Nib-3-tin superconducting wire with stable RRR value and preparation method of Nib-3-tin superconducting wire

Abstract

The invention belongs to the technical field of superconducting wires, and discloses a Ni3Sn superconducting wire with a stable RRR value and a preparation method of the Ni3Sn superconducting wire. An oxygen-free copper rod, a Ta sheet and a thin-wall oxygen-free copper sheath are prepared into a Cu / Ta / Cu composite tube, meanwhile, subcomponents are densely arranged and loaded into a Ta barrier layer, then the Ta barrier layer is loaded into the prepared Cu / Ta / Cu composite tube, a final Nb3Sn blank with a double-layer Ta structure is obtained, and the Nb3Sn superconducting wire is prepared through multiple times of stretching. According to the invention, a double-Ta barrier layer structure in the Nb3Sn superconducting wire is realized, and the risk that an original single Ta barrier layer structure is broken in a stretching process to cause diffusion of Sn to a copper stable layer and reduce the RRR value of the wire is reduced. Compared with a traditional single-layer Ta tube superconducting wire, the RRR value of the Nb3Sn superconducting wire prepared through the method is obviously increased, and the Nb3Sn superconducting wire is more stable.

Description

Technical Field

[0001] The invention belongs to the technical field of superconducting wires and relates to a niobium-tin superconducting wire with a stable RRR value and a preparation method thereof. Background Art

[0002] Niobium-tin (Nb3Sn) superconducting wire has a high critical current density and is an important raw material for manufacturing high-field magnets. The internal tin method is one of the main methods for preparing Nb3Sn superconducting wire. At present, the Nb3Sn superconducting wires with the highest performance and the widest application are all prepared by the internal tin method. The composite wire is usually prepared by a single composite method, that is, the subcomponents are bundled into an oxygen-free copper tube and drawn multiple times to obtain the Nb3Sn composite wire. The Nb3Sn composite wire is mainly composed of four parts: a copper-free Nb3Sn superconducting layer, a copper-tin mixture matrix, a Ta barrier layer, and a copper stabilization layer. The copper-tin mixture is the main medium for the heat treatment of Nb3Sn. During the heat treatment process, Sn diffuses in the solid state to form a copper-tin mixture, and then reacts with the Nb rod to form a Nb3Sn superconducting phase. However, the presence of crystal defects, impurities, grain boundaries, etc. in superconducting wires will lead to the appearance of non-uniform resistance areas inside the material, and the residual resistivity (RRR value) of the wire must be stable.

[0003] For Nb3Sn composite wire, the RRR value is greatly affected by the structure and composition of the Cu stabilizing layer outside the Ta barrier layer, so the integrity of the Ta barrier layer must be ensured to reduce the risk of Sn diffusing to the Cu stabilizing layer during heat treatment. However, during the drawing process of the composite wire, the Ta tube is prone to barrier layer damage due to twisting and other drawing processes, causing Sn to diffuse to the Cu stabilizing layer during heat treatment, thereby reducing the RRR value. Therefore, it is necessary to design a new composite wire structure to reduce the risk of Ta barrier layer rupture. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing a Nb3Sn superconducting wire with a stable RRR value in view of the above-mentioned deficiencies in the prior art, so as to solve the problems existing in the above-mentioned background technology. To this end, the present invention provides the following technical solutions: The present invention provides a method for preparing a Nb3Sn superconducting wire with a stable RRR value, comprising: S1. Wrap the cleaned Ta sheet on the cleaned oxygen-free copper rod, put it into the cleaned thin-walled oxygen-free copper sheath, and then add copper covers at both ends and seal them with vacuum electron beam to obtain a Cu / Ta / Cu composite sheath; S2. The Cu / Ta / Cu composite sheath obtained in S1 is extruded, stretched multiple times, and then cut to length to obtain a Cu / Ta / Cu composite rod; S3. The Cu / Ta / Cu composite rod obtained in S2 is deep-drilled to obtain a Cu / Ta / Cu composite tube; S4. After cleaning the Ta barrier layer and subcomponents, they are bundled and loaded into the cleaned Cu / Ta / Cu composite tube, and finally loaded into the cleaned thin-walled oxygen-free copper tube to obtain the final Nb3Sn billet, which is then stretched multiple times to obtain the Nb3Sn superconducting wire.

