R-Fe-B permanent magnet materials, manufacturing methods and applications

Abstract

The present invention discloses an R-Fe-B-based permanent magnet material, its manufacturing method and applications. The above permanent magnet material has the performance of Br≧13.3 KGs, Hcj≧25.1 Koe, HAST weight loss ≦3 mg / cm² for 20 days 2 , and a bending strength >440 Mpa. By means of accurate formulation design and method design, on the premise of strictly controlling elements such as O, C, N, etc. in the permanent magnet material, elements such as Ti, Ga, Cu, etc. that are beneficial to the Hcj, weight loss performance, and mechanical properties of the permanent magnet material are contained in the grain boundary phase of the permanent magnet material. These elements are uniformly distributed in the grain boundary phase at a certain ratio, not only playing a role in refining the crystal grains, increasing the wettability and corrosion resistance of the grain boundaries, and preventing abnormal growth of the crystal grains, but also by combining the optimized jet mill powder-making process and the sintering process, improving the microstructure of the main phase and the grain boundary phase of the permanent magnet material, thereby manufacturing an R-Fe-B-based permanent magnet material with excellent comprehensive performance.

Description

Detailed Description of the Invention

[0001] This application claims priority from a prior patent application filed by the applicant with the State Intellectual Property Office of the People's Republic of China on May 24, 2022, bearing application number 202210576133.8 and entitled "R-Fe-B based permanent magnet material, manufacturing method and application," which is incorporated herein by reference in its entirety.

[0002] [Technical Field] The present invention belongs to the technical field of R-Fe-B based permanent magnetic materials, and in particular to R-Fe-B based permanent magnetic materials, their manufacturing methods, and applications.

[0003] [Background technology] Due to their excellent magnetic properties, sintered R-Fe-B permanent magnets are widely used in power motors, computers, electronic products, etc. As products improve, the requirements for the temperature coefficient of magnets in these fields are increasing. In particular, with the development of related fields such as air conditioners and electric vehicles, there is an increasing demand for NdFeB magnets to be used in a variety of fields, and the requirements for their performance are also becoming increasingly higher.

[0004] At the same time, the most obvious drawback of R-Fe-B sintered magnets compared to Sm-Co permanent magnets is their poor corrosion resistance, which limits their application in high-temperature, high-humidity environments, making research into the corrosion resistance of R-Fe-B sintered magnets of great significance.In particular, with increasing awareness of environmental protection and energy conservation in countries around the world in recent years, there is an increasing demand for high-performance R-Fe-B sintered magnets with excellent corrosion resistance for permanent magnet motors such as environmentally friendly, energy-saving, and highly efficient wind turbines that are used in humid environments such as seaside and grassland.

[0005] However, at present, the formulation of magnetic materials in conventional technology does not fully utilize the improvement in magnetic performance due to each element of the neodymium-iron-boron magnetic material, and it is not possible to obtain a magnetic material that combines high magnetic performance with relatively good weight loss performance and mechanical performance.

[0006] Summary of the Invention In order to improve the above-mentioned problems, the present invention provides an R—Fe—B based permanent magnet material, Br≧13.3 KGs, Hcj≧25.1 Koe, 20-day HAST weight loss ≤3 mg / cm 2 , The present invention provides an R-Fe-B based permanent magnet material characterized by a bending strength of >440 MPa.

[0007] According to an embodiment of the present invention, the 20-day HAST weight loss of the permanent magnet material is ≦1 mg / cm 2 is.

[0008] According to an embodiment of the present invention, the R—Fe—B based permanent magnet material has a Br of 13.3 to 15.0 KGs, an Hcj of 25 to 34 Koe, and a 20-day HAST weight loss of 0.1 to 0.5 mg / cm 2 The bending strength is 445 to 470 MPa.

[0009] According to an embodiment of the present invention, the composition of the R—Fe—B based permanent magnet material contains Ti and Ga, in which the Ti content is ≧0.2 wt% and the Ga content is ≧0.2 wt%, and 1 <Ti / Ga<2である。

[0010] According to an embodiment of the present invention, the R—Fe—B based permanent magnet material has a composition, in mass percentage 100%, of 26.0 to 32.0% R, 0.3 to 4.0% RH, 0.5 to 3.0% Co, 0.1 to 0.25% Cu, 0.2 to 0.4% Ga, 0.2 to 0.4% Ti, 0 to 0.4% Al, 0.95 to 1.05% B, and the balance being Fe and unavoidable impurities, wherein R is neodymium (Nd) and / or praseodymium (Pr), and RH is dysprosium (Dy) and / or terbium (Tb), The mass percentage of the above element contents is: 1)1 <Ti / Ga<2、 2) 5≦Co / Cu<15, The relationship must be satisfied.

