JP7524664B2 - Fe-based alloy composition, powder and magnetic core of the Fe-based alloy composition - Google Patents

Description

The present invention relates to an Fe-based alloy composition, a powder of the Fe-based alloy composition, and a magnetic core.

Fe-based nanocrystalline alloys, such as FeCuNbSiB alloys, are used in magnetic parts, especially in the high frequency range, due to their excellent magnetic properties of low loss and high magnetic permeability.

The Fe-based nanocrystalline alloy can have excellent magnetic properties by obtaining a ribbon of amorphous alloy by rapidly solidifying the molten alloy using a single roll method or the like, and then precipitating fine crystal grains of the (Fe-Si) bcc phase by heat treatment (see, for example, Patent Document 1). Hereinafter, the fine crystals of the (Fe-Si) bcc phase may be referred to as fine crystals, and the grains may be referred to as fine crystal grains.

Because the alloy obtained by the single roll method is in the form of a thin ribbon, the shape of the magnetic cores that can be made using it is limited. For example, in the case of a wound magnetic core, which is formed by slitting the alloy ribbon to a width corresponding to the desired height of the magnetic core and winding the alloy ribbon to match the desired inner and outer diameters, the shape is limited to annular shapes such as a toroidal shape or a racetrack shape.

On the other hand, the required magnetic core shape is not limited to annular, but is various. For this reason, powdering of Fe-based nanocrystalline alloys including the FeCuNbSiB system is being studied so that magnetic cores of complex shapes can be manufactured by applying molding methods such as pressing and extrusion.
As a method for powderization, for example, a high-pressure water atomization method or a high-speed rotating water jet atomization method (Patent Document 2) can be used. There is also an attempt to adopt a method of spraying a flame jet to a molten metal (hereinafter also referred to as a jet atomization method) disclosed in Patent Document 3.

Special Publication No. 4-4393 JP 2017-95773 A JP 2014-136807 A

However, compared to obtaining a thin alloy ribbon using the single roll method, the above-mentioned method has the following problems in obtaining alloy powder, which is a precursor to an Fe-based nanocrystalline alloy:

(a) In the case of alloy ribbons obtained by the single roll method, the molten alloy being cast is rapidly solidified by direct contact with a roll of cooled copper alloy. On the other hand, in atomization methods such as the high-pressure water atomization method described above, the particles of the molten alloy are cooled by contacting water, which is a cooling medium. The water vapor film that is generated during cooling inhibits the transfer of heat from the alloy to the water, limiting the cooling rate. In the high-speed rotating water flow atomization method, a high-speed water flow is supplied to suppress the formation of a water vapor film, but since the generation of the water vapor film cannot be eliminated in principle, the cooling rate tends to be limited compared to the single roll method.

In addition, in the case of an alloy ribbon obtained by the single roll method, by controlling the thickness of the alloy ribbon to about 20 μm, it is easy to maintain a constant cooling rate with good reproducibility and to obtain an amorphous alloy. In contrast, in the case of an alloy powder obtained by the atomization method, it is difficult to control the particle size or to make the particle size uniform, and the particle size tends to vary, resulting in a powder with a particle size distribution of sub-μm to several hundreds of μm.
The ideal structure of the obtained alloy powder is an amorphous phase or a mixed structure in which a fine crystalline (Fe-Si) bcc phase is precipitated in part of the amorphous phase (primary fine crystalline alloy with a nanoheterostructure).
Generally, small particles have a fast cooling rate, while large particles (especially the interior) have a slow cooling rate. Relatively small particles tend to produce alloy powder with an ideal structure. On the other hand, large particles tend to have an insufficient cooling rate, which tends to result in an alloy in which Fe ₂ B crystals are precipitated, which deteriorates the magnetic properties.
In alloy powder containing a large amount of Fe ₂ B crystals in the structure, even if fine crystal grains are precipitated by heat treatment in a later step, the magnetic properties may not achieve low core loss.

(b) When used in magnetic cores for high frequency applications, the phenomenon in which high frequency magnetic flux flows only near the surface of the particles (skin effect) becomes prominent. In powder form, the larger the particle size and the smaller the specific surface area, the greater the impact. If the powder surface reaches magnetic saturation, the particles will lose their function as a magnetic material, so it is preferable to use particles made of an alloy composition with a high saturation magnetic flux density Bs. However, such alloy compositions have a high Fe content, making it difficult to obtain an alloy with an ideal structure.

Therefore, an object of the present invention is to provide an Fe-based alloy composition that can stably provide an alloy powder having an amorphous phase or a mixed structure of an amorphous phase and a fine crystalline phase and in which the formation of Fe ₂ B crystals is suppressed when the molten metal is rapidly solidified to form an alloy powder. It is also an object of the present invention to provide a powder of the Fe-based alloy composition obtained by heat treating the above-mentioned alloy powder. It is also an object of the present invention to provide a magnetic core having excellent magnetic properties by using the powder of the Fe-based alloy composition.

As a result of intensive research in view of the above object, the inventors discovered that the above problems could be solved by the following Fe-based alloy composition, powder of the Fe-based alloy composition, and magnetic core, and arrived at the present invention.

That is, the present invention provides:
The Fe-based alloy composition has an alloy composition of Fe _{100-a-b-c-d-e-f} Cu _a Si _b B _c Cr _d Sn _e M _f (wherein M is at least one of Nb and Mo, and a, b, c, d, e and f satisfy, in atomic %, 0.6≦a≦1.8, 2.0≦b≦10.0, 11.0≦c≦17.0, 0≦d≦2.0, 0.01≦e≦1.5, and 0<f<1.0), and contains 77 atomic % or more of Fe.

In addition, it is preferable that the alloy powder has a Cr content of 0.1≦d≦2.0, or the M content of 0.1≦f<1.0.

The powder made of the Fe-based alloy composition preferably has an average particle size d50, which is the particle size corresponding to an accumulated frequency of 50 volume %, of 30 μm or less in an accumulated distribution curve showing the relationship between particle size and accumulated frequency from the small particle size side, determined by a laser diffraction method.
The powder is preferably an Fe-based alloy composition having 20% by volume or more of fine crystal grains of the (Fe-Si) bcc phase with an average crystal grain size of 10 to 50 nm in the alloy structure.

The magnetic core of the present invention is a magnetic core made using powder of the Fe-based alloy composition.

The magnetic core preferably has a core loss (2 MHz, 30 mT) of less than 10,000 kW/ ^m3 .

