Metal powder and method for producing metal powder

Abstract

To provide a metal powder to be a green compact that has a low eddy current loss and can be used as a magnetic core for an inductor even when the green compact is produced from a metal powder having an average particle diameter of 1 μm or less.SOLUTION: Disclosed is a metal powder comprising 1.0%-13.0% of Si and 0.10%-8.00% of Cr in mass concentration, and the remainder Fe and inevitable impurities. The product of X and Y (X×Y) is 1.50 or less where X (m2 / g) is a value of the specific surface area of the metal powder measured by the BET method, Y (μm) is a number reference primary particle diameter D50 in SEM measurement, and Z (%) is the mass concentration of the oxygen content. The product of Z and Y (Z×Y) is 0.90-1.70 when the Cr content is less than 3.50% and 0.70-1.70 when the Cr content is 3.50% or more, and Y is 0.10 μm-1.00 μm. Thus, a green compact having a low core loss can be easily obtained.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a metal powder and a method for manufacturing the metal powder, and more particularly to a metal powder made of an iron alloy suitable for use in inductors and a method for manufacturing the metal powder. [Background technology]

[0002] In recent years, small portable devices such as smartphones and tablet PCs have become increasingly multifunctional and sophisticated. Accordingly, there is a growing demand for inductors in the power supply circuits to handle the increasing number of devices they are equipped with and the larger currents that accompany the increasingly sophisticated integrated circuits (ICs). In addition, to meet the demand for smaller and thinner portable devices, there is also a growing demand for smaller and thinner inductors.

[0003] Ferrite materials have traditionally been used for the magnetic cores of inductors. However, because ferrite has a low saturation magnetic flux density, when the inductor is made small, the DC superposition characteristics deteriorate due to saturation magnetism, making it impossible to pass large currents. For this reason, metal powder, which is an iron-based metal magnetic fine particle with a high saturation magnetic flux density, has recently been attracting attention as a magnetic core material for small inductors. Furthermore, there is a trend toward higher frequencies for the operation of electric circuits in order to realize smaller and lighter passive elements including inductors and to reduce noise caused by magnetostriction of inductors. Accordingly, it is important to improve the energy core loss (also called "core loss") caused by increased eddy current loss in inductors that use a green compact made by compressing and molding metal powder as a magnetic core.

[0004] For example, Patent Document 1 discloses a "soft magnetic alloy powder." It is described that this soft magnetic alloy powder has an insulating layer formed by adhering a silica film or silica fine particles obtained by hydrolysis of alkyl silicate to the powder surface, thereby increasing the resistivity of a green compact made by compression molding the soft magnetic gold alloy powder and reducing eddy current loss.

[0005] Patent Document 2 also discloses "Si oxide film coated soft magnetic powder". In this Si oxide film coated soft magnetic powder, a SiOx (x=1-2) deposited oxide film is formed on the surface of iron powder via a diffusion layer of Si-Fe-O ternary oxide consisting of Si, Fe and O. The diffusion layer of the Si-Fe-O ternary oxide has a concentration gradient in which the concentration of Fe is high and the concentration of Si is low at the interface with the iron powder, and the concentration of Fe is low and the concentration of Si is high at the interface with the SiOx (x=1-2) deposited oxide film. This allows the oxide film to adhere firmly to the surface of the soft magnetic powder, and solves the problem that in the process of manufacturing conventional soft magnetic materials, the silicate film peels off or breaks during press molding, making it impossible to exert a sufficient insulating effect and therefore not obtaining a sufficiently high specific resistance.

[0006] Patent Document 3 discloses a "soft magnetic powder material." This soft magnetic powder material is characterized by having a coating layer, the main component of which is silicon oxide, coated on the surface of iron powder particles, the main component of which is Fe. It is described that this increases the resistivity of a soft magnetic compact using the soft magnetic powder material, suppresses eddy currents generated in the soft magnetic compact even when used in an alternating magnetic field, and suppresses energy loss due to eddy currents.

[0007] Patent Document 4 discloses a "soft magnetic material powder." This soft magnetic material powder includes soft magnetic material particles having a core containing an Fe-based soft magnetic material and an insulating film covering the core's surface, the insulating film containing an inorganic oxide and a water-soluble polymer. It is described that molding this soft magnetic material powder into a magnetic core can provide a sufficient density and increase the magnetic permeability of the magnetic core, and that the insulating film and binder contained in the soft magnetic material powder can provide a magnetic core with high electrical resistance.

[0008] Furthermore, Patent Document 5 discloses a "metal powder" suitable for inductors. This metal powder contains 1.0 to 13.0 mass% Si, 0.10 to 8.00 mass% Cr, with the remainder being Fe and unavoidable impurities, and has an insulating coating of metal oxide on the surface of the metal powder. Furthermore, when the number-based primary particle diameter D50 (X) of the metal powder is 0.10 to 1.50 μm and the volume-based secondary particle diameter D50 (Y μm), the ratio of Y to X (Y / X) is 1.50 or less. As a result, it is described that a metal powder with low coercive force, high saturation magnetization, and excellent rust resistance can be obtained, and further, a green compact with low core loss can be easily obtained.

