Soft magnetic sintered member and method for manufacturing soft magnetic sintered member

Abstract

The present disclosure relates to a soft magnetic sintered member including a sintered body that contains a soft magnetic matrix containing 1.0-6.5% by mass of Si and has a porosity of 7.9% or more.

Description

Soft magnetic sintered member and method for manufacturing the same

[0001] FIELD Embodiments of the present invention relate to a soft magnetic sintered member and a method for manufacturing the soft magnetic sintered member.

[0002] Soft magnetic materials such as silicon steel plates have high saturation magnetic flux density, high electrical resistivity, and low iron loss, and are therefore widely used as iron cores (cores, yokes, etc.) for relays, transformers, etc. When soft magnetic materials are used as electromagnetic drive components in actuators that convert electrical energy into drive energy, the conversion efficiency can be significantly improved compared to when other materials are used.

[0003] A powder metallurgical method is known as a method for producing soft magnetic members such as silicon steel plates. Patent Document 1 discloses a method for producing raw material particles for an Fe—Si-based soft magnetic sintered alloy, which comprises granulating a fine Fe powder of 350 mesh (about 40 μm) or less and a fine Fe—Si-based powder of 350 mesh (about 40 μm) or less using an organic binder and / or an organic solvent to form granules with an average particle size of 40 μm to 1 mm, and optionally further crushing the granules to form granules with an average particle size of 100 mesh (about 150 μm) or less, and further discloses a method for producing an Fe—Si-based soft magnetic sintered alloy member, which comprises firing the raw material particles for the Fe—Si-based soft magnetic sintered alloy at 1150 to 1350° C. to sinter them.

[0004] Japanese Patent Application Laid-Open No. 2000-212679

[0005] An object of one embodiment of the present invention is to provide a soft magnetic sintered member having good magnetic properties and high strength. Another object of another embodiment of the present invention is to provide a method for manufacturing a soft magnetic sintered member having good magnetic properties and high strength.

[0006] One embodiment relates to a soft magnetic sintered member including a sintered body having a soft magnetic matrix containing 1.0 to 6.5 mass% Si and a porosity of 7.9% or less. Another embodiment relates to a method for producing a soft magnetic sintered member, the method comprising: preparing a raw material powder containing soft magnetic powder having an average particle size of 10 μm to 150 μm and Si powder having an average particle size of 0.5 μm to less than 10 μm, the Si powder content being 1.0 to 6.5 mass% based on the total mass of the soft magnetic powder and the Si powder, and at least a portion of the Si powder adhering to the surface of the soft magnetic powder; compacting the raw material powder to obtain a green body; and heating the green body using a mesh belt furnace or a pusher furnace to obtain a sintered body.

[0007] According to the embodiments of the present invention, it is possible to provide a soft magnetic sintered member having good magnetic properties and high strength. Also, according to the embodiments of the present invention, it is possible to provide a method for manufacturing a soft magnetic sintered member having good magnetic properties and high strength.

[0008] Fig. 1 is a scanning electron microscope photograph showing an example of Si powder before and after pulverization. Fig. 2 is an optical microscope photograph of the sintered bodies obtained in Example 1 and Comparative Example 1 (upper row: 200x magnification, lower row: 500x magnification). Fig. 3 is a schematic plan view of the sintered bodies produced in the examples.

[0009] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0010] In the present specification, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in the present specification, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another staged numerical range. Furthermore, in numerical ranges described in the present specification, the upper or lower limit value of that numerical range may be replaced with a value shown in the Examples. A staged numerical range may be created by selecting a certain numerical value from the upper and lower limit values ​​described in stages in the present specification. Furthermore, the upper and lower limit values ​​described in the present specification may be replaced with a value shown in the Examples. In the present specification, each component may contain multiple corresponding substances. When multiple substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified. In the present specification, the term "layer" includes cases where, when the region in which the layer exists is observed, the layer is formed over the entire region, as well as cases where the layer is formed only in a portion of the region. In this specification, the term "step" includes not only an independent step but also a step that cannot be clearly distinguished from other steps as long as the intended function is achieved. When embodiments are described in this specification with reference to drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of components in each drawing are conceptual, and the relative size relationships between components are not limited to the relationships shown in the drawings.

[0011] <Soft Magnetic Sintered Member> In an embodiment of the present invention, the soft magnetic sintered member includes a sintered body having a porosity of 7.9% or less, and the sintered body includes a soft magnetic matrix containing 1.0 to 6.5 mass % of Si.

[0012] [Sintered body] The sintered body includes a soft magnetic matrix. The soft magnetic matrix contains 1.0 to 6.5 mass% Si based on the mass of the soft magnetic matrix. When the Si content is 1.0 mass% or more, the effect of increasing the specific resistance and reducing iron loss tends to be easily obtained. When the Si content is 6.5 mass% or less, a sufficiently high saturation magnetic flux density tends to be easily obtained, and the sintered body tends to be prevented from becoming too hard and brittle. The Si content may be, for example, 1.5 mass% or more, 1.8 mass% or more, or 2.0 mass% or more based on the mass of the soft magnetic matrix. The Si content may be, for example, 6.0 mass% or less, 5.5 mass% or less, 4.5 mass% or less, or 3.0 mass% or less based on the mass of the soft magnetic matrix. The Si content may be, for example, 1.5 to 6.0 mass %, 1.8 to 4.5 mass %, or 2.0 to 3.0 mass % based on the mass of the soft magnetic matrix.

[0013] The soft magnetic matrix is ​​preferably an iron-based matrix containing Fe as a main component. The saturation magnetic flux density tends to increase as the Fe content increases. The Fe content, based on the mass of the soft magnetic matrix, may be, for example, more than 50.0 mass%, 90.0 mass% or more, 93.5 mass% or more, or 95.0 mass% or more. The Fe content, based on the mass of the soft magnetic matrix, may be, for example, 99.0 mass% or less, 98.0 mass% or less, or 97.0 mass% or less. The Fe content, based on the mass of the soft magnetic matrix, may be, for example, 90.0 to 99.0 mass%, 95.0 to 99.0 mass%, or 97.0 to 98.0 mass%.

