Soft magnetic powder, magnetic core, and magnetic component

Abstract

The invention relates to a soft magnetic powder, a magnetic core, and a magnetic component. The soft magnetic powder contains Fe and C. And the content of C is from 0.01% by mass to 0.5% by mass (inclusive). The soft magnetic powder contains special soft magnetic particles. The special soft magnetic particles contain both a phase having a symmetry of a space group Im-3m or Pm-3m and a phase having a symmetry of a space group Pnam.

Description

Technical Field

[0001] This invention relates to a soft magnetic powder, a magnetic core, and a magnetic component. Background Art

[0002] Magnetic components such as inductors require high DC superposition characteristics. This is because when using magnetic components in power supply components such as DC-DC converters, a high inductance must be maintained even when DC current is superimposed on the magnetic components.

[0003] Patent document 1 describes an invention related to a soft magnetic material containing a total of 90% by mass or more of Fe and Co, characterized in that it contains precipitates of compounds containing iron and nitrogen.

[0004] Existing technical documents

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2022-070508 Summary of the Invention

[0007] Technical problem to be solved by the invention

[0008] The purpose of this invention is to provide a soft magnetic powder that can provide a magnetic core and magnetic components with high DC superposition characteristics.

[0009] Solutions for solving technical problems

[0010] The soft magnetic powder involved in this invention is a soft magnetic powder containing Fe and C.

[0011] The content of C is between 0.01% and 0.5% by mass.

[0012] The soft magnetic powder contains special soft magnetic particles.

[0013] The special soft magnetic particles comprise both phases with symmetry of space group Im-3m or Pm-3m and phases with symmetry of space group Pnam.

[0014] The soft magnetic powder may also contain Co.

[0015] In the soft magnetic powder, the content of Fe relative to the total content of Fe and Co can be more than 25% by mass and less than 99% by mass.

[0016] The phase with symmetry of space group Im-3m or Pm-3m can also be a (Fe,Co) phase.

[0017] The phase with the symmetry of space group Pnam can also be the (Fe,Co)3C phase.

[0018] The proportion of the special soft magnetic particles can also be 10% or more.

[0019] The average particle size of the soft magnetic particles contained in the soft magnetic powder can also be above 0.1 μm and below 50 μm.

[0020] The soft magnetic powder may also contain secondary components, and the content of the secondary components in 100% by mass of the soft magnetic powder may be less than 15% by mass.

[0021] The secondary components may also be one or more selected from B, Si, P, Cu, V, Ti, Zr, Hf, Nb, Ta, Mo, W, Cr, Ni, Al, Mn, Ag, Zn, S, Sn, As, Sb, Bi, N, O and rare earth elements.

[0022] The magnetic core of the present invention comprises the above-mentioned soft magnetic powder.

[0023] The magnetic component of the present invention comprises the aforementioned soft magnetic powder. Attached Figure Description

[0024] Figure 1 It is a bright-field image obtained by observing the cross-section of a soft magnetic powder containing special soft magnetic particles using STEM.

[0025] Figure 2 Photographed using selected area diffraction. Figure 1 Electron diffraction image of soft magnetic particle 1.

[0026] Figure 3 Photographed using selected area diffraction. Figure 1 Electron diffraction image of soft magnetic particle 2.

[0027] Figure 4 Photographed using selected area diffraction. Figure 1 Electron diffraction images of soft magnetic particles 3.

[0028] Figure 5 It is an electron diffraction image obtained by taking pictures of soft magnetic particles that are not special soft magnetic particles using the selected area diffraction method. Detailed Implementation

[0029] The present invention will now be described based on its embodiments.

[0030] (Composition of soft magnetic powder)

[0031] The soft magnetic powder contains Fe and C. Furthermore, the C content is between 0.01% and 0.5% by mass. The soft magnetic powder may also contain Co, and the proportion of Fe to the total content of Fe and Co may be between 25% and 99% by mass.

[0032] When the carbon content in the soft magnetic powder is too low, it is difficult for the powder to contain the special soft magnetic particles described later, and the DC superposition characteristics of the magnetic core tend to decrease. When the carbon content in the soft magnetic powder is too high, the number of soft magnetic particles containing only phases with space group Pnam symmetry and not phases with space group Im-3m or Pm-3m symmetry tends to increase along with the special soft magnetic particles described later. Therefore, the saturation magnetization of the soft magnetic powder tends to decrease, and the DC superposition characteristics of the magnetic core tend to decrease.

[0033] When the total Fe content relative to Fe and Co is 25% by mass or more, the DC superposition characteristics of the magnetic core using this soft magnetic powder are easily improved. When the total Fe content relative to Fe and Co is 99% by mass or less, it is easy to form a soft magnetic powder with a good balance of coercivity, saturation flux density, and corrosion resistance.

