JPH08138468A - Nb3sn superconductive wire material and manufacture of it - Google Patents

Abstract

PURPOSE: To uniformly disperse remaining Nb cores after heat treatment so as to prevent attenuation and the like in a permanent current by altering a cross sectional area ratio according to a position of a Nb wire from the center in a secondary stack material in a bronze processing method. CONSTITUTION: A primary stack material constructed of a group of wire materials, in which plural primary stack materials are bound, and the heat treatment of the secondary stack materials is executed after a wire drawing processing so as to be turned into a Nb3 Sn superconductive wire material. In the secondary stack material, a cross sectional area ratio t(ri) of a Nb wire buried in the primary stack material separated from the center by a distance ri is constructed according to expressions I, II, III. By this constitution, a degree of dispersion of remaining Nb cores is unified, although a Sn quantity on the circumference is varied on the basis of the distance ri, and a breakage rate in a Nb3 Sn filament is suppressed low, so that deterioration in a critical current density Jc or a (n) value can be prevented. (In the expressions, r1 >r2 , an inferior out/in means an outermost/innermost side from the center. SNB(r) and SBZ(r) mean cross sectional areas of a Nb wire and a Cu-Sn group alloy part in the primary stack material positioned in the (r) position).

Description

Detailed Description of the Invention

[0001]

The present invention relates to relates to a Nb ₃ Sn superconducting wire and its manufacturing method used for a superconducting magnet structure material, Nb ₃ Sn superconducting wire and a Such having a particularly stable high field critical current characteristics The present invention relates to a useful method for obtaining a wire rod.

[0002]

2. Description of the Related Art A superconducting magnet which utilizes a permanent current phenomenon realized by a superconducting material and allows a large current to flow without consuming electric power to generate a magnetic field in a coil is known as a nuclear magnetic resonance (NMR) device. In addition to various physical property measurement devices, application to magnetic levitation trains, nuclear fusion devices, etc. is being promoted. As a constituent material of the above-mentioned superconducting magnet, a Nb ₃ Sn superconducting wire has been conventionally used as a typical one.

As a method for producing a Nb ₃ Sn superconducting wire, an internal diffusion method, a tube method, an in-situ (in
-Situ) method, powder method, bronze method and the like are known, but the most typical method is a so-called bronze method, which is a composite processing method. The general method of the bronze method will be described in more detail with reference to the drawings.

First, as shown in FIG. 1, made of a Cu--Sn based alloy.
Nb wire 1 is embedded in pipe 2 and subjected to cross-section reduction processing to make a hexagon
Manufacture the single core wire 3 formed into
And insert it into the Cu-Sn based alloy linear matrix 4 and reduce the cross-section.
Worked to form a hexagonal shape to form the primary stack material 5.
It Next, bundle the plurality of primary stack materials 5 into a cylindrical shape.
To form a wire rod group 10, and as shown in the drawing, Cu or Cu-Sn alloy
Inserted in a substantially cylindrical outer layer case 9 (outermost layer) made of gold
In the final shape, 3000-10000 Nb wires
A secondary stack material 11 containing 2 is formed. Secondary
In the tack material 11, as shown in FIG.
Assembled with oxygen-free copper 6 (stabilized copper) in the form of wires and rods that serves as a stabilizing material
The wire group 10 of the stack material 5 and the oxygen-free
Between the copper 6 is a cylindrical inside made of Cu-Sn based alloy.
Layer 7, and Nb₃ S during the diffusion heat treatment for producing Sn
Cylindrical Nb layer or Ta layer 8 serving as n diffusion barrier layer
Are formed. Of these, the diffusion barrier layer 8 is
Oxygen copper 6 has a function to prevent contamination by Sn.
Volatile. Finally, Sn is diffused by heat treatment, and Nb wire is
1 near the surface (ie, Cu-Sn based alloy pipe 2 and Nb wire)
(At the interface of 1), Nb ₃ Generate Sn to Nb₃ Over Sn
Use conductive wire.

In the above structure, a plurality of single core wires 3 are bundled to form Cu.
-Sn-based alloy linear base material 4 is inserted into the primary stack material 5
Although the case where the above is configured is shown, for example, in FIG.
As shown in, a plurality of Nb wires 1 are directly embedded in the Cu-Sn base alloy linear base material 4 to form the primary stack material 5.
In the same manner, the vicinity of the surface of the Nb wire 1 (in this case, Cu
At the interface between the Sn-based alloy linear base material 4 and the Nb wire 1), N
There is also a case where b ₃ Sn is generated to be an Nb ₃ Sn superconducting wire.