[0005] Furthermore, in S1 of the above method, the Ta sheet has a length of 200-1000 mm, a width of 300-600 mm, and a thickness of 1-50 mm.

[0006] Furthermore, in S1 of the above method, the specifications of the oxygen-free copper rod are: diameter 100~300mm, length 200~1000mm.

[0007] Furthermore, in S1 of the above method, the specifications of the thin-walled oxygen-free copper sheath are: inner diameter 100~300mm, outer diameter 120~320mm, and length 200~1000mm.

[0008] Furthermore, in S2 of the above method, the specifications of the Cu / Ta / Cu composite rod are: diameter 30~60mm, length 1500~4000mm.

[0009] Furthermore, in S3 of the above method, the diameter of the deep hole drilled in the Cu / Ta / Cu composite rod is 20-40 mm.

[0010] Further, in S4 of the above method, the subcomponents include: hexagonal subcomponents, fan-shaped subcomponents, and semicircular subcomponents; the distance between opposite sides of the hexagonal subcomponents is 2~15mm, the farthest distance between the arc and the opposite side of the fan-shaped subcomponents is 2~15mm, and the distance between two parallel sides of the semicircular subcomponents is 2~15mm; the length of the subcomponents is 600~4000mm.

[0011] Furthermore, in S4 of the above method, the thin-walled oxygen-free copper tube has specifications of: inner diameter 15-60 mm, outer diameter 20-75 mm, and length 1500-4000 mm.

[0012] Furthermore, in S4 of the above method, the stretching pass processing rate is 2-30%, and the stretching speed is 1-100 m / min.

[0013] The present invention also claims protection for the Nb3Sn superconducting wire with stable RRR value obtained by the above preparation method.

[0014] Compared with the prior art, the present invention "a niobium-tin superconducting wire with a stable RRR value and a preparation method thereof" has at least the following beneficial effects: The present invention uses a Cu / Ta / Cu composite tube instead of an oxygen-free copper tube to assemble Nb3Sn wires, which can realize a double-layer Ta barrier layer structure inside the composite wire, reduce the risk of the original single Ta barrier layer structure breaking during the stretching process, thereby causing Sn to diffuse into the copper stabilization layer, and reduce the RRR value of the wire. Specifically: oxygen-free copper rods, Ta sheets, and thin-walled oxygen-free copper sheaths are prepared into Cu / Ta / Cu composite tubes by assembling-welding-extrusion-stretching-drilling, and the subcomponents are densely packed into the Ta barrier layer, which is then loaded into the prepared Cu / Ta / Cu composite tube to obtain a Nb3Sn final billet with a double-layer Ta structure, and the Nb3Sn superconducting wire is obtained after multiple stretching. Compared with traditional single-layer Ta tube superconducting wires, the RRR value of the Nb3Sn superconducting wire prepared by the present invention is significantly improved, and it is more stable.

[0015] In addition, the present invention obtains a Cu / Ta / Cu composite rod by assembling the Ta sheet with an oxygen-free copper rod and a thin-walled oxygen-free copper sheath and then extruding it. Compared with the traditional process of rolling the Ta sheet into a Ta tube and then assembling it, it can obtain better Cu / Ta interface bonding, improve the molding integrity of Cu and Ta, and effectively reduce the risk of rupture at the overlap of the Ta barrier layer due to twisting and other processes in the subsequent composite wire processing.

[0016] Finally, the Ta sheet specifications used in the assembly process of the Cu / Ta / Cu composite tube (length 200~1000mm, width 300~600mm, thickness 1~50mm) are larger than those used in traditional Nb3Sn composite wires, which effectively reduces the difficulty of cleaning and reduces foreign impurities during the assembly process of the composite wire. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the cross section of the Cu / Ta / Cu composite rod obtained for S1. Figure 1 Middle: 1-Ta sheet, 2-oxygen-free copper rod, 3-thin-wall oxygen-free copper sheath.

[0018] Figure 2 Schematic diagram of the cross section of the final Nb3Sn billet. Figure 2 Middle: 410 hexagonal subcomponent, 420 fan-shaped subcomponent, 430 semicircular subcomponent, 5-Ta barrier layer, 6-Cu / Ta / Cu composite tube, 7-thin-wall oxygen-free copper tube.

