Soft magnetic powder, magnetic core, and magnetic component

Abstract

To provide a soft magnetic powder that can provide magnetic cores and magnetic parts with excellent DC bias characteristics.SOLUTION: Soft magnetic powder contains Fe and C. The C content is 0.01 mass% or more and 0.5 mass% or less. The soft magnetic powder contains special soft magnetic particles. The special soft magnetic particles contain both a phase having symmetry of space group Im-3m or Pm-3m and a phase having symmetry of space group Pnam.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a soft magnetic powder, a magnetic core, and a magnetic component. [Background technology]

[0002] Magnetic components such as inductors are required to have high DC bias characteristics. This is because when magnetic components are used in power supply components such as DC-DC converters, they need to maintain high inductance even when a DC current is superimposed on them.

[0003] Patent Document 1 describes an invention relating to a soft magnetic material containing Fe and Co in a total amount of 90 mass % or more, and characterized in that it contains precipitates of compounds of iron and nitrogen. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2022-070508 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a soft magnetic powder that can provide magnetic cores and magnetic parts with excellent DC bias characteristics. [Means for solving the problem]

[0006] The soft magnetic powder according to the present invention is a soft magnetic powder containing Fe and C, The C content is 0.01% by mass or more and 0.5% by mass or less, The soft magnetic powder contains special soft magnetic particles, The special soft magnetic particles include both a phase having the symmetry of the space group Im-3m or Pm-3m and a phase having the symmetry of the space group Pnam.

[0007] The soft magnetic powder may further contain Co, In the soft magnetic powder, the content of Fe relative to the total content of Fe and Co may be 25% by mass or more and 99% by mass or less.

[0008] The phase having space group Im-3m or Pm-3m symmetry may be FeCo; The phase having the symmetry of the space group Pnam may be a (Fe,Co)3C phase.

[0009] The proportion of the special soft magnetic particles may be 10% or more.

[0010] The soft magnetic particles contained in the soft magnetic powder may have an average particle size of 0.1 μm or more and 50 μm or less.

[0011] The soft magnetic powder may further contain a subcomponent, and the content of the subcomponent in 100% by mass of the soft magnetic powder may be 15% by mass or less.

[0012] The auxiliary component may be one or more selected from the group consisting of 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.

[0013] The magnetic core of the present invention contains the soft magnetic powder described above.

[0014] The magnetic component of the present invention contains the soft magnetic powder described above. [Brief explanation of the drawings]

[0015] [Figure 1] This is a bright-field image obtained by observing the cross section of soft magnetic powder containing special soft magnetic particles using STEM. [Figure 2] 2 is an electron beam diffraction image obtained by photographing the soft magnetic particle 1 of FIG. 1 using a selected area diffraction method. [Figure 3] 2 is an electron beam diffraction image obtained by photographing the soft magnetic particle 2 of FIG. 1 using a selected area diffraction method. [Figure 4] 2 is an electron beam diffraction image obtained by photographing the soft magnetic particle 3 of FIG. 1 using a selected area diffraction method. [Figure 5] 1 is an electron beam diffraction image obtained by photographing soft magnetic particles that are not special soft magnetic particles using a selected area diffraction method. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described below based on embodiments.

[0017] (Composition of soft magnetic powder) The soft magnetic powder contains Fe and C. The C content is 0.01% by mass or more and 0.5% by mass or less. The soft magnetic powder may further contain Co, and the Fe content relative to the total content of Fe and Co may be 25% by mass or more and 99% by mass or less.

[0018] If the C content in the soft magnetic powder is too low, the soft magnetic powder will be less likely to contain the special soft magnetic particles described below, and the DC bias characteristics of the magnetic core will be more likely to deteriorate. If the C content in the soft magnetic powder is too high, the soft magnetic powder will be more likely to contain soft magnetic particles that contain only phases with symmetry of space group Pnam and no phases with symmetry of space group Im-3m or Pm-3m, along with the special soft magnetic particles described below. As a result, the saturation magnetization of the soft magnetic powder will be more likely to decrease, and the DC bias characteristics of the magnetic core will be more likely to deteriorate.

[0019] When the Fe content is 25% by mass or more relative to the total content of Fe and Co, the DC bias characteristics of a magnetic core using the soft magnetic powder are likely to be improved.When the Fe content is 99% by mass or less relative to the total content of Fe and Co, it is easy to obtain a suitable soft magnetic powder with a good balance of coercive force, saturation magnetic flux density, and corrosion resistance.

