CN1610956A - Manufacturing method of oxide superconducting wire - Google Patents

Abstract

An oxide superconducting wire producing method comprising a step of producing a wire having a form in which the material powder of an oxide superconductor is covered with a metal (S1, S2) and a step of heat-treating the wire in a pressurized atmosphere (S4, S6), wherein the total pressure of the pressurized atmosphere lies in the range from 1 to 50 MPa. In such a way, voids among the oxide superconducting crystals and bulging of the oxide superconducting wire are prevented, and the partial pressure of oxygen during the heat treatment can be easily controlled, thereby improving the critical current density.

Description

Manufacturing method of oxide superconducting wire

technical field

The present invention relates to a method for producing an oxide superconducting wire, and more particularly, to a method for producing an oxide superconducting wire from a wire in the form of a material powder of an oxide superconductor coated with a metal.

Background technique

Hitherto, as a method for producing an oxide superconducting wire, it is known that after filling a metal tube with raw material powder of an oxide superconductor, heat-treating the wire rod obtained by drawing or rolling the metal tube to remove the oxide superconducting wire. A method in which superconductor raw material powder is sintered to obtain an oxide superconducting wire. However, in the above-mentioned heat treatment step for sintering, there is a problem that the superconducting properties of the obtained oxide superconducting wire are lowered due to expansion in the wire.

Therefore, in Japanese Unexamined Patent Publication No. 5-101723, the following method for producing an oxide superconducting wire is proposed, which is characterized in that a metal tube or a metal tube formed by filling an oxide superconductor powder in a pressurized atmosphere is proposed. The flat body is heat-treated to sinter the oxide superconductor sub-powder. It is described in the above-mentioned gazette that, according to this method, a wire rod having good superconducting properties can be obtained by performing heat treatment under pressure.

Specifically, the following test was done: a metal tube filled with oxide superconductor powder was accommodated in a heat-resistant and pressure-resistant airtight container, and the internal pressure was increased by increasing the temperature in the airtight container. To prevent expansion during sintering. The internal pressure at this time can be obtained from the equation of state of the gas. For example, it is described in the above publication that an internal pressure of about 4 atmospheres can be obtained at a heating temperature of about 900°C.

In addition, in Japanese Patent No. 2592846 (Japanese Unexamined Patent Publication No. 1-301114), the following method for producing an oxide superconductor is proposed, which is characterized in that at least one of the heat treatment and the heat treatment is filled with A metal tube filled with oxide superconducting powder, etc. is kept under high pressure. It is described in the above-mentioned gazette that, according to this method, the peeling of the portion at the interface between the oxide superconductor and the metal tube that occurs during sintering can be eliminated by placing it under a high pressure state.

Specifically, during at least one of the heat treatment and the heat treatment, by maintaining the metal tube filled with the oxide superconducting powder in a high pressure state of 500 to 2000 kg/cm ² (about 50 to 200 MPa), it is possible to Crimp the metal tube to one side of the sintered body. Accordingly, when the quenching phenomenon partially occurs in the superconductor, the generated heat can be rapidly removed by the quenching phenomenon. In addition, in addition to this, the peeled part becomes a stress concentration part, and performance deterioration of superconducting characteristics due to generation of deformation can also be prevented.

However, in JP-A-5-101723, the internal pressure obtained with the temperature rise in the airtight container is about 4 atmospheres (0.4 MPa). As a result, voids are formed between the oxide superconducting crystals during sintering, and there is a problem that the critical current density decreases.

In addition, since the internal pressure is about 4 atmospheres (0.4 MPa), the expansion of the oxide superconducting wire generated during sintering cannot be sufficiently suppressed, resulting in a problem that the critical current density decreases.

In addition, in Patent No. 2592846, since the applied pressure is as high as 500 to 2000 kg/cm ² (approximately 50 to 200 MPa), it becomes difficult to control the oxygen partial pressure during heat treatment, and the critical current density decreases.

disclosure of invention

An object of the present invention is to provide an oxide superconducting oxide capable of increasing the critical current density by suppressing the formation of voids between oxide superconducting crystals and the expansion of the oxide superconducting wire, and at the same time facilitating the control of the oxygen partial pressure during heat treatment. Manufacturing method of wire rod.

The method for producing an oxide superconducting wire of the present invention has the following features.

A wire rod in the form of a raw material powder of an oxide superconductor covered with a metal is produced. Also, the wire rod is heat-treated in a pressurized atmosphere. The total pressure of the pressurized atmosphere is 1 MPa or more and less than 50 MPa.

According to the production method of the oxide superconducting wire rod of the present invention, since the pressure outside the wire rod is as large as 1 MPa or more, the plastic flow and creep deformation of the superconducting crystal generated during the heat treatment are caused, so the reduction of the oxide superconducting wire is reduced. Voids between superconducting crystals. In addition, since the pressure from the outside of the metal pipe can be used to suppress the expansion of the gas in the gap of the oxide superconducting crystal powder generated during the heat treatment or the gas adhering to the oxide superconducting crystal powder generated during the heat treatment during the heat treatment, it is possible The generation of swelling of the oxide superconducting wire is suppressed. As a result of the above, the critical current density was increased.

In addition, in order to generate a stable oxide superconducting phase, it is necessary to control the oxygen partial pressure within a constant range regardless of the value of the total pressure in the pressurized atmosphere. However, at this time, when the total pressure in the pressurized atmosphere exceeds 50 MPa, the partial pressure of oxygen relative to the total pressure decreases. Therefore, since the value of the oxygen concentration in the pressurized atmosphere is very small, it is greatly affected by measurement errors and the like, so there is a problem that control of the oxygen partial pressure becomes difficult. According to the method for producing an oxide superconducting wire of the present invention, since the heat treatment is performed in a pressurized atmosphere of less than 50 MPa, the partial pressure of oxygen relative to the total pressure in the pressurized atmosphere will not be too small. Since the value of the oxygen concentration is high to some extent, it is less affected by measurement errors and the like, and the control of the oxygen partial pressure becomes easy.

In the above-mentioned method for producing an oxide superconducting wire, it is preferable to perform a heat treatment step using a hot isostatic pressing method (HIP: Hot Isostatic Pressing).

Thus, since the oxide superconducting wire is pressurized uniformly, voids and expansion of the wire are prevented.

In the above-mentioned method for producing an oxide superconducting wire, it is preferable that the oxide superconductor comprises bismuth, lead, strontium, calcium and copper in a ratio of (bismuth and lead):strontium:calcium:copper approximately 2:2: A Bi-Pb-Sr-Ca-Cu-O series oxide superconductor of the Bi2223 phase represented by an atomic ratio of 2:3.

This suppresses the formation of voids between crystals and swelling of the oxide superconducting wire, and as a result, the critical current density can be increased.

In the above-mentioned method for producing an oxide superconducting wire, it is preferable that the heat treatment step is performed in an oxygen atmosphere, and that the oxygen partial pressure is 0.003 MPa to 0.02 MPa.

In this way, by keeping the oxygen partial pressure in the range of 0.003 MPa to 0.02 MPa, a stable oxide superconducting phase can be formed and the critical current density can be increased. In addition, when the oxygen partial pressure exceeds 0.02 MPa, heterogeneous phases are formed, and when it is less than 0.003 MPa, it is difficult to form an oxide superconducting phase, and the critical current density decreases.

In the above-mentioned method of producing an oxide superconducting wire, it is preferable to control such that the oxygen partial pressure increases as the temperature rises in the pressurized atmosphere during the temperature rise before the heat treatment in the heat treatment step.

The optimum oxygen partial pressure value for the formation of the oxide superconducting phase increases with increasing temperature. As a result, since an appropriate oxygen partial pressure is obtained even during the temperature rise before the heat treatment in the heat treatment process, a stable oxide superconducting phase can be formed, and the critical current density can be increased.

In the above-mentioned method for producing an oxide superconducting wire, it is preferable to control the heat treatment such that the total pressure in the pressurized atmosphere is kept constant.

Oxygen consumption during heat treatment due to oxidation of the supporting device supporting the wire rod in the pressurized container, or vibration during pressure control of a pressure regulator such as a pressure-holding valve, or when additional gas is introduced to compensate for the consumed oxygen. Due to pressure fluctuations, etc., the total pressure may show a tendency to decrease. Therefore, if a sudden decompression occurs in the container, the pressure inside the wire rod becomes higher than the pressure outside the wire rod, thus causing expansion of the wire rod. However, in a more desirable aspect of the present invention, the total pressure during heat treatment is controlled to be constant, so that the generation of expansion of the wire rod due to sudden decompression during heat treatment can be prevented.

In the above-mentioned method for producing an oxide superconducting wire, it is preferable to perform the heat treatment step in an oxygen atmosphere, and to control such that the oxygen partial pressure during the heat treatment is kept constant within a fluctuation range of 10%. .

Thus, even if there is a fluctuation in temperature, the oxygen partial pressure can be kept in the range of the optimum oxygen partial pressure for the formation of the oxide superconducting phase, so a stable oxide superconducting phase can be formed, and the critical current can be increased. density.

In the above-mentioned method of producing an oxide superconducting wire, it is preferable to inject a gas when the temperature is lowered immediately after the heat treatment in order to compensate for a drop in pressure due to the lowering of the temperature.

When the temperature is lowered after the heat treatment, a pressure drop accompanied by a temperature change is caused. If the pressure is reduced rapidly in the heating container at this time, the pressure inside the wire rod will be higher than the pressure outside the wire rod, thus causing expansion of the wire rod. However, in a more desirable aspect of the present invention, the gas is injected to compensate for the drop in pressure caused by temperature drop, so that the generation of expansion of the wire rod due to the rapid decompression when the temperature is dropped immediately after heat treatment can be prevented.

