JP5343526B2 - Superconducting wire manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem wherein, while a critical current value is required to be further improved in an oxide superconducting wire, a crystal grain of a precursor in a superconducting phase is small, so that the orientation of the crystal grain is sometimes disturbed when a multicore wire of the superconducting wire is rolled, the disturbance of the orientation of the crystal grain may become a factor of preventing a critical current and a critical current density from being improved, and therefore, the crystal grain of the precursor in the superconducting phase is required to be increased. <P>SOLUTION: Flattering processing is performed so as to improve a reactivity of crystal grains of a precursor in a superconducting phase. Thereafter, an intermediate heat treatment is carried out before full-scale rolling so that the crystal grains of the precursor in the superconducting phase having the improved reactivity are bonded together by a reaction and the grain size of the crystal grains is increased. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method for manufacturing a superconducting wire, and more particularly to a method for manufacturing a superconducting wire that improves the critical current and the critical current density by improving the crystal orientation of an oxide superconductor. Is.

  Conventionally, a tape-shaped superconducting wire (superconducting tape) made of a multi-core wire in which an oxide superconductor having a Bi2223 phase or the like is coated with a sheath portion such as silver can be used at a liquid nitrogen temperature and is relatively high. Since a critical current density can be obtained and lengthening is relatively easy, application to superconducting coils and magnets is expected.

  A technique of forming such a superconducting wire having a long shape by processing an oxide superconductor such as a Bi2223 phase by a powder-in-tube method is known. Here, the long shape means a band-like or bar-like shape extending in one direction. In the conventional powder-in-tube method, first, raw material powder such as Bi2212 is filled into the first metal tube having a long shape. Next, the first metal tube is drawn by subjecting the first metal tube to wire drawing. Then, a plurality of drawn strands are bundled and inserted into another metal tube (second metal tube), and the second metal tube is formed into a multi-core wire by drawing the wire. To do. By rolling this multifilamentary wire, a tape-shaped wire having a long shape is obtained. The tape-shaped wire is heat treated to form the desired superconducting phase. These rolling and heat treatments may be performed only once, but are usually performed twice. By performing the above steps, a superconducting wire in which a plurality of superconducting filaments are contained in the metal sheath formed by the above-described metal tube is obtained.

  However, due to recent technological advancement, higher Jc (critical current density) and Ic (critical current) are required particularly for superconducting wires applied to applications such as superconducting coils and cables.

  A so-called high-temperature superconductor that has a Bi2223 phase and can be used at a liquid nitrogen temperature is an oxide ceramic. For this reason, Jc, Ic, and the like of the high-temperature superconducting wire are affected by all manufacturing conditions such as raw material powder, filament arrangement, processing process, rolling conditions, and heat treatment conditions. Therefore, in order to realize higher Jc and Ic, it is necessary to optimize each of these manufacturing conditions.

  Here, regarding the filament arrangement and rolling conditions, in the above-described conventional superconducting wire manufacturing method, the cross section intersecting the major axis direction (extending direction) of the second metal tube having a long shape is circular or regular hexagonal. For example, the rolling process for compressing the multifilament wire so as to have a rectangular cross section is performed randomly without specifying the direction of compression (pressurization). For this reason, a plurality of first metal tubes arranged inside the multi-core wire and the multi-core wire may be displaced in a direction crossing the direction in which the multi-core wire is pressed, and shearing may occur. That is, a plurality of first metal tubes arranged inside the multi-core wire may cause a load collapse by generating shear when pressurizing the multi-core wire. The collapse of the first metal tube due to the shearing deteriorates the filament arrangement after the heat treatment, that is, the orientation of the crystal of the superconducting wire. Deteriorating the orientation of the superconducting wire crystal results in a decrease in Jc and Ic.

Therefore, for example, in Japanese Patent Application Laid-Open No. 2003-303519 (hereinafter referred to as “Patent Document 1”), prior to the step of rolling the second metal tube, the multicore wire is pressed to increase the cross section of the multicore wire. A method of manufacturing a superconducting wire is disclosed, in which a flattening process is performed so that the dimension in the measured direction is reduced. In this way, if the multifilamentary wire is processed into a flat shape in advance, shearing that is likely to occur at the initial stage of rolling in the conventional process of rolling the second metal tube following the flattening is performed. It is possible to suppress the occurrence of the displacement of the position of the first metal tube. For this reason, it is said that the electrical characteristics such as the critical current and critical current density of the superconducting wire can be improved. In fact, as disclosed in Patent Document 1, if flat processing is performed on a multi-core wire, the position of the plurality of first metal tubes arranged inside the multi-core wire due to shearing of the strand is determined. By suppressing the deviation, the effect of improving the critical current and the critical current density is recognized.
JP 2003-303519 A

  However, considering the needs from the future market, further improvement of critical current and critical current density is desired. Specifically, a current value of at least 220 A or more is required. However, when performing the flattening process previously disclosed in Patent Document 1 to process a multicore wire into a flat shape, the crystal grains of the material (precursor) to be superconductive inside the multicore wire are compressed. It is crushed. For this reason, the crystal grains of the precursor of the superconducting phase are reduced. If the crystal grains are small, the orientation of the crystal grains may be disturbed when the conventional process of rolling the second metal tube is performed following the flattening process. Disturbance of crystal grain orientation can be a factor that hinders improvement of critical current and critical current density.

  The present invention has been made in view of the above problems, and its purpose is to improve the crystal orientation of the oxide superconductor further than the above-described superconducting wire manufacturing method, thereby making it possible to achieve critical current and critical current density. It is providing the manufacturing method of the superconducting wire which improves this.

  The method of manufacturing a superconducting wire according to the present invention includes a step of drawing a first metal tube filled with a raw material powder constituting the superconducting wire to form a single core wire, and a single core wire as a first metal tube. Are drawn to form a multi-core wire, a step of processing the multi-core wire into a flat shape, and a flat shape. It comprises a step of rolling the processed multi-core wire and a step of heat-treating the rolled multi-core wire. And the process of carrying out the intermediate heat processing of a multi-core wire is performed between the process of processing a multi-core wire so that it may become flat, and the process of rolling the multi-core wire processed so that it may become flat.

  If it does in this way, when carrying out flat processing before a full-scale rolling process, raw material powders, such as Bi2212 phase, will be stuck beforehand by pressurization, and it will be densified. In this way, if the raw powder is densified, if the step of intermediate heat treatment of the multifilamentary wire is performed, the raw material powders that have become more reactive due to densification are combined to form a precursor crystal composed of the raw powder The particle size of can be increased. When the crystal grain size is increased in this way, the crystal tends to fall down in the rolling direction in the subsequent full-scale rolling process. As a result, it is possible to satisfactorily align the orientation of the crystal grains of the formed superconducting phase by a heat treatment process that is a post-treatment.

  In addition, as described above, prior to the step of rolling the multifilamentary wire, flattening is performed in which the multifilamentary wire is pressed to compress the cross section of the multifilamentary wire so that the dimension in the pressurized direction is reduced. If it does in this way, the 1st metal pipe (element wire) with which the inside of a multi-core wire is filled will be in the position by shear by the full-scale rolling process (process which presses a multi-core wire) performed after flat processing. It is possible to suppress the occurrence of deviation. Suppressing the displacement of the position due to shearing is achieved by performing a full-scale rolling process thereafter, so that the raw material powder such as Bi2212 filling the inside of the first metal tube eventually becomes a superconducting filament. Contributes to a good alignment.

  The step of processing the above-described multifilament wire into a flat shape is preferably carried out using any one of the rolling methods of rectangular rolling or rectangular die drawing. When any one of these processing methods is used, the length of the superconducting wire can be increased.

