KR20160134548A - Soft magnetic metal powder and soft magnetic metal dust core - Google Patents

Abstract

An objective of the present invention is to provide a soft magnetic metal powder having a low coercive force in order to improve loss of a soft magnetic metal dust core. The present invention relates to a soft magnetic metal powder comprising: Fe, or Fe and Ni as a main component by making carbon content of the soft magnetic metal powder particles from 100-1000 ppm; providing soft magnetic metal powder having a low coercive force; and enabling an improvement in a loss of soft magnetic metal powder core using the soft magnetic metal powder.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soft magnetic metal powder core and a soft magnetic metal powder core,

TECHNICAL FIELD The present invention relates to a soft magnetic metal powder and a soft magnetic metal pressurized core used for a press compaction core or the like.

There is a demand for a soft magnetic metal pressure core having a low loss and a high saturation magnetic flux density as a core material for a motor, a reactor, and an inductor.

It is known to reduce the coercive force of the soft magnetic metal powder constituting the core in order to reduce the loss of the soft magnetic metal powder core. The core loss is divided into a hysteresis loss and an eddy current (eddy current) loss. Since the hysteresis loss depends on the coercive force, loss of the core can be reduced by reducing the coercive force.

The coercive force can be reduced by heat-treating the soft magnetic metal powder compact core at a high temperature at which the crystal grain diameter becomes large.

For example, Patent Document 1 discloses a technique of mixing a iron oxide and a carbide and performing a high-temperature heat treatment at 1150 占 폚 or more to deposit a heat resistant coating on the surface in the course of solid-phase reduction.

Japanese Patent Application Laid-Open No. 2013-79412

In the technique of Patent Document 1, the mixed powder of the iron oxide powder and the carbon powder is heat-treated to form a carbon insulating film on the particles of the soft magnetic metal powder, and the reduction and grain growth of the iron oxide are carried out. However, when a carbon film is formed on the surface of the particles, the carbon that has penetrated in a large amount does not solid-solubilize but forms an abnormal phase and increases the coercive force.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to improve the coercive force of the soft magnetic metal powder and to improve the loss of the soft magnetic metal pressure core using the coercive metal powder.

In order to solve the above-mentioned problems, the soft magnetic metal powder according to claim 1 is a soft magnetic metal powder mainly composed of iron or iron and Ni, wherein the content of carbon in the metal particles of the soft magnetic metal powder is 100 to 1000 ppm .

By using the soft magnetic metal powder having the above-described constitution, the coercive force can be reduced.

The soft magnetic metal powder according to claim 2 is the soft magnetic metal powder according to claim 1, wherein the soft magnetic metal powder has a Si content of 0 to 15 mass%.

By using the soft magnetic metal powder having the above-described constitution, the coercive force can be further reduced.

The soft magnetic metal powder according to claim 3 is the soft magnetic metal powder according to claim 1, wherein the content of Ni is 30 to 80 mass%, and the total content of Fe and Ni is 90 mass% or more.

By using the soft magnetic metal powder having the above-described constitution, the coercive force can be further reduced.

The soft magnetic metal powder according to claim 4 is the soft magnetic metal powder according to any one of claims 1 to 3, wherein at least 90% of the particles constituting the soft magnetic metal powder are composed of one crystal grain.

By using the soft magnetic metal powder having the above-described constitution, the coercive force can be further reduced.

The soft magnetic metal powder according to claim 5 is the soft magnetic metal powder according to any one of claims 1 to 4, characterized in that the amount of oxygen contained in the particles is 500 ppm or less.

By using the soft magnetic metal powder having the above-described constitution, the coercive force can be further reduced.

The soft magnetic metal powder according to claim 6 is the soft magnetic metal powder according to any one of claims 1 to 5, characterized in that the soft magnetic metal powder has a Cr content of 10 mass% or less.

By using the soft magnetic metal powder having the above-described constitution, it is possible to provide an extremely small loss, and at the same time to improve the rustproofing property and the electric resistance.

The soft magnetic metal powder according to claim 7 is the soft magnetic metal powder according to any one of claims 1 to 6, wherein the circularity of the cross section of 90% or more of the particles constituting the soft magnetic metal powder is 0.80 or more .

