JP2021150555A - Powder magnetic core and method of manufacturing the same - Google Patents

Abstract

To provide a powder magnetic core that has particularly high magnetic permeability and that can contribute to miniaturization of a magnetic component such as a reactor, and a method of manufacturing the same.MEANS FOR SOLVING THE PROBLEM: A powder magnetic core includes a pressurized powder body that is made from malleable powder and nanocrystal powder in which the ratio (L1/L2) between a major axis L1 and a minor axis L2 is in the range of 1.1-5.0. The ratio of powder, in which an orientation angle of the nanocrystal powder with respect to a direction perpendicular to a molding direction of the pressurized powder body is less than 45°, is in the range of 65-85%.SELECTED DRAWING: None

Description

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

There is a dust core as a magnetic core for a reactor used in the region from several kHz to several hundred kHz. The dust core is formed by insulating the surface of the magnetic powder and then processing and molding it. The insulation treatment suppresses the occurrence of eddy current loss.

In particular, hybrid vehicles, which have begun to spread rapidly, have high-power electric motors, and the power supply circuit that drives them requires a reactor that can withstand high voltage and large current. This reactor is strongly required to be miniaturized, reduced in noise, reduced in loss, and durable, and the magnetic core material used in the reactor is required to have a high magnetic permeability μ in addition to a high saturation magnetic flux density Bs.

As a reactor magnetic core for a large current, there is one using the above-mentioned dust core. Amorphous mixed powder and nanocrystal mixed powder are used for the dust core, which is required to have low loss (see Patent Document 1). However, since the initial magnetic permeability of an amorphous mixed powder or the like has a negative coefficient with respect to temperature, Joule heat is generated when a large current is passed through a conductor of a conventional magnetic component such as a reactor or a motor core, and the reactor's initial magnetic permeability is increased. There is a problem that the magnetic performance of the saturation magnetic flux density Bs and the inductance L deteriorates.

Further, even in a reactor using an amorphous mixed powder or the like, the magnetic permeability may have a negative coefficient with respect to the temperature depending on the composition, and there is a problem that the inductance L also decreases.

Furthermore, with the above-mentioned amorphous mixed powder and the like, the absolute magnetic permeability is insufficient, the inductor L cannot be increased, and the reactor inevitably increases in size as the number of coil turns increases. There was a problem.

Japanese Unexamined Patent Publication No. 2016-27656

An object of the present invention is to provide a dust core having a particularly high magnetic permeability and capable of contributing to miniaturization of magnetic parts such as a reactor, and a method for producing the same.

In order to achieve the above object, the present inventors have conducted diligent studies. As a result, a nanocrystal powder having a ratio (L1 / L2) of the major axis L1 to the minor axis L2 in the range of 1.1 to 5.0 is prepared, and the expandable powder is mixed with the nanocrystal powder to prepare a mixed powder. After that, the mixed powder is molded to form a green compact, and a powder magnetic core containing the green compact is produced. It has been found that the crystal powder is oriented, that is, the major axis of the nanocrystal powder is oriented and exhibits high magnetic permeability in the orientation direction.

