JP6398138B2 - Manufacturing method of iron-based superconducting wire - Google Patents

Description

  The present invention relates to a method for producing an iron-based superconducting wire.

The iron-based superconductor discovered in 2008 has high critical temperature (T _c ) and high critical magnetic field (H _c2 ), so it is expected to be applied as a superconducting wire for high magnetic field generation. There are attempts to make wire rods using the PIT (Powder-in-tube) method.

In the PIT method, the raw material powder is usually packed in a metal tube such as silver and then processed into a final shape by rolling or the like, and then heat treatment for reacting or sintering the raw material powder is performed. Regarding the iron-based superconducting wire, the inventors of the present invention report the production of (Ba, K) Fe ₂ As ₂ + Ag wire by the PIT method using a silver tube in the following Non-Patent Document 1. .

However, rolling tends to cause cracks, and the generated cracks inhibit current from flowing in the longitudinal direction of the wire. Therefore, currently, the iron-based superconductors, the critical current density can flow in the superconducting state (J _c) is not sufficiently high, the improvement of J _c is, is urgent the practical application of iron-based superconductors ing.

Matsumoto Akiyoshi et al., “Microstructure and superconducting properties of Ag-sheathed (Ba, K) Fe2As2 + Ag superconducting wires fabricated by an exsitu powder-in-tube process”, Supercond. Sci. & Technol., 25 (2012) 125010

The present invention has been made in view of the circumstances as described above, of the iron-based _{superconductors,} a T c ~38K, composition _{(Ba, K) Fe 2 As} 2 and (Sr, K) An object of the present invention is to provide a method for producing an iron-based superconducting wire that realizes excellent _Jc characteristics with respect to a so-called 122-based superconductor represented by Fe ₂ As ₂ .

In order to solve the above-mentioned problems, the inventors of the present invention reduced the occurrence of cracks and the fine grains by performing rolling and intermediate heat treatment one or more times in the production of 122 series superconducting wire. And found that the filling factor of the superconductor increases. In addition, by performing uniaxial compression and final heat treatment subsequent to this uniaxial compression at the final stage of production, cracks perpendicular to the length direction of the wire that are likely to occur during rolling can be eliminated. , J _c is also found that further improved. Furthermore, intermediate processing is performed by filling the raw material powder of the superconductor into a silver tube and processing it into a wire, and then performing secondary processing that inserts it into a metal tube having a hardness higher than silver and processes it into a wire. It has been found that even when heat treatment is not performed, the generation of cracks is suppressed and the filling rate of the superconductor is further increased. Based on these findings, the highest _Jc has been achieved so far as an iron-based PIT wire.

That is, in the method for producing an iron-based superconducting wire of the present invention, the composition is (Ba _x , K _1-x ) Fe ₂ As ₂ (0 <x <1) or (Sr _x , K _1-x ) Fe ₂ As. ₂ Rolling in which the thickness is reduced to 30% to 80% after primary processing is performed in which the iron-based superconductor powder represented by 0 (0 <x <1) is filled into a silver tube and processed into a wire. An intermediate heat treatment was performed one to several times in a temperature range of 700 ° C. to 900 ° C., and then uniaxial compression was performed to reduce the thickness to 60% to 90% of the thickness after the previous heat treatment. Thereafter, a final heat treatment is performed in a temperature range of 700 ° C. to 900 ° C. for 5 hours to 15 hours.

  Further, in this method for producing an iron-based superconducting wire, after the secondary processing in which the wire obtained by the primary processing is inserted into a metal tube having a hardness higher than silver and processed into a wire, Rolling to reduce it to 30% to 80% and intermediate heat treatment for 1 hour to 3 hours at a temperature range of 700 ° C. to 900 ° C. one or more times, and then the thickness is 60 to 60% of the thickness after the previous heat treatment. After performing uniaxial compression which reduces to 90%, it is preferable to perform a final heat treatment for 5 hours to 15 hours in a temperature range of 700 ° C to 900 ° C.

