JP2017054910A - Soft magnetic metal powder compact core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for achieving a soft magnetic metal powder compact core which is superior in DC superposing characteristic.SOLUTION: A soft magnetic metal powder compact core comprises: Fe-Si based soft magnetic metal powder; and an insulating material. In the powder compact core, the sectional circularity of 80% or more of particles forming the soft magnetic metal powder is 0.75-1.0 on any section thereof. In the particles forming the soft magnetic metal powder, a coefficient of the variation in Si concentration near the center of each particle is 0.050-0.120; and the difference between the maximum and minimum of the Si concentration is within 6 times the standard deviation thereof.SELECTED DRAWING: Figure 2

Description

The present invention relates to a reactor and an inductor used for a power supply circuit and the like, and more particularly to improvement of DC superposition characteristics of inductance of a soft magnetic metal dust core.

Ferrite cores, laminated electrical steel sheets, soft magnetic metal dust cores (cores made by mold molding, injection molding, sheet molding, etc.) as core materials for reactors and inductors used in applications where large currents are applied Is used. Although the laminated magnetic steel sheet has a high saturation magnetic flux density, there is a problem that when the driving frequency of the power supply circuit exceeds several tens of kHz, the core loss increases and the efficiency decreases. On the other hand, the ferrite core is a magnetic core material with a small high-frequency loss, but there is a problem that the shape is increased because the saturation magnetic flux density is low. On the other hand, soft magnetic metal dust cores are widely used because the high-frequency core loss is smaller than that of laminated electromagnetic steel sheets and the saturation magnetic flux density is larger than that of ferrite. However, the core loss of the soft magnetic metal dust core is not sufficiently small, and a low loss soft magnetic metal dust core is required.

The current waveform applied to the reactor and the inductor is a waveform in which an AC component is superimposed on the DC component, and when the DC component increases, the inductance of the reactor or the inductor generally decreases. As a characteristic required for reactors and inductors, a reduction in inductance is required to be small even under DC superposition, and the DC superposition characteristics are good even for the magnetic core material used therefor, that is, inductance under DC current superposition. Is required to be small, and hence the permeability is small.

In Patent Document 1, as a technique for improving the saturation magnetic flux density and iron loss of a soft magnetic metal dust core, a composite soft magnetic material in which Fe-3Si alloy particles and pure iron particles are consolidated and fired, An Fe-3Si alloy particle phase and a plurality of pure iron particle phases present at a grain boundary surrounded by at least three Fe-3Si alloy particle phases, and an average particle of the Fe-3Si alloy particle phase A composite soft magnetic material having a diameter of 100 to 145 μm and a content of the pure iron particle phase with respect to the total amount of the dust core of 3% by mass or more and less than 10% by mass is disclosed.

In Patent Document 2, as a technique for improving the saturation magnetic flux density, magnetic permeability, and iron loss of a soft magnetic metal dust core, insulated iron powder, 2.5-8 mass% Si-residual Fe alloy powder, and binder are used. Mainly composed of a main phase in which the iron powder and the 2.5-8 mass% Si-residual Fe alloy powder are consolidated and fired, and a binder formed around the main phase. And a ratio of 2.5 to 8 mass% Si-residual Fe alloy in the main phase is 10 mass% or more and less than 44 mass%, and a saturation magnetic flux at a magnetic field of 10 kA / m. A composite soft magnetic material having a density of 1.1 T or more, a coercive force of 220 A / m or less, and an iron loss (at 0.1 T, 10 kHz) of 20 W / kg or less is disclosed.

In Patent Document 3, as a technique for improving the magnetic flux density and the coercive force of a soft magnetic metal dust core, it can be obtained by compacting a mixture of iron powder and Fe-Si powder containing iron and silicon. A magnetic material is disclosed. The content of Fe and Si in the Fe—Si based alloy is not particularly limited, but Fe is, for example, 85 to 99 parts by weight, preferably 93 to 99 parts by weight with respect to 100 parts by weight of the Fe—Si based alloy. Si is, for example, 1 to 10 parts by mass, preferably 1 to 7 parts by mass. The mixing ratio of the iron powder and the Fe-Si powder is such that the iron powder is, for example, 20 to 80 parts by mass, preferably 40 to 80 parts by mass with respect to 100 parts by mass of the total amount of the iron powder and Fe-Si powder. Parts, more preferably 40-60 parts by mass, and the Fe-Si powder is, for example, 20-80 parts by mass, preferably 20-60 parts by mass, and more preferably 40-60 parts by mass.