[0009] Patent Document 6 discloses a "soft magnetic particle powder." This is characterized in that soft magnetic metal particle powder and oxide fine particles are premixed, and then mechanical energy consisting of compression and shear force is applied to form an insulating layer on the particle surface of the soft magnetic metal particle powder. It is described that this makes it possible to form a uniform insulating layer with excellent adhesion to the surface of the soft magnetic metal particles. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2003-282317 A [Patent Document 2] JP 2007-123703 A [Patent Document 3] JP 2007-254768 A [Patent Document 4] International Publication No. WO2016 / 056351 [Patent Document 5] JP 2022-119746 A [Patent Document 6] Patent No. 5310988 Summary of the Invention [Problem to be solved by the invention]

[0011] In order to further miniaturize inductors that use green compacts made by compressing metal powder as their magnetic cores, it is important to use finer grain metal powders. Conventionally, green compacts for inductor magnetic cores have been manufactured using metal powders with an average particle size of 2μm to 50μm, and small multilayer inductors with dimensions of 1.0mm length x 0.5mm width x 0.5mm height have been manufactured. However, to manufacture inductors that are smaller in size and operate at high frequencies, finer metal powders with an average particle size of 1μm or less are required.

[0012] Here, the term "average particle size" refers to the cumulative 50% primary particle size D50 based on the number of particles, which is determined by observing and photographing a metal powder with a scanning electron microscope (SEM) at a magnification of 5,000 times or more, at which the outline of the particles is clear, and analyzing the SEM images of 1,000 to 2,000 measured particles. This is also simply called "D50 of the number-based primary particle size measured by SEM." Furthermore, the "primary particle size" refers to the size of a particle whose outline can be identified in an SEM image, and is different from the "secondary particle size," which is the size of an aggregate in which primary particles are aggregated and behave like a single particle. Furthermore, the "number-based" is a standard for creating a particle size distribution, and indicates the distribution of the number percentage by range among the total number of particles.

[0013] In the techniques described in the above Patent Documents 1 to 4, metal powders with an average particle size of 1.0 μm or less have a large specific surface area, so when a thick surface coating is formed, the weight ratio of the non-metallic surface coating portion to the weight of the metal portion of the powder may become too large. This may deteriorate the magnetic properties of the magnetic core of the inductor formed from a compact of the metal powder, so it is necessary to make the thickness of the surface coating thin. With a thin surface coating, the coating on the particle surface may peel off due to the pressure when the magnetic core is press-molded, and the surfaces of the particles that are not surface-coated may come into contact with each other, causing electrical conduction, which may cause a problem that eddy current loss cannot be reduced.

[0014] Furthermore, in the case of the technology described in the above-mentioned Patent Document 5, although a considerable improvement effect was achieved, there was a demand for achieving even further reduction in core loss.

[0015] Furthermore, in the technology described in the above-mentioned Patent Document 6, it is extremely difficult to uniformly mix soft magnetic metal particles and oxide fine particles in a premix, resulting in a problem that the oxide fine particles do not adhere uniformly to the surface of all of the soft magnetic metal particles. For this reason, even when mechanical energy consisting of compression and shear forces is applied, soft magnetic metal particles that are not covered with an insulating coating or soft magnetic metal particles having a partially uncovered surface may be produced.

[0016] The present invention aims to solve the problems of the conventional technology and to provide a metal powder that can produce a green compact with low eddy current loss and usable as a magnetic core for an inductor, even when the green compact is produced using a metal powder with an average particle size of 1.0 μm or less. [Means for solving the problem]

[0017] In order to achieve the above object, the present inventors have intensively studied the composition of the metal powder with iron as the main component, the surface shape of the oxide coating intended for insulating the particles, the oxygen content of the metal powder related to the amount of the oxide coating, and the particle size of the metal powder. As a result, it was found that it is essential to contain an appropriate amount of Si and Cr in Fe, to coat the metal powder with an appropriate amount of oxide according to the average particle size of the metal powder, and to make the surface irregularities of the oxide-coated metal powder smaller than a certain size according to the average particle size of the metal powder. In particular, the specific surface area of ​​the metal powder related to the surface irregularities of the oxide-coated metal powder is made smaller than a certain size according to the average particle size of the metal powder. This makes it possible to suppress the decrease in electrical resistance of the compact caused by peeling of the oxide coating on the metal powder surface due to press processing when forming the metal powder into a compact. And, it was newly discovered that it is easy to manufacture a compact with less core loss due to eddy current by ensuring the electrical resistance of the oxide coating.

[0018] They also discovered that a metal powder containing appropriate amounts of Si and Cr in Fe can be easily produced by oxidizing the surface of the metal powder in a liquid and coating it with an appropriate amount of oxide according to the average particle size of the metal powder, by dry stirring in an inert gas atmosphere with a controlled oxygen partial pressure, and adjusting the temperature of the metal powder by cooling the container to release the frictional heat.

