Soft magnetic powder, dust core, magnetic element, and electronic device

Abstract

To provide soft magnetic powder with which a dust core having a high density and a high withstand voltage can be produced, a dust core having a high density and a high withstand voltage, a magnetic element including such a dust core, and an electronic device including the magnetic element.SOLUTION: Soft magnetic powder contains: Fe as a main component; Si having a content of 2.5 mass% or more and 7.5 mass% or less; Cr having a content of 1.0 mass% or more and 10.0 mass% or less; Sn having a content of 0.05 mass% or more and 1.10 mass% or less; and impurities. A mass ratio Sn / Cr of a content amount of Sn to a content amount of Cr is 0.02 or more and 0.30 or less, an average particle diameter is 1.5 μm or more and 11.0 μm or less, and, when a heat treatment is applied to the soft magnetic power in an air atmosphere, Sn-substituted hematite in which a part of Fe atoms forming hematite is substituted by Sn atoms is precipitated. A dust core 1 includes soft magnetic particles 3 that are particles of the soft magnetic powder and a binding portion 4 that is made of an Fe oxide and binds the soft magnetic particles 3 together.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a soft magnetic powder, a dust core, a magnetic element, and an electronic device. [Background technology]

[0002] Patent Document 1 discloses a soft magnetic powder having a composition represented by Fe-2%Si-1%Cr-1%Sn and an average particle size of 55 μm or 200 μm. Furthermore, the crystal grain size of this soft magnetic powder is optimized. This allows for the realization of a powder magnetic core with low core loss when excited at a predetermined excitation frequency. It also discloses that when manufacturing a powder magnetic core, a silicone resin is added to perform an insulating coating treatment. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-124270 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses that an insulating material such as a silicone resin is added when manufacturing a powder core using soft magnetic powder. The addition of the silicone resin ensures insulation between particles. However, insulating materials such as silicone resin do not have sufficient insulating properties and are unable to sufficiently increase the withstand voltage of the powder core. While the withstand voltage can be increased by adding a large amount of silicone resin, this reduces the density of the powder core (the proportion of soft magnetic powder), resulting in a decrease in magnetic properties.

[0005] Therefore, it is an issue to realize a soft magnetic powder that can be used to manufacture a dust core with high density and high voltage resistance. [Means for solving the problem]

[0006] The soft magnetic powder according to the application example of the present invention is Fe as the main component, Si having a content of 2.5 mass% or more and 7.5 mass% or less, Cr having a content of 1.0 mass% or more and 10.0 mass% or less; Sn having a content of 0.05% by mass or more and 1.10% by mass or less; Impurities and It consists of The mass ratio of the Sn content to the Cr content is Sn / Cr of 0.02 or more and 0.30 or less, The average particle size is 1.5 μm or more and 11.0 μm or less, By heat treatment in an air atmosphere, some of the Fe atoms constituting the hematite are substituted with Sn atoms to precipitate Sn-substituted hematite.

[0007] A powder magnetic core according to an application example of the present invention includes: Fe as the main component, Si having a content of 2.5 mass% or more and 7.5 mass% or less, Cr having a content of 1.0 mass% or more and 10.0 mass% or less; Sn having a content of 0.05% by mass or more and 1.10% by mass or less; Impurities and It consists of The mass ratio of the Sn content to the Cr content is Sn / Cr of 0.02 or more and 0.30 or less, A soft magnetic powder having an average particle size of 1.5 μm or more and 11.0 μm or less; a binding portion made of Fe oxide that binds the particles of the soft magnetic powder together; and The Fe oxides include Sn-substituted hematite in which some of the Fe atoms constituting hematite are substituted with Sn atoms.

[0008] The magnetic element according to the application example of the present invention includes: The dust core according to the application example of the present invention is provided.

[0009] The electronic device according to the application example of the present invention includes: The magnetic element according to the application example of the present invention is provided. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is an example of an X-ray diffraction pattern obtained by performing crystal structure analysis by X-ray diffraction (XRD) on the soft magnetic powder after heat treatment. [Figure 2] FIG. 2 is a partially enlarged cross-sectional view showing a powder magnetic core according to an embodiment. [Figure 3] 1 shows the results of element mapping analysis of a cross section of a powder magnetic core performed using an energy dispersive X-ray fluorescence analyzer (EDX), focusing on Si. [Figure 4] 1 shows the results of element mapping analysis of a cross section of a powder magnetic core performed using an energy dispersive X-ray fluorescence analyzer (EDX), focusing on Sn. [Figure 5] FIG. 1 is a plan view schematically showing a toroidal type coil component. [Figure 6] FIG. 1 is a transparent perspective view schematically showing a closed magnetic circuit type coil component. [Figure 7] 1 is a perspective view showing a mobile personal computer as an electronic device according to an embodiment. [Figure 8] FIG. 1 is a plan view showing a smartphone as an electronic device according to an embodiment. [Figure 9] 1 is a perspective view showing a digital still camera as an electronic device according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] The soft magnetic powder, dust core, magnetic element, and electronic device of the present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings.

[0012] 1. Soft magnetic powder The soft magnetic powder according to the embodiment is a metal powder exhibiting soft magnetism. Such soft magnetic powder can be used for any purpose, but for example, the particles are bound together via a binder and used to produce various compacts such as dust cores and electromagnetic wave absorbers.

[0013] 1.1. Composition The soft magnetic powder is composed primarily of Fe (iron), with Si (silicon) content of 2.5% by mass or more and 7.5% by mass or less, Cr (chromium) content of 1.0% by mass or more and 10.0% by mass or less, Sn (tin) content of 0.05% by mass or more and 1.10% by mass or less, and impurities.

[0014] The main component is the element with the highest atomic ratio. Fe is the main component of soft magnetic powder and has a significant impact on the basic magnetic properties of the soft magnetic powder.

[0015] The Fe content is not particularly limited, but is preferably 80% by mass or more, and more preferably 90% by mass or more.

[0016] The Si content is set to 2.5% by mass or more and 7.5% by mass or less, preferably 2.7% by mass or more and 5.0% by mass or less, and more preferably 3.0% by mass or more and 4.5% by mass or less. If the Si content is within the above range, a green compact with higher magnetic permeability can be obtained. Note that if the Si content is below the lower limit, magnetic properties such as magnetic permeability and DC bias characteristics will decrease. On the other hand, if the Si content is above the upper limit, the soft magnetic powder will become hard, resulting in a decrease in the density of the green compact.

[0017] The Cr content is 1.0% by mass or more and 10.0% by mass or less, preferably 3.0% by mass or more and 6.0% by mass or less, and more preferably 4.0% by mass or more and 5.0% by mass or less. When the Cr content is within this range, the oxidation resistance of the soft magnetic powder can be improved. This keeps the oxide occupancy rate particularly low during compaction, resulting in a soft magnetic powder that can be used to produce a compact with excellent magnetic properties such as magnetic permeability and DC bias characteristics. If the Cr content is below the lower limit, the oxidation resistance of the soft magnetic powder decreases. On the other hand, if the Cr content exceeds the upper limit, magnetic properties such as magnetic permeability and DC bias characteristics decrease.