[0019] Figure 3 The RRR value test results of the Nb3Sn superconducting wire prepared in Example 1 and the conventional wire.

[0020] Figure 4 The RRR value test results of the Nb3Sn superconducting wire prepared in Example 2 and the conventional wire.

[0021] Figure 5 The RRR value test results of the Nb3Sn superconducting wire prepared in Example 3 and the conventional wire. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] The embodiment of the present invention provides a method for preparing a Nb3Sn superconducting wire with a stable RRR value, comprising: S1. Wrap the cleaned Ta sheet 1 on the cleaned oxygen-free copper rod 2, put it into the cleaned thin-walled oxygen-free copper sheath 3, then add copper covers on both ends and seal them with vacuum electron beam to obtain a Cu / Ta / Cu composite sheath.

[0024] S2. The Cu / Ta / Cu composite sheath obtained in S1 is extruded, stretched multiple times, and then cut to a fixed length to obtain a Cu / Ta / Cu composite rod; the cross section of the Cu / Ta / Cu composite rod is as follows Figure 1 shown.

[0025] S3. The Cu / Ta / Cu composite rod obtained in S2 is deep-hole drilled to obtain a Cu / Ta / Cu composite tube 6.

[0026] S4. After cleaning the Ta barrier layer 5 and the subcomponents, they are bundled and loaded into the cleaned Cu / Ta / Cu composite tube 6, and finally loaded into the cleaned thin-walled oxygen-free copper tube 7 to obtain the final Nb3Sn billet (cross section as shown in FIG. Figure 2 As shown), and then stretched multiple times to produce Nb3Sn superconducting wire.

[0027] Illustratively, in S1 of the above method, the Ta sheet 1 has a length of 200-1000 mm, a width of 300-600 mm, and a thickness of 1-50 mm.

[0028] For example, in S1 of the above method, the specifications of the oxygen-free copper rod 2 are: diameter 100-300 mm, length 200-1000 mm.

[0029] For example, in S1 of the above method, the specifications of the thin-walled oxygen-free copper sheath 3 are: inner diameter 100-300 mm, outer diameter 120-320 mm, and length 200-1000 mm.

[0030] Illustratively, in S2 of the above method, the specifications of the Cu / Ta / Cu composite rod are: diameter 30~60mm, length 1500~4000mm.

[0031] Exemplarily, in S3 of the above method, the diameter of the deep hole drilled in the Cu / Ta / Cu composite rod is 20-40 mm.

[0032] Exemplarily, in S4 of the above method, the subcomponents include: a hexagonal subcomponent 410, a fan-shaped subcomponent 420, and a semicircular subcomponent 430; the distance between opposite sides of the hexagonal subcomponent 410 is 2~15mm, the farthest distance between the arc and the opposite side of the fan-shaped subcomponent 420 is 2~15mm, and the distance between two parallel sides of the semicircular subcomponent 430 is 2~15mm; the length of the subcomponent is 600~4000mm.

[0033] For example, in S4 of the above method, the specifications of the thin-walled oxygen-free copper tube 7 are: inner diameter 15-60 mm, outer diameter 20-75 mm, and length 1500-4000 mm.

[0034] Illustratively, in S4 of the above method, the stretching pass processing rate is 2-30%, and the stretching speed is 1-100 m / min.

[0035] Example 1 This embodiment provides a method for preparing a Nb3Sn superconducting wire with a stable RRR value.

[0036] S1. Wrap the cleaned Ta sheet 1 on the cleaned oxygen-free copper rod 2, put it into the cleaned thin-walled oxygen-free copper sheath 3, then add copper covers on both ends and seal them with vacuum electron beam to obtain a Cu / Ta / Cu composite sheath.

[0037] In the above S1, the length of the Ta sheet 1 is 500 mm, the width is 500 mm, and the thickness is 17.5 mm. The specifications of the oxygen-free copper rod 2 are: diameter 150 mm, length 500 mm. The specifications of the thin-walled oxygen-free copper sheath 3 are: inner diameter 165 mm, outer diameter 300 mm, length 500 mm.

[0038] S2. Extrude the Cu / Ta / Cu composite sheath obtained in S1, and perform multiple stretching and then cut to a predetermined length to obtain a Cu / Ta / Cu composite rod. The Cu / Ta / Cu composite rod has a diameter of 45 mm and a length of 1500 mm.