By using the soft magnetic metal powder having the above-described constitution, the coercive force can be further reduced.

The soft magnetic metal meal core according to claim 8 is a soft magnetic metal meal core made using the soft magnetic metal powder according to any one of claims 1 to 7.

By using the soft magnetic metal pressure powder cores having the above-described constitution, the loss of the core becomes extremely small.

The soft magnetic metal dust core according to claim 9 is the core for an inductor or the core for a reactor according to claim 8.

By using the soft magnetic metal powder core of the present invention, a reactor or an inductor having a good withstand voltage can be obtained.

According to the present invention, a soft magnetic metal powder having a low coercive force can be obtained, and the loss of the soft magnetic metal powder core can be improved by using the soft magnetic metal powder.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a heat treatment process of a soft magnetic metal powder in an embodiment of the present invention. FIG.

As a method for reducing the coercive force of soft magnetic metal particles, the most effective method is to coarsen crystal grains in the grains, and preferably to monocrystalline grains. The crystal grain growth requires heat treatment of the soft magnetic metal particles. The higher the treatment temperature, the easier the coarsening of the crystal grain size becomes and the closer to the single crystal grain. In the present invention, by controlling the carbon content after the heat treatment to 100 to 1000 ppm with respect to the soft magnetic metal material containing iron or iron and Ni as a main component, the crystal grains grow greatly during the heat treatment and low coercive force can be obtained. Hereinafter, details of the carbon addition effect, the method of producing metal particles having coarse crystal grains, and the mechanism of low coercive force of soft magnetic metal powder in the present invention will be described in detail.

Among soft magnetic metal materials mainly composed of iron or iron and Ni, carbon is known as an impurity which hinders the movement of the magnetic wall and increases the coercive force. When the amount of carbon is increased, the effect of increasing the coercive force is increased by precipitation of cementite phase or pearlite phase.

However, by adding a small amount of carbon to the soft magnetic metal powder particles, it has been found that the diffusion of carbon in the soft magnetic metal powder promotes bonding between the crystal grains during heat treatment, resulting in a soft magnetic metal powder having a large crystal grain size. When the carbon content in the soft magnetic metal powder particles after the heat treatment is 100 ppm or more and 1000 ppm or less, carbon can be sufficiently dissolved in the soft magnetic metal powder, and the effect of accelerating the crystal growth and reducing the coercive force becomes remarkable .

Hereinafter, an embodiment of the present invention will be described.

(With respect to the characteristics of the soft magnetic metal powder of the present invention)

The soft magnetic metal powder in the embodiment of the present invention is a soft magnetic metal powder mainly composed of iron or iron and Ni, and the content of carbon is 100 to 1000 ppm.

When the carbon content exceeds 1000 ppm, the coercive force becomes large. If the content of carbon in the grain of the soft magnetic metal powder is 100 to 1000 ppm, the grain growth is promoted by the diffusion of carbon at the high temperature treatment. If it is less than 100 ppm, the effect of grain growth can not be sufficiently obtained. The carbon content in the soft magnetic metal powder particles is preferably 200 to 800 ppm. More preferably from 200 to 550 ppm, even more preferably from 200 to 400 ppm.

The carbon content in the soft magnetic metal powder particles in the embodiment of the present invention can be quantified by using a carbon sulfur simultaneous analyzer (model CS600, manufactured by LECO Corporation) by the non-dispersive infrared absorption method.

The soft magnetic metal powder of the present embodiment may contain Si in an amount of up to 15% by mass, if necessary. By adding Si, a soft magnetic metal powder having a lower coercive force can be obtained. When the content of Si is more than 15 mass%, the coercive force increases or the hardness of the soft magnetic metal powder becomes too high, so that the density of the green compact becomes low when the soft magnetic metal powder core is used and a good soft magnetic metal green compact core can not be obtained . The Si content is more preferably 2 to 15% by mass. The Si content in the soft magnetic metal powder particles of the present invention can be quantified using an ICP light emission analyzer (Inductively Coupled Plasma Atomic Emission Spectroscopy).