[0014] The iron-based matrix may contain at least one element selected from the group consisting of Cr, Co, P, Mo, and Ni. Examples of the iron-based matrix include an Fe—P-based matrix, an Fe—Cr-based matrix, an Fe—Co-based matrix, an Fe—Mo-based matrix, and an Fe—Ni-based matrix.

[0015] The iron-based matrix may contain P. When the iron-based matrix contains P, the soft magnetic matrix has crystal grains of an appropriate size, and magnetic permeability tends to be improved. From the viewpoint of improving magnetic permeability, the P content may be, for example, 0.2 mass% or more based on the mass of Fe. From the viewpoint of preventing embrittlement of the iron-based matrix, the P content may be, for example, 1.2 mass% or less based on the mass of Fe. The P content may be, for example, 0.2 to 1.2 mass% based on the mass of Fe.

[0016] Specific examples of the soft magnetic matrix include the following: A matrix consisting of 1.0 to 6.5 mass% of Si, Fe, and unavoidable impurities based on the mass of the soft magnetic matrix A matrix consisting of 1.0 to 6.5 mass% of Si, P, Fe, and unavoidable impurities based on the mass of the soft magnetic matrix

[0017] The porosity of the sintered body is 7.9% or less. When the porosity of the sintered body is 7.9% or less, good magnetic properties and high strength can be obtained, and when the sintered body is plated, the plating solution can be prevented from blowing out of the pores. The porosity of the sintered body may be, for example, 7.5% or less, 7.0% or less, 6.8% or less, 6.5% or less, 6.0% or less, 5.8% or less, or 5.5% or less. The lower limit of the porosity of the sintered body is not particularly limited, and may be, for example, 1.0% or more, 2.0% or more, 3.0% or more, 4.0% or more, or 5.0% or more. The porosity of the sintered body may be, for example, 1.0 to 7.9%, 3.0 to 7.5%, or 5.0 to 7.0%.

[0018] The porosity of the sintered body can be adjusted by, for example, changing the particle size of the raw material powder, molding conditions, sintering conditions, etc. For example, the porosity of the sintered body tends to be reduced by reducing the particle size of the raw material powder, increasing the molding pressure, increasing the sintering temperature, extending the sintering time, using the manufacturing method described below, etc.

[0019] The porosity of a sintered body can be measured by the following method. The sintered body is cut and the cross section is mirror-polished. An image of the polished surface is observed and the area of ​​pores contained in any measurement area on the polished surface is measured. The porosity is determined by calculating the ratio of the area of ​​pores to the area of ​​the measurement area (porosity (%) = pore area / area of ​​measurement area × 100). For example, image analysis software (WinROOF manufactured by Mitani Shoji Co., Ltd.) can be used to observe the image. The measurement area may be, for example, any one location or any 10 locations. When the measurement area is 10 locations, the arithmetic average of the porosities of the 10 locations is defined as the porosity in this specification.

[0020] The pore diameter is preferably 7.0 μm or less. When the pore diameter is 7.0 μm or less, it is possible to prevent the plating solution from blowing out from the pores when the sintered body is plated. The pore diameter may be, for example, 6.0 μm or less, 5.0 μm or less, or 4.5 μm or less. The lower limit of the pore diameter is not particularly limited, but may be, for example, 0.1 μm or more, 0.4 μm or more, or 0.5 μm or more. The pore diameter may be, for example, 0.1 to 7.0 μm, 0.1 to 6.0 μm, or 0.1 to 5.0 μm.

[0021] The pore diameter can be measured by the following method. The sintered body is cut and the cross section is mirror-polished. An image of the polished surface is observed and the maximum diameter of each pore contained in any measurement area of ​​the polished surface is measured. The maximum diameter measured for each pore is taken as the pore diameter of that pore. The measurement area may be, for example, any one location or any 10 locations.

[0022] "The pore diameter of the pores contained in the soft magnetic matrix is ​​7.0 μm or less" preferably means that more than 50% of the number of pores contained in an arbitrarily selected measurement area satisfy the above pore diameter range. It is more preferable that 70% or more of the number of pores contained in an arbitrarily selected measurement area satisfy the above pore diameter range, and even more preferable that 90% or more satisfy the above pore diameter range. All of the pores contained in an arbitrarily selected measurement area (i.e., 100% of the number of pores) may satisfy the above pore diameter range.

[0023] The soft magnetic matrix includes crystal grains. The grain size of the crystal grains may be, for example, 500 μm or less, 400 μm or less, or 300 μm or less, and is preferably 200 μm or less. From the viewpoint of the strength of the sintered body, it is desirable that the grain size of the crystals is not too large. In particular, when the grain size is 200 μm or less, the sintered body tends to have high strength. The grain size of the crystal grains may be, for example, 180 μm or less, or 150 μm or less. There is no particular restriction on the lower limit of the grain size of the crystal grains, but it may be, for example, 20 μm or more, 30 μm or more, or 50 μm or more. The grain size of the crystal grains may be, for example, 20 to 500 μm, 20 to 400 μm, 20 to 300 μm, 30 to 200 μm, 30 to 180 μm or less, or 50 to 150 μm.

[0024] The grain size of the crystal grains can be measured by the following method. The sintered body is cut and the cross section is mirror-polished. An image of the polished surface is observed and the maximum diameter of each crystal grain contained in an arbitrary measurement area of ​​the polished surface is measured. The maximum diameter measured for each crystal grain is taken as the grain size of that crystal grain. The measurement area may be, for example, any one location or any 10 locations.

[0025] "The grain size of the crystal grains contained in the soft magnetic matrix is ​​200 μm or less" preferably means that more than 50% of the number of crystal grains contained in an arbitrarily selected measurement area meet the above grain size range. It is more preferable that 70% or more of the number of crystal grains contained in an arbitrarily selected measurement area meet the above grain size range, and even more preferable that 90% or more meet the above grain size range. All of the crystal grains contained in an arbitrarily selected measurement area (i.e., 100% of the number of crystal grains) may meet the above grain size range. The same applies to "The grain size of the crystal grains contained in the soft magnetic matrix is ​​500 μm or less."