[0034] Soft magnetic powder contains soft magnetic particles. The average particle size of the soft magnetic particles in the soft magnetic powder can be between 0.1 μm and 50 μm. With an average particle size of 0.1 μm or larger, the filling rate of the magnetic core is easily increased, and the relative permeability is easily increased. With an average particle size of 50 μm or smaller, the eddy current loss of the magnetic core is less likely to increase.

[0035] There are no particular limitations on the method for determining the average particle size of soft magnetic particles. For example, the observation range of a STEM can be set to include more than 20,000 soft magnetic particles, and the cross-section of the soft magnetic particles can be observed. The average of the circular equivalent diameters of each soft magnetic particle can then be taken as the average particle size. The observation range can be a single field of view containing more than 20,000 soft magnetic particles, or multiple fields of view containing a total of more than 20,000 soft magnetic particles can be taken as the observation range. The circular equivalent diameter of a soft magnetic particle is the diameter of a circle whose area is equal to the cross-sectional area of ​​the soft magnetic particle.

[0036] In addition to Fe, Co, and C, the soft magnetic powder of this embodiment may also contain secondary components. These secondary components may be, for example, one or more selected from B, Si, P, Cu, V, Ti, Zr, Hf, Nb, Ta, Mo, W, Cr, Ni, Al, Mn, Ag, Zn, S, Sn, As, Sb, Bi, N, O, and rare earth elements. The rare earth elements are Sc, Y, and lanthanides.

[0037] By including the aforementioned byproducts in the soft magnetic powder, the relative permeability and eddy current loss of the magnetic core made using this soft magnetic powder can be easily controlled. The total content of the aforementioned byproducts can be less than 25% by mass, less than 15% by mass, or less than 5% by mass. By keeping the content of the byproducts within the above ranges, the saturation magnetization of the soft magnetic powder can be easily improved.

[0038] Soft magnetic powders may also contain elements other than those mentioned above, specifically elements other than those contained in the group consisting of Fe, Co, C, B, Si, P, Cu, V, Ti, Zr, Hf, Nb, Ta, Mo, W, Cr, Ni, Al, Mn, Ag, Zn, S, Sn, As, Sb, Bi, N, O, and rare earth elements, as unavoidable impurities. There is no particular limit to the content of unavoidable impurities; if the entire soft magnetic powder is considered to be 100% by mass, the total content of unavoidable impurities can also be less than 1% by mass.

[0039] The total content of by-products and unavoidable impurities in the soft magnetic powder can be less than 26% by mass, less than 16% by mass, or less than 6% by mass. That is, the total content of Fe, Co and C can be more than 74% by mass, more than 84% by mass, or more than 94% by mass.

[0040] (Special soft magnetic particles)

[0041] The soft magnetic powder of this embodiment comprises soft magnetic particles, which are classified into special soft magnetic particles and other soft magnetic particles.

[0042] The soft magnetic powder of this embodiment contains special soft magnetic particles. Special soft magnetic particles refer to soft magnetic particles that contain both a phase with symmetry of space group Im-3m or Pm-3m and a phase with symmetry of space group Pnam.

[0043] Furthermore, the proportion of special soft magnetic particles in the soft magnetic powder can also be 10% or more. There is no particular upper limit to the proportion of special soft magnetic particles in the soft magnetic powder. For example, the proportion of special soft magnetic particles in the soft magnetic powder can also be less than 100%. That is, all the soft magnetic particles contained in the soft magnetic powder can be special soft magnetic particles.

[0044] The following is an example of a method for confirming whether a soft magnetic particle is a special soft magnetic particle.

[0045] First, the cross-section of the soft magnetic powder is observed using STEM (Scanning Transmission Electron Microscopy). TEM (Transmission Electron Microscopy) can also be used instead of STEM. To observe the cross-section of the soft magnetic powder, a cross-sectional observation sample is prepared. There are no particular limitations on the method for preparing the cross-sectional observation sample. It can also be prepared by cutting the soft magnetic powder after mixing it with resin. Alternatively, it can be prepared by cutting a magnetic core containing the soft magnetic powder.

[0046] exist Figure 1 The image shows a bright-field image obtained by observing a cross-section of a soft magnetic powder containing special soft magnetic particles using STEM.

[0047] Next, electron diffraction images are taken for the soft magnetic particles that are to be confirmed as special soft magnetic particles. There are no particular restrictions on the method for taking electron diffraction images. Selected area diffraction can also be used to take electron diffraction images.