[0019] The present invention has been completed based on these findings and through further investigation. [1] A metal powder containing, by mass concentration, 1.0% to 13.0% Si, 0.10% to 8.00% Cr, the balance being Fe and unavoidable impurities; The metal powder has a metal oxide coating on a surface thereof, The specific surface area of ​​the metal powder measured by the BET method is X (m 2 / g), D50 of the number-based primary particle diameter measured by SEM is Y (μm), and O (oxygen) content is Z (%) by mass concentration. The product (X × Y) of X and Y is 1.50 or less, The product (Z × Y) of Z and Y is 0.90 to 1.70 when the Cr content is less than 3.50%, and is 0.70 to 1.70 when the Cr content is 3.50% or more; The Y is 0.10 μm to 1.00 μm. 1. A metal powder comprising: [2] In the above [1], the metal powder further comprises, in mass concentration: S (sulfur): 5 ppm to 2000 ppm, Ni: 10.0% or less and Al: 5.0% or less Contains one or more of the following: 1. A metal powder comprising: [3] The electrical resistivity of the powder obtained by crushing a powder compact obtained by pressing and compressing only the metal powder described in [1] or [2] above without adding a binder is 10 5 A metal powder characterized by having a density of Ω·cm or more. [4] A step of producing a metal material powder containing, in mass concentration, 1.0% to 13.0% Si, 0.10% to 8.00% Cr, the remainder being Fe and unavoidable impurities (metal material powder production step); a step of oxidizing the metallic material powder in a liquid to coat the surface of the metallic material powder with an oxide to form an oxide-coated metallic powder (oxide coating step); A step of dry-stirring the oxide-coated metal powder in an inert gas atmosphere with a controlled oxygen partial pressure while controlling the temperature (dry-stirring step); A method for producing a metal powder comprising the steps of: [5] In the above [4], the specific surface area of ​​the metal powder measured by the BET method is expressed as X (m 2 / g), D50 of the number-based primary particle diameter measured by SEM is Y (μm), and O (oxygen) content is Z (%) by mass concentration. The product (X × Y) of X and Y is 1.50 or less, The product (Z × Y) of Z and Y is 0.90 to 1.70 when the Cr content is less than 3.50%, and is 0.70 to 1.70 when the Cr content is 3.50% or more; The Y is 0.10 μm to 1.00 μm. A method for producing metal powder comprising the steps of: [6] In the above [4] or [5], the metal material powder further comprises, in mass concentration: S (sulfur): 5 ppm to 2000 ppm, Ni: 10.0% or less and Al: 5.0% or less Contains one or more of the following: A method for producing metal powder comprising the steps of: Effect of the Invention

[0020] According to the present invention, metal powder having an average particle size of 1.0 μm or less is coated with an oxide film with minimal surface irregularities, and when molded into a powder compact, it has the excellent effect of producing a magnetic core for an inductor that is small and has high electrical resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, the embodiments of the present invention will be described in detail.

[0022] [Metal powder] The metal powder according to the present invention is a metal powder (Fe alloy powder) mainly composed of Fe. The chemical composition of the metal powder is, by mass concentration, Si: 1.0% to 13.0%, Cr: 0.10% to 8.00%, with the balance being Fe and unavoidable impurities (Fe-Si-Cr alloy powder). Furthermore, the metal powder may contain, by mass concentration, one or more selected from S (sulfur): 5 ppm to 2000 ppm, Ni: 10.0% or less, and Al: 5.0% or less.

[0023] The surface properties of the metal powder are as follows: the metal powder has a metal oxide coating on its surface. The specific surface area of ​​the metal powder measured by the BET method is expressed as X(m 2 When the mass concentration of oxygen (O) in the metal powder is Z (%), the product of Z and Y (Z×Y) is in the range of 0.90 to 1.70 when the Cr content is less than 3.50%, and in the range of 0.70 to 1.70 when the Cr content is 3.50% or more. Furthermore, the above Y (μm) is in the range of 0.10 μm to 1.00 μm.

[0024] [Chemical composition of metal powder] Next, the reasons for limiting the chemical composition will be explained. In the following, % in the composition means mass concentration.

[0025] [Si: 1.0%~13.0%] The Si content of the alloying elements contained in the metal powder is measured by wet analysis (silicon dioxide gravimetry). In metal powders mainly composed of Fe, Si is an element that dissolves in the base Fe and contributes to a decrease in the coercive force of the metal powder. In order to achieve a desired low coercive force, it is necessary to contain 1.0% or more of Si. On the other hand, if the Si content exceeds 13.0%, the coercive force increases and the saturation magnetization decreases. For this reason, the Si content is limited to a range of 1.0% to 13.0%. The Si content is preferably 3.0% to 11.0%, and more preferably 4.0% to 9.0%.

[0026] [Cr:0.10%~8.00%] The Cr content of the alloying elements contained in the metal powder is measured using ICP (inductively coupled plasma). Cr is an element that reduces the magnetic properties of the metal powder but improves the corrosion resistance, and in the metal powder of the present invention, it is necessary to contain 0.10% or more. If the Cr content is less than 0.10%, rust is likely to occur on the particle surface. On the other hand, if it is contained in a large amount exceeding 8.00%, the saturation magnetization decreases. For this reason, the Cr content is limited to the range of 0.10% to 8.00%. It is preferably 0.50% to 6.00%, and more preferably 0.70% to 4.00%. Here, the corrosion resistance refers to the rust resistance described later.

[0027] [Optional elements] Further optional elements that can be mixed include S (sulfur), Ni and Al.