[0020] The soft magnetic powder contains soft magnetic particles. The soft magnetic particles contained in the soft magnetic powder may have an average particle size of 0.1 μm or more and 50 μm or less. When the average particle size is 0.1 μm or more, the filling rate of the magnetic core is easily improved, and the relative permeability is easily improved. When the average particle size is 50 μm or less, the eddy current loss of the magnetic core is less likely to increase.

[0021] There are no particular limitations on the method for measuring the average particle diameter of soft magnetic particles. For example, the STEM observation range can be set so that the entirety of 20,000 or more soft magnetic particles is included in the observation range, and the cross-section of the soft magnetic particles can be observed, and the average of the circle-equivalent diameters of each soft magnetic particle can be used as the average particle diameter of the soft magnetic particles. The observation range can be a single field of view that includes the entirety of 20,000 or more soft magnetic particles, or multiple fields of view that include the entirety of 20,000 or more soft magnetic particles in total. The circle-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.

[0022] The soft magnetic powder according to this embodiment may further contain an auxiliary component in addition to Fe, Co, and C. The auxiliary component may be, for example, one or more selected from the group consisting of 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 lanthanoids.

[0023] By including the above-mentioned subcomponents in the soft magnetic powder, it becomes easier to control the relative permeability and eddy current loss of the magnetic core produced using the soft magnetic powder. The total content of the above-mentioned subcomponents may be 25% by mass or less, 15% by mass or less, or 5% by mass or less. By having the content of the subcomponents within the above range, the saturation magnetization of the soft magnetic powder is likely to be improved.

[0024] The soft magnetic powder may contain, as inevitable impurities, elements other than those listed above, i.e., elements other than those included 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. There are no particular restrictions on the content of the inevitable impurities, but the total may be 1% by mass or less, assuming that the entire soft magnetic powder is 100% by mass.

[0025] The total content of the minor components and unavoidable impurities in the soft magnetic powder may be 26% by mass or less, 16% by mass or less, or 6% by mass or less. That is, the total content of Fe, Co, and C may be 74% by mass or more, 84% by mass or more, or 94% by mass or more.

[0026] (Special soft magnetic particles) The soft magnetic powder according to this embodiment includes soft magnetic particles, which are divided into special soft magnetic particles and other soft magnetic particles.

[0027] The soft magnetic powder according to this embodiment contains special soft magnetic particles, which refer to soft magnetic particles containing both a phase having the symmetry of the space group Im-3m or Pm-3m and a phase having the symmetry of the space group Pnam.

[0028] Furthermore, the number ratio of the special soft magnetic particles in the soft magnetic powder may be 10% or more. There is no particular upper limit to the number ratio of the special soft magnetic particles in the soft magnetic powder. For example, the number ratio of the special soft magnetic particles in the soft magnetic powder may be 100% or less. In other words, all of the soft magnetic particles contained in the soft magnetic powder may be special soft magnetic particles.

[0029] An example of a method for determining whether soft magnetic particles are special soft magnetic particles will be described below.

[0030] First, the cross section of the soft magnetic powder is observed using a STEM (scanning transmission electron microscope). A TEM (transmission electron microscope) may be used instead of a STEM. In order to observe the cross section of the soft magnetic powder, a sample for cross section observation is prepared. There are no particular restrictions on the method for preparing the sample for cross section observation. It may be prepared by kneading the soft magnetic powder with a resin and then cutting it. It may also be prepared by cutting a magnetic core containing the soft magnetic powder.

[0031] Figure 1 shows a bright-field image obtained by observing the cross section of a soft magnetic powder containing special soft magnetic particles with a STEM.

[0032] Next, an electron beam diffraction image is taken of the soft magnetic particles to be confirmed as being special soft magnetic particles. There are no particular limitations on the method for taking the electron beam diffraction image. The electron beam diffraction image may be taken by selected area diffraction.

[0033] FIG. 2 shows an electron beam diffraction image of the soft magnetic particle 1 in FIG. 1 taken by the selected area diffraction method.

