JP5682724B1 - Soft magnetic metal powder and soft magnetic metal powder core - Google Patents

Abstract

A soft magnetic metal powder with improved saturation magnetization and coercive force, and a soft magnetic metal powder core with improved loss using the same. A soft magnetic metal powder 4 containing Fe as a main component and containing Al, wherein the Fe content is 96% by mass or more, and the Al content in the metal particles of the soft magnetic metal powder 4 is 0.1%. It is ˜1% by mass and has a nitrided aluminum film 5 on the surface of the metal particles. By using the soft magnetic metal powder 4, the saturation magnetization of the soft magnetic metal powder is increased and the coercive force is reduced. By producing a soft magnetic metal powder core using this soft magnetic metal powder 4, the loss of the core is improved. [Selection] Figure 2

Description

The present invention relates to a soft magnetic metal powder used for a dust core and the like, and a soft magnetic metal dust core.

As core materials for reactors and inductors used in applications where large currents are applied, ferrite cores, laminated electrical steel sheets, soft magnetic metal dust cores (cores made by mold molding, injection molding, sheet molding, etc.), etc. Is used. Although the laminated magnetic steel sheet has a high saturation magnetic flux density, there is a problem that when the driving frequency of the power supply circuit exceeds several tens of kHz, the iron loss increases and the efficiency decreases. On the other hand, the ferrite core is a magnetic core material with a small high-frequency loss, but there is a problem that the shape is increased because the saturation magnetic flux density is low.

Soft magnetic metal dust cores, especially dust cores using iron powder, are widely used because the high-frequency iron loss is smaller than that of laminated electrical steel sheets and the saturation magnetic flux density is higher than that of laminated electrical steel sheets. . However, although the loss is superior to that of laminated electrical steel sheets, it cannot be said that the loss is as low as that of ferrite, and reduction of the loss is desired.

In order to reduce the loss of the soft magnetic metal dust core, it is known to reduce the coercive force of the soft magnetic metal powder constituting the core. The core loss is divided into hysteresis loss and eddy current loss. Since the hysteresis loss depends on the coercive force, the core loss can be reduced by reducing the coercive force.

In order to reduce the coercive force of the soft magnetic metal powder, it has been attempted to heat-treat the soft magnetic metal powder at a high temperature at which the crystal grain size becomes large. For example, Patent Document 1 discloses a technique in which inorganic powder for preventing sintering is mixed with iron powder and heat-treated at a high temperature. Patent Document 2 discloses a technique in which a soft magnetic alloy powder is heat-treated at a high temperature while mixing an inorganic insulator and suppressing the adhesion of the powder.

JP-A-9-260126 JP 2002-57020 A

In the techniques of Patent Document 1 and Patent Document 2, a large amount of inorganic powder is mixed with the soft magnetic metal powder to prevent sintering, and heat treatment is performed at a high temperature. Since covering is impossible, it is inevitable that the powder adheres when heat treatment is performed at 1000 ° C. or higher. Since the powder that has been fixed needs to be crushed and distorted, the coercive force of the resulting powder is not sufficiently small. 950 ° C. is the limit for heat treatment without fixing, and crystal grain growth is insufficient at this heat treatment temperature. That is, in the conventional technique, the effect on the increase of the crystal grain size is insufficient, and therefore, the coercive force of the obtained soft magnetic metal powder cannot be said to be sufficiently reduced, and is produced using it. There was a problem that the loss of the soft magnetic metal dust core also increased.

The present invention has been devised in order to solve the above-mentioned problems, and improves the saturation magnetization and coercive force of the soft magnetic metal powder, and reduces the loss of the soft magnetic metal dust core using the soft magnetic metal powder. The issue is to improve.

In order to solve the above problems, the soft magnetic metal powder of the present invention is a soft magnetic metal powder containing Fe as a main component and containing Al, and the Fe content in the soft magnetic metal powder is 96 mass% or more, The content of Al in the metal particles of the soft magnetic metal powder is 0.1 to 1% by mass, and an aluminum nitride film is provided on the surface of the metal particles.