JP 2010-153638 A JP 2010-185126 A JP 2011-187634 A

In the techniques of Patent Documents 1 to 3, an attempt is made to improve the DC superposition characteristics by increasing the saturation magnetic flux density of the dust core by mixing pure iron powder with Fe-Si alloy powder. However, by simply mixing pure iron powder in a ratio that is preferred in Patent Documents 1 to 3, the uniformity of the composition of the dust core is impaired, so that a sufficiently good DC superposition characteristic cannot be obtained.

Thus, in the conventional technology, even if Fe powder is mixed with Fe-Si alloy powder in an attempt to increase the saturation magnetic flux density of the soft magnetic metal dust core, the uniformity of the composition of the dust core is impaired. There is a problem that a sufficiently good DC superposition characteristic cannot be obtained. Therefore, there is a need for a technique for realizing a soft magnetic metal dust core having more excellent direct current superposition characteristics.

The present invention has been devised in order to solve the above-described problems, and an object thereof is to realize excellent direct current superposition characteristics in a soft magnetic metal dust core.

The soft magnetic metal dust core of the present invention is a dust core comprising an Fe-Si soft magnetic metal powder and an insulator, and the soft magnetic metal core is formed on any cross section of the dust core. The circularity of the cross section of 80% or more of the particles constituting the metal powder is 0.75 to 1.0, and the variation coefficient of the Si concentration near the center of each particle constituting the soft magnetic metal powder is 0.05 or more. 0.12 or less, and the difference between the maximum value and the minimum value of the Si concentration is within 6 times the standard deviation. By doing in this way, it can be set as the soft magnetic metal dust core excellent in the direct current superposition characteristic.

The soft magnetic metal dust core of the present invention is characterized in that the insulator includes a silicon compound. By doing in this way, eddy current loss can be suppressed effectively.

According to the present invention, in a soft magnetic metal dust core, by suppressing a decrease in permeability under a DC magnetic field superimposition, when used as a reactor or an inductor, an inductance decrease when a DC current is superimposed is improved. be able to.

FIG. 1 is a schematic cross-sectional view showing the structure of a soft magnetic metal dust core according to an embodiment of the present invention. FIG. 2 is a graph showing the relationship between the coefficient of variation of Si concentration and the magnetic permeability μ when a DC magnetic field of 5 kA / m is applied in the soft magnetic metal dust core of the present invention.

The present invention is a dust core containing Fe-Si based soft magnetic metal powder and an insulator, wherein a cross section of 80% or more of the particles constituting the soft magnetic metal powder on an arbitrary cross section of the dust core. The circularity of 0.75 to 1.0 and the coefficient of variation of the Si concentration near the center of each particle constituting the soft magnetic metal powder is 0.05 or more and 0.12 or less, Since the difference between the maximum value and the minimum value is within 6 times the standard deviation, it is possible to improve the inductance under DC current superposition.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a view showing a cross section of a soft magnetic metal dust core 10. The soft magnetic metal dust core 10 is composed of a soft magnetic metal powder 11 and an insulating layer 12 that covers the surface of most of the particles constituting the soft magnetic metal powder 11. The soft magnetic metal powder 11 is a soft magnetic metal containing iron as a main component, and an Fe—Si alloy can be used.

The raw powder of the soft magnetic metal powder 11 can be produced by a gas atomization method, a water atomization method, or the like. Generally, it is easier to obtain particles with a high degree of circularity when using the gas atomization method, but even when using the water atomization method, particles with a high degree of circularity can be obtained by appropriately adjusting the spraying conditions and the like. .
By classifying the raw material powder, a soft magnetic metal powder 11 having a predetermined particle size can be obtained. For classification, a vibrating sieve or an air classifier can be used.

