Classifications

• • 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
• • 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
• • 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
  • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
• • 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
  • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
  • B22F1/102—Metallic powder coated with organic material
• • 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
  • B22F1/14—Treatment of metallic powder
• • 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
  • B22F1/16—Metallic particles coated with a non-metal
• • 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
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
• • 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
• • 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
  • H01F1/147—Alloys characterised by their composition
• • 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

Definitions

• Magnetic cores used in motors, transformers, etc. require high magnetic flux density and low iron loss.
• motor cores have been made from laminated electromagnetic steel sheets, but in recent years, powder magnetic cores have been attracting attention.
• Patent Documents 1 and 2 disclose technology for obtaining dust cores with low hysteresis loss by reducing the strain in soft magnetic powder measured by X-ray diffraction.
• An iron-based soft magnetic powder for dust cores An iron-based soft magnetic powder for dust cores, comprising at least one element selected from the group consisting of Al, Si, Cr, and Mn, and having a number density of inclusions having a particle diameter of 150 nm or less of 500 pieces/ ⁇ m3 or less .
• Al content Al is an easily oxidizable metal element, and if it is contained in excess, the number density of oxide-based inclusions may become excessively high. Therefore, when Al is contained, the Al content is preferably 0.010% or less. Since the lower the Al content, the better, there is no lower limit for the Al content, and it may be 0%, or Al may not be contained at all. However, from the viewpoint of production costs, an Al content of 0.001% or more is preferable.
• Si content Si is an easily oxidizable metal element, and if it is contained in excess, the number density of oxide-based inclusions may become excessively high. Therefore, when Si is contained, the Si content is preferably 0.010% or less. Since the lower the Si content, the better, there is no lower limit for the Si content, and it may be 0%, or Si may not be contained at all. However, from the viewpoint of production costs, a content of 0.001% or more is preferable.
• Mn content Mn is an easily oxidizable metal element, and if contained in excess, the number density of oxide-based inclusions may become excessively high. Therefore, when Mn is contained, the Mn content is preferably 0.100% or less, and more preferably 0.070% by mass or less. Since the lower the Mn content, the better, there is no restriction on the lower limit of the Mn content; it may be 0%, or Mn may not be contained at all. However, from the viewpoint of production costs, a content of 0.010% or more is preferred.
• P content Since P is an easily oxidizable metal element, when P is contained, the P content is preferably 0.015% or less. Since the lower the P content, the better, there is no lower limit for the P content, and it may be 0%, or P may not be contained. However, from the viewpoint of production costs, a P content of 0.001% or more is preferable.
• Ti content Since Ti is an easily oxidizable metal element, when Ti is contained, the Ti content is preferably 0.005% or less. Since the lower the Ti content, the better, the lower limit of the Ti content is not limited, and it may be 0%, or Ti may not be contained.
• inclusions with a particle size of 150 nm or less have a greater effect on suppressing grain growth than coarse inclusions with a particle size of more than 150 nm, and therefore have a greater impact on hysteresis loss.
• the surface of the observation area of the sample is 1 ⁇ m x 1 ⁇ m or more and a thickness of 200 nm or less.
• elemental mapping is performed on the sample using a scanning transmission electron microscope and an energy dispersive X-ray fluorescence analyzer to obtain mapping data of Al, Si, Mn, and Cr.
• the resolution of the elemental mapping is 5 nm or less.
• an STEM such as the Talos F200X manufactured by FEI can be used.
• the accelerating voltage during observation is approximately 200 kV.
• the mapping data is superimposed and binarized, and image analysis is performed to calculate the equivalent circle diameter of each particle corresponding to an inclusion.
• the binarization and image analysis can be performed using image analysis software such as ImageJ.
• the maximum particle size of the iron-based soft magnetic powder is not particularly limited, but is preferably 600 ⁇ m or less in order to suppress an increase in eddy current loss.
• the maximum particle size can be measured by a sieving method.