The soft magnetic metal powder of the present embodiment can add up to 80% by mass of Ni to the composition, if necessary. By adding Ni, a soft magnetic metal powder having a low magnetic anisotropy and a small magnetostriction constant and a lower coercive force can be obtained. If the content of Ni is more than 80 mass%, the magnetocrystalline anisotropy and the magneto-static constant become large, and the coercive force increases, so that good magnetic characteristics can not be obtained. The Ni content is more preferably 30 mass% or more and 80 mass% or less. The Ni content in the soft magnetic metal powder particles of the present invention can be quantified using an ICP emission spectrometer.

The soft magnetic metal powder in the embodiment of the present invention is a soft magnetic metal powder in which at least 90% of the particles constituting the soft magnetic metal powder are composed of one crystal grain to obtain a soft magnetic metal powder having a smaller coercive force . As the heat treatment step described later is performed at a high temperature and a long time, grains composed of one grain tend to stretch. Depending on the grain size of the soft magnetic metal powder, heat treatment is usually performed at 1300 캜 for 30 min. It can be made into a crystal grain. The resulting soft magnetic metal powder is fixed with a cold embedding resin, the cross section is cut out, mirror-polished, and then the crystal grain boundary can be observed by etching with NaOH (ethanol + 1% nitric acid). When 20 or more, preferably 100 or more of the cross sections of the thus prepared particles are observed at random, and the number of particles in which grain boundaries are not observed is calculated as particles consisting of one crystal grain, 90% ≪ / RTI > There are some particles whose grain growth sites in the heat treatment furnace are incomplete, so that all the grains do not consist of one grain. An optical microscope or SEM can be used for observation.

The soft magnetic metal powder in the embodiment of the present invention can obtain a soft magnetic metal powder having a smaller coercive force when the amount of oxygen contained in the particles is 500 ppm or less. The amount of oxygen contained in the particles can be made to be 500 ppm or less by performing heat treatment in a reducing atmosphere.

If necessary, the soft magnetic metal powder of this embodiment may contain up to 10% by mass of Cr in its composition. Cr is added to the soft magnetic metal powder particles without deteriorating the coercive force and good rust resistance can be imparted to the soft magnetic metal powder particles and also the effect of increasing the electrical resistance of the soft magnetic metal powder particles, It is known that the eddy current loss can be reduced. Even when Cr is more than 10% by mass, the effect of imparting rustproofing does not change, and the saturation magnetization becomes smaller by the portion where Cr is added. Therefore, the upper limit of Cr is set to 10% by mass. The amount of Cr added is preferably 1 to 10% by mass.

In the soft magnetic metal powder in the embodiment of the present invention, when the circularity of the cross section of 90% or more of the particles constituting the soft magnetic metal powder is 0.80 or more, a soft magnetic metal powder having a smaller coercive force is obtained . The soft magnetic metal powder thus obtained is fixed with a cold embedding resin, and its cross-section is cut out and subjected to mirror-surface polishing, whereby the cross-sectional shape of the particles can be observed. At least 20, preferably 100 or more, cross-sections of the thus-prepared particles are observed at random to obtain the circularity of each particle. As an example of the circularity, Wadell's circularity can be used and is defined as the ratio of the diameter of the circle equal to the projected area of the particle cross-section to the diameter of the circle circumscribing the particle cross-section. In the case of a true circle, the circularity of Wadell is 1, and the closer to 1, the higher the roundness. If it is 0.80 or more, it can be regarded as a true sphere. An optical microscope or SEM (Scanning Electron Microscope) can be used for observation, and an image analysis can be used for calculating the circularity.

The average particle diameter of the soft magnetic metal powder in the embodiment of the present invention is preferably 0.5 to 200 mu m. When the thickness is 0.5 mu m or more, the coercive force is small, hysteresis loss can be suppressed when the core is used, and a high filling rate can be obtained. On the other hand, if the average particle diameter exceeds 200 mu m, the eddy current loss in the grain of the soft magnetic metal dust core is increased. By setting the average particle diameter to 0.5 to 200 占 퐉, the soft magnetic metal powder having low coercive force can be obtained, and the soft magnetic metal pressurized core to be produced can be made low in loss. Preferably, the average particle diameter is 1 to 150 mu m, and more preferably the average particle diameter is 1 to 100 mu m.

