WO2014097556A1 - 圧粉磁芯用鉄粉 - Google Patents
圧粉磁芯用鉄粉 Download PDFInfo
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- WO2014097556A1 WO2014097556A1 PCT/JP2013/007055 JP2013007055W WO2014097556A1 WO 2014097556 A1 WO2014097556 A1 WO 2014097556A1 JP 2013007055 W JP2013007055 W JP 2013007055W WO 2014097556 A1 WO2014097556 A1 WO 2014097556A1
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- 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
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/05—Metallic powder characterised by the size or surface area of the particles
- B22F1/052—Metallic powder characterised by the size or surface area of the particles characterised by a mixture of particles of different sizes or by the particle size distribution
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- B22—CASTING; POWDER METALLURGY
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- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/08—Metallic powder characterised by particles having an amorphous microstructure
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- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
- B22F1/102—Metallic powder coated with organic material
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- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
- B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
- B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
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- B22—CASTING; POWDER METALLURGY
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- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/16—Making metallic powder or suspensions thereof using chemical processes
- B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
- B22F9/20—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from solid metal compounds
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
- C21D3/02—Extraction of non-metals
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
- C21D3/02—Extraction of non-metals
- C21D3/04—Decarburising
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- 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
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- 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
- H01F1/24—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 the particles being insulated
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F3/00—Cores, Yokes, or armatures
- H01F3/08—Cores, Yokes, or armatures made from powder
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
- B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
- B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
- B22F2009/0824—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid with a specific atomising fluid
- B22F2009/0828—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid with a specific atomising fluid with water
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- B22F2301/00—Metallic composition of the powder or its coating
- B22F2301/35—Iron
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- B22F2304/00—Physical aspects of the powder
- B22F2304/10—Micron size particles, i.e. above 1 micrometer up to 500 micrometer
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
- B22F2998/10—Processes characterised by the sequence of their steps
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C2202/00—Physical properties
- C22C2202/02—Magnetic
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/02—Making ferrous alloys by powder metallurgy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F27/00—Details of transformers or inductances, in general
- H01F27/24—Magnetic cores
Definitions
- the present invention relates to an iron powder for a dust core in which a powder core having a low iron loss and a high density can be obtained.
- Magnetic cores used in motors and transformers are required to have high magnetic flux density and low iron loss.
- a laminate of electromagnetic steel sheets has been used as such a magnetic core, but in recent years, a dust core has attracted attention as a magnetic core material for motors.
- the biggest feature of the dust core is that a three-dimensional magnetic circuit can be formed. Since magnetic steel sheets form magnetic cores by lamination, there is a limit to the degree of freedom in shape. However, in the case of a dust core, since the soft magnetic particles coated with insulation are pressed and molded, if there is only a mold, the degree of freedom of the shape exceeding that of the electromagnetic steel sheet can be obtained.
- press forming has a short process and low cost compared to the lamination of steel plates, and it combines with the low cost of the base powder to demonstrate excellent cost performance. Furthermore, since the magnetic steel sheets are laminated with the steel plate surfaces insulated, the magnetic characteristics are different between the steel sheet surface direction and the surface vertical direction, and the magnetic properties in the surface vertical direction are poor. Since each particle is covered with an insulating coating, the magnetic properties are uniform in all directions, and it is suitable for use in a three-dimensional magnetic circuit.
- the dust core is an indispensable material for designing a three-dimensional magnetic circuit and has excellent cost performance. From this point of view, research and development of a motor having a three-dimensional magnetic circuit using a dust core has been actively conducted.
- Patent Document 1 and Patent Document 2 as impurities, mass%, C: 0.005% or less, Si: more than 0.01% Iron powder containing 0.03% or less, Mn: 0.03% or more and 0.07% or less, P: 0.01% or less, S: 0.01% or less, O: 0.10% or less, and N: 0.001% or less,
- a technology relating to a highly compressible iron powder having an average number of crystal grains of 4 or less and a micro Vickers hardness HV of 80 or less on average is disclosed.
