JP2017011073A - Powder-compact magnetic core and method of manufacturing power-compact magnetic core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a powder-compact magnetic core whose soft magnetic particle is made of an Fe-Si-based alloy and which has a high density and a low coercive force.SOLUTION: Disclosed is a powder-compact magnetic core which includes: a plurality of soft magnetic particles; and an insulation coating covering each surface of the soft magnetic particles. The soft magnetic particle contains Si of 3 mass% or more and 10 mass% or less, and P of 0.4 mass% or more and 1.8 mass% or less, and the balance is an Fe-Si-based alloy particle composed of Fe and inevitable impurities. The insulation coating is an oxide material containing an oxide of Fe, an oxide of Si and an oxide of P. In the powder-compact magnetic core, the relative density is 93% or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a dust core used for a magnetic core provided in a circuit component such as a reactor or an inductor, and a method for manufacturing a dust core. In particular, the present invention relates to a dust core in which soft magnetic particles are made of an Fe-Si-P alloy and have a high density and a low coercive force.

  As a component provided in a circuit for converting energy, such as a switching power supply or a DC / DC converter, there is a magnetic component including a coil formed by winding a winding and a magnetic core in which the coil is disposed to form a closed magnetic circuit. As the magnetic core, there is a powder magnetic core manufactured using a powder made of a soft magnetic material. A dust core is typically manufactured by press-molding a powder of coated soft magnetic particles having an insulating layer on the surface of soft magnetic particles into a predetermined shape, and subjecting the formed product to heat treatment. Is done.

  Among soft magnetic materials, iron-based alloys such as Fe-Si-Al alloys and Fe-Si alloys typified by Sendust are particularly easy to reduce iron loss compared to pure iron, for example. Therefore, the powder magnetic core comprised from the said iron-base alloy can construct | assemble a lower-loss magnetic core (for example, patent document 1).

JP 2012-107330 A

  However, the iron-based alloy described above is very hard and inferior in plastic deformability compared to pure iron due to solid solution hardening of the additive element. Therefore, the iron-base alloy particles are not substantially plastically deformed by the above-described pressure forming. Therefore, voids increase between the individual iron-base alloy particles constituting the dust core, leading to a decrease in the density of the dust core, resulting in a decrease in magnetic properties.

  The present invention has been made in view of the above circumstances, and one of the objects of the present invention is to provide a dust core having a high density and a low coercive force, in which soft magnetic particles are made of an Fe-Si-P alloy. It is in. Another object of the present invention is to provide a method for producing a dust core in which soft magnetic particles are made of an Fe-Si-P alloy, and a dust core with high density and low coercivity can be efficiently obtained. It is in.

  A dust core according to an aspect of the present invention includes a plurality of soft magnetic particles and an insulating coating that covers the surface of each of the soft magnetic particles. The soft magnetic particles are Fe-Si-P based alloy particles containing 3 mass% to 10 mass% of Si, 0.4 mass% to 1.8 mass% of P, and the balance being Fe and inevitable impurities. The insulating coating is an oxide material containing an oxide of Fe, an oxide of Si, and an oxide of P, and has a relative density of 93% or more.

  The manufacturing method of the powder magnetic core which concerns on 1 aspect of this invention is equipped with a preparatory process, a formation process, and a sintering process. The preparation step includes, as a raw material powder, a low Si powder composed of an Fe—Si based alloy having a Si content of 2% by mass or less and a high Si composed of an Fe—Si based alloy having a Si content of 9% by mass or more. A mixed powder is prepared by mixing Si powder, Fe-P alloy powder having a P content of 15% by mass to 36% by mass, and oxide powder containing Si oxide. In the molding step, the mixed powder is pressed and compressed to form a molded body. A sintering process sinters the said molded object at the temperature of 1000 degreeC or more and 1300 degrees C or less. The sintering process includes a primary sintering process and a secondary sintering process. In the primary sintering step, sintering is performed in an atmosphere substantially free of oxygen, and the Si content is 3% by mass or more and 10% by mass or less, and the P content is low. A plurality of soft magnetic particles made of an Fe—Si—P-based alloy having a content of 0.4 mass% to 1.8 mass%. In the secondary sintering step, after the primary sintering step, sintering is performed in an atmosphere containing oxygen, and around each of the soft magnetic particles, an Fe oxide, a Si oxide, and a P And an oxide material containing the oxide.

  In the dust core, soft magnetic particles are made of an Fe-Si-P alloy, and have a high density and a low coercive force.

  In the method of manufacturing the dust core, a soft magnetic particle is made of an Fe-Si-P alloy, and a dust core having a high density and a low coercive force can be manufactured with high productivity.

It is explanatory drawing which illustrates typically the state which manufactures the powder magnetic core which concerns on embodiment.

[Description of Embodiment of the Present Invention]
It is known that the coercive force of the Fe—Si alloy is the smallest when the Si content is around 6.5 mass%. In manufacturing a dust core having a low coercive force, for example, it is conceivable to sinter using an alloy powder made of a Fe-6.5 mass% Si alloy. However, in Fe-Si alloys, the higher the Si content, the higher the hardness and the poorer the plastic deformability, so it is difficult to obtain a high-density dust core. Therefore, when manufacturing a dust core made of a Fe-Si based alloy (hereinafter sometimes referred to as a Fe-6.5Si based alloy) having a Si content of around 6.5 mass%, It was studied to improve plastic deformability by using a low Si powder made of an Fe—Si based alloy having a Si content of 2% by mass or less. At this time, in order to obtain a powder magnetic core made of coated soft magnetic particles having alloy particles made of Fe-6.5Si alloy and an insulating coating covering the surface of the alloy particles, a low Si powder is used as a raw material powder. Then, it was considered to use a mixed powder obtained by mixing a high Si powder made of an Fe—Si based alloy having a high Si content and an oxide powder serving as an insulating coating. By compressing and compressing this mixed powder, the constituent elements of the low Si powder and the high Si powder are mutually diffused to become a powder composed of Fe-6.5Si alloy particles, which becomes a liquid phase by sintering. This is because it is considered that the oxide powder covers the surface of each Fe-6.5Si alloy particle to form an insulating coating.

