A rare earth permanent magnet, its preparation method and application

Abstract

This invention relates to a rare-earth permanent magnet, its preparation method, and its application, belonging to the technical field of rare-earth permanent magnets. The rare-earth permanent magnet of this invention comprises a first rare-earth layer, a central rare-earth layer, and a second rare-earth layer. This invention forms a gradient-distributed rare-earth permanent magnet by layering and pressing neodymium iron boron rare-earth layers with defined heavy rare-earth element content and mass ratio, followed by isostatic pressing and sintering. This fully utilizes the eddy current effect during magnet operation, ensuring sufficient surface performance to resist demagnetization, and meeting the core requirements of wind turbines. Furthermore, the central rare-earth layer uses low-cost, low-performance magnet powder with a low rare-earth content and uses little or no heavy rare-earth elements, thus significantly saving rare-earth resources and reducing production costs.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet technology, specifically relating to a rare earth permanent magnet, its preparation method, and its application. Background Technology

[0002] Wind power generation converts the kinetic energy of wind into mechanical kinetic energy, and then into electrical kinetic energy. The principle of wind power generation is to use wind to drive the rotation of windmill blades, and then use a speed increaser to increase the rotational speed, thereby driving a generator to produce electricity. Wind power generation requires a large amount of rare-earth permanent magnet neodymium iron boron (NdFeB) magnets, and these magnets are relatively large, consuming a significant amount of rare-earth resources. During operation, the magnets can demagnetize due to heat, and in severe cases, this can cause the magnets to fail, leading to generator malfunction. Therefore, it is necessary to improve the demagnetization resistance of NdFeB magnets. The simplest way is to increase the grade of NdFeB magnets to enhance their coercivity, but this requires a large amount of rare-earth resources, especially the scarce dysprosium-terbium rare-earth resources. During wind turbine operation, the magnets heat up because they generate eddy currents. These eddy currents make the demagnetizing field on the surface of the magnet stronger, while the demagnetizing field in the core is weaker. Therefore, if magnets with a gradient distribution of properties can be manufactured, with high coercivity on the surface sufficient to resist the demagnetizing field and weaker properties in the core to meet the magnetic field required for normal wind turbine operation, this method can reduce the cost of the magnet core. The core magnets do not need to consume rare earth metals such as dysprosium and terbium, thus saving a large amount of rare earth resources and reducing production costs.

[0003] Rare earth permanent magnets are widely used in wind power generation, new energy vehicles, and white goods. With the increasing demands for magnet performance in various applications, the usage of heavy rare earth elements (Tb and Dy) is constantly rising. How to significantly improve the performance of rare earth permanent magnets while reducing the amount of heavy rare earth elements used has become a pressing issue for the rare earth permanent magnet industry. Grain boundary diffusion technology is a recently developed process for improving magnet performance. This process can significantly increase the intrinsic coercivity of the magnet, while significantly reducing the amount of heavy rare earth elements used compared to traditional processes. However, this process has a drawback: it cannot be applied to thicker magnets. As the magnet becomes thicker, the amount of heavy rare earth elements penetrating into the magnet along the grain boundaries decreases with thickness, resulting in uneven magnet performance. Magnets used in wind power generation generally have large thickness and volume in the magnetic field orientation direction. Currently, the rare earth permanent magnet industry can only produce such large magnets using traditional processes. This production process limits the application of grain boundary diffusion technology in the manufacture of NdFeB magnets for wind power generation, resulting in high rare earth usage and high costs. Therefore, there is an urgent need to develop a rare earth permanent magnet with a gradient performance distribution, so that its surface has high coercivity to resist demagnetization, and the core uses low-performance magnets with lower cost, which can meet the magnetic field required for the normal operation of wind turbines, and can save a lot of rare earth resources and reduce production costs. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a rare earth permanent magnet with gradient performance, which can effectively save rare earth resources and reduce costs.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a rare earth permanent magnet, comprising a first rare earth layer, a central rare earth layer, and a second rare earth layer; the first rare earth layer, the central rare earth layer, and the second rare earth layer are all composed of neodymium iron boron material.