[0011] According to an embodiment of the present invention, the R—Fe—B based permanent magnet material includes a grain boundary phase, and the grain boundary phase contains R a RH b Ti c Ga d Cu e Al F C Og Fe 残り , 33≦a≦45, 0.1≦b≦16, 3≦c≦12, 0.4≦d≦2, 0.3≦e≦2.0, 0.01≦f≦0.1, 0.4≦g≦16, a+b+c+d+e+f+g+remainder=100, The above R occupies the above permanent magnet material a RH b Ti c Ga d Cu e Al F C Og Fe 残り The mass ratio of is 6 to 11 wt%.

[0012] According to an embodiment of the present invention, the R is Nd or PrNd, and the content of the R is preferably 26.5% to 31.0%, preferably 26.5%, 27.0%, 27.5%, 28%, 28.5%, 29.0%, 29.5%, 30.0%, 30.5%, or 31%.

[0013] According to an embodiment of the present invention, the RH is at least one of Dy and Tb, and the RH content range is preferably 0.3% to 3.5%, for example, 0.5%, 0.8%, 1.0%, 1.3%, 1.5%, 1.8%, 2.5%, 2.8%, 3.0%, 3.1%, or 3.5%.

[0014] According to an embodiment of the present invention, the Co content is 1.0 to 3.0%, and preferably 0.5%, 1%, 1.5%, 2.0%, 2.5% or 3.0%.

[0015] According to an embodiment of the present invention, the Cu content is 0.1 to 0.25%, and preferably 0.1%, 0.12%, 0.15%, 0.17%, 0.18%, 0.2%, 0.23% or 0.25%.

[0016] According to an embodiment of the present invention, the Ga content is 0.2 to 0.4%, and preferably 0.2%, 0.25%, 0.3%, 0.35% or 0.4%.

[0017] According to an embodiment of the present invention, the Ti content is 0.2 to 0.4%, and preferably 0.2%, 0.25%, 0.28%, 0.30%, 0.32%, 0.35%, 0.38% or 0.40%.

[0018] According to an embodiment of the present invention, the Al content is 0.05 to 0.35%, and preferably 0.1%, 0.15%, 0.2%, 0.25%, 0.3% or 0.35%.

[0019] According to an embodiment of the present invention, the B content is 0.97 to 1.03%, and preferably 0.97%, 0.98%, 0.99%, 1.0%, 1.01%, 1.02%, or 1.03%.

[0020] According to an embodiment of the present invention, the unavoidable impurities are, for example, at least one of C, N, O, etc., and preferably, the oxygen content is 300 to 900 ppm, the carbon content is 400 to 800 ppm, and the nitrogen content is 200 to 600 ppm.

[0021] The present invention further provides a method for producing a Re-Fe-B based permanent magnetic material, comprising the steps of smelting and casting, coarsely pulverizing, finely pulverizing, molding, sintering, processing, and diffusing raw materials for the Re-Fe-B based permanent magnetic material to obtain the Re-Fe-B based permanent magnetic material.

[0022] According to an embodiment of the present invention, the above smelting and casting process is carried out in a medium frequency vacuum induction rapid solidification melt spinning furnace, the linear speed of the casting and quenching roll is 1 m / s to 2 m / s, the casting temperature is 1380 to 1480°C, and the average thickness of the flakes after smelting and casting is 0.20 to 0.30 mm.

[0023] According to an embodiment of the present invention, the coarse grinding process is carried out in a hydrogen grinding furnace by the steps of hydrogen absorption, dehydrogenation, and cooling, the pressure of the hydrogen absorption process is 90 to 110 KPa, the temperature of the dehydrogenation process is 550 to 620°C, and the dehydrogenation time is 3 to 6 hours.

[0024] According to an embodiment of the present invention, the pulverization is carried out using an inert gas jet mill, and the inert gas is, for example, nitrogen gas or argon gas. Preferably, the oxygen content during the pulverization process is controlled to ≦50 ppm, and the particle size SMD is 2.3-2.7 μm, preferably 2.5 μm, X90 / X10≦4.5, and X100≦12.5 μm. In the present invention, when X90 / X10≦4.5 and X100≦12.5 μm are satisfied, higher Br and Hcj can be obtained, while the weight loss level and bending strength are also improved.