[0039] S3. The Cu / Ta / Cu composite rod obtained in S2 is deep-hole drilled to obtain a Cu / Ta / Cu composite tube 6. The diameter of the deep-hole drilled on the Cu / Ta / Cu composite rod is 20 mm.

[0040] S4. After cleaning the Ta barrier layer 5 and the subcomponents, they are bundled and loaded into the cleaned Cu / Ta / Cu composite tube 6, and finally loaded into the cleaned thin-walled oxygen-free copper tube 7 to obtain the final Nb3Sn billet, which is then stretched multiple times to obtain the Nb3Sn superconducting wire.

[0041] In the above S4, the subcomponents include: hexagonal subcomponent 410, fan-shaped subcomponent 420, and semicircular subcomponent 430; the distance between opposite sides of the hexagonal subcomponent 410 is 10 mm, the maximum distance between the arc and the opposite side of the fan-shaped subcomponent 420 is 7 mm, and the distance between two parallel sides of the semicircular subcomponent 430 is 10 mm; the length of the subcomponent is 1500 mm. The specifications of the thin-walled oxygen-free copper tube 7 are: inner diameter 46.3 mm, outer diameter 65 mm, and length 1500 mm. The stretching pass processing rate is 2-30%, and the stretching speed is 1-100 m / min.

[0042] It should be noted that, for the processing rate of the stretching pass, since the blank needs to be stretched for multiple passes, the processing rate of each stretching pass is different. The first three passes use a processing rate of 5%, and above φ45 uses a processing rate of about 15%, above φ35 uses a processing rate of about 20%, above φ5 ​​uses a processing rate of about 18%, and below φ5 uses a processing rate of about 12%. Therefore, the processing rate in S4 is not a fixed value. For the stretching speed, 5m / min is used for φ45 and above, 12m / min is used for φ17 and above, 20~30m / min is used for φ5 and above, 50~80m / min is used for φ1.0 and above, and 100m / min is used for the final molding. Therefore, the stretching speed in S4 is not a fixed value, and the following embodiments will not be repeated.

[0043] Among them, after the wire was stretched to a diameter of 0.818mm, 100m was selected for corrosion. No Ta cracking was found in the selected 100m wire. Another 100m wire was heat treated and RRR value tested in sections. The test conditions were 273K / 20K, and the test results were all above 250 ( Figure 3 ). The same specification subcomponents were used to prepare single-layer Ta tube superconducting wires. The same processing method was used. After the wires were stretched to 0.818 mm, 100 m were also selected for corrosion. One Ta crack was found. Another 100 m wire was heat treated and RRR value tests were performed in sections. The test conditions were 273K / 20K. The test results were all below 170, and some were below 100. The specific test results are shown in Figure 3 .

[0044] Example 2 This embodiment provides a method for preparing a Nb3Sn superconducting wire with a stable RRR value.

[0045] S1. Wrap the cleaned Ta sheet 1 on the cleaned oxygen-free copper rod 2, put it into the cleaned thin-walled oxygen-free copper sheath 3, then add copper covers on both ends and seal them with vacuum electron beam to obtain a Cu / Ta / Cu composite sheath.

[0046] In the above S1, the length of the Ta sheet 1 is 400 mm, the width is 530 mm, and the thickness is 16.8 mm. The specifications of the oxygen-free copper rod 2 are: diameter 160 mm, length 530 mm. The specifications of the thin-walled oxygen-free copper sheath 3 are: inner diameter 174 mm, outer diameter 290 mm, length 530 mm.

[0047] S2. Extrude the Cu / Ta / Cu composite sheath obtained in S1, and perform multiple stretching and then cut to a predetermined length to obtain a Cu / Ta / Cu composite rod. The Cu / Ta / Cu composite rod has a diameter of 50 mm and a length of 1750 mm.

[0048] S3. The Cu / Ta / Cu composite rod obtained in S2 is deep-hole drilled to obtain a Cu / Ta / Cu composite tube 6. The diameter of the deep-hole drilled on the Cu / Ta / Cu composite rod is 24 mm.

