Samarium iron nitride magnetic powder and a method for preparing the same

Abstract

The application relates to the technical field of rare earth permanent magnet materials, in particular to a samarium-iron-nitrogen magnetic powder and a preparation method thereof, the preparation method comprising the following steps: 1) smelting samarium and iron elements, then pouring the smelting product on a cooling roller and dropping the smelting product on a water cooling tray to obtain samarium-iron alloy flakes; 2) homogenizing the samarium-iron alloy flakes, then hydrogenating the samarium-iron alloy flakes to obtain samarium-iron coarse powder; and 3) nitriding the samarium-iron coarse powder to obtain samarium-iron-nitrogen coarse powder, then adding the samarium-iron-nitrogen coarse powder into an air flow classifier to perform screening and ball milling. The preparation method of the samarium-iron-nitrogen magnetic powder can not only effectively prevent the samarium-iron magnetic powder from being oxidized before nitriding, but also obtain samarium-iron-nitrogen magnetic powder with uniform particle size and excellent performance, so as to meet the demand of magnetic components on high-performance magnetic powder; meanwhile, the preparation method also has the advantages of high production efficiency, low energy consumption and environmental friendliness, and can meet the demand of large-scale production.

Description

Technical Field

[0001] This invention relates to the field of rare earth permanent magnet materials technology, specifically to a samarium iron nitrogen magnetic powder and its preparation method. Background Technology

[0002] Samarium iron nitrogen (SMR) magnetic powder, as an important functional material, is widely used in various magnetic components. Currently, the main methods for preparing SMR magnetic powder include the high-density magnetic flux distillation (HDDR) method, the melt quenching method, and the reduction-diffusion method. While the HDDR method can yield SMR magnetic powder with high magnetocrystalline anisotropy, it is complex, energy-intensive, and has low production efficiency, making it unsuitable for large-scale production. The reduction-diffusion method has attracted attention due to its simple equipment, low raw material cost, and easy implementation of process conditions; however, it suffers from drawbacks such as excessive samarium volatilization and difficulties in achieving a complete diffusion reaction.

[0003] Existing technologies also have some other problems. For example, the method of crushing samarium iron alloy sheets using hydrogen breaking and air jet milling is prone to oxidation of samarium iron magnetic powder during the transfer process, leading to a decrease in performance after subsequent nitriding. Utilizing the principle of hydrogen disproportionation to crush samarium iron alloy sheets into powder through hydrogen filling and dehydrogenation avoids oxidation, but there is a problem of uneven powder particle size after hydrogen breaking, with coarse powder failing to saturate the nitriding process, resulting in lower performance.

[0004] Patent CN114012096A discloses a method for preparing anisotropic Sm-Fe-N magnetic powder. This method employs a rapid solidification process to obtain rapidly solidified flakes with a network-like distribution of Sm-rich phase at grain boundaries and uniform grain size. Hydrogen breakage before nitriding induces volume expansion of the main phase alloy, generating microcracks and pores within the particles, which facilitates the nitriding and regrinding processes. However, in practical operation, this method still requires further optimization of the hydrogen breakage conditions, such as increasing hydrogen pressure and temperature, and extending the hydrogen treatment time, to obtain finer magnetic powder particles and higher coercivity.

[0005] CN 118969491 B discloses a method for preparing isotropic samarium iron nitride (SmFe) magnetic powder. The method involves weighing metallic Sm and Fe according to a Sm2Fe17 ratio, with an excess of 5%~10% Sm, and then rapidly solidifying the mixture to form samarium iron alloy sheets. The samarium iron alloy sheets are then crushed to prepare powdered samarium iron alloy. The powdered samarium iron alloy is subjected to high-temperature nitriding (HDDR) treatment to obtain isotropic alloy blocks. These isotropic alloy blocks are then crushed and aged to obtain isotropic alloy powder. Finally, the aged isotropic alloy powder is subjected to high-temperature nitriding treatment to obtain Sm2Fe. 17N3 isotropic magnetic powder. The preparation method for samarium iron alloy flakes is hydrogen crushing combined with air jet milling. However, during this process, samarium iron magnetic powder is highly susceptible to oxidation due to its reaction with oxygen in the air during transfer. Once the magnetic powder is oxidized, even subsequent nitriding treatment will significantly reduce its final performance.

