0.010 and 0.015 mm, and the grain size deviation between the edge and center of the finished copper tube should be controlled within 0.005 mm. If the average grain size is less than 0.010 mm, the copper tube is too hard and is prone to bending cracks during the bending of U-tubes at the customer's site. If the average grain size of the finished product is greater than 0.015 mm, the copper tube grains are too large, the strength is reduced, and its fatigue resistance is decreased. Similarly, if the grain size of the finished copper tube is uneven, and the grain size deviation between the edge and center is greater than 0.005 mm, some grains are too large, and fatigue cracks will occur at the grain boundaries of the large grains during fatigue resistance testing, resulting in leakage.

[0018] When the annealing temperature of the finished product provided by this invention is less than 330℃ or the annealing cycle time is less than 45min, the internal stress of the copper tube is not fully released, and the copper tube grain size is less than 0.01mm. When the annealing temperature is higher than 380℃ or the annealing cycle time exceeds 60min, the copper tube grain growth rate is faster, the grain production is uneven, and the overall grain size is coarse, resulting in insufficient strength of the copper tube and easy fatigue leakage.

[0019] Furthermore, in step (1), the mass percentages of each component in the ingot are as follows: P is 0.03-0.04%, Ni is 0.01-0.02%, Cu is ≥99.9%, and the remainder is unavoidable impurities. Among them, P has little effect on the plasticity of the ingot, but it can improve the weldability of the finished product and refine the ingot grains; adding 0.01-0.02% Ni can form a solid solution with copper, which can refine the grains and improve the strength of the ingot.

[0020] Furthermore, in step (1), two water cooling processes are required during the horizontal continuous casting process. During the first water cooling, the cooling water is located outside the graphite crystallizer to cool the molten copper inside the graphite crystallizer. During the second water cooling, the cooling water comes into contact with the detached ingot to cool the detached ingot. During the second cooling, after the ingot has completely detached from the crystallizer, the ingot temperature has reached below the recrystallization temperature. In order to quickly reduce the overall temperature of the ingot, the cooling water is directly sprayed onto the surface of the ingot.

[0021] Furthermore, in step (1), during the first water cooling, the cooling water temperature is 20-45℃, and the water flow rate is 2-6 m³ / h. 3 / h. If the water temperature is below 20℃ or the water flow rate is greater than 6 m³ / h. 3 A high cooling rate ( / h) will cause the crystallization zone to shift towards the furnace opening, deepening the liquid cavity, increasing the pulling resistance, and making the ingot surface prone to cold shuts or cracks; conversely, if the water temperature is above 45℃ or the water flow rate is less than 2 m³ / h, the cooling intensity will be high, causing the crystallization zone to shift towards the furnace opening, thus deepening the liquid cavity, increasing the pulling resistance, and making the ingot surface prone to cold shuts or cracks. 3 The cooling intensity is low, which easily leads to the formation of coarse equiaxed and dendritic crystals. In addition, the solidified layer on the surface of the ingot is relatively thin, making the ingot prone to leakage and resulting in copper liquid leakage.

[0022] Furthermore, in step (4), the online induction annealing process is as follows: the current is 4850-5125A and the online induction annealing time is 0.2-0.25s.

[0023] The present invention also provides a fatigue-resistant internally threaded copper tube prepared according to the aforementioned method for preparing fatigue-resistant internally threaded copper tubes.

[0024] Furthermore, the average grain size of the fatigue-resistant internally threaded copper tube is 0.010-0.015 mm, with a grain size deviation within 0.005 mm. The fatigue-resistant internally threaded copper tube provided by this invention did not develop fatigue cracks under pressures of 5-8 MPa and pulse cycles of up to 200,000, demonstrating good fatigue resistance.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) By controlling the parameters of each process of rolling, online induction annealing and coil drawing, the present invention enables the tube blanks produced by the above processes to have suitable grain size and grain size deviation. Based on the reasonable control of the grain size and grain size deviation of the tube blanks by the preceding processes, the final annealing process can produce an internal spiral copper tube with a grain size deviation between the edge and the center within 0.005 mm and an average grain size of 0.010-0.015 mm. Thus, the internally threaded copper tubes produced by the present invention have good fatigue resistance.

[0027] (2) The high fatigue-resistant internal threaded copper tube provided by the present invention has high strength and fatigue resistance under suitable grain size and grain size deviation. It can meet the requirements of air conditioners using new environmentally friendly CO2 refrigerant. The two devices prepared by the internal threaded copper tube provided by the present invention did not leak in the fatigue resistance test with more than 200,000 pulse tests at a pressure of 5-8 MPa. Attached Figure Description

[0028] Figure 1 The images show the grain morphology of the ingots obtained in Example 1 and Comparative Example 2.