[0026] The tensile strength of the sintered body is, for example, 400 MPa or more or 450 MPa or more, and preferably 480 MPa or more. The tensile strength of the sintered body may be, for example, 490 MPa or more, 500 MPa or more, 510 MPa or more, 520 MPa or more, 530 MPa, or 540 MPa or more. The upper limit of the tensile strength of the sintered body is not particularly limited, but may be, for example, 600 MPa or less or 580 MPa or less. The tensile strength of the sintered body can be measured by the method specified in JIS Z 2241:2011. The tensile strength of the sintered body may be, for example, 400 to 600 MPa, 480 to 580 MPa, or 500 to 580 MPa.

[0027] The tensile strength of a sintered body can be adjusted, for example, by changing molding conditions, sintering conditions, pore size, crystal grain size, additives, etc. For example, the tensile strength of a sintered body tends to be increased by increasing the molding pressure, increasing the sintering temperature, extending the sintering time, suppressing coarsening of pores, suppressing coarsening of crystal grains, etc. When the tensile strength of a sintered body is high, the soft magnetic sintered member exhibits excellent durability.

[0028] [Plating Layer] The soft magnetic sintered member may have a sintered body and a plating layer on at least a part of the surface of the sintered body. The plating layer may be a copper plating layer, a nickel plating layer, a gold plating layer, a chromium plating layer, or the like.

[0029] [Applications] Soft magnetic sintered members can be used in electromagnetically driven components of actuators that convert electrical energy into drive energy, various sensor components, and the like. Soft magnetic sintered members having a plating layer on at least a portion of the surface of the sintered body are rust-resistant and therefore suitable for applications such as sensors used in the atmosphere. It is generally known that the formation of rust is accelerated by the escape of treatment liquid from pores after plating to form a plating layer. According to some embodiments of the present invention, the escape of treatment liquid from pores after plating can be prevented, and therefore the soft magnetic sintered member can have a plating layer formed in good condition on its surface. Therefore, soft magnetic sintered members having a plating layer have particularly excellent reliability when used in the atmosphere or in harsh environments.

[0030] [Manufacturing Method] The manufacturing method of the soft magnetic sintered member is not particularly limited, and the soft magnetic sintered member can be manufactured by a known powder metallurgy method using soft magnetic powder as raw material powder. For example, the soft magnetic sintered member can be efficiently manufactured by the following manufacturing method of the soft magnetic sintered member.

[0031] <Method for manufacturing soft magnetic sintered member> According to an embodiment of the present invention, a method for manufacturing a soft magnetic sintered member includes: preparing a raw material powder containing soft magnetic powder having an average particle size of 10 μm or more and 150 μm or less and Si powder having an average particle size of 0.5 μm or more and less than 10 μm, wherein the content of the Si powder is 1.0 to 6.5 mass% based on the total mass of the soft magnetic powder and the Si powder, and at least a portion of the Si powder adheres to the surface of the soft magnetic powder (hereinafter, this may be referred to as a "step of preparing raw material powder"); compacting the raw material powder to obtain a molded body (hereinafter, this may be referred to as a "molding step"); and heating the molded body using a mesh belt furnace or a pusher furnace (hereinafter, this may be referred to as a "heating step").

[0032] [Step of Preparing Raw Material Powder] The raw material powder contains at least a soft magnetic powder having an average particle size of 10 μm or more and 150 μm or less, and a Si powder having an average particle size of 0.5 μm or more and less than 10 μm. The content of the Si powder is 1.0 to 6.5 mass% based on the total mass of the soft magnetic powder and the Si powder, and at least a portion of the Si powder adheres to the surface of the soft magnetic powder. The raw material powder may further contain any powder.

[0033] The average particle size of the soft magnetic powder is 10 μm or more and 150 μm or less. When the average particle size of the soft magnetic powder is 10 μm or more, the raw material powder exhibits good fluidity, improving moldability and making it easier to obtain a high-density molded body. Furthermore, when the average particle size of the soft magnetic powder is 10 μm or more, the amount of shrinkage after sintering can be reduced, and when molding into a complex shape, the shape can be easily maintained. When the average particle size of the soft magnetic powder is 150 μm or less, sufficient diffusion of Si is achieved, making it easier to obtain a uniform soft magnetic matrix. The average particle size of the soft magnetic powder may be, for example, 20 μm or more, 30 μm or more, 40 μm or more, 50 μm or more, or 60 μm or more. The average particle size of the soft magnetic powder may be, for example, 130 μm or less, 120 μm or less, 110 μm or less, 100 μm or less, or 90 μm or less. The average particle size of the soft magnetic powder may be, for example, 20 to 130 μm, 30 to 120 μm, 40 to 110 μm, 50 to 100 μm, or 60 to 90 μm.

[0034] The average particle size of the soft magnetic powder can be measured by laser diffraction. In this specification, the average particle size of the soft magnetic powder is the median diameter (D50) in the volume-based particle size distribution.

[0035] The soft magnetic powder is preferably iron powder, iron alloy powder, or iron mixed powder. Examples of iron alloy powders include Fe—P alloy powder, Fe—Cr alloy powder, Fe—Co alloy powder, Fe—Mo alloy powder, and Fe—Ni alloy powder. When the iron alloy powder contains P, the magnetic permeability of the resulting soft magnetic sintered member tends to be improved. From the viewpoint of improving magnetic permeability, the P content may be, for example, 0.2 mass% or more based on the mass of the iron alloy powder. From the viewpoint of preventing embrittlement of the iron matrix, the P content may be, for example, 1.2 mass% or less based on the mass of the iron alloy powder. Examples of iron mixed powders include Fe—P mixed powder, Fe—Cr mixed powder, Fe—Co mixed powder, Fe—Mo mixed powder, and Fe—Ni mixed powder. When the iron mixed powder contains P, the magnetic permeability of the resulting soft magnetic sintered member tends to be improved. The P content may be, for example, 0.2 mass% or more based on the mass of the iron mixed powder from the viewpoint of improving magnetic permeability. The P content may be, for example, 1.2 mass% or less based on the mass of the iron mixed powder from the viewpoint of preventing embrittlement of the iron-based matrix. The P content may be, for example, 0.2 to 1.2 mass%.