[0006] CN 117912795 A discloses an in-situ multi-stage preparation method for SmFeN magnetic powder. Under a protective atmosphere, samarium iron alloy sheets are obtained through induction melting and rapid solidification. The samarium iron alloy sheets are then added to a reaction vessel, and using the principle of hydrogen disproportionation decomposition, the samarium iron alloy sheets are crushed into powder through hydrogen filling and dehydrogenation. High-pressure nitrogen gas is then introduced into the reaction vessel to perform in-situ nitriding treatment on the samarium iron alloy powder to obtain Sm2Fe. 17 N3 magnetic powder. While this method effectively avoids oxidation during the crushing process, it introduces new challenges. The resulting powder exhibits uneven particle size, containing a significant amount of coarse powder. This coarse powder cannot achieve saturated nitriding in the subsequent nitriding process. The larger particle size of the coarse powder restricts the diffusion and reaction of nitrogen atoms, leading to insufficient nitriding and ultimately lower overall performance of the magnetic powder. This uneven particle size and inadequate nitriding also limit the use of samarium iron nitride magnetic powder in applications requiring high performance consistency and stability.

[0007] Therefore, there is an urgent need for a method to prepare samarium iron nitrogen magnetic powder to overcome the above-mentioned technical problems. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing hydrogen-based methods for preparing samarium iron (SMI) magnetic powder. While these methods overcome the oxidation problem of coarse SMI powder, the resulting powder exhibits uneven particle size and poor nitriding performance, leading to low magnetic properties. Furthermore, existing hydrogen-based methods, such as hydrogen pressure, temperature, and time, require further optimization to obtain finer particles and higher coercivity. This invention provides a samarium iron nitride (SMI) magnetic powder and its preparation method. This method effectively prevents oxidation of the SMI powder before nitriding and produces uniformly sized, high-performance powder, meeting the demands of magnetic components for high-performance magnetic powder. Moreover, this preparation method is characterized by high production efficiency, low energy consumption, and environmental friendliness, making it suitable for large-scale production.

[0009] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing samarium iron nitrogen magnetic powder, characterized in that the preparation method comprises: 1) Smelt elemental samarium and elemental iron, then cast them onto cooling rollers and drop them onto a water-cooling pan to obtain samarium-iron alloy sheets; 2) The samarium iron alloy sheets are homogenized and then hydrogenated to obtain samarium iron coarse powder; 3) Nitride the samarium iron coarse powder to obtain samarium iron nitrogen coarse powder, and then add the samarium iron nitrogen coarse powder to an air classifier for sieving and ball milling.

[0010] Preferably, in step 1), the molar ratio of samarium to iron is 2.2-3.0:17.

[0011] Preferably, in step 1), the melting conditions include: pressure < 1 Pa, temperature 1400-1600 °C, and time 20-40 min.

[0012] Preferably, the smelting process further includes first smelting elemental iron with 50% elemental samarium, and then adding the remaining elemental samarium for further smelting.

[0013] Preferably, in step 1), the casting conditions include: the rotation speed of the cooling roller is 3-5 rpm.

[0014] Preferably, in step 2), the homogenization treatment conditions include: a pressure of 1×10⁻⁶. -2 Pa, temperature 900-1100℃, time 6-10h.

[0015] Preferably, in step 2), the hydrogenation conditions include: a pressure of 1 × 10⁻⁶. -2 The temperature is 250-350℃, the absolute pressure of hydrogen is 0.10-0.20MPa, and the time is 1.5-3h.

[0016] Preferably, in step 3), the nitriding treatment conditions include: first, raising the temperature to 350-450°C at a heating rate of 5-15°C / min, filling with nitrogen gas to a nitrogen pressure of 0.2-0.8 MPa, holding at this temperature for 0.5-1.5 h, then raising the temperature to 500-600°C at a heating rate of 5-15°C / min, holding at this temperature for 8-12 h, and then cooling to 15-30°C.

[0017] Preferably, in step 3), the screening conditions include: particle size < 10 μm is grade H samarium iron nitrogen coarse powder, 10 μm ≤ particle size ≤ 30 μm is grade M samarium iron nitrogen coarse powder, and particle size > 30 μm is grade L samarium iron nitrogen coarse powder.

[0018] Preferably, in step 3), the D50 of the ball-milled samarium iron nitrogen magnetic powder is ≤2.0μm.

[0019] Preferably, the preparation method further includes: after adding the sample to an air classifier for sieving, for the obtained L-grade samarium iron nitrogen coarse powder with a nitrogen content ≤2.8% and a particle size >30μm, steps 2) and 3) can be repeated for secondary nitriding treatment.