- Patent Document 3 discloses that the impurity content is C ⁇ 0.005%, Si ⁇ 0.010%, Mn ⁇ 0.050%, P ⁇ 0.010%, S ⁇ 0.010%, O ⁇ 0.10% and N ⁇ 0.0020%, and the balance.
- Is substantially composed of Fe and inevitable impurities, and its particle size composition is sieving weight ratio (%) using a sieve defined in JIS Z 8801, -60 / + 83 mesh is 5% or less, and -83 / + 100 mesh is 4 % To 10%, -100 / + 140 mesh is 10% to 25%, 330 mesh passage is 10% to 30%, and the average grain size of -60 / + 200 mesh is specified in JIS G 0052 Coarse crystal grains of 6.0 or less according to the ferrite crystal grain size measurement method, when 0.75% of zinc stearate is blended as a lubricant for powder metallurgy and molded at a molding pressure of 5 t / cm 2 , 7.05 g / A pure iron powder for powder metallurgy excellent in compressibility and magnetic properties capable of obtaining a green compact density of cm 3 or more is disclosed.
- the particle size distribution of the iron powder is mass% obtained by sieving using a sieve defined in JIS Z 8801, passing through a sieve having a nominal size of 1 mm and passing through a sieve having a nominal size of 250 ⁇ m.
- the upper limit of the micro Vickers hardness of the iron powder having a particle size that does not pass through a 150 ⁇ m sieve is 110 or less, and the impurity content of the iron powder is mass%, C ⁇ 0.005%, Si ⁇ 0.01%, Mn ⁇ 0.05 %, P ⁇ 0.01%, S ⁇ 0.01%, O ⁇ 0.10% and N ⁇ 0.003% are disclosed. It is.
- Patent Document 4 discloses that the particle size composition of iron powder is a mass% obtained by sieving using a sieve defined in JIS Z 8801, passing through a sieve having a nominal size of 1 mm and passing through a sieve having a nominal size of 180 ⁇ m.
- Non-granular particles with a particle size exceeding 0% and 2% or less, passing through a sieve with a nominal size of 180 ⁇ m, and those having a particle size not passing through a sieve with a nominal size of 150 ⁇ m The upper limit of the micro Vickers hardness of the iron powder with a particle size that does not pass through the sieve having a nominal size of 150 ⁇ m is 110 or less, and the iron powder contains impurities.
- Technology related to highly compressible iron powder 2 in which the amount is% by mass, C ⁇ 0.005%, Si ⁇ 0.01%, Mn ⁇ 0.05%, P ⁇ 0.01%, S ⁇ 0.01%, O ⁇ 0.10% and N ⁇ 0.003% Are also disclosed.
- Patent Document 1 and Patent Document 2 can obtain a high-density molded body, there is no mention of iron loss, and studies on reducing iron loss are insufficient. Further, in Patent Document 3, as in Patent Documents 1 and 2, studies relating to higher density are mainly described, and the description relating to lowering iron loss is still insufficient. Furthermore, the highly compressible iron powders 1 and 2 of Patent Document 4 are both specialized for increasing the magnetic flux density, as in the techniques described in Patent Documents 1 to 3, and are concerned with reducing iron loss. Has not been made.
- the present invention has been developed in view of the above-described present situation, and an object thereof is to provide iron powder for a dust core having excellent compressibility and low iron loss after molding.
- the gist configuration of the present invention is as follows. 1. An iron powder for a dust core made of pure iron powder obtained by a water atomization method, The pure iron powder contains Si: 0.01 mass% or less, Apparent density: 3.8g / cm 3 or more, Iron powder particle size: the ratio of 45 ⁇ m or less is 10mass% or less, Iron powder particle size: The ratio of more than 180 ⁇ m and less than 250 ⁇ m is less than 30mass%, The ratio of iron powder particle size over 250 ⁇ m is 10mass% or less, Iron powder for dust cores with a Vickers hardness (test force: 0.245 N) of the powder cross section of 80 Hv or less.