[0028] [S(Sulfur): 5ppm~2000ppm] The amount of S (sulfur) contained in the metal powder is measured using a combustion method. The metal powder of the present invention may contain 5 ppm to 2000 ppm of S (sulfur) as an optional mixed element. The metal powder (Fe-Si-Cr alloy powder) of the present invention, which contains Fe as a main component and Si and Cr as described above, is a metal magnetic fine particle having a number-based primary particle diameter D50 of 0.10 μm to 1.00 μm as measured by SEM, and can be mainly manufactured by the CVD method or PVD method described below. The CVD method or PVD method is a method for forming particles in a gas phase at high temperatures, but when the metal powder flies through the gas and grows into crystals, polyhedral particles in which a specific crystal face grows preferentially are mixed in. S (sulfur) is concentrated on the surface of the generated particles, but this surface-concentrated layer of S suppresses the preferential growth of a specific crystal face, so that uniform crystal growth occurs in all directions, and the presence rate of particles grown into a spherical shape can be increased. If the S content is less than 5 ppm, the effect of suppressing the generation of polyhedrons is insufficient, and if it exceeds 2000 ppm, the amount of S concentrated on the particle surface becomes excessive, the growth of the particles is extremely suppressed, and only particles finer than the target particle size range can be obtained. Therefore, it is preferable that S (sulfur) is contained in an amount of 5 ppm to 2000 ppm. More preferably, it is 10 ppm to 1500 ppm, and even more preferably, it is 20 ppm to 1000 ppm.

[0029] [Ni:10.0% or less] The Ni content of the alloying element contained in the metal powder is measured using ICP (inductively coupled plasma). The metal powder of the present invention may contain 10.0% or less (not including 0%) of Ni as an optional mixed element. Ni is an element that dissolves in the metal powder and reduces the saturation magnetization of the metal powder when the Fe content is reduced, and it is preferable to reduce it as much as possible, but Ni has an effect of suppressing heat generation due to oxidation of the Fe alloy powder compared to other elements. Therefore, it is preferable to contain 10.0% or less because the safety of handling of the Fe alloy powder can be ensured and the action of reducing the saturation magnetization is slow. Note that, in order to improve the saturation magnetic flux density as a core, it is more preferable that it is 5.0% or less, and even more preferable that it is 3.0% or less.

[0030] [Al: 5.0% or less] The Al content of the alloying element contained in the metal powder is measured using ICP (inductively coupled plasma). The metal powder of the present invention may contain 5.0% or less (excluding 0%) of Al as an optional optional element that can be mixed. Like Ni, when Al is mixed into the metal powder and the Fe content is reduced, the saturation magnetization of the metal powder is reduced, so it is preferable to reduce it as much as possible. However, compared to other elements, Al has an effect of suppressing heat generation due to oxidation of the Fe alloy powder, and in order to ensure the safety of handling the Fe alloy powder, it is preferable to contain 5.0% or less. More preferably, it is 1.0% or less, and even more preferably, it is 0.5% or less.

[0031] [Remaining composition] The balance other than the above composition is Fe and unavoidable impurities. Examples of unavoidable impurity elements include elements such as C, N, P, Mn, and Cu. These elements reduce the saturation magnetization of the metal powder, and if they are contained in a total amount of 3% or less, the magnetic properties are not deteriorated to a degree that would be fatal in practical use, so this is acceptable. From the viewpoint of improving the saturation magnetic flux density of the core, it is more preferable that the content of the above elements is 1% or less in total. More preferably, it is 0.5% or less.

[0032] [Metal powder average particle size] (D50(Y) of number-based primary particle size measured by SEM: 0.10μm to 1.00μm) As described above, if the number-based primary particle diameter D50 obtained by SEM measurement of the metal powder is Y (μm), Y is set to a range of 0.10 μm to 1.00 μm. The reason for setting this range is that if Y is less than 0.10 μm, the coercive force becomes too large. In order to manufacture an inductor that is smaller than the conventional inductor using a metal powder with an average particle diameter of more than 1 μm (up to 50 μm) as a magnetic core material, it is necessary to reduce the particle diameter of the metal powder in order to suppress eddy current loss generated in the metal powder in the magnetic core in order to increase the operating frequency of the inductor. For this purpose, the primary particle diameter D50 (Y) of the metal powder used in the magnetic core is set to 1.00 μm or less. It is preferably 0.20 μm to 0.90 μm, and more preferably 0.30 μm to 0.80 μm.

[0033] (Product of specific surface area (X) and primary particle size (Y)) The specific surface area of ​​metal powder is determined using the gas adsorption method. The specific surface area is calculated from the adsorption of nitrogen gas using the BET (Brunauer-Emmett-Teller) equation. This specific surface area is expressed as X (m 2 / g), the product (X × Y) of the number-based primary particle diameter D50(Y) measured by SEM mentioned above should be in the range of 1.50 or less. X = a × (1 / Y) (1) (where a is a constant) However, when the average particle size is the same, as the unevenness of the metal powder surface increases and the specific surface area increases, a gradually increases. On the other hand, as described above, since the range of the average particle size D50(Y) is 0.10 μm to 1.00 μm, the product of X and Y (X×Y) is defined as a relational expression that holds for all average particle sizes within this range. When the product of X and Y (X×Y) exceeds 1.50, the unevenness of the surface of the oxide coating covering the surface of the metal powder is too large, so that the oxide coating is damaged and peeled off due to the contact friction between the metal powders under the pressure of press molding. And, since the phenomenon that the surfaces of the particles that are not surface-coated come into contact with each other and electrical conduction occurs in many cases in the green compact, the electrical resistance of the green compact decreases and the core loss due to the eddy current of the inductor cannot be reduced. In addition, it is preferably 1.40 or less, and more preferably 1.30 or less.

[0034] (The product of the oxygen content (Z) and the primary particle size (Y) of the metal powder) O (oxygen) exists as an oxide on the surface of the metal powder, and the oxygen content of the metal powder is measured by a combustion method. If the oxygen content of the metal powder is Z (%) in mass concentration and D50 of the number-based primary particle diameter of the above-mentioned SEM measurement is Y (μm), the product of Z and Y (Z×Y) is 0.90 to 1.70 when the Cr content of the metal powder is less than 3.50%, and is 0.70 to 1.70 when the Cr content is 3.50% or more.

