High-performance copper alloy tube and method for manufacturing the same

Abstract

To provide a high-performance copper alloy tube and its manufacturing method.SOLUTION: By adding Sn, Ni and P elements to Cu, adjusting the content and proportion of each element, and introducing a high proportion of Σ 3, Σ 9 and Σ 27 coincidence grain boundaries in combination with a recrystallization treatment process, a copper alloy tube having high strength, high formability, excellent pressure resistance, corrosion resistance and high-temperature softening resistance at the same time is produced. Further, by adding Zr, Co, and B (optional addition) elements in addition to the above alloy components, the performance of the copper alloy tube is further improved. Compared with the TP2 copper tube and the existing high-strength copper tube of the same specification, the copper-alloy tube of the present invention is much higher in tensile strength, formability, pressure resistance, corrosion and high-temperature softening resistance, and meets the requirements of the high-pressure and thin-wall seamless copper tube.SELECTED DRAWING: FIG. 3 (a)

Description

Technical Field

[0001] This application relates to the field of alloys, and particularly to high-performance copper alloy tubes and their manufacturing methods.

Background Art

[0002] Copper materials have become important materials in fields such as electronic communication and advanced thermal management, new energy and power transmission, and high-end equipment manufacturing due to their excellent thermal conductivity, electrical conductivity, processing formability, and corrosion resistance. Their importance and scope of application continue to improve with the progress of technology. Taking the heat exchange field as an example, as the core material of heat exchangers and pipeline systems in refrigeration and air conditioning, copper materials not only have high processing process performance such as bending, flaring, tube expanding, and welding to meet the increasingly demanding development requirements of high pressure resistance and thinning, but also need to have higher strength.

[0003] Conventional phosphor deoxidized copper tubes (TP2) have excellent bending, flaring, and tube expanding performance. By adding a small amount of P element to electrolytic copper, oxygen is removed, and its ductility, weldability, and corrosion resistance are improved. However, TP2 copper tubes have low burst pressure and cannot meet the safety requirements in the development context of lightweight and thin-walled copper tubes.

[0004] To solve the problem that the burst pressure of TP2 copper tubes is too low, various high-strength copper tubes have been researched and developed in recent years. However, the currently researched and developed high-strength copper tubes generally have high contents of Sn, Zn, and Ni. Although the burst pressure requirements can be met to some extent after wall thickness reduction, they generally have low processing formability and insufficient plastic deformation ability (specifically, expressed as low bending, flaring, and tube expanding performance).

[0005] Patent CN101469961B discloses a copper alloy material containing Sn and P, which contains 0.1% to 3.0% Sn and 0.005% to 0.1% P, has a tensile strength of 250 MPa or more, and improves the circumferential tensile strength of the copper alloy and further improves the burst pressure by limiting the proportion of Goss texture and increasing the proportion of small-angle grain boundaries. However, small-angle grain boundaries are essentially dislocation accumulations, and if their content is too high, it intensifies the material's brittleness, reduces its workability, and deteriorates its cold workability, such as bending, flaring, and expanding.

[0006] Patent CN107739880A discloses a high-strength copper alloy material containing Ni, Sn, and P, which has a tensile strength of 262-290 MPa, can be processed into a jointed copper pipe using a rolling and welding process, and ensures that no wrinkles or cracks occur in the copper material during the pipe bending process by controlling the elongation at break of the copper material to 40-50%. However, under these conditions, the workability of the copper pipe cannot be effectively ensured, the risk of flaring and expansion is extremely high, and its elongation at break is lower than that of TP2 copper pipe.

[0007] Therefore, in the current research and development and application of high-strength copper alloys, how to achieve a balance between material strength and workability is a technical challenge in the development of copper alloy tubes for heat exchange. Among the many indicators used to evaluate the performance of copper alloy tubes, the yield ratio is an important indicator for measuring the balance between material strength and workability. Generally, a low yield ratio indicates that the material has both high tensile strength and low yield strength. As a result, the material has excellent uniform deformation ability and low rebound elasticity, making it easy to process and deform, while also being able to withstand high fracture stress. Furthermore, it resolves the problem of difficulty in achieving both high strength and excellent workability simultaneously.

[0008] The yield ratio of TP2 copper tubes is generally 0.30 to 0.35, while the yield ratio of high-strength copper tubes is generally in the range of 0.4 to 0.6. As a result, high-strength copper tubes are significantly inferior to TP2 copper tubes in performance such as bending, flaring, and bulging. To solve the problem of balancing the strength and workability of high-strength copper alloy materials, it is necessary to develop new high-performance copper tubes with high strength and low yield ratio as research and development goals, and to adapt to the development trend of lightweight and compact modern refrigeration equipment.

[0009] Furthermore, when using thin-walled copper pipes, copper pipes face the following two technical challenges. Firstly, as the wall thickness decreases, the pitting corrosion resistance life is significantly reduced, and the thinner the wall thickness, the more severe the damage becomes. Secondly, in bent sections of pipes where residual stress exists, the stress corrosion effect further accelerates the progression of corrosion. In addition, the high-temperature softening phenomenon during the brazing process becomes more pronounced, and the decrease in burst pressure in the heat-affected zone of thin-walled copper pipes can reach 15% to 30%, and the thinner the wall thickness, the higher the risk of overheating, leading to a more serious decrease in pressure resistance.

[0010] Based on the above challenges, there is a need to develop high-performance copper alloy tubes with high tensile strength, low yield ratio, excellent pitting corrosion resistance, and high-temperature softening resistance. This will solve the problem of the poor workability of conventional high-strength copper tubes, meet the requirements for high corrosion resistance and high-temperature softening resistance for copper alloy materials in the context of increasing wall thickness, and promote the development of heat exchange materials toward high efficiency, energy saving, greening, and low carbon emissions. [Overview of the project]

[0011] The present invention aims to provide high-performance copper alloy tubes and methods for manufacturing the same. In this invention, by designing the composition of the copper alloy and combining it with an improved recrystallization process, the copper alloy tubes have high strength, high workability, excellent corrosion resistance and high-temperature softening resistance, and can overcome many of the problems associated with the use of conventional copper alloy tubes in the heat exchange field.

[0012] The design concept of this invention is as follows:

[0013] The copper alloy tube designed in this invention possesses both high tensile strength and a low yield ratio to meet the requirements for high pressure resistance and excellent workability of copper materials in the heat exchange field. In this invention, the yield ratio of the copper material is reduced mainly by improving the tensile strength of the copper material and maintaining the yield strength at a nearly constant level. For this purpose, the copper material needs to meet the requirements of (1) having a single face-centered cubic (FCC) crystal structure phase without the precipitation of hard and brittle phases, (2) having an appropriate grain size, and (3) having a high proportion of low Σ-value corresponding grain boundaries.

[0014] Low-Σ-value grain boundaries possess low-energy and coherent properties, exhibiting lower inhibition of dislocations in the initial stages of deformation compared to random high-angle grain boundaries, thus limiting the improvement of yield strength. As plastic deformation progresses, dislocations gradually accumulate at the interface, and the elastic strain field of preceding dislocations inhibits subsequent dislocation motion, thereby strengthening the dislocation storage capacity and causing an increase in rheological stress, which manifests as an increase in strain hardening rate. This results in copper alloys having higher tensile strength and achieving a lower yield ratio.

[0015] Because the mobility of low-Σ grain boundaries is low, abnormal grain growth during the welding process of copper alloy pipes can be prevented, thereby improving the resistance to high-temperature softening.

[0016] Low-Σ-value grain boundaries are purer than random high-angle grain boundaries, and their coherent properties make them less likely to retain solute atoms, resulting in lower susceptibility to intergranular corrosion. By increasing the ratio of (Σ9 + Σ27) / Σ3, they effectively reduce the connectivity of random high-angle grain boundary grids, inhibiting the spread of intergranular corrosion along the grain boundaries. This helps mitigate the problem of intergranular corrosion promoting pitting corrosion and extends the corrosion resistance life.

[0017] In the present invention, a copper alloy is strengthened by a method of adding a plurality of elements in trace amounts in combination, and by controlling the blending ratio and addition amount of each element, precipitation of brittle phases in the copper alloy is prevented, the copper alloy has a single face-centered cubic crystal structure α-phase, the stacking fault energy of the alloy system is reduced, the copper alloy has thermodynamic conditions for forming a high proportion of low-Σ value corresponding grain boundaries, and based on this, a recrystallization treatment process is combined to introduce a high proportion of low-Σ value corresponding grain boundaries. In the present invention, by further adjusting the annealing process to control the grain size of the copper alloy, a copper alloy tube having high strength, low yield ratio, corrosion resistance and high temperature softening resistance is obtained.

[0018] The high-performance copper alloy tube according to the first aspect of the present invention contains, as components by mass percentage, 0.05% ≦ Sn ≦ 0.6%, 0.08% ≦ Ni < 0.3%, 0.015% ≦ P ≦ 0.045%, the balance being Cu and inevitable impurities, f1 = [Sn] + 10[P], f2 = [Sn] / [Ni], and f1 and f2 satisfy 0.5% ≦ f1 ≦ 1.05%, 1 < f2 ≦ 5, where [Sn], [P] and [Ni] are the mass percentages of the Sn, P and Ni contents respectively. The copper alloy tube has a single face-centered cubic crystal structure α-phase, the average grain size excluding twin grain boundaries is 10 - 25 μm, the average grain size including twin grain boundaries is 5 - 20 μm, the total proportion of Σ3, Σ9 and Σ27 corresponding grain boundaries ≧ 50%, and the ratio of the proportion of Σ9 and Σ27 to the proportion of Σ3 corresponding grain boundaries satisfies (Σ9 + Σ27) / Σ3 ≧ 3.5%.

[0019] In the present invention, the Sn element can be largely dissolved in the Cu matrix, and no second phase precipitates when added in trace amounts.

[0020] In this invention, the element Sn can improve the strength of copper alloy tubes through solid solution strengthening. The solid solution strengthening effect of alloying elements on copper alloy tubes mainly depends on the lattice misfit coefficient and the shear modulus misfit coefficient between solute atoms and matrix atoms. The larger the two misfit coefficients, the stronger the solid solution strengthening effect. The difference in atomic radii between Sn and Cu is 23.4%, and the increase in the shear modulus of the Cu matrix due to Sn is approximately 1.35 GPa / at.%. This indicates that the two misfit coefficients of Sn and Cu are large, and that the solid solution strengthening effect of Sn on the Cu matrix is ​​high. Therefore, adding Sn can effectively perform solid solution strengthening.

[0021] In this invention, the Sn element can effectively reduce the stacking fault energy of copper alloy systems, thereby forming a large number of stacking faults during the recrystallization process. These stacking faults act as nucleation sites for annealed twins, expanding into complete annealed twins through atomic rearrangement. The annealed twin grain boundaries, during their migration, encounter and react with random high-angle grain boundaries to generate a large number of low-Σ-value corresponding grain boundaries (Σ3, Σ9, and Σ27 corresponding grain boundaries, where Σ27 is divided into Σ27a and Σ27b), thereby reducing random high-angle grain boundaries and increasing the proportion of low-Σ-value corresponding grain boundaries.