(Relative to raw material powder)

The method for producing the soft magnetic metal powder in the embodiment of the present invention is not particularly limited, and for example, methods such as water atomization method, gas atomization method, and casting milling method can be used. When granulating the raw material powder, it is preferable that the particle diameter of the raw material powder is finer, but raw material powder having a particle diameter of 0.5 탆 or less is not practically usable because it is difficult to obtain or manufacture as an industrial material.

The raw material powder is a metal powder mainly composed of iron or iron and Ni. The composition of the raw material powder may be adjusted according to the composition of the desired soft magnetic metal powder.

The carbon content in the raw material powder is preferably 100 ppm or more and 1000 ppm or less. When the carbon content in the raw material powder is less than 100 ppm, the effect of grain growth can not be sufficiently obtained at the time of heat treatment. When the carbon content in the raw material powder is more than 1000 ppm, the carbon content in the soft magnetic metal powder obtained after the heat treatment becomes more than 1000 ppm.

Pure iron, Fe-Si alloy, Fe-Ni alloy, or the like can be used as the raw material alloy for preparing the raw material powder. At this time, it is necessary to select the raw material metal so that the carbon content of the obtained raw material powder is 100 ppm or more and 1000 ppm or less. Since carbon is an element contained as an impurity in a raw metal, for example, pure iron, the soft magnetic metal powder of the present invention can be obtained by selecting the impurity level of the raw metal. The carbon content of the present invention can be obtained by appropriately adding carbon to the raw material metal without selecting the impurity level of the raw metal.

(For resin coating)

The raw material powder is preferably coated or granulated with a resin to produce a granulated powder. When the raw material powder coated or assembled by the resin is heat-treated, the resin is burned at a high temperature. When the resin is burned, part of the carbon in the soft magnetic metal powder is also used for combustion, so that the diffusion of carbon in the soft magnetic metal powder is promoted. As a result, the growth of the crystal grains of the soft magnetic metal powder is promoted, And becomes a magnetic metal powder.

As the resin coating, a resin such as polyvinyl alcohol or epoxy can be used. The kind of resin is not particularly limited. If the amount of the resin used is too large, it becomes difficult to handle the raw material powder after coating or granulating the raw material powder. If necessary, the particle size of the resin-coated granules is adjusted by classification, sizing, and the like.

The shape of the soft magnetic metal powder obtained after the heat treatment is similar to that of the granulated powder. In order to obtain spherical soft magnetic metal powder, it is preferable to prepare spherical granules by a spray dryer or the like.

A heat resistant powder may be mixed into the granulated powder. When the granulated powder is heat-treated at a high temperature of 1000 ° C or more, coarse powder is produced due to adhesion between the metals, but it is possible to prevent sticking by mixing the heat-resistant powder. Examples of the powder to be mixed include oxide powders such as Al ₂ O ₃ powder and SiO ₂ powder, and nitride powders such as AlN powder, Si ₃ N ₄ powder and BN powder. The mixing ratio of the heat resistant powder to the coarse powder is preferably 2 to 10% by mass based on the amount of the coarse powder because the cost increases in the step of removing the mixed heat resistant powder after the heat treatment.

(About heat treatment)

Fig. 1 is a schematic view of a heat treatment process of a soft magnetic metal powder according to an embodiment of the present invention.

Fig. 1 (a) is a schematic diagram of the raw material powder to be assembled. In Fig. 1 (a), 1 is an Fe-Si-based powder to be a raw material and is composed of many crystal grains. 2 (a), 2 is a resin used for granulation, and 3 (a) is a heat resistant powder. Heat treatment is carried out in a non-oxidizing atmosphere at a maximum temperature of 1000 to 1500 占 폚 and a holding time of 30 to 600 min, preferably 60 to 600 min. (B) and (c) are schematic diagrams of changes in the granules in this heat treatment process. 4 (b), the resin used in the assembly is the residue left after burning. As the resin is burned, a part of the trace carbon in the raw material powder moves so as to be pulled out to the outside of the raw material particles. This promotes the growth of grains inside the raw material particles and the discharge of vacancies. The soft magnetic metal powder obtained by this heat treatment has a large grain size of the particles constituting the soft magnetic metal powder and has a low coercive force. As the heat treatment temperature is high and the holding time is prolonged, the crystal growth is promoted in a state in which a plurality of crystal grains in the raw material powder have one crystal grain as shown in Fig. If the heat treatment temperature does not reach 1000 占 폚, the grain growth becomes insufficient and the coercive force is not sufficiently lowered. When the heat treatment temperature exceeds 1500 ° C, the grain growth progresses rapidly, and therefore, even if the temperature is raised above that, it is not effective. The high-temperature heat treatment is carried out in a non-oxidizing atmosphere. The heat treatment in the non-oxidizing atmosphere is performed in order to prevent oxidation of the soft magnetic metal powder.