Furthermore, in the method for producing an iron-based superconducting wire of the present invention, the composition is (Ba _x , K _1-x ) Fe ₂ As ₂ (0 <x <1) or (Sr _x , K _1-x ) Fe ₂ As. ₂ Perform the primary processing of filling the iron-based superconductor powder represented by (0 <x <1) into a silver tube and processing it into a wire, and then insert it into a metal tube with hardness higher than silver Then, after the secondary processing to process the wire, the rolling is performed to reduce the thickness to 30% to 80%, and then the uniaxial compression to reduce the thickness to 20 to 90% of the thickness after the previous rolling. After being performed, a final heat treatment is performed in a temperature range of 700 ° C. to 900 ° C. for 5 hours to 15 hours.

The iron-based superconducting wire of the present invention has a structure in which a superconductor whose composition is represented by (Ba, K) Fe ₂ As ₂ is coated with silver, and the superconductor has a Vickers hardness of 100 to 100. 150, and the critical current density under the conditions of 4.2 K and 10 T is 1.0 × 10 ^{4 to} 2.5 × 10 ⁴ A / cm ² .

The iron-based superconducting wire of the present invention has a structure in which a superconductor whose composition is represented by (Sr, K) Fe ₂ As ₂ is coated with silver, and the superconductor has a Vickers hardness of 100 to 150. The critical current density under the conditions of 20K and 5T is 2.5 × 10 ^{3 to} 2.0 × 10 ⁴ A / cm ² .

The iron-based superconducting wire of the present invention has a structure in which a superconductor having a composition of (Ba, K) Fe ₂ As ₂ is coated with silver and further coated with a metal having a hardness higher than silver, The superconductor has a Vickers hardness of 170 to 200, and has a critical current density of 1.5 × 10 ^{4 to} 1.0 × 10 ⁵ A / cm ² under the conditions of 4.2K and 10T. To do.

The iron-based superconducting wire of the present invention has a structure in which a superconductor having a composition of (Sr, K) Fe ₂ As ₂ is coated with silver and further coated with a metal having a hardness higher than silver, The superconductor has a Vickers hardness of 170 to 200, and a critical current density under the conditions of 20K and 5T is 2.5 × 10 ^{3 to} 2.0 × 10 ⁴ A / cm ² .

According to the manufacturing method of the iron-based superconducting wire of the present invention, 122 based superconducting wires with an improved J _c it is achieved.

The powder X-ray-diffraction pattern and magnetization-temperature curve of Ba-122 superconductor obtained in Example 1 are shown. (A) and (b) show the voltage-current curve of the tape-shaped Ba-122 superconductor wire obtained in Example 1, respectively, and J _c of three tape-shaped wires having different thicknesses. Are plotted. It shows the magnetic field dependence of J _c. (A), (b), and (c) are the optical microscope image which observed the cross section of a square-shaped wire and a tape-shaped wire, respectively, and the X-ray-diffraction pattern of a superconducting part. (A), (b), and (c) show the polished surfaces of the cross-section in the length direction of the tape-shaped wire, and (a) and (b) are those of the rolled tape-shaped wire, respectively. Yes, (c) is a tape-shaped wire material that has been uniaxially compressed.

In one embodiment of the method for producing an iron-based superconducting wire of the present invention, the composition is (Ba _x , K _1-x ) Fe ₂ As ₂ (0 <x <1) or (Sr _x , K _1-x ) Fe. After the primary processing of filling the iron superconductor powder represented by ₂ As ₂ (0 <x <1) into a silver tube and processing it into a wire rod, the thickness is reduced to 30% to 80%. Rolling and intermediate heat treatment for 1 hour to 3 hours in a temperature range of 700 ° C. to 900 ° C. are performed one or more times. Next, uniaxial compression is performed to reduce the thickness to 60% to 90% of the thickness after the previous heat treatment, and then a final heat treatment is performed at a temperature range of 700 ° C. to 900 ° C. for 5 hours to 15 hours.