[0036] Specific examples of soft magnetic powders include: Iron powder consisting of Fe and unavoidable impurities; Iron alloy powder consisting of P, Fe, and unavoidable impurities; Mixed iron powder consisting of P, Fe, and unavoidable impurities.

[0037] The average particle size of the Si powder is 0.5 μm or more and less than 10 μm. When the average particle size of the Si powder is 1 μm or more, a high-density sintered body is easily obtained. When the average particle size of the Si powder is less than 10 μm, a high-density sintered body is easily obtained. The average particle size of the Si powder may be, for example, 1.0 μm or more, 1.5 μm or more, 2 μm or more, 3 μm or more, or 5 μm or more. The average particle size of the Si powder may be, for example, 9 μm or less, 7 μm or less, 6 μm or less, 4 μm or less, 2 μm or less, or 1.5 μm or less. The average particle size of the Si powder may be, for example, 0.5 to 9 μm, 1.0 to 7 μm, 1.5 to 6 μm, or 2 to 6 μm.

[0038] The average particle size of the Si powder can be measured by laser diffraction. In this specification, the average particle size of the Si powder is the median diameter (D50) in the volume-based particle size distribution.

[0039] The content of Si powder is 1.0 to 6.5% by mass based on the total mass of the soft magnetic powder and the Si powder. When the content of Si powder is 1.0% by mass or more, the effect of increasing the specific resistance and reducing iron loss tends to be obtained. When the content of Si powder is 6.5% by mass or less, a sufficiently high saturation magnetic flux density tends to be obtained and the sintered body tends to be prevented from becoming too hard and brittle. The content of Si powder may be, for example, 1.5% by mass or more, 1.8% by mass or more, 2.0% by mass or more, or 2.5% by mass or more based on the total mass of the soft magnetic powder and the Si powder. The content of Si powder may be, for example, 6.0% by mass or less, 5.5% by mass or less, 4.5% by mass or less, or 3.0% by mass or less based on the total mass of the soft magnetic powder and the Si powder. The content of the Si powder may be, for example, 1.5 to 6.0 mass%, 1.8 to 5.5 mass%, 1.8 to 4.5 mass%, or 2.0 to 3.0 mass%, based on the total mass of the soft magnetic powder and the Si powder.

[0040] The Si powder is preferably a powder having a shape including corners. The Si powder having a shape including corners can adhere to the surface of the soft magnetic powder while being stuck into the soft magnetic powder. When the Si powder is stuck into the soft magnetic powder, the Si powder is likely to remain attached to the surface of the soft magnetic powder. By using soft magnetic powder with Si powder attached to its surface, the sinterability of the sintered body tends to be improved.

[0041] A Si powder having an average particle size of 0.5 μm or more and less than 10 μm and having a shape including corners can be obtained by pulverizing a Si powder having an average particle size of 10 μm or more. The pulverization may be dry pulverization or wet pulverization, and is preferably dry pulverization. Examples of dry pulverizers that can be used for dry pulverization include a ball mill, a bead mill, a hammer mill, a pellet mill, a roller mill, and a jet mill. The average particle size of the Si powder used for pulverization is, for example, 10 μm or more and 30 μm or less.

[0042] It is preferable to use a ball mill for pulverization because it is easy to obtain Si powder with fine and sharp corners. When using a ball mill, the average particle size of the Si powder can be adjusted by changing the hardness, diameter, material, etc. of the media; the pulverization time, etc. Figure 1 is an SEM photograph showing an example of Si powder before pulverization and Si powder after pulverization.

[0043] At least a portion of the Si powder adheres to the surface of the soft magnetic powder. The soft magnetic powder may be partially or entirely coated with Si powder. The Si powder may adhere to the surface of the soft magnetic powder via a binder that is solid at room temperature. By using the binder, the Si powder adheres uniformly to the surface of the soft magnetic powder. There are no particular limitations on the method for obtaining soft magnetic powder with Si powder adhered to its surface. For example, a method can be used in which a dispersion liquid in which Si powder is dispersed in water or ethanol is used, and the dispersion liquid and the soft magnetic powder are mixed and dried.

[0044] More specifically, the following methods (1) to (3) can be mentioned: (1) A method in which the soft magnetic powder is immersed in a dispersion liquid and dried by evaporating or vaporizing the water or ethanol while the powder is flowing; (2) A method in which the dispersion liquid is gradually added in small amounts to the soft magnetic powder and dried by evaporating or vaporizing the water or ethanol while the powder is flowing; (3) A method in which the dispersion liquid is sprayed onto the soft magnetic powder and dried by evaporating or vaporizing the water or ethanol while the powder is flowing.

[0045] Among the above methods (1) to (3), soft magnetic powder with more uniformly adhered Si powder is more likely to be obtained in the order (3), (2), and (1). On the other hand, the steps and equipment tend to become more complicated in the order (3), (2), and (1).

[0046] A binder may be further added to the dispersion in which Si powder is dispersed in water or ethanol. When the dispersion contains a binder, the adhesion of the Si powder to the surface of the soft magnetic powder is also achieved by the binder. The binder is preferably one that is solid at room temperature, volatilizes during the temperature rise process during sintering, and does not remain in the final product. Examples of binders that are solid at room temperature, volatilizes during the temperature rise process during sintering, and do not remain in the final product include polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA).

[0047] The amount of binder added to the dispersion is preferably 0.5% by mass or less, based on the mass of the dispersion. At 0.5% by mass or less, a decrease in the density of the compact can be prevented, resulting in a high-density sintered body. Furthermore, at 0.5% by mass or less, the binder can be sufficiently volatilized and removed, preventing the remaining binder from diffusing into the soft magnetic matrix as carbon, resulting in good magnetic properties.

