WO2023085187A1 - 磁性体及び磁性体の製造方法 - Google Patents

磁性体及び磁性体の製造方法 Download PDF

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Publication number
WO2023085187A1
WO2023085187A1 PCT/JP2022/041013 JP2022041013W WO2023085187A1 WO 2023085187 A1 WO2023085187 A1 WO 2023085187A1 JP 2022041013 W JP2022041013 W JP 2022041013W WO 2023085187 A1 WO2023085187 A1 WO 2023085187A1
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Prior art keywords
magnetic
powder
iron
region
magnetic material
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PCT/JP2022/041013
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English (en)
French (fr)
Japanese (ja)
Inventor
翼 上田
哲矢 小川
宏明 近藤
有紗 平良
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Resonac Corp
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Resonac Corp
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Priority to JP2023559592A priority Critical patent/JPWO2023085187A1/ja
Priority to CN202280072993.6A priority patent/CN118251584A/zh
Publication of WO2023085187A1 publication Critical patent/WO2023085187A1/ja
Anticipated expiration legal-status Critical
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L3/00—Measuring torque, work, mechanical power, or mechanical efficiency, in general
    • G01L3/02—Rotary-transmission dynamometers
    • G01L3/04—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft
    • G01L3/10—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
    • H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
    • H01F1/20—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of particles, e.g. powder
    • H01F1/22—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of particles, e.g. powder pressed, sintered, or bound together
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F17/00—Fixed inductances of the signal type
    • H01F17/04—Fixed inductances of the signal type with magnetic core
    • H01F17/06—Fixed inductances of the signal type with magnetic core with core substantially closed in itself, e.g. toroid
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
    • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets

Definitions

  • the present invention relates to a magnetic material and a method for manufacturing a magnetic material.
  • a magnetostrictive sensor that utilizes the magnetostrictive effect is known as a measurement technique, and a ferromagnetic material is incorporated in the magnetostrictive sensor.
  • Patent Document 1 discloses a torque sensor 1 , and a sensor section 2 of the torque sensor 1 includes a coil 21 and a magnetic ring 22 .
  • the sensor portion 2 of the torque sensor 1 is attached around a magnetostrictive torque sensor shaft 101 having magnetostrictive characteristics.
  • the magnetic material used in the sensor is integrated with a resin bobbin on which a coil is wound by resin molding.
  • the magnetic material when operating the sensor in a high frequency band of 100 kHz or higher, the magnetic material is desired to have high complex magnetic permeability and low iron loss. Therefore, a powder magnetic core, a ferrite magnetic core, or the like, which has low iron loss, is applied as a magnetic material.
  • a powder magnetic core, a ferrite magnetic core, or the like which has low iron loss, is applied as a magnetic material.
  • it is effective to reduce the cross-sectional area of the magnetic path.
  • it is conceivable to reduce the thickness but if the thickness is reduced, cracks are likely to occur in the magnetic body.
  • the surface covered with the iron oxide film containing triiron tetroxide is included in the area where the magnetic path is formed on the inner diameter surface of the green compact after the steam treatment.
  • the eddy current loss of the powder as a whole is suppressed, and it becomes possible to realize a magnetic material for a sensor used at an operating frequency of 100 kHz or higher.
  • One embodiment includes a green compact containing an iron-based powder having an insulating coating on the surface and triiron tetroxide, has a cylindrical shape, and has four regions on the inner diameter surface where the magnetic path is formed.
  • the present invention relates to a magnetic body comprising a surface covered with an iron oxide film containing triiron oxide and intended for sensors used at operating frequencies of 100 kHz or higher.
  • Another embodiment is a method for producing a magnetic material, comprising: compressing and molding a raw material powder containing an iron-based powder having an insulating coating on its surface to obtain a green compact; heat treatment in a water vapor atmosphere, wherein the magnetic body has a cylindrical shape and a surface covered with an iron oxide film containing triiron tetraoxide in a region where a magnetic path is formed on an inner diameter surface;
  • the present invention relates to a method of manufacturing magnetic materials, including for sensors used at operating frequencies of 100 kHz and above.
  • a magnetic material having good magnetic properties and high strength is provided.