[0007] The first and second rare earth layers are identical and symmetrical about the central rare earth layer as an axis of symmetry.

[0008] The content of heavy rare earth elements in the neodymium iron boron material in the first and second rare earth layers gradually decreases from the edge to the center of the rare earth permanent magnet.

[0009] The mass percentage of heavy rare earth elements in the neodymium iron boron materials of the first and second rare earth layers is 0.2-3%, and the mass percentage of heavy rare earth elements in the neodymium iron boron materials of the central rare earth layer is 0-0.5%.

[0010] The mass ratio of the first rare earth layer, the second rare earth layer, and the central rare earth layer is: first rare earth layer: second rare earth layer: central rare earth layer = 1:1:(0.001~1).

[0011] The inventors of this invention discovered through extensive research that the surface of the rare earth permanent magnet steel of this invention consists of a first rare earth layer and a second rare earth layer with a high content of heavy rare earth elements and good performance, while the core consists of a central rare earth layer with a low content of heavy rare earth elements and lower performance. Simultaneously, ensuring that the heavy rare earth element content of the first and second rare earth layers gradually decreases from the edge to the center of the rare earth permanent magnet steel allows for a gradient distribution of the rare earth permanent magnet steel's performance. Furthermore, the surface of the rare earth permanent magnet steel possesses high coercivity sufficient to resist demagnetization, while the core uses low-cost, low-performance magnets, meeting the magnetic field requirements for normal operation of wind turbines. The lower rare earth element content in the core of the rare earth permanent magnet steel significantly saves rare earth resources and reduces production costs. In contrast, when the first and second rare earth layers are made of NdFeB material with low heavy rare earth element content, and the central rare earth layer is made of NdFeB material with high heavy rare earth element content, although costs can be reduced, the performance of the rare earth permanent magnet steel deteriorates, failing to meet application requirements. In addition, the first and second rare earth layers are identical and placed symmetrically about the central rare earth layer, which enables the performance of the rare earth permanent magnet to have a symmetrical gradient distribution, which is beneficial to meeting the performance requirements of the magnet.

[0012] In a preferred embodiment of the rare earth permanent magnet steel of the present invention, the first rare earth layer and the second rare earth layer each include at least one layer of neodymium iron boron material, and the central rare earth layer is one layer of neodymium iron boron material.

[0013] In a preferred embodiment of the rare earth permanent magnet steel described in this invention, both the first rare earth layer and the second rare earth layer include at least two layers of neodymium iron boron material.

[0014] The inventors of this invention have discovered that the first and second rare earth layers of this invention require at least one layer of neodymium iron boron (NdFeB) material with high coercivity (SH) to meet the application performance requirements of the magnet. However, when the outermost layer of the first and second rare earth layers is a NdFeB material with medium coercivity (M) or low coercivity (N), the performance of the prepared rare earth permanent magnet decreases significantly and cannot meet its application requirements. Furthermore, the NdFeB material in the central rare earth layer of this invention can be a layer of NdFeB material with low coercivity (N), which ensures that the rare earth permanent magnet has good performance, while also saving on the amount of heavy rare earth elements used and reducing the cost of the rare earth permanent magnet.

[0015] As a preferred embodiment of the rare earth permanent magnet steel of the present invention, the mass percentage of heavy rare earth elements in the neodymium iron boron materials of the first rare earth layer and the second rare earth layer is 0.5% to 2.5%, and the mass percentage of heavy rare earth elements in the neodymium iron boron material of the central rare earth layer is 0% to 0.4%.

[0016] The inventors discovered that by controlling the content of heavy rare earth elements in each layer of the rare earth permanent magnet steel described in this invention within the above-mentioned range, compared with magnet steel that uses a higher content of heavy rare earth elements throughout, it is possible not only to effectively reduce the amount and cost of rare earth elements in the core, but also to make the performance of the rare earth permanent magnet steel comparable.