[0034] In Figure 2, the strong spots indexed 11-0 in upright font, 000 in upright font, and 01-3 in upright font are diffraction spots due to phases with space group Im-3m symmetry. The weak spots indexed 201 in italic font, 021 in italic font, and 2-01 in italic font are diffraction spots due to phases with space group Pnam symmetry. Numbers and letters with a trailing hyphen (-) are synonymous with the numbers and letters with a preceding hyphen (-) in Figure 2.

[0035] Therefore, FIG. 2 confirms that the soft magnetic particle 1 of FIG. 1 contains a phase having the symmetry of the space group Im-3m, and that the soft magnetic particle 1 of FIG. 1 contains a phase having the symmetry of the space group Pnam.

[0036] By analyzing the soft magnetic particles 1 by energy dispersive X-ray spectroscopy using STEM-EDS, it is possible to determine what elements are contained in each phase contained in the soft magnetic particles 1. If the soft magnetic particles contained in the soft magnetic powder all have substantially the same composition, it is possible to determine what elements are contained in each phase contained in the soft magnetic particles 1 from the composition of the soft magnetic powder.

[0037] A phase having symmetry of the space group Im-3m may exist as crystalline grains within the special soft magnetic particles.

[0038] From the above, "soft magnetic particles contain a phase having the symmetry of a specific space group" means that spots that can be indexed to a specific space group are observed in an electron beam diffraction image obtained by photographing the soft magnetic particles using selected area diffraction.

[0039] An electron beam diffraction image taken by the selected area diffraction method for soft magnetic particle 2 in Fig. 1 is shown in Fig. 3. An electron beam diffraction image taken by the selected area diffraction method for soft magnetic particle 3 in Fig. 1 is shown in Fig. 4.

[0040] As in Figure 2, in the electron beam diffraction images of Figures 3 and 4, the strong spots indexed with upright solids are diffraction spots due to a phase having the symmetry of the space group Im-3m. Also, the weak spots indexed with italics are diffraction spots due to a phase having the symmetry of the space group Im-3m. As with soft magnetic particle 1 in Figure 1, it can be confirmed that soft magnetic particles 2 and 3 in Figure 1 are special soft magnetic particles.

[0041] In FIGS. 2 to 4, the spots indexed 000 are spots generated by transmitted electrons.

[0042] Figure 5 shows an electron diffraction image of soft magnetic particles that are not special soft magnetic particles, taken by the selected area diffraction method. In Figure 5, strong diffraction spots due to a phase having symmetry of space group Im-3m are confirmed, but weak spots due to symmetry of space group Pnam are not confirmed. Therefore, Figure 5 confirms that the soft magnetic particles contain a phase having symmetry of space group Im-3m, and that the soft magnetic particles do not contain a phase having symmetry of space group Pnam.

[0043] Soft magnetic powder containing special soft magnetic particles can be used to produce magnetic cores with high relative permeability and excellent DC bias characteristics. Special soft magnetic particles are harder than other soft magnetic particles. This is because the special soft magnetic particles contain a phase with the symmetry of the space group Pnam. Therefore, when producing a magnetic core using soft magnetic powder containing special soft magnetic particles, the soft magnetic powder is less likely to deform during production of the magnetic core, the fluidity of the soft magnetic powder is improved, and the soft magnetic powder is distributed more uniformly in the magnetic core.

[0044] For the above reasons, when soft magnetic powder containing special soft magnetic particles is used, a magnetic core with excellent DC bias characteristics can be obtained.

[0045] The phase having the symmetry of the space group Im-3m may be a (Fe,Co) phase, and the phase having the symmetry of the space group Pnam may be a (Fe,Co)3C phase.

[0046] When the phase having symmetry of space group Im-3m contains Fe and Co, i.e., when soft magnetic particle 1 contains Fe and Co, the phase having symmetry of space group Im-3m can be identified as the (Fe,Co) phase. The (Fe,Co) phase is a magnetic phase. When the phase having symmetry of space group Pnam contains Fe, Co, and C, i.e., when soft magnetic particle 1 contains Fe, Co, and C, the phase having symmetry of space group Pnam can be identified as the (Fe,Co)3C phase. The (Fe,Co)3C phase is a magnetic phase with a lower saturation magnetization than the (Fe,Co) phase. This confirms that soft magnetic particle 1 in Figure 1 is a special soft magnetic particle.

