A method for preparing Bi2212 superconducting wire / magnet by low-pressure melting recrystallization heat treatment

Abstract

The present invention discloses a method for preparing Bi2212 superconducting wire / magnet by low-pressure melting recrystallization heat treatment, the method comprising: 1. putting Bi2212 precursor powder into an Ag sheath for heating and vacuum degassing; 2. bunching and drawing to obtain multi-core Bi2212 wire; 3. pre-high-pressure heat treatment of the multi-core Bi2212 wire; 4. low-pressure melting recrystallization heat treatment of the Bi2212 wire or winding it into a magnet. The present invention first uses heating and vacuum removal to reduce the air pressure in the wire, and then compresses the wire by pre-high-pressure heat treatment to make it close to the theoretical density, so that low-pressure melting recrystallization heat treatment can be performed at a conventional pressure of 1 / 5 to 1 / 10, which greatly reduces the difficulty of high-pressure heat treatment, improves the current-carrying performance of Bi2212 superconducting wire or Bi2212 superconducting magnet, reduces the research and development threshold, and is conducive to the application of Bi2212 superconducting wire in fusion magnets.

Description

Technical Field

[0001] The invention belongs to the technical field of high-temperature superconducting wires and strips, and in particular relates to a method for preparing Bi2212 superconducting wires / magnets by low-pressure melting and recrystallization heat treatment. Background Art

[0002] Since Bi2212 superconducting wire is the only high-temperature superconducting material that can be prepared into round wire and has high current-carrying performance, it will become one of the preferred materials for large-scale ultra-strong magnetic field magnets such as future fusion.

[0003] Usually, Bi2212 superconducting wires are prepared by powder tube loading, that is, the precursor ceramic oxide powder is loaded into a silver tube to form a single-core composite, and then single-core wire drawing, multi-core wire bundle drawing and heat treatment are performed to form high-performance Bi2212 superconducting wires. In order to achieve the high texture of Bi2212 superconducting wires, Bi2212 superconducting wires are melted at a high temperature of 880℃~900℃, and Bi2212 superconducting wires with molten texture are obtained in the subsequent cooling process. In addition, during the micron-scale powder tube loading process, a large amount of gas in the powder gap and on the powder surface is loaded and sealed in the Ag sheath together with the powder. These gases expand during the heat treatment, resulting in a large number of pores inside the wire, which seriously affects the connectivity between superconducting grains and leads to a significant decrease in wire performance. Therefore, at present, Bi2212 superconducting wires and Bi2212 superconducting magnets are both subjected to 50atm~100atm high-pressure partial melting recrystallization heat treatment.

[0004] The high-pressure partial melting recrystallization heat treatment of Bi2212 superconducting wire and superconducting magnet has the following two disadvantages:

[0005] (1) The gas pressure of 50atm to 100atm greatly increases the difficulty of heat treatment of large Bi2212 superconducting magnets, and even makes the sintering of large magnets almost impossible. The largest application market for Bi2212 superconducting magnets will be magnetic confinement nuclear fusion test devices and even commercial magnetic confinement nuclear fusion power generation devices. However, the diameter of fusion Bi2212 superconducting magnets reaches 3 to 5 meters. At present, Bi2212 superconducting magnets can only be made by winding wires into magnets and then heat treating the magnets. To perform high-pressure heat treatment on fusion magnets, a large-caliber high-pressure heat treatment furnace is required. According to calculations by professionals, no company can currently produce a high-pressure heat treatment furnace that meets 100atm, 5m diameter and 900℃. According to the current largest-caliber high-pressure furnace (the largest-caliber high-pressure furnace currently developed internationally has a diameter of 2m and costs hundreds of millions of RMB), the price of a high-pressure sintering furnace for fusion Bi2212 superconducting magnets will increase several times. This will become the biggest obstacle to the application of Bi2212 superconducting wire fusion devices.