[0018] The Sn content is 0.05% by mass or more and 1.10% by mass or less, preferably 0.07% by mass or more and 0.80% by mass or less, and more preferably 0.10% by mass or more and 0.40% by mass or less. When the Sn content is within this range, the particle shape of the soft magnetic powder can be made more spherical. This allows for improved packing of the soft magnetic powder even with a small particle size, thereby increasing the density of the compact. Note that if the Sn content is below the lower limit, the circularity of the particle shape decreases, resulting in a decrease in packing. This results in a decrease in the density of the compact, and magnetic properties such as magnetic permeability and DC bias characteristics deteriorate. On the other hand, if the Sn content exceeds the upper limit, the soft magnetic powder becomes more susceptible to oxidation, resulting in an increase in the oxygen content. The oxides produced by oxidation reduce the metal occupancy rate in the compact, resulting in a decrease in the density of the compact and a decrease in magnetic properties such as magnetic permeability and DC bias characteristics.

[0019] The mass ratio of the Sn content to the Cr content is defined as Sn / Cr. The mass ratio Sn / Cr is 0.02 or more and 0.30 or less, preferably 0.03 or more and 0.25 or less, and more preferably 0.04 or more and 0.20 or less. When the mass ratio Sn / Cr is within the above range, the balance between the Cr content and the Sn content can be optimized. This allows for both improved packing due to the particle shape and improved magnetic properties due to the optimized composition. As a result, a green compact with particularly excellent magnetic properties can be obtained. Furthermore, when the mass ratio Sn / Cr is within the above range, the amount of Sn-substituted hematite produced during heat treatment can be optimized. As described below, Sn-substituted hematite improves the insulating properties of the soft magnetic powder after heat treatment. Therefore, when subjected to heat treatment, a soft magnetic powder can be obtained that can be used to produce a green compact with excellent voltage resistance.

[0020] If the mass ratio Sn / Cr is below the lower limit, the oxidation resistance of the soft magnetic powder improves, but the circularity of the particle shape decreases, and the packing ability of the soft magnetic powder deteriorates. Furthermore, the relative amount of Sn decreases, and the amount of Sn-substituted hematite produced during heat treatment decreases. On the other hand, if the mass ratio Sn / Cr exceeds the upper limit, the soft magnetic powder becomes spherical, but the oxidation resistance decreases and the metal occupancy rate in the compact decreases. Furthermore, the relative amount of Sn becomes excessive, and the magnetic properties of the soft magnetic powder deteriorate.

[0021] In addition to the elements described above, the soft magnetic powder may contain other elements as impurities. The term "impurities" refers to elements other than the elements described above.

[0022] The impurity concentration is preferably 0.10% by mass or less for each element, and more preferably 0.05% by mass or less. The total impurity concentration is preferably 1.00% by mass or less. Within this range, the inclusion of other elements is permissible because it does not affect the effects of the soft magnetic powder.

[0023] The soft magnetic powder according to the embodiment may contain oxygen as an impurity. Oxygen may be mixed in the raw materials or during the manufacturing process. The oxygen content of the soft magnetic powder is preferably 3000 ppm or less by mass, more preferably 2000 ppm or less, and even more preferably 1500 ppm or less. This prevents the particle shape from being deformed due to oxides adhering to the surface, resulting in a soft magnetic powder with high packing properties during compaction. This also prevents a decrease in the space factor of the alloy in the powder core. While a lower limit need not be set, from the viewpoint of ensuring interparticle insulation, it is preferably 300 ppm or more, more preferably 500 ppm or more. This ensures sufficient interparticle insulation and allows for a compact with reduced eddy current loss.

[0024] The above composition is determined by the following analytical method. Examples of analytical methods include iron and steel - atomic absorption spectrometry specified in JIS G 1257:2000, iron and steel - inductively coupled plasma (ICP) atomic emission spectrometry specified in JIS G 1258:2007, iron and steel - spark discharge atomic emission spectrometry specified in JIS G 1253:2002, iron and steel - X-ray fluorescence analysis specified in JIS G 1256:1997, and gravimetric / titration / absorptiometry specified in JIS G 1211 to G 1237.

[0025] Specific examples include a solid-state optical emission spectrometer manufactured by SPECTRO, in particular a spark discharge optical emission spectrometer, model: SPECTROLAB, type: LAVMB08A, and an ICP device, model CIROS120 manufactured by Rigaku Corporation.

[0026] In particular, for the identification of carbon (C) and sulfur (S), the oxygen flow combustion (high-frequency induction heating furnace combustion) - infrared absorption method specified in JIS G 1211:2011 is also used. Specifically, the LECO CS-200 carbon and sulfur analyzer can be used.

[0027] Furthermore, for the identification of N (nitrogen) and O (oxygen), the iron and steel - nitrogen determination method specified in JIS G 1228:1997 and the general method for oxygen determination in metallic materials specified in JIS Z 2613:2006 are also used.Specific examples include the LECO oxygen and nitrogen analyzer TC-300 / EF-300 and the LECO oxygen, nitrogen and hydrogen analyzer ONH836.

[0028] 1.2.Powder characteristics The soft magnetic powder has an average particle size of 1.5 μm to 11.0 μm, preferably 3.0 μm to 10.0 μm, and more preferably 4.0 μm to 9.0 μm, which provides a soft magnetic powder that has high packing properties during compaction and can suppress eddy current loss in the compact.

[0029] If the average particle size of the soft magnetic powder is below the lower limit, the soft magnetic powder tends to aggregate, reducing the packing ability and the density of the green compact, whereas if the average particle size of the soft magnetic powder is above the upper limit, the eddy current loss of the green compact may increase.

[0030] The average particle size refers to the particle size D50 at which the cumulative frequency is 50% from the smallest diameter side in the cumulative particle size distribution on a volume basis of the soft magnetic powder obtained using a laser diffraction particle size distribution analyzer.

[0031] The average circularity of the soft magnetic powder is preferably 0.80 or more and 0.95 or less, more preferably 0.82 or more and 0.92 or less, and even more preferably 0.85 or more and 0.90 or less. This results in a soft magnetic powder with particularly good packing properties during compaction. Furthermore, when an insulating coating is formed on the surface of the soft magnetic powder particles, it can be formed uniformly and without unevenness. This allows for the production of a green compact with excellent interparticle insulation. Furthermore, by forming the coating uniformly and without unevenness, the specific surface area can be reduced, and the amount of binder covering the surface can also be reduced. Therefore, a smaller amount of binder is required to bond the particles together, thereby improving the magnetic properties of the green compact.

[0032] If the average circularity is below the lower limit, the soft magnetic powder may have poor packing properties during compaction. Also, the insulating coating may have poor thickness uniformity. On the other hand, if the average circularity is above the upper limit, the soft magnetic powder may be difficult to manufacture.

[0033] The average circularity of the soft magnetic powder is measured as follows. First, an image (secondary electron image) of the soft magnetic powder is taken using a scanning electron microscope (SEM). Next, the obtained image is loaded into image processing software. For example, image analysis particle size distribution measurement software "Mac-View" manufactured by Mountech Co., Ltd. is used as the image processing software. The imaging magnification is adjusted so that 50 to 100 particles are captured in one image. Then, multiple images are taken so that a total of 300 or more particle images are obtained.

