A sintered NdFeB magnet and its preparation method

Abstract

The present invention provides a sintered NdFeB and a preparation method thereof, and belongs to the technical field of rare earth permanent magnet materials. The present invention uses a tooling made of pure iron material to bake the crucible before use, which can avoid the problem that the crucible structure is loose due to the use of graphite core baking, which affects the service life in the later period, and the problem that impurities are continuously generated during use due to the loose structure and affect the purity of the melt in the later period, thereby significantly improving the microstructure of the casting; during refining, stopping heating for 30 to 90 seconds every 5 to 8 minutes can promote the generation of crystal nuclei, thereby improving the microstructure of the casting; during pouring, the argon partial pressure is set to 5 to 10 KPa, which reduces the argon partial pressure, reduces the disturbance of the melt pouring surface during pouring, promotes the growth of columnar crystals in the melt, and thus significantly improves the microstructure of the sintered NdFeB. The experimental results show that, according to the metallographic pictures of the embodiment, it can be seen that the preparation method provided by the present invention can significantly improve the microstructure of the sintered NdFeB.

Description

Technical Field

[0001] The invention belongs to the technical field of rare earth permanent magnet materials, and specifically relates to a sintered NdFeB and a preparation method thereof. Background Art

[0002] NdFeB is a tetragonal crystal formed by neodymium, iron and boron. NdFeB can be divided into sintered NdFeB and bonded NdFeB. Sintered NdFeB permanent magnets have the advantages of high magnetic energy product, small size and light weight, and have been widely used in defense aviation, communications, electronic medical and machinery. However, due to the limitations of NdFeB powder metallurgy process, further improvement of magnetic properties requires improvement of material microstructure.

[0003] At present, the production process of sintered NdFeB is batching, casting, powder making, molding and sintering. It is very difficult to improve the microstructure of the sintered NdFeB. The microstructure has poor columnar crystal penetration, uneven thickness, and uneven distribution of neodymium-rich phase. Therefore, how to improve the microstructure of sintered NdFeB has become a problem to be solved in this field. Summary of the invention

[0004] The purpose of the present invention is to provide a sintered NdFeB and a preparation method thereof. The preparation method provided by the present invention can significantly improve the microstructure of the sintered NdFeB, with good columnar crystal penetration, uniform thickness, and uniform distribution of the neodymium-rich phase, thereby greatly improving the magnetic properties of the sintered NdFeB.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing sintered NdFeB, comprising the following steps:

[0007] (1) melting and refining the alloy raw materials in a crucible in sequence to obtain an alloy melt; the crucible is prepared by baking and sintering using a tooling made of pure iron; during the refining, heating is stopped for 30 to 90 seconds every 5 to 8 minutes;

[0008] (2) pouring the alloy melt obtained in step (1) under argon protection to obtain a casting; the argon partial pressure during the argon protection pouring is 5 to 10 KPa;

[0009] (3) The casting obtained in step (2) is subjected to hydrogen crushing, air flow grinding, pressing, sintering and tempering in sequence to obtain sintered NdFeB.

[0010] Preferably, the refining temperature in step (1) is 1350-1500° C., and the refining time is 10-20 min.

[0011] Preferably, the refining time is 15 to 18 minutes.

[0012] Preferably, the interval time for stopping heating during refining in step (1) is 6 to 7 minutes, and the time for stopping heating is 50 to 80 seconds.

[0013] Preferably, the temperature of the argon protection pouring in step (2) is 1430-1480°C.

[0014] Preferably, in step (2), the partial pressure of argon is 6 to 8.5 KPa.

[0015] Preferably, the sintering in step (3) is carried out under vacuum conditions.

[0016] Preferably, the sintering temperature in step (3) is 1323-1383 K, and the sintering time is 3-6 h.

[0017] Preferably, the tempering treatment in step (3) is firstly kept at 1073-1213K for 2-3 hours, and then kept at 733-913K for 3-5 hours.

[0018] The present invention also provides sintered NdFeB prepared by the preparation method described in the above technical solution.