When the soft magnetic metal powder core 10 is embedded and polished in a resin, the cross section is observed, and the circularity of the soft magnetic metal powder 11 is measured, the circularity of 80% or more of the constituent particles is 0. .75-1.0. As an example of circularity, Wadell's circularity can be used, which is defined by the ratio of the diameter of a circle equal to the projected area of the particle cross section to the diameter of the circle circumscribing the particle cross section. In the case of a perfect circle, Wadell's circularity is 1, and the closer to 1, the higher the roundness. An optical microscope or a scanning electron microscope can be used for observation, and image analysis can be used for calculating the circularity.

Particles with a low degree of circularity have a non-uniform curvature on the particle surface, so that the stress is not uniform during molding. Therefore, when many particles with low circularity are included, a portion with a large amount of plastic deformation and a portion with no plastic deformation are generated, so that the magnetization process becomes non-uniform, and as a result, the direct current superposition characteristics deteriorate. That is, when the circularity of 80% or more of the particles is 0.75 to 1.0, good direct current superposition characteristics can be obtained.

The Si concentration of the soft magnetic metal powder 11 can be easily measured by embedding the powder core 10 in a resin and polishing it, and analyzing the cross section with an energy dispersive X-ray spectrometer (EDS) of a scanning electron microscope. Other analysis methods such as an electron beam microanalyzer can also be used.
In order to quantitatively represent the variation in the Si concentration of the soft magnetic metal powder 11, the following may be performed. About 100 points are selected in the form of a lattice at intervals of about 500 μm on the cross section of the dust core 10, and spot analysis is performed with an energy dispersive X-ray spectrometer (EDS) near the center of the particle closest to each lattice point. A standard deviation and an average value are calculated from the Si concentration data obtained as a result. The coefficient of variation is defined as the standard deviation divided by the mean value. The variation of the Si concentration can be quantitatively represented by this variation coefficient. Further, the maximum value and the minimum value of this series of data are regarded as the maximum value and the minimum value of the Si concentration of the soft magnetic metal powder 11.

By setting the coefficient of variation of the Si concentration of the soft magnetic metal powder 11 to 0.05 to 0.12, and making the difference between the maximum value and the minimum value of the Si concentration within 6 times the standard deviation, the Si concentration is relatively low and soft. Since the particles are plastically deformed to fill the gaps between the hard particles having a relatively high Si concentration, the uniformity of the gap between the particles of the dust core 10 is improved and each particle is applied when a DC magnetic field is applied. Since the demagnetizing field is uniform, the entire dust core 10 is uniformly magnetized, so that excellent DC superposition characteristics can be realized. Further, by setting the coefficient of variation of the Si concentration of the soft magnetic metal powder 11 to 0.05 to 0.12, uniformity of the composition of the powder core 10 can be maintained, so that the coercive force is extremely large or small. There is no particle to be applied, and when the DC magnetic field is applied, the entire dust core 10 is magnetized uniformly, so that excellent DC superposition characteristics can be realized.

Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.
The soft magnetic metal powder 11 is composed of soft magnetic metal powders 11-a and 11-b having different Si concentrations. The particle diameters of the soft magnetic metal powders 11-a and 11-b are desirably 1 μm or more and 200 μm or less. By setting the particle size to 1 μm or more, the coercive force of the powder can be 800 A / m or less, and the low-frequency core loss is reduced. By setting the particle size to 200 μm or less, eddy current loss is reduced, and high-frequency core loss is reduced. The Si concentration of the soft magnetic metal powders 11-a and 11-b is preferably 1 wt% or more and 10 wt% or less. By setting the Si concentration to 10 wt% or less, the saturation magnetization of the powder becomes 1.5 T or more, and the DC superposition characteristics are improved. By setting the Si concentration to 1 wt% or more, the electrical resistivity of the powder is increased to 20 μΩcm or more, and the core loss is reduced. The Si concentration and the mixing ratio of the soft magnetic metal powders 11-a and 11-b are adjusted so that the variation coefficient of the Si concentration is 0.05 to 0.12 in calculation. However, the difference between the maximum value and the minimum value of the Si concentration of the soft magnetic metal powders 11-a and 11-b is set to be within 6 times the standard deviation.