Regardless of which configuration is adopted, the primary stack material 5 and the Nb wire 1 buried therein are generally made to have the same cross-sectional area in the secondary stack material 11. Further, as the Cu—Sn base alloy pipe 2 and the Cu—Sn base alloy linear base material 4, a Cu—Sn alloy or Cu—S is used.
An n-Ti alloy or the like is generally used.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The method is made of Cu-Sn based alloy pipe 2 or Cu-Sn based alloy.
By diffusing Sn in the linear matrix 4 into the Nb wire 1.
Nb near the surface of Nb line 1₃ What produces Sn
However, at this time, all of Nb line 1 is completely Nb ₃ Sn
Remains ductile and high in strength in the center of Nb wire 1
Nb core remains and only the periphery is Nb₃ The method to make Sn
Used. That is, a superconducting magnet is used to generate a magnetic field.
Hoop force on the superconducting wire that composes the magnet.
The outward force called "Nb" works, and the entire Nb line 1 is
b₃ When reacted with Sn, this Nb₃ Sn is intermetallic
Since it is a brittle compound, it is sometimes Nb due to the hoop force.₃ To Sn
Cracks will occur and the characteristics of the superconducting wire and eventually the magnet
May cause significant deterioration. To prevent such deterioration
Therefore, all of the Nb line 1 is completely Nb₃ N without converting to Sn
Residual Nb core with ductility and high strength is left in the center of b wire 1.
Let only the surroundings Nb₃ Since the method of making Sn is used
is there.

If the residual Nb core remains unevenly in the cross section of the wire, the critical current density Jc, n value, etc. will be significantly deteriorated due to distortion caused by external force such as electromagnetic stress. Eventually, the operating current of the superconducting magnet will be attenuated in the permanent current mode. Therefore, it is desirable that the residual amount of the residual Nb core is uniform in the cross section of the wire.

However, in the wire rod in which the Nb wire 1 having a uniform cross-sectional area is buried before the final heat treatment as in the conventional case, the amounts of Sn around the Nb wires 1 on the inner side and the outer side are different from each other. , The remaining Nb core was reduced or hardly remained on the outer side where the Sn content was large, and it was difficult to make the remaining Nb core uniform after the final heat treatment.

By the way, the superconducting magnet used in the NMR apparatus is required to have extremely high accuracy in spatial uniformity and temporal stability of the magnetic field. The former is a subject that depends on the design of the magnet, and the latter is a subject that largely depends on the performance of the superconducting wire used. That is, the temporal instability of the magnetic field is caused by the decay of the persistent current flowing in the superconducting wire. Such a phenomenon is more remarkable in the Nb ₃ Sn wire rod used in a higher magnetic field than in the NbTi superconducting wire rod. The attenuation of about 0.1 to 100 ppm / h in the commonly used Nb ₃ Sn superconducting wire has not been a serious problem for the applied equipment until now, but it is a slight attenuation especially in the NMR apparatus. However, the performance as an analytical instrument is greatly deteriorated, which is a very serious problem. This disadvantage is caused by the decay of the permanent current in the superconducting magnet of the NMR apparatus, that is, the slight decay of the magnetic field (about 0.1-10).
It was found to appear as 0 ppm / h). However,
As described above, this attenuation greatly deteriorates the performance as an analytical instrument, and the Nb ₃ Sn superconducting wire thus far has some problems as a superconducting wire for an NMR apparatus.

The present invention has been made in order to solve the technical problems of the conventional Nb ₃ Sn superconducting wire as described above, and its purpose is to eliminate the residual Nb core as a strength member after the final heat treatment. By evenly dispersing,
A Nb ₃ Sn superconducting wire useful as a material for a superconducting magnet for an NMR apparatus, which prevents deterioration of the critical current density Jc, n value, etc., and does not cause problems such as decay of permanent current, and such Nb. ₃ To provide a useful method for manufacturing a Sn superconducting wire.