  Further, in the method of manufacturing a superconducting wire according to the present invention, in the step of processing the above-described multi-core wire into a flat shape, the size of the multi-core wire in a direction in which the multi-core wire is compressed so as to become flat has a flat shape. It is preferable to perform processing so that it is 30% or more and 45% or less of the dimension of the multi-core wire before processing. That is, it is preferable to perform the processing under a condition that the rolling reduction is 55% or more and 70% or less.

  If the multi-core wire is processed into a flat shape (processing by pressing) so that it is 30% or less of the dimension of the multi-core wire before it is processed into a flat shape, it becomes a multi-core wire in the same way as a full-scale rolling process. On the other hand, since pressurization is performed and the pressurization pressure increases, for example, the second metal tube constituting the multi-core wire may break. In addition, there is a high possibility that the first metal tube will generate shear in the process.

  Also, if the multi-core wire is processed into a flat shape (processed by pressing) so that it is 45% or more of the dimension of the multi-core wire before processing into a flat shape, the powder filled in the first metal tube Therefore, the raw material powder such as the Bi2212 phase cannot be sufficiently densified. Therefore, in order to form the densified raw material powder by the process of processing the multi-core wire into a flat shape, as described above, the dimensions of the multi-core wire in the compressing direction so that the multi-core wire is flattened, It is preferable to process the multi-core wire so that it is 30% or more and 45% or less of the dimension of the multi-core wire before processing into a flat shape.

Moreover, in the manufacturing method of the superconducting wire which concerns on this invention, it is preferable to heat a multi-core wire in the process of carrying out the intermediate heat processing of a multi-core wire so that it may become temperature lower than the process of heat-processing the subsequent multi-core wire. When the multicore wire is heated to a higher temperature than the step of heat treating the multicore wire in the step of intermediate heat treatment of the multicore wire, the process of crystal growth of the raw material powder such as Bi2212 in the superconducting phase is promoted, but at the same time, for example, A non-superconducting phase such as (Ca, Sr) ₂ CuO ₃ may grow. If the subsequent full-scale rolling process is performed in a state where the non-superconducting phase is formed, the orientation of crystal grains of the formed superconducting phase may be disturbed. Therefore, in the step of performing the intermediate heat treatment on the multi-core wire, it is preferable to heat the multi-core wire at a temperature lower than that in the subsequent step of heat-treating the multi-core wire to such an extent that the non-superconducting phase does not grow.

More specifically, in the step of performing the intermediate heat treatment on the multicore wire described above, the multicore wire is preferably heated to 740 ° C. or higher and 780 ° C. or lower. If the multi-core wire is subjected to an intermediate heat treatment at a heating temperature of less than 740 ° C., the raw material powder such as Bi2212 cannot be sufficiently grown. Further, when the heating temperature is 780 ° C. or higher, as described above, the process of crystal growth of the raw material powder such as Bi2212 in the superconducting phase is promoted, but at the same time, for example, (Ca, Sr) ₂ CuO ₃ etc. The superconducting phase may grow crystals. If the subsequent full-scale rolling process is performed in a state where the non-superconducting phase is formed, the orientation of crystal grains of the formed superconducting phase may be disturbed. Therefore, it is preferable to heat the multifilamentary wire to 740 ° C. or higher and 780 ° C. or lower.

Further, in the step of performing the intermediate heat treatment on the multi-core wire, it is preferable to heat the multi-core wire in a time range of 1.5 hours or more and 3 hours or less under the temperature condition described above. If heating is performed in a time range of less than 1.5 hours, the raw material powder such as Bi2212 cannot be sufficiently grown. In addition, when it is performed in a time range of 3 hours or more, as described above, the process of crystal growth of raw material powder such as Bi2212 in the superconducting phase is promoted, but at the same time, for example, (Ca, Sr) ₂ CuO ₃ or the like The superconducting phase may grow crystals. If the subsequent full-scale rolling process is performed in a state where the non-superconducting phase is formed, the orientation of crystal grains of the formed superconducting phase may be disturbed. Therefore, it is preferable to heat the multifilamentary wire in a time range of 1.5 hours or more and 3 hours or less. Among them, it is more preferable to heat the multifilamentary wire in a time range of 2 hours to 2.5 hours.

  In the method for producing a superconducting wire according to the present invention, it is preferable to repeat the step of rolling the multi-core wire and the step of heat-treating the multi-core wire several times following the step of performing the intermediate heat treatment on the multi-core wire described above. .

  The above-described step of rolling the multi-core wire and the step of heat-treating the multi-core wire may be performed only once each, but are preferably performed a plurality of times as described above. For example, when both steps are performed twice, a multi-core wire is processed into a tape-shaped wire in the first rolling step (primary rolling). In the first heat treatment step (primary heat treatment), raw material powder such as Bi2212 is reacted, and a superconducting phase such as Bi2223 phase is mainly generated inside the strand that is the first metal tube. Further, in the second rolling step (secondary rolling), the voids formed in the superconducting phase by the reaction by the primary heat treatment are crushed. As a result, it becomes easy to firmly bond the crystals of the superconductor in the subsequent secondary heat treatment. Then, in the second heat treatment step (secondary heat treatment), as described above, the superconductor crystals are firmly bonded in a state in which the orientation of the crystal grains is kept good to form a superconducting phase such as a Bi2223 phase. To do. As described above, a high-quality superconducting phase can be formed stepwise by performing each step a plurality of times.

  Therefore, the superconducting wire formed by using the method of manufacturing a superconducting wire according to the present invention has a superconducting phase such as a high-quality Bi2223 phase that is firmly bonded in a state where the orientation is kept good, and is critical. The current and critical current density are improved.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the superconducting wire which improved the critical current and the critical current density by improving the crystal orientation of an oxide superconductor further than before can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each embodiment, portions having the same function are denoted by the same reference numerals, and the description thereof will not be repeated unless particularly necessary.

(Embodiment)
FIG. 1 is a flowchart showing a procedure for manufacturing a superconducting wire in an embodiment of the present invention. As shown in FIG. 1, as a method of manufacturing a superconducting wire according to the present invention, first, preparation of raw material powder (S10) is performed. Next, the first metal tube is drawn (S20). Next, fitting to the second metal tube (S30) is performed. Next, the second metal pipe is drawn (S40). And flattening (S51) is implemented. Next, an intermediate heat treatment (S52) is performed. And primary rolling (S53) is implemented. Further, a primary heat treatment (S60) is performed. In the case where the step of rolling the multi-core wire and the step of heat-treating the multi-core wire are performed twice, secondary rolling (S70) and secondary heat treatment (S80) are further performed as shown in FIG. Next, each process mentioned above is explained in full detail.

  As shown in FIG. 1, first, raw material powder is prepared (S10). Specifically, this is a step of preparing a raw material powder as a raw material for forming the superconducting phase of the oxide superconductor (finally) after performing each step.

  As the raw material powder, it is necessary to use a powder blended so as to form a high-quality superconductor having excellent superconducting characteristics at a liquid nitrogen temperature when forming a superconducting phase, that is, having a high critical temperature of 77 K or higher. preferable. This raw material powder includes not only a powder obtained by mixing a composite oxide so as to have a predetermined composition ratio, but also a powder obtained by sintering and pulverizing the mixed powder.

