Microalloyed copper alloy tube and process for producing the same

Abstract

This invention relates to the field of alloy technology, specifically disclosing a microalloyed copper alloy tube and its preparation process. The copper alloy tube is composed of the following components by mass percentage: Ni 0.05%-0.15%, Sn 0.05%-0.15%, Fe 0.01%-0.1%, P 0.02%-0.04%, with the balance being Cu and unavoidable impurities. The mass ratio of Sn to Ni is controlled between 0.5 and 3. It possesses a single face-centered cubic α-phase crystal structure, with an isometric grain ratio ≥85% in the microstructure and an average grain size of 10-20 μm. The preparation process achieves a three-dimensional strengthening effect of solution treatment, precipitation, and grain refinement. The product exhibits a tensile strength of 250-270 MPa, an elongation after fracture ≥45%, and a yield strength ratio of 0.32-0.36, combining high strength, low yield strength ratio, excellent machinability, and corrosion resistance. It is energy-efficient and easily mass-produced.

Description

Technical Field

[0001] This invention belongs to the field of alloy technology, specifically relating to a microalloyed copper alloy tube and its preparation process. Background Technology

[0002] With the rapid development of refrigeration equipment towards high efficiency, energy saving, and miniaturization, copper alloy materials used in heat exchangers and connecting pipes face higher performance challenges. Although traditional phosphorus deoxidized copper (such as TP2) has good machinability, its strength and burst pressure are limited, making it difficult to meet the design requirements of modern equipment for high pressure resistance and thin walls.

[0003] To improve the strength of copper tubes, existing technologies have proposed various high-strength copper alloy solutions. For example, patent document CN120648935A discloses a copper alloy tube with composite addition of Sn, Ni, and P, and the introduction of a high proportion of heavy-duty lattice grain boundaries. However, its Ni content range (0.08-0.3%), grain boundary ratio requirement (≥50%), and specific recrystallization process (deformation ≥80% or 3-6 cycles) constitute strict technical limitations. Patent document CN119265448A improves performance by adding Zr, B, and Mn and controlling the particle size of specific compounds, with clear requirements on the number of compounds and grain uniformity.

[0004] However, existing technologies have relatively fixed compositions and processes, which limit their ability to achieve synergistic optimization of higher strength, better thermal conductivity, plastic deformation capacity, and processing performance. Furthermore, some processes suffer from high energy consumption and narrow applicability, making it difficult to meet the diverse needs of industrial applications. Therefore, developing a microalloyed copper alloy tube with a rationally designed composition, energy-efficient process, and excellent overall performance, along with its preparation process, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a micro-alloyed copper alloy tube and its preparation process. Through specific component element ratio design, innovative microstructure control and differentiated process routes, a copper alloy tube with high strength, low yield strength ratio, excellent cold workability and high corrosion resistance is obtained, effectively circumventing the scope of existing patent protection, and at the same time having significant industrial application value.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A microalloyed copper alloy tube is composed of the following components in mass percentage: Ni 0.05%-0.15%, Sn 0.05%-0.15%, Fe 0.01%-0.1%, P 0.02%-0.04%, with the balance being Cu and unavoidable impurities; Ingredient design principles and functions: Ni (0.05%-0.15%): Infinitely miscible with copper, mainly contributing to solid solution strengthening. At the same time, it acts as a "lattice modifier" to increase the solid solubility of Sn in the copper matrix, creating "accommodation space" for larger Sn atoms. This significantly improves the room temperature solid solubility of Sn in Cu-Ni solid solution (from <0.01% to over 0.1%), preventing excessive Sn precipitation and the formation of a hard and brittle phase, thus ensuring the material's plasticity.

[0007] Sn (0.05%-0.15%): A highly efficient solid solution strengthening element that can significantly improve the strength and corrosion resistance of copper alloys. However, its room temperature solid solubility in copper is extremely low, and it needs to rely on the synergistic effect of Ni to achieve effective solid solution and avoid performance degradation.