By using the soft magnetic metal powder having the above configuration, both high saturation magnetization and low coercive force can be achieved.

More preferably, the soft magnetic metal powder of the present invention is characterized in that the circularity of the cross section of 90% or more of the metal particles constituting the soft magnetic metal powder is 0.80 or more.

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

More preferably, the soft magnetic metal powder of the present invention is characterized in that 90% or more of the metal particles constituting the soft magnetic metal powder are composed of one crystal grain.

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

The soft magnetic metal powder of the present invention is more preferably characterized in that the amount of oxygen contained in the metal particles is 500 ppm or less.

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

The soft magnetic metal powder of the present invention is characterized by having at least one of aluminum oxide particles and aluminum hydroxide particles on the surface of the metal particles in the soft magnetic metal powder.

By using the soft magnetic metal powder having the above-described configuration, the soft magnetic metal powder core can be stably produced while keeping the coercive force low.

The soft magnetic metal dust core of the present invention is a soft magnetic metal dust core produced using the soft magnetic metal powder of the present invention.

The soft magnetic metal dust core produced using the soft magnetic metal powder of the present invention has a very small core loss.

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

First, the mechanism by which the soft magnetic metal powder of the present invention has a low coercive force will be described.

In the conventional technology, the oxide and nitride fine particles mixed to prevent sintering during high-temperature heat treatment are unevenly distributed without covering the surface of the metal particles, or unstable at high temperatures. In the heat treatment at a high temperature of 1000 ° C. or more, there is a problem that the particles adhere to each other and a powder cannot be obtained. Therefore, in order to improve this, a technique for coating the entire surface of the metal particles in the soft magnetic metal powder with an aluminum nitride film having a high melting point and extremely low reactivity with the metal even at a high temperature was studied, and the present invention was applied. It was.

The fundamental problem of the conventional technology is that a member for preventing sintering (powder or coating) is formed from the outside of the soft magnetic metal powder. It is inevitable that the distribution becomes non-uniform. Therefore, it was considered that a uniform and stable sintering prevention layer can be formed by diffusing and precipitating components contained in the metal particles on the surface and reacting with the atmosphere. Therefore, in the present invention, a raw material powder containing Fe as a main component and containing Al is prepared, and this raw material powder is subjected to high-temperature heat treatment in a non-oxidizing atmosphere containing nitrogen. By this high-temperature heat treatment, Al in the raw material powder particles diffuses to the metal particle surface and reacts with nitrogen at the particle surface portion to form aluminum nitride. After the high-temperature heat treatment, a soft magnetic metal powder having an aluminum nitride precipitate on the particle surface and a structure containing 0.1 to 1% by mass of Al in the metal portion inside the particle is obtained.

The cross-sectional form of the metal particles of the raw material powder is illustrated in FIG. 1, and the cross-sectional form of the metal particles of the soft magnetic metal powder is illustrated in FIG. The metal particles of the raw material powder in FIG. 1 are polycrystals composed of fine crystal grains, and Al is dissolved in the metal matrix. An aluminum nitride film is formed on the surface of the metal particles of the soft magnetic metal powder in FIG. 2 so as to uniformly cover the entire surface of the particles. As the size of the crystal grains increases, Al in the metal particles decreases, and 0.1 to 1% by mass of Al is dissolved in the metal matrix.