In the above-mentioned method for producing an oxide superconducting wire, preferably, the metal covering the raw material powder contains silver, and the ratio of the area of the metal portion to the area of the oxide superconductor in the cross section of the wire after the heat treatment step is ( Hereinafter, when the silver ratio) is 1.5, the depressurization rate at the time of temperature drop immediately after the heat treatment is controlled to be 0.05 MPa/min or less.

Accordingly, when the silver ratio is 1.5, the effect of preventing the expansion of the wire rod due to rapid decompression becomes more remarkable.

In the above-mentioned method for producing an oxide superconducting wire, it is preferable that the metal covering the raw material powder contains silver, and in the case of a silver ratio of 1.5, the temperature in the pressurized atmosphere in the heat treatment step is 200°C Or in the case of 200° C. or higher, control is performed such that the decompression rate of the total pressure in the pressurized atmosphere is 0.05 MPa/min or less.

When the temperature in the atmosphere is 200° C. or higher and the pressure in the heating container is reduced rapidly, the pressure inside the wire becomes higher than the pressure outside the wire, thus causing expansion of the wire. Therefore, when the silver ratio is 1.5, the effect of suppressing the expansion of the wire rod due to sudden decompression during the heat treatment process (before heat treatment, during heat treatment, and after heat treatment) becomes more remarkable.

In the above-mentioned method for producing an oxide superconducting wire, it is preferable that the metal covering the raw material powder contains silver, and when the silver ratio is 3.0, the depressurization rate when the temperature is lowered immediately after the heat treatment is controlled to be 0.03 MPa/min. Or below 0.03MPa/min.

Accordingly, when the silver ratio is 3.0, the effect of preventing the expansion of the wire rod due to sudden decompression becomes more remarkable.

In the above-mentioned method for producing an oxide superconducting wire, it is preferable that the metal covering the raw material powder contains silver, and in the case of a silver ratio of 3.0, in the heat treatment step, the temperature in the atmosphere is 200° C. or 200° C. When the temperature is higher than °C, it is controlled so that the decompression rate of the total pressure in the pressurized atmosphere is 0.03 MPa/min or less.

When the temperature in the atmosphere is 200° C. or higher and the pressure in the heating container is reduced rapidly, the pressure inside the wire becomes higher than the pressure outside the wire, thereby causing expansion of the wire. Therefore, when the silver ratio is 3.0, the effect of suppressing the expansion of the wire rod due to sudden decompression during the heat treatment process (before heat treatment, during heat treatment, and after heat treatment) becomes more remarkable.

In the above-mentioned method for producing an oxide superconducting wire, it is preferable that in the heat treatment step, when the total pressure in the pressurized atmosphere is 1 MPa or more, control is performed such that the pressure in the pressurized atmosphere The decompression rate of the total pressure is 0.05MPa/min or less.

When the total pressure in the atmosphere is 1 MPa or more, the pressure in the heating container is reduced rapidly, and the pressure inside the wire becomes higher than the pressure outside the wire, thereby causing expansion of the wire. Thereby, the effect of suppressing the generation of expansion of the wire rod due to sudden decompression in the heat treatment process (before heat treatment, during heat treatment, and after heat treatment) becomes more remarkable.

In the above-mentioned method for producing an oxide superconducting wire, preferably, after the step of producing the wire rod and before the step of heat treatment, a step of rolling the wire rod with a roll is further included, and the sheath thickness of the wire rod after the rolling step is 200 μm or more.

The pinhole is mainly formed in such a way that the surface of the wire is damaged and roughened due to the friction between the wire and the calender roll, and the pinhole penetrates the oxide superconductor filament from the outside. However, if the oxide superconducting wire is rolled in a state where the thickness of the sheath of the oxide superconducting wire is 200 μm or more in any part after the rolling process, even if the surface of the wire is damaged and roughened by the rolling, pinholes will be formed. It also does not penetrate the oxide superconductor filament from the outside, so pinholes are not generated. Accordingly, the generation of voids and swelling can be suppressed by the above-mentioned heat treatment process, and the critical current density can be increased. In this specification, a pinhole means a hole having a diameter of 100 μm or more penetrating through the oxide superconductor filament from the outside. In addition, the wire rod having a pinhole means a wire rod including two or more holes having a diameter of 100 μm or more in a wire rod of 4 mm×10 mm.

In the above-mentioned method for producing an oxide superconducting wire, it is preferable to further include a step of adhering silver or a silver alloy to the wire after the step of producing the wire and before the step of heat treatment.

In order to increase the superconducting current that can flow per unit area, the silver ratio of the oxide superconducting wire is reduced as much as possible. However, since the proportion of the metal portion of the wire rod having a small silver ratio is small, the sheath thickness cannot be increased. In particular, pinholes are likely to be formed at the time of processing such as rolling before the heat treatment process for wires having a sheath thickness of less than 200 μm after the heat treatment process. Even in the step of heat-treating the wire rod having pinholes in the above-mentioned pressurized atmosphere, the pressurized gas penetrates into the inside of the wire rod from the pinholes. Therefore, there is no pressure difference between the inside and outside of the wire, and the effect of suppressing the generation of voids or swelling by pressurization to prevent a decrease in the critical current density is small. Therefore, by attaching silver or silver alloy to the surface of the wire rod after the step of producing the wire rod and before the step of heat treatment, the pinholes are covered with silver or silver alloy and disappear from the surface. Therefore, since the heat treatment step is performed after the wire rod having no pinholes is produced, the gas pressurized during the heat treatment step does not enter the inside of the wire rod through the pinholes. Thus, the critical current density can be increased by suppressing the formation of voids and swelling by the heat treatment step in the pressurized atmosphere.

In the above-mentioned method for producing an oxide superconducting wire, preferably, after the step of producing the wire rod and before the step of heat treatment, a step of rolling the wire rod with a roll is further included, and the portion of the roll in contact with the wire rod is The surface roughness Ry is 320 μm or less.

Thereby, since the friction between the wire rod and the roller is small, the surface of the wire rod is less likely to be damaged and roughened, and a wire rod without pinholes can be obtained regardless of the thickness of the sheath of the wire rod. Therefore, during the heat treatment process, the pressurized gas does not intrude into the inside of the wire rod through the pinholes. Thus, irrespective of the sheath thickness of the wire rod, the generation of voids or swelling can be suppressed by the above-mentioned heat treatment step in a pressurized atmosphere, and the critical current density can be increased. In addition, the so-called surface roughness Ry is the maximum height prescribed|regulated by JIS (Japanese Industrial Standard (Japanese Industrial Standard)).

In the above-mentioned method for producing an oxide superconducting wire, it is preferable that the temperature rise before the heat treatment in the heat treatment step is controlled so that the pressure increases stepwise as the temperature in the atmosphere rises.

In the case of a wire rod having pinholes, the pressurized gas penetrates into the inside of the wire rod through the pinholes even when heat treatment is performed in a pressurized atmosphere by a usual pressurization method. Therefore, there is no pressure difference between the inside and outside of the wire, and the effect of suppressing the generation of voids or swelling by pressurization to prevent the decrease of the critical current density is small. However, by controlling the pressure to increase stepwise with the increase in temperature in the atmosphere, the external pressure is increased before the pressurized gas penetrates into the inside of the wire rod from the pinhole. As a result, a pressure difference between inside and outside of the wire rod is generated regardless of whether there are pinholes in the wire rod before the heat treatment process, and the generation of voids and swelling can be suppressed, and the critical current density can be increased.

In the above-mentioned method for producing an oxide superconducting wire, it is preferable that, during the temperature rise before the heat treatment in the heat treatment step, the total pressure in the atmosphere is controlled to be 0.05 MPa/min or 0.05 MPa/min. The above speed increases.

The inventors of the present application found that the rate at which pressurized gas intrudes from the pinholes into the inside of the wire rod was less than 0.05 MPa/min in the heat treatment process of the wire rod. Therefore, by controlling the total pressure of the atmosphere to continuously increase at a rate of 0.05 MPa/min or more during the temperature rise before heat treatment, the pressure in the atmosphere can be kept higher than the pressure inside the wire for a long time. high. As a result, a compressive force can be applied to the wire rod during the temperature rise before the heat treatment regardless of the presence or absence of pinholes in the wire rod before the heat treatment process, thereby suppressing the generation of voids or expansion. As a result, the decrease in the critical current density can be effectively suppressed by heat treatment in a pressurized atmosphere of 1 MPa or more than 1 MPa and less than 50 MPa.

In the above-mentioned method for producing an oxide superconducting wire, it is preferable that the heat treatment in the heat treatment step be controlled so that the total pressure in the atmosphere is continuously increased.

Accordingly, during heat treatment, the state where the pressure inside the wire rod is equal to the pressure in the atmosphere can be delayed, and the state where the pressure in the atmosphere is higher than the pressure inside the wire rod can be maintained for a longer period of time. Therefore, the generation of voids or swelling is suppressed during the heat treatment, and the decrease of the critical current density can be effectively suppressed by heat treatment in a pressurized atmosphere of 1 MPa or more and less than 50 MPa.

In the above-mentioned method for producing an oxide superconducting wire, preferably, after the step of producing the wire rod and before the step of heat treatment, a step of rolling the wire rod is further provided, and the reduction ratio of the wire rod in the rolling step is 84% or less, preferably 80% or less.

