Iron-based soft magnetic composite powder and method for producing the same

Abstract

The present application relates to the technical field of metal powder preparation, and particularly relates to a kind of iron-based soft magnetic composite powder and its preparation method.The present application carries out smelting to iron-based matrix under inert atmosphere, obtains iron-based molten liquid;Iron-based molten liquid is impacted by high-pressure atomization medium, and iron-based composite powder is obtained;Iron-based composite powder is reduced under reducing atmosphere, and iron-based soft magnetic composite powder is obtained;The atomization medium includes iron nitride and water.Iron-based matrix powder is prepared by iron-based raw material through arc furnace smelting-water atomization or water-steam combined atomization process, uses the mixture of iron nitride and water as atomization medium, combines the atomization process parameters and post-processing technology of accurate control, realizes the efficient preparation of flaky iron-based soft magnetic composite powder, can significantly improve the yield (>=50%) of particle size <=15 μm powder, and simultaneously optimizes the soft magnetic performance of composite powder.

Description

Technical Field

[0001] This invention relates to the field of metal powder preparation technology, and in particular to an iron-based soft magnetic composite powder and its preparation method. Background Technology

[0002] Iron-based soft magnetic composite powder is a core raw material for the preparation of soft magnetic components. Due to its excellent magnetic properties, processing performance, and cost advantages, it is widely used in power electronics, new energy vehicles, 5G communications, and metal additive manufacturing. As terminal devices develop towards higher frequencies and smaller sizes, higher performance requirements are placed on iron-based soft magnetic composite powder. It not only needs to possess high saturation magnetic flux density, low coercivity, and high resistivity, but also requires a flake-like powder morphology (to optimize permeability and reduce high-frequency losses), and a significantly improved yield of fine powder with a particle size ≤15 μm to meet the application needs in high-frequency scenarios.

[0003] Currently, the preparation of iron-based soft magnetic composite powders in the industry mostly adopts traditional water atomization or gas atomization processes. The smelting and atomization processes of the iron-based matrix powder are disconnected, and the atomization medium is mostly pure water or a simple gas-liquid mixture, resulting in the following significant technical defects: First, the yield of fine powder is low. In traditional water atomization processes, the yield of powder with a particle size ≤15 μm is usually less than 30%, and a large amount of fine powder is wasted due to agglomeration, oxidation, and other problems, leading to increased production costs. Second, it is difficult to precisely control the powder morphology. Powders prepared by traditional atomization processes are mostly spherical or near-spherical, and it is difficult to prepare sheet-like powders. An additional shaping process is required, and the performance of the powder is easily damaged after shaping. Third, the soft magnetic properties need further optimization. Traditional powders are prone to oxidation and component segregation, resulting in a decrease in saturation magnetic flux density and an increase in coercivity, which cannot meet the requirements of high-frequency applications. Fourth, existing atomization processes lack effective means of adding phase control. Iron nitride is not combined with water as an atomization medium, making it difficult to achieve the dual goals of improving the yield of fine powder and controlling its morphology simultaneously through the atomization process.

[0004] Iron nitride powder possesses excellent magnetic properties and surface activity, and can be used as an additive phase to improve the microstructure and magnetic properties of iron-based soft magnetic materials. However, in existing technologies, iron nitride is mostly used as a dopant phase directly mixed into the powder matrix, without being combined with water as an atomizing medium for integrated electric arc furnace smelting-atomization processes. This fails to fully leverage its role in controlling atomization effects, powder morphology, and particle size distribution. Furthermore, existing water-steam combined atomization processes primarily focus on improving the compositional uniformity of alloy powders, without combining iron nitride and water as a mixed atomizing medium to achieve synergistic optimization of fine powder yield and flake morphology. Therefore, developing a method for preparing flake-shaped iron-based soft magnetic composite powders by smelting and atomizing iron-based matrix powders in an electric arc furnace, using a mixture of iron nitride and water as the atomizing medium, has become an urgent technical need in the industry. Summary of the Invention

[0005] The purpose of this invention is to provide an iron-based soft magnetic composite powder and its preparation method, so as to solve the technical problems existing in the preparation process of existing iron-based soft magnetic composite powders, such as low yield of fine powder with particle size ≤15 μm, difficulty in accurately controlling the powder morphology to be flake-like, and poor soft magnetic properties.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: One of the technical solutions of this invention provides a method for preparing iron-based soft magnetic composite powder, comprising the following steps: (1) The iron-based matrix is ​​smelted under an inert atmosphere to obtain an iron-based molten liquid; (2) Iron-based composite powder is obtained by atomizing the iron-based molten liquid with a high-pressure atomizing medium; (3) The iron-based composite powder was subjected to reduction treatment under a reducing atmosphere to obtain iron-based soft magnetic composite powder; The atomizing medium includes iron nitride and water.