  • ADVANTAGE OF THE INVENTION the manufacturing method of the magnetic substance which has a favorable magnetic characteristic and high intensity
  • FIG. 1 is a schematic diagram showing an example of a magnetic body.
  • FIG. 2 is an optical micrograph of a cross section of a magnetic material produced in Examples.
  • each component may contain a plurality of corresponding substances.
  • the content rate or content of each component is the total content rate or content of the multiple types of substances present in the composition unless otherwise specified. means quantity.
  • the term “coating” includes the case where the coating is formed over the entire region when the region where the coating is present is observed, and the case where the coating is formed only in part of the region. included.
  • the term “process” includes not only an independent process, but also a process that achieves an intended effect even if it cannot be clearly distinguished from other processes.
  • a method for producing a magnetic material comprises compression-molding a raw material powder containing an iron-based powder having an insulating coating on the surface to obtain a compact, and placing the compact in a steam atmosphere. heat treating in.
  • a method for manufacturing a magnetic material is a method for manufacturing a magnetic material for use in a sensor used at an operating frequency of 100 kHz or higher (sometimes referred to as a "sensor magnetic material"). The method for manufacturing the magnetic body for sensors may further include any step.
  • the magnetic body has a cylindrical shape, and the region of the inner diameter surface where the magnetic path is formed may include a surface covered with an iron oxide film containing triiron tetraoxide. In some embodiments, the magnetic body may have a cylindrical shape, and the radial thickness of the region where the magnetic path is formed may be 3 mm or less.
  • a method for manufacturing a magnetic material for a sensor includes compression molding of raw material powder containing iron-based powder having an insulating coating on the surface to obtain a green compact (sometimes referred to as a "molding step").
  • the raw material powder contains an iron-based powder (sometimes simply referred to as "iron-based powder") having an insulating coating on its surface.
  • the iron-based powder having an insulating coating on its surface includes metal powder containing iron and an insulating coating covering at least part of the surface of the metal powder.
  • the insulating coating can suppress eddy currents.
  • the raw material powder may contain one type of iron-based powder alone, or may contain two or more types in combination.
  • the metal powder may contain, for example, at least one selected from the group consisting of a single powder of iron and an alloy powder containing iron.
  • the metal powder may be a powder made of at least one selected from the group consisting of a single powder of iron and an alloy powder containing iron.
  • the iron-containing alloy may contain at least one selected from the group consisting of solid solutions, eutectics, and intermetallic compounds.
  • the alloy may be, for example, stainless steel (Fe--Cr alloy, Fe--Ni--Cr alloy, etc.).
  • the metal powder may be amorphous.
  • the metal powder may contain multiple types of metal elements.
  • the metal powder may contain, in addition to iron, at least one element selected from the group consisting of base metal elements, noble metal elements, transition metal elements, and rare earth elements.
  • the alloy powder containing iron may be, for example, a soft magnetic alloy containing iron as a main component.
  • the content of iron in the metal powder may be, for example, 50% by mass or more, 70% by mass or more, or 90% by mass or more based on the mass of the metal powder.
  • the metal powder includes Fe—Si alloy powder, Fe—Si—Al alloy powder, Fe—Ni alloy powder, Fe—Cu—Ni alloy powder, Fe—Co alloy powder, Fe—Cr - At least one selected from the group consisting of Si-based alloy powder, iron-based amorphous alloy powder, and the like may be included. From the viewpoint of maintaining the iron oxide film on the inner diameter surface to be formed later, pure iron, which is a material with high dimensional stability, is preferable.
  • the shape of individual metal particles contained in the metal powder is not particularly limited. Individual metal particles are, for example, flattened, spherical, or acicular.
  • the average particle size of the iron-based powder is, for example, 60 ⁇ m or more and 250 ⁇ m or less.
  • the average particle size of the metal powder can be measured according to the metal powder-dry sieving particle size test method (ISO 4497:2020). When the average particle size of the iron-based powder is 60 ⁇ m or more, there is a tendency that sufficient strength of the magnetic material can be secured.
  • the average particle size may be 80 ⁇ m or more, or 100 ⁇ m or more. When the average particle size of the iron-based powder is 250 ⁇ m or less, it is easy to obtain a magnetic material having a high density and good magnetic properties.
