JP2021002555A - Powder magnetic core and manufacturing method of powder magnetic core - Google Patents

Abstract

To provide a powder magnetic core and a manufacturing method of a powder magnetic core that can obtain excellent magnetic properties by reducing iron loss.SOLUTION: A powder magnetic core includes an FeSiAl alloy powder, and an insulating resin that coats the FeSiAl alloy powder, and when the total of the weight of the FeSiAl alloy powder and the weight of Fe2O3 is 100 wt.%, the weight ratio of Fe2O3 is 0.1 wt.% or more.SELECTED DRAWING: Figure 1

Description

The present invention relates to a dust core and a method for producing a powder core.

Reactors are used in various applications such as drive systems for hybrid vehicles, electric vehicles and fuel cell vehicles. As the core of this reactor, for example, a dust core is used. The dust core is formed by pressure molding the soft magnetic powder and the insulating film covering the soft magnetic powder.

The dust core is required to have a magnetic characteristic of low energy loss in order to improve energy exchange efficiency and generate low heat. Specifically, the magnetic property related to energy loss is iron loss (Pcv). The iron loss (Pcv) is the hysteresis loss (Phv) and the eddy current loss (Phv).
It is represented by the sum of Pev).

Japanese Patent No. 5027945

Conventionally, it has been said that when strain occurs in the particles of the soft magnetic powder, the coercive force of the soft magnetic powder increases and the hysteresis loss increases. Therefore, in order to remove the strain in the particles of the soft magnetic powder and reduce the coercive force, the molded product after pressure molding is heat-treated at a high temperature to reduce the hysteresis loss due to the removal of the strain. .. However, in recent years, due to the diversification of reactor applications, further reduction of hysteresis loss is required.

An object of the present invention is to provide a powder magnetic core and a method for producing a powder magnetic core, which can obtain excellent magnetic properties by reducing iron loss.

As a result of diligent research, the present inventor, unlike the above-mentioned common general technical knowledge, dared to cause a certain degree of strain in the soft magnetic powder by oxidizing a part of the soft magnetic powder in the molded product, thereby causing hysteresis. It was found that the loss and eventually the iron loss can be reduced.

The powder magnetic core of the present invention is a powder magnetic core containing a FeSiAl alloy powder and an insulating resin coating the FeSiAl alloy powder, and the total of the weight of the FeSiAl alloy powder and the weight of Fe ₂ O ₃ is 100 wt. When% is taken, the weight ratio of Fe ₂ O ₃ is 0.1 wt% or more.

Further, the method for producing a powder metallurgy of the present invention comprises an insulation treatment step of coating a FeSiAl alloy powder with an insulating resin, a molding step of molding the insulated FeSiAl alloy powder, and the molded FeSiAl alloy powder. It includes a heat treatment step of heat treatment in an oxidizing atmosphere.

According to the present invention, it is possible to provide a powder magnetic core and a method for producing a powder magnetic core that can obtain excellent magnetic characteristics by reducing iron loss.

It is a flowchart which shows the manufacturing process of the dust core which concerns on embodiment. It is a graph which shows the relationship between the ratio of Fe ₂ O ₃ layers, iron loss, hysteresis loss, and eddy current loss. Iron loss after the heat treatment under N ₂ atmosphere, the hysteresis loss, the graph showing the eddy current loss, iron loss after the heat treatment in the air after heat treatment under N ₂ atmosphere, hysteresis loss, eddy current loss Is.

The present embodiment is a powder magnetic core in which an oxide layer is formed on a part of the soft magnetic powder in a pressure-molded body containing a soft magnetic powder and an insulating resin covering the soft magnetic powder. The dust core is used, for example, as a magnetic material of a reactor. Here, the layer includes the case of covering the entire powder and the case of covering a part of the powder.

[Soft magnetic powder]
The soft magnetic powder used in this embodiment is a FeSiAl alloy powder containing iron, silicon, and aluminum as main components, so-called sendust alloy powder. The average particle size (D50) of the soft magnetic powder is, for example, preferably 10 μm or more and 50 μm or less, preferably 15 μm or more and 25 μm or less. In the present specification, the "average particle size" refers to D50, that is, the median diameter, unless otherwise specified.

The soft magnetic powder preferably has a small surface area. That is, it is preferable that the degree of sphericity is high. This is because when the surface area is small, a uniform oxide layer can be efficiently formed with a small amount of oxygen. Further, when the surface area is reduced, the gaps between the soft magnetic powders are reduced, and the density and magnetic permeability can be improved. When the circularity of the soft magnetic powder is used as an index indicating that the sphericity is high, the circularity is preferably 0.95 or more. Further, it is more preferable that the circularity is 0.98 or more.

