RTB-based permanent magnets, their manufacturing methods, and applications

Abstract

The present invention discloses an RTB-based permanent magnet, its manufacturing method, and applications. The RTB permanent magnet has a nitrogen content of X ppm, where X satisfies 500≦X≦1300, an average crystal grain size of D μm, where D satisfies −2.6lnX+20≦D≦−2.3lnX+19.6, and includes main phase crystal grains and a grain boundary phase. The main phase crystal grains are R2Fe 14 The grain boundary phase is distributed between the main phase crystal grains, and the RN-rich regions of the grain boundary phase account for less than 10% by volume. The nitrogen element in the RTB permanent magnet according to the present invention is uniformly distributed at the grain boundaries and does not form NdN aggregates or the content of such aggregates is extremely low, which increases the coercive force Hcj of the magnet, reduces high-temperature magnetic loss, and simultaneously improves corrosion resistance.

Description

[Technical Field]

[0001] The present invention relates to an RTB-based permanent magnet, a manufacturing method thereof, and applications thereof. [Background technology]

[0002] In conventional RTB rare earth permanent magnet materials, nitrogen is an unavoidable impurity, mainly resulting from raw material impurities, organic additives added during processing, and the nitrogen gas atmosphere used in each process. Based on nitrogen content management and control capabilities, the possible nitrogen content range for RTB rare earth permanent magnet materials is 0.01-0.15%, with most measured nitrogen contents in this field ranging from 0.02-0.05%. High nitrogen content can easily form NdN aggregates, resulting in reduced coercivity (Hcj) due to rare earth consumption, while the increase in heterophases reduces the volume fraction of the main phase, resulting in reduced remanence (Br), high R activity, and reduced corrosion resistance of high-concentration aggregate materials. To improve performance, it is best to minimize the nitrogen impurity. In the prior art CN103875047A, the nitrogen content of magnets is reduced by changing the ambient atmosphere during the manufacturing process and using inert gases such as He and Ar instead of N2. However, this method is costly and unsuitable for large-scale mass production. Summary of the Invention [Problem to be solved by the invention]

[0003] The technical problem solved by the present invention is to provide an RTB-based permanent magnet, a manufacturing method thereof, and applications thereof, to overcome the drawback of prior art RTB-based permanent magnets, which have an excessively high nitrogen content, resulting in the formation of NdN agglomerates at grain boundaries and a reduced Hcj of the magnet. The RTB-based permanent magnet of the present invention can tolerate a higher nitrogen content without the need to specifically reduce the nitrogen content, thereby overcoming the limitations of the prior art. The nitrogen element in the RTB-based permanent magnet of the present invention is uniformly distributed at grain boundaries, and does not form NdN agglomerates, or the NdN agglomerates are present at an extremely low content, thereby increasing the magnet's coercive force Hcj, reducing high-temperature magnetic loss, and simultaneously improving corrosion resistance. [Means for solving the problem]

[0004] The present invention solves the above technical problems by the following technical solutions.

[0005] The present invention provides an RTB permanent magnet, the RTB permanent magnet having a nitrogen content of X ppm, where X satisfies 500≦X≦1300; The RTB permanent magnet has an average crystal grain size of D μm, and D satisfies -2.6lnX+20≦D≦-2.3lnX+19.6; The RTB permanent magnet includes main phase crystal grains and a grain boundary phase, and the main phase crystal grains are R2Fe 14 B, the grain boundary phase is distributed between the main phase crystal grains, and the volume fraction of the R—N rich regions of the grain boundary phase is less than 10%.

[0006] In the present invention, the volume fraction of the RN-rich region in the grain boundary phase may be calculated by detecting with an FE-EPMA device and combining it with image processing software commonly used in this field (for example, ImageJ).

[0007] In the present invention, the X preferably satisfies 550≦X≦1200, and more preferably 600≦X≦1000.

[0008] In the present invention, the above D preferably satisfies 1.6≦D≦5.0, and more preferably satisfies 2.1≦D≦4.8.

[0009] In one preferred embodiment of the present invention, X is 557 and D is 4.1.

[0010] In one preferred embodiment of the invention, X is 685 and D is 3.5.

[0011] In a preferred embodiment of the present invention, X is 812 and D is 3.2.

[0012] In one preferred embodiment of the present invention, X is 956 and D is 3.3.

[0013] In one preferred embodiment of the present invention, X is 1105 and D is 3.

[0014] In the present invention, the volume fraction of the RN-rich region in the grain boundary phase is preferably less than 5%, more preferably less than 3%, for example, 1% or 2%.

[0015] The present invention further provides a method for producing the RTB permanent magnet, which includes the following steps: S1: The raw material composition of the RTB permanent magnet is melted and refined to obtain a molten liquid. S2, the molten liquid is cast to obtain alloy flakes. S3: Hydrogen crushing the alloy flakes to obtain coarse powder. S4: The coarse powder is pulverized by a jet mill to obtain a fine powder. S5: The fine powder is molded to obtain a molded body. S6: Sintering the green body to obtain a sintered body. S7: The sintered body is subjected to a heat treatment to obtain the RTB-based permanent magnet.