  • the average particle size may be 220 ⁇ m or less, or 200 ⁇ m or less.
  • the average particle size of the iron-based powder may be, for example, 80-220 ⁇ m, or 100-200 ⁇ m.
  • the insulating coating may contain at least one coating selected from the group consisting of inorganic compound coatings and organic compound coatings.
  • the insulating coating may be a single layer coating or a coating comprising multiple layers.
  • Inorganic compound coatings include phosphates such as aluminum phosphate, zinc phosphate, iron phosphate, manganese phosphate, and calcium phosphate; borates such as lithium borate, magnesium borate, and calcium borate; aluminum silicate, silicon At least one selected from the group consisting of silicates such as potassium acid and calcium silicate; carbonates such as lithium carbonate, sodium carbonate, aluminum carbonate, calcium carbonate and barium carbonate; and oxides such as silicon oxide and tungsten oxide. Contains seeds.
  • the organic compound film contains, for example, at least one selected from the group consisting of silicone resins, polyimide resins, polyamide resins, polyamideimide resins, phenol resins, epoxy resins, and fatty acids.
  • the insulating coating is preferably a coating containing phosphate.
  • the insulating coating may be formed on a part of the surface of each metal particle contained in the metal powder, or may be formed on the entire surface. That is, the iron-based powder has an insulating coating on at least part of the surface or the entire surface.
  • the raw material powder may contain any powder in addition to the iron-based powder.
  • powders for example, soft magnetic powders not having an insulating coating; metal powders, alloy powders and metal oxides mainly composed of chromium, copper, etc.; Additives such as viscosity improvers can be used. Among them, it is preferable to contain a powder lubricant in order to reduce the ejection pressure after molding.
  • powdery lubricants examples include metal soaps such as zinc stearate and calcium stearate; amide-based lubricants such as stearamide, stearamide bisamide, and ethylenebisstearate amide.
  • metal soaps such as zinc stearate and calcium stearate
  • amide-based lubricants such as stearamide, stearamide bisamide, and ethylenebisstearate amide.
  • the powder lubricant it is preferable to use a compound with a small molecular weight because it has good degreasing properties. Powder lubricants may be used singly or in combination of two or more.
  • the content of the powder lubricant in the raw material powder is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, more preferably 0.2% by mass or more, based on the mass of the iron-based powder, from the viewpoint of obtaining a sufficient effect by use. 0.3 mass % or more is more preferable. From the viewpoint of obtaining sufficient magnetic properties, the content of the powder lubricant is preferably 3% by mass or less, more preferably 2% by mass or less, further preferably 1% by mass or less, based on the mass of the iron-based powder. 0.5% by mass or less is particularly preferred.
  • the powder lubricant content may be, for example, 0.1-2% by weight, 0.2-1% by weight, or 0.3-0.5% by weight.
  • compression molding By compression molding, the raw material powder is molded to obtain a green compact. For example, raw material powder is compressed by upper and lower punches. At the time of molding, a mold lubricating agent may be applied to the mold to carry out mold lubrication molding.
  • the shape of the green compact is, for example, cylindrical, and the cylindrical shape may be hollow.
  • the molding pressure is, for example, 400 MPa or more, 500 MPa or more, or 600 MPa or more from the viewpoint of obtaining a green compact with high accuracy and obtaining good magnetic properties.
  • the molding pressure is, for example, 1,000 MPa or less, 900 MPa or less, or 800 MPa or less from the viewpoint of durability of the mold. Molding pressures may be, for example, 400-1,000 MPa, 500-900 MPa, or 600-800 MPa.
  • the mold may be heated, or the raw material powder and the mold may be heated to perform warm molding.
  • the heating temperature is, for example, 80 to 140°C.
  • the density of the powder compact is, for example, 6.5 g/cm 3 or more, 6.8 g/cm 3 or more, or 7.2 g/cm 3 or more from the viewpoint of obtaining good magnetic properties.
  • the density of the compact is, for example, 7.8 g/cm 3 or less, 7.6 g/cm 3 or less, or 7.4 g/cm 3 or less.
  • the density of the green compact can be measured according to Metal Powders Except for Cemented Carbide—Measurement of Uniaxial Compressibility (ISO 3927:2001).