According to the Fe-based alloy composition of the present invention, when a molten metal is rapidly solidified to obtain an alloy powder, it is possible to obtain an alloy powder having an amorphous phase or a mixed structure of an amorphous phase and a fine crystalline phase, and in which the formation of crystals of Fe ₂ B is suppressed. By using the powder of the Fe-based alloy composition obtained by heat treating this alloy powder, a magnetic core having excellent magnetic properties can be obtained.

1 is a transmission electron microscope (TEM) image of a cross section of the Fe-based nanocrystalline alloy powder after heat treatment of the alloy powder of Example 2. 2 is a transmission electron microscope (TEM) image of a cross section of the Fe-based nanocrystalline alloy powder after heat treatment of the alloy powder of Example 2, which is an enlarged view of FIG. 1. FIG. 4 is an electron diffraction pattern observed by a transmission electron microscope (TEM) of a cross section of the Fe-based nanocrystalline alloy powder after the heat treatment of the alloy powder of Example 2. 1 is a transmission electron microscope (TEM) image of a cross section of the Fe-based nanocrystalline alloy powder after heat treatment of the alloy powder of Example 7. FIG. 5 is a transmission electron microscope (TEM) image of a cross section of the Fe-based nanocrystalline alloy powder after heat treatment of the alloy powder of Example 7, which is an enlarged view of FIG. 1 shows an electron diffraction pattern observed by a transmission electron microscope (TEM) of a cross section of the Fe-based nanocrystalline alloy powder after the heat treatment of the alloy powder of Example 7. 2 is a transmission electron microscope (TEM) image of a cross section of the Fe-based nanocrystalline alloy powder after heat treatment of the alloy powder of Comparative Example 1. 8 is a transmission electron microscope (TEM) image of a cross section of the Fe-based nanocrystalline alloy powder after heat treatment of the alloy powder of Comparative Example 1, which is an enlarged view of FIG. 7. FIG. 2 is an electron diffraction pattern observed by a transmission electron microscope (TEM) of a cross section of the Fe-based nanocrystalline alloy powder after the heat treatment of the alloy powder of Comparative Example 1. 1 shows X-ray diffraction patterns of the Fe-based nanocrystalline alloy powders after heat treatment in Example 2 and Comparative Example 1, with the upper side showing Example 2 and the lower side showing Comparative Example 1.

Hereinafter, the Fe-based alloy composition, the powder of the Fe-based alloy composition, and the magnetic core of the present invention will be described in detail with reference to embodiments thereof. However, the present invention is not limited to these embodiments and can be appropriately modified within the scope of the technical concept.
In this specification, a numerical range expressed using "to" means a range including the numerical values described before and after "to" as the lower and upper limits. In the numerical ranges described in stages in this specification, the upper limit or lower limit described in one numerical range may be replaced with the upper limit or lower limit of another numerical range described in stages. In addition, in the numerical ranges described in this specification, the upper limit or lower limit of the numerical range may be replaced with a value shown in the examples.

[1] Composition The Fe-based alloy composition of this embodiment has an alloy composition of Fe _{100-a-b-c-d-e-f} Cu _a Si _b B _c Cr _d Sn _e M _f (wherein M is at least one of Nb and Mo, and a, b, c, d, e, and f satisfy, in atomic %, 0.6≦a≦1.8, 2.0≦b≦10.0, 11.0≦c≦17.0, 0≦d≦2.0, 0.01≦e≦1.5, and 0<f<1.0), and contains 77 atomic % or more of Fe. The alloy composition of the powder of the Fe-based alloy composition of this embodiment is also the same.

According to the Fe-based alloy composition, even in the atomization method in which the cooling rate is more likely to be limited than in the single roll method, it is easy to obtain an ideal amorphous phase (single phase) alloy or an alloy with a mixed structure in which the (Fe-Si) bcc phase of a fine crystal phase is precipitated in a part of the amorphous phase (nanoheterostructure primary microcrystalline alloy) by rapidly solidifying the molten metal. The (Fe-Si) bcc phase is an FeSi solid solution with a body-centered cubic structure. In addition, it is possible to obtain a powder of the Fe-based alloy composition in which the formation of Fe ₂ B crystals is suppressed in the alloy structure.
The fine crystal phase is a fine (Fe-Si) bcc phase, and in the state where the molten metal is rapidly solidified, it is observed in the form of grains of less than 10 nm by a transmission electron microscope (TEM). It is also called a cluster, and is an area rich in Fe and Si. In this specification, unless otherwise specified, the alloy powder of the Fe-based alloy composition obtained by rapid solidification from the molten metal is called "alloy powder", and as described later, the alloy powder obtained by heat treating this "alloy powder" and having an alloy structure containing a relatively large amount of the fine crystalline phase (Fe-Si) bcc phase in the alloy structure compared to the alloy powder is called "Fe-based nanocrystalline alloy powder".

Here, the alloy powder in which the formation of Fe ₂ B crystals is suppressed refers to a state in which no Fe ₂ B crystals are formed or a state in which an extremely small amount of fine Fe ₂ B crystals are precipitated.
The state where Fe ₂ B crystals are not generated refers to a state where, as a result of X-ray diffraction (XRD) measurement, no Fe ₂ B peak is confirmed, and the peak intensity of the diffraction peak is equal to or lower than the noise level (X-ray scattering obtained unavoidably) forming the baseline. The state where a very small amount of Fe ₂ B fine crystals are precipitated refers to a state where the peak intensity of the Fe ₂ B diffraction peak is slightly higher than the noise level (X-ray scattering obtained unavoidably) forming the baseline. In the case of a mixed phase, the state where, in the X-ray diffraction (XRD) measurement of the alloy powder, the intensity of the diffraction peak of the (002 plane) of Fe ₂ B is 3% or less with respect to the intensity (100%) of the diffraction peak of the (Fe-Si) bcc phase (110 plane). In the alloy powder of this embodiment, the intensity of these diffraction peaks is more preferably 2% or less.

By subjecting the alloy powder to the heat treatment described below, it is possible to obtain a Fe-based nanocrystalline alloy powder having a fine crystalline phase with an average crystal grain size D of 10 to 50 nm. The fine crystalline phase is a (Fe-Si) bcc phase, which is obtained by crystallizing an amorphous phase from a Cu cluster (Cu-rich region) as the starting point, or is a phase in which the fine crystalline phase of the mixed structure has grown. The alloy structure of the Fe-based nanocrystalline alloy powder of this embodiment may consist of only a fine crystalline phase, or may be a mixed structure consisting of a fine crystalline phase and an amorphous phase. In other words, the Fe-based nanocrystalline alloy powder does not need to have a fine crystalline structure with an average crystal grain size D of 10 to 50 nm in all regions of the alloy structure of the powder, and it is sufficient that it has 20 vol% or more. It is sufficient that the fine crystalline structure has an average crystal grain size D of 10 to 50 nm in the region of preferably 30 vol% or more, more preferably 40 vol% or more, more preferably 50 vol% or more, and most preferably 60 vol% or more.