That is, the present invention is as shown below.
(1) A green compact having a ratio (L1 / L2) of a major axis L1 to a minor axis L2 (L1 / L2) in the range of 1.1 to 5.0 and a spread powder is contained in the green compact. A powder magnetic core, characterized in that the proportion of the powder having an orientation angle of the nanocrystal powder less than 45 ° with respect to a direction perpendicular to the molding direction is 65 to 85%.
Molding (2) The dust core according to (1), wherein the malleable powder has a Vickers hardness Hv of 500 or less.
(3) The dust core according to (1) or (2), wherein the ratio of the malleable powder in the powder is 10 to 90%.
(4) The dust core according to any one of (1) to (3), wherein the malleable powder has a particle size ratio of 1 or less to the nanocrystal powder. ..
(5) The dust core according to any one of (1) to (4), wherein the nanocrystal powder has a crystallinity of 25% or more.
(6) The dust core according to any one of (1) to (5), wherein the nanocrystal powder has a crystal grain size of 45 nm or less.
(7) The composition of the nanocrystal powder is atomic%.
Si: 0-17%,
B: 2 to 15%,
P: 0-15%,
Cr + Nb: 0-5%,
Cu: 0.2-2%,
The powder magnetic core according to any one of (1) to (6), wherein the balance is Fe + an unavoidable impurity.
(8) The step of preparing a nanocrystal powder in which the ratio (L1 / L2) of the major axis L1 to the minor axis L2 is in the range of 1.1 to 5.0, and the nanocrystal powder and the expandable powder are mixed. Manufacture of a powder magnetic core, which comprises a step of adjusting a mixed powder and a step of molding the mixed powder to form a green compact and producing a powder magnetic core containing the green powder. Method.
(9) The method for producing a dust core according to (8), wherein the malleable powder has a Vickers hardness Hv of 500 or less.
(10) The method for producing a powder magnetic core according to (8) or (9), wherein the ratio of the malleable powder in the powder is 10 to 90%.
(11) The dust core according to any one of (8) to (10), wherein the malleable powder has a particle size ratio of 1 or less to the nanocrystal powder. Manufacturing method.
(12) The method for producing a dust core according to any one of (8) to (11), wherein the nanocrystal powder has a crystallinity of 25% or more.
(13) The method for producing a dust core according to any one of (8) to (12), wherein the nanocrystal powder has a crystal grain size of 45 nm or less.
(14) The composition of the nanocrystal powder is atomic%.
Si: 0-17%,
B: 2 to 15%,
P: 0-15%,
Cr + Nb: 0-5%,
Cu: 0.2-2%,
The method for producing a dust core according to any one of (8) to (13), wherein the balance is Fe + an unavoidable impurity.

Generally, a green compact is produced by filling a mold having a plurality of surfaces with a magnetic powder such as nanocrystal powder or malleable powder and a binder, and applying molding pressure. Of these surfaces, the molding pressure is applied in the direction connecting the surface to which the molding pressure is applied and the surface of the mold facing the surface. In other words, since the molding pressure is applied to the green compact from any of the outer surfaces of the green compact corresponding to these surfaces, the direction perpendicular to the outer surface is generally the molding direction. The molding direction is generally perpendicular to the direction in which the major axis of the nanocrystal powder is oriented. The molding direction is generally perpendicular to the magnetic path.

According to the present invention, it is possible to provide a dust core and a method for producing the same, which have a particularly high magnetic permeability and can contribute to the miniaturization of magnetic parts such as reactors.

Hereinafter, the details and other features of the present invention will be described based on the mode for carrying out the invention.

The nanocrystal powder used in the present invention preferably has a ratio (L1 / L2) of a major axis L1 to a minor axis L2 in the range of 1.1 to 5.0, preferably in the range of 1.2 to 3.5. It is preferable to have. When the ratio (L1 / L2) of the major axis L1 and the minor axis L2 of the nanocrystal powder is within the above range, the nanocrystal powder is oriented in the direction perpendicular to the molding direction of the powder magnetic core (compact powder), that is, The long axis of the nanocrystal powder is oriented and exhibits high magnetic permeability in the orientation direction.

If the ratio (L1 / L2) is less than 1.1, the orientation of the nanocrystal powder deteriorates and the magnetic permeability in the orientation direction decreases. Further, when the above ratio (L1 / L2) exceeds 5.0, the packing property of the nanocrystal powder in the green compact decreases, and the density of the green compact, that is, the powder magnetic core decreases, so that the powder is saturated. Magnetic characteristics such as magnetic flux density and magnetic permeability deteriorate.

The malleable powder used in the present invention is not particularly limited as long as it is softer than the nanocrystal powder and has excellent malleability, but preferably has a Vickers hardness Hv of 500 or less, more preferably less than 450, and more preferably. Is less than 250. As a result, the expandable powder functions as an auxiliary agent that facilitates the orientation of the nanocrystal powder in the direction perpendicular to the molding direction of the dust core (compact), so that the nanocrystal powder is pressed. It is oriented in a direction perpendicular to the molding direction of the powder magnetic core (compact powder), that is, the major axis of the nanocrystal powder is oriented and exhibits high magnetic permeability in the orientation direction.