[0007] Optionally, the smelting temperature is 1550~1700 ℃ and the time is 25~45 min.

[0008] Optionally, the iron-based matrix includes one or more of iron, iron-silicon alloys, and iron-silicon-aluminum alloys.

[0009] Optionally, the iron nitride is Fe4N or Fe3N; the concentration of the iron nitride mixed with water is 5~20 g / L.

[0010] Optionally, the atomizing medium further includes compressed air; the volume ratio of water to compressed air in the atomizing medium is 1:0.3 to 1:0.8.

[0011] Optionally, the amount of iron nitride added is 0.5 to 5% of the mass of the iron-based matrix powder.

[0012] Optionally, the parameters for the high-pressure atomization impact on the iron-based molten liquid are: atomization pressure of 80~150 MPa, atomization distance of 150~300 mm, and a cooling rate of 10 during atomization. 3 ~10 4 ℃ / s.

[0013] Optionally, the reducing atmosphere is hydrogen and nitrogen; the volume ratio of hydrogen to nitrogen is 1:3 to 1:9.

[0014] Optionally, the reduction treatment temperature is 300~500 ℃, the reduction treatment pressure is 0.1~0.3 MPa, and the reduction treatment time is 1~2 h.

[0015] The second technical solution of the present invention provides iron-based soft magnetic composite powder prepared by the above-mentioned iron-based soft magnetic composite powder preparation method.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses a mixture of iron nitride and water as the atomizing medium, combined with an integrated electric arc furnace smelting-atomization process. The iron nitride component can reduce the surface tension of the molten iron-based droplets, effectively promoting droplet breakage and refinement. This increases the yield of powder with a particle size ≤15 μm from less than 30% in the traditional process to more than 50%, significantly improving raw material utilization, reducing production costs, and solving the technical problem of serious fine powder waste in the traditional atomization process. 2. This invention adds a hydrogen reduction process in a hydrogen-nitrogen combined atmosphere, which can effectively remove oxidative impurities on the surface and inside of the initial powder. Combined with the synergistic effect of the iron nitride additive phase, it further refines the powder grains and inhibits oxidation, giving the composite powder excellent soft magnetic properties such as high saturation magnetic flux density (≥1.5 T), low coercivity (≤80 A / m) and high resistivity (≥100 μΩ·cm). It is especially suitable for high-frequency scenarios of 10~100 MHz, solving the problems of high high-frequency loss and insufficient purity of traditional iron-based soft magnetic powders, which is in line with the development trend of high frequency and miniaturization of terminal equipment. 3. The iron nitride of the present invention, as the core component of the atomizing medium, can induce the molten droplets to extend laterally during the cooling process, so that the composite powder forms a uniform sheet shape (thickness 1~5 μm, aspect ratio 5~20). It eliminates the need for complicated additional shaping processes, simplifies the process, improves the magnetic permeability of the powder, reduces high-frequency loss, and adapts to the application requirements of high-frequency soft magnetic components, overcoming the defect that the traditional atomized powder morphology is difficult to control into a sheet shape. 4. This invention adopts an integrated smelting-atomization process, where the iron-based matrix powder is directly obtained from smelting followed by atomization, eliminating the need for additional matrix powder preparation steps. The atomization medium is a mixture of iron nitride and water, which is simple to prepare and requires no additional specialized equipment. It can be directly adapted to existing water atomization and water-vapor combined atomization production equipment. The process parameters are simple and controllable, and the operation is convenient, enabling large-scale continuous industrial production. The coarse powder on the sieve can be recycled, further reducing production costs and conforming to the concept of green production. 5. The sheet-like iron-based soft magnetic composite powder prepared by this invention can be widely used in high-frequency inductors, transformer cores, new energy vehicle motor cores, 5G communication equipment magnetic components, additive manufacturing and other fields. It is especially suitable for the preparation needs of high-frequency and miniaturized soft magnetic components and has broad market application prospects. Attached Figure Description