The average crystal grain size D of the fine crystal phase was determined by determining the half-width (radian angle) of the peak in the diffraction plane (110) of (Fe-Si) bcc from the X-ray diffraction (XRD) pattern of the Fe-based nanocrystalline alloy powder, and using the following Scherrer formula:
D = 0.9 × λ / ((half width) × cos θ)
[λ: X-ray wavelength of the X-ray source. For example, λ = 0.1789 nm for the CoKα X-ray source, λ = 0.15406 nm for the CuKα1 X-ray source, and θ represents the Bragg angle (half of the diffraction angle 2θ).]
It can be calculated by:
The volume fraction of the fine crystal phase is a value calculated by observing the alloy structure with a transmission electron microscope (TEM), adding up the areas of the fine crystal phases, and calculating the ratio of this to the area of the observed field.

In the Fe-based nanocrystalline alloy powder of this embodiment, the volume fraction of the fine crystalline phase with an average crystal grain size D of 10 to 50 nm is 20% or more relative to the entire region of the alloy structure of the powder, but may be approximately 20% to 60%, or may be 60% or more. The portion other than the fine crystalline structure is mainly an amorphous phase structure. In addition, coarse crystal grains such as a dendrite phase may be present in some areas to the extent that they do not affect the magnetic properties.

The composition range of the Fe-based alloy composition described above is explained in detail below.

Fe is the main element that determines the saturation magnetic flux density Bs. To obtain a high saturation magnetic flux density Bs, the Fe content is preferably 77.0 atomic % or more. More preferably, the Fe content is 79.0 atomic % or more. In addition to Fe, the value of (100-a-b-c-d-e-f) in the formula representing the alloy composition includes impurities other than the elements that define the alloy composition. The total content of these impurities is preferably 0.2 atomic % or less, and more preferably 0.1 atomic % or less.

In order to uniformly generate Cu clusters in the alloy structure, which are the starting points for the formation of a fine crystal phase from an amorphous phase, the Cu content is set to 0.6 atomic % or more. The Cu content is preferably 0.7 atomic % or more, more preferably 0.8 atomic % or more, more preferably 1.0 atomic % or more, and even more preferably 1.15 atomic % or more. On the other hand, if the Cu content exceeds 1.8 atomic %, relatively large crystals are likely to be generated in the alloy powder after rapid solidification (before heat treatment), which may grow into coarse crystal grains after heat treatment, leading to deterioration of the magnetic properties of the Fe-based nanocrystalline alloy powder. Therefore, in order to suppress the generation of coarse crystal grains after heat treatment, the Cu content is set to 1.8 atomic % or less. The Cu content is preferably 1.6 atomic % or less, and even more preferably 1.5 atomic % or less.

Sn is an element that enhances the effect of uniformly generating Cu clusters, which are the starting points for the formation of fine crystal phases, within the alloy structure. It also has the effect of suppressing the generation of coarse crystal grains after heat treatment. In other words, even in areas where the Cu concentration is relatively low in the amorphous phase, the presence of Sn can facilitate the generation of uniform fine crystals within the alloy structure. Furthermore, magnetic cores made using Fe-based nanocrystalline alloy powder containing Sn tend to have small core loss.

The Sn content is 0.01 atomic % or more to realize the above-mentioned action and effect. The Sn content is preferably 0.05 atomic % or more, more preferably 0.10 atomic % or more, even more preferably 0.15 atomic % or more, and even more preferably 0.20 atomic % or more. On the other hand, the Sn content is 1.5 atomic % or less to obtain a high saturation magnetic flux density. The Sn content is more preferably 1.0 atomic % or less, even more preferably 0.8 atomic % or less, and even more preferably 0.7 atomic % or less. If the Sn content exceeds the Cu content, the above-mentioned action and effect are suppressed, so it is preferable that Sn does not exceed the Cu content (i.e., e≦a).

Si is an element that forms an alloy with Fe as a fine crystal phase by heat treatment, forming the (Fe-Si) bcc phase. It is also an element that affects the ability to form an amorphous phase during rapid solidification. In order to reproducibly form an amorphous phase after rapid solidification, the Si content is set to 2.0 atomic % or more. The Si content is preferably 3.0 atomic % or more, and more preferably 3.5 atomic % or more. On the other hand, in order to ensure reproducibility of the viscosity of the molten alloy and uniformity and reproducibility of the particle size of the alloy powder generated by rapid solidification, the Si content is set to 10.0 atomic % or less. The Si content is preferably 8.0 atomic % or less, and more preferably 7.0 atomic % or less.

B (boron) is an element that acts on the amorphous forming ability during rapid solidification, similar to Si. In addition, B is also a major element in the action of making Cu atoms, which are the nuclei of fine crystals, uniformly present in the alloy structure (in the amorphous phase) without uneven distribution. In order to form an amorphous phase after rapid solidification with good reproducibility and to make Cu atoms uniformly present in the amorphous phase, the B content is set to 11.0 atomic % or more. The B content is preferably 11.5 atomic % or more, and more preferably 11.7 atomic % or more. In addition, in order to obtain a high saturation magnetic flux density Bs, the B content is set to 17.0 atomic % or less, although it is related to the total amount with the Si content described later. The B content is preferably 15.5 atomic % or less.

Since the contents of Si and B in the alloy composition are relatively high, they have a large effect on the Fe content. In other words, as the Si content and B content increase, the Fe content decreases relatively, and the saturation magnetic flux density Bs of the resulting Fe-based nanocrystalline alloy powder decreases. To obtain a high saturation magnetic flux density Bs, the total amount of Si content and B content is preferably 20.0 atomic % or less (i.e., b + c ≦ 20.0), more preferably 19.0 atomic % or less (b + c ≦ 19.0), and even more preferably 18.5 atomic % or less (b + c ≦ 18.5).

Cr is effective in improving the corrosion resistance of the alloy powder. In addition, Cr is effective in improving the DC superposition characteristics of the magnetic core made using the Fe-based nanocrystalline alloy powder. Therefore, in order to obtain the above effect, it is preferable to contain Cr. Note that Cr is a selective element and may be 0 atomic %. When Cr is contained, in order to obtain the above effect, it is preferable that the Cr content is 0.1 atomic % or more. The Cr content is more preferably 0.2 atomic % or more, even more preferably 0.3 atomic % or more, and even more preferably 0.4 atomic % or more. On the other hand, since Cr does not contribute to improving the saturation magnetic flux density, it is set to 2.0 atomic % or less. The Cr content is preferably 1.5 atomic % or less, more preferably 1.3 atomic % or less, more preferably 1.2 atomic % or less, and more preferably 1.0 atomic % or less.