When the step of heat-treating the wire rod is performed in a pressurized atmosphere of 1 MPa or more to less than 50 MPa, the oxide superconducting wire rod is compressed even during the heat-treatment step. Therefore, even if the wire rolling process is performed at a reduction rate of 84% or less than the conventional reduction rate, the raw material powder is also compressed in the subsequent heat treatment process, so as a result, the superconducting fineness can be improved The density of the silk. On the other hand, by performing the rolling process of the wire rod at a reduction ratio of 84% or less than the conventional reduction ratio, since it is difficult to generate voids in the raw material powder, it is possible to suppress the friction between the oxide superconducting wire rod and the oxide superconducting wire rod. Occurrence of voids extending in a direction perpendicular to the longitudinal direction. From the above reasons, the critical current density of the oxide superconducting wire can be increased. In addition, by performing the rolling process of the wire rod at a reduction rate of 80% or less, since voids are not generated in the raw material powder, it is possible to further suppress the possibility of extending in the direction perpendicular to the longitudinal direction of the oxide superconducting wire rod. voids occur.

In addition, in this specification, the reduction ratio (%) is defined by the following formula.

Reduction rate (%)={1-(thickness of wire rod after calendering/thickness of wire rod before calendering)}×100

In the above-mentioned method for producing an oxide superconducting wire, it is preferable that the wire is subjected to multiple heat treatments, and at least one of the multiple heat treatments is pressurized at a total pressure of 1 MPa or more and less than 50 MPa. in the atmosphere.

Thus, the generation of voids between oxide superconducting crystals and expansion of the oxide superconducting wire that occur during heat treatment can be suppressed.

A brief description of the drawings

FIG. 1 is a partial cross-sectional perspective view conceptually showing the structure of an oxide superconducting wire.

FIG. 2 is a diagram showing one manufacturing process of an oxide superconducting wire.

Fig. 3 is a schematic sectional view of a hot isobaric pressing (HIP) apparatus.

4A to 4D are conceptual diagrams showing the state of voids between oxide superconducting crystals step by step.

Fig. 5 is a graph showing the relationship between the total pressure P (MPa) of the pressurized atmosphere and the number of wires expanded (number/10m).

Fig. 6 is a graph showing the total pressure and oxygen partial pressure of a mixed gas in which nitrogen is about 80% and oxygen is about 20%.

Fig. 7 is a graph showing the relationship between the total pressure and the oxygen concentration value when the oxygen partial pressure is kept constant.

8A is a graph showing the relationship between the time and the temperature of the wire rod when the decompression rate is controlled immediately after the heat treatment, and FIG. 8B is a graph showing the time and the total volume in the container when the decompression rate is controlled immediately after the heat treatment. Diagram of the relationship of pressure.

9A is a graph showing the wire thickness of the oxide superconducting wire without pinholes before and after heat treatment in a pressurized atmosphere, and FIG. 9B is a graph showing the wire thickness of the oxide superconducting wire with pinholes.

FIG. 10 is a partial cross-sectional perspective view conceptually showing the structure of a pinhole-containing oxide superconducting wire.

FIG. 11 is a schematic sectional view showing a rolling method in Embodiment 2. FIG.

Fig. 12 is a diagram showing another manufacturing process of the oxide superconducting wire.

13 is a partial cross-sectional perspective view conceptually showing the structure of the oxide superconducting wire after the step of electroplating the wire with silver or a silver alloy.

FIG. 14 is a graph showing the relationship between temperature and pressure and time during heat treatment in the fourth method of Embodiment 2. FIG.

15A is a graph showing the relationship between temperature and time in the heat treatment process in the case of the silver ratio in Embodiment 2 being 1.5, and FIG. 15B is a graph showing the heat treatment process in the case of the silver ratio in Embodiment 2 being 1.5. Figure 15C is a graph showing the relationship between pressure and time. Figure 15C is a graph showing the relationship between oxygen concentration and time in the heat treatment process in the case where the silver ratio in Embodiment 2 is 1.5. Figure 15D shows the relationship between the silver ratio in Embodiment 2. It is a diagram of the relationship between oxygen partial pressure and time in the heat treatment process in the case of 1.5.

FIG. 16 is a graph showing the relationship between temperature and pressure and time during heat treatment in the fifth method of Embodiment 2. FIG.

Fig. 17 is a graph showing the optimum combination of temperature and oxygen partial pressure during heat treatment.

Fig. 18 is a partial cross-sectional perspective view conceptually showing the structure of an oxide superconducting wire in which voids remain.

FIG. 19 is a graph schematically showing the relationship between the reduction ratio and the critical current density in one rolling of an oxide superconducting wire.

Best way to practice the invention

Embodiments of the present invention will be described below using the drawings.

Implementation 1

Referring to FIG. 1 , an example of an oxide superconducting wire of a multi-core wire will be described. The oxide superconducting wire 1 has a plurality of oxide superconductor filaments 2 extending in the longitudinal direction and a sheath portion 3 covering the oxide superconductor filaments 2 . The respective materials of the plurality of oxide superconductor filaments 2 are, for example, preferably a composition of Bi-Pb-Sr-Ca-Cu-O system, and particularly include (bismuth and lead): strontium: calcium: copper in an atomic ratio of approximately The material of the Bi2223 phase represented approximately by the ratio of 2:2:2:3 is optimal. The material of the sheath portion 3 is, for example, silver.

In addition, although a multi-core wire has been described above, an oxide superconducting wire having a single-core wire structure in which one oxide superconductor filament 2 is covered with a sheath portion 3 may also be used.

Next, a method for producing the above-mentioned oxide superconducting wire will be described.

Referring to FIG. 2 , first, a metal tube is filled with raw material powder of an oxide superconductor (step S1 ). The raw material powder of the oxide superconductor is composed of a material containing a Bi2223 phase, for example.

In addition, it is preferable to use silver or silver alloy with high thermal conductivity as the metal tube. As a result, when the superconductor is partially quenched, the generated heat can be rapidly removed from the metal tube.

Next, the metal tube filled with the raw material powder is formed into a wire rod having a desired diameter by wire drawing (step S2). Thereby, a wire rod having a form in which the raw material powder of the oxide superconductor is covered with the metal can be obtained. This wire rod is rolled once (step S3), and then heat-treated for the first time (step S4). These operations are used to generate oxide superconducting phases from raw material powders. The heat-treated wire rod is rolled twice (step S5). In this way, voids generated in the first heat treatment are removed. The second heat treatment is performed on the wire rod that has been rolled twice (step S6). In the second heat treatment, the oxide superconducting phase is single-phased simultaneously with the sintering of the oxide superconducting phase.

Using the above-described manufacturing method, an oxide superconducting wire such as that shown in FIG. 1 can be manufactured.

In this embodiment, at least one of the first heat treatment (step S4) and the second heat treatment (step S6) is performed in a pressurized atmosphere with a pressure of 1 MPa or more and less than 50 MPa as the total pressure. .

Heat treatment in this pressurized atmosphere is performed, for example, by hot isobaric pressing (HIP). The hot isobaric pressing method will be described below.

With reference to Fig. 3, the device 13 that carries out hot isobaric pressurization method is made up of following parts: pressure vessel cylinder 6; The loam cake 5 and lower cover 11 that seals the two ends of this pressure vessel cylinder 6; The gas inlet 4 provided on the upper cover 5 in the cylinder 6 ; the heater 9 for heating the processed product 8 ; the heat insulating layer 7 ; and the supporting device 10 for supporting the processed product 8 .

In the present embodiment, the metal tube is filled with raw material powder and then drawn and rolled as the processed product 8 and supported by the supporting tool 10 in the pressure vessel cylinder 6 . In this state, by introducing a predetermined gas from the gas inlet 4 into the pressure vessel cylinder 6, the inside of the pressure vessel cylinder 6 becomes a pressurized atmosphere of 1 MPa or more than 1 MPa and less than 50 MPa. Next, the wire 8 is heated to a predetermined temperature by the heater 9 . This heat treatment is preferably performed in an oxygen atmosphere, and the oxygen partial pressure is preferably 0.003 MPa to 0.02 MPa. In this way, the wire rod 8 is subjected to heat treatment by a hot isobaric pressing method.

According to the present embodiment, by performing heat treatment in a pressurized atmosphere of 1 MPa or more and less than 50 MPa as described above, the following three effects can be mainly obtained.

First, voids generated between oxide superconducting crystals during heat treatment can be reduced.

The inventors of the present application found that by performing heat treatment in a pressurized atmosphere of 1 MPa or more, the voids between oxide superconducting crystals that are mainly generated during heat treatment can be particularly reduced compared to the case of less than 1 MPa.

That is, referring to FIGS. 4A to 4D , if the heat treatment is performed in a pressurized atmosphere, the contact area between the oxide superconducting crystals formed during the heat treatment increases due to plastic flow, and the area of several μm to tens of micrometers existing between the superconducting crystals The voids on the order of μm are reduced (Fig. 4A → 4B). If kept in this state, creep deformation occurs as shown in FIG. 4C , voids present at the bonding interface shrink, and at the same time, a part of the contaminated portion such as the oxide film is destroyed and decomposed, and atomic diffusion occurs, and sintering proceeds. And finally, as shown in FIG. 4D , the voids between the superconducting crystals are almost eliminated, and a stable joint interface is formed.

