JPS5871508A - Method of producing nb3sn series extrefine multicore superconductive wire - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an Nb B S n-based ultrafine multifilamentary superconducting wire comprising a large number of ultrafine filaments of Nb38n, which is a superconducting intermetallic compound, and particularly relates to an intermediate annealing heat treatment during the manufacturing process. It is something.

As is well known, Nb s S n has excellent superconducting properties as a superconducting intermetallic compound, but on the other hand, it has problems with workability, especially low ductility and malleability.
When manufacturing s S n-based superconducting wire, Nb s S
Since it is difficult to process the wire in a state in which n is generated, processing is performed in a state in which no intermetallic compound has been generated, that is, in a composite state where Nb and Sn exist separately, to obtain the desired wire diameter. After that, diffusion heat treatment was performed to form Nb s
It is usual to generate S n.

By the way, as conventional methods for manufacturing Nb s S n-based ultrafine multicore superconducting wires, the bronze method and the Sn method are known. The former bronze method involves arranging one or more Nb cores in a base of Cu-8n alloy (bronze) to create a composite strand, and usually involves diameter-reducing after gathering multiple composite strands. The molded multicore composite wire with the desired wire diameter was obtained by applying diffusion heat treatment to the ultrafine multicore composite wire to form Cu-8n.
This is a method of diffusing Sn in an alloy base to generate a large number of Nb3Sn filaments, and the latter Sn method is a composite method in which one or more Nb core materials are placed in a copper base. A strand is made, usually a plurality of the composite strands are gathered together, the optical diameter is reduced to the desired wire diameter, and the outer circumferential surface is coated with Sn and scratched to obtain an ultra-fine multicore composite wire. The ultra-fine multifilamentary composite wire is subjected to diffusion heat treatment to diffuse Sn from the Sm layer and the Cu layer through the Cu base, and then the NJ
This is a method of producing n filaments. However, each of these conventional methods has advantages and disadvantages, and the reality is that none of them is satisfactory.

In other words, the former bronze method has the advantage of being able to generate Nb s Sn with a relatively simple heat treatment and does not require S-plating. There is a serious problem that is inferior to gender. In other words, in the bronze method, a sufficient amount of Nb5S
In order to generate s, it is necessary to use a Cu-Sn alloy with a fairly high Sn concentration of about 10 to 16 as the base, but work hardening is extremely likely to occur in a Cm-Sn alloy with such a high Sn concentration. Therefore, intermediate annealing must be performed frequently, and in particular, in the production of ultrafine multifilamentary superconducting wires, diameter reduction processing must be performed until the diameter of one Nb core material becomes a filament of about the size of a filament. There is a problem that the number of man-hours increases significantly, resulting in a significant decrease in productivity. On the other hand, in the latter method, the Sn method uses pure copper with good workability as the base, so the number of annealing times during diameter reduction processing can be significantly reduced compared to the bronze method. On the other hand, in order to generate a sufficient amount of Nb s S n, a fairly thick Sn layer is required, and in order to generate such a thick plating layer, a considerable amount of time is required for plating. However, there is a problem in that it is difficult to control the plating thickness, and in this method, the Sn for producing Nl)sSa is quite far from the Nb filament and requires a long diffusion distance. In order to increase the production efficiency of Nb5Sn, a long time is required for diffusion heat treatment.
Furthermore, it is necessary to make various adjustments to the heat treatment conditions.

The drawback of this Sn plating method is that it is particularly
This becomes noticeable when manufacturing bsSn-based superconducting wires. In other words, as the wire diameter becomes thicker, a larger amount of wire is required, so the thickness of the Sn plating layer needs to be significantly increased, and the gap between the Nb7' filament at the center of the ring and the Sn plating layer becomes larger. As the distance increases, the distance Sn must diffuse over is long. Therefore, in order to diffuse a large amount of Bm over a long distance and generate a sufficient amount of Nb 318m, preliminary heat treatment is required before the normal diffusion heat treatment. In addition, significant inconveniences arise, such as the need for preliminary heat treatment to be carried out in several stages.

In order to solve the above-mentioned problems, several improved methods have been proposed that combine the bronze method and the Sm plating method. That is, a method in which a Cu-8m alloy base with a low Sti concentration of less than 10wt1 is used instead of the pure copper base in the Sm plating method, and Sn plating is applied after gathering and diameter reduction processing in the same way as in the Sn plating method, or a method in which the base is made of Cu -B
! L alloy is used, but pure copper is placed on the outside, and Srs is used after assembly and diameter reduction processing.