Both Nb and Mo are elements that, when contained in the amorphous phase, have the effect of improving the thermal stability of the amorphous phase. By replacing Fe with Nb, it becomes easier to avoid the precipitation of Fe ₂ B during the quenching process in which the molten metal is rapidly solidified to form an alloy powder. In addition, there is an effect of raising the temperature at which Fe ₂ B starts to precipitate from the amorphous phase (precipitation start temperature Tx2) by about 30°C per atomic %. When Fe is replaced with Mo, the effect is slightly inferior, but there is an effect of raising Tx2 by about 15 to 20°C per atomic %. As a result, in addition to making it easier to avoid the precipitation of Fe ₂ B during the quenching process, the heat treatment temperature range is also widened during heat treatment for the purpose of crystallization, so the temperature control range during heat treatment is also widened, and the effect of improving manufacturing efficiency can be expected. In addition, the inventor's research has confirmed that Mo not only has the effect of increasing Tx2, but also has a tendency to make the shape of the powder more spherical, which is considered to be effective in increasing the packing rate when the alloy powder is compressed. On the other hand, since both Nb and Mo are paramagnetic elements with large atomic weights, the saturation magnetic flux density decreases by about 4% when substituted with 1 atomic %. Considering the above tendency, the content of M (at least one of Nb and Mo) is preferably 0<f<1.0 atomic %, and in order to fully obtain the effects of increasing Tx2 and stabilizing the shape, it is preferably 0.1 atomic % or more, and more preferably 0.25 atomic % or more. On the other hand, in order to reduce the effect of the drop in saturation magnetic flux density, it is preferably 0.9 atomic % or less, and more preferably 0.75 atomic % or less.

[2] Alloy Powder (1) Manufacturing Method The alloy powder of this embodiment can be obtained by rapidly solidifying a molten alloy having the above-mentioned alloy composition by an atomization method, etc. This manufacturing method will be described in detail below.

First, the raw elements of pure iron, ferroboron, ferrosilicon, etc. are mixed to obtain the desired alloy composition, and then heated in an induction heating furnace or the like and melted above the melting point to obtain a molten alloy having the alloy composition.

This molten alloy is rapidly cooled and solidified by atomization or other methods to produce alloy powder. Various types of atomization are known, and the production conditions can be appropriately selected from known production techniques.

The alloy powder of the Fe-based alloy composition obtained by the above method has a single amorphous phase or a mixed structure in which fine crystals of the (Fe-Si) bcc phase are precipitated in the amorphous phase, and the formation of Fe ₂ B crystals is suppressed.

The particles obtained by the atomization method are close to spherical, and it is known that the cooling rate is highly dependent on the particle size. When the pulverized molten metal passes at high speed through a liquid or gas (e.g., water, He, or steam) that has a higher heat exchange efficiency than air, the surface is cooled at a high cooling rate. The inside is also cooled due to heat conduction, but the cooling rate varies, and a difference occurs between the cooling rate of the surface layer, which solidifies first, and the cooling rate of the center, which solidifies later. The larger the diameter of the obtained alloy particles, the more noticeable the variation in cooling rate becomes. For this reason, the Fe-based alloy composition of the present invention has a composition range that is compatible with this manufacturing method.

[3] Fe-based nanocrystalline alloy powder (1) Heat treatment The Fe-based nanocrystalline alloy powder of the present embodiment is obtained by heat treating the alloy powder to form fine crystals. The heat treatment conditions for the fine crystallization are as follows.

(a) Heating Rate 1) When carrying out the heat treatment required for fine crystallization, a heating rate of about 0.1 to 1000° C./sec is preferred.
2) The alloy powder is placed in a container that does not react with the alloy powder and heat-treated as one batch. When the depth of the alloy powder per unit area exceeds 10 mm, it is preferable to control the heating rate to about 0.1 to 1°C/sec, taking into consideration the temperature rise due to heat generation caused by microcrystallization.
3) When the alloy powder is continuously heat-treated in a rotary grinder or the like, it is preferable to control the heat treatment rate to 1 to 1000° C./sec depending on the volume of alloy powder transported per unit time (flow rate of alloy powder).

(b) Holding temperature (fine crystallization temperature)
The holding temperature is the temperature Tx1 (the temperature at which the first (lower temperature side) exothermic peak (the exothermic peak due to the precipitation of the fine crystalline phase) appears, as measured by a differential scanning calorimeter (DSC) (heating rate: 20° C./min). The temperature is preferably equal to or higher than the crystallization temperature and lower than the temperature Tx2 at which the second (higher temperature) exothermic peak (exothermic peak due to the precipitation of Fe ₂ B crystals or coarse crystals) appears.

(c) Holding Time When the alloy powder is heat-treated in one batch, the holding time at the holding temperature may be appropriately set depending on the processing amount so that the alloy powder reaches the holding temperature, and is preferably 5 to 60 minutes. When the alloy powder is heat-treated continuously, a shorter time is sufficient than when the alloy powder is heat-treated in one batch. The time for holding at the maximum reaching temperature is preferably between 1 and 300 seconds.

(d) Cooling rate The Fe-based nanocrystalline alloy powder is cooled to a temperature of about 100° C. or less, but the cooling rate does not have a significant effect on the magnetic properties of the alloy powder, so there is no need to control it. Considering productivity, the cooling rate may be, for example, 200 to 1000° C./hour.

(e) Heat Treatment Atmosphere The heat treatment atmosphere is preferably a non-oxidizing atmosphere such as nitrogen gas.

The above heat treatment conditions allow for stable and reproducible production of Fe-based nanocrystalline alloy powder.

(f) Average particle diameter d50
The Fe-based nanocrystalline alloy powder of the present embodiment preferably has an average particle size d50 of 30 μm or less. Note that the average particle size d50 of the Fe-based nanocrystalline alloy powder is substantially the same before and after the heat treatment for microcrystallization. Since this does not change, it can also be regarded as the average particle size d50 of the alloy powder.
The alloy powder of the present embodiment obtained by a method such as atomization often has a wide particle size distribution, with the particle size not being uniform. The average particle size d50 is the value at which the cumulative frequency reaches 50% by volume in a cumulative distribution curve showing the relationship between particle size and cumulative frequency from the small particle size side, which is determined by a laser diffraction method. The median diameter is the corresponding particle diameter. A laser diffraction/scattering type particle size distribution measuring device (for example, LA-920 manufactured by Horiba, Ltd.) can be used as the measuring device.