[0049] S4. After cleaning the Ta barrier layer 5 and the subcomponents, they are bundled and loaded into the cleaned Cu / Ta / Cu composite tube 6, and finally loaded into the cleaned thin-walled oxygen-free copper tube 7 to obtain the final Nb3Sn billet, which is then stretched multiple times to obtain the Nb3Sn superconducting wire.

[0050] In the above S4, the subcomponents include: hexagonal subcomponent 410, fan-shaped subcomponent 420, and semicircular subcomponent 430; the distance between opposite sides of the hexagonal subcomponent 410 is 11 mm, the maximum distance between the arc and the opposite side of the fan-shaped subcomponent 420 is 9 mm, and the distance between two parallel sides of the semicircular subcomponent 430 is 11 mm; the length of the subcomponent is 2000 mm. The specifications of the thin-walled oxygen-free copper tube 7 are: inner diameter 51.3 mm, outer diameter 66 mm, and length 2000 mm. The stretching pass processing rate is 2-30%, and the stretching speed is 1-100 m / min.

[0051] Among them, after the wire was stretched to a diameter of 0.818mm, 100m was selected for corrosion. No Ta cracking was found in the selected 100m wire. Another 100m wire was heat treated and RRR value tested in sections. The test conditions were 273K / 20K, and the test results were all above 260 ( Figure 4). The same specification subcomponents were used to prepare single-layer Ta tube superconducting wires. The same processing method was used. After the wires were stretched to 0.818 mm, 100 m were also selected for corrosion. Three Ta cracks were found. Another 100 m wire was heat treated and RRR values ​​were tested in sections. The test conditions were 273K / 20K. The test results were all below 170, and some were below 100. The specific test results are shown in Figure 4 .

[0052] Example 3 This embodiment provides a method for preparing a Nb3Sn superconducting wire with a stable RRR value.

[0053] S1. Wrap the cleaned Ta sheet 1 on the cleaned oxygen-free copper rod 2, put it into the cleaned thin-walled oxygen-free copper sheath 3, then add copper covers on both ends and seal them with vacuum electron beam to obtain a Cu / Ta / Cu composite sheath.

[0054] In the above S1, the length of the Ta sheet 1 is 600 mm, the width is 500 mm, and the thickness is 4.5 mm. The specifications of the oxygen-free copper rod 2 are: diameter 150 mm, length 600 mm. The specifications of the thin-walled oxygen-free copper sheath 3 are: inner diameter 164.5 mm, outer diameter 285 mm, length 600 mm.

[0055] S2. Extrude the Cu / Ta / Cu composite sheath obtained in S1, and perform multiple stretching and then cut to a predetermined length to obtain a Cu / Ta / Cu composite rod. The Cu / Ta / Cu composite rod has a diameter of 47 mm and a length of 2000 mm.

[0056] S3. The Cu / Ta / Cu composite rod obtained in S2 is deep-hole drilled to obtain a Cu / Ta / Cu composite tube 6. The diameter of the deep-hole drilled on the Cu / Ta / Cu composite rod is 25 mm.

[0057] S4. After cleaning the Ta barrier layer 5 and the subcomponents, they are bundled and loaded into the cleaned Cu / Ta / Cu composite tube 6, and finally loaded into the cleaned thin-walled oxygen-free copper tube 7 to obtain the final Nb3Sn billet, which is then stretched multiple times to obtain the Nb3Sn superconducting wire.

[0058] In the above S4, the subcomponents include: hexagonal subcomponent 410, fan-shaped subcomponent 420, and semicircular subcomponent 430; the distance between opposite sides of the hexagonal subcomponent 410 is 9 mm, the maximum distance between the arc and the opposite side of the fan-shaped subcomponent 420 is 7 mm, and the distance between the two parallel sides of the semicircular subcomponent 430 is 9 mm; the length of the subcomponent is 3000 mm. The specifications of the thin-walled oxygen-free copper tube 7 are: inner diameter 48.3 mm, outer diameter 63.5 mm, and length 3000 mm. The stretching pass processing rate is 2-30%, and the stretching speed is 1-100 m / min.