- Si content When Si is contained in molten steel, pure iron powder obtained by the water atomization method (hereinafter also simply referred to as powder or iron powder) is oxidized during water atomization to produce oxide inclusions in the grains. As a result, hysteresis loss increases. Moreover, since the fine Si oxide produced
- the iron powder is plastically deformed by press molding to form a high-density molded body.
- fine iron powder with a grain size of 45 ⁇ m or less is possible because it greatly increases hysteresis loss. It is necessary to reduce as much as possible.
- the apparent density of the powder is 3.8 g / cm 3 or more. It is essential and is preferably 4.0 g / cm 3 or more.
- the apparent density is an index indicating the degree of powder filling rate and can be measured by a test method defined in JIS Z 2504.
- the iron powder according to the present invention mainly has a particle size of more than 45 ⁇ m and a particle size of 180 ⁇ m or less (50 mass% or more and may be 100 mass%), but a fine iron powder having a particle diameter of 45 ⁇ m or less has a hysteresis loss.
- 10 mass% or less is essential, Preferably it is 5 mass% or less. It may be 0 mass%.
- the proportion of iron powder of 45 ⁇ m or less can be determined by sieving using a sieve defined in JIS Z 8801-1.
- coarse iron powder having a particle size of more than 180 ⁇ m has high compressibility, so it needs to be contained at a certain ratio.
- excessive inclusion causes an increase in eddy current loss. Therefore, it is necessary that the iron powder having a particle size of more than 180 ⁇ m and 250 ⁇ m or less is less than 30 mass%, and the iron powder of more than 250 ⁇ m is 10 mass% or less.
- the iron powder having a particle size of more than 180 ⁇ m and 250 ⁇ m or less is 25 mass% or less, and the iron powder of more than 250 ⁇ m is 5 mass% or less.
- 0 mass% may be sufficient respectively.
- iron powder which is the object to be measured, is mixed with thermoplastic resin powder to make a mixed powder, then this mixed powder is charged into an appropriate mold, heated to melt the resin, and then cooled and solidified. , Iron powder-containing resin solids.
- the surface of the iron powder-containing resin solid material cut with an appropriate cross section is polished, and after the processed layer is removed by corrosion, a micro Vickers hardness tester (test force: 0.245 N (25 gf)) is used. Then measure the hardness of the iron powder. The measurement is performed at one point for each particle, and it is preferable to measure the hardness of at least 10 powders and use the average value.
- the powder to be measured needs to have a size that can accommodate the indentation, so that the powder particle size is preferably 100 ⁇ m or more. Except for the above procedure, measurement is performed according to JIS Z2244.
- the iron powder for a dust core in the present invention is obtained by a water atomizing method, and the molten steel has a normal pure iron powder composition except Si, C, O, S and N.
- Si Si ⁇ 0.01 mass%
- C may be added to the composition of pure iron powder or more for deoxidation, but it is preferable to decarburize in a subsequent process and finally reduce it to 0.01 mass% or less.
- the composition of the pure iron powder is equivalent to 300A, which is a pure iron powder for powder metallurgy commercially available from JFE Steel Corporation.
- this powder is subjected to reduction annealing.
- the reduction annealing is preferably performed in a reducing atmosphere containing hydrogen, and is preferably performed at a temperature of 800 ° C. or higher and lower than 1100 ° C. for 1 h or longer and 5 h or shorter.
- the iron powder after atomization contains a large amount of C, it is carried out by including water vapor in hydrogen.
- the amount of water vapor is not particularly limited and can be appropriately changed according to the amount of C in the iron powder. However, it is general to add water vapor so that the dew point is about 30 to 60 ° C.
- the agglomeration is solved by a crushing step, and sieved so that particles of 45 ⁇ m or less become 10 mass% or less. Also, coarse powder can be removed by appropriate sieving.
- sieving there is a method of sieving using a sieve defined in JIS Z 8801-1.
- the apparent density of the iron powder after sieving is less than 3.8 g / cm 3
- the apparent density is reduced to 3.8 g by adjusting the particle size or spheroidizing (Japanese Patent Publication No. 64-21001). / cm 3 or more.
- the spheroidizing treatment it is preferable to perform strain relief annealing in a hydrogen atmosphere at a temperature of 700 ° C. to 850 ° C. for about 1 to 5 hours in order to remove strain during processing.