[0034] Next, using software, the circularity of 300 or more particle images is calculated and the average value is obtained. The obtained average value is the average circularity of the soft magnetic powder. Note that when the circularity is e, the area of ​​the particle image is S, and the perimeter of the particle image is L, the circularity e can be calculated using the following formula. e=4πS / L 2

[0035] The particles of the soft magnetic powder may contain a plurality of crystal grains. In other words, the particles of the soft magnetic powder may contain a polycrystalline structure. The number of crystal grains per unit area of ​​the cross section of the particle is 0.10 [particles / (μm) 2 ] or more 0.45[pcs / (μm) 2 ] or less, and 0.14 [pieces / (μm) 2 ] or more 0.38[pcs / (μm) 2 ] or less, and more preferably 0.16 [pieces / (μm) 2 ] or more 0.35[pcs / (μm) 2] or less. If the number of crystal grains per unit area of ​​the cross section of the particle is within the above range, the number density of the crystal grains can be optimized, and as a result, the crystal grain size can be optimized. This allows the particles to deform appropriately during compaction, resulting in a soft magnetic powder that can be used to produce a high-density compact. Furthermore, the soft magnetic powder obtained has a sufficiently high magnetic permeability that depends on the crystal grain size, and low eddy current loss.

[0036] The number of crystal grains per unit area of ​​the cross section of a particle of the soft magnetic powder is measured as follows.

[0037] First, the cross section of the soft magnetic powder particles is corroded with a 3% nital etchant (3% nitric acid, 97% ethanol). Next, the cross section of the particles is imaged using a scanning transmission electron microscope (STEM). The obtained image is then loaded into image processing software. For example, the image processing software used may be "Mac-View," an image analysis particle size distribution measurement software manufactured by Mountech Co., Ltd.

[0038] Next, the cross-sectional area of ​​the particle is calculated. The cross-sectional area is calculated using the following formula after calculating the major and minor axes of the cross section. Cross-sectional area = major axis × minor axis × π ÷ 4

[0039] Furthermore, image processing software is used to detect the crystal grains contained in the cross-sectional image. Next, the number of crystal grains contained in the cross-section of one particle is counted. The counted number of crystal grains is then divided by the cross-sectional area to calculate the number of crystal grains per unit area of ​​the cross-section (number density of crystal grains). The unit is number / (μm). 2 Let's say.

[0040] 1.3.Insulating Coating If necessary, an insulating coating may be provided on the surface of the soft magnetic powder particles. By providing such an insulating coating, the insulation between the soft magnetic powder particles can be improved. As a result, eddy currents flowing between the particles can be suppressed, and eddy current loss in the compact can be suppressed. Examples of insulating coatings include glass materials, ceramic materials, and resin materials.

[0041] 1.4.Crystal structure analysis by X-ray diffraction When the soft magnetic powder according to the embodiment is heat-treated in an air atmosphere and then subjected to crystal structure analysis by X-ray diffraction, the resulting X-ray diffraction pattern includes peaks derived from Sn-substituted hematite. Sn-substituted hematite is a compound in which some of the Fe atoms constituting hematite (iron oxide represented by Fe2O3) are replaced with Sn atoms. Even if the content of such Sn-substituted hematite is small, it imparts good insulating properties to the soft magnetic powder after heat treatment. Therefore, by using the heat-treated soft magnetic powder, a compact with high density and excellent voltage resistance can be obtained. The heat treatment is, for example, a treatment in which the substrate is heated at 600° C. for 1 hour in an air atmosphere.

[0042] FIG. 1 shows an example of an X-ray diffraction pattern obtained by performing crystal structure analysis by X-ray diffraction (XRD) on the soft magnetic powder after heat treatment.

[0043] FIG. 1 shows four X-ray diffraction patterns: XRD-1, XRD-2, XRD-3, and XRD-4.

[0044] XRD-1 is an X-ray diffraction pattern obtained before heat treatment of soft magnetic powder having a composition of Fe-3.5Si-4.5Cr. In the formula representing the composition, the numbers before each element symbol represent the mass concentration of each element. The content of Fe is the balance of the other elements.

[0045] XRD-2 is an X-ray diffraction pattern obtained after heat treatment of soft magnetic powder having a composition of Fe-3.5Si-4.5Cr.

[0046] XRD-3 is an X-ray diffraction pattern obtained before heat treatment of soft magnetic powder having a composition of Fe-3.5Si-4.5Cr-1.0Sn.

[0047] XRD-4 is an X-ray diffraction pattern obtained after heat treatment of soft magnetic powder having a composition of Fe-3.5Si-4.5Cr-1.0Sn.

[0048] Four strong peaks P(Fe-Si) derived from Fe-Si alloy crystals are observed in all four X-ray diffraction patterns XRD-1, XRD-2, XRD-3, and XRD-4 shown in Figure 1. Here, the peak P(Fe-Si) located at 2θ=77°±1° is defined as the reference peak P0.

[0049] In the XRD-4 shown in Figure 1, in addition to four peaks P(Fe-Si) derived from the crystals of the Fe-Si alloy, multiple peaks P(Sn) scattered in the range of 2θ = 35 to 75° are observed. These peaks P(Sn) are peaks derived from the crystal structure of Sn-substituted hematite. Here, the peak P(Sn) located near 2θ = 39° ± 1° is designated as index peak P1. Index peak P1 is a peak derived from the crystal plane of Sn-substituted hematite represented by Miller index (104).

[0050] In XRD-4, when the peak top intensity of the reference peak P0 is set to 1, the peak top intensity of the index peak P1 is preferably 0.100 to 0.700, more preferably 0.150 to 0.600, and even more preferably 0.200 to 0.500. When the intensity ratio of the index peak P1 to the reference peak P0 is within the above range, the ratio of Sn-substituted hematite contained in the soft magnetic powder after heat treatment is optimized. This makes it possible to realize a soft magnetic powder that can be used to produce a green compact with excellent voltage resistance without compromising magnetic properties.

[0051] If the intensity ratio of the index peak P1 to the reference peak P0 is below the lower limit, the proportion of Sn-substituted hematite in the heat-treated soft magnetic powder will decrease, which may result in a decrease in the voltage resistance of the green compact. On the other hand, if the intensity ratio of the index peak P1 to the reference peak P0 is above the upper limit, the amount of Sn-substituted hematite will become excessive, which may result in a decrease in the magnetic properties of the green compact.

[0052] The intensity ratio can be adjusted by adjusting the Sn content and whether or not heat treatment is performed. For example, the intensity ratio can be increased by increasing the Sn content. Furthermore, the intensity ratio can be increased by subjecting the soft magnetic powder to heat treatment.

[0053] In the example shown in FIG. 1, no significant peak P(Sn) is observed in XRD-1, XRD-2, and XRD-3.

[0054] 1.5.Tap Density The tap density of the soft magnetic powder is 3.80 g / cm 3 More than 5.10g / cm 3 Preferably, it is 3.90 g / cm or less. 3 More than 5.00g / cm 3 More preferably, it is 4.00 g / cm or less. 3 More than 5.00g / cm 3 It is more preferable that the tap density is less than or equal to 1000 MPa. If the tap density is within the above range, a soft magnetic powder with particularly good packing properties can be obtained. This makes it possible to produce a higher density green compact. If the tap density is below the above lower limit, the packing properties of the soft magnetic powder may decrease, resulting in a decrease in the density of the green compact. On the other hand, if the tap density is above the above upper limit, it may be more difficult to produce the soft magnetic powder.