  In order to produce a PIT wire, the rolling process is an essential process. However, since the rolling process performs compressive deformation in one direction using friction on the roll surface, the wire is subjected to nonuniform deformation in the thickness direction. As a result, the degree of deformation may differ between the sheath material silver and the internal superconducting portion. When silver is soft, the deviation between the silver and the superconducting portion is alleviated at the interface between them. However, when the silver is hardened by work hardening, the deviation cannot be alleviated at the interface, and a crack occurs in the brittle superconducting portion. Since this crack occurs in a direction crossing the longitudinal direction of the wire, the flow of superconducting current is hindered, and the critical current density is remarkably reduced.

  Therefore, in the method for producing an iron-based superconducting wire according to the present invention, in order to suppress the generation of cracks, the rolling is not performed at a stretch, but heat treatment is performed in the middle of rolling to suppress the extreme hardening of silver. In this way, by carrying out rolling and intermediate heat treatment one or more times, pulverization and recombination of crystal grains occur and uniform fine crystals are obtained, and an ideal structure with an increased superconductor filling rate is obtained. It is done.

Moreover, in another embodiment of the manufacturing method of the iron-type superconducting wire of this invention, the secondary process which inserts the wire obtained by the said primary process into a metal pipe with hardness higher than silver, and processes it into a wire is performed. Thus, by processing into a wire using two types of metal tubes, an ideal structure with a further increased superconductor filling rate can be obtained. In this case, even if the intermediate heat treatment is not performed, by performing the rolling process, the uniaxial compression, and the final heat treatment, the generation of cracks is suppressed and the filling rate of the superconductor further increases. , Higher _Jc is achieved. In the case of a wire covered only with silver, the wire may be extremely soft due to the complete annealing of the silver by heat treatment. Therefore, for example, when processing into a coil winding, troubles such as bending of the wire with a small curvature and deteriorating superconducting characteristics may occur. On the other hand, in the case of a wire with the outer surface of the silver coating coated with a metal having a hardness higher than that of silver, the wire is maintained in a moderate hardness even after heat treatment and processed into a coil winding or the like while maintaining superconducting properties. There are advantages such as making it easier to do.

  In the case of using two types of metal tubes, a silver tube and a metal tube having a hardness higher than silver may be used separately, or a metal having a double structure of a silver tube and a metal tube having a hardness higher than silver. A tube may be used. As the double-structured metal tube, for example, a double-structured metal tube composed of a silver tube provided on the inside and a metal tube having higher hardness than silver provided on the outside can be used. The metal having a higher hardness than silver is not particularly limited as long as it has a Vickers hardness higher than that of silver. An example is stainless steel.

  On the other hand, the occurrence of cracks in the superconducting portion cannot be sufficiently suppressed only by rolling. Therefore, in the method for producing an iron-based superconducting wire of the present invention, uniaxial compression is performed before the final heat treatment to remove cracks remaining in the superconducting portion. Uniaxial compression is a processing method in which a wire is sandwiched between two plates and compressed in one direction using a press, and can uniformly deform the wire in the thickness direction. By this uniaxial compression, cracks remaining in the superconducting portion can be reduced, and the critical current density can be remarkably improved.

  As the rolling conditions, the outer diameter and inner diameter of the silver tube and the metal tube having a hardness higher than silver, the filling amount of the iron-based superconductor, and the like are considered, and the thickness is reduced within a range of 30% to 80%. It can be selected appropriately. Moreover, as conditions for the intermediate heat treatment performed alternately with rolling, 1 hour to 3 hours can be used as a rough standard in a temperature range of 700 ° C to 900 ° C. Also, the uniaxial compression conditions are not particularly limited, and for example, the thickness can be reduced to 60% to 90% of the thickness after the heat treatment performed before. On the other hand, when two types of metal tubes are used and no intermediate heat treatment is performed, the uniaxial compression condition is, for example, 20% to 90% of the thickness after the previous rolling performed. It can be reduced to a level that can be reduced. Furthermore, although it does not specifically limit about final heat processing, It can select suitably in the range of 5 hours-15 hours in the temperature range of 700 to 900 degreeC.

  An example is shown below and the manufacturing method of the iron system superconducting wire of the present invention is explained in detail. In addition, the manufacturing method of the iron-type superconducting wire of this invention is not limited to a following example.