When the soft magnetic metal powders 11-a and 11-b are mixed and molded, the gap between the soft magnetic metal powders having a high Si concentration and relatively hard (11-a in FIG. 1) is compared with a low Si concentration. Soft magnetic metal powder (11-b in FIG. 1) is considered to be plastically deformed and filled. When the variation coefficient of Si concentration is larger than 0.12, the filling rate of the dust core tends to increase, but the uniformity of the composition is impaired and the direct current superimposition characteristic is deteriorated. On the other hand, when the variation coefficient of the Si concentration is less than 0.05, the composition uniformity is high, but the soft magnetic metal powder 11-b does not undergo plastic deformation so much that the gap cannot be sufficiently filled. Since the uniformity of the gap between the powders is impaired, the direct current superposition characteristics are deteriorated. Further, when the difference between the maximum value and the minimum value of the Si concentration of the soft magnetic metal powders 11-a and 11-b is larger than 6 times the standard deviation, the coefficient of variation of the Si concentration is 0.05 to 0.12. The state is a state in which one of the mixing ratios is extremely small, and the packing ratio of the dust core cannot be increased, so that the direct current superimposition characteristics are deteriorated.

The coefficient of variation of the Si concentration of the soft magnetic metal powders 11-a and 11-b is 0.05 to 0.12, and the difference between the maximum value and the minimum value of the Si concentration is within 6 times the standard deviation. Since the composition of the powder core 10 and the uniformity of the gap can be compatible, excellent direct current superposition characteristics can be realized.

The surface of the soft magnetic metal powders 11-a and 11-b is covered with the insulating layer 12. The insulating layer 12 may use either an inorganic material or an organic material having a low electrical conductivity, or may be a composite thereof. The insulating layer 12 preferably contains a silicon compound. Since a silicon compound can form a uniform insulating layer, generation of eddy current can be suppressed and core loss can be reduced even when the density is high.

A method for producing the soft magnetic metal powder core 10 using the soft magnetic metal powders 11-a and 11-b may be in accordance with a general method for producing the soft magnetic metal powder core 10, but an example is described below. Show.

An insulating material is coated on the soft magnetic metal powder to obtain a granular granulated product. As the insulator, a resin such as a silicone resin or an epoxy resin can be used, and it is preferable to have a shape-retaining property at the time of molding and an electrical insulating property and can be uniformly applied to the surface of the soft magnetic metal powder. A predetermined amount of these solutions is added to the soft magnetic metal powders 11-a and 11-b, and after kneading with a kneader or the like, the aggregate obtained by drying can be crushed to obtain granules. .

The obtained granule is filled into a mold having a desired shape, and pressure-molded to obtain a molded body. The molding pressure can be appropriately selected depending on the composition of the soft magnetic metal powder and the desired molding density, but is generally in the range of 600 to 1600 MPa. A lubricant may be used as necessary. The obtained molded body is heat-cured to form a powder core. Or heat processing is performed in order to remove distortion at the time of fabrication, and it is set as a soft magnetic metal dust core. The heat treatment is preferably performed at a temperature of 500 to 800 ° C. in a non-oxidizing atmosphere such as a nitrogen atmosphere or an argon atmosphere. When a silicone resin is used as the insulator, an insulator containing a silicon compound can be formed after the heat treatment, which is preferable because eddy current loss can be further suppressed.

The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. The present invention can be variously modified without departing from the gist thereof. For example, the soft magnetic metal powder 11 may be composed of three or more types of soft magnetic metal powders having different Si concentrations.

The content of the present invention will be described in detail below using examples and comparative examples, but the present invention is not limited to the following examples.

Example 1
As a raw material powder, a target composition of Fe-4.0 wt% Si and Fe-3.0 wt% Si alloy powder was prepared by a gas atomization method. After adjusting the particle size distribution by classifying the Fe-4.0 wt% Si and Fe-3.0 wt% Si alloy powder to 20 μm to 90 μm, the ratio of the Fe-3.0 wt% Si alloy powder is 20 wt%. Mixed.

Fe-4.0 wt% Si and Fe-3.0 wt% Si mixed powder is added to 100 wt% diluted with xylene so that the silicone resin is 1.5 wt%, kneaded with kneader and dried The agglomerates thus obtained were sized so as to be 355 μm or less to obtain granules. This was filled in a toroidal mold having an outer diameter of 17.5 mm and an inner diameter of 11.0 mm, and pressed at a molding pressure of 1180 MPa to obtain a molded body. The core weight was 5 g. The obtained compact was heat treated in a belt furnace at 750 ° C. for 30 minutes in a nitrogen atmosphere to obtain a soft magnetic metal dust core.