[0022] Furthermore, if the amount of Sn element added is too small, neither the reduction of stacking fault energy of the alloy nor the improvement of solid solution strengthening is evident, but if it is added in excess, a hard and brittle δ phase (Cu 41 Sn 11 The precipitation of δ phase, microsegregation of Sn elements, and grain boundary segregation cause a decrease in grain boundary bonding strength and a reduction in the hot workability of the alloy. Therefore, in this invention, the Sn element content is controlled to 0.05% ≤ Sn ≤ 0.6%, and a high proportion of low Σ-value corresponding grain boundaries are introduced to improve the solid solution strengthening ability of the alloy, while avoiding phenomena such as the precipitation of hard and brittle δ phase, a decrease in grain boundary bonding strength, and a decrease in hot workability.

[0023] Therefore, in the present invention, by adding Sn element to dissolve and strengthen the copper alloy, reducing the stacking fault energy of the alloy system, and introducing a high proportion of low-Σ corresponding grain boundaries, the copper alloy tube has the characteristics of high strength and low yield ratio, thereby realizing a high-level synergy of high strength and excellent processing formability, and improving the corrosion resistance and high-temperature softening resistance to a certain extent.

[0024] In the present invention, by adding Ni element, the pitting corrosion resistance of the Cu matrix is improved. Ni ions can fill the defects in the cuprous oxide film layer on the surface of the copper alloy, making the oxide layer on the surface of the copper alloy more stable and dense, thereby reducing the pitting corrosion rate of the copper alloy, and with the increase of the Ni content, the pitting corrosion resistance of the copper alloy is improved.

[0025] In the present invention, Ni has the same crystal form as Cu and has an infinite solid solution characteristic, so it does not precipitate a brittle second phase that has the effect of reducing ductility.

[0026] In the present invention, although the Ni element also has a certain solid solution strengthening effect, the difference in atomic radius from Cu is only 3.2%, and the increase in the shear modulus of elasticity of the Cu matrix by Ni is only 0.19 GPa / at.%, and both of the two misfit coefficients are much lower than the Sn element, and the solid solution strengthening effect is limited. Therefore, it only strengthens the copper alloy as a supplement to the Sn element.

[0027] In addition, the addition of Ni element can slightly improve the stacking fault energy of the alloy system, which is not helpful for introducing low-Σ value corresponding grain boundaries, that is, it is not helpful for reducing the yield ratio of the copper alloy. Therefore, its addition amount should not be too much, and the mixing ratio of Sn and Ni should be controlled to ensure a high proportion of low-Σ value corresponding grain boundaries.

[0028] Therefore, in order to significantly improve the pitting corrosion resistance of the copper alloy and maintain the yield ratio, ductility, and processing performance such as bending, flaring, and tube expansion of the alloy, in the present invention, the content of Ni element is controlled to be 0.08% ≤ Ni < 0.3%.

[0029] In this invention, the pitting corrosion resistance of copper alloys is improved by adding Ni, and a high degree of synergy between mechanical properties and corrosion resistance is achieved by adding Sn and Ni in combination. Ni compensates for the problem that Sn cannot significantly improve the pitting corrosion resistance of thin-walled copper alloy tubes, and Sn compensates for the negative problem that Ni increases the stacking fault energy of the alloy system.

[0030] In this invention, by adding a small amount of element P, not only is the molten copper deoxidized, but the stacking fault energy of the alloy system can be further reduced by element P. The stacking fault energy reduction effect of element P is stronger than that of element Sn, and can compensate to some extent for the problem that the reduction in stacking fault energy is limited due to the limited content of element Sn. In addition, element P improves the fluidity of molten copper, which can compensate for the problem that element Sn reduces the fluidity of molten copper.

[0031] Furthermore, since element P has a low maximum solid solubility, if added in excess, it forms a Cu3P phase, and if it is unevenly distributed at grain boundaries, it reduces the ductility of the copper alloy. Therefore, in this invention, the amount of element P added is limited and controlled to 0.015% ≤ P ≤ 0.045%.

[0032] In this invention, by weighting and controlling the total amount of Sn and P elements added and the blending ratio of Sn and Ni elements, and setting the f1 value to ≥ 0.5% and the f2 value to > 1, the alloy has a certain low stacking fault energy. Furthermore, by combining this with a subsequent recrystallization process, the proportion of low Σ-value corresponding grain boundaries is set to ≥ 50%, achieving even higher strength and a lower yield ratio. The ratio of (Σ9 + Σ27) / Σ3 is controlled to ≥ 3.5%, further improving corrosion resistance. In addition, in this invention, by controlling f1 ≤ 1.05 and f2 ≤ 5, if the amount of Sn element added and the total amount of elements added are too high, the concentration of solute atoms in the matrix will exceed a certain limit, the pinning spacing will be too small, and the deformation ability of the matrix will be severely reduced, which will not help in maintaining a low yield ratio. Controlling the upper limits of the values ​​of f1 and f2 also helps the copper alloy of this invention have a single face-centered cubic crystal structure α phase.

[0033] The copper alloy tube has a single face-centered cubic crystal structure α phase, which can avoid the occurrence of micro-cracking due to deformation mismatch between the matrix and the second phase. Furthermore, the face-centered cubic crystal structure phase has abundant slip systems, resulting in high plastic deformation capacity, making it less prone to stress concentration. This helps promote plastic deformation and maintain low yield strength, providing a microstructural foundation for achieving a low yield ratio.

[0034] According to the Hall-Petch relationship, grain refinement increases the grain boundary area, increases resistance to dislocation motion, and can improve yield strength and tensile strength to some extent. In this invention, the average grain size excluding twin grain boundaries is controlled to 10-25 μm to prevent an excessive increase in yield strength. Twin grain boundaries divide the original grains and further reduce the grain size, but because they have low-energy and coherent properties, the increase in yield strength is small, avoiding strain concentration and significantly improving strain hardening ability. However, the average grain size including twin grain boundaries must not be too small; otherwise, it will similarly lead to an improvement in yield strength. Therefore, in this invention, the average grain size including twin grain boundaries is controlled to 5-20 μm to maintain low yield strength, provide a certain level of strain hardening ability, and promote improvement in tensile strength.

[0035] In this invention, the proportion of grain boundaries corresponding to Σ3, Σ9, and Σ27 is controlled to 50% or more to achieve high strength and a low yield ratio, thereby improving the workability of the alloy. Furthermore, the ratio of (Σ9 + Σ27) / Σ3 is controlled to ≥ 3.5%, thereby improving the corrosion resistance of the alloy.

[0036] In the present invention, by controlling the elemental composition, blending ratio, and microstructure parameters within the above ranges, the manufactured copper alloy tube has a yield strength of 60 - 90 MPa, a tensile strength of ≥ 260 MPa, a yield ratio of 0.23 - 0.30, and an elongation at break of ≥ 50%. Compared with TP2 copper tubes of the same specification, the bursting pressure is improved by ≥ 7%, the wall thickness can be made ≥ 10% thinner under the condition of maintaining the bursting pressure without decreasing, and the bursting pressure attenuation rate after welding is ≤ 10%. After repeating heating and cooling in an atmosphere of a 0.4% formic acid aqueous solution for 21 days of corrosion, the maximum corrosion depth of a single tube is ≤ 170 μm, and the maximum corrosion depth at the tube bending part is ≤ 190 μm. The pitting corrosion resistance of a single tube is improved by ≥ 15% compared with TP2 copper tubes of the same specification, and the corrosion resistance attenuation rate at the tube bending part is ≤ 15%.

[0037] The high-performance copper alloy tube according to the second aspect of the present invention contains, by mass percentage, as components, 0.05% ≤ Sn ≤ 0.6%, 0.08% ≤ Ni < 0.3%, 0.015% ≤ P ≤ 0.045%, with the balance being Cu and inevitable impurities, where f1 = [Sn] + 10[P], f2 = [Sn] / [Ni], and f1 and f2 satisfy 0.5% ≤ f1 ≤ 1.05%, 1 < f2 ≤ 5. Here, [Sn], [P], and [Ni] are the mass percentages of the Sn, P, and Ni contents respectively, The copper alloy tube has a single face-centered cubic crystal structure α-phase, the average grain size excluding twin grain boundaries is 10 - 25 μm, the average grain size including twin grain boundaries is 5 - 20 μm, the total proportion of Σ3, Σ9, and Σ27 corresponding grain boundaries is ≥ 68%, and the ratio of the proportion of Σ9 and Σ27 to the Σ3 corresponding grain boundary satisfies (Σ9 + Σ27) / Σ3 ≥ 10%.

[0038] In the present invention, while maintaining the chemical components and contents as they are, by adjusting the single recrystallization process to a repeated recrystallization process, the total proportion of Σ3, Σ9, and Σ27 corresponding grain boundaries and the (Σ9 + Σ27) / Σ3 value in the copper alloy can be further increased, thereby further improving the strength, corrosion resistance, and high-temperature softening resistance of the material and reducing the yield ratio.

[0039] In this invention, by controlling the elemental composition, blending ratio, and microstructure parameters within the above range, the manufactured copper alloy pipe has a yield strength of 65-90 MPa, a tensile strength of ≥285 MPa, a yield ratio of 0.21-0.28, and a fracture elongation of ≥50%. Compared to TP2 copper pipe of the same specifications, the burst pressure is improved by ≥20%, the wall thickness is reduced by ≥18% under conditions that maintain the burst pressure, and the burst pressure decay rate after welding is ≤5%. After corrosion for 21 days by repeatedly heating and cooling in an atmosphere of 0.4% formic acid aqueous solution, the maximum corrosion depth of the single pipe is ≤155 μm, and the maximum corrosion depth of the pipe bend is ≤165 μm. The pitting corrosion resistance of the single pipe is improved by more than 20% compared to TP2 copper pipe of the same specifications, and the corrosion resistance decay rate of the pipe bend is ≤10%.

[0040] In the high-performance copper alloy tubes according to the first and second embodiments of the present invention, it is preferable that f1 and f2 satisfy the conditions 0.65% ≤ f1 ≤ 1.05% and 3.4 ≤ f2 ≤ 5.

[0041] In the present invention, by further increasing the values ​​of f1 and f2 and increasing the content of solid solution elements, the tensile strength is further improved, the stacking fault energy of the alloy system is reduced, the proportion of grain boundaries corresponding to low Σ values ​​and an increase in the (Σ9+Σ27) / Σ3 value are achieved, and a low yield ratio is maintained, thereby reducing the rate of decay of burst pressure and the rate of decay of corrosion resistance at the pipe bending section to some extent.

[0042] Taking the single recrystallization process as an example, in the present invention, by controlling the values of f1 and f2 within the above ranges, the obtained copper alloy still has a single face-centered cubic crystal structure α-phase, the average grain size excluding twin grain boundaries is 10 - 25 μm, the average grain size including twin grain boundaries is 5 - 20 μm, and a microstructure basis can be provided to achieve a low yield ratio. Also, in the present invention, by further increasing the values of f1 and f2, the ratio of low Σ-value corresponding grain boundaries can be increased to ≧60%, and the ratio of (Σ9 + Σ27) / Σ3 can be increased to ≧3.8%. The manufactured copper alloy has a yield strength of 65 - 90 MPa, a tensile strength of ≧270 MPa, a yield ratio of 0.23 - 0.30, and an elongation at break of ≧50%. Compared with copper tubes of the same specification, the burst pressure is improved by ≧13%, the wall thickness can be made ≧14% thinner under the condition of maintaining the burst pressure from decreasing, and the burst pressure attenuation rate after welding is ≦7%. After repeating heating and cooling in an atmosphere of a 0.4% formic acid aqueous solution for 21 days of corrosion, the maximum corrosion depth of a single tube is ≦165 μm, and the maximum corrosion depth of the tube bending part is ≦180 μm. Compared with TP2 copper tubes of the same specification, the pitting corrosion resistance of a single tube is improved by more than 17%, and the corrosion resistance attenuation rate of the tube bending part is ≦12%.

