Method for improving performance of sintered NdFeB magnets

Abstract

The present disclosure relates generally to a method for improving the performance of sintered NdFeB magnet. A method of preparing a sintered NdFeB magnet therefore comprises the steps of: a) preparing alloy flakes from a raw material of the NdFeB magnet by a strip casting process; and b) preparing a coarse alloy powder from the alloy flakes by a hydrogen decrepitation process, the hydrogen decrepitation process including treatment of the alloy flakes under a hydrogen pressure of 0.10 MPa to 0.25 MPa for a duration of 1 to 3.5 hours, then degassing the hydrogen at a predetermined temperature between 300° C. to 400° C. for a duration time of 0.5 to 5 hours, and then mixing the resulting coarse alloy powder with a lubricant.

Claims

1. A method of preparing a sintered NdFeB magnet, said method comprising the steps of: a) preparing alloy flakes from a raw material of the NdFeB magnet by a strip casting process; and b) preparing an alloy powder from the alloy flakes by a hydrogen decrepitation process, the hydrogen decrepitation process including treatment of the alloy flakes under a hydrogen pressure of 0.10 MPa to 0.25 MPa for a duration of 1 to 3.5 hours, then degassing the hydrogen at a predetermined temperature between 300° C. to 400° C. for a duration time of 0.5 to 5 hours, and then mixing the resulting alloy powder with a lubricant; c) preparing a magnetic powder from the alloy powder by a jet milling process, wherein nitrogen is used as carrier gas in the jet milling process and the magnetic powder is mixed with a lubricant; d) molding the magnetic powder mixed with lubricant into a compact, wherein the step of molding includes orienting the powder under a magnetic field and then subjecting the compact to a cold isostatic treatment; e) sintering and aging the compact to obtain the sintered NdFeB magnet, wherein the step of sintering further includes a step of heating to and holding at 250° C. for a duration of 2 hours, then heating to and holding at 550° C. for a duration of 2 hours, then heating to and holding at 750° C. for a duration of 2 hours, and finally raising the temperature to 1010° C. to 1040° C. and holding at the temperature for a duration of 2 to 5 hours; wherein a heating rate from 550° C. to 750° C. is between 1° C./min to 4° C./min.

2. The method of claim 1, wherein in step b) degassing hydrogen is performed at a temperature between 340° C. to 380° C. for a duration of 1 to 3 hours.

3. The method of claim 1, wherein in step b) degassing hydrogen is performed until the hydrogen content in the alloy powder is between 300 ppm to 850 ppm.

4. The method of claim 2, wherein in step b) degassing hydrogen is performed until the hydrogen content in the alloy powder is between 300 ppm to 850 ppm.

5. The method of claim 1, wherein said step of molding is defined as after the forming process the unit weight of the compact is no more than 600 g.

6. The method of claim 1, wherein a heating rate from 550° C. to 750° C. is between 2° C./min to 3° C./min.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) In step b), firstly the alloy flakes are performed in a hydrogen decrepitation process under a predetermined hydrogen pressure of between 0.10 MPa to 0.25 MPa and for a duration time of 1 to 3.5 hours. Then the dehydrogenation temperature is set to be between 300° C. to 400° C. and the dehydrogenation time is between 0.5 to 5 hours. The main reaction occurring under such a condition is Re.sub.2Fe.sub.14BH.sub.x+Re—H.sub.y—Re.sub.2Fe.sub.14B+x/2H.sub.2+Re—H.sub.y. Thus, the dehydrogenation reaction occurs mainly in Re.sub.2Fe.sub.14BH.sub.x phase (e.g. Nd.sub.2Fe.sub.14BH.sub.2), while the dehydrogenation reaction of Re—H.sub.y phase (e.g. NdH.sub.2) hardly occurs. In the process of jet milling following step b), the rare earth-rich phase which is easier to be oxidized and azotized, exists in the form of Re—H.sub.y. Thus, the specific degasing conditions can effectively reduce the oxidation and nitridation rate of the fine magnetic powder achieved by the jet milling. At the same time, the rare earth-rich phase in the form of hydride can improve the milling efficiency.