By containing a sufficient amount of Al in the raw powder particles, nitriding the Al, and precipitating aluminum nitride on the particle surface, a uniform and gap-free film can be formed. Even if oxide powder such as SiO2, Al2O3, B2O3, or nitride powder such as boron nitride is mixed in the raw material powder, even if a large amount of oxide powder or nitride powder is mixed, the surface of the raw material powder particles Although contact is unavoidable, contact between the surfaces of the raw material powder particles can be prevented by forming a film that is uniform and has no gaps. Aluminum nitride is stable in a nitrogen atmosphere, and aluminum nitride itself is a hardly sinterable substance. Therefore, when performing high-temperature heat treatment, metal particles adhere to each other through the oxide in the oxide film, but do not adhere to the aluminum nitride film. Since aluminum nitride has a lower density than the raw material powder that is a metal, if aluminum nitride is formed on the surface portion of the raw material powder particles, there is an effect of increasing the distance between the surfaces of the metal portions of the adjacent raw material powder. This action is also effective in preventing sintering of the raw material powder particles. Due to the above effects, it becomes possible to perform heat treatment at a high temperature of 1000 ° C. or higher, which was impossible in the past, and the coercive force can be reduced.

Another effect on the coercive force due to the inclusion of Al in the raw material powder particles is considered. That is, the diffusion of Al inside the raw material powder particles toward the surface of the raw material powder particles facilitates the movement of the crystal grain boundary toward the surface of the raw material powder particles, and promotes the growth of crystal grains. By including Al in the raw material powder particles, the effect of forming a good anti-sintering film that can withstand high temperatures, the effect of promoting crystal grain growth, and the dual effect are obtained, and the softness with extremely low coercivity is obtained. Magnetic metal powder can be obtained.

Embodiments of the present invention will be described below.

(About the characteristics of the soft magnetic metal powder of the present invention)
The soft magnetic metal powder of the present invention is a soft magnetic metal powder containing Fe as a main component and containing Al, wherein the soft magnetic metal powder has a Fe content of 96% by mass or more, and the metal particles of the soft magnetic metal powder. The content of Al is 0.1 to 1% by mass, and an aluminum nitride film is formed on the surface of the metal particles. By setting the content of Al in the metal particles of the soft magnetic metal powder to 0.1 to 1% by mass, the coercive force becomes sufficiently small. When high-temperature heat treatment is performed in a non-oxidizing atmosphere containing nitrogen, Al in the raw material powder particles is nitrided on the particle surface to become aluminum nitride, so the Al content in the raw material powder and the amount of aluminum nitride deposited on the particle surface The Al content in the metal particles varies depending on the balance. Since Al has a wide solid solubility limit in the parent phase (bcc) of the metal particles, a certain amount of Al remains in the metal particles. When the Al content in the metal particles is less than 0.1% by mass, the Al content is insufficient, so the amount of aluminum nitride deposited on the surface of the metal particles becomes insufficient, and the powder in the heat treatment Will sinter. On the other hand, if 1% by mass or more of Al is present in the metal particles, the magnetostriction increases, which causes a deterioration in coercive force.

The Al content in the metal particles of the soft magnetic metal powder of the present invention can be quantified using, for example, an electron beam microanalyzer (EPMA). The soft magnetic metal powder is fixed with cold embedding resin, the cut out is polished, the cross section of the particle is exposed, and the Al content in the particle can be quantified with EPMA.

The Fe content of the soft magnetic metal powder is adjusted to be 96% by mass or more. If the Fe content is less than 96%, the saturation magnetization is lowered. The Fe content of the soft magnetic metal powder can be calculated by reducing the content of alloy components and impurity components other than Fe from 100%.

The soft magnetic metal powder of the present invention is a soft magnetic material having a smaller coercive force when the circularity of the cross section of 90% or more of the metal particles constituting the soft magnetic metal powder is 0.80 or more. Metal powder can be obtained. By fixing the obtained soft magnetic metal powder with cold embedding resin, cutting out the cross section and mirror polishing, the cross sectional shape of the metal particles can be observed. At least 20 (preferably 100 or more) cross sections of the metal particles thus prepared are observed at random, and the circularity of each particle is obtained. As an example of circularity, Wadell's circularity can be used, which is defined by the ratio of the diameter of a 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 perfect circle, Wadell's circularity is 1, and the closer to 1, the higher the roundness, and if it is 0.80 or more, it can be regarded as a substantially spherical appearance. An optical microscope or SEM can be used for observation, and image analysis can be used for calculation of circularity.