[0035] When the product of Z and Y (Z×Y) is less than the lower limit (0.90 or 0.70), the amount of oxide coating on the surface of the metal powder is insufficient, resulting in scattered areas of insufficient insulation on the surface of the metal powder. As a result, the surfaces of particles that are not surface-coated come into contact with each other, causing electrical conduction in many places in the compact, which reduces the electrical resistance of the compact and makes it impossible to reduce the core loss due to eddy currents in the inductor. The lower limit of (Z×Y) is preferably 1.00 or more when the Cr content is less than 3.50%, and is preferably 0.80 or more when the Cr content is 3.50% or more. On the other hand, when the product of Z and Y (Z×Y) exceeds the upper limit (1.70), the weight ratio of the non-metallic surface coating portion to the weight of the metal portion of the metal powder becomes too large, resulting in a decrease in the magnetic properties of the magnetic core of the inductor formed from the compact of the metal powder, such as the saturation magnetic flux density. The upper limit of (Z×Y) is preferably 1.50 or less.

[0036] [Metal powder compact] Next, the metal powder compact according to the present invention will be described. The produced metal powder alone is inserted into a die without adding a binder, and pressed (pressed) at a load of 600 MPa to obtain a compact. The pressing (pressed) method is not particularly limited, and is performed by a normal pressing method. The load is set to 600 MPa, which is approximately equivalent to the pressing pressure used when manufacturing the magnetic core of an inductor compact.

[0037] The obtained green compact is crushed into a powder, and the powder is subjected to electrical resistance measurement. In the present invention, the electrical resistivity of the crushed green compact measured under a load of 59 MPa is 10 5 It is preferable that the electrical resistivity is Ω·cm or more. When the green compact is crushed into powder form, the degree of crushing is determined by measuring the laser diffraction particle size in water, comparing the volumetric particle sizes D10, D50, and D90 of the powder before green compact molding with those of the powder crushed after green compact molding, and the difference in the values ​​is preferably 20% or less. 5If the resistivity is less than Ω·cm, when the metal powder is pressed to form the iron core of an inductor, the oxide coating on the surface peels off under the pressure of the press, causing the surfaces of the particles that are not surface-coated to come into contact with each other, resulting in electrical conduction, which occurs frequently within the green compact. This causes the electrical resistance of the green compact to decrease, making it impossible to reduce core loss due to eddy currents in the inductor. Therefore, the electrical resistivity of the green compact is 10 5 It is preferable that the resistance is 10 Ω·cm or more. 6 Ω·cm or more.

[0038] [Metal powder manufacturing method] Next, a method for producing metal powder according to the present invention will be described.

[0039] As described above, the metal powder of the present invention can be manufactured by the CVD method or the PVD method, which are methods for forming particles in a gas phase at high temperatures. In particular, the CVD method is a chemical vapor deposition method, and the present invention is preferably manufactured using this CVD method. Specific manufacturing steps using the CVD method are described below. The steps include a metal material powder generating step, an oxide coating step, and a dry mixing step.

[0040] (Metal material powder generation process) First, in the metal material powder production process, alloy elements such as Fe, Si, and Cr are reacted with high-temperature chlorine gas to produce chloride gases of each element, or chloride gases obtained by heating and vaporizing the chlorides of each element such as Fe, Si, and Cr to a high temperature are mixed in a predetermined ratio. Hydrogen is reacted with the mixed gas at an appropriate temperature to reduce the chlorides, thereby obtaining a metal material powder of the desired composition containing Si, Cr, etc. In the production method of the present invention, it is preferable to adjust the concentration, reaction temperature, and reaction time of the chloride gas by mixing nitrogen gas so as to obtain the desired particle size.

[0041] (Oxide coating process) The next oxide coating step is a step of carrying out a dechlorination treatment, in which the metal material powder obtained after the reaction (reduction reaction) in the above-mentioned metal material powder production step is oxidized in a liquid to coat the surface of the metal material powder with an oxide. When the oxidation method is to oxidize in a liquid, the chlorine concentration is reduced by washing with a liquid and then drying in a vacuum to adjust the amount of oxide coating on the surface of the metal material powder. Here, the liquid is preferably water (H2O). When water (H2O) is used, its purity is preferably such that the conductivity of the water is 5 mS / m or less in order to suppress the aggregation of the metal powder in the water. The amount of oxide coating the metal material powder is adjusted by adjusting the dissolved oxygen concentration in the water used for washing in this step to 1 mg / L to 40 mg / L. That is, the product (Z×Y) of the oxygen content (Z%) and the primary particle diameter D50 (Y μm) of the metal material powder described above is adjusted to 0.90 to 1.70 when the Cr content of the metal material powder is less than 3.50%, and to 0.70 to 1.70 when the Cr content is 3.50% or more. Here, if (Z×Y) exceeds 1.70, excessive oxide is formed in the final process, deteriorating the magnetic properties of the magnetic core, and if (Z×Y) is less than the lower limit (0.90 or 0.70), the amount of surface oxide is insufficient in the final process, resulting in insufficient insulation and increased eddy current loss. In liquid, metal powder is easily dispersed, and each metal particle can be oxidized evenly. In this way, an oxide coating having an appropriate oxygen content can be formed on the surface of the metal material powder, and an oxide-coated metal powder can be obtained.