(2) During the subsequent forming and orientation process, the Nd.sub.2Fe.sub.14B phase basically does not contain hydrogen, which is beneficial to improve the orientation of the magnetic powder and increase the remanence of the magnet. Cold isostatic treatment can make the green body more uniform in density and stress, especially when the hydrogen content is higher.

(3) During the sintering process, the reaction Re—H.sub.y-Re+y/2H.sub.2 occurs around a temperature of 750° C. The released hydrogen may combine with the remaining carbon elements in the magnetic powder to form hydrocarbons and discharge from the blanks, reducing the content of carbon in the blanks. This is beneficial to increase magnetic performance of the magnet.

(4) When heating from 550° C. to 750° C., controlling the heating rate in a special range can effectively prevent the occurrence of micro-cracks in the magnet due to excessive dehydrogenation, thus ensuring the mechanical properties of the magnet.

DESCRIPTION OF EMBODIMENTS

(5) To have a better understanding of the present disclosure, the examples set forth below provide illustrations of the present disclosure. The examples are only used to illustrate the present disclosure and do not limit the scope of the present disclosure.

Implementing Example 1

(6) A raw material is used including Nd—Pr being present at 31.0 wt. %, B being present at 0.96 wt. %, Al being present at 0.45 wt. %, Co being present at 1.0 wt. %, Cu being present at 0.15 wt. %, Ga being present at 0.10 wt. %, Dy being present at 1.50 wt. %, Ti being present at 0.08 wt. %, and Fe being present as a balance, and unavoidable impurities. The raw material is made into alloy flakes by a strip casting process and then coarsely broken by a mechanical method and then the alloy flakes are disintegrated to produce an alloy powder. The step of disintegrating is further defined as subjecting the alloy flakes in a hydrogen decrepitation process under a hydrogen pressure of 0.10 MPa for a duration of 3.5 hours. The step of disintegrating further includes a step of degassing the hydrogen at a predetermined temperature of 300° C. for a duration of 0.5 hour. After dehydrogenation the hydrogen content in the hydrogen treatment alloy powder is tested. The hydrogen treatment alloy powder is then mixed with a conventional ester lubricant having a weight content of 0.05 wt. %. Next, the coarse alloy powder with the lubricant is pulverized by subjecting the coarse alloy powder to a jet milling process using a carrier gas of nitrogen to produce a fine magnetic powder having an average particle size of 3.8 μm. Then, the fine magnetic powder is mixed with the conventional ester lubricant having a weight content of 0.10 wt. %. The fine magnetic powder mixed with lubricant is then molded into a compact. The step of molding includes orienting the powder under a magnetic field of 1.8 T. The unit weight of the compact is 600 g and then subjected to a cold isostatic treatment. The sintering and aging processes are carried out in a vacuum furnace, and the vacuum degree is below 5×10.sup.−1 Pa. The step of sintering further includes a step of heating to 250° C. for a duration of 2 hours, then heating to 550° C. for a duration of 2 hours, and then heating to 750° C. for a duration of 2 hours. While the temperature rises from 550° C. to 750° C., the heating rate is controlled as 1° C./min. Finally, the temperature is raised to 1010° C. for a duration of 5 hours. After sintering a conventional aging treatment is subjected. Concentration of carbon and nitrogen and hydrogen element in the finally magnet is detected. The magnetic performance of the magnet is also tested. The magnet is cut into size of 5 mm*5 mm**35 mm for bending strength testing. Five samples have been tested separately.

