WO2014171105A1 - 圧粉磁芯用鉄粉および圧粉磁芯用絶縁被覆鉄粉 - Google Patents
圧粉磁芯用鉄粉および圧粉磁芯用絶縁被覆鉄粉 Download PDFInfo
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- WO2014171105A1 WO2014171105A1 PCT/JP2014/002008 JP2014002008W WO2014171105A1 WO 2014171105 A1 WO2014171105 A1 WO 2014171105A1 JP 2014002008 W JP2014002008 W JP 2014002008W WO 2014171105 A1 WO2014171105 A1 WO 2014171105A1
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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
- 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
- H01F1/26—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 by macromolecular organic substances
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- 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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- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/16—Metallic particles coated with a non-metal
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- C22C33/00—Making ferrous alloys
- C22C33/02—Making ferrous alloys by powder metallurgy
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- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
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- 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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- C—CHEMISTRY; METALLURGY
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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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
- C22C38/06—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
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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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
- H01F27/255—Magnetic cores made from particles
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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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- 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
- H01F41/0206—Manufacturing of magnetic cores by mechanical means
- H01F41/0246—Manufacturing of magnetic circuits by moulding or by pressing powder
Definitions
- the present invention relates to a dust core iron powder and a dust core insulating coating iron powder from which a dust core having excellent magnetic properties 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 magnetic steel sheets are laminated with the steel plate surfaces insulated, the magnetic properties are different between the steel plate 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.
- iron loss characteristics after molding are required. It is affected by residual strain, impurities, crystal grain size, etc.
- oxygen is one of the elements that have a large effect on iron loss, but iron powder has a higher oxygen content than steel sheets, and it has been found preferable to reduce it as much as possible. Yes.
- Patent Document 1 discloses a technique for reducing the iron loss of a magnetic core material after molding by reducing the amount of oxygen in the iron powder to less than 0.05 wt%. It is disclosed.
- the present invention has been developed in view of the above-described situation, and provides a powder magnetic core iron powder and a powder magnetic core insulating coated iron powder for producing a powder magnetic core with low iron loss. Objective.
- the gist configuration of the present invention is as follows. 1. A powder containing iron as a main component obtained by an atomizing method, wherein the amount of oxygen in the powder is 0.05% by mass or more and 0.20% by mass or less, and inclusions occupying the area of the parent phase in the cross section of the powder Iron powder for dust cores with an area fraction of 0.4% or less.
- the iron powder for dust core and the dust magnet for producing a dust core with low iron loss by adjusting the inclusions in the iron powder grains and the oxygen content of the iron powder, the iron powder for dust core and the dust magnet for producing a dust core with low iron loss. Insulation-coated iron powder for the core can be obtained.
- a powder containing iron as a main component is used.
- a powder containing iron as a main component means that iron is contained in an amount of 50% by mass or more.
- the other components may be component compositions and ratios used for conventionally known iron powders for dust cores.
- the iron loss is roughly divided into two types: hysteresis loss and eddy current loss.
- the hysteresis loss is a loss that occurs due to the presence of a factor that hinders magnetization in the magnetic core when the magnetic core is magnetized. Magnetization is caused by the movement of the domain wall in the structure of the magnetic core. At this time, if fine nonmagnetic particles exist in the structure, the domain walls are trapped by the nonmagnetic particles and are separated therefrom. Extra energy is required. As a result, the hysteresis loss increases. For example, since oxide particles are basically non-magnetic, they cause an increase in hysteresis loss for the reasons described above.
- inclusions such as oxide particles are present in the powder, it becomes a pinning site at the time of recrystallization, which is not preferable for suppressing grain growth, and the inclusion itself becomes a nucleation site for recrystallized grains, Refine crystal grains after forming and strain relief annealing. And as above-mentioned, the inclusion itself becomes an increase factor of a hysteresis loss.
- the inventors have intensively studied the relationship between inclusions and hysteresis loss, and found that when the area fraction of inclusions was 0.4% or less, preferably 0.2% or less of the area of the parent phase of the powder, It has been found that the hysteresis loss of the magnetic core can be sufficiently reduced.