[0016] In the present invention, the raw material composition for the RTB permanent magnet preferably contains the following components: Light rare earth elements RL, RL contains 24-30 wt% Nd and 0 wt% ≦ Pr ≦ 8 wt% Pr; heavy rare earth elements RH, RH including Dy and / or Tb, where 0 wt%≦RH≦0.9 wt%; Co: 0 to 1.5 wt% Al: 0.03 to 0.3 wt%, X: 0 to 0.6 wt%, where X is one or more of Zr and Ti; Cu: 0.1 to 0.4 wt% Ga: 0.1 to 0.4 wt% B: 0.92~0.98wt%, The balance is Fe, Here, wt% represents the mass percentage in the RTB permanent magnet, and the total of all components is 100 wt%.

[0017] In step S1, the melting and smelting can be carried out by a method commonly used in the art, for example, by melting and smelting in a high-frequency vacuum induction melting furnace.

[0018] Here, the degree of vacuum in the high frequency vacuum induction melting furnace is, for example, 5×10 -2 It is Pa.

[0019] Here, the temperature of the melting and smelting may be 1500°C or less, for example, 1480°C or less.

[0020] The melting and smelting is generally carried out in an alumina crucible, which introduces a portion of Al into the RTB permanent magnet.

[0021] In step S2, the casting process may be a conventional casting process in the art, for example, by casting and quenching in an Ar atmosphere in an intermediate frequency vacuum induction rapid solidification strip furnace to obtain alloy flakes.

[0022] Here, the pressure of the Ar atmosphere is preferably 5.5×10 4 It is Pa.

[0023] Here, the cooling rate of the rapid cooling is preferably 10 2 ℃ / sec~10 4 °C / sec.

[0024] In step S3, the hydrocracking is carried out in a hydrocracking furnace. The hydrocracking process can be a conventional hydrocracking process in the art, for example, it can only include hydrogen absorption, dehydrogenation and cooling.

[0025] Here, the hydrogen absorption can be carried out under the condition of a hydrogen pressure of 0.05 to 0.25 MPa, for example, 0.15 MPa.

[0026] Here, the dehydrogenation may be carried out under conditions of evacuation and temperature increase.

[0027] Here, the cooling can be carried out under a nitrogen gas atmosphere or an argon gas atmosphere.

[0028] When cooling is performed under a nitrogen gas atmosphere, the nitrogen gas atmosphere can be realized by introducing nitrogen gas, preferably 1 to 5 times, and the pressure of the nitrogen gas introduction is preferably 0.08 MPa.

[0029] In step S4, the jet mill pulverization is carried out in a jet mill.

[0030] The jet mill pulverization can be carried out in a nitrogen gas atmosphere containing 150 ppm or less of an oxidizing gas, where the oxidizing gas means oxygen and / or moisture.

[0031] The rotation speed of the jet mill pulverization is preferably 3500 to 6000 rpm.

[0032] The nozzle pressure of the jet mill pulverization is preferably 0.35 to 0.45 MPa, for example, 0.38 MPa.

[0033] The jet milling may be carried out for a period of 3 hours.

[0034] The particle size D50 of the fine powder obtained from the powder after the jet mill pulverization is preferably 2.5 to 5.0 μm.

[0035] Preferably, the method further comprises a step of uniformly mixing the fine powder with a lubricant after the jet mill pulverization, or a step of uniformly mixing the coarse powder with a lubricant before the jet mill pulverization. Here, the lubricant may be, for example, zinc stearate and benzotriazole, and the amount of the lubricant added may be 0.10 to 0.15%, for example, 0.12%, of the powder weight after mixing. Here, the mixing is preferably performed thoroughly using a V-type mixer.

[0036] In step S5, the molding process may be a conventional molding process in the art, such as magnetic field orientation molding. A preferred operation of the magnetic field orientation molding method is to use a perpendicular orientation type magnetic field molding machine, and apply 0.35 ton / cm in an orientation magnetic field of 1.6 T. 2 The powder was first compacted under a compacting pressure of 1.3 ton / cm, and then demagnetized in a 0.2 T magnetic field. The compact was sealed and then subjected to an isostatic press at a pressure of 1.3 ton / cm. 2 The secondary molding is carried out at a pressure of 0.05.

[0037] In step S6, the sintering is carried out in a sintering furnace. The sintering process may be a typical sintering process in the art, for example, by performing preheating, sintering, and cooling under vacuum conditions.

[0038] Here, the vacuum condition is, for example, 5×10 ‐3 It is Pa.

[0039] Here, the preheating temperature may be 300 to 600° C. The preheating time may be 1 to 2 hours. Preferably, the preheating is performed at temperatures of 300° C. and 600° C. for 1 hour each.

[0040] Here, the sintering temperature may be a normal sintering temperature in this field, for example, 1040 to 1090°C.

[0041] Here, the sintering time may be a normal sintering time in this field, for example, 4 hours.

[0042] Here, the cooling can be carried out under a nitrogen gas atmosphere or an argon gas atmosphere.