(7) TABLE-US-00001 TABLE 1 Testing results of Implementing Example 1 H content H C N in coarse content content content alloy in in in bending powder magnet magnet magnet Hcj strength (ppm) (ppm) (ppm) (ppm) Br(T) (kA/m) (MPa) 1 850 3 550 322 1.315 1791 420 2 835 4 575 363 1.320 1783 416 3 795 3 569 344 1.309 1799 433 4 816 6 565 375 1.316 1807 417 5 785 8 535 368 1.314 1807 418 ave 816 5 559 354 1.315 1797 421

Implementing Example 2

(8) A raw material is used including Nd—Pr being present at 31.0 wt. %, B being present at 0.96 wt. %, Al being present at 0.45 wt. %, Co being present at 1.0 wt. %, Cu being present at 0.15 wt. %, Ga being present at 0.10 wt. %, Dy being present at 1.50 wt. %, Ti being present at 0.08 wt. %, and Fe being present as a balance, and unavoidable impurities. The raw material is made into alloy flakes by a strip casting process and then coarsely broken by a mechanical method. Then the alloy flakes are disintegrated to produce a coarse alloy powder. The step of disintegrating is further defined as subjecting the alloy flakes in a hydrogen decrepitation process under a hydrogen pressure of 0.25 MPa for a duration of 1 hours. The step of disintegrating further includes a step of degassing the hydrogen at a predetermined temperature of 400° C. for a duration of 5 hour. After dehydrogenation, the hydrogen content in the hydrogen treatment alloy powder is tested. The hydrogen treated coarse alloy powder is then mixed with a conventional ester lubricant having a weight content of 0.05 wt. %. Next, the coarse alloy powder with the lubricant is pulverized by subjecting the coarse alloy powder to a jet milling process using a carrier gas of nitrogen to produce a fine magnetic powder having an average particle size of 3.8 μm. Then, the fine magnetic powder is mixed with a conventional ester lubricant having a weight content of 0.10 wt. %. The powder mixed with lubricant is then molded into a compact. The step of molding includes orienting the powder under a magnetic field of 1.8 T. The unit weight of the compact is 600 g and then subjected to a cold isostatic treatment. The sintering and aging processes are carried out in a vacuum furnace, and the vacuum degree is below 5×10.sup.−1 Pa. The step of sintering further includes a step of heating to 250° C. for a duration of 2 hours, then heating to 550° C. for a duration of 2 hours, and then heating to 750° C. for a duration of 2 hours. While the temperature rises from 550° C. to 750° C., the heating rate is controlled as 4° C./min. Finally, the temperature is raised to 1040° C. for a duration of 2 hours. After sintering a conventional aging treatment is subjected. Concentration of carbon and nitrogen and hydrogen element in the finally magnet is detected. The magnetic performance of the magnet is also tested. The magnet is cut into size of 5 mm*5 mm**35 mm for bending strength testing. Test five sets of data separately.

(9) TABLE-US-00002 TABLE 2 Testing results of Implementing Example 2 H content H C N in coarse content content content alloy in in in bending powder magnet magnet magnet Br Hcj strength (ppm) (ppm) (ppm) (ppm) (T) (kA/m) (MPa) 1 350 3 625 422 1.325 1759 417 2 335 4 675 463 1.322 1783 416 3 375 3 664 434 1.319 1743 423 4 316 3 665 475 1.318 1775 410 5 300 7 635 432 1.324 1767 418 ave 335 4 653 445 1.322 1766 417