[0019] The invention provides a preparation method of sintered NdFeB, comprising the following steps: melting and refining alloy raw materials in a crucible in sequence to obtain an alloy melt; baking and sintering the crucible using a tooling made of pure iron during preparation; stopping heating for 30 to 90 seconds every 5 to 8 minutes during refining; pouring the alloy melt with argon protection to obtain a casting; the argon partial pressure during the argon protection pouring is 5 to 10 KPa; and hydrogen crushing, air flow grinding, pressing and sintering the casting in sequence to obtain sintered NdFeB. The present invention improves the baking and sintering process of the crucible during preparation, and uses a tooling made of pure iron to bake and sinter the crucible, which can avoid the problem of using a graphite core to bake and sinter, resulting in the continuous generation of impurities in the crucible during use that affects the purity of the melt, thereby reducing the influence of the crucible on the purity of the melt, and thus significantly improving the microstructure of the casting; during refining, the static process of stopping heating for 30 to 90 seconds every 5 to 8 minutes can promote the generation of crystal nuclei, thereby improving the microstructure of the casting; during pouring, the argon partial pressure is set to 5 to 10 KPa, which reduces the argon partial pressure compared to the traditional pouring process, reduces the disturbance of the melt pouring surface during pouring, and promotes the growth of columnar crystals in the melt, thereby improving the microstructure of the casting, and then significantly improving the microstructure of the sintered NdFeB. The experimental results show that, according to the metallographic pictures of the embodiment, it can be seen that the preparation method provided by the present invention can significantly improve the microstructure of the sintered NdFeB. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1It is a structural schematic diagram of the tooling made of pure iron material of the present invention;

[0021] Figure 2 This is a metallographic picture of the sintered NdFeB prepared in Example 1;

[0022] Figure 3 This is a metallographic picture of the sintered NdFeB prepared in Comparative Example 1;

[0023] Figure 4 This is a metallographic picture of the sintered NdFeB prepared in Example 2. DETAILED DESCRIPTION

[0024] The present invention provides a method for preparing sintered NdFeB, comprising the following steps:

[0025] (1) melting and refining the alloy raw materials in a crucible in sequence to obtain an alloy melt; the crucible is prepared by baking and sintering using a tooling made of pure iron; during the refining, heating is stopped for 30 to 90 seconds every 5 to 8 minutes;

[0026] (2) pouring the alloy melt obtained in step (1) under argon protection to obtain a casting; the argon partial pressure during the argon protection pouring is 5 to 10 KPa;

[0027] (3) The casting obtained in step (2) is subjected to hydrogen crushing, air flow grinding, pressing, sintering and tempering in sequence to obtain sintered NdFeB.

[0028] The invention melts and refines alloy raw materials in a crucible in sequence to obtain an alloy melt.

[0029] The present invention has no special limitation on the ratio of the alloy raw materials, which can be adjusted according to actual needs.

[0030] In the present invention, the crucible is baked and sintered using a tooling made of pure iron during preparation. The present invention improves the baking and sintering process of the crucible during preparation, and uses a tooling made of pure iron for baking and sintering, which can avoid the problem of using a graphite core for baking and sintering, which causes the crucible to continuously generate impurities during use and affects the purity of the melt, thereby reducing the influence of the crucible on the purity of the melt, and further significantly improving the microstructure of the casting.

[0031] In the present invention, the shape of the tooling made of pure iron is preferably a plurality of cylinders arranged outside a hollow cylinder; the plurality of cylinders are arranged around the hollow cylinder. The present invention has no special limitation on the size of the tooling made of pure iron, and it can be adjusted according to the actual size of the crucible required. The present invention has no special limitation on the chemical composition of the pure iron material, and pure iron materials well known to those skilled in the art can be used.

[0032] The structural schematic diagram of the tooling made of pure iron material of the present invention is as follows Figure 1 As shown. Figure 1 It can be seen that the tooling made of pure iron material includes a hollow cylinder and a plurality of cylinders arranged outside the hollow cylinder, and the plurality of cylinders are arranged around the hollow cylinder.

[0033] The present invention has no special limitation on the process parameters for baking and sintering the tooling made of pure iron, and the process parameters for baking and sintering well known to those skilled in the art can be used.

[0034] In the present invention, the melting and refining are preferably carried out under vacuum conditions; the vacuum degree is preferably ≤ 0.5 Pa. The present invention performs melting, i.e., melting and refining, under vacuum conditions, which can avoid the influence of external air on the purity of the alloy and can also reduce the gas and low-melting-point harmful metal impurities in the alloy.