For example, when a Bi2223 series superconducting wire that is an oxide superconductor is obtained after each step (finally), for example, Bi ₂ O ₃ , PbO, SrCO ₃ , CaCO ₃ , CuO may be used as the raw material powder. preferable. A mixture of these powders is sintered at 700 ° C. to 870 ° C. for 10 to 40 hours in an air atmosphere or a reduced pressure atmosphere at least once. By such sintering, a raw material powder mainly composed of the Bi2212 phase rather than the Bi2223 phase can be obtained. At this point, a superconducting phase with good electrical characteristics (mainly Bi2223 phase) can be obtained in a later step if the raw material powder mainly consisting of Bi2212 phase is prepared rather than Bi2223 phase.

Specific composition _ratio, when the _{Bi a Pb b Sr c Ca d} Cu e (a + b): c: d: e = 1.7~2.8: 1.7~2.5: 1.7 Those satisfying ˜2.8: 3 are preferred. In particular, the composition ratio is preferably in the vicinity of (Bi or Bi + Pb): Sr: Ca: Cu = 2: 2: 2: 3, Bi is about 1.8, Pb is 0.3 to 0.4, and Sr is It is particularly preferable that the vicinity is 2, Ca is about 2.2, and Cu is about 3.0.

  The raw material powder preferably has a maximum particle size of 0.1 μm or more and 2.0 μm or less and an average particle size of 0.5 μm or more and 1.0 μm or less. By using such a fine powder, a high-quality high-temperature superconducting phase having a high critical temperature can be easily generated. Among these, it is more preferable that the maximum particle size is 0.1 μm or more and 1.0 μm or less, and the average particle size is 0.6 μm or more and 0.9 μm or less.

  Next, the first metal tube is drawn (S20). Specifically, this is a process in which the raw material powder prepared in the previous step (S10) is filled into a metal pipe (first metal pipe) serving as a stabilizer, and the metal pipe is drawn. is there.

  FIG. 2 is a schematic view showing a process of filling a raw material powder into a metal pipe which is a first metal pipe. As shown in FIG. 2, the raw material powder 2 prepared in the previous step (S10) is filled into a metal pipe 1 having a cylindrical shape, for example. The material of the metal pipe 1 used here is any one or more selected from the group consisting of Ag, Cu, Fe, Ni, Cr, Ti, Mo, W, Pt, Pd, Rh, Ir, Ru, and Os. It is preferable to use an alloy containing. In FIG. 2, the metal pipe 1 has a circular cross-sectional shape. However, in addition to the circular shape, for example, a metal pipe 1 having a polygonal cross-sectional shape may be used. It is particularly preferable to use a polygon having a regular polygon, particularly a regular hexagonal cross section. Thus, the strand 3 as a single core wire which is the metal pipe 1 filled with the raw material powder 2 is formed.

  Then, the wire 3 is drawn so as to have a desired cross-sectional area. FIG. 3 is a schematic view showing a process of thinning the wire filled with the raw material powder using a round die. As shown in FIG. 3, the wire 3 is passed through a round die 4 to perform wire drawing so that the wire 3 has a desired cross-sectional area (thinner than the original). By this wire drawing, a strand 3 having a desired cross-sectional area and a long shape is formed in which a raw material powder 2 of a superconducting phase is arranged in a single core in a metal pipe 1 that is a stabilizing material. Similarly to the metal pipe 1, the cross section of the strand 3 may be circular or polygonal.

  Subsequently, fitting to the second metal tube (S30) is performed. Specifically, a plurality of strands 3 formed in the previous step (S20) are bundled and inserted (fitted) inside a metal pipe (second metal pipe) different from the metal pipe 1 described above. ) And forming a multi-core wire.

  As the cross-sectional shape of the metal pipe (second metal tube) forming the multicore wire, any shape such as a circle or a regular polygon can be used. In particular, when the cross-sectional shape is a regular polygon, a shape having parallel opposite sides such as a square, a regular hexagon, and a regular octagon is preferable. In view of ease of manufacture and stability as a superconducting wire, it is particularly preferable to use a regular hexagonal cross-sectional shape.

  FIG. 4 is a schematic diagram showing the state of the multifilamentary wire after fitting (S30) to the second metal tube. 4 to 7 and FIGS. 10 to 13, the left side of each figure is a schematic diagram of a multi-core wire having a regular hexagonal cross section, and the right side of each figure is a circular cross section. The schematic of a multi-core wire is shown.

  As shown in FIG. 4, each of the hexagonal pipe 5 as the second metal tube having a regular hexagonal cross section and the cylindrical pipe 7 as the second metal tube having a circular cross section has a plurality of elements. It has a size that can accommodate a bundle of wires 3. The material of the hexagonal pipe 5 and the cylindrical pipe 7 is the same as that of the metal pipe 1. When the strands 3 are stored inside the second metal tube, as shown in FIG. 4, a plurality of strands 3 are arranged in a polygonal shape inside a hexagonal pipe 5 having a regular hexagonal cross section. Alternatively, a plurality of strands 3 may be arranged in a polygonal shape inside a cylindrical pipe 7 having a circular cross-sectional shape. Further, a plurality of strands 3 may be arranged in a circular shape inside each second metal tube. Thus, the hexagonal multicore wire 6 and the cylindrical multicore wire 8 can be formed as the multicore wire shown in FIG.

  After fitting to the second metal tube in the above procedure, the second metal tube is drawn (S40). Specifically, this is a step of drawing the multifilamentary wire formed in the previous step (S30). Similarly to the previous step (S20), for example, by using a round die, a multi-core wire such as a hexagonal multi-core wire 6 or a cylindrical multi-core wire 8 is drawn so that the multi-core wire has a desired cross-sectional area (from the beginning). The wire is drawn so that it also becomes thinner. FIG. 5 is a schematic diagram showing the state of the multi-core wire after the second metal tube is drawn (S40). By performing the step (S40), as shown in FIG. 5, a hexagonal multicore wire 6 and a cylindrical multicore wire 8 having a long shape with a desired cross-sectional area are formed. These hexagonal multicore wire 6 and cylindrical multicore wire 8 finally form a configuration of the superconducting wire.

  Next, flattening (S51) is performed. Specifically, this is a step of processing the multicore wires such as the hexagonal multicore wire 6 and the cylindrical multicore wire 8 formed in the previous step (S40) into a flat shape. By performing this step, the raw material powder 2 of the plurality of strands 3 arranged inside the multi-core wire is densified before the primary rolling (S53), which is a full-scale rolling performed later, and the reactivity is good. It can be in a state. Since the reactivity is improved, the grain size of the Bi2212 crystal formed by the raw material powder 2 in the subsequent intermediate heat treatment (S52) is increased, for example, and the orientation of the Bi2212 crystal is improved when primary rolling (S53) is performed. It can be. If the crystal orientation is good, the critical current and critical current density of the formed superconducting phase can be improved.

  FIG. 6 is a schematic diagram showing a cross-sectional state of the multifilamentary wire before flattening (S51). That is, the cross-sectional view of FIG. 6 is a schematic view showing the state of the cross section of the multifilamentary wire after performing the step (S40) shown in FIG. FIG. 7 is a schematic diagram showing a cross-sectional state of the multifilamentary wire after flattening (S51).