[0043] The high-performance copper alloy tube according to the third aspect of the present invention contains, in mass percentage, as components, 0.05% ≦ Sn ≦ 0.6%, 0.08% ≦ Ni < 0.3%, 0.015% ≦ P ≦ 0.045%, 0.001% ≦ Zr < 0.03%, 0.001% ≦ Co < 0.01%, 0 ≦ B < 0.01%, with the balance being Cu and unavoidable impurities. f1 = [Sn] + 10[P] + 10[Zr], f2 = [Sn] / [Ni], f"1" and f2 satisfy 0.65% ≦ f1 < 1.15%, 1 < f2 ≦ 5, and [Sn], [P], [Zr], [Ni] are the mass percentages of the Sn, P, Zr, Ni contents respectively, The copper alloy tube has a single face-centered cubic crystal structure α-phase, the average grain size excluding twin grain boundaries is 10 - 25 μm, the average grain size including twin grain boundaries is 5 - 20 μm, the total ratio of Σ3, Σ9 and Σ27 corresponding grain boundaries is ≧60%, and the ratio of the ratio of Σ9 and Σ27 to Σ3 corresponding grain boundaries satisfies (Σ9 + Σ27) / Σ3 ≧ 4.0%.

[0044] In addition to the composite strengthening of copper alloys by Sn, Ni, and P, this invention further reduces the stacking fault energy of the alloy system by adding Zr, significantly increasing the proportion of low-Σ grain boundaries, thereby achieving further strength improvement and a reduction in the yield ratio. By adding Co, the high-temperature softening resistance of the copper alloy is improved with precision, and the rate of rupture pressure decay of copper pipes after welding is significantly reduced. Furthermore, by optionally adding B, the quality of the cast billet is improved, the oxygen content is reduced, and the corrosion resistance of the finished copper pipe is further improved.

[0045] Specifically, in this invention, by adding a small amount of Zr, the stacking fault energy of the copper alloy system is further reduced, a higher proportion of stacking faults are activated, a higher proportion of low-Σ corresponding grain boundaries are formed, and the performance of the copper alloy is further optimized. The stacking fault energy reduction effect of Zr is much stronger than that of Sn and P, and not only can it reduce stacking fault energy to a lower level in conjunction with Sn and P, but it can also replace Sn to some extent, reducing the amount of Sn used and improving the economics of the alloy.

[0046] Furthermore, the solid solubility of Zr in a Cu matrix is ​​extremely limited. According to the Cu-Zr binary phase diagram, the maximum solid solubility of Zr in Cu at room temperature is less than 0.11%, and in actual use, in order to ensure that a brittle Zr-containing second phase does not precipitate, the Zr content needs to be reduced to 0.03% or less. Therefore, in order to ensure that the element Zr can significantly reduce stacking fault energy and to ensure that a brittle Zr-containing second phase does not precipitate, the amount of Zr added in this invention is strictly controlled to 0.001% ≤ Zr < 0.03%.

[0047] In this invention, the Co element, due to its high melting point, significantly increases the recrystallization temperature of the copper alloy and also has the function of pinning random high-angle grain boundaries. This effectively restricts the rapid movement of random high-angle grain boundaries during the welding process, suppresses abnormal grain growth, and improves the high-temperature softening resistance of the copper alloy. However, the solid solubility of the Co element in the Cu matrix is ​​also extremely low. Therefore, in this invention, the amount of Co element added is controlled to 0.001% ≤ Co < 0.01% in order to improve high-temperature softening resistance while maintaining a single face-centered cubic crystal structure.

[0048] In this invention, element B has a dual effect: oxygen removal from molten copper and refinement of the dendritic structure of the cast billet. Element B reacts with cuprous oxide and free oxygen in the molten copper to produce boron trioxide, which forms slag and floats to the surface, achieving the oxygen removal effect. However, since the maximum solid solubility of element B in the Cu matrix at room temperature is only 0.01%, in order to perform the effects of oxygen removal and crystal refinement while maintaining a single face-centered cubic crystal structure phase, the amount of element B added is controlled to less than 0.01% in this invention.

[0049] In this invention, by weighting and controlling the total amount of Sn, P, and Zr elements added, the blending ratio of Sn and Ni elements, and the separate amounts of Co and B elements added, and setting f1≧0.65% and f2>1, the stacking fault energy is further reduced due to the strong effect of Zr in reducing stacking fault energy, or by reducing the amount of Sn element added and, in combination with the subsequent recrystallization process, increasing the proportion of low Σ-value corresponding grain boundaries to ≧60%, thereby improving strength while maintaining a low yield ratio, and increasing the ratio of (Σ9+Σ27) / Σ3 to ≧4.0%, which helps improve corrosion resistance. Furthermore, in this invention, by controlling the separate amounts of each element added and setting f1 <1.15% and f2 ≦5, the copper alloy can maintain a single α phase.

[0050] In the present invention, by controlling the composition, blending ratio and microstructure parameters of the elements within the above ranges, the produced copper alloy tube has a yield strength of 65 - 90 MPa, a tensile strength ≥ 275 MPa, a yield ratio of 0.22 - 0.29, an elongation at break ≥ 50%. Compared with TP2 copper tubes of the same specifications, the burst pressure is improved by ≥ 18%, the wall thickness can be reduced by ≥ 15% under the condition of maintaining the burst pressure from decreasing, and the burst pressure attenuation rate after welding is ≤ 6%. After repeating heating and cooling for 21 days in an atmosphere of 0.4% formic acid aqueous solution, the maximum corrosion depth of a single tube is ≤ 165 μm, and the maximum corrosion depth of the tube bending part is ≤ 180 μm. The pitting corrosion resistance of a single tube is improved by more than 18% compared with TP2 copper tubes of the same specifications, and the corrosion resistance attenuation rate of the tube bending part is ≤ 11%.

[0051] Preferably, in the copper alloy of the present invention, in terms of mass percentage of the content, 0.001% ≤ B < 0.01%.

[0052] In the present invention, by controlling the B content within the above range, the dendrite structure of the casting billet can be refined, and the oxygen content in the copper alloy can be reduced to 15 ppm or less, thereby improving its pitting corrosion resistance. After adding the B element, after repeating heating and cooling for 21 days in an atmosphere of 0.4% formic acid aqueous solution, the maximum corrosion depth of a single tube is ≤ 155 μm, and the maximum corrosion depth of the tube bending part is ≤ 170 μm. The pitting corrosion resistance of a single tube is improved by more than 21% compared with TP2 copper tubes of the same specifications, and the corrosion resistance attenuation rate of the tube bending part is ≤ 10%.

[0053] The high-performance copper alloy tube according to the fourth aspect of the present invention contains, in terms of mass percentage, as components, 0.05% ≤ Sn ≤ 0.6%, 0.08% ≤ Ni < 0.3%, 0.015% ≤ P ≤ 0.045%, 0.001% ≤ Zr < 0.03%, 0.001% ≤ Co < 0.01%, 0 ≤ B < 0.01%, with the balance being Cu and unavoidable impurities, f1 = [Sn] + 10[P] + 10[Zr], f2 = [Sn] / [Ni], and f1 and f2 satisfy 0.65% ≤ f1 < 1.15%, 1 < f2 ≤ 5, where [Sn], [P], [Zr], [Ni] are the mass percentages of the Sn, P, Zr, Ni contents respectively, The copper alloy tube has a single face-centered cubic crystal structure α phase, with an average grain size of 10-25 μm excluding twin grain boundaries, and an average grain size of 5-20 μm including twin grain boundaries. The total proportion of grain boundaries corresponding to Σ3, Σ9, and Σ27 is ≥ 72%, and the ratio of grain boundaries corresponding to Σ9 and Σ27 to Σ3 satisfies (Σ9 + Σ27) / Σ3 ≥ 12%.

[0054] In the present invention, by combining the compound addition of the above alloying elements with a repeated recrystallization process, the total proportion of Σ3, Σ9, and Σ27 grain boundaries in the alloy is further increased so that (Σ9+Σ27) / Σ3≧12%, improving strength while maintaining a sufficiently low yield ratio, and effectively reducing the rate of decay of burst pressure after welding and the rate of decay of corrosion resistance at the pipe bending section.

[0055] In this invention, by controlling the elemental composition, mixing ratio, and microstructure parameters within the above range, the manufactured copper alloy pipe has a yield strength of 65-90 MPa, a tensile strength of ≥295 MPa, a yield ratio of 0.20-0.27, and a fracture elongation of ≥50%. Compared to TP2 copper pipe of the same specifications, the burst pressure is improved by ≥25%, the wall thickness is reduced by ≥20% under conditions that maintain the burst pressure, and the burst pressure decay rate after welding is ≤2%. After corrosion for 21 days by repeatedly heating and cooling in an atmosphere of 0.4% formic acid aqueous solution, the maximum corrosion depth of the single pipe is ≤150 μm, and the maximum corrosion depth of the pipe bend is ≤160 μm. The pitting corrosion resistance of the single pipe is improved by more than 23% compared to TP2 copper pipe of the same specifications, and the corrosion resistance decay rate of the pipe bend is ≤7%.

[0056] Preferably, based on the above repeated recrystallization process, the oxygen content in the copper alloy can be reduced to 15 ppm or less by controlling the content of element B to 0.001% ≤ B < 0.01%. After corrosion for 21 days by repeatedly heating and cooling in an atmosphere of 0.4% formic acid aqueous solution, the maximum corrosion depth of the single pipe is ≤ 145 μm, and the maximum corrosion depth of the pipe bend is ≤ 155 μm. The pitting corrosion resistance of the single pipe is improved by more than 25% compared to TP2 copper pipe of the same specifications, and the corrosion resistance decay rate of the pipe bend is ≤ 5%.

[0057] The method for manufacturing the high-performance copper alloy tube according to the fifth aspect of the present invention can manufacture seamless copper alloy tubes, can be implemented using a conventional production line, and has strong compatibility with conventional equipment.

[0058] Specifically, the method for manufacturing high-performance copper alloy tubes of the present invention includes the steps of compounding and melting → continuous casting → rolling → continuous drawing → recrystallization treatment, In compounding and dissolving, raw materials are dissolved according to the appropriate mixing ratio. In continuous casting, molten metal is continuously cast to form billets. In rolling, a billet is rolled to obtain a rolled tube. In continuous drawing, the rolled raw tube is reduced in diameter, In the recrystallization process, the amount of deformation and annealing parameters are controlled to obtain a product with the target performance.

