CN115188578A - Grain boundary diffusion method for improving magnetic property of neodymium iron boron magnetic steel - Google Patents
Grain boundary diffusion method for improving magnetic property of neodymium iron boron magnetic steel Download PDFInfo
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- H—ELECTRICITY
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- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
- H01F41/0293—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
- C21D1/773—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material under reduced pressure or vacuum
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
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- H01F1/053—Alloys characterised by their composition containing rare earth metals
- H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
- H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
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Abstract
The invention belongs to the field of permanent magnet materials, and discloses a grain boundary diffusion method for improving the magnetic property of neodymium iron boron magnetic steel. The method of the invention comprises the following steps: melting the rare earth metal raw material, casting the melted raw material into a mold, and cooling to obtain a rare earth metal plate; and placing the neodymium iron boron magnetic steel on the rare earth metal plate, and performing high-temperature heat treatment and tempering treatment to obtain the neodymium iron boron magnetic steel containing rare earth metal. According to the invention, the rare earth metal diffusion source is prepared in a rare earth metal plate mode, the crystal boundary diffusion process is improved, the process flow is shortened, the production efficiency is improved, the magnetic property of the neodymium iron boron magnetic steel can be obviously improved, the rare earth metal resource is saved, and the production cost is further reduced.
Description
Technical Field
The invention belongs to the field of permanent magnet materials, and particularly relates to a grain boundary diffusion method for improving the magnetic property of neodymium iron boron magnetic steel.
Background
Since the advent of the rare earth permanent magnet material, especially neodymium iron boron rare earth permanent magnet material, it has been widely used in the fields of new energy automobiles, white home appliances, wind power generation, elevator traction machines, etc. because of its excellent magnetic properties. Along with the increase of high-quality requirements of downstream terminal product performance in the permanent magnet industry, the performance requirements on the neodymium iron boron are also continuously improved. In order to improve the magnetic performance of the neodymium iron boron, heavy rare earth Tb or Dy is generally required to be added, the Tb and Dy are scarce in resources and expensive in price, and the addition can greatly improve the production cost of the magnetic steel. Therefore, the magnetic steel performance is improved by adopting a grain boundary diffusion process in the industry, specifically, tb and Dy are made into powder, the powder and resin colloid are uniformly stirred and then uniformly coated on the surface of the magnetic steel, and the Tb and Dy powder are melted and permeate into the magnetic steel along the grain boundary of the magnetic steel through heat treatment, so that the purpose of improving the magnetic steel performance is achieved. For example, patent document CN 109887696A discloses a preparation method of an organic slurry coated on a neodymium iron boron magnet and a high-coercivity neodymium iron boron magnet, in the preparation method, heavy rare earth powder and thermoplastic resin are uniformly stirred, then glue solution is uniformly coated on the surface of magnetic steel, and the neodymium iron boron magnetic steel with improved performance is obtained after heat treatment. Patent document CN 113096910A discloses a sheet magnet with gradient performance and a preparation method thereof, wherein a mixture (including heavy rare earth substances and a solvent) is coated on the surface of the sheet substrate and then heat treatment is performed to obtain the sheet magnet with gradient performance.
However, the process has the following disadvantages: (1) The method needs to use high-molecular glue or solvent and remove the high-molecular glue or solvent in the heat treatment process, on one hand, harmful waste gas is generated to the environment, and meanwhile, the glue or solvent is deposited in a mechanical pump in the vacuum pumping process to cause the blockage and damage of the mechanical pump; on the other hand, in the heat treatment process, the products are close together, so that the products are easily bonded together to cause product scrap; (2) During mass production, the glue solution or mixture containing rare earth metal is loaded on the surface of the magnetic steel in a coating mode, so that the problem of large final performance fluctuation of the product caused by uneven loading exists; the coating process has long flow and low production efficiency, and part of the coating process can only aim at the planar magnetic steel and cannot be applied to arc-shaped and tile-shaped products; (3) Tb and Dy need to be prepared into powder, complex processes such as hydrogen crushing, grinding, sieving and the like are needed, and the powder has high activity, is easy to catch fire and has potential safety hazards.