[0017] Figure 1 SEM image of the iron-based soft magnetic composite powder prepared in Example 1; Figure 2SEM image of the iron-based soft magnetic composite powder prepared in Example 2; Figure 3 SEM image of the iron-based soft magnetic composite powder prepared in Example 3; Figure 4 SEM image of the iron-based soft magnetic composite powder prepared in Comparative Example 1. Detailed Implementation

[0018] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0019] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0020] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0021] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0022] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0023] All raw materials used in this invention can be obtained commercially or prepared using existing technologies.

[0024] This invention provides a method for preparing iron-based soft magnetic composite powder. The core innovation focuses on the synergistic effect of "integrated preparation of iron-based matrix powder through electric arc furnace smelting and atomization" and "using a mixture of iron nitride and water as the atomization medium," achieving a unified approach that improves fine powder yield, controls flake morphology, and optimizes soft magnetic properties. Specifically, the method includes the following steps: (1) The iron-based matrix is ​​smelted under an inert atmosphere to obtain an iron-based molten liquid; (2) Iron-based composite powder is obtained by atomizing the iron-based molten liquid with a high-pressure atomizing medium; (3) The iron-based composite powder was subjected to reduction treatment under a reducing atmosphere to obtain iron-based soft magnetic composite powder; The atomizing medium includes iron nitride and water.

[0025] In this invention, the type of atomizing medium is selected according to production needs: when a water atomization process is used, the atomizing medium is a mixture of iron nitride and water; when a water-vapor combined atomization process is used, the atomizing medium is a mixture of iron nitride, water and compressed air.

[0026] In a preferred embodiment of the present invention, the atomizing medium is prepared by adding iron nitride to water and stirring with ultrasonic waves to ensure that the iron nitride powder is uniformly dispersed in water without agglomeration, thus forming a stable iron nitride-water suspension system. The ultrasonic stirring frequency is 20~40 kHz, for example, 20 kHz, 25 kHz, 30 kHz, 35 kHz or 40 kHz, and the time is 15~30 min, for example, 15 min, 20 min, 25 min or 30 min.

[0027] In this invention, iron nitride powder, as the core component of the atomizing medium, can change the impact characteristics and surface tension of the atomizing medium, promote the fragmentation and refinement of iron-based molten droplets, and induce the formation of a plate-like morphology during the cooling process of the droplets, thus laying the foundation for improving the yield of fine powder and controlling its morphology.

[0028] In a preferred embodiment of the present invention, the iron-based matrix must undergo strict impurity removal treatment before smelting to remove non-metallic inclusions and oxide impurities from the raw materials to ensure that the purity meets the standards; the purity of the iron-based matrix is ​​≥99.0% to ensure that the matrix powder has good soft magnetic properties.

[0029] In a preferred embodiment of the present invention, the iron nitride needs to be pretreated before use. The pretreatment method is as follows: the iron nitride is pulverized by airflow and sent into a vacuum drying oven to dry thoroughly to remove the moisture adsorbed on the powder surface, so as to avoid agglomeration when preparing the atomizing medium later.

[0030] In this invention, the particle size of the pulverized material is ≤5 μm; the drying temperature is 80~100 ℃, for example, it can be 80 ℃, 85 ℃, 90 ℃, 95 ℃ or 100 ℃, etc., and the time is 1 h.

[0031] In this invention, the purification and pretreatment of the iron-based matrix and iron nitrides can effectively improve the purity of the raw materials, thus ensuring the stability of the subsequent electric arc furnace smelting and atomization processes.

[0032] In a preferred embodiment of the present invention, step (1) involves adding the iron-based matrix into an electric arc furnace, closing the furnace door, drawing a vacuum, and then introducing an inert atmosphere for protection to prevent oxidation during the melting of the raw materials. The iron-based matrix is ​​then heated and smelted to completely melt the iron-based matrix, forming a uniformly composed iron-based molten liquid.