[0025] According to an embodiment of the present invention, an antioxidant can be added during the milling process and mixed for 3 to 6 hours. The mass of the antioxidant is 1 to 2% of the total mass of the permanent magnet material, and the antioxidant is one or more selected from 1,3,5-trichlorotoluene, dibutylhydroxytoluene, and 4-hexylresorcinol. The antioxidant has a lubricating function. The milling process produces fine powder with a uniform particle size distribution, and the use of an inert gas jet mill ensures that the nitrogen content of the powder is relatively low.

[0026] According to an embodiment of the present invention, the above molding process is a magnetic field-oriented pressing process of ≧1.5 T, and during the pressing process, the powder is in a completely sealed press and is continuously protected by filling it with nitrogen gas.

[0027] According to an embodiment of the present invention, the sintering process is carried out by first subjecting the green compact produced by the compacting process to decarburization and degassing treatment in 2 to 10 temperature zones, then vacuum sintering, then sintering in an inert atmosphere, and cooling.

[0028] Preferably, the temperatures in the 2 to 10 temperature zones are different from one another, and preferably, the decarburization degassing treatment can be performed at an increasing temperature gradient. For example, when the decarburization degassing treatment is performed sequentially in 2 to 10 temperature zones, the decarburization degassing treatment is first performed in a first temperature zone, and then the next temperature zone is sequentially entered, for example, the decarburization degassing treatment is performed in a second temperature zone, the decarburization degassing treatment is performed in a third temperature zone, or the decarburization degassing treatment is performed in more than one temperature zone. For example, the temperature in the first temperature zone may be 200 to 380°C, preferably 280 to 320°C, for example 300°C, the temperature in the second temperature zone may be higher than that in the first temperature zone, for example 450 to 720°C, preferably 580 to 620°C, for example 600°C, and the temperature in the third temperature zone may be higher than that in the second temperature zone, for example 750 to 1000°C, preferably 880 to 920°C, for example 900°C. By employing the decarburization and degassing treatment process of the present invention, elements such as C, N, and H in the antioxidant can be sequentially desorbed from the permanent magnet material.

[0029] Preferably, the temperature of the vacuum sintering is 1000 to 1020° C., and the time of the vacuum sintering is 1 to 2 hours.

[0030] Preferably, the sintering temperature in the inert atmosphere is 1030 to 1050°C, the sintering time in the inert atmosphere is 2 to 4 hours, and the pressure during sintering in the inert atmosphere is 10 to 30 KPa. The inert atmosphere is, for example, nitrogen gas or argon gas.

[0031] Preferably, after sintering in an inert atmosphere, the mixture can be cooled to 50° C. or less using a blower at 100 KPa.

[0032] According to an embodiment of the present invention, the sintering process involves placing the green compact produced by the molding process in a sintering furnace under nitrogen gas protection, passing through a first temperature zone of 200-380°C, a second temperature zone of 450-720°C, and a third temperature zone of 750-1000°C, each of which undergoes decarburization and degassing treatment for 1-3 hours, followed by vacuum sintering at 1000-1020°C for 1-2 hours, and then filling with argon gas at 10-30 KPa and performing pressure-holding sintering at 1030-1050°C for 2-4 hours. The argon gas is then filled at approximately 100 KPa, and the blower is started to cool the compact to below 50°C.

[0033] The present invention employs a decarburization / outgassing process, vacuum sintering, and pressure sintering process to reduce the contents of elements such as C, N, and O in the permanent magnet material to relatively low levels, while at the same time further increasing the density and bending strength of the permanent magnet material.

[0034] According to an embodiment of the present invention, the diffusion treatment is a grain boundary diffusion treatment, and is performed according to a process commonly used in the art, such as Tb or Dy vapor diffusion. The temperature of the diffusion treatment may be 850-950°C, for example, 900°C, and the diffusion time may be 10-50 hours, for example, 36 hours. After the diffusion treatment, a stress relief aging treatment may be performed at a temperature of 450-650°C, for example, 550°C, for 3-6 hours.

[0035] According to an embodiment of the present invention, the Re—Fe—B based permanent magnet material has an oxygen content of 300 to 900 ppm, a carbon content of 400 to 800 ppm, and a nitrogen content of 200 to 600 ppm.