  In the flattening process (S51), the compression process is performed so that the multicore wires, for example, the hexagonal multicore wires 6 and the cylindrical multicore wires 8 are flattened. Here, the direction of compression is the direction that intersects the major axis direction (extending direction) of the multicore wire. For example, in the case of the hexagonal multicore wire 6 shown on the left side of FIG. 6, it intersects the opposite side of the regular hexagon forming the cross section. It is preferable to compress the hexagonal multifilamentary wire 6 in a direction (for example, perpendicular to the opposite side). This compressive stress is applied to the long axis of the hexagonal multicore wire 6. If it does in this way, it can suppress that the strand 3 arrange | positioned in the inside of a multicore wire raise | generates a position shift by shearing. As a result, the cross section of the multifilamentary wire is deformed so as to be flatter than the shape before compression shown in FIG. Similarly, in the case of the cylindrical multicore wire 8 shown on the right side of FIGS. 6 and 7, the cylindrical multicore wire 8 extends in the direction intersecting the major axis direction (extending direction) of the cylindrical multicore wire 8 (for example, perpendicular to the opposite side). It is preferable to apply a compressive stress to the long axis. Similarly, in the case of a multifilamentary wire having a cross-sectional shape other than a regular polygon or a circle, similarly, the stress compressing the major axis of the multifilamentary wire in the direction intersecting the major axis direction (extending direction). Is preferably added.

  In the flattening process (S51), the dimension of the multicore wire in the compressing direction so that the multicore wire is flattened is 30% or more and 45% or less of the multicore wire dimension before the multicore wire is processed into a flat shape. It is preferable to perform the processing as described above. That is, for example, the vertical direction of the cross section of the hexagonal multifilamentary wire 6 after the compression by the flattening process (S51) shown in FIG. 7 (here, the direction in which the compression is performed) is the flattening process (S51) shown in FIG. It is preferable to perform compression so that it is 30% or more and 45% or less of the vertical dimension of the cross section of the hexagonal multi-core wire 6 before performing. The same applies to the cross-sectional views of the cylindrical multicore wire 8 shown in FIGS. 6 and 7.

  The flattening process (S51) described above is preferably performed using, for example, a rolling method or a rectangular die drawing method. FIG. 8 is a schematic view showing flattening (S51) by roll rolling. FIG. 9 is a schematic diagram showing flattening (S51) by rectangular die drawing.

  As shown in FIG. 8, roll rolling refers to, for example, the roll 11 from one end A of the multifilamentary wire 12 in a state where the multifilamentary wire 12 is sandwiched by using a pair of rolls 11 from both sides with respect to the long axis of the multifilamentary wire 12. The multi-end B is moved relatively in the direction along the long axis direction. Specifically, the multifilamentary wire 12 is sandwiched between a pair of rolls 11 whose positions are fixed, the roll 11 is rotated, and the multifilamentary wire 12 is pulled out from one end A side of the multifilamentary wire 12. Then, the multifilamentary wire 12 sandwiched between the rolls 11 is rolled to form a flat tape-shaped precursor wire 13 as shown in FIG. Since the compressing stress at this time is increased and the multifilamentary wire 12 is compressed with a compressive stress that does not cause breakage, the multifilamentary wire 12 in the direction in which the multifilamentary wire 12 is compressed after the flattening (S51) described above is performed. It is preferable to compress the core wire 12 so that the dimension is 30% or more of the dimension before the compression.

  In addition, the rectangular die drawing is a processing method for reducing the cross-sectional area of a multi-core wire using a die in the same manner as the step of drawing in the steps (S20) and (S40) described above. For example, the multi-core wire 15 is moved from the A side to the B side in FIG. 9 through the atypical die 14 using the odd-shaped die 14 shown in FIG. Wire drawing is performed so that the precursor wire 16 is obtained. In particular, when performing this wire drawing, in order to prevent the multi-core wire 15 from being disconnected by the wire drawing, the multi-core wire 15 in the direction in which the multi-core wire 15 after the flattening (S51) is compressed is compressed. It is preferable to carry out the processing under the condition that the dimension of is 30% or more of the dimension before compression.

  Moreover, even if it uses any method of the above-mentioned roll rolling and rectangular die wire drawing, it will exceed 45% of the multi-core wire dimensions before processing a multi-core wire into a flat shape (that is, the reduction ratio is less than 55%). In addition, when the multifilamentary wire is processed into a flat shape, the raw material powder such as the Bi2212 phase cannot be sufficiently densified. Therefore, it is preferable to perform the compression process so that the dimension of the multi-core wire in the direction in which the multi-core wire is compressed after the flattening process (S51) described above is 45% or less of the dimension before the compression. If the processing is performed under the condition of 45% or less of the dimension before compression, the raw material powder 2 (see FIG. 2) can be sufficiently densified.

  As described above, in flattening (S51), the dimension of the multicore wire in the compression direction so that the multicore wire becomes flat is 30% or more and 45% of the multicore wire dimension before the multicore wire is processed into a flat shape. It is preferable to perform processing so as to be as follows. However, among these, processing is performed so that the dimension of the multi-core wire in the compression direction so that the multi-core wire is flattened is 35% or more and 40% or less of the multi-core wire dimension before the multi-core wire is processed into a flat shape. It is more preferable.

  For the reasons described above, the tape-shaped precursor wires 13 and 16 which are multi-core wires processed into a flat shape by the step (S51) have a ratio expressed by a rectangular width / thickness forming a cross section thereof. The aspect ratio is preferably 2.0 or more and 4.0 or less. Among these, it is more preferable to perform processing so that the above-described aspect ratio is 2.5 or more and 3.5 or less. At this time, with respect to the strands 3 arranged inside the multi-core wire, the dimension of the strand 3 in the direction in which the strand 3 is compressed is about 50% of the dimension of the strand 3 before being compressed. Specifically, it is more preferable to perform the processing so that it is 40% or more and 60% or less. Among these, it is more preferable to perform the processing so that the above-described dimensions are 45% or more and 55% or less.

  Here, for example, as shown in the cross-sectional views of FIGS. 6 and 7, when a plurality of strands 3 are arranged in a polygon to obtain a hexagonal multicore wire 6 or a cylindrical multicore wire 8, the diagonal of the strand 3 is obtained. The hexagonal multicore wire 6 and the cylindrical multicore wire 8 are preferably roll-rolled or drawn in a rectangular die so as to maintain the direction or the opposite direction. For this purpose, for example, in the case of performing rectangular die drawing in flat processing (S51), a flat tape shape obtained by the opposite side direction or diagonal direction (that is, flat processing (S51) of the modified die 14 used for drawing). The opposite direction or diagonal direction of the outer shape of the cross section in the direction perpendicular to the extending direction of the precursor wires 13 and 16, and the strand 3 (see FIG. 5) in the multifilamentary wire 15 (see FIG. 8) for flattening. It is preferable that the wire drawing is performed after arranging them so that the opposite side direction or the opposite direction of each of them substantially coincides. In this way, the multifilamentary wire 15 can be drawn while maintaining the aligned state of the strands 3 arranged in a polygon as shown in the sectional views of FIGS. 6 and 7. Similarly, in the flat processing (S51), for example, when roll rolling is performed, the direction in which one roll 11 and the other roll 11 are connected, that is, the direction in which rolling (compression) is performed, and the multifilamentary wire 12 sandwiched between the rolls 11 are used. It is preferable to perform the wire drawing after arranging the wires 3 (see FIG. 5) in FIG. In this way, the multifilamentary wire 15 can be rolled while maintaining the aligned state of the strands 3 arranged in a polygon as shown in the cross-sectional views of FIGS. 6 and 7.

  By the above procedure, an intermediate heat treatment (S52) is performed on the multifilamentary wires (tape-like precursor wires 13 and 16) in which the raw material powder 2 is densified. Specifically, the raw material powder 2 included in the strand 3 of the tape-like precursor wire 13 or the tape-like precursor wire 16 is a multi-core wire that has been densified in the previous step (S51). On the other hand, it is a process of heat-treating the raw material powder 2 so as to form crystals having a large particle diameter by heating.