[0020] In a second aspect, the present invention provides a samarium iron nitrogen magnetic powder, which is prepared by the preparation method described in the first aspect.

[0021] In the above technical solution, the preparation method of samarium iron nitrogen magnetic powder of the present invention adopts the airflow classification method after nitriding, which classifies the nitrided samarium iron nitrogen magnetic powder into samarium iron nitrogen coarse powder with a particle size of <10μm, 10μm≤particle size≤30μm and particle size>30μm, and then ball-mills them to D50≤2.0μm respectively, so as to obtain samarium iron nitrogen magnetic powder with different properties of H grade, M grade and L grade in one go. This not only reduces the production cost, but also allows them to be used separately or compounded according to the required ratio to meet the needs of different application scenarios.

[0022] Meanwhile, the samarium iron nitrogen magnetic powder prepared by this method has uniform particle size and excellent performance. It also has the advantages of simple process, low raw material cost, high production efficiency, low energy consumption and environmental friendliness, and has broad application prospects, making it suitable for large-scale industrial production.

[0023] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0024] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a particle size distribution diagram of the H-grade samarium iron nitrogen magnetic powder after ball milling in Example 1. Detailed Implementation

[0025] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0026] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0027] In a first aspect, the present invention provides a method for preparing samarium iron nitrogen magnetic powder, characterized in that the preparation method includes: 1) Smelt elemental samarium and elemental iron, then cast them onto cooling rollers and drop them onto a water-cooling pan to obtain samarium-iron alloy sheets; 2) The samarium iron alloy sheets are homogenized and then hydrogenated to obtain samarium iron coarse powder; 3) Nitride the samarium iron coarse powder to obtain samarium iron nitrogen coarse powder, and then add the samarium iron nitrogen coarse powder to an air classifier for sieving and ball milling.

[0028] The preparation method of samarium iron nitrogen magnetic powder of the present invention adopts the air-flow classification method after nitriding, which classifies the nitrided magnetic powder into samarium iron nitrogen coarse powder with particle size <10μm, 10μm≤particle size≤30μm and particle size >30μm, and then ball-mills them to D50≤2.0μm respectively, so as to obtain samarium iron nitrogen magnetic powder with different properties of H grade, M grade and L grade in one go. This not only reduces the production cost, but also allows them to be used separately or compounded according to the required ratio to meet the needs of different application scenarios.

[0029] Meanwhile, the samarium iron nitrogen magnetic powder prepared by this method has uniform particle size and excellent performance. It also has the advantages of simple process, low raw material cost, high production efficiency, low energy consumption and environmental friendliness, and has broad application prospects, making it suitable for large-scale industrial production.

[0030] In a preferred embodiment of the present invention, in order to ensure the magnetic properties of the obtained samarium-iron-nitrogen magnetic powder, in step 1), the molar ratio of samarium to iron is 2.2-3.0:17.

[0031] In a preferred embodiment of the present invention, the samarium is provided by samarium particles with a purity of 99.9% and a particle size of 1~10 mm.

[0032] In a preferred embodiment of the present invention, in order to ensure the magnetic properties of the obtained samarium iron nitrogen magnetic powder, the smelting conditions in step 1) include: pressure < 1 Pa, temperature of 1400-1600 °C, and time of 20-40 min.

[0033] In a preferred embodiment of the present invention, in order to ensure the magnetic properties of the obtained samarium iron nitrogen magnetic powder, the smelting process further includes first smelting elemental iron with 50% samarium, and then adding the remaining samarium for further smelting.

[0034] In a preferred embodiment of the present invention, in step 1), the casting conditions include: the rotation speed of the cooling roller is 3-5 rpm.

[0035] In a preferred embodiment of the present invention, because the alloy sheet obtained after casting includes Sm2Fe 17 The homogenization process involves removing the samarium-rich and α-Fe phases to obtain purer Sm2Fe. 17In step 2), the homogenization process is carried out under the following conditions: pressure of 1×10-2 Pa, temperature of 900-1100℃, and time of 6-10 h.

[0036] In a preferred embodiment of the present invention, to prevent the alloy sheet from being too coarse and thick, making nitriding impossible, hydrogenation can be used to break the alloy sheet into particles of 10-100 μm to facilitate nitriding. In step 2), the hydrogenation conditions include: a pressure of 1×10⁻⁶. -2 The temperature is 250-350℃, the absolute pressure of hydrogen is 0.10-0.20MPa, and the time is 1.5-3h.