[0006] (2) The gas pressure of 50atm to 100atm limits the research and development of Bi2212 superconducting wires and Bi2212 superconducting magnets. To carry out the research and development of Bi2212 superconducting wires or Bi2212 superconducting magnets, a 100atm high-pressure furnace is required. The high pressure of 100atm places high demands on the supporting materials of the furnace cavity, greatly increases the laboratory research and development costs, and increases the risk of the experiment. These reasons have prevented many laboratories from carrying out the research and development of Bi2212 superconducting wires and superconducting magnets, thus restricting the research and development progress of Bi2212 superconducting wires and superconducting magnets. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a method for preparing Bi2212 superconducting wire / magnet by low-pressure melting recrystallization heat treatment in view of the deficiencies of the above-mentioned prior art. The method first uses heating vacuum removal to reduce the air pressure in the wire, and then compresses the wire through pre-high-pressure heat treatment to make it close to the theoretical density, so that low-pressure melting recrystallization heat treatment can be performed at a pressure of 1 / 5 to 1 / 10 of the conventional pressure, which greatly reduces the difficulty of high-pressure heat treatment, improves the current-carrying performance of Bi2212 superconducting wire or Bi2212 superconducting magnet, and is conducive to the application of Bi2212 superconducting wire in fusion magnets.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing Bi2212 superconducting wire / magnet by low-pressure melting recrystallization heat treatment, characterized in that the method comprises the following steps:

[0009] Step 1: Heating and vacuum degassing of Bi2212 precursor powder: The Bi2212 precursor powder is loaded into the Ag sheath by the vibration method, and then the inside of the Ag sheath is vacuum degassed through the powder loading port, and the Ag sheath is heated to 400°C to 500°C, and then the exhaust port is sealed by in-situ welding, so that the Bi2212 precursor powder in the Ag sheath is in a vacuum state, and a single-core Bi2212 composite is obtained;

[0010] Step 2: Processing of Bi2212 wires: Bundle drawing of the single-core Bi2212 composite obtained in step 1 to obtain multi-core Bi2212 wires;

[0011] Step 3: Pre-high pressure heat treatment of Bi2212 wire: The multi-core Bi2212 wire obtained in step 2 is pre-high pressure heat treated at a pressure of more than 250 atm and a temperature of 800° C. to 870° C. to obtain a pre-treated Bi2212 wire;

[0012] Step 4. Low-pressure melting recrystallization heat treatment of Bi2212 wire or magnet: Wind the pretreated Bi2212 wire obtained in step 3 into a Bi2212 magnet, and then heat the pretreated Bi2212 wire or Bi2212 magnet to 885℃~900℃ under a constant gas pressure of 10atm~11atm until the Bi2212 precursor powder in the core wire melts, and then cool down to 830℃~850℃ at a rate of 2℃ / min~5℃ / min and keep warm for 10h~24h, and obtain Bi2212 superconducting wire or Bi2212 superconducting magnet after cooling to room temperature.

[0013] The present invention firstly heats and vacuum degasses the Bi2212 precursor powder after loading it into a tube, so as to fully desorb the gas on the surface of the Bi2212 precursor powder, and seals and welds the exhaust port to obtain a single-core Bi2212 complex with a low impurity gas content, and then obtains a multi-core Bi2212 wire by bundle drawing. Since the core wire density in the multi-core Bi2212 wire is only 70% to 80%, there are a large number of gaps between the Bi2212 precursor powders in the core wire, resulting in poor connectivity between the final superconducting grains, which affects the current-carrying performance of the Bi2212 superconducting wire. Therefore, the prior art needs to use a pressure P out Overcome the support of the wire's sheath material and precursor powder to compress the gas inside the wire, i.e. P out ≥P in +σ Ag +σ core , where σ Ag is the yield strength of the sheath material, σ core is the yield strength of the precursor powder, P in is the internal air pressure, usually P out A pressure of 50 atm to 100 atm is required to overcome the sheath material, precursor powder and internal air pressure, compress the wire to the theoretical density, and perform partial melting recrystallization heat treatment under pressure holding. The high pressure and high temperature conditions greatly increase the difficulty of heat treatment. Based on this, the present invention first performs a pre-high pressure heat treatment on the multi-core Bi2212 wire, compresses it to a near theoretical density, and then performs a low pressure melting recrystallization heat treatment on it or after winding it into a magnet. In this process, it is only necessary to avoid the expansion of the Bi2212 wire, that is, to meet P' out ≥P in -σ Ag -σ core The pressure used is the external air pressure P' out It only needs to be greater than the difference between the internal pressure and the yield strength of the sheath material and the yield strength of the precursor powder. The minimum external pressure difference (P out -P' out ) reaches 2(σ Ag +σcore ), therefore, in the low-pressure melting recrystallization heat treatment process of the present invention, a pressure of only 1 / 5 to 1 / 10 times the conventional pressure in the prior art, i.e., 10atm to 11atm, is used to achieve the melting recrystallization treatment of the Bi2212 wire or Bi2212 magnet, thereby improving the connectivity between the superconducting grains, thereby improving the current-carrying performance of the Bi2212 superconducting wire or Bi2212 superconducting magnet, greatly reducing the difficulty of high-pressure heat treatment of the Bi2212 superconducting wire or Bi2212 superconducting magnet, and facilitating the application of the Bi2212 superconducting wire in fusion magnets.