[0043] When the cooling is performed under a nitrogen gas atmosphere, the nitrogen gas atmosphere can be realized by introducing nitrogen gas, where the number of times of introducing nitrogen gas is preferably 1 to 5, and the pressure of introducing nitrogen gas is preferably 0.05 to 0.1 MPa, for example 0.1 MPa.

[0044] In step S7, the temperature of the heat treatment is preferably 430 to 600°C, for example 500°C.

[0045] Preferably, the heat treatment is 9×10 ‐3 The reaction is carried out under a vacuum of 0.5 Pa.

[0046] The heat treatment may last for 3 hours.

[0047] The heat treatment further includes a cooling step, which can be performed under a nitrogen gas atmosphere or an argon gas atmosphere.

[0048] In some preferred embodiments, for the cooling in step S3, the cooling in step S6, and the cooling in step S7, at most one of the cooling steps is performed under a nitrogen gas atmosphere.

[0049] In a preferred embodiment of the present invention, the cooling in step S3 is performed under an argon gas atmosphere, the cooling in step S6 is performed under an argon gas atmosphere, and the cooling in step S7 is performed under an argon gas atmosphere.

[0050] In a preferred embodiment of the present invention, the cooling in step S3 is performed in a nitrogen gas atmosphere, the cooling in step S6 is performed in an argon gas atmosphere, and the cooling in step S7 is performed in an argon gas atmosphere.

[0051] In a preferred embodiment of the present invention, the cooling in step S3 is performed in an argon gas atmosphere, the cooling in step S6 is performed in a nitrogen gas atmosphere, and the cooling in step S7 is performed in an argon gas atmosphere.

[0052] In a preferred embodiment of the present invention, the cooling in step S3 is performed under an argon gas atmosphere, the cooling in step S6 is performed under an argon gas atmosphere, and the cooling in step S7 is performed under a nitrogen gas atmosphere.

[0053] In a more preferred embodiment of the present invention, the cooling in step S3 is performed under an argon gas atmosphere, the cooling in step S6 is performed under an argon gas atmosphere, and the cooling in step S7 is performed under an argon gas atmosphere, the rotation speed of the jet mill grinding in step S4 is 4500 to 5500 rpm, and the nozzle pressure of the jet mill grinding in step S4 is 0.35 to 0.45 MPa.

[0054] In a more preferred embodiment of the present invention, the cooling in step S3 is performed under a nitrogen gas atmosphere, the cooling in step S6 is performed under an argon gas atmosphere, and the cooling in step S7 is performed under an argon gas atmosphere, the rotation speed of the jet mill grinding in step S4 is 5000 to 6000 rpm, and the nozzle pressure of the jet mill grinding in step S4 is 0.35 to 0.45 MPa.

[0055] In a more preferred embodiment of the present invention, the cooling in step S3 is performed under an argon gas atmosphere, the cooling in step S6 is performed under a nitrogen gas atmosphere, and the cooling in step S7 is performed under an argon gas atmosphere, the rotation speed of the jet mill grinding in step S4 is 5000 to 6000 rpm, and the nozzle pressure of the jet mill grinding in step S4 is 0.35 to 0.45 MPa.

[0056] In a more preferred embodiment of the present invention, the cooling in step S3 is performed under an argon gas atmosphere, the cooling in step S6 is performed under an argon gas atmosphere, and the cooling in step S7 is performed under a nitrogen gas atmosphere, the rotation speed of the jet mill grinding in step S4 is 5500 to 6000 rpm, and the nozzle pressure of the jet mill grinding in step S4 is 0.35 to 0.45 MPa.

[0057] In a more preferred embodiment of the present invention, the cooling in step S3 is performed under an argon gas atmosphere, the cooling in step S6 is performed under an argon gas atmosphere, and the cooling in step S7 is performed under an argon gas atmosphere; the rotation speed of the jet mill grinding in step S4 is 4500 to 5500 rpm; the nozzle pressure of the jet mill grinding in step S4 is 0.35 to 0.45 MPa; and the amount of the lubricant added in step S4 is 0.25 to 0.35% of the powder weight after mixing.

[0058] In a more preferred embodiment of the present invention, the cooling in step S3 is performed under a nitrogen gas atmosphere, the cooling in step S6 is performed under an argon gas atmosphere, and the cooling in step S7 is performed under an argon gas atmosphere; the rotation speed of the jet mill grinding in step S4 is 5000 to 6000 rpm; the nozzle pressure of the jet mill grinding in step S4 is 0.35 to 0.45 MPa; and the amount of the lubricant added in step S4 is 0.10 to 0.20% of the weight of the powder after mixing.

[0059] In a more preferred embodiment of the present invention, the cooling in step S3 is performed under an argon gas atmosphere, the cooling in step S6 is performed under a nitrogen gas atmosphere, and the cooling in step S7 is performed under an argon gas atmosphere; the rotation speed of the jet mill grinding in step S4 is 5000 to 6000 rpm; the nozzle pressure of the jet mill grinding in step S4 is 0.35 to 0.45 MPa; and the amount of the lubricant added in step S4 is 0.10 to 0.20% of the weight of the powder after mixing.