[0033] In this invention, the vacuum is evacuated to ≤1×10⁻⁶. -2 Pa; the inert gas is nitrogen; the flow rate of the inert gas is 0.5~1.0 L / min, for example, 0.5 L / min, 0.6 L / min, 0.7 L / min, 0.8 L / min, 0.9 L / min or 1.0 L / min, etc.; the smelting temperature is 1550~1700 ℃, for example, 1550 ℃, 1600 ℃, 1650 ℃ or 1700 ℃, etc., and the time is 25~45 min, for example, 25 min, 30 min, 35 min, 40 min or 45 min, etc.

[0034] In this invention, the iron-based matrix includes one or more of iron, iron-silicon alloys, and iron-silicon-aluminum alloys.

[0035] In a preferred embodiment of the present invention, step (2) involves introducing the prepared atomizing medium into a dual-flow atomizing nozzle to impact the iron-based molten liquid with high-pressure atomization, causing the molten liquid droplets to break up rapidly, cool and solidify, until iron-based sheet-like composite powder is obtained.

[0036] In this invention, the orifice diameter of the dual-flow atomizing nozzle is 15~25 mm.

[0037] In this invention, iron nitride, as an atomizing medium component, can reduce the surface tension of molten droplets, promote the breakup of droplets into fine particles, and guide the droplets to extend laterally during the cooling process to form a sheet-like shape, significantly improving the yield of fine powder with a particle size ≤15 μm.

[0038] In this invention, the iron nitride is Fe4N or Fe3N; the concentration of the iron nitride mixed with water is 5~20 g / L, for example, it can be 5 g / L, 8 g / L, 10 g / L, 12 g / L, 15 g / L, 16 g / L or 20 g / L, etc.

[0039] In a preferred embodiment of the present invention, the purity of the iron nitride is ≥98.0%, the nitrogen content of the iron nitride is 5.0%~8.0%, and the particle size after pulverization is ≤5 μm.

[0040] In this invention, iron nitride, as the core component of the atomizing medium, can effectively control the droplet breakup effect during the atomization process, promote the formation of flake powder, and enhance the soft magnetic properties of the composite powder. In this invention, the atomizing medium further includes compressed air; the volume ratio of water to compressed air in the atomizing medium is 1:0.3 to 1:0.8, for example, it can be 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7 or 1:0.8, etc.

[0041] In this invention, the amount of iron nitride added is 0.5-5% of the mass of the iron-based matrix powder, for example, it can be 0.5%, 1%, 1.2%, 1.5%, 2%, 2.5%, 3%, 35%, 4%, 4.5% or 5%, etc.

[0042] In this invention, the parameters of the high-pressure atomization impact on the iron-based molten liquid are as follows: the atomization pressure is 80~150 MPa, for example, it can be 80 MPa, 90 MPa, 100 MPa, 110 MPa, 120 MPa, 130 MPa, 140 MPa or 150 MPa, etc.; the atomization distance is 150~300 mm, for example, it can be 150 mm, 200 mm, 250 mm or 300 mm, etc.; and the cooling rate during atomization is 10. 3 ~10 4 ℃ / s, for example, can be 1×10 3 ℃ / s, 2×10 3 ℃ / s, 4×10 3 ℃ / s, 6×10 3 ℃ / s, 8×10 3 ℃ / s or 1×10 4 ℃ / s, etc.

[0043] In a preferred embodiment of the present invention, the iron-based composite powder is fed into a reduction furnace, a reducing atmosphere is introduced, and a reduction treatment is performed to complete the deoxidation and reduction treatment of the iron-based composite powder. This effectively removes oxidized impurities from the powder surface and interior, further improving the soft magnetic properties and purity of the composite powder, and preventing oxidized impurities from affecting subsequent processing and performance.

[0044] In this invention, the reducing atmosphere is hydrogen and nitrogen; the volume ratio of hydrogen to nitrogen is 1:3 to 1:9, for example, it can be 1:3, 1:4, 1:5, 1:6, 1:7, 1:8 or 1:9, etc.; the purity of the reducing atmosphere is ≥99.99%, wherein the impurity oxygen content is ≤0.001%, so as to prevent the introduction of new impurities during the reduction process.

