METHOD FOR PRODUCE AN IRON CORE AND RAW MATERIAL POWDER FOR AN IRON CORE

Abstract

Methods for producing an iron core, comprising: a step for the preparation of a raw material powder comprising a coated pure iron powder formed from a variety of pure iron particles, each having an insulating coating layer, a coated iron alloy powder formed from a variety of iron alloy particles, each having an insulating coating layer, and a metal soap; a step towards the production of a molded part by compression molding of the raw material powder filled into a mold; and a step to carry out a heat treatment of the molded part in order to eliminate deformations in the coated pure iron powder and in the coated iron alloy powder, wherein a difference Tm-Td between a melting point Tm of the metal soap and a temperature Td of the mold in the step to produce the molded part is greater than or equal to 90 °C, the temperature Td of the mold is equal to the temperature of a raw material powder contact section of the mold immediately before the raw material powder is poured in, a proportion of metal soap in the raw material powder is greater than or equal to 0.02% by mass and less than or equal to 0.80% by mass, Each of the iron alloy particles contains at least one additional element, selected from Si and Al, the insulating coating layer contains a phosphoric acid compound which contains a phosphate salt as its main component, the metal soap contains at least one substance selected from the group consisting of lithium stearate, barium stearate, sodium stearate, zinc stearate and aluminium stearate, a forming pressure of the compression molding process is greater than or equal to 500 MPa and less than or equal to 3000 MPa, the temperature Td of the mold is higher than or equal to 60 °C and lower than or equal to 130 °C and The step involves carrying out a heat treatment of the molded part in an atmosphere with an oxygen concentration greater than 0 volume ppm and less than or equal to 10,000 volume ppm at a temperature greater than or equal to 400 °C and less than or equal to 1,000 °C and with a residence time greater than or equal to 10 minutes and less than or equal to 60 minutes.

Description

Technical field

[0001] The present invention relates to a method for producing an iron core and a raw material powder for an iron core. State of the art

[0002] A method for producing an iron core that can be used in various electromagnetic components is known and is disclosed in patent literature 1. The method for producing an iron core disclosed in patent literature 1 comprises, for example, a manufacturing step, a coating step, a mixing step, a pressurization step, and a heat treatment step, as explained below.

[0003] In the manufacturing step, soft magnetic particles are produced.

[0004] In the coating step, each of the surfaces of the soft magnetic particles is coated with an insulating layer.

[0005] In the mixing step, a coated soft magnetic powder, consisting of a multitude of soft magnetic particles, each coated with the insulating layer, is mixed with a resin powder for molding (as a lubricant) to form a mixed powder.

[0006] In the pressurization step, the mixed powder is pressurized in a molding tool to produce a molded part.

[0007] In the heat treatment step, the molded part undergoes heat treatment to eliminate deformations that occur in the soft magnetic particles during the pressurization step. Citation list of patent literature

[0008] PTL1: Japanese Disclosure Document No. JP 2012-107330A

[0009] Document JP 2005-303 006 A describes a manufacturing process for a powder composite core. First, a mixed powder is produced from coated iron particles with a saturation flux density of at least 1.5 T and further coated iron particles containing additional elements such as Al, Si, Cr, Ni, or Co. This powder is then pressed into a green compact and heat-treated at 500–900 °C.

[0010] Document US 2010 / 0188179A1 concerns an iron-based soft magnetic powder with a multilayer coating consisting of an Fe / Co layer, a phosphoric acid-based conversion layer, and a silicone resin layer. Alternatively, a two-layer insulation is provided (phosphate and silicone resin, each 100–280 nm thick) with particle sizes of 45–180 µm. A powder composite core is produced from this powder by pressing.

[0011] Document JP 2011-029 302 A discloses a powder composite core produced by compression molding a mixture of soft magnetic powder and at least 0.1 wt% of an insulating powder lubricant. The pressing process is carried out at a maximum pressure of 800 MPa, achieving a volume filling of at least 93%. The core has a resistivity of at least 10,000 µD·cm; metal salts of fatty acids, such as barium or lithium stearate, serve as lubricants.