[0048] exist Figure 2 The diagram shows the effect of selected area diffraction. Figure 1 Electron diffraction image of soft magnetic particle 1.

[0049] Figure 2 In the diagram, the strong light spots labeled 11-0 (rectangular), 000 (rectangular), and 01-3 (rectangular) are diffraction points caused by phases with space group Im-3m symmetry. The weak light spots labeled 201 (italic), 021 (italic), and 2-01 (italic) (italic) are diffraction points caused by phases with space group Pnam symmetry. The numbers and text marked with a hyphen (-) are... Figure 2 The numbers and text marked with a hyphen (-) above have the same meaning.

[0050] Therefore, through Figure 2 confirm Figure 1 The soft magnetic particles 1 contain a phase with symmetry of space group 1m-3m, and Figure 1 The soft magnetic particles 1 contain a phase with symmetry of space group Pnam.

[0051] Using STEM-EDS, the soft magnetic particles 1 were analyzed by energy-dispersive X-ray spectroscopy, which allowed for the identification of the elements contained in each phase of the soft magnetic particles 1. Furthermore, if the soft magnetic particles contained in the soft magnetic powder have virtually identical compositions, then the elements contained in each phase of the soft magnetic particles 1 can be identified based on the composition of the soft magnetic powder.

[0052] Phases with space group symmetry of 1m-3m can also exist as grains within special soft magnetic particles.

[0053] Based on the above, "soft magnetic particles contain phases with symmetry of specific space groups" refers to the observation of light spots that can be indexed for specific space groups in electron diffraction images of soft magnetic particles obtained by selected area diffraction.

[0054] exist Figure 3 The image shows a photograph taken using the selected area diffraction method. Figure 1 The electron diffraction pattern obtained from soft magnetic particle 2. Figure 4 The image shows a photograph taken using the selected area diffraction method. Figure 1 Electron diffraction images of soft magnetic particles 3.

[0055] and Figure 2 Similarly, in Figure 3 and Figure 4 In the electron diffraction pattern, the strong bright spots, indexed in rectangular planes, are also diffraction spots caused by phases with symmetry of space group Im-3m. Conversely, the weak bright spots, indexed in italics, are diffraction spots caused by phases with symmetry of space group Im-3m. Figure 1 Similarly, the soft magnetic particles 1 can be confirmed. Figure 1 The soft magnetic particles 2 and 3 are special soft magnetic particles.

[0056] exist Figures 2-4 In the diagram, the light spot indexed as 000 is a light spot produced by transmitted electrons.

[0057] exist Figure 5 The image shows an electron diffraction pattern obtained by selected area diffraction of soft magnetic particles that are not special soft magnetic particles. Figure 5 In the study, strong diffraction spots caused by phases with space group Im-3m symmetry were confirmed, but weak diffraction spots with space group Pnam symmetry were not confirmed. Therefore, according to Figure 5 It was confirmed that the soft magnetic particle contains a phase with symmetry of space group Im-3m, and that the soft magnetic particle does not contain a phase with symmetry of space group Pnam.

[0058] Soft magnetic powder containing special soft magnetic particles can be used to fabricate magnetic cores with high relative permeability and high DC superposition characteristics. These special soft magnetic particles are harder than other soft magnetic particles. This is because they contain phases with symmetry of the space group Pnam. Therefore, when using soft magnetic powder containing these special soft magnetic particles to fabricate magnetic cores, the powder is less prone to deformation during fabrication, its flowability is improved, and the distribution of the powder within the magnetic core becomes more uniform.

[0059] Based on the above reasons, when using soft magnetic powder containing special soft magnetic particles, a magnetic core with high DC superposition characteristics can be obtained.

[0060] The phase with space group Im-3m symmetry mentioned above can be the (Fe,Co) phase, and the phase with space group Pnam symmetry mentioned above can be the (Fe,Co)3C phase.

[0061] When the phase with space group 1m-3m contains Fe and Co, i.e., when the soft magnetic particle 1 contains Fe and Co, the phase with space group 1m-3m symmetry can be identified as the (Fe,Co) phase. Furthermore, the (Fe,Co) phase is a magnetic phase. When the phase with space group 1m-3m symmetry contains Fe, Co, and C, i.e., when the soft magnetic particle 1 contains Fe, Co, and C, the phase with space group 1m symmetry can be identified as the (Fe,Co)3C phase. Furthermore, the (Fe,Co)3C phase is a magnetic phase with a lower saturation magnetization than the (Fe,Co) phase. Moreover, it can be confirmed that… Figure 1 The soft magnetic particles 1 are special soft magnetic particles.