[0045] In this invention, the temperature of the reduction treatment is 300~500 ℃, for example, 300 ℃, 350 ℃, 400 ℃, 450 ℃ or 500 ℃, the pressure of the reduction treatment is 0.1~0.3 MPa, for example, 0.1 MPa, 0.2 MPa or 0.3 MPa, and the time of the reduction treatment is 1~2 h, for example, 1 h, 1.5 h or 2 h.

[0046] In a preferred embodiment of the present invention, the iron-based soft magnetic composite powder obtained after hydrogen reduction is subjected to vacuum filtration, vacuum drying, and grading and sieving in sequence to obtain the iron-based soft magnetic composite powder.

[0047] In this invention, the vacuum drying temperature is 80~100℃, for example, 80℃, 85℃, 90℃, 95℃ or 100℃, etc., and the time is 2~3 hours, for example, 2 hours, 2.5 hours or 3 hours, etc.; the grading and screening is carried out by an ultrasonic sieve to collect fine powder with a particle size ≤15μm, and the coarse powder on the sieve can be returned to the electric arc furnace for re-smelting and atomization to improve the raw material utilization rate; the frequency of the ultrasonic sieve is 25~35 kHz, for example, 25 kHz, 30 kHz or 35 kHz, etc., and the screen aperture is 15μm.

[0048] In a preferred embodiment of the present invention, the integrated process of electric arc furnace smelting-water atomization or water-steam combined atomization includes core processes such as raw material pretreatment, atomization medium preparation, electric arc furnace smelting-atomization, hydrogen reduction treatment, and post-treatment, wherein atomization medium preparation and electric arc furnace smelting-atomization are the core innovative processes.

[0049] The present invention also provides iron-based soft magnetic composite powder prepared by the above-mentioned iron-based soft magnetic composite powder preparation method.

[0050] In this invention, the iron-based soft magnetic composite powder is prepared from iron-based raw materials through electric arc furnace smelting, water atomization, or water-steam combined atomization process.

[0051] In this invention, a laser particle size analyzer is used to detect the particle size distribution of the composite powder, ensuring that the yield of powder with a particle size ≤15μm is ≥50%; a scanning electron microscope is used to observe the powder morphology, confirming that it is uniformly flaky; an energy dispersive spectroscopy (EDS) analyzer is used to detect the powder composition, ensuring that the iron nitride additive phase is uniformly distributed and the impurity content meets the requirements; a vibrating sample magnetometer is used to detect the soft magnetic properties, ensuring that the saturation magnetic flux density, coercivity, and resistivity meet the design specifications. After passing the tests, the powder is vacuum-sealed with Ar inert gas to prevent oxidation, resulting in the finished flaky iron-based soft magnetic composite powder, which can be directly used for the preparation of soft magnetic components.

[0052] In this invention, the iron-based soft magnetic composite powder is in a uniform flake shape with a thickness of 1~5 μm and an aspect ratio of 5~20; the yield of powder with a particle size ≤15 μm is ≥50%, which is significantly higher than that of traditional processes; the soft magnetic properties meet the following requirements: saturation magnetic flux density ≥1.5 T, coercivity ≤80 A / m, resistivity ≥100 μΩ·cm, which is suitable for high-frequency applications; the impurity content is strictly controlled: oxygen content ≤0.05% and carbon content ≤0.03% to avoid the adverse effects of impurities on the soft magnetic properties.

[0053] The sheet-like iron-based soft magnetic composite powder prepared by this invention has a uniform morphology and concentrated particle size distribution, and combines the advantages of high saturation magnetic flux density, low coercivity and high resistivity, which can meet the application requirements of high-frequency soft magnetic components. The preparation process is simple and controllable, low cost, and does not require additional special equipment, which can realize large-scale industrial production. It effectively solves the technical bottleneck of traditional atomization process for preparing iron-based soft magnetic powder, and promotes the development of iron-based soft magnetic materials towards high frequency and miniaturization.

[0054] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0055] Example 1 (1) Raw material pretreatment: Pure iron raw material (purity 99.2%) undergoes strict impurity removal treatment to remove non-metallic inclusions and oxide impurities from the raw material; Fe4N powder (purity 98.5%, nitrogen content 6.2%) was pulverized to a particle size ≤5μm using an air jet milling process. The pulverized Fe4N powder was then sent to a vacuum drying oven and kept at 90℃ for 1 hour to completely remove the adsorbed moisture on the powder surface. (2) Mix Fe4N with water and stir for 20 minutes at a frequency of 30 kHz to make the iron nitride powder uniformly dispersed in the water and make the system uniform and stable to obtain an iron nitride-water suspension system (atomizing medium); the concentration of Fe4N powder in water is 12 g / L, and the amount of Fe4N added is 2% of the mass of pure iron raw material.