[0042] In the above drying step, the metal powder is dried and agglomerated, so the powder is put into a dry disperser (e.g., a pin mill or a dry jet mill) to break down or remove the coarse agglomerates, and then put into a classifier (e.g., a dry cyclone) to remove the coarse particles.

[0043] (Dry stirring process) In the next dry stirring step, the oxide-coated metal powder obtained above can be kept in an inert gas with an adjusted oxygen partial pressure, and is introduced into a container equipped with a cooling means by providing a cooling device, and is stirred in a dry state. The temperature of the oxide-coated metal powder rises due to frictional heat caused by stirring, but by adjusting the temperature of the oxide-coated metal powder to 40°C to 150°C with a cooling device, the surface oxide film is smoothed by friction, and the final metal powder with less surface unevenness can be produced. If the temperature is less than 40°C, the effect of surface friction may be insufficient, resulting in a metal powder with large unevenness of the surface oxide film, and if the temperature exceeds 150°C, the surface oxide film may peel off due to excessive frictional force, and the metal powder may be thermally fused to each other to form coarse particles.

[0044] Examples of inert gases include nitrogen gas, Ar gas, and He gas, but from the viewpoint of equipment costs, it is preferable to use nitrogen gas, and the purity of the gas is preferably 99.9% by volume or more.

[0045] When a gas that oxidizes metals, for example, a gas with a high partial pressure of oxygen, is used as the inert gas and stirred in a dry state, excess oxides are generated, and when the product of Z and Y (Z×Y) exceeds 1.70, excess oxides are formed and the magnetic properties of the magnetic core deteriorate. In addition, since excess oxides are formed, it becomes impossible to manufacture metal powder with less unevenness in the surface oxide coating. Therefore, it is necessary to measure the oxygen partial pressure in the inert gas surrounding the oxide-coated metal powder during dry stirring and control it to an oxygen partial pressure that does not form excess oxides. A specific range of oxygen partial pressure is preferably 5% by volume or less. More preferably, it is 2% by volume or less. EXAMPLES

[0046] The present invention will be specifically described below with reference to examples, although the present invention is not limited thereto.

[0047] As raw materials, Fe chloride, Si chloride, Cr chloride and S (sulfur) were prepared. Then, these chlorides and S (sulfur) were heated to a high temperature (1100°C) in a reaction device to vaporize the chlorides and S (sulfur), and chloride gas and S (sulfur) gas of each element were generated. The generated chloride gas and S (sulfur) gas of each element were mixed in different ratios to obtain various mixed gases with the chemical composition of each metal powder shown in Table 1. The obtained mixed gas was reacted with hydrogen at a predetermined reaction temperature (1100°C to 1200°C) to reduce the chloride gas and generate a metal material powder (Fe-Si-Cr alloy powder) (metal material powder generation process).

[0048] The obtained metal powders were then subjected to a dechlorination process in which they were washed with pure water at 25°C in which the dissolved oxygen concentration was adjusted to 1mg / L to 40mg / L, to remove residual chlorine and coat the surface of the metal powder with a predetermined amount of oxide (oxide coating process).Then, the water slurry of the oxide-coated metal powder after the dechlorination process was dehydrated and dried while heating to 150°C in a vacuum.

[0049] After drying, the oxide-coated metal powders were dispersed in a dry jet mill and then classified in a dry cyclone to remove coarse particles.

[0050] Next, the oxide-coated metal powder obtained above was added to an electric mortar held in nitrogen gas with an oxygen partial pressure of 0.1% by volume, and the temperature of the mortar was adjusted with cooling water, and the powder was dry-stirred (dry-stirring step). As a result, the temperature of the oxide-coated metal powder rose due to frictional heat, but the temperature of the oxide-coated metal powder was adjusted with cooling water to be 40°C to 150°C.

[0051] The final metal powders were examined for element content, content in the oxide film, primary particle size D50, magnetic properties, and core loss of the green compact. (1) Elemental content of metal powder The Si content of the alloying element contained in the metal powder was measured by wet analysis (silicon dioxide gravimetric method). The Cr content of the alloying element was measured by ICP (inductively coupled plasma). Furthermore, the oxygen content of the metal powder was measured by a combustion method. (2) Number-based primary particle diameter D50 The obtained metal powder was observed and photographed using a scanning electron microscope (SEM) at a magnification of 5,000 times or more at which the outlines of the particles were clearly visible, and the primary particle diameter D50 based on the number of particles was determined by SEM image analysis of 1,000 to 2,000 particles. For the image analysis, WinRoof image analysis software manufactured by Mitani Shoji Co., Ltd. was used. (3) Specific surface area The specific surface area of ​​the obtained metal powder was determined using a gas adsorption method. The specific surface area was calculated from the adsorption of nitrogen gas using the BET (Brunauer-Emmett-Teller) equation. A Macsorb Automatic Surface Area Analyzer manufactured by Mountech was used for the measurement, and as a pretreatment for the measurement, the metal powder was heated to 200°C while flowing He gas mixed with 30% N2 by volume at 25 NmL / min, and degassed for 10 minutes. (4) Magnetic properties The coercive force and saturation magnetization of each of the obtained metal powders were measured using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.). (5) Core loss of powder compact The obtained various metal powders were mixed and dispersed in resin (epoxy resin) to obtain various mixed powders. These mixed powders were filled into a ring-shaped mold (outer diameter: 13 mm, inner diameter: 8 mm) and press-molded at 600 MPa, after which the resin was cured to produce a toroidal core with a thickness of 3 mm. The obtained core was given a winding of 20 turns on the primary side and 20 turns on the secondary side, and the core loss was measured using a BH analyzer (SY-8218 manufactured by Iwatsu Measurement Co., Ltd.) under the conditions of a magnetic flux density of 10 mT and a frequency of 1 MHz.