The method for producing the soft magnetic powder does not matter. However, it is preferable that the sphericity is high as described above. The soft magnetic powder produced by the gas atomization method becomes substantially spherical particles. Therefore, the gas atomizing powder formed by the gas atomizing method can be used as it is without processing.

Further, the pulverized powder produced by the pulverization method, the water atomizing powder produced by the water atomizing method, and the water gas atomizing powder produced by the water gas atomizing method have irregular surface particles and are distorted and have many irregularities. Therefore, when these powders are used, it is preferable to perform a process for improving the average circularity of the particles. In this case, the average circularity of the particles can be increased by smoothing the surface irregularities using a ball mill, mechanical alloying, jet mill, attritor or surface modifier.

[Manufacturing process]
FIG. 1 is a flowchart showing a manufacturing process of the dust core of the present embodiment. As shown in FIG. 1, the powder magnetic core manufacturing steps of the present embodiment include (1) powder heat treatment step, (2) insulation treatment step, (3) lubricant mixing step, (4) molding step, and (5). It has a heat treatment process.

(1) Powder heat treatment step (step S01)
The powder heat treatment step is a step of heat-treating the soft magnetic powder. That is, the crystal structure of the FeSiAl alloy powder is changed by heat-treating the FeSiAl alloy powder.

Specifically, the crystal structure of the FeSiAl alloy powder before the powder heat treatment is a bcc structure (body-centered cubic lattice structure), and includes a DO ₃ structure and an irregular structure, which are regular structures. Then, by heat-treating the FeSiAl alloy powder, the ratio of the irregular structure can be set to a desired value. The ratio of the irregular structure and the DO ₃ structure can be calculated by X-ray diffraction by the Rietveld analysis method. The distinction between the irregular structure and the DO ₃ structure can be judged by the lattice constant calculated by X-ray diffraction.

In the powder heat treatment step, for example, heating is performed in a vacuum atmosphere, an inert gas atmosphere, a non-oxidizing atmosphere, or an air atmosphere for 1 to 6 hours. Examples of the inert gas include H ₂ and N ₂ . The heat treatment temperature is preferably 500 ° C. or higher and 700 ° C. or lower. By setting the heat treatment temperature within this range, the ratio of the irregular structure to the crystal structure of the FeSiAl alloy powder can be reduced to 14.6 wt% or more and 43.7 wt% or less, and iron loss can be reduced. ..

The coercive force of the FeSiAl alloy powder is preferably 0.43 A / cm or more and 1.81 A / cm or less. When the coercive force is set in this range, the hysteresis loss can be reduced.

(2) Insulation treatment step (step S02)
The insulation treatment step is a step of forming an insulating film on the surface of the soft magnetic powder. That is, the insulating treatment step is performed by mixing an insulating resin with the soft magnetic powder, drying the mixture, and sieving the mixture. As the insulating film, a silicone oligomer, a silicone resin, a silane coupling agent, or the like is used. Of these, a two-layer insulating film may be formed by forming an insulating layer of the first layer with a silicone oligomer or a silane coupling agent and forming an insulating layer of the second layer with a silicone resin. Hereinafter, the process for each material will be described.

(A) Silicone oligomer mixing step The silicone oligomer mixing step is a step of mixing silicone oligomers and coating the surface of the heat-treated FeSiAl alloy powder. Silicone oligomers have an alkoxysilyl group. Alkoxysilyl groups include methoxy-based, ethoxy-based, and methoxy / ethoxy-based groups. If it is a silicone oligomer having an alkoxysilyl group, it is a methyl type or a methylphenyl type having no reactive functional group, or an epoxy type, an epoxymethyl type, a mercapto type or a mercapto having an alkoxysilyl group and a reactive functional group. Methyl-based, acrylic-methyl-based, methacryl-methyl-based, vinylphenyl-based, and the like can be used. In particular, a thick and hard insulating layer can be formed by using a methyl-based or methylphenyl-based silicone oligomer.

The amount of the silicone oligomer added is preferably 0.1 wt% or more and 2.0 wt% or less with respect to the soft magnetic powder. If the amount added is less than 0.1 wt%, the DC superimposition characteristics may deteriorate. If the amount added is more than 2.0 wt%, the density may decrease, so that the initial magnetic permeability may decrease and the hysteresis loss may increase.