The lower limit of the Vickers hardness Hv is not particularly limited, but may be, for example, 50. Even if it is smaller than the lower limit, it no longer affects the orientation of the nanocrystal powder and does not contribute to the increase in magnetic permeability.

As the expandable powder as described above, pure iron powder, carbonyl iron powder, sentust powder, Fe-Ni powder, Fe-Si-Cr powder, Fe-Si powder, Fe-Cr-based soft magnetic powder and the like can be used. can.

The ratio of the malleable powder in the green compact is preferably 10 to 90%, more preferably 30 to 70%. When the ratio of the expandable powder is in the above range, as described above, the expandable powder serves as an auxiliary agent that facilitates the orientation of the nanocrystal powder in the direction perpendicular to the molding direction of the powder magnetic core (compact powder). Since it becomes functional, the nanocrystal powder is oriented in a direction perpendicular to the molding direction of the dust core (compact powder), that is, the long axis of the nanocrystal powder is oriented and is high in the orientation direction. Indicates magnetic permeability.

If the proportion of the malleable powder is less than 10%, the above-mentioned action effect becomes small and a sufficient magnetic permeability may not be obtained. If it exceeds 90%, nanocrystals that contribute to the magnetic permeability by orientation. Similarly, it may not be possible to obtain sufficient magnetic permeability because the proportion of powder is reduced.

The ratio of the expandable powder described above is obtained by defining a region of 500 μm × 500 μm in the electron micrograph of the powder magnetic core and determining it from the area ratio of the expandable powder to the nanocrystal powder in the region.

The particle size ratio of the expandable powder to the nanocrystal powder (particle size of the expandable powder / nanocrystal powder) is preferably 1 or less, and more preferably less than 0.45. In this case, the nanocrystal powder tends to be oriented in the direction perpendicular to the molding direction of the dust core (compact powder), so that the nanocrystal powder is perpendicular to the molding direction of the dust core (compact powder). It is oriented in the direction, that is, the major axis of the nanocrystal powder is oriented, and exhibits high magnetic permeability in the orientation direction.

The lower limit of the particle size ratio is not particularly limited, but may be, for example, 0.02. Even if the particle size ratio is made smaller than the lower limit, the orientation is no longer affected and the magnetic permeability is not affected.

The degree of crystallization of the nanocrystal powder is preferably 25% or more, and more preferably 35% or more. In this case, since the crystal ratio of bcc—Fe (−Si) increases, the magnetic characteristics such as the saturation magnetic flux density and the magnetic permeability become good.

The upper limit of the crystallinity of the nanocrystal powder is not particularly limited, but is, for example, 70%. Even if the crystallinity increases beyond the upper limit, it no longer affects the magnetic properties.

The crystal grain size of the nanocrystal powder is preferably 45 nm or less, and more preferably 30 nm or less. In this case, since the coercive force becomes small, the magnetic characteristics as the dust core become good. Even if it is less than 10 nm, it no longer affects the decrease in coercive force, so that value is the lower limit.

Next, the compositional components of the nanocrystal powder of the present invention will be described. Unless otherwise specified,% shown below is atomic%.

Si: 0-17%
Si is an element for stably performing heat treatment by expanding ΔT (difference between compound precipitation temperature and bcc-Fe (-Si) precipitation temperature). If Si exceeds 17%, the amorphous forming ability is lowered, it becomes difficult to obtain a powder containing amorphous as the main phase, and the soft magnetic properties after heat treatment are deteriorated.

B: 2 to 15%
If B is less than 2%, it becomes difficult to form an amorphous phase by quenching, and the soft magnetic properties after heat treatment deteriorate. If B exceeds 15%, the melting point becomes high, which is not preferable in manufacturing, and the amorphous forming ability is also lowered, and the soft magnetic properties are deteriorated, which is not preferable.

P: 0 to 15%
P is an element for easily forming fine and uniform nanocrystal powder and obtaining good magnetic properties. When P exceeds 15%, the balance with other metalloid elements is deteriorated, the amorphous forming ability is lowered, and the saturation magnetic flux density is lowered.