[0012]

According to the method of the present invention which has achieved the above object, a wire / rod-shaped stabilized copper, a cylindrical diffusion barrier layer, a substantially cylindrical Cu-Sn based alloy inner layer, Cu-S
A wire rod group in which a plurality of primary stack members in which a plurality of Nb wires are embedded in a linear base material made of an n-based alloy are bundled in a cylindrical shape, and a cylindrical C
The outermost layer made of u or Cu-Sn base alloy is arranged in the above-mentioned mounting order from the center side in the radial direction to the outside to form a secondary stack material, and the secondary stack material is wire-drawn, and then heat treated. Then, in the method for producing an Nb ₃ Sn superconducting wire for producing Nb ₃ Sn near the surface of the Nb wire, the Nb wire is embedded in a primary stack material at a distance of r ₁ , r ₂ (where r ₁ > r ₂ ) from the center. The cross-sectional area ratios of the Nb lines thus formed are t (r
₁ ), t (r ₂ ) and the cross-sectional area ratios of the Nb wires embedded in the primary stack material at the distances r _out and r _in from the center to the outermost side and the innermost side, respectively, T (r)
_out ), t (r _in ), the Nb ₃ Sn superconducting material is characterized in that a secondary stack material is formed so that these satisfy the following expressions (1) and (2) and the heat treatment is performed. It is a manufacturing method of a wire rod. t (r ₁ ) ≧ t (r ₂ ) ... (1) t (r _out )> t (r _in ) ... (2)

Further, the Nb _{3 of} the present invention capable of achieving the above object
The Sn superconducting wire has a point that the residual Nb cores dispersedly present in the Nb ₃ Sn superconducting wire satisfy the following formula (3). Such an Nb ₃ Sn superconducting wire is, for example, It is obtained by the method as described above. 0.05 ≦ σ / x ≦ 0.4 (3) where σ: standard deviation of the diameter of the remaining Nb core x: average value of the diameter of the remaining Nb core

[0014]

The present invention is constructed as described above, but in short,
A primary stack material is formed by reducing the cross-sectional area ratio of the Nb wire 1 on the inner side with a small amount of Sn and increasing the cross-sectional area ratio of the Nb wire 1 on the outer side with a large amount of Sn. By arranging them to form a secondary stack material, and by subjecting this secondary stack material to a final heat treatment, a Nb ₃ Sn superconducting wire rod with the remaining Nb cores left as evenly as possible can be manufactured, and this superconducting wire rod has desired characteristics. That is, the present invention has been completed.

As described above, the present invention is basically designed such that the cross-sectional area ratio increases toward the outer side. However, in order to satisfy this requirement in all regions of the wire rod, the constitution is There is a possibility that the process for achieving the above may become complicated. Therefore, in the present invention, as shown in Examples described later, for example, as shown in three parts of an inner layer, an intermediate layer and an outer layer, even if the distances r ₁ and r ₂ are different, the same sectional area is obtained. Assuming that it may be a ratio, the equal sign (=) is also included in the above formula (1). However, even in this case, since it is necessary to finally satisfy the above expression (2), the above expression (2) is defined as a requirement of the present invention.

The above-mentioned "cross-sectional area ratio of Nb wire" means the cross-sectional area ratio of Nb wires in the primary stack material 5, and Cu-S in the primary stack material 5 at the position r from the center.
When the sectional area of the n-based alloy portion (including that portion when the Cu-Sn-based alloy pipe 2 is used) is S _BZ (r) and the sectional area of the Nb wire 1 is S _NB (r), It is defined by the equation (4). t (r) = S _NB (r) / [S _NB (r) + S _BZ (r)] (4)

FIG. 3 shows the radial distribution of Sn concentration in the Nb ₃ Sn superconducting wire produced by the conventional method.
Here, the wire rod group 10 was divided into three parts, an inner layer part, a middle layer part, and an outer layer part. Looking at the Sn concentration of the wire rod group 10 after the reaction, it can be seen that the Sn concentration increases from the inner layer portion to the outer layer portion. Therefore, the generated Nb
The amount of ₃ Sn was also larger in the outer layer portion than in the inner layer portion, and the residual Nb core was smaller in the outer layer portion.

FIG. 4 shows a typical radial distribution of Sn concentration in the Nb ₃ Sn superconducting wire produced by the method of the present invention. In the method of the present invention, since the cross-sectional area ratio of the Nb line of the primary stack material 5 is distributed in the radial direction, a gradient is formed in the Sn concentration in the wire rod group 10 before the reaction (before the final heat treatment). Therefore, after reaction (after final heat treatment)
It is understood that the Sn concentration distribution in the wire rod group 10 is almost uniform.

Further, an Nb ₃ Sn superconducting wire having a uniform degree of dispersion of the remaining Nb cores is obtained such that the remaining Nb cores dispersedly present in the Nb ₃ Sn superconducting wire satisfy the above expression (3). Such wire rods exhibit the desired superconducting properties.