[0012] Document WO 2016 / 158336A1 concerns a process for the heat treatment of a pressed body made of coated soft magnetic particles. After forming with an auxiliary material, a two-stage heat treatment is carried out: First, heating takes place in the decomposition range of the auxiliary material, followed by heating at a higher temperature to stress-relieve the particles. Summary of the invention

[0013] The method for producing an iron core according to the present invention comprises: a step to produce a raw material powder comprising a coated pure iron powder formed from a plurality of pure iron particles, each having an insulating coating layer, a coated iron alloy powder formed from a plurality of iron alloy particles, each having an insulating coating layer, and a metal soap; a step towards the production of a molded part by pressing the raw material powder filled into a mold; and a step towards carrying out a heat treatment of the molded part to eliminate deformations in the coated pure iron powder and in the coated iron alloy powder, where the difference Tm-Td between a melting point Tm of the metal soap and a temperature Td of the mold in the step to produce the molded part is greater than or equal to 90 °C, the temperature Td of the mold is equal to the temperature of a raw material powder contact section of the mold immediately before the raw material powder is poured in, a proportion of metal soap in the raw material powder is greater than or equal to 0.02% by mass and less than or equal to 0.80% by mass, Each of the iron alloy particles contains at least one additional element, selected from Si and Al, the insulating coating layer contains a phosphoric acid compound which contains a phosphate salt as its main component, the metal soap contains at least one substance selected from the group consisting of lithium stearate, barium stearate, sodium stearate, zinc stearate and aluminium stearate, a forming pressure of the compression molding process is greater than or equal to 500 MPa and less than or equal to 3000 MPa, the temperature Td of the mold is higher than or equal to 60 °C and lower than or equal to 130 °C and The step involves carrying out a heat treatment of the molded part in an atmosphere with an oxygen concentration greater than 0 volume ppm and less than or equal to 10,000 volume ppm at a temperature greater than or equal to 400 °C and less than or equal to 1,000 °C and with a residence time greater than or equal to 10 minutes and less than or equal to 60 minutes.

[0014] The raw material powder for an iron core according to the present invention comprises: a coated pure iron powder formed from a multitude of pure iron particles, each having an insulating coating layer; a coated iron alloy powder formed from a multitude of iron alloy particles, each having an insulating coating layer; and a metal soap that has a melting point Tm of at least 200 °C, where the Vickers hardness of the iron alloy particles is greater than or equal to 200 HV and less than or equal to 1000 HV, a content of the coated iron alloy powder greater than or equal to 15 wt% and less than or equal to 40 wt%, and a metal soap content greater than or equal to 0.02 mass % and less than or equal to 0.80 mass % Each of the iron alloy particles contains at least one additional element, selected from Si and Al, the insulating coating layer contains a phosphoric acid compound which contains a phosphate salt as its main component, the metal soap contains at least one substance selected from the group consisting of lithium stearate, barium stearate, sodium stearate, zinc stearate and aluminium stearate, the coated pure iron powder and / or the coated iron alloy powder has a double-layer structure consisting of both the insulating coating layer and an insulating outer layer formed on an outer circumference of the insulating coating layer, and the insulating outer layer contains a silica compound containing Si and O as its main components. Detailed description [The problem to be solved by the present invention]

[0015] There is a need to further reduce the core loss of an iron core. In particular, there is a need to reduce the core loss (iron loss) of an iron core by reducing the eddy current loss of the iron core.

[0016] Under these circumstances, it is a challenge to provide an iron core manufacturing process that makes it possible to produce an iron core with low core loss.

[0017] Another task is to provide a raw material powder for an iron core with which it is possible to form an iron core with low iron loss. [Advantageous effect of the present invention]

[0018] The previously mentioned iron core manufacturing process enables the production of an iron core with low core loss.