Cr + Nb: 0-5%
Cr forms an oxide film on the powder surface and has an action of improving corrosion resistance. Further, Nb has an action of suppressing the growth of bcc crystal grains and forming fine nanocrystal powder during nanocrystallization. However, by adding Cr and Nb, the amount of Fe is relatively reduced and the saturation magnetic flux density is reduced. Further, since the amorphous forming ability is lowered, it is preferably 5% or less.

Cu: 0.2-2%
If Cu is less than 0.2%, cluster precipitation during nanocrystallization heat treatment is small, and uniform nanocrystallization becomes difficult. On the other hand, if the amount of Cu exceeds 2%, the amount of Cu becomes excessive, so that the amorphous forming ability is lowered and the soft magnetic property is lowered.

Inevitable Impurities Examples of unavoidable impurities include Co, Ni, Zn, Zr, Hf, Mo, Ta, W, Ag, Au, Pd, K, Ca, Mg, Sn, Ti, V, Mn, Al, S, C, O. , N, Bi, and at least one selected from rare earth elements. By including such an element, a uniform nanocrystal powder can be easily obtained after the heat treatment.

The nanocrystal powder can be obtained by dissolving raw materials such as pure iron, ferrosilicon, ferroline, ferroboron, ferrochrome and electrolytic copper at a temperature of 1.25 to 1450 ° C. and pulverizing the powder.

Further, pulverization can be performed by various pulverization methods such as water atomization method, gas atomization method, rotating water flow atomizing method, spray method, cavitation method, spark erosion method, etc., but water atomizing method, gas atomizing method, rotation An atomizing method such as a water flow atomizing method is preferable. In the atomizing method, the mother alloy is melted by a high-frequency induction heating device, and the molten alloy is injected at high speed from a nozzle, and the cooling medium (liquid or gas) is made to collide with the flow of the molten alloy to make the molten alloy fine. This is a method of obtaining nanocrystal powder by alloying and quenching. According to such a method, extremely fine nanocrystal powder can be efficiently produced.

In order to obtain the desired nanocrystal powder, as described above, for example, the powder obtained by the atomizing method is appropriately used in an inert atmosphere for a predetermined time, for example, 0 to 180 minutes at a predetermined temperature. For example, the heat treatment may be performed at 350 to 600 ° C. The heat treatment temperature of 0 minutes means that the reaction is completed during the temperature rise. The heat treatment atmosphere is preferably an inert atmosphere in order to suppress surface oxidation of the powder, but it can also be an oxidizing atmosphere such as air or a reducing atmosphere such as hydrogen for a specific purpose.

In order to obtain the powder magnetic core of the present invention, the nanocrystalline powder obtained as described above and the expandable powder are mixed to prepare a mixed powder, and then the mixed powder is prepared at a molding pressure of, for example, 190 to 2000 MPa. By forming the green compact, the desired green compact can be obtained from the green compact.

At this time, the proportion of the powder in which the orientation angle of the nanocrystal powder is less than 45 ° with respect to the direction perpendicular to the molding direction of the green compact is 65 to 85%, preferably 70 to 80%. Therefore, it is possible to provide a dust core and a method for producing the same, which have a particularly high magnetic permeability and can contribute to the miniaturization of magnetic parts such as reactors.

When molding the mixed powder, the binder is appropriately mixed, the green compact is heat-treated to cure the binder, and the nanocrystal powder and the malleable powder are bonded via the binder. It can also be.

Examples of the binder include organic materials such as silicone resins, epoxy resins, phenol resins, polyamide resins, polyimide resins, polyphenylene sulfide resins, magnesium phosphate, calcium phosphate, zinc phosphate, and manganese phosphate. , Phosphates such as cadmium phosphate, thermosetting inorganic materials such as silicates (water glass) such as sodium silicate, and the like.

(Examples 1 to 5 and Comparative Examples 1 to 2)
A raw material composed of industrial pure iron, ferrosilicon, ferroline, ferroboron, and electrolytic copper _{is weighed so as to have a predetermined alloy composition (Fe 81.9} Si ₄ B ₇ P _6.5 Cu _0.6 ), and an inert atmosphere is obtained. It was melted at 1450 ° C. using medium and high frequency melting. Then, the melted molten alloy was treated by a water atomizing method and classified into −63 μm, ± 90 μm, ± 150 μm, and ± 250 μm to prepare an alloy powder.