A composition ratio of (Ba _0.6 , K _0.4 ) Fe ₂ As ₂ superconductor (hereinafter referred to as Ba-122 superconductor) using Ba, K, Fe and As as constituent elements. It was prepared by mixing in an Ar atmosphere at 0.6: 0.4: 2: 2.02, reacting at 900 ° C. for 10 hours in a niobium tube, and cooling in a furnace.

  FIG. 1 shows a powder X-ray diffraction pattern and a magnetization-temperature curve of the obtained Ba-122 superconductor.

  As shown in the powder X-ray diffraction pattern, all diffraction peaks were identified as being from the Ba-122 superconductor, and no peaks due to the impurity phase were observed. The (00) peak is higher in intensity than the other diffraction peaks, which indicates that the crystal grains are single crystals having a plate-like form, and their c-axis is oriented to some extent. . The magnetization-temperature curve is obtained from the measurement by the SQUID magnetometer, and a sharp superconducting transition is confirmed at about 37K. From these results, the Ba-122 superconductor is evaluated as a high-quality superconductor.

  Next, the Ba-122 superconductor was powdered, packed into a silver tube having an outer diameter of 6 mm and an inner diameter of 4 mm, and processed into a square wire having a cross section of about 2 mm square by the groove roll method. This rectangular wire was subjected to an intermediate heat treatment at 850 ° C. for 2 hours. After this heat treatment, the rectangular wire rod was rolled into a tape shape having a thickness of 0.6 mm to 0.7 mm using a rolling mill, and an intermediate heat treatment was performed again at 850 ° C. for 2 hours. After this heat treatment, the tape-shaped wire was again rolled to a thickness of 0.4 mm to 0.5 mm using a rolling mill, and an intermediate heat treatment was performed at 850 ° C. for 2 hours. After the obtained tape-shaped wire is cut into a length of 35 mm, the tape-shaped wire is uniaxially compressed using a press machine so that the thickness is 60% to 90% of the thickness after the previous heat treatment. A tape-shaped wire having a thickness of about 0.35 mm was produced. The tape-shaped wire thus obtained was finally subjected to heat treatment at 850 ° C. for 10 hours. The furnace was cooled after the final heat treatment.

A tape-shaped wire after final heat treatment, were measured critical current _{I c} at 4.2 K, 10T conditions. The magnetic field was applied perpendicular to the length direction of the tape-like wire and perpendicular to the surface of the tape-like wire. I _c was determined using a voltage reference of 1 μ / cm. FIG. 2A shows a voltage-current curve. Moreover, the cross-sectional photograph of the tape-shaped wire was shown in the figure of Fig.2 (a). I _c it was confirmed that the 122A. The I _c was determined the critical current density J _c is divided by the cross-sectional area of the superconducting portion of the tape-shaped wire. 2 (b) is a plot of J _c of the three tape-shaped wires of different thicknesses. For comparison, FIG. 2 (b) shows a J-shaped wire having a cross section of about 2 mm square and a tape-shaped wire having a thickness of 0.4 mm that has been subjected to final heat treatment without uniaxial compression. _c is also shown.

As apparent from FIG. 2 (b), _{J c} of angular wire rod, ~1000A / cm ² as low as about. Meanwhile, J _c is increased by repeating the rolling and intermediate heat treatment behind it. Increase of J _c is remarkable under strong magnetic fields. Further, increase of J _c is most pronounced by uniaxial compression. The three tape-shaped wires subjected to uniaxial compression before the final heat treatment exceed 10000 A / cm ² at 10T. This indicates that the high _Jc realization has good reproducibility. With a tape-like wire having a thickness of 0.4 mm, 21000 A / cm ² was obtained.

Next, than 4.2K at high temperatures was measured _{I c.} Figure 3 shows the magnetic field dependence of J _c. As apparent from FIG. 3, the magnetic field dependence of _{J c} of the tape-shaped wire is kept small to 20K, _{J c} at 10T maintains a high value of more than 1000A / cm ^2. This result shows that application of the tape-shaped wire rod to a magnet is promising even in an intermediate temperature range cooled by liquid hydrogen or the like as in liquid helium.