As described above, according to the present invention, the cross-sectional area of the residual Nb core after the final heat treatment can be made uniform, and the stress applied to the superconducting wire rod by the excitation after magnetizing is applied to the residual Nb core in the wire rod. Since it is evenly shared, Nb ₃ S
The disconnection rate of the n-filament can be suppressed to a low level. This prevents deterioration of the critical current density Jc, n value, etc. due to strain generated in the superconducting wire, and does not cause problems such as permanent current attenuation in particular, and Nb ₃ in a high magnetic field to which a large electromagnetic stress is applied. It means to facilitate the use of Sn superconducting wire.

The n value is an amount showing the sharpness of the transition from the superconducting state to the normal conducting state. This value reflects the degree of uniform processing of the filament, and it is said that the larger the value, the better the characteristic. It is what That is, when an electric current is passed through the superconducting wire, a resistance is generated and a voltage is generated at a certain current value (critical current) or more, but the relationship between the current and the generated voltage is empirically shown in (5) below. It is represented by an approximate expression like the expression, and the value of n in this expression is called the n value. V = V ₀ (I / Ic) ⁿ (5) where V: generated voltage V ₀ : constant Ic: critical current

The present invention will be described in more detail with reference to the following examples. The following examples are not intended to limit the scope of the present invention, and any modification of the design can be made according to the gist of the preceding and the following. It is included in the target range.

[0023]

【Example】

Example 1 A superconducting wire of the present invention was prepared by the procedure shown in FIG. First, the Nb wire 1 is embedded in a Cu-Sn base alloy tube 2 having a composition of Cu-13% Sn-0.3% Ti, and subjected to cross-section reduction processing, and then molded into a hexagonal shape to form a single core wire 3. It was made. At this time, the sectional area ratio t defined by the above equation (4)
Three types (r) of 0.22, 0.42, and 0.54 were prepared. A plurality of these are stacked (primary stack), embedded in a Cu—Sn based alloy base material 4 having a composition of Cu—13% Sn—0.3% Ti, and subjected to cross-section reduction processing. A primary stack material 5 was produced by forming it into a rectangular shape.

Next, a plurality of primary stack materials 5 are Cu-1
The secondary stack material 11 was assembled by inserting it into a Cu-Sn based alloy tube (outermost layer 9) having a composition of 3% Sn-0.3% Ti. Here, the central three-layer structure member is Cu-13%.
For an alloy pipe of Sn-0.3% Ti composition (inner layer 7),
A Ta pipe (diffusion barrier layer 8) and oxygen-free copper (stabilized copper 6) were used. Primary stack material 5
As shown in FIG. 5, the cross-sectional area ratio t (r) is 0.
No. 22 having a cross-sectional area ratio t (r) of 0.42 was arranged in the middle layer, and one having a cross-sectional area ratio t (r) of 0.54 was arranged in the outer layer. The obtained secondary stack material 11 was subjected to cross-section reduction processing to obtain a wire material having a wire diameter of 0.7 mmφ.

On the other hand, for comparison, the secondary stack material 11 was assembled by the same method as the conventional one as shown in FIG. That is, the single core wire 3 having the sectional area ratio t (r) of 0.42
Secondary stack material 11 was assembled in the same manner as above except that a plurality of sheets were stacked to produce primary stack material 5. Then, the cross-section reduction processing is applied to this and the wire diameter is 0.7 m.
It was a wire of mφ.

After these wires were subjected to a final heat treatment (Nb ₃ Sn formation heat treatment) at 680 ° C. for 50 hours, the diameter of the remaining Nb core in each layer was observed with an electron microscope. The results are shown in Table 1 below, and it can be seen that the distribution of the residual Nb core is more uniform in the wire produced by the method of the present invention than in the conventional method.

[0027]

[Table 1]

Next, the critical current densities Jc and n of the superconducting wire are
The effect of strain on the values was measured. The results are shown in FIG. 7 in comparison with the wire produced by the conventional method. The superconducting wire produced by the method of the present invention has a critical current density Jc or n higher than that of the superconducting wire produced by the conventional method.
It can be seen that the strain resistance characteristics are improved as well as the superconducting characteristics such as values are improved.

Further, a magnet was constructed by using two types of wire rods for these, and the degree of current attenuation (drift amount) in the persistent current mode was measured. As a result, the drift amount of the magnet composed of the wire produced by the conventional method is 0.
While it was 045 ppm / h, the drift amount was 0.008 ppm / h in the magnet constituted by the wire rod manufactured by the method of the present invention. From this, it is understood that the method of the present invention is effective in reducing the operating current attenuation of the superconducting magnet in the permanent current mode.