The obtained alloy powder was heated in an inert atmosphere using an infrared heating device. The alloy powder was heated to 440 ° C. at a heating rate of 30 ° C. per minute, held for 20 minutes, and then air-cooled. When the powder (nanocrystal powder) after the heat treatment was analyzed by XRD, the crystallinity of each powder was 45% and the crystal grain size was 35 nm.

Next, Fe-Si-Cr powder (expandable powder) having a Vickers hardness Hv of 350 was mixed with the nanocrystal powder at a ratio of 30% by mass so that the mass ratio was 3% with respect to the obtained mixed powder. A binder was added to the mixture, and the mixture was stirred and mixed. Here, a silicone resin was used as the binder.

Next, the particle size of the mixed powder mixed with the binder was adjusted using a mesh having a mesh size of 500 μm to obtain a granulated powder. 2.0 g of this granulated powder was weighed, placed in a mold, and molded at a pressure of 294 MPa by a hydraulic automatic press to produce a cylindrical green compact having an outer diameter of 13 mm and an inner diameter of 8 mm.

Next, the green compact was placed in a constant temperature bath and kept in the air at 150 ° C. for 2 hours to cure the binder.

As an evaluation of the magnetic characteristics of the prepared dust core, the initial magnetic permeability μ at a frequency of 1 MHz was measured using an impedance analyzer. In addition, the cross section of the dust core was observed using an electron microscope, and the direction perpendicular to the molding direction of the powder in the major axis direction in the shape of the nanocrystal powder (ratio of major axis L1 to minor axis L2: L1 / L2). The orientation angle, which is the angle formed with respect to the object, was measured. Specifically, the dust core was embedded in a cold resin, cured, and polished perpendicular to the magnetic path of the dust core to prepare a cross section of the dust core. From elemental mapping by EDX (Energy Dispersive X-ray spectrum), 30 or more nanocrystal powders in the powder magnetic core cross section are randomly selected, and the major axis L1 and minor axis L2 of each powder are measured. At the same time, the orientation angle was examined. The major axis L1 is the longest line segment in each powder, and the minor axis L2 is the longest line segment perpendicular to the major axis.

For the orientation angle, for nanocrystal powder with an L1 / L2 ratio of 1.1 or more, measure the angle of L1 with respect to the direction perpendicular to the molding direction for about 100 pieces, and calculate the proportion of powder with an L1 / L2 ratio of less than 45 °. bottom.

Table 1 shows the magnetic characteristics and powder shape of the dust core and the ratio of the orientation angle of less than 45 degrees when alloy powder classified by -63 μm, ± 90 μm, ± 150 μm, and ± 250 μm is used as the nanocrystal powder. ..

From this, it can be seen that the powder classified by a sieve having a large opening has a higher initial magnetic permeability and L1 / L2 ratio, and a higher proportion of orientation angles of less than 45 degrees. That is, it can be seen that the long axis of the irregularly shaped nanocrystal powder is oriented in the direction perpendicular to the molding direction of the dust core. Further, when the L1 / L2 ratio is too large, the filling rate is lowered and the initial magnetic permeability is lowered.

The larger the opening during classification, the more irregularly shaped powder, and the reason why the long axis of the nanocrystal powder is oriented in the direction perpendicular to the molding direction of the dust core is that the alloy separated by water during atomization. This is because when the molten metal is small, it tends to become spherical due to surface tension, but the large split molten metal solidifies before it becomes spherical.

(Examples 6 to 8 and Comparative Example 3)
A raw material composed of industrial pure iron, ferrosilicon, ferroline, ferroboron, ferrochrome and electrolytic copper is adjusted to have a predetermined alloy composition (Fe _81.4 Si _2.5 B ₆ P _8.5 Cr _1.0 Cu _0.6 ). Weighed in, and dissolved in an inert atmosphere at 1.25 to 1550 ° C. using high frequency dissolution. Then, the melted molten alloy was treated by a water atomizing method and classified at −45 μm to prepare an alloy powder.

