JP2019090103A - Soft magnetic metal powder, production method thereof and soft magnetic metal dust core - Google Patents

Abstract

To provide a soft magnetic metal powder having a small coercive force, a high circularity and a reduced amount of fine powder, to provide a production method thereof and to provide a soft magnetic metal dust core using the soft magnetic metal powder.SOLUTION: The production method of a soft magnetic metal powder has: a raw material powder preparation step of preparing a metal raw material powder having a plurality of metal raw material particles including iron, silicon and boron; a mixing step of mixing the metal raw material powder with a carbon source substance to produce a mixed powder; and a heat treatment step of subjecting the mixed powder to heat treatment at 1,250°C or higher in a non-oxidation atmosphere including nitrogen to spheroidize the metal raw material particles.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a soft magnetic metal powder, a method of producing the same, and a soft magnetic metal powder core, and in particular, a soft magnetic metal powder suitably used for a core of an electromagnetic circuit component such as an inductor or reactor, a method of producing the soft magnetic metal It relates to a dust core.

  Ferrite cores, dust cores made of soft magnetic metal powder, laminated electromagnetic steel plates using silicon steel plates, etc. are used as reactors and core materials for inductors used in applications where large currents are applied.

  Among these magnetic core materials, soft magnetic metal compacted cores are widely used as magnetic core materials because their core loss is smaller than that of laminated electromagnetic steel sheets and their saturation magnetic flux density is larger than that of ferrite cores.

  The reactor and the inductor are required to be compatible with the miniaturization and the magnetic characteristics. As the magnetic characteristics, in particular, it is required to have high inductance even if direct current is superimposed. Therefore, the soft magnetic metal green compact core is required to have high magnetic permeability even when a DC superimposed magnetic field is applied, that is, excellent in DC superimposed characteristics.

  In order to improve the DC bias characteristics of the soft magnetic metal green compact core, it is known that increasing the density of the core, increasing the circularity of the soft magnetic metal powder used, and the like are effective. For example, Patent Document 1 describes that a powder magnetic core having excellent direct current superposition characteristics is obtained by using a soft magnetic metal powder having a high degree of circularity and a small amount of fine powder.

  In addition, since the reactor and the inductor are required to have high efficiency, the soft magnetic metal powder compact core is required to have a small core loss.

  In order to reduce the core loss of the soft magnetic metal green compact core, it is necessary to reduce both the hysteresis loss and the eddy current loss that constitute the core loss. In order to reduce the hysteresis loss, it is known that reducing the coercivity of the soft magnetic metal powder used is effective. For example, Patent Document 2 describes that the soft magnetic metal powder is heat-treated at a high temperature to reduce the coercivity and to obtain a soft magnetic metal powder core having a reduced core loss. On the other hand, in order to reduce the eddy current loss, it is effective to reduce the particle size of the soft magnetic metal powder to be used, and it is particularly effective to reduce the coarse powder.

  Therefore, the soft magnetic metal powder used for the soft magnetic metal powder compact core is required to have a small coercive force, a high degree of circularity, and a small amount of fine powder.

JP, 2016-139748, A JP, 2015-233119, A

  Patent Document 1 describes that a powder magnetic core having excellent direct current superposition characteristics can be obtained by using a soft magnetic metal powder having a high degree of circularity and a small amount of fine powder. However, Patent Document 1 only describes a method of removing fine powder by classification from metal powder having high circularity such as gas atomized powder as a specific method of obtaining such soft magnetic metal powder.

  Patent Document 2 describes that the coercivity can be reduced by heat treating the soft magnetic metal powder at a high temperature. However, the shape of the particles and the particle size distribution are determined by the properties of the raw metal powder, and these can not be improved by heat treatment.

  A water atomizing method, a gas atomizing method, etc. are known as a general manufacturing method for obtaining said metal powder.

  According to the water atomizing method, water atomized powder can be manufactured at low cost. Further, according to the water atomization method, particles are obtained by rapidly cooling and solidifying the droplets of the molten metal, so it is possible to obtain a powder having a small average particle diameter. However, the shape of the particles is indeterminate, and it is difficult to obtain particles having a spherical shape by water atomization.

  On the other hand, gas atomized powder produced by gas atomization is more expensive than water atomized powder. However, according to the gas atomization method, since the particles are obtained by relatively slowly cooling and solidifying the droplets of the molten metal, it is possible to obtain particles having a shape close to a true spherical shape. However, there is a problem that only a powder having a large average particle size can be obtained as compared to a water atomized powder produced by a water atomization method.

  Furthermore, in either of the water atomizing method and the gas atomizing method, there is a problem that the particle size distribution of the produced powder is wide and the content of fine powder is large. For example, as described in Patent Document 1, the gas atomized powder is classified, the coarse particles are removed, and the average particle diameter of the powder is reduced while the fine particles are removed, whereby the degree of circularity is high, the average A metal powder having a small particle size and a small amount of fine powder can be obtained. However, since it is necessary to remove both coarse particles and fine particles, it is not practical because the cost for classification and the waste loss of powder due to classification occur.

  Therefore, there is a problem that it is very difficult to obtain a soft magnetic metal powder having a small coercive force, a high degree of circularity, and a small amount of fine powder.

  The present invention has been made in view of such circumstances, and an object thereof is a soft magnetic metal powder having a small coercive force, a high degree of circularity and a small amount of fine powder, a method for producing the same, and a soft magnetic metal powder Providing a soft magnetic metal green compact core using the

In order to achieve the above object, a method of producing a soft magnetic metal powder according to the present invention is
[1] A raw material powder preparation step of preparing a metal raw material powder having a plurality of metal raw material particles containing iron, silicon and boron,
Mixing the metal raw material powder and the carbon source material to obtain a mixed powder;
A heat treatment step of subjecting the mixed powder to a heat treatment temperature of at least 1250 ° C. in a non-oxidizing atmosphere containing nitrogen to make the metal raw material particles into a spheroidizing method; It is.

  [2] The method of producing a soft magnetic metal powder according to [1], including a boron nitride removing step of removing a part of boron nitride contained in the soft magnetic metal powder after the heat treatment step.

  [3] In the raw material powder preparation step, the content of boron contained in 100% by mass of the metal raw material powder is 0.4% by mass or more and 2.0% by mass or less [1] or [2] It is a manufacturing method of the soft-magnetic metal powder as described in these.

  [4] The raw material powder preparation step, characterized in that the content of oxygen contained in 100% by mass of the metal raw material powder is 0.100% by mass or more and 1.000% by mass or less [1] to [3] It is a manufacturing method of the soft-magnetic metal powder in any one of these.

  [5] In the heat treatment step, a coated portion containing boron nitride is formed on the surface of the metal source particles, which is the method for producing a soft magnetic metal powder according to any one of [1] to [4].

[6] A soft magnetic metal powder having a plurality of metal particles containing iron, silicon, boron and carbon,
The content of boron contained in 100% by mass of the soft magnetic metal powder is 0.010% by mass or more and 2.0% by mass or less,
The content of carbon contained in 100% by mass of the soft magnetic metal powder is 0.010% by mass or more and 0.350% by mass or less,
Boron nitride is formed on the surface of the metal particles,
Among the metal particles, the circularity of the metal particles of 80% or more is 0.80 or more,
Among the metal particles, 85% or more of the metal particles consist of one crystal grain, which is a soft magnetic metal powder.