Furthermore, the method of applying Cu-
In this method, 8m alloy is used, and a Cu-Sn composite with a low Sn concentration, which has good workability, is arranged on the outer spool, and Sn plating is applied in the same manner as described above. All of these methods have better workability than the bronze method and can reduce the number of intermediate annealing operations, and the Sn plating method allows for easier diffusion heat treatment, but they are still not fully satisfactory. There wasn't. Particularly in the case of thick wire diameters, some degree of diffusion heat treatment had to be devised. In addition, a common drawback of the conventional Sn plating method and each of the above-mentioned improved methods is that after the wire has been reduced to a predetermined diameter, Sn plating is applied to the outer peripheral surface and diffusion heat treatment is performed. There is a problem that it cannot be applied to the production of ultrafine multicore superconducting wires with copper. That is, in the case of the bronze method, one or more Nb
A plurality of composite wires with a core material arranged in a Cu-8rs alloy base are assembled, and a diffusion barrier layer made of Nb and Ta is formed on the outside of the composite wire, and a diffusion barrier layer made of Nb and Ta is further formed on the outside of the diffusion barrier layer. A method of manufacturing an ultrafine multicore superconducting wire with a Cu layer for stabilization is known by forming a stabilizing steel layer, reducing the diameter to the desired wire diameter, and then performing diffusion heat treatment. In this case, the presence of the diffusion barrier layer prevents 8n from diffusing into the outer Cu layer, so that the purity of the Cm layer can be kept high and play a sufficient role in stabilization. However, even if an attempt is made to manufacture an ultrafine multicore superconducting wire with a stabilizing steel and a diffusion barrier layer as described above by applying the Sn plating method or each of the above-mentioned improved methods, the distance from the outside of the round where the diffusion barrier layer is present is 8 m.・It is impossible to diffuse the oxygen-free steel provided outside the /4 rear layer for stabilization, and therefore it is impossible to do so. The reality is that it is limited to the law.

Based on the above circumstances, the present inventors have developed a stabilized steel that can easily perform diffusion heat treatment even for thick wire diameters, can reduce the number of intermediate annealing operations during diameter reduction processing, and has a diffusion delta rear. Nb s suitable for manufacturing ultrafine multicore superconducting wire with
We have developed a standard manufacturing method for Sn-based ultrafine multicore superconducting wire and proposed it in a separate application. That is, in the conventional Sm plating method and each of the improved methods described above, after gathering the composite wires as described above and performing diameter reduction processing to obtain the final number of wire cores,
In contrast, in the method proposed above, Sm holes and holes are applied at the stage where the final number of wire cores has not yet been assembled, and Sm holes and holes are applied to the outermost circumferential side. This is a method that can be called an internal plating method in which the Sm layer and the layer are located inside the base at the stage of the reduced diameter ultrafine multicore composite wire.

To explain the internal plating method proposed above in more detail with reference to FIGS. 1 to 6, first, as shown in FIG. Insert the wire into two hollow 71 ide made of Cu-8m alloy or Cu, and perform diameter reduction processing such as swaging, wire drawing, or drawing as necessary to make the Cu
A composite wire 3 is prepared in which a tooth core material 1 is embedded in a base 2 made of -8m alloy or Cu. Alternatively, as shown in FIG. The wire is inserted into the base 2 made of Cu-8m alloy or Cu by extrusion, swaging, wire drawing and drawing to reduce the diameter. Create a composite wire τ that material 1 has longed to embed. Next, as shown in FIG. 1 (Q) or FIG. 2 (C), the outer layer of the composite wires 3, 3', that is, the outer surface of the base 2 made of Cu-Bn alloy or Cu, is coated with a required thickness by electroplating or the like. Sm Me, Ki layer 5
Figure 1 (2)
Or, as shown in Figure 2 (2), collect multiple Cu
- Insert /4'ide 2CK made of 8m alloy or Cu, and repeat diameter reduction processes such as swaging, wire drawing and drawing, and intermediate annealing until the desired wire diameter, that is, the final wire diameter to be obtained. The diameter is reduced to obtain an ultrafine multifilamentary composite wire 7 as shown in FIG. 1 (2) or FIG. 2 (G). As shown in Fig. 3 and Fig. 4, this ultra-fine multifilamentary composite wire 7 has a large number of extremely thin n-core materials (Nb filaments) 1 arranged at intervals in a base 2 made of Cu-8m alloy or Cu. The Nb filament 1 is placed and buried inside the base 2, and an Sm layer 5 is arranged in a cross-sectional mesh shape so as to surround the Nb filament 1. By applying diffusion heat treatment to the ultra-fine multi-core composite wire 7 as described above, Sn is diffused from the Sn plating layer 5 inside the base 2, Nb and Sn are generated around the Nb filament 1, and the ultra-fine multi-core composite wire 7 is A superconducting wire is obtained. In addition, when producing ultrafine multicore superconducting wire with stabilized copper accompanied by a diffusion barrier,
The method shown in Figure C).