The soft magnetic metal powder of the present invention is a soft magnetic metal powder in which 90% or more of the metal particles constituting the soft magnetic metal powder are composed of one crystal grain, thereby obtaining a soft magnetic metal powder having a smaller coercive force. be able to. By performing a high-temperature heat treatment exceeding 1200 ° C., 90% or more of the metal particles constituting the soft magnetic metal powder can be made into a soft magnetic metal powder composed of one crystal grain. The obtained soft magnetic metal powder is fixed with a cold embedding resin, a cross section is cut out, mirror-polished, and then etched with nital (ethanol + 1% nitric acid), whereby crystal grain boundaries can be observed. The cross section of the metal particles thus prepared is observed at least 20 randomly, preferably 100 or more, and the number of metal particles in which no crystal grain boundary is observed is counted as a metal particle composed of one crystal grain. Since some of the metal particles have incomplete crystal grain growth, all the metal particles do not consist of one crystal grain. An optical microscope or SEM (scanning electron microscope) can be used for observation.

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

The average particle size of the soft magnetic metal powder of the present invention is 1 to 200 μm. When the average particle size is less than 1 μm, the magnetic permeability of the soft magnetic metal dust core decreases. On the other hand, if the average particle size exceeds 200 μm, the intra-grain eddy current loss of the soft magnetic metal dust core increases.

(About raw material powder)
The method for producing the raw material powder of the soft magnetic metal powder is not particularly limited, and for example, a water atomizing method, a gas atomizing method, a casting pulverization method, or the like can be used. If the raw material powder produced by the gas atomization method is used, it is easy to obtain a soft magnetic metal powder in which the circularity of the cross section of 90% or more of the metal particles constituting the soft magnetic metal powder is 0.80 or more. Therefore, it is preferable.

The raw material powder is a metal powder mainly composed of Fe and contains Al. The Fe content of the raw material powder is adjusted to be 97% by mass or more. The content of Al in the raw material powder is 1.0% by mass or more and 3.0% by mass or less. If the amount is less than 1.0% by mass, the content of Al is too small, the amount of aluminum nitride deposited becomes insufficient, and a uniform film cannot be formed. Resulting in. As the Al content of the raw material powder increases, Al remaining in the metal particles of the soft magnetic metal powder increases and the magnetostriction constant increases.

(About heat treatment)
The raw material powder containing Al is subjected to high temperature heat treatment in a non-oxidizing atmosphere containing nitrogen. This heat treatment releases the strain and increases the crystal grain size. In order to sufficiently reduce the coercive force, the heat treatment is performed in a non-oxidizing atmosphere containing nitrogen at a heating rate of 5 ° C./min or less, a temperature of 1000 to 1300 ° C., and a holding time of 30 to 600 min. By performing this heat treatment, nitrogen in the atmosphere reacts with Al in the raw material powder to form an aluminum nitride film on the surface of the metal particles and to grow crystal grains of the metal particles. When the heat treatment temperature is less than 1000 ° C., the crystal grain growth of the raw material powder becomes insufficient. When the heat treatment temperature exceeds 1300 ° C., the nitridation proceeds promptly to complete the reaction, and the crystal grain growth also proceeds rapidly to form a single crystal. Therefore, even if the temperature is raised further, there is no effect. The high temperature heat treatment is performed in a non-oxidizing atmosphere containing nitrogen. The heat treatment is performed in a non-oxidizing atmosphere to prevent the soft magnetic metal powder from being oxidized. If the heating rate is too high, the temperature reaches the temperature at which the raw material powder particles sinter before a sufficient amount of aluminum nitride is produced, and the raw material powder is sintered. The following.