  By compressing in the previous step (S51), the particles of the raw material powder 2 contained in the strand 3 of the tape-shaped precursor wire 13 or the tape-shaped precursor wire 16 are in close contact with each other. Since the grains are in close contact with each other, for example, if heat treatment or the like is performed in this state, the reactivity of the individual raw material powders 2 is better than when heating is performed in a state where the grains of the raw material powder 2 are not in close contact with each other. It has become.

  However, by compressing in the previous step (S51), the particles of the raw material powder 2 are brought into close contact with each other to improve the reactivity, and at the same time, the individual raw material powders 2 are pulverized by the compression. . For this reason, at the stage where the step (S51) is finished, the raw material powder 2 is densified, but the crystals forming the grains of the raw material powder 2 are pulverized and become minute. If the crystal is fine, the orientation of the crystal is disturbed when primary rolling (S53), which is the subsequent full rolling, is performed. Therefore, in order to easily improve the crystal orientation in the primary rolling (S53), the step of heating the raw material powder 2 in order to increase the crystal grain size is the intermediate heat treatment (S52). . If the raw material powder 2 is heated by the intermediate heat treatment (S52) in a state where the flattening (S51) is finished, individual raw material powders are compared with the case where the raw material powder 2 is heated in a state where the particles of the raw material powder 2 do not adhere to each other. As a result of the favorable reactivity of No. 2, the grains of the raw material powder 2 can be easily bonded to form crystals having a large grain size.

Note that the heating in this step (S52) is heating in the previous stage of forming, for example, the Bi2223 phase, which is the superconducting phase that is the final purpose. For this reason, in the intermediate heat treatment (S52), the tape-like precursor is formed so that the Bi2223 phase or the like is not formed, that is, lower than the heat treatment temperature in the subsequent primary heat treatment (S60) or secondary heat treatment (S80). It is preferable to heat the body wires 13 and 16. More specifically, in the step (S52), it is preferable to heat the tape-shaped precursor wire 13 or the tape-shaped precursor wire 16 which is a multi-core wire to 740 ° C. or higher and 780 ° C. or lower. Moreover, it is preferable that the time range which performs a heating shall be 1.5 hours or more and 3 hours or less. As described above, the raw material powders 2 react with each other to form crystals having a large particle size, but a non-superconducting phase such as (Ca, Sr) ₂ CuO ₃ is not formed inside the precursor of the superconducting phase. Of temperature or time. When the non-superconducting phase such as (Ca, Sr) ₂ CuO ₃ described above grows, the orientation of the superconducting conductor portion may be disturbed in the subsequent first rolling (S53). Therefore, it is preferable that the heating conditions are such that the non-superconducting phase such as (Ca, Sr) ₂ CuO ₃ described above does not grow crystals. Among these, it is more preferable to heat the tape-shaped precursor wire 13 or the tape-shaped precursor wire 16 which is a multi-core wire to 750 ° C. or higher and 770 ° C. or lower. More preferably, it is 5 hours or less.

  FIG. 10 is a schematic diagram showing a cross-sectional state of the multifilamentary wire after performing the intermediate heat treatment (S52). Since the intermediate heat treatment (S52) is a process for increasing the particle size of the raw material powder 2, in the schematic diagram of the macro dimension than the raw material powder 2 shown in FIG. 10, after the previous step (S51) is performed. There is no significant change with respect to FIG.

  In the step (S52), primary rolling (S53) is performed on the multifilamentary wire in which the crystal grains forming the superconducting phase precursor have a large grain size. Specifically, the tape-shaped precursor wires 13 and 16 which are multi-core wires processed in advance in the previous step (S51) in advance are rolled (compressed) in earnest, and finally This is a step of establishing the outer shape of a tape-shaped wire as a superconducting wire to be formed. Moreover, by performing this primary rolling (S53), the direction of the superconducting phase crystals of the finally formed superconducting wire is aligned. Here, since the grain size of the crystal of the precursor of the superconducting phase is increased by the previous step (S52), the crystal orientation of the precursor of the superconducting phase can be made better.

  For example, when the particles of the raw material powder 2 described above are bonded to form a crystal having a large particle size, 1 is used for the tape-shaped precursor wire 13 or the tape-shaped precursor wire 16 in which a large number of crystals having a large particle size are present. If the next rolling (S53) is performed, a crystal having a large grain size is rolled, and the crystal takes a shape close to a long shape. Then, the long axis direction of the crystal having a long shape is aligned in substantially the same direction between the plurality of crystals. That is, the rolled tape-shaped precursor wire 13 or the tape-shaped precursor wire 16 is a tape-shaped wire, which has a long shape, but its major axis direction and the major axis direction of a plurality of crystals having a large grain size. Are aligned in almost the same direction. On the other hand, for example, if primary rolling (S53) is performed on a tape-shaped precursor wire in which crystals having a small grain size are present, even if the crystals having a small grain size are rolled, the major axis direction of the major axis shape thereof Are difficult to align in a direction along one direction. For the above reason, when the crystal grain size is increased in the intermediate heat treatment (S52), when the subsequent primary rolling (S53) is performed, the individual crystals are aligned in the direction along the major axis direction of the tape-shaped wire. It becomes easy to make the orientation of the same.

  As described above, by primary rolling (S53), it is finally formed by aligning the crystal orientation of the precursor of the superconducting phase constituting the tape-shaped wire (making the orientation good and improving). It is possible to increase the critical current density of the superconducting wire. In general, oxide-based superconducting conductors have a large difference in current density that can be passed depending on the direction of crystal. For this reason, the value of the current flowing in the major axis direction of the finally formed superconducting wire can be improved by aligning the orientation of the individual crystals.

  When a plurality of the above-described strands 3 are bundled and inserted (fitted) into the second metal tube to form a multi-core wire, for example, the strands 3 are arranged in a polygon as shown in FIG. When rolling the multifilamentary wire manufactured in this manner, it is preferable that the rolling (compression) direction is a direction along the diagonal direction or the opposite side direction of the strands 3 arranged in a polygonal shape.

  FIG. 11 is a schematic diagram showing a cross-sectional state of the multifilamentary wire after primary rolling (S53). As shown in FIG. 11, when a multi-core wire (tape-like wire) is rolled in a direction along the diagonal direction of the strand 3 (that is, a direction along the vertical direction in FIG. 11), the superconductivity included in the strand 3 Filaments containing phase precursors (that is, filaments 3 compressed) are aligned in the thickness direction of the tape-shaped wire. As a result, the largest number of filaments are laminated at the center of the tape-shaped wire in the width direction (the left-right direction in FIG. 11), and the number of laminated filaments is reduced at both ends. Especially, since the filament of a center part is compressed most, the tape-shaped wire material with especially favorable electrical characteristics of a center part can be obtained.

  On the other hand, a multi-core wire (tape-shaped wire) is rolled in a direction along the opposite side direction of the strand 3, that is, in a direction along the direction from one side to the other of the opposite sides of the strand 3 arranged in a polygonal shape. In this case, the filaments are alternately arranged in the thickness direction of the tape-shaped wire. As a result, the filaments are arranged almost evenly over most of the tape-shaped wire in the width direction. For this reason, a tape-shaped wire with good Jc characteristics (critical current density characteristics) can be obtained. In particular, when rolling in the direction along the opposite side direction described above, rolling is easy to perform, and rolling can be performed with a smaller force.

  Further, as described above, when the strand 3 is inserted (fitted) into a second metal tube by bundling a plurality of strands into a polygonal shape to form a multi-core wire, It is preferable to replace the strand 3 positioned at the vertex of the polygon with a filler wire that does not contain a raw material to be a superconducting phase. As the filler wire, it is preferable to use a filler wire made of a material that is more easily compressed and deformed than a clad wire that is a strand 3 containing a raw material that should become a normal superconducting phase. In general, a metal wire can be used. More specifically, for example, Ag wire or Ag alloy wire is preferably used. In addition, a metal wire including any one selected from the group consisting of Cu, Fe, Ni, Cr, Ti, Mo, W, Pt, Pd, Rh, Ir, Ru, and Os, or of two or more metals An alloy is preferable.