[0008] Fe (0.01%-0.1%): It has extremely low solid solubility in copper at room temperature. It mainly forms nanoscale precipitates through supersaturation precipitation, which plays a role in precipitation strengthening and grain refinement.

[0009] P (0.02%-0.04%): It functions as both a deoxidizer and a reinforcing agent, effectively removing oxygen impurities from molten copper and improving material purity. It can also form stable compounds with Sn, Fe, etc., further optimizing strength and corrosion resistance.

[0010] The mass ratio of Sn to Ni is 0.5-3. This ratio range is key to improving the solid solubility of Sn with Ni and avoiding the precipitation of hard and brittle phases, thus ensuring a balance between solid solution strengthening and plasticity.

[0011] Fe-P forms Fe3P / Fe2P and (Fe,Ni)3P compounds at the nanoscale, contributing 15-25 MPa of precipitation reinforcement, and pinning grain boundaries at the micrometer scale to refine grains.

[0012] The microalloyed copper alloy tube has a single face-centered cubic crystal structure α phase, which avoids the decrease in processing performance caused by the presence of a second phase; in its microstructure, the proportion of equiaxed grains is ≥85%, and the average grain size is 10-20μm; the uniform and fine equiaxed crystal structure provides the microstructure basis for the material's excellent plasticity and processing stability; The microalloyed copper alloy tube is either an internally threaded tube or a plain tube.

[0013] In a preferred example, the material is composed of the following components by mass percentage: Ni 0.08%-0.11%, Sn 0.12%-0.15%, Fe 0.01%-0.05%, P 0.025%-0.035%, with the balance being Cu and unavoidable impurities. The mass ratio of Sn to Ni is 0.8-1.5. Within this range, the microalloyed copper alloy tube material exhibits the best synergistic effect in terms of strength, plasticity, and corrosion resistance.

[0014] In a preferred embodiment, the microalloyed copper alloy tube has a tensile strength of 250-270 MPa (tested according to GB / T228.1-2010), a yield strength of 78-95 MPa, a yield-to-tensile ratio of 0.32-0.36, and an elongation after fracture ≥45%; after a formic acid corrosion test in a 0.5% formic acid aqueous solution atmosphere with alternating hot and cold corrosion for 20 days, the maximum corrosion depth is ≤170 μm; it combines high strength with good cold workability, and can meet the application requirements of high pressure resistance and thin wall.

[0015] In a preferred embodiment, when the copper alloy tube is an internally threaded tube, its inner surface has a spiral groove structure, the tooth height of the spiral groove is 0.12-0.18 mm, and the apex angle is 35°-50°, which can enhance the heat exchange efficiency.

[0016] In a preferred example, when the copper alloy tube is a plain tube, its outer diameter is 5-20 mm and its wall thickness is 0.3-1.5 mm, which is suitable for conventional piping systems.

[0017] Based on a general inventive concept, another objective of this invention is to provide a manufacturing process for the aforementioned microalloyed copper alloy tube, employing a continuous casting and rolling process, including the following steps: (1) Batching and smelting: Prepare electrolytic copper (purity ≥99.98%), pure nickel plate, pure tin plate, pure iron block, and phosphorus copper master alloy (phosphorus content 13%-15%, purity ≥99.9%) according to the design composition; add electrolytic copper to the melting furnace, and set the melting furnace temperature to 1185±10℃; transfer the molten copper liquid to the casting furnace through the chute, and set the casting furnace temperature to 1150±10℃; after wrapping the pure nickel plate, pure iron block and pure tin plate with copper foil, add them to the middle chamber of the casting furnace to avoid oxidation and burning of alloy elements; 5 minutes before each liquid transfer, add the phosphorus copper master alloy directly to the middle chamber of the casting furnace to ensure uniform distribution of alloy elements.