Disclosure of Invention
Aiming at the problems of polluting waste gas, large magnetic steel performance fluctuation, low production efficiency and the like in the production related to the prior art, the invention provides a grain boundary diffusion method for improving the magnetic performance of the neodymium iron boron magnetic steel.
A grain boundary diffusion method for improving the magnetic property of NdFeB magnetic steel comprises the following steps: melting the rare earth metal raw material, casting the melted raw material into a mold, and cooling to obtain a rare earth metal plate; and placing the neodymium iron boron magnetic steel on the rare earth metal plate, and performing high-temperature heat treatment and tempering treatment to obtain the neodymium iron boron magnetic steel containing rare earth metal.
According to the invention, rare earth metal raw materials are made into plates, a diffusion source of the rare earth metal plate is formed, and then grain boundary diffusion of the neodymium iron boron magnetic steel is carried out, so that the traditional loading mode after mixing rare earth metal powder and high polymer adhesive is replaced, the waste gas pollution in production is avoided, the production environment is improved, and the problems of product adhesion, diffusion pump blockage and the like in grain boundary diffusion are solved; meanwhile, the production flow is simplified, and the production efficiency is improved; the rare earth metal is melted and diffused into the magnetic steel in the high-temperature heat treatment process, so that the purpose of improving the performance of the magnetic steel is achieved. In addition, the rare earth metal content required to be diffused is less by the rare earth metal plate mode, the rare earth metal resource is saved, and the degree of improving the performance of the magnetic steel is higher.
In a preferred embodiment of the present invention, the rare earth metal raw material includes at least one of elemental terbium, elemental dysprosium, a terbium-containing alloy, and a dysprosium-containing alloy.
Tb or Dy or alloy thereof is melted and cast in a special mould, and then cooled to obtain the thin plate. Place low performance magnet steel and sheet metal in turn in the graphite box to put into the vacuum diffusion furnace with the graphite box, through thermal treatment back, tb or Dy steam is waved out to the sheet metal, and along the magnet steel grain boundary, inside the diffusion gets into the magnet steel, thereby reaches the purpose that promotes magnet steel magnetic property. Meanwhile, after the heat treatment is finished, the Tb or Dy thin plate can be used for next production, is recycled, and is convenient and efficient.
In a preferred embodiment of the present invention, the heat treatment temperature is 700 to 1000 ℃ and the holding time is 8 to 24 hours.
In a preferred embodiment of the present invention, the heat treatment temperature is 700 to 920 ℃ and the holding time is 8 to 24 hours.
In a further preferred embodiment of the present invention, the heat treatment temperature is 900 ℃ and the holding time is 12 hours.
Under the heat treatment condition, the rare earth metal is diffused into the magnetic steel, so that the effect of improving the performance of the magnetic steel is better.
In a preferred embodiment of the present invention, the tempering treatment is performed at a temperature of 400 to 600 ℃ for 4 to 8 hours.
In a preferred embodiment of the present invention, the tempering temperature is 420 to 520 ℃ and the tempering time is 4 to 8 hours.
In a further preferred embodiment of the present invention, the tempering temperature is 505 ℃ and the tempering time is 6 hours.
Under the tempering condition, the rare earth metal infiltrated into the magnetic steel is more uniform, so that the performance of the magnetic steel is better.
In a preferred embodiment of the present invention, the thickness of the rare earth metal plate is 1 to 10mm.
In a more preferred embodiment of the present invention, the thickness of the rare earth metal plate is 3 to 5mm.
In a preferred embodiment of the present invention, the thickness of the ndfeb magnetic steel is 2 to 5mm.
As a preferred embodiment of the present invention, the heat treatment and the tempering treatment are also performed under a vacuum condition in which the effect of the oxidation of the rare earth metal on the infiltration and diffusion effects is avoided.
Compared with the prior art, the invention has the following beneficial effects:
(1) The rare earth metal diffusion source is prepared by preparing the rare earth metal plate, so that the crystal boundary diffusion process is improved, the process flow is shortened, the problem of product adhesion in crystal boundary diffusion is solved, and the production efficiency is improved.