[0019] The previously mentioned raw material powder for an iron core enables the formation of an iron core with low core loss. [Description of the embodiments of the present invention]

[0020] Depending on the intended use of the iron core and the properties required for it, either pure iron particles or iron alloy particles are generally used as soft magnetic particles for an iron core. Pure iron particles are more easily deformable and denser compared to an iron alloy. In contrast, iron alloy particles exhibit lower magnetic coercivity, higher specific electrical resistivity, and lower eddy current loss compared to pure iron. The present inventors have considered producing an iron core that exhibits the properties of both pure iron particles and iron alloy particles by combining the two.The inventors then investigated the production of an iron core with high density, low magnetic coercivity, and low eddy current loss (iron loss). However, it was found that the eddy current loss of the iron core was frequently elevated. The following factors can be considered as causes for this phenomenon. Pure iron particles are softer and therefore deform more easily compared to an iron alloy powder. Consequently, the pure iron particles are severely deformed by the iron alloy particles during compression molding. Due to this excessive deformation of the pure iron particles, the insulating layers covering their surfaces are damaged, thus reducing the insulation between the particles.Under these circumstances, the present inventors have conducted extensive studies on a manufacturing process that makes it possible to reduce eddy current loss (iron loss), even when both pure iron particles and iron alloy particles are present. As a result, it was found that eddy current loss, and thus iron loss, can be reduced if the melting point Tm of a metal soap used as a lubricant and the temperature Td of a mold used in compression molding satisfy a certain relationship. The present invention is based on this finding. First, embodiments of the present invention are described. (1) The method for producing an iron core according to an embodiment of the present invention comprises: a step to produce a raw material powder comprising a coated pure iron powder formed from a variety of pure iron particles, each having an insulating coating layer, a coated iron alloy powder formed from a variety of iron alloy particles, each having an insulating coating layer, and a metal soap; a step towards the production of a molded part by pressing the raw material powder filled into a mold; and a step towards carrying out a heat treatment of the molded part to eliminate deformations in the coated pure iron powder and in the coated iron alloy powder, where the difference Tm-Td between a melting point Tm of the metal soap and a temperature Td of the mold in the step to produce the molded part is greater than or equal to 90 °C.

[0021] According to the previously mentioned configuration, it is possible to produce an iron core with low core loss. This is thought to be due to the fact that damage to the insulating coating layer in the coated pure iron powder can be prevented during the forming step. This increases the insulation between the particles, thereby reducing eddy current loss and thus promoting the reduction of iron loss.

[0022] The following reasons can be considered as reasons why damage to the insulating coating layers in coated pure iron powder can be prevented. By setting the temperature difference Tm-Td to greater than or equal to 90 °C, the raw material powder can be subjected to compression molding, preventing the melting of the metal soap during the molding process. In other words, the raw material powder can be compression molded under conditions that allow the metal soap to maintain a certain degree of hardness. The action of the metal soap makes it easier to reduce the stress exerted by the iron alloy particles on the pure iron particles, while simultaneously increasing lubricity during compression molding.This prevents damage to the insulating coating layers in the coated pure iron powder, even if the iron alloy particles deform the pure iron particles during compression molding.

[0023] The proportion of metal soap in the raw material powder is greater than or equal to 0.02% by mass and less than or equal to 0.80% by mass.

[0024] If the metal soap content is greater than or equal to 0.02 wt%, it is easy to achieve a satisfactory improvement in lubricity. This can significantly reduce the stress acting on the pure iron particles. Consequently, damage to the insulating coating layers in the coated pure iron powder can be prevented. If the metal soap content is less than or equal to 0.80 wt%, it is not too high. This prevents a decrease in the proportion of the metal component in the molded part.

[0025] Each of the iron alloy particles contains at least one additional element, selected from Si and Al.

[0026] According to the previously mentioned configuration, it is easy to produce an iron core with low core loss. This is because the iron alloy particles containing the additional element have a high electrical resistance, which reduces eddy current loss. This is also due to the low hysteresis loss of the iron alloy particles.