[0059] In this invention, in addition to designing the alloying components and their content, the proportion of low-Σ-value grain boundaries is increased by improving the recrystallization process. The recrystallization process is divided into a single-step recrystallization process and a repeated recrystallization process, and the essence of both types of recrystallization processes is to increase the formation rate of low-Σ-value grain boundaries by strain-induced grain boundary movement.

[0060] Preferably, the recrystallization process is a single-step recrystallization process consisting of "block drawing → finished product annealing," wherein the total deformation amount of the block drawing is 80% or more, the temperature of the finished product annealing is 500 to 750°C, and the annealing time is 30 to 150 minutes.

[0061] In this invention, single recrystallization results in a large deformation and a high annealing temperature. During the annealing process, the low stacking fault energy of the alloy system forms a large amount of strain-induced annealing twins. The formed annealing twin grain boundaries (Σ3) encounter random high-angle grain boundaries during the migration process and react to generate a large amount of low-Σ-value corresponding grain boundaries (Σ3, Σ9, Σ27a, and Σ27b), thereby increasing the proportion of low-Σ-value corresponding grain boundaries. The Σ9 and Σ27-corresponding grain boundaries occupy the positions of random high-angle grain boundaries, disrupting the random high-angle grain boundary network.

[0062] In this invention, by controlling the total deformation amount of a single recrystallization to 80% or more, sufficient strain energy is accumulated, high-density dislocations are introduced, and the original grain boundary structure is destroyed. Furthermore, based on the high strain energy structure, annealing treatment is performed at 500 to 750°C for 30 to 150 minutes to drive large-scale recrystallization and grain boundary migration, forming low-Σ value corresponding grain boundaries with a proportion of 50% or more.

[0063] Preferably, the recrystallization process is a repeating recrystallization process in which the "block drawing → annealing" cycle is repeated multiple times after 1 to 3 passes of block drawing, the total deformation amount of the 1 to 3 passes of block drawing prior to the cycle is ≤ 72%, the number of "block drawing → annealing" cycles in the multiple "block drawing → annealing" cycles is 3 to 6 times, the deformation amount of block drawing in a single cycle is 25 to 35%, the annealing temperature is 500 to 600°C, and the annealing time is 10 to 70 min.

[0064] In this invention, the repeated recrystallization process is characterized by a single pass, small deformation, and low annealing temperature. At lower temperatures, selective recrystallization is preferentially induced in areas with many defects, strain-induced annealing twins are generated, and the annealing twin grain boundaries move similarly, reacting with random high-angle grain boundaries under conditions that do not introduce strong crystal orientation to form low-Σ-value corresponding grain boundaries, while controlling the growth of crystal grains to prevent excessive growth. When the recrystallized structure is deformed again, the low-energy low-Σ-value corresponding grain boundaries are less likely to break, and the random high-angle grain boundaries are continuously activated and moved by deformation and annealing, allowing them to form new annealing twins and low-Σ-value corresponding grain boundaries. The low-Σ-value corresponding grain boundaries superimpose and accumulate, increasing the proportion of low-Σ-value corresponding grain boundaries.

[0065] In this invention, by controlling the amount of deformation in a single pass of the cycle to a range of 25% to 35%, controllable strain energy is introduced, preferentially fracturing high-energy, random, high-angle grain boundaries while avoiding the fracturing of existing low-energy interfaces. Furthermore, by controlling the annealing temperature and annealing time of the cycle, strain energy is gradually released, selectively driving the high-strain-energy structure to preferentially recrystallize, thereby forming low-energy interfaces. Through the cycling process, a higher proportion of low-Σ-value corresponding grain boundaries are accumulated, allowing for more precise control of low-Σ-value corresponding grain boundaries.

[0066] In the repeated recrystallization process of the present invention, after 3 to 6 cycles, the number of low-Σ-value grain boundaries can be significantly increased compared to general processes and single-cycle annealing processes. The proportion of low-Σ-value grain boundaries exceeds 65%, and the proportions of Σ9, Σ27a, and Σ27b also increase significantly, with (Σ9+Σ27) / Σ3 > 10.3%, effectively reducing the connectivity of random high-angle grain boundary networks. However, after more than 6 cycles, the proportion of low-Σ-value grain boundaries does not increase significantly because they reach a saturation state.

[0067] Preferably, in the blending and melting process, the raw materials suitable for the blending ratio are first dried and then melted at 1170-1350°C. The elements Ni, Co, B, Zr, P, and Sn are added in the form of commercially available copper-nickel master alloy, copper-cobalt master alloy, copper-boron master alloy, copper-zirconium master alloy, phosphorus-copper master alloy, and copper-tin master alloy, respectively. After the raw materials are completely melted, the mixture is kept warm for 45-90 minutes to allow the trace elements to diffuse sufficiently and become homogenized. Adding the trace elements in the form of master alloys promotes melting and diffusion and reduces burnout. Subsequently, the molten copper is poured into a casting furnace under the protection of nitrogen gas, and the furnace is kept warm at 1180-1190°C for 8-12 minutes, after which continuous casting is performed on the raw pipes.

[0068] Preferably, the continuous casting process is horizontal continuous casting, with a traction speed of 330-380 mm / min, a primary cooling water flow rate of 30-35 L / min, and a secondary cooling water flow rate of 65-75 L / min. The outer diameter of the raw pipes to be horizontally continuously cast can be designed according to actual needs, for example, 88-98 mm, and preferably 92 mm.

[0069] Preferably, in the rolling process, the rolling speed is 1.2 to 2.2 m / min, and rolled raw tubes are obtained after the rolling is completed. The dimensions of the rolled raw tubes can be designed according to actual requirements, for example, the outer diameter of the rolled raw tubes is 50 to 55 mm and the wall thickness is 2.3 to 2.7 mm.

[0070] Preferably, the continuous drawing process provides a semi-finished product that meets dimensional requirements for the subsequent processing process, controls the speed of the continuous drawing to 70-92 m / min, and obtains a precision raw tube with a significantly reduced outer diameter after continuous drawing. For example, continuous drawing reduces the outer diameter of a rolled raw tube with an outer diameter of 50-55 mm and a wall thickness of 2.3-2.7 mm to 30-35 mm and the wall thickness to 1.4-1.7 mm.

[0071] After a continuous drawing process, the obtained precision raw tubes are subjected to a single recrystallization process or a repeated recrystallization process to produce high-performance copper alloy tube materials having a high proportion of low Σ-value corresponding grain boundaries. The produced tube materials are not limited by specifications or dimensions and include, but are not limited to, smooth tubes and female threaded tubes.

[0072] In a single-pass recrystallization process, the block drawing passes and specific process parameters can be flexibly adjusted according to actual production needs to ensure that the final product meets the target specifications and dimensional requirements. However, to store sufficient strain energy, it is necessary to ensure that the total deformation of the block drawing is ≥ 80%. This effectively promotes the formation of a dimensionally uniform recrystallized structure in the finished product during the annealing process and significantly increases the proportion of low-Σ-value corresponding grain boundaries. For example, after performing 6 to 9 block drawing passes on a rolled raw tube with an outer diameter of 30 to 35 mm and a wall thickness of 1.4 to 1.7 mm, a smooth tube with an outer diameter of 5 to 12 mm and a wall thickness of 0.40 to 0.65 mm is produced, with a total deformation of 81.5% to 96.7% and a block drawing speed of 450 to 700 m / min.

[0073] In the repeated recrystallization process, the total deformation of the block drawing process in the first 1-3 passes prior to the cycle is ≤72%, and the deformation distribution between specific passes and specific process parameters can be flexibly adjusted according to actual production needs. In the "block drawing → annealing" cycle process, the block drawing passes and specific process parameters can also be flexibly adjusted according to actual production needs in a single cycle, but it is necessary to ensure that the total deformation of block drawing in a single cycle is 25%-35%, the annealing temperature in a single cycle is 500-600°C, the annealing time is 10-70 min, and the number of cycles is 3-6, thereby accumulating a high proportion of low Σ-value corresponding grain boundaries and increasing the (Σ9+Σ27) / Σ3 ratio. For example, a rolled raw tube with an outer diameter of 30-35 mm and a wall thickness of 1.4-1.7 mm is subjected to a block drawing process of 1-2 passes to produce an intermediate raw tube with an outer diameter of 20-26 mm and a wall thickness of 0.85-1.2 mm. Then, a "block drawing-annealing" cycle is performed to produce a smooth tube with an outer diameter of 5-12 mm and a wall thickness of 0.40-0.65 mm, with a block drawing speed of 450-700 m / min.

[0074] When manufacturing female threaded tubes using a single-cycle recrystallization process flow, it is necessary to soften the raw tubes using an online annealing method after the block drawing process, preferably with online annealing process parameters of 300-450 m / min speed and 3600-5000 A current. Next, female thread spinning is performed on the raw tubes obtained by inline annealing, with a spinning speed of preferably 480-650 r / m, and more preferably 550-600 r / m. After that, a finished product annealing treatment is performed to obtain female threaded tubes, preferably with a finished product annealing temperature of 510-650°C and an annealing time of 30-120 min.

[0075] When manufacturing female threaded tubes using a repeated recrystallization process flow, the "block drawing → annealing" cycle step in the final pass is replaced with the "female thread forming → female threaded tube annealing" step. The female thread forming spinning speed is preferably 480 to 650 r / m, more preferably 550 to 600 r / m. Preferably, the female threaded tube annealing temperature is 500 to 580°C and the annealing time is 10 to 70 min.

[0076] Furthermore, the copper alloy components according to the present invention are not only applicable to the production of pipes, but also to the manufacture of various copper alloy products such as wires, rods, plates, and strips. The production process may utilize conventional mature processing technologies such as extrusion, rolling, drawing, and forging. Depending on the specific product performance requirements and application scenarios, process parameters may be optimized and adjusted, or new processing methods may be developed, to meet the diverse needs for copper alloy materials in different industries. The high-performance copper alloy pipes are applicable not only to heat exchange fields but also to fields such as marine construction and the energy chemical industry, and are particularly excellent in scenarios with complex environments and high requirements for material performance.

[0077] Compared to the prior art, the present invention has at least the following technical effects.

[0078] (1) In the present invention, by compounding elements of Sn, Ni, and P with Cu, adjusting the content and blending ratio of each element, and combining this with a subsequent recrystallization process, the strength of the copper alloy is enhanced, it has a high proportion of low Σ-value compatible grain boundaries, effectively reduces the yield ratio, maintains high processing and forming ability, exhibits excellent performance in applicable processes such as bending, flaring, and tube expansion, and has superior pressure resistance, corrosion resistance, and high-temperature softening resistance.

[0079] (2) In the present invention, in addition to the elements Cu, Sn, Ni, and P, the elements Zr, Co, and B (optional addition) are added, and the content and blending ratio of each element are controlled, and by combining this with a subsequent improved recrystallization process, the strength, plastic deformation capacity, pressure resistance, corrosion resistance, and high-temperature softening resistance of the alloy are further improved compared to copper alloys made from the elements Cu, Sn, Ni, and P.