  4A and 4B are optical microscope images obtained by observing the cross sections of the rectangular wire and the tape-shaped wire, respectively. As described above, the rectangular wire is obtained by performing heat treatment after processing by the groove roll method, and the tape-shaped wire is repeatedly subjected to rolling and intermediate heat treatment and subjected to uniaxial compression and then subjected to final heat treatment. It was obtained by performing. Both optical microscope images are after heat treatment.

As is clear from FIG. 4A, the microstructure of the rectangular wire has a large non-uniform distribution with a crystal grain size exceeding several μm to 10 μm. On the other hand, as is clear from FIG. 4B, the microstructure of the tape-shaped wire has a uniform crystal grain size of 2 to 4 μm. Finer tissue, results in a greater pinning force due to the grain boundary, is believed to achieve higher J _c in a magnetic field. Moreover, although the Ba-122 superconductor packed in the silver tube was a plate-like crystal, the crystal grains of the superconducting portion in the tape-like wire have a substantially equiaxed form. FIG. 4C shows the X-ray diffraction pattern of the superconducting portion. From the comparison with FIG. 1A, it is confirmed that the (00) peak is not so high. Moreover, in the figure of FIG.4 (c), the magnetization-temperature curve of the superconducting part was shown collectively. A sharp superconducting transition is confirmed at about 35K.

Next, the cross-section in the length direction of the tape-shaped wire was polished, and the state of cracks was confirmed by observing the polished surface. FIGS. 5 (a) and 5 (b) are polished surfaces of the rolled tape-shaped wire, and cracks from the silver interface as the sheath material toward the inside of the superconducting portion are confirmed on each polished surface. FIG.5 (c) is the grinding | polishing surface of the tape-shaped wire which performed uniaxial compression. As confirmed in FIG. 5 (c), cracks in the superconducting portion that are perpendicular to the silver interface are suppressed, and instead, small cracks are generated in the length direction of the tape-shaped wire. ing. Differences in how to enter such cracks are considered to reflect the difference in the size of J _c. That is, cracks towards the inside of the superconducting portion, and inhibits the current flowing along the length of the tape-shaped wire, as a result, but leads to a decrease in J _c, tape-shaped wire shown in FIG. 5 (c) Cracks that occur in the length direction of do not disturb the current.

Furthermore, the filling rate of the superconductor in the wire was evaluated by measuring the Vickers hardness H _v. That is, it is considered that the higher the Vickers hardness value of the superconductor in the wire, the higher the filling factor of the superconductor in the wire. The Vickers hardness can be measured according to JIS B 7725. The Vickers hardness of the superconductor in the rectangular wire and the tape-shaped wire was 75 to 90 for the rectangular wire and 110 to 125 for the tape-shaped wire, respectively. As a result, it can be seen that the filling rate of the superconductor in the tape-shaped wire is significantly improved as compared with the rectangular wire.

A (Sr _0.6 , K _0.4 ) Fe ₂ As ₂ superconductor (hereinafter referred to as Sr-122 superconductor) was prepared in the same manner as in Example 1 and powdered. It was packed into a silver tube having an inner diameter of 4 mm and processed into a square wire having a cross section of about 2 mm square by the groove roll method. This rectangular wire was subjected to an intermediate heat treatment at 850 ° C. for 2 hours. After this heat treatment, the rectangular wire was rolled into a tape-like wire having a thickness of 0.6 mm to 0.7 mm using a rolling mill, and an intermediate heat treatment was again performed at 850 ° C. for 2 hours. After this heat treatment, the tape-shaped wire was again rolled to a thickness of 0.4 mm to 0.5 mm using a rolling mill, and an intermediate heat treatment was performed at 850 ° C. for 2 hours. After the obtained tape-shaped wire is cut into a length of 35 mm, the tape-shaped wire is uniaxially compressed using a press machine so that the thickness is 60% to 90% of the thickness after the previous heat treatment. A tape-shaped wire having a thickness of about 0.35 mm was produced. The tape-shaped wire thus obtained was finally subjected to heat treatment at 850 ° C. for 10 hours. The furnace was cooled after the final heat treatment.