[0055] The tap density of the soft magnetic powder is measured as follows. First, the soft magnetic powder is treated with a coupling agent. Phenyltrimethoxysilane is used as the coupling agent. Next, the tap density of the treated soft magnetic powder is measured using a powder property evaluation device. The powder property evaluation device used is a Powder Tester (registered trademark) PT-X manufactured by Hosokawa Micron Corporation.

[0056] 1.6.Specific surface area The specific surface area of ​​the soft magnetic powder is 0.170m 2 / g or more 0.320m 2 / g or less, and 2 / g or more 0.300m 2 / g or less is more preferable, and 0.190m 2 / g or more 0.280m 2 / g or less is even more preferable. If the specific surface area is within the above range, the packing property of the soft magnetic powder is improved, and the density of the green compact can be increased. If the specific surface area is below the above lower limit, the particle size of the soft magnetic powder may be too large, and the core loss of the green compact may be high. On the other hand, if the specific surface area is above the above upper limit, the packing property of the soft magnetic powder may be reduced, and the density of the green compact may be reduced.

[0057] The specific surface area of ​​the soft magnetic powder is measured by the BET method. An example of a specific surface area measuring device is the BET specific surface area measuring device HM1201-010 manufactured by Mountech Co., Ltd. The amount of sample is 5 g.

[0058] 1.7.Coercive Force The soft magnetic powder according to the embodiment preferably has a coercive force of 12.0 [Oe] or less (955 [A / m] or less), more preferably 10.0 [Oe] or less (796 [A / m] or less), and even more preferably 8.0 [Oe] or less (637 [A / m] or less). If the coercive force is within the above range, hysteresis loss in the compact can be suppressed. Furthermore, from the viewpoint of ease of production of the soft magnetic powder, the coercive force is preferably 2.0 [Oe] or more (159 [A / m] or more), and more preferably 3.0 [Oe] or more (239 [A / m] or more).

[0059] The coercive force of the soft magnetic powder can be measured using a vibrating sample magnetometer, etc. The maximum magnetic field applied when measuring the coercive force is, for example, 15 kOe.

[0060] 2. Manufacturing method of soft magnetic powder Next, an example of a method for producing the soft magnetic powder will be described.

[0061] The soft magnetic powder may be a powder produced by any method. Examples of production methods include various atomization methods such as water atomization, rotary water flow atomization, and gas atomization, as well as pulverization. Of these, powder produced by atomization is preferably used for the soft magnetic powder. The atomization method makes it possible to efficiently produce high-quality metal powder with particle shapes closer to perfect spheres and with less formation of oxides, etc. Therefore, the atomization method makes it possible to produce metal powder with a smaller specific surface area.

[0062] Atomization is a method for producing metal powder by atomizing and cooling molten metal by colliding it with a high-speed jet of liquid or gas. After atomization, the molten metal becomes more spherical during the solidification process, making it possible to produce particles that are closer to perfect spheres.

[0063] The water atomization method uses a liquid such as water as a coolant, sprays it in an inverted cone shape so that it converges at one point, and then causes molten metal to flow down toward this convergence point and collide with it, thereby producing metal powder from molten metal.

[0064] The rotary water atomization method is a method for producing metal powder by supplying a cooling liquid along the inner surface of a cooling cylinder and rotating it along the inner surface, while spraying a liquid or gas jet onto molten metal, and incorporating the scattered molten metal into the cooling liquid.

[0065] The gas atomization method uses gas as a cooling medium, spraying it in an inverted cone shape that converges to one point, while allowing molten metal to flow down and collide with this convergence point, producing metal powder from molten metal.

[0066] In these atomization methods, the particle size, circularity, and number density of crystal grains in the cross section of the soft magnetic powder particles can be adjusted depending on the conditions.

[0067] The melting temperature, or casting temperature, is preferably set to Tm + 200°C or higher, where Tm [°C] is the melting point of the constituent material of the soft magnetic powder, more preferably Tm + 220°C or higher and Tm + 350°C or lower, and even more preferably Tm + 250°C or higher and Tm + 300°C or lower. This reduces the viscosity of the molten metal, allowing for more efficient production of smaller particles. Furthermore, when the particles are refined by various atomization methods and solidify, they remain as molten metal for a longer period than conventional methods. This increases the circularity of the soft magnetic powder particles and allows the number density of crystal grains in the particle cross section to be adjusted within the aforementioned range.

[0068] In the atomization method, molten metal is allowed to flow down through a narrow opening, and the resulting stream of molten metal is collided with a fluid jet. The outer diameter of the stream of molten metal is not particularly limited, but is preferably 2.5 mm or less, more preferably 0.3 mm to 2.0 mm, and even more preferably 0.5 mm to 1.5 mm. This facilitates uniform application of the fluid jet to the molten metal, facilitating the uniform scattering of droplets of appropriate size. As a result, the average particle size and average circularity of the soft magnetic powder can be adjusted within the aforementioned ranges. Furthermore, the cooling rate is relatively fast, allowing the oxygen content of the soft magnetic powder to be adjusted within the aforementioned ranges. Furthermore, since the amount of molten metal supplied per unit time is reduced, the cooling rate of each droplet is also uniform, making it easier to adjust the number density of crystal grains in the cross section of the soft magnetic powder within the aforementioned ranges.

[0069] The produced soft magnetic powder may be classified as needed. Examples of classification methods include dry classification such as sieving classification, inertial classification, and centrifugal classification, and wet classification such as sedimentation classification.

[0070] 3.Powder magnetic core Next, a powder magnetic core according to an embodiment will be described. FIG. 2 is a partially enlarged cross-sectional view showing the powder magnetic core 1 according to the embodiment.

[0071] The powder magnetic core 1 shown in FIG. 2 has soft magnetic particles 3 (particles of the soft magnetic powder according to the embodiment) and binders 4 that bind the soft magnetic particles 3 together. The binders 4 are made of Fe oxide. The binders 4 made of such an inorganic material are distributed so as to fill the gaps between the soft magnetic particles 3, and therefore the powder magnetic core 1 has good mechanical strength. Furthermore, because the binders 4 are chemically and thermally stable, the powder magnetic core 1 has good durability and heat resistance.

[0072] 2 is produced by molding the soft magnetic powder according to the embodiment together with a binder and heat treating it. During the heat treatment, Fe oxide precipitates from the soft magnetic particles 3, forming binders 4. This firmly bonds the soft magnetic particles 3 together.

[0073] The heat treatment temperature is preferably 500° C. or higher and 800° C. or lower, and more preferably 550° C. or higher and 700° C. or lower. If the heat treatment temperature is below the lower limit, the formation of the binder 4 may be insufficient, and the insulating properties of the powder core 1 may be reduced. On the other hand, if the heat treatment temperature exceeds the upper limit, the magnetic properties of the soft magnetic particles 3 may be reduced.

[0074] The heat treatment time, during which the temperature is maintained within the above range, is preferably 0.5 hours or more and 10 hours or less, and more preferably 1 hour or more and 3 hours or less.