Implementing Example 3

(10) A raw material is used including Nd—Pr being present at 31.0 wt. %, B being present at 0.96 wt. %, Al being present at 0.45 wt. %, Co being present at 1.0 wt. %, Cu being present at 0.15 wt. %, Ga being present at 0.10 wt. %, Dy being present at 1.50 wt. %, Ti being present at 0.08 wt. %, and Fe being present as a balance, and unavoidable impurities. The raw material is made into alloy flakes by a strip casting process and then coarsely broken by a mechanical method. Then the alloy flakes are disintegrated to produce a coarse alloy powder. The step of disintegrating is further defined as subjecting the alloy flakes in a hydrogen decrepitation process under a hydrogen pressure of 0.1 MPa for a duration of 3.5 hours. The step of disintegrating further includes a step of degassing the hydrogen at a predetermined temperature of 360° C. for a duration of 2 hour. After dehydrogenation, the hydrogen content in the hydrogen treatment alloy powder is tested. The hydrogen treated coarse alloy powder is then mixed with a conventional ester lubricant having a weight content of 0.05 wt. %. Next, the coarse alloy powder with the lubricant is pulverized by subjecting the coarse alloy powder to a jet milling process using a carrier gas of nitrogen to produce a fine magnetic powder having an average particle size of 3.8 μm. Then, the fine magnetic powder is mixed with a conventional ester lubricant having a weight content of 0.10 wt. %. The powder mixed with lubricant is then molded into a compact. The step of molding includes orienting the powder under a magnetic field of 1.8 T. The unit weight of the compact is 400 g and then subjected to a cold isostatic treatment. The sintering and aging processes are carried out in a vacuum furnace, and the vacuum degree is below 5×10.sup.−1 Pa. The step of sintering further includes a step of heating to 250° C. for a duration of 2 hours, then heating to 550° C. for a duration of 2 hours, and then heating to 750° C. for a duration of 2 hours. While the temperature rises from 550° C. to 750° C., the heating rate is controlled as 2.5° C./min. Finally, the temperature is raised to 1040° C. for a duration of 2 hours. After sintering a conventional aging treatment is subjected. Concentration of carbon and nitrogen and hydrogen element in the finally magnet is detected. The magnetic performance of the magnet is also tested. The magnet is cut into size of 5 mm*5 mm**35 mm for bending strength testing. Test five sets of data separately.

(11) TABLE-US-00003 TABLE 3 Testing results of Implementing Example 3 H content H C N in coarse content content content alloy in in in bending powder magnet magnet magnet Br Hcj strength (ppm) (ppm) (ppm) (ppm) (T) (kA/m) (MPa) 1 480 3 625 422 1.322 1791 416 2 515 5 575 413 1.322 1783 427 3 475 3 611 434 1.319 1775 431 4 516 5 635 375 1.316 1775 417 5 523 7 620 395 1.322 1791 419 ave 502 5 613 408 1.320 1783 422

Implementing Example 4

(12) A raw material is used including Nd—Pr being present at 31.0 wt. %, B being present at 0.96 wt. %, Al being present at 0.45 wt. %, Co being present at 1.0 wt. %, Cu being present at 0.15 wt. %, Ga being present at 0.10 wt. %, Dy being present at 1.50 wt. %, Ti being present at 0.08 wt. %, and Fe being present as a balance, and unavoidable impurities. The raw material is made into alloy flakes by a strip casting process and then coarsely broken by a mechanical method. Then the alloy flakes are disintegrated to produce a coarse alloy powder. The step of disintegrating is further defined as subjecting the alloy flakes in a hydrogen decrepitation process under a hydrogen pressure of 0.2 MPa for a duration of 2 hours. The step of disintegrating further includes a step of degassing the hydrogen at a predetermined temperature of 350° C. for a duration of 3 hour. After dehydrogenation, the hydrogen content in the hydrogen treatment alloy powder is tested. The hydrogen treated coarse alloy powder is then mixed with a conventional ester lubricant having a weight content of 0.05 wt. %. Next, the coarse alloy powder with the lubricant is pulverized by subjecting the coarse alloy powder to a jet milling process using a carrier gas of nitrogen to produce a fine magnetic powder having an average particle size of 3.8 μm. Then, the fine magnetic powder is mixed with a conventional ester lubricant having a weight content of 0.10 wt. %. The powder mixed with lubricant is then molded into a compact. The step of molding includes orienting the powder under a magnetic field of 1.8 T. The unit weight of the compact is 500 g and then subjected to a cold isostatic treatment. The sintering and aging processes are carried out in a vacuum furnace, and the vacuum degree is below 5×10.sup.−1 Pa. The step of sintering further includes a step of heating to 250° C. for a duration of 2 hours, then heating to 550° C. for a duration of 2 hours, and then heating to 750° C. for a duration of 2 hours. While the temperature rises from 550° C. to 750° C., the heating rate is controlled as 2° C./min. Finally, the temperature is raised to 1040° C. for a duration of 3 hours. After sintering a conventional aging treatment is subjected. Concentration of carbon and nitrogen and hydrogen element in the finally magnet is detected. The magnetic performance of the magnet is also tested. The magnet is cut into size of 5 mm*5 mm**35 mm for bending strength testing. Test five sets of data separately.