- an insulating coating on the surface of the iron powder.
- This insulating coating may be anything as long as it can maintain the insulating properties between the particles, but as such an insulating coating, a glassy insulating amorphous based on a silicone resin, a metal phosphate or a metal borate is used. Examples include layers, metal oxides such as MgO, forsterite, talc and Al 2 O 3 , or crystalline insulating layers based on SiO 2 .
- the iron powder coated with the insulating coating is inserted into a mold and press-molded into a desired size and shape (a dust core shape) to form a dust core.
- the pressure molding method any ordinary molding method such as a room temperature molding method or a mold lubrication molding method can be applied.
- the preferred molding pressure is 981 MPa (10 t / cm 2 ) or more, more preferably 1471 MPa (15 t / cm 2 ) or more.
- the upper limit of the molding pressure is not particularly limited, but is about 1960 MPa (20 t / cm 2 ) due to equipment limitations.
- a preferable mold temperature is 80 ° C. or higher, more preferably 100 ° C. or higher.
- the upper limit of the mold temperature is not particularly limited, but is about 300 ° C. due to equipment limitations.
- die wall surface or adding to a powder as needed can be taken.
- the friction between the mold and the powder can be reduced at the time of pressure molding, the decrease in the density of the molded body can be suppressed, and the friction at the time of extraction from the mold can be reduced. It is possible to prevent cracking of the molded body (dust core) at the time.
- Preferred lubricants include metal soaps such as lithium stearate, zinc stearate and calcium stearate, and waxes such as fatty acid amides.
- the dust core is subjected to heat treatment for the purpose of reducing the hysteresis loss due to strain relief and increasing the strength of the compacted body after pressure molding.
- the heat treatment time is preferably in the range of 5 to 120 minutes.
- the heating atmosphere may be in the air, in an inert atmosphere, in a reducing atmosphere, or in a vacuum, but there is no problem even if any of them is adopted. Moreover, what is necessary is just to determine an atmospheric dew point suitably according to a use. Furthermore, a step of holding at a constant temperature when the temperature is raised or lowered during the heat treatment may be provided.
- the powders shown in Table 1 were each provided with an insulating coating with a silicone resin. After the silicone resin is dissolved in toluene and a resin dilution solution is prepared so that the resin content is 0.9 mass%, the powder and the resin dilution solution are mixed so that the resin addition ratio to the powder is 0.1 mass%, Dry in air. After drying, a silicone resin-coated iron powder was obtained by performing a resin baking treatment at 200 ° C. for 120 minutes in the air. These powders were molded by molding pressure: 1471 MPa (15 t / cm 2 ) and die lubrication to produce ring-shaped test pieces having an outer diameter of 38 mm, an inner diameter of 25 mm, and a height of 6 mm.
- Table 2 shows the measurement results of the density and magnetic properties of the molded body together with the molded body density.
- the acceptance criterion for magnetic flux density was B 100 ⁇ 1.70 T
- the acceptance criterion for iron loss was W 10 / 1K ⁇ 80 W / kg.
- Table 2 also shows the crystal grain measurement results.
- the invention examples (sample numbers: 1 and 2) according to the present invention not only have a high density of the compact, but both the magnetic flux density (B 100 ) and the iron loss (W 10 / 1K ) are acceptable. It can be seen that it has excellent magnetic properties.
- Sample Nos. 3 to 6 having a larger amount of Si than the invention examples did not reach the acceptance standards for both magnetic flux density and iron loss. Further, it can be seen from the results of sample numbers 3 to 6 that the magnetic flux density tends to decrease and the iron loss tends to increase as the Si amount increases. This is considered to be due to the fact that the powder hardens as the Si content increases and that the fine oxides generated during water atomization increased.
- Sample No. 7 containing a large amount of iron powder of 45 ⁇ m or less as compared with Invention Examples and Sample No. 8 having a high powder hardness did not reach the acceptance criteria for both magnetic flux density and iron loss.