[0075] The heat treatment atmosphere may be a reducing atmosphere or an inert atmosphere, but an oxidizing atmosphere is preferable, and an air atmosphere is more preferable. This promotes the precipitation of Fe oxides and allows the efficient production of the binding portion 4. Furthermore, an air atmosphere contains nitrogen, which prevents excessive oxidation and prevents the magnetic properties of the soft magnetic powder from deteriorating after the heat treatment.

[0076] The Fe oxide includes Sn-substituted hematite, in which some Fe atoms are substituted with Sn atoms. Even a small amount of Sn-substituted hematite imparts good insulation to the powder magnetic core 1. This allows for a powder magnetic core 1 with high density and excellent voltage resistance. The Sn-substituted hematite also suppresses eddy currents between the soft magnetic particles 3. This allows for a powder magnetic core 1 with low iron loss. The Fe oxide may also contain elements other than Fe, O, and Sn. In this case, the content of each element is preferably less than the respective contents of Fe, O, and Sn in terms of atomic ratio.

[0077] 3 and 4 show the results of elemental mapping analysis performed on a cross section of powder core 1 using an energy dispersive X-ray fluorescence analyzer (EDX). Fig. 3 shows the results of elemental mapping analysis focusing on Si, and Fig. 4 shows the results of elemental mapping analysis focusing on Sn. The concentrations of Si and Sn are represented by color intensity in Figs. 3 and 4.

[0078] As shown in FIGS. 3 and 4 , the powder magnetic core 1 preferably has a segregation layer 5 located at the boundary between the soft magnetic particles 3 and the binder parts 4. The segregation layer 5 is a layer in which Si and Sn are segregated. "Si and Sn are segregated" refers to a state in which the Si concentration in the segregation layer 5 is higher than both the soft magnetic particles 3 and the binder parts 4, and the Sn concentration is also higher than both the soft magnetic particles 3 and the binder parts 4. The provision of such a segregation layer 5 can improve the adhesion between the soft magnetic particles 3 and the binder parts 4. This can further increase the mechanical strength of the powder magnetic core 1.

[0079] 3 shows that Si is segregated in an annular shape between the soft magnetic particles 3 and the binder 4. Similarly, FIG. 4 shows that Sn is segregated in an annular shape between the soft magnetic particles 3 and the binder 4. These annular regions correspond to the segregation layer 5.

[0080] 3.1. Crystal structure analysis by X-ray diffraction When powder magnetic core 1 is subjected to crystal structure analysis by X-ray diffraction, the resulting X-ray diffraction pattern contains peaks derived from Sn-substituted hematite.

[0081] An example of an X-ray diffraction pattern obtained from powder core 1 is the X-ray diffraction pattern XRD-4 shown in FIG. 1. In XRD-4, when the peak top intensity of reference peak P0 is defined as 1, the peak top intensity of index peak P1 is preferably 0.100 or more and 0.700 or less, more preferably 0.150 or more and 0.600 or less, and even more preferably 0.200 or more and 0.500 or less. When the intensity ratio of index peak P1 to reference peak P0 is within the above range, the proportion of Sn-substituted hematite contained in powder core 1 is optimized. This makes it possible to achieve powder core 1 with excellent voltage resistance without compromising magnetic properties.

[0082] If the intensity ratio of index peak P1 to reference peak P0 is below the lower limit, the proportion of Sn-substituted hematite decreases, which may result in a decrease in the withstand voltage of powder core 1. On the other hand, if the intensity ratio of index peak P1 to reference peak P0 exceeds the upper limit, the amount of Sn-substituted hematite becomes excessive, which may result in a decrease in the magnetic properties of powder core 1.

[0083] 3.2. Green density The density of powder core 1 is 5.30 g / cm 3 More than 6.10g / cm 3 Preferably, it is 5.50 g / cm or less. 3 More than 6.00g / cm 3 It is more preferable that the above condition is satisfied: This makes it possible to obtain a powder magnetic core 1 with high density and excellent magnetic properties.

[0084] 3.3.Magnetic permeability The magnetic permeability of the powder magnetic core 1 at a measurement frequency of 1 MHz is preferably 30 or more, and more preferably 32 or more. This makes it possible to obtain a powder magnetic core 1 that can be easily miniaturized.

[0085] The magnetic permeability of the powder magnetic core 1 is measured as follows. First, the powder magnetic core 1 is formed into a ring shape with an outer diameter of 14 mm, an inner diameter of 8 mm, and a thickness of 3 mm. Next, the obtained powder magnetic core 1 is placed in a resin case, and a conductor wire with a wire diameter of 0.6 mm is wound around the case seven times to prepare a test specimen. Next, the magnetic permeability of the test specimen is measured at a frequency of 1 MHz. To measure the magnetic permeability, an impedance analyzer (Keysight Technologies, Inc., 4194A) or the like is used.

[0086] 3.4. DC Superimposition Characteristics Powder magnetic core 1 has high DC superposition characteristics. Magnetic elements using powder magnetic core 1 often have a DC current superimposed on an AC signal. For this reason, powder magnetic core 1 is required to have good magnetic permeability characteristics in a DC magnetic field. In this specification, when the magnetic permeability when a DC magnetic field is superimposed on an AC signal drops by 30% from the magnetic permeability when no DC magnetic field is applied, the strength of the DC magnetic field at that point is considered to be the DC superposition characteristics. If the DC superposition characteristics according to this definition are high, high magnetic permeability can be maintained even in high applied magnetic fields. The frequency of the AC signal when measuring the DC superposition characteristics is 10 kHz.

[0087] The DC bias characteristic of the powder magnetic core 1 is preferably 15,000 [A / m] or more, more preferably 16,000 [A / m] or more, and even more preferably 17,000 [A / m] or more. A powder magnetic core 1 having such DC bias characteristics is suitable for high current applications. In other words, a powder magnetic core 1 having such DC bias characteristics can realize a magnetic element that exhibits excellent operational stability even when a high current is passed through it.

[0088] The DC bias characteristics are evaluated as follows. First, the powder magnetic core 1 is formed into a ring shape with an outer diameter of 14 mm, an inner diameter of 8 mm, and a thickness of 3 mm. Next, the obtained powder magnetic core 1 is placed in a resin case, and a conductor wire with a wire diameter of 1.25 mm is wound 50 times around the case to prepare a test specimen. Next, an AC signal with a frequency of 10 kHz is passed through the test specimen, and the magnetic permeability when no DC bias current is superimposed is taken as the reference value. Next, the magnetic permeability is measured while gradually increasing the DC bias current superimposed on the test specimen. Then, when the measured value drops 30% from the reference value, the magnetic field strength due to the DC bias current (DC magnetic field strength) at that point is measured.

[0089] 3.5.Voltage resistance When the withstand voltage of the powder magnetic core 1 is measured with an inter-electrode distance of 3 mm, the powder magnetic core 1 preferably has a withstand voltage of 1000 V or more. When the powder magnetic core 1 satisfies this withstand voltage, a powder magnetic core 1 can be obtained that can realize a magnetic element with a high rated voltage even though it is small.

[0090] The withstand voltage is more preferably 1000V or more and 5000V or less, further preferably 1500V or more and 4000V or less, and particularly preferably 2000V or more and 3000V or less.