Here, flowing a current in a superconducting wire means flowing a current between superconducting crystals constituting the superconducting wire. Generally, in a cold medium (such as liquid nitrogen or helium or a freezer) using a superconducting wire, the limit on the amount of current that can flow to maintain a superconducting state (no resistance) is the inter-crystal contact between superconducting crystals with a weak superconducting state. Junction (the superconductivity of the superconducting crystal is stronger than the superconductivity of the junction between crystals). In normal atmosphere sintering, gaps at the junction between superconducting crystals remain anyway. Therefore, by reducing the gap between superconducting crystals, the performance of the superconducting wire can be improved, and the decrease of the critical current density can be prevented.

Specifically, for an oxide superconducting wire containing a Bi2223 phase, the sintered density of the oxide superconductor in the case of heat treatment at atmospheric pressure is 80 to 90%, and when the total pressure of the pressurized atmosphere is set at 10 MPa The sintered density of the oxide superconductor produced by the production method of the present invention was 93 to 96%, and the reduction of voids formed between the crystals of the oxide superconductor was observed.

Second, expansion of the oxide superconducting wire generated during heat treatment can be prevented.

The inventors of the present application studied the expansion number generated in the heat-treated wire rod when the total pressure was changed when the oxide superconducting wire rod was heat-treated in a pressurized atmosphere. Referring to FIG. 5, if the total pressure of the pressurized atmosphere exceeds 0.5 MPa, the expansion in the oxide superconducting wire is greatly reduced, and if it is 1 MPa or more, it can be seen that the swelling in the oxide superconducting wire is almost eliminated. swell. The reason why such a result was obtained is considered to be as follows.

Since the oxide superconductor in the metal tube usually has a theoretical density of about 80% filling rate before sintering, there is gas in the interstices of the powder. When the temperature becomes high during the heat treatment, the volume of the gas in the gaps of the powder expands, and the wire rod expands. However, in this embodiment, since the heat treatment is performed in a pressurized atmosphere of 1 MPa or more, the pressure outside the metal tube is higher than the pressure inside the metal tube. Therefore, it is considered that the expansion of the wire rod caused by the gas in the gaps of the powder is prevented.

In addition, the inventors of the present application further studied the cause of the expansion of the wire rod and found that adsorbed substances such as carbon (C), water (H ₂ O), oxygen (O ₂ ) attached to the raw material powder of the oxide superconductor Gasification occurs during sintering, and the volume in the metal tube expands due to the gas, thereby causing expansion of the wire rod. However, by performing heat treatment in a pressurized atmosphere of 1 MPa or more, since the external pressure can be increased to be greater than the internal pressure between the metals, it is considered that the gasification of the adsorbate of the powder can also be prevented. expansion of the wire.

From the above, by setting it at 1 MPa or more, it is considered that not only the expansion caused by the gas existing in the gaps of the raw material powder of such an oxide superconductor can be eliminated, but also the adsorption caused by the surface of the particle can be eliminated. Expansion caused by gasification of matter. Since the expansion of the oxide superconducting wire is a cause of a decrease in the critical current density, the decrease in the critical current density can be prevented by preventing the expansion of the wire.

Third, control of the oxygen partial pressure during heat treatment can be facilitated.

The inventors of the present application found that the 2223 phase of a Bi-based oxide superconductor can be stably formed by controlling the oxygen partial pressure to 0.003 MPa to 0.02 MPa regardless of the total pressure. That is, if the oxygen partial pressure exceeds 0.02 MPa, a heterogeneous phase such as Ca ₂ PbO ₄ is formed, and if it is less than 0.003 MPa, it is difficult to form a Bi2223 phase, and the critical current density decreases.

Referring to Fig. 6, for example, in the case where the total pressure of the pressurized atmosphere is 1 atmosphere (0.1 MPa), even if the control of the oxygen partial pressure is not carried out, since the oxygen partial pressure is different from the 0.2 atmosphere shown by the dotted line (0.02 MPa) at the same level, the Bi2223 phase is stably formed. However, as the total pressure of the pressurized atmosphere increases to 2 atmospheres, 3 atmospheres, . As a result, the Bi2223 phase cannot be stably formed. Therefore, as shown in FIG. 7 , it is necessary to control the oxygen partial pressure at 0.003 MPa to 0.02 MPa by changing the mixing ratio of oxygen in the mixed gas. In addition, the dotted line in FIG. 7 shows the level of 0.2 atmospheres (0.02 MPa) similarly to the dotted line in FIG. 6 .

The actual partial pressure of oxygen is controlled by detecting the total pressure and oxygen concentration. That is, the oxygen partial pressure is calculated by multiplying the oxygen concentration by the value of the total pressure.

Therefore, for example, when the total pressure is 50 MPa and the heat treatment is performed with an oxygen partial pressure of 0.005 MPa, the oxygen concentration is 0.01%. Therefore, it is necessary to measure the oxygen concentration of 0.01% to control the injected mixed gas. However, since the oxygen concentration of 0.01% is equivalent to a measurement error, it is difficult to accurately measure the oxygen concentration to control the oxygen in the injected mixed gas. In this embodiment, by reducing the total pressure in the pressurized atmosphere to less than 50 MPa, the influence of the measurement error of the oxygen concentration can be reduced, and the concentration of oxygen in the injected mixed gas can be kept at a certain high level. , so the partial pressure of oxygen can be easily controlled.

However, when the heat treatment is performed in a pressurized atmosphere of 1 MPa or higher, it is preferable to control the decompression rate so as not to cause sudden decompression in the pressurized atmosphere during and after the heat treatment.

That is, when the heat treatment is carried out in a pressurized atmosphere of 1 MPa or more, it is considered that external gas enters the interior of the wire through the fine pores on the surface of the wire, making the internal pressure the same as the external pressure. In such a high-pressure atmosphere, the inventors of the present application have found that if the external pressure drops due to sudden decompression, the release of gas from the inside cannot keep up with the decrease in external pressure, and the internal pressure becomes high and Generate bloat.

Therefore, in order to prevent such expansion, it is preferable to inject a mixed gas of an inert gas such as Ar (argon) or N ₂ (nitrogen) and O ₂ gas into the container during heat treatment so that the total pressure becomes constant. In addition, when the temperature is lowered immediately after the heat treatment, a mixed gas such as an inert gas and O ₂ gas is injected into the container to compensate for the pressure drop caused by the temperature drop. By controlling the decompression rate during the heat treatment and when the temperature is lowered immediately after the heat treatment, the generation of expansion due to the sudden decompression can be prevented.

Referring to FIGS. 8A and 8B , during the heat treatment of FIG. 8A (temperature of about 800° C.), as shown in FIG. 8B , the total pressure is controlled to be constant. That is, since the oxygen in the container is consumed due to the oxidation of the supporter supporting the wire in the heating container during the heat treatment, the pressure in the container decreases. To prevent this, the container is filled with a gas mixture to keep the pressure constant. Moreover, when the temperature is lowered immediately after the heat treatment in FIG. 8A (temperature range of about 800°C to about 300°C), as shown in FIG. The decompression speed is controlled to be equal to or lower than a certain speed. That is, at the time of temperature drop, due to the sudden drop in temperature, the pressure of the gas also drops sharply according to the equation of state of the gas. Therefore, it is necessary to inject the mixed gas to make the temperature drop gentle. In addition, at 300°C or below, since the temperature is lower than the case of about 800°C to about 300°C, the pressure inside the wire is sufficiently low. Therefore, it is considered that the expansion of the wire rod does not occur even if the decompression rate is not controlled.

In addition, the inventors of the present application have found that the range of the decompression rate necessary to prevent the generation of swelling of the oxide superconducting wire depends on the area of the metal part in the cross section of the wire rod after heat treatment to the area of the oxide superconductor part The ratio (silver ratio) varies with each other. That is, it is preferable that when the silver ratio is 1.5, the decompression rate when the temperature is lowered immediately after the heat treatment (temperature range of 800° C. to 300° C.) is 0.05 MPa/min or less. In the case of 3.0, the decompression rate when the temperature is lowered immediately after the heat treatment (temperature range of 800° C. to 300° C.) is 0.03 MPa/min or less.

Embodiment 2

The heat treatment conditions in FIGS. 9A and 9B were a total pressure of 20 MPa, an oxygen partial pressure of 0.008 MPa, an atmosphere temperature of 825° C., and a heat treatment time of 50 hours. Referring to FIG. 9A , the thickness of the oxide superconducting wire without pinholes was reduced by about 0.006 mm to 0.01 mm after heat treatment. This is because the heat treatment in a pressurized atmosphere with a total pressure of 20 MPa suppressed the formation of voids between oxide superconducting crystals and swelling of the oxide superconducting wire. On the other hand, referring to FIG. 9B , the thickness of the oxide superconducting wire with pinholes is only reduced by about 0.002 mm to 0.005 mm after heat treatment, which does not sufficiently suppress the gap between the oxide superconducting crystals and the thickness of the oxide superconducting wire. The generation of bloat. In addition, the thickness after the heat treatment was thicker than the thickness before the heat treatment for the portion having pinholes (A portion) in the wire rod.

According to the above, in the absence of pinholes, if the heat treatment is performed within the pressure range (1MPa or more than 1MPa to less than 50MPa) of Embodiment 1, the generation of voids and expansion can be effectively suppressed, but in the presence of pinholes In the case of pores, it was found that within the pressure range of Embodiment 1, the generation of voids and swelling could not be sufficiently suppressed only by heat treatment.

In the heat treatment in the pressurized atmosphere of the present invention, since the plastic flow and creep deformation of the superconducting crystals generated during the heat treatment are caused by utilizing the pressure outside the wire rod as large as 1 MPa or more, the heat treatment generated during the heat treatment is suppressed. Voids between oxide superconducting crystals. In addition, since the pressure from the outside of the metal tube can be used to suppress the expansion of the gas in the gap of the oxide superconducting crystal powder generated during the heat treatment or the gas attached to the oxide superconducting crystal powder generated during the heat treatment, it is suppressed. The generation of the expansion of the oxide superconducting wire. As a result of the above, a decrease in critical current density due to voids or expansion is prevented.