• the insulating-coated soft magnetic powder for dust cores of the present invention has an insulating coating on the surfaces of the particles that make up the iron-based soft magnetic powder.
• the insulating coating ensures insulation between particles and can suppress short circuits between particles.
• the insulating coating may consist of one coating or two or more coatings. When the insulating coating consists of two or more coatings, the insulating coating may consist of the same type of coating or different types of coatings.
• the insulating coating may be layered. That is, the insulating coating may be a single-layer coating or a multi-layer coating consisting of two or more layers.
• the multi-layer coating may be a multi-layer coating consisting of the same type of coating or a multi-layer coating consisting of different types of coatings.
• the inorganic insulating coating can use one or both of an amorphous material and a crystalline material as the inorganic insulating material.
• the amorphous material include metal phosphates and metal borates.
• the metal phosphate is preferably condensed aluminum phosphate.
• the crystalline material include metal oxides and SiO2 .
• the metal oxides include MgO, forsterite, talc, and Al2O3 .
• the inorganic insulating coating is a coating containing the inorganic insulating material, and is preferably made of the inorganic insulating material.
• the organic insulating coating is a coating containing an organic resin, and is preferably made of an organic resin.
• Silicone resin is preferably used as the organic resin. Silicone resin forms Si-O bonds with excellent heat resistance when heat treated, so excellent insulation properties can be maintained even when the compact is subjected to stress relief heat treatment at high temperatures (e.g., 600°C) during the production of the dust core.
• silicone resins include resin-based silicone resins, such as those containing 60 mol% or more of T units (trifunctional siloxane units).
• silicone resins in which 50 mol% or more of the functional groups on the Si are methyl groups are preferred, such as methylphenyl silicone resins (KR-255, KR-311, KR-300, etc., manufactured by Shin-Etsu Chemical Co., Ltd.) and methyl silicone resins (KR-251, KR-400, KR-220L, KR-220LP, KR-242A, KR-240, KR-500, KC-89, etc., manufactured by Shin-Etsu Chemical Co., Ltd.).
• SR2400 and Trefil R-910 manufactured by Dow Corning Toray Co., Ltd. can also be used.
• the insulating coating comprises, from the surface of the particle toward the outside, a first coating containing condensed aluminum phosphate and a second coating containing a silicone resin, in this order. That is, the insulating coated soft magnetic powder preferably comprises, from the inside, the iron-based soft magnetic powder, the first coating, and the second coating, in this order. It is more preferable that the insulating coating be composed of the first coating and the second coating.
• the insulating coated soft magnetic powder contains the insulating coating and the iron-based soft magnetic powder, and is preferably composed of the insulating coating and the iron-based soft magnetic powder.
• the content of the insulating coating is preferably 0.2 parts by mass or more per 100 parts by mass of the iron-based soft magnetic powder.
• the content of the insulating coating is preferably 1.0 part by mass or less per 100 parts by mass of the iron-based soft magnetic powder.
• lubricant materials include organic lubricants such as fatty acid amides, and inorganic lubricants such as MoS 2 , WS, BN, and talc.
• organic lubricants such as fatty acid amides
• inorganic lubricants such as MoS 2 , WS, BN, and talc.
• fatty acid amides include stearamide, EBS (ethylene bisstearamide), erucamide, and oleamide. These may be used alone or in combination.
• Powders obtained by the oxide reduction method and the electrolytic deposition method have low apparent densities, and even if additional processing such as crushing is performed to increase the apparent density, sufficient apparent density cannot be achieved. Therefore, from the perspective of improving the density of the resulting powder core, it is preferable to manufacture the above iron-based soft magnetic powder using an atomization method.
• the atomization method involves pulverizing molten metal and cooling it to solidify it. Any of water atomization, gas atomization, and centrifugal atomization can be used. Water atomization involves spraying water onto molten metal to pulverize it, while gas atomization involves spraying gas to pulverize it. Powdering can also be performed by spraying both water and gas.