[0047] The arrangement of Fe and Co contained in the phase having the symmetry of space group Im-3m may be ordered. When the arrangement of Fe and Co is ordered, weak diffraction spots due to forbidden reflection appear, and the weak diffraction spatial spots due to forbidden reflection have the symmetry of space group Pm-3m. It is also possible that no diffraction spots due to the phase having the symmetry of space group Im-3m are observed, and only diffraction spatial spots due to the phase having the symmetry of space group Pm-3m are observed.

[0048] The proportion of the special soft magnetic particles in the soft magnetic powder may be 5% or more, 10% or more, or 20% or more. The higher the proportion of the special soft magnetic particles, the easier it is for the hardness of the soft magnetic powder to be improved, and the easier it is for the soft magnetic powder to be distributed uniformly during the production of the magnetic core, which in turn improves the DC bias characteristics of the magnetic core.

[0049] (Method of manufacturing soft magnetic powder) A method for producing the soft magnetic powder according to this embodiment will be described, but the method for producing the soft magnetic powder according to this embodiment is not limited to the method described below.

[0050] The soft magnetic powder containing the special soft magnetic particles can be produced, for example, by a water+organic solvent atomization method.

[0051] Water atomization is a well-known method for producing soft magnetic powder. In typical water atomization, raw material metals are melted and the molten metal is powdered using high-pressure water to produce soft magnetic powder.

[0052] In the water + organic solvent atomization method, the water used to powder the molten metal in the water atomization method is replaced with a liquid mixture of water and an organic solvent (hereinafter sometimes referred to as a mixed liquid).In other words, in the water + organic solvent atomization method, the molten metal obtained by melting the raw material metal is powdered using a high-pressure mixed liquid to produce soft magnetic powder.

[0053] In the water + organic solvent atomization method, first, an inert gas atmosphere is created inside the cooling tank into which the molten metal is dropped. The inert gas is preferably nitrogen or a rare gas such as Ar or He, and nitrogen is more preferable from the viewpoint of cost reduction. The molten metal dropped into the cooling tank is then powdered using a high-pressure mixed liquid.

[0054] The organic solvent contained 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 absorbed into the molten metal. As a result, even if the molten metal does not contain carbon, the soft magnetic powder that is finally obtained contains carbon.

[0055] The present inventors have found that soft magnetic powders produced by the water+organic solvent atomization method using molten metal containing Fe tend to contain special soft magnetic particles. Below, we will explain why soft magnetic powders produced by the water+organic solvent atomization method using molten metal containing Fe tend to contain special soft magnetic particles.

[0056] In the following description, part of Fe may be substituted with Co. When part of Fe is substituted with Co, the term "phase having symmetry of space group Im-3m" may be read as "(Fe,Co) phase." The term "phase having symmetry of space group Pnam" may be read as "(Fe,Co)3C phase."

[0057] In high-temperature molten metal, the Fe metal phase exists as a phase with space group symmetry of Fm3m. Therefore, the gaps between atoms in the Fe metal phase are relatively large. Furthermore, the Fe metal phase can contain up to 2% by mass of carbon as a solid solution.

[0058] As the molten metal cools, the phase with symmetry of space group Fm3m becomes a phase with symmetry of space group Im-3m. Compared to the phase with symmetry of space group Fm3m, carbon is less likely to dissolve in the phase with symmetry of space group Im-3m. The dissolved carbon, together with the Fe contained in the soft magnetic powder, forms a phase with symmetry of space group Pnam. Then, the phase with symmetry of space group Pnam precipitates between the phases with symmetry of space group Im-3m.

[0059] The reason why the DC bias characteristics of the magnetic core obtained when the soft magnetic powder according to this embodiment is used to manufacture the magnetic core is improved will be explained below.

[0060] 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. This makes phases with space group Pnam symmetry extremely hard. In contrast, phases with space group Im-3m or Pm-3m symmetry are relatively soft.

[0061] In the special soft magnetic particles, phases with space group Pnam symmetry are precipitated between phases with space group Im-3m or Pm-3m symmetry. This makes the special soft magnetic particles both hard and soft, making them less susceptible to cracking or deformation. When magnetic cores are made using soft magnetic powder containing the special soft magnetic particles, the distribution of the soft magnetic particles tends to be more uniform, improving the DC bias characteristics of the magnetic cores.

[0062] Even if carbon is added to the raw metal, the molten metal will contain carbon, and the soft magnetic powder obtained will also contain carbon. However, even if soft magnetic powder is produced from molten metal containing carbon using the water atomization method, the special soft magnetic particles will not be included.