(2) The invention uses the rare earth metal plate as a rare earth metal diffusion source, does not generate powder metal, is relatively safe, does not need to be mixed with glue, does not generate the problems of waste gas pollution or blockage of a glue pump caused by diffusion and the like, and is environment-friendly.
(3) The invention uses the rare earth metal plate as the rare earth metal diffusion source, not only can obviously improve the magnetic property of the magnetic steel, but also can reduce the input amount of the rare earth metal, saves the rare earth metal resource, reduces the production cost, and lays a foundation for further production and popularization.
Drawings
The schematic view is placed to 1 ~ 7 heavy rare earth metal sheet metal and neodymium iron boron magnetic steel of the embodiment of fig. 1, and on the heavy rare earth metal sheet metal was placed in to the magnet steel, magnet steel and heavy rare earth metal sheet metal placed in turn simultaneously, all had heavy rare earth infiltration on the two sides of magnet steel, can improve product magnetic property homogeneity, increased the tray in the middle of magnet steel and the sheet metal, the purpose is the operation of being convenient for.
Detailed Description
To better illustrate the objects, technical solutions and advantages of the present invention, the present invention will be further illustrated by specific comparative examples and examples.
Example 1
Taking rare earth raw material terbium (Tb purity is more than or equal to 99.5%, melting temperature is generally 1450-1500 ℃), after melting, casting the molten material terbium into a mold with the thickness of 100-30-3mm, cooling, and taking out the terbium plate to obtain the terbium plate with the thickness of 3mm. In addition, the low-performance neodymium iron boron magnetic steel is prepared by a powder metallurgy method, the method is consistent with the traditional method for preparing the neodymium iron boron magnetic steel, namely the low-performance neodymium iron boron magnetic steel is prepared by smelting, hydrogen crushing, airflow grinding, profiling, isostatic pressing and sintering, the low-performance neodymium iron boron magnetic steel is machined into a semi-finished product magnetic steel with the specification of grain boundary diffusion, the magnetic performance of the semi-finished product magnetic steel is 45H (Br: 13.2kGs, hcj.
Placing the terbium plate into a graphite box, placing the semi-finished magnetic steels on a tray at an interval of 5mm, and then placing the terbium plate on the terbium plate to enable the terbium plate to be in contact with the semi-finished magnetic steels; another terbium plate is covered on the semi-finished magnetic steel, and meanwhile, the semi-finished magnetic steel is continuously stacked on the terbium plate, and 3 layers of magnetic steel are repeatedly and alternately placed in the mode. And (3) putting the graphite box filled with the terbium plate and the semi-finished magnetic steel into a vacuum sintering furnace, heating to raise the temperature for carrying out high-temperature heat treatment, wherein the temperature for the high-temperature heat treatment is 900 ℃, the heat preservation time is 12h, cooling to the normal temperature after the high-temperature heat treatment is finished, carrying out tempering treatment, wherein the temperature for the tempering treatment is 505 ℃, the heat preservation time is 6h, cooling to the room temperature after the tempering treatment is finished, and discharging to obtain the terbium-containing neodymium-iron-boron magnetic steel. The performance of the terbium-containing neodymium-iron-boron magnetic steel is tested by adopting an NIM62000 magnetic tester, and the terbium content of the magnetic steel is tested by adopting an ICP-MS (inductively coupled plasma-mass spectrometry), and the performance and the terbium content are summarized in a table 1. And collecting the terbium plate after the heat treatment, and using the collected terbium plate for next production.
Example 2
Taking rare earth raw material dysprosium (Dy purity is more than or equal to 99.5 percent, melting temperature is generally 1450-1500 ℃), casting the dysprosium into a mold with the thickness of 100-30-3mm after melting, and taking the dysprosium plate out after cooling to prepare the dysprosium plate with the thickness of 3mm. In addition, the low-performance neodymium iron boron magnetic steel is prepared by a powder metallurgy method, the method is consistent with the traditional method for preparing the neodymium iron boron magnetic steel, namely the low-performance neodymium iron boron magnetic steel is prepared by smelting, hydrogen crushing, airflow grinding, profiling, isostatic pressing and sintering, the low-performance neodymium iron boron magnetic steel is machined into a semi-finished product magnetic steel with the specification of grain boundary diffusion, the magnetic performance of the semi-finished product magnetic steel is 45H (Br: 13.2kGs, hcj.