Example 2 A superconducting wire of the present invention was produced by the procedure shown in FIG. First, a plurality of Nb wires 1 are embedded in a Cu-Sn-based alloy linear base material 4 having a composition of Cu-13% Sn-0.3% Ti, and subjected to cross-section reduction processing, and then formed into a hexagonal shape. It shape | molded and produced the primary stack material 5. At this time, the cross-sectional area ratio t (r) defined by the equation (4) is 0.22, 0.42,
Three types of 0.54 were prepared.

Next, a plurality of primary stack materials 5 are Cu-1.
The secondary stack material 11 was assembled by inserting it into a Cu-Sn based alloy tube (outermost layer 9) having a composition of 3% Sn-0.3% Ti. Here, the central three-layer structure member is Cu-13%.
For an alloy pipe of Sn-0.3% Ti composition (inner layer 7),
A Ta pipe (diffusion barrier layer 8) and oxygen-free copper (stabilized copper 6) were used. Primary stack material 5
As shown in FIG. 8, the cross-sectional area ratio t (r) is 0.
No. 22 having a cross-sectional area ratio t (r) of 0.42 was arranged in the middle layer, and one having a cross-sectional area ratio t (r) of 0.54 was arranged in the outer layer. The obtained secondary stack material 11 was subjected to cross-section reduction processing to obtain a wire material having a wire diameter of 0.7 mmφ.

On the other hand, for comparison, the secondary stack material 11 was assembled by the same method as the conventional one as shown in FIG. That is, the secondary stack material 11 was assembled in the same manner as above except that the primary stack material 5 having a cross-sectional area ratio t (r) of 0.42 was used. Then, this was subjected to cross-section reduction processing to obtain a wire rod having a wire diameter of 0.7 mmφ. .

After these wires were subjected to a final heat treatment (Nb ₃ Sn formation heat treatment) at 680 ° C. for 50 hours, the diameter of the remaining Nb core in each layer was observed with an electron microscope. The results are shown in Table 2 below, and it can be seen that the distribution of the residual Nb core is more uniform in the wire produced by the method of the present invention than in the conventional method.

[0034]

[Table 2]

Next, a magnet was constructed by using two kinds of wire rods for these, and the degree of current attenuation (drift amount) in the permanent current mode was measured. As a result, the drift amount of the magnet composed of the wire produced by the conventional method is 0.
While it was 025 ppm / h, the drift amount was 0.007 ppm / h in the magnet constituted by the wire rod manufactured by the method of the present invention. From this, it is understood that the method of the present invention is effective in reducing the operating current attenuation of the superconducting magnet in the permanent current mode.

Example 3 A superconducting wire according to the present invention was produced by the procedure shown in FIGS. First, a plurality of Nb is added to the Cu-Sn based alloy linear base material 4 having a composition of Cu-13% Sn-0.3% Ti.
After embedding the wire 1 and reducing the cross section, a hexagonally shaped primary stack material 5 was produced. At this time, as shown in FIG. 10, the cross-sectional area ratio t (r) is 0.20, 0.45, 0.
60 sets of 3 types (this is called the method A of the present invention)
Then, as shown in FIG. 11, the cross-sectional area ratio t (r) is 0.2.
Two sets of three kinds of sets of 2, 0.47 and 0.55 (this is called the method B of the present invention) were prepared.

Cu-1 was used as the primary stack material for these two sets.
In two alloy pipes (outermost layer 9 and inner layer 7) having a composition of 3% Sn-0.3% Ti and different inner diameters, the cross-sectional area ratio t (r) from the inner layer portion to the outer layer portion is small in order. Stacked (see FIG. 10 and FIG. 11), oxygen-free copper (stabilized copper) is provided in the central portion, and a diffusion barrier layer 8 made of Ta is provided in the periphery thereof to reduce the cross-section, and the wire diameter is 0.7 m.
m wire rod. 50 at 680 ° C for these two types of wire
After heat treatment for a time, the remaining Nb core in each layer of each wire was observed with an electron microscope. Table 3 shows the results.

[0038]

[Table 3]

Further, a magnet was produced using these wire rods and the amount of drift was measured. The above results are shown in FIG. 12 together with the results of Examples 1 and 2 above. From this graph, it can be seen that extremely high magnetic field stability with a drift amount of 0.01 ppm / h can be realized when the ratio value (σ / x) is in the range of 0.05 to 0.4. From this result, it is understood that the method of the present invention makes it possible to provide a wire rod effective for reducing the current attenuation in the persistent current mode of the superconducting magnet.