[0017] In a preferred embodiment of the rare earth permanent magnet steel of the present invention, the mass percentage of heavy rare earth elements in the neodymium iron boron materials of the first rare earth layer and the second rare earth layer is 2%, and the mass percentage of heavy rare earth elements in the neodymium iron boron material of the central rare earth layer is 0%.

[0018] The inventors of this invention have surprisingly discovered that by employing a method that simultaneously controls the mass ratio and performance gradient distribution of different rare earth layers in rare earth permanent magnet steel, when the heavy rare earth element content of both the first and second rare earth layers is 2% and the heavy rare earth element content of the central rare earth layer is 0%, the prepared rare earth permanent magnet steel exhibits superior performance while significantly reducing the amount of heavy rare earth elements used, thus lowering the cost of the rare earth permanent magnet steel. Furthermore, when both the first and second rare earth layers contain ≥2 layers of NdFeB material and the heavy rare earth element content of the central rare earth layer is 0%, the amount of heavy rare earth elements used in the rare earth permanent magnet steel can be minimized while still maintaining good performance.

[0019] As a preferred embodiment of the rare earth permanent magnet steel of the present invention, the mass ratio of the first rare earth layer, the second rare earth layer and the central rare earth layer is the first rare earth layer: second rare earth layer: central rare earth layer = 1:1:(0.67~1).

[0020] The inventors discovered that, within the mass ratio range of the first rare earth layer, the second rare earth layer, and the central rare earth layer, this invention can simultaneously reduce the amount of rare earth elements in rare earth permanent magnets while maintaining good performance, effectively saving rare earth resources and reducing the cost of rare earth permanent magnets. However, when the amount of the central rare earth layer exceeds that of the first or second rare earth layer, although it can further reduce the amount and cost of heavy rare earth elements in the rare earth permanent magnet, the excessive use of low-coercivity NdFeB material in the core leads to a decline in the performance of the rare earth permanent magnet, and its surface cannot meet the performance requirements for demagnetization.

[0021] In a preferred embodiment of the rare earth permanent magnet steel of the present invention, the mass ratio of the first rare earth layer, the second rare earth layer and the central rare earth layer is the first rare earth layer: second rare earth layer: central rare earth layer = 1:1:1.

[0022] The inventors discovered that when the mass ratio of the first rare earth layer, the second rare earth layer, and the central rare earth layer is 1:1:1, not only can the rare earth permanent magnet steel achieve better performance, but the content of rare earth elements can also be better controlled, effectively saving rare earth resources and reducing the cost of rare earth permanent magnet steel.

[0023] Secondly, the present invention also provides a method for preparing the above-mentioned rare earth permanent magnet steel, comprising the following steps: placing the first rare earth layer, the central rare earth layer and the second rare earth layer into a press in sequence, isostatically pressing to obtain a green blank, sintering to obtain the rare earth permanent magnet steel.

[0024] As a preferred embodiment of the preparation method of the rare earth permanent magnet steel of the present invention, the first rare earth layer, the second rare earth layer and the central rare earth layer are placed by first placing the powder in layers and then oriented and pressing it into shape, or by first oriented and pressing the powder of each layer into shape and then placing it in layers.

[0025] The inventors have discovered that rare earth permanent magnets obtained by the above-mentioned placement method of this invention are conducive to better bonding of rare earth layers with different properties. This not only solves the problem that the bonding layer of magnets with gradient performance distribution obtained by traditional bonding methods is prone to falling off during use, but also overcomes the inability of using grain boundary diffusion to increase the diffusion depth for thicker magnets.