  [7] The soft magnetic metal powder according to [6], wherein the content of chromium contained in 100 mass% of the soft magnetic metal powder is 1 mass% or more and 10 mass% or less.

  [8] When the total content of iron and nickel contained in the soft magnetic metal powder is 100% by mass, the content of nickel is 40% by mass to 80% by mass [6] ] Or the soft-magnetic metal powder as described in [7].

  [9] The soft magnetic metal powder according to any one of [6] to [8], wherein the content of carbon contained in the metal particles is 0.010 mass% to 0.150 mass%. is there.

  [10] The soft magnetic metal powder according to any one of [6] to [9], wherein the content of oxygen contained in 100 mass% of the soft magnetic metal powder is 0.1000 mass% or less. is there.

  [11] A soft magnetic metal powder core comprising the soft magnetic metal powder according to any one of [6] to [10].

  According to the present invention, a soft magnetic metal powder having a small coercive force, a high degree of circularity, and a small amount of fine powder, a method for producing the same, and a soft magnetic metal powder compact core using the soft magnetic metal powder are provided. be able to.

FIG. 1 is a process chart showing a manufacturing method according to the present embodiment. FIG. 2 is a cross-sectional schematic view of particles constituting the metal source powder. FIG. 3 is a schematic cross-sectional view of particles constituting the mixed powder. FIG. 4 is a schematic view for explaining that boron nitride is formed on the particle surface in the initial process of the heat treatment step. FIG. 5 is a schematic view for explaining that particles are spheroidized in the spheroidizing process of the heat treatment step. FIG. 6A is a schematic view for explaining that particles are bonded in the spheroidizing process of the heat treatment step. FIG. 6B is a schematic view for explaining that particles are integrated to form one spherical particle in the spheroidizing process of the heat treatment step. FIG. 7 is a schematic cross-sectional view of particles constituting the soft magnetic metal powder after the heat treatment step. FIG. 8A is a SEM image of the appearance of the powder according to sample No. 2 in an example of the present invention. FIG. 8B is a SEM image of the appearance of the powder according to sample number 6-2 in the example of the present invention.

Hereinafter, the present invention will be described in detail in the following order based on the embodiments shown in the drawings.
1. Method of manufacturing soft magnetic metal powder 1.1. Raw material powder preparation process 1.2. Mixing process 1.3. Heat treatment process 1.3.1. Initial process 1.3.2. Spheroidization process 1.3.3. Late process 1.4. Boron nitride removal step Soft magnetic metal powder 2.1. Boron content 2.2. Carbon content 2.3. Oxygen content 2.4. Nitrogen content 2.5. Circularity of particles 2.6. Grain size of particles 2.7. Particle size distribution3. Soft magnetic metal dust core

  A method of manufacturing a soft magnetic metal powder according to the present embodiment includes: metal raw material powder composed of a plurality of metal raw material particles containing iron (Fe), silicon (Si), boron (B) and oxygen (O); The mixed powder obtained by mixing the additive serving as the source is heat-treated in a non-oxidizing atmosphere containing nitrogen. Hereinafter, the manufacturing method of the said soft-magnetic metal powder is demonstrated in detail using process drawing shown in FIG.

(1.1. Raw material powder preparation process)
First, the raw material powder is prepared. In the present embodiment, the raw material powder is a metal raw material powder having a plurality of metal raw material particles containing iron, silicon and boron.

  Since the metal source powder is an Fe-Si based alloy powder containing iron and silicon, oxygen is inevitably contained. In addition, the metal source powder may further contain chromium (Cr). The metal source powder may further contain nickel (Ni).

  In the present embodiment, in addition to the effect of reducing the magnetocrystalline anisotropy and the magnetostriction constant of the soft magnetic metal powder, silicon plays a part in the role of spheroidizing metal raw material particles in the heat treatment step described later. .

  It is preferable that it is 1.0 mass% or more, and, as for content of the silicon contained in 100 mass% of metal raw material powder, it is more preferable that it is 3.0 mass% or more. Moreover, it is preferable that it is 10.0 mass% or less, and, as for content of a silicon, it is more preferable that it is 7.0 mass% or less. If the content of silicon is too low, the spheroidization of the metal source particles tends to be insufficient. On the other hand, when the content of silicon is too large, the hardness of the metal particles obtained by spheroidizing the metal raw material particles becomes too large, and the density of the soft magnetic metal green compact core tends to decrease.

  Boron, which is contained in the soft magnetic metal, is not preferable because it generally tends to increase the coercivity of the powder. However, in the present embodiment, as described later, the boron contained in the metal source particles in the heat treatment step is used for spheroidizing the particles, and is discharged as boron nitride to the outside of the metal source particles. Therefore, the amount of boron contained in the metal particles constituting the soft magnetic metal powder finally obtained is smaller than the amount of boron contained in the metal raw material particles constituting the metal raw material powder. Therefore, even when the metal raw material powder contains a predetermined amount of boron and the coercive force of the metal raw material powder is high, the coercive force of the soft magnetic metal powder finally obtained can be lowered.

  The content of boron contained in 100% by mass of the metal raw material powder is preferably 0.4% by mass or more, and more preferably 0.8% by mass or more. The content of boron is preferably 2.0% by mass or less, more preferably 1.6% by mass or less, and still more preferably 1.2% by mass or less. If the content of boron is too low, the boron necessary for spheroidizing the metal particles tends to be insufficient. On the other hand, when the content of boron is too high, the time for which spheroidization is completed tends to be long.

  Chromium has the effect of increasing the antirust effect and the electrical resistance of the soft magnetic metal powder. The content of chromium contained in 100% by mass of the metal source powder is preferably in the range of 1% by mass to 10% by mass.

  Nickel has the effect of reducing the magnetocrystalline anisotropy and the magnetostriction constant of the soft magnetic metal powder. In the present embodiment, when the content of iron and nickel contained in the metal raw material powder is 100% by mass, the content of nickel (Ni / (Fe + Ni) mass ratio) is 40% by mass or more and 80% by mass or less It is preferable that it is a range.

  When oxygen is contained in the soft magnetic metal, oxygen is generally recognized as an impurity because it increases the coercivity. Therefore, the oxygen content is required to be small. However, in the present embodiment, as described later, when oxygen contained in the metal raw material particles is utilized for spheroidizing the particles in the heat treatment step, oxygen is separated from the particles and becomes a gas, so The amount of oxygen contained in the metal particles constituting the soft magnetic metal powder obtained can be lower than the amount of oxygen contained in the metal raw material particles constituting the metal raw material powder. Therefore, even when the metal raw material powder contains a predetermined amount of oxygen and the coercive force of the metal raw material powder is high, the coercive force of the soft magnetic metal powder finally obtained can be lowered.

  The content of oxygen contained in 100% by mass of the metal raw material powder is preferably 0.100% by mass or more, and more preferably 0.200% by mass or more. In addition, the content of oxygen is preferably 1.000% by mass or less, and more preferably 0.600% by mass or less.

  The average particle size of the metal source powder is not particularly limited, but it needs to be smaller than the intended average particle size of the soft magnetic metal powder produced by the method according to the present embodiment. Although mentioned later, in this embodiment, it is because it spheroidizes on the occasion of the coupling | bonding of metal raw material particle | grains which comprise metal raw material powder. Therefore, the shape of the metal source particles constituting the metal source powder is not particularly limited, and may be indeterminate.