• Centrifugal atomization involves powdering molten metal using centrifugal force generated by rotation. Powders obtained using two or more of these methods can also be combined.
• water atomization the particle surfaces have numerous irregularities, making them more likely to become entangled. This improves the strength of the powder core when molded into a powder core.
• water atomization is inexpensive. Therefore, water atomization is preferable from the standpoint of the strength and cost of the resulting dust core.
• gas atomization allows for relatively large-scale production, so gas atomization is preferable from the perspective of mass production. Below, we will explain a manufacturing method using water atomization as an example.
• the molten steel is used as the molten metal.
• the molten steel may have a composition consisting of Fe, alloying elements, and unavoidable impurities, and the composition of the molten steel preferably consists of Fe and unavoidable impurities.
• the Al, Si, Mn, and Cr contents of the molten steel are preferably Al: 0-0.010 mass%, Si: 0-0.010 mass%, Mn: 0-0.100 mass%, and Cr: 0-0.050 mass%, respectively.
• the contents of each element are more preferably Al: 0-0.010 mass%, Si: 0-0.010 mass%, Mn: 0-0.070 mass%, and Cr: 0-0.040 mass%, respectively.
• the reduction annealing is preferably carried out in one or more heat treatment stages. Reduction annealing can reduce the number density of the inclusions and coarsen the crystal grain size in the resulting iron-based soft magnetic powder. Particle size adjustment, such as pulverization, may be carried out before or after each heat treatment stage.
• the temperature of the heat treatment is preferably 700°C or higher, more preferably 800°C or higher, and even more preferably 900°C or higher.
• the temperature of the heat treatment is preferably less than 1200°C, more preferably less than 1100°C.
• the holding time of the heat treatment is preferably 1 hour or longer.
• the holding time of the heat treatment is preferably 7 hours or shorter, more preferably 5 hours or shorter.
• the atmosphere used for the heat treatment is typically a reducing atmosphere, preferably an atmosphere containing hydrogen.
• the upper limit of the dew point of the atmosphere is not particularly limited, but is preferably 30°C or lower.
• the lower limit of the dew point of the atmosphere is not particularly limited, but may be, for example, -40°C or higher.
• the decarburization is preferably performed as a heat treatment in a wet hydrogen atmosphere.
• a wet hydrogen atmosphere refers to an atmosphere containing water vapor and hydrogen, specifically an atmosphere containing hydrogen and having a dew point of over 30°C.
• the dew point of the heat treatment in the wet hydrogen atmosphere is preferably 60°C or lower.
• the temperature and holding time of the heat treatment in the wet hydrogen atmosphere can be the same as those of the heat treatment for reduction annealing.
• the heat treatment for the reduction annealing it is preferable to perform the heat treatment for the reduction annealing at least once under the conditions of a hydrogen-containing atmosphere with a dew point of 30°C or less, a temperature of 800°C or more, and a holding time of 1 hour or more.
• a hydrogen-containing atmosphere with a dew point of 30°C or less, a temperature of 800°C or more, and a holding time of 1 hour or more.
• the decarburization and reduction annealing can be performed in a two-stage heat treatment, with the first stage being a heat treatment in a wet hydrogen atmosphere and the second stage being a heat treatment in a hydrogen-containing atmosphere with a dew point of 30°C or less, at a temperature of 800°C or more, and a holding time of 1 hour or more.
• the order of the heat treatments for the decarburization and reduction annealing is not limited as long as the above conditions are met.
• the iron-based soft magnetic powder can be crushed and sieved as needed to adjust the apparent density and particle size distribution.
• the content of Al, Si, Cr, Mn, P, B, and Ti in the final iron-based soft magnetic powder is equivalent to the chemical composition of the molten steel.
• the insulating coated soft magnetic powder can be produced by forming the insulating coating on the iron-based soft magnetic powder.
• the insulating coating can be formed by any method, including wet and dry methods.
• the wet method is a method in which the material used for the insulating coating is mixed with the iron-based soft magnetic powder using a solvent such as water or an organic solvent.