[0062] The arrangement of Fe and Co in a phase with space group Im-3m can also be ordered. When Fe and Co are ordered, weak diffraction spots caused by forbidden reflection appear, and these weak diffraction spatial spots have space group P-3m symmetry. Alternatively, only diffraction spatial spots caused by phases with space group P-3m symmetry can be identified, while diffraction spots caused by phases with space group Im-3m symmetry cannot be identified.

[0063] The proportion of special soft magnetic particles in soft magnetic powder can be 5% or more, 10% or more, or even 20% or more. The higher the proportion of special soft magnetic particles, the easier it is to increase the hardness of the soft magnetic powder. When making a magnetic core, the distribution of the soft magnetic powder is more likely to become uniform, thus improving the DC superposition characteristics of the magnetic core.

[0064] (Method for manufacturing soft magnetic powder)

[0065] The method for manufacturing the soft magnetic powder of this embodiment will be described, but the method for manufacturing the soft magnetic powder of this embodiment is not limited to the method described below.

[0066] Soft magnetic powders containing special soft magnetic particles can be produced, for example, by atomization using water and organic solvents.

[0067] One known method for producing soft magnetic powder is water atomization. In the conventional water atomization method, molten metal, formed by melting the raw material metal, is atomized into powder using high-pressure water to produce soft magnetic powder.

[0068] In the water + organic solvent atomization method, the water used for pulverizing molten metal in the water atomization method is replaced with a liquid mixed with water and organic solvent (hereinafter, sometimes referred to as a mixture). That is, in the water + organic solvent atomization method, molten metal formed by melting the raw material metal is pulverized by a high-pressure mixture to produce soft magnetic powder.

[0069] In the water + organic solvent atomization method, firstly, the cooling tank where the molten metal is dropped is set to an inert gas atmosphere. Nitrogen or rare gases such as Ar or He are preferred as the inert gas; from a cost reduction perspective, nitrogen is more preferred. Then, the molten metal dropped into the cooling tank is pulverized using a high-pressure mixture.

[0070] The organic solvent in the mixture is decomposed into carbon dioxide and hydrogen by the high-temperature molten metal. The carbon dioxide is reduced by the hydrogen to produce carbon. Some of the produced carbon is incorporated into the molten metal. As a result, even if the molten metal does not contain carbon, the final soft magnetic powder will contain carbon.

[0071] The inventors have discovered that soft magnetic powder prepared by atomizing molten metal containing Fe using a water + organic solvent method readily contains specific soft magnetic particles. The reasons why soft magnetic powder prepared by atomizing molten metal containing Fe using a water + organic solvent method readily contains specific soft magnetic particles will be explained below.

[0072] In the following description, a portion of Fe may be replaced with Co. When a portion of Fe is replaced with Co, the term "phase with symmetry of space group Im-3m" may be used instead of "(Fe,Co) phase". The term "phase with symmetry of space group Pnam" may also be used instead of "(Fe,Co)3C phase".

[0073] In molten metal at high temperatures, the Fe metallic phase exists as a phase with space group Fm3m symmetry. Therefore, the interatomic spacing within the Fe metallic phase is relatively large. Furthermore, a maximum of approximately 2% by mass of carbon can be dissolved in the Fe metallic phase.

[0074] As the molten metal cools, the phase with space group Fm3m symmetry transforms into a phase with space group Im-3m symmetry. Carbon is more difficult to dissolve in the phase with space group Im-3m symmetry compared to the phase with space group Fm3m symmetry. The dissolved carbon, together with Fe contained in the soft magnetic powder, forms a phase with space group Pnam symmetry. Then, the phase with space group Pnam symmetry precipitates between the phases with space group Im-3m symmetry.

[0075] The following explains the reasons for the improved DC superposition characteristics of the magnetic core obtained when using the soft magnetic powder of this embodiment to fabricate the magnetic core.

[0076] Phases with space group Pnam symmetry have a crystal structure containing 12 Fe atoms and 4 C atoms in the unit cell. The Fe and C atoms are bonded by strong covalent bonds. Therefore, phases with space group Pnam symmetry are very hard. In contrast, phases with space group Im-3m or Pm-3m symmetry are softer.

[0077] In special soft magnetic particles, phases with space group Pnam symmetry precipitate between phases with space group Im-3m or Pm-3m symmetry. Therefore, these special soft magnetic particles possess both hardness and flexibility, making them resistant to breakage or deformation. When using soft magnetic powder containing these special soft magnetic particles to fabricate magnetic cores, the distribution of the soft magnetic particles tends to become more uniform, improving the DC superposition characteristics of the magnetic core.

[0078] Even when carbon is added to the raw metal, the molten metal still contains carbon, and the resulting soft magnetic powder also contains carbon. However, even when soft magnetic powder is produced from molten metal containing carbon using water atomization, it does not contain any special soft magnetic particles.