[0080] (3) The recrystallization process of the present invention includes single recrystallization and repeated recrystallization, can be implemented on a conventional production line, and has strong compatibility with conventional equipment. In the present invention, by designing the alloy composition and combining it with a single recrystallization process, a copper alloy with superior performance can be obtained. By combining it with a repeated recrystallization process, the proportion of grain boundaries corresponding to low Σ values ​​and the ratio of (Σ9 + Σ27) / Σ3 are significantly increased, and the strength, plastic deformation capacity, pressure resistance, corrosion resistance, and high-temperature softening resistance of the alloy are further improved compared to copper alloys produced by a single recrystallization process. [Brief explanation of the drawing]

[0081] [Figure 1] This is a process flow diagram of the present invention. [Figure 2] These are the X-ray diffraction (XRD) spectra of Examples 2, 5, 12, 15, and Comparative Example 1 of the present invention. [Figure 3(a)]The images show the inverse pole figure (IPF figure) and grain boundary distribution figures obtained by electron backscatter diffraction (EBSD) testing of the sample from Example 2 of the present invention, the sample after repeated recrystallization in three cycles from Example 5, the sample after repeated recrystallization in four cycles from Example 5, and the sample from Comparative Example 1. (a) is the IPF figure of Comparative Example 1. [Figure 3(b)] Figure 3(b) is the grain boundary distribution diagram for Comparative Example 1. [Figure 3(c)] Figure 3(c) is the IPF diagram for Example 2. [Figure 3(d)] Figure 3(d) is the grain boundary distribution diagram for Example 2. [Figure 3(e)] Figure 3(e) is the IPF diagram after three cycles of repeated recrystallization in Example 5. [Figure 3(f)] Figure 3(f) shows the grain boundary distribution diagram after three cycles of repeated recrystallization in Example 5. [Figure 3(g)] Figure 3(g) is the IPF diagram after four cycles of repeated recrystallization in Example 5. [Figure 3(h)] Figure 3(h) shows the grain boundary distribution diagram after four cycles of repeated recrystallization in Example 5. [Figure 4] These are the nominal stress-strain curves for Examples 2, 5, 12, 15, and Comparative Example 1 of the present invention. [Figure 5] These are typical corrosion morphologies of the cross-sections of samples after pitting corrosion in Example 2 and Comparative Example 1 of the present invention, and also show the corrosion depth. (a) is a cross-sectional morphology of the sample of Comparative Example 1 after a pitting corrosion test, (b) is a cross-sectional morphology of the pipe bending sample of Comparative Example 1 after a pitting corrosion test, (c) is a cross-sectional morphology of the sample of Example 2 after a pitting corrosion test, and (d) is a cross-sectional morphology of the pipe bending sample of Example 2 after a pitting corrosion test. [Figure 6]The images show the rupture ports of the samples from Example 2 and Comparative Example 1 of the present invention after hydrostatic rupture testing, and the rupture ports of the welded samples after hydrostatic rupture testing. (a) is a photograph of the rupture port of the sample from Comparative Example 1 after hydrostatic rupture testing, (b) is a photograph of the rupture port of the welded sample from Comparative Example 1 after hydrostatic rupture testing, (c) is a photograph of the rupture port of the sample from Example 2 after hydrostatic rupture testing, and (d) is a photograph of the rupture port of the welded sample from Example 2 after hydrostatic rupture testing. [Figure 7(a)] These are the kernel mean orientation difference diagrams (KAM diagrams) measured after 5% tensile deformation of Example 2 and Comparative Example 1 of the present invention, and Figure 7(a) is the KAM diagram measured after 5% tensile deformation of Comparative Example 1. [Figure 7(b)] Figure 7(b) is the KAM diagram measured after 5% tensile deformation in Example 2. [Modes for carrying out the invention]

[0082] The technical means and advantages of the present application will be described more clearly and completely below with reference to the drawings and specific embodiments of the embodiments of the present application. Clearly, the embodiments described are some, but not all, embodiments of the present application. All other embodiments that a person skilled in the art could obtain without creative effort based on the embodiments of the present application are all within the scope of the protection of the present application.

[0083] Unless otherwise specified in the examples, general conditions or conditions suggested by the manufacturer were followed. All raw materials and reagents used are commercially available, common products.

[0084] The performance parameters according to the embodiments of the present invention were measured by the following method.

[0085] The average grain size of the metal microstructure was tested according to the GB / T 6394-2017 method for determining the average grain size of metals.

[0086] Room-temperature mechanical properties such as yield strength, critical tensile strength, and elongation at break were tested using an electronic universal mechanical properties tester in accordance with "GB / T 228.1-2010 Part 1 of Tensile Testing for Metallic Materials: Room Temperature Test Methods," with a tensile gauge, a standard distance of 50 mm, a tensile speed of 5 mm / min, and three parallel samples.

[0087] The burst pressure was determined by conducting a pressure resistance test according to the "GB / T 241-2007 Hydraulic Test Method for Metal Pipes" to obtain the burst pressure of the copper alloy pipe. The same pressure resistance test was then performed after the copper pipe was welded to obtain the burst pressure after welding. The rate of decay of the burst pressure after welding is defined as follows.

[0088] The rate of decrease in burst pressure after welding = (burst pressure - burst pressure after welding) / burst pressure * 100%.

[0089] Bending tests for process performance were conducted according to GB / T 244-2008, "Method for Bending Metal Tubes." After bending 180° under conditions where the mandrel diameter was 1.5 times the outer diameter of the copper tube, the inner and outer surfaces were smooth and free of wrinkles or cracks. Flaring tests were conducted according to GB / T 17791-1999, "Seamless Copper Tubes for Air Conditioning and Refrigeration." When a 60° punch cone was selected for flaring, and the flare ratio was 40%, or when the distance between the two walls after crushing was equal to the wall thickness, the absence of visible cracks or fissures in the sample indicated superior process performance.

[0090] In the pitting corrosion test, thirteen parallel samples, each 10 cm long, were used for each copper alloy. First, the copper tube samples were pre-treated by ultrasonic cleaning with anhydrous ethanol, acetone, and deionized water for 3 minutes each to remove oil stains from the copper tube surface. Then, both ends of the copper tube samples were sealed, and only the outer surface of the copper tube was exposed to a formic acid atmosphere. The pre-treated copper tubes were suspended in a sealed box containing a 0.4% formic acid aqueous solution, and the ratio of the solution volume to the sample area was set to 5 cm². 3 / cm 2The samples were then heated in a water bath to 40°C and kept warm for 48 hours, followed by being left at room temperature for another 48 hours. This cooling and heating process was repeated for 21 days. After the corrosion test, seven cross-sections were selected at equal intervals from each sample and subjected to corrosion depth tests. The seven data points with the largest corrosion depths were recorded for each sample, and the average value was taken as the maximum corrosion depth for that sample. Next, the average of the maximum corrosion depths of 13 parallel samples was calculated as the maximum corrosion depth of the single pipe of the copper alloy under the above test conditions.

[0091] In the pipe bending corrosion test, pipe bending samples were prepared based on the pipe bending test conditions. Each sample was 15 cm long, with the pipe bending center located at the axial center of the sample. Samples were pretreated and sealed according to the pitting corrosion test steps described above. The outer portion of the pipe bending section of the sample was suspended downwards in a sealed box containing a formic acid aqueous solution to corrode it. After the corrosion test, samples were taken from each sample at 5 mm intervals from the pipe bending center toward both sides, and three cross-sections were taken from each sample, for a total of seven cross-sections including the cross-section of the pipe bending center, and the corrosion depth test was performed. The remaining test and data processing requirements were the same as those for the pitting corrosion test. This allowed us to obtain the maximum corrosion depth of the pipe bending section.

[0092] The corrosion resistance decay rate of the pipe bend is defined as follows:

[0093] Corrosion resistance attenuation rate of pipe bends = (Maximum corrosion depth of pipe bend - Maximum corrosion depth of single pipe) / Maximum corrosion depth of single pipe * 100%.

[0094] For the XRD pattern testing, a Smartlab X-ray diffractometer manufactured by Rigaku Corporation was used. The continuous scanning speed was 1° / min, and the 2θ range was 35° to 100°. A copper target was used for the testing.

[0095] For the EBSD test, a Carl Zeiss Sigma 300 field emission scanning electron microscope equipped with a Ushizu Symmetry S2 EBSD probe was used. The scanning step size was 0.5 μm. AZtec Crystal 2.1 software was used for data analysis. The type of corresponding grain boundary was determined based on the Brandon standard. Note that 60° / <111> Grain boundaries with orientation differences, angular deviation ≤ 8.7°, and axial deviation ≤ 8.2° are defined as Σ3 corresponding grain boundaries, and 38.9° / <110> Grain boundaries with orientation differences, angular deviation ≤ 5.0°, and axial deviation ≤ 2.7° are defined as Σ9 corresponding grain boundaries, and 31.6° / <110> and 35.4° / <210> Grain boundaries that have an orientation difference, an angular deviation ≤ 2.9°, and an axial deviation ≤ 0.9° are defined as the grain boundaries corresponding to Σ27a and Σ27b.

[0096] (Examples 1-4) Examples 1 to 4 provide a smooth tube made of a copper alloy material containing Sn, Ni, and P, and a manufacturing method using a single recrystallization process flow. The specific manufacturing method of Example 1 includes the following steps S1 to S5.

[0097] S1.Blending and dissolving Based on the chemical composition of the designed copper alloy, the raw materials—electrolytic copper (purity ≥ 99.98%), copper-nickel master alloy (Cu-42%Ni), phosphorus-copper master alloy (Cu-14%P), and copper-tin master alloy (Cu-50%Sn)—were prepared, dried, and dried for use. By supplying the raw materials in the master alloy manner, it was possible to lower the melting temperature of high-melting-point elements, accelerate melting, and reduce elemental burnout and oxidation.

[0098] After melting the electrolytic copper plate, the temperature of the molten copper was adjusted to 1200°C, and copper-nickel matrix alloy, phosphorus-copper matrix alloy, and copper-tin matrix alloy were added in appropriate proportions. The molten copper was stirred using a graphite rod, and the surface of the molten copper was covered with charcoal to prevent oxidation and suppress burnout. The mixture was kept warm for 60 minutes to allow sufficient diffusion of the elements, promote the homogenization of elements in the molten copper, and provide time for gas and nonmetallic inclusions to float to the surface and escape, thereby promoting deoxidation and degassing. The molten copper was poured into the casting furnace to prepare for casting. During the pouring process, it was protected with nitrogen gas to physically isolate it from the air, reducing the risk of oxidation and impurity absorption during the pouring process. To prevent oxidation of the molten copper, the surface of the molten copper in the casting furnace was covered with graphite flakes. The holding temperature of the molten copper in the casting furnace was 1185°C, and the holding time was 10 minutes.

[0099] S2. Continuous Casting Molten copper was continuously cast horizontally in a casting furnace to form a raw tube. The traction speed was 350 mm / min, the primary cooling water flow rate was 35 L / min, and the secondary cooling water flow rate was 69 L / min. The outer diameter of the raw tube was 92 mm, the inner diameter was 38.5 mm, and the fixed length was 8 m. Subsequently, the raw tube was milled to remove surface oxide scale and to prevent surface defects from entering the interior of the material during the subsequent rolling process. The milling depth was 1 mm.

[0100] S3. Rolling The continuously cast tubes were reduced in diameter by a three-roll planetary rolling process. During the rolling process, the tubes generated heat due to friction, which aided in deformation. The rolling speed was 1.4 m / min. As a result, the outer diameter was reduced to 51 mm and the wall thickness to 2.4 mm.