The alloy powder or Fe-based nanocrystalline alloy powder is classified and overcut to remove large particles, thereby adjusting the average particle size d50 to 30 μm or less. It is more preferable that the average particle size d50 is 29 μm or less, and even more preferable that the average particle size d50 is 28 μm or less.

The average particle size d50 of this alloy powder or Fe-based nanocrystalline alloy powder can be, for example, 20 μm or less, 15 μm or less, 10 μm or less, or even 5 μm or less, or 1 μm or less, by classification. On the other hand, if the average particle size d50 is too small, it may not be possible to obtain the desired magnetic properties of the Fe-based nanocrystalline alloy powder. For example, the average particle size d50 is 0.1 μm or more, which exceeds 0.05 μm, which is generally defined as the magnetic domain width, and is preferably 0.3 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more.

The suitable size of the alloy powder or Fe-based nanocrystalline alloy powder varies depending on the application, so it is preferable to classify the powder to obtain a suitable particle size depending on the application. Therefore, the average particle size d50 of the alloy powder or Fe-based nanocrystalline alloy powder can be set appropriately depending on the application. In addition, the particle size range (upper and lower limits of the particle size) can be set appropriately by classification.

(g) Alloy powder with adjusted particle size For example, the alloy powder (or Fe-based nanocrystalline alloy powder) can be classified with a sieve so that the powder with a particle size of more than 40 μm is 10% by mass or less of the entire powder, the powder with a particle size of more than 20 μm and less than 40 μm is 30% by mass or more and 90% by mass or less of the entire powder, and the powder with a particle size of 20 μm or less is 5% by mass or more and 60% by mass or less of the entire powder. Since it may be difficult to obtain a stable amorphous phase or a mixed structure of an amorphous phase and a fine crystal phase with an alloy powder with a particle size of more than 40 μm, it is preferable that the powder with a particle size of more than 40 μm is 10% by mass or less. It is more preferable that the powder with a particle size of more than 40 μm is 5% by mass or less, and most preferably 0% by mass. In other words, the alloy powder and the Fe-based nanocrystalline alloy powder of this embodiment may contain powder that is not in an amorphous phase or a mixed structure of an amorphous phase and a fine crystalline phase, or powder that does not have a structure in which the alloy structure contains 20 volume % or more of fine crystal grains of the (Fe-Si) bcc phase with an average crystal grain size of 10 to 50 nm.

By adjusting the particle size distribution of the Fe-based nanocrystalline alloy powder, the desired magnetic properties can be obtained. For example, if the powder contains a large number of particles with a particle size of 20 μm or less, an Fe-based nanocrystalline alloy powder suitable for magnetic cores for high frequency applications can be obtained, and if the powder contains a large number of particles with a particle size of more than 20 μm and less than 40 μm, an Fe-based nanocrystalline alloy powder suitable for magnetic cores with high initial permeability μi and excellent DC superposition properties can be easily obtained.

[4] Magnetic core (1) Magnetic core powder The Fe-based nanocrystalline alloy powder of this embodiment can be used alone as a magnetic core powder. In addition, by mixing the Fe-based nanocrystalline alloy powder of this embodiment with powder of another soft magnetic material, the different magnetic characteristics of each material can be utilized and complemented, and when used as a magnetic core, the magnetic core powder can be used to improve the superposition characteristics while suppressing the increase in magnetic core loss and the decrease in magnetic permeability.

Other examples of soft magnetic material powders include Fe-based amorphous alloy powders, and powders of crystalline metal-based soft magnetic materials such as pure iron, Fe-Si, and Fe-Si-Cr.

(2) Preparation of magnetic core: Fe-based nanocrystalline alloy powder is mixed with a binder such as silicone resin and an organic solvent, granulated, and then the organic solvent is evaporated to obtain granules. The granules are filled into a press die and pressed into a molded body. The molded body is heated to harden the binder, and the magnetic core is obtained.

Other examples of binders include, but are not limited to, epoxy resin, unsaturated polyester resin, phenol resin, xylene resin, diallyl phthalate resin, polyamide-imide, polyimide, water glass, etc. A lubricant such as zinc stearate may be mixed into the mixture of magnetic core powder and binder, if necessary. The mixture is molded into a desired shape at a molding pressure of about 1 MPa to 2 GPa using a hydraulic press molding machine or the like. The molded body is then heat-treated for about 1 hour at a temperature of 300°C to a temperature lower than the microcrystallization temperature Tx1 to remove molding distortion and harden the binder to obtain a magnetic core. The heat treatment atmosphere in this case may be an inert atmosphere or an oxidizing atmosphere. The obtained magnetic core may be an annular body such as a circular ring or a rectangular frame, or may be a rod or plate, or may have a more complex shape, and the shape can be selected in various ways depending on the purpose.

The coil may be embedded in a mixture containing magnetic core powder and a binder and molded as a single unit. For example, if a thermoplastic resin or a thermosetting resin is appropriately selected as the binder, a metal composite core (coil component) with a coil sealed therein can be easily produced by known molding methods such as injection molding.

In either case, the resulting magnetic core has excellent magnetic properties and is suitable for use in inductors, noise filters, choke coils, transformers, reactors, etc.

(3) Saturation magnetic flux density Bs
The Fe-based nanocrystalline alloy powder of this embodiment preferably has a saturation magnetic flux density Bs of 1.45 T or more. More preferably, it is 1.47 T or more, even more preferably, it is 1.48 T or more, and even more preferably, it is 1.50 T or more. The saturation magnetic flux density Bs is the maximum value of B in a B-H loop obtained by applying a magnetic field H up to 800 kA/m. It may also be calculated from the saturation magnetization Ms in an M-H loop (magnetization curve) obtained by applying a magnetic field H up to 800 kA/m using a VSM (vibrating sample magnetometer).

(4) Core Loss The magnetic core produced using the Fe-based nanocrystalline alloy powder of this embodiment preferably has a core loss of less than 10,000 kW/ ^m3 under conditions of a frequency of 2 MHz and a magnetic flux density of 30 mT. More preferably, the core loss is 9,500 kW/ ^m3 or less, and even more preferably, the core loss is 9,000 kW/ ^m3 or less.