[0060] In a more preferred embodiment of the present invention, the cooling in step S3 is performed under an argon gas atmosphere, the cooling in step S6 is performed under an argon gas atmosphere, and the cooling in step S7 is performed under a nitrogen gas atmosphere; the rotation speed of the jet mill grinding in step S4 is 5500 to 6000 rpm; the nozzle pressure of the jet mill grinding in step S4 is 0.35 to 0.45 MPa; and the amount of the lubricant added in step S4 is 0.10 to 0.20% of the weight of the powder after mixing.

[0061] In a specific embodiment of the present invention, the cooling in step S3 is performed under an argon gas atmosphere, the cooling in step S6 is performed under an argon gas atmosphere, and the cooling in step S7 is performed under an argon gas atmosphere; the rotation speed of the jet mill grinding in step S4 is 5000 rpm; the nozzle pressure of the jet mill grinding in step S4 is 0.38 MPa; and the amount of lubricant added in step S4 is 0.30% of the powder weight after mixing.

[0062] In a specific embodiment of the present invention, the cooling in step S3 is performed under a nitrogen gas atmosphere, the cooling in step S6 is performed under an argon gas atmosphere, and the cooling in step S7 is performed under an argon gas atmosphere; the rotation speed of the jet mill grinding in step S4 is 5500 rpm; the nozzle pressure of the jet mill grinding in step S4 is 0.38 MPa; and the amount of lubricant added in step S4 is 0.12% of the powder weight after mixing.

[0063] In a specific embodiment of the present invention, in step S3, the cooling is performed under an argon gas atmosphere, in step S6, the cooling is performed under an argon gas atmosphere, in step S7, the cooling is performed under an argon gas atmosphere, the rotation speed of the jet mill grinding in step S4 is 4800 rpm, the nozzle pressure of the jet mill grinding in step S4 is 0.48 MPa, and the amount of lubricant added in step S4 is 0.30% of the powder weight after mixing.

[0064] In a specific embodiment of the present invention, the cooling in step S3 is performed under an argon gas atmosphere, the cooling in step S6 is performed under a nitrogen gas atmosphere, and the cooling in step S7 is performed under an argon gas atmosphere; the rotation speed of the jet mill grinding in step S4 is 5500 rpm; the nozzle pressure of the jet mill grinding in step S4 is 0.38 MPa; and the amount of lubricant added in step S4 is 0.12% of the powder weight after mixing.

[0065] In a specific embodiment of the present invention, the cooling in step S3 is performed under an argon gas atmosphere, the cooling in step S6 is performed under an argon gas atmosphere, and the cooling in step S7 is performed under a nitrogen gas atmosphere; the rotation speed of the jet mill grinding in step S4 is 6000 rpm; the nozzle pressure of the jet mill grinding in step S4 is 0.38 MPa; and the amount of lubricant added in step S4 is 0.12% of the powder weight after mixing.

[0066] In the present invention, preferably, after step S6 and before step S7, the manufacturing method further includes a step of grain boundary diffusion.

[0067] In the present invention, the grain boundary diffusion treatment can be carried out according to a conventional process in this field, for example, by depositing, coating or sputtering a diffusion source material on the surface of the sintered body obtained after the sintering, and then carrying out a diffusion heat treatment.

[0068] The diffusion source material is preferably a substance containing a heavy rare earth element. The substance containing a heavy rare earth element may be a heavy rare earth element metal, or a compound or alloy containing a heavy rare earth element. The heavy rare earth element preferably includes Tb and / or Dy.

[0069] Here, the temperature of the diffusion heat treatment may be 800 to 950°C, for example, 920°C.

[0070] Here, the duration of the diffusion heat treatment may be 12 to 48 hours, for example, 24 hours.

[0071] The present invention further provides the application of the above-mentioned RTB-based permanent magnet as an electronic component in a motor.

[0072] By arbitrarily combining the above-mentioned preferred conditions in accordance with common knowledge in this field, each preferred embodiment of the present invention can be obtained.

[0073] All of the reagents and raw materials used in the present invention are commercially available. [Effects of the Invention]

[0074] The positive and inventive effects of the present invention are as follows:

[0075] In the present invention, by controlling the relationship between the average crystal grain size and nitrogen content of an RTB-based permanent magnet, a uniform distribution of nitrogen elements is ensured, and the formation of RN-rich regions is avoided or reduced as much as possible. The volume fraction of the RN-rich regions in the grain boundary phase is less than 10%, and even less than 2%, thereby increasing the coercive force Hcj (Hcj ≥ 22.6 kOe, and even reaching 28.5 kOe), reducing high-temperature magnetic loss (thermal demagnetization at 120°C does not exceed 0.5%, and thermal demagnetization at 150°C does not exceed 1.0%), and improving corrosion resistance (in the HAST test, the weight change ΔM before and after the test was 0.57 mg / cm). 2 (not exceeding 100%). [Brief explanation of the drawings]

[0076] [Figure 1] FIG. 1 is a Nd and N distribution diagram obtained by FE-EPMA surface scanning of the RTB permanent magnet produced in Example 3. [Figure 2] FIG. 2 is a Nd and N distribution map obtained by FE-EPMA surface scanning of the RTB permanent magnet produced in Comparative Example 3, where point 1 is the Nd-rich region. DETAILED DESCRIPTION OF THE INVENTION

[0077] The present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the above examples. In the following examples, experimental methods for which specific conditions are not specified are selected according to conventional methods and conditions or product specifications.