The obtained alloy powder was heated in an inert atmosphere using an infrared heating device. The alloy powder was heated to 430 ° C. at a heating rate of 30 ° C. per minute, held for 20 minutes, and then air-cooled. When the powder (nanocrystal powder) after the heat treatment was analyzed by XRD, the crystallinity of each powder was 40% and the crystal grain size was 24 nm.

Next, carbonyl iron powder (expandable powder) having a Vickers hardness Hv of 110 was mixed with the nanocrystal powder at a ratio of 40% by mass so that the mass ratio was 2.5% with respect to the obtained mixed powder. The binder was added, and the mixture was stirred and mixed. Here, a phenol resin was used as the binder.

Next, the particle size of the mixed powder mixed with the binder was adjusted using a mesh having a mesh size of 500 μm to obtain a granulated powder. 2.5 g of this granulated powder was weighed, placed in a mold, and molded at a pressure of 294 MPa by a hydraulic automatic press to produce a cylindrical green compact having an outer diameter of 13 mm and an inner diameter of 8 mm. Next, the green compact was placed in a constant temperature bath and kept in the air at 150 ° C. for 2 hours to cure the binder.

Next, as in the case of Example 1 and the like, the initial magnetic permeability μ at a frequency of 1 MHz was measured using an impedance analyzer as an evaluation of the magnetic characteristics of the produced dust core. Further, the cross section of the dust core was observed using an electron microscope, and the shape (ratio of major axis L1 to minor axis L2: L1 / L2) and orientation angle of the nanocrystal powder were measured.

Table 2 shows the initial magnetic permeability, the L1 / L2 ratio, and the ratio of the orientation angle of less than 45 degrees when the alloy powder melted at 1.25 to 1550 ° C. was used as the nanocrystal powder.

From Table 2, it can be seen that the powder having a lower melting temperature has a larger L1 / L2 ratio, a higher proportion of orientation angles of less than 45 degrees, and a higher initial magnetic permeability. The lower the melting temperature, the shorter the time it takes for the molten alloy to solidify, and the molten alloy solidifies before spheroidization due to surface tension and becomes deformed. This is because it is oriented in the vertical direction.

(Examples 9 to 15)
Raw materials composed of industrial pure iron, ferrosilicon, ferroline, ferrobolon, ferroniobium, ferrochrome and electrolytic copper are weighed so as to have an alloy composition as shown in Table 3 and at 1450 ° C. in an inert atmosphere using high frequency dissolution. Dissolved. Then, the melted molten alloy was treated by a water atomizing method and classified at −150 μm to prepare an alloy powder.

The obtained alloy powder was heated in an inert atmosphere using an infrared heating device. The alloy powder was heated to 440 ° C. at a heating rate of 30 ° C. per minute, held for 20 minutes, and then air-cooled. Next, a powder having a Vickers hardness Hv (expandable powder) as shown in Table 3 was mixed with the nanocrystal powder at a ratio of 40% by mass so as to have a mass ratio of 3% with respect to the obtained mixed powder. The binder was added, and the mixture was stirred and mixed. Here, a phenol resin was used as the binder.

Next, the particle size of the mixed powder mixed with the binder was adjusted using a mesh having a mesh size of 500 μm to obtain a granulated powder. 2.5 g of this granulated powder was weighed, placed in a mold, and molded at a pressure of 780 MPa by a hydraulic automatic press to produce a cylindrical green compact having an outer diameter of 13 mm and an inner diameter of 8 mm. Next, the green compact was placed in a constant temperature bath and held at 160 ° C. for 4 hours in an inert atmosphere to cure the binder.

Next, as in the case of Example 1 and the like, the initial magnetic permeability μ at a frequency of 1 MHz was measured using an impedance analyzer as an evaluation of the magnetic characteristics of the produced dust core. Further, the cross section of the dust core was observed using an electron microscope, and the shape (ratio of major axis L1 to minor axis L2: L1 / L2) and orientation angle of the nanocrystal powder were measured.