• the dry method is a method in which the material used for the insulating coating is mixed with the iron-based soft magnetic powder without using a solvent.
• the mixing can be carried out using a mixer, which may be, for example, a rotary blade mixer. Examples of rotary blade mixers include the FM Mixer series (manufactured by Nippon Coke) and the High Speed Mixer series (manufactured by EarthTechnica).
• the insulating coating comprises, from the surface of the particle outward, a first coating made of condensed aluminum phosphate and a second coating made of silicone resin, in that order.
• a continuous coating can be formed as a complete or partial coating, but it is distinguished from a state in which the powder is fused together to form a continuous coating, as opposed to a state in which the powder is simply attached in a scattered manner. It is preferable that the continuous coating covers most of the surface of the iron-based soft magnetic powder, and more preferably, it covers substantially the entire surface. Furthermore, the heat mixing can achieve excellent adhesion of the first coating to the surface of the iron-based soft magnetic powder. This is presumably due to a reaction occurring at the interface between the condensed aluminum phosphate continuous coating and the iron-based soft magnetic powder.
• the average particle size of the condensed aluminum phosphate powder may be 1 ⁇ m or more, preferably 1.5 ⁇ m or more.
• the average particle size may be 10 ⁇ m or less, preferably 7.5 ⁇ m or less.
• the mixer described above can be used for the mixing.
• the rotation speed of the mixer is preferably 100 rpm or higher, and more preferably 200 rpm or higher.
• the rotation speed is preferably 1000 rpm or lower, and more preferably 800 rpm or lower.
• the maximum temperature reached during mixing is not particularly limited. However, to facilitate the formation of the first coating as a continuous film, the maximum temperature is preferably 100°C or higher, more preferably 130°C or higher, and even more preferably 150°C or higher. On the other hand, because high temperatures can cause condensed aluminum phosphate to deteriorate, the maximum temperature is preferably 200°C or lower. Note that the "temperature” referred to here refers to the temperature of the powder during mixing. When using a rotary blade mixer, it refers to the temperature indicated by a thermocouple protruding from the wall of the mixing vessel to a degree that does not come into contact with the rotary blades.
• the maximum temperature reached during mixing refers to the highest temperature of the powder during mixing, and can be the highest temperature measured by the thermocouple of the powder containing the iron-based soft magnetic powder and the condensed aluminum phosphate powder.
• the mixing is preferably performed in an inert gas atmosphere, such as a nitrogen atmosphere.
• a second coating made of silicone resin is formed on the powder obtained by the above-mentioned method.
• the second coating can be formed by, for example, a wet method using an organic solvent or a dry method without using a solvent, either of which can be used to form a layer of silicone resin coating.
• the dry method is preferred because it does not require safety measures associated with the use of organic solvents and is advantageous in terms of cost, equipment, and workability.
• At least one silicone resin selected from the group consisting of SR2400 manufactured by Dow Corning Toray Co., Ltd., and KR-311 and LR-220L manufactured by Shin-Etsu Chemical Co., Ltd.
• the solid silicone resin is not particularly limited, and either or both of powder and flake silicone resins can be used. It is preferable to use a solid silicone resin that softens when heated. When using the dry method, it is preferable to use at least one silicone resin selected from the group consisting of, for example, Toray Dow Corning Toray's Trefil R-910 and Shin-Etsu Chemical's KR-220LP.
• the silicone resin After the silicone resin has been applied by a wet or dry method, it may be subjected to a heat treatment to increase the hardness of the applied silicone resin.
• the heat treatment temperature may be, for example, 150°C or higher and 250°C or lower.
• the heat treatment may be performed in air or in an inert gas atmosphere (e.g., a nitrogen atmosphere).
• the mixed powder can be produced by adding, for example, the lubricant to the insulating coated soft magnetic powder.
• the type and amount of the lubricant to be added are as described above.
• the iron-based soft magnetic powder is coated with the insulating coating and, if necessary, mixed with a lubricant, and then loaded into a mold and pressure-molded to the desired dimensions and shape.