[0026] As a preferred embodiment of the preparation method of the rare earth permanent magnet steel of the present invention, the method of first placing powder in layers and then oriented and pressing it into shape includes the following steps:

[0027] (1) Different NdFeB materials were hydrogen-crushed to obtain coarse powders of different NdFeB materials with a fineness of 80-120 μm;

[0028] (2) The coarse powder obtained in step (1) is subjected to air jet milling to obtain fine powder of different NdFeB materials with a fineness of 3 to 5 μm;

[0029] (3) The fine powder described in step (2) is placed into a press in layers and oriented and pressed into shape.

[0030] As a preferred embodiment of the method for preparing rare earth permanent magnet steel according to the present invention, the method of first orienting and pressing the powder of each layer into shape and then placing them in layers includes the following steps:

[0031] (1) Different NdFeB materials were hydrogen-crushed to obtain coarse powders of different NdFeB materials with a fineness of 80-120 μm;

[0032] (2) The coarse powder obtained in step (1) is subjected to air jet milling to obtain fine powder of different NdFeB materials with a fineness of 3 to 5 μm;

[0033] (3) The fine powder described in step (2) is placed into a press and oriented and pressed into shape;

[0034] (4) The NdFeB material pressed in step (3) is placed into the press in layers.

[0035] As a preferred embodiment of the preparation method of the rare earth permanent magnet steel of the present invention, the sintering process is as follows: the green blank is sintered at 1060°C under vacuum for 8 hours, followed by a two-stage tempering treatment.

[0036] In a preferred embodiment of the method for preparing rare earth permanent magnet steel according to the present invention, the temperature of the first stage of tempering is 890°C and the tempering time is 3 hours; the temperature of the second stage of tempering is 520°C and the tempering time is 5 hours.

[0037] Thirdly, the present invention also provides the application of the above-mentioned rare earth permanent magnet steel in the preparation of wind turbine generators.

[0038] The rare earth permanent magnet steel described in this invention is formed by pressing powders with different properties and compositions in layers, followed by isostatic pressing and sintering to create rare earth permanent magnet steel with a gradient distribution. This fully utilizes the eddy current effect during the operation of the magnet steel, making its surface properties sufficiently resistant to demagnetization, and ensuring that the core meets the operating requirements of wind turbines. This significantly saves rare earth resources and reduces the production cost of rare earth permanent magnet steel.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] (1) The present invention provides a rare earth permanent magnet with gradient performance distribution. The surface of the rare earth permanent magnet has high coercivity and can resist a strong demagnetizing field. The core has low coercivity and contains less or no heavy rare earth elements, which can effectively save the amount of heavy rare earth metal elements and reduce the cost of rare earth permanent magnets.

[0041] (2) The first rare earth layer, the second rare earth layer and the central rare earth layer of the present invention, through a specific order and placement method, are conducive to better combination of neodymium iron boron rare earth layers with different properties, and can be applied to thicker magnets, and can prepare rare earth permanent magnets with gradient performance distribution and meet the overall performance requirements. Detailed Implementation

[0042] The technical solution of the present invention will be further described below with reference to the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the methods or operations used in the embodiments are conventional methods or operations in the art.

[0043] Example 1

[0044] One embodiment of the rare earth permanent magnet steel of the present invention, wherein the raw material of the rare earth permanent magnet steel described in this embodiment is:

[0045] (1) Both the first and second rare earth layers are composed of a layer of neodymium iron boron material with the grade N42SH. Specifically, the total mass percentage of rare earth in the N42SH neodymium iron boron material is 31.2% (of which the mass percentage of heavy rare earth elements is 2%, and the heavy rare earth element is dysprosium).

[0046] (2) The central rare earth layer consists of a layer of NdFeB material with grade N45, specifically: the total rare earth mass percentage of NdFeB material is 31% (of which the mass percentage of heavy rare earth elements is 0), and 6% cerium is used to replace 6% neodymium.

[0047] The method for preparing rare earth permanent magnet steel described in this embodiment includes the following steps:

[0048] (1) The neodymium iron boron material in the first and second rare earth layers is hydrogen-crushed to obtain coarse powder A; the neodymium iron boron material in the central rare earth layer is hydrogen-crushed to obtain coarse powder B; the fineness of coarse powder A and coarse powder B is 100 μm.