[0091] If the withstand voltage of the powder core 1 is below the lower limit, it may be difficult to miniaturize the magnetic element if the rated voltage is set high. On the other hand, the withstand voltage of the powder core 1 may be above the upper limit, but in that case, it may become more difficult to manufacture the soft magnetic powder, which may lead to an increase in manufacturing costs and a decrease in manufacturing yield.

[0092] The method for measuring the withstand voltage is as follows. First, the powder magnetic core 1 is crushed in a mortar or the like to obtain a crushed material. 0.5 g of the crushed material obtained is subjected to pressure of 0.02 MPa (20 kg / cm 2) pressure to form a cylindrical shape 5 mm in height, to obtain a green body. During the press forming process, 1 mm thick copper electrodes are embedded on the top and bottom of the cylinder. Next, each electrode is connected to a power supply, and a DC voltage is applied between the electrodes. The electrical resistance between the electrodes is measured while the voltage is increased in 50 V increments. The voltage when the electrical resistance falls to 1 MΩ or less is taken as the "voltage resistance."

[0093] 3.6. Radial crushing strength The radial crushing strength of the powder magnetic core 1 is preferably 45 MPa or more, more preferably 50 MPa or more and 150 MPa or less, even more preferably 60 MPa or more and 130 MPa or less, and particularly preferably 70 MPa or more and 120 MPa or less. A powder magnetic core 1 having such a radial crushing strength is less likely to suffer from defects such as chipping or cracking even when subjected to a load such as an impact.

[0094] If the radial crushing strength is below the lower limit, defects such as chipping or cracking may occur when a load such as a strong impact is applied to the powder magnetic core 1. On the other hand, the radial crushing strength may exceed the upper limit, but in that case, the mechanical strength of the powder magnetic core 1 may vary greatly.

[0095] The radial crushing strength was measured as follows. First, the powder magnetic core 1 is formed into a ring shape with an outer diameter of 14 mm, an inner diameter of 8 mm, and a thickness of 3 mm. Next, the radial crushing strength of the obtained powder magnetic core 1 is measured. The method for measuring the radial crushing strength is a method conforming to the radial crushing strength test method specified in JIS Z 2507:2000. Specifically, when the radial crushing strength is K, the outer diameter is D, the radial thickness (half the difference between the outer diameter and the inner diameter) is t, the thickness is L, and the breaking load is F, the radial crushing strength K is given by K=F(Dt) / (Lt 2 ) can be calculated using

[0096] 4. Magnetic elements Next, the magnetic element according to the embodiment will be described.

[0097] The magnetic element according to the embodiment includes the above-described powder magnetic core 1. Specific examples of such magnetic elements include choke coils, inductors, noise filters, reactors, transformers, motors, actuators, solenoid valves, and generators.

[0098] Two types of coil components will be described below as representative examples of magnetic elements. 4.1.Toroidal type FIG. 5 is a plan view schematically illustrating a toroidal-type coil component 10. The coil component 10 shown in FIG. 5 has a ring-shaped powder magnetic core 11 and a conductive wire 12 wound around the powder magnetic core 11. The powder magnetic core 1 described above is used for the powder magnetic core 11. This allows for the powder magnetic core 11 to have high density and high withstand voltage. As a result, a coil component 10 with excellent magnetic properties and capable of supporting high voltages can be realized. Furthermore, when the coil component 10 is installed in an electronic device or the like, the electronic device or the like can be made more compact and have higher performance.

[0099] The shape of the powder magnetic core 11 is not limited to the ring shape shown in FIG. 5, but may be, for example, a shape in which a part of the ring is missing, a shape in which the longitudinal direction is linear, a sheet shape, a film shape, or the like.

[0100] 4.2.Closed magnetic circuit type FIG. 6 is a see-through perspective view that schematically shows a coil component 20 of a closed magnetic circuit type.

[0101] The closed magnetic circuit type coil component 20 will be described below, but the following description will focus on the differences from the toroidal type coil component 10, and a description of similar points will be omitted.

[0102] Coil component 20 shown in Fig. 6 is formed by embedding a conductor wire 22 formed into a coil shape inside powder magnetic core 21. Powder magnetic core 1 described above is used for powder magnetic core 21. This makes it possible to realize powder magnetic core 21 with high density and high withstand voltage. As a result, coil component 20 with excellent magnetic properties and capable of being applied with high voltage can be realized.

[0103] The shape of the powder magnetic core 21 is not limited to the shape shown in FIG. 6, but may be a sheet, a film, or the like.

[0104] 5.Electronic equipment Next, an electronic device including the magnetic element according to the embodiment will be described with reference to FIGS.

[0105] Fig. 7 is a perspective view showing a mobile personal computer 1100, which is an electronic device according to an embodiment. The personal computer 1100 shown in Fig. 7 includes a main body 1104 having a keyboard 1102, and a display unit 1106 having a display unit 100. The display unit 1106 is rotatably supported on the main body 1104 via a hinge structure. Such a personal computer 1100 includes a magnetic element 1000, such as a choke coil or inductor for a switching power supply, or a motor.

[0106] Fig. 8 is a plan view showing a smartphone 1200, which is an electronic device according to an embodiment. The smartphone 1200 shown in Fig. 8 includes a plurality of operation buttons 1202, an earpiece 1204, and a mouthpiece 1206. A display unit 100 is disposed between the operation buttons 1202 and the earpiece 1204. Such a smartphone 1200 includes a built-in magnetic element 1000, such as an inductor, a noise filter, or a motor.

[0107] 9 is a perspective view showing an electronic device according to an embodiment, namely, a digital still camera 1300. The digital still camera 1300 photoelectrically converts an optical image of a subject using an imaging element such as a CCD (Charge Coupled Device) to generate an imaging signal.

[0108] 9 includes a display unit 100 provided on the back of a case 1302. The display unit 100 functions as a viewfinder that displays an object as an electronic image. A light receiving unit 1304 including an optical lens, a CCD, etc. is provided on the front side of the case 1302, i.e., the back side in the figure.

[0109] When the photographer checks the subject image displayed on the display unit 100 and presses the shutter button 1306, the image signal from the CCD at that time is transferred to and stored in memory 1308. This digital still camera 1300 also incorporates magnetic elements 1000 such as inductors and noise filters.

[0110] The above-described powder magnetic core 1 is used for these magnetic elements 1000. This makes it possible to realize magnetic elements 1000 that have excellent magnetic properties and can be applied with high voltages. Furthermore, the electronic devices shown in FIGS. 7 to 9 are equipped with the magnetic element 1000. This allows the effects of the magnetic element 1000 to be enjoyed, and makes it possible to improve the performance and miniaturize the electronic devices.

[0111] Examples of electronic devices according to the embodiments include a personal computer 1100 in FIG. 7, a smartphone 1200 in FIG. 8, and a digital still camera 1300 in FIG. 9, as well as mobile phones, tablet terminals, watches, inkjet ejection devices such as inkjet printers, laptop personal computers, televisions, video cameras, video tape recorders, car navigation devices, pagers, electronic organizers, electronic dictionaries, calculators, electronic game devices, word processors, workstations, videophones, security television monitors, electronic binoculars, POS terminals, medical devices such as electronic thermometers, blood pressure monitors, blood glucose meters, electrocardiogram measuring devices, ultrasound diagnostic devices, and electronic endoscopes, fish finders, various measuring devices, instruments for vehicles, aircraft, and ships, mobile object control devices such as automobile control devices, aircraft control devices, railway vehicle control devices, and ship control devices, and flight simulators.