[0014] The above-mentioned method for preparing Bi2212 superconducting wire / magnet by low-pressure melting recrystallization heat treatment is characterized in that the vacuum degree of vacuum degassing in step 1 does not exceed 10 -3 Pa. The present invention reduces the internal gas pressure of the single-core Bi2212 complex by vacuum degassing the interior of the Ag sheath and controlling the vacuum degree, which is conducive to realizing low-pressure melting recrystallization heat treatment at a lower pressure.

[0015] The above-mentioned method for preparing Bi2212 superconducting wire / magnet by low-pressure melting recrystallization heat treatment is characterized in that the number of cores of the multi-core Bi2212 wire in step 2 is 342 to 1530, and the diameter of the multi-core Bi2212 wire is 0.8 mm to 1.4 mm. The pre-high-pressure heat treatment effect of the multi-core Bi2212 wire with the preferred number of cores and diameter is better, and the pressure used is smaller, which effectively ensures the improvement of the current carrying performance of the Bi2212 superconducting wire or Bi2212 superconducting magnet.

[0016] The above-mentioned method for preparing Bi2212 superconducting wire / magnet by low-pressure melting recrystallization heat treatment is characterized in that the holding time of the pre-high-pressure heat treatment in step 3 is more than 2 hours. By controlling the above-mentioned holding time, the multi-core Bi2212 is fully compressed and reduced in diameter under the action of pressure, which improves the effect of pre-high-pressure heat treatment, reduces the number of pores, improves the connectivity between superconducting grains, and avoids adverse effects on the current-carrying performance of Bi2212 superconducting wire or Bi2212 superconducting magnet.

[0017] The above-mentioned method for preparing Bi2212 superconducting wire / magnet by low-pressure melting recrystallization heat treatment is characterized in that the oxygen partial pressure in the gas in step 4 is 1 atm, and the remaining gas is argon. The gas composition not only promotes the melting of Bi2212 precursor powder in the core wire, but also facilitates the formation of Bi2212 superconducting phase, thereby improving the current carrying performance of Bi2212 superconducting wire or Bi2212 superconducting magnet.

[0018] The above-mentioned method for preparing a Bi2212 superconducting wire / magnet by low-pressure melting recrystallization heat treatment is characterized in that the superconducting transition temperature of the Bi2212 superconducting wire or Bi2212 superconducting magnet in step 4 is less than 80 K. The current carrying performance of the superconducting wire has a corresponding relationship with its superconducting transition temperature Tc, and the superconducting transition temperature of the Bi2212 superconducting wire or Bi2212 superconducting magnet of the present invention is less than 80 K, indicating that it has a higher current carrying performance.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. The present invention reduces the pressure of the low-pressure melting recrystallization heat treatment process to 1 / 5 to 1 / 10 of the conventional pressure by first subjecting the multi-core Bi2212 wire to a pre-high-pressure heat treatment to compress it to a near-theoretical density, and then subjecting it to a low-pressure melting recrystallization heat treatment after it is wound into a magnet. This greatly reduces the difficulty of high-pressure heat treatment, improves the current-carrying performance of the Bi2212 superconducting wire or the Bi2212 superconducting magnet, and is conducive to the application of the Bi2212 superconducting wire in fusion magnets.

[0021] 2. During the pre-high-pressure heat treatment process of the present invention, the core wire in the multi-core Bi2212 wire is in a powder state, and bending it will not affect the superconducting performance. Therefore, the pre-high-pressure heat treatment of the multi-core Bi2212 wire can be completed using the currently commonly used small-caliber high-pressure heat treatment equipment, which reduces the difficulty of the pre-high-pressure heat treatment and ensures the smooth implementation of the low-pressure melting recrystallization heat treatment.