The raw material powder is loaded in a container such as a crucible or a sagger. The material of the container should not be deformed at a high temperature of 1500 DEG C nor react with the metal. For example, alumina may be used. The heat treatment furnace may be a continuous furnace, a box furnace, a tubular furnace, a vacuum furnace, or the like, such as a pusher furnace or a roller-hearth furnace.

After the heat treatment, the mixed heat-resistant powder can be easily removed by separation by wind power classification or sieve, or washing with alcohol or water. Even if the heat resistant powder remains, a highly efficient soft magnetic metal pressurized core can be obtained. However, by removing the heat resistant powder, the density and permeability of the soft magnetic metal pressurized core to be produced can be increased.

(For a soft magnetic metal meal core)

The soft magnetic metal powder obtained in the present invention exhibits a low coercive force, so that the loss is small when the soft magnetic metal powder is used in the soft magnetic metal powder core. The manufacturing method of the soft magnetic metal dust core can be manufactured by a general manufacturing method except that the soft magnetic metal powder obtained in the present invention is used as the soft magnetic metal powder.

With respect to the soft magnetic metal powder in the embodiment of the present invention, the resin is mixed to produce a granulated powder for molding. An epoxy resin or a silicone resin can be used for the resin, and it is preferable that the resin can be uniformly applied to the surface of the soft magnetic metal powder because it has a shape-retaining property and electrical insulation property. The obtained molding granules are loaded into a mold having a desired shape and subjected to pressure molding to obtain a molded article. The forming pressure can be appropriately selected according to the composition of the soft magnetic metal powder and the desired molding density, but is generally in the range of 600 to 1600 MPa. A lubricant may be used if necessary. The obtained compact is thermally cured to obtain a soft magnetic metal pressurized core. Alternatively, heat treatment is carried out to remove deformation during molding to obtain a soft magnetic metal pressurized core. The temperature of the heat treatment is preferably 500 to 800 占 폚 in a non-oxidizing atmosphere such as a nitrogen atmosphere or an argon atmosphere.

While the present invention has been described with respect to the specific embodiments thereof, it is to be understood that the invention is not limited to the embodiments. The present invention can be modified in various ways without departing from the gist of the invention.

[Example]

≪ Example 1 >

The amount of resin at the time of assembly, the carbon content of the raw material powder, and the carbon content after the heat treatment

A raw material powder having various carbon contents whose main composition is Fe was prepared by water atomization method. The obtained raw material powder was sieved to adjust the particle size to have an average particle diameter of 20 mu m. These powders were each assembled by a spray dryer using an aqueous solution of PVA (polyvinyl alcohol) of 10 mass% with respect to the raw material powder. The mean particle size of the granules was 20 mu m. This granulated powder was mixed with 5% by mass of AlN powder, then charged into a crucible made of alumina, placed in a tubular furnace, and subjected to a high-temperature heat treatment in which it was held at 1,300 캜 for 300 minutes in a nitrogen atmosphere. The amount of PVA used in the granulation and the carbon content of the raw material powder were set as shown in Table 1. (Samples 1-1, 1-8, 1-9, and Samples 1-2 to 1-7)

The mixed AlN powder was rinsed with ethanol for the samples 1-1, 1-8, 1-9, and 1-2-1 to 1-7, and the carbon content in the soft magnetic metal powder particles was measured by using a non-dispersive infrared absorption (CS600 type, manufactured by LECO Corporation). Further, the oxygen amount was quantified by using an oxygen analyzer (TC600, manufactured by LECO). The results are shown in Table 1.