[0029] Figure 2 The image shows the morphology of the rolled grains obtained in Example 1.

[0030] Figure 3 The image shows the morphology of the rolled grains obtained in Comparative Example 2.

[0031] Figure 4 The image shows the grain morphology of the finished product obtained in Example 1.

[0032] Figure 5 The image shows the grain morphology of the finished product obtained from the disc pulling process in Comparative Example 2.

[0033] Figure 6 The image shows the grain morphology of the online annealed product obtained in Example 1.

[0034] Figure 7 The image shows the grain morphology of the online annealed product obtained in Comparative Example 2.

[0035] Figure 8 The image shows the grain morphology of the fatigue-resistant internally threaded copper tube prepared in Example 1.

[0036] Figure 9 The image shows the grain morphology of the fatigue-resistant internally threaded copper tube prepared in Comparative Example 2. Detailed Implementation

[0037] The present invention will be further described in detail below with reference to the accompanying drawings, embodiments, and comparative examples.

[0038] The preparation methods used in Examples 1 to 4 include the following steps:

[0039] 1) Horizontal continuous casting: Electrolytic copper, phosphor bronze alloy, copper-nickel alloy, and other raw materials are melted, cast, and drawn into ingots. During the process, the primary cooling water temperature is 20-45℃ and the water flow rate is 2-6m³ / h. 3 / h, the chemical composition of the ingot is Cu≥99.9%, P content is 0.03-0.04%, Ni content is 0.01-0.02%, and the remainder is the sum of unavoidable impurities;

[0040] 2) Milling, rolling and drawing: The ingot is successively milled, rolled and drawn into a hardened tube blank. The rolling elongation coefficient is 5-8, the primary cooling water temperature is 35-55℃ and the water flow rate is 5-10 m³ / h. 3 / h;

[0041] 3) Coil drawing: The rigid tube blank is continuously drawn to obtain the rigid internal threaded mother tube of the target size. The elongation coefficient of the first two passes of the coil drawing is 1.6-1.8.

[0042] 4) Online annealing: The hard-state internally threaded mother tube is softened by online induction annealing to obtain a soft-state internally threaded mother tube. The average grain size of the copper tube after annealing is 0.010-0.020mm.

[0043] 5) Internal thread forming: The annealed mother tube is internally threaded and spun.

[0044] 6) Horizontal rewinding: The internally threaded copper tube after internal threading is finished and wound up on a horizontal rewinding machine;

[0045] 7) Finished product annealing: The finished copper tubes are placed in a roller hearth furnace for static annealing at a temperature of 330-380℃ and a cycle time of 45-60 minutes.

[0046] The key process parameters in the preparation steps of Examples 1-4 are shown in Tables 1 and 2.

[0047] The difference between Comparative Example 1 and Example 1 is that the P content in the chemical composition of the ingot in the horizontal continuous casting process is not within the scope of this invention, and the P content is 200 ppm.

[0048] The difference between Comparative Example 2 and Example 1 is that the Ni content in the ingot chemical composition of the horizontal continuous casting process is not within the scope of this invention, and the Ni content is 30 ppm.

[0049] The difference between Comparative Example 3 and Example 2 is that the primary cooling water temperature and flow rate in the horizontal continuous casting process are not within the range of this invention; the water temperature is 50°C and the water flow rate is 1.5 m³ / h. 3 / h.

[0050] The difference between Comparative Example 4 and Example 2 is that the elongation coefficient during rolling is not within the range of the present invention, and the processing elongation coefficient is 4.

[0051] The difference between Comparative Example 5 and Example 3 is that the primary cooling water temperature and flow rate during the rolling process are not within the range of this invention; the water temperature is 20°C and the water flow rate is 12 m³. 3 / h.

[0052] The difference between Comparative Example 6 and Example 3 is that the elongation coefficients of the first and second passes during the stretching process are not within the scope of the present invention. The elongation coefficient of the first pass is 1.56 and the elongation coefficient of the second pass is 1.53.

[0053] The difference between Comparative Example 7 and Example 4 is that the grain size of the online annealing is not within the scope of this invention, and the grain size of the online annealing is 0.025 mm.

[0054] The difference between Comparative Example 8 and Example 4 is that the annealing temperature and annealing cycle during the annealing process of the finished product are not within the scope of the present invention. The annealing temperature is 400°C and the annealing time is 70 min.