  Here, from the phase diagram of the Fe—Si based alloy, at the sintering temperature (around 1200 ° C.) at which the oxide powder becomes a liquid phase, the Fe—Si based alloy whose Si content is 2 mass% or less is the γ phase. It is known that In the γ phase, since Fe self-diffusion is very slow, mutual diffusion of each constituent element hardly occurs between the low Si powder and the high Si powder as described above, and sintering does not proceed easily. Therefore, even if the above mixed powder is pressed, compressed, and sintered, it is a compact made of coated soft magnetic particles having alloy particles made of Fe-6.5Si alloy and an insulating coating covering the surface of the alloy particles. It has proved difficult to manufacture the magnetic core. Therefore, as a result of intensive studies by the present inventors, P-containing alloy powder containing P is further mixed with the above mixed powder, and the mixed powder is pressed, compressed and sintered, so that P is dissolved. The present inventors have found that a dust core including coated soft magnetic particles having alloy particles made of Fe-6.5Si alloy and an insulating coating covering the surface of the alloy particles can be obtained. The contents of the embodiments of the present invention will be listed and described below.

  (1) A dust core according to an embodiment includes a plurality of soft magnetic particles and an insulating coating covering each surface of the soft magnetic particles. The soft magnetic particles are Fe-Si-P based alloy particles containing 3 mass% to 10 mass% of Si, 0.4 mass% to 1.8 mass% of P, and the balance being Fe and inevitable impurities. The insulating coating is an oxide material containing an oxide of Fe, an oxide of Si, and an oxide of P, and has a relative density of 93% or more.

  According to the said structure, although a soft magnetic particle is Fe-Si-P type alloy particle containing 3 mass% or more and 10 mass% or less of Si, relative density is as high as 93% or more. Therefore, the dust core has a low coercive force.

  (2) As an example of the dust core, the oxide material may have a content of 0.5% by mass or more and 2.0% by mass or less.

  When the content of the oxide material is 0.5% by mass or more, the insulating coating is easily provided uniformly on the surface of each soft magnetic particle. Due to the presence of the uniform insulation coating, the eddy current loss of the dust core can be reduced. On the other hand, since the content of the oxide material is 2.0% by mass or less, the insulation coating amount in the dust core becomes an appropriate amount, and the amount of soft magnetic particles can be sufficient, so that a high-density dust core is obtained. easy.

  (3) As an example of the powder magnetic core, a form in which a majority of the soft magnetic particles are single crystals in an arbitrary cross section of the powder magnetic core.

  The fact that the soft magnetic particles are single crystals can reduce the coercive force because there are no crystal grain boundaries that inhibit magnetization reversal.

  (4) As an example of the powder magnetic core, when the soft magnetic particle is a single crystal, the average crystal grain size of the single crystal of the soft magnetic particle may be 40 μm or more and 300 μm or less.

  When the average crystal grain size of the single crystal of soft magnetic particles is 40 μm or more, the coercive force can be reduced. On the other hand, when the average crystal grain size of the single crystal of soft magnetic particles is 300 μm or less, an increase in eddy current loss can be easily reduced.

  (5) The manufacturing method of the powder magnetic core which concerns on embodiment is equipped with a preparatory process, a formation process, and a sintering process. The preparation step includes, as a raw material powder, a low Si powder composed of an Fe—Si based alloy having a Si content of 2% by mass or less and a high Si composed of an Fe—Si based alloy having a Si content of 9% by mass or more. A mixed powder is prepared by mixing Si powder, Fe-P alloy powder having a P content of 15% by mass to 36% by mass, and oxide powder containing Si oxide. In the molding step, the mixed powder is pressed and compressed to form a molded body. A sintering process sinters the said molded object at the temperature of 1000 degreeC or more and 1300 degrees C or less. The sintering process includes a primary sintering process and a secondary sintering process. In the primary sintering step, sintering is performed in an atmosphere substantially free of oxygen, and the Si content is 3% by mass or more and 10% by mass or less, and the P content is low. A plurality of soft magnetic particles made of an Fe—Si—P-based alloy having a content of 0.4 mass% to 1.8 mass%. In the secondary sintering step, after the primary sintering step, sintering is performed in an atmosphere containing oxygen, and around each of the soft magnetic particles, an Fe oxide, a Si oxide, and a P And an oxide material containing the oxide.

  According to the above configuration, by mixing the raw material powder with low Si powder having excellent plastic deformability, the plastic powder has excellent plastic deformability at the time of compression molding, can have good moldability, and a high-density dust core can be obtained. Can be manufactured. Therefore, a molding binder or the like can be eliminated. Mainly in the primary sintering step, the constituent elements of the low Si powder and the high Si powder are mutually diffused, so that the soft magnetic particles constituting the dust core have a Si content of 3 mass% or more and 10 mass% or less. The Fe—Si—P-based alloy can be made, and a dust core having a low coercive force can be manufactured. In addition, since the periphery of each soft magnetic particle can be covered with an oxide material derived from the raw material powder mainly in the secondary sintering step, an insulating coating is formed on the surface of each powder particle at the raw material powder stage. There is no need to consider, and the step of forming the insulating coating can be omitted. As mentioned above, according to the said structure, the high-density and low coercive-force powder magnetic core can be manufactured with sufficient productivity.

  In the sintering process, it is considered that the following phenomenon occurs by performing sintering at a temperature of 1000 ° C. or higher and 1300 ° C. or lower. First, in the primary sintering step, sintering is performed in an atmosphere substantially free of oxygen, so that the Fe-P alloy powder becomes a liquid phase, and the Fe-P alloy in the liquid phase is a low Si powder. And enters the grain boundary of each particle of the high Si powder. At this time, Fe and Si are interdiffused between the low Si powder and the high Si powder, and P dissolved from the Fe-P alloy in the liquid phase is dissolved in the low Si powder and the high Si powder. A plurality of soft magnetic particles made of an Fe-Si-P alloy having a Si content of 3% by mass to 10% by mass and a P content of 0.4% by mass to 1.8% by mass. Generated. By mixing the Fe—P alloy powder with the raw material powder, even if the Fe—Si alloy is a γ phase (Fe self-diffusion is very slow), the self-diffusion coefficient of Fe can be improved and low Fe and Si can easily diffuse each other between the Si powder and the high Si powder, and the sintering proceeds. Since the Fe-P alloy in the liquid phase enters the crystal grain boundary of each soft magnetic particle, it becomes an insulating coating that covers the surface of each soft magnetic particle and insulates each soft magnetic particle from each other. When the Fe-P alloy in the liquid phase enters the crystal grain boundary of each soft magnetic particle, each soft magnetic particle moves in a direction approaching each other, and the gap between each soft magnetic particle is narrowed.