[0035] The present invention has no special limitation on the melting temperature, as long as the raw material is melted. The present invention has no special limitation on the heating rate, as long as the heating rate known in the art is used and the raw material is melted.

[0036] In the present invention, the refining temperature is preferably 1350-1500°C; the refining time is preferably 10-20 minutes, more preferably 15-18 minutes. The present invention can further improve the degree of refining by controlling the refining temperature and time.

[0037] In the present invention, the heating is stopped for 30 to 90 seconds every 5 to 8 minutes during refining; the interval time of stopping heating during refining is preferably 6 to 7 minutes; the time of stopping heating during refining is preferably 50 to 80 seconds, and more preferably 60 to 70 seconds. The present invention adopts a static process of stopping heating for 30 to 90 seconds every 5 to 8 minutes during refining to promote the generation of crystal nuclei and form a large number of short-range ordered structures, thereby improving the microstructure of the casting and achieving the purpose of significantly improving the microstructure of sintered NdFeB.

[0038] After obtaining the alloy melt, the present invention uses argon protection to cast the alloy melt to obtain a casting sheet. The present invention uses argon protection to cast, which can effectively reduce secondary oxidation during the casting process, especially significantly reduce the content of inclusions.

[0039] In the present invention, the temperature of the argon protection pouring is preferably 1430-1480°C; the argon partial pressure during the argon protection pouring is 5-10KPa, preferably 6-8.5KPa, and more preferably 7-8KPa. The present invention sets the argon partial pressure to 5-10KPa during pouring, which reduces the argon partial pressure compared to the traditional pouring process (25-30KPa), reduces the disturbance of the melt pouring surface during pouring, promotes the growth of columnar crystals in the melt, and thus improves the microstructure of the casting, achieving the purpose of significantly improving the microstructure of the sintered NdFeB, so that the columnar crystals in the metallographic phase have good penetration, uniform thickness, and uniform distribution of the neodymium-rich phase.

[0040] In the present invention, the cooling method of the argon protection casting is air cooling. In the present invention, the rotation speed of the copper roller of the smelting furnace during the argon protection casting is preferably 30 to 35 revolutions per minute; the linear speed of the copper roller during the argon protection casting is preferably 1.2 to 1.6 m / s. In the present invention, the thickness of the casting is preferably 0.25 to 0.5 mm.

[0041] After obtaining the casting sheet, the present invention sequentially performs hydrogen crushing, air flow grinding, pressing, sintering and tempering treatment on the casting sheet to obtain sintered NdFeB.

[0042] The present invention has no special limitation on the operations of hydrogen crushing and air flow milling, and the operations of hydrogen crushing and air flow milling well known to those skilled in the art can be used.

[0043] In the present invention, the product obtained by airflow grinding is preferably subjected to orientation molding in a magnetic field press before the compression molding; the magnetic field strength of the magnetic field press is preferably 1280-1600KA / m. The present invention has no special limitation on the model of the magnetic field press, and instruments and equipment familiar to those skilled in the art can be used. The present invention has no special limitation on other process parameters of the orientation molding, and processes familiar to those skilled in the art can be used. In the present invention, the product obtained by airflow grinding is subjected to orientation molding in a magnetic field press, so that the powder particles can be oriented.

[0044] In the present invention, the compression molding is preferably cold isostatic pressing. The present invention has no special restrictions on the process parameters of the cold isostatic pressing, and the process parameters well known to those skilled in the art are adopted, and the density of the obtained product is ensured to be 4.1-4.3 g / cm 3 That's it.

[0045] In the present invention, the sintering is preferably carried out under vacuum conditions; the vacuum degree is preferably <5×10 -2Pa; the sintering temperature is preferably 1323-1383 K, more preferably 1350-1379 K; the sintering time is preferably 3-6 hours. The present invention can further improve the compactness of sintered NdFeB by controlling the sintering process parameters.

[0046] After sintering, the present invention preferably cools the sintered product. In the present invention, the cooling is preferably gas quenching cooling. The present invention has no special limitation on the operation of the gas quenching cooling, and the gas quenching cooling well known to those skilled in the art can be used.

[0047] In the present invention, the tempering treatment is preferably carried out by first keeping the temperature at 1073-1213K for 2-3 hours and then keeping the temperature at 733-913K for 3-5 hours; more preferably, the tempering treatment is carried out by first keeping the temperature at 1100-1200K for 2.5 hours and then keeping the temperature at 800-850K for 3.5-4 hours; the cooling method of the tempering treatment is preferably air cooling.