[0052] The results obtained above are shown in Table 1. In the chemical composition column, "-" indicates "below the detection limit" or "1 ppm or less."

[0053] [Table 1]

[0054] All of the examples of the present invention have a low coercive force of 1200 A / m or less and a high saturation magnetization of 120 emu / g or more. Furthermore, when compacted, the core loss is 110 kW / m 3 It was possible to produce a green compact with low core loss, which is as follows:

[0055] On the other hand, if the magnetic material falls outside the preferred range of the present invention, the coercive force is high, exceeding 1200 A / m, the saturation magnetization is low, being less than 120 emu / g, or when compacted, the core loss is less than 110 kW / m 3 The resulting green compact had a high core loss.

[0056] As for the manufacturing conditions shown in Table 1, the purity of the pure water used was 0.5 mS / m in electrical conductivity, and the dissolved oxygen concentration was 1.0 mg / L to 2.0 mg / L for metal powders No. 1 to No. 25, No. 27, No. 28, No. 31, No. 33, No. 35, and No. 37 to No. 41, 0.0 mg / L to 0.5 mg / L for metal powders No. 44 and No. 48, and 0.0 mg / L to 0.5 mg / L for metal powders No. 32, No. 45, and No. 46. In metal powder No. 9, the dissolved oxygen concentration was set to 0.5 mg / L to 1.0 mg / L, in metal powder No. 26, No. 34, and No. 36, the dissolved oxygen concentration was set to 2.0 mg / L to 3.0 mg / L, in metal powder No. 29, No. 42, No. 46, and No. 50, the dissolved oxygen concentration was set to 3.0 mg / L to 4.0 mg / L, and in metal powder No. 30, No. 43, No. 47, and No. 51, the dissolved oxygen concentration was set to 4.0 mg / L to 8.0 mg / L.

[0057] Metal powder No. 1 in Table 1 has an insufficient Si content, resulting in large coercive force, large hysteresis loss and large eddy current loss, and an insufficient S content, resulting in non-spherical particles, a low filling rate, and low saturation magnetization.

[0058] Nos. 2 and 3 have a low S content, are non-spherical, and have a low filling factor and low saturation magnetization.

[0059] In No. 4, the saturation magnetization was reduced due to an excess of Si, and the S content was too low, resulting in non-spherical particles with a low packing rate and low saturation magnetization.

[0060] No. 5 had too little Cr, resulting in a lot of rust, low resistance due to the formation of magnetite, large eddy current loss, and too little S, resulting in non-spherical shapes, a low filling factor, and low saturation magnetization.

[0061] Conversely, No. 6 has an excess of Cr, resulting in low saturation magnetization, large magnetostriction, and high coercive force, while it has an insufficient amount of S, resulting in non-spherical shape, a low packing factor, and low saturation magnetization.

[0062] No. 7 does not contain Ni or Al, but contains a large amount of Fe, resulting in a large saturation magnetization.

[0063] No. 8 has a small amount of S, is non-spherical, has a low packing rate, and Ni, which is mixed in addition to Fe, is magnetic, so the saturation magnetization is slightly low.

[0064] Also, No. 9 similarly has a small amount of S, is non-spherical, and has a low packing rate. Since the Al mixed in addition to Fe is non-magnetic, the saturation magnetization is low.

[0065] In No. 10, Ni, which is mixed in addition to Fe, is magnetic, and the saturation magnetization is slightly low.

[0066] In addition, No. 11 has low saturation magnetization because the Al mixed in with other elements besides Fe is non-magnetic. No. 12 has low S content, is non-spherical, and has a low packing ratio, and the Al mixed in with other elements besides Fe is non-magnetic, so the saturation magnetization is low.

[0067] Metal powder No. 13 had an insufficient Si content, which resulted in a large coercive force and therefore a large core loss.

[0068] In No. 17, the Si content was excessive, so the Fe composition was low and the saturation magnetization was small.

[0069] In No. 18, the Cr content was too low, which caused a lot of rust and magnetite formation, resulting in low resistance and increased core loss due to increased eddy current loss.

[0070] No. 21 had an excessively high Cr content, resulting in large magnetostriction and a large coercive force, while the low Fe content resulted in low saturation magnetization and large core loss.

[0071] No. 22 has a low S (sulfur) content, but the specific surface area measured by the BET method of the metal powder is X (m 2 The product (X × Y) of the oxygen content Z (mass %) of the metal powder and Y (μm) of the number-based primary particle diameter D50 measured by SEM was 1.50 or less, and the product (Z × Y) of the oxygen content Z (mass %) of the metal powder and Y (μm) was 0.90 or more, and the magnetic properties were good.

[0072] Conversely, No. 25 has an excessively high S (sulfur) content and a small primary particle diameter (Y), resulting in high coercivity and high core loss, as well as many aggregates, low packing density, and low saturation magnetization.