As shown in FIG. 5 (4) or FIG. The T& is inserted into the nozzle 8, and the entire body is inserted into the oxygen-free steel base 9 which is to become the stabilizing steel layer, and then the diameter reduction process and intermediate annealing are repeated several times in the same manner as described above. As shown in Figure (B) or Figure 4, an ultrafine multifilamentary composite wire 7' with a stabilizing copper layer 9' accompanied by a diffusion barrier layer 8' is obtained with a desired wire diameter, and then subjected to diffusion heat treatment in the same manner as described above. By applying this, Nb 5 Sn is generated without the internal Sm and the Sm in the middle layer being diffused to the outside.

In the stage of forming the ultrafine multicore composite wire immediately before the diffusion heat treatment in the method proposed above, the Sn plating layer is placed inside the base so as to surround the Nb filament, as described above. , such as the key method and its improvement method.
Compared to the case where the n and g layers are located on the outermost side, the Sn layer, which is the main source for island ssn generation,
The distance between the Ki layer and the island filament is extremely short, in other words, the distance that KSn must diffuse and move to generate island s Sn is significantly short compared to the conventional method, and therefore the diffusion generation of NbjSn is significantly shortened. It is easy to perform preheat treatment during diffusion heat treatment, and there is no need to perform preheat treatment in multiple stages, and a sufficient amount of Nb and Sn can be generated with simple heat treatment. This effect is particularly noticeable when the wire diameter is large.

In other words, in the conventional Sn method, as the wire diameter increases, the distance between the outer plating layer and the central filament increases, but in the method proposed above, the distance between the outer plating layer and the central filament increases. Regardless of this, the distance through which Sn must diffuse and move is always short, so even when the wire diameter is large, a simple heat treatment is sufficient in the same way as when the wire diameter is small. Furthermore, N
b The base in which the core material is embedded is C as in the conventional Sn plating method.
In the case of Cu-Sn alloys, Cu-Sn alloys with low Sn concentrations (preferably less than Sn 10 wt%, more optimally Sn 8 wt% or less) can be used, so composite wires and ultra-fine wires can be used. It is possible to improve the workability of the multicore composite wire and reduce the number of intermediate annealing operations during diameter reduction processing. Furthermore, as the base Cu-Sn alloy, one containing a small amount of P, that is, so-called phosphor bronze can be used.

Furthermore, in order to obtain an ultrafine multicore superconducting wire with a large number of Nb filaments, it is possible to assemble the composite strands intermediately even before the composite strands are assembled to the final number of Nb filaments. For example, a secondary composite wire is created by assembling multiple composite wires that do not make any noise when assembled at all (hereinafter referred to as primary composite wires), and then multiple secondary composite wires are assembled to create a secondary composite wire. By reducing the diameter, the final Nb
An ultrafine multifilamentary composite wire having a number of filaments may be obtained. In this case, the Sn metal in the internal plating method proposed above,
Ki may be performed at either the −th order composite wire stage or the second order composite wire stage, or may be performed at both stages.
In short, it is sufficient to apply 8n filaments and kiss at a stage before the final number of filaments is assembled.