(13) TABLE-US-00004 TABLE 4 Testing results of Implementing Example 4 H content H C N in coarse content content content alloy in in in bending powder magnet magnet magnet Br Hcj strength (ppm) (ppm) (ppm) (ppm) (T) (kA/m) (MPa) 1 501 4 595 431 1.323 1767 419 2 478 6 605 423 1.321 1783 426 3 475 3 618 439 1.316 1759 433 4 511 7 629 390 1.319 1775 417 5 503 4 633 401 1.324 1767 427 ave 494 5 616 417 1.321 1770 424

Comparative Example 1

(14) A raw material is used including Nd—Pr being present at 31.0 wt. %, B being present at 0.96 wt. %, Al being present at 0.45 wt. %, Co being present at 1.0 wt. %, Cu being present at 0.15 wt. %, Ga being present at 0.10 wt. %, Dy being present at 1.50 wt. %, Ti being present at 0.08 wt. %, and Fe being present as a balance, and unavoidable impurities. The raw material is made into alloy flakes by a strip casting process and then coarsely broken by a mechanical method. Then the alloy flakes are disintegrated to produce a coarse alloy powder. The step of disintegrating is further defined as subjecting the alloy flakes in a hydrogen decrepitation process under a hydrogen pressure of 0.1 MPa for a duration of 3.5 hours. The step of disintegrating further includes a step of degassing the hydrogen at a predetermined temperature of 550° C. for a duration of 5 hour. After dehydrogenation, the hydrogen content in the hydrogen treatment alloy powder is tested. The hydrogen treated coarse alloy powder is then mixed with a conventional ester lubricant having a weight content of 0.05 wt. %. Next, the coarse alloy powder with the lubricant is pulverized by subjecting the coarse alloy powder to a jet milling process using a carrier gas of nitrogen to produce a fine magnetic powder having an average particle size of 3.8 μm. Then, the fine magnetic powder is mixed with a conventional ester lubricant having a weight content of 0.10 wt. %. The powder mixed with lubricant is then molded into a compact. The step of molding includes orienting the powder under a magnetic field of 1.8 T. The unit weight of the compact is 600 g and then subjected to a cold isostatic treatment. The sintering and aging processes are carried out in a vacuum furnace, and the vacuum degree is below 5×10.sup.−1 Pa. The step of sintering further includes a step of heating to 250° C. for a duration of 2 hours, then heating to 550° C. for a duration of 2 hours, and then heating to 750° C. for a duration of 2 hours. While the temperature rises from 550° C. to 750° C., the heating rate is controlled as 2.5° C./min. Finally, the temperature is raised to 1040° C. for a duration of 2 hours. After sintering a conventional aging treatment is subjected. Concentration of carbon and nitrogen and hydrogen element in the finally magnet is detected. The magnetic performance of the magnet is also tested. The magnet is cut into size of 5 mm*5 mm**35 mm for bending strength testing. Test five sets of data separately.

(15) TABLE-US-00005 TABLE 5 Testing results of Comparative Example 1 H content H C N in coarse content content content alloy in in in bending powder magnet magnet magnet Br Hcj strength (ppm) (ppm) (ppm) (ppm) (T) (kA/m) (MPa) 1 70 6 881 699 1.321 1695 426 2 77 4 842 645 1.322 1727 418 3 65 4 831 703 1.319 1703 435 4 69 3 902 721 1.321 1727 426 5 69 5 876 706 1.324 1711 419 ave 70 4 866 695 1.321 1713 425