[0073] For Nos. 26, 35, and 36, an aqueous slurry of the metal material powder that had been subjected to the above-mentioned dechlorination treatment was dispersed in an ultrasonic disperser, and then ethyl silicate, an oxide containing Si, was added to the aqueous slurry of the metal material powder as an agent for forming an oxide surface coating. While dispersing the metal material powder in the ultrasonic disperser, the slurry was stirred for a predetermined time, after which it was dehydrated and dried while heating to 50°C in a vacuum, forming a coating of Si oxide on the surface of the metal material powder. The insulating coating on the surface had large surface irregularities, and the specific surface area value X(m2) of the metal powder measured by the BET method was 100%. 2 The product (X × Y) of the powder diameter (X / g) and the number-based primary particle diameter D50 (Y (μm) measured by SEM) exceeded 1.50. Furthermore, the surface coating peeled off due to friction between the powder particles during pressing, so the electrical resistance of the green compact after pressing was low and the core loss was high.

[0074] In No. 27 and No. 40, the Cr content was less than 3.50%, and the product (Z x Y) of the oxygen content Z (mass%) of the metal powder and Y (μm) was less than 0.90, so the amount of oxide coating on the metal powder surface was insufficient and there were scattered areas where the insulation of the metal powder surface was insufficient. Furthermore, the surfaces of particles that were not surface-coated came into contact with each other, causing electrical conduction in many places in the green compact, so the electrical resistance of the green compact after pressing was low and the core loss was large.

[0075] For Nos. 30, 43, 47, and 51, the aforementioned (Z × Y) exceeded 1.70, so the weight ratio of the non-metallic surface coating portion to the weight of the metal (material) portion of the metal powder became too large, resulting in low saturation magnetization.

[0076] In No. 31, since the above Y (μm) was small, the coercive force was large and the core loss was large. In addition, there were many aggregates, and the packing density was low, resulting in low saturation magnetization.

[0077] In No. 34, the above-mentioned Y (μm) was large, and the generation of eddy currents caused a large core loss.

[0078] No. 38 had an excessively high Ni content and thus exhibited large magnetostriction, but the aforementioned (X×Y) was 1.50 or less and the aforementioned (Z×Y) was 0.90 or more, and the magnetic properties were good.

[0079] No. 39 had an excessively high Al content and thus exhibited large magnetostriction, but the aforementioned (X×Y) was 1.50 or less and the aforementioned (Z×Y) was 0.90 or more, and the magnetic properties were good.

[0080] In No. 44 and No. 48, the Cr content was 3.50% or more, and the aforementioned (Z × Y) was less than 0.70, so the amount of oxide coating on the metal powder surface was insufficient, resulting in scattered areas of insufficient insulation on the metal powder surface. Furthermore, the surfaces of particles that were not surface-coated came into contact with each other, causing electrical conduction in many places in the green compact, so the electrical resistance of the green compact after pressing was low and the core loss was large.

Claims

1. A metal powder containing, by mass concentration, Si: 1.0% to 13.0%, Cr: 0.10% to 8.00%, with the remainder being Fe and unavoidable impurities. The metal powder has a metal oxide film on its surface. The specific surface area of ​​the aforementioned metal powder, measured by the BET method, is X(m ２ If the number-based primary particle size D50 for SEM measurement is Y (μm) and the O (oxygen) content is Z (%) in mass concentration, The product of X and Y (X × Y) is 1.50 or less. The product of Z and Y (Z × Y) is 0.90 to 1.70 when the Cr content is less than 3.50%, and 0.70 to 1.70 when the Cr content is 3.50% or more. The above Y is 0.10 μm to 1.00 μm. A metal powder characterized by the following features.

2. The aforementioned metal powder is further, in terms of mass concentration, S (sulfur): 5 ppm to 2000 ppm Ni: 10.0% or less and Al: 5.0% or less It contains one or more types selected from among them. The metal powder according to feature 1.

3. The electrical resistivity of the powder obtained by crushing a compact obtained by pressing and compressing only the metal powder described in claim 1 or 2 without adding a binder is 10 ５ A metal powder characterized by having a density of Ω·cm or greater.

4. A process for producing a metal material powder containing Si: 1.0% to 13.0% by mass concentration, Cr: 0.10% to 8.00%, with the remainder being Fe and unavoidable impurities (metal material powder production process), The process involves oxidizing the metal material powder in a liquid, coating the surface of the metal material powder with an oxide, and forming an oxide-coated metal powder (oxide coating process), A step of dry stirring the oxide-coated metal powder in an inert gas atmosphere with controlled oxygen partial pressure while controlling the temperature (dry stirring step) A method for producing metal powder, characterized by having the following features.

5. The specific surface area of ​​the aforementioned metal powder, measured by the BET method, is X(m ２ If the number-based primary particle size D50 for SEM measurement is Y (μm) and the O (oxygen) content is Z (%) in mass concentration, The product of X and Y (X × Y) is 1.50 or less. The product of Z and Y (Z × Y) is 0.90 to 1.70 when the Cr content is less than 3.50%, and 0.70 to 1.70 when the Cr content is 3.50% or more. The above Y is 0.10 μm to 1.00 μm. The method for producing metal powder according to feature 4.

6. The aforementioned metal material powder is further, in terms of mass concentration, S (sulfur): 5 ppm to 2000 ppm Ni: 10.0% or less and Al: 5.0% or less It contains one or more types selected from among them. A method for producing metal powder according to claim 4 or 5, characterized by the above.