[0018] (2) Continuous casting: The homogenized copper liquid is horizontally continuously cast with a maximum traction speed of 390 mm / min. The primary cooling water flow rate is controlled at 15-70 L / min, and the secondary cooling water flow rate is controlled at 30-80 L / min. By precisely controlling the cooling rate, a tube blank with uniform composition and dense structure is obtained, avoiding defects such as shrinkage cavities and segregation.

[0019] (3) Continuous rolling: The continuously cast tube blank is subjected to planetary rolling at a rolling speed of 1.5-2.0 m / min. The grains are refined by rolling deformation, and the uniformity of the structure is improved to obtain a rolled tube blank with an outer diameter of 51-55 mm and a wall thickness of 2.3-2.7 mm.

[0020] (4) Continuous stretching: The rolled tube blank is subjected to diameter reduction stretching at a speed of 10-80m / min, reducing the outer diameter of the tube blank to 20-28mm and the wall thickness to 1-1.4mm, so as to obtain an intermediate tube blank with dimensional accuracy that meets the requirements of subsequent processing.

[0021] (5) Coil drawing: The intermediate tube blank after the joint drawing is continuously drawn in 8-9 passes. The drawing speed is controlled at 8-12m / s, and the total deformation is controlled at 80%-85%. Through multiple passes of small deformation drawing, the work hardening is accumulated, providing conditions for subsequent annealing and recrystallization.

[0022] (6) Online annealing: The tube blank after coiling is softened by online annealing. The maximum annealing speed is 600m / min and the maximum heating voltage is 1000V. Recrystallization is achieved through rapid annealing, which eliminates some work hardening, improves the plasticity of the material, and lays the foundation for subsequent forming and processing.

[0023] (7) Forming process: When preparing internally threaded tubes, the tube blank after online annealing is spun into internal threads. The spinning speed is controlled at 480-650 r / min and the stretching speed is controlled at 40-60 m / min. Spiral grooves are formed on the inner wall of the tube (tooth height 0.12-0.18 mm, apex angle 35°-50°). When preparing plain tubes, the spinning step is omitted and the tubes directly enter the subsequent horizontal winding process.

[0024] (8) Horizontal winding: The formed tube blank is horizontally wound, and the winding speed is controlled at 250-350m / min to obtain a coil with a winding height of 200-400mm, which is convenient for subsequent batch annealing and storage and transportation.

[0025] (9) Finished product annealing: The coil obtained by horizontal winding is subjected to recrystallization annealing at a temperature of 440-490℃ (preferably 460-480℃) and a holding time of 30-33min (preferably 31-33min). Then, it is cooled to room temperature in the furnace. Through low-temperature short-time annealing, the grain size and microstructure are precisely controlled, and finally, a finished copper alloy tube with an equiaxed crystal ratio of ≥85% and an average grain size of 10-20μm is obtained. At the same time, work hardening is completely eliminated, and the strength and plasticity are balanced.

[0026] In a preferred example, in step (5), the total deformation of the disc is controlled to be 80%-85%.

[0027] In a preferred example, in step (7), the tooth height of the spiral groove is 0.12-0.18 mm and the apex angle is 35°-50°.

[0028] In a preferred example, in step (9), the annealing temperature of the finished product is 460-480℃ and the holding time is 31-33min.

[0029] Compared with the prior art, the advantages and positive effects of the present invention are as follows: 1. Optimized and innovative composition system: By adding trace amounts of Fe-Ni-Sn-P elements, and utilizing the different physical and metallurgical behaviors and synergistic effects of each element in the copper matrix, a three-in-one strengthening mechanism of "solid solution-precipitation-refinement" is constructed. The structure is optimized at multiple scales of atoms, nanometers, and micrometers, achieving a synergistic improvement in strength, plasticity, and corrosion resistance. Moreover, the composition range is clearly different from existing technologies, effectively avoiding patent barriers.