From Table 3, it can be seen that the softer the added powder, the larger the L1 / L2 ratio, the higher the ratio of the orientation angle of less than 45 degrees, and the higher the initial magnetic permeability. This is because the added powder functions as an auxiliary agent for facilitating the nanocrystal powder to be oriented in the direction perpendicular to the molding direction of the dust core (compact), so that the nanocrystal powder is the dust core. This is because the powder is oriented in a direction perpendicular to the molding direction of the (compact powder), that is, the major axis of the nanocrystal powder is oriented so as to exhibit high magnetic permeability in the orientation direction.

(Examples 16 to 22)
Raw materials consisting of industrial pure iron, ferrosilicon, ferroline, ferrobolon, ferroniobium, ferrocarbon, ferrochrome and electrolytic copper are weighed so as to have an alloy composition as shown in Table 4, and 1450 is used in an inert atmosphere using high frequency dissolution. Dissolved at ° C. Then, the melted molten alloy was treated by a water atomizing method and classified at −150 μm to prepare an alloy powder.

The obtained alloy powder was heated in an inert atmosphere using an infrared heating device. The alloy powder was heated to 440 ° C. at a heating rate of 30 ° C. per minute, held for 20 minutes, and then air-cooled. Next, the powder (expandable powder) as shown in Table 4 was mixed with the nanocrystal powder at the ratio shown in Table 4, and the binder was added so as to have a mass ratio of 1.5% with respect to the obtained mixed powder. In addition, it was stirred and mixed. Here, a phenol resin was used as the binder.

Next, the particle size of the mixed powder mixed with the binder was adjusted using a mesh having a mesh size of 500 μm to obtain a granulated powder. 4.5 g of this granulated powder was weighed, placed in a mold, and molded at a pressure of 294 MPa by a hydraulic automatic press to produce a cylindrical green compact having an outer diameter of 20 mm and an inner diameter of 13 mm. Next, the green compact was placed in a constant temperature bath and held at 160 ° C. for 4 hours in an inert atmosphere to cure the binder.

Next, as in the case of Example 1 and the like, the initial magnetic permeability μ at a frequency of 1 MHz was measured using an impedance analyzer as an evaluation of the magnetic characteristics of the produced dust core. Further, the cross section of the dust core was observed using an electron microscope, and the shape (ratio of major axis L1 to minor axis L2: L1 / L2) and orientation angle of the nanocrystal powder were measured. Further, the addition ratio of the expandable powder was determined from the area ratio of the expandable powder to the nanocrystal powder in the region defined in the electron micrograph of the dust core in a region of 500 μm × 500 μm.

From Table 4, when the ratio of the expandable powder in the green compact is 10 to 90%, particularly 30 to 70%, the expandable powder, the nanocrystal powder, and the molding direction of the powder magnetic core (compact). Since it functions as an auxiliary agent that facilitates orientation in the vertical direction, the nanocrystal powder is oriented in a direction perpendicular to the molding direction of the dust core (compact powder), that is, the length of the nanocrystal powder. It can be seen that the axes are oriented and exhibit high magnetic permeability in the orientation direction.

(Examples 23 to 28)
Raw materials consisting of industrial pure iron, ferrosilicon, ferroline, ferrobolon, ferroniobium, ferrocarbon, ferrochrome and electrolytic copper are weighed so as to have an alloy composition as shown in Table 5, and 1450 is used in an inert atmosphere using high frequency dissolution. Dissolved at ° C. Then, the melted molten alloy was treated by a water atomizing method and classified at −150 μm to prepare an alloy powder.

The obtained alloy powder was heated in an inert atmosphere using an infrared heating device. The alloy powder was heated to 440 ° C. at a heating rate of 30 ° C. per minute, held for 20 minutes, and then air-cooled. Next, the powder (expandable powder) is mixed with the nanocrystal powder at the ratio shown in Table 5, a binder is added so as to have a mass ratio of 1.5% with respect to the obtained mixed powder, and the mixture is stirred and mixed. bottom. Here, a phenol resin was used as the binder.