When a plurality of composite wires that have been Sn-metalized and skimmed as described above are assembled and reduced in diameter using a ζ-rotation process, intermediate annealing must be performed at the stage where the cross-sectional area has been reduced to a certain degree.・In particular, when suspending a base of Cu-an alloy with MIh workability, it is necessary to increase the number of intermediate annealing, and Co-8m alloy with low Sn concentration or Co-8m alloy with relatively good workability is required. C1
Even when base I is used, intermediate annealing a certain number of times is unavoidable. Such intermediate annealing is performed by general K Cu
-400~ based on the softening temperature of Sn alloys and Cu
It is normal to perform the annealing at a temperature of about 550°C, but if the intermediate annealing is performed excessively at such a temperature, S! l IJ y chi na Cu
−8m phase, i.e. β phase, r phase, δ phase, C phase, ζ phase, η
Equivalent intermetallic phases are formed. These Sn I
J, the strong Cu-Sn intermetallic compound phase is the original Cm-
It is harder and has poor workability compared to Sn alloy bases and Cm bases, so if the Cu-8a-based gold metal compound phase develops, it becomes difficult to work9, and it may eventually lead to wire breakage during wire drawing. be. Even if the entire round wire does not break, the hard hCu-
If the an-based intermetallic compound phase develops in the base, the Nb core material is locally compressed by the hard phase during wire drawing, resulting in Nb
If unevenness occurs on the surface of the Nb core material and the wire drawing process continues, the Nb core material portion may break, and as a result, the desired superconducting properties may not be obtained. It was considered difficult to apply wire processing.

This invention was made against the background of the above-mentioned circumstances, and was designed to manufacture Nb s Sn-based ultrafine multicore superconducting wire by the internal plating method as proposed above, and during the diameter reduction process, Cu-Sn based superconducting wire was produced. Due to the formation and development of intermetallic compound phases! The purpose of this method is to enable the diameter to be reduced to a desired diameter without causing breakage of the wire rod itself or breakage of the Nbt material in the base of the wire rod.

In other words, the present invention replaces one or more core materials made of Nb with C.
A composite strand is made by placing it in a base made of u-Sn alloy or Cu, and after forming a So layer and a layer on the surface of the composite strand, a plurality of the composite strands are assembled, and then the diameter is reduced. Processing and intermediate annealing are repeated multiple times to obtain an ultrafine multifilamentary composite wire with a desired wire diameter, and then a diffusion heat treatment is performed to generate Nb 8ts. 'Jb s S In the manufacturing method of n-based ultrafine multifilamentary superconducting wire, when a plurality of composite strands are assembled and the diameter reduction process and intermediate annealing are repeated multiple times, the inside of the intermediate annealing after the second intermediate annealing is 700℃ at least once
It is characterized in that it is carried out by heating at the above temperature for 5 minutes to 1 hour.

The method of the present invention will be explained in more detail above.

In the method of the present invention, when a plurality of composite wires having been Sn-plated and skimmed as described above are assembled and subjected to diameter reduction processing and intermediate annealing multiple times, during the second and subsequent intermediate annealing, Heat treatment is performed at least once at a temperature of 700°C or higher for 5 minutes to 1 hour, but intermediate annealing other than the heat treatment at 700°C or higher is carried out at 400 to 55°C as in the past.
Heat treatment at about 0° C. may be performed, however, as will be described later, it is preferable that the first intermediate annealing be performed by short-time electrical heating of about several seconds to several minutes.

As mentioned above, at a temperature of 700°C or higher for 5 minutes to 1:1,
If heat-treated for a period of
Most of the □Cu-8n intermetallic compound generated by the intermediate annealing (degree) is decomposed, and the base becomes a Cu-Sn alloy phase with a substantially uniform concentration. Since the Cu-8n intermetallic compound phase is almost completely decomposed when heated at 790° C. or higher within the above temperature range, it is particularly desirable to heat at 790° C. or higher for 5 minutes to 1 hour. Once the hard Cu-8nn gold compound phase generated in this way decomposes, the wire itself may break during wire drawing or the spacing material may break due to the presence of the intermetallic compound phase. Therefore, it becomes possible to repeat the wire drawing process.

Note that if the assembled composite wires are heat-treated at a high temperature of about 700°C or higher, Nb 5 S a should be produced, but it takes an extremely long time to actually produce Nb s S n. In short, if the heat treatment is within 1 hour as described above, N
The phenomenon of generation of b s S n is hardly observed.