For the tape-shaped wire after the final heat treatment, I _c was measured under the conditions of 4.2 K and 10 T in the same manner as in Example 1. I _c was 130A. J _c was 2950 A / cm ² under the conditions of 20K and 5T, and 1940 A / cm ² under the conditions of 20K and 10T. The tape-like Ba-122 superconducting wire, 20K, conditions 2290A / cm ^2, 20K of 5T, so was 1430A / cm ² under the conditions of 10T, the production of higher Sr-122 superconducting wires of _{J c} Is confirmed to be possible. In addition, the Vickers hardness of the superconductor in the tape-shaped wire was the same level as that of the tape-shaped wire of Example 1.

  The Ba-122 superconductor powder produced in Example 1 was packed in a silver tube having an outer diameter of 6 mm and an inner diameter of 4 mm, and processed into a square wire having a cross section of about 2 mm square by the groove roll method. This square wire was further drawn into a wire wire having a diameter of 1.3 mm. This 1.3 mm diameter wire-like wire was rolled into a tape shape having a thickness of 0.62 mm using a rolling mill. This tape-shaped wire was inserted into a stainless steel tube (SUS316) having an outer diameter of 3.2 mm and an inner diameter of 1.7 mm, and further rolled into a tape having a thickness of 1.5 mm using a rolling mill. This tape-shaped wire was subjected to an intermediate heat treatment at 850 ° C. for 2 hours, and further rolled into a 0.98 mm tape using a rolling mill. The obtained tape-shaped wire was cut into a length of 35 mm, and then the tape-shaped wire was uniaxially compressed using a press to produce a tape-shaped wire having a thickness of about 0.78 mm. The tape-shaped wire thus obtained was finally subjected to heat treatment at 850 ° C. for 10 hours. The furnace was cooled after the final heat treatment.

A tape-shaped wire material after heat treatment, 4.2 K in the same manner as in Example 1, was measured I _c under conditions of 10T. I _c was 58A. J _c was a high value of 48,000 A / cm ² . The Vickers hardness of the superconductor in the tape-shaped wire was 193. This value is higher than that of the silver-coated tape-like wire of Example 1, and is considered to be due to the improvement in the filling rate of the superconductor by adopting two types of metal tubes.

  The Ba-122 superconductor powder produced in Example 1 was packed in a silver tube having an outer diameter of 6 mm and an inner diameter of 4 mm, and processed into a square wire having a cross section of about 2 mm square by the groove roll method. This rectangular wire is further drawn into a wire-like wire with a diameter of 1.3 mm, inserted into a stainless steel tube (SUS316) with an outer diameter of 3.2 mm and an inner diameter of 1.7 mm, and the cross section is about 2 mm square by the groove roll method. It was processed into a square wire. The rectangular wire was rolled into a tape shape having a thickness of 1.25 mm using a rolling mill. The obtained tape-shaped wire was cut into a length of 35 mm, and then the tape-shaped wire was uniaxially compressed using a press to produce a tape-shaped wire having a thickness of about 0.35 mm. The tape-shaped wire thus obtained was subjected to heat treatment at 850 ° C. for 10 hours. The furnace was cooled after the heat treatment.

A tape-shaped wire material after heat treatment, 4.2 K in the same manner as in Example 1, was measured I _c under conditions of 10T. I _c was 19A. J _c was 17,000 A / cm ² .

  The wire wire with a diameter of 1.3 mm produced in Example 4 was rolled into a tape shape having a thickness of 0.62 mm using a rolling mill. This tape-shaped wire was inserted into a stainless steel tube (SUS316) having an outer diameter of 3.2 mm and an inner diameter of 1.7 mm, and further rolled into a tape shape having a thickness of 0.98 mm using a rolling mill. The obtained tape-shaped wire was cut into a length of 35 mm, and then the tape-shaped wire was uniaxially compressed using a press to produce a tape-shaped wire having a thickness of about 0.78 mm. The tape-shaped wire thus obtained was subjected to heat treatment at 850 ° C. for 10 hours. The furnace was cooled after the heat treatment.