[0048] The present invention has no particular limitation on the rate of heating to 1073-1213 K, and any heating rate known to those skilled in the art may be used. The present invention has no particular limitation on the rate of cooling to 733-913 K, and any cooling rate known to those skilled in the art may be used.

[0049] The present invention improves the baking and sintering process of the crucible during preparation, and adopts a tooling made of pure iron material to bake and sinter the crucible, which can avoid the problem that the crucible continuously generates impurities and affects the purity of the melt during use due to the baking and sintering of a graphite core, thereby reducing the influence of the crucible on the purity of the melt, and further significantly improving the microstructure of the casting; during refining, a static process of stopping heating for 30 to 90 seconds every 5 to 8 minutes can promote the generation of crystal nuclei, thereby improving the microstructure of the casting; during pouring, the argon partial pressure is set to 5 to 10 KPa, which reduces the argon partial pressure compared with the traditional pouring process, reduces the disturbance of the pouring surface of the melt during pouring, and promotes the growth of columnar crystals in the melt, thereby improving the microstructure of the casting, and further significantly improving the microstructure of the sintered NdFeB.

[0050] The present invention integrates the improvement of process and tooling equipment, and proposes a process method for improving the microstructure of NdFeB, which significantly improves the magnet performance under the premise of the same formula, and is specifically achieved through the following three improvements:

[0051] 1. Improve the baking and sintering process of the crucible, minimize the impact on the strength of the crucible, reduce the impact of the crucible material on the purity of the charge, and thereby improve the microstructure of the material casting: The first step in the preparation of sintered NdFeB is to cast the prepared raw materials into alloy sheets. The crucible used in this process requires high strength, good stability, and not easy to introduce impurities into the molten steel. The alumina crucible currently used uses a graphite core for crucible baking. The graphite core is mainly composed of carbon elements, which will have a certain reduction reaction on the crucible at high temperatures, causing the strength of the crucible to slowly decrease. There is a risk of continuous falling off and mixing into the melt in the later stage. The present application uses a tooling made of pure iron material to bake and sinter the crucible, which can avoid the problem of using a graphite core for baking and sintering, which causes the crucible to continuously produce impurities during use and affects the purity of the melt, thereby reducing the impact of the crucible on the purity of the melt, and significantly improving the microstructure of the casting.

[0052] 2. Use multiple static processes when casting: stop heating for 30 to 90 seconds every 5 to 8 minutes during refining, which can promote the formation of crystal nuclei and improve the microstructure of the casting.

[0053] 3. Add a vacuum process before pouring to reduce the argon partial pressure during pouring, reduce the disturbance of the melt pouring surface during pouring, promote the growth of melt columnar crystals, and improve the microstructure of the casting.

[0054] The present invention also provides sintered NdFeB prepared by the preparation method described in the above technical solution.

[0055] The microstructure of the sintered NdFeB provided by the present invention is significantly improved, and the columnar crystals in the metallographic phase have good penetration, uniform thickness, and uniform distribution of the Nd-rich phase.

[0056] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] Example 1

[0058] A method for preparing sintered NdFeB, comprising the following steps:

[0059] (1) melting and refining the alloy raw materials in a crucible under vacuum conditions to obtain an alloy melt; wherein the formula of the alloy raw materials is designed as follows (by weight ratio): Pr-Nd 26 Dy 4.2 Fe bal Co 1.58 B 0.98 Al 0.25 Cu 0.1 Nb0.2 Ga 0.2 ; The crucible is prepared by baking and sintering with a tool made of pure iron; the shape of the tool made of pure iron is that a plurality of cylinders are arranged outside a hollow cylinder; the plurality of cylinders are arranged around the hollow cylinder; the vacuum degree before heating is 0.50Pa; the refining temperature range is 1350-1480°C, and the refining time is 15min; during refining, the heating is stopped for 30s every 5min;

[0060] (2) The alloy melt obtained in the step (1) is cast by argon protection, and air-cooled to obtain a casting sheet with a thickness of 0.25 to 0.50 mm; wherein the temperature of the argon protection casting is 1430° C.; the argon partial pressure during the argon protection casting is 8.5 KPa; the rotation speed of the copper roller of the smelting furnace during the argon protection casting is 30 revolutions per minute; and the linear speed of the copper roller during the argon protection casting is 1.3 m / s;