[0101] S4. Continuous extraction The rolled intermediate tube was subjected to continuous drawing to reduce its diameter. The continuous drawing speed was 72 m / min. As a result, the outer diameter of the tube was reduced to 31 mm and the wall thickness was reduced to 1.4 mm.

[0102] S5. Single recrystallization process Seven-pass block drawing was performed on the intermediate raw tube that had undergone continuous drawing. The block drawing speed for the first pass was 450 m / min, the block drawing speeds for the second to sixth passes were 660 m / min, and the block drawing speed for the seventh pass was 620 m / min. As a result, a smooth tube with an outer diameter of 9.52 mm and a wall thickness of 0.55 mm was produced. The total deformation amount of the block drawing was 88.1%. Subsequently, the raw tube was annealed in a vacuum atmosphere. The annealing temperature was 580°C and the annealing time was 90 min. As a result, the copper alloy tube of Example 1 was obtained. Its specific chemical composition is shown in Table 1.

[0103] Example 2 follows the same manufacturing method as Example 1, except that in step S1, the chemical composition of the copper alloy and the mixing ratio of the raw materials are different. The specific chemical composition is shown in Table 1.

[0104] Example 3 differs from Example 1 in the following respects.

[0105] In step S1 described above, the chemical composition of the copper alloy and the mixing ratio of the raw materials differ, and the specific chemical composition is shown in Table 1.

[0106] In step S5 above, the annealing temperature was set to 600°C and the annealing time to 90 min. The purpose of changing the annealing temperature was to equalize the degree of complete recrystallization in each example after the change in chemical composition, that is, to make the average grain size similar when the twin grain boundaries are removed.

[0107] (Example 4) This embodiment differs from Embodiment 1 in the following respects.

[0108] In step S1 described above, the chemical composition of the copper alloy and the mixing ratio of the raw materials differ, and the specific chemical composition is shown in Table 1.

[0109] In step S5 above, the annealing temperature was set to 600°C and the annealing time to 90 min.

[0110] (Examples 5-6) Examples 5-6 provided a smooth tube made of a copper alloy material containing Sn, Ni, and P, and a manufacturing method using a repeated recrystallization process flow.

[0111] Example 5 differs from Example 1 in the following respects.

[0112] In step S1 described above, the chemical composition of the copper alloy and the mixing ratio of the raw materials differ, and the specific chemical composition is shown in Table 1.

[0113] Step S5 described above is a repeated recrystallization process, and the specific steps are as follows.

[0114] Two-pass block drawing was performed on the intermediate raw tube that had undergone continuous drawing. The block drawing speed in the first pass was 450 m / min, and the block drawing speed in the second pass was 660 m / min. As a result, the outer diameter was reduced to 21 mm and the wall thickness was reduced to 0.98 mm. The total deformation amount of block drawing was 52.7%. Next, the "block drawing-annealing" cycle process was carried out. In the first cycle, the deformation amount of block drawing was 30.3%, the block drawing speed was 600 m / min, the annealing temperature was 530°C, and the annealing time was 20 min. In the second cycle, the deformation amount of block drawing was 29.4%, the block drawing speed was 600 m / min, the annealing temperature was 530°C, and the annealing time was 20 min. In the third cycle, the deformation amount of block drawing was 29.2%, the block drawing speed was 600 m / min, the annealing temperature was 530°C, and the annealing time was 20 min. In the fourth cycle, the block drawing deformation was 27.9%, the block drawing speed was 600 m / min, the annealing temperature was 530°C, and the annealing time was 20 min. This yielded the copper alloy tube of Example 5. The specific chemical composition is shown in Table 1.

[0115] Example 6 differs from Example 5 in the following respects.

[0116] In step S1 described above, the chemical composition of the copper alloy and the mixing ratio of the raw materials differ, and the specific chemical composition is shown in Table 1.

[0117] In step S5 described above, the annealing temperature was 540°C in all cases.

[0118] (Examples 7-10) Examples 7-10 provided smooth tubes made of copper alloys containing Sn, Ni, P, Zr, and Co, and a manufacturing method using a single recrystallization process flow.

[0119] Examples 7 and 9 differ from Example 1 in the following respects.

[0120] In step S1 described above, the chemical composition of the copper alloy and the mixing ratio of the raw materials differed. In addition to adding copper-nickel matrix alloy, phosphorus-copper matrix alloy, and copper-tin matrix alloy in the designed mixing ratios, copper-cobalt matrix alloy (Cu-10%Co) and copper-zirconium matrix alloy (Cu-10%Zr) were also added. The specific chemical composition is shown in Table 1.

[0121] Examples 8 and 10 differ from Example 7 in the following respects.

[0122] In step S1 described above, the chemical composition of the copper alloy and the mixing ratio of the raw materials differ, and the specific chemical composition is shown in Table 1.

[0123] In step S5 described above, the annealing temperature was 620°C in all cases.

[0124] (Example 11) This embodiment provides a smooth tube made of a copper alloy containing Sn, Ni, P, Zr, Co, and B, and a manufacturing method using a single-cycle recrystallization process flow.

[0125] This embodiment differs from Embodiment 7 in the following respects.

[0126] In step S1 above, the chemical composition of the copper alloy and the mixing ratio of the raw materials differed. In addition to the addition of copper-nickel matrix alloy, copper-cobalt matrix alloy, copper-zirconium matrix alloy, phosphorus-copper matrix alloy, and copper-tin matrix alloy in the designed mixing ratios, copper-boron matrix alloy (Cu-5%B) was also added. The specific chemical composition is shown in Table 1.

[0127] (Examples 12-15) Examples 12-15 provided smooth copper alloy tubes containing Sn, Ni, P, Zr, Co, and optionally added B, and a manufacturing method using a repeated recrystallization process flow.

[0128] Example 12 has the same chemical composition as Example 7 (same batch of cast billets), but differs in that step S5 is a repeated recrystallization process.

[0129] The repeated recrystallization process used in Example 12 is the same as that used in Example 5.

[0130] Example 13 differs from Example 12 in the following respects.

[0131] In step S1 described above, the chemical composition of the copper alloy and the mixing ratio of the raw materials differ, and the specific chemical composition is shown in Table 1.

[0132] In the repeated recrystallization process of step S5 described above, the annealing temperature for the "block drawing-annealing" cycle was set to 540°C and the annealing time to 20 min in order to completely recrystallize the alloy.

[0133] Examples 14 and 15 differ from Example 13 in the following respects. In step S1 above, the chemical composition of the copper alloy and the mixing ratio of the raw materials are different, and the specific chemical composition is shown in Table 1.

[0134] (Example 16) This embodiment provides a female threaded tube made of a copper alloy containing Sn, Ni, P, Zr, Co, and B, and a manufacturing method using a repeated recrystallization process flow.

[0135] This embodiment has the same chemical composition as Example 15 (same batch of cast billets), but differs in the following respects.

[0136] In step S5 described above, the fourth cycle was replaced with the "female thread forming → female thread tube annealing" process, and the raw tube after the third cycle was spun. The spinning speed was 550 r / m. This produced a female thread tube with dimensions of 7 mm * 0.23 mm + 0.1 mm (outer diameter * bottom wall thickness + tooth height), which was then annealed. The annealing temperature was 570°C and the annealing time was 30 min.

[0137] (Comparative Example 1) This comparative example uses a conventional copper tube sample provided by Zhejiang Hailiang Co., Ltd. The material is TP2 smooth tube, with specifications of 9.52 mm * 0.55 mm (outer diameter * wall thickness), and its specific composition is shown in Table 2.

[0138] (Comparative Example 2) This comparative example uses a conventional copper pipe sample provided by Zhejiang Hailiang Co., Ltd. The material is a TP2 female threaded pipe with specifications of 7mm*0.23mm+0.1mm, and its specific components are shown in Table 2.

[0139] (Comparative Example 3) This comparative example provides a Cu-Sn-Ni-P copper alloy material with high Sn content and f2 value, and specific steps for its manufacture using a single-cycle recrystallization process flow.

[0140] This comparative example differs from Example 1 in the following respects.

[0141] In step S1 described above, the chemical composition of the copper alloy and the mixing ratio of the raw materials differ, and the specific chemical composition is shown in Table 2.

[0142] In step S5 described above, the annealing temperature was 620°C and the annealing time was 90 min.

[0143] (Comparative Example 4) This comparative example provides a smooth tube made of Cu-Sn-Ni-P copper alloy with low f1 and f2 values, and specific steps for manufacturing using a single recrystallization process flow.

[0144] This comparative example differs from Example 1 in the following respects.

[0145] In step S1 described above, the chemical composition of the copper alloy and the mixing ratio of the raw materials differ, and the specific chemical composition is shown in Table 2.

[0146] In step S5 described above, the annealing temperature was 620°C and the annealing time was 90 min.

[0147] (Comparative Example 5) This comparative example provides a smooth tube made of Cu-Sn-Ni-P copper alloy with a high Ni content and a low f2 value, and specific steps for its manufacture using a single-cycle recrystallization process flow.

[0148] This comparative example differs from Example 1 in the following respects.

[0149] In step S1 described above, the chemical composition of the copper alloy and the mixing ratio of the raw materials were different, and the specific chemical composition is shown in Table 2. In addition, the melting temperature was increased to 1250°C.

[0150] In step S5 described above, the block drawing speed for the 2nd to 6th passes was 600 m / min, the block drawing speed for the 7th pass was 550 m / min, the annealing temperature of the finished product was 650°C, and the annealing time was 90 min.

[0151] (Comparative Example 6) This comparative example provides a smooth tube made of Cu-Sn-Ni-P copper alloy with high Sn content and high f1 and f2 values, and specific steps for its manufacture using a single recrystallization process flow.

[0152] This comparative example differs from Example 1 in the following respects.

[0153] In step S1 described above, the chemical composition of the copper alloy and the mixing ratio of the raw materials were different, and the specific chemical composition is shown in Table 2. In addition, the melting temperature was increased to 1250°C.

[0154] In step S5 described above, the block drawing speed for the 2nd to 6th passes was 600 m / min, the block drawing speed for the 7th pass was 550 m / min, the annealing temperature of the finished product was 650°C, and the annealing time was 90 min.

[0155] (Comparative Example 7) This comparative example provides a smooth tube made of a Cu-Sn-Ni-P-Zr-Co copper alloy with high Co and Zr content, and specific steps for its manufacture using a single-cycle recrystallization process flow.

[0156] This comparative example differs from Example 7 in the following respects.

[0157] In step S1 described above, the chemical composition of the copper alloy and the mixing ratio of the raw materials differ, and the specific chemical composition is shown in Table 2.

[0158] In step S5 described above, the block drawing speed for the 2nd to 6th passes was 600 m / min, the block drawing speed for the 7th pass was 550 m / min, the annealing temperature of the finished product was 650°C, and the annealing time was 90 min.

[0159] (Comparative Example 8) This comparative example provides a smooth tube made of a Cu-Sn-Ni-P-Zr-Co-B copper alloy with high Zr, Co, and B content, and specific steps for its manufacture using a single-cycle recrystallization process flow.