[0055] Table 1. Process parameters of Examples 1-4 of the present invention

[0056]

[0057] Table 2 Process parameters of Examples 1-4 of the present invention

[0058]

[0059] As shown in Tables 3 and 4, the larger the grain size deviation of the rolled billet, the larger the grain size deviation of the finished product. Furthermore, the grain size deviation of the internally threaded copper tube gradually decreases with each processing step. However, due to limited processing correction capabilities, when the grain size deviation of the preceding process exceeds a certain limit, the grain size deviation of the finished copper tube will exceed the target value of no more than 0.005 mm specified in this invention. For example, the difference between Comparative Example 2 and Example 1 is that the Ni content in the ingot chemical composition of the horizontal continuous casting process is not within the range of this invention; the Ni content is 30 ppm. Ni can form a solid solution with copper, which can refine the grains. The fatigue-resistant internally threaded copper tube developed in this invention requires the Ni content of the ingot to be 0.01%~0.02%. The Ni content in Comparative Example 2 is 30ppm, which is too low and cannot refine the grains. This results in a rolling grain deviation of 0.041mm (exceeding the requirement of no more than 0.02mm for the rolling grain deviation in this invention) and a finished product grain size deviation of 0.011mm (exceeding the requirement of no more than 0.005mm for the finished product grain deviation in this invention). Ultimately, this leads to the finished copper tube of Comparative Example 2 only passing 181,000 fatigue tests under 6MPa pressure, which cannot meet the standard of more than 200,000 tests.

[0060] like Figure 1 As shown, Figure 1 (a) shows the ingot grains obtained in Example 1, which are uniform in size and have no transgranularity. Figure 1 (b) shows the ingot grains obtained in Comparative Example 2. Due to the low Ni content, the grains were not refined, resulting in larger grains in some parts of the ingot and the appearance of transgranular phenomena.

[0061] like Figure 2 As shown, Example 1 shows the grain size of the rolled tube billet. Figure 2 (a) shows the edge grains of the rolled tube blank. Figure 2 (b) shows the central grains of the rolled tube blank. During the rolling process, the edges of the tube blank are directly processed in contact with the die, resulting in significant microstructural refinement. The central grains undergo dynamic recrystallization at the deformation temperature of 700-800℃ during rolling, further homogenizing the tube blank grains. Therefore, the edge grain size is 0.031 mm, and the central grain size is 0.045 mm, indicating a certain degree of grain deviation.

[0062] Figure 3 The rolled tube blank obtained in Comparative Example 2 is shown as having a grain size. Figure 3 (a) shows the grain size at the edge of the rolled tube blank. Figure 3(b) shows the central grain of the rolled tube blank. Because the Ni content in the rolled tube blank obtained in Comparative Example 2 is low and the grain of the ingot itself is large, the rolling process can refine the uniform grain to a certain extent, but the deviation between the edge and the center grain is large. The edge grain is 0.041 mm and the center grain is 0.082 mm, with a grain deviation of 0.041 mm, which exceeds the requirement of no more than 0.02 mm for the rolled tube blank of this invention.

[0063] Figure 4 The image shows the finished grains of the disc-pulled product obtained in Example 1. Figure 4 (a) shows the edge grains of the finished product. Figure 4 (b) shows the central grain size of the finished product. After the rolled billet undergoes two-stage drawing and multiple passes of coil drawing, the grain size gradually becomes finer and more uniform, with an edge grain size of 0.0037 mm and a central grain size of 0.0052 mm, with a deviation of 0.0015 mm.

[0064] Figure 5 The image shows the grains of the finished product obtained from the disc-pulled method in Comparative Example 2. Figure 5 (a) shows the edge grains of the finished product. Figure 5 (b) shows the center grain of the coiled product. Compared with the coiled product obtained in Example 1, the edge and center grain deviations are larger, and the overall average grain size is also larger, with edge grains of 0.0043 mm, center grains of 0.0096 mm, and a deviation of 0.0053 mm.

[0065] Figure 6 The online annealed finished grains obtained in Example 1 are shown. Figure 6 (a) shows the edge grains of the finished product after online annealing. Figure 6 (b) shows the central grain of the online annealed finished product. After being heated online by induction electromagnetic heating, the coiled finished product undergoes recrystallization, and the grains grow rapidly, with the edge grains reaching 0.012 mm and the central grains reaching 0.018 mm, and the grain deviation being 0.006 mm, which meets the requirement of the present invention that the grain deviation of online annealing does not exceed 0.01 mm.