  Next, in the secondary sintering step, sintering is performed in an atmosphere containing oxygen, so that the Si oxide becomes a liquid phase, and the liquid phase Fe-P alloy is oxidized. Insulating coating is produced with an oxide material containing a material, an oxide of Fe, and an oxide of P. Thereafter, as the oxide material transitions from the liquid phase to the solid phase, the soft magnetic particles are rearranged, and the voids between the soft magnetic particles are further reduced to produce a high-density powder magnetic core. it can.

[Details of the embodiment of the present invention]
Details of the embodiment of the present invention will be described below. First, the manufacturing method of a dust core will be described, and then the dust core will be described. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to the claim are included. For example, in the test examples described later, the mixing ratio of the raw material powder, the molding pressure of the molded body, the sintering temperature / time of the molded body, and the like can be appropriately changed.

<Method of manufacturing a dust core>
The manufacturing method of the powder magnetic core of the embodiment includes the following preparation process, molding process, and sintering process. Hereinafter, each step will be described in order based on FIG.

[Preparation process]
As shown in the upper left figure of FIG. 1, as raw material powder, a low Si powder 21 made of Fe-Si alloy having a low Si content and a high Si powder made of Fe-Si alloy having a high Si content. A mixed powder 2 is prepared by mixing 22, Fe—P-based alloy powder 23, and oxide powder 24.

Low Si powder and high Si powder The content of Si in the low Si powder (low Si soft magnetic particles) 21 is 2% by mass or less. If the Si content is in the vicinity of 6.5% by mass, it contributes to a low coercive force. However, the higher the Si content, the higher the hardness and the lower the plastic deformability. Therefore, when the Si content is 2% by mass or less, it is excellent in plastic deformability in the molding process described later, and can have good moldability. The content of Si is preferably 1% by mass or less, and more preferably pure iron containing substantially no Si. Pure iron is less expensive and more economical than iron alloys.

  In the Fe—Si based alloy, in a region of about 900 ° C. to 1400 ° C., there is a region that undergoes phase transformation between the α phase and the γ phase depending on the Si content. The γ phase is a region where the self-diffusion of Fe is very slow. In the sintering process described later, mutual diffusion of each constituent element is difficult to occur between the low Si powder and the high Si powder, and the sintering is difficult to proceed. is there. The low Si powder mentioned here consists of an Fe—Si based alloy in which the Si content is located in the region of the γ phase at the sintering temperature of the primary sintering process (described in the sintering process described later). This γ-phase region typically has a Si content of about 2% by mass or less at a sintering temperature at which the Fe—P-based alloy powder 23 and the oxide powder 24 become a liquid phase.

  The Si content in the high Si powder (high Si soft magnetic particles) 22 is 9% by mass or more. When the Si content is 9% by mass or more, Si sufficiently diffuses from the high Si powder 22 to the low Si powder 21 in the sintering step described later, and the Si content is 3% by mass or more and 10% by mass. It is easy to manufacture a dust core made of the following Fe-Si-P alloy. As the Si content increases, the amount of Si that diffuses during sintering increases, and it is easier to obtain an Fe—Si—P-based alloy having a Si content of around 6.5% by mass, preferably 12% by mass or more. 15 mass% or more is more preferable.

  Typically, the low Si powder 21 and the high Si powder 22 include Si in the above-described range, and the balance is made of a Fe—Si two-phase alloy of Fe and inevitable impurities.

  Each compounding amount (mass) of the low Si powder 21 and the high Si powder 22 is preferably low Si powder: high Si powder = 2: 1 to 15: 1, and more preferably 3: 1 to 10: 1. The blending amounts of the low Si powder 21 and the high Si powder 22 are combined with the contents of the Fe—P alloy powder 23 and the oxide powder 24 described later, and the soft magnetic particles 10 (Fe—Si) constituting the dust core. What is necessary is just to select according to Si content of each powder so that it may become desired value (value selected from 3 mass% or more and 10 mass% or less) in Si content in -P type alloy. In consideration of obtaining a high-density powder magnetic core, the content of the low Si powder 21 is preferably larger than the content of the high Si powder 22.

  The size of each particle of the low Si powder 21 and the high Si powder 22 can be appropriately selected. In consideration of moldability and sinterability, the average particle size is preferably 150 μm or less. In particular, the high Si powder 22 has a higher hardness than the low Si powder 21 and is inferior in moldability, so that it is preferably smaller than the low Si powder 21. Specifically, when the average particle size of the high Si powder (each high Si soft magnetic particle) 22 is 45 μm or less, the raw material powder (mixed powder 2) is preferably excellent in moldability, and further 30 μm or less and 20 μm or less. Is preferred. However, if the high Si powder 22 is too small, it is difficult to handle and the workability is inferior. Therefore, the average particle size of the high Si powder (each high Si soft magnetic particle) 22 is preferably 1 μm or more, more preferably 3 μm or more, particularly 5 μm. The above is more preferable because of excellent handling properties.

  When the average particle size of the low Si powder (low Si soft magnetic particles) 21 is 45 μm or more, the raw material powder (mixed powder 2) is preferably excellent in moldability, and more preferably 50 μm or more and 70 μm or more. When the average particle size of the low Si powder (low Si soft magnetic particles) 21 is 150 μm or less, in the sintering process described later, Si can be sufficiently diffused into each particle made of a low Si alloy and sintered. Excellent in properties. Furthermore, when the average particle size of the low Si powder (low Si soft magnetic particles) 21 is 125 μm or less, particularly 100 μm or less, Si can be sufficiently diffused even in a short time, and the sinterability can be further enhanced. The average particle size of the low Si powder (low Si soft magnetic particles) 21 is not less than 3 times, more preferably not less than 5 times the average particle size of the high Si powder (each high Si soft magnetic particle) 22. The powder is large enough and has excellent moldability.

  The low Si powder 21 and the high Si powder 22 can be manufactured using a known Fe—Si alloy powder manufacturing method, for example, an atomizing method. Commercially available powder satisfying the above-described Si content and average particle diameter may be used.