The coercive force of the powders was measured for Samples 1-1, 1-8, 1-9, and Samples 1-2 to 1-7. The coercive force of the powder was measured by a coercive force meter (model K-HC1000, manufactured by Tohoku Kogyo Kabushiki Kaisha) in which 20 mg of powder was placed in a plastic case of 6 mm x 5 mm and the paraffin was melted and solidified and fixed. The measuring magnetic field was 150kA / m. The measurement results are shown in Table 1. Here, when the value of the coercive force was 350 A / m or less, it was judged that the coercive force was low.

Powders of Samples 1-1, 1-8, 1-9, and Samples 1-2 to 1-7 were fixed with a cold embedding resin, and their cross sections were cut out to perform mirror polishing. The cross-section of the mirror-polished particles was etched away with Na (ethanol + 1% nitric acid). The grain boundaries of 100 randomly selected grains were observed and the ratio of the grains composed of one grain was calculated. The results are shown in Table 1.

A compacted core was prepared using powders of Samples 1-1, 1-8, 1-9, and Samples 1-2 to 1-7. 2.4% by mass of a silicone resin was added to 100% by mass of the powder, kneaded with a kneader, and the resulting mixture was sieved with a mesh of 355 占 퐉 to prepare molding granules. This was filled in a troidal mold having an outer diameter of 17.5 mm and an inner diameter of 11.0 mm and pressed at a molding pressure of 980 MPa to obtain a molded article. The core weight was 5 g. The compact thus obtained was heat treated in a nitrogen furnace at 750 캜 for 30 minutes to form a compacted core.

Core loss was evaluated with respect to the obtained press compaction core. The core loss was measured using a BH analyzer (SY-8258 manufactured by Iwatsu Instrument Co., Ltd.) under the conditions of a frequency of 20 kHz and a measurement magnetic flux density of 50 mT. The results are shown in Table 1.

In samples 1-2 to 1-7, coercive force lower than that of samples 1-1, 1-8, 1-9 was obtained by setting the carbon content of the soft magnetic metal powder to 100 to 1000 ppm. In the samples 1-3, 1-4, and 1-5, the coercive force is further reduced by setting the amount of carbon contained in the soft magnetic metal powder to 200 to 500 ppm. In Sample 1-1, the effect of growing crystal grains is small because of a small amount of carbon, and the coercive force is larger than that of Samples 1-2 to 1-7. In Samples 1-8 and 1-9, the coercive force is larger than that of Samples 1-2 to 1-7 because the carbon content of the soft magnetic metal powder exceeds 1000 ppm.

Comparing the core loss of Samples 1-2 to 1-7 with Samples 1-1, 1-8, and 1-9, the soft magnetic metal pressure cores using the soft magnetic metal powder of the present invention showed improved core loss .

≪ Example 2 >

The amount of Si, the amount of Ni and the amount of Cr in the soft magnetic metal powder

The amount of Si, the amount of Ni and the amount of Cr, and the raw material powder containing iron or iron and Ni as main components in the composition shown in Table 2 were prepared by water atomization method, respectively. For Fe-3.0% Si and Fe-4.5% Si, raw material powders having various carbon contents were prepared by water atomization method. The obtained raw material powder was sieved to adjust the particle size to have an average particle diameter of 20 mu m. A 10% by mass aqueous solution of PVA was slurried by using PVA in a concentration of 0.8% by mass of the solid content of the raw material powder, and the resulting slurry was assembled by a spray dryer. The mean particle size of the granules was 20 mu m. The granulated powder was mixed with 5% by mass of Al ₂ O ₃ powder, then charged into a crucible made of alumina, placed in a tubular furnace, and subjected to a high-temperature heat treatment at 1300 ° C for 60 minutes in a nitrogen atmosphere. The carbon content in the metal molecules of the obtained soft magnetic metal powder was measured by washing the mixed Al ₂ O ₃ powder with ethanol and then using a carbon sulfur simultaneous analyzer (CS600 type manufactured by LECO Corporation) by a non-dispersion type infrared absorption method , And quantified in the same procedure as in Sample 1. (Samples 2-1 to 28)

The coercive force of the powders was measured for Samples 2-1 to 2-28. The coercive force of the powder was measured by a coercive force meter (model K-HC1000, manufactured by Tohoku Kogyo Kabushiki Kaisha) in which 20 mg of powder was placed in a plastic case of 6 mm x 5 mm and the paraffin was melted and solidified and fixed. The measuring magnetic field was 150kA / m. The measurement results are shown in Table 2.