[0066] Figure 7 The online annealed finished grains obtained in Comparative Example 2 are shown. Figure 7 (a) shows the edge grains of the finished product after online annealing. Figure 7 (b) shows the central grain size of the online annealed product. The average grain size of the online annealed product obtained in Comparative Example 2 is consistent with that of the online annealed product obtained in Example 1, with the edge grain size reaching 0.009 mm, the central grain size reaching 0.028 mm, and the grain deviation reaching 0.019 mm.

[0067] Figure 8 The annealed finished grains obtained in Example 1 are shown. Figure 8 (a) shows the edge grains of the annealed finished product. Figure 8(b) shows the central grain of the annealed finished product. After low-temperature, long-cycle annealing of the finished product, the copper tube grains grow and gradually become more uniform, with the edge grains reaching 0.013 mm, the central grains reaching 0.016 mm, and the grain deviation reaching 0.003 mm.

[0068] Figure 9 The annealed finished grains obtained in Comparative Example 2 are shown. Figure 9 (a) shows the edge grains of the annealed finished product. Figure 9 (b) shows the central grain of the annealed finished product. The edge grain is 0.01 mm and the central grain is 0.021 mm, with a deviation of 0.011 mm. Even if the low-temperature, long-cycle annealing of the finished product further reduces the deviation between the edge and the central grain, it still cannot meet the requirement that the grain deviation of the finished product does not exceed 0.005 mm.

[0069] Table 3. Process data and fatigue resistance properties of finished products in the embodiments and comparative examples of the present invention.

[0070]

[0071] Table 4. Process data and fatigue resistance of finished products in the embodiments and comparative examples of the present invention.

[0072]

[0073] Note: In Comparative Example 5, due to the low cooling water temperature and high cooling water flow rate during the rolling process, the grains were small and the properties were hard, resulting in tube breakage during the rolling process, which prevented normal subsequent production.

Claims

1. A method of producing a fatigue resistant internal threaded copper pipe, characterized by, The method comprises the following steps: (1) horizontally casting the copper liquid into ingots; (2) the ingot is sequentially subjected to face milling, rolling and two-step drawing to form a hard-state two-step drawn pipe blank, the rolling process is as follows: the deformation temperature is 700-800 DEG C, the elongation coefficient is 5-8, the rolling water flow is 5-10 m 3 / h, and the water temperature is 35-55 DEG C; (3) stretching the hard-state coupled pipe blank in multiple passes to obtain an inner threaded mother pipe, wherein the stretching coefficient of the first pass and the second pass is 1.6-1.8; (4) on-line induction annealing the inner threaded mother pipe to obtain a soft-state inner threaded mother pipe; (5) sequentially performing inner thread forming, horizontal rewinding and finished product annealing on the soft-state inner threaded mother pipe to obtain the fatigue-resistant inner threaded copper pipe, wherein the finished product annealing process is as follows: the finished product annealing temperature is 330-380℃, and the annealing cycle time is 45-60min; After rolling, the average grain size of the pipe blank is 0.025-0.05mm, and the grain size deviation is not more than 0.02mm; The average grain size of the inner threaded mother pipe is 0.003-0.006mm, and the grain size deviation is not more than 0.003mm; The average grain size of the fatigue-resistant inner threaded copper pipe is 0.010-0.015mm, and the grain size deviation is within 0.005mm.

2. The method of producing a fatigue resistant interior threaded copper tube according to claim 1, characterized by, In step (1), the mass percentage of each component of the ingot is as follows: P is 0.03-0.04%, Ni is 0.01-0.02%, Cu is ≥99.9%, and the rest is inevitable impurities.

3. The method of producing a fatigue resistant interior threaded copper tube according to claim 1, characterized by, In step (1), two water cooling processes are needed during the horizontal continuous casting, wherein in the first water cooling process, the cooling water is located outside the graphite crystallizer to cool the copper liquid inside the graphite crystallizer; and in the second water cooling process, the cooling water is in contact with the separated ingot to cool the separated ingot.

4. The method of producing a fatigue resistant interior threaded copper tube according to claim 3, characterized by, In horizontal continuous casting process, the first time water cooling, the cooling water temperature is 20-45℃, the water flow is 2-6m 3 / h.

5. The method of producing a fatigue resistant interior threaded copper tube according to claim 1, characterized by, In step (4), the on-line induction annealing process is as follows: the current is 4850-5125A, and the on-line induction annealing time is 0.2-0.25s.

6. A fatigue-resistant inner threaded copper pipe prepared by the method according to any one of claims 1-5.

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