[0048] The dispersion may contain at least one selected from the group consisting of a dispersant, a surfactant, and a rust inhibitor. When the dispersion contains a dispersant, the dispersibility of the Si powder in the dispersion is improved, preventing sedimentation of the Si powder. This allows the Si powder to adhere uniformly to the soft magnetic powder. When the dispersion contains a surfactant, the wettability of the surface of the soft magnetic powder with the dispersion is improved, allowing the Si powder to adhere uniformly to the soft magnetic powder. When the dispersion contains a rust inhibitor, if the dispersion medium is water, rusting of the soft magnetic powder is suppressed.

[0049] An example of an optional powder that can be contained in the raw material powder is a powder lubricant. When the raw material powder contains a powder lubricant, it is possible to prevent the occurrence of galling, chipping, and the like during the molding process. The powder lubricant may be, for example, a powder lubricant containing an amide-based lubricant such as stearic acid amide, stearic acid bisamide, or ethylene bisstearic acid amide; a metal soap; or a wax such as a polyolefin-based wax or an ester-based wax.

[0050] [Forming Step] The method for manufacturing a soft magnetic sintered member includes compacting a raw material powder to obtain a green body. For example, the raw material powder is compressed using upper and lower punches in a die. During compaction, a die lubricant may be applied to the die to perform die lubrication compaction.

[0051] The molding pressure is preferably 400 MPa or more, more preferably 500 MPa or more, and even more preferably 600 MPa or more, from the viewpoint of obtaining a soft magnetic sintered member with high precision and obtaining good magnetic properties, etc. Furthermore, from the viewpoint of mold durability, etc., the molding pressure is preferably 1,000 MPa or less, more preferably 900 MPa or less, and even more preferably 800 MPa or less.

[0052] [Heating Step] The method for producing a soft magnetic sintered member includes heating the compact using a mesh belt furnace or a pusher furnace. When using a mesh belt furnace or a pusher furnace, heating is performed under atmospheric pressure. By heating, optional binders, dispersants, powder lubricants, etc. are removed (degreasing step), sintering progresses, and a sintered body is obtained (sintering step). By using a mesh belt furnace or a pusher furnace, crystal grain growth is suppressed, making it possible to produce a soft magnetic sintered member with good magnetic properties and high strength. Furthermore, according to a preferred embodiment, when a plating process is performed, the spraying of the treatment solution after the process can be suppressed.

[0053] For example, in the debinding step, before sintering, binders and the like are removed in an atmosphere below the heating temperature during sintering. Debinding is preferably carried out in a non-oxidizing atmosphere. The heating temperature is preferably below the sintering temperature, more preferably 700°C or lower. The heating temperature is preferably at or above the decomposition temperature of the compounds to be debound, such as the binder and any powder lubricant used. In one example, when the molded body contains PVA, which has a decomposition temperature of 300°C, the debinding treatment can be carried out at 300°C or higher. The heating temperature may be, for example, 300 to 700°C.

[0054] The heating time in the degreasing step is preferably 1 to 6 hours in order to thoroughly remove binders and the like, and more preferably 4 to 6 hours in order to more thoroughly remove them.

[0055] In the sintering step, the compact is sintered to obtain a sintered body. Sintering is preferably carried out in a non-oxidizing atmosphere. Sintering conditions are appropriately selected depending on the soft magnetic powder contained in the raw material powder. When an iron alloy is used as the soft magnetic powder, it is preferable to heat and sinter the sintered body to 1,000°C or higher in order to improve the density of the sintered body. Furthermore, in order to sufficiently improve the density of the sintered body, the heating temperature is more preferably 1,100°C or higher. Considering wear and tear on the sintering furnace, the heating temperature is preferably 1,400°C or lower, and more preferably 1,200°C or lower. The heating temperature may be, for example, 1,000 to 1,400°C or 1,100 to 1,200°C.

[0056] The heating time in the sintering step is preferably 1 to 6 hours, more preferably 4 to 6 hours, in order to promote sintering and improve the density of the sintered body.

[0057] In the heating step, a dimensional change adjusting member can be used. Examples of the dimensional change adjusting member include a dimensional change adjusting member A used to place the molded body thereon and a dimensional change adjusting member B used to cover the molded body. Preferred embodiments include heating the molded body while it is placed on the dimensional change adjusting member A; heating the molded body while it is covered with the dimensional change adjusting member B; and heating the molded body while it is placed on the dimensional change adjusting member A and covered with the dimensional change adjusting member B.

[0058] The dimensional change rate adjusting member is a member for adjusting the dimensional change rate of the compact, and by using dimensional change rate adjusting member A, dimensional change rate adjusting member B, or both, it is possible to suppress the dimensional change between the compact and the sintered body. In this specification, the term "dimensional change" is a concept that includes both a case where the dimensions of the sintered body become larger than those of the compact (expansion) and a case where the dimensions of the sintered body become smaller than those of the compact (contraction). The dimensional change rate can be expressed, for example, by [(dimension of compact - dimension of sintered body) / dimension of compact] x 100 (%).

[0059] When dimensional change rate adjusting member A is used, the dimensional change rate of the molded body when sintered is adjusted by the dimensional change rate adjusting member A on which the molded body is placed. The dimensional change rate can be adjusted simply by placing the molded body on the dimensional change rate adjusting member A. When dimensional change rate adjusting member B is used, the dimensional change rate of the molded body when sintered is adjusted by the dimensional change rate adjusting member B covering the molded body. The dimensional change rate can be adjusted simply by covering the molded body with the dimensional change rate adjusting member B. For these reasons, even if the dimensional change rate of the molded body varies depending on the location, a metal product with excellent dimensional accuracy can be obtained. Compared to adjusting the dimensions by polishing, cutting, etc. after sintering, a metal product with excellent dimensional accuracy can be obtained by a simpler method.