[0049] (2) The coarse powder A and coarse powder B obtained in step (1) are subjected to air jet milling to obtain fine powder A and fine powder B; 600g of fine powder A and 300g of fine powder B are taken, and the fine powder A is divided into two equal parts; the fineness of fine powder A and fine powder B is 4μm.

[0050] (3) In order, the first fine powder A, fine powder B and the second fine powder A from step (2) are placed into the press, oriented and pressed into shape, with an orientation magnetic field ≥16000Gs, isostatic pressing, to obtain a green body.

[0051] (4) The green blank obtained in step (3) is sintered in a vacuum atmosphere. The sintering process is sintering at 1060℃ for 8 hours, 890℃ for 3 hours and 520℃ for 5 hours to obtain a blank.

[0052] (5) Polish the sintered blank to a bright finish and perform surface anti-corrosion treatment to obtain the rare earth permanent magnet steel.

[0053] Example 2

[0054] This invention provides an embodiment of rare earth permanent magnet steel, wherein the raw materials of the rare earth permanent magnet steel described in this embodiment are the same as those in Embodiment 1.

[0055] The difference between the preparation method of the rare earth permanent magnet steel described in this embodiment and that in embodiment 1 is only that 675g of fine powder A and 225g of fine powder B are taken in step (2). The other components, dosages and preparation methods are the same as in embodiment 1.

[0056] Example 3

[0057] This invention provides an embodiment of rare earth permanent magnet steel, wherein the raw materials of the rare earth permanent magnet steel described in this embodiment are the same as those in Embodiment 1.

[0058] The difference between the preparation method of the rare earth permanent magnet steel described in this embodiment and that in embodiment 1 is that 650g of fine powder A and 250g of fine powder B are taken in step (2). The other components, dosages and preparation methods are the same as in embodiment 1.

[0059] Example 4

[0060] This invention provides an embodiment of rare earth permanent magnet steel, wherein the raw materials of the rare earth permanent magnet steel described in this embodiment are the same as those in Embodiment 1.

[0061] The difference between the preparation method of the rare earth permanent magnet steel described in this embodiment and that in embodiment 1 is that 700g of fine powder A and 200g of fine powder B are taken in step (2). The other components, dosages and preparation methods are the same as in embodiment 1.

[0062] Example 5

[0063] One embodiment of the rare earth permanent magnet steel of the present invention, wherein the raw material of the rare earth permanent magnet steel described in this embodiment is:

[0064] (1) Both the first rare earth layer and the second rare earth layer are composed of a layer of NdFeB material with the grade N42SH. Specifically, the NdFeB material of this embodiment has the same composition as the NdFeB material of Example 1.

[0065] (2) The central rare earth layer consists of a layer of neodymium iron boron material with the grade N42H. Specifically, the total mass percentage of rare earth in the N42H neodymium iron boron material is 31.4% (of which the mass percentage of heavy rare earth elements is 0.2%, and the heavy rare earth element is dysprosium).

[0066] The rare earth permanent magnet steel described in this embodiment is the same as that in Embodiment 1.

[0067] Example 6

[0068] One embodiment of the rare earth permanent magnet steel of the present invention, wherein the raw material of the rare earth permanent magnet steel described in this embodiment is:

[0069] (1) Both the first rare earth layer and the second rare earth layer are composed of a layer of NdFeB material with the grade N42SH. Specifically, the NdFeB material of N42SH in this embodiment has the same composition as the NdFeB material of N42SH in Example 1.

[0070] (2) The central rare earth layer consists of a layer of neodymium iron boron material with grade N45M. Specifically, the total mass percentage of rare earth in the N45M neodymium iron boron material is 31% (of which the mass percentage of heavy rare earth elements is 0.5%, and the heavy rare earth element is dysprosium), and 3% cerium is used to replace 3% neodymium.