[0037] In a preferred embodiment of the present invention, in order to ensure the magnetic properties of the obtained samarium iron nitrogen magnetic powder, the nitriding treatment conditions in step 3) include: first, raising the temperature to 350-450°C at a heating rate of 5-15°C / min, filling with nitrogen gas to make the nitrogen pressure 0.2-0.8 MPa, holding at the temperature for 0.5-1.5 h, then raising the temperature to 500-600°C at a heating rate of 5-15°C / min, holding at the temperature for 8-12 h, and then cooling to 15-30°C.

[0038] In a preferred embodiment of the present invention, in order to obtain uniformly sized samarium iron nitrogen magnetic powder, the sieving conditions in step 3) include: particle size < 10 μm is grade H samarium iron nitrogen coarse powder, 10 μm ≤ particle size ≤ 30 μm is grade M samarium iron nitrogen coarse powder, and particle size > 30 μm is grade L samarium iron nitrogen coarse powder.

[0039] In a preferred embodiment of the present invention, in order to obtain uniformly sized samarium iron nitrogen magnetic powder, in step 3), the D50 of the ball-milled samarium iron nitrogen magnetic powder is ≤2.0μm.

[0040] In a preferred embodiment of the present invention, for cases where samarium iron coarse powder cannot be sufficiently nitrided after hydrogenation, after air classification, the obtained L-grade samarium iron nitrogen magnetic powder with a nitrogen content ≤2.8% is subjected to secondary nitriding to improve the nitrogen content and magnetic properties of the samarium iron nitrogen magnetic powder, from L-grade to M-grade or even H-grade, thereby increasing its usability. The preparation method further includes: after adding the powder to an air classifier for sieving, the obtained L-grade samarium iron nitrogen coarse powder with a nitrogen content ≤2.8% and a particle size >30μm can be subjected to secondary nitriding by repeating steps 2) and 3).

[0041] In a second aspect, the present invention provides a samarium iron nitrogen magnetic powder, which is prepared by the preparation method described in the first aspect.

[0042] In this invention, the room temperature is 15-30℃.

[0043] The present invention will be described in detail below through examples. In the following examples, the pharmaceuticals and agents are all conventional commercially available products.

[0044] Example 1 (1) According to Sm2Fe 17 Raw materials were prepared using a stoichiometric ratio, with samarium in 30% excess, to prepare 100 kg of samarium-iron alloy. 75.95 kg of 99% pure iron rods and 31.26 kg of 99.9% pure samarium particles (1-10 mm in size) were weighed. The weighed iron rods and 50% of the samarium particles were placed in a crucible, while the remaining 50% were placed in a secondary feeding hopper. A vacuum of less than 1 Pa was applied, and the raw materials in the crucible were melted at 1500°C. The samarium particles from the secondary feeding hopper were then added. After complete melting, smelting continued for 30 minutes. The molten samarium-iron alloy was then poured through an tundish and runner onto a cooling roller rotating at 3 r / min, allowing the samarium-iron alloy to form Sm₂Fe during cooling. 17 The phase falls onto the water-cooling plate below, resulting in a samarium iron alloy sheet; (2) After the samarium-iron alloy sheet from step (1) has cooled to room temperature, it is placed in a vacuum heat treatment furnace and evacuated to a vacuum level of 1×10⁻⁶. -2 Pa, and heat to 1000℃ and stop heating. After holding at this temperature for 8 hours, cool to 300℃ and hold at this temperature. In a vacuum environment, introduce hydrogen into the furnace. The absolute pressure of the hydrogen is controlled at 0.15MPa, and the hydrogenation time is 2 hours. (3) The temperature is raised to 400°C at a heating rate of 10°C / min, nitrogen is introduced and the nitrogen pressure is 0.5MPa. The temperature is held for 1 hour, and then the temperature is raised to 530°C at a heating rate of 10°C / min. The temperature is held for 10 hours. Then the furnace temperature is lowered to room temperature to obtain nitrided samarium iron nitrogen coarse powder. (4) Add the samarium iron nitrogen coarse powder from step (3) into the feed inlet of the air classifier. Through the rotating classifying disc of the air classifier, the samarium iron nitrogen coarse powder is classified into H grade samarium iron nitrogen coarse powder with a particle size <10μm, M grade samarium iron nitrogen coarse powder with a particle size ≤30μm and L grade samarium iron nitrogen coarse powder with a particle size >30μm. (5) Add the three grades of samarium iron nitrogen coarse powder obtained in step (4) into a ball mill and ball mill until D50≤2μm to obtain the corresponding H grade, M grade and L grade of samarium iron nitrogen magnetic powder, which are denoted as B1H, B1M and B1L respectively.