Next, the particle size of the mixed powder mixed with the binder was adjusted using a mesh having a mesh size of 500 μm to obtain a granulated powder. 4.5 g of this granulated powder was weighed, placed in a mold, and molded at a pressure of 294 MPa by a hydraulic automatic press to produce a cylindrical green compact having an outer diameter of 20 mm and an inner diameter of 13 mm. Next, the green compact was placed in a constant temperature bath and held at 160 ° C. for 4 hours in an inert atmosphere to cure the binder.

Next, as in the case of Example 1 and the like, the initial magnetic permeability μ at a frequency of 1 MHz was measured using an impedance analyzer as an evaluation of the magnetic characteristics of the produced dust core. In addition, the cross section of the dust core was observed using an electron microscope, and the shape (ratio of major axis L1 to minor axis L2: L1 / L2) and orientation angle of the nanocrystal powder were measured. Further, the addition ratio of the expandable powder was determined from the area ratio of the expandable powder to the nanocrystal powder in the region defined in the electron micrograph of the dust core in a region of 500 μm × 500 μm.

From Table 5, when the particle size ratio of the expandable powder to the nanocrystal powder (particle size of the expandable powder / nanocrystal powder) is 1 or less, particularly less than 0.45, the nanocrystal powder is a dust core (compact powder). Since it is easy to orient in the direction perpendicular to the molding direction of the body), the nanocrystal powder is oriented in the direction perpendicular to the molding direction of the dust core (compact), that is, the major axis of the nanocrystal powder is It is oriented and exhibits high magnetic permeability in the orientation direction.

Although some embodiments of the present invention have been described above, these embodiments are shown as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

Claims (14)

It contains a green compact having a ratio (L1 / L2) of a major axis L1 to a minor axis L2 (L1 / L2) in the range of 1.1 to 5.0 and a malleable powder.
A powder magnetic core, wherein the proportion of the powder having an orientation angle of the nanocrystal powder of less than 45 degrees with respect to a direction perpendicular to the molding direction of the powder is 65 to 85%. The dust core according to claim 1, wherein the malleable powder has a Vickers hardness Hv of 500 or less. The powder magnetic core according to claim 1 or 2, wherein the ratio of the malleable powder to the powder is 10 to 90%. The dust core according to any one of claims 1 to 3, wherein the powder size ratio of the expandable powder to the nanocrystal powder in the green compact is 1 or less. The dust core according to any one of claims 1 to 4, wherein the nanocrystal powder has a crystallinity of 25% or more. The dust core according to any one of claims 1 to 5, wherein the nanocrystal powder has a crystal grain size of 45 nm or less. The composition of the nanocrystal powder is atomic%.
Si: 0-17%,
B: 2 to 15%,
P: 0-15%,
Cr + Nb: 0-5%,
Cu: 0.2-2%,
The powder magnetic core according to any one of claims 1 to 6, wherein the balance is Fe + an unavoidable impurity. A step of preparing nanocrystal powder in which the ratio (L1 / L2) of the major axis L1 to the minor axis L2 is in the range of 1.1 to 5.0, and
The step of mixing the nanocrystal powder and the malleable powder to prepare a mixed powder, and
A process of molding the mixed powder to form a green compact and producing a green compact magnetic core containing the green compact.
A method for producing a dust core, which comprises. The method for producing a dust core according to claim 8, wherein the malleable powder has a Vickers hardness Hv of 500 or less. The method for producing a powder magnetic core according to claim 8 or 9, wherein the ratio of the malleable powder to the powder is 10 to 90%. The method for producing a powder magnetic core according to any one of claims 8 to 10, wherein the particle size ratio of the expandable powder to the nanocrystal powder in the powder is 1 or less. The method for producing a dust core according to any one of claims 8 to 11, wherein the nanocrystal powder has a crystallinity of 25% or more. The method for producing a dust core according to any one of claims 8 to 12, wherein the nanocrystal powder has a crystal grain size of 45 nm or less. The composition of the nanocrystal powder is atomic%.
Si: 0-17%,
B: 2 to 15%,
P: 0-15%,
Cr + Nb: 0-5%,
Cu: 0.2-2%,
The method for producing a dust core according to any one of claims 8 to 13, wherein the balance is Fe + an unavoidable impurity.