However, for wires with pinholes, even if the above-mentioned heat treatment in a pressurized atmosphere is performed, the pressurized gas intrudes into the inside of the wires from the pinholes, so the pressure difference between the inside and outside of the wires is eliminated, and pressurization cannot be used. Generation of voids or swelling is sufficiently suppressed. As a result, the effect of preventing the decrease of the critical current density is small.

Therefore, the inventors of the present application conducted intensive studies, and as a result, found a method in which the generation of voids and swelling can be sufficiently suppressed by forming a wire rod without pinholes before heat treatment.

The first method is to set the sheath thickness ω of the oxide superconducting wire after rolling (step S3 or S5 ) in FIG. 2 and before heat treatment (step S4 or step S6 ) to 200 μm or more.

The second method is to set the surface roughness Ry of the portion where the wires of the rollers used in the rolling (step S3 or S5 ) of FIG. 2 are in contact with 320 μm or less.

The third method is to electroplate silver or a silver alloy on the oxide superconducting wire after rolling (step S3 or S5 ) in FIG. 2 and before heat treatment (step S4 or step S6 ).

Hereinafter, these methods will be specifically described.

As a first method, the inventors of the present application found that by setting the thickness W of the oxide superconducting wire after rolling (step S3 or S5) in FIG. 2 and before heat treatment (step S4 or step S6) at which All parts are 200 μm or more, and no pinholes are formed during rolling (step S3 or S5 ). Here, the sheath thickness W means, as shown in FIG. 10 , the distance W after rolling between the oxide superconductor filaments 2 aligned on the outer periphery in the cross section of the wire 1 and the outer surface of the wire 1 . The reason why pinholes are not generated by making the skin thickness W 200 μm or more is considered to be as follows.

The pinholes 14 are mainly formed by breaking the surface of the wire 1 due to friction between the wire 1 and the calender roll, and penetrating through the oxide superconductor filament 2 from the outside. However, if the oxide superconducting wire 1 is rolled in a state where the thickness W of the sheath of the oxide superconducting wire 1 is 200 μm or more in all parts, even if the surface of the wire 1 is damaged by rolling, the pores will not emerge from the surface. Since the outside penetrates the oxide superconductor filament 2, it is considered that the pinhole 14 will not be formed. In addition, since the structure other than the above of FIG. 10 is substantially the same as the structure shown in FIG. 1, the same code|symbol is attached|subjected to the same member, and the description is abbreviate|omitted.

In addition, even if the sheath thickness W of the rolled oxide superconducting wire is less than 200 μm, if the above-mentioned second and third methods are used, a wire without pinholes 14 can be obtained before heat treatment. As a result, the present application The inventors have found that by performing heat treatment in a pressurized atmosphere, generation of voids or swelling is suppressed, and a decrease in critical current density is effectively prevented.

Referring to FIG. 11 , calendering is a processing method of passing a plate-shaped or rod-shaped material between multiple (usually 2) rotating rollers 15, reducing its thickness or cross-sectional area, and simultaneously forming the cross-section into a desired shape. At the time of calendering, the oxide superconducting wire 1 is drawn between a plurality of rolls 15 by frictional force from the rolls 15 , where it is deformed by compressive force from the surfaces 15 a of the rolls 15 .

In the second method, the surface roughness Ry of the surface 15a of the portion that is in contact with the wire rod 1 in at least one of the primary rolling (step S3) and the secondary rolling (step S5) shown in FIG. 2 is used. The roller 15 is 320 μm or less.

That is, if the surface roughness Ry of the surface 15a of the roll 15 used during rolling is 320 μm or less, since the friction between the wire 1 and the surface 15a of the roll 15 becomes smaller, the surface of the wire 1 is less likely to be damaged, and it can be used with Regardless of the sheath thickness of the wire 1 , a wire 1 without pinholes is obtained. Therefore, it is difficult for the pressurized gas to penetrate into the inside of the wire rod 1 during the heat treatment process. Accordingly, generation of voids and swelling can be suppressed by the step of heat treatment in the pressurized atmosphere regardless of the sheath thickness W of the wire rod 1 , and a decrease in the critical current density can be effectively prevented.

In addition, in the third method, as shown in FIG. 12, after rolling (step S3 or S5) and before heat treatment (step S4 or S6), the process of electroplating silver or silver alloy on the surface of the wire rod (step S11 or S12). In addition, since it is substantially the same as the method of FIG. 2 except for the process of additional electroplating (step S11 or S12), corresponding symbols are assigned to corresponding processes, and descriptions thereof are omitted.

Referring to FIG. 13 , silver or silver alloy 16 is plated on the outer peripheral portion of sheath portion 3 , whereby pinholes 14 opened outside are blocked with silver or silver alloy 16 . In addition, since the structure other than this is substantially the same as the structure shown in FIG. 1, the same code|symbol is attached|subjected to the same member, and the description is abbreviate|omitted.

In general, in order to increase the superconducting current that can flow per unit area, the silver ratio of the oxide superconducting wire 1 is reduced as much as possible. However, since the ratio of the metal portion of the wire 1 having a small silver ratio is small, the sheath thickness W cannot be increased. Therefore, the wire rod 1 having a small silver ratio has a sheath thickness of less than 200 μm, and pinholes 14 are likely to be formed in a process (such as rolling) before the heat treatment process. In the wire 1 having the pinholes 14, as described above, the generation of voids and swelling cannot be sufficiently suppressed by pressurization, and as a result, the effect of preventing a decrease in the critical current density is small. Therefore, by electroplating silver or silver alloy 16 on the surface of wire rod 1 before the heat treatment process, pinholes 14 are blocked with silver or silver alloy 16 to disappear from the surface. Therefore, since the heat treatment step is performed after removing the pinholes 14 from the wire rod 1 , pressurized gas does not intrude into the inside of the wire rod 1 during the heat treatment step. Thus, regardless of the value of the sheath thickness W of the wire rod 1 and the value of the surface roughness Ry of the roll 15 used for rolling, the process of performing heat treatment in the pressurized atmosphere suppresses the generation of voids or swelling, and effectively Prevents a drop in critical current density.

In addition, the inventors of the present application have found that by using the fourth method or the fifth method described below, even in the wire 1 having pinholes 14, the generation of voids or swelling can be suppressed, and the critical current density can be effectively prevented. Decline. In the fourth method, in at least one of the first heat treatment (step S4) and the second heat treatment (step S6) shown in FIG. The pressure is increased stepwise as the temperature rises. In addition, in the fifth method, in at least one of the first heat treatment (step S4) and the second heat treatment (step S6) shown in FIG. Control so that the total pressure of the atmosphere increases at a rate of 0.05MPa/min or more. Also, during heat treatment, control is performed such that the total pressure in the atmosphere is continuously increased. In addition, when the temperature is lowered immediately after the heat treatment, it is controlled so as to compensate for the drop in pressure (additional pressure) caused by the temperature lowering. First, the fourth method will be described.

Referring to FIG. 14 , heat treatment was performed at a heat treatment temperature of 800° C. and a pressure of 20 MPa. At this time, control is performed such that the pressure increases in a stepwise manner as the temperature rises. That is, the pressure is controlled in such a way that when the pressure is increased, the pressure is increased after being maintained for a certain period of time at a certain pressure, and then the pressure is maintained for a certain period of time again at the increased pressure. Specifically, during the pressure increase, the pressure was maintained at about 7 MPa, 10 MPa, 12.5 MPa, 15 MPa, and 17 MPa for a certain time. In addition, the sequence of increasing the pressure after maintaining the pressure for a certain period of time is performed based on the measured value of the temperature in the atmosphere. That is, the pressure is controlled in this way: the pressure is increased to about 7 MPa at room temperature, the pressure is increased to about 10 MPa when the temperature reaches about 400 °C, and the pressure is increased to about 12.5 MPa when the temperature reaches about 500 °C. MPa, when the temperature reaches about 600°C, the pressure is increased to about 15MPa, and when the temperature reaches about 700°C, the pressure is increased to about 17MPa. In addition, in order to generate a stable oxide superconducting phase, the oxygen partial pressure is constantly controlled to be in the range of 0.003 to 0.008 MPa.

For wires with pinholes, even if heat treatment is carried out in a pressurized atmosphere using the usual pressurization method, the pressurized gas will intrude into the inside of the wire from the pinholes, so there is no pressure difference between the inside and outside of the wire. Pressurization is less effective in preventing a drop in critical current density due to voids or expansion. However, by controlling such that the pressure increases stepwise as the temperature rises as in the fourth method, the external pressure increases before the pressurized gas enters the inside of the wire rod from the pinhole. As a result, a pressure difference between inside and outside of the wire rod is generated regardless of whether there are pinholes in the wire rod before the heat treatment process, and the generation of voids and swelling can be suppressed, and the decrease of the critical current density can be effectively prevented.

Furthermore, by combining the following methods with the above-mentioned methods 1 to 4, it is possible to more effectively suppress the generation of voids or swelling of the wire rod. Hereinafter, this method will be described.

In this method, in at least one of the first heat treatment (step S4) shown in FIG. 2 and the second heat treatment (step S6), in the heat treatment process, the temperature in the atmosphere is 200 °C or more than 200 °C, control is performed so that the decompression rate of the total pressure in the pressurized atmosphere does not reach a certain rate.