[0060] The method for adjusting the dimensional change rate of a molded article using the dimensional change rate adjusting member A is not particularly limited. For example, the dimensional change rate may be adjusted by adjusting the surface roughness of the region where the dimensional change rate adjusting member A contacts the molded article. The method for adjusting the surface roughness of the dimensional change rate adjusting member A is not particularly limited. For example, the surface roughness may be adjusted by methods such as forming scratches, protrusions, or the like on the surface of the dimensional change rate adjusting member A, or roughening the surface by etching. Alternatively, an object with an uneven surface, such as a mesh or porous material, may be used as the dimensional change rate adjusting member A.

[0061] The shape of the dimensional change rate adjusting member A may be, for example, plate-like, rectangular parallelepiped-like, cylindrical, etc., and is preferably plate-like. The material of the dimensional change rate adjusting member A is not particularly limited as long as it is heat-resistant to the heat treatment temperature. Examples include ceramics such as alumina, silica, zirconia, earthenware, and porcelain, metal, stone, and carbon. Among these, it is preferable that the dimensional change rate adjusting member A contains ceramics, and from the viewpoint of ease of handling of the material, it is more preferable that it contains alumina.

[0062] The method for quantifying the surface roughness of the dimensional change rate adjusting member A is not particularly limited. For example, it may be quantified by the arithmetic mean height (Ra) of the roughness curve defined in JIS B0601:2013. The range of Ra is not particularly limited, but is selected taking into consideration, for example, the components and size of the molded body. For example, it may be 0.1 to 5.0 μm, 0.2 to 3.0 μm, or 0.3 to 1.0 μm.

[0063] The shape of the dimensional change rate adjusting member B may be, for example, a container, a box, or the like, and the outer shape of these may be a rectangular parallelepiped, a cube, a cylinder, a hemisphere, or the like. The material of the dimensional change rate adjusting member B is not particularly limited as long as it is heat resistant to the heat treatment temperature. Examples include ceramics such as alumina, silica, zirconia, earthenware, and porcelain, metal, stone, and carbon. Among these, the dimensional change rate adjusting member B preferably contains ceramics, carbon, or both, and more preferably contains carbon from the viewpoint of ease of handling. For example, the dimensional change rate adjusting member B includes a bottomless box body and a box lid. The box body may be made of alumina, and the lid may be made of carbon.

[0064] The dimensional change rate of the molded body can be adjusted by covering the molded body with the dimensional change rate adjusting member B. For example, a box-shaped dimensional change rate adjusting member B may be placed over the molded body. The box is preferably sized so that the inner surface of the box does not come into contact with the molded body. When a box body without a bottom and a box lid are used, the inner surfaces of the box and lid are preferably sized so that they do not come into contact with the molded body.

[0065] [Optional Steps] The method for producing a soft magnetic sintered member may further include optional steps such as cooling the high-temperature sintered body (cooling step) and forming a plating layer on at least a portion of the surface of the sintered body (plating step).

[0066] In the plating step, the method for forming the plating layer is not particularly limited, and may be either electrolytic plating or electroless plating. The type of metal used to form the plating layer is not particularly limited, and examples thereof include copper, nickel, gold, and chromium.

[0067] <Examples of Embodiments> Preferred examples of embodiments of the present invention are listed below. The embodiments of the present invention are not limited to the following examples. (1) A soft magnetic sintered member comprising a sintered body including a soft magnetic matrix containing 1.0 to 6.5 mass % Si and having a porosity of 7.9% or less. (2) The soft magnetic sintered member according to (1) above, in which the pores included in the soft magnetic matrix have a pore size of 7.0 μm or less. (3) The soft magnetic sintered member according to (1) or (2) above, in which the crystal grains included in the soft magnetic matrix have a grain size of 200 μm or less. (4) The soft magnetic sintered member according to any one of (1) to (3) above, in which the tensile strength is 400 MPa or more. (5) The soft magnetic sintered member according to any one of (1) to (4) above, wherein the soft magnetic matrix is ​​composed of 1.0 to 6.5 mass% of Si, Fe, and unavoidable impurities based on the mass of the soft magnetic matrix, or 1.0 to 6.5 mass% of Si, P, Fe, and unavoidable impurities based on the mass of the soft magnetic matrix. (6) The soft magnetic sintered member according to any one of (1) to (5) above, having a plating layer on at least a part of the surface of the sintered body. (7) A method for producing a soft magnetic sintered member, comprising: preparing a raw material powder containing soft magnetic powder having an average particle size of 10 μm or more and 150 μm or less and Si powder having an average particle size of 0.5 μm or more and less than 10 μm, wherein the Si powder content is 1.0 to 6.5 mass% based on the total mass of the soft magnetic powder and the Si powder, and at least a portion of the Si powder adheres to the surface of the soft magnetic powder; compacting the raw material powder to obtain a green body; and heating the green body in a mesh belt furnace or a pusher furnace to obtain a sintered body. (8) The method for producing a soft magnetic sintered member according to (7) above, wherein the Si powder has a shape including corners. (9) The method for producing a soft magnetic sintered member according to (7) or (8) above, wherein the soft magnetic powder is a powder consisting of Fe and unavoidable impurities, or an alloy powder or a mixed powder consisting of P, Fe, and unavoidable impurities. (10) The method for producing a soft magnetic sintered member according to any one of (7) to (9) above, further comprising forming a plating layer on at least a part of the surface of the sintered body. (11) The method for producing a soft magnetic sintered member according to any one of (7) to (10) above, wherein the sintered body has a porosity of 7.9% or less.(12) The method for producing a soft magnetic sintered member according to any one of (7) to (11) above, wherein the soft magnetic sintered member has a tensile strength of 400 MPa or more. (13) The method for producing a soft magnetic sintered member according to any one of (7) to (12) above, comprising heating the compacted body in a state where the compacted body is placed on a dimensional change rate adjusting member A. (14) The method for producing a soft magnetic sintered member according to any one of (7) to (13) above, comprising heating the compacted body in a state where the compacted body is covered with a dimensional change rate adjusting member B.