[0063] When soft magnetic powder is produced by water atomization, carbon is incorporated into a phase having the symmetry of space group Im-3m as a martensite phase or a residual austenite phase, and a phase having the symmetry of space group Pnam is not precipitated. As a result, even if a magnetic core is produced using soft magnetic powder produced by water atomization, the distribution of the soft magnetic particles is unlikely to be sufficiently uniform, and the DC bias characteristics of the magnetic core are not sufficiently high.

[0064] From the above, the present inventors have found that soft magnetic powder containing special soft magnetic particles can be suitably produced by using the water+organic solvent atomization method for producing soft magnetic powder.

[0065] The type of organic solvent used in the water + organic solvent atomization method is not particularly limited. Examples include monohydric alcohols such as methanol and ethanol, dihydric alcohols such as ethylene glycol, trihydric alcohols such as glycerin, and carboxylic acids such as formic acid and acetic acid. In particular, from the viewpoints of ease of handling and cost, it is preferable to use ethanol as the organic solvent.

[0066] The magnetic powder according to this embodiment may be used in any applications, including, for example, magnetic components used in sensors, motor stator cores, inductors, voltage transformers, EMI filters, magnetic heads, and the like.

[0067] (magnetic core) The magnetic core according to this embodiment contains the soft magnetic powder described above. The soft magnetic powder may be coated with an insulating material.

[0068] The magnetic core according to this embodiment may contain other powders in addition to the soft magnetic powder described above. There are no particular restrictions on the composition and microstructure of the other powders. They may be selected appropriately depending on the application of the magnetic core. If the other powders have an amorphous structure and / or a nanocrystalline structure, the relative permeability of the magnetic core is likely to be improved and the core loss is likely to be reduced.

[0069] A soft magnetic powder having an average particle diameter of more than 3 μm is called a large-diameter powder, and a soft magnetic powder having an average particle diameter of 3 μm or less is called a small-diameter powder. The magnetic core according to this embodiment may be made using only a large-diameter powder, only a small-diameter powder, or a mixture of a large-diameter powder and a small-diameter powder. The large-diameter powder and / or the small-diameter powder may be coated with an insulating material.

[0070] Both the large-diameter powder and the small-diameter powder may contain the special soft magnetic particles, only the large-diameter powder may contain the special soft magnetic particles, or only the small-diameter powder may contain the special soft magnetic particles.

[0071] When a magnetic core is produced using a powder in which large-diameter powder and small-diameter powder are mixed, the packing density of the magnetic core is more likely to be improved and the relative permeability is more likely to be improved than when a magnetic core is produced using only large-diameter powder or only small-diameter powder, because the gaps between the soft magnetic powder particles derived from the large-diameter powder can be filled with the soft magnetic powder derived from the small-diameter powder.

[0072] The magnetic core may further contain a 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 amount of resin contained. For example, the amount may be 0.5% by mass or more and 5% by mass or less of the entire magnetic core.

[0073] (Magnetic core manufacturing method) There are no particular limitations on the method for manufacturing the magnetic core according to this embodiment. An example of a method for manufacturing the magnetic core (dust core) will be described below.

[0074] First, a soft magnetic powder containing special soft magnetic particles is mixed with a thermosetting resin to produce a resin compound. Next, the resin compound is filled into a mold. Next, the resin compound filled into the mold is pressure-molded to obtain a green compact. Finally, the resin contained in the green compact is thermally cured to obtain a magnetic core (green dust core).

[0075] The magnetic core may be made of soft magnetic powder obtained by mixing large-diameter powder and small-diameter powder.

[0076] There are no particular limitations on the applications of the magnetic core according to this embodiment. Examples include coil components such as inductors, choke coils, and transformers. In particular, when the magnetic core according to this embodiment is used in a coil component, a coil component that satisfies both high inductance and good DC bias characteristics can be obtained. [Example]

[0077] The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

[0078] (Experimental Example 1) Fe, Co, C, and / or each of the minor components were weighed out so as to obtain a master alloy having the composition shown in the charge composition column of Table 1. After evacuating the chamber, the contents were melted by high-frequency heating to produce a master alloy.

[0079] The charged compositions and analyzed compositions shown in Table 1 are both listed in wt% units. In addition, when the composition is 100 wt% Fe, it is simply listed as Fe.