[0071] The preparation method of the rare earth permanent magnet steel described in this embodiment is the same as that in Embodiment 1.

[0072] Example 7

[0073] This invention provides an embodiment of rare earth permanent magnet steel, wherein the raw materials of the rare earth permanent magnet steel described in this embodiment are the same as those in embodiment 6.

[0074] The preparation method of the rare earth permanent magnet steel described in this embodiment is the same as that in Embodiment 4.

[0075] Example 8

[0076] (1) Both the first rare earth layer and the second rare earth layer are composed of a layer of NdFeB material with grade N42SH and a layer of NdFeB material with grade N45M. Specifically, the NdFeB material of N42SH in this embodiment has the same composition as the NdFeB material of N42SH in Example 1; the NdFeB material of N45M in this embodiment has the same composition as the NdFeB material of N45M in Example 6.

[0077] (2) The central rare earth layer is composed of a layer of NdFeB material with grade N45. Specifically, the composition of NdFeB material in this embodiment is the same as that of NdFeB material in Example 1.

[0078] The method for preparing rare earth permanent magnet steel described in this embodiment includes the following steps:

[0079] (1) The NdFeB material with grade N42SH and the NdFeB material with grade N45M in the first and second rare earth layers are hydrogen-crushed to obtain coarse powder A and coarse powder B respectively; the NdFeB material in the central rare earth layer is hydrogen-crushed to obtain coarse powder C; the fineness of coarse powder A, coarse powder B and coarse powder C is 100μm.

[0080] (2) The coarse powder A, coarse powder B and coarse powder C obtained in step (1) are respectively subjected to air jet milling to obtain fine powder A, fine powder B and fine powder C; 600g fine powder A, 200g fine powder B and 100g fine powder C are taken, and fine powder A and fine powder B are divided into 2 equal parts; the fineness of fine powder A, fine powder B and fine powder C is 4μm.

[0081] (3) In order, put the first fine powder A, the first fine powder B, the fine powder C, the second fine powder B, and the second fine powder A from step (2) into the press, orient and press them into shape, with an orienting magnetic field ≥16000Gs, and isostatic pressing to obtain a green body.

[0082] (4) The green blank obtained in step (3) is sintered in a vacuum atmosphere. The sintering process is sintering at 1060℃ for 8 hours, 890℃ for 3 hours and 520℃ for 5 hours to obtain a blank.

[0083] (5) Polish the sintered blank to a bright finish and perform surface anti-corrosion treatment to obtain the rare earth permanent magnet steel.

[0084] Example 9

[0085] This invention provides an embodiment of rare earth permanent magnet steel, wherein the raw materials of the rare earth permanent magnet steel described in this embodiment are the same as those in embodiment 8.

[0086] The difference between the preparation method of rare earth permanent magnet steel described in this embodiment and that in embodiment 8 is only that step (3) is as follows: the first fine powder A, the first fine powder B, the fine powder C, the second fine powder B, and the second fine powder A from step (2) are respectively placed into a press for orientation and pressing, and the orientation magnetic field is ≥16000Gs. Then, the pressed neodymium iron boron material is placed into the press in the above order and isostatically pressed to obtain a green blank; the remaining components, dosages, and preparation methods are the same as in embodiment 8.

[0087] Comparative Example 1

[0088] This invention provides a comparative example of a rare-earth permanent magnet steel. The raw material for the rare-earth permanent magnet steel described in this comparative example is:

[0089] The first rare earth layer, the second rare earth layer, and the central rare earth layer are all composed of a layer of NdFeB material with the grade N42SH. Specifically, the NdFeB material of N42SH in this comparative example has the same composition as the NdFeB material of N42SH in Example 1.

[0090] The preparation method of the rare earth permanent magnet steel described in this comparative example is the same as that in Example 1.