- the lower limit is not particularly limited and may be 0%.
- the area of the parent phase of the powder is obtained by subtracting the area of the pores in the grain boundary of the powder from the area surrounded by the grain boundary of the powder when a cross section of the powder is observed.
- inclusions contained in iron powder oxides containing one or more of Mg, Al, Si, Ca, Mn, Cr, Ti, Fe and the like are conceivable.
- the area fraction of inclusions can be obtained by the following method.
- iron powder which is the object to be measured, is mixed with thermoplastic resin powder to obtain a mixed powder.
- the mixed powder is filled into an appropriate mold, heated to melt the resin, and then solidified by cooling to obtain an iron powder-containing resin solid.
- This iron powder-containing resin solid material is cut in an appropriate cross section, the cut surface is polished and corroded, and then the cross-sectional structure of the iron powder particles is determined using a scanning electron microscope (magnification: 1k to 5k times). Observation and imaging with a backscattered electron image. Since inclusions appear as black contrast in the obtained image, the area fraction of the inclusions can be obtained by performing image processing on the image. In the present invention, this is performed in at least five visual fields, the area fraction of inclusions in these observation visual fields is determined, and the average value is used.
- Eddy current loss which is another factor of iron loss, is a loss affected by the insulation between particles. Therefore, if the insulation between the particles is insufficient, the eddy current loss increases significantly.
- the inventors have examined the insulation between the particles, and when the oxygen content in the iron powder is less than 0.05 mass%, the insulation between the particles after the insulation coating is applied and the strain relief annealing is performed. It was found that the eddy current loss increased instead of maintaining the properties.
- oxygen in iron powder exists in the state of thin iron oxide covering the surface of iron powder, so if there is no oxygen content in iron powder, It is considered that the double insulating layer by the insulating coating cannot increase the insulation between the particles. Therefore, oxygen must be contained at 0.05% by mass or more. Preferably, oxygen is 0.08% by mass or more.
- oxygen content is preferably about 0.20% by mass at the maximum. More preferably, the oxygen content is less than 0.15% by mass.
- the product of the present invention may be obtained by a method other than the method described later.
- the iron-based powder used in the present invention is produced using an atomizing method. The reason is that the powder obtained by the oxide reduction method and the electrolytic deposition method has a low apparent density, even when the inclusion area fraction and oxygen content satisfy the conditions of the present invention. This is because the insulation coating is peeled off and the eddy current loss is greatly increased due to large plastic deformation.
- the type of gas, water, gas + water, centrifugal method, etc. is not limited. It is preferable to use a gas atomizing method that can be produced in large quantities.
- the manufacturing method when the water atomizing method is applied will be described as a representative example.
- the composition of the molten steel to be atomized is not particularly limited as long as it contains iron as a main component.
- the amount of easily oxidizable metal elements Al, Si, Mn, Cr, etc.
- Al ⁇ 0.01% by mass Si ⁇ 0.07 mass%, Mn ⁇ 0.1 mass%, and Cr ⁇ 0.05 mass% are preferable.
- the reduction annealing is preferably a high-load treatment in a reducing atmosphere containing hydrogen, for example, at a temperature of 900 ° C. or more and less than 1200 ° C., preferably 1000 ° C. or more and less than 1100 ° C. in a reducing atmosphere containing hydrogen.
- Heat treatment with a holding time of 1 to 7 hours, preferably 2 to 5 hours, and an introduction amount of reducing atmosphere gas containing hydrogen of 3 L / min or more, preferably 4 L / min or more with respect to 1 kg of iron powder.
- an additional heat treatment for adjusting the oxygen amount can be performed. Since the amount of oxygen after finish reduction annealing is lower than the target, when the amount of oxygen in the powder is increased, heat treatment in a hydrogen atmosphere containing water vapor may be performed.
- the heat treatment conditions may be selected according to the amount of oxygen after the finish reduction annealing, but the dew point is 0 to 60 ° C., the heat treatment temperature is 400 to 1000 ° C., and the soaking time is 0 to 120 min. It is preferable to carry out.