[0027] The step of performing heat treatment of the molded part is carried out in an atmosphere with an oxygen concentration greater than 0 volume ppm and less than or equal to 10,000 volume ppm at a temperature greater than or equal to 400 °C and less than or equal to 1,000 °C and with a residence time of more than or equal to 10 minutes and less than or equal to 60 minutes.

[0028] According to the aforementioned configuration, it becomes possible to satisfactorily eliminate deformations in the coated pure iron powder and the iron alloy powder. Consequently, the hysteresis loss can be reduced. Therefore, it becomes easy to produce an iron core with low iron loss.

[0029] Furthermore, the insulating coating layer contains a phosphoric acid compound with a phosphate salt as its main component. The metal soap contains at least one substance selected from the group consisting of lithium stearate, barium stearate, sodium stearate, zinc stearate, and aluminum stearate. The mold pressure is greater than or equal to 500 MPa and less than or equal to 3000 MPa, and the mold temperature Td is greater than or equal to 60 °C and less than or equal to 130 °C.

[0030] (2) According to one embodiment of the method for producing an iron core, the melting point Tm of the metal soap is greater than or equal to 200 °C and less than or equal to 252 °C.

[0031] According to the aforementioned configuration, damage to the insulating coating layers in the coated pure iron powder is prevented. Furthermore, the density of the molded part can be increased. Consequently, the density of the iron core can be increased. Since the melting point Tm of the metal soap is high, the temperature difference Td between the melting point and the mold temperature can be increased. Thus, it is possible to impart a certain hardness to the metal soap during compression molding. This enhances the effectiveness in preventing damage to the insulating coating layers in the coated pure iron powder. In addition, due to the high melting point Tm of the metal soap, the raw material powder can be compression molded at a higher mold temperature Td. This facilitates the deformation of the coated pure iron powder and the iron alloy powder. Consequently, it is possible to increase the density of the molded part.

[0032] (3) According to one embodiment of the method for producing an iron core, the Vickers hardness of the iron alloy particles is greater than or equal to 200 HV and less than or equal to 1000 HV.

[0033] According to the aforementioned configuration, damage to the insulating coating layers in the coated pure iron powder can be prevented. Damage to the insulating coating layers in the coated pure iron powder occurs more readily with an increase in the Vickers hardness of the iron alloy particles. However, if the temperature difference (Tm-Td) between the melting point Tm of the metal soap and the temperature Td of the mold falls within the previously mentioned range, damage to the insulating coating layers in the coated pure iron powder can be prevented even at high Vickers hardness.

[0034] (4) According to one embodiment of the method for producing an iron core, the Vickers hardness of the iron alloy particles is greater than or equal to 200 HV and less than or equal to 1000 HV, the melting point Tm of the metal soap is greater than or equal to 200 °C and less than or equal to 252 °C, and the temperature Td of the mold is greater than or equal to 60 °C and less than or equal to 130 °C.

[0035] According to the aforementioned configuration, damage to the insulating coating layers in the coated pure iron powder can be prevented. Furthermore, the density of the iron core can also be increased.

[0036] (5) According to one embodiment of the process for producing an iron core, the content of the coated iron alloy powder in the raw material powder is greater than or equal to 15 wt% and less than or equal to 40 wt%.

[0037] If the coated iron alloy powder content is greater than or equal to 15 wt%, the proportion of the iron alloy component in the molded part can be increased. The specific electrical resistivity of an iron alloy is high. Therefore, a reduction in eddy current losses is possible. Increasing the proportion of the iron alloy component also reduces the magnetic coercivity of the iron core. If the coated iron alloy powder content is less than or equal to 40 wt%, the proportion of the iron alloy component in the molded part is not too high. This prevents excessive deformation of the coated pure iron powder, which is normally prone to deformation. Consequently, damage to the insulating coating layers in the coated pure iron powder can be prevented. Furthermore, the proportion of the pure iron component, which is normally prone to deformation, can be increased. Consequently, the density of the molded part can be increased.Consequently, the density of the iron core can be increased.