  • the density of the compact may be, for example, 6.5-7.8 g/cm 3 , 6.8-7.6 g/cm 3 , or 7.2-7.4 g/cm 3 .
  • a method for manufacturing a magnetic material for a sensor includes heat-treating a powder compact in a steam atmosphere (sometimes referred to as a "steam treatment step").
  • triiron tetroxide Fe 3 O 4
  • Triiron tetroxide usually forms on the surface of iron-based powders exposed to water vapor. Due to the intimate contact of the individual iron-based particles contained in the iron-based powder, the iron-based powder may also contain surfaces that are not exposed to water vapor. Iron-based powder surfaces that are not exposed to water vapor generally do not form triiron tetroxide.
  • the heat treatment temperature is, for example, 300-600°C.
  • the heat treatment time is, for example, 5 to 60 minutes.
  • the heat treatment in a water vapor atmosphere may be exposing the green compact to high temperature water vapor.
  • As a method of exposing to water vapor there is a method of injecting water vapor onto the powder compact. Water vapor permeates from the surface of the green compact into the internal pores, and triiron tetroxide is generated on the surface of the green compact and at the interface between the iron-based powder and the pores.
  • the temperature of steam is, for example, 300-600.degree.
  • the exposure time to steam is, for example, 5 to 60 minutes. From the viewpoint of concentrating the iron oxide film containing triiron tetraoxide on the surface of the powder compact, it is preferable to perform the treatment at a high temperature of 500° C. or higher for a short time of 30 minutes or less, for example.
  • a pressurized furnace or normal pressure furnace can be used for heat treatment in a steam atmosphere.
  • belt furnaces such as a pot-type furnace and a mesh belt furnace that can maintain high pressure can be used.
  • the magnetic material obtained by heat-treating the powder compact in a water vapor atmosphere has high strength. It is believed that the triiron tetraoxide produced by the oxidation of the iron-based powder enhances the strength of the magnetic material.
  • a magnetic body having high strength can withstand the pressure during resin molding, and can prevent cracks from occurring during molding.
  • the surface of the magnetic material obtained by heat-treating the green compact in a water vapor atmosphere is covered with an iron oxide film containing triiron tetraoxide.
  • the thickness of the iron oxide film containing triiron tetroxide can be adjusted by changing the conditions such as the atmosphere, temperature and time when the green compact is heat-treated in the steam atmosphere.
  • steps that the method for manufacturing a magnetic material for a sensor may include, preparing a raw material powder, heat-treating the green compact (heat treatment step), and cutting the green compact into a desired shape (cutting process) and the like.
  • Heat treatment process In the heat treatment step, heat is applied to the green compact to impart desired properties to the green compact according to the application. Heat treatment can improve properties such as, for example, strength, hardness, and impact resistance.
  • the heat treatment here does not include heat treatment of the green compact in a steam atmosphere.
  • the atmosphere in which the heat treatment is performed may be the air, but a gas atmosphere in which the green compact is less likely to oxidize is preferable.
  • non-oxidizing gas such as nitrogen gas, reducing gas such as cracked ammonia gas, carburizing gas (for example, a mixture of hydrogen, nitrogen, and carbon monoxide with a carbon potential within the range of 0.1 to 1.2%) gas), etc.
  • the heat treatment temperature is, for example, 300 to 600.degree.
  • the heat treatment time is, for example, 5 to 60 minutes.
  • the magnetic material manufacturing method includes a heat treatment step between the molding step and the steam treatment step.
  • the method for producing the magnetic material may include compression molding of the raw material powder to obtain a green compact; heat treatment of the green compact; and heat treatment of the green compact in a steam atmosphere.
  • the compact is cut into a desired shape.
  • cutting may be turning, milling, or both.
  • Materials for cutting tools include cermet, ceramics, cemented carbide, high-speed tool steel, diamond sintered bodies, cBN sintered bodies, and the like.
  • the magnetic body may include a molded surface.
  • the manufacturing method of the magnetic body does not include cutting the green compact, or cuts only a part of the surface of the green compact.
  • may contain When the green compact is cylindrical, for example, the part of the surface may be the outer peripheral surface of the cylindrical green compact.
  • the magnetic body has a cylindrical shape, and the region of the inner diameter surface where the magnetic path is formed may include a surface covered with an iron oxide film containing triiron tetraoxide.