[0112] 6. Effects of the above embodiment The soft magnetic powder according to the embodiment is composed of Fe as a main component, Si with a content of 2.5% by mass or more and 7.5% by mass or less, Cr with a content of 1.0% by mass or more and 10.0% by mass or less, Sn with a content of 0.05% by mass or more and 1.10% by mass or less, and impurities. The soft magnetic powder according to the embodiment has a mass ratio of Sn to Cr (Sn / Cr) of 0.02 to 0.30, and an average particle size of 1.5 μm to 11.0 μm. Furthermore, when the soft magnetic powder according to the embodiment is heat-treated in an air atmosphere, Sn-substituted hematite is precipitated, in which some of the Fe atoms constituting hematite are substituted with Sn atoms.

[0113] According to this configuration, by heat treatment in an air atmosphere, Sn-substituted hematite precipitates, resulting in a soft magnetic powder that bonds particles together. In other words, by heat treatment in an air atmosphere, the soft magnetic powder described above can be used to produce a powder magnetic core that is strong and has excellent insulating properties. Such a powder magnetic core has high density and high voltage resistance, making it possible to realize a magnetic element that has excellent magnetic properties and can be used to apply high voltages.

[0114] The soft magnetic powder according to the embodiment has an Sn content of 0.10% by mass or more and 0.60% by mass or less, and the number of crystal grains per unit area of ​​the cross section of the particle is 0.10 [particles / (μm) 2 ] or more 0.45[pcs / (μm) 2 ] is as follows.

[0115] This configuration allows the number density of crystal grains to be optimized, resulting in an optimized crystal grain size. This allows the particles to deform appropriately during compaction, resulting in a soft magnetic powder that can be used to produce high-density powder cores. Furthermore, the soft magnetic powder has sufficiently high magnetic permeability, which depends on the crystal grain size, and low eddy current loss.

[0116] The soft magnetic powder according to the embodiment has an oxygen content of 300 ppm or more and 3000 ppm or less.

[0117] This configuration prevents the particle shape from being deteriorated due to the adhesion of oxides to the surface, thereby obtaining a soft magnetic powder with high packing properties during compaction. Also, it is possible to prevent a decrease in the space factor of the alloy in the powder magnetic core.

[0118] The powder magnetic core 1 according to the embodiment includes a soft magnetic powder and a binder 4 made of Fe oxide that binds the soft magnetic powder particles together (soft magnetic particles 3 together). The soft magnetic powder contains Fe as a main component, Si at a content of 2.5 to 7.5 mass%, Cr at a content of 1.0 to 10.0 mass%, Sn at a content of 0.05 to 1.10 mass%, and impurities. The mass ratio of Sn to Cr (Sn / Cr) is 0.02 to 0.30, and the average particle size is 1.5 to 11.0 μm. The Fe oxide also contains Sn-substituted hematite, in which some of the Fe atoms constituting hematite are substituted with Sn atoms.

[0119] According to this configuration, the Sn-substituted hematite imparts good insulating properties to the powder magnetic core 1. This makes it possible to obtain a powder magnetic core 1 that is high in density and has excellent withstand voltage.

[0120] Furthermore, since the binder parts 4 are made of an inorganic material and are distributed so as to fill the gaps between the soft magnetic particles 3, the resulting powder core 1 has good mechanical strength. Furthermore, since the binder parts 4 are chemically and thermally stable, the resulting powder core 1 has good durability and heat resistance.

[0121] The powder magnetic core 1 according to the embodiment is crushed, and the crushed material is crushed under a pressure of 49.0 MPa (0.5 t / cm 2 ) and the resulting molded body has a withstand voltage of 1000V or more when the electrode distance is 3mm. With this configuration, a dust core 1 with excellent voltage resistance can be obtained.

[0122] When the powder magnetic core 1 according to the embodiment is subjected to crystal structure analysis by X-ray diffraction, the resulting X-ray diffraction pattern includes a reference peak P0 and an index peak P1. The reference peak P0 is located in the range of 2θ=77°±1° and is derived from Fe—Si alloy crystals. The index peak P1 is located in the range of 2θ=39°±1° and is derived from Sn-substituted hematite. When the peak top intensity of the reference peak P0 is taken as 1, the intensity ratio of the index peak P1 is 0.100 or more and 0.700 or less.

[0123] This configuration optimizes the ratio of Sn-substituted hematite contained in the powder magnetic core 1. This makes it possible to realize a powder magnetic core 1 that has excellent voltage resistance without impairing the magnetic properties.

[0124] The powder magnetic core 1 according to the embodiment has a radial crushing strength of 45 MPa or more, measured by a method conforming to the radial crushing strength test method specified in JIS Z 2507:2000. With this configuration, a dust core 1 can be obtained that is less susceptible to defects such as chipping and cracking even when subjected to a load such as an impact.

[0125] The powder magnetic core 1 according to the embodiment has a segregation layer 5. The segregation layer 5 is located at the boundary between the soft magnetic particles 3 (particles of soft magnetic powder) and the binding portion 4. In the segregation layer 5, Si and Sn are segregated.

[0126] This configuration makes it possible to obtain a powder magnetic core 1 with improved adhesion between the soft magnetic particles 3 and the binder parts 4. This allows the mechanical strength of the powder magnetic core 1 to be further increased.

[0127] The magnetic element according to the embodiment includes the powder magnetic core 1 according to the embodiment. With this configuration, a magnetic element having excellent magnetic properties and capable of being applied with a high voltage can be realized.

[0128] The electronic device according to the embodiment includes the magnetic element 1000 according to the embodiment. With this configuration, an electronic device with high performance and small size can be obtained.

[0129] The soft magnetic powder, powder magnetic core, magnetic element, and electronic device of the present invention have been described above based on preferred embodiments, but the present invention is not limited thereto. For example, the shapes of the powder magnetic core and magnetic element are not limited to those shown in the drawings and may be any shape. [Example]

[0130] Next, specific examples of the present invention will be described. 7. Manufacturing of soft magnetic powder 7.1. Sample No. 1 First, soft magnetic powder was obtained by water atomization. The composition of the obtained soft magnetic powder is shown in Table 1.

[0131] A portion of the obtained soft magnetic powder was also sampled and subjected to heat treatment at 600°C for 1 hour in an air atmosphere. The X-ray diffraction pattern of the heat-treated soft magnetic powder was obtained by XRD, and the presence of Sn-substituted hematite was confirmed. The XRD intensity ratio (the intensity ratio of the index peak P1 to the reference peak P0) obtained by the above-mentioned method is shown in Table 1.

[0132] Furthermore, the average particle size, average circularity, oxygen content, and number of crystal grains per unit area of ​​the obtained soft magnetic powder were measured. The measurement results are shown in Table 1.

[0133] Table 1 also shows the manufacturing conditions for the soft magnetic powder, such as the difference between the pouring temperature and the melting point, and the outer diameter of the molten metal stream.