• the pressure-molding method is not particularly limited, and any conventional molding method, such as room-temperature molding or die-lubricated molding, can be used.
• the die-lubricated molding method is a method in which a lubricant is applied to the mold wall surface before pressure molding, thereby improving ejection properties. This method can also be used effectively when no lubricant is added to the insulating-coated soft magnetic powder.
• Suitable lubricants for application to the wall surface include metal soaps such as lithium stearate, zinc stearate, and calcium stearate, and waxes such as fatty acid amides.
• the molding pressure is determined appropriately depending on the application. Since increasing the molding pressure increases the density of the resulting dust core, the molding pressure is preferably 10 t/ cm2 or higher, more preferably 15 t/ cm2 or higher.
• the heat treatment temperature is not particularly limited.
• the holding time for the heat treatment is also not particularly limited, but is preferably 5 to 120 minutes. A stage of holding the temperature at a constant temperature during temperature increase or decrease during the heat treatment may be provided.
• the atmosphere for the heat treatment is not particularly limited, and may be, for example, air, an inert atmosphere, a reducing atmosphere, or a vacuum.
• the dew point of the atmosphere is not particularly limited, and may be determined appropriately depending on the application.
• Example 1 First, an iron-based powder was produced from molten steel by water atomization. The resulting iron-based powder was then subjected to a two-stage heat treatment. First, heat treatment was performed in a wet hydrogen atmosphere (dew point 40°C) for decarburization. The holding temperature was 950°C and the holding time was 1 hour. The resulting agglomerates were pulverized. Next, to reduce fine inclusions, heat treatment was performed in a hydrogen atmosphere (dew point 20°C). The holding temperature was 950°C and the holding time was 1 hour.
• a wet hydrogen atmosphere decarburization
• the holding temperature was 950°C and the holding time was 1 hour.
• the resulting iron-based soft magnetic powder had a maximum particle size measured by the above-mentioned method of less than 250 ⁇ m, and a volume-based median diameter D50 measured by laser diffraction and a mass-based average particle size measured by sieving were both 100 to 180 ⁇ m.
• the iron-based soft magnetic powder had a composition containing the components listed in Table 1, with the balance consisting of Fe and other unavoidable impurities.
• the C content was measured by the above-mentioned method using a CS844 manufactured by LECO Corporation. It was also confirmed that the contents of Al, Si, Mn, and Cr were the same as the contents of each component in the iron-based powder before the heat treatment.
• an insulating coating was formed on these iron-based soft magnetic powders.
• aluminum tripolyphosphate powder with an average particle size of 5 ⁇ m was heated and mixed to form a coating made of aluminum tripolyphosphate.
• a high-speed mixer (Earth Technica (formerly Fukae Powtec Co., Ltd.) LFS-GS-2J model) was used for mixing.
• the atmosphere inside the mixing vessel was nitrogen, the heater temperature of the mixing vessel was set to 190°C, and the rotating blades were rotated at 500 rpm for 20 minutes while stirring and mixing was carried out. The mixture was then cooled to 60°C inside the mixing vessel and the powder was removed.
• Silicone resin was dissolved in toluene to prepare a diluted resin solution with a silicone resin solids concentration of 2.0% by mass.
• the heated and mixed powder and the diluted resin solution were mixed, dried, and then heat-treated in air at 200°C for 120 minutes.
• the insulating coating content was adjusted so that 0.3 parts by mass of aluminum tripolyphosphate coating and 0.3 parts by mass of silicone resin coating per 100 parts by mass of the iron-based soft magnetic powder. Ring-shaped test specimens were fabricated by pressure molding using these powders and heat treatment.
• the pressure molding was performed using a die-lubricated molding method at a molding pressure of 980 MPa, resulting in a shape with an outer diameter of 38 mm, an inner diameter of 25 mm, and a height of 6 mm.
• the heat treatment was performed in nitrogen at 600°C for 45 minutes.