Putting the dysprosium plates into a graphite box, arranging the semi-finished magnetic steels on a tray at an interval of 5mm, and then placing the dysprosium plates on the dysprosium plates to enable the dysprosium plates to be in contact with the semi-finished magnetic steels; and covering another dysprosium plate on the semi-finished magnetic steel, and continuously stacking the semi-finished magnetic steel on the dysprosium plate, and repeatedly and alternately placing 3 layers of magnetic steel in such a way. And (3) placing the graphite box filled with the dysprosium plate and the semi-finished magnetic steel into a vacuum sintering furnace, heating to raise the temperature for carrying out high-temperature heat treatment at 900 ℃ for 12h, cooling to normal temperature after finishing the high-temperature heat treatment, then carrying out tempering treatment at 505 ℃ for 6h, cooling to room temperature after finishing the tempering treatment, and discharging to obtain the Dy-Nd-containing Fe-B magnetic steel. The performance of the steel containing dysprosium-neodymium-iron-boron magnetic steel and the content of the dysprosium magnetic steel in the ICP-MS test are tested by an NIM62000 magnetic tester, and the results are summarized in Table 1. Collecting the dysprosium plate after heat treatment and using the collected dysprosium plate for next production.
Example 3
Taking a rare earth raw material terbium (the purity of Tb is more than or equal to 99.5 percent, and the melting temperature is generally 1450-1500 ℃), melting, casting into a mold of 100-30-5mm, cooling, and taking out the terbium plate to prepare the terbium plate with the thickness of 5mm. In addition, the low-performance neodymium iron boron magnetic steel is prepared by a powder metallurgy method, the method is consistent with the traditional method for preparing the neodymium iron boron magnetic steel, namely the low-performance neodymium iron boron magnetic steel is prepared by smelting, hydrogen crushing, airflow grinding, profiling, isostatic pressing and sintering, the low-performance neodymium iron boron magnetic steel is machined into a semi-finished product magnetic steel with the specification of grain boundary diffusion, the magnetic performance of the semi-finished product magnetic steel is 45H (Br: 13.2kGs, hcj.
Placing the terbium plate into a graphite box, placing the semi-finished magnetic steels on a tray at an interval of 5mm, and then placing the terbium plate on the terbium plate to enable the terbium plate to be in contact with the semi-finished magnetic steels; and covering the other terbium plate on the semi-finished magnetic steel, and continuously stacking the semi-finished magnetic steel on the thin plate, and repeatedly and alternately placing 3 layers of magnetic steel in the mode. And (3) placing the graphite box filled with the terbium plate and the semi-finished magnetic steel into a vacuum sintering furnace, heating to raise the temperature for carrying out high-temperature heat treatment at 900 ℃ for 12h, cooling to normal temperature after finishing, carrying out tempering treatment at 505 ℃ for 6h, cooling to room temperature after finishing, and discharging to obtain the terbium-containing neodymium-iron-boron magnetic steel. The performance of the terbium-containing neodymium iron boron magnetic steel is tested by an NIM62000 magnetic tester, and the terbium content of the magnetic steel is tested by ICP-MS, and the performance and the terbium content are summarized in a table 1. And collecting the terbium plate after the heat treatment is finished, and using the collected terbium plate for next production.
Example 4
The terbium plate with the thickness of 3mm improves the magnetic performance of the magnetic steel with the thickness of 5mm.
Taking rare earth raw material terbium (Tb purity is more than or equal to 99.5%, melting temperature is generally 1450-1500 ℃), after melting, casting the molten material terbium into a mold with the thickness of 100-30-3mm, cooling, and taking out the terbium plate to obtain the terbium plate with the thickness of 3mm. In addition, the low-performance neodymium iron boron magnetic steel is prepared by a powder metallurgy method, the method is consistent with the traditional method for preparing the neodymium iron boron magnetic steel, namely the low-performance neodymium iron boron magnetic steel is prepared by smelting, hydrogen crushing, airflow grinding, profiling, isostatic pressing and sintering, the low-performance neodymium iron boron magnetic steel is machined into a semi-finished product magnetic steel with the specification of grain boundary diffusion, the magnetic performance of the semi-finished product magnetic steel is 45H (Br: 13.2kGs, hcj.