Cl-8 again! In order to decompose the l-based intermetallic compound, it is necessary to heat it for at least about 5 minutes. For these reasons, the above-mentioned heat treatment time at 700° C. or higher is set to 5 minutes to 1 hour. The upper limit of the heating temperature in this heat treatment is not particularly determined, but it is usually desirably about 850° C. or lower in order to avoid Nb3Sn formation due to excessively high temperatures.

Furthermore, if the 9Cm-8n intermetallic compound once generated in the matrix is decomposed by the above-mentioned heat treatment at 700°C or higher, the uniform 8n concentration in the matrix will increase, and if compared with the state before the start of diameter reduction processing, (Of course, Cu-8El
Processability is much better than in a state where intermetallic compounds have developed). Therefore, it is desirable to insert the above-mentioned heat treatment at 700° C. or higher as late as possible in the processing. However, if this heat treatment is delayed too much, the temperature will rise to 400-550℃.
By ordinary intermediate annealing of
The system intermetallic phase develops too much, and as a result, the wire itself breaks, and the Nb filament becomes uneven, causing the Nb filament to break.
It is sufficient to determine the stage at which heat treatment at temperatures above 0.degree. C. is to be performed.

Further, it is desirable that the first annealing, which is performed after Sn plating is performed and the composite strands are assembled and subjected to diameter reduction processing, be carried out by electrical heating for a short period of several seconds to several minutes.

In this way, a certain amount of Cu-Sn intermetallic compound phase is generated by the current annealing, so that the subsequent 400 to 55
Intermediate annealing at about 0°C melts the internal ST1 and G layers and prevents the Sn from melting out from the terminals or seeping out from the outer circumferential surface. The amount of Sn that contributes to the generation of Nb 3 Sn may be insufficient, and sufficient cold S a may not be generated, or wire breakage may occur during wire drawing due to voids formed in the portion of Sn that has been molten. can be prevented. However, if electrical annealing is carried out for a long time, Cu-Sn intermetallic compounds will develop excessively, which may cause early wire breakage.
Since there is a risk that unevenness may occur in the Nb filament and the Nb filament may break, it is desirable that the current annealing be carried out for a short time of several minutes at most. In addition, in this beak, as mentioned above, among the multiple intermediate annealing steps after the second, at least one is performed by heat treatment at 700C or higher to remove Sn.
Since this is a step to decompose the Cu-Sn-based intermetallic compound phase, even if the first annealing is electrically heated, the Cu-Sn-based intermetallic phase generated thereby will be
It will be decomposed by heat treatment above 'C. Then, at the stage where this heat treatment at 700°C or higher is completed, the Sn metal
Most of the Sn in the Q layer is the base (Cu or Cu-
Since FJn is diffused at a uniform concentration into the Sn alloy (Sn alloy), it is unlikely that FJn will be dissolved during the subsequent intermediate annealing.

Figure 7 shows an example of the diameter reduction process when the first annealing is electrical annealing as described above.In this way, an ultra-fine multifilamentary composite wire is obtained. If heat treatment is performed to generate Nb58n, an Nb5Bn-based ultrafine multicore superconducting wire can be obtained.

This Nb s S! Specifically, the diffusion heat treatment to prepare for the formation of l is performed in a vacuum or in an inert gas atmosphere.
Heat treatment may be performed at a temperature of about 50 to 850° C. for about 20 to 150 hours.

In addition, when manufacturing a Nb s S n ultrafine multicore superconductor with a large number of island filaments, -order composite strands (Cu-Sn
At least one Nb core material is embedded in the alloy base or Cu base, and a plurality of Nb core materials have not yet been assembled). After applying ki and assembling a plurality of these, performing a diameter reduction process on it to obtain a secondary composite strand, applying Sn and ki to the secondary composite strand again, multiple strands of this are assembled. The wire may be subjected to diameter reduction processing and then subjected to diffusion heat treatment to form an ultra-fine multifilamentary composite wire with a desired wire diameter. In this case, it is normal to repeat the diameter reduction process such as wire drawing and intermediate annealing in both the diameter reduction process after the secondary composite strand assembly and the diameter reduction process after the secondary composite strand assembly. However, in this case, in the diameter reduction process after the second composite strand assembly, any of the second and subsequent intermediate annealing is heat treated at 700°C or higher as described above, and the reduction process after the second composite strand assembly is performed. In the diameter machining step, it is also desirable that any of the intermediate annealing steps after FIG. 2 be heat treated at 700° C. or higher in the same manner as described above.