Comparative Example 2

(16) A raw material is used including Nd—Pr being present at 31.0 wt. %, B being present at 0.96 wt. %, Al being present at 0.45 wt. %, Co being present at 1.0 wt. %, Cu being present at 0.15 wt. %, Ga being present at 0.10 wt. %, Dy being present at 1.50 wt. %, Ti being present at 0.08 wt. %, and Fe being present as a balance, and unavoidable impurities. The raw material is made into alloy flakes by a strip casting process and then coarsely broken by a mechanical method. Then the alloy flakes are disintegrated to produce a coarse alloy powder. The step of disintegrating is further defined as subjecting the alloy flakes in a hydrogen decrepitation process under a hydrogen pressure of 0.1 MPa for a duration of 3.5 hours. No dehydrogenation was performed after the hydrogen decrepitation process. The hydrogen treated coarse alloy powder is then mixed with a conventional ester lubricant having a weight content of 0.05 wt. %. Next, the coarse alloy powder with the lubricant is pulverized by subjecting the coarse alloy powder to a jet milling process using a carrier gas of nitrogen to produce a fine magnetic powder having an average particle size of 3.8 μm. The fine magnetic powder is treated at a predetermined temperature of 550° C. for a duration of 5 hour for degassing the hydrogen. After dehydrogenation, the hydrogen content in the fine magnetic powder is tested. Then, the fine magnetic powder is mixed with a conventional ester lubricant having a weight content of 0.10 wt. %. The powder mixed with lubricant is then molded into a compact. The step of molding includes orienting the powder under a magnetic field of 1.8 T. The unit weight of the compact is 600 g and then subjected to a cold isostatic treatment. The sintering and aging processes are carried out in a vacuum furnace, and the vacuum degree is below 5×10.sup.−1 Pa. The step of sintering further includes a step of heating to 250° C. for a duration of 2 hours, then heating to 550° C. for a duration of 2 hours, and then heating to 750° C. for a duration of 2 hours. While the temperature rises from 550° C. to 750° C., the heating rate is controlled as 2.5° C./min. Finally, the temperature is raised to 1040° C. for a duration of 2 hours. After sintering a conventional aging treatment is subjected. Concentration of carbon and nitrogen and hydrogen element in the finally magnet is detected. The magnetic performance of the magnet is also tested. The magnet is cut into size of 5 mm*5 mm**35 mm for bending strength testing. Test five sets of data separately.

(17) TABLE-US-00006 TABLE 6 Testing results of Comparative Example 2 H content H C N in fine content content content magnet in in in bending powder magnet magnet magnet Br Hcj strength (ppm) (ppm) (ppm) (ppm) (T) (kA/m) (MPa) 1 55 3 887 338 1.322 1743 418 2 65 6 832 343 1.322 1759 418 3 58 5 831 344 1.319 1727 429 4 58 4 865 319 1.316 1759 427 5 59 4 896 321 1.322 1735 432 ave 59 4 862 333 1.320 1745 425