  The method for producing the metal raw material powder is not particularly limited, and in the present embodiment, a water atomizing method, a gas atomizing method, a casting pulverizing method and the like are exemplified, but a water atomizing method from which a fine powder can be easily obtained is preferable.

The schematic diagram of the cross section of the metal raw material particle which comprises metal raw material powder is shown in FIG. The cross-sectional shape of the metal source particles 1 constituting the metal source powder is indeterminate. Inside the particle 1, there exist crystal grains 4a made of an Fe-Si alloy and Fe ₂ B phase 2 which is an alloy of iron and boron, and between the crystal grains 4a and between the crystal grains 4a and the Fe ₂ B phase Grain boundaries 4 b are present between the two. Further, boron 3 contained in the Fe—Si alloy is present in the crystal grains 4 a. The surface of particle 1 is covered with oxide 5.

(1.2. Mixing process)
In the mixing step, the metal powder and the carbon source material are mixed to produce a mixed powder. The carbon source material is not particularly limited as long as it can supply carbon in the heat treatment step described later. In the present embodiment, the carbon source material is carbon and / or an organic compound.

  Examples of carbon include carbon powders such as graphite, carbon black and amorphous carbon. As the organic compound, a substance which is thermally decomposed when heated in a non-oxidizing atmosphere to generate carbon is exemplified. Specifically, hydrocarbons, alcohols, resins and the like are exemplified.

  In the heat treatment step to be described later, the carbon source substance causes fine particles containing carbon to adhere to the surface of metal raw material particles constituting the metal raw material powder. The fine particles containing the attached carbon can play a part of the role of spheroidizing the particles. When the carbon source substance is an organic compound, the organic compound is thermally decomposed by being heated in a non-oxidative atmosphere to form carbon-containing fine particles, which are attached to the particle surface.

  The carbon source material may be composed only of carbon, may be composed only of an organic compound, or may be composed of carbon and an organic compound. In addition, carbon and organic compounds may each contain two or more of the exemplified substances.

  In the present embodiment, the carbon source material is preferably carbon powder. This is because carbon adheres to the particle surface without being thermally decomposed, so that the control of the amount of carbon contributing to the spheroidization reaction is easy.

  When the form of the carbon source material is a powder, it is preferable to use the metal source powder coated with the carbon source material. By coating, the dispersibility of the raw material powder and the carbon source substance can be enhanced, and the effect of spheroidization in the heat treatment process can be enhanced. The coating method is not particularly limited as long as it is a known method, and for example, a method in which a solvent obtained by dispersing a powder of a carbon source material in an organic solvent is mixed with metal powder and dried is exemplified. Be done. In addition, an organic compound such as a resin may be used as a coating aid.

  The content of the carbon source substance contained in the mixed powder is preferably 30% by mass or more, more preferably 90% by mass or more in carbon conversion, with respect to 100% by mass of the oxygen contained in the metal raw material powder. It is preferable to By being contained in said range, the spheroidization of metal raw material particle is accelerated | stimulated in the heat processing mentioned later. The cross-sectional schematic diagram of the metal raw material particle which comprises mixed powder is shown in FIG. A carbon source material 7 is present around the metal source particles 1a and 1b constituting the mixed powder.

(1.3. Heat treatment process)
In the heat treatment step, the prepared mixed powder is heat-treated in a stream of a non-oxidizing atmosphere containing nitrogen. In the present embodiment, the heat treatment process can be divided into three processes of an initial process, a spheroidization process and a late process.

(1.3.1. Initial process)
In the initial process, the mixed powder is heated in a nonoxidizing atmosphere containing nitrogen. As the temperature rises, the nitrogen in the atmosphere and a part of the boron contained in the metal raw material particles of the metal raw material powder constituting the mixed powder react with each other to form a coated portion containing boron nitride on the surface of the metal raw material particles. It is formed. The boron source of boron nitride to be formed is both boron contained in crystal grains 4a of Fe-Si based alloy in metal raw material particles and boron contained in Fe ₂ B phase 2 which is an alloy of iron and boron. .

Most of the boron contained in the Fe ₂ B phase is consumed in the formation of boron nitride. As a result, as shown in FIG. 4, the Fe ₂ B phase is decomposed and almost disappears. On the other hand, the crystal grains 4a made of Fe-Si-based alloy, while release boron contained in the crystal grains 4a, grain growth while taking in iron constituted the Fe 2 _B phase. As a result, although the number of crystal grains contained in the particles 1a and 1b decreases, the particles 1a and 1b still contain a plurality of crystal grains 4a. Further, in the initial process, the cross-sectional shapes of the particles 1a and 1b are indeterminate and substantially similar to the cross-sectional shape of the metal material particles of the raw material powder before the heat treatment step shown in FIG.

The total amount of boron contained in the crystal grains 4a and boron contained in the Fe ₂ B phase may not be used to form boron nitride, and boron may remain in the particles. The remaining boron is mainly present inside the crystal grains 4a or in the grain boundaries 4b.

  Further, as shown in FIG. 4, in the present embodiment, this covering portion is a thin piece 8 of boron nitride. The flakes 8 may cover at least a part of the surfaces of the particles 1a and 1b, but as shown in FIG. 4, it is preferable to cover the entire surface.

  The content of boron in each metal raw material particle constituting the metal raw material powder is almost constant, and the smaller the particle diameter, the larger the specific surface area. Therefore, the thickness of the boron nitride flakes formed in the initial process is smaller for particles having a smaller particle size.

  The carbon source substance is present as fine particles of carbon between the metal source particles 1a and 1b, but a part of carbon is diffused inside the metal source particles 1a and 1b to promote the spheroidization of the metal source particles Do. When the carbon source substance is an organic compound, in the initial process, the organic compound is thermally decomposed to generate carbon fine particles on the surfaces of the metal material particles 1a and 1b constituting the metal material powder. A part of generated carbon diffuses inside the metal raw material particles.

(1.3.2. Spheroidization process)
In the spheroidization process, oxygen contained in particles constituting the metal raw material powder is reduced by carbon to generate carbon monoxide (CO) gas. As shown to FIGS. 2-4, the oxygen contained in metal raw material powder combines with metal elements, such as a silicon, and becomes an oxide, and the said oxide exists on the surface of metal raw material particle | grains. The oxide present on the particle surface is reduced to metal by carbon contained in the above mixed powder or carbon generated in the initial process. Since oxygen generated by reduction reacts with carbon to generate carbon monoxide gas, the content of oxygen contained in metal source particles is reduced.

  In addition, when the carbon monoxide gas is generated, the partial pressure of the carbon monoxide gas in the vicinity of the particle surface becomes high, so that the partial pressure of nitrogen around the particle relatively decreases. Boron nitride can be stably present when the nitrogen partial pressure is high, but tends to be unstable when the nitrogen partial pressure is reduced and to decompose into boron and nitrogen.

  Therefore, in the spheroidization process, part of boron nitride formed on the surface of the metal source particles in the initial process is decomposed as carbon monoxide is generated. The generated boron is incorporated into the metal raw material particles, and reacts with a metal component such as iron to form an alloy containing boron. Since the melting point of this alloy is low, it is present as the liquid phase 9 of the alloy containing boron in the surface layer of the metal material particles. In the initial process, carbon diffused to the inside of the metal raw material particles can lower the melting point of the liquid phase 9 and can further promote spheroidization.