Using an LCR meter (Agilent Technology 4284A) and a DC bias power supply (Agilent Technology 42841A), the inductance of the soft magnetic dust core was measured, and the permeability of the soft magnetic dust core was calculated from the inductance. . The measurement was performed when the DC superimposed magnetic field was 0 A / m and 5000 A / m, which were 90 and 55, respectively.

Further, the soft magnetic metal dust core after the DC superposition characteristics measurement was fixed with a cold embedding resin, the cross section was cut out, and mirror polishing was performed. 100 points were selected in a lattice pattern at intervals of 500 μm on the cross section of the powder core, spot analysis was performed with an energy dispersive X-ray spectrometer (EDS) near the center of the particle closest to each lattice point, and the Si concentration was measured. When the average value and the standard deviation were obtained from these Si concentration data, they were 3.7 wt% and 0.32 wt%, and the coefficient of variation was calculated to be 0.089. Of these Si concentration data, the maximum value was 4.5 wt% and the minimum value was 2.7 wt%. Since the difference was 1.8 wt%, it was within 6 times the standard deviation.

Furthermore, the Wadell circularity of each particle whose Si concentration was measured was measured, and the ratio of the particles having a circularity of 0.75 or more was calculated to be 85%.

(Example 2)
As a raw material powder, the target composition Fe-5.5 wt% Si and Fe-5.0 wt% Si alloy powder prepared by gas atomization method is classified into 20 μm to 63 μm to adjust the particle size distribution, and then Fe-5.0 wt. A soft magnetic dust core was produced in the same manner as in Example 1 except that the mixing was performed so that the ratio of the% Si alloy powder was 30 wt%. The magnetic permeability when the DC superimposed magnetic field was 0 A / m and 5000 A / m was 69 and 51, respectively. The variation coefficient of Si concentration was 0.051, and the proportion of particles having a circularity of 0.75 or more was 89%.

(Example 3)
As raw material powder, target composition Fe-5.0Siwt% and Fe-4.0wt% Si alloy powder prepared by gas atomization method were mixed so that the ratio of Fe-4.0wt% Si alloy powder was 30wt%. A soft magnetic dust core was produced in the same manner as in Example 1 except for the above. The magnetic permeability when the DC superimposed magnetic field was 0 A / m and 5000 A / m was 69 and 54, respectively. The variation coefficient of Si concentration was 0.108, and the ratio of particles having a circularity of 0.75 or more was 83%.

Example 4
As a raw material powder, a target composition Fe-6.5 wt% Si and Fe-5.0 wt% Si alloy powder prepared by gas atomization method are mixed so that the ratio of Fe-5.0 wt% Si alloy powder is 35 wt% A soft magnetic powder core was produced in the same manner as in Example 1 except that. The magnetic permeability when the DC superimposed magnetic field was 0 A / m and 5000 A / m was 63 and 50, respectively. The variation coefficient of Si concentration was 0.120, and the ratio of particles having a circularity of 0.75 or more was 80%.

(Example 5)
As a raw material powder, target composition Fe-5.5 wt% Si and Fe-4.5 wt% Si alloy powder produced by a gas atomization method is classified into 20 μm to 106 μm and the particle size distribution is adjusted, and then Fe-4.5 wt. A soft magnetic dust core was produced in the same manner as in Example 1 except that the mixing was performed so that the ratio of the% Si alloy powder was 25 wt%. The magnetic permeability when the DC superimposed magnetic field was 0 A / m and 5000 A / m was 79 and 55, respectively. The variation coefficient of the Si concentration was 0.071, and the proportion of particles having a circularity of 0.75 or more was 85%.

(Example 6)
Other than mixing the target composition Fe-5.2wt% Si and Fe-4.5wt% Si alloy powder prepared by gas atomization method as raw material powder so that the ratio of Fe-4.5wSi alloy powder is 35wt% Produced a soft magnetic dust core in the same manner as in Example 1. The magnetic permeability when the DC superimposed magnetic field was 0 A / m and 5000 A / m was 60 and 52, respectively. The variation coefficient of the Si concentration was 0.066, and the proportion of particles having a circularity of 0.75 or more was 87%.