-Fe-P-based alloy powder Fe-P-based alloy powder (Fe-P-based alloy particles) 23 typically contains 15 mass% or more and 36 mass% or less of P, with the balance being Fe and inevitable impurities. Examples thereof include those made of a two-phase alloy of -P. The Fe-P-based alloy powder is in a liquid phase state in a sintering step described later, and covers the periphery of the Fe-Si-P-based alloy particles (soft magnetic particles) derived from the Fe-P alloy in the liquid phase state. Produces an insulation coating. In addition, the Fe—P-based alloy powder plays a role of promoting the mutual diffusion of the constituent elements of the low Si powder 21 and the high Si powder 22 generated in the sintering process described later.

  When the content of P is 15% by mass or more, the low Si powder becomes an α phase in the vicinity of the sintering temperature, so that the self-diffusion coefficient of Fe can be improved. Therefore, the mutual diffusion of the constituent elements of the low Si powder 21 and the high Si powder 22 can be easily performed in the sintering step described later, and the sintering can be promoted. Specifically, when the content of P is 15% by mass or more, the self-diffusion coefficient of Fe can be improved to about 100 times the self-diffusion coefficient in the γ phase, which is equivalent to the self-diffusion coefficient in the α phase. And can. On the other hand, when the content of P is 36% by mass or less, the influence of P on the coercive force does not substantially occur. The content of P is preferably 20% by mass to 33% by mass, and more preferably 25% by mass to 30% by mass.

  When the average particle size of the Fe-P alloy powder (Fe-P alloy particles) 23 is 45 μm or less, the raw material powder (mixed powder 2) is preferably excellent in moldability, and more preferably 30 μm or less and 20 μm or less. . However, if the Fe-P alloy powder 23 is too small, it is difficult to handle and the workability is inferior. Therefore, the average particle diameter of the Fe-P alloy powder (Fe-P alloy particles) 23 is preferably 1 μm or more, Furthermore, it is more preferable that it is 3 μm or more, particularly 5 μm or more because of excellent handling properties.

  The blending amount of the Fe—P-based alloy powder 23 is preferably 1% by mass or more and 7% by mass or less in the mixed powder 2. When the content of the Fe—P based alloy powder 23 in the mixed powder 2 is 1% by mass or more, the Fe—Si—P based alloy particles (soft magnetic particles) are uniformly distributed around the Fe—Si—P based alloy particles after the primary sintering. A P-based grain boundary layer can be formed. On the other hand, when the content in the mixed powder 2 of the Fe-P alloy powder 23 is 7% by mass or less, the content of the low Si powder 21 and the high Si powder 22 can be made appropriate, and Fe— The content of Si-P alloy particles (soft magnetic particles) can be sufficiently secured.

  The Fe-P alloy powder 23 may be a commercially available Fe-P alloy powder having a desired size, or may be obtained by pulverizing a commercially available powder and selecting a desired size by sieving. Good.

-Oxide powder The oxide powder (oxide particle | grains) 24 can utilize the appropriate oxide which has insulation, and contains the oxide of Si. The oxide powder 24 is in a liquid phase state in a sintering process to be described later, and is derived from the oxide in the liquid phase state, together with the Fe—P based alloy particles ( An insulating coating covering the periphery of the soft magnetic particles is generated. The oxide powder 24 is either (1) a solid solution that does not dissolve in the Fe—Si alloy or the Fe—Si—P alloy, or that does not affect the magnetic properties even if dissolved. (2) a Fe—Si alloy Or a Fe—Si—P-based alloy having a small contact angle (good wettability) and easily entering the liquid phase into the crystal grain boundary of the soft magnetic particles.

  As for the size of the oxide powder (oxide particles) 24, the average particle diameter is 1 μm or more and 40 μm or less. Since the average particle diameter of the oxide powder (oxide particles) 24 is 1 μm or more, it is easily distributed uniformly around the low Si powder 21 and the high Si powder 22 and is further handled as a raw material powder (mixed powder 2). easy. On the other hand, when the average particle diameter of the oxide powder (oxide particles) 24 is 40 μm or less, it is easy to suppress variation in the thickness of the insulating coating that is generated from the oxide, leading to a decrease in magnetic properties. hard. The average particle size of the oxide powder (oxide particles) 24 is preferably 5 μm or more and 30 μm or less, and more preferably 10 μm or more and 30 μm or less.

  The blending amount of the oxide powder 24 is preferably 0.5% by mass or more and 2.0% by mass or less in the mixed powder 2. When the content of the oxide powder 24 in the mixed powder 2 is 0.5% by mass or more, it is easy to be uniformly distributed around the low Si powder 21 and the high Si powder 22, and the Fe—Si—P alloy. The periphery of the particles (soft magnetic particles) can be uniformly coated with an insulating coating. On the other hand, when the content of the oxide powder 24 in the mixed powder 2 is 2.0% by mass or less, the content of the low Si powder 21 and the high Si powder 22 can be set to appropriate amounts, and Fe—Si in the dust core. The content of -P alloy particles (soft magnetic particles) can be sufficiently secured. The content of the oxide powder 24 in the mixed powder 2 is further 1% by mass or more and 1.5% by mass or less.

  The blending amount of the oxide powder 24 can be more than 2.0 mass% and 10 mass% or less in the mixed powder 2. Since the content of the oxide powder 24 in the mixed powder 2 is more than 2.0% by mass, the content of the insulating coating produced from the oxide can be increased, and a low magnetic permeability powder core and it can. On the other hand, when the content of the oxide powder 24 in the mixed powder 2 is 10% by mass or less, the content of the low Si powder 21 and the high Si powder 22 can be made appropriate, and the soft magnetic particles are contained in the dust core. A sufficient amount can be secured.

The oxide powder 24 can include an oxide of Ca. Since Ca does not form a solid solution in the Fe—Si based alloy or Fe—Si—P based alloy, it is difficult to lower the magnetic properties. Further, the oxide powder 24 to which Ca oxide is added is preferable in that the surface tension becomes small in the liquid phase state, and therefore, the oxide powder 24 easily enters between crystal grain boundaries. In addition, the oxide powder 24 may include Al ₂ O ₃ . Although Al dissolves in a Fe—Si based alloy or a Fe—Si—P based alloy, it is difficult to cause a decrease in magnetic properties due to the solid solution.

  As the oxide powder 24, a commercially available oxide powder having a desired size may be used, or a commercially available powder may be pulverized and screened for a desired size.