(5) DC Superposition Characteristics After winding an insulating coated conductor wire with a predetermined number of turns around a magnetic core made using the Fe-based nanocrystalline alloy powder of this embodiment, the two ends of the conductor wire are connected to an LCR meter and a DC current source, and the inductance L at each superposition current can be measured. The magnetic path length and cross-sectional area are calculated from the magnetic core shape, and the magnetic permeability μ can be obtained from the inductance L. When no DC superposition current is applied, the initial magnetic permeability μi (magnetic field strength H=0 A/m) can be measured. In addition, with a superposition current that generates a DC magnetic field with a magnetic field strength H=10 kA/m, the magnetic permeability μ10k can be measured.

In the magnetic core of this embodiment, the magnetic permeability μ10k of the magnetic core is preferably 12.5 or more, more preferably 12.8 or more, and more preferably 13.5 or more. μ10k/μi (an index also known as incremental magnetic permeability Δμ) is preferably 0.88 or more, more preferably 0.89 or more, and even more preferably 0.90 or more. The initial magnetic permeability μi is preferably 9.0 or more, more preferably 10.0 or more, even more preferably 11.0 or more, even more preferably 12.0 or more, even more preferably 13.0 or more, even more preferably 14.0 or more, even more preferably 14.5 or more, and even more preferably 15.0 or more.

The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

(1) Examples 1 to 5 and Comparative Example 1
The Fe-based alloy compositions were prepared by blending the various elemental raw materials such as pure iron, ferroboron, and ferrosilicon so as to obtain the alloy compositions A to F shown in Table 1, heating them in an induction heating furnace, and melting the molten alloy at or above the melting point, followed by rapid solidification using the rapid solidification device (jet atomization device) described in Patent Document 3, to obtain alloy powders. The estimated temperature of the flame jet was 1300 to 1600° C., and the amount of water injected was 4 to 5 liters/min.
Table 1 also shows the temperature Tx1 (microcrystallization temperature) at which the first exothermic peak appears and the temperature Tx2 at which the second (higher temperature) exothermic peak appears, which were measured by a differential scanning calorimeter (DSC) (heating rate: 20° C./min).

The obtained alloy powder was classified using a sieve with 32 μm mesh. The particle size distribution of each alloy powder that passed through the sieve was evaluated using a laser diffraction scattering type particle size distribution measuring device (LA-920 manufactured by Horiba, Ltd.). The average particle size d50 of each alloy powder was the value shown in Table 2. Table 2 also shows d90, which is the particle size corresponding to an accumulated frequency of 90% by volume.

As a result of X-ray diffraction (XRD) measurement, it was confirmed that the alloy powders of Examples 1 to 5 were composed of a mixed structure of an amorphous phase and a (Fe-Si) bcc peak of a fine crystal phase. The peak of Fe ₂ B could not be confirmed. Here, the (Fe-Si) bcc peak refers to the diffraction peak of the above-mentioned (Fe-Si) bcc phase (110 plane), and the peaks of Fe ₂ B (near 2θ=50° and near 67°) refer to the diffraction peak of the (002 plane) of Fe ₂ B, and the diffraction peak of the composite of the (022 plane) and (130 plane), respectively.
The alloy powder of alloy F in Comparative Example 1 was confirmed to be an amorphous phase by the above-mentioned XRD measurement, and no peak of Fe ₂ B was confirmed.

When the alloy powders of the above-mentioned classified alloys A to F were observed at 500 times magnification using a scanning electron microscope (SEM), the alloy powder within the field of view was found to be roughly spherical. Here, roughly spherical means a shape including an egg shape where the maximum diameter divided by the minimum diameter is 1.25 or less.

The alloy powders of Examples 1 to 5 and Comparative Example 1 were placed in containers made of alumina, which does not react with the alloy powder, and were heated between 300 and 400°C at an average heating rate of 0.1 to 0.2°C/sec, held at 400°C for 30 minutes, and then cooled to room temperature in about 1 hour, resulting in heat treatment to obtain Fe-based nanocrystalline alloy powder. This heat treatment was carried out in a non-oxidizing atmosphere using a batch-type electric furnace.

<Evaluation of Fe-based nanocrystalline alloy powder>
The cross sections of the obtained Fe-based nanocrystalline alloy powders of Examples 1 to 5 and Comparative Example 1 were observed. In addition, the half-width (radian angle) of the (Fe-Si) bcc peak (near 2θ = 53°) was obtained from the diffraction pattern by X-ray diffraction measurement (XRD), and the average crystal grain size was calculated by Scherrer's formula.

Figures 1 and 2 are transmission electron microscope (TEM) images of the cross section of the Fe-based nanocrystalline alloy powder of Example 2. In Figure 1, the length of the black bar at the bottom right is 100 nm. Figure 2 is an enlarged view of Figure 1, where the length of the black bar at the bottom right is 50 nm. Although it is unclear in Figure 2, a nearly spherical shape with a particle size of 10 to 50 nm can be seen in the TEM image observed directly.

Fig. 3 is an electron diffraction pattern of the cross section of the Fe-based nanocrystalline alloy powder of Example 2 observed by a transmission electron microscope (TEM). Fig. 10 shows the X-ray diffraction pattern of the Fe-based nanocrystalline alloy powder of Example 2. Fig. 10 also shows the X-ray diffraction pattern of the Fe-based nanocrystalline alloy powder of Comparative Example 1. In Fig. 10, the upper side is Example 2 and the lower side is Comparative Example 1. In Example 2, the peak of Fe ₂ B is hardly observed at the noise level. It can be seen that Example 2 does not have an Fe ₂ B phase, and is a mixed phase of a fine crystal phase and an amorphous phase.

The average crystal grain size D of the Fe-based nanocrystalline alloy powder of Example 2, calculated using Scherrer's formula, was 22 nm.

Similarly to Example 2, the Fe-based nanocrystalline alloy powders of Examples 1 and 3 to 5 also had fine crystalline structures, and no Fe ₂ B was observed. Similarly to Example 2, the average crystal grain sizes D of the fine crystalline alloy powders of Examples 1 and 3 to 5 calculated by the Scherrer formula were 30 nm, 22 nm, 26 nm, and 25 nm, respectively.

The average crystal grain size of the Fe-based nanocrystalline alloy powder of Comparative Example 1, calculated using Scherrer's formula, was 23 nm.

Transmission electron microscope (TEM) images of the cross section of the Fe-based nanocrystalline alloy powder of Comparative Example 1 are shown in Figures 7 and 8. In Figure 7, the length of the black bar at the bottom right is 100 nm. Figure 8 is an enlarged view of Figure 7, in which the length of the black bar at the bottom right is 50 nm. Also, Figure 9 shows the electron diffraction pattern of the cross section of the Fe-based nanocrystalline alloy powder of Comparative Example 1 observed with a transmission electron microscope (TEM). According to this, a clear pattern is observed, and coarsening of the crystal grains is expected.