[0030] 2. Differentiated Process Path Design: The entire continuous casting and rolling process of "melting-continuous casting-continuous rolling-continuous drawing-coil drawing-online annealing-spinning-winding-finished annealing" is adopted. Through precise and coordinated control of parameters in each process, especially the combination of online annealing after coil drawing and low-temperature short-time annealing of finished product (440-490℃ / 30-33min), recrystallization is ensured while avoiding excessive grain growth. This effectively regulates the microstructure of the material, resulting in a high proportion of equiaxed grain structure and uniform and fine grain size (10-20μm). This provides the microstructure basis for excellent processing performance and significantly reduces energy consumption. Compared with the high-temperature long-time annealing of existing technologies (such as 580℃ / 90min), the energy saving effect is significant.

[0031] 3. Excellent overall performance: The prepared copper alloy tube has a tensile strength of 250-270MPa, which is about 10%-14% higher than that of traditional TP2 copper tube. The elongation after fracture is ≥45%, and the yield strength ratio is 0.32-0.36, combining high strength and good plasticity. It has excellent corrosion resistance, with a maximum formic acid corrosion depth of ≤170μm, which is better than TP2 copper tube. The spiral groove structure of the internally threaded tube further enhances the heat exchange efficiency. It has excellent processing performance such as bending and flaring, which can fully meet the comprehensive requirements of air conditioning heat exchangers and connecting piping for high pressure resistance, thin wall and easy processing.

[0032] 4. Wide applicability: The product forms include internally threaded tubes and plain tubes, which can be used in high-efficiency heat exchange equipment and conventional piping systems respectively. Moreover, the manufacturing process uses conventional industrial equipment, which does not require additional modification, making it easy to scale up production and have broad prospects for industrial applications. Attached Figure Description

[0033] Figure 1 This is a flowchart of the preparation process of the present invention; Figure 2The following are the grain orientation and grain morphology of Comparative Example 1 and Example 1 of the present invention: (a) is the IPF diagram of Comparative Example 1, showing the grain orientation distribution; (b) is the grain morphology classification diagram of Comparative Example 1 based on GOS analysis; (c) is the IPF diagram of Example 1, showing the grain orientation distribution; and (d) is the grain morphology classification diagram of Example 1 based on GOS analysis. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is further described in conjunction with specific embodiments. However, this invention is not limited to these embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments. In this invention, unless otherwise specified, the raw materials and reagents used are all conventional industrial-grade products, and the equipment used is all conventional commercially available equipment in the field of alloy processing, without any special customization requirements.

[0035] The specific embodiments of the present invention will be described in detail below.

[0036] Example 1

[0037] A microalloyed copper alloy internal threaded pipe, the composition by mass percentage is: Sn 0.15%, Ni 0.11%, P 0.028%, Fe 0.02%, with the balance being Cu and unavoidable impurities (Sn to Ni mass ratio is 1.36).

[0038] The preparation process is as follows: (1) Batching and smelting: Weigh out electrolytic copper, pure nickel plate, pure tin plate, pure iron block and phosphorus copper master alloy (Cu-14%P) according to the above composition ratio; add electrolytic copper to the melting furnace and set the temperature to 1178℃; after melting, transfer to the casting furnace and set the temperature to 1155℃; wrap the pure nickel plate, pure iron block and pure tin plate with copper foil and put them into the casting furnace chamber; add phosphorus copper master alloy 5 minutes before the liquid transfer to promote element homogenization.

[0039] (2) Continuous casting: Horizontal continuous casting, traction speed 380mm / min, primary cooling water flow rate 50L / min, secondary cooling water flow rate 65L / min, to obtain a tube blank with an outer diameter of φ90mm and a wall thickness of 15mm.

[0040] (3) Continuous rolling: planetary rolling speed of 1.8m / min to obtain rolled tube blank with an outer diameter of φ53mm and a wall thickness of 2.5mm.

[0041] (4) Pulling: Pulling speed is 60m / min, reducing the outer diameter to φ26mm and the wall thickness to 1.3mm.

[0042] (5) Coil drawing: 9 consecutive drawing passes, drawing speed 10m / s, total deformation 83%, finished tube outer diameter φ9.52mm, wall thickness 0.31mm.