(Comparative Example 1)
As a raw material powder, target composition Fe-5.0 wt% Si and Fe-4.0 wt% Si alloy powder produced by water atomization method is used so that the ratio of Fe-4.0 wt% Si alloy powder is 25 wt%. A soft magnetic dust core was produced in the same manner as in Example 1 except that the mixing pressure was changed to 1480 MPa. The magnetic permeability when the DC superimposed magnetic field was 0 A / m and 5000 A / m was 120 and 46, respectively. The variation coefficient of Si concentration was 0.101, and the ratio of particles having a circularity of 0.75 or more was 72%.

(Comparative Example 2)
The target composition Fe-4.0 wt% Si and Fe-2.5 wt% Si alloy powder prepared by gas atomization method as raw material powder is classified into 20 μm to 53 μm to adjust the particle size distribution, and then Fe-2.5 wt. A soft magnetic dust core was produced in the same manner as in Example 1 except that the mixing was performed so that the ratio of the% Si alloy powder was 15 wt%. The magnetic permeability when the DC superimposed magnetic field was 0 A / m and 5000 A / m was 66 and 44, respectively. The coefficient of variation of the Si concentration was 0.152, and the proportion of particles having a circularity of 0.75 or more was 80%.

(Comparative Example 3)
As a raw material powder, target composition Fe-5.0 wt% Si and Fe-3.5 wt% Si alloy powder prepared by gas atomization method are mixed so that the ratio of Fe-3.5 wt% Si alloy powder is 20 wt% A soft magnetic powder core was produced in the same manner as in Example 1 except that. The magnetic permeability when the DC superimposed magnetic field was 0 A / m and 5000 A / m was 92 and 47, respectively. The variation coefficient of Si concentration was 0.125, and the ratio of particles having a circularity of 0.75 or more was 82%.

(Comparative Example 4)
As raw material powder, target composition Fe-5.0wt% Si and Fe-3.0wt% Si alloy powder prepared by gas atomization method are mixed so that the ratio of Fe-3.0wt% Si alloy powder is 20wt% A soft magnetic powder core was produced in the same manner as in Example 1 except that. The magnetic permeability when the DC superimposed magnetic field was 0 A / m and 5000 A / m was 146 and 40, respectively. The variation coefficient of Si concentration was 0.175, and the ratio of particles having a circularity of 0.75 or more was 80%.

(Comparative Example 5)
As a raw material powder, target composition Fe-5.5 wt% Si and Fe-5.2 wt% Si alloy powder prepared by gas atomization method is classified into 20 μm to 150 μm, and the particle size distribution is adjusted, and then Fe-5.2 wt. A soft magnetic dust core was produced in the same manner as in Example 1 except that the mixing was performed so that the ratio of the% Si alloy powder was 50 wt%. The magnetic permeability when the DC superimposed magnetic field was 0 A / m and 5000 A / m was 69 and 48, respectively. The variation coefficient of Si concentration was 0.029, and the proportion of particles having a circularity of 0.75 or more was 88%.

(Comparative Example 6)
As a raw material powder, target composition Fe-5.5 wt% Si and Fe-5.4 wt% Si alloy powder prepared by gas atomization method are mixed so that the ratio of Fe-5.4 wt% Si alloy powder is 30 wt% A soft magnetic powder core was produced in the same manner as in Example 1 except that. The magnetic permeability when the DC superimposed magnetic field was 0 A / m and 5000 A / m was 49 and 40, respectively. The variation coefficient of Si concentration was 0.008, and the proportion of particles having a circularity of 0.75 or more was 87%.

(Comparative Example 7)
As raw material powder, target composition Fe-5.5 wt% Si and Fe-2.0 wt% Si alloy powder prepared by gas atomization method are mixed so that the ratio of Fe-2.0 wt% Si alloy powder is 1 wt% A soft magnetic powder core was produced in the same manner as in Example 1 except that. The magnetic permeability when the DC superimposed magnetic field was 0 A / m and 5000 A / m was 45 and 39, respectively. The variation coefficient of the Si concentration was 0.064, and the proportion of particles having a circularity of 0.75 or more was 93%.