Referring to FIGS. 15A to 15D , the temperature rise before the heat treatment is controlled so that the pressure increases stepwise as the temperature in the atmosphere rises, as in the fourth method described above. In addition, in Fig. 15B, it is not seen that the predetermined pressure is maintained for a certain period of time, but this is because the scale of the elapsed time in Fig. 15B is much larger than that of Fig. 14, so it is only seen that the pressure maintaining part is omitted, and the actual In the same manner as in the case of FIG. 14, a predetermined pressure is maintained for a certain period of time. In this heating step, the temperature was set at 815° C., the pressure was set at 20 MPa, and heat treatment was performed for 50 hours in this state. During the temperature rise before the heat treatment and during the heat treatment, when the temperature in the atmosphere is 200°C or higher, control is performed so that the decompression rate of the total pressure in the pressurized atmosphere is 0.05MPa/min or Below 0.05MPa/min. Therefore, the thermal energy lowers the temperature at a rate of 50°C/h after the heat treatment. Even after the heat treatment, when the temperature in the atmosphere is 200° C. or higher, control is performed so that the decompression rate of the total pressure in the pressurized atmosphere is 0.05 MPa/min or less. In addition, when the cooling rate after heat treatment is 50°C/h, since the natural decompression rate accompanying the temperature drop is always 0.05 MPa/min or less, it is not necessary to control the decompression rate. Furthermore, by keeping the oxygen concentration at 0.04% before, during, and after heat treatment, the oxygen partial pressure is kept in the range of 0.003 to 0.008 MPa for a constant time, and a stable oxide superconducting phase can be formed.

When the temperature in the atmosphere is 200° C. or higher and the pressure in the heating container is reduced rapidly, the pressure inside the wire becomes higher than the pressure outside the wire, thereby causing expansion of the wire. Therefore, by controlling the decompression speed of the total pressure in the pressurized atmosphere to be less than a certain speed, the effect of suppressing the generation of expansion of the wire rod due to the rapid decompression during heat treatment (before heat treatment, during heat treatment, and after heat treatment) become more pronounced.

In addition, when the temperature in the atmosphere is 200° C. or higher for a wire rod having a silver ratio of 3.0, the depressurization rate is controlled to be 0.03 MPa/min or less.

Next, the fifth method will be described. In the fifth method, in at least one of the heat treatment for the first time (step S4) and the heat treatment for the second time (step S6), when the temperature is raised before the heat treatment, it is controlled so that the total pressure in the atmosphere Continuously increase at a speed of 0.05MPa/min or above. Also, during the heat treatment, the total pressure in the atmosphere is controlled to increase continuously. In addition, when the temperature is lowered after the heat treatment, it is controlled so as to compensate for the drop in pressure (additional pressure) caused by the temperature lowering.

Referring to FIG. 16 , when the temperature is raised before heat treatment, when the temperature of the atmosphere is, for example, 700° C. or lower, the pressure gradually increases according to the gas equation of state. Also, when the temperature of the atmosphere exceeds 700° C., the pressure in the atmosphere increases to about 10 MPa. At this time, the pressure in the atmosphere is increased at one go at a pressurization rate of 0.05 MPa/min or more.

Here, the inventors of the present application have found that when an oxide superconducting wire rod having pinholes is heat-treated in a pressurized atmosphere, the rate at which pressurized gas penetrates from the pinholes into the wire rod is less than about 0.05 MPa. /min. Therefore, when the temperature is raised before the heat treatment, the total pressure of the atmosphere is continuously increased by controlling the total pressure of the atmosphere at a speed of 0.05 MPa/min or more, so the pressure in the atmosphere can be continuously maintained when the temperature is raised before the heat treatment. higher than the inside of the wire.

Thereafter, during the heat treatment, the temperature is kept at, for example, 830°C. On the other hand, the pressure in the atmosphere continues to increase. The pressurization rate during heat treatment is preferably as fast as possible, but since the total pressure exceeds 50 MPa if the pressurization rate is too fast, the pressure must be continuously maintained at an appropriate pressurization rate such that the total pressure during heat treatment does not exceed 50 MPa. Increase. In Figure 16, the pressure has increased to about 30 MPa. Thereby, the time at which the pressure inside the wire rod becomes equal to the pressure in the atmosphere can be delayed from time t ₁ to time t ₂ compared with the case where the pressure is kept constant during heat treatment. In this way, the state where the pressure in the atmosphere is higher than the pressure inside the wire rod can be maintained for a long time during the heat treatment.

Thereafter, when the temperature is lowered immediately after the heat treatment, according to the equation of state of a gas, the temperature in the atmosphere is lowered and the pressure is also lowered. At this time, the pressure is controlled so as to compensate for the drop in pressure due to temperature drop (additional pressure). In addition, in order to generate a stable oxide superconducting phase, the oxygen partial pressure is constantly controlled to be in the range of 0.003 to 0.02 MPa.

According to the fifth method, since the pressure in the atmosphere is higher than the pressure inside the wire rod when the temperature is raised before heat treatment, a compressive force is applied to the wire rod. In addition, during the heat treatment, the pressure in the atmosphere can be kept higher than the pressure inside the wire rod for a long time. As a result, the generation of voids or swelling can be suppressed during the temperature rise before and during the heat treatment, and the decrease of the critical current density can be effectively suppressed by heat treatment in a pressurized atmosphere of 1 MPa or more to less than 50 MPa.

Embodiment 3

In order to further increase the critical current density of the oxide superconducting wire. The inventors of the present application conducted intensive studies on the optimum oxygen partial pressure during temperature rise before heat treatment and heat treatment. Thus, the results shown in FIG. 17 can be obtained.

Referring to FIG. 17 , for example, when the oxygen partial pressure is 0.007 MPa, as long as the temperature ranges from 815° C. to 825° C., it can be seen that a stable oxide superconducting phase can be formed and the critical current density can be increased. In addition, although not shown, in the case of an oxygen partial pressure of 0.0003 MPa, as long as it is in the temperature range of 750°C to 800°C, preferably equal to or greater than the temperature range of 770°C to 800°C, stable The oxide superconducting phase, and increase the critical current density. In addition, in the case of an oxygen partial pressure of 0.02MPa, as long as it is in the temperature range of 820°C to 850°C, preferably in the temperature range of 830°C to 845°C, a stable oxide superconducting phase can be formed and the critical current can be increased. density. Furthermore, when the temperature is 650° C. or lower, it can be seen that the oxygen partial pressure must be controlled within the range of 0.00005 MPa to 0.02 MPa.

From the above relationship between temperature and oxygen partial pressure, the optimum value of oxygen partial pressure in the formation of the oxide superconducting phase increases as the temperature rises. Therefore, by controlling the oxygen partial pressure to increase as the temperature in the atmosphere rises during the temperature rise before the heat treatment, the oxygen partial pressure can be brought into an optimum range for the formation of the oxide superconducting phase. Thereby, a stable oxide superconducting phase can be generated, and the critical current density can be increased.

In addition, when the wire rod is held at a constant temperature during heat treatment, fluctuations (errors) of several degrees Celsius often occur with respect to the temperature. Considering the relationship between the change in temperature and the range of the optimum partial pressure of oxygen, for example, when the wire is kept at 822.5°C, the optimum partial pressure of oxygen is 0.006MPa to 0.01MPa, but when the temperature fluctuates at 825°C Under the circumstances, the optimum oxygen partial pressure is 0.007MPa to 0.011MPa. In addition, when the temperature fluctuation is 820° C., the optimum oxygen partial pressure is 0.005 MPa to 0.009 MPa. Therefore, in order to obtain the optimum oxygen partial pressure over time even with such temperature fluctuations, the oxygen partial pressure was controlled within a fluctuation range of 0.007MPa to 0.009MPa while maintaining the wire rod at 822.5°C (Fig. The slashed part in 17) can be constant.

However, the fluctuation range of this oxygen partial pressure is about 10% of the value of the oxygen partial pressure. Therefore, by controlling the oxygen partial pressure during heat treatment to be within a fluctuation range of 10%, since the oxygen partial pressure can be kept in the optimum oxygen partial pressure range even if there is a temperature fluctuation, stable oxide superconducting materials can be produced. phase and increase the critical current density.

Embodiment 4

In order to further increase the critical current density of the oxide superconducting wire, the inventors of the present application controlled the decompression rate of the total pressure in the heat treatment to 0.05 MPa/min, and conducted a study on the relationship between the value of the total pressure and the generation of expansion of the wire. in-depth research.

Raw material powder adjusted to a composition ratio of Bi:Pb:Sr:Ca:Cu=1.82:0.33:1.92:2.01:3.02. After heat-processing this raw material powder at 750 degreeC for 10 hours, it heat-processed at 800 degreeC for 8 hours. Thereafter, the powder obtained by pulverization was heat-treated at 850° C. for 4 hours, and then pulverized again. The pulverized powder was heat-treated under reduced pressure, and filled into a metal tube made of silver with an outer diameter of 36 mm and an inner diameter of 31 mm. Next, wire drawing was performed on the powder-filled metal tube. Furthermore, 61 drawn wires were bundled and fitted into a metal tube with an outer diameter of 36 mm and an inner diameter of 31 mm. Next, wire drawing and primary rolling were performed to obtain a strip-shaped Bi2223 phase superconducting wire having a thickness of 0.25 mm and a width of 3.6 mm. Next, the first heat treatment is performed on the wire rod. The first heat treatment was performed in the atmosphere, the heat treatment temperature was set at 842° C., and the heat treatment time was set at 50 hours. Next, the second heat treatment was performed after the rolling was performed twice. In the second heat treatment, the oxygen partial pressure is controlled to be 0.008MPa, the heat treatment temperature is controlled to be 825°C, the heat treatment time is controlled to be 50 hours, and the decompression rate of the total pressure in the heat treatment is controlled to be 0.05MPa/min, such as The total pressure was varied as shown in Table 1. After the second heat treatment, the presence or absence of expansion of the wire rod was examined. In Table 1, the total pressure and the presence or absence of expansion of the wire rod are shown together.