  By providing this filler wire, the opposite side direction and the diagonal direction of the plurality of strands 3 arranged in a polygonal shape can be easily visually confirmed. In the case of forming a multi-core wire, the above-described second metal tube is formed by arranging a plurality of strands 3 in a polygonal shape in the above-described fitting to the second metal tube (S30). Insert into the hexagonal pipe 5 and the cylindrical pipe 7. However, when stress is applied to each of the strands 3 in the subsequent drawing (S40) of the second metal tube, all the strands 3 are arranged in a shape close to a circle by breaking the original orderly polygonal shape. Of the strands 3 arranged in a polygonal shape, it may be difficult to distinguish the strand 3 positioned at the apex from the other strands 3. For this reason, the position of the vertex can be easily identified by identifying the strand 3 positioned at the vertex of the polygonal shape as a filler wire not including the superconducting phase, and the opposite side direction and the diagonal direction can be identified.

  Further, by using the filler wire, even when rolling without regard to the diagonal direction and the opposite direction of the strands 3 arranged on the polygon when performing the primary rolling (S53), the diagonal direction is almost the same. Can be rolled from. This is because the filler wire is more easily compressed and deformed than the clad wire, and therefore, even if the multifilamentary wire is rolled from any direction, first, among the polygonal diagonal lines, 1 is located on the diagonal line most along the compression direction axis. It will be compressed from a pair of filler wires. As a result, it is considered that the multifilamentary wire is rolled from substantially the diagonal direction, for example, by rotating. However, even if you are not aware of the rolling direction, if you accidentally roll (compress) the direction along the opposite side, it is not first compressed from the filler wire at the diagonal position, but the direction along the opposite side. It is thought that compression will be performed.

  In the primary rolling (S53), the dimension of the multifilamentary wire in the direction of compressing the multifilamentary wire is 16% or more and 17.5% or less of the multifilamentary wire dimension before the flattening (S51) is performed. It is preferable to perform processing. If the step (S53) is performed under the rolling conditions such that the above-described dimension is 17.5% or more, it is difficult to improve the orientation of Bi2212 because the amount of deformation is small. Further, if the step (S53) is performed under rolling conditions such that the above-mentioned dimension is 16% or less, the amount of deformation is excessively large, so that cracks may occur in the raw material powder 2. For this reason, it is preferable to perform primary rolling (S53) so that it may become the multifilamentary wire dimension in the range mentioned above.

  And primary heat processing (S60) is performed following primary rolling (S53). Specifically, this is a step of heating the multifilamentary wire whose outer shape as the tape-shaped wire has been determined in the previous step (S53). By performing this step, the filament containing the raw material to form the superconducting conductor contained in the strand 3 can be made into a superconducting phase such as mainly a Bi2223 phase.

  FIG. 12 is a schematic diagram showing a cross-sectional state of the multifilamentary wire after the primary heat treatment (S60). The primary heat treatment (S60) is a treatment for making the filament contained in the strand 3 into a superconducting phase such as mainly a Bi2223 phase. For this reason, in the schematic diagram of a macro dimension rather than the raw material powder 2 shown in FIG. 12, there is no big change with respect to FIG. 9 which shows the state after performing the previous process (S53).

  The heat treatment temperature here is preferably higher than the intermediate heat treatment (S52) in order to generate a superconducting phase such as Bi2223 phase, and is preferably 815 ° C. or higher and 860 ° C. or lower. In addition, it is more preferable to set it as 830 degreeC or more and 850 degrees C or less. The time range for performing the heat treatment is preferably 50 hours or more and 250 hours or less.

  The primary heat treatment (S60) can be performed in an air atmosphere. However, it is more preferable to perform the heat treatment in an air stream composed of the same components as the atmosphere. At that time, it is more preferable to lower the moisture content in the atmosphere in which the heat treatment is performed than the normal moisture content in the atmosphere.

  Although the primary rolling (S53) and the primary heat treatment (S60) described above may be performed only once, it is more preferable to repeat the plurality of times. That is, as shown in FIG. 1, it is preferable to perform secondary rolling (S70) and secondary heat treatment (S80) following the primary heat treatment (S60).

  FIG. 13 is a schematic diagram showing a cross-sectional state of the multifilamentary wire after secondary rolling (S70). The primary rolling (S53) was a step of establishing the outer shape of the multifilamentary wire as a tape-shaped wire, whereas the secondary rolling (S70) was specifically performed during the previous primary heat treatment (S60). In this step, the voids formed in the superconducting phase are crushed and rolled again in order to firmly bond the crystals inside the superconducting conductor (superconducting phase) in the subsequent secondary heat treatment (S80). Therefore, as shown in FIG. 13, in the schematic diagram of a macro dimension than the raw material powder 2, there is no big change with respect to FIG. 12 which shows the state after performing the previous process (S60). For this reason, FIG. 13 is depicted similarly to FIG.

  Specifically, the secondary heat treatment (S80) is the following process. That is, the crystal grain size is increased in the previous intermediate heat treatment (S52), and a superconducting phase as a superconducting conductor is formed in the primary heat treatment (S60). Thereafter, the voids in the superconducting phase are crushed by secondary rolling (S70). The purpose of the secondary heat treatment (S80) is to mainly bond crystal grains such as the Bi2223 phase firmly and improve the electrical property values such as Jc of the superconducting phase. Therefore, as shown in FIG. 13 above, in the schematic diagram of the macro dimension than the raw material powder 2, there is no significant change from FIG. 12 showing the state after the previous step (S60). Therefore, the state after performing the step (S80) is the same as the state after performing the step (S70) in the schematic diagram of the macro dimension than the raw material powder 2, and after performing the step (S80). This state is collectively shown in FIG. 13 as in the state after the step (S70).

  The heat treatment temperature in the secondary heat treatment (S80) is preferably 815 ° C. or higher and 860 ° C. or lower, similarly to the primary heat treatment (S60). In addition, it is more preferable to set it as 830 degreeC or more and 850 degrees C or less. However, in particular, it is more preferable to perform the above-described primary heat treatment (S60) by heating to 840 ° C to 850 ° C and heating the secondary heat treatment (S80) to a temperature of 830 ° C to 840 ° C. If it does in this way, there exists an effect that the crystal grains of Bi2223 phase become stronger. Further, the secondary heat treatment (S80) may be performed in multiple stages (particularly in two stages) at different temperatures within the above-described temperature range. In this way, there is an effect that good superconducting characteristics can be obtained.

  Moreover, also about the time range which performs heat processing, it is preferable to set it as 50 hours or more and 250 hours or less similarly to primary heat processing (S60). However, the secondary heat treatment (S80) is more preferably 100 hours or more and 250 hours or less. If it does in this way, there exists an effect that the crystal grains of Bi2223 phase become stronger.

  Also, the secondary heat treatment (S80) can be performed in an air atmosphere as in the case of the primary heat treatment (S60). However, it is more preferable to perform the heat treatment in an air stream composed of the same components as the atmosphere. At that time, it is more preferable to reduce the moisture content in the atmosphere in which the heat treatment is performed. By following the above procedure, a superconducting wire (tape-like wire) having the Bi2223 phase as the superconducting phase in the embodiment of the present invention can be obtained.

  Based on the manufacturing procedure of the superconducting wire in the embodiment of the present invention described above, samples of the superconducting wire were actually manufactured under various conditions, and the value of Ic (critical current) was evaluated.