[0068] The embodiments of the present invention will be described in more detail with reference to examples, but the embodiments of the present invention are not limited to the following examples.

[0069] <Preparation of Raw Material Powders> A Si powder dispersion liquid was prepared by dispersing 2% by mass of the Si powder shown in Table 1 in a 0.25% by mass aqueous polyvinyl alcohol solution. The Si powder dispersion liquid was sprayed onto a soft magnetic powder while flowing, volatilizing the water, and drying to obtain raw material powders 1 to 4 containing soft magnetic powder to which the Si powder shown in Table 1 had adhered. The average particle sizes (D50) of the soft magnetic powder and Si powder were measured by laser diffraction. The soft magnetic powder used in raw material powders 1 to 4 was pure iron powder. The Si powder used in raw material powders 1 to 3 was a powder having a shape including acute angles on its outer shape, obtained by pulverizing Si powder having a particle size of 10 to 30 μm using a dry bead mill.

[0070]

[0071] <Preparation I of Sintered Body (Soft Magnetic Sintered Member)> Raw material powders 1 to 4 were used, and compacted into a test piece shape at a compacting pressure of 686 MPa to prepare a compacted body (φ30 mm × φ20 mm × t5 mm). Next, in Examples 1 to 5, the compacted body was sintered using a mesh belt furnace under conditions of a conveying speed of 40 mm / min, a heating temperature of 1,160°C, and an atmosphere containing ammonia decomposition gas, to obtain a sintered body. The heating times were as follows: Example 1: 60 minutes, Example 2: 120 minutes, Example 3: 30 minutes, and Examples 4 and 5: 60 minutes. In Comparative Example 1, the compacted body was sintered using a vacuum furnace ("VHSgr" manufactured by Shimadzu Corporation) at a heating temperature of 1,200°C, a heating time of 60 minutes, and a heating time of 10 minutes. －３The mixture was sintered under a reduced pressure gas atmosphere of Torr to obtain a sintered body.

[0072] <Formation of plating layer> Oil and foreign matter adhering to the obtained sintered body was removed with an alkaline solvent. Next, the sintered body was washed with 10% hydrochloric acid and washed with water. After that, oil and foreign matter adhering to the sintered body was removed by electrolytic degreasing and washed with water. After drying, the sintered body was immersed in a plating solution tank, and a plating layer was formed on the surface of the sintered body by electrolytic treatment. The sintered body with the plating layer formed was washed with water, dried, and then immersed in a chromate solution tank, and a chromate layer was formed on the surface of the plating layer. The sintered body was further washed with water and dried to obtain a sintered body with a plating layer formed on its surface.

[0073] <Porosity, etc. of sintered body (soft magnetic sintered member)> The sintered density, porosity, pore diameter, and crystal grain size were measured for the sintered bodies of Examples 1 to 5 and Comparative Example 1. The measurement methods are as follows. Sintered bodies without a plating layer formed on the surface were used for measuring the sintered density, porosity, pore diameter, and crystal grain size. The measurement results of sintered density and porosity are shown in Table 2.

[0074] (Sintered density) Measured by Archimedes' method. (Porosity, pore size, and crystal grain size) Measurements were made according to the above-mentioned measurement methods. One measurement area was used. For the sintered bodies of Examples 1 to 5, more than 50% of the pores contained in an arbitrarily selected measurement area had a pore size of 7.0 μm or less. For the sintered body of Comparative Example 1, more than 50% of the pores contained in an arbitrarily selected measurement area had a pore size of more than 7.0 μm. For the sintered bodies of Examples 1 to 5, more than 50% of the crystal grains contained in an arbitrarily selected measurement area had a grain size of 200 μm or less. For the sintered body of Comparative Example 1, more than 50% of the crystal grains contained in an arbitrarily selected measurement area had a grain size of more than 500 μm. Figure 2 shows cross-sectional photographs of the sintered bodies of Example 1 and Comparative Example 1.

[0075] <Evaluation of Sintered Bodies (Soft Magnetic Sintered Members)> The sintered bodies of Examples 1 to 5 and Comparative Example 1 were evaluated for DC magnetic flux density, strength (tensile strength), and the presence or absence of red rust. The evaluation methods are as follows. For the evaluation of DC magnetic flux density and strength (tensile strength), sintered bodies without a plated layer formed on the surface were used, and for the evaluation of the presence or absence of red rust, sintered bodies with a plated layer formed on the surface were used. The evaluation results are shown in Table 2.

[0076] (DC Magnetic Flux Density) The value at a magnetizing force of 2000 A / m was measured and evaluated using a DC BH analyzer manufactured by Riken Electronics Co., Ltd. The winding was performed using a winding machine (GORMAN MODEL 900A) with 100 turns on the primary side (φ0.5 mm) and 20 turns on the secondary side (φ0.27 mm). The test specimens were insulated before winding. Lumirror 50 (film thickness 50 μm) was used for the insulation treatment. (Strength (Tensile Strength)) Measured according to the tensile strength measurement method described above. (Red Rust Formation) The sintered compacts with the plating layer formed were left in a thermo-hygrostat (Espec Corporation's "PL-3K P") under atmospheric conditions of 60°C and 95% humidity, and the presence or absence of red rust after 72 hours was visually confirmed. Observation of red rust is considered to be due to plating solution blowout during the plating layer formation process.

[0077]

[0078] The sintered bodies of Examples 1 to 5 contained a soft magnetic matrix containing 1.0 to 6.5 mass % of Si and had a porosity of 7.9% or less, and therefore had good magnetic properties and high strength.

[0079] By using specific raw material powders and a mesh belt furnace to heat the compacts, it was possible to easily obtain the sintered bodies of Examples 1 to 5, which have a porosity of 7.9% or less, crystal grains of 500 μm or less, and tensile strengths of 400 MPa or more. Sintered bodies produced in the same manner as Examples 1 to 5, except that the heating method for the compacts was changed to the method of Comparative Example 1, had porosities exceeding 7.9%, crystal grain sizes exceeding 500 μm, and tensile strengths of less than 400 MPa.