[0056] (3) Place the pure iron raw material in the electric arc furnace, close the furnace door, and evacuate to a vacuum level of ≤1×10. -2 Pa, Ar inert gas is introduced for protection, the Ar gas flow rate is 0.8 L / min, and then heated to 1580℃ and held for 30 min to completely melt the iron-based raw material, thus preparing a uniform iron-based molten liquid. (4) The atomizing medium is introduced into a dual-flow atomizing nozzle (orifice diameter 22 mm) to impact the molten iron-based liquid with high-pressure atomization. The atomization pressure is 120 MPa, the atomization distance is 220 mm, and the cooling rate is controlled at 5 × 10⁻⁶ during the atomization process. 3 ℃ / s, to rapidly break up and cool the molten droplets to solidify them, thus obtaining iron-based sheet-like composite powder; (5) The iron-based sheet composite powder is fed into a reduction furnace and a combined reducing atmosphere of hydrogen and nitrogen is introduced. The volume ratio of the hydrogen and nitrogen combined reducing atmosphere is 1:5. The reduction is carried out at a temperature of 400℃ and a pressure of 0.2MPa for 1.5h to obtain the deoxidized and reduced iron-based sheet composite powder. (6) The deoxidation-reduction treated iron-based flake composite powder was vacuum dried at 90°C for 2.5 h, and then sieved using an ultrasonic sieve classifier at a frequency of 30 kHz to collect powder with a particle size ≤ 15 μm to obtain iron-based soft magnetic composite powder.

[0057] Finished product testing results: The powder morphology was observed using a scanning electron microscope; the iron-based soft magnetic composite powder was found to be in uniform flake form. Figure 1 The composite powder has a thickness of 2-4 μm and an aspect ratio of 8-15. The particle size distribution of the composite powder was detected using a laser particle size analyzer, and the yield of powder with a particle size ≤15 μm was 56%. The soft magnetic properties were detected using a vibrating sample magnetometer, with a saturation magnetic flux density of 1.58 T, coercivity of 72 A / m, and resistivity of 115 μΩ·cm. The powder composition was detected using an energy dispersive spectroscopy analyzer, with an oxygen content of 0.04% and a carbon content of 0.02%. All properties meet the design requirements and can be used for the preparation of high-frequency inductors.

[0058] Example 2 (1) Raw material pretreatment: The iron-silicon alloy raw material (silicon content 4.5%, purity 99.0%) is subjected to strict impurity removal treatment to remove non-metallic inclusions and oxide impurities from the raw material; Fe3N powder (purity 98.0%, nitrogen content 7.5%) was pulverized to a particle size ≤5μm using an air jet milling process. The pulverized Fe3N powder was then sent to a vacuum drying oven and kept at 100 ℃ for 1 h to completely remove the adsorbed moisture on the powder surface. (2) Mix Fe3N with water and stir for 25 min at a frequency of 35 kHz to uniformly disperse the iron nitride powder in the water and make the system homogeneous and stable to obtain an iron nitride-water suspension system; introduce compressed air into the iron nitride-water suspension system to obtain an atomization mechanism; wherein the concentration of Fe3N powder in water is 18 g / L, and the volume ratio of water to compressed air is 1:0.5; wherein the amount of Fe3N added is 3.5% of the mass of the iron-silicon alloy raw material.