-Others contained in raw material powder The raw material powder (mixed powder 2) can contain a lubricant. In this case, (1) a mold with improved moldability and excellent dimensional accuracy can be obtained. (2) Since the friction during molding can be reduced, the molded article can be easily extracted from the mold and has excellent surface properties. It has the advantage that it is obtained. Examples of the lubricant include metal soaps such as lithium stearate and zinc stearate, fatty acid amides such as stearic acid amide, organic substances such as higher fatty acid amides such as ethylenebisstearic acid amide, and inorganic substances such as boron nitride and graphite. . The content of the lubricant is 0.1% by mass or more and 1.0% by mass or less with respect to the total amount of the low Si powder and the high Si powder used for the raw material powder (the amount of only the Si powder not containing the lubricant). In addition, the above advantages can be sufficiently obtained, and a decrease in the proportion of the alloy in the raw material can be prevented.

[Molding process]
The prepared mixed powder 2 is compressed under pressure to form a compact. The formed body is formed by filling the mixed powder 2 into a forming space of a mold having a desired shape. As the mold, a general mold used for manufacturing a dust core can be used. A typical mold includes a cylindrical die provided with a through hole, and an upper punch and a lower punch that are inserted into the through hole and compress the raw material powder under pressure. After filling the above-mentioned mixed powder 2 into the molding space formed by the inner peripheral surface of the through hole of the die and the lower punch inserted into one opening of this through hole, the other opening of the above through hole The raw powder is pressed and compressed at a predetermined pressure with the upper punch inserted into the upper punch and the lower punch to form a molded body, and the molded body is extracted from the die. When this mold is used, a columnar shaped body corresponding to the contour shape of the die and the end face shapes of the upper punch and the lower punch is obtained. When a mold including a core rod inserted and disposed in the above-described cylindrical die is used, a molded body having a through hole or a groove corresponding to the shape of the core rod can be formed. The core rod is inserted and disposed in at least one of the upper punch and the lower punch.

Examples of the molding pressure include 5 ton / cm ² (≈490 MPa) to 15 ton / cm ² (≈1470 MPa). By setting it to 5 ton / cm < ² > or more, even if it is the mixed powder 2 containing high hardness high Si powder, it can fully compress, and a mold life does not become excessively short by setting it to 15 ton / cm < ² > or less. This pressurization / compression is preferably performed at room temperature.

  When the pressure compression is performed under the above-described conditions, as shown in the upper right diagram of FIG. 1, the low Si powder 21 (plural low Si soft magnetic particles) is plastically deformed, and a molded body 3 excellent in moldability can be obtained.

[Sintering process]
The molded body 3 is sintered at a temperature of 1000 ° C. or higher and 1300 ° C. or lower to form a dust core. When the sintering temperature is in the above range, the Fe-P alloy powder 23 and the oxide powder 24 become a liquid phase, and Fe, Si between the low Si powder 21 and the high Si powder 22 through this liquid phase. Can be interdiffused. When the sintering temperature is 1000 ° C. or higher, Fe and Si are easily diffused between the low Si powder 21 and the high Si powder 22, and the content of Si in the Fe—Si alloy is a desired value ( A dust core having a value selected from 3% by mass to 10% by mass) is obtained. Further, the Fe—P-based alloy powder 23 and the oxide powder 24 become a liquid phase and can enter the liquid phase between the soft magnetic particles, thereby providing an insulating coating that appropriately insulates the soft magnetic particles. On the other hand, when the sintering temperature is 1300 ° C. or lower, it is possible to suppress elution before the high Si alloy having a low melting point (liquidus point) is sintered. The sintering temperature is more preferably 1100 ° C. or more and 1275 ° C. or less, particularly preferably 1150 ° C. or more and 1250 ° C. or less. The holding time is 5 minutes or more, preferably 30 minutes or more.

  In the method for manufacturing a powder magnetic core according to the present embodiment, the primary sintering step ⇒ the secondary sintering step is performed within the above-described sintering temperature and holding time. Hereinafter, the mechanism generated by performing the primary sintering process and the secondary sintering process will be described in detail based on the lower diagram of FIG.

≪Primary sintering process≫
In the primary sintering step, sintering is performed in an atmosphere substantially free of oxygen. The atmosphere that does not substantially contain oxygen here means that the oxygen partial pressure is less than 1 × 10 ⁻⁵ atm (1 Pa). When primary sintering is performed, first, as shown in the lower left diagram of FIG. 1, the Fe—P alloy powder 23 becomes a liquid phase (liquid phase interposing member 44), and the low Si powder 21 and the high Si powder Fe and Si are interdiffused between the two, and both Si powders are powders composed of polycrystalline soft magnetic particles 40 containing 3 mass% or more and 10 mass% or less of Si. At this time, P contained in the liquid phase interposing member 44 is dissolved in the low Si powder, so that the low Si powder becomes an α phase, and the mutual diffusion of each constituent element between the low Si powder 21 and the high Si powder 22. Is promoted and sintering proceeds. Due to the above solid solution, the polycrystalline soft magnetic particles 40 contain 0.4 mass% or more and 1.8 mass% or less of P.

  Next, the liquid phase intervening member 44 enters the crystal grain boundary of the polycrystalline soft magnetic particle 40. Then, as shown in the lower middle diagram of FIG. 1, the polycrystalline soft magnetic particles 40 are divided by the liquid phase intervening member 44 that has penetrated into the crystal grain boundaries, and become a plurality of single crystal soft magnetic particles 10. In the process in which the liquid phase intervening member 44 penetrates into the crystal grain boundary, between the polycrystalline soft magnetic particles 40, 40, between the soft magnetic particles 10, 10, and between the polycrystalline soft magnetic particles 40 and the soft magnetic particles 10. Then, Fe and Si are interdiffused, and liquid phase sintering further proceeds while Fe and P are mutually dissolved between the particles 10 and 40 and the liquid phase intervening member 44. The liquid phase intervening member 44 penetrates into the crystal grain boundary of the polycrystalline soft magnetic particles 40 to cover the entire surface of each soft magnetic particle 10 and becomes an insulating coating that insulates the soft magnetic particles 10 from each other. . As the liquid phase sintering proceeds, the divided soft magnetic particles 10 move toward each other, and the gaps between the soft magnetic particles 10 are narrowed.

  In the primary sintering, it is possible to easily diffuse each constituent element between the low Si powder 21 and the high Si powder 22 by making the atmosphere substantially free of oxygen and to promote the sintering. it can. This is because, if oxygen is contained in the atmosphere during the primary sintering, an oxide of Fe is generated, and diffusion of Fe is not performed.