  The liquid phase 9 has very poor wettability with boron nitride. Therefore, at the interface between the boron nitride 8 remaining on the particle surface and the liquid phase 9, the liquid phase 9 does not adhere to the boron nitride 8, and when the liquid phase 9 reduces the surface area by surface tension, Wrap the crystal grains 4a present inside. As a result, even if the shape of the metal source particles is indeterminate before the spheroidizing process, as shown in FIG. 5, the metal source particles are spheroidized to be metal particles.

  As described above, the smaller the diameter of the metal raw material particle, the thinner the thickness of boron nitride formed on the surface. Therefore, in the metal raw material particle having a small particle diameter, the probability that undecomposed boron nitride is present around liquid phase 9 generated due to the decomposition of boron nitride is low, and liquid phase 9 is It is easy to expose outside. As a result, metal particles having a small particle size contact with metal particles having a small particle size in the surrounding through the liquid phase 9 more frequently.

  As shown in FIGS. 6A and 6B, the liquid phase of two spherical metal particles in contact with each other tries to reduce the surface area by surface tension, that is, it tries to become spherical, so that the two metal particles are integrated. Form spherical metal particles. In the spherical metal particles, crystal grains 4a of a metal which has not reacted with boron exist inside the liquid phase of the alloy containing boron, but in order to lower the interface free energy of the liquid phase 9 and the crystal grains 4a, The grains 4 a are spheroidized, and single crystallization proceeds in which a plurality of crystal grains become one crystal grain. Therefore, in the spheroidization process, the surface layer is formed of the liquid phase of the alloy containing boron, and the inside is formed of spherical metal particles composed of one crystal grain.

  In addition, when two metal particles unify, at least one part of the boron nitride adhering to the surface of each metal particle peels, and the thin piece of the boron nitride liberated from the metal particles is produced.

  In the spheroidization process, as described above, since the metal particles having a smaller particle size are preferentially bonded to other metal particles, the metal particles having a smaller particle size are larger than the particle size before the spheroidization process. It becomes frequent. On the other hand, in the case of metal particles having a large particle size, the thickness of boron nitride formed on the surface is relatively thicker than the thickness of boron nitride formed on the surface of metal particles having a small particle size. Although spheroidization proceeds inside the large particle metal particles, the frequency of contact between liquid phases is lower than that of small particle metal particles, so the frequency with which they are combined with other metal particles and integrated is low. . Therefore, the frequency with which particles having a large particle size become larger than the particle size before the spheroidization process is low.

  Therefore, comparing the particle size distribution of the metal raw material particles contained in the metal raw material powder with the particle size distribution of the metal particles contained in the obtained soft magnetic metal powder, the particle size distribution of the metal particles contained in the soft magnetic metal powder The small diameter particles decrease and the large diameter particles hardly increase. Therefore, soft magnetic metal powder with a small dispersion of the particle diameter of metal particles can be obtained.

  It is generally known that the reduction of oxides of silicon by carbon is very difficult. For example, even if a mixture of silicon oxide and carbon is heated in a nonoxidizing atmosphere, no reduction reaction occurs.

  However, as described above, the inventor has found that the oxide of silicon present on the surface of the iron alloy containing silicon can be reduced by carbon by heating in a non-oxidizing atmosphere. Furthermore, the present inventor has found that the spheroidization of particles proceeds only when the temperature at which the reduction reaction proceeds and the temperature at which boron forms a liquid phase with other components are approximately the same.

(1.3.3. Late process)
When the above-mentioned reduction reaction of the oxide proceeds and oxygen and carbon are consumed for carbon monoxide generation, the content of one or both of oxygen and carbon decreases. As a result, the generation of carbon monoxide ends, and along with this, the spheroidization process also ends and shifts to the later stage process.

  In the later stage, when the generation of carbon monoxide ends, the nitrogen partial pressure around the carbon dioxide rises again, and as shown in FIG. 7, boron contained in the liquid phase located in the surface layer of the metal particles is in the atmosphere. React again with nitrogen to form boron nitride on the surface of the metal particles. When the amount of boron contained in the liquid phase decreases with the formation of boron nitride, the amount of liquid phase of the alloy containing boron decreases, and the component dissolved in the liquid phase crystallizes on the surface of the crystal grains present inside. Get out.

  When the boron contained in the liquid phase is consumed and almost disappears in the nitriding reaction, the reaction for forming boron nitride is terminated, and as shown in FIG. 7, boron nitride is formed on the surface of the single crystal spherical particles. Metal particles can be obtained. After the late process, most of the boron contained in the metal particles is discharged out of the metal particles as boron nitride flakes 8b, but a trace amount of boron remains inside the metal particles.

  Furthermore, by cooling in a non-oxidizing atmosphere containing nitrogen, a soft magnetic metal powder with a low oxygen content can be obtained which is composed of metal particles in which boron nitride is formed on the surface of spherical particles consisting of single crystals.

  The initial process, the spheroidization process and the late process described above are preferably performed continuously in one heat treatment process, but each process can be performed independently by dividing into several heat treatment processes. Further, in the present embodiment, in the heat treatment step, in order to allow the above reaction to proceed uniformly and smoothly, it is preferable that the mixed powder be filled in a container with a lid and heat treated. Further, it is preferable to control the flow rate of the atmosphere gas (nitrogen gas or the like).

  In the heat treatment step, the nitrogen partial pressure in the atmosphere is preferably 0.5 atm or more, more preferably 0.9 atm or more, and preferably 1.0 atm or more. When the pressure of the atmosphere is atmospheric pressure, the nitrogen concentration is preferably 50% or more, more preferably 90% or more, and particularly preferably 100%, that is, pure nitrogen. Further, the oxygen partial pressure in the atmosphere is preferably 0.0001 atm or less. When the oxygen partial pressure is too high, in parallel with the nitriding reaction, the oxidation reaction of the metal proceeds, and the formation of the coating tends to be uneven.

  In the heat treatment step, the heat treatment temperature is 1250 ° C. or more, and preferably 1300 ° C. or more. Moreover, it is preferable that the heat processing temperature is 1500 degrees C or less. If the heat treatment temperature is too low, a series of reactions involving spheroidization tends not to proceed. On the other hand, if the heat treatment temperature is too high, the decomposition reaction of boron nitride proceeds too much, or the amount of liquid phase alloy formation increases too much, which tends to make control difficult.

  At a high temperature of 1000 ° C. or more, metal raw material particles of the metal raw material powder adhere to each other to be easily sintered. However, in the present embodiment, a coating portion containing boron nitride is rapidly formed on the surface of the metal raw material particles in the initial process, and carbon particles derived from the mixed powder are also interposed between the particles. As a result, the adhesion between the metal raw material particles is sufficiently suppressed and sintering does not occur. Boron nitride and carbon have high heat resistance, are difficult to sinter, and inhibit sintering between particles.

(1.4. Boron nitride removal process)
As is clear from FIG. 7, since boron nitride is formed on the surface of the metal particles after the heat treatment step, the soft magnetic metal powder after the heat treatment step contains flakes of boron nitride. When the powder magnetic core is formed using this soft magnetic metal powder, thin pieces of boron nitride exist between the soft magnetic metal particles. Since the density of boron nitride is lower than that of metal particles, the relative density of the dust core tends to decrease slightly. In addition, since boron nitride is nonmagnetic, boron nitride present between soft magnetic metal particles generates a demagnetizing field in the soft magnetic metal particles, and as a result, the magnetic permeability of the dust core decreases. Therefore, when the magnetic permeability of the dust core is required to be high, it is preferable to perform the boron nitride removing step on the soft magnetic metal powder after the spheroidizing step.