[0160] This comparative example differs from Example 11 in the following respects.

[0161] In step S1 described above, the chemical composition of the copper alloy and the mixing ratio of the raw materials were different, and the specific chemical composition is shown in Table 2. In addition, the melting temperature was increased to 1250°C.

[0162] In step S5 described above, the block drawing speed for the 2nd to 6th passes was 600 m / min, the block drawing speed for the 7th pass was 550 m / min, the annealing temperature of the finished product was 650°C, and the annealing time was 90 min.

[0163] Tables 1 and 2 show the chemical composition and f1 and f2 values ​​of the copper alloys of the examples and comparative examples of the present invention. Table 3 shows the proportion of low-Σ corresponding grain boundaries and the average grain size of the copper alloys of the examples and comparative examples of the present invention. Table 4 shows a detailed table of the proportion of low-Σ corresponding grain boundaries of the copper alloys of the examples and comparative examples of the present invention, and the effect of the number of cycles of the repeated recrystallization process on the proportion of corresponding grain boundaries. Table 5 shows the mechanical properties, burst pressure and workability of the copper alloys of the examples and comparative examples of the present invention. Table 6 shows the pitting corrosion resistance of the copper alloys of the examples and comparative examples of the present invention.

[0164] As can be seen from Examples 1-3 and Comparative Example 1, when the Ni and P content remains substantially unchanged, the values ​​of f1 and f2 increase with increasing Sn content, and the proportions of grain boundaries corresponding to Σ3, Σ9, and Σ27 increase to 57.36%, 61.12%, and 62.97%, respectively (see Table 3 and Figures 3(a), 3(b), 3(c), and 3(d)), and the XRD test results indicate the presence of a single α phase (see Figure 2). Furthermore, as can be seen from Examples 1-3, the yield strength and tensile strength of the copper alloy improve simultaneously with increasing Sn content (see Table 5), proving that the element Sn has a significant solid solution strengthening effect and can simultaneously improve yield strength and tensile strength. Compared to Comparative Example 1, the tensile strengths of Examples 1, 2, and 3 increased by 12.1%, 17.7%, and 21.1%, respectively. However, the yield strength of Example 1 did not exceed that of Comparative Example 1. This indicates that a high proportion of Σ3, Σ9, and Σ27 corresponding grain boundaries contribute to providing a high proportion of low-energy coherent Σ-value corresponding grain boundaries. These grain boundaries have a lower limiting ability against dislocation motion in the initial stages of plastic deformation compared to random high-angle grain boundaries. By mitigating the initial inhibition of dislocation motion at the interface, it was possible to maintain a low yield strength to some extent and reduce the yield ratio to within 0.30.

[0165] As can be seen from Table 5, the burst pressure of copper alloy pipes of the same specifications increased with increasing Sn content, and Examples 1, 2, and 3 showed burst pressures that were 7.3%, 14.2%, and 20.7% higher than Comparative Example 1, respectively. The post-welding burst pressure decay rate for Examples 1, 2, and 3 was less than 10.0% in all cases. This is because the introduction of a high proportion of low-Σ-value compatible grain boundaries suppressed grain boundary migration and abnormal grain growth at high temperatures to some extent, thereby reducing the post-welding burst pressure decay rate. The burst location and morphology of the sample after the hydraulic burst test and after the post-welding hydraulic burst test for Example 2 are shown in Figure 6.

[0166] As can be seen from Table 6, under the same formic acid atmosphere corrosion conditions, Examples 1, 2, and 3 showed a gradual decrease in maximum corrosion depth compared to Comparative Example 1, with improvement rates of corrosion resistance of 15.8%, 17.9%, and 21.5%, respectively. Compared to Comparative Example 1, Examples 1-3 have a consistent Ni content, which contributes to improved corrosion resistance. Although the Ni content of Examples 1-3 is similar, Example 3 has a higher total amount of Σ3, Σ9, and Σ27, resulting in higher coherence of these low-Σ-value corresponding grain boundaries, lower energy, and segregation of extremely few impurity elements, creating pathways where corrosion is less likely to spread and which do not promote the corrosion of random high-angle grain boundaries. Furthermore, with an increase in (Σ9+Σ27) / Σ3 (see data for Examples 1-3 and Comparative Example 1 in Table 4), the original random high-angle grain boundary lattice is destroyed, the original grain boundary corrosion pathways are blocked, and as a result, the progression of pitting corrosion is slowed to a certain extent.

[0167] Examples 1, 2, and 3 all showed improved corrosion resistance after pipe bending compared to Comparative Example 1, with corrosion resistance decay rates of less than 17.0% in the pipe bending section in all cases. This indicates that a high total amount of Σ3, Σ9, and Σ27 has a certain inhibitory effect even against conditions that promote pitting corrosion through a combination of stress corrosion and intergranular corrosion. As can be seen from Figure 7, compared to Comparative Example 1, Example 2 showed a more uniform strain distribution after 5% tensile deformation, a lower average KAM value, meaning that the degree of strain concentration was much lower than that of TP2 copper. This indicates that finer grain size (including twin grain boundaries) and a high proportion of low Σ-value corresponding grain boundaries help promote a uniform strain distribution, thereby reducing stress and intergranular corrosion effects.

[0168] In Example 4, the Ni content was increased and the f2 value was decreased compared to Example 2. As a result, the total amounts of Σ3, Σ9, and Σ27 decreased to 57.42%, but due to the higher Ni content, it exhibited higher pitting corrosion resistance, with an improvement of 8.8% compared to Example 2. However, due to the slightly lower total amounts of Σ3, Σ9, and Σ27, the corrosion resistance decay rate at the pipe bend increased compared to Example 2.

[0169] As can be seen from Examples 2 and 3, by controlling the values ​​of f1 and f2 to the preferred ranges of 0.65% ≤ f1 ≤ 1.05% and 3.4 ≤ f2 ≤ 5, the tensile strength of the copper alloy can be further improved to 275 MPa or higher while maintaining a low yield ratio. This allows the copper alloy to meet the requirements of pipe bending, expansion, and flaring processes, while further improving pressure resistance, corrosion resistance, and heat softening resistance. Compared to Comparative Example 1, Example 1 showed improvements of only 7.3% and 15.8% in burst pressure and single-pipe corrosion resistance, respectively, while Example 3 showed improvements of 20.7% and 21.5%, respectively, demonstrating a significant improvement in both the pressure resistance and corrosion resistance of the preferably manufactured copper alloy pipe. Furthermore, compared to Example 1, Example 3 showed a decrease in both burst pressure decay rate and corrosion resistance decay rate.

[0170] As can be seen from Comparative Example 3, when the concentration of Sn atoms reaches the limit of solute atoms in a dilute solid solution, the distance between solute atoms decreases, and the ability to inhibit the dislocation motion of solute atoms increases dramatically. Therefore, the beneficial effect of the low-Σ-value grain boundaries in Comparative Example 3, which reduces the yield ratio, is almost canceled out by the hardening effect of the solute atoms. As a result, the pipe bending test was good, but the flare test was unsuccessful.

[0171] As is clear from Comparative Example 4, when the values ​​of f1 and f2 are too low, the total amount of Σ3, Σ9, and Σ27 does not exceed 50%, making it difficult to maintain high workability. Therefore, in Comparative Example 4, although the strength improved and the pipe bending test was passed, the flare performance was low.

[0172] As can be seen from Comparative Example 5, copper alloys with a high Ni content, even if they have an appropriate f1 value, exhibit a significantly reduced elongation at break, a high yield ratio of 0.40, extremely low flaring performance, and inability to meet the pipe bending requirements.

[0173] As can be seen from Comparative Example 6, a high Sn content can result in a strong hardening effect. Due to this hardening effect, Comparative Example 6 has a high yield ratio of 0.39 and extremely poor flare performance, and its pipe bending performance also fails to meet the requirements.

[0174] As can be seen by comparing Examples 5 and 6 with Examples 2 and 3, copper alloys with similar chemical compositions were repeatedly produced through a recrystallization process, and the total amounts of Σ3, Σ9, and Σ27 were effectively accumulated through the cycle, increasing from approximately 60% to 72-75% (see Table 3), while the average grain size (including twin grain boundaries) was slightly reduced. Taking Examples 2 and 5 as examples, the ratio of (Σ9+Σ27) / Σ3 increased from 4.3% to 12.5% ​​(see Table 4), and in Example 5, when the yield strength was close to that of Example 2, the tensile strength and pressure resistance performance improved significantly, and the yield ratio decreased. In Example 5, the rate of rupture pressure decay after welding was only 3.2%, and the rate of corrosion resistance decay at the pipe bend was only 6.2%. This indicates that a high proportion of grain boundaries corresponding to Σ3, Σ9, and Σ27, and a high (Σ9+Σ27) / Σ3 ratio, contribute to improving the high-temperature softening resistance of the copper alloy and reducing corrosion accelerated by grain boundaries and stress.

[0175] As can be seen by comparing Examples 7 and 9 with Example 2, and Examples 8 and 10 with Example 3, by adding a compound of Sn, Ni, and P, and then adding a small amount of Zr, the f1 value of the alloy is further increased, the proportion of grain boundaries corresponding to Σ3, Σ9, and Σ27 is increased, the tensile strength and burst pressure are further improved, and a low yield ratio of approximately 0.22 to 0.29 can be maintained. By adding a small amount of Co, the decay rate after welding can generally be reduced to within 6%. As can be seen by comparing Example 10 with Example 8, further increasing the Zr and Co content further improves the pressure resistance, corrosion resistance, and high-temperature softening resistance of the alloy. Particularly noteworthy is the significant reduction in the burst pressure decay rate of the alloy with the addition of Co and Zr.

[0176] As can be seen from Comparative Example 7, when the Sn and Ni content is appropriate, if the amount of Zr and Co added is too high, a hard and brittle second phase is introduced, which reduces the elongation at break, increases the yield ratio, and reduces the pipe bending and flaring performance.

[0177] As can be seen by comparing Example 11 with Example 7, by adding a small amount of element B, the oxygen content in the alloy can be effectively reduced to 15 ppm or less, and the dimensions of the cast dendrite structure can be significantly refined. Compared to Example 7, Example 11 showed an improvement in pitting corrosion resistance from 18.7% to 23.5% compared to the TP2 alloy.

[0178] As can be seen from Comparative Example 8, the amounts of Zr, Co, and B added should not be too high. Otherwise, the formed hard and brittle phase inclusions will significantly increase the yield strength and yield ratio, and decrease ductility, thereby reducing workability and significantly decreasing pipe bending and flaring performance.