[0080] The prepared master alloy was heated to 1500°C and melted to obtain a molten alloy. Soft magnetic powder with the analyzed composition shown in Table 1 was then prepared. The "Atomized high-pressure liquid" column indicates the high-pressure liquid (high-pressure water or high-pressure mixed liquid) used to prepare the soft magnetic powder. Samples with "100% water" listed in the high-pressure liquid column were prepared using the water atomization method, which uses high-pressure water as the high-pressure liquid. Samples with "Water + X% ethanol" listed in the high-pressure liquid column were prepared using the water + organic solvent atomization method, which uses a high-pressure mixed liquid as the high-pressure liquid. In Experimental Example 1, X is 20 for all samples.

[0081] Next, the powder was classified to obtain soft magnetic powders having the average particle diameters shown in Table 1. To obtain powders having an average particle diameter of 0.30 μm or more, classification was performed using a swirling air classifier (Aero Fine Classifier manufactured by Nisshin Engineering Co., Ltd.). To obtain powders having an average particle diameter of less than 0.30 μm, classification was performed using a differential electrostatic classifier (Model 3082 manufactured by TSI Co., Ltd.).

[0082] It was confirmed that the average particle diameter of the obtained soft magnetic powder was the value shown in Table 1 using a laser diffraction particle size distribution measuring device (HELOS&RODOS, Sympatec).

[0083] The contents of elements other than carbon in the obtained soft magnetic powders were measured by quantitative analysis using ICP-AES (Shimadzu Corporation, ICPS-8100CL). The carbon content was measured by quantitative analysis using oxygen flow combustion-infrared absorption method (LECO Corporation, CS-844). From the content of each element in each soft magnetic powder, it was confirmed that the composition of each soft magnetic powder matched the analyzed composition shown in Table 1.

[0084] The true density of the obtained soft magnetic powder was measured by the Archimedes method using a Wardon type pycnometer.

[0085] The soft magnetic powder was mixed with epoxy resin to prepare a resin compound. The mass ratio of the resin in the resin compound was set to 2.5 mass%. The epoxy resin used was YSLV-80XY manufactured by Nippon Steel Chemical & Material Co., Ltd.

[0086] The obtained resin compound was filled into a mold of a predetermined toroidal shape. Then, the molding pressure was controlled so that the filling rate of the finally obtained magnetic core (toroidal core) would be about 80%, and pressure molding was performed to obtain a molded body. Specifically, the molding pressure was 1 to 10 ton / cm. 2 was controlled within the range.

[0087] The resin contained in the molded body was thermally cured at 180°C for 60 minutes to produce a toroidal core (outer diameter 11 mm, inner diameter 6.5 mm, thickness 2.5 to 3.0 mm).

[0088] The filling rate η of the soft magnetic powder in the toroidal core was calculated by dividing the density of the toroidal core, calculated from the dimensions and mass of the toroidal core, by the theoretical density of the toroidal core, calculated from the true densities of the various materials contained in the toroidal core (the true density of the soft magnetic powder in Experimental Example 1).

[0089] The inductance of the toroidal core at a frequency of 1 MHz was measured using an LCR meter (Agilent Technologies 4284A) and a DC bias power supply (Agilent Technologies 42841A). The relative permeability of the toroidal core was then calculated from the inductance. The number of winding turns was 24. The relative permeability when the DC bias current was 0 A was defined as μ0, and the DC bias current when the relative permeability was 90% of μ0 was defined as Isat. The higher Isat, the better the DC bias characteristics.

[0090] The Isat improvement rate of sample No. 1 was defined as the improvement rate from the Isat of a comparative example having the same analyzed composition as the example, i.e., sample No. 3. The Isat improvement rate of sample No. 2 was also stated as the improvement rate from the Isat of sample No. 3. Hereinafter, examples with an Isat improvement rate of 5% or more were considered to have good DC bias characteristics, examples with an Isat improvement rate of 10% or more were considered to have even better DC bias characteristics, and examples with an Isat improvement rate of 20% or more were considered to have particularly good DC bias characteristics.