[0078] The manufacturing method for RTB permanent magnets is as follows. Examples 1, 2, 4, and 5 and Comparative Examples 1, 2, and 4

[0079] S1, Melting and smelting process: The raw material composition prepared according to the ingredients in Table 1 was placed in an alumina crucible and melted in a 5 × 10 -2 Vacuum melting and smelting is carried out under conditions of a vacuum of 100 Pa and 1480°C.

[0080] S2, introduce Ar into the intermediate frequency vacuum induction rapid solidification strip furnace, and 5.5 × 10 4 Casting was performed in an Ar atmosphere with a pressure of 10 Pa and rapid cooling (rate was 10 2 ℃ / sec~10 4 °C / sec) to obtain alloy pieces.

[0081] S3. Hydrogen crushing process: The hydrogen crushing furnace containing the alloy flakes is evacuated at room temperature, and then hydrogen gas with a purity of 99.9% is introduced into the hydrogen crushing furnace. The hydrogen gas pressure is maintained at 0.15 MPa, and after sufficient hydrogen is absorbed, the furnace is heated while being evacuated to fully dehydrogenate. Argon gas or nitrogen gas is then introduced to cool the alloy flakes, and the coarse powder after hydrogen crushing is taken out.

[0082] S4. Jet mill grinding process: In a nitrogen gas atmosphere with an oxidizing gas (oxygen or moisture) content of 150 ppm or less, the coarse powder after hydrogen crushing is jet milled for 3 hours under the conditions of a constant jet mill winding wheel rotation speed and jet mill grinding nozzle pressure to obtain a fine powder with a D50 of 2.5 to 5.0 μm. The lubricants zinc stearate and benzotriazole are added in certain amounts to the fine powder, which is then thoroughly mixed in a V-type mixer.

[0083] S5. Magnetic field molding process: Using a perpendicular magnetic field molding machine, in a 1.6T magnetic field, 0.35 ton / cm 2 The mixed powder is subjected to primary molding under a molding pressure of 1.3 ton / cm. After primary molding, the primary molding is demagnetized in a magnetic field of 0.2 T. The primary molding is sealed to prevent contact with air, and then subjected to a hydrostatic pressing machine under a pressure of 1.3 ton / cm. 2 Secondary molding is performed at a pressure of .

[0084] S6, sintering process: Each compact is carried into a sintering furnace and sintered to 5 × 10 -3 The mixture is sintered under a vacuum of 100 Pa, maintained at temperatures of 300°C and 600°C for 1 hour each, and then sintered at a temperature of 1040°C for 2 hours. Argon gas or nitrogen gas is then introduced to adjust the pressure to 0.1 MPa, and the mixture is then cooled to room temperature.

[0085] S7, heat treatment process: 9 x 10-3 The sintered body is tempered for 3 hours at a heat treatment temperature of 500°C under a vacuum of 100 Pa, and then cooled to room temperature by introducing argon gas or nitrogen gas and then removed to obtain an RTB-based permanent magnet. Example 3 and Comparative Example 3

[0086] A step of grain boundary diffusion is further included between step S6 and step S7.

[0087] Each set of sintered body was processed into a magnet measuring 50mm long x 39mm wide and 4.5mm thick, with the thickness direction being the magnetic field orientation direction. After surface cleaning, a raw material made from Tb fluoride was applied to the entire surface of the magnet. After coating, the magnet was dried and then subjected to a diffusion heat treatment at 920°C for 24 hours in a high-purity argon gas atmosphere, after which it was cooled to room temperature.

[0088] The raw material component compositions and manufacturing process parameters (lubricant addition amount, dehydrogenation gas, rotation speed of the jet mill winding wheel, jet mill nozzle pressure, sintering cooling gas, and heat treatment cooling gas) of the RTB permanent magnets in Examples 1 to 5 and Comparative Examples 1 to 4 are shown in Tables 1 and 2.

[0089] Table 1. Components and content (wt%) of raw material composition of RTB permanent magnet JPEG2025535824000002.jpg33161

[0090] Table 2: Compositions and process parameters of Examples 1 to 5 and Comparative Examples 1 to 4 JPEG2025535824000003.jpg120161 Effect Example 1

[0091] The characteristics of the RTB permanent magnets obtained in Example 3 and Comparative Example 3 were evaluated using an FE-EPMA device, and the results are shown in FIGS. 1 and 2, respectively.

[0092] The different colors represent the higher or lower concentration of each element, with darker colors indicating lower concentrations and pinker colors indicating higher concentrations, as shown on the scale on the right.