≪Secondary sintering process≫
In the secondary sintering step, sintering is performed in an atmosphere containing oxygen after the primary sintering. As a result, the oxide powder 24 becomes a liquid phase, and the liquid phase intervening member 44 is oxidized, and an insulating coating made of an oxide material containing an oxide of Si, an oxide of Fe, and an oxide of P is generated. . As for the atmosphere of secondary sintering, it is mentioned that oxygen partial pressure is more than 1 × 10 ⁻² atm (1013 Pa), more preferably 1 × 10 ⁻¹ atm (101 Pa) or more, and an air atmosphere is particularly preferable.

  Thereafter, as the oxide material transitions from the liquid phase to the solid phase, the soft magnetic particles 10 are rearranged, and the gaps between the soft magnetic particles 10 are further reduced. This liquid-phase oxide material becomes an insulating coating 14 that insulates the soft magnetic particles 10, and insulates a plurality of soft magnetic particles 10 from each soft magnetic particle 10 as shown in the lower right diagram of FIG. 1. A dust core 1 having an insulating coating 14 can be obtained. As described above, each soft magnetic particle 10 is an Fe—Si—P-based alloy particle containing 3% by mass to 10% by mass of Si and 0.4% by mass to 1.8% by mass of P.

  Examples of the primary sintering and the secondary sintering described above include performing secondary sintering continuously after the primary sintering. That is, the secondary sintering process is performed without cooling to room temperature after the primary sintering process. In this case, for example, the sintering temperature can be the same in primary sintering and secondary sintering, and liquid phase sintering can be performed efficiently. In addition, after the primary sintering process, the secondary sintering process may be performed by cooling to room temperature and reheating from room temperature, or the sintering temperature may be different between the primary sintering process and the secondary sintering process. May be.

<Dust core>
The dust core obtained by the above-described method for manufacturing a dust core includes a plurality of soft magnetic particles and an insulating coating that covers the surface of each soft magnetic particle. Each of the soft magnetic particles contains 3% by mass to 10% by mass of Si, 0.4% by mass to 1.8% by mass of P, and the balance is Fe—Si—P based alloy particles composed of Fe and inevitable impurities. It is. The insulating coating is an oxide material containing an oxide of Fe, an oxide of Si, and an oxide of P.

  The soft magnetic particles have the smallest coercive force when the Si content is around 6.5% by mass. The Si content of the soft magnetic particles is preferably 4% by mass to 9% by mass, more preferably 5% by mass to 8% by mass, and particularly preferably 6% by mass to 7% by mass. Further, the content of P in the soft magnetic particles is preferably 0.6% by mass or more and 1.5% by mass or less, and more preferably 0.8% by mass or more and 1.2% by mass or less.

  It can be mentioned that the majority of the soft magnetic particles are single crystals in any cross section of the dust core. In the above-described method for manufacturing a powder magnetic core, an insulating coating is formed by allowing the Fe-P alloy powder and oxide powder in a liquid phase to enter the crystal grain boundaries of the polycrystalline soft magnetic particles in the sintering process. Therefore, the majority of soft magnetic particles in the dust core are single crystals. More preferably, 80% or more of the soft magnetic particles, and substantially all the soft magnetic particles are single crystals. The state of the soft magnetic particles can be confirmed or measured by observing an arbitrary cross section of the dust core with an optical microscope or a scanning electron microscope (SEM). For example, in an arbitrary cross section of the dust core, five or more fields of 200 μm × 300 μm are obtained, and the average of the proportion of soft magnetic particles that are single crystals in each field of view is used as the ratio of single crystal particles. .

  In the above-described method for manufacturing a powder magnetic core, high-temperature heat treatment is performed in the sintering process. Therefore, when each constituent element of the low Si powder and the high Si powder is interdiffused, each particle easily grows, It tends to be larger than the size of the particles. Thereafter, the liquid-phase Fe-P alloy powder and oxide powder penetrate into the crystal grain boundaries of the polycrystalline soft magnetic particles and divide the polycrystalline soft magnetic particles to form a plurality of single crystal soft magnetic particles. . Examples of the average crystal grain size of the single crystal soft magnetic particles generated by the grain growth and separation include 40 μm or more and 300 μm or less. In particular, when the average crystal grain size of the single crystal soft magnetic particles is 75 μm or more, the magnetization reversal becomes easy and it is easy to contribute to the reduction of the coercive force. Examples of the average crystal grain size of the single crystal soft magnetic particles include 50 μm to 200 μm and 100 μm to 150 μm.

  It is mentioned that content of the oxide material which comprises insulation coating is 0.5 mass% or more and 2.0 mass% or less. When the content of the oxide material is 0.5% by mass or more, the soft magnetic particles can be sufficiently insulated. On the other hand, when the content of the oxide material is 2.0% by mass or less, the amount of soft magnetic particles in the dust core can be sufficiently secured. The content of the oxide material is preferably 0.7% by mass or more and 1.8% by mass or less, and more preferably 1.0% by mass or more and 1.5% by mass or less.

  Content of the oxide material which comprises insulation coating can also be more than 2.0 mass% and 10 mass% or less. When the content of the oxide material is more than 2.0% by mass, the content of the oxide material can be increased, and a dust core having a low magnetic permeability can be obtained. On the other hand, the amount of soft magnetic powder in the dust core can be sufficiently ensured by being 10% by mass or less.

  The powder magnetic core of the present embodiment includes (1) improvement in plastic deformability by mixing raw material powder with low Si powder having excellent plastic deformability, and (2) by forming an insulating coating by liquid phase sintering. High density due to reduction of voids between soft magnetic particles. The relative density of the dust core is 93% or more. The relative density of the powder magnetic core is, for example, 95% or more, further 97% or more, depending on the mixing ratio of the low Si powder in the raw material powder, the sintering temperature and the holding time, and the like. The dust core of this embodiment has a high density and a low coercive force.

  Further, the dust core of the present embodiment has a high strength because an insulating coating is formed by liquid phase sintering, and each soft magnetic particle is bonded by an oxide material that has undergone a liquid phase.

<Test example>
A powder magnetic core (sample No. 1) comprising a plurality of soft magnetic particles and an insulating coating covering each surface of the soft magnetic particles by pressure-compressing and sintering a mixed powder containing an Fe-Si based alloy powder. To 12), and the relative density and coercive force of each obtained dust core were examined.