First, as preparation of raw material powder (S10), Bi ₂ O ₃ , PbO, SrCO ₃ , CaCO ₃ , and CuO powders were mixed at a molar ratio of 1.81: 0.40: 1.98: 2.20: 3.01. What was mixed by ratio was prepared as the raw material powder 2 (refer FIG. 2). The raw material powder 2 was first heat-treated in the atmosphere at 700 ° C. for 8 hours and 800 ° C. for 10 hours, and then sequentially heat-treated in a reduced pressure atmosphere of 133 Pa (1 Torr) at 760 ° C. for 8 hours. The raw material powder 2 was adjusted by subjecting the raw material powder 2 thus obtained to a heat treatment at 845 ° C. for 12 hours.

  In the subsequent wire drawing (S20) of the first metal tube, the raw material powder 2 is filled into a cylindrical cylindrical pipe 7 (see FIG. 4) made of Ag having a cross-sectional shape of an outer diameter of 25 mm and an inner diameter of 22 mm. The wire was drawn using a round die 4 (see FIG. 3). In this way, a strand 3 (clad wire, see FIG. 3) that was drawn so that the outer diameter of the circular cross-section was 2.4 mm was formed.

  As fitting to the second metal tube (S30), 61 strands 3 as the clad wires were bundled to form a hexagonal shape (see FIG. 4). Then, the assembly of the strands 3 was inserted into an Ag cylindrical pipe 7 (see FIG. 4) having a circular cross section with an outer diameter of 25 mm and an inner diameter of 22 mm. Then, as the second metal pipe drawing (S40), drawing is performed using a round die 4 (see FIG. 3), and the cylindrical multi-core wire 8 having a circular shape with a diameter of 1.58 mm (see FIG. 4). Got. The 61-core strand 3 (cladding wire) was arranged so as to have a hexagonal shape inscribed in the inner diameter of the cylindrical pipe 7 as shown in FIG. 4 when inserted into the Ag cylindrical pipe 7. When processing was performed so far, a part of the cylindrical pipe 7 which is each sample was cut out, and the density (powder density) of the raw material powder 2 was measured.

  And flat processing (S51) was performed with respect to each sample. As described above, the diameter of the cross section of each sample (multifilamentary wire) before performing flattening (S51) is 1.58 mm, but the conditions for performing the processing in flattening (S51) are changed for each sample. In the processing (S51), flat processing (S51) is performed by roll rolling shown in FIG. 7 so that the dimensions of the multi-core wires in the direction of compression so that the multi-core wires are flattened (this is defined as “wire thickness”) are various. ) Was performed. Even when the treatment was performed so far, a part of the cylindrical pipe 7 as each sample was cut out, and the density (powder density) of the raw material powder 2 was measured.

Subsequently, an intermediate heat treatment (S52) was performed. As will be described later, the temperature and the heating time for the heat treatment were changed for each sample as described later. And after performing intermediate heat processing (S52), the Bi2212 particle size of Bi2212 phase of each sample, and the ratio (mass%) which Bi2223 produced | generated by heating were measured. The Bi2212 particle size is measured by using an imaging method, and the Bi2223 generation ratio is determined by the XRD, θ-2θ method. Bi2212 (0012) peak intensity (I ₂₂₁₂ ) and Bi2223 (0014) peak intensity ( I ₂₂₂₃ ) and I ₂₂₂₃ / (I ₂₂₁₂ + I ₂₂₂₃ ) were calculated from the method.

  Next, primary rolling (S53) was performed. As will be described later, as in flat processing (S51), the processing conditions are changed for each sample, and the processing is performed so that the wire thickness after the primary rolling (S53) varies for each sample. Carried out. In addition, this process rolled in the direction along the diagonal direction of the strand 3 arrange | positioned at hexagonal shape. And after processing, a part of cylindrical pipe 7 which is each sample was cut off, and the Bi2212 orientation deviation angle which shows the degree of deviation of orientation of Bi2212 phase was measured. The misorientation angle was measured by the method of (XRD, half of rocking curve half width).

  Each tape sample obtained by primary rolling (S53) was subjected to a primary heat treatment (S60) to generate a superconducting phase mainly composed of Bi2223 phase. In this method, the sample was heated to 840 ° C. to 850 ° C. in an air atmosphere and subjected to heat treatment for 50 hours. Then, by performing secondary rolling (S70), voids formed inside the superconducting phase were removed. The secondary rolling (S70) was performed under a processing condition that the rolling reduction was 8%, that is, the dimension in the direction of compression was 92% before performing the process. For this reason, the dimension of each sample after secondary rolling (S70) is a value close to the dimension of each sample after primary rolling (S53). Finally, as a secondary heat treatment (S80), each sample was heat-treated at 840 ° C. for 100 hours.

  The critical current Ic at 77K was measured for each sample of the tape-shaped oxide superconducting wire after the above steps without applying an external magnetic field. Further, a part of each sample was cut out, and a Bi2223 misalignment angle indicating the degree of misalignment of crystals of the Bi2223 phase which is a superconducting phase was measured. In addition, the measuring method of an orientation shift angle here is the same as the measuring method of the Bi2212 orientation shift angle after performing primary rolling (S53).

  Table 1 is a table showing each processing condition and measurement result in each step of a sample whose critical current measurement result was less than 220A. Table 2 is a table showing each processing condition and measurement result in each step of a sample whose critical current measurement result was 220 A or more. Each sample in Table 1 is numbered A1 to A12, and each sample in Table 2 is numbered B1 to B14.

The “multi-core wire diameter” before flattening (S51) in each table indicates the diameter (mm) of the multi-core wire after drawing (S40) of the second metal tube. “Powder density” indicates the density (g / cm ³ ) of the raw material powder filled in the strands inside the multifilamentary wire just before flattening (S51).

Each table shows the wire thickness (mm) and multi-core wire dimensions (%) of each sample after the flattening (S51). The multi-core wire dimension is the multi-core wire dimension (mm) in the direction in which the multi-core wire after flattening (S51) is compressed by flattening (S51) with respect to the multi-core wire diameter before flattening (S51). The ratio is shown in%. Also here, the powder density (g / cm ³ ) of the Bi2212 phase is shown.

  In the intermediate heat treatment (S52), the conditions (heating temperature (holding temperature) and heating time (holding time)) are changed for each sample, and the conditions of the crystals constituting the Bi2212 phase that is the superconducting phase precursor after the processing. We are investigating the effects on particle size. Moreover, the ratio of the mass by which Bi2223 was produced | generated from Bi2212 in the said process is investigated. Those conditions and data are shown.

  Moreover, also about primary rolling (S53) and secondary rolling (S70), similarly to flat processing (S51), the wire thickness (mm) after performing a process is shown, and also about primary rolling (S53) The multi-core wire dimensions (%) are shown. Further, for primary rolling (S53), a Bi2212 misalignment angle (°) representing how much the orientation of the major axis direction of Bi2212 crystal, which is a superconducting phase precursor after the process, is displaced. Is shown. In addition, since the misalignment angle after the primary rolling (S53) dominates the misalignment angle after the secondary heat treatment (S80), the misalignment angle after the secondary rolling (S70) is performed. The orientation misalignment angle is omitted in Tables 1 and 2.

  Further, in the columns after the secondary heat treatment (S80) in Tables 1 and 2, the value (A) of the critical current (Ic) of the superconducting wire finally completed up to the secondary heat treatment (S80), and the superconducting wire A Bi2223 misalignment angle (°) indicating how much the orientation of the Bi2223 phase crystal, which is a superconducting phase, is displaced in the major axis direction is shown.