[0079] When soft magnetic powders are prepared by water atomization, carbon is incorporated as a martensitic or retained austenitic phase into the interior of a phase with a space group of 1m-3m, without precipitating a phase with a space group of Pnam. As a result, even when using soft magnetic powders prepared by water atomization to fabricate magnetic cores, the distribution of soft magnetic particles is difficult to achieve a sufficiently uniform state, and the DC superposition characteristics of the magnetic core cannot be adequately improved.

[0080] Based on the above, the inventors have discovered that by using a water + organic solvent atomization method in the preparation of soft magnetic powder, it is possible to appropriately produce soft magnetic powder containing special soft magnetic particles.

[0081] There are no particular restrictions on the types of organic solvents used in water + organic solvent atomization methods. Examples include monohydric alcohols such as methanol or ethanol, dihydric alcohols such as ethylene glycol, trihydric alcohols such as glycerol, and carboxylic acids such as formic acid or acetic acid. In particular, from the viewpoints of ease of operation and cost, ethanol is preferred as the organic solvent.

[0082] The application of the magnetic powder in this embodiment is not particularly limited. Examples include magnetic components used in sensors, motor stator cores, inductors, transformers, EMI filters, and magnetic heads.

[0083] (Magnetic core)

[0084] The magnetic core of this embodiment comprises the soft magnetic powder described above. The soft magnetic powder may also be coated with an insulating material.

[0085] In addition to the soft magnetic powder described above, the magnetic core of this embodiment may also contain other powders. There are no particular limitations on the composition and microstructure of these other powders. They can be appropriately selected based on the intended use of the magnetic core. When the other powders have an amorphous structure and / or a nanocrystalline structure, the relative permeability of the magnetic core is easily increased, and the core loss is easily reduced.

[0086] Soft magnetic powder with an average particle size exceeding 3 μm is designated as large-diameter powder, and soft magnetic powder with an average particle size of less than 3 μm is designated as small-diameter powder. The magnetic core of this embodiment can be fabricated using only large-diameter powder, only small-diameter powder, or a mixture of both. Furthermore, large-diameter powder and / or small-diameter powder can also be coated with an insulating coating.

[0087] Large-diameter powder and small-diameter powder may contain special soft magnetic particles, or only large-diameter powder may contain special soft magnetic particles, or only small-diameter powder may contain special soft magnetic particles.

[0088] When using powders that combine large-diameter and small-diameter powders to fabricate magnetic cores, the filling rate and relative permeability of the magnetic core are more easily improved compared to using only large-diameter powder or only small-diameter powder. This is because soft magnetic powder derived from small-diameter powder can fill the gaps between soft magnetic powders derived from large-diameter powder.

[0089] The magnetic core may also contain resin. There are no particular restrictions on the type of resin. Examples include epoxy resin and phenolic resin. There are also no particular restrictions on the resin content. For example, it can be between 0.5% and 5% by mass relative to the total magnetic core.

[0090] (Manufacturing method of magnetic core)

[0091] The method for manufacturing the magnetic core in this embodiment is not particularly limited. Hereinafter, an example of a method for manufacturing a magnetic core (powder core) is shown.

[0092] First, a resin mixture is prepared by mixing soft magnetic powder containing special soft magnetic particles with a thermosetting resin. Next, the resin mixture is filled into a mold. Then, the resin mixture in the mold is pressurized to obtain a pressed powder. Finally, the resin contained in the pressed powder is thermosetting to obtain a magnetic core (pressed powder core).

[0093] Soft magnetic powder, obtained by mixing large-diameter powder and small-diameter powder, can also be used in the fabrication of magnetic cores.

[0094] The application of the magnetic core in this embodiment is not particularly limited. Examples include inductors, choke coils, transformers, and other coil components. In particular, when the magnetic core of this embodiment is used in coil components, coil components that satisfy both high inductance and good DC superposition characteristics can be obtained.

[0095] Example

[0096] The present invention will be further described below based on more detailed embodiments, but the present invention is not limited to these embodiments.

[0097] (Experimental Example 1)

[0098] To obtain the master alloy with the composition listed in the Added Components column of Table 1, elemental Fe, elemental Co, elemental C, and / or the elemental components of the secondary components were weighed. Then, after evacuating the chamber, the master alloy was melted by high-frequency heating.

[0099] The added and analytical compositions shown in Table 1 are all listed in wt%. Additionally, for a composition of 100wt% Fe, it is simply listed as Fe.