[0091] Comparative Example 2

[0092] This invention provides a comparative example of a rare-earth permanent magnet steel. The raw material for the rare-earth permanent magnet steel described in this comparative example is:

[0093] The first rare earth layer, the second rare earth layer, and the central rare earth layer are all composed of a single layer of NdFeB material with the grade N45. Specifically, the NdFeB material of N45 in this comparative example has the same composition as the NdFeB material of N45 in Example 1.

[0094] The preparation method of the rare earth permanent magnet steel described in this comparative example is the same as that in Example 1.

[0095] Comparative Example 3

[0096] This invention provides a comparative example of a rare-earth permanent magnet steel. The raw material for the rare-earth permanent magnet steel described in this comparative example is:

[0097] (1) Both the first rare earth layer and the second rare earth layer are composed of a layer of NdFeB material with grade N45. Specifically, the composition of the NdFeB material of N45 in this comparative example is the same as that of the NdFeB material of N45 in Example 1.

[0098] (2) The central rare earth layer is composed of a layer of neodymium iron boron material with the grade N42SH. Specifically, the composition of the N42SH neodymium iron boron material in this comparative example is the same as that of the N42SH neodymium iron boron material in Example 1.

[0099] The preparation method of the rare earth permanent magnet steel described in this comparative example is the same as that in Example 1.

[0100] Comparative Example 4

[0101] This invention provides a comparative example of rare earth permanent magnet steel, wherein the raw materials of the rare earth permanent magnet steel described in this comparative example are the same as those in Example 1.

[0102] The preparation method of the rare earth permanent magnet described in this comparative example differs from that in Example 1 only in that 550g of fine powder A and 350g of fine powder B are taken in step (2). The remaining components, dosages and preparation methods are the same as in Example 1.

[0103] Comparative Example 5

[0104] This invention provides a comparative example of rare earth permanent magnet steel, wherein the raw materials of the rare earth permanent magnet steel described in this comparative example are the same as those in Example 1.

[0105] The preparation method of the rare earth permanent magnet described in this comparative example differs from that in Example 1 only in that 810g of fine powder A and 90g of fine powder B are taken in step (2). The other components, dosages and preparation methods are the same as in Example 1.

[0106] Comparative Example 6

[0107] This invention provides a comparative example of a rare-earth permanent magnet steel. The raw material for the rare-earth permanent magnet steel described in this comparative example is:

[0108] (1) Both the first rare earth layer and the second rare earth layer are composed of a layer of NdFeB material with the grade N45M. Specifically, the composition of the NdFeB material in this comparative example is the same as that of the NdFeB material in Example 6.

[0109] (2) The central rare earth layer is composed of a layer of neodymium iron boron material with the grade N42SH. Specifically, the composition of the N42SH neodymium iron boron material in this comparative example is the same as that of the N42SH neodymium iron boron material in Example 1.

[0110] The preparation method of the rare earth permanent magnet steel described in this comparative example is the same as that in Example 1.

[0111] Comparative Example 7

[0112] This invention provides a comparative example of rare earth permanent magnet steel, wherein the raw materials of the rare earth permanent magnet steel described in this comparative example are the same as those in Comparative Example 6.

[0113] The preparation method of the rare earth permanent magnet described in this comparative example differs from that in Example 1 only in that 90g of fine powder A and 810g of fine powder B are taken in step (2). The remaining components, dosages and preparation methods are the same as in Example 1.

[0114] Example 1

[0115] To further verify the performance of the rare earth permanent magnets of the present invention, the rare earth permanent magnets of Examples 1-9 and Comparative Examples 1-7 of the present invention were tested using a NIM62000 instrument. The specific testing method was as follows: the blanks obtained above were prepared into D10*10mm cylinders using a single-wire cutting machine, and then the outer surface of the cylinder was rounded by a centerless grinder. Finally, the rounded cylinder was tested for magnetic properties to obtain the remanence (Br), coercivity (Hcj), and squareness of the demagnetization curve (HK / Hcj). The test results are shown in Table 1 below.