  Regarding samples A1 to A12 shown in Table 1, as can be seen from Table 1, the flattening process (S51) is performed, the crystals are brought into close contact with each other, and the heat treatment is performed after the reactivity is improved. It has been shown that the properties of the critical current are improved and the characteristics of the critical current are improved. As for samples A1 to A4, since the value of multi-core wire dimension% is large (being 45% or more), crystals are not sufficiently adhered to each other in the step (S51). It seems to be a cause of deterioration.

  Conversely, for A8 and A9, the value of the multi-core wire dimension% is small. That is, since compression was performed under strong conditions in flat processing (S51), Ag constituting the metal tube was broken. As described above, in order not to cause problems such as A1 to A4, A8, and A9, as shown by the data of each sample in Table 2, the value of the multi-core wire dimension (%) after flattening (S51) is performed. Is preferably 30% or more and 45% or less.

  A5 and A6 continue to be heated for 3 hours or longer in the intermediate heat treatment (S52). For A7, an intermediate heat treatment (S52) is performed at 780 ° C. As a result, for A5, A6, and A7, Bi2223 was generated in the course of the intermediate heat treatment (S52), and this seems to be a cause of lowering the value of the critical current Ic. In the Bi2223 phase formed by the intermediate heat treatment (S52), since the orientation of the Bi2223 crystal grains is lowered, the value of the critical current Ic is lowered. Therefore, the heating holding time in the intermediate heat treatment (S52) is preferably 3 hours or less. In Sample B7 in Table 2, since the holding time is 1.5 hours, it is considered preferable to perform heating for 1.5 hours or more.

  In A10 and A11, since the value of the multi-core wire dimension (S53) in the first rolling (S53) is as large as 17.5% or more, the crystals cannot be sufficiently adhered to each other in the step (S53). This seems to be the cause of the deterioration of the critical current characteristics. On the contrary, in A12, the value of the multi-core wire dimension (S53) in the first rolling (S53) is as small as 16% or less. For this reason, it is considered that the compressing force was too strong and cracks were generated in the Bi2223 phase crystal, which caused the critical current characteristics to deteriorate. Therefore, in B1 to B14 of Table 2, since the multi-core wire dimensions are 16% or more and 17.5% or less, the multi-core wire dimension (%) value after the first rolling (S53) is initially set. It is preferable to be 16% or more and 17.5% or less of the multi-core wire dimensions.

  In the samples B1 to B14 shown in Table 2 in which each condition in each step was selected well and the value of the critical current Ic of 220 A or more was output, the grain size of the Bi2212 crystal after the intermediate heat treatment (S52) Is 5.5 μm or more except for a part. Here, the maximum dimension in the major axis direction of each crystal grain is defined as “grain size”. Conventionally, since the grain size of the crystal after performing the heat treatment step was 3.5 μm or more, the intermediate heat treatment (S51) after improving the crystal reactivity in the flat processing disclosed in the present invention ( By performing S52), it is shown that the crystal reaction is promoted and crystals having a large particle size are generated.

  In the data in Table 2, only the sample B2 has a particle size of Bi2212 as small as 3.3 μm. This is because the temperature at which the intermediate heat treatment (S52) was performed was as low as 738 ° C., so the reaction of the crystal grains was accelerated. It is thought that it was not done. Therefore, in the intermediate heat treatment (S52), it is preferable to perform heating at a temperature of 740 ° C. or higher and 780 ° C. or lower. The reason why the temperature is 780 ° C. or lower is to suppress the formation of Bi2223.

  Samples A1 to A12 shown in Table 1 have a Bi2212 orientation deviation angle of 14% or more after the first rolling (S53), but Samples B1 to B14 shown in Table 2 have the Bi2212 orientation. The deviation angles are all 12.5% or less. Samples A1 to A12 shown in Table 1 all had a Bi2223 orientation deviation angle of 5% or more after the completion of the second heat treatment (S80). However, Samples B1 to B14 shown in Table 2 (2) The Bi2223 misorientation angle after completing the heat treatment (S80) was 5% or less. Thus, it is considered that the value of the critical current Ic is improved as a result of the improvement in the orientation of the crystal in the superconducting phase.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention is particularly excellent as a technique for producing a superconducting wire that improves electrical characteristics such as critical current.

It is a flowchart which shows the manufacture procedure of the superconducting wire in embodiment of this invention. It is the schematic which shows the process of filling raw material powder inside the metal pipe which is a 1st metal pipe. It is the schematic which shows the process of thinning the strand filled with raw material powder using a round die. It is the schematic which shows the state of a multi-core wire after fitting to a 2nd metal pipe (S30). It is the schematic which shows the state of the multi-core wire after performing the wire drawing (S40) of the 2nd metal pipe. It is the schematic which shows the state of the cross section of the multi-core wire before performing flat processing (S51). It is the schematic which shows the state of the cross section of a multi-core wire after performing flat processing (S51). It is the schematic which shows the flat process (S51) by roll rolling. It is the schematic which shows the flat process (S51) by rectangular die drawing. It is the schematic which shows the state of the cross section of a multi-core wire after performing intermediate heat processing (S52). It is the schematic which shows the state of the cross section of a multi-core wire after performing primary rolling (S53). It is the schematic which shows the state of the cross section of a multi-core wire after performing primary heat processing (S60). It is the schematic which shows the state of the cross section of a multifilamentary wire after performing secondary rolling (S70).

Explanation of symbols

  1 metal pipe, 2 raw material powder, 3 strand, 4 round die, 5 hexagonal pipe, 6 hexagonal multicore wire, 7 cylindrical pipe, 8 cylindrical multicore wire, 11 roll, 12,15 multicore wire, 13,16 tape-like precursor Wire rod, 14 Atypical dies.

Claims (4)

A step of drawing a first metal tube filled with a raw material powder constituting a superconducting wire to form a single core wire;
Drawing a plurality of single-core wires assembled in a second metal pipe different from the first metal pipe to form a multi-core wire;
A step of processing the multifilamentary wire into a flat shape;
Rolling the multifilament wire that has been processed to be flat;
Heat-treating the rolled multifilamentary wire,
A step of processing so that the multifilamentary wire the flat, between the step of rolling the multifilamentary wire, have rows a step of intermediate annealing the multifilamentary wire,
In the step of processing the multi-core wire into a flat shape, the dimension of the multi-core wire in the compression direction so that the multi-core wire becomes flat is the size of the multi-core wire before processing the multi-core wire into a flat shape. Processing to be 30% to 45%,
In the step of intermediate heat treatment of the multifilamentary wire, the multifilamentary wire is heated in a time range of 1.5 hours or more and 3 hours or less, and the multifilamentary wire is heated to 740 ° C. or more and 770 ° C. or less,
In the step of rolling the multi-core wire, the dimension of the multi-core wire in the direction in which the multi-core wire is compressed is 16% or more of the dimension of the multi-core wire before the step of processing the multi-core wire into a flat shape 17 cormorant line processing so that .5% or less, the manufacturing method of a superconducting wire.   The method of manufacturing a superconducting wire according to claim 1, wherein the step of processing the multi-core wire into a flat shape is performed using any one of a rolling method and a rectangular die drawing method. The method for producing a superconducting wire according to claim 1 or 2 , wherein, in the step of performing the intermediate heat treatment on the multicore wire, the multicore wire is heated to a temperature lower than that in the step of heat treating the multicore wire. The method for producing a superconducting wire according to any one of claims 1 to 3 , wherein the step of rolling the multi-core wire and the step of heat-treating the multi-core wire are repeated a plurality of times.

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