[0045] Example 2 The method described in Example 1 was implemented, except that "30% excess samarium" in step (1) was changed to "50% excess samarium", while other conditions remained unchanged, and samarium iron nitrogen magnetic powder of three grades, namely H grade, M grade and L grade, was obtained, which were denoted as B2H, B2M and B2L respectively.

[0046] Example 3 The method described in Example 1 was implemented, except that "30% excess samarium" in step (1) was changed to "10% excess samarium", while other conditions remained unchanged, and samarium iron nitrogen magnetic powder of three grades, namely H grade, M grade and L grade, was obtained, which were denoted as B3H, B3M and B3L respectively.

[0047] Example 4 The three grades of samarium iron nitrogen magnetic powder (H, M, and L) obtained in Example 1 were compounded in a weight ratio of 2:2:1 to prepare samarium iron nitrogen magnetic powder, denoted as B4.

[0048] Example 5 The samarium iron nitrogen magnetic powder of grade L in Example 3 was subjected to the hydrogenation treatment in step (2) and the nitridation reaction in step (3) of Example 1, and ball-milled until D50≤2μm to obtain samarium iron nitrogen magnetic powder, which was denoted as B5.

[0049] Comparative Example 1 The method described in Example 1 was implemented, except that the airflow classification in step (4) was not performed. After obtaining the samarium iron nitrogen coarse powder, it was directly ball-milled to obtain samarium iron nitrogen magnetic powder, which was denoted as D1.

[0050] Detection Example 1 The samarium iron nitrogen magnetic powders prepared in Examples 1-4 and Comparative Example 1 were tested for magnetic properties and nitrogen content using VSM. The results are shown in Table 1.

[0051] Table 1

[0052] As shown in Table 1, the smaller the particle size of the magnetic powder after air classification in Examples 1-3, the higher the magnetic properties after ball milling. This is because for the samarium iron coarse powder after hydrogenation, the smaller the particle size, such as samarium iron coarse powder with a particle size ≤10μm, the easier it is to nitrid, the nitrogen content can be nitrided to saturation, and relatively pure Sm2Fe can be obtained after nitriding. 17 N3 phase, Sm2Fe 17 Samarium iron has relatively few impurities, including α-Fe, resulting in higher performance. However, in coarse Samarium iron powder with a particle size >30μm, nitrogen has difficulty diffusing into its interior, allowing for nitriding on the surface of the magnetic powder. In contrast, the nitrogen content in the core of the magnetic powder is lower than that on the surface, and there may even be residual Sm2Fe. 17 Phase, while Sm2Fe 17 The phase is non-magnetic, which leads to a decrease in both remanence and coercivity, resulting in lower magnetic properties.

[0053] Meanwhile, based on the data from Examples 1-3, it can be seen that the higher the samarium content, the higher the coercivity of the samarium-iron-nitrogen magnetic powder, and the lower the samarium content, the higher the remanence of the samarium-iron-nitrogen magnetic powder. This is because when the samarium content increases, there will be more samarium-rich phases in the quick-setting sheet. The samarium-rich phase is a non-magnetic phase and does not contribute to the remanence. However, when the samarium-rich phase is evenly distributed around the samarium-iron phase, it plays a role in magnetic isolation and can improve the coercivity.

[0054] Furthermore, comparing the data of Example 1 and Comparative Example 1, Comparative Example 1 did not use airflow classification, and the magnetic properties of the prepared samarium iron nitrogen magnetic powder were lower than those of the M-grade samarium iron nitrogen magnetic powder prepared in Example 1. It not only failed to provide the high-performance H-grade samarium iron nitrogen magnetic powder of Example 1, but was also less economical.

[0055] Furthermore, as shown by the data from Example 4, after the air-flow graded samarium iron nitrogen magnetic powder is compounded in a specific ratio, samarium iron nitrogen magnetic powder with performance far exceeding that of the original samarium iron nitrogen coarse powder can be obtained. Moreover, compared with pure H-grade samarium iron nitrogen magnetic powder, the cost can be significantly reduced while maintaining similar performance.