[0179] As can be seen from Examples 12 to 15, the overall performance of copper alloy pipes can be effectively improved by comprehensively adjusting the content of Sn, Ni, P, Zr, Co, and B, maintaining the values ​​of f1 and f2 at optimal levels, and manufacturing them through a repeated recrystallization process. Compared to Comparative Example 1, Example 12 showed an improvement of approximately 27.6% in tensile strength (see Figure 4), the copper alloy pipe had a yield ratio of 0.25 or less and excellent workability, and its burst pressure improved by more than 30%, while the burst pressure decay rate after welding was less than 2%. Under the same test conditions, the maximum corrosion depth of the single pipe was less than 150 μm, and the maximum corrosion depth of the pipe bend was less than 160 μm. As can be seen from the XRD spectrum, by rationally controlling the content of Zr, Co, and B, it is possible to ensure that the copper alloy forms a single α-phase solid solution and that a hard and brittle second phase does not precipitate (see Figure 2). Example 12 has nearly the same Sn and Ni content as Example 2, but significantly higher Zr, Co, and B content. The addition of Zr helps to counteract the hardening effect of Ni, Co, and B, and gives the copper alloy a high total amount of Σ3, Σ9, and Σ27, while maintaining a low yield ratio of 0.25. Co helps to improve the high-temperature softening resistance of the copper alloy, and due to the action of Co, the burst pressure decay rate of Example 12 is only 1.8%. B mainly improves the quality of the ingot, reduces the oxygen content, and ensures that low-oxygen copper alloy material without casting defects can be produced using conventional equipment.

[0180] As is evident from Example 16, the combination of the high-performance copper alloy tube and the recrystallization process of the present invention can be applied to the manufacture of female threaded tubes, and each of the performance indicators can achieve the desired effect.

[0181] As can be seen from Table 4 and Figure 3, the number of recrystallization cycles in the repeated recrystallization process flow significantly affects the proportion of grain boundaries corresponding to Σ3, Σ9, and Σ27. Analysis of the grain boundary distribution maps of samples after 3 and 4 cycles of repeated recrystallization in Examples 5, 13, and 15 shows that increasing the number of recrystallization cycles not only increases the proportion of grain boundaries corresponding to Σ3, but also significantly increases the proportion of grain boundaries corresponding to Σ9, Σ27a, and Σ27b, thereby increasing the ratio of (Σ9+Σ27) / Σ3 and reducing the connectivity of random high-angle grain boundary networks. However, it is clear that if the number of cycles is too low, for example, less than 3 recrystallization cycles, the overall performance-to-cost balance of the repeated recrystallization process is inferior to that of the single-cycle recrystallization process. Similarly, when the number of cycles reaches 6, the proportion of low-Σ-value corresponding grain boundaries tends to saturate, and it becomes difficult to increase the total amounts of Σ3, Σ9, and Σ27 even with recrystallization cycles. Therefore, beyond 6 cycles, the balance between overall performance and cost of the repeated recrystallization process is inferior to that of the repeated recrystallization process with 3 to 6 cycles.

[0182] Finally, it should be noted that the above embodiments are merely for illustrating the technical means of the present application and do not limit the present application. Although the present application has been described in detail with reference to the embodiments described above, those skilled in the art can modify the technical means described in the embodiments described above or make equivalent substitutions for some or all of their technical features, and such modifications or substitutions do not cause the essence of the corresponding technical means to deviate from the scope of the technical means of the embodiments of the present application.

[0183] [Table 1]

[0184] [Table 2]

[0185] Table 3

[0186] Table 4

[0187] Table 5-1

[0188] Table 5-2

[0189] Table 6

Claims

1. In terms of mass percentage, the composition includes 0.05% ≤ Sn ≤ 0.6%, 0.08% ≤ Ni < 0.3%, and 0.015% ≤ P ≤ 0.045%, with the remainder being Cu and unavoidable impurities, where f1 = [Sn] + 10 [P] and f2 = [Sn] / [Ni], satisfying 0.5% ≤ f1 ≤ 1.05% and 1 < f2 ≤ 5, where [Sn], [P], and [Ni] are the mass percentages of Sn, P, and Ni content, respectively. A high-performance copper alloy tube characterized by having a single face-centered cubic α-phase, an average grain size of 10 to 25 μm excluding twin grain boundaries, an average grain size of 5 to 20 μm including twin grain boundaries, the total proportion of grain boundaries corresponding to Σ3, Σ9, and Σ27 being ≥ 50%, and the ratio of grain boundaries corresponding to Σ9 and Σ27 to Σ3 being (Σ9 + Σ27) / Σ3 ≥ 3.5%.

2. The high-performance copper alloy pipe according to claim 1, characterized in that it has a tensile strength of ≥ 260 MPa, a yield ratio of 0.23 to 0.30, a burst pressure decay rate of ≤ 10%, and after corrosion for 21 days by repeatedly heating and cooling in an atmosphere of 0.4% formic acid aqueous solution, the maximum corrosion depth of the single pipe is ≤ 170 μm, and the maximum corrosion depth of the pipe bend is ≤ 190 μm.

3. In terms of mass percentage, the composition includes 0.05% ≤ Sn ≤ 0.6%, 0.08% ≤ Ni < 0.3%, and 0.015% ≤ P ≤ 0.045%, with the remainder being Cu and unavoidable impurities, where f1 = [Sn] + 10 [P] and f2 = [Sn] / [Ni], satisfying 0.5% ≤ f1 ≤ 1.05% and 1 < f2 ≤ 5, where [Sn], [P], and [Ni] are the mass percentages of Sn, P, and Ni content, respectively. A high-performance copper alloy tube characterized by having a single face-centered cubic α-phase, an average grain size of 10 to 25 μm excluding twin grain boundaries, an average grain size of 5 to 20 μm including twin grain boundaries, a total proportion of grain boundaries corresponding to Σ3, Σ9, and Σ27 ≥ 68%, and a ratio of grain boundaries corresponding to Σ9 and Σ27 to Σ3 that satisfies (Σ9 + Σ27) / Σ3 ≥ 10%.

4. The high-performance copper alloy pipe according to claim 3, characterized in that it has a tensile strength of ≥ 285 MPa, a yield ratio of 0.21 to 0.28, a burst pressure decay rate of ≤ 5%, and after corrosion for 21 days by repeatedly heating and cooling in an atmosphere of 0.4% formic acid aqueous solution, the maximum corrosion depth of the single pipe is ≤ 155 μm, and the maximum corrosion depth of the pipe bend is ≤ 165 μm.

5. In terms of mass percentage, the composition includes 0.05% ≤ Sn ≤ 0.6%, 0.08% ≤ Ni < 0.3%, 0.015% ≤ P ≤ 0.045%, 0.001% ≤ Zr < 0.03%, 0.001% ≤ Co < 0.01%, and 0 ≤ B < 0.01%, with the remainder being Cu and unavoidable impurities, where f1 = [Sn] + 10[P] + 10[Zr] and f2 = [Sn] / [Ni], satisfying 0.65% ≤ f1 < 1.15% and 1 < f2 ≤ 5, where [Sn], [P], [Zr], and [Ni] are the mass percentages of Sn, P, Zr, and Ni content, respectively. A high-performance copper alloy tube characterized by having a single face-centered cubic α-phase, an average grain size of 10 to 25 μm excluding twin grain boundaries, an average grain size of 5 to 20 μm including twin grain boundaries, a total proportion of grain boundaries corresponding to Σ3, Σ9, and Σ27 ≥ 60%, and a ratio of grain boundaries corresponding to Σ9 and Σ27 to Σ3 that satisfies (Σ9 + Σ27) / Σ3 ≥ 4.0%.

6. The high-performance copper alloy pipe according to claim 5, characterized in that it has a tensile strength of ≥ 275 MPa, a yield ratio of 0.22 to 0.29, a burst pressure decay rate of ≤ 6%, and after corrosion for 21 days by repeatedly heating and cooling in an atmosphere of 0.4% formic acid aqueous solution, the maximum corrosion depth of the single pipe is ≤ 165 μm or less, and the maximum corrosion depth of the pipe bend is ≤ 180 μm.

7. The high-performance copper alloy tube according to claim 5 or 6, characterized in that 0.001% ≤ B < 0.01%.

8. The high-performance copper alloy pipe according to claim 7, characterized in that, after being corroded for 21 days by repeatedly heating and cooling in an atmosphere of a 0.4% formic acid aqueous solution, the maximum corrosion depth of the single pipe is ≤ 155 μm, and the maximum corrosion depth of the pipe bend is ≤ 170 μm.

9. In terms of mass percentage, the composition includes 0.05% ≤ Sn ≤ 0.6%, 0.08% ≤ Ni < 0.3%, 0.015% ≤ P ≤ 0.045%, 0.001% ≤ Zr < 0.03%, 0.001% ≤ Co < 0.01%, and 0 ≤ B < 0.01%, with the remainder being Cu and unavoidable impurities, where f1 = [Sn] + 10[P] + 10[Zr] and f2 = [Sn] / [Ni], satisfying 0.65% ≤ f1 < 1.15% and 1 < f2 ≤ 5, where [Sn], [P], [Zr], and [Ni] are the mass percentages of Sn, P, Zr, and Ni content, respectively. A high-performance copper alloy tube characterized by having a single face-centered cubic α-phase, an average grain size of 10 to 25 μm excluding twin grain boundaries, an average grain size of 5 to 20 μm including twin grain boundaries, a total proportion of grain boundaries corresponding to Σ3, Σ9, and Σ27 ≥ 72%, and a ratio of grain boundaries corresponding to Σ9 and Σ27 to Σ3 that satisfies (Σ9 + Σ27) / Σ3 ≥ 12%.

10. The high-performance copper alloy pipe according to claim 9, characterized in that it has a tensile strength of ≥ 295 MPa, a yield ratio of 0.20 to 0.27, a burst pressure decay rate of ≤ 2%, and after corrosion for 21 days by repeatedly heating and cooling in an atmosphere of 0.4% formic acid aqueous solution, the maximum corrosion depth of the single pipe is ≤ 150 μm, and the maximum corrosion depth of the pipe bend is ≤ 160 μm.

11. The high-performance copper alloy tube according to claim 9 or 10, characterized in that 0.001% ≤ B < 0.01%.

12. The high-performance copper alloy pipe according to claim 11, characterized in that, after being corroded for 21 days by repeatedly heating and cooling in an atmosphere of a 0.4% formic acid aqueous solution, the maximum corrosion depth of the single pipe is ≤ 145 μm, and the maximum corrosion depth of the pipe bend is ≤ 155 μm.

13. A blending and dissolving step in which raw materials are dissolved to match the blending ratio, A continuous casting step in which molten metal is continuously cast to form a billet, A rolling step in which a billet is rolled to obtain a rolled tube, A continuous drawing step to reduce the diameter of the rolled raw tube, A method for manufacturing a high-performance copper alloy tube according to any one of claims 1 to 6, 9, and 10, characterized by comprising a recrystallization step to obtain a product with target performance by controlling the amount of deformation and annealing parameters.

14. The method for manufacturing a high-performance copper alloy tube according to claim 13, characterized in that the recrystallization treatment is a single recrystallization of "block drawing → finished product annealing", the total deformation amount of the block drawing is 80% or more, the temperature of the finished product annealing is 500 to 750°C, and the annealing time is 30 to 150 min.

15. The method for manufacturing a high-performance copper alloy tube according to claim 13, characterized in that the recrystallization treatment is a repeated recrystallization in which a block drawing cycle of "block drawing → annealing" is performed multiple times after a block drawing of one to three passes, the total deformation amount of the block drawing in the first to three passes prior to the cycle is ≤ 72%, the number of "block drawing → annealing" cycles in the multiple "block drawing → annealing" cycles is 3 to 6 times, the deformation amount of block drawing in a single cycle is 25 to 35%, the annealing temperature is 500 to 600°C, and the annealing time is 10 to 70 min.

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