The samples 2-1 to 2-28 were tested for rust resistance. The powder was fixed with a cold embedding resin, and the cross section was cut out to polish the mirror. It was allowed to stand in a constant temperature and humidity bath at 60 DEG C and a relative humidity of 95% for 2,000 hours. Thereafter, 20 cross sections of the metal particles were randomly observed, and the ratios of the rusted metal particles were calculated. The results thereof are shown in Table 2.

The samples 2-4 to 2-8, 2-11 to 2-15, 2-17 and 2-18 had a very low coercive force of less than 230 A / m because the Si content was in the range of 2 to 15 mass% It is. On the other hand, in the samples 2-9, 2-10 and 2-16, the Si content was within the range of 2 to 15% by mass, but the carbon content was not appropriate, so that the coercive force of the powder was increased. Further, the sample 2-19 had a coercive force greater than 250 A / m because the Si content was as high as 18 mass%. The metal powder compositions of Samples 2-20 to 2-23 were obtained by adding Cr to the metal powder composition of Sample 2-12, and it was found that even when Cr was added, the coercive force of the powder was hardly affected . By adding Cr in an amount of 1.0% by mass or more, the ratio of particles generating rust can be made 0%.

≪ Example 3 >

Evaluation of Circularity, Grain Size, Oxygen Content and Powder Core

The raw material powder having the composition of Fe-6.5% Si was prepared by the water atomization method. The raw material powder was sieved to adjust its particle size to have an average particle size of 75 탆. The raw material powder having a carbon content of 250 ppm was selected. The raw material powder was slurried by adding a resin solution of 10 mass% to the raw material powder and then assembled by a spray dryer. The resin solution was an epoxy-acetone solution, and the amount of the epoxy resin was 0.3% by mass of the solid content of the raw material powder. The mean particle size of the granules was 75 탆. This granulated powder was mixed with a 5 mass% BN powder, then charged into a crucible made of alumina, placed in a tubular furnace, subjected to a high-temperature heat treatment in a nitrogen atmosphere, washed with ethanol to remove the mixed BN powder, A metal powder was obtained. These soft magnetic metal powders were subjected to heat treatment at the temperature and time shown in Table 3. (Samples 3-1 to 3-3)

The soft magnetic metal powder of the sample 3-3 was subjected to a reduction treatment at 600 ° C for 1 hour in a hydrogen atmosphere to obtain a soft magnetic metal powder. (Sample 3-4)

The Fe-6.5% Si raw material powder was prepared by the gas atomization method. The raw material powder was sieved to adjust the particle size, and the average particle size was set to 75 탆. The raw material powder was slurried by adding a resin solution of 10 mass% to the raw material powder and then assembled by a spray dryer. The resin solution was an epoxy-acetone solution, and the amount of the epoxy resin was 0.3% by mass of the solid content of the raw material powder. The mean particle size of the granules was 75 탆. This granulated powder was mixed with a 5 mass% BN powder, then charged into a crucible made of alumina, placed in a tubular furnace, subjected to a high-temperature heat treatment in a nitrogen atmosphere, washed with ethanol to remove the mixed BN powder, A metal powder was obtained. This soft magnetic metal powder was subjected to heat treatment at the temperature and time shown in Table 3. Thereafter, the soft magnetic metal powder was subjected to a reduction treatment at 600 DEG C for 1 hour in a hydrogen atmosphere to obtain a soft magnetic metal powder (Sample 3-5)

The C content in the obtained soft magnetic metal powder particles was quantified using a carbon sulfur simultaneous analyzer (model CS600, manufactured by LECO Corporation) by a non-dispersion type infrared absorption method. The amount of oxygen was quantified using an oxygen analyzer (TC600, manufactured by LECO). The results are shown in Table 3.