• the ring-shaped test specimens were wound (100 turns for the primary winding, 20 turns for the secondary winding), and hysteresis loss was measured using a DC magnetization measuring device (Metron Giken SK-110).
• the magnetization curve was evaluated using a DC power supply at a frequency of 1 Hz and an excitation magnetic flux density of 1.0 T, and the hysteresis loss at 400 Hz was calculated by multiplying the loop area at 1 Hz by 400.
• a hysteresis loss of 30.0 W/kg or less was considered pass, and anything over 30.0 W/kg was considered fail.
• Powder magnetic cores are said to have high hysteresis loss at 400 Hz due to their higher hysteresis loss compared to conventional iron cores made from electromagnetic steel sheet. Therefore, by keeping the hysteresis loss at 30.0 W/kg or less, iron loss is at the same level as when electromagnetic steel sheet with a thickness of 0.35 mm is used, making them suitable for use in motors, for example.
• Example 2 The iron-based powder was produced by water atomization using the same molten steel as Sample No. 4 used in Example 1, but the reduction annealing conditions were changed from those in Example 1.
• the first heat treatment was performed in a wet hydrogen atmosphere (dew point 40°C), as in Example 1.
• the holding temperature was 950°C, and the holding time was 1 hour.
• the conditions for the subsequent heat treatments were changed to the holding temperature and dew point shown in Table 2 below.
• the obtained iron-based soft magnetic powder was evaluated for C content and number density of inclusions containing at least one element selected from the group consisting of Al, Si, Cr, and Mn and having a particle size of 150 nm or less, using the above-mentioned method.
• the measurement results are also shown in Table 2.
• ring-shaped test pieces were prepared using these powders using the same method as in Example 1, and hysteresis loss was evaluated.
• Example 3 The iron-based soft magnetic powder No. 2 in Example 1 was used, and the amount of aluminum tripolyphosphate and silicone resin added when forming the insulating coating was changed from that in Example 1 to adjust the content of the insulating coating.
• Table 3 shows the content of the aluminum tripolyphosphate coating and the silicone resin coating in parts by mass per 100 parts by mass of the iron-based soft magnetic powder.
• Ring-shaped test pieces were prepared from the obtained insulating-coated soft magnetic powder using the same method as in Example 1. In addition to evaluating the hysteresis loss of the obtained ring-shaped test pieces using the method described above, the density was calculated from the dimensions and mass, and the resistivity was measured using the four-terminal method.
• the density of the ring-shaped test pieces is preferably 7.30 g/cm or more to ensure a practical saturation magnetic flux density (2 T or more) for use as an iron core for a motor.
• Example 4 An insulating coating was formed in the same manner as in Example 1 using the iron-based soft magnetic powder No. 2 in Example 1.
• the types of lubricants shown in Table 4 were added to the obtained insulating-coated soft magnetic powder, and the contents (parts by mass per 100 parts by mass of the insulating-coated soft magnetic powder) shown in Table 4 were adjusted to obtain mixed powders.
• Ring-shaped test pieces were produced using the mixed powders by pressure molding and heat treatment under the same conditions as in Example 1. The hysteresis loss of the obtained test pieces was evaluated using the method described above, and all were 30.0 W/kg or less.
• Tablet-shaped test pieces with an outer diameter of 25 mm and a height of 20 mm were prepared using the mixed powder.
• the ejection energy was calculated from the history of the ejection load when the test piece was ejected, and the density was measured from the dimensions and mass of the resulting tablet-shaped test piece.
• the ejection energy refers to the integral value of the load history curve obtained when the horizontal axis represents the sliding distance during ejection and the vertical axis represents the ejection load. If the density of the tablet-shaped test piece is less than 7.30 g/ cm3 , it is difficult to ensure a practical saturation magnetic flux density (2 T or more) for a motor iron core. Furthermore, if the ejection energy exceeds 300 kJ/ m2 , significant damage to the mold occurs, reducing mass productivity.

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