[0038] (6) According to one embodiment of the method for producing an iron core, the thickness of both the insulating coating layer in the coated pure iron powder and the insulating coating layer in the coated iron alloy powder is greater than or equal to 30 nm and less than or equal to 300 nm.

[0039] If the thickness of both insulating coating layers is greater than or equal to 30 nm, it is possible to improve the insulation between the particles. If the thickness of each insulating coating layer is less than or equal to 120 nm, it becomes easy to produce a high-density iron core. °C °C

[0040] (7) A raw material powder for an iron core according to one embodiment of the present invention comprises: a coated pure iron powder formed from a multitude of pure iron particles, each having an insulating coating layer; a coated iron alloy powder formed from a multitude of iron alloy particles, each having an insulating coating layer; and a metal soap that has a melting point Tm of at least 200 °C, where the Vickers hardness of the iron alloy particles is greater than or equal to 200 HV and less than or equal to 1000 HV, a content of the coated iron alloy powder greater than or equal to 15 wt% and less than or equal to 40 wt%, and a metal soap content greater than or equal to 0.02 mass-% and less than or equal to 0.80 mass-%, Each of the iron alloy particles contains at least one additional element, selected from Si and Al, the insulating coating layer contains a phosphoric acid compound which contains a phosphate salt as its main component, the metal soap contains at least one substance selected from the group consisting of lithium stearate, barium stearate, sodium stearate, zinc stearate and aluminium stearate, the coated pure iron powder and / or the coated iron alloy powder has a double-layer structure consisting of both the insulating coating layer and an insulating outer layer formed on an outer circumference of the insulating coating layer, and the insulating outer layer contains a silica compound containing Si and O as its main components.

[0041] According to the previously mentioned configuration, it becomes possible to produce an iron core with low core loss. [Detailed description of the embodiment of the present invention]

[0042] The following describes the details of the method for producing an iron core according to the embodiment of the present invention. [Method for producing the iron core]

[0043] The method for manufacturing an iron core according to the embodiment comprises: a step for manufacturing a raw material powder (that is, a raw material powder for an iron core) (hereinafter also referred to as a "raw material manufacturing step"); a step for manufacturing a shaped part (hereinafter also referred to as a "shaping step"); and a step for performing a heat treatment of the shaped part (hereinafter also referred to as a "heat treatment step"). In the manufacturing step, a raw material powder is manufactured, comprising a coated pure iron powder, a coated iron alloy powder, and a metal soap. In the shaping step, the raw material powder, which is filled into a mold, is subjected to compression forming to manufacture a shaped part.In the heat treatment step, the deformations that occur in the coated pure iron powder and the iron alloy powder that form the molded part are eliminated. A characteristic feature of the process for manufacturing an iron core is that the difference (Tm-Td) between the melting point Tm of the metal paste and the temperature Td of the mold during the forming step falls within a specific range. That is, the type of metal paste is selected and the temperature Td of the mold is set so that this specific range is met. The details of the steps are described sequentially below. [Manufacturing step]

[0044] In the manufacturing step, a raw material powder is produced that includes a coated pure iron powder, a coated iron alloy powder, and a metal soap. [Raw material powder]<Beschichtetes reines Eisenpulver, beschichtetes Eisenlegierungspulver>

[0045] The coated pure iron powder contains: a multitude of pure iron particles (that is, a pure iron powder) consisting of pure iron (purity: greater than or equal to 99% by mass; the remainder being unavoidable impurities); and insulating coating layers, each covering the outer surfaces of the pure iron particles. The coated pure iron powder consists of a multitude of pure iron particles, each having an insulating coating layer. The coated iron alloy powder contains: a multitude of iron alloy particles (that is, an iron alloy powder) consisting of an iron alloy; and insulating coating layers, each covering the outer surfaces of the iron alloy particles. The coated iron alloy powder consists of a multitude of iron alloy particles, each having an insulating coating layer.The phrase "composed of pure iron particles" means that "no components other than pure iron particles are included." The phrase "composed of iron alloy particles" means that "no component other than iron alloy particles is included." The production of coated pure iron powder and coated iron alloy powder is carried out, for example, by producing a large number of pure iron particles and a large number of iron alloy particles, and subsequently forming an insulating coating layer on each of the outer circumferences of the pure iron particles and each of the outer circumferences of the iron alloy particles. • Pure iron particles