- heat treatment may be performed in a hydrogen atmosphere containing no water vapor.
- the heat treatment conditions at that time can be selected according to the amount of oxygen after the finish reduction annealing, but the heat treatment temperature is preferably 400 to 1000 ° C. and the soaking time is preferably 0 to 120 min. This is because if the heat treatment temperature is lower than 400 ° C., the reduction is insufficient, and if it is higher than 1000 ° C., the reduction speed is fast and it becomes difficult to control the oxygen amount. In addition, if the soaking time is longer than 120 min, the powder is sintered and it becomes difficult to disintegrate. In addition, when implementing the stress relief annealing mentioned later, it does not matter as a target oxygen amount by adjusting the conditions of stress relief annealing.
- pulverization is performed by an impact pulverizer such as a hammer mill or a jaw crusher after decarburization or reduction annealing described above.
- the pulverized powder can be subjected to additional pulverization and strain relief annealing as necessary.
- the above-described iron powder becomes an insulating coated iron powder for a dust core by applying an insulating coating.
- Any insulating coating may be applied to the powder as long as the insulation between the particles can be maintained.
- Such insulating coatings include glassy insulating amorphous layers based on silicone resins, metal phosphates and borate salts, metal oxides such as MgO, forsterite, talc and Al 2 O 3 , Alternatively, there is a crystalline insulating layer based on SiO 2 .
- the insulation coating at least 0.1% by mass or more in terms of the addition rate (mass ratio) with respect to the iron powder for dust core.
- the upper limit of the addition rate is not particularly limited, but is preferably about 0.5% by mass from the viewpoint of production cost.
- the insulating coating is preferably a silicone resin in terms of heat resistance and flexibility (it is necessary to follow the plastic deformation of the powder during molding).
- Insulation-coated iron powder for dust cores with an insulating coating on the particle surface is filled in a mold and pressed into a desired dimensional shape (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 die lubrication molding method can be applied.
- the molding pressure is appropriately determined depending on the application. However, if the molding pressure is increased, the green density becomes higher. Therefore, the preferred molding pressure is 10 t / cm 2 (981 MPa) or more, more preferably 15 t / cm 2. (1471 MPa) or more.
- a lubricant can be applied to the mold wall surface or added to the powder as necessary.
- the friction between the mold and the powder during pressure molding can be reduced, so that the decrease in the density of the molded body can be suppressed, and the friction during extraction from the mold can also be reduced. It is possible to effectively prevent cracking of the green body (dust core).
- Preferred lubricants at that time include metal soaps such as lithium stearate, zinc stearate and calcium stearate, and waxes such as fatty acid amides.
- the molded powder magnetic core is subjected to heat treatment for the purpose of reducing the hysteresis loss due to strain removal and increasing the strength of the molded body after pressure molding.
- the heat treatment time for this heat treatment is preferably about 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.
- Iron powder No. 1-7 atomized iron powder with different Si content was used.
- the amount of Si in each iron powder is as shown in Table 1.
- Components other than Si are C ⁇ 0.2 mass%, O ⁇ 0.3 mass%, N ⁇ 0.2 mass%, Mn ⁇ 0.05 mass%, P ⁇ 0.02 mass%, S ⁇ 0.01 mass%, Ni ⁇ 0.05% in all iron powders.
- iron powder No. 1 has dew points of 40, 50 and 60 ° C, 3 levels of hydrogen flow rate and 2 levels of hydrogen flow rate of 3L / min / kg and 1L / min / kg, other iron powders All were annealed with a dew point of 60 ° C. wet hydrogen and a hydrogen flow rate of 3 L / min / kg.
- the sintered body after annealing was pulverized with a hammer mill to obtain 10 types of pure iron powder.
- Table 2 shows the iron powder No. used as the basis for the 10 types of pure iron powders A to J and the conditions for reduction annealing.
- the iron powder obtained in the above procedure was crushed at 1000rpm ⁇ 30min using a high-speed mixer (Fukae Pautech LFS-GS-2J type), and strain relief annealing at 850 ° C x 60min in dry hydrogen Were carried out respectively.