Table 1 Total pressure (MPa) Wire expansion 0.1 none 0.2 none 0.3 none 0.4 none 0.5 none 0.8 none 1.0 have 2.0 have 3.0 have 5.0 have 10.0 have 20.0 have 30.0 have

According to the results in Table 1, in the case where the total pressure was 1 MPa or more, expansion of the wire rod occurred. Therefore, in order to suppress the expansion of the wire rod, it is necessary to control the decompression rate in the pressurized atmosphere to 0.05 MPa/min or less when the total pressure is 1 MPa or more.

Next, the heat treatment temperature of the second heat treatment was set at 500° C., and the presence or absence of expansion of the wire rod was similarly examined. In Table 1, the total pressure and the presence or absence of expansion of the wire rod are shown together.

Table 2 Total pressure (MPa) Wire expansion 0.1 none 0.2 none 0.3 none 0.4 none 0.5 none 0.8 none 1.0 have 2.0 have 3.0 have 5.0 have 10.0 have 20.0 have 30.0 have

As can be seen from the results in Table 2, even when the heat treatment temperature is 500° C., the expansion of the wire occurs when the total pressure is 1 MPa or more. Therefore, even when the heat treatment temperature is 500°C, in order to suppress the expansion of the wire rod, the decompression rate in the pressurized atmosphere must be controlled to 0.05MPa/min or 0.05MPa/min when the total pressure is 1MPa or more. below min.

Embodiment 5

Referring to FIG. 18, in the superconductor filament 2 of the oxide superconducting wire 1 after heat treatment in a pressurized atmosphere with a total pressure of 1 MPa or more than 1 MPa and less than 50 MPa, in the longitudinal direction (horizontal direction in FIG. 18 ) The long voids are nearly eliminated, leaving only a small amount of extended voids 20 in the direction perpendicular to the long side direction. In addition, in FIG. 18 , an oxide superconducting wire having a single superconducting filament is shown.

That is, the inventors of the present application found that it is difficult to reduce voids 20 extending in a direction perpendicular to the longitudinal direction of oxide superconducting wire 1 even by heat treatment in a pressurized atmosphere. This is considered to be based on the following reasons. In a pressurized atmosphere, pressure is applied equally to the entire surface of the oxide superconducting wire. Then, due to this pressure, the oxide superconducting crystal undergoes creep deformation, and voids present at the bonding interface between the crystals contract. Thus, voids generated between oxide superconducting crystals are reduced. However, since the oxide superconducting wire 1 has a shape extending long in the longitudinal direction, it is difficult to transmit force in the longitudinal direction, and it is difficult for the wire 1 to be compressed in the longitudinal direction. As a result, it is difficult to reduce voids 20 extending in a direction perpendicular to the longitudinal direction of oxide superconducting wire 1 by heat treatment in a pressurized atmosphere.

Since the voids 20 extending in the direction perpendicular to the longitudinal direction of the oxide superconducting wire 1 shield the current in the superconducting filaments, this is one of the causes of the decrease in the critical current density of the oxide superconducting wire 1 . Therefore, if the generation of the voids 20 can be suppressed, the critical current density of the oxide superconducting wire 1 can be further increased.

Therefore, the inventors of the present application have found that, in the primary rolling (step S5) of FIG. % or less, the generation of voids extending in the direction perpendicular to the longitudinal direction of the oxide superconducting wire can be suppressed before heat treatment, and as a result, the critical current density of the oxide superconducting wire can be increased. The reason for this will be described below.

The primary rolling is a process performed to increase the density of the raw material powder filled in the metal tube. In one rolling, the higher the reduction rate of the oxide superconducting wire rod (the higher the processing rate), the higher the density of the raw material powder filled in the metal tube. If the density of the raw material powder increases, the density of the superconducting crystals generated by the subsequent heat treatment (steps S4 and S5 ) increases, thereby increasing the critical current density of the oxide superconducting wire.

On the other hand, when the reduction rate of the oxide superconducting wire rod is increased in one rolling, the following three phenomena may be observed due to an increase in the working rate. First, cracks are generated in the raw material powder. Second, it is easy to produce a sausage shape in which the shape of the filaments in the oxide superconducting wire is uneven in the longitudinal direction. Third, due to the occurrence of a sausage shape, a lapping phenomenon in which a superconducting filament is in contact with another superconducting filament is likely to occur in a portion where the cross-sectional area of the superconducting filament increases locally. All of these phenomena may cause the critical current density of the oxide superconducting wire to decrease.

Therefore, primary rolling must be performed at such a reduction rate that the density of the raw material powder is increased and no voids or the like are generated in the raw material powder. In conventional primary rolling, the oxide superconducting wire is rolled at a rolling reduction of 86 to 90%.

However, when the heat treatment is performed in a pressurized atmosphere of 1 MPa or more and less than 50 MPa, the effect of compressing the oxide superconducting wire rod can be obtained even during the heat treatment. Therefore, even if one rolling is performed with a rolling reduction of 84% or less, since the raw material powder is compressed in the subsequent heat treatment in a pressurized atmosphere, the superconducting fineness of the oxide superconducting wire can be improved as a result. The density of the silk. On the other hand, by performing one-pass rolling with a rolling reduction of 84% or less, since voids are less likely to be generated in the raw material powder, it is possible to suppress the occurrence of stretching in the direction perpendicular to the longitudinal direction of the oxide superconducting wire. gap. Furthermore, by performing one rolling at a rolling reduction of 80% or less, voids are not generated in the raw material powder at all. From the above reasons, the critical current density of the oxide superconducting wire can be increased.

Referring to FIG. 19 , when the heat treatment is performed in the air, the critical current density of the oxide superconducting wire is the highest when one rolling is performed at a reduction ratio of about 86%. On the other hand, when the heat treatment is performed in the pressurized atmosphere of the present invention, the critical current density of the oxide superconducting wire material is the highest when one rolling is performed at a reduction ratio of about 82%. In this way, when heat treatment is performed in a pressurized atmosphere of 1 MPa or more than 1 MPa and less than 50 MPa, it can be seen that the reduction ratio of the first rolling for increasing the critical current density of the oxide superconducting wire is toward the low reduction ratio. Offset on one side.

In order to confirm the above-mentioned effects, the inventors of the present application produced the oxide superconducting wire of the present embodiment under the following conditions, and measured the critical current density.

According to the manufacturing process of the oxide superconducting wire shown in FIG. 2 , raw material powder was filled in a metal tube, and wire drawing was performed. Next, rolling was performed once to obtain a tape-shaped superconducting wire. One rolling was performed at two reduction ratios of 82% and 87%. In addition, a roll with a diameter of 100 mm was used in one rolling, and lubricating oil with a dynamic viscosity of 10 mm ² /s was used. Next, the first heat treatment was performed on the wire rod. The oxygen partial pressure was set at 0.008 MPa, the heat treatment temperature was set at 830° C., the heat treatment time was set at 30 hours, and the first heat treatment was performed. Next, rolling was performed twice. The rolling was performed twice without lubricating oil at a rolling reduction of 5 to 30% using a roll with a diameter of 300 mm. Next, a second heat treatment is performed. The oxygen partial pressure was set at 0.008 MPa, the heat treatment temperature was set at 820° C., the heat treatment time was set at 50 hours, and the second heat treatment was performed. After the second heat treatment, the critical current density of the obtained oxide superconducting wire was detected.

As a result, the critical current density of 30 kA/cm ² was obtained in the oxide superconducting wire rod at a reduction ratio of 87% in one rolling. On the other hand, in the oxide superconducting wire having a reduction ratio of 82%, the critical current density was 40 kA/cm ² . In addition, from the above results, by making the rolling reduction of the oxide superconducting wire 84% or less in the primary rolling (step S5), it is possible to suppress the difference between the oxide superconducting wire and the oxide superconducting wire before heat treatment. As a result of the generation of voids extending in a direction perpendicular to the side direction, it is known that the critical current density of the oxide superconducting wire can be increased.

In addition, in each of the above-mentioned embodiments, the method for producing the oxide superconducting wire rod having the Bi2223 phase obtained by the hot isobaric pressing method has been described. The method of performing heat treatment in a pressurized atmosphere, the present invention can also be carried out by a pressurization method other than the hot isobaric pressurization method. In addition, the present invention is also applicable to a method for producing an oxide superconducting wire having a composition other than bismuth, such as yttrium-based.

In Embodiment 2 of the present invention, the case where the step of electroplating silver or silver alloy to the wire rod is shown, but as long as it is a step of attaching silver or silver alloy to the wire rod, the present invention can also be implemented by, for example, a sputtering step. In addition, in Fig. 14 and Fig. 15A to 15D, specific control conditions of temperature, pressure, oxygen concentration, and oxygen partial pressure are shown, but the present invention is not limited to these conditions. When the temperature in the atmosphere is equal to or higher than 200° C., the decompression rate of the total pressure in the pressurized atmosphere may be controlled to be 0.05 MPa/min or less.

By combining the first to fifth methods of Embodiment 2 of the present invention with the heat treatment conditions of Embodiment 1, the occurrence of pinholes can be prevented, or even when pinholes occur, the cracking of the wire rod can be effectively suppressed. Creation of voids or swelling.