The average value and standard deviation of Si concentration of the soft magnetic metal dust core produced as described above, coefficient of variation, maximum value, minimum value, ratio of particles having a circularity of 0.75 or more, core density, and direct current Table 1 shows a summary of the magnetic permeability when the superposed magnetic field is 0 A / m and 5000 A / m.

Further, FIG. 2 is a graph in which the data in Table 1 is plotted with the coefficient of variation of Si concentration on the horizontal axis and the magnetic permeability when the DC superimposed magnetic field is 5000 A / m on the vertical axis. From FIG. 2, the circularity of the cross section of 80% or more of the particles constituting the soft magnetic metal powder is 0.75 to 1.0, and the variation coefficient of Si concentration is in the range of 0.05 to 0.12. When the direct current superposition magnetic field is 5000 A / m, the magnetic permeability is 50 or more, and it can be confirmed that excellent direct current superposition characteristics are exhibited.

In Example 1, Example 2, Example 3, Example 4, Example 5, and Example 6, the relatively soft Fe-Si alloy powder was plastically deformed in the gaps between the relatively hard Fe-Si alloy powders. The filling rate is increased by entering, and the gap uniformity of the dust core is improved. In addition, since the variation coefficient of the Si concentration is within an appropriate range of 0.089, 0.051, 0.108, 0.120, 0.071, 0.066, the uniformity of the composition of the dust core is not so much The magnetic permeability with a DC superimposed magnetic field of 5000 A / m is as high as 55, 51, 54, 50, 55, and 52 without being damaged.

In Comparative Example 1, the coefficient of variation of the Si concentration is within an appropriate range of 0.101, but the proportion of particles having a circularity of 0.75 or more is as low as 72%, and the particle surface curvature is not constant. There are many ratios. For this reason, the stress applied at the time of molding becomes non-uniform, and a portion with a large amount of plastic deformation and a portion with no plastic deformation are generated, so the magnetization process becomes non-uniform, and as a result, the DC superimposition magnetic field has a permeability of 5000 A / m. 46 and low.

In Comparative Example 2, Comparative Example 3, and Comparative Example 4, the coefficient of variation of the Si concentration is as high as 0.152, 0.125, and 0.175. For this reason, the uniformity of the composition of the dust core is impaired, and the magnetic permeability with a DC superimposed magnetic field of 5000 A / m is as low as 44, 47, and 40.

In Comparative Examples 5 and 6, the coefficient of variation of the Si concentration is as low as 0.029 and 0.008. For this reason, the uniformity of the composition of the dust core is high, but the uniformity of the gap is impaired, and the magnetic permeability at a DC superimposed magnetic field of 5000 A / m is as low as 48 and 40.

In Comparative Example 7, the variation coefficient of the Si concentration is 0.064, which is within an appropriate range, but the difference between the maximum value and the minimum value of the Si concentration of the Fe-5.5Si powder and the Fe-2.0Si powder is the standard. It exceeds 6 times the deviation. For this reason, the density of the dust core is low, the gap uniformity is impaired, and the magnetic permeability with a DC superimposed magnetic field of 5000 A / m is as low as 39.

As described above, the soft magnetic metal dust core of the present invention has a high inductance even under DC current superposition, and thus can be miniaturized. Therefore, it is widely used in electric and magnetic devices such as inductors and reactors such as power circuits. And can be used effectively.

10: Soft magnetic metal powder core 11-a, 11-b: Soft magnetic metal powder 12: Insulator

Claims (4)

A powder core including an Fe-Si soft magnetic metal powder and an insulator, wherein a circularity of a cross section of 80% or more of the particles constituting the soft magnetic metal powder on an arbitrary cross section of the powder core. The variation coefficient of Si concentration near the center of each particle constituting the soft magnetic metal powder is 0.75 to 1.0, and is 0.050 or more and 0.120 or less, and the maximum value and the minimum value of the Si concentration are A soft magnetic metal dust core characterized in that the difference in values is within 6 times the standard deviation. 2. The soft magnetic metal powder core according to claim 1, wherein a particle diameter of the soft magnetic metal powder is 1 μm or more and 200 μm or less. The soft magnetic metal dust core according to claim 1, wherein the Si concentration of the soft magnetic metal powder is 1 wt% or more and 10 wt% or less. The soft magnetic metal dust core according to claim 1, wherein the insulator includes a silicon compound.

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