- Table 3 shows the measurement results of the inclusion area fraction determined by analyzing the oxygen content of these iron powders and observing the cross section with a scanning electron microscope.
- these iron powders were classified with a sieve specified in JIS Z 8801-1 to obtain a particle size of 45 to 250 ⁇ m. Further spread over a part of the classified iron powder: classifying with 63 ⁇ m, 75 ⁇ m, 106 ⁇ m, 150 ⁇ m and 180 ⁇ m sieves, measuring the powder weight on the sieves, obtaining the particle size distribution, and obtaining the particle size From the distribution, the weight average particle diameter D50 was calculated. Further, the apparent density was measured by a test method specified in JIS Z 2504. As a result, D50: 95 to 120 ⁇ m and apparent density ⁇ 3.8 g / cm 3 for all powders.
- an insulating coating with a silicone resin was applied to these iron powders. Dissolve the silicone resin in toluene to prepare a resin diluted solution with a resin content of 0.9% by mass, and then mix the powder and the resin diluted solution so that the resin addition rate to the powder is 0.15% by mass And dried in air. After drying, an insulating coated iron powder for powder magnetic core (coated iron-based soft magnetic powder) was obtained by performing a resin baking process at 200 ° C. for 120 minutes in the air.
- Table 4 shows the measurement results obtained by performing magnetic measurements on the samples.
- the acceptance criteria for iron loss at 1.0 T, 400 Hz is 30 W / kg, which is lower than the acceptance criteria (50 W / kg or less) shown in the examples of Patent Document 1 and Patent Document 2.
- the iron loss acceptance standard at 1.0 T and 1 kHz is set to 90 W / kg or lower, which is lower than the minimum iron loss value (117.6 W / kg) shown in the example of Patent Document 3. .
- the comparative example with a low oxygen content was not able to meet the acceptance criteria because the eddy current loss was significantly increased compared to the inventive example. It can be seen that the comparative examples with high amounts and inclusion area fractions did not satisfy the acceptance criteria because either or both of the hysteresis loss and eddy current loss increased compared to the inventive examples.
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Abstract
Description
すなわち、
(I) 酸素量の増加によって鉄損が増加するのは、酸素が介在物の形態で粒内に存在しているためであり、粒内介在物が十分に低減されていれば、たとえ酸素を多く含んでいても鉄損の低い圧粉磁芯が得られること、