[0093] As can be seen from Figure 1, the RTB permanent magnet produced in Example 3 has a relatively uniform distribution of Nd and N in the grain boundary phase, with little Nd-N concentration. As can be seen from Figure 2, the RTB permanent magnet produced in Comparative Example 3 has Nd and N concentrated in the same region in the grain boundary phase, with numerous Nd-N rich regions formed. Effect Example 2

[0094] (1) N content test: The surfaces of the RTB permanent magnets manufactured in Examples 1 to 5 and Comparative Examples 1 to 4 were ground to remove the oxide layer, and then a nitrogen content test was performed using an oxygen / nitrogen analyzer (Horiba, EMGA-620W). (2) Test of average crystal grain size D: The vertically oriented surfaces of the RTB permanent magnets produced in Examples 1 to 5 and Comparative Examples 1 to 4 were polished, and after etching with a 5% nitric acid solution, images were taken using a metallographic microscope at an amplified magnification of 1000 times. Three straight lines of length L were drawn at the top, middle, and bottom of the image, and the number of crystal grains per line segment n, the crystal grain size = L / n, was measured. The average crystal grain size was the average value of the three lines. (3) Volume fraction of RN-rich regions in the grain boundary phase: The vertically oriented surfaces of the RTB permanent magnets produced in Examples 1 to 5 and Comparative Examples 1 to 4 were polished, and surface scanning was performed using a field emission electron probe microanalyzer FE-EPMA (JEOL, 8530F). Proportional statistics were then performed using commonly used image processing software (e.g., ImageJ). (4) Magnetic property test: The magnetic properties (residual magnetic flux density Br, coercive force Hcj) of the RTB permanent magnets produced in Examples 1 to 5 and Comparative Examples 1 to 4 were measured using the NIM-2000 model permanent magnet material precision measurement system from the China Academy of Metrology. The test temperature was 20°C. (5) Thermal demagnetization test: The RTB permanent magnets produced in Examples 1 to 5 and Comparative Examples 1 to 4 were processed into 50 mm × 39 mm × 4.5 mm, and the permanent magnets were heated to 120°C or 150°C under semi-open conditions on a 2 mm thick iron plate with the 4.5 mm orientation direction, kept warm in an oven for 2 hours, and then cooled to room temperature. The magnetic flux before and after heating was measured using a magnetometer, and thermal demagnetization = (magnetic flux before heating - magnetic flux after heating) / magnetic flux before heating × 100%. (6) Corrosion Resistance HAST Test: The RTB permanent magnets manufactured in the examples and comparative examples were processed into 50mm x 39mm x 4.5mm pieces, with the 4.5mm orientation. They were then placed in a high-pressure accelerated aging tester with a humidity of 95% and a temperature of 130°C, and held for 240 hours. The samples were weighed before and after the test. Corrosion resistance was measured by the weight change per unit area (ΔM), where ΔM = (weight before test - weight after test) / surface area of ​​the sample.

[0095] The test results are shown in Table 3.

[0096] As can be seen from Table 3, by changing the amount of lubricant added, the type of dehydrogenation gas, the rotational speed of the jet mill winding wheel, the jet mill nozzle pressure, the type of sintering cooling gas, and the type of heat-treatment cooling gas, the N content and grain size of the manufactured RTB permanent magnet can be changed, which in turn affects the volume fraction of the RN-rich region in the grain boundary phase, the magnetic properties, and the corrosion resistance.

[0097] As can be seen from the effect data for Examples 1, 2, 4, and 5 and Comparative Examples 1, 2, and 4, the volume fraction of the RN-rich region in the grain boundary phase in the four Examples does not exceed 2%, while Comparative Examples 1, 2, and 4 reach 27%, 46%, and 58%, respectively. The remanence Br reaches 13.83 kGs in Example 2, but is a maximum of 13.73 kGs in the Comparative Example. The coercivity Hcj exceeds 22 kOe in all four Examples, while it does not exceed 20.2 kOe in the Comparative Example. The thermal demagnetization at 120°C does not exceed 0.4% in all four Examples, while it reaches 4.5%, 4.8%, and 4.3% in Comparative Examples 1, 2, and 4, respectively. Regarding corrosion resistance, the weight change per unit area for the four Examples is 0.57 mg / cm. 2 In contrast, the weight change per unit area of ​​the comparative example was 1.9 mg / cm 2 Exceeds.

[0098] The RTB permanent magnets manufactured in Example 3 and Comparative Example 3, which underwent grain boundary diffusion, also tend to increase or decrease in magnetic parameters similar to those of the RTB permanent magnets not underwent grain boundary diffusion. Specifically, the volume fraction of the RN-rich region in the grain boundary phase in Example 3 is only 1%, while in Comparative Example 3 it reaches 38%. The remanence Br and coercivity Hcj of Comparative Example 3 decrease compared to Example 3. The thermal demagnetization at 150°C is 0.90% in Example 3, while in Comparative Example 3 it reaches 4.2%. Regarding corrosion resistance, the weight change per unit area of ​​Example 3 is 0.564 mg / cm. 2 In contrast, the weight change per unit area of ​​Comparative Example 3 was 1.815 mg / cm 2 is.

[0099] Table 3 Comparison of magnet parameters between Examples 1 to 5 and Comparative Examples 1 to 4 JPEG2025535824000004.jpg65161

[0100] In the present invention, the N content and grain size of the RTB permanent magnet are adjusted by using the process conditions described above, thereby reducing the volume fraction of the N-rich region in the grain boundary phase, increasing the remanence Br and coercivity Hcj, and reducing thermal demagnetization and weight change per unit area under hot and humid conditions, thereby having a positive effect on both the magnetic properties and corrosion resistance.