[0100] The master alloy was heated to 1500°C to melt it, resulting in a molten alloy. Then, soft magnetic powders with the analytical compositions shown in Table 1 were prepared. The high-pressure liquid (high-pressure water or a high-pressure mixture) used in the preparation of the soft magnetic powders is shown in the "Atomized High-Pressure Liquid" column. Samples listed as "100% Water" in the high-pressure liquid column were prepared using a water atomization method using high-pressure water as the high-pressure liquid. Samples listed as "Water + Ethanol X%" in the high-pressure liquid column were prepared using a water + organic solvent atomization method using a high-pressure mixture as the high-pressure liquid. In Experimental Example 1, X was always 20.

[0101] Next, classification was performed to obtain soft magnetic powders with the average particle sizes shown in Table 1. For powders with an average particle size of 0.30 μm or larger, classification was performed using a rotary airflow classifier (NISSHIN ENGINEERING Inc. Aerofine Classifier). For powders with an average particle size of less than 0.30 μm, classification was performed using a differential electrostatic classifier (TSI Model 3082).

[0102] The average particle size of the obtained soft magnetic powder is shown in Table 1 and confirmed using a laser diffraction particle size distribution measuring device (HELOS & RODOS, Sympatec).

[0103] The obtained soft magnetic powders were quantitatively analyzed using ICP-AES (Shimadzu ICPS-8100CL) to determine the content of elements other than carbon. The carbon content was determined using oxygen flow combustion-infrared absorption spectrometry (LECO CS-844). Based on the content of each element in each soft magnetic powder, the composition of each soft magnetic powder was confirmed to be consistent with the analytical compositions shown in Table 1.

[0104] The true density of the obtained soft magnetic powder was determined using Archimedes' method with a WADON-type specific gravity bottle.

[0105] Soft magnetic powder and epoxy resin were mixed to prepare a resin mixture. The resin content in the resin mixture was set to 2.5% by mass. YSLV-80XY manufactured by NIPPON STEEL Chemical & Material Co., Ltd. was used as the epoxy resin.

[0106] The obtained resin mixture is filled into a mold of a specified annular shape. Then, molding is performed under pressure, controlling the filling rate of the final magnetic core (annular iron core) to approximately 80%, to obtain the molded body. Specifically, the molding pressure is controlled between 1 and 10 ton / cm². 2 Within the range.

[0107] The resin contained in the molded body is heat-cured at 180℃ for 60 minutes to produce a ring-shaped iron core (outer diameter 11mm, inner diameter 6.5mm, thickness 2.5~3.0mm).

[0108] The filling rate η of the soft magnetic powder in the toroidal core is calculated by dividing the density of the toroidal core, which is calculated based on the size and mass of the toroidal core, by the theoretical density of the toroidal core, which is calculated based on the true density of the various materials contained in the toroidal core (in Experimental Example 1, the true density of the soft magnetic powder).

[0109] The inductance of the toroidal core at 1 MHz was measured using an LCR meter (Agilent Technologies Inc. 4284A) and a DC bias power supply (Agilent Technologies Inc. 42841A). The relative permeability of the toroidal core was then calculated based on its inductance. The number of turns in the winding was set to 24. The relative permeability at a DC superposition current of 0 A was defined as μ0, and the DC superposition current at 90% of μ0 was defined as Isat. A higher Isat indicates better DC superposition characteristics.

[0110] The Isat improvement rate of sample number 1 is described as the Isat improvement rate of the comparative example, sample number 3, which has the same analytical composition as the example. Furthermore, the Isat improvement rate of sample number 2 is also described as the Isat improvement rate of sample number 3. Hereinafter, the DC superposition characteristics of examples with an Isat improvement rate of 5% or more are described as good, the DC superposition characteristics of examples with an Isat improvement rate of 10% or more are described as better, and the DC superposition characteristics of examples with an Isat improvement rate of 20% or more are described as particularly good.

[0111] The toroidal iron cores of each sample were cut off, and a TEM mesh grid of Mo#200 was embedded in epoxy resin and cured at 130°C. The samples were then thinned using ion milling (Gatan PIPS) at an accelerating voltage of 4 kV and a milling angle of 4°–5° to obtain samples for observation. Bright-field images were then observed using a STEM (JEM-2100F, NEC) with a field of view of approximately 3 μm × 3 μm. Electron diffraction images of approximately 20 particles within the field of view were captured using selected area diffraction. The area size was set to 300 nmΦ. The proportion of special soft magnetic particles was calculated by dividing the number of special soft magnetic particles by the total number of soft magnetic particles. Furthermore, in the captured electron diffraction images, soft magnetic particles exhibiting diffraction spots caused by phases with space group Im-3m or Pm-3m symmetry, and those with diffraction spots caused by phases with space group Pnam symmetry, were designated as special soft magnetic particles.