[0036] The present invention further provides an application of the above-mentioned Re-Fe-B based permanent magnet material as magnetic steel for a motor rotor in a motor.

[0037] [Beneficial Effects of the Present Invention] This invention, on the premise of strictly controlling elements such as O, C, and N in permanent magnet materials through precise formulation and process design, allows elements such as Ti, Ga, and Cu to be contained in the grain boundary phase of the permanent magnet material, which are beneficial to the Hcj, weight loss performance, and mechanical performance of the permanent magnet material. These elements are uniformly distributed in the grain boundary phase at a certain ratio, which not only refines the crystal grains, increases the wettability and corrosion resistance of the grain boundaries, and prevents abnormal grain growth, but also improves the microstructure of the main phase and grain boundary phase of the permanent magnet material by combining an optimized jet milling process and sintering process, thereby producing an R-Fe-B system permanent magnet material with excellent comprehensive performance. This Re-Fe-B system permanent magnet material has a 20-day HAST weight loss of ≦3 mg / cm under the conditions of Br≧13.3 kgs and Hcj≧25.1 Koe. 2 It has excellent weight loss performance, bending strength >440 Mpa, and excellent overall performance.

[0038] BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a backscattered scanning electron microscope analysis diagram of the permanent magnet material in Example 1.

[0039] [Mode for Carrying Out the Invention] The technical solutions of the present invention will be described in more detail below with reference to specific examples. It should be understood that the following examples are merely for illustrative purposes and should not be construed as limiting the scope of the claims of the present invention. Any technology realized based on the above content of the present invention is included within the scope of the claims of the present invention.

[0040] Unless otherwise specified, all raw materials and reagents used in the following examples are commercially available or may be prepared by known methods.

[0041] Examples 1 to 10 and Comparative Examples 1 to 9 The mass percentages of elements in the permanent magnet materials of Examples 1 to 10 and Comparative Examples 1 to 9 are shown in Table 1 below.

[0042] [Table 1] [Table 2]

[0043] The R—Fe—B based permanent magnet materials in Examples 1 to 10 and Comparative Examples 1 to 6 were produced by the following methods.

[0044] 1) Smelting According to the formulation shown in Table 1, the prepared raw materials were taken and placed in a crucible, and then the process was carried out in a medium-frequency vacuum induction rapid solidification melt spinning furnace, with the linear speed of the casting quench roll being 1.5 m / s, the casting temperature being 1450°C, and the average thickness of the smelted flakes being 0.25 mm.

[0045] 2) HD processing (coarse crushing) The material was subjected to hydrogen absorption, dehydrogenation and cooling treatments in a hydrogen pulverization furnace, with the pressure for the hydrogen absorption treatment being 100 KPa, the temperature for the dehydrogenation treatment being 580°C and the dehydrogenation time being 4.5 hours.

[0046] 3) Jet mill (fine grinding) By optimizing the jet mill grinding process parameters, the oxygen content during grinding was reduced to 50 ppm or less, and the particle size was controlled to 2.5 μm, with X90 / X10 = 4.0 and X100 = 10 μm. To produce the powder, 1.5% of the total mass of the permanent magnet material was added with dibutylhydroxytoluene and mixed for 5 hours.

[0047] 4) Molding The 1.8 T magnetic field oriented pressing method is used, and during the pressing process, the powder is in a completely sealed press and is continuously protected by filling it with nitrogen gas.

[0048] 5) Sintering The compact was placed in a sintering furnace under nitrogen gas protection, and decarburized and degassed for 2 hours at 300°C, 600°C, and 900°C, respectively. It was then vacuum sintered at 1015°C for 1.5 hours, and then filled with argon gas at 20 KPa and sintered at 1040°C for 3 hours. The furnace was then filled with argon gas at approximately 100 KPa, and the blower was started to cool the compact to below 50°C.

[0049] 6) Diffusion The permanent magnet material further required grain boundary diffusion treatment, which was carried out according to the Tb vapor diffusion process commonly used in the art, where the diffusion temperature was 900°C and the diffusion time was 30 hours. After the diffusion treatment, stress relief aging treatment was carried out at a temperature of 550°C for 4 hours to produce the permanent magnet material.

[0050] Comparative Example 7 3) Jet mill (fine grinding) By optimizing the jet milling process parameters, the oxygen content during the milling process was ≦50 ppm, and the particle size control SMD was 2.5 μm, X90 / X10 = 5.0, and X100 = 25 μm. To produce the powder, 1.5% dibutylhydroxytoluene was added and mixed for 5 hours. The remaining blending, smelting, HD, pressing, sintering, and diffusion processes were the same as in Example 1.