[0040]

The present invention is constructed as described above, and the distribution of the remaining Nb cores of the superconducting wire after the final thermomagnetic treatment can be made uniform. As a result, Nb ₃ S
n superconducting wire strength is increased and the critical current density due to strain J
It is possible to prevent the deterioration of the c and n values and also to improve the critical current density Jc and the n value itself. Further, the superconducting wire of the present invention can be a constituent material of an excellent superconducting magnet, which can be expected to improve the performance of devices in a wide range of fields such as analysis and medical treatment.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining a procedure of a bronze method.

FIG. 2 is a schematic diagram for explaining another procedure of the bronze method.

FIG. 3 is a graph showing a radial distribution of Sn concentration in a Nb ₃ Sn superconducting wire manufactured by a conventional method.

FIG. 4 is a graph showing a typical radial distribution of Sn concentration in a Nb ₃ Sn superconducting wire manufactured by the method of the present invention.

FIG. 5 is a schematic view for explaining the procedure of the method of the present invention performed in Example 1.

FIG. 6 is a schematic diagram for explaining the procedure of the conventional method performed in Example 1.

FIG. 7 is a graph showing the effect of strain on the critical current density Jc and n value of a superconducting wire.

FIG. 8 is a schematic diagram for explaining the procedure of the method of the present invention performed in Example 2.

FIG. 9 is a schematic diagram for explaining the procedure of the conventional method performed in Example 2.

FIG. 10 is a schematic diagram for explaining the procedure of the method A of the present invention performed in Example 3.

FIG. 11 is a schematic view for explaining the procedure of the method B of the present invention performed in Example 3.

FIG. 12 is a graph showing the relationship between σ / x and the amount of drift.

[Explanation of symbols]

 1 Nb wire 2 Cu-Sn group alloy pipe 3 Single core wire 4 Cu-Sn group alloy linear matrix 5 Primary stack material 6 Oxygen-free copper (stabilized copper) 7 Inner layer 8 Nb or Ta layer (diffusion barrier layer) ) 9 outer layer case (outermost layer) 10 wire group 11 secondary stack material

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiko Inoue 1-5-5 Takatsukadai, Nishi-ku, Kobe-shi, Hyogo Kobe Steel Co., Ltd. Kobe Research Institute (72) Inventor Hidefumi Kurahashi Takatsuka, Nishi-ku, Kobe-shi, Hyogo 1-5-5 Taiwan Kobe Works, Kobe Steel Co., Ltd. (72) Inventor Kazukazu Hakukura 1-5-5 Takatsukadai, Nishi-ku, Kobe-shi, Hyogo Kobe Steel Works, Kobe Steel Co., Ltd.

Claims (2)

[Claims] 1. A wire / rod-shaped stabilized copper, a cylindrical diffusion barrier layer, a substantially cylindrical inner layer made of a Cu—Sn based alloy, and Cu—S.
A wire rod group in which a plurality of primary stack materials in which a plurality of Nb wires are embedded in an n-base alloy linear base material are bundled in a cylindrical shape, and a substantially cylindrical Cu or Cu-Sn base alloy outermost layer are provided on the radial center side. From the above to the outside to configure the secondary stack material arranged in the above-mentioned mounting order, and after drawing the secondary stack material,
In a method for producing an Nb ₃ Sn superconducting wire which is heat-treated to generate Nb ₃ Sn near the surface of the Nb wire, in a primary stack material at a distance of r ₁ , r ₂ (where r ₁ > r ₂ ) from the center, The cross-sectional area ratios of the buried Nb wires are t (r
₁ ), t (r ₂ ) and the cross-sectional area ratios of the Nb wires embedded in the primary stack material at the distances r _out and r _in from the center to the outermost side and the innermost side, respectively, T (r)
_out ), t (r _in ), the Nb ₃ Sn superconducting material is characterized in that the heat treatment is performed by forming a secondary stack material so that these satisfy the following expressions (1) and (2). Manufacturing method of wire. t (r ₁ ) ≧ t (r ₂ ) ... (1) t (r _out )> t (r _in ) ... (2) 2. A Nb ₃ Sn superconducting wire, characterized in that the residual Nb cores dispersedly present in the Nb ₃ Sn superconducting wire satisfy the following formula (3). 0.05 ≦ σ / x ≦ 0.4 (3) where σ: standard deviation of the diameter of the remaining Nb core x: average value of the diameter of the remaining Nb core