10, a peak of Fe ₂ B was observed in Comparative Example 1. The intensity of the diffraction peak of the (002 plane) of Fe ₂ B was 6.4% of the intensity of the diffraction peak of the (Fe-Si) bcc phase (110 plane) (100%).

In Examples 1 to 5 and Comparative Example 1, X-ray diffraction measurements (XRD) were carried out using the following apparatus and under the following measurement conditions.
Device:
Rigaku Corporation RINT2500PC
Measurement condition:
X-ray source: CoKα (wavelength λ = 0.1789 nm)
Scan axis: 2θ/θ
Sampling width: 0.020°
Scan speed: 2.0°/min Divergence slit: 1/2°
Divergence vertical slit: 5 mm
Scattering slit: 1/2°
Receiving slit: 0.3 mm
Voltage: 40 kV
Current: 200mA

The saturation magnetic flux density Bs of each Fe-based nanocrystalline alloy powder in Examples 1 to 5 and Comparative Example 1 was calculated from the saturation magnetization Ms in the M-H loop (magnetization curve) obtained by applying a magnetic field H up to 800 kA/m using a VSM (vibrating sample magnetometer) manufactured by Riken Electronics Co., Ltd., and the true density of alloys A to F shown in Table 1.

The results are summarized in Table 3.

The saturation magnetic flux density Bs of Examples 1 to 5 is high, ranging from 1.48 to 1.54 T. On the other hand, Comparative Example 1, which does not contain Nb, also has a high saturation magnetic flux density of 1.55 T. In Examples 1 to 5, even though Fe was replaced with Nb to improve the amorphous forming ability, the decrease in saturation magnetic flux density Bs was kept to a minimum, and values of 95% or more were obtained compared to the comparative examples.

<Measurement of magnetic properties of magnetic core using Fe-based nanocrystalline alloy powder>
The Fe-based nanocrystalline alloy powder (Examples 1 to 5 and Comparative Example 1), silicone resin (H44 manufactured by Wacker Asahi Kasei Silicone) and ethanol were mixed in a mass ratio of 100 alloy powder, 5 silicone resin and 5.8 ethanol, and the ethanol was evaporated to form granules, which were then press molded at a pressure of 1 MPa to obtain a compact in the shape of a magnetic core with an outer diameter of 13.5 mm, an inner diameter of 7 mm and a height of 2 mm. The resin was then heated and cured at 300°C to obtain a magnetic core for measurement.

18 turns were wound around the magnetic core on both the primary and secondary sides. Using a B-H analyzer (SY-8218) manufactured by Iwasaki Electric Co., Ltd., the core loss was measured at three frequencies, 0.5 MHz, 1 MHz, and 2 MHz, and at a magnetic flux density of 30 mT. The measurement results are shown in Table 4.

In addition, 30 turns were wound around the magnetic core. A DC current in the range of 0 A to 10.5 A was superimposed using an Agilent Technologies 4284A LCR meter and an Agilent Technologies 4184A Bias Current Source. Under conditions of an applied voltage of 1 V and a frequency of 100 kHz, the inductance L (H) was determined at superimposed currents of 0 A and 10.5 A (I _DC =0 A and 10.5 A). The superimposition of a 10.5 A DC current generates a DC magnetic field with a magnetic field strength H = 10 kA/m.

From the dimensions and shape of the magnetic core, the magnetic path length (m) and the cross-sectional area (m ² ) were calculated.

The magnetic permeability μ was calculated using the formula: magnetic permeability μ=(L(H)×magnetic path length (m))/(4π×10 ⁻⁷ ×cross-sectional area (m ² )×(number of turns: 30 turns) ² ), where (4π×10 ⁻⁷ ) is the magnetic permeability μ ₀ of a vacuum (unit: H/m).

The initial permeability μi was obtained from the measured value of inductance L under the condition I _DC = 0 A, and the permeability μ10k was obtained from the measured value under the condition I _DC = 10.5 A. Table 4 shows the initial permeability μi, the permeability μ10k, and the value obtained by dividing the permeability μ10k by the initial permeability μi: μ10k/μi.

In Examples 1 to 5, the initial permeability μi (100 kHz) was 14.16 to 15.25. In addition, μ10k (100 kHz) in Examples 1 to 5 was 12.96 to 13.57, and μ10k/μi (100 kHz) was also 0.89 to 0.92, and the same results as Comparative Example 1 were obtained. On the other hand, the core loss was smaller in all of Examples 1 to 5 compared to Comparative Example 1, and in Comparative Example 1, the core loss at a frequency of 2 MHz was 10890 kW/m ³ , which exceeded 10000 kW/m ³ , but in Examples 1 to 5, values less than 10000 kW/m ³ were obtained. In Examples 1 to 5, a core loss of 9000 kW/m ³ or less was obtained.
The reason why the core loss in Examples 1 to 5 is smaller than that in Comparative Example 1 is presumably because the content of structures with high crystalline magnetic anisotropy, such as Fe ₂ B compounds, is low in Examples 1 to 5, which is significantly lower than that in Comparative Example 1.

As described above, the Fe-based nanocrystalline alloy powder of the present invention has a high saturation magnetic flux density Bs of 1.45 T or more, even though Fe is replaced with Nb to improve the amorphous forming ability, and a magnetic core with low core loss was obtained under the conditions of a frequency of 0.5 kHz to 2 MHz and a magnetic flux density of 30 mT.

(2) Examples 6 and 7, Comparative Example 2
As an Fe-based alloy composition, each element raw material such as pure iron, ferroboron, ferrosilicon, etc. was mixed so as to obtain the alloy compositions of alloys G and H shown in Table 5, and the mixture was heated in an induction heating furnace and melted at or above the melting point. The molten alloy was then rapidly solidified using the rapid solidification device (jet atomization device) described in Patent Document 3 to obtain an alloy powder. The estimated temperature of the flame jet was 1300 to 1600°C, and the amount of water injected was 4 to 5 liters/min.
Table 5 also shows the temperature Tx1 at which the first exothermic peak appears and the temperature Tx2 at which the second exothermic peak appears, as measured by a differential scanning calorimeter (DSC).

The obtained alloy powders of alloys G and H and the alloy powder of alloy F were classified using a sieve with a mesh size of 53 μm. The average particle size d50 of each alloy powder that passed through the sieve was the value shown in Table 6. Also shown in Table 6 is the d90, which is the particle size corresponding to an integrated frequency of 90 volume %. All evaluations were performed using the evaluation device and measurement conditions used in Examples 1 to 5 and Comparative Example 1.
As a result of X-ray diffraction (XRD) measurement, it was confirmed that the alloy powders of Examples 6 and 7 were composed of a mixed structure of an amorphous phase and a fine crystalline (Fe-Si) bcc phase. No peak of Fe ₂ B was confirmed.