A tape-shaped wire material after heat treatment, 4.2 K in the same manner as in Example 1, was measured I _c under conditions of 10T. I _c was 56.5A. J _c was a high value of 90,000 A / cm ² . The Vickers hardness of the superconductor in the tape-shaped wire was the same level as in Example 3.

Claims (7)

The composition has a structure in which a superconductor represented by (Ba _x , K _1-x ) Fe ₂ As ₂ (0 <x <1) is coated with silver, and the superconductor has a Vickers hardness of 100 to 150 An iron-based superconducting wire characterized by having a critical current density of 1.0 × 10 ^{4 to} 2.5 × 10 ⁴ A / cm ² under conditions of 4.2K and 10T. The superconductor has a structure in which a superconductor represented by (Sr _x , K _1-x ) Fe ₂ As ₂ (0 <x <1) is coated with silver, and the superconductor has a Vickers hardness of 100 to 150 An iron-based superconducting wire characterized by having a critical current density of 2.5 × 10 ^{3 to} 2.0 × 10 ⁴ A / cm ² under conditions of 20K and 5T. A superconductor having a composition represented by (Ba _x , K _1-x ) Fe ₂ As ₂ (0 <x <1) is coated with silver, and further has a structure coated with a metal having higher hardness than silver; The superconductor has a Vickers hardness of 170 to 200, and a critical current density of 1.5 × 10 ^{4 to} 1.0 × 10 ⁵ A / cm ² under the conditions of 4.2K and 10T. Iron-based superconducting wire. A superconductor having a composition represented by (Sr _x , K _1-x ) Fe ₂ As ₂ (0 <x <1) is coated with silver, and further has a structure coated with a metal having a higher hardness than silver; The superconductor has a Vickers hardness of 170 to 200, and a critical current density under conditions of 20K and 5T is 2.5 × 10 ^{3 to} 2.0 × 10 ⁴ A / cm ^2. Iron-based superconducting wire. A method for producing an iron-based superconducting wire according to claim 1 or 2,
Iron-based superconductivity whose composition is represented by (Ba _x , K _1-x ) Fe ₂ As ₂ (0 <x <1) or (Sr _x , K _1-x ) Fe ₂ As ₂ (0 <x <1) After performing the primary processing of filling the body powder into a silver tube and processing it into a wire rod, rolling to reduce the thickness to 30% to 80% and the temperature range of 700 ° C to 900 ° C for 1 hour to 3 hours The intermediate heat treatment is performed one or more times, and then the uniaxial compression is performed to reduce the thickness to 60% to 90% of the thickness after the previous heat treatment, and then the temperature is 700 ° C to 900 ° C for 5 hours to 15 A method for producing an iron-based superconducting wire characterized by performing a final heat treatment for a period of time. After performing the secondary processing of inserting the wire obtained by the primary processing into a metal tube having a hardness higher than silver and processing it into a wire, rolling to reduce the thickness to 30% to 80% and 700 ° C. to 900 ° C. 1 to 3 hours of intermediate heat treatment in the temperature range of 1 ° C to 3 ° C, and then uniaxial compression to reduce the thickness to 60 to 90% of the thickness after the previous heat treatment, followed by 700 ° C to The method for producing an iron-based superconducting wire according to claim 5 , wherein a final heat treatment is performed at a temperature range of 900 ° C for 5 hours to 15 hours. A method for producing an iron-based superconducting wire according to claim 3 or 4,
Iron-based superconductivity whose composition is represented by (Ba _x , K _1-x ) Fe ₂ As ₂ (0 <x <1) or (Sr _x , K _1-x ) Fe ₂ As ₂ (0 <x <1) After performing the primary processing of filling the body powder into a silver tube and processing it into a wire, and then performing the secondary processing of inserting it into a metal tube with a hardness higher than silver and processing it into a wire, Rolling is performed to reduce the thickness to 30% to 80%, and then uniaxial compression is performed to reduce the thickness to 20 to 90% of the thickness after the previous rolling, and then at a temperature range of 700 ° C. to 900 ° C. for 5 hours. A method for producing an iron-based superconducting wire, characterized by performing a heat treatment for -15 hours.