[0061] (3) The cast sheet obtained in step (2) is subjected to hydrogen crushing and air flow grinding in sequence to prepare fine powder with an average particle size of 2.8 μm and a particle size distribution of d[9,0] / d[1,0]=3.8-4.2;

[0062] (4) The fine powder obtained in step (3) is oriented and formed in a 1280-1600KA / m magnetic field press, and then cold isostatically pressed to obtain a density of 4.2 g / cm 3 of greenware;

[0063] (5) Sintering the green compact obtained in step (4) under vacuum conditions, followed by gas quenching and cooling, and then tempering to obtain sintered NdFeB; wherein the vacuum degree is less than 5×10 -2 Pa; the sintering temperature is 1338K, and the sintering time is 6h; the tempering treatment is first heated to 1173K and kept warm for 3h, and then cooled to 773K and kept warm for 4h; the cooling method of the tempering treatment is air cooling.

[0064] Comparative Example 1

[0065] A method for preparing sintered NdFeB, comprising the following steps:

[0066] (1) melting and refining the alloy raw materials in a crucible under vacuum conditions to obtain an alloy melt; wherein the formula of the alloy raw materials is designed as follows (by weight ratio): Pr-Nd 26 Dy 4.2 Fe bal Co 1.58 B 0.98 Al 0.25 Cu 0.1 Nb 0.2 Ga 0.2; The crucible is prepared by baking and sintering with a tool made of pure iron; the shape of the tool made of pure iron is that a plurality of cylinders are arranged outside a hollow cylinder; the plurality of cylinders are arranged around the hollow cylinder; the vacuum degree before heating is 0.50Pa; the refining temperature range is 1350-1480°C, and the refining time is 15min;

[0067] (2) The alloy melt obtained in the step (1) is cast by argon protection, and air-cooled to obtain a casting sheet with a thickness of 0.25 to 0.5 mm; wherein the temperature of the argon protection casting is 1430° C.; the argon partial pressure during the argon protection casting is 25 KPa; the rotation speed of the copper roller of the smelting furnace during the argon protection casting is 30 revolutions / min; and the linear speed of the copper roller during the argon protection casting is 1.3 m / s;

[0068] (3) The cast sheet obtained in step (2) is subjected to hydrogen crushing and air flow grinding in sequence to prepare fine powder with an average particle size of 2.8 μm and a particle size distribution of d[9,0] / d[1,0]=3.8-4.2;

[0069] (4) The fine powder obtained in step (3) is oriented and formed in a 1280-1600KA / m magnetic field press, and then cold isostatically pressed to obtain a density of 4.2 g / cm 3 of greenware;

[0070] (5) Sintering the green compact obtained in step (4) under vacuum conditions, followed by gas quenching and cooling, and then tempering to obtain sintered NdFeB; wherein the vacuum degree is less than 5×10 -2 Pa; the sintering temperature is 1338K, and the sintering time is 6h; the tempering treatment is first heated to 1173K and kept warm for 3h, and then cooled to 773K and kept warm for 4h; the cooling method of the tempering treatment is air cooling.

[0071] The metallographic images of the sintered NdFeB prepared in Example 1 and Comparative Example 1 are as follows: Figure 2 and 3 shown.

[0072] from Figure 2 and 3 It can be seen that the metallographic structure of the sintered NdFeB prepared in Example 1 of the present invention has good columnar crystal penetration, uniform thickness, and uniform distribution of neodymium-rich phase, while the metallographic structure of the sintered NdFeB prepared in Comparative Example 1 using traditional technology has poor columnar crystal penetration, uneven thickness, and uneven distribution of neodymium-rich phase, indicating that the preparation method provided by the present invention can significantly improve the microstructure of sintered NdFeB.