[0091] The toroidal core of each sample was cut and embedded in a TEM mesh grid Mo#200 with epoxy resin and cured at 130°C. This was then sliced ​​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 in a field of view of approximately 3 μm × 3 μm using a STEM (JEOL JEM-2100F), and electron diffraction images were taken of approximately 20 particles within the field of view using the selected area diffraction method. The area size was 300 nmΦ. The percentage of special soft magnetic particles was calculated by dividing the number of special soft magnetic particles by the total number of soft magnetic particles. Soft magnetic particles that exhibited diffraction spots attributable to phases with space group Im-3m or Pm-3m symmetry and diffraction spots attributable to phases with space group Pnam symmetry in the captured wire diffraction images were defined as special soft magnetic particles.

[0092] [Table 1]

[0093] Sample No. 2 has the same feed composition as Sample No. 1, but was prepared using the water atomization method. Therefore, the carbon content in the analyzed composition differs from that of Sample No. 1. Sample No. 3 was prepared using the water atomization method, but carbon was added to the molten metal so that the carbon content in the analyzed composition was equivalent to that of Sample No. 1.

[0094] The soft magnetic powder of sample No. 1 contained special soft magnetic particles. As a result, the magnetic core containing the soft magnetic powder of sample No. 1 had the same μ0 and improved DC bias characteristics as the magnetic core containing the soft magnetic powder of sample No. 3, which was an equivalent soft magnetic powder except that it did not contain the special soft magnetic particles.

[0095] Samples 4, 7, and 10 were run under the same conditions as sample 1, except that the feed composition and analytical composition were changed. Samples 5, 8, and 11 were run in the same manner as sample 2. Samples 6, 9, and 12 were run in the same manner as sample 3.

[0096] Sample numbers 4 to 6, sample numbers 7 to 9, and sample numbers 10 to 12 all gave results similar to those of sample numbers 1 to 3.

[0097] (Experimental Example 2) Under the condition that the analyzed compositions were the same, a comparison was made between an example performed using the water+organic solvent atomization method (only sample number 43 was a comparative example) and a comparative example performed using the water atomization method. Specifically, a comparison was made similar to the comparison between the example of sample number 1 and the comparative example of sample number 3 in Experimental Example 1. The results are shown in Tables 2 to 6.

[0098] [Table 2]

[0099] [Table 3A]

[0100] [Table 3B]

[0101] [Table 4]

[0102] [Table 5]

[0103] [Table 6]

[0104] Table 2 shows experimental results for compositions generally referred to as Fe-Si based. Table 3A shows experimental results for compositions in which part or all of the Fe in sample numbers 19 and 20 in Table 2 is substituted with Co. Table 3B shows experimental results for compositions in which part or all of the Fe in sample numbers 1 and 3 in Table 1 is substituted with Co. Table 4 shows experimental results for compositions in which Fe and / or Si in sample numbers 19 and 20 are substituted with Cr. Tables 5 and 6 show experimental results for compositions in which part of the Fe in Table 4 is substituted with Co and the contents of Fe, Co, and / or Si are varied.

[0105] When the composition of the soft magnetic powder was within a specific range, the results were the same as in Experimental Example 1. However, when the soft magnetic powder did not contain Fe, the special soft magnetic particles were not included in the soft magnetic powder even when the water + organic solvent atomization method was used.

[0106] (Experimental Example 3) Samples 10 and 12 in Experimental Example 1 were run under the same conditions, except that the carbon content in the analyzed composition was varied. In each example, the carbon content in the analyzed composition was varied by changing the composition of the mixed solution. In each comparative example, the carbon content in the analyzed composition was varied by changing the carbon content in the feed composition. The results are shown in Table 7.

[0107] [Table 7]

[0108] Table 7 confirms that when using the water + organic solvent atomization method, the higher the proportion of organic solvent in the mixed solution and the higher the carbon content in the analyzed composition, the higher the proportion of special soft magnetic particles and the better the DC bias characteristics.

[0109] In contrast, when water atomization was used, the soft magnetic powder obtained did not contain special soft magnetic particles, regardless of the carbon content in the feed composition. Furthermore, the effect of carbon on μ0 and Isat of the magnetic core was also small.

[0110] (Experimental Example 4) Soft magnetic powders and magnetic cores were produced under the same conditions as Sample Nos. 10 and 12 in Experimental Example 1, except that the average particle size of the soft magnetic powder was changed.

[0111] In Experimental Example 4, the eddy current loss of the magnetic core was also evaluated. The eddy current loss was measured using a BH analyzer (SY-8218 manufactured by Iwatsu Measurement Co., Ltd.) under the following conditions: the number of turns in the primary winding was 24, the number of turns in the secondary winding was 12, the frequency was 3 MHz, and the measurement magnetic flux density was 10 mT. The results are shown in Table 8.