・ Sample No. 1 to Sample No. 12
As raw material powders, Si powders composed of two types of Fe—Si alloys having different Si contents, Fe—P alloy powders, and oxide powders were prepared. Si powder is a low Si powder of pure iron powder (Fe: 99.7 mass% or more, balance: inevitable impurities), one of which contains substantially no Si, the other contains 18 mass% of Si, and the balance is It is a high Si powder (Fe-18Si alloy powder) made of Fe and inevitable impurities. The pure iron powder becomes an α phase at the primary sintering temperature because P is dissolved at the primary sintering temperature described later. The average particle size of the low Si powder is 75 μm, and the average particle size of the high Si powder is 10 μm. The Fe—P-based alloy powder is an alloy powder containing a predetermined amount of P shown in Table 1, with the balance being Fe and inevitable impurities, and the average particle size is 10 μm. The oxide powder is an oxide of Si: SiO ₂ powder, and the average particle size is 30 μm. In this test example, the average particle diameter is a 50% particle diameter (cumulative mass) measured by a commercially available measuring device. Table 1 shows the blending amount (mass) of the raw material powder. Table 1 also shows the composition of the soft magnetic particles produced by the blending amount of the raw materials.

  A lubricant was added to the raw material powder and mixed well with a V-type mixer to prepare a mixed powder. The lubricant was ethylene bis-stearic acid amide, and the content thereof was 0.6% by mass with respect to the total amount of the low Si powder, high Si powder, Fe—P alloy powder, and oxide powder.

The mixed powder is fed into the molding space of the mold, pressed and compressed at a molding pressure of 8 ton / cm ² (≈784 MPa), and a ring-shaped molded body (outer diameter: 34 mm × inner diameter: 20 mm × thickness: 5 mm). This molded body could be molded satisfactorily.

The obtained molded body was heat-treated at 600 ° C. for 1 hour in a vacuum atmosphere substantially free of oxygen (oxygen partial pressure: 1 × 10 ⁻³ Pa) to remove the lubricant, and then 1200 ° C. × Heat treatment (primary sintering) for 1 hour was performed. Furthermore, following the primary sintering, heat treatment (secondary sintering) at 1250 ° C. for 1 hour was performed in an air atmosphere to produce a dust core.

・ Sample No. 111
As raw material powders, Si powders made of two types of Fe—Si alloys having different Si contents and oxide powders were prepared. The Si powder was sample No. 1 and a low Si powder and a high Si powder. The oxide powder is a powder obtained by mixing Fe oxide: FeO and Si oxide: SiO ₂ at a ratio (mass) of FeO: SiO ₂ = 2: 1. The average particle size of the oxide powder is 30 μm. The blending amount (mass) of the raw material powder was low Si powder: high Si powder: oxide powder = 63: 36: 1. That is, sample no. In 111, the raw material powder does not contain Fe-P alloy powder.

  Sample no. The same lubricant as in No. 1 was added to prepare a mixed powder. And sample no. Similarly to 1, a ring-shaped molded body (outer diameter: 34 mm × inner diameter: 20 mm × thickness: 5 mm) was produced.

  The molded body thus obtained was subjected to heat treatment at 600 ° C. for 1 hour in an air atmosphere to remove the lubricant, and then subjected to heat treatment (sintering) at 1250 ° C. for 1 hour to produce a dust core.

・ Sample No. 112
A dust core was prepared by a conventional method (preparation of soft magnetic powder → formation of an insulating coating on the surface of each soft magnetic particle → pressing and compressing the coated soft magnetic powder → sintering). First, as a raw material powder, a soft magnetic powder of an Fe-6.5Si alloy having a Si content of 6.5% by mass was prepared, and a silicone insulating coating was formed on the surface of each soft magnetic particle to coat the soft magnetic powder. A powder was prepared. The coating conditions for the insulation coating were the same as in Patent Document 1. A molding resin is added to the coated soft magnetic powder to form a granulated powder, and this granulated powder is pressed and compressed with a molding pressure of 8 ton / cm ² (≈784 MPa) to form a ring-shaped molded body (outer diameter: 34 mm). X inner diameter: 20 mm x thickness: 5 mm). This molded body was heat-treated at 775 ° C. for 1 hour in a nitrogen atmosphere to obtain a dust core.

  Sample No. Relative densities were measured for powder cores 1-12, 111, and 112. The relative density is a density ratio represented by (apparent density / true density) × 100. The apparent density was determined using the Archimedes method. For the true density, a component analysis of the powder magnetic core was performed, and the composite density of the constituent components (here, alloy particles and oxide) was used. The component analysis utilizes a known method (such as energy dispersive X-ray spectroscopy or inductively coupled plasma (ICP) emission spectroscopy). The results are shown in Table 2.

  Sample No. The coercive force was measured for the dust cores 1 to 12, 111, and 112. The coercive force (Oe) was measured using a BH tracer (DCBH tracer manufactured by Riken Denshi Co., Ltd.) by arranging the same winding on the ring-shaped dust core of each sample. The results are shown in Table 2.

  As shown in Table 2, pure iron powder (low Si powder) and high Si powder as raw material powder, Fe-P alloy powder containing 15 mass% or less and 36 mass% or less of P, mixed powder containing oxide powder 、 Pressure compression ⇒ Sample No. in which two-stage sintering (primary sintering and secondary sintering) was performed to produce a powder magnetic core composed of powder of Fe-Si-P alloy particles (soft magnetic particles) . 2-7, 10 and 11 were found to have high density and very low coercivity. Sample No. 2-7, 10 and 11, (1) The plastic deformability was improved by mixing pure iron powder (low Si powder) excellent in plastic deformability with the raw material powder. (2) Insulation by two-step sintering It can be considered that the density was increased because the gap between the soft magnetic particles was reduced by forming the coating. Sample No. In Nos. 2-7, 10 and 11, the Fe-P alloy powder containing an appropriate amount of P can be mixed to improve the self-diffusion coefficient of Fe, and each composition of the low Si powder and the high Si powder in the sintering process. It is considered that interdiffusion of elements could be easily performed and sintering could be promoted. Furthermore, sample no. In Nos. 2-7, 10 and 11, pure iron powder and high Si powder are made into soft magnetic particle powder made of Fe-Si alloy having a Si content of around 6.5% by mass by two-stage sintering. It is considered that an insulating coating can be formed around each soft magnetic particle by the Fe—P alloy powder and oxide powder in a liquid phase, and a dust core having a low coercive force was obtained.