The drying temperature of the silicone oligomer layer is preferably 25 ° C. or higher and 200 ° C. or lower. This is because if the drying temperature is less than 25 ° C., the film formation is incomplete and the eddy current loss may increase. On the other hand, if the drying temperature exceeds 200 ° C., decomposition proceeds and it becomes difficult to form a film, which may reduce the density and magnetic permeability of the molded product. The drying time is about several hours, for example, about 1 hour to 2 hours.

(B) Silane Coupling Agent Mixing Step The silane coupling agent mixing step is a step of mixing the silane coupling agent and coating the surface of the heat-treated FeSiAl alloy powder. As the silane coupling agent, for example, aminosilane-based, epoxysilane-based, isocyanurate-based, ethoxysilane-based, emexisilane-based, and methoxysilane-based can be used, and in particular, 3-aminopropyltriethoxysilane and 3-glycid. Xipropyltrimethoxysilane and tris- (3-trimethoxysilylpropyl) isocyanurate are preferable.

The amount of the silane coupling agent added is preferably 0.25 wt% or more and 1.0 wt% or less. By setting the amount of the silane coupling agent added in this range, the standard deviation, magnetic characteristics, and strength characteristics of the density of the molded dust core can be improved.

The drying temperature of the silane coupling agent is preferably 25 ° C. or higher and 200 ° C. or lower. This is because if the drying temperature is lower than 25 ° C., the solvent may remain and the film may be incomplete. On the other hand, if the drying temperature exceeds 200 ° C., decomposition may proceed and the film may not be formed. The drying time is about 2 hours.

(C) Silicone Resin Mixing Step In the silicone resin mixing step, a predetermined amount of silicone resin is added to the FeSiAl alloy powder coated with a silicone oligomer or a silane coupling agent, and the mixture is dried in an air atmosphere at a predetermined temperature. Is. By the silicone resin mixing step, a silicone resin layer is formed on the outside of the coating film made of the silane coupling agent.

Silicone resin is a resin having a siloxane bond (Si—O—Si) in its main skeleton. By using a silicone resin, a film having excellent flexibility can be formed. As the silicone resin, methyl type, methylphenyl type, propylphenyl type, epoxy resin modified type, alkyd resin modified type, polyester resin modified type, rubber type and the like can be used. Among these, in particular, when a methylphenyl-based silicone resin is used, it is possible to form a silicone resin layer having less heat loss and excellent heat resistance.

The amount of the silicone resin added is preferably 1.0 wt% or more and 3.0 wt% or less with respect to the soft magnetic powder. This is because if the amount added is less than 1.0 wt%, it does not function as an insulating film, and the magnetic characteristics may deteriorate due to an increase in eddy current loss. This is because if the amount added is more than 3.0 wt%, the core expands and the density of the molded product decreases, which may reduce the magnetic permeability.

The drying temperature of the silicone resin is preferably 100 ° C. or higher and 200 ° C. or lower. This is because if the drying temperature is lower than 100 ° C., the film formation is incomplete and the eddy current loss may increase. On the other hand, if the drying temperature is higher than 200 ° C., it becomes an inorganic substance and does not play a role as a binder, the retention is deteriorated, and the density and magnetic permeability of the molded product may decrease. The drying time is about 2 hours.

(3) Lubricant mixing step (step S03)
The lubricant mixing step is a step of adding a lubricant to the insulated FeSiAl alloy powder and mixing the mixture. By going through this step, the surface of the silicone resin layer is coated with the lubricant. By adding a lubricant to the soft magnetic powder, the sliding between the soft magnetic powders can be improved, so that the density at the time of mixing can be improved and the molding density can be increased. Further, it is possible to reduce the withdrawal pressure of the upper punch during molding and prevent the generation of vertical streaks on the core wall surface due to the contact between the mold and the powder.

As the lubricant, stearic acid and its metal salt and wax such as ethylene bis are used. For example, ethylene bisstealamide, ethylene bisstealamide, calcium stearate, lithium stearate, aluminum stearate, zinc stearate, and mixtures thereof can be used. The amount of the lubricant added is preferably about 0.1 wt% or more and 0.6 wt% or less with respect to the soft magnetic powder.

(4) Molding step (step S04)
The molding step is a step of forming a molded body by pressure molding a soft magnetic powder having an insulating film formed on its surface. The pressure during molding is 10ton / cm ² or more and 20ton / cm ² or less, about 15 ton / cm ² on average are preferred.