Claims

1. An RTB based permanent magnet, The nitrogen content of the R-T-B system permanent magnet is set to X ppm, and X satisfies 500≦X≦1300, The average crystal grain size of the R-T-B based permanent magnet is defined as D μm, and D satisfies -2.6 lnX + 20≦D≦-2.3 lnX + 19.6, The R-T-B system permanent magnet includes main phase crystal grains and a grain boundary phase. The main phase crystal grains are R ２ Fe １４ B, the grain boundary phase is distributed between the main phase crystal grains, and the volume fraction of the R—N rich region of the grain boundary phase in the grain boundary phase is less than 10%. An RTB-based permanent magnet characterized by:

2. wherein X satisfies 550≦X≦1200, preferably 600≦X≦1000, and / or The D satisfies 1.6≦D≦5.0, preferably 2.1≦D≦4.8, and / or The volume fraction of the R-N rich region in the grain boundary phase is less than 5%, preferably less than 3%, for example, 1% or 2%.

2. The RTB system permanent magnet according to claim 1.

3. said X is 557 and said D is 4.1; or said X is 685 and said D is 3.5; or said X being 812 and said D being 3.2; or said X being 956 and said D being 3.3; or said X is 1105 and said D is 3; 3. The RTB system permanent magnet according to claim 2.

4. A method for producing an R-T-B system permanent magnet according to any one of claims 1 to 3, comprising the steps of: Step S1: Melting and refining the raw material composition of the R-T-B system permanent magnet to obtain a molten liquid; Step S2: casting the molten liquid to obtain alloy flakes; Step S3: subjecting the alloy flakes to hydrogen crushing to obtain coarse powder; Step S4: Jet mill pulverization of the coarse powder to obtain fine powder; Step S5: forming the fine powder into a compact; Step S6 of sintering the compact to obtain a sintered body; and step S7 of heat treating the sintered body to obtain the R-T-B based permanent magnet. A method for producing an RTB based permanent magnet.

5. In step S1, the melting and smelting may be performed in a high-frequency vacuum induction melting furnace. Here, the degree of vacuum in the high frequency vacuum induction melting furnace is preferably 5×10 －２ Pa, the smelting temperature is preferably 1500°C or less, for example 1480°C or less, and the smelting is preferably carried out in an alumina crucible; and / or In step S2, the casting step is performed in an intermediate frequency vacuum induction rapid solidification strip furnace in an Ar atmosphere to obtain alloy flakes, and the pressure of the Ar atmosphere is preferably 5.5×10 ４ Pa, and the cooling rate of the quenching is preferably 10 ２ °C / sec ~ 10 ４ °C / sec, In step S5, the molding process is a magnetic field orientation molding method, and preferably, the magnetic field orientation molding method is performed using a perpendicular orientation type magnetic field molding machine in an orientation magnetic field of 1.6 T at 0.35 ton / cm ２ The powder was first compacted under a compacting pressure of 1.3 ton / cm, and then demagnetized in a magnetic field of 0.2 T. The compact was sealed and then compressed using an isostatic press. ２ The secondary molding is performed at a pressure of 5. The method for producing an RTB system permanent magnet according to claim 4.

6. In step S3, the hydrocrushing process may only include hydrogen absorption, dehydrogenation, and cooling, wherein the hydrogen absorption is preferably carried out under a hydrogen pressure of 0.05 to 0.25 MPa, for example 0.15 MPa, the dehydrogenation is preferably carried out under a condition of increasing the temperature while evacuating, the cooling is preferably carried out under a nitrogen gas atmosphere or an argon gas atmosphere, and preferably, when the cooling is carried out under a nitrogen gas atmosphere, the nitrogen gas atmosphere is achieved by introducing nitrogen gas, wherein the number of times of introducing nitrogen gas is preferably 1 to 5, and the pressure of introducing nitrogen gas is preferably 0.08 MPa; and / or In step S4, the jet milling is carried out in a nitrogen gas atmosphere having an oxidizing gas content of 150 ppm or less, and the oxidizing gas is preferably oxygen and / or moisture, and / or In step S4, the rotation speed of the jet mill is 3500 to 6000 rpm, and / or In step S4, the nozzle pressure of the jet milling is 0.35 to 0.45 MPa, for example, 0.38 MPa; and / or In step S4, the particle size D50 of the fine powder obtained from the powder after the jet mill pulverization is 2.5 to 5.0 μm, and / or In step S4, the method may further comprise a step of uniformly mixing the fine powder and a lubricant after the jet milling, or may further comprise a step of uniformly mixing the coarse powder and a lubricant before the jet milling, wherein the lubricant is, for example, zinc stearate and benzotriazole, and the amount of the lubricant added is preferably 0.10 to 0.15% of the powder weight after mixing, for example 0.12%, and wherein the mixing is preferably performed thoroughly using a V-type mixer; and / or In step S6, the sintering step may be performed by preheating, sintering, and cooling under vacuum conditions. The vacuum conditions are preferably 5×10 ‐３ Pa, the preheating temperature is preferably 300 to 600°C, the preheating time is preferably 1 to 2 hours, more preferably, the preheating is performed at temperatures of 300°C and 600°C for 1 hour each, the sintering temperature is preferably 1040 to 1090°C, the cooling is performed in a nitrogen gas atmosphere or an argon gas atmosphere, preferably, when the cooling is performed in a nitrogen gas atmosphere, the nitrogen gas atmosphere is achieved by introducing nitrogen gas, wherein the number of times of introducing nitrogen gas is preferably 1 to 5 times, and the pressure of introducing nitrogen gas is preferably 0.05 to 0.1 MPa, for example 0.1 MPa, and / or In step S7, the temperature of the heat treatment is 430 to 600°C, for example 500°C, and / or In step S7, the heat treatment is performed at 9×10 ‐３ and / or In step S7, the heat treatment further includes a cooling step, and the cooling is preferably performed under a nitrogen gas atmosphere or an argon gas atmosphere.