Placing terbium plates into a graphite box, placing the semi-finished magnetic steels on a tray at an interval of 5mm, and then placing the terbium plates on the terbium plates so that the terbium plates are in contact with the semi-finished magnetic steels; and covering the other terbium plate on the semi-finished magnetic steel, and continuously stacking the semi-finished magnetic steel on the thin plate, and repeatedly and alternately placing 3 layers of magnetic steel in the mode. And (3) putting the graphite box filled with the terbium plate and the semi-finished magnetic steel into a vacuum sintering furnace, heating to raise the temperature for carrying out high-temperature heat treatment at 900 ℃, keeping the temperature for 12h, cooling to normal temperature after finishing, then carrying out tempering treatment at 505 ℃, keeping the temperature for 6h, cooling to room temperature after finishing, and discharging to obtain the terbium-containing neodymium-iron-boron magnetic steel. And collecting the terbium plate after the heat treatment is finished, and using the collected terbium plate for next production.
Example 5
Taking a rare earth raw material terbium (the purity of Tb is more than or equal to 99.5 percent, and the melting temperature is generally 1450-1500 ℃), melting, casting into a mold of 100-30-3mm, cooling, and taking out the terbium plate to prepare the terbium plate with the thickness of 3mm. In addition, the low-performance neodymium iron boron magnetic steel is prepared by a powder metallurgy method, the method is consistent with the traditional method for preparing the neodymium iron boron magnetic steel, namely the low-performance neodymium iron boron magnetic steel is prepared by smelting, hydrogen crushing, airflow grinding, profiling, isostatic pressing and sintering, the low-performance neodymium iron boron magnetic steel is machined into a semi-finished product magnetic steel with the specification of grain boundary diffusion, the magnetic performance of the semi-finished product magnetic steel is 45H (Br: 13.2kGs, hcj.
Placing terbium plates into a graphite box, placing the semi-finished magnetic steels on a tray at an interval of 5mm, and then placing the terbium plates on the terbium plates so that the terbium plates are in contact with the semi-finished magnetic steels; and covering the other terbium plate on the semi-finished magnetic steel, and continuously stacking the semi-finished magnetic steel on the thin plate, and repeatedly and alternately placing 3 layers of magnetic steel in the mode. And (3) placing the graphite box filled with the terbium plate and the semi-finished magnetic steel into a vacuum sintering furnace, heating to raise the temperature for carrying out high-temperature heat treatment at 920 ℃ for 24 hours, cooling to normal temperature after finishing, carrying out tempering treatment at 505 ℃ for 6 hours, cooling to room temperature after finishing, and discharging to obtain the terbium-containing neodymium-iron-boron magnetic steel.
And collecting the terbium plate after the heat treatment, and using the collected terbium plate for next production.
Example 6
Taking a rare earth raw material terbium (the purity of Tb is more than or equal to 99.5 percent, and the melting temperature is generally 1450-1500 ℃), melting, casting into a mold of 100-30-3mm, cooling, and taking out the terbium plate to prepare the terbium plate with the thickness of 3mm. In addition, the low-performance neodymium iron boron magnetic steel is prepared by a powder metallurgy method, the method is consistent with the traditional method for preparing the neodymium iron boron magnetic steel, namely the low-performance neodymium iron boron magnetic steel is prepared by smelting, hydrogen crushing, jet milling, profiling, isostatic pressing and sintering, the low-performance neodymium iron boron magnetic steel is machined into a semi-finished product magnetic steel with the specification of grain boundary diffusion, the magnetic performance of the semi-finished product magnetic steel is 45H (Br: 13.2kGs, hcj.