  Such boron nitride flakes can be separated from the soft magnetic metal particles in a predetermined operation. In the case where high permeability is not required, it is possible to mainly separate the easily peelable flakes using a classifier such as sieving, cyclone, electrostatic separation, magnetic classification, air classification, wet sedimentation separation and the like.

  When a high magnetic permeability is required, for example, the soft magnetic metal particles are crushed to give a small impact force to the soft magnetic metal particles to forcibly separate the boron nitride flakes from the soft magnetic metal particles. can do. For crushing, a general crushing apparatus such as a wet ball mill, a dry ball mill and a jet mill can be used. In addition, a composite device such as a crusher having a classification function may be used.

  In the present embodiment, it is preferable to forcibly separate a thin piece of boron nitride from soft magnetic metal particles by combining crushing and separation. For example, pulverization using a wet ball mill may be performed, and magnetic separation may forcibly separate soft magnetic metal particles and boron nitride flakes. In addition, pulverization by dry pulverization may be performed, and soft magnetic metal particles and thin pieces of boron nitride may be forcibly separated by wet magnetic separation. Furthermore, it is possible to carry out crushing by dry crushing and forcibly separate the soft magnetic metal particles and the boron nitride flakes by classification using a wind force.

  Although the removal rate of boron nitride changes depending on the conditions of the crushing step or the separation step, the removal of the boron nitride does not necessarily completely remove the boron nitride flakes. Therefore, the soft magnetic metal powder after the boron nitride removing step contains at least a slight amount of boron nitride. Therefore, the boron nitride may be removed by controlling classification, crushing and the like according to the desired magnetic properties.

  Moreover, the carbon powder contained in the soft magnetic metal powder can also be removed by performing the above-described boron nitride removing step. Incidentally, even if the boron nitride removing step is performed, the carbon powder can not be completely removed. Therefore, the soft magnetic metal powder after the boron nitride removing step contains at least a slight amount of carbon.

(2. Soft magnetic metal powder)
Through the above steps, the soft magnetic metal powder according to the present embodiment can be obtained. The soft magnetic metal powder according to the present embodiment has the following characteristics.

(2.1. Amount of boron)
The form of boron contained in the soft magnetic metal powder according to the present embodiment is composed of boron contained in the metal particles and boron nitride present outside the metal particles. As described above, the majority of boron is boron nitride in the later stage of the heat treatment process, but a trace amount of boron remains in the metal particles. Therefore, although the amount of boron contained in the metal particles of the soft magnetic metal powder is much smaller than the amount of boron contained in the metal raw material particles of the metal raw material powder, the soft magnetic metal powder after the heat treatment step It contains the same amount of boron as that contained. Also, as described above, part of boron nitride may be removed in the boron nitride removing step. The soft magnetic metal powder after the boron nitride removing step contains a smaller amount of boron than the boron contained in the metal source powder.

  As described above, the amount of boron contained in 100% by mass of the metal raw material powder is preferably 0.4% by mass or more and 2.0% by mass or less in order to smoothly advance the reaction of the heat treatment step. Therefore, 0.4% by mass or more and 2.0% by mass or less of boron is also contained in 100% by mass of the soft magnetic metal powder after the heat treatment step.

  When soft magnetic metal powder is used to form a dust core, a boron nitride removing step may be performed to remove a part of boron nitride in order to adjust the magnetic permeability. However, it is extremely difficult to completely remove boron nitride, and boron nitride remains on the surface of the metal particles. In addition, a trace amount of boron is also contained in the metal particles, and therefore, 100% by mass of the soft magnetic metal powder after the boron nitride removing step contains 0.010% by mass or more of boron.

  It is preferable that the amount of boron contained in the metal particles of the soft magnetic metal be smaller because the soft magnetic metal, in particular, the coercive force of the soft magnetic metal increases as the amount of boron contained in the crystalline soft magnetic metal increases. . In the present embodiment, although a predetermined amount of boron is intentionally contained in the metal raw material particles of the metal raw material powder, in the heat treatment step, the boron contained in the particles is discharged as boron nitride to the outside of the metal particles, Boron contained in the metal particles after heat treatment can be reduced. Therefore, it is preferable to discharge boron as boron nitride out of the metal particles in the above heat treatment step as much as possible.

  However, as the boron contained in the metal particles is reduced by the nitriding reaction, the nitriding reaction is less likely to proceed thermodynamically. Therefore, it is extremely difficult to completely discharge the boron remaining in the particles. In particular, it is known that a certain amount of boron is solid-solved in the metal phase (for example, about 15 ppm at 900 ° C. for Fe), and metal particles composed of a soft magnetic metal phase mainly composed of Fe It is difficult to reduce the content of boron to 15 ppm or less. On the other hand, the present inventors found that the influence on the coercive force is limited if the amount of boron in the metal particles is 150 ppm or less. The amount of boron in the metal particles is more preferably 100 ppm or less.

  The boron content of the soft magnetic metal powder can be measured by ICP. The boron of the soft magnetic metal powder comprises boron contained in the metal particles and boron contained in boron nitride. In the case of measuring the content of boron contained in the metal particles of the soft magnetic metal powder, it is necessary to remove the influence of boron detected from boron nitride. Since most of the nitrogen contained in the soft magnetic metal powder is present as boron nitride, the amount of boron nitride can be quantified to calculate the amount of boron in the particles.

(2.2. Carbon content)
The form of carbon contained in the soft magnetic metal powder according to the present embodiment is composed of carbon contained in the metal particles and carbon present outside the metal particles.

  Since the coercivity of the soft magnetic metal increases as the amount of carbon contained in the soft magnetic metal increases, the amount of carbon contained in the metal particles is preferably smaller. In the present embodiment, although the carbon source material is intentionally added to the raw material powder and adhered to the surface of the metal raw material particles in the heat treatment step, the outside of the soft magnetic metal powder using carbon as carbon monoxide in the spheroidization process. Discharged into In the present embodiment, the amount of carbon contained in 100% by mass of the soft magnetic metal powder after the heat treatment is 0.010% by mass or more and 0.350% by mass or less.

  Further, in the heat treatment step, part of carbon derived from the carbon source material is diffused into the inside of the metal source particles. The amount of carbon contained in the metal particles constituting the soft magnetic metal powder after the heat treatment is 0.010% by mass or more and 0.150% by mass or less.

(2.3. Amount of oxygen)
Since the coercivity of the soft magnetic metal increases as the amount of oxygen contained in the soft magnetic metal increases, the amount of oxygen contained in the metal particles is preferably smaller. In the present embodiment, although the metal raw material particles of the metal raw material powder intentionally contain a predetermined amount of oxygen, in the heat treatment step, oxygen is reduced by reducing the oxide formed on the surface of the metal raw material particles. Out of the metal particles, and the discharged oxygen reacts with carbon to form carbon monoxide. Therefore, the oxygen separated from the metal raw material particles by the reduction of the oxide is not present in the soft magnetic metal powder after the heat treatment step.