5. The method for producing an RTB system permanent magnet according to claim 4.

7. With regard to the cooling in step S3, the cooling in step S6, and the cooling in step S7, the cooling in at most one step is performed under a nitrogen gas atmosphere; Preferably, in step S3, the cooling is performed under an argon gas atmosphere, in step S6, the cooling is performed under an argon gas atmosphere, and in step S7, the cooling is performed under an argon gas atmosphere; more preferably, in step S4, the rotation speed of the jet mill pulverization is 4500 to 5500 rpm, and in step S4, the nozzle pressure of the jet mill pulverization is 0.35 to 0.45 MPa; and even more preferably, in step S4, the amount of lubricant added is 0.25 to 0.35% of the weight of the powder after mixing; Preferably, in step S3, the cooling is performed under a nitrogen gas atmosphere, in step S6, the cooling is performed under an argon gas atmosphere, and in step S7, the cooling is performed under an argon gas atmosphere; more preferably, in step S4, the rotation speed of the jet mill pulverization is 5000 to 6000 rpm, and in step S4, the nozzle pressure of the jet mill pulverization is 0.35 to 0.45 MPa; and even more preferably, in step S4, the amount of lubricant added is 0.10 to 0.20% of the weight of the powder after mixing. Preferably, in step S3, the cooling is performed under an argon gas atmosphere, in step S6, the cooling is performed under a nitrogen gas atmosphere, and in step S7, the cooling is performed under an argon gas atmosphere; more preferably, in step S4, the rotation speed of the jet mill pulverization is 5000 to 6000 rpm, and in step S4, the nozzle pressure of the jet mill pulverization is 0.35 to 0.45 MPa; and even more preferably, in step S4, the amount of lubricant added is 0.10 to 0.20% of the weight of the powder after mixing. Preferably, in step S3, the cooling is performed under an argon gas atmosphere, in step S6, the cooling is performed under an argon gas atmosphere, and in step S7, the cooling is performed under a nitrogen gas atmosphere; more preferably, in step S4, the rotation speed of the jet mill grinding is 5500 to 6000 rpm, and in step S4, the nozzle pressure of the jet mill grinding is 0.35 to 0.45 MPa; and even more preferably, in step S4, the amount of lubricant added is 0.10 to 0.20% of the weight of the powder after mixing.

7. The method for producing an RTB system permanent magnet according to claim 6.

8. After step S6 and before step S7, further comprising a step of grain boundary diffusion; Preferably, the grain boundary diffusion step may be performed by depositing, applying, or sputtering a diffusion source material on the surface of the sintered body, followed by a diffusion heat treatment; Here, the diffusion source material is preferably a substance containing a heavy rare earth element, and the substance containing a heavy rare earth element is preferably a heavy rare earth element metal, or a compound or alloy containing a heavy rare earth element, and the heavy rare earth element preferably contains Tb and / or Dy; Here, the temperature of the diffusion heat treatment is preferably 800 to 950°C, for example, 920°C. Here, the duration of the diffusion heat treatment is preferably 12 to 48 hours, for example, 24 hours.

5. The method for producing an RTB system permanent magnet according to claim 4.

9. The raw material composition of the R-T-B based permanent magnet contains the following components: The light rare earth elements RL, RL contain 24 to 30 wt% Nd and 0 wt%≦Pr≦8 wt% Pr, The heavy rare earth elements RH, RH include Dy and / or Tb, where 0 wt%≦RH≦0.9 wt%; Co: 0 to 1.5 wt%, Al: 0.03 to 0.3 wt%, X: 0 to 0.6 wt%, where X is one or more of Zr and Ti; Cu: 0.1 to 0.4 wt%, Ga: 0.1-0.4wt%, B: 0.92-0.98wt%, The balance is Fe, Here, wt% represents the mass percentage of the R-T-B system permanent magnet, and the total of each component is 100 wt%.

5. The method for producing an RTB system permanent magnet according to claim 4.

10. 4. The RTB system permanent magnet according to claim 1, wherein the RTB system permanent magnet is used as an electronic component in a motor.

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