[0112] [Table 1]

[0113]

[0114] Sample No. 2 was prepared using the same composition as Sample No. 1 but via water atomization. Therefore, the carbon content in its analytical composition differs from that of Sample No. 1. Sample No. 3 was prepared using water atomization, but carbon was added to the molten metal in a manner that ensured the carbon content in its analytical composition was equal to that of Sample No. 1.

[0115] The soft magnetic powder of sample number 1 contains special soft magnetic particles. As a result, the magnetic core containing the soft magnetic powder of sample number 1 has the same μ0 as the magnetic core containing the same soft magnetic powder, namely sample number 3, except that it does not contain special soft magnetic particles, and the DC superposition characteristics are improved.

[0116] Samples 4, 7, and 10 were administered under the same conditions, except that the added and analytical compositions were changed from those in sample 1. Samples 5, 8, and 11 were administered in the same manner as sample 2. Samples 6, 9, and 12 were administered in the same manner as sample 3.

[0117] Sample numbers 4-6, 7-9, and 10-12 all yielded the same results as sample numbers 1-3.

[0118] (Experimental Example 2)

[0119] Under conditions where the analytical compositions were identical, examples implemented by the water + organic solvent atomization method (only sample number 43 was a comparative example) and comparative examples implemented by the water atomization method were compared. Specifically, the same comparisons were performed as those for example sample number 1 and comparative example sample number 3 of Experimental Example 1. The results are shown in Tables 2 to 6.

[0120] [Table 2]

[0121]

[0122] [Table 3A]

[0123]

[0124] [Table 3B]

[0125]

[0126] [Table 4]

[0127]

[0128] [Table 5]

[0129]

[0130] [Table 6]

[0131]

[0132] Table 2 shows the experimental results for the composition commonly referred to as the Fe-Si system. Table 3A shows the experimental results for the composition of samples 19 and 20 in Table 2, where some or all of the Fe was replaced by Co. Table 3B shows the experimental results for the composition of samples 1 and 3 in Table 1, where some or all of the Fe was replaced by Co. Table 4 shows the experimental results for the composition of samples 19 and 20, where Fe and / or Si were replaced by Cr. Tables 5 and 6 show the experimental results for the composition of samples 4, where some of the Fe was replaced by Co, and the contents of Fe, Co, and / or Si were further varied.

[0133] When the composition of the soft magnetic powder is within a specific range, the same results as in Experimental Example 1 are obtained under any circumstances. However, when the soft magnetic powder does not contain Fe, even when using the water + organic solvent atomization method, the soft magnetic powder does not contain any special soft magnetic particles.

[0134] (Experimental Example 3)

[0135] For samples 10 and 12 of Experimental Example 1, the experiments were conducted under the same conditions, except that the carbon content in the analytical composition was changed. In each example, the carbon content in the analytical composition was changed by altering the composition of the mixture. In each comparative example, the carbon content in the analytical composition was changed by altering the carbon content in the added components. The results are shown in Table 7.

[0136] [Table 7]

[0137]

[0138] According to Table 7, it was confirmed that when using the water + organic solvent atomization method, the higher the proportion of organic solvent in the mixture and the higher the carbon content in the analytical composition, the higher the proportion of special soft magnetic particles and the better the DC superposition characteristics.

[0139] In contrast, when using the water atomization method, regardless of the carbon content in the composition, the resulting soft magnetic powder does not contain any special soft magnetic particles. Furthermore, carbon has minimal impact on the μ0 and Isat of the magnetic core.

[0140] (Experimental Example 4)

[0141] Except for changing the average particle size of the soft magnetic powder, the soft magnetic powder and magnetic core were prepared under the same conditions as the samples 10 and 12 of Experimental Example 1.

[0142] In Experiment 4, the eddy current loss of the magnetic core was also evaluated. Eddy current loss was measured using a BH analyzer (SY-8218 manufactured by Iwatsu Measurement Co., Ltd.) under the following conditions: 24 turns in the primary winding, 12 turns in the secondary winding, a frequency of 3 MHz, and a measured magnetic flux density of 10 mT. The results are shown in Table 8.

[0143] [Table 8]

[0144]

[0145] Table 8 confirms that when using soft magnetic powder with an average particle size of less than 50.0 μm, the larger the average particle size, the larger the μ0 of the magnetic core, and the higher the improvement rate of Isat. However, when using soft magnetic powder with an average particle size exceeding 50.0 μm, the increase in μ0 and Isat reaches its peak, leading to an increase in eddy current loss.