  Therefore, the oxygen amount of the metal particles of the soft magnetic metal powder after the heat treatment step, that is, the oxygen amount of the soft magnetic metal powder after the heat treatment step is the oxygen amount contained in the metal raw material particles of the metal raw material powder, that is, before the heat treatment step The amount of oxygen of the soft magnetic metal powder can be reduced. Specifically, the amount of oxygen contained in 100% by mass of the soft magnetic metal powder after the heat treatment step is preferably 0.1000% by mass or less. By adjusting the conditions of the heat treatment step, the amount of oxygen contained in the soft magnetic metal powder can be made to be not more than 0.0300 mass%. In addition, when the soft magnetic metal powder is handled in the atmosphere, oxidation of the surface is inevitable, so the soft magnetic metal powder contains oxygen of several ppm or more.

(2.4. Nitrogen content)
Nitrogen contained in the soft magnetic metal powder according to the present embodiment is present in the form of boron nitride on the surface of the metal particles. Although nitrogen is hardly contained in the metal raw material powder, most of the boron contained in the metal particles is reacted with nitrogen contained in the atmosphere to form boron nitride in the later stage of the heat treatment process. The soft magnetic metal powder contains nitrogen taken from the atmosphere. The mass ratio (N / B) of nitrogen to boron constituting boron nitride is 14.0 / 10.8 = 1.30. Therefore, the amount of nitrogen contained in the soft magnetic metal powder is 100 to 150% by mass of the amount of boron contained in the soft magnetic metal powder.

(2.5. Circularity of particles)
By performing the above-described heat treatment step, it is possible to obtain a powder having a circularity of 0.80 or more of the soft magnetic metal particles of 80% or more among the soft magnetic metal particles constituting the soft magnetic metal powder. By adjusting the conditions of the heat treatment step, it is possible to obtain a powder having a circularity of 0.80 or more of the cross section of the soft magnetic metal particles of 90% or more. That is, it is possible to obtain a soft magnetic metal powder including particles having a spherical shape or a shape close to a spherical shape.

  The method of measuring the degree of circularity may be as follows. First, the obtained soft magnetic metal powder is embedded in a cold embedding resin and fixed, and mirror polishing is performed so that the cross section of the particles constituting the powder is exposed. Next, the particles whose cross section is exposed are observed by an optical microscope, a scanning electron microscope (SEM) or the like, and the observation image is image-processed to measure the circularity of the particles. The number of particles to be measured is preferably 20 or more, and more preferably 100 or more. Further, it is preferable to use Wadell's circularity as the circularity. That is, the diameter of a circle equal to the projected area of the particle cross section relative to the diameter of the circle circumscribing the particle cross section is evaluated. In the case of a perfect circle, Wadell's circularity is 1. Therefore, the closer the circularity of Wadell is to 1, the closer the shape of the particle cross section will be to a perfect circle.

  In the present embodiment, the shape of the particles after heat treatment is improved by heat treating the metal material powder instead of using the metal material powder in which the shape of the metal material particles is improved. Therefore, even if the shape of the metal source particles is indeterminate, it is possible to obtain particles having a true spherical shape or a near spherical shape after heat treatment.

(2.6. Grain size of particles)
By performing the above-mentioned heat treatment step, it is possible to obtain a soft magnetic metal powder in which 85% or more, preferably 90% or more of metal particles among the metal particles constituting the soft magnetic metal powder consist of one crystal grain. . Since there is no grain boundary that hinders the movement of the domain wall in the metal particle consisting of one crystal grain, a soft magnetic metal powder having a small coercive force can be obtained.

  The observation method of crystal grains may be as follows. First, the obtained soft magnetic metal powder is embedded in a cold embedding resin, fixed, and mirror-polished so that the cross section of the particles constituting the powder is exposed. Then, grain boundaries can be observed by etching the particles whose cross section is exposed with an etchant such as nital (ethanol + 1% nitric acid). An optical microscope or an electron microscope (SEM) can be used for observation. The observation conditions of the grain boundaries are previously confirmed using polycrystalline alloy powder having similar components, and it is preferable to carry out the conditions according thereto. At least 20, preferably 100 or more of the cross sections of the metal particles prepared in this manner were observed, and metal particles with no crystal grain boundaries counted were counted as metal particles consisting of one crystal grain, and the observed metal particles You can calculate the ratio to the number.

(2.7. Particle size distribution)
By performing the above-mentioned heat treatment step, it is possible to obtain a soft magnetic metal powder having a small standard deviation of the particle size distribution of the metal particles. In the present embodiment, the particle size distribution of the soft magnetic metal powder is a particle size distribution obtained from the volume-based particle size calculated using a laser diffraction scattering method. In such a particle size distribution, the standard deviation σ can be expressed by the following equations 1 to 3.
Standard deviation σ = (σ1 + σ2) / 2 Equation 1
σ 1 = ln (d 50 / d 16) equation 2
σ 2 = ln (d 84 / d 50) equation 3
d16, d50 and d84 represent 16% cumulative particle size, 50% cumulative particle size and 84% cumulative particle size, respectively, in the particle size distribution.

  The soft magnetic metal powder of the present embodiment contains a thin piece of boron nitride liberated in the spheroidizing process of the heat treatment process. Since the boron nitride flakes are smaller than the size of the metal particles, they are detected as fine particles when the particle size distribution is measured. When essentially measuring the particle size distribution of the metal particles of the soft magnetic metal powder, it is preferable to carry out the separation operation of the above-mentioned boron nitride removing step to remove loose boron nitride flakes and then measure. The boron nitride fixed to the metal particles does not have a large influence on the particle size distribution.

  The standard deviation σ ((σ1 + σ2) / 2) of the particle size distribution of the soft magnetic metal powder after removing the liberated boron nitride flakes by producing the soft magnetic metal powder by performing the above heat treatment step is 0 .65 or less. That is, the particle size distribution is sharp. By using a powder with such a small standard deviation, a powder core having a high relative density and a small core loss can be produced.

(3. Soft magnetic metal dust core)
The soft magnetic metal powder obtained in the present invention exhibits low coercivity, so when it is used for a soft magnetic metal green compact core, core loss becomes small. The soft magnetic metal powder core can be produced by a general production method except that the soft magnetic metal powder obtained above is used as the soft magnetic metal powder. An example is shown below.

  First, a resin is mixed with the soft magnetic metal powder obtained above to prepare granules. As the resin, a known resin such as an epoxy resin or a silicone resin can be used, which has shape retention property at the time of molding and electrical insulation, and can be uniformly applied on the surface of soft magnetic metal powder particles. preferable. The resulting granules are filled into a mold of the desired shape and pressed to obtain a shaped body. The molding pressure can be appropriately selected according to the composition of the soft magnetic metal powder and the desired molding density, but is generally in the range of 600 to 1600 MPa. A lubricant may be used as needed. The resulting molded product is thermally cured to form a soft magnetic metal powder core. Alternatively, a heat treatment is performed to remove distortion during molding to form a soft magnetic metal powder core. The heat treatment is preferably performed at a temperature of 500 to 800 ° C. in a non-oxidizing atmosphere such as a nitrogen atmosphere or an argon atmosphere.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and may be modified in various aspects within the scope of the present invention.

  Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to the following examples.

(Experimental example 1)
First, a metal raw material powder was produced by a water atomizing method such that the composition of the metal raw material particles is as shown in Table 1, and the contents of boron and oxygen contained in the metal raw material particles are as shown in Table 1. . The particle size distribution of the produced metal raw material powder was equivalent.