  A pure iron powder (low Si powder) was mixed as a raw material powder, and an insulating coating was formed by sintering, but the sample no. The dust core of No. 111 has a low relative density of about 86% and a coercive force of 2.1 Oe. Higher than 2-7, 10 and 11. Even if Fe-P alloy powder is included, Sample No. 1 also has a low relative density of about 86% and a coercive force of 2.1 Oe. Higher than 2-7. This is considered to be due to the fact that the pure iron powder is in the γ phase when the sintering temperature is around 1200 ° C. In the γ phase, since Fe self-diffusion is very slow, mutual diffusion of each constituent element hardly occurs between pure iron powder and high Si powder, and sintering does not proceed easily. Therefore, sample no. In 111, 1, even if the mixed powder mixed with pure iron powder is pressed and compressed ⇒ sintered, it does not contain Fe-P alloy powder or its content is low, so that sintering does not proceed. This is probably because the voids of the soft magnetic particles cannot be reduced.

  Sample No. with a large content of Fe-P alloy powder. The dust cores of Nos. 8 and 9 have a coercive force of Sample No. Higher than 2-7, 10 and 11. This is presumably because the influence of P on the coercive force has increased. Even when the content of the Fe-P-based alloy powder is large, the sample No. 1 in which the content of P in the Fe-P-based alloy powder is an appropriate amount. 8 was high density. This is considered to be because the self-diffusion coefficient of Fe was improved by P and the relative density was improved by promoting the mutual diffusion of each constituent element between the pure iron powder and the high Si powder. On the other hand, sample No. 2-7, 10 and 11, since an appropriate amount of Fe-P alloy powder is mixed as a raw material powder, P is dissolved in a low Si powder and transformed from a γ phase to an α phase. It is considered that the self-diffusion coefficient was improved and the mutual diffusion of each constituent element was promoted between the pure iron powder and the high Si powder.

  Even if an appropriate amount of Fe-P alloy powder is mixed, Sample No. with a high P content in the Fe-P alloy powder. The dust core of No. 12 has a relative density as low as about 85% and a coercive force of 2.1 Oe. Higher than 2-7, 10 and 11. This is presumably because the influence of P on the coercive force is increased because the content of P in the Fe-P alloy powder is too large. Sample No. It is considered that the dust core of No. 12 has a high content of P in the Fe-P alloy powder, so that a stable compound called FeP is formed, P becomes difficult to diffuse into Fe, and the relative density is lowered.

  Sample No. obtained by the conventional method The dust core No. 112 has a low relative density of about 85% and a coercive force of 2.1 Oe. Higher than 2-7, 10 and 11. This is because the soft powder of Fe-6.5Si alloy having a Si content of 6.5% by mass is used as the raw material powder, so that the plastic deformability is inferior and the relative density was not improved during molding. Conceivable.

Sample No. The cross sections of the powder magnetic cores 2 to 7, 10, and 11 were observed. When the cross section of the dust core is mirror-polished and observed with an SEM, each single crystal can be identified by the difference in contrast. As a result, sample no. In the dust cores of 2 to 7, 10, and 11, it was confirmed that the majority of the soft magnetic particles were single crystals. Sample No. In the SEM backscattered electron image of the cross section of the dust cores 2-7, 10 and 11, the area of each single crystal particle was measured for 10 arbitrarily selected single crystal particles, and a circle having the same area as this area was measured. The diameter was taken as the particle size of each single crystal particle, and the average crystal particle size of the single crystal particle was determined. As a result, the average crystal grain size of the single crystal particles was 122 μm. Furthermore, by energy dispersive X-ray spectroscopy, each soft magnetic particle is a Fe-6.5 mass% Si alloy having a uniform composition, and FeO—SiO ₂ —P ₂ O ₅ is formed on the surface of each soft magnetic particle. It was confirmed that an insulating coating made of

  The dust core of the present invention can be used as a magnetic member for applications where low coercivity is desired. Moreover, the manufacturing method of the powder magnetic core of this invention can be utilized suitably for obtaining the powder magnetic core used for various inductors.

DESCRIPTION OF SYMBOLS 1 Powder magnetic core 2 Mixed powder 3 Molded body 10 Soft magnetic particle (single crystal soft magnetic particle) 14 Insulation coating 21 Low Si soft magnetic particle (low Si powder)
22 High Si soft magnetic particles (High Si powder)
23 Fe-P alloy particles (Fe-P alloy powder)
24 Oxide particles (oxide powder)
40 Polycrystalline soft magnetic particles 44 Liquid phase intervening member

Claims (5)

A dust core comprising a plurality of soft magnetic particles and an insulating coating covering the surface of each of the soft magnetic particles,
The soft magnetic particles are Fe-Si-P based alloy particles containing 3 mass% to 10 mass% of Si, 0.4 mass% to 1.8 mass% of P, and the balance being Fe and inevitable impurities. And
The insulating coating is an oxide material containing an oxide of Fe, an oxide of Si, and an oxide of P,
A dust core having a relative density of 93% or more.   The dust core according to claim 1, wherein the content of the oxide material is 0.5 mass% or more and 2.0 mass% or less.   The powder magnetic core according to claim 1 or 2, wherein a majority of the soft magnetic particles are single crystals in an arbitrary cross section of the powder magnetic core.   The powder magnetic core according to claim 3, wherein an average crystal grain size of the single crystal of the soft magnetic particles is 40 μm or more and 300 μm or less. As raw material powder, a low Si powder composed of an Fe-Si based alloy having a Si content of 2% by mass or less, and a high Si powder composed of a Fe-Si based alloy having a Si content of 9% by mass or more, A preparation step of preparing a mixed powder in which an Fe-P alloy powder having a P content of 15% by mass to 36% by mass and an oxide powder containing an oxide of Si is prepared;
A molding step of compressing and pressing the mixed powder to form a molded body;
A sintering step of sintering the molded body at a temperature of 1000 ° C. or higher and 1300 ° C. or lower,
The sintering step includes
Sintering is performed in an atmosphere substantially free of oxygen, and the low Si powder and the high Si powder have a Si content of 3% by mass to 10% by mass and a P content of 0.4% by mass. A primary sintering step in which a plurality of soft magnetic particles composed of an Fe-Si-P-based alloy having a mass of 1.8% by mass or less;
After the primary sintering step, sintering is performed in an atmosphere containing oxygen, and each of the soft magnetic particles is oxidized including an oxide of Fe, an oxide of Si, and an oxide of P. A secondary sintering step of covering with a material.

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