The raw material powder is loaded into a container such as a crucible or a mortar. The material of the container is required not to be deformed at a high temperature of 1300 ° C., and it is necessary that the material does not react with a metal. As an example, alumina can be used. The heat treatment furnace may be a continuous furnace such as a pusher furnace or a roller hearth furnace, or a batch furnace such as a box furnace, a tubular furnace, or a vacuum furnace.

(Decomposition of aluminum nitride)
In the soft magnetic metal powder of the present invention, even if a part of the aluminum nitride formed on the surface of the metal particles is modified to aluminum hydroxide or aluminum oxide, the effect is not affected. Aluminum nitride easily reacts with moisture in the air to produce aluminum hydroxide, but has no effect on the coercivity of the powder. In addition, when a powder magnetic core produced using the soft magnetic metal powder of the present invention is heat-treated, aluminum hydroxide may be decomposed into aluminum oxide, but this has no effect on the coercive force of the powder. Never give. Since aluminum nitride is unstable with respect to moisture, the characteristics of the soft magnetic metal dust core can be stabilized by making some aluminum nitride into the form of aluminum hydroxide or aluminum oxide.

(About soft magnetic metal dust core)
Since the soft magnetic metal powder obtained in the present invention exhibits a low coercive force, the loss is reduced when it is used for a soft magnetic metal dust core. The method for producing the soft magnetic metal dust core can be produced by a general production method except that the soft magnetic metal powder obtained in the present invention is used as the soft magnetic metal powder, but an example is shown.

The soft magnetic metal powder of the present invention is mixed with a resin to produce granules. As the resin, an epoxy resin or a silicone resin can be used, and those having shape retention and electrical insulation during molding and preferably capable of being uniformly applied to the surface of the soft magnetic metal powder are preferable. The obtained granule is filled into a mold having a desired shape, and pressure-molded to obtain a molded body. The molding pressure can be appropriately selected depending on the composition of the soft magnetic metal powder and the desired molding density, but is generally in the range of 600 to 1200 MPa. A lubricant may be used as necessary. The obtained molded body is heat-cured to form a powder core. Or heat processing is performed in order to remove distortion at the time of fabrication, and it is set as a soft magnetic metal dust core. The heat treatment is preferably performed at a temperature of 500 to 650 ° C. in a non-oxidizing atmosphere such as a nitrogen atmosphere or an argon atmosphere.

The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. The present invention can be variously modified without departing from the gist thereof.

<Example 1> About the amount of Fe and the amount of Al

A raw material powder having a composition with a main composition of Fe-2.0% Al was prepared by a water atomization method. The particle size of the raw material powder was adjusted by sieving so that the average particle size was 70 μm. This powder was loaded into an alumina crucible, placed in a tubular furnace, and subjected to high-temperature heat treatment at 1100 ° C. in a nitrogen atmosphere to obtain a soft magnetic metal powder. The holding time of 1100 ° C. during the heat treatment was set as the time shown in Table 1, and the Al content in the metal particles of the soft magnetic metal powder was adjusted. ( Examples 1-1 and 1-2, Reference Example 1-3, Comparative Examples 1-4 to 1-5)

The raw material powder which added the quantity of Al shown in Table 1 with respect to Fe was produced by the water atomization method. The particle size of the raw material powder was adjusted by sieving so that the average particle size was 70 μm. This powder was loaded into an alumina crucible, placed in a tubular furnace, and subjected to high temperature heat treatment at 1100 ° C. for 300 minutes in a nitrogen atmosphere to obtain a soft magnetic metal powder. (Examples 1-7 to 1-9, Comparative Examples 1-6, 1-10 to 1-11)

A raw material powder made of pure iron was prepared by a water atomization method. The particle size of the powder was adjusted by sieving so that the average particle size was 70 μm. This powder was loaded into an alumina crucible, placed in a tubular furnace, and subjected to high temperature heat treatment for 300 minutes in a nitrogen atmosphere to obtain a soft magnetic metal powder. The heat treatment temperature was set to 700 ° C. as a result of examining the highest possible temperature at which the powder was not sintered. (Comparative Example 1-12)