[0022] 3. The pressure used in the low-pressure melting recrystallization heat treatment of the present invention is as low as 10atm-11atm, which facilitates R&D personnel to optimize the process of Bi2212 superconducting wire or Bi2212 superconducting magnet under safer conditions, lowers the research threshold, and the furnace of the corresponding low-pressure melting recrystallization heat treatment equipment can be prepared using conventional 316 or 304 stainless steel, reducing equipment costs.

[0023] 4. The present invention heats the interior of the Ag sheath containing the Bi2212 precursor powder for vacuum degassing and in-situ sealing, thereby reducing the internal pressure of the multi-core Bi2212 wire and facilitating low-pressure melting recrystallization heat treatment at a lower pressure.

[0024] 5. The preparation of the present invention is simple and the process design is reasonable. The low-pressure melting recrystallization heat treatment of Bi2212 wire or Bi2212 magnet, especially large magnet, can be achieved by using existing equipment. It is easy to implement and suitable for promotion.

[0025] 6. The wire preparation method of the present invention, which can perform partial melting heat treatment of large magnets under lower pressure, breaks through the barrier of high-pressure heat treatment of large Bi2212 magnets, while lowering the threshold of Bi2212 wire and magnets, and promoting the rapid development of Bi2212 wire technology and industry.

[0026] The technical solution of the present invention is further described in detail below through embodiments. DETAILED DESCRIPTION

[0027] Example 1

[0028] This embodiment includes the following steps:

[0029] Step 1: Heating and vacuum degassing of Bi2212 precursor powder: The Bi2212 precursor powder is loaded into the Ag package by a vibration method, and then the inside of the Ag package is vacuum degassed through the powder loading port, and the Ag package is heated to 400°C, and then the exhaust port is sealed by in-situ welding, so that the Bi2212 precursor powder in the Ag package is in a vacuum state, and a single-core Bi2212 composite is obtained; the vacuum degree of the vacuum degassing is 0.9×10 -3 Pa;

[0030] Step 2, processing of Bi2212 wire: the single-core Bi2212 composite obtained in step 1 is bundled and drawn to obtain a multi-core Bi2212 wire; the number of cores of the multi-core Bi2212 wire is 342, and the diameter of the multi-core Bi2212 wire is 0.8 mm;

[0031] Step 3: Pre-high pressure heat treatment of Bi2212 wire: The multi-core Bi2212 wire obtained in step 2 is pre-high pressure heat treated at a pressure of 250 atm and a temperature of 800° C. for 2 h to obtain a pre-treated Bi2212 wire;

[0032] Step 4. Low-pressure melting recrystallization heat treatment of Bi2212 wire: Heat the pretreated Bi2212 wire prepared in step 3 to 885°C under a constant gas pressure of 10atm and an oxygen partial pressure of 1atm until the Bi2212 precursor powder in the core wire melts, then cool down to 830°C at a rate of 2°C / min and keep warm for 10h, and obtain Bi2212 superconducting wire after cooling to room temperature.

[0033] After testing, the critical current density of the Bi2212 superconducting wire prepared in this embodiment is close to the critical current density of the Bi2212 superconducting wire prepared by the conventional method only by partial melting and recrystallization heat treatment at 100atm, both of which are close to 5000A / mm 2(4.2K, 5T), the superconducting transition temperature of Bi2212 superconducting wire is 79K, which means that the present invention adopts the process of pre-high pressure heat treatment and then low pressure melting recrystallization heat treatment, and can prepare high-density and high-current Bi2212 superconducting wire under the condition of 1 / 10 of the pressure of the conventional method, which greatly reduces the difficulty of melting recrystallization treatment.

[0034] Example 2

[0035] This embodiment includes the following steps:

[0036] Step 1: Heating and vacuum degassing of Bi2212 precursor powder: The Bi2212 precursor powder is loaded into the Ag package by a vibration method, and then the inside of the Ag package is vacuum degassed through the powder loading port, and the Ag package is heated to 450°C, and then the exhaust port is sealed by in-situ welding, so that the Bi2212 precursor powder in the Ag package is in a vacuum state, and a single-core Bi2212 composite is obtained; the vacuum degree of the vacuum degassing is 0.98×10 -3 Pa;

[0037] Step 2, processing of Bi2212 wire: the single-core Bi2212 composite obtained in step 1 is bundled and drawn to obtain a multi-core Bi2212 wire; the number of cores of the multi-core Bi2212 wire is 666, and the diameter of the multi-core Bi2212 wire is 1.0 mm;

[0038] Step 3: Pre-high pressure heat treatment of Bi2212 wire: The multi-core Bi2212 wire obtained in step 2 is pre-high pressure heat treated at a pressure of 255 atm and a temperature of 830° C. for 3 h to obtain a pre-treated Bi2212 wire;

[0039] Step 4. Low-pressure melting recrystallization heat treatment of Bi2212 wire: Heat the pretreated Bi2212 wire prepared in step 3 to 888°C under a constant gas pressure of 10atm and an oxygen partial pressure of 1atm until the Bi2212 precursor powder in the core wire melts, then cool down to 840°C at a rate of 2.5°C / min and keep warm for 18h, and obtain Bi2212 superconducting wire after cooling to room temperature.