  • the magnetic body manufacturing method includes cutting the compact. It may not include, or it may include cutting only a portion of the surface of the green compact.
  • the part of the surface may be the outer peripheral surface of the cylindrical green compact.
  • the magnetic material obtained by the method for manufacturing a magnetic material for sensors includes a green compact heat-treated in a water vapor atmosphere. Magnetic materials are used in sensors used at operating frequencies above 100 kHz.
  • the description of the magnetic body for sensor which is an embodiment of the present invention described below can also be applied to the magnetic body obtained by the method for manufacturing the magnetic body for sensor.
  • a magnetic material that is an embodiment of the present invention includes a powder compact containing an iron-based powder having an insulating coating on its surface and triiron tetroxide (Fe 3 O 4 ).
  • the sensor magnetic material may further contain any component. The above explanations regarding the iron-based powder, green compact, magnetic material, etc. can also be applied to the magnetic material of this embodiment.
  • triiron tetroxide in the powder compact can be confirmed using, for example, X-ray photoelectric spectroscopy (XPS). If a peak occurs between binding energies of 711 eV and 708 eV in a spectrum obtained by analysis by X-ray photoelectric spectroscopy (XPS), it can be said that the green compact contains triiron tetroxide.
  • XPS X-ray photoelectric spectroscopy
  • a magnetic material that is an embodiment of the present invention is a magnetic material for use in a sensor that is used at an operating frequency of 100 kHz or higher.
  • the operating frequency may be 200 kHz or higher.
  • the upper limit of the operating frequency is not particularly limited, it is, for example, 1 MHz or less.
  • the sensor may be a magnetostrictive torque sensor.
  • FIG. 1 is a schematic diagram showing an example of a magnetic body.
  • (a) is a schematic front view
  • (b) is a schematic cross-sectional view taken along the line AA of the magnetic body shown in (a).
  • t represents the radial thickness of the region where the magnetic path is formed.
  • the magnetic body shown in FIG. 1 is arranged outside a resin bobbin around which a coil is wound, and is used in a state of being mounted around a torque sensor shaft together with the resin bobbin.
  • the radial thickness of the region where the magnetic path of the magnetic material is formed is, for example, 8 mm or less, or 5 mm or less. There is a tendency that the thinner the radial thickness of the region where the magnetic path is formed, the more the eddy current loss can be suppressed. From the viewpoint of obtaining good magnetic properties, the radial thickness of the region where the magnetic path is formed is preferably 3 mm or less. From the viewpoint of strength, the radial thickness of the region where the magnetic path is formed is, for example, 1 mm or more.
  • At least part of the surface of the magnetic body may be a molded surface.
  • the region of the inner diameter surface of the magnetic body where the magnetic path is formed includes a molded surface.
  • the region in which a magnetic path is formed means a magnetic path formed by a magnetostrictive material (for example, a shaft) to which torque is applied and a magnetic body when the magnetic body is incorporated in a sensor and used. It may be a certain area.
  • the region of the inner diameter surface where the magnetic path is formed refers to the portion of the inner diameter surface of the magnetic body that corresponds to the region where the magnetic path is formed.
  • the molded surface refers to the surface that has not been subjected to processing such as cutting after compression molding and extrusion from the mold. If the region of the inner diameter surface where the magnetic path is formed is a molded surface, eddy current loss tends to be suppressed.
  • Whether or not the green compact before steam treatment has a molded surface can be confirmed by checking whether an insulating coating is present on the surface of the green compact. Whether or not the insulating coating is present can be determined, for example, by measuring the specific resistance of the surface of the green compact. The specific resistance of the molded surface is large, and the specific resistance of the surface subjected to processing such as cutting tends to be about the same as that of the iron-based powder.
  • whether or not the magnetic material has a molded surface can be confirmed by checking whether triiron tetroxide is present on the surface of the magnetic material. Whether or not triiron tetraoxide is present can be determined, for example, by visual observation. In the presence of triiron tetroxide, the surface of the magnetic material assumes a dark gray or black color.
  • the magnetic body has a cylindrical shape, and the region of the inner diameter surface where the magnetic path is formed may include a surface covered with an iron oxide film containing triiron tetraoxide.