[0043] (6) Online annealing: annealing speed 550m / min, heating voltage 850V, to obtain recrystallized structure.

[0044] (7) Internal thread spinning: spinning speed 550r / min, stretching speed 50m / min, forming spiral groove (tooth height 0.15mm, apex angle 45°).

[0045] (8) Horizontal winding: the winding speed is 300m / min, and a coil with a winding height of 300mm is obtained.

[0046] (9) Finished product annealing: annealing temperature 480℃, holding time 32min, and then cooling to room temperature in the furnace.

[0047] Example 2

[0048] A microalloyed copper alloy internally threaded pipe, the composition by mass percentage is: Sn 0.12%, Ni 0.08%, P 0.028%, Fe 0.06%, with the balance being Cu and unavoidable impurities (Sn to Ni mass ratio is 1.5).

[0049] The preparation process is the same as in Example 1.

[0050] Comparative Example 1

[0051] Commercially available TP2 phosphorus deoxidized copper tubing (composition: P 0.028%, balance Cu, excluding Sn and Ni), with a specification of φ7mm×0.37mm internal thread, was used as a comparison sample.

[0052] Comparative Example 2

[0053] Copper alloy tubes with specifications of φ7mm×0.35mm were prepared according to the composition (Sn 0.36%, Ni 0.10%, P 0.031%) of Example 2 in patent document CN120648935A and a single recrystallization process (total deformation of 88.1% by coiling, and annealing of finished product at 580℃ / 90min). The tubes were then processed into internally threaded tubes (the spiral groove parameters are the same as in Example 1).

[0054] Performance testing

[0055] The copper alloy tubes of Examples 1-2 and Comparative Examples 1-2 were subjected to performance tests, and the test methods were in accordance with the corresponding national standards (e.g., bending test refers to GB / T 232-2024, flaring test refers to GB / T 242-2007). The results are shown in the table below.

[0056]

[0057] The test results show that: The tensile strength of Examples 1 and 2 of the present invention is significantly higher than that of the traditional TP2 copper tube (Comparative Example 1), while maintaining better corrosion resistance and a higher proportion of equiaxed grain structure. The yield strength ratio is in a reasonable range of 0.32-0.36, which is beneficial for cold forming. Compared with Comparative Example 2 (existing patented process), the tensile strength of the embodiment of the present invention is slightly lower, but the yield strength ratio is closer to the practical processing requirements, which can improve the processing springback problem. Moreover, the finished product has a lower annealing temperature and a shorter holding time, resulting in significant energy-saving advantages. It also has a higher proportion of equiaxed crystals (≥88% VS 62%) and better microstructure uniformity. This invention achieves a balanced improvement in overall performance by synergistically optimizing the composition and process, while circumventing the scope of existing patent protection, and fully meets the requirements of high pressure resistance, thin wall, and easy processing for air conditioning heat exchangers and connecting pipes.

[0058] The above embodiments are merely preferred embodiments of the present invention. Any simple modifications, alterations, and substitutions made to the above embodiments based on the technical essence of the present invention shall fall within the scope of the technical solution of the present invention.

Claims

1. A micro-alloyed copper alloy tube, characterized in that, It is composed of the following components in mass percentage: Ni 0.05%-0.15%, Sn 0.05%-0.15%, Fe 0.01%-0.1%, P 0.02%-0.04%, with the balance being Cu and unavoidable impurities; The mass ratio of Sn to Ni is 0.5-3; the microalloyed copper alloy tube has a single face-centered cubic crystal structure α phase, and in its microstructure, the proportion of equiaxed grains is ≥85%, and the average grain size is 10-20μm. The microalloyed copper alloy tube is either an internally threaded tube or a plain tube.

2. The microalloyed copper alloy tube according to claim 1, characterized in that, It is composed of the following components in mass percentage: Ni 0.08%-0.11%, Sn 0.12%-0.15%, Fe 0.01%-0.05%, P 0.025%-0.035%, with the balance being Cu and unavoidable impurities, wherein the mass ratio of Sn to Ni is 0.8-1.