[0146] Furthermore, even when the combination of sample numbers 10 and 12 was changed to other combinations of samples from Experimental Examples 1 to 3 and 6, the same trend was observed. That is, it was confirmed that when using soft magnetic powder with an average particle size of 50.0 μm or less, the larger the average particle size, the larger the μ0 of the magnetic core, and the higher the improvement rate of Isat. However, when using soft magnetic powder with an average particle size exceeding 50.0 μm, the increase in μ0 and the improvement rate of Isat reaches its peak, and eddy current loss increases accordingly.

[0147] (Experimental Example 5)

[0148] In Experiment 5, except for the small average particle size, the powder prepared in the same manner as the soft magnetic powder prepared in Experiments 1-4 was designated as a small-diameter powder. Furthermore, the amorphous powder was designated as a large-diameter powder. The large-diameter powder had an average particle size of 22 μm and a composition of Fe. 73 B 11 Si 11 C3Cr2. Furthermore, soft magnetic powder is prepared by mixing small-diameter and large-diameter powders. The content of small-diameter powder in the soft magnetic powder is set to the values ​​shown in the respective tables.

[0149] Tables 9A and 9B show examples and comparative examples using small-diameter powders with the same analytical composition as the soft magnetic powders of samples 1 and 3. Table 10 shows examples and comparative examples using small-diameter powders with the same analytical composition as the soft magnetic powders of samples 4 and 6. Table 11 shows examples and comparative examples using small-diameter powders with the same analytical composition as the samples 7 and 9. Table 12 shows examples and comparative examples using small-diameter powders with the same analytical composition as the samples 10 and 12.

[0150] [Table 9A]

[0151]

[0152] [Table 9B]

[0153]

[0154] [Table 10]

[0155]

[0156] [Table 11]

[0157]

[0158] [Table 12]

[0159]

[0160] Based on Tables 9A, 9B, and 10–12, it was confirmed that the larger the average particle size of the small-diameter powder, the higher the μ0 of the magnetic core. Furthermore, it was confirmed that when the soft magnetic powder used as the small-diameter powder contains special soft magnetic particles, the DC superposition characteristics are improved.

[0161] (Experimental Example 6)

[0162] In Experiment 6, the experiment was conducted under identical conditions, except that the contents of each component, including byproducts, in the analytical composition were appropriately changed. The results are shown in Tables 13 to 20.

[0163] [Table 13]

[0164]

[0165] [Table 14]

[0166]

[0167] [Table 15]

[0168]

[0169] [Table 16]

[0170]

[0171] [Table 17]

[0172]

[0173] [Table 18]

[0174]

[0175] [Table 19]

[0176]

[0177] [Table 20]

[0178]

[0179] According to the tables, even when the composition of the soft magnetic powder is changed within the specified range, the μ0 of the magnetic core containing soft magnetic powder with special soft magnetic particles is higher, and the DC superposition characteristics are improved compared with the magnetic core containing soft magnetic powder without special soft magnetic particles.

Claims

1. A soft magnetic powder, wherein, The soft magnetic powder contains Fe and C. The content of C is between 0.01% and 0.5% by mass. The soft magnetic powder contains special soft magnetic particles. The special soft magnetic particles comprise both a phase with symmetry of space group Im-3m or Pm-3m and a phase with symmetry of space group Pnam.

2. The soft magnetic powder according to claim 1, wherein, The soft magnetic powder also contains Co. In the soft magnetic powder, the content of Fe relative to the total content of Fe and Co is more than 25% by mass and less than 99% by mass.

3. The soft magnetic powder according to claim 2, wherein, The phase with symmetry of space group Im-3m or Pm-3m is the (Fe,Co) phase. The phase with the symmetry of space group Pnam is the (Fe,Co)3C phase.

4. The soft magnetic powder according to any one of claims 1 to 3, wherein, The proportion of the special soft magnetic particles is more than 10%.

5. The soft magnetic powder according to any one of claims 1 to 3, wherein, The soft magnetic powder contains soft magnetic particles with an average particle size of 0.1 μm to 50 μm.

6. The soft magnetic powder according to any one of claims 1 to 3, wherein, The soft magnetic powder also contains secondary components, and the content of the secondary components in 100% by mass of the soft magnetic powder is less than 15% by mass.

7. The soft magnetic powder according to claim 6, wherein, The secondary components are selected from one or more of the following: B, Si, P, Cu, V, Ti, Zr, Hf, Nb, Ta, Mo, W, Cr, Ni, Al, Mn, Ag, Zn, S, Sn, As, Sb, Bi, N, O, and rare earth elements.

8. A magnetic core, wherein, It comprises the soft magnetic powder according to any one of claims 1 to 7.

9. A magnetic component, wherein, It comprises the soft magnetic powder according to any one of claims 1 to 7.

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