Comparative Example 3

(18) A raw material is used including Nd—Pr being present at 31.0 wt. %, B being present at 0.96 wt. %, Al being present at 0.45 wt. %, Co being present at 1.0 wt. %, Cu being present at 0.15 wt. %, Ga being present at 0.10 wt. %, Dy being present at 1.50 wt. %, Ti being present at 0.08 wt. %, and Fe being present as a balance, and unavoidable impurities. The raw material is made into alloy flakes by a strip casting process and then coarsely broken by a mechanical method. Then the alloy flakes are disintegrated to produce a coarse alloy powder. The step of disintegrating is further defined as subjecting the alloy flakes in a hydrogen decrepitation process under a hydrogen pressure of 0.1 MPa for a duration of 3.5 hours. The step of disintegrating further includes a step of degassing the hydrogen at a predetermined temperature of 360° C. for a duration of 2 hour. After dehydrogenation, the hydrogen content in the hydrogen treatment alloy powder is tested. The hydrogen treated coarse alloy powder is then mixed with a conventional ester lubricant having a weight content of 0.05 wt. %. Next, the coarse alloy powder with the lubricant is pulverized by subjecting the coarse alloy powder to a jet milling process using a carrier gas of nitrogen to produce a fine magnetic powder having an average particle size of 3.8 μm. Then, the fine magnetic powder is mixed with a conventional ester lubricant having a weight content of 0.10 wt. %. The powder mixed with lubricant is then molded into a compact. The step of molding includes orienting the powder under a magnetic field of 1.8 T. The unit weight of the compact is 750 g and then subjected to a cold isostatic treatment. The sintering and aging processes are carried out in a vacuum furnace, and the vacuum degree is below 5×10.sup.−1 Pa. The step of sintering further includes a step of heating to 250° C. for a duration of 2 hours, then heating to 550° C. for a duration of 2 hours, and then heating to 750° C. for a duration of 2 hours. While the temperature rises from 550° C. to 750° C., the heating rate is controlled as 7° C./min. Finally, the temperature is raised to 1040° C. for a duration of 2 hours. After sintering a conventional aging treatment is subjected. Concentration of carbon and nitrogen and hydrogen element in the finally magnet is detected. The magnetic performance of the magnet is also tested. The magnet is cut into size of 5 mm*5 mm**35 mm for bending strength testing. Test five sets of data separately.

(19) TABLE-US-00007 TABLE 7 Testing results of Comparative Example 3 H content H C N in coarse content content content alloy in in in bending powder magnet magnet magnet Br Hcj strength (ppm) (ppm) (ppm) (ppm) (T) (kA/m) (MPa) 1 500 4 625 412 1.312 1767 388 2 502 4 575 413 1.309 1751 404 3 484 5 611 394 1.315 1743 395 4 512 6 635 393 1.311 1759 389 5 529 6 620 395 1.307 1767 411 ave 505 5 613 401 1.311 1758 397

(20) Comparing Implementing Examples 1, 2, 3, 4 with Comparative Example 1, when the dehydrogenation process of the present disclosure is used, the hydrogen content in the hydrogen treatment powder is significantly higher than that after the conventional dehydrogenation process, which can effectively suppress the nitriding ratio of rare earth phase during the jet milling. This can significantly reduce the N content in the final magnet. The average N content corresponding to the Implementing Examples 1, 2, 3, and 4 are 354 ppm, 445 ppm, 408 ppm, and 417 ppm. Respectively, the N content of Comparative Example 1 is as high as 695 ppm.

(21) The C content of the Implementing Examples 1, 2, 3, and 4 is also significantly lower than it in Comparative Example 1, indicating that the presence of a certain amount of hydrogen in the magnetic powder can play a role in decarburization during the sintering process.

(22) At the same time, because the residual hydrogen in the magnetic powder does not exist in the main phase, it will not affect the orientation of the magnetic powder during the molding orientation process. Therefore, the Br of the sample of the Implementing Examples 1, 2, 3, and 4 has almost no decrease compared with the Comparative Example 1 and Comparative Example 2. However, the coercivity is greatly improved due to the decrease of N and C content.

(23) Comparing Implementing Examples 1, 2, 3, 4 and Comparative Example 3, what can be seen is that controlling the heating rate from 550° C. to 750° C. between 1° C./min to 4° C./min can avoid the occurrence of microcracks in the magnet due to excessive dehydrogenation. The bending strength of magnet in the samples of Implementing Examples 1, 2, 3, and 4 is significantly higher than that of Comparative Example 3.

(24) The control of the unit weight of the compact in the Implementing Examples is also to achieve better dehydrogenation during the sintering process and to improve the mechanical properties. Comparing the Implementing Examples with Comparative Example 2, also Comparative Example 2 reduces the N content in the magnet. But after dehydrogenation and the jet milling, the H content in the magnetic powder is too low to have the effect of decarburization. Therefore, the magnet of Comparative Example 2 has a higher carbon content and a lower coercivity.

(25) In summary, the method provided in the present disclosure can effectively reduce the content of N and C in the magnet, which can improve the magnetic properties of sintered NdFeB magnet.