[0040] After testing, the critical current density of the Bi2212 superconducting wire prepared in this embodiment is close to the critical current density of the Bi2212 superconducting wire prepared by the conventional method only by partial melting and recrystallization heat treatment at 100atm, both of which are close to 5000A / mm 2(4.2K, 5T), the superconducting transition temperature of Bi2212 superconducting wire is 79.5K, which means that the present invention adopts the process of pre-high pressure heat treatment and then low pressure melting recrystallization heat treatment, and can prepare high-density and high-current-carrying Bi2212 superconducting wire under the condition of 1 / 10 of the pressure of the conventional method, which greatly reduces the difficulty of melting recrystallization treatment.

[0041] Example 3

[0042] This embodiment includes the following steps:

[0043] Step 1: Heating and vacuum degassing of Bi2212 precursor powder: The Bi2212 precursor powder is loaded into the Ag package by a vibration method, and then the inside of the Ag package is vacuum degassed through the powder loading port, and the Ag package is heated to 500°C, and then the exhaust port is sealed by in-situ welding, so that the Bi2212 precursor powder in the Ag package is in a vacuum state, and a single-core Bi2212 composite is obtained; the vacuum degree of the vacuum degassing is 0.97×10 -3 Pa;

[0044] Step 2, processing of Bi2212 wire: the single-core Bi2212 composite obtained in step 1 is bundled and drawn to obtain a multi-core Bi2212 wire; the number of cores of the multi-core Bi2212 wire is 1530, and the diameter of the multi-core Bi2212 wire is 1.4 mm;

[0045] Step 3: Pre-high pressure heat treatment of Bi2212 wire: The multi-core Bi2212 wire obtained in step 2 is pre-high pressure heat treated at a pressure of 255 atm and a temperature of 870° C. for 2 h to obtain a pre-treated Bi2212 wire;

[0046] Step 4. Low-pressure melting recrystallization heat treatment of Bi2212 wire: The pretreated Bi2212 wire obtained in step 3 is wound into a Bi2212 magnet, and the Bi2212 magnet is heated to 900°C under a constant gas pressure of 10atm and an oxygen partial pressure of 1atm until the Bi2212 precursor powder in the core wire is melted, and then the temperature is reduced to 850°C at a rate of 5°C / min and kept at this temperature for 24h, and a Bi2212 superconducting magnet is obtained after it is cooled to room temperature.

[0047] After testing, the critical current density of the Bi2212 superconducting magnet prepared in this embodiment is similar to the critical current density of the Bi2212 superconducting magnet prepared by the conventional method only through partial melting recrystallization heat treatment at 100atm, and the superconducting transition temperature of the Bi2212 superconducting magnet is 79K, which means that the present invention adopts a process of pre-high-pressure heat treatment and then low-pressure melting recrystallization heat treatment, and can prepare a high-density and high-current Bi2212 superconducting magnet under 1 / 10 of the pressure of the conventional method, which greatly reduces the difficulty of the melting recrystallization treatment.

[0048] Example 4

[0049] This embodiment includes the following steps:

[0050] Step 1: Heating and vacuum degassing of Bi2212 precursor powder: The Bi2212 precursor powder is loaded into the Ag package by the vibration method, and then the inside of the Ag package is vacuum degassed through the powder loading port, and the Ag package is heated to 450°C, and then the exhaust port is sealed by in-situ welding, so that the Bi2212 precursor powder in the Ag package is in a vacuum state, and a single-core Bi2212 composite is obtained; the vacuum degree of the vacuum degassing is 10 -3 Pa;

[0051] Step 2, processing of Bi2212 wire: the single-core Bi2212 composite obtained in step 1 is bundled and drawn to obtain a multi-core Bi2212 wire; the number of cores of the multi-core Bi2212 wire is 1053, and the diameter of the multi-core Bi2212 wire is 1.2 mm;