[0056] Finally, in the art, the nitrogen content of generally qualified samarium iron nitrogen magnetic powder should be higher than 3.0%. Samarium iron nitrogen magnetic powder with a nitrogen content lower than 3.0% has too low coercivity and therefore has very low use value. Even if high remanence materials are required in certain specific scenarios, such as the H grade samarium iron nitrogen magnetic powder in Example 3, the L grade samarium iron nitrogen magnetic powder in Example 3 has virtually no use value due to its low nitrogen content and coercivity. However, as can be seen from the performance of the samarium iron nitrogen magnetic powder obtained in Example 5, the preparation method of the present invention can perform secondary nitriding on samarium iron nitrogen magnetic powder that has not been fully nitrided, thereby increasing the nitrogen content and magnetic properties of the samarium iron nitrogen magnetic powder. This allows unusable low-performance materials to be upgraded to high-performance materials for use, thereby reducing costs.

[0057] In summary, the preparation method of samarium iron nitride magnetic powder of the present invention avoids oxidation of samarium iron magnetic powder before nitriding by classifying it after nitriding. Furthermore, the airflow classification method after nitriding allows for the simultaneous acquisition of three grades of magnetic powder with different properties, resulting in lower cost and higher efficiency. Moreover, the different grades of samarium iron nitride magnetic powder obtained by the present invention can not only be used separately and independently, but also be compounded in different proportions, providing flexible solutions for more complex and diversified applications. This meets the specific performance requirements of magnetic powder in different application scenarios, thereby achieving adjustable performance of samarium iron nitride magnetic powder and efficient resource utilization. This innovative preparation method not only solves the problems existing in the prior art, but also enriches the performance levels of samarium iron nitride magnetic powder, making its performance more diverse and greatly expanding its application range, thus possessing broad application prospects.

[0058] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0059] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0060] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing samarium iron nitrogen magnetic powder, characterized in that, The preparation method includes: 1) Smelt elemental samarium and elemental iron, then cast them onto cooling rollers and drop them onto a water-cooling pan to obtain samarium-iron alloy sheets; 2) The samarium iron alloy sheets are homogenized and then hydrogenated to obtain samarium iron coarse powder; 3) The samarium iron coarse powder is subjected to nitriding treatment to obtain samarium iron nitrogen coarse powder, and then the samarium iron nitrogen coarse powder is added to an air classifier for sieving and ball milling; In step 1), the molar ratio of samarium to iron is 2.2-3.0:17; In step 1), the melting conditions include: pressure < 1 Pa, temperature 1400-1600 °C, and time 20-40 min; and / or, The smelting process also includes first smelting elemental iron with 50% elemental samarium, and then adding the remaining elemental samarium for further smelting. In step 2), the hydrogenation conditions include: a pressure of 1 × 10⁻⁶. -2 Pa, temperature 250-350℃, absolute pressure of hydrogen 0.10-0.20MPa, time 1.5-3h; In step 3), the sieving conditions include: particle size < 10 μm is grade H samarium iron nitrogen coarse powder, 10 μm ≤ particle size ≤ 30 μm is grade M samarium iron nitrogen coarse powder, and particle size > 30 μm is grade L samarium iron nitrogen coarse powder; and / or, The D50 of the ball-milled samarium iron nitrogen magnetic powder is ≤2.0μm; The preparation method further includes: after adding the mixture to an air classifier for sieving, for the obtained L-grade samarium iron nitrogen coarse powder with a nitrogen content ≤2.8% and a particle size >30μm, steps 2) and 3) can be repeated for secondary nitriding treatment; In step 3), the nitriding treatment conditions include: first, raising the temperature to 350-450°C at a heating rate of 5-15°C / min, filling with nitrogen gas to a nitrogen pressure of 0.2-0.8 MPa, holding at this temperature for 0.5-1.5 h, then raising the temperature to 500-600°C at a heating rate of 5-15°C / min, holding at this temperature for 8-12 h, and then cooling to 15-30°C.

2. The preparation method according to claim 1, characterized in that, In step 1), the casting conditions include: the rotation speed of the cooling roller is 3-5 rpm.

3. The preparation method according to claim 1, characterized in that, In step 2), the conditions for the homogenization process include: a pressure of 1 × 10⁻⁶. -2 Pa, temperature 900-1100℃, time 6-10h.

4. A samarium iron nitrogen magnetic powder, characterized in that, The samarium iron nitrogen magnetic powder is prepared by the preparation method described in any one of claims 1-3.

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