  The amount of the carbon source material shown in Table 1 was added to the prepared metal material powder shown in Table 1 to prepare a mixed powder. Using a carbon black as a carbon source substance, mixing a solution in which carbon black is dispersed in acetone with a metal material powder, and drying, carbon black is made to adhere to the surface of particles constituting the metal material powder, which is simple The coating was done. Moreover, the sample 7 used PVA (polyvinyl alcohol) as a carbon source substance. The amount of carbon derived from PVA is obtained by putting PVA in a container with a lid, performing heat treatment at 750 ° C. in a nitrogen atmosphere, estimating the effective carbon amount from the weight of the residue, and using this amount the carbon amount to the oxygen amount shown in Table 1 Calculated.

  The prepared mixed powder was filled in a crucible made of alumina and placed in a tubular furnace, and a heat treatment step was performed under the heat treatment temperature conditions and heat treatment atmosphere conditions shown in Table 1. In addition, the sample numbers 1 and 2 did not add a carbon source substance, and the heat processing process was not performed, either. That is, sample numbers 1 and 2 are water atomized powders.

  The form of the soft magnetic metal powder after the heat treatment step is shown in Table 1. From Table 1, in the sample numbers 34, 14 and 15, the particles contained in the powder were sintered after the heat treatment.

  The proportion of particles having a degree of circularity of 0.80 or more and one particle for samples 1 to 2, 5 to 13 and 16 to 22 in which the form of the metal raw material powder and the soft magnetic metal powder after heat treatment is powder The ratio of 1 to 3 was measured.

  The powder was fixed with cold embedding resin and mirror polishing was performed so that the cross section of the particles was exposed. The obtained cross section was observed with a scanning electron microscope (SEM), 50 particle cross sections were randomly selected, the degree of circularity was measured, and the proportion of particles having a degree of circularity of 0.80 or more was calculated. The circularity of Wadell was used as the circularity. The results are shown in Table 2.

  In addition, after etching the cross section of the mirror-polished particle with nital, 50 particle cross sections are randomly selected, and it is evaluated whether or not there is a grain boundary in the particle, and one crystal is selected. The proportion of particles consisting of particles was calculated. The results are shown in Table 2.

  The coercivity of each of the samples 1 to 2, 5 to 13 and 16 to 22 was measured as follows. 20 mg of soft magnetic metal powder was put in a φ6 mm × 5 mm plastic case, and paraffin was melted, solidified, and fixed to measure with a coercometer (K-HC 1000 type manufactured by Tohoku Special Steel Co., Ltd.). The measured magnetic field was 150 kA / m. The results are shown in Table 2.

  The amount of boron in the powder was measured by ICP for samples 1 to 2, 5 to 13 and 16 to 22. The results are shown in Table 2. In addition, the amount of oxygen in the powder was measured by an oxygen analyzer (TC600 manufactured by LECO). The results are shown in Table 2. In addition, the carbon content of the powder was measured by a carbon analyzer (CS-600 manufactured by LECO). The results are shown in Table 2.

  Samples 6 to 12 and 16 to 22 were prepared by mixing raw material powder having a plurality of raw material particles containing iron, silicon and boron with a carbon source material, and obtaining the obtained mixed powder in a non-oxidizing atmosphere containing nitrogen Heat treatment at a heat treatment temperature of 1250.degree. C. or higher to obtain a soft magnetic metal powder having a high degree of circularity, a large amount of metal particles consisting of one crystal grain, and a low coercive force of 350 A / m or less. It could be confirmed that

  Moreover, in samples 6 to 7, 9 to 11, 16 to 21, the boron content of the soft magnetic metal powder is 0.01 to 2.0% by mass, and the carbon content is 0.010 to 0.300% by mass And boron nitride is formed on the surface of the metal particles, the circularity of the metal particles of 80% or more is 0.80 or more, and the metal particles of 85% or more consist of one crystal grain. It can be seen that a particularly low coercivity of 250 A / m or less is obtained.

  Furthermore, in samples 6 to 7 and 10 to 11, since the oxygen content of the soft magnetic metal powder is 0.100 mass% or less, it is possible to obtain lower coercivity than sample 9 of the same silicon content. Recognize.

  Furthermore, with respect to sample 6, the amount of boron in particles and the amount of carbon in particles were measured as follows. The resulting soft magnetic metal powder is crushed in a ball mill, and acetone is added and stirred to suspend boron nitride and carbon fine particles attached to the metal particle surface in acetone and separate and remove the supernatant acetone. As a result, a soft magnetic metal powder after heat treatment from which boron nitride and carbon were removed was obtained.

  The nitrogen content, the boron content, and the carbon content were measured for those in which the crushing time was changed to 1 hour, 2 hours, 13 hours, and 18 hours.

  The nitrogen content was measured by a nitrogen analyzer (TC600 manufactured by LECO) in the same manner as the nitrogen content of the powder. The boron content was measured by ICP in the same manner as the boron content of the powder. The carbon content was measured by a carbon analyzer (CS-600, manufactured by LECO) in the same manner as the carbon content of the powder.

  Since the boron nitride is removed and the amount of boron nitride decreases as the crushing time increases, the nitrogen content and the boron content both decrease, but the boron content in the particles does not change. Therefore, the correlation between the nitrogen content and the boron content is determined, the boron content when the nitrogen content is 0 is extrapolated, and the value is 0.009 mass% when the value is the boron amount in the particles. there were.

  In addition, since carbon attached to the surface decreases as the crushing time increases, the carbon content existing outside the particle decreases, but since it gradually approaches a certain value, its convergence value is The carbon content in the particles was 0.08% by mass.

  The particle size distribution of the powder and the standard deviation thereof were measured for the metal raw material powder and the samples 1 to 2, 5 to 13 and 16 to 22 in which the form of the soft magnetic metal powder after heat treatment was powder.

  Since the soft magnetic metal powder after the heat treatment contains liberated boron nitride as described above, fine powder derived from liberated boron nitride is detected. Therefore, the particle size distribution of the soft magnetic metal powder is changed. Therefore, in order to measure the particle size distribution of the metal particles contained in the soft magnetic metal powder, first, the liberated boron nitride was removed by the boron nitride removing step described below.

  The soft magnetic metal powder after heat treatment is placed in a container, acetone is added and stirred, the liberated boron nitride is suspended in acetone, only metal particles are precipitated using a magnet, and the cloudy acetone containing boron nitride is The removing operation was repeated, and this operation was performed until the white turbidity disappeared. The particle size distribution of the soft magnetic metal powder from which liberated boron nitride has been removed is measured using a laser diffraction particle size distribution measuring apparatus HELOS & RODOS (manufactured by Nippon Laser Co., Ltd.), and the particle size distribution and its standard deviation are calculated from the obtained particle size distribution. did. The results are shown in Table 2.

  In addition, when a magnet was put into acetone of the cloudy supernatant and stirred, and the weight of the metal particle adhering to the magnet was measured, it was 1 mass% or less with respect to the weight of the soft magnetic metal powder charged. The metal particles contained in the soft magnetic metal powder after heat treatment and the metal particles after the boron nitride removing step for removing liberated boron nitride may be considered to be substantially the same.