- the increase in fine powder led to an increase in total iron loss due to a decrease in compressibility and an increase in hysteresis loss.
- the hardness of the powder is high because the crystal grains in the powder are fine or strain is accumulated, thereby reducing the compressibility and increasing the hysteresis loss. This is thought to have led to an increase in total iron loss.
- Sample No. 9 is considered to have increased hysteresis loss as a result of accumulation of many strains during molding due to a decrease in apparent density, resulting in an increase in iron loss.
- Sample Nos. 10 and 11 have high compressibility because they contain a lot of coarse powder, and although the compact density and magnetic flux density exceed the values of the invention examples, the coarse powder increased eddy current loss. It is considered that the iron loss did not meet the acceptance criteria.
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Abstract
Description
また、特許文献3には、特許文献1及び2と同様に、主に高密度化等に関する検討が記載され、低鉄損化に関する記載はやはり不十分である。
さらに、特許文献4の高圧縮性鉄粉1及び2は、特許文献1~特許文献3に記載された技術のように、いずれも高磁束密度化に特化しており、低鉄損化に関する配慮がなされていない。
(1) Siが、溶鋼中にある程度以上含まれてしまうと、鉄粉の圧縮性が劣化して鉄損が増加すること、
(2) 見掛密度が低いと鉄損が増加すること、
(3) 鉄粉の粒度分布には適正な範囲があって、粗粉が多すぎても微粉が多すぎても鉄損が増加すること、及び
(4) 鉄粉断面の硬度が高いと圧縮性が低下すること
を見出した。
本発明は、上記知見を基に得られたものである。
1.水アトマイズ法によって得られる純鉄粉からなる圧粉磁芯用鉄粉であって、
上記純鉄粉が、Siの含有量:0.01mass%以下、
見掛密度:3.8g/cm3以上、
鉄粉粒径:45μm以下の割合が10mass%以下、
鉄粉粒径:180μm超250μm以下の割合が30mass%未満、
鉄粉粒径250μm超の割合が10mass%以下であって、
粉末断面のビッカース硬さ(試験力:0.245N)が80Hv以下
である圧粉磁芯用鉄粉。
まず、本発明の数値の限定理由について述べる。
〔Si量〕
Siが溶鋼中に含まれると、水アトマイズ法で得られる純鉄粉(以下、単に、粉末または鉄粉とも言う)は、水アトマイズ時に酸化して、その粒内に酸化物系介在物を生成するため、ヒステリシス損が増加してしまう。また、水アトマイズ時に生成した微細なSi酸化物及びアトマイズ時に酸化せずに固溶したSiが粉末を硬化させるために、圧縮性が低下する。以上のことから、Siは可能な限り低減することが必須であって、本発明では、0.01mass%以下とする。0mass%であっても良い。
鉄粉は、プレス成形により塑性変形して高密度の成形体となる。この成形時の塑性変形量が小さいほど、歪取焼鈍後の結晶粒が粗大になるが、後述するように、粒径:45μm以下の微細な鉄粉は、ヒステリシス損を大きく増加させるため、可能な限り低減する必要が有る。
ここで、成形時の粉末の塑性変形量を低減するためには、金型への粉末の充填率を上げる必要が有るが、本発明では、粉末の見掛密度で3.8g/cm3以上が必須であって、4.0g/cm3以上とするのが好ましい。見掛密度が3.8g/cm3を下回ると、成形時、粉末に多量の歪が導入されて、歪取焼鈍後の結晶粒が微細化するからである。なお、上記見掛密度とは、粉末の充填率の程度を示す指標であり、JIS Z 2504に規定される試験方法によって測定することができる。