[0046] The pure iron particles in the coated pure iron powder are composed of pure iron (purity: greater than or equal to 99% by mass; the remainder consisting of unavoidable impurities). Therefore, compared to iron alloy particles, the pure iron particles are softer and can be deformed more easily. •• Average particle diameter

[0047] The mean diameter of the pure iron particles is preferably greater than or equal to 50 µm and less than or equal to 400 µm. If the mean diameter of the pure iron particles is greater than or equal to 50 µm, it becomes easier to produce a high-density iron core. If the mean diameter of the pure iron particles is less than or equal to 400 µm, the eddy current loss of the pure iron particles themselves is more likely to be reduced. Thus, it becomes easier to produce an iron core with low core loss. The mean diameter of the pure iron particles is even more preferably greater than or equal to 50 µm and less than or equal to 250 µm, and particularly preferably greater than or equal to 50 µm and less than or equal to 200 µm.The mean particle diameter refers to a particle diameter (D50) at which the cumulative volume in a bulk particle size distribution, as measured with a laser diffraction particle size distribution instrument, is 50%. This also applies to the mean particle diameter of the iron alloy particles mentioned below. • Iron alloy particles

[0048] The iron alloy particles in the coated iron alloy powder contain an additional element, and therefore have a lower purity compared to pure iron. Consequently, the iron alloy particles are harder and less deformable than pure iron particles. The iron alloy particles can have a single-component chemical composition or a multi-component chemical composition. This means that all iron alloy particles can have the same chemical composition, or they can contain iron alloy particles with different chemical compositions. •• Chemical composition

[0049] The additional element in the iron alloy is preferably at least one element selected from Si (silicon) and Al (aluminum). The iron alloy containing the additional element exhibits high electrical resistance, and thus its eddy current loss is more likely to be reduced. Consequently, the iron alloy exhibits low hysteresis loss. This makes it easier to produce an iron core with low core loss. The proportion of the additional element is, for example, more than or equal to 1.0 wt% and less than or equal to 30.0 wt%. The remainder of the iron alloy consists of Fe and unavoidable impurities.

[0050] Examples of the iron alloy include an Fe-Si-Al-based alloy, an Fe-Si-based alloy, and an Fe-Al-based alloy. In the Fe-Si-Al-based alloy, for example, the Si content is more than or equal to 1.0 wt% and less than or equal to 15.0 wt%, more preferably more than or equal to 3.0 wt% and less than or equal to 12.0 wt%, and the Al content is, for example, more than or equal to 1.0 wt% and less than or equal to 10.0 wt%, more preferably more than or equal to 2.0 wt% and less than or equal to 8.0 wt%. In the Fe-Si-based alloy, for example, the Si content is more than or equal to 1.0 wt% and less than or equal to 18.0 wt%, more preferably more than or equal to 2.0 wt% and less than or equal to 10.0 wt%.In the Fe-Al-based alloy, the Al content is, for example, more than or equal to 1.0 wt% and less than or equal to 20.0 wt%, or more preferably more than or equal to 2.0 wt% and less than or equal to 15.0 wt%. The chemical composition of the iron alloy can be analyzed by energy-dispersive X-ray spectroscopy (EDX) using a TEM. •• Vickers hardness