  Samples 6 to 12 and 16 to 22 have a standard deviation σ of the particle size distribution of the soft magnetic metal powder of 0.70 or less, and have a smaller amount of fine powder compared to the water atomized powder of the raw material (σ = 0.78) It has been confirmed that magnetic metal powder can be obtained. In addition, the particle diameter on the coarse powder side is 58 to 67 μm at d 90%, and hardly changes or remains at 20% or less as compared with the water atomized powder (d 90% = 57 μm) of the raw material Therefore, the eddy current loss does not increase.

  Furthermore, samples 6 to 7, 9 to 11 and 16 to 21 can obtain soft magnetic metal powder in which the standard deviation σ of the particle size distribution of the soft magnetic metal powder is 0.65 or less and the amount of fine powder is further small. It could be confirmed.

  In samples 5 to 13 and 16 to 22, the white supernatant acetone was dried and the obtained white powder was measured by XRD. As a result, it was confirmed that boron nitride was generated. The appearance of the powder after heat treatment was observed by SEM, and it was confirmed that boron nitride was attached to the surface of the metal particles.

(Experimental example 2)
The soft magnetic metal powder of sample 6 was subjected to a boron nitride removing step of removing free boron nitride and boron nitride attached to the surface of the metal particles. The heat-treated soft magnetic metal powder, zirconia medium and ethanol as a solvent are placed in a ball mill, and the mixture is stirred for 0.5 hours (Sample 6-2), 1.0 hour (Sample 6-3), 3 hours (Sample 6-). When the crushing process of 4) was performed, ethanol became cloudy and a suspension was obtained. Ethanol was added to the obtained suspension, and the heat-treated metal powder and the suspension of the supernatant were magnetically separated to obtain a heat-treated soft magnetic metal powder from which boron nitride was removed.

  With respect to the obtained soft magnetic metal powder after removal of boron nitride, the circularity, the ratio of metal particles consisting of one crystal grain, the oxygen content of the soft magnetic metal powder, the carbon content, as in the case of the above sample 6. The boron content and coercivity were measured and are shown in Table 3. As is apparent from Table 3, even when the boron nitride removing step is performed, it is confirmed that a high degree of circularity, many metal particles consisting of one crystal grain, and a low coercive force of 300 A / m or less can be obtained. The

  Moreover, the SEM photograph of the external appearance of the metal raw material powder (sample 2) and the soft-magnetic metal powder (sample 6-2) after the boron nitride removal process of this embodiment was respectively shown to FIG. 8A and FIG. 8B. As is apparent from these, even if the raw material powder having an irregular particle shape and containing a large amount of fine powder is used, according to the manufacturing method of the present embodiment, the softness is high and the amount of fine powder is small. Magnetic metal powder can be obtained.

(Experimental example 3)
Powdered powder cores were produced using the soft magnetic metal powders of Sample 1 and Sample 6 and Samples 6-2 to 6-4, respectively, and used as Samples 2-1 to 2-5. To 100% by mass of the soft magnetic metal powder, 1.0% by mass of a silicone resin was added, and the mixture was kneaded with a kneader to prepare granules. The resultant was filled in a toroidal mold having an outer diameter of 17.5 mm and an inner diameter of 11.0 mm, and was pressurized under a molding pressure of 1180 MPa to obtain a molded body. The core weight was 5 g. The obtained molded product was heat-treated in a nitrogen atmosphere at 750 ° C. for 30 minutes in a belt furnace to form a dust core.

  The permeability and the core loss of the obtained dust core were evaluated. The magnetic permeability and the core loss were measured under the conditions of a frequency of 50 kHz and a measured magnetic flux density of 50 mT using a BH analyzer (SY-8258 manufactured by Iwatsu Keisoku Co., Ltd.). In addition, the inductance of the soft magnetic metal powder core at a frequency of 100 kHz is measured using an LCR meter (Agilent Technology 4284A) and a DC bias power supply (Agilent Technology 42841A), and the inductance is determined from the soft magnetic metal powder. The permeability of the magnetic core was calculated. The measurements were conducted for the cases where the DC superimposed magnetic field was 0 A / m and 8000 A / m, and the magnetic permeability was shown in Table 4 as μ (0 A / m) and μ (8 kA / m). Moreover, the change rate was calculated and shown in Table 4.

  From Table 4, when Sample 2-1 and Samples 2-2 to 2-5 are compared, the soft magnetic metal green compact core using the soft magnetic metal powder of the present invention can improve the core loss, and the DC magnetic field can be improved. It was confirmed that the rate of change of permeability when superposed was small, and that the direct current superposition characteristics were excellent.

1 ... metallic material particles 2 ... Fe 2 _B phase 3 ... boron 4a ... grain 4b ... grain boundary 5 ... oxide 7 ... carbon source material 8 ... flakes 9 ... liquid

Claims (11)

A raw material powder preparation step of preparing a metal raw material powder having a plurality of metal raw material particles containing iron, silicon and boron;
Mixing the metal raw material powder and the carbon source material to obtain a mixed powder;
A heat treatment step of subjecting the mixed powder to a heat treatment temperature of 1250 ° C. or more in a non-oxidizing atmosphere containing nitrogen to make the metal raw material particles into a spheroidizing powder; Production method.   The method for treating soft magnetic metal powder according to claim 1, further comprising a boron nitride removing step of removing a part of boron nitride contained in the soft magnetic metal powder after the heat treatment step.   In the said raw material powder preparation process, content of the said boron contained in 100 mass% of said metal raw material powder is 0.4 mass% or more and 2.0 mass% or less, It is characterized by the above-mentioned. Method of soft magnetic metal powder.   The said raw material powder preparation process WHEREIN: Content of the oxygen contained in 100 mass% of said metal raw material powder is 0.100 mass% or more and 1.000 mass% or less, It is characterized by the above-mentioned. The manufacturing method of the soft magnetic metal powder as described in-.   The method for producing a soft magnetic metal powder according to any one of claims 1 to 4, wherein in the heat treatment step, a coating portion containing boron nitride is formed on the surface of the metal raw material particles. A soft magnetic metal powder comprising a plurality of metal particles comprising iron, silicon, boron and carbon,
The content of boron contained in 100% by mass of the soft magnetic metal powder is 0.010% by mass or more and 2.0% by mass or less,
The content of carbon contained in 100% by mass of the soft magnetic metal powder is 0.010% by mass or more and 0.350% by mass or less,
Boron nitride is formed on the surface of the metal particles,
Among the metal particles, the circularity of the metal particles of 80% or more is 0.80 or more,
Soft magnetic metal powder characterized in that 85% or more of metal particles among the metal particles consist of one crystal grain.   The soft magnetic metal powder according to claim 6, wherein the content of chromium contained in 100% by mass of the soft magnetic metal powder is 1% by mass or more and 10% by mass or less.   The total content of iron and nickel contained in the soft magnetic metal powder is 100% by mass, and the content of nickel is 40% by mass or more and 80% by mass or less. The soft magnetic metal powder according to 7.   The soft magnetic metal powder according to any one of claims 6 to 8, wherein a content of carbon contained in the metal particles is 0.010% by mass or more and 0.150% by mass or less.   The soft magnetic metal powder according to any one of claims 6 to 9, wherein the content of oxygen contained in 100 mass% of the soft magnetic metal powder is 0.1000 mass% or less.   A soft magnetic metal green compact core comprising the soft magnetic metal powder according to any one of claims 6 to 10.

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