  • the magnetic body has an iron oxide film containing triiron tetroxide in the region where the magnetic path is formed on the inner diameter surface, eddy current loss tends to be suppressed.
  • the ratio of the area of the surface covered with the iron oxide film containing triiron tetraoxide to the area of the region where the magnetic path is formed on the inner diameter surface is most preferably 100%, but depending on the application, it may be 90% or more, or , 95% or more.
  • the ratio of the area of the surface covered with the iron oxide film containing triiron tetraoxide to the area of the region where the magnetic path is formed on the inner diameter surface is, for example, the area of the surface not subjected to cutting etc. and the area of cutting etc. It can be calculated from the area of the surface on which the
  • the thickness of the iron oxide film containing triiron tetraoxide is, for example, 1 ⁇ m or less.
  • the thickness of the iron oxide film containing triiron tetroxide can be measured by taking an SEM photograph and enlarging it appropriately. Eddy current loss tends to be suppressed when the thickness of the iron oxide film containing triiron tetraoxide is 2 ⁇ m or less.
  • the thickness may be 3 ⁇ m or less, or 5 ⁇ m or less.
  • the thickness of the iron oxide film containing triiron tetraoxide is 0.1 ⁇ m or more, it has a high density and good magnetic properties are easily obtained.
  • the thickness of the iron oxide film containing triiron tetroxide may be, for example, 0.1-5 ⁇ m, 0.1-3 ⁇ m, or 0.1-1 ⁇ m.
  • eddy currents can be suppressed by including a surface covered with an iron oxide film containing triiron tetroxide in the region where the magnetic path is formed on the inner diameter surface of the magnetic body. It is possible to use magnetic materials at operating frequencies as high as 100 kHz or higher.
  • the sensor magnetic body can be manufactured, for example, by the method for manufacturing the sensor magnetic body of the above embodiment.
  • a magnetic material for a sensor used at an operating frequency of 100 kHz or higher comprising an iron-based powder having an insulating coating on its surface and a green compact containing triiron tetroxide.
  • the magnetic body according to (1) above which has a cylindrical shape, and wherein the region of the inner diameter surface where the magnetic path is formed includes a surface covered with an iron oxide film containing triiron tetroxide.
  • the magnetic body according to any one of (1) to (5) above, which has a cylindrical shape and wherein the region of the inner diameter surface where the magnetic path is formed includes a molded surface.
  • the sensor is a magnetostrictive torque sensor.
  • a method for manufacturing a magnetic material Compressing a raw material powder containing an iron-based powder having an insulating coating on the surface to obtain a compact, and heat-treating the powder compact in a water vapor atmosphere;
  • a method of manufacturing a magnetic material for sensors used at operating frequencies of 100 kHz or higher comprising: (9) The above-described (8), wherein the magnetic body has a cylindrical shape, and the region of the inner diameter surface where the magnetic path is formed includes a surface covered with an iron oxide film containing triiron tetraoxide.
  • Example 1 Evaluation of strength
  • a dust core material (“Somaloy 700 3P” manufactured by Höganäs AB) containing a pure iron powder having a phosphate coating as an insulating coating on the surface and a powder lubricant (“Lube 3P”). : about 0.3 to 0.4% by mass with respect to the pure iron powder having a phosphate coating).
  • the average particle size of the pure iron powder (spherical) with a phosphate coating was 150 ⁇ m. The average particle size was measured according to the metal powder-dry sieving particle size test method (ISO 4497:2020).
  • the powder magnetic core material was compression-molded using a hydraulic press to obtain a rectangular parallelepiped powder compact.
  • the compacting pressure was 686 MPa, and the density of the green compact was 7.4 g/cm 3 .
  • the rectangular parallelepiped compact had a short side of 12 mm, a long side of 34 mm, and a thickness of 5 mm.
  • the green compact was heated in a nitrogen atmosphere at 500° C. for 30 minutes to obtain a powder magnetic core of Sample No. 01, which is a magnetic material.
  • the compact was heated in a nitrogen atmosphere at 500° C. for 30 minutes and then heated in a water vapor atmosphere at 530° C. for 20 minutes to obtain a powder magnetic core of sample number 02. .