[0080] <Preparation of Sintered Body (Soft Magnetic Sintered Member) II> In Example 6, a compact obtained by the same method as above using raw material powder 1 was placed on an alumina plate (Ra: 0.48 μm) and heated under the same conditions as in Example 1 to obtain a sintered body. The heating time was 60 minutes. In Example 7, the compact was placed on a mesh belt and heated with a lidded bottomless box placed on top, while in Example 8, the compact was placed on an alumina plate and heated with another lidded bottomless box placed on top. The box lid was made of carbon, and the box body was made of alumina.

[0081] <Porosity, etc. of Sintered Body (Soft Magnetic Sintered Member)> The sintered density, porosity, pore diameter, and crystal grain size were measured by the same methods as above for the sintered bodies of Examples 6 to 8. The measurement results of sintered density and porosity are shown in Table 3.

[0082] (Pore diameter and crystal grain diameter) In the sintered bodies of Examples 6 to 8, more than 50% of the pores contained in an arbitrarily selected measurement area had a pore diameter of 7.0 μm or less, and more than 50% of the crystal grains contained in an arbitrarily selected measurement area had a grain diameter of 200 μm or less.

[0083] <Evaluation of sintered bodies (soft magnetic sintered members)> The sintered bodies of Examples 6 to 8 were evaluated for DC magnetic flux density, strength (tensile strength), and the presence or absence of red rust by the same methods as above. The evaluation results for DC magnetic flux density and strength (tensile strength) are shown in Table 3. The evaluation result for red rust was "not present" for all of the sintered bodies of Examples 6 to 8.

[0084] <Evaluation of dimensional accuracy> A schematic plan view of the sintered body is shown in Figure 3. The length x1 of the lower surface of the sintered body in the direction of line X was measured, and the dimensional change rate X relative to the length x2 of the lower surface of the molded body in the direction of line X before sintering was calculated using the following formula: Dimensional change rate X (%) = {(x2 - x1) / x2} x 100

[0085] The length y1 of the lower surface of the sintered body in the direction of line Y was measured, and the dimensional change rate Y relative to the length y2 of the lower surface of the molded body before sintering in the direction of line Y was calculated using the following formula: Dimensional change rate Y (%) = {(y2 - y1) / y2} × 100

[0086] The length z1 of the lower surface of the sintered body in the direction of line Z was measured, and the dimensional change rate Z relative to the length z2 of the lower surface of the molded body before sintering in the direction of line Z was calculated using the following formula: Dimensional change rate Z (%) = {(z2 - z1) / z2} × 100

[0087] The arithmetic mean values ​​of the dimensional change rates X, Y, and Z were calculated and used as the dimensional change rates (%) for Examples 6 to 8. If the molded body shrinks due to sintering, the value of the dimensional change rate will be positive, and if the molded body expands due to sintering, the value of the dimensional change rate will be negative. The results are shown in Table 3.

[0088]

[0089] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2021-170314, filed on October 18, 2021, the entire disclosure of which is incorporated herein by reference.

[0090] 10 Sintered body 1 Through hole

Claims

1. A soft magnetic sintered member includes a sintered body having a soft magnetic matrix containing 1.0 to 6.5 mass % of Si and a porosity of 7.9% or less.

2. 2. The soft magnetic sintered member according to claim 1, wherein the pores contained in the soft magnetic matrix have a diameter of 7.0 μm or less.

3. 2. The soft magnetic sintered member according to claim 1, wherein the grain size of the crystal grains contained in the soft magnetic matrix is ​​500 [mu]m or less.

4. 4. The soft magnetic sintered member according to claim 1, wherein the soft magnetic sintered member has a tensile strength of 400 MPa or more.

5. The soft magnetic sintered member according to any one of claims 1 to 3, wherein the soft magnetic matrix is ​​composed of 1.0 to 6.5 mass% of Si, Fe, and unavoidable impurities based on the mass of the soft magnetic matrix, or 1.0 to 6.5 mass% of Si, P, Fe, and unavoidable impurities based on the mass of the soft magnetic matrix.

6. The soft magnetic sintered member according to any one of claims 1 to 3, wherein the sintered body has a plating layer on at least a portion of a surface thereof.

7. A raw material powder is prepared, the raw material powder containing soft magnetic powder having an average particle size of 10 μm or more and 150 μm or less and Si powder having an average particle size of 0.5 μm or more and less than 10 μm, the content of the Si powder being 1.0 to 6.5 mass% based on the total mass of the soft magnetic powder and the Si powder, and at least a part of the Si powder adhering to the surface of the soft magnetic powder. compacting the raw material powder to obtain a compact; heating the compact using a mesh belt furnace or a pusher furnace to obtain a sintered body; A method for producing a soft magnetic sintered member, comprising:

8. The method for producing a soft magnetic sintered member according to claim 7 , wherein the Si powder has a shape including corners.

9. 8. The method for producing a soft magnetic sintered member according to claim 7, wherein the soft magnetic powder is a powder containing Fe and unavoidable impurities, or an alloy powder or a mixed powder containing P, Fe, and unavoidable impurities.

10. The method for producing a soft magnetic sintered member according to any one of claims 7 to 9, further comprising forming a plating layer on at least a part of a surface of the sintered body.

11. The method for producing a soft magnetic sintered member according to any one of claims 7 to 9, wherein the sintered body has a porosity of 7.9% or less.

12. The method for producing a soft magnetic sintered member according to any one of claims 7 to 9, wherein the soft magnetic sintered member has a tensile strength of 400 MPa or more.

13. The method for producing a soft magnetic sintered member according to any one of claims 7 to 9, comprising heating the compact in a state where the compact is placed on a dimensional change rate adjusting member (A).

14. The method for producing a soft magnetic sintered member according to any one of claims 7 to 9, comprising heating the compact in a state where the compact is covered with a dimensional change rate adjusting member (B).