[0059] (3) Place the iron-silicon alloy raw material in the electric arc furnace, close the furnace door, and evacuate to ≤1×10⁻⁶. -2 Pa was introduced with Ar inert gas for protection at a flow rate of 0.6 L / min, and then heated to 1620 °C and held for 25 min to completely melt the iron-silicon alloy raw material, thus preparing a uniform iron-based molten liquid. (4) The atomizing medium is introduced into a dual-flow atomizing nozzle (orifice diameter 22 mm) to impact the molten iron-based liquid with high-pressure atomization. The atomization pressure is 150 MPa, the atomization distance is 250 mm, and the cooling rate is controlled at 8 × 10⁻⁶ during the atomization process. 3 ℃ / s, to rapidly break up and cool the molten droplets to solidify them, thus obtaining iron-based sheet-like composite powder; (5) The iron-based sheet composite powder is fed into a reduction furnace and a combined reducing atmosphere of hydrogen and nitrogen is introduced. The volume ratio of the hydrogen and nitrogen reducing atmosphere is 1:7. The reduction is carried out at a temperature of 450 ℃ and a pressure of 0.25 MPa for 1.2 h to obtain the deoxidized and reduced iron-based sheet composite powder. (6) The deoxidation-reduction treated iron-based flake composite powder was vacuum dried at 100 °C for 2 h, and then sieved at a frequency of 32 kHz using an ultrasonic sieve classifier to collect powder with a particle size ≤15 μm to obtain iron-based soft magnetic composite powder.

[0060] Finished product testing results: The powder morphology was observed using a scanning electron microscope; the iron-based soft magnetic composite powder was found to be in uniform flake form. Figure 2 The composite powder has a thickness of 1~3 μm and an aspect ratio of 10~18. The particle size distribution of the composite powder was detected by a laser particle size analyzer, and the yield of powder with a particle size ≤15μm was 53%. The soft magnetic properties were detected by a vibrating sample magnetometer, with a saturation magnetic flux density of 1.62 T, coercivity of 68 A / m, and resistivity of 122 μΩ·cm. The powder composition was detected by an energy dispersive spectroscopy analyzer, with an oxygen content of 0.03% and a carbon content of 0.02%. All properties meet the design requirements and are fully compatible with the large-scale production needs of magnetic cores for new energy vehicle motors.

[0061] Example 3 (1) Raw material pretreatment: The iron-silicon-aluminum alloy raw material (silicon content 3.5%, aluminum content 2.0%, purity 99.1%) is subjected to strict impurity removal treatment to remove non-metallic inclusions and oxide impurities from the raw material; Fe4N powder (purity 98.2%, nitrogen content 5.8%) was pulverized to a particle size ≤5μm using an air jet milling process. The pulverized Fe4N powder was then sent to a vacuum drying oven and kept at 80 ℃ for 1 h to completely remove the adsorbed moisture on the powder surface. (2) Mix Fe4N with water and stir for 18 min at a frequency of 25 kHz to uniformly disperse the iron nitride powder in the water and make the system homogeneous and stable to obtain an iron nitride-water suspension system; introduce compressed air into the iron nitride-water suspension system to obtain an atomization mechanism; wherein the concentration of Fe4N powder in water is 8 g / L, and the volume ratio of water to compressed air is 1:0.7; wherein the amount of Fe4N added is 1% of the mass of the iron-silicon-aluminum alloy raw material.

[0062] (3) Place the iron-silicon-aluminum alloy raw material in the electric arc furnace, close the furnace door, and evacuate to ≤1×10. -2 Pa was introduced with Ar inert gas for protection at a flow rate of 0.9 L / min, and then heated to 1550 °C and held for 35 min to completely melt the iron-silicon-aluminum alloy raw material, thus preparing a uniform iron-based molten liquid. (4) The atomizing medium is introduced into a dual-flow atomizing nozzle (orifice diameter 22 mm) to impact the molten iron-based liquid with high-pressure atomization. The atomization pressure is 100 MPa, the atomization distance is 180 mm, and the cooling rate is controlled at 6 × 10⁻⁶ during the atomization process. 3 ℃ / s, to rapidly break up and cool the molten droplets to solidify them, thus obtaining iron-based sheet-like composite powder; (5) The iron-based sheet composite powder is fed into a reduction furnace and a combined reducing atmosphere of hydrogen and nitrogen is introduced. The volume ratio of the hydrogen and nitrogen reducing atmosphere is 1:4. The reduction is carried out at a temperature of 380 ℃ and a pressure of 0.15 MPa for 1.8 h to obtain the deoxidized and reduced iron-based sheet composite powder. (6) The deoxidation-reduction treated iron-based flake composite powder was vacuum dried at 85 °C for 3 h, and then sieved using an ultrasonic sieve classifier at a frequency of 28 kHz to collect powder with a particle size ≤15 μm to obtain iron-based soft magnetic composite powder.