[0073] Example 2

[0074] A method for preparing sintered NdFeB, comprising the following steps:

[0075] (1) melting and refining the alloy raw materials in a crucible under vacuum conditions to obtain an alloy melt; wherein the formula of the alloy raw materials is designed as follows (by weight ratio): Pr-Nd 26 Dy 4.2 Fe bal Co 1.58 B 0.98 Al 0.25 Cu 0.1 Nb 0.2 Ga 0.2 ; The crucible is prepared by baking and sintering with a tool made of pure iron; the shape of the tool made of pure iron is that a plurality of cylinders are arranged outside a hollow cylinder; the plurality of cylinders are arranged around the hollow cylinder; the vacuum degree before heating is 0.50Pa; the refining temperature range is 1350-1480℃, and the refining time is 20min; during refining, the heating is stopped for 60s every 7min;

[0076] (2) The alloy melt obtained in the step (1) is cast by argon protection, and air-cooled to obtain a casting sheet with a thickness of 0.25 to 0.5 mm; wherein the temperature of the argon protection casting is 1430° C.; the argon partial pressure during the argon protection casting is 10 KPa; the rotation speed of the copper roller of the smelting furnace during the argon protection casting is 30 revolutions / min; and the linear speed of the copper roller during the argon protection casting is 1.3 m / s;

[0077] (3) The cast sheet obtained in step (2) is subjected to hydrogen crushing and air flow grinding in sequence to prepare fine powder with an average particle size of 2.8 μm and a particle size distribution of d[9,0] / d[1,0]=3.8-4.2;

[0078] (4) The fine powder obtained in step (3) is oriented and formed in a 1280-1600KA / m magnetic field press, and then cold isostatically pressed to obtain a density of 4.2 g / cm 3 of greenware;

[0079] (5) Sintering the green compact obtained in step (4) under vacuum conditions, followed by gas quenching and cooling, and then tempering to obtain sintered NdFeB; wherein the vacuum degree is less than 5×10 -2 Pa; the sintering temperature is 1338K, and the sintering time is 6h; the tempering treatment is first heated to 1173K and kept warm for 3h, and then cooled to 773K and kept warm for 4h; the cooling method of the tempering treatment is air cooling.

[0080] The metallographic picture of the sintered NdFeB prepared in Example 2 is as follows Figure 4 shown.

[0081] from Figure 4It can be seen that the metallographic phase of the sintered NdFeB prepared in Example 2 of the present invention has good columnar crystal penetration, uniform thickness, and uniform distribution of neodymium-rich phase, indicating that the preparation method provided by the present invention can significantly improve the microstructure of the sintered NdFeB.

[0082] It can be seen from the above embodiments and comparative examples that the preparation method provided by the present invention can significantly improve the microstructure of sintered NdFeB, thereby greatly improving the magnetic properties of sintered NdFeB.

[0083] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing sintered NdFeB, comprising the following steps: (1) melting and refining the alloy raw materials in a crucible in sequence to obtain an alloy melt; the crucible is prepared by baking and sintering using a tooling made of pure iron; during the refining, heating is stopped for 30 to 90 seconds every 5 to 8 minutes; (2) pouring the alloy melt obtained in step (1) under argon protection to obtain a casting; the argon partial pressure during the argon protection pouring is 5 to 10 KPa; (3) The casting obtained in step (2) is subjected to hydrogen crushing, air flow grinding, pressing, sintering and tempering in sequence to obtain sintered NdFeB.

2. The preparation method according to claim 1, characterized in that: The refining temperature in step (1) is 1350-1500° C., and the refining time is 10-20 min.

3. The preparation method according to claim 2, characterized in that: The refining time is 15 to 18 minutes.

4. The preparation method according to claim 1, characterized in that: The interval time for stopping heating during refining in the step (1) is 6 to 7 minutes, and the time for stopping heating is 50 to 80 seconds.

5. The preparation method according to claim 1, characterized in that: The temperature of the argon protection pouring in step (2) is 1430-1480°C.

6. The preparation method according to claim 1, characterized in that: In the step (2), the partial pressure of argon is 6 to 8.5 KPa.

7. The preparation method according to claim 1, characterized in that: The sintering in step (3) is carried out under vacuum conditions.

8. The preparation method according to claim 1, characterized in that: The sintering temperature in the step (3) is 1323-1383 K, and the sintering time is 3-6 h.

9. The preparation method according to claim 1, characterized in that: The tempering treatment in step (3) is firstly to keep the temperature at 1073-1213K for 2-3 hours, and then to keep the temperature at 733-913K for 3-5 hours.

10. Sintered NdFeB prepared by the preparation method according to any one of claims 1 to 9.

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