In addition, by appropriately combining the first to fifth methods of Embodiment 2 of the present invention, it is possible to more effectively suppress the generation of voids or swelling in the wire rod.

In the fifth method of Embodiment 2 of the present invention, the case where the temperature drop immediately after the heat treatment is controlled so as to compensate for the drop in pressure (additional pressure) caused by the temperature drop is shown, but the present invention is not limited to such a case. At least during the heat treatment, it is sufficient to control the pressure in the atmosphere to continuously increase.

In Embodiment 3 of the present invention, an example of the numerical range of the optimum oxygen partial pressure at the time of temperature rise before heat treatment and at the time of heat treatment is shown, but the present invention is not limited to the method of controlling the oxygen partial pressure within this numerical range. In some cases, it is only necessary to control so that the oxygen partial pressure increases as the temperature in the atmosphere increases.

In Embodiment 5, an example of the dynamic viscosity of lubricating oil during rolling or the diameter of the roll used in rolling was shown, but the present invention is not limited to such rolling conditions, as long as the rolling of the wire rod in the rolling process The pass rate is 84% or less.

The above-disclosed embodiments should be considered in all respects as illustrative rather than restrictive. The scope of the present invention is shown not only by the above-mentioned embodiment but also by the scope of claims, and it is intended that all modifications and variations within the meaning and range equivalent to the scope of claims are included.

Possibility of industrial use

As described above, the method for producing an oxide superconducting wire according to the present invention is applicable to a method for producing an oxide superconducting wire capable of preventing a decrease in critical current density.

Claims (22)

1. the manufacture method of an oxide superconducting wire rod is characterized in that:

This method comprises:

Make the operation (S1, S2) of wire rod, this wire rod has the form that has covered the raw material powder of oxide superconductor with metal; And

The operation (S4, S6) of in pressurization atmosphere, above-mentioned wire rod being heat-treated,

The total pressure of above-mentioned pressurization atmosphere is that 1MPa or 1MPa are above extremely less than 50MPa.

2. the manufacture method of the oxide superconducting wire rod described in claim 1 is characterized in that:

Each carries out above-mentioned heat treated operation (S4, S6) to the isobar pressurization method to utilize heat.

3. the manufacture method of the oxide superconducting wire rod described in claim 1 is characterized in that:

Above-mentioned oxide superconductor comprises bismuth, lead, strontium, calcium and copper, is to comprise (bismuth and lead): strontium: calcium: copper is approximately 2: 2: 2: the oxide superconductor of the 3 Bi2223 Bi-Pb-Sr-Ca-Cu-O series of recently representing as its atom mutually.

4. the manufacture method of the oxide superconducting wire rod described in claim 1 is characterized in that:

In oxygen atmosphere, carry out above-mentioned heat treated operation (S4, S6), and partial pressure of oxygen is 0.003MPa to 0.02MPa.

5. the manufacture method of the oxide superconducting wire rod described in claim 4 is characterized in that:

Control during intensification before the heat treatment in above-mentioned heat treated operation (S4, S6), so that above-mentioned oxygen partial pressure is followed temperature in the above-mentioned pressurization atmosphere to rise and increased.

6. the manufacture method of the oxide superconducting wire rod described in claim 1 is characterized in that:

When heat treatment, control, so that the total pressure in the above-mentioned pressurization atmosphere becomes constant.

7. the manufacture method of the oxide superconducting wire rod described in claim 1 is characterized in that:

In oxygen atmosphere, carry out above-mentioned heat treated operation (S4, S6), and control, so that the partial pressure of oxygen during heat treatment is constant 10% in interior mobility scale.

8. the manufacture method of the oxide superconducting wire rod described in claim 1 is characterized in that:

Injecting gas when lowering the temperature at once after heat treatment is to remedy the decline of the pressure that causes because of cooling.

9. the manufacture method of the oxide superconducting wire rod described in claim 8 is characterized in that:

The above-mentioned metal that covers above-mentioned raw material powder comprises silver, and the area of the above-mentioned metal part (3) in the cross section of the above-mentioned wire rod (1) after the above-mentioned heat treated operation is 1.5 for the ratio of the area of above-mentioned oxide superconducting body portion (2),

Decompression rate when lowering the temperature at once after the above-mentioned heat treatment is 0.05MPa/min or below the 0.05MPa/min.

10. the manufacture method of the oxide superconducting wire rod described in claim 9 is characterized in that:

The above-mentioned metal that covers above-mentioned raw material powder comprises silver, and the area of the above-mentioned metal part (3) in the cross section of the above-mentioned wire rod (1) after the above-mentioned heat treated operation is 1.5 for the ratio of the area of above-mentioned oxide superconducting body portion (2),

In above-mentioned heat treated operation (S4, S6), the temperature in above-mentioned pressurization atmosphere is to control under the situation more than 200 ℃ or 200 ℃, so that the decompression rate of the total pressure in the above-mentioned pressurization atmosphere is 0.05MPa/min or below the 0.05MPa/min.

11. the manufacture method of the oxide superconducting wire rod described in claim 8 is characterized in that:

The above-mentioned metal that covers above-mentioned raw material powder comprises silver, and the area of the above-mentioned metal part (3) in the cross section of the above-mentioned wire rod (1) after the above-mentioned heat treated operation (S4, S6) is 3.0 for the ratio of the area of above-mentioned oxide superconducting body portion (2),

Decompression rate during cooling after the above-mentioned firm heat treatment is 0.03MPa/min or below the 0.03MPa/min.

12. the manufacture method of the oxide superconducting wire rod described in claim 11 is characterized in that:

The above-mentioned metal that covers above-mentioned raw material powder comprises silver, and the area of the above-mentioned metal part (3) in the cross section of the above-mentioned wire rod (1) after the above-mentioned heat treated operation (S4, S6) is 3.0 for the ratio of the area of above-mentioned oxide superconducting body portion (2),

In above-mentioned heat treated operation (S4, S6), the temperature in above-mentioned pressurization atmosphere is to control under the situation more than 200 ℃ and 200 ℃, so that the decompression rate of the total pressure in the above-mentioned pressurization atmosphere is 0.03MPa/min or below the 0.03MPa/min.

13. the manufacture method of the oxide superconducting wire rod described in claim 1 is characterized in that:

In above-mentioned heat treated operation (S4, S6), the total pressure in above-mentioned pressurization atmosphere is to control under 1MPa or the situation more than the 1MPa, so that the decompression rate of the total pressure in the above-mentioned pressurization atmosphere is 0.05MPa/min or below the 0.05MPa/min.

14. the manufacture method of the oxide superconducting wire rod described in claim 1 is characterized in that:

In the operation (S1, S2) of making above-mentioned wire rod afterwards and before in above-mentioned heat treated operation (S4, S6), also have the operation (S3) of utilizing roller (15) that above-mentioned wire rod is rolled, the skin thickness of the above-mentioned wire rod (1) after the operation of above-mentioned calendering (S3) is 200 μ m or more than the 200 μ m.

15. the manufacture method of the oxide superconducting wire rod described in claim 1 is characterized in that:

In the operation (S1, S2) of making above-mentioned wire rod afterwards and before, also have and make silver or silver alloy (16) be attached to the lip-deep operation (S11) of above-mentioned wire rod (1) in above-mentioned heat treated operation (S4, S6).

16. the manufacture method of the oxide superconducting wire rod described in claim 1 is characterized in that:

In the operation (S1, S2) of making above-mentioned wire rod afterwards and before, also have the operation (S3) of utilizing roller (16) that above-mentioned wire rod is rolled in above-mentioned heat treated operation (S4, S6),

Maximum height Ry with the surface roughness contacted part of above-mentioned wire rod (1) above-mentioned roller (16) is 320 μ m or below the 320 μ m.

17. the manufacture method of the oxide superconducting wire rod described in claim 1 is characterized in that:

Control during intensification before the heat treatment in above-mentioned heat treated operation (S4, S6), so that pressure is followed temperature in the atmosphere to rise and increased steppedly.

18. the manufacture method of the oxide superconducting wire rod described in claim 1 is characterized in that:

Control during intensification before the heat treatment in above-mentioned heat treated operation (S4, S6), so that the total pressure in the atmosphere increases with 0.05MPa/min or the speed more than the 0.05MPa/min.

19. the manufacture method of the oxide superconducting wire rod described in claim 18 is characterized in that:

Control during heat treatment in above-mentioned heat treated operation (S4, S6), so that the total pressure in the above-mentioned atmosphere increases constantly.

20. the manufacture method of the oxide superconducting wire rod described in claim 1 is characterized in that:

In the operation (S1, S2) of making above-mentioned wire rod afterwards and before in above-mentioned heat treated operation (S4, S6), also have the operation (S3) that above-mentioned wire rod is rolled, the reduction ratio of the above-mentioned wire rod (1) in the operation of above-mentioned calendering (S3) is below 84% or 84%.

21. the manufacture method of the oxide superconducting wire rod described in claim 20 is characterized in that:

The reduction ratio of the above-mentioned wire rod (1) in the operation of above-mentioned calendering (S3) is below 80% or 80%.

22. the manufacture method of the oxide superconducting wire rod described in claim 1 is characterized in that:

Above-mentioned wire rod is carried out repeatedly heat treatment (S4, S6), be 1MPa or carry out at least 1 heat treatment in the above-mentioned repeatedly heat treatment (S4, S6) more than the 1MPa to the pressurization atmosphere less than 50MPa in total pressure.

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