A raw material powder made of pure iron was prepared by a water atomization method. The particle size of the powder was adjusted by sieving so that the average particle size was 70 μm. This powder was loaded into an alumina crucible, placed in a tubular furnace, and subjected to high-temperature heat treatment at 1100 ° C. for 5 minutes in a nitrogen atmosphere to obtain a soft magnetic metal powder. (Comparative Example 1-13)

About Example 1-1, 1-2, Reference Example 1-3, Examples 1-7 to 1-9 and Comparative Examples 1-4 to 1-6, 1-10 to 1-11, soft magnetic metal powder The Al content in the metal particles was quantified. After the heat treatment, the soft magnetic metal powder fixed with the cold embedding resin was cut, and the cut surface was mirror-polished. Next, using an electron beam microanalyzer (EPMA), the Al content inside the particle was quantified in the portion where the cross section of the metal particle appeared.

About Example 1-1, 1-2, Reference Example 1-3, 1-7 to 1-9 and Comparative Examples 1-4 to 1-6 , 1-10 to 1-13, Fe content of soft magnetic metal powder The amount was quantified. The amount of Al in the soft magnetic metal powder is determined by ICP, the amount of oxygen and the amount of nitrogen are determined by an oxygen / nitrogen analyzer (TC600 manufactured by LECO), and the amount of carbon is determined by a carbon analyzer (CS600 manufactured by LECO). The Fe content in the soft magnetic metal powder was calculated by subtracting from%.

In Examples 1-1 and 1-2, Reference Example 1-3, 1-7 to 1-9 and Comparative Examples 1-4 to 1-6 and 1-10 to 1-11, aluminum nitride is formed on the surface of the metal particles. Was formed. In Comparative Example 1-13, since Al was not contained at all, the film that prevented sintering was not formed on the particle surface, and the entire powder was sintered. In Comparative Example 1-6, although Al was contained in the raw material powder, since the Al content was small, the powder was partially sintered and no powder was obtained. This is probably because the amount of aluminum nitride formed on the particle surface is insufficient when the Al content is so low that Al in the metal particles is reduced to less than 0.1% by mass.

Cold embedding of soft magnetic metal powders of Examples 1-1 and 1-2, Reference Example 1-3, 1-7 to 1-9 and Comparative Examples 1-4 to 1-5 and 1-10 to 1-12 It fixed with resin, cut out the cross section, and mirror-polished. The mirror-polished metal particle cross section was etched with nital (ethanol + 1% nitric acid). The crystal grain boundary of 100 randomly selected metal particles was observed, and the ratio of metal particles composed of one crystal grain was calculated. The results are shown in Table 1.

About Examples 1-1, 1-2, Reference Example 1-3, 1-7 to 1-9 and Comparative Examples 1-4 to 1-5 and 1-10 to 1-12 obtained as powder The coercive force and saturation magnetization of were measured. The coercive force of the powder was measured with a coercive force meter (K-HC1000 type, manufactured by Tohoku Special Steel Co., Ltd.) in which 20 mg of powder was put in a plastic case of φ6 mm × 5 mm, and paraffin was melted and solidified. The measurement magnetic field is 150 kA / m. The saturation magnetization was measured by VSM. The measurement results are shown in Table 1.

In Examples 1-1 and 1-2, Reference Example 1-3, 1-7 to 1-9, and Comparative Example 1-10, the Al content in the metal particles is 0.1 to 1% by mass. A low coercive force of 300 A / m or less is obtained. On the other hand, in Comparative Examples 1-4 to 1-5 and 1-11, since the Al content in the metal particles exceeds 1 mass%, only a large coercive force of 350 A / m or more can be obtained. In Examples 1-1 to 1-2, Reference Example 1-3, and Comparative Examples 1-4 to 1-5, the smaller the Al content in the metal particles, the higher the proportion of metal particles composed of one crystal grain. It can be seen that Al in the metal particles is nitrided and moves to the surface, and crystal grain growth proceeds.