[0051] Comparative Example 8 5) Sintering First, the green compact was placed in a sintering furnace under nitrogen gas protection, and decarburized and degassed at 600°C and 900°C for 2 hours each, then vacuum sintered at 1015°C for 1.5 hours, and then filled with argon gas at 20 KPa and sintered at 1040°C for 3 hours. After that, the furnace was filled with argon gas at approximately 100 KPa, and the blower was started to cool the compact to below 50°C.

[0052] The remaining steps of compounding, smelting, HD, press molding, sintering, and diffusion were the same as in Example 1.

[0053] Comparative Example 9 5) Sintering First, the green compacts were placed in a sintering furnace under nitrogen gas protection, and then decarburized and degassed at 900°C for 2 hours. They were then vacuum sintered at 1015°C* for 1.5 hours, and then filled with argon gas at 20 KPa and sintered at 1040°C for 3 hours. The furnace was then filled with argon gas at approximately 100 KPa, and the blower was started to cool the compacts to below 50°C.

[0054] The remaining steps of compounding, smelting, HD, press molding, sintering, and diffusion were the same as in Example 1.

[0055] The permanent magnet materials manufactured in each of Examples 1 to 10 and Comparative Examples 1 to 9 were taken and their magnetic properties, weight loss properties and bending strength were measured. The results are shown in Table 2 below.

[0056] The residual magnetism (Br), coercive force (Hcj), and magnetic energy product (BH (max) ) The magnetic properties were detected using the NIM-62000 rare earth permanent magnet measuring system of the Institute of Metrology, the weight loss properties were determined using the D10-10 sample column and the German HAST high temperature and humidity tester (130℃, 0.26 atm, 100% RH, 480 h), and the bending strength was determined using a three-point bending device and tested in accordance with the GB / T 14452-93 (three-point bending) standard.

[0057] [Table 3] [Table 4]

[0058] As can be seen from the table above, the present invention precisely designs the formulation to incorporate elements such as Ti, Ga, and Cu into the grain boundary phase of this system's permanent magnet material, which are beneficial to the permanent magnet's Hcj, weight loss, and mechanical properties. These elements are uniformly distributed throughout the grain boundary phase at a certain ratio, reducing grain size, improving grain boundary wettability and corrosion resistance, and preventing abnormal grain growth. Furthermore, the optimized jet milling and sintering processes improve the microstructure of the main phase and grain boundary phase of the permanent magnet material, and rigorously control the O, C, and N contents in the permanent magnet material through strict process design, resulting in an R-Fe-B system permanent magnet material with excellent overall performance. The O, C, and N elements occupy the effective neodymium-rich phase in high-end permanent magnet materials, making the grain boundary phase brittle, which tends to reduce the Hcj and strength of the permanent magnet material. That is, by accurate formulation and process design, the present invention can achieve Br≧1.33 T, Hcj≧2000 KA / m, and 20-day HAST weight loss≦0.5 mg / cm. 2 , bending strength > 440 Mpa, making it a permanent magnet material with excellent overall performance.

[0059] FIG. 1 is a backscattered scanning electron microscope analysis diagram of the permanent magnet material in Example 1.

[0060] The grain boundary phase in different areas of Figure 1 was selected and subjected to EDS energy spectrum analysis at 2000x magnification to obtain the content (mass percentage) of each element in the grain boundary. From Figure 1 and the results of the EDS energy spectrum analysis, it is clear that the magnet of Example 1 is NdFe 14 It consists of a B main phase (gray area) and a grain boundary phase (silver-white area), of which the grain boundary phase contains Nd 33~45 Tb 0.1~1 Ti 4~8 Ga 0.4~1.5 Cu 0.3~1 Al 0.01~0.06 C O0.4~3 Fe 残り The percentage of the area of ​​the grain boundary phase in different regions to the total area of ​​the observation region of the selected microstructure was calculated, and it was found that the area of ​​the grain boundary phase / total area of ​​the observation region was 6.2-8.9%, that is, the density of the permanent magnet material was uniform.

[0061] In Table 3, the specific detection results of the grain boundary phase content are as follows:

[0062] [Table 5]

[0063] Although the embodiments of the present invention have been described above as examples, the scope of the claims of the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art without departing from the spirit and principles of the present invention should be included within the scope of the claims of the present invention. [Brief explanation of the drawings]

[0064] [Figure 1] 1 is a backscattered scanning electron microscope analysis diagram of the permanent magnet material in Example 1. FIG.