(5) Heat treatment step (step S05)
The heat treatment step is a step of heat-treating a molded product that has undergone the molding step in an oxidizing atmosphere. This heat treatment is also called annealing. By going through this heat treatment step, a dust core is produced. The oxidative atmosphere is a gas containing oxygen, and also includes the atmosphere. By performing the heat treatment in an oxidizing atmosphere, a Fe ₂ O ₃ (hematite) layer can be formed on the surface of the powder on which the insulating layer is formed. By forming the Fe ₂ O ₃ layer, stress is generated inside the powder, and a slight strain is generated. As a result, the effect of reducing the hysteresis loss can be obtained. It is presumed that this is because when an oxide layer is formed on the surface of the powder, stress is applied to the powder, the width of the magnetic domain in the crystal is narrowed, and the coercive force is lowered.

When the total of the weight of the FeSiAl alloy powder and the weight of Fe ₂ O ₃ in the powder magnetic core is 100 wt%, the ratio of the weight of Fe ₂ O ₃ may be relatively small and is preferably not excessive. For example, the weight ratio of Fe ₂ O ₃ is preferably 0.1 wt% or more. Further, the weight ratio of Fe ₂ O ₃ is preferably 0.79 wt% or less. The heat treatment temperature is preferably 600 ° C. or higher and 900 ° C. or lower. The amount of oxygen in the oxidizing atmosphere is preferably equal to that in the atmosphere.

When heat treatment is performed in the air, the silicone resin reacts quickly with oxygen, which may cause cracks. Therefore, first, the silicone resin is stabilized by performing the first heat treatment in a nitrogen atmosphere in which the atmosphere is purged with nitrogen. Then, the Fe ₂ O ₃ layer can be formed by further performing a _second heat treatment in the atmosphere. Thereby, the occurrence of cracks can be prevented.

[Example]
(First Example)
A first embodiment according to the present embodiment will be described below. The sample used in the first example was prepared as follows.

(1) Powder Heat Treatment FeSiAl powder having an average particle diameter (D50) of 21.0 μm obtained by the gas atomization method was subjected to powder heat treatment at a temperature of 700 ° C. for 2 hours in a nitrogen atmosphere.

(2) Insulation Treatment 0.5 wt% of silicone oligomer was mixed with FeSiAl powder after powder heat treatment, heat-dried at 200 ° C. for 2 hours, and passed through a sieve having a mesh size of 250 μm. Then, 1.5% of silicone resin (methylphenyl type) was mixed, heat-dried at 150 ° C. for 2 hours, and passed through a sieve having a mesh size of 250 μm.

(3) Lubricant Mixing Treatment After the insulation treatment, 0.5 wt% of ethylene bis (Acrawax (registered trademark)) was mixed as a lubricant and heat-dried at 150 ° C. for 2 hours. Then, it was passed through a sieve having a mesh size of 250 μm.

(4) Molding FeSiAl powder after insulation treatment and lubricant mixing treatment on the molding surface was pressure-molded at 12 ton / cm ² at room temperature using a mold to form an EER core-shaped molded product.

(5) Heat Treatment The molded product was heat-treated in the air at 750 ° C. for 2 hours to prepare a dust core of Sample 1 (Example 1). Further, a dust core of Sample 2 and Sample 3 under the same conditions except that the amount of air was adjusted by flowing N ₂ was prepared (Examples 2 and 3). Sample 2 has a flow rate of N ₂ of 0.5 L / min, and sample 3 has a flow rate of N ₂ of 1.0 L / min.

On the other hand, by setting the flow rate of N ₂ to 4.0 L / min, a dust core of Sample 4 which was heat-treated in a nitrogen atmosphere where the atmosphere was purged was prepared (Comparative Example 1). Comparative Example 1 is the same as Example 1, Example 2, and Example 3 except that the atmosphere in which the heat treatment is performed is different.

(Measurement result)
For Examples 1-3 and Comparative Example 1 prepared as described above, the ratio of the DO ₃ structure to the Fe ₂ O ₃ in the crystal structure of the dust core and the iron loss Pcv (hysteresis loss Ph and eddy current loss Pe) were determined. It was measured. The DO ₃ structure referred to here corresponds to FeSiAl alloy powder.

More specifically, the above (1) to (5) after passing through the process, the powder magnetic core was produced, DO ₃ in the case where the total weight of DO ₃ weight structures and _Fe 2 _{O 3} and 100 wt% Each ratio of the weight of the structure and the weight of Fe ₂ O ₃ was calculated by performing a crystal structure evaluation by X-ray diffraction on the molded product. As the X-ray diffractometer, an apparatus manufactured by Bruker (BRUKER D2 PHASER 2nd Gen, X-ray: Cu-Kα ray) was used.