Placing terbium plates into a graphite box, placing the semi-finished magnetic steels on a tray at an interval of 5mm, and then placing the terbium plates on the terbium plates so that the terbium plates are in contact with the semi-finished magnetic steels; and covering the other terbium plate on the semi-finished magnetic steel, and continuously stacking the semi-finished magnetic steel on the thin plate, and repeatedly and alternately placing 3 layers of magnetic steel in the mode. And (3) putting the graphite box filled with the terbium plate and the semi-finished magnetic steel into a vacuum sintering furnace, heating to raise the temperature for high-temperature heat treatment, keeping the temperature for 8h, cooling to the normal temperature after finishing, then tempering, keeping the temperature for 4h, cooling to the room temperature after finishing, and discharging to obtain the terbium-containing neodymium-iron-boron magnetic steel.
And collecting the terbium plate after the heat treatment, and using the collected terbium plate for next production.
Example 7
Taking a rare earth raw material terbium (the purity of Tb is more than or equal to 99.5 percent, and the melting temperature is generally 1450-1500 ℃), melting, casting into a mold of 100-30-3mm, cooling, and taking out the terbium plate to prepare the terbium plate with the thickness of 3mm. In addition, the low-performance neodymium iron boron magnetic steel is prepared by a powder metallurgy method, the method is consistent with the traditional method for preparing the neodymium iron boron magnetic steel, namely the low-performance neodymium iron boron magnetic steel is prepared by smelting, hydrogen crushing, jet milling, profiling, isostatic pressing and sintering, the low-performance neodymium iron boron magnetic steel is machined into a semi-finished product magnetic steel with the specification of grain boundary diffusion, the magnetic performance of the semi-finished product magnetic steel is 45H (Br: 13.2kGs, hcj.
Placing the terbium plate into a graphite box, placing the semi-finished magnetic steels on a tray at an interval of 5mm, and then placing the terbium plate on the terbium plate to enable the terbium plate to be in contact with the semi-finished magnetic steels; another terbium plate is covered on the semi-finished magnetic steel, and meanwhile, the semi-finished magnetic steel is continuously stacked on the thin plate, and 3 layers of magnetic steel are repeatedly and alternately placed in the mode. And (3) putting the graphite box filled with the terbium plate and the semi-finished magnetic steel into a vacuum sintering furnace, heating to raise the temperature for carrying out high-temperature heat treatment, wherein the temperature for the high-temperature heat treatment is 900 ℃, the heat preservation time is 12h, cooling to the normal temperature after the high-temperature heat treatment is finished, carrying out tempering treatment, wherein the temperature for the tempering treatment is 520 ℃, the heat preservation time is 8h, cooling to the room temperature after the tempering treatment is finished, and discharging to obtain the terbium-containing neodymium-iron-boron magnetic steel.
And collecting the terbium plate after the heat treatment is finished, and using the collected terbium plate for next production.
Comparative example 1
And the magnetic performance of the magnetic steel with the thickness of 3mm is improved by adopting the traditional spraying process.
The low-performance neodymium iron boron magnetic steel is prepared by a powder metallurgy method by adopting the same process as that of the embodiment 1, the method is consistent with the traditional preparation of the neodymium iron boron magnetic steel, namely the low-performance neodymium iron boron magnetic steel is prepared by smelting, hydrogen crushing, airflow milling, compression, isostatic pressing and sintering, the low-performance neodymium iron boron magnetic steel is machined into a semi-finished product magnetic steel with the specification of grain boundary diffusion, the magnetic performance of the semi-finished product magnetic steel is 45H (Br: 13.2kGs, hcj.
Terbium is melted in a smelting furnace and then is spun to prepare a cast sheet, the cast sheet is placed in a hydrogen crushing furnace to be hydrogen crushed, and then is made into fine powder through a powder making device, the fine powder is mixed with high polymer glue under the protection of nitrogen to form a colloidal diffusion source (the mass ratio of the fine powder to the high polymer glue is 2). According to the traditional process, a jelly diffusion source is sprayed on the surface of magnetic steel (the mass of fine powder accounts for 0.7% of the weight of the magnetic steel) by a spraying method, the magnetic steel is dried and then put into a graphite box, the graphite box is put into a vacuum sintering furnace, the heating and the temperature rise are carried out for high-temperature heat treatment, the temperature of the high-temperature heat treatment is 900 ℃, the heat preservation time is 12 hours, the temperature is reduced to normal temperature, then tempering treatment is carried out, the tempering treatment temperature is 505 ℃, the heat preservation time is 6 hours, the temperature is reduced to room temperature, and then the steel is taken out of the furnace to obtain the terbium-containing neodymium-iron-boron magnetic steel, wherein the performance test results are shown in table 2.