It was confirmed by the above-mentioned XRD measurement that the alloy powder of Alloy F in Comparative Example 2 had a structure in which the Fe ₂ B phase was precipitated in part of the fine crystal phase and the amorphous phase.

When the alloy powders of the above-mentioned classified alloys G to F were observed at 500x magnification using a scanning electron microscope (SEM), the alloy powder within the field of view was generally spherical.

The alloy powders of Examples 6 and 7 and Comparative Example 2 were placed in containers made of alumina, which does not react with the alloy powder, and heated to 300°C to 400°C at an average heating rate of 0.1 to 0.2°C/sec., held at 400°C for 30 minutes, and then cooled to room temperature in about 1 hour, thereby performing heat treatment and obtaining Fe-based nanocrystalline alloy powder. This heat treatment was performed in a non-oxidizing atmosphere using a batch-type electric furnace.

<Evaluation of Fe-based nanocrystalline alloy powder>
When the cross sections of the obtained Fe-based nanocrystalline alloy powders of Examples 6 and 7 and Comparative Example 2 were observed, it was found that the particles had a nearly spherical shape with a particle size of 10 to 50 nm.
In addition, the half-width (radian angle) of the (Fe-Si) bcc peak (near 2θ = 53°) was obtained from the diffraction pattern by X-ray diffraction measurement (XRD), and the average crystal grain size was calculated by Scherrer's formula. The evaluation was performed using the evaluation device and measurement conditions used in Examples 1 to 5 and Comparative Example 1.

Figures 4 and 5 show transmission electron microscope (TEM) images of the cross section of the Fe-based nanocrystalline alloy powder of Example 7. In Figure 4, the length of the black bar at the bottom right is 100 nm, and Figure 5 is an enlarged view of Figure 4, where the length of the black bar at the bottom right is 50 nm. Figure 6 shows the electron diffraction pattern of the cross section of the Fe-based nanocrystalline alloy powder of Example 7 observed with a transmission electron microscope (TEM).

The average crystal grain size D of the Fe-based nanocrystalline alloy powders of Example 6 (Alloy G) and Example 7 (Alloy H), calculated using Scherrer's formula, was 23 nm. The average crystal grain size of the Fe-based nanocrystalline alloy powder of Comparative Example 2 was 24 nm.

No Fe ₂ B was observed in the Fe-based nanocrystalline alloy powders of Examples 6 and 7. In Comparative Example 2, a peak of Fe ₂ B was observed in X-ray diffraction measurement (XRD). The intensity of the diffraction peak of the (002 plane) of Fe ₂ B was 3.5% of the intensity of the diffraction peak of the (Fe-Si) bcc phase (110 plane) (100%).

The saturation magnetic flux density Bs of the Fe-based nanocrystalline alloy powders in Examples 6 and 7 and Comparative Example 2 was calculated based on the saturation magnetization Ms.

The results are summarized in Table 7.

The saturation magnetic flux density Bs of Examples 6 and 7 was high at 1.53 T and 1.57 T, despite the replacement of Fe with Nb and Mo to improve the amorphous forming ability.

<Measurement of magnetic properties of magnetic core using Fe-based nanocrystalline alloy powder>
The Fe-based nanocrystalline alloy powder (Examples 6, 7 and Comparative Example 2), silicone resin (H44 manufactured by Asahi Kasei Wacker Silicone) and ethanol were mixed in a mass ratio of 100 alloy powder, 5 silicone resin and 5.8 ethanol, the ethanol was evaporated to form granules, and the granules were press molded under a pressure of 1 MPa to obtain a molded body having an outer diameter of 13.5 mm, an inner diameter of 7 mm and a height of 2 mm. The resin was then heated and cured at 300°C to obtain a magnetic core for measurement.

The core loss (kW/m ³ ) was measured using this magnetic core. In addition, the inductance L (H) was calculated at superimposed currents of 0 A and 10.5 A (I _DC = 0 A and 10.5 A). The initial permeability μi was calculated from the inductance L value under the measurement condition I _DC = 0 A, and the permeability μ10k was calculated from the inductance L value under the measurement condition I _DC = 10.5 A. Table 8 shows the measurement results.

In Examples 6 and 7, the initial permeability μi (100 kHz) was 15.6, μ10k (100 kHz) was 13.8 and 14.0, respectively, and μ10k/μi (100 kHz) was 0.89 and 0.90. Thus, the initial permeability μi was higher than that of Comparative Example 2. The core loss was smaller than that of Comparative Example 2, and both Examples 6 and 7 had smaller core losses than Examples 1 to 5.
In particular, in Example 6, the amount of Nb is half or less of the other examples, and the saturation magnetic flux density Bs is high. Example 7 uses Mo as the M element, but compared to Example 2 using Nb, the saturation magnetic flux density Bs and initial permeability μi are high, and a small core loss is obtained, resulting in a high effect of improving the soft magnetic properties.

Claims (6)

An Fe-based alloy composition having an alloy composition of Fe _{100-a-b-c-d-e-f} Cu _a Si _b B _c Cr _d Sn _e M _f (wherein M is at least one of Nb and Mo, and a, b, c, d, e and f satisfy, in atomic %, 0.6≦a≦1.8, 2.0≦b≦10.0, 11.0≦c≦17.0, 0≦d≦2.0, 0.01≦e≦1.5, and 0<f<1.0), and containing 77 atomic % or more of Fe. The Fe-based alloy composition according to claim 1, wherein the amount of Cr is 0.1≦d≦2.0, or the amount of M is 0.1≦f<1.0. A powder made of the Fe-based alloy composition according to claim 1 or 2,
A powder of an Fe-based alloy composition, in which an average particle size d50, which is the particle size corresponding to a cumulative frequency of 50 volume %, is 30 μm or less in a cumulative distribution curve showing the relationship between particle size and cumulative frequency from the small particle size side, obtained by a laser diffraction method. A powder of the Fe-based alloy composition according to claim 3,
A powder of an Fe-based alloy composition having 20% by volume or more of fine crystal grains of (Fe-Si) bcc phase with an average crystal grain size of 10 to 50 nm in the alloy structure. A magnetic core using powder of the Fe-based alloy composition according to claim 3 or 4. 6. The magnetic core according to claim 5, having a core loss (2 MHz, 30 mT) of less than 10,000 kW/ ^m3 .

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