The coercive force of the powder was measured for the samples 3-1 to 3-5 obtained as a powder. The coercive force of the powder was measured with a coercive force meter (model K-HC1000, manufactured by Tohoku Kogyo Kabushiki Kaisha) in which 20 mg of powder was placed in a plastic case of 6 mm x 5 mm and the paraffin was melted and solidified and fixed. The measuring magnetic field is 150 kA / m. The measurement results are shown in Table 3.

Fixed with the cold embedding resin of Samples 3-1 to 3-5, and the cross-section was cut out to perform mirror-surface polishing. 100 cross sections of the particles were randomly observed and the circularity of Wadell of each particle was measured to calculate the ratio of particles having a circularity of 0.80 or more. The results are shown in Table 3.

Powders of Samples 3-1 to 3-5 were fixed with a cold embedding resin, and their cross-sections were cut out to perform mirror-surface polishing. The cross-section of the mirror-polished particles was etched away with Na (ethanol + 1% nitric acid). The grain boundaries of 100 randomly selected grains were observed and the ratio of the grains composed of one grain was calculated. The results are shown in Table 3.

Powders of samples 3-1 to 3-5 were used to prepare compacted cores. 2.4% by mass of a silicone resin was added to 100% by mass of the powder, kneaded with a kneader, and the resulting mixture was sieved with a mesh of 355 占 퐉 to prepare molding granules. This was filled in a toroidal mold having an outer diameter of 17.5 mm and an inner diameter of 11.0 mm and pressed at a molding pressure of 980 MPa to obtain a molded article. The core weight was 5 g. The obtained molded body was heat treated in a nitrogen atmosphere at 750 캜 for 30 minutes using a belt furnace to obtain a compacted core.

Core loss was evaluated with respect to the obtained press compaction core. The core loss was measured using a BH analyzer (SY-8258 manufactured by Iwatsu Instrument Co., Ltd.) under the conditions of a frequency of 20 kHz and a measurement magnetic flux density of 50 mT. The results are shown in Table 3.

Comparing the samples 3-1 to 3-3, 90% or more of the particles constituting the soft magnetic metal powder were able to obtain one crystal grain by setting the heat treatment temperature at a high temperature and the heat treatment time to 60 minutes or more. In addition, when at least 90% of the particles constituting the soft magnetic metal powder are one crystal grain, a low coercive force can be obtained. From the comparison of Samples 3-3 and 3-4, the coercive force becomes smaller when the ratio of the particles having a circularity of the particle cross section of 0.80 or more is 90% or more. From the comparison of Samples 3-4 and 3-5, when the oxygen amount is 500 ppm or less, the coercive force is further reduced.

INDUSTRIAL APPLICABILITY As described above, the soft magnetic metal powder of the present invention has a low coercive force, and by using the soft magnetic metal powder, a soft magnetic metal pressurized core can be produced, and a low loss core can be obtained. The soft magnetic metal powder or the soft magnetic metal pressurized core can be widely and effectively used for an electric or magnetic device such as a power supply circuit because it can realize high efficiency from a low loss.

1: raw material powder
2: Resin
3: Heat resistant powder
4: Residue after combustion of resin

Claims (9)

1. A soft magnetic metal powder comprising carbon or iron, or iron and Ni as a main component,
Characterized in that the content of carbon in the metal particles of the soft magnetic metal powder is 100 to 1000 ppm. The soft magnetic metal powder according to claim 1, which contains Si and has a Si content of 2 to 15 mass%. The method according to claim 1,
The content of Ni is 30 to 80 mass%
Wherein the total content of Fe and Ni is 90 mass% or more. The soft magnetic metal powder according to any one of claims 1 to 3, wherein at least 90% of the particles constituting the soft magnetic metal powder are composed of one crystal grain. The soft magnetic metal powder according to any one of claims 1 to 4, characterized in that the amount of oxygen contained in the particles is 500 ppm or less. The soft magnetic metal powder according to any one of claims 1 to 5, characterized by containing Cr and having a Cr content of 10 mass% or less. The soft magnetic metal powder according to any one of claims 1 to 6, wherein a circularity of 90% or more of the metal powder is 0.80 or more. A soft magnetic metal powder core produced by using the soft magnetic metal powder according to any one of claims 1 to 7. The soft magnetic metal dust core according to claim 8, which is used as a core for an inductor or a core for a reactor.

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