Claims

1. An R-Fe-B based permanent magnet material, the R-Fe-B based permanent magnet material having a composition, in mass percentage 100%, of 26.0 to 32.0% R, 0.3 to 4.0% RH, 0.5 to 3.0% Co, 0.1 to 0.25% Cu, 0.2 to 0.4% Ga, 0.2 to 0.4% Ti, 0.05 to 0.4% Al, 0.95 to 1.05% B, and the balance being Fe and unavoidable impurities, wherein R is neodymium (Nd) and / or praseodymium (Pr), and RH is dysprosium (Dy) and / or terbium (Tb), The mass percentage of the content of the elements is: 1) 1<Ti / Ga<2, 2) The relationship 5≦Co / Cu<15 must be satisfied; Br≧13.3 KGs, Hcj≧25.1 Koe, 20-day HAST weight loss of 0.1-0.5 mg / cm 2 , It is characterized by having a bending strength of more than 440 MPa. R-Fe-B permanent magnet material.

2. The R-Fe-B based permanent magnet material is characterized by having the following properties: Br is 13.3 to 15.0 KGs, Hcj is 25 to 34 Koe, and bending strength is 445 to 470 MPa. The permanent magnet material of claim 1 .

3. The R-Fe-B based permanent magnet material includes a grain boundary phase, and the composition of the grain boundary phase is R a RH b Ti c Ga d Cu e Al F CO g Fe 残り , 33≦a≦45, 0.1≦b≦16, 3≦c≦12, 0.4≦d≦2, 0.3≦e≦2.0, 0.01≦f≦0.1, 0.4≦g≦16, a+b+c+d+e+f+g+remainder=100, The R occupies the permanent magnet material a RH b Ti c Ga d Cu e Al F CO g Fe 残り is characterized in that the mass ratio of is 6 to 11 wt%; The permanent magnet material of claim 1 .

4. The unavoidable impurities are at least one of C, N, and O, and the oxygen content is 300 to 900 ppm, the carbon content is 400 to 800 ppm, and the nitrogen content is 200 to 600 ppm. The permanent magnet material of claim 1 .

5. A method for producing a permanent magnet material according to any one of claims 1 to 4, comprising smelting and casting raw materials for a Re-Fe-B based permanent magnet material, coarsely pulverizing, finely pulverizing, molding, sintering, processing, and diffusing the raw materials, During the fine grinding process, the particle size SMD is 2.3-2.7 μm, X90 / X10≦4.5, X100≦12.5 μm; The sintering process includes the steps of first subjecting a green compact produced by a molding process to decarburization and degassing treatment in 3 to 10 temperature zones, then vacuum sintering, then sintering in an inert atmosphere, and cooling to obtain the Re-Fe-B based permanent magnet material. Manufacturing method.

6. The coarse pulverization process is carried out in a hydrogen pulverization furnace by the steps of hydrogen absorption, dehydrogenation, and cooling, the pressure of the hydrogen absorption process is 90 to 110 KPa, the temperature of the dehydrogenation process is 550 to 620°C, and the dehydrogenation time is 3 to 6 hours; The fine pulverization is carried out by an inert gas jet mill, and the inert gas is nitrogen gas or argon gas. The oxygen content is controlled to ≦50 ppm during the milling process, and the particle size SMD of the particles is 2.5 μm during the milling process. The method of claim 5.

7. A method for heating a heating system, characterized in that the temperatures of the 3 to 10 temperature zones are different from each other. The method of claim 6.

8. When the decarburization and degassing treatment is carried out sequentially in 3 to 10 temperature zones, the decarburization and degassing treatment is first carried out in a first temperature zone, and then the treatment is moved to the next temperature zone in sequence. The method of claim 7.

9. The decarburization / venting treatment is performed in a first temperature zone, followed by a second temperature zone and a third temperature zone, wherein the temperature in the first temperature zone is 200-380°C, the temperature in the second temperature zone is higher than that in the first temperature zone, being 450-720°C, and the temperature in the third temperature zone is higher than that in the second temperature zone, being 750-1000°C. The method of claim 8.

10. A magnetic material comprising the Re-Fe-B based permanent magnet material according to any one of claims 1 to 4. Motor rotor magnetic steel.

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