本発明に従う鉄粉は、粒径:45μm超で粒径:180μm以下が主体(50mass%以上であって100mass%でも良い)となるが、粒径:45μm以下の微細な鉄粉はヒステリシス損を大きく増加させるため、可能な限り低減する必要が有り、10mass%以下が必須であって、好ましくは5mass%以下である。0mass%であっても良い。なお、45μm以下の鉄粉の割合については、JIS Z 8801-1に規定される篩を用いて篩い分けすることにより求めることができる。
なお、粒径:180μm超250μm以下の鉄粉は25mass%以下とし、250μm超の鉄粉は5mass%以下とするのが好ましい。また、それぞれ0mass%であっても良い。
粉末が硬いと、成形体の密度を高めるのに、より大きな成形圧が必要となる。そのため、粉末は可能な限り軟化させる必要があり、ビッカース硬さ試験において試験力0.245Nでの硬さ(Hv)は80以下とすることが必須である。好ましくは、Hvで75以下である。なお、ビッカース硬さについては以下記載の方法で測定することができる。
本発明における圧粉磁芯用鉄粉は、水アトマイズ法によって得られ、溶鋼は、Si、C、O、S及びN以外は通常の純鉄粉組成とし、Siについては、Si≦0.01mass%としたものとする。また、Cについては、脱酸の為に、純鉄粉の組成以上に添加しても構わないが、後工程で脱炭し最終的には0.01mass%以下まで低減することが好ましい。さらに、O、S及びNについては、後工程で水素雰囲気での焼鈍を実施することで除去することができるため、純鉄粉の組成に比べて多少多めに混入していても構わないが、多すぎると還元焼鈍の負荷が増えるため可能な限り純鉄粉の組成に近づけておくことが好ましい。
ここで、上記純鉄粉の組成とは、JFEスチール株式会社が市販している粉末冶金用純鉄粉である300Aと同等の組成である。
これにより、加圧成形時に、金型と粉末との間の摩擦を低減することができ、成形体密度の低下を抑制するとともに、金型から抜出す際の摩擦も低減することができ、取出時の成形体(圧粉磁芯)の割れを防止することができる。なお、好ましい潤滑材としては、ステアリン酸リチウム、ステアリン酸亜鉛、ステアリン酸カルシウムなどの金属石鹸、脂肪酸アミド等のワックスが挙げられる。
これらの粉末を、成形圧:1471MPa(15t/cm2)、金型潤滑で成形し、外形:38mm、内径:25mm、高さ:6mmのリング状試験片を作製した。作製した試験片は、窒素中で600℃、45minの熱処理を行った後、巻き線を行い(1次巻100ターン、二次巻40ターン)、直流磁化装置による磁束密度測定(H=10000A/m、メトロン技研製 直流磁化測定装置)と鉄損測定装置による鉄損測定(1.0T、1kHz、メトロン技研製 高周波鉄損測定装置)を行なった。
表2に、成形体の密度と磁気特性の測定結果を、成形体密度と共に示す。本実施例では、磁束密度の合格基準をB100≧1.70T、鉄損の合格基準をW10/1K≦80W/kgとした。
また、表2に結晶粒の測定結果を併記する。
試料番号:7については、微細な粉末の増加が、圧縮性の低下とヒステリシス損の増加による総鉄損の増加を招いたと推察される。一方、試料番号:8については、粉末内の結晶粒が微細、もしくは歪が蓄積していた為に粉末の硬度が高くなっていると考えられ、それにより圧縮性が低下し、ヒステリシス損の増加による総鉄損の増加を招いたものと考えられる。
試料番号:9は、見掛密度の低下によって成形時に多くの歪が蓄積されることで、ヒステリシス損が増加し、結果的に鉄損が増加したものと考えられる。他方、試料番号:10及び11は、粗粉を多く含むために圧縮性が高く、成形体密度と磁束密度は発明例を上回る値を示すものの、粗粉が渦電流損を増加させたために、鉄損は合格基準を満たさなかったものと考えられる。
Claims (1)
- 水アトマイズ法によって得られる純鉄粉からなる圧粉磁芯用鉄粉であって、
上記純鉄粉が、Siの含有量:0.01mass%以下、
見掛密度:3.8g/cm3以上、
鉄粉粒径:45μm以下の割合が10mass%以下、
鉄粉粒径:180μm超250μm以下の割合が30mass%未満、
鉄粉粒径:250μm超の割合が10mass%以下であって、
粉末断面のビッカース硬さ(試験力:0.245N)が80Hv以下
である圧粉磁芯用鉄粉。
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