On the other hand, a reactor having a dust core as a core was prepared through the steps (1) to (5) above, and measurement was performed to obtain the iron loss Pcv. That is, a BH analyzer (Iwadori Measurement Co., Ltd .: SY-8219), which is a magnetic measuring device, is wound around a dust core with a copper wire of φ0.5 mm for 16 turns of the primary winding and 8 turns of the secondary winding. ) Was used for measurement. The measurement conditions were a frequency of 100 kHz and a maximum magnetic flux density of Bm = 100 mT, and the hysteresis loss (Ph) and the eddy current loss (Pe) were calculated. This calculation was performed by calculating the hysteresis loss coefficient (Kh) and the eddy current loss coefficient (Ke) by the least squares method using the following equations (1) to (3) for the frequency curve of the loss.

Pcv = Kh x f + Ke x f ² ... (1)
Ph = Kh x f ... (2)
Pe = Ke × f ² ... (3)
Pcv: Iron loss Kh: Hysteresis loss coefficient Ke: Eddy current loss coefficient f: Frequency Ph: Hysteresis loss Pe: Eddy current loss The above measurement results are shown in Table 1 and FIG.

Table 1 is a table showing the relationship between the ratio of Fe ₂ O ₃ and iron loss (Pcv), hysteresis loss (Ph), and eddy current loss (Pe), and FIG. 2 is a graph corresponding to Table 1. .. First, in Comparative Example 1 in which the ratio of Fe ₂ O ₃ was 0%, the hysteresis loss (Ph) was 309 kW / m ³ and the eddy current loss (Pe) was 227 kW / m ³ . On the other hand, as the proportions of Fe ₂ O ₃ in Example 3, Example 2, and Example 1 increase, both the hysteresis loss (Ph) and the eddy current loss (Pe) decrease. In particular, the rate of decrease in hysteresis loss (Ph) is large. Comparing Comparative Example 1 with Example 1 in which Fe ₂ O ₃ is 0.79 wt%, the hysteresis loss (Ph) is reduced to about 30% from 309 kW / m ³ to 101 kW / m ³ . Therefore, the iron loss is also significantly reduced from 536 kW / m ³ to 291 kW / m ³ . Also Comparative Example 1 and _Fe 2 _{O 3} is compared with the third embodiment of the 0.10 wt%, hysteresis loss (Ph) is reduced from 309kw / ^{m 3} and about 65% to 200 kW / ^{m 3} .. Therefore, the iron loss is also reduced from 536 kW / m ³ to 409 kW / m ³ . That is, when the ratio of Fe ₂ O ₃ is 0.1 wt% or more, the hysteresis loss (Ph) and the eddy current loss (Pe) are clearly reduced. Further, it can be seen that the hysteresis loss (Ph) and the eddy current loss (Pe) clearly decrease at 0.79 w% or less. If the amount of Fe ₂ O ₃ is too large, the amount of FeSiAl alloy is reduced, so that the characteristics are deteriorated.

(Second Example)
Next, a second embodiment according to the present embodiment will be described below. The sample used in the second example was prepared as follows.

(1) Powder Heat Treatment FeSiAl powder having an average particle diameter (D50) of 19.8 μm obtained by the gas atomization method was subjected to powder heat treatment in a nitrogen atmosphere at a temperature of 700 ° C. for 2 hours.

(2) Insulation treatment 1.0 wt% of a silane coupling agent (tetraethoxysilane) is mixed with the FeSiAl powder after the powder heat treatment, and the mixture is heat-dried at 200 ° C. for 2 hours, and then a sieve having a mesh size of 250 μm. Passed through. Then, 1.5% of silicone resin (methylphenyl type) was mixed, heat-dried at 150 ° C. for 2 hours, and passed through a sieve having a mesh size of 250 μm.

(3) Lubricant Mixing Treatment After the insulation treatment, 0.5 wt% of ethylene bis (Acrawax (registered trademark)) was mixed as a lubricant, and the mixture was heat-dried at 150 ° C. for 2 hours. Then, it was passed through a sieve having a mesh size of 250 μm.

(4) Molding FeSiAl powder after insulation treatment and lubricant mixing treatment on the molding surface was pressure-molded at 12 ton / cm ² at room temperature using a mold to form an EER core-shaped molded product.