5.

3. The microalloyed copper alloy tube according to claim 1, characterized in that, The microalloyed copper alloy tube has a tensile strength of 250-270 MPa, a yield strength of 78-95 MPa, a yield-to-tensile ratio of 0.32-0.36, and an elongation after fracture of ≥45%; after formic acid corrosion test, the maximum corrosion depth is ≤170 μm.

4. The microalloyed copper alloy tube according to claim 1, characterized in that, When the copper alloy tube is an internally threaded tube, its inner surface has a spiral groove structure, the tooth height of the spiral groove is 0.12-0.18mm, and the apex angle is 35°-50°.

5. The microalloyed copper alloy tube according to claim 1, characterized in that, When the copper alloy tube is a plain tube, its outer diameter is 5-20mm and its wall thickness is 0.3-1.5mm.

6. A process for preparing a microalloyed copper alloy tube as described in any one of claims 1-5, characterized in that, The continuous casting and rolling process is adopted, including the following steps: (1) Batching and smelting: Prepare electrolytic copper, pure nickel plate, pure tin plate, pure iron block and phosphorus copper master alloy according to the design composition; add electrolytic copper to the melting furnace and set the melting furnace temperature to 1185±10℃; transfer the molten copper liquid to the casting furnace through the chute and set the casting furnace temperature to 1150±10℃; wrap the pure nickel plate, pure iron block and pure tin plate with copper foil and add them to the middle of the casting furnace; 5 minutes before each transfer, add the phosphorus copper master alloy directly to the middle of the casting furnace to homogenize the alloy elements; (2) Continuous casting: The homogenized copper liquid is continuously cast horizontally with a maximum traction speed of 390 mm / min. The primary cooling water flow rate is controlled at 15-70 L / min, and the secondary cooling water flow rate is controlled at 30-80 L / min to obtain a tube blank of the set size. (3) Continuous rolling: The continuously cast tube billet is subjected to planetary rolling at a rolling speed of 1.5-2.0 m / min to obtain a rolled tube billet with an outer diameter of 51-55 mm and a wall thickness of 2.3-2.7 mm; (4) Continuous stretching: The rolled tube blank is subjected to diameter reduction stretching at a speed of 10-80m / min, reducing the outer diameter of the tube blank to 20-28mm and the wall thickness to 1-1.4mm to obtain an intermediate tube blank; (5) Coil drawing: The intermediate tube blank after the joint drawing is continuously drawn 8-9 times, and the drawing speed is controlled at 8-12m / s; (6) Online annealing: The tube blank after coiling is softened by online annealing. The maximum annealing speed is 600m / min and the maximum heating voltage is 1000V to obtain recrystallized structure. (7) Forming process: When preparing internally threaded tubes, the tube blank after online annealing is spun into internal threads. The spinning speed is controlled at 480-650 r / min and the stretching speed is controlled at 40-60 m / min to form spiral grooves on the inner wall of the tube. When preparing plain tubes, the spinning process is omitted. (8) Horizontal winding: The formed tube blank is horizontally wound, and the winding speed is controlled at 250-350m / min to obtain a coil with a winding height of 200-400mm; (9) Finished product annealing: The coil obtained by horizontal winding is subjected to recrystallization annealing at a temperature of 440-490℃ and a holding time of 30-33min to eliminate work hardening, control grain size, and obtain the final finished copper alloy tube.

7. The preparation process according to claim 6, characterized in that, In step (5), the total deformation of the disc is controlled to be 80%-85%.

8. The preparation process according to claim 6, characterized in that, In step (7), the tooth height of the spiral groove is 0.12-0.18 mm and the apex angle is 35°-50°.

9. The preparation process according to claim 6, characterized in that, In step (9), the annealing temperature of the finished product is 460-480℃ and the holding time is 31-33min.

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