[0112] [Table 8]

[0113] Table 8 confirms that when soft magnetic powder with an average particle size of 50.0 μm or less is used, the larger the average particle size, the larger the μ0 of the magnetic core and the higher the improvement rate of Isat. However, when soft magnetic powder with an average particle size exceeding 50.0 μm is used, the increase in μ0 and Isat improvement rate plateaus, and eddy current loss also increases.

[0114] The same tendency was observed when the combination of samples 10 and 12 was replaced with any of the other combinations of samples in Experimental Examples 1 to 3 and 6. That is, when soft magnetic powder with an average particle size of 50.0 μm or less was used, the larger the average particle size, the larger the μ0 of the magnetic core and the higher the improvement rate of Isat. However, when soft magnetic powder with an average particle size exceeding 50.0 μm was used, the increase in μ0 and Isat improvement rate plateaued, and eddy current loss further increased.

[0115] (Experimental Example 5) In Experimental Example 5, the small-diameter powder was prepared in the same manner as the soft magnetic powder prepared in Experimental Examples 1 to 4, except that the average particle diameter was smaller. The large-diameter powder was an amorphous powder. The average particle diameter of the large-diameter powder was 22 μm, and the composition of the large-diameter powder was Fe 73 B 11 Si 11 The soft magnetic powder was prepared by mixing the small-diameter powder and the large-diameter powder together. The content of the small-diameter powder in the soft magnetic powder was adjusted to the value shown in each table.

[0116] Tables 9A and 9B show examples and comparative examples using small diameter powders whose analytical compositions are the same as those of the soft magnetic powders of sample numbers 1 and 3. Table 10 shows examples and comparative examples using small diameter powders whose analytical compositions are the same as those of the soft magnetic powders of sample numbers 4 and 6. Table 11 shows examples and comparative examples using small diameter powders whose analytical compositions are the same as those of sample numbers 7 and 9. Table 12 shows examples and comparative examples using small diameter powders whose analytical compositions are the same as those of sample numbers 10 and 12.

[0117] [Table 9A]

[0118] [Table 9B]

[0119] [Table 10]

[0120] [Table 11]

[0121] [Table 12]

[0122] Tables 9A, 9B, 10 to 12 confirm that the larger the average particle diameter of the small-diameter powder, the higher the μ0 of the magnetic core. It was also confirmed that the DC bias characteristics are improved when the soft magnetic powder used as the small-diameter powder contains special soft magnetic particles.

[0123] (Experimental Example 6) In Experimental Example 6, the conditions were the same except that the contents of each component, such as the subcomponents, in the analyzed composition were changed as appropriate. The results are shown in Tables 13 to 20.

[0124] [Table 13]

[0125] [Table 14]

[0126] [Table 15]

[0127] [Table 16]

[0128] [Table 17]

[0129] [Table 18]

[0130] [Table 19]

[0131] [Table 20]

[0132] As can be seen from each table, even when the composition of the soft magnetic powder is changed within the specified range, the magnetic core containing the soft magnetic powder containing the special soft magnetic particles has a high μ0 and improved DC bias characteristics compared to the magnetic core containing the soft magnetic powder without the special soft magnetic particles.

Claims

1. A soft magnetic powder containing Fe and C, The C content is 0.01% by mass or more and 0.5% by mass or less, The soft magnetic powder contains special soft magnetic particles, The special soft magnetic particles are soft magnetic powders containing both a phase having the symmetry of space group Im-3m or Pm-3m and a phase having the symmetry of space group Pnam.

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

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

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

5. 4. The soft magnetic powder according to claim 1, wherein the average particle size of the soft magnetic particles contained in the soft magnetic powder is 0.1 μm or more and 50 μm or less.

6. The soft magnetic powder according to any one of claims 1 to 3, wherein the soft magnetic powder further contains a subcomponent, and the content of the subcomponent in 100% by mass of the soft magnetic powder is 15% by mass or less.

7. 7. The soft magnetic powder according to claim 6, wherein the auxiliary component is one or more selected from the group consisting of 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 comprising the soft magnetic powder according to any one of claims 1 to 3.

9. A magnetic part comprising the soft magnetic powder according to any one of claims 1 to 3.

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