[0063] Finished product testing results: The powder morphology was observed using a scanning electron microscope; the iron-based soft magnetic composite powder was found to be in uniform flake form. Figure 3The composite powder has a thickness of 3-5 μm and an aspect ratio of 6-12. The particle size distribution of the composite powder was detected using a laser particle size analyzer, and the yield of powder with a particle size ≤15μm was 51%. The soft magnetic properties were detected using a vibrating sample magnetometer, with a saturation magnetic flux density of 1.55 T, coercivity of 76 A / m, and resistivity of 108 μΩ·cm. The powder composition was detected using an energy dispersive spectroscopy analyzer, with an oxygen content of 0.04% and a carbon content of 0.03%. The product has stable performance and can meet the technical requirements of high-frequency transformer cores.

[0064] Comparative Example 1 The only difference from Example 1 is that the atomizing medium is water only, and no Fe4N powder is added. All other preparation steps and process parameters are completely consistent with Example 1.

[0065] Finished product testing results: Powder morphology was observed using a scanning electron microscope; the iron-based soft magnetic composite powder was found to be spherical. Figure 4 The powder has a thickness of 5-8 μm and an aspect ratio of 2-5; the yield of powder with a particle size ≤15 μm is 28%; the saturation magnetic flux density is 1.42 T, the coercivity is 95 A / m, and the resistivity is 88 μΩ·cm; the oxygen content is 0.08% and the carbon content is 0.04%. Due to the absence of Fe4N as an atomizing medium component, it is impossible to promote the breakup and refinement of molten droplets and lateral extension. The yield of fine powder is much lower than that of Example 1, the powder morphology cannot form flakes, the soft magnetic properties are significantly reduced, and the oxygen and carbon contents exceed the standards, which cannot meet the application requirements of high-frequency inductors and other high-frequency scenarios.

[0066] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an iron-based soft magnetic composite powder, characterized in that, Includes the following steps: (1) The iron-based matrix is ​​smelted under an inert atmosphere to obtain an iron-based molten liquid; (2) Iron-based composite powder is obtained by atomizing the iron-based molten liquid with a high-pressure atomizing medium; (3) The iron-based composite powder was subjected to reduction treatment under a reducing atmosphere to obtain iron-based soft magnetic composite powder; The atomizing medium includes iron nitride and water.

2. The method for preparing iron-based soft magnetic composite powder according to claim 1, characterized in that, The smelting temperature is 1550~1700 ℃, and the time is 25~45 min.

3. The method for preparing iron-based soft magnetic composite powder according to claim 1, characterized in that, The iron-based matrix includes one or more of iron, iron-silicon alloys, and iron-silicon-aluminum alloys.

4. The method for preparing iron-based soft magnetic composite powder according to claim 1, characterized in that, The iron nitride is Fe4N or Fe3N; the concentration of the iron nitride mixed with water is 5~20 g / L.

5. The method for preparing iron-based soft magnetic composite powder according to claim 1 or 4, characterized in that, The atomizing medium also includes compressed air; the volume ratio of water to compressed air in the atomizing medium is 1:0.3 to 1:0.

8.

6. The method for preparing iron-based soft magnetic composite powder according to claim 1, characterized in that, The amount of iron nitride added is 0.5 to 5% of the mass of the iron-based matrix powder.

7. The method for preparing iron-based soft magnetic composite powder according to claim 1, characterized in that, The parameters for the high-pressure atomization impact on the iron-based molten liquid are: atomization pressure of 80~150 MPa, atomization distance of 150~300 mm, and cooling rate during atomization of 10. 3 ~10 4 ℃ / s.

8. The method for preparing iron-based soft magnetic composite powder according to claim 1, characterized in that, The reducing atmosphere is hydrogen and nitrogen; the volume ratio of hydrogen to nitrogen is 1:3 to 1:

9.

9. The method for preparing iron-based soft magnetic composite powder according to claim 1, characterized in that, The reduction treatment is performed at a temperature of 300-500 ℃, a pressure of 0.1-0.3 MPa, and a time of 1-2 h.

10. The iron-based soft magnetic composite powder prepared by the method for preparing iron-based soft magnetic composite powder according to any one of claims 1 to 9.

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