[0052] Step 3: Pre-high pressure heat treatment of Bi2212 wire: The multi-core Bi2212 wire obtained in step 2 is pre-high pressure heat treated at a pressure of 255 atm and a temperature of 845° C. for 3 h to obtain a pre-treated Bi2212 wire;

[0053] Step 4. Low-pressure melting recrystallization heat treatment of Bi2212 wire: Heat the pretreated Bi2212 wire prepared in step 3 to 888°C under a constant gas pressure of 11atm and an oxygen partial pressure of 1atm until the Bi2212 precursor powder in the core wire melts, then cool down to 840°C at a rate of 2.5°C / min and keep warm for 24h, and obtain Bi2212 superconducting wire after cooling to room temperature.

[0054] After testing, the critical current density of the Bi2212 superconducting wire prepared in this embodiment is close to the critical current density of the Bi2212 superconducting wire prepared by the conventional method only by partial melting and recrystallization heat treatment at 100atm, both of which are close to 5000A / mm 2(4.2K, 5T), the superconducting transition temperature of Bi2212 superconducting wire is 79.8K, which means that the present invention adopts the process of pre-high pressure heat treatment and then low pressure melting recrystallization heat treatment, and can prepare high-density and high-current-carrying Bi2212 superconducting wire under the condition of 1 / 10 of the pressure of the conventional method, which greatly reduces the difficulty of melting recrystallization treatment.

[0055] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing Bi2212 superconducting wire / magnet by low-pressure melting recrystallization heat treatment, characterized in that: The method comprises the following steps: Step 1: Heating and vacuum degassing of Bi2212 precursor powder: The Bi2212 precursor powder is loaded into the Ag sheath by the vibration method, and then the inside of the Ag sheath is vacuum degassed through the powder loading port, and the Ag sheath is heated to 400°C to 500°C, and then the exhaust port is sealed by in-situ welding, so that the Bi2212 precursor powder in the Ag sheath is in a vacuum state, and a single-core Bi2212 composite is obtained; Step 2: Processing of Bi2212 wires: Bundle drawing of the single-core Bi2212 composite obtained in step 1 to obtain multi-core Bi2212 wires; Step 3: Pre-high pressure heat treatment of Bi2212 wire: The multi-core Bi2212 wire obtained in step 2 is pre-high pressure heat treated at a pressure of more than 250 atm and a temperature of 800° C. to 870° C. to obtain a pre-treated Bi2212 wire; Step 4. Low-pressure melting recrystallization heat treatment of Bi2212 wire or magnet: Wind the pretreated Bi2212 wire obtained in step 3 into a Bi2212 magnet, and then heat the pretreated Bi2212 wire or Bi2212 magnet to 885℃~900℃ under a constant gas pressure of 10atm~11atm until the Bi2212 precursor powder in the core wire melts, and then cool down to 830℃~850℃ at a rate of 2℃ / min~5℃ / min and keep warm for 10h~24h, and obtain Bi2212 superconducting wire or Bi2212 superconducting magnet after cooling to room temperature.

2. The method for preparing Bi2212 superconducting wire / magnet by low pressure melting recrystallization heat treatment according to claim 1, characterized in that: The vacuum degree of the vacuum degassing in step 1 does not exceed 10 -3 Pa.

3. The method for preparing Bi2212 superconducting wire / magnet by low pressure melting recrystallization heat treatment according to claim 1, characterized in that: The number of cores of the multi-core Bi2212 wire in step 2 is 342 to 1530, and the diameter of the multi-core Bi2212 wire is 0.8 mm to 1.4 mm.

4. The method for preparing Bi2212 superconducting wire / magnet by low pressure melting recrystallization heat treatment according to claim 1, characterized in that: The holding time of the pre-high pressure heat treatment in step 3 is more than 2 hours.

5. The method for preparing Bi2212 superconducting wire / magnet by low pressure melting recrystallization heat treatment according to claim 1, characterized in that: The oxygen partial pressure in the gas in step 4 is 1 atm, and the remaining gas is argon.

6. The method for preparing Bi2212 superconducting wire / magnet by low pressure melting recrystallization heat treatment according to claim 1, characterized in that: The superconducting transition temperature of the Bi2212 superconducting wire or Bi2212 superconducting magnet described in step 4 is less than 80K.