TABLE 1 EXAMPLES 1-3 summary of the properties of the heavy rare earth terbium/dysprosium magnetic steels
The final 10 terbium-containing neodymium iron boron magnetic steel sheets in example 1 and comparative example 1 were taken for performance testing, and the results of the performance testing at room temperature and 20 ℃ are summarized in table 2.
Table 2 summary of properties of terbium (heavy rare earth) magnetic steels of example 1 and comparative example 1
Generally, in a certain range, the more the content of heavy rare earth dysprosium or terbium which permeates into the magnetic steel through grain boundary diffusion or permeates into the magnetic steel, the greater the magnetic steel performance improvement degree, but dysprosium and terbium are very expensive, the more dysprosium or terbium which needs to permeate into the magnetic steel, the higher the production cost, and the driving force problems such as concentration difference and the like exist due to grain boundary diffusion, and the improvement of the magnetic steel performance by increasing the content of the dysprosium or terbium which permeates into the magnetic steel is quite limited.
As can be seen from table 2, after grain boundary diffusion, the average performance of the terbium-containing ndfeb magnetic steel obtained in example 1 is better than that of comparative example 1. Therefore, in the invention, the performance of the magnetic steel can be further improved by improving the process.
In the invention, the plate form of the heavy rare earth metal is used as a diffusion source, and the heavy rare earth metal does not need to be crushed into powder, so that the problems that the heavy rare earth metal in a powder state is easy to oxidize and needs to be gelatinized or added with a solvent, and the subsequent diffusion and permeation effects are poor are avoided; on the other hand, the content of dysprosium or terbium which is diffused and infiltrated into the magnetic steel by the heavy rare earth metal plate is less than that of the dysprosium or terbium which is diffused and infiltrated into the magnetic steel by the traditional coating method, but the performance of the magnetic steel is improved to a greater extent finally; and the requirement for improving the magnetic steel can be met due to less content of heavy rare earth metal needing to be infiltrated, and the used heavy rare earth metal plate can be reused, so that the utilization rate of the rare earth metal is increased, the rare earth metal resource is saved, and the production cost is further reduced.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope of the present invention, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.
Claims (10)
1. A grain boundary diffusion method for improving the magnetic property of neodymium iron boron magnetic steel is characterized by comprising the following steps: melting the rare earth metal raw material, casting the molten rare earth metal raw material into a mold, and cooling to obtain a rare earth metal plate; and placing the neodymium iron boron magnetic steel on the rare earth metal plate, and performing heat treatment and tempering treatment to obtain the neodymium iron boron magnetic steel containing rare earth metal.
2. The grain boundary diffusion method of claim 1, wherein the rare earth metal feedstock comprises at least one of elemental terbium, elemental dysprosium, terbium-containing alloys, and dysprosium-containing alloys.
3. The grain boundary diffusion method according to claim 1 or 2, wherein the heat treatment temperature is 700 ℃ to 1000 ℃ and the holding time is 8h to 24h.
4. The grain boundary diffusion method according to claim 3, wherein the heat treatment temperature is 900 ℃ and the holding time is 12 hours.
5. The grain boundary diffusion method according to claim 1 or 2, wherein the tempering temperature is 400 to 600 ℃ and the tempering time is 4 to 8 hours.
6. The grain boundary diffusion method according to claim 5, wherein the tempering temperature is 505 ℃ and the tempering time is 6 hours.
7. The grain boundary diffusion method according to claim 1 or 2, wherein the thickness of the rare earth metal plate is 1 to 10mm.
8. The grain boundary diffusion method according to claim 7, wherein the thickness of the rare earth metal plate is 3 to 5mm.
9. The grain boundary diffusion method according to claim 1 or 2, wherein the thickness of the neodymium iron boron magnetic steel is 2 to 5mm; the heat treatment and tempering treatment are also performed under vacuum conditions.
10. The neodymium-iron-boron magnetic steel containing rare earth metal prepared by the grain boundary diffusion method of any one of claims 1 to 9.
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