[0051] The Vickers hardness of the iron alloy particles can be greater than or equal to 200 HV. When the Vickers hardness of the iron alloy particles is greater than or equal to 200 HV, it becomes easier to prevent damage to the insulating coating layers in the coated pure iron powder. The iron alloy particles are harder than the pure iron particles. The pure iron particles deform more easily than the iron alloy particles. Thus, during the forming step, the pure iron particles are deformed by the iron alloy particles. Excessive deformation of the coated pure iron powder during the forming step can occur more easily with increasing Vickers hardness of the iron alloy particles. If the deformation of the coated pure iron powder is too great, the insulating coating layers in the coated pure iron powder can be damaged.However, if, as described in detail below, the requirement is met that the temperature difference (Tm-Td) between the melting point Tm of the metal soap contained in the raw material powder and the temperature Td of the mold during the forming step lies within a certain range, damage to the insulating coating layers in the coated pure iron powder can be prevented even when iron alloy particles with a high Vickers hardness are used. The Vickers hardness of the iron alloy particles is preferably greater than or equal to 250 HV, and particularly preferably greater than or equal to 300 HV. The upper limit of the Vickers hardness of the iron alloy particles is, for example, less than or equal to 1,000 HV.Vickers hardness is a value determined by embedding iron alloy powder in a resin, subsequently grinding the resin to expose the iron alloy particles in the resin, measuring the hardness of the exposed iron alloy particles, and then averaging the measured values ​​(n = 10). •• Average particle diameter

[0052] Like the average particle diameter of the pure iron particles, the mean particle diameter of the iron alloy particles is preferably greater than or equal to 50 µm and less than or equal to 400 µm, more preferably greater than or equal to 50 µm and less than or equal to 250 µm, and particularly preferably greater than or equal to 50 µm and less than or equal to 200 µm. The mean particle diameter of the pure iron particles and the mean particle diameter of the iron alloy particles may be the same or different, as long as the aforementioned range is satisfied. In the case where the mean particle diameters of the two particles differ, the relationship between the mean particle diameters may be "(pure iron particles) < (iron alloy particles)" or "(pure iron particles) > (iron alloy particles)".If the relationship between these mean particle diameters is "(pure iron particles) < (iron alloy particles)" and the relationship between the proportions is "(pure iron particles) > (iron alloy particles)", it becomes easier to increase the density of the molded part. This is because, if the pure iron particles, which have a higher proportion and are more easily deformable, are smaller, and the iron alloy particles, which can deform the pure iron particles, are larger, it becomes possible to arrange the pure iron particles sufficiently among the iron alloy particles, thus enabling the pure iron particles to be sufficiently deformed by the iron alloy particles.Conversely, if the relationship between these mean particle diameters is "(pure iron particles) > (iron alloy particles)" and the relationship between the proportions is "(pure iron particles) > (iron alloy particles)", it becomes easier to reduce eddy current losses. This is because if the pure iron particles, which are more abundant and more easily deformed, are larger, and the iron alloy particles, which can deform the pure iron particles, are smaller, it becomes possible to prevent excessive deformation of the pure iron particles.

[0053] The production of pure iron particles and iron alloy particles can be carried out by producing these particles through an atomization process, such as a gas atomization process and a water atomization process, or by purchasing commercially available pure iron powder and commercially available iron alloy powder. • Insulating coating layer

[0054] Each insulating coating layer in the coated pure iron powder and the coated iron alloy powder can increase the insulation between the pure iron particles, the insulation between the iron alloy particles, and the insulation between the pure iron particles and the iron alloy particles. Each insulating coating layer is formed directly on the surface of both the pure iron particles and the iron alloy particles. The materials for the insulating coating layers of the coated pure iron powder and the insulating coating materials of the coated iron alloy powder can be the same or different. •• Material

[0055] An example of the material for the insulating coating layer is a phosphoric acid compound containing a phosphate salt as its main component. A specific example of the phosphate salt is iron phosphate. The chemical composition of the insulating coating layer preferably has, for example, a phosphorus content of more than or equal to 10 atomic percent and less than or equal to 15 atomic percent, an iron content of more than or equal to 15 atomic percent and less than or equal to 20 atomic percent, and a remainder consisting of oxygen and unavoidable impurities. By using an insulating coating layer that meets the aforementioned chemical composition, it becomes easy to produce an iron core with low core loss. The iron content in the insulating coating layer may preferably be greater than or equal to 16 atomic percent and less than or equal to 19 atomic percent, and particularly preferably greater than or equal to 17 atomic percent and less than or equal to 19 atomic percent.The chemical composition of the insulating coating layer can be analyzed using EDX with a TEM. •• Thickness