[0059] Among them, after the wire was stretched to a diameter of 0.818mm, 100m was selected for corrosion. No Ta cracking was found in the selected 100m wire. Another 100m wire was heat treated and RRR value tested in sections. The test conditions were 273K / 20K, and the test results were all above 280 ( Figure 5 ). The same specification subcomponents were used to prepare single-layer Ta tube superconducting wires. The same processing method was used. After the wires were stretched to 0.818 mm, 100 m were also selected for corrosion. One Ta crack was found. Another 100 m wire was heat treated and RRR value tests were performed in sections. The test conditions were 273K / 20K. The test results were all below 170, and some were below 100. The specific test results are shown in Figure 5 .

[0060] In summary, the present invention provides a niobium-tin superconducting wire with a stable RRR value and a preparation method thereof. The present invention uses a Cu / Ta / Cu composite tube instead of an oxygen-free copper tube to assemble the Nb3Sn wire, realizing a double-layer Ta barrier layer structure inside the Nb3Sn superconducting wire, reducing the risk of the original single Ta barrier layer structure breaking during the stretching process and causing Sn to diffuse into the copper stabilization layer, thereby reducing the risk of the wire's RRR value. Compared with the traditional single-layer Ta tube Nb3Sn superconducting wire, the RRR value of the Nb3Sn superconducting wire prepared by the present invention is significantly improved and more stable.

[0061] The embodiments described above are only some embodiments of the present invention, not all embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but only represents selected embodiments of the present invention. All other embodiments obtained without creative work and related deductions and substitutions made by ordinary technicians in the field under the conditions of the concept of the present invention belong to the scope of protection of the present invention.

Claims

1. A method for preparing a Nb3Sn superconducting wire with a stable RRR value, characterized in that: include: S1. Wrap the cleaned Ta sheet (1) on the cleaned oxygen-free copper rod (2), place it in the cleaned thin-walled oxygen-free copper sheath (3), then add copper covers to both ends and seal them with vacuum electron beam welding to obtain a Cu / Ta / Cu composite sheath; S2. The Cu / Ta / Cu composite sheath obtained in S1 is extruded, stretched multiple times, and then cut to length to obtain a Cu / Ta / Cu composite rod; S3. The Cu / Ta / Cu composite rod obtained in S2 is deep-drilled to obtain a Cu / Ta / Cu composite tube (6); S4. After cleaning the Ta barrier layer (5) and the subcomponents, they are bundled and loaded into a cleaned Cu / Ta / Cu composite tube (6), and finally loaded into a cleaned thin-walled oxygen-free copper tube (7) to obtain a final Nb3Sn billet, which is then stretched multiple times to obtain a Nb3Sn superconducting wire.

2. The preparation method according to claim 1, characterized in that: In S1, the length of the Ta sheet (1) is 200~1000mm, the width is 300~600mm, and the thickness is 1~50mm.

3. The preparation method according to claim 1, characterized in that: In S1, the specifications of the oxygen-free copper rod (2) are: diameter 100~300mm, length 200~1000mm.

4. The preparation method according to claim 1, characterized in that: In S1, the thin-walled oxygen-free copper sheath (3) has specifications of inner diameter 100-300 mm, outer diameter 120-320 mm, and length 200-1000 mm.

5. The preparation method according to claim 1, characterized in that: In S2, the specifications of the Cu / Ta / Cu composite rod are: diameter 30~60mm, length 1500~4000mm.

6. The preparation method according to claim 1, characterized in that: In S3, the Cu / Ta / Cu composite rod is deep-drilled with a diameter of 20-40 mm.

7. The preparation method according to claim 1, characterized in that: In S4, the sub-components include: a hexagonal sub-component (410), a fan-shaped sub-component (420), and a semicircular sub-component (430); The distance between opposite sides of the hexagonal sub-component (410) is 2-15 mm, the maximum distance between the arc and the opposite side of the fan-shaped sub-component (420) is 2-15 mm, and the distance between two parallel sides of the semicircular sub-component (430) is 2-15 mm; the length of the sub-component is 600-4000 mm.

8. The preparation method according to claim 1, characterized in that: In S4, the thin-walled oxygen-free copper tube (7) has specifications of inner diameter 15-60 mm, outer diameter 20-75 mm, and length 1500-4000 mm.

9. The preparation method according to claim 1, characterized in that: In S4, the processing rate of the stretching pass is 2~30%, and the stretching speed is 1~100m / min.

10. A Nb3Sn superconducting wire with a stable RRR value obtained by the preparation method of claim 1.

Images