(II) 介在物が十分に低減された鉄粉の場合、酸素量が低いものよりも、一定量の酸素を含有している鉄粉の方がむしろ低鉄損となること、
である。
本発明は、上記知見に基づいてなされたものである。
1.アトマイズ法によって得られる鉄を主成分とする粉末であって、該粉末中の酸素量が0.05質量%以上、0.20質量%以下で、かつ該粉末の断面において、母相の面積に占める介在物の面積分率が0.4%以下である圧粉磁芯用鉄粉。
このうち、ヒステリシス損は、磁芯を磁化した際、磁芯中に磁化の妨げとなる因子が存在することによって発生する損失である。磁化は、磁芯の組織内を磁壁が移動することによって起こるが、このとき、組織内に微細な非磁性粒子が存在すると、磁壁が非磁性粒子にトラップされてしまい、そこから離脱するために余分なエネルギーが必要となる。その結果、ヒステリシス損が大きくなる。例えば、酸化物粒子は、基本的に非磁性であるため、上記した理由によりヒステリシス損増加の要因となる。
なお、下限に特に限定はなく0%であっても良い。また、粉末の母相の面積とは、ある粉末の断面を観察したとき、当該粉末の粒界により囲まれた面積から当該粉末の粒界内の空孔部の面積を引いたものである。
発明者らが粒子間の絶縁性につき検討したところ、鉄粉中の酸素量を0.05質量%未満としてしまうと、絶縁被覆を施して成形し、さらに歪取焼鈍を行った後の粒子間の絶縁性が保たれずに、かえって、渦電流損が増加してしまうことが分かった。
一方、鉄粉に対し、過度に酸素を含有させると、鉄粉表面の酸化鉄が過度に厚くなって、成形時に絶縁被覆ごと剥離してしまうことで渦電流損が増加することに加え、鉄粉粒内にも非磁性の酸化鉄粒子が生成することで、ヒステリシス損が増加してしまうおそれがある。そのため、酸素の含有量は最大で0.20質量%程度とするのが好ましい。より好ましくは、酸素の含有量は0.15質量%未満である。
本発明に用いる鉄を主成分とする粉末は、アトマイズ法を用いて製造する。その理由は、酸化物還元法、電解析出法によって得られる粉末は、見掛密度が低く、たとえ介在物の面積分率や酸素量が、本発明の条件を満たしていたとしても、成形時に大きく塑性変形するために、絶縁被覆が剥離して渦電流損が大きく増加してしまうからである。
仕上還元焼鈍後の酸素量が目標を下回っているために、粉末中の酸素量を増加させる場合は、水蒸気を含む水素雰囲気中での熱処理を実施すれば良い。その際、熱処理条件は、仕上還元焼鈍後の酸素量に応じて選択されれば良いが、露点:0~60℃、熱処理温度:400~1000℃、均熱時間:0~120minの範囲内で実施するのが好ましい。露点が0℃よりも低いと、脱酸が起こって酸素量が更に下がってしまい、60℃よりも高いと、粉末の内部まで酸化してしまうからである。また、熱処理温度が400℃より低いと酸化が不十分となる一方で、1000℃より高いと酸化のスピードが早く、酸素量の制御が難しくなる。さらに、均熱時間が120minよりも長いと、粉末の焼結が進み解砕が困難になる。
なお、後述の歪取焼鈍を実施する場合は、歪取焼鈍の条件を調整することで目標酸素量としても構わない。
粉末に施す絶縁被覆は、粒子間の絶縁性を保てるものであれば何でも良い。その様な絶縁被覆としては、シリコーン樹脂、リン酸金属塩やホウ酸金属塩をベースとしたガラス質の絶縁性アモルファス層や、MgO、フォルステライト、タルクおよびAl2O3などの金属酸化物、或いはSiO2をベースとした結晶質の絶縁層などがある。
一方、上記添加率の上限は、特に限定されないものの、0.5質量%程度とするのが、製造コストなどの点から好ましい。
これらの鉄粉の酸素量分析値および走査電子顕微鏡による断面観察により求めた介在物面積分率の測定結果を、それぞれ表3に示す。
その結果、全ての粉末でD50:95~120μm、見掛密度≧3.8g/cm3であった。
かようにして作製した試験片に、窒素中で650℃、45minの熱処理を行い、試料とした後、巻き線を行い(1次巻:100ターン、2次巻:40ターン)、直流磁化装置によるヒステリシス損測定(1.0T、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、400Hz及び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4に、試料の磁気測定を行なって得た測定結果を示す。
なお、本実施例では、1.0T、400Hzでの鉄損の合格基準を、特許文献1および特許文献2の実施例に示された合格基準(50W/kg以下)よりも、さらに低い30W/kg以下とし、加えて、1.0T、1kHzでの鉄損合格基準を、特許文献3の実施例に示された鉄損の最小値(117.6W/kg)よりもさらに低い、90W/kg以下とした。
Claims (4)
- アトマイズ法によって得られる鉄を主成分とする粉末であって、該粉末中の酸素量が0.05質量%以上、0.20質量%以下で、かつ該粉末の断面において、母相の面積に占める介在物の面積分率が0.4%以下である圧粉磁芯用鉄粉。
- 請求項1に記載の圧粉磁芯用鉄粉に、さらに絶縁被覆を施した圧粉磁芯用絶縁被覆鉄粉。
- 前記絶縁被覆が、前記圧粉磁芯用鉄粉に対する添加率で、少なくとも0.1質量%以上である請求項2に記載の圧粉磁芯用絶縁被覆鉄粉。
- 前記絶縁被覆がシリコーン樹脂である請求項2または3に記載の圧粉磁芯用絶縁被覆鉄粉。
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