In Examples 1-1 and 1-2, Reference Example 1-3, and 1-7 to 1-9, since the Fe content of the soft magnetic metal powder is 96% by mass or more, a high saturation magnetization of 200 emu / g or more is exhibited. Has been obtained. On the other hand, in Comparative Examples 1-10 to 1-11, since the Fe content of the soft magnetic metal powder is 96 mass% or more, only a low saturation magnetization of less than 200 emu / g can be obtained.

In Comparative Example 1-12, the heat treatment was attempted without addition of Al. However, since the heat treatment temperature recoverable with powder is as low as 700 ° C., only a large coercive force of 620 A / m can be obtained.

From these results, the soft magnetic metal powder has a high saturation magnetization and a low coercive force by controlling the Fe content of the soft magnetic metal powder to 96% by mass and controlling the Al content in the metal particles to 0.1 to 1% by mass. It can be seen that a powder can be obtained.

<Example 2> Effect of circularity, crystal grain size, oxygen content and evaluation of dust core

Raw material powders having a composition with a main composition of Fe-1.5% Al were prepared by a water atomizing method and a gas atomizing method, respectively. The particle size of the raw material powder was adjusted by sieving so that the average particle size was 70 μm. This powder was loaded into an alumina crucible, placed in a tubular furnace, and subjected to high temperature heat treatment in a nitrogen atmosphere to obtain a soft magnetic metal powder. The heat treatment temperature and heat treatment time are shown in Table 2. (Examples 2-1 to 2-4)

Further, the obtained soft magnetic metal powder was subjected to a reduction treatment at 600 ° C. for 60 minutes in a hydrogen atmosphere to obtain a soft magnetic metal powder having a reduced amount of oxygen. (Examples 2-5 to 2-8)

Raw material powder of pure iron composition was produced by water atomization method and gas atomization method. The particle size of the raw material powder was adjusted by sieving so that the average particle size was 70 μm. Each of these powders was loaded into an alumina crucible, placed in a tubular furnace, and heat-treated at 700 ° C. for 300 minutes in a nitrogen atmosphere to obtain a soft magnetic metal powder. (Comparative Examples 2-9 to 2-10)

For Examples 2-1 to 2-8 and Comparative Examples 2-9 to 2-10, the Fe content of the soft magnetic metal powder and the Al content in the metal particles were quantified in the same procedure as in Example 1. The oxygen content of the soft magnetic metal powder was quantified with an oxygen analyzer (TC600 manufactured by LECO). The results are shown in Table 2.

For Examples 2-1 to 2-8 and Comparative Examples 2-9 to 2-10, the coercive force and saturation magnetization of the soft magnetic metal powder were measured in the same manner as in Example 1. The saturation magnetization was 200 emu / g or more. The coercive force of the powder is shown in Table 2.

The powders of Examples 2-1 to 2-8 and Comparative Examples 2-9 to 2-10 were fixed with a cold embedding resin, the cross section was cut out, and mirror polishing was performed. 100 cross sections of the metal particles were randomly observed, the Wadell circularity of each particle was measured, and the ratio of the metal particles having a circularity of 0.80 or more was calculated. The results are shown in Table 2.

The powders of Examples 2-1 to 2-8 and Comparative Examples 2-9 to 2-10 were fixed with a cold embedding resin, the cross section was cut out, and mirror polishing was performed. The mirror-polished metal particle cross section was etched with nital (ethanol + 1% nitric acid). The crystal grain boundary of 100 randomly selected metal particles was observed, and the ratio of metal particles composed of one crystal grain was calculated. The results are shown in Table 2.