Implementation i of this invention will be described below.

Example 6 8 in Cws-8r1 alloy base containing excellent Snf
After forming a 30 μm thick Sn layer and a thin layer on the outer peripheral surface of a composite wire with an outer diameter of 0.8 φ in which five island core materials were embedded, 85 composite wires were assembled. , outer diameter 1o, inner diameter 9
It was inserted into the Cu-8m alloy Δear'' (6% Sn) of (2).

After wire-drawing this to an outer diameter of 4.6 mm, it was annealed by electricity, and then wire-processed and heated at 500°C in a nitrogen atmosphere.
x 1 hour annealing was repeated, and the outer diameter was 2.0 mm. At this stage, heat treatment was performed at 820'CX for 10 minutes in a nitrogen atmosphere, followed by wire drawing and 500°C in a nitrogen atmosphere.
C. for 1 hour was repeated to finally obtain an ultrafine multifilamentary composite wire with an outer diameter of 0.5 .phi. 750℃ for this ultra-fine multicore composite wire
A diffusion heat treatment was performed for 100 hours to generate Nb58m, thereby obtaining an Nbl1lsn-based ultrafine multifilamentary superconducting wire. The critical current value of this superconducting wire was measured and was 4.2, 10
I hope I can get a good value of 120mm at 0KG.

In the above example, when the cross-sectional condition of the ultra-fine multicore composite wire was observed after it was drawn to 0.5■φ, it was found that the base had C.
No u-8n intermetallic compound phase was observed, and uniform Cu-
It was confirmed that it was an 8o alloy phase and that the Nb filaments were arranged in a normal state. On the other hand, when the wire drawing and annealing were repeated without the heat treatment at 820°C for 10 minutes as in the above example (with the other conditions being the same as in the example), the outer diameter was 1.2 m. I was worried that the wire would break when this happened. When the cross section of the broken wire was observed, it was confirmed that a Sn'J-type Cu-Sn intermetallic compound had developed, and that this compound had caused significant unevenness on the surface of the Nb filament. Ta.

As is clear from the above dispersion, according to the method of this invention,
When producing 'Nb 5 S a -based ultrafine multifilamentary superconducting wires using the internal plating method, Sn generated and developed by intermediate annealing during the diameter reduction process during the manufacturing process.
') By effectively preventing unevenness from occurring on the surface of the di-Nb filament whose wire itself is f+7r wire due to the thick Cu-8n intermetallic compound phase and causing the Nb filament to break, it is possible to form the desired wire. In addition to being able to smoothly reduce the diameter until it reaches the same diameter, it is also possible to effectively prevent the occurrence of a situation where good superconducting characteristics cannot be obtained due to breakage of the internal Nb filament.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing step-by-step an example of the internal plating method that is the premise of this invention; Fig. 2 is an explanatory diagram showing step-by-step another example of the same internal plating method; Fig. 3; Figure 1■
), Figure 4 is an enlarged cross-sectional view of the compound line shown in Figure 2 @)
The enlarged cross-sectional view of the composite wire shown in FIGS. 5 and 6 are step-by-step explanatory diagrams in the case of manufacturing an ultrafine multicore superconducting wire with stabilizing steel according to the internal plating method described above, respectively. FIG. 7 is a flowchart showing an example of the diameter reduction process in the method of the present invention. 1...Nb core material, 2...base, 3...composite wire,
5... Sm plating layer, 7... Ultra-fine multicore composite wire. Figure 1 Figure 2 4 31- Figure 3 Figure 4

Claims (1)

[Claims] After making a composite wire by arranging one or more core materials made of Nb in a base made of Cu-8n alloy or C1I, and forming an Sfi plating layer on the surface of the composite wire, , a plurality of the composite wires are assembled, and then diameter reduction processing and intermediate annealing are repeated multiple times to obtain an ultrafine multifilamentary composite wire with a desired wire diameter, and then a diffusion heat treatment is performed to produce Nb s S n.
bs In the method for manufacturing a Sn-based ultrafine multifilamentary superconducting wire, tJ
Nb, Sn characterized in that at least one intermediate annealing after /cz times is performed at a temperature of 700 ° C. or higher for 5 minutes to 1 hour.
A method for manufacturing ultrafine multicore superconducting wire.