[0116] Table 1

[0117]

[0118]

[0119] As can be seen from Table 1, the rare earth permanent magnet steel with gradient performance of the present invention has good performance. Compared with Comparative Example 1, which uses high-performance neodymium iron boron materials in the first rare earth layer, the second rare earth layer and the central rare earth layer, the proportion of heavy rare earth elements in the rare earth permanent magnet steel of Examples 1 to 9 can be reduced by 16.5% to 44.5%, which effectively reduces the production cost of rare earth permanent magnet steel.

[0120] By comparing Examples 1 to 9, it can be seen that when the selection, mass ratio, and content of heavy rare earth elements of neodymium iron boron materials in the first rare earth layer, the second rare earth layer, and the central rare earth layer are within the range described in this invention, the performance of rare earth permanent magnets is comparable. However, the amount of heavy rare earth elements used and the cost have a greater impact. Among them, the formulation of Example 1 can minimize the overall cost while ensuring performance, and the proportion of heavy rare earth elements in the magnet can be reduced to 1.33%.

[0121] By comparing Example 1 with Comparative Examples 2-3 and 6-7, it can be seen that the performance of the rare earth permanent magnet steel described in this invention exhibits a gradient distribution, and the surface of the magnet steel is composed of high-performance neodymium iron boron material. The performance gradually decreases from the surface of the magnet steel to the core, which can fully utilize the eddy current effect during the operation of the magnet steel, making the surface performance of the magnet steel sufficient to resist the demagnetizing field, and the core meeting the working requirements of the wind turbine. Although the performance of the rare earth permanent magnet steels in Comparative Examples 2-3 and Comparative Example 6 also exhibits a gradient distribution, the use of low-performance neodymium iron boron material on their surfaces leads to a decrease in the performance of the rare earth permanent magnet steel. Comparative Example 7 increases the coercivity of the rare earth permanent magnet steel by increasing the amount of high-performance neodymium iron boron material in the central rare earth layer, but its cost is higher.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A rare-earth permanent magnet steel, characterized in that, It includes a first rare earth layer, a central rare earth layer, and a second rare earth layer; all three rare earth layers are composed of neodymium iron boron material. The first and second rare earth layers are identical and symmetrical about the central rare earth layer as an axis of symmetry. The mass percentage of heavy rare earth elements in the neodymium iron boron materials of the first and second rare earth layers gradually decreases from the edge to the center of the rare earth permanent magnet. The mass percentage of heavy rare earth elements in the neodymium iron boron materials of the first and second rare earth layers is 2%, while the mass percentage of heavy rare earth elements in the neodymium iron boron materials of the central rare earth layer is 0%. The mass ratio of the first rare earth layer, the second rare earth layer, and the central rare earth layer is: first rare earth layer: second rare earth layer: central rare earth layer = 1:1:(0.67~1); The rare earth permanent magnet steel is prepared by the following steps: The first rare earth layer, the central rare earth layer, and the second rare earth layer are sequentially placed into a press and isostatically pressed to obtain a green blank, which is then sintered to obtain the rare earth permanent magnet steel. The sintering process is as follows: the green blank is sintered at 1060℃ under vacuum for 8 hours, followed by a two-stage tempering treatment; the first stage tempering temperature is 890℃ and the tempering time is 3 hours; the second stage tempering temperature is 520℃ and the tempering time is 5 hours.

2. The rare earth permanent magnet steel as described in claim 1, characterized in that, The first and second rare earth layers each include at least one layer of neodymium iron boron material; the central rare earth layer is one layer of neodymium iron boron material.

3. The rare earth permanent magnet steel as described in claim 2, characterized in that, Both the first and second rare earth layers include at least two layers of neodymium iron boron material.

4. The rare earth permanent magnet steel as described in claim 1, characterized in that, The mass ratio of the first rare earth layer, the second rare earth layer, and the central rare earth layer is 1:1:

1.

5. The application of rare earth permanent magnets as described in any one of claims 1 to 4 in the manufacture of wind turbine generators.

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