The compact magnetic core of Sample 5 was prepared by heat-treating the molded product at 750 ° C. for 2 hours in a nitrogen atmosphere (Comparative Example 2). The flow rate of N ₂ is 4 L / min. The dust core of Sample 6 was prepared by further heat-treating this Sample 5 at 750 ° C. for 2 hours in the air (Example 4).

(Measurement result)
For Comparative Examples 2 and 4 prepared as described above, the ratio of DO ₃ structure and Fe ₂ O _{3 to} the crystal structure and iron loss Pcv (hysteresis loss Ph and eddy current loss Pe) were measured. The measurement items, measuring devices, and measuring methods of the second embodiment are the same as those of the first embodiment. The above measurement results are shown in Table 2 and FIG.

Table 2 is a table showing the relationship between the ratio of Fe ₂ O ₃ and iron loss (Pcv), and FIG. 3 is a graph corresponding to Table 2. In FIG. 3, the values of the hysteresis loss (Ph) and the eddy current loss (Pe) in the iron loss (Pcv) are displayed. First, in Comparative Example 2 in which the ratio of Fe ₂ O ₃ was 0%, the hysteresis loss (Ph) was 230 kW / m ³ and the eddy current loss (Pe) was 147 kW / m ³ . On the other hand, in Example 4 in which Fe ₂ O ₃ is 0.51 wt%, the hysteresis loss (Ph) is reduced to 161 kW / m ³ and the eddy current loss (Pe) is reduced to 132 kW / m ³ . In particular, the rate of decrease in hysteresis loss (Ph) is large. Therefore, the iron loss (Pcv) is significantly reduced from 377 kW / m ³ to 293 kW / m ³ . This is because even if the dust core is heat-treated (annealed) once after pressure molding, it is further heat-treated in the atmosphere, that is, in an oxygen atmosphere, resulting in hysteresis loss (Ph) and iron loss (Ph). It means that the reduction effect of Pcv) can be obtained.

[Other Embodiments]
The present invention is not limited to the above embodiment as it is, and at the implementation stage, the components can be modified and embodied without departing from the gist thereof. In addition, various inventions can be formed by an appropriate combination of the plurality of components disclosed in the above-described embodiment. For example, some components may be removed from all the components shown in the embodiments. In addition, components across different embodiments may be combined as appropriate.

For example, the powder heat treatment step may not be performed. That is, even when the powder is not heat-treated, the heat treatment of the molded product of the present invention can obtain the effect of reducing iron loss. However, since the effect of reducing iron loss can be obtained by powder heat treatment, there is an advantage that the effect of reducing iron loss is further enhanced by the heat treatment of the molded product of the present invention.

Further, for example, the present invention is not limited to the powder magnetic core of the reactor produced in Examples 1 to 4 as described above, and a choke coil is produced by winding a coil around the powder magnetic core. Also includes embodiments. As a result, the effects obtained in Examples 1 to 4 as described above can be similarly exerted in the choke coil.

Claims (8)

A powder magnetic core containing a FeSiAl alloy powder and an insulating resin that coats the FeSiAl alloy powder.
When the total of the weight of the FeSiAl alloy powder and the weight of Fe ₂ O ₃ is 100 wt%, the powder magnetic core is characterized in that the ratio of the weight of Fe ₂ O ₃ is 0.1 wt% or more. The dust core according to claim 1, wherein the FeSiAl alloy powder is an atomized powder. The powder magnetic core according to claim 1, wherein the FeSiAl alloy powder is a spheroidized powder. The powder magnetic core according to any one of claims 1 to 3, wherein the FeSiAl alloy powder has a circularity of 0.95 or more. The proportion of the weight of Fe ₂ O ₃ is 0.79 wt% or less when the total of the weight of the FeSiAl alloy powder and the weight of Fe ₂ O ₃ is 100 wt%, according to claims 1 to 4. The powder magnetic core described in either. Insulation treatment process of coating FeSiAl alloy powder with insulating resin,
A molding process for molding the insulated FeSiAl alloy powder, and
A heat treatment step of heat-treating the molded FeSiAl alloy powder in an oxidizing atmosphere, and
A method for producing a dust core, which comprises. The heat treatment step is
The first heat treatment performed in a nitrogen atmosphere and
After the first heat treatment, the second heat treatment performed in an oxidizing atmosphere,
The method for producing a dust core according to claim 6, wherein the powder magnetic core comprises. The method for producing a powder magnetic core according to claim 6 or 7, wherein a powder heat treatment step of heat-treating the FeSiAl alloy powder is included before the insulation treatment step.

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