[0134] 7.2. Samples No. 2 to 23 A soft magnetic powder was obtained in the same manner as Sample No. 1, except that the composition of the soft magnetic powder was changed as shown in Table 1, Table 2 or Table 3.

[0135] In Tables 1 to 3, among the soft magnetic powders of each sample number and the powder magnetic cores produced using the soft magnetic powders, those that correspond to the present invention are designated as "Examples," and those that do not correspond to the present invention are designated as "Comparative Examples."

[0136] 8. Evaluation of soft magnetic powder 8.1. Tap Density of Soft Magnetic Powder The tap density of the soft magnetic powder of each sample No. was measured by the method described above. The measurement results are shown in Tables 1 to 3.

[0137] 8.2. Specific surface area of ​​soft magnetic powder The specific surface area of ​​the soft magnetic powder of each sample No. was measured by the method described above. The measurement results are shown in Tables 1 to 3.

[0138] 8.3. Coercive force of soft magnetic powder The coercive force was measured by the method described above for the soft magnetic powder of each sample No. The measurement results are shown in Tables 1 to 3.

[0139] 9. Evaluation of powder cores The soft magnetic powders of each of the examples and comparative examples were used to prepare powder magnetic cores by the following method.

[0140] First, the soft magnetic powder was mixed with an epoxy resin equivalent to 2.0 mass % of the soft magnetic powder to obtain a mixture. The obtained mixture was subjected to a pressure of 294.2 MPa (3 t / cm 2 ) to obtain two ring-shaped compacts each having an outer diameter of 14 mm, an inner diameter of 8 mm, and a thickness of 3 mm.

[0141] The resulting compact was then heat-treated in air at 600°C for 1 hour. This removed the epoxy resin and formed bonds, resulting in a powder magnetic core. One of the two powder magnetic cores was cut, and the cross section was observed with a scanning electron microscope and subjected to elemental mapping analysis. The results showed that Fe oxide was distributed in the gaps between the soft magnetic particles.

[0142] 9.1. Density The mass and volume of each powder magnetic core of each example and comparative example were measured, and the density was calculated. The calculation results are shown in Tables 1 to 3.

[0143] 9.2. Radial crushing strength The radial crushing strength of each of the powder magnetic cores of the examples and comparative examples was measured by the method described above. The measurement results are shown in Tables 1 to 3.

[0144] 9.3. DC Superimposition Characteristics The DC bias characteristics of each of the powder magnetic cores of the examples and comparative examples were measured by the method described above. The measurement results are shown in Tables 1 to 3.

[0145] 9.4.Voltage resistance The withstand voltage of each of the powder magnetic cores of the examples and comparative examples was measured by the method described above. The measurement results are shown in Tables 1 to 3.

[0146] [Table 1]

[0147] [Table 2]

[0148] [Table 3]

[0149] As shown in Tables 1 to 3, the soft magnetic powders of each example had high tap density and small specific surface area despite their small particle size, demonstrating high packing properties. It was also confirmed that the soft magnetic powders of each example had relatively low coercive force. Furthermore, it was found that high-density powder cores could be obtained by using the soft magnetic powders of each example. Furthermore, it was also found that these powder cores had excellent DC bias characteristics. Furthermore, by optimizing the composition, particle size, and cross-sectional grain density of the soft magnetic powder, it was possible to increase the withstand voltage of the powder core. [Explanation of symbols]

[0150] 1... powder core, 3... soft magnetic particles, 4... binding portion, 5... segregation layer, 10... coil component, 11... powder core, 12... conducting wire, 20... coil component, 21... powder core, 22... conducting wire, 100... display unit, 1000... magnetic element, 1100... personal computer, 1102... keyboard, 1104... main body, 1106... display unit, 1200... smartphone, 1202... operation button, 1204... receiver Mouth, 1206...mouthpiece, 1300...digital still camera, 1302...case, 1304...light receiving unit, 1306...shutter button, 1308...memory, P(Fe-Si)...peak, P(Sn)...peak, P0...reference peak, P1...index peak, XRD-1...X-ray diffraction pattern, XRD-2...X-ray diffraction pattern, XRD-3...X-ray diffraction pattern, XRD-4...X-ray diffraction pattern

Claims

1. Fe as the main component, Si having a content of 2.5% by mass or more and 7.5% by mass or less; Cr having a content of 1.0 mass% or more and 10.0 mass% or less; Sn having a content of 0.05% by mass or more and 1.10% by mass or less; Impurities and It consists of a mass ratio (Sn / Cr) of the Sn content to the Cr content is 0.02 or more and 0.30 or less; The average particle size is 1.5 μm or more and 11.0 μm or less, A soft magnetic powder characterized in that, when heat-treated in an air atmosphere, Sn-substituted hematite is precipitated, in which some of the Fe atoms constituting the hematite are substituted with Sn atoms.

2. The Sn content is 0.10 mass% or more and 0.60 mass% or less, The number of crystal grains in a unit area of ​​the cross section of the particle is 0.10 [particles / (μm) ２ ] or more 0.45 [pcs / (μm) ２ 2. The soft magnetic powder according to claim 1, wherein the average particle diameter is 1 / 2 or less.

3. 3. The soft magnetic powder according to claim 1, wherein the oxygen content is 300 ppm or more and 3,000 ppm or less.

4. Fe as the main component, Si having a content of 2.5% by mass or more and 7.5% by mass or less; Cr having a content of 1.0 mass% or more and 10.0 mass% or less; Sn having a content of 0.05% by mass or more and 1.10% by mass or less; Impurities and It consists of a mass ratio (Sn / Cr) of the Sn content to the Cr content is 0.02 or more and 0.30 or less; A soft magnetic powder having an average particle size of 1.5 μm or more and 11.0 μm or less; a binding portion made of Fe oxide that binds the particles of the soft magnetic powder together; and The powder magnetic core is characterized in that the Fe oxide contains Sn-substituted hematite in which some of the Fe atoms constituting hematite are substituted with Sn atoms.

5. The crushed material is crushed under a pressure of 49.0 MPa (0.5 t / cm ２ 5. The powder magnetic core according to claim 4, wherein the powder magnetic core is compacted at a pressure of 1000 V or more, and the resulting compact has a withstand voltage of 1000 V or more at an inter-electrode distance of 3 mm.

6. When subjected to crystal structure analysis by X-ray diffraction, the resulting X-ray diffraction pattern is a reference peak located in the range of 2θ=77°±1° and attributable to crystals of an Fe—Si-based alloy; An index peak located in the range of 2θ = 39 ° ± 1 ° and derived from the Sn-substituted hematite; Including, 6. The powder magnetic core according to claim 4, wherein the intensity ratio of the index peak is 0.100 or more and 0.700 or less when the peak top intensity of the reference peak is taken as 1.

7. 6. The powder magnetic core according to claim 4, wherein the radial crushing strength measured according to the radial crushing strength test method specified in JIS Z 2507:2000 is 45 MPa or more.

8. 6. The powder magnetic core according to claim 4, further comprising a segregation layer located at the boundary between the particles of the soft magnetic powder and the binder portion, in which Si and Sn are segregated.

9. A magnetic element comprising the powder magnetic core according to claim 4 or 5.

10. An electronic device comprising the magnetic element according to claim 9.

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