In each of Examples 2-1 to 2-8, a low coercive force of 300 A / m or less was obtained. When Examples 2-1 and 2-3 and Examples 2-2 and 2-4 are compared, the ratio of the metal particles having a circularity of the cross section of the metal particles of 0.80 or more is 90% or more. It can be seen that the coercive force can be further reduced. In addition, when Examples 2-1 and 2-2 and Examples 2-3 and 2-4 are compared, 90% or more of the metal particles constituting the soft magnetic metal powder are formed as one crystal grain, thereby providing a coercive force. It can be seen that can be made smaller. Moreover, when Examples 2-1 to 2-4 and Examples 2-5 to 2-8 are compared, it can be seen that the coercive force can be further reduced by setting the amount of oxygen contained in the soft magnetic metal powder to 500 ppm or less. .

The compacting core was produced using Examples 2-1 to 2-8 and Comparative Examples 2-9 to 2-10. What added 2.4 mass% of silicone resin with respect to 100 mass% of metal powder, knead | mixed with the kneader was sized with a 355-micrometer mesh, and the granule was produced. 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 with a molding pressure of 780 MPa to obtain a molded body. The core weight was 5 g. The obtained molded body was heat-treated in a belt furnace at 600 ° C. for 30 minutes in a nitrogen atmosphere to obtain a powder core. In addition, there was an ammonia odor during kneading of Examples 2-1 to 2-8, and it was considered that at least a part of aluminum nitride reacted with moisture in the air and decomposed into aluminum hydroxide and ammonia. By doing so, it is considered that aluminum oxide is generated.

The core loss was evaluated about the obtained powder core. The core loss was measured using a BH analyzer (SY-8258 manufactured by Iwadori Measurement Co., Ltd.) under conditions of a frequency of 20 kHz and a measurement magnetic flux density of 50 mT. The results are shown in Table 2.

When comparing the core loss of Examples 2-1 to 2-8 and Comparative Examples 2-9 and 2-10, the soft magnetic metal dust core using the soft magnetic metal powder of the present invention has a core loss of 25% or more. It can be seen that it can be reduced.

As described above, the soft magnetic metal powder of the present invention has a high saturation magnetization and a low coercive force, and a soft magnetic metal powder core is produced using this soft magnetic metal powder to obtain a low-loss core. Can do. Since this soft magnetic metal powder or soft magnetic metal powder core has high saturation magnetization and low loss, it can realize high efficiency and can be used widely and effectively for electric and magnetic devices such as power supply circuits. .

FIG. 1 is a schematic diagram of a cross section of metal particles constituting the raw material powder of the present invention. FIG. 2 is a schematic view of a cross section of metal particles constituting the soft magnetic metal powder of the present invention.

1 ... Raw material powder particles 2 ... Al in the matrix
3 ... Grain boundary 4 ... Soft magnetic metal powder particles 5 ... Aluminum nitride film

Claims (6)

A soft magnetic metal powder containing Fe as a main component and containing Al, wherein the soft magnetic metal powder has an Fe content of 96% by mass or more, and the Al content in the metal particles of the soft magnetic metal powder is 0.00. A soft magnetic metal powder having a content of 1 to 0.65 % by mass and having an aluminum nitride film on the surface of the metal particles. 2. The soft magnetic metal powder according to claim 1, wherein a circularity of a cross section of 90% or more of the metal particles constituting the soft magnetic metal powder is 0.80 or more. Soft magnetic metal powder. 3. The soft magnetic metal powder according to claim 1, wherein 90% or more of the metal particles constituting the soft magnetic metal powder are composed of one crystal grain. 4. . The soft magnetic metal powder according to any one of claims 1 to 3, wherein the amount of oxygen contained in the metal particles is 500 ppm or less. 5. The soft magnetic metal powder according to claim 1, wherein the soft magnetic metal powder has at least one of aluminum oxide particles and aluminum hydroxide particles on the surface of the metal particles in the soft magnetic metal powder. Magnetic metal powder. A soft magnetic metal dust core produced by using the soft magnetic metal powder according to claim 1.

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