  • the surfaces of the dust cores were evaluated by XPS, and it was confirmed that the dust core of sample number 01 did not contain triiron tetroxide, and the dust core of sample number 02 contained triiron tetroxide.
  • an XPS apparatus was used to measure the peak of iron, which is the main element contained in the surface of the powder magnetic core, and after deconvolution, the presence or absence of the peak of triiron tetraoxide was confirmed.
  • the density of the green compact was measured in accordance with the method for measuring uniaxial compressibility (ISO 3927:2001) for metal powders other than those for cemented carbide.
  • Table 1 shows that the strength of the dust core is improved by including triiron tetraoxide.
  • Example 2 Evaluation of magnetic properties
  • the same powder magnetic core material as the powder magnetic core material used in Example 1 was prepared.
  • the powder magnetic core material was compression-molded using a hydraulic press to obtain cylindrical powder compacts of sample numbers 03 to 07.
  • the compacting pressure was 686 MPa, and the density of the green compact was 7.4 g/cm 3 .
  • the cylindrical compact had an inner diameter of 20 mm and a total length of 5 mm.
  • the radial thickness of the ring-shaped compact is 5 mm for the compact of sample number 03, 4 mm for the compact for sample number 04, 3 mm for the compact for sample number 05, and 3 mm for the compact for sample number 06.
  • the body was 2 mm, and the green compact of sample number 07 was 1 mm.
  • sample numbers 03 to 07 were heated in a nitrogen atmosphere at 500 ° C. for 30 minutes, and then heated in water vapor at 530 ° C. for 20 minutes to form cylinders of sample numbers 03 to 07.
  • a powder magnetic core with a shape was obtained.
  • the surfaces of the powder magnetic cores of sample numbers 03 to 07 were evaluated by XPS, and it was confirmed that all the powder magnetic cores contained triiron tetroxide. Further, the powder magnetic cores of sample numbers 03 to 07 had molded surfaces.
  • FIG. 2 shows an optical microscope photograph (magnification: 300) of the cross section of the powder magnetic core of sample number 06. As shown in FIG. In the photograph, the black line indicates the insulating film, the black area indicates pores, the dark gray indicates triiron tetroxide, and the light gray indicates iron-based powder.
  • Table 2 shows that the magnetic properties improve as the radial thickness of the cylindrical dust core decreases.
  • Example 3 The same powder magnetic core material as the powder magnetic core material used in Example 1 was prepared.
  • the powder magnetic core material was compression-molded using a hydraulic press to obtain cylindrical powder compacts of sample numbers 08 and 09.
  • the compacting pressure was 686 MPa, and the density of the green compact was 7.4 g/cm 3 .
  • the green compact of sample number 08 had an outer diameter of 24 mm, an inner diameter of 19 mm, and an overall length of 5 mm.
  • the green compact of sample number 09 had an outer diameter of 24 mm, an inner diameter of 20 mm, and an overall length of 5 mm.
  • the compacts of sample numbers 08 and 09 were heated in a nitrogen atmosphere at 500 ° C.
  • a dust core of No. 09 was obtained.
  • the heat-treated body of sample number 08 was cut into a cylindrical shape having an outer diameter of 24 mm, an inner diameter of 20 mm, and a total length of 5 mm by cutting using a lathe, and a dust core of sample number 08 was obtained. Obtained.
  • the surfaces of the powder magnetic cores of sample numbers 08 and 09 were evaluated by XPS, and it was confirmed that the powder magnetic cores contained triiron tetroxide.
  • the primary and secondary coils were wound 12 times in the poloidal direction of the cylindrical dust core.
  • the complex magnetic permeability was measured at a frequency of 200 kHz and an excitation magnetic flux density of 0.01 T using an AC magnetic property measuring device.
  • "SY-8258" manufactured by Iwasaki Tsushinki Co., Ltd. was used as an AC magnetization property measuring device. The measured results are shown in Table 3 below.
  • Table 3 shows that, in the powder magnetic core, the magnetic properties are improved by forming the area where the magnetic path is formed on the inner diameter surface is a molded surface. Table 3 shows that in the powder magnetic core, the magnetic properties are improved by including the surface covered with the iron oxide film containing triiron tetroxide in the region where the magnetic path is formed on the inner diameter surface. .

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