[0056] The thickness of the insulating coating layer is preferably greater than or equal to 30 nm and less than or equal to 300 nm. If the thickness of the insulating coating layer is greater than or equal to 30 nm, it is easier to increase the insulation between the particles. If the thickness of the insulating coating layer is less than or equal to 300 nm, it is easier to produce an iron core with a high density. The density of the insulating coating layer is preferably greater than or equal to 40 nm and less than or equal to 250 nm, and particularly preferably greater than or equal to 50 nm and less than or equal to 200 nm. The thickness of the insulating coating layer can be measured as follows: The coated pure iron powder and the coated iron alloy powder are embedded in a resin.A cross-section of both the coated pure iron powder and the coated iron alloy powder within the insulating coating layer of the resulting embedded product is examined using TEM. The observed image is analyzed. Alternatively, the thickness of the insulating coating layer can also be measured as follows: The raw material powder is formed under the forming conditions described below. A cross-section of an iron core, which is heat-treated under the heat treatment conditions described below, is examined using TEM. The observed image is analyzed.This is because the thicknesses of the insulating coating layer in the coated pure iron powder in a powdered form and the insulating coating layer in the coated iron alloy powder in a powdered form are essentially the same before compression molding as the thicknesses of the insulating coating layer in the coated pure iron powder and the insulating coating layer in the coated iron alloy powder in the iron core after compression molding. In each of these methods, the number of observation fields is greater than or equal to 20, and the magnification is greater than or equal to 50,000 and less than or equal to 300,000. The mean thickness across the entire observation field is determined from the mean thicknesses in the observed fields. The mean thickness of the entire observation field is defined as the thickness of the insulating coating layer.In cases where there are some parts where the insulating coating layer is missing (or peeling off), the thicknesses of the parts are excluded from the measuring range. • Outer insulating layer

[0057] In coated pure iron powder and coated iron alloy powder, an outer insulating layer can be formed around the perimeter of the insulating coating layer. The material of the outer insulating layer for coated pure iron powder and the material of the outer coating layer for coated iron alloy powder can be the same or different. It is possible to form a single-layer structure consisting only of the insulating coating layer in coated pure iron powder and coated iron alloy powder, and a multi-layer (two-layer) structure consisting of both the insulating coating layer and the outer insulating layer in the other.It is also possible to form a multi-layered (two-layered) structure, consisting of both an insulating coating layer and an outer insulating layer, in both the coated pure iron powder and the coated iron alloy powder. •• Material

[0058] The material for the outer insulating layer is preferably a silica compound containing silicon (Si) and oxygen (O) as its main constituents. Using a silica compound for the outer insulating layer can facilitate the reduction of core loss from the iron core. Examples of silica compounds include potassium silicate (K₂SiO₃), sodium silicate (Na₂SiO₃, also known as liquid glass or soda ash), lithium silicate (Li₂SiO₂), and magnesium silicate (MgSiO₃). The analysis of the outer insulating layer material can be performed using the same method as described previously for analyzing the chemical composition of the insulating coating layer. ••• Thickness

[0059] The thickness of the outer insulating layer is preferably greater than or equal to 10 nm and less than or equal to 100 nm. If the thickness of the outer insulating layer is greater than or equal to 10 nm, it is easy to increase the insulation between the particles. If the thickness of the outer insulating layer is less than or equal to 100 nm, it is easy to increase the density of the iron core. The thickness of the outer insulating layer is even more preferably greater than or equal to 20 nm and less than or equal to 90 nm, and particularly preferably greater than or equal to 30 nm and less than or equal to 80 nm. The thickness of the outer insulating layer can be measured in the same way as in the previously mentioned method for measuring the thickness of the insulating coating layer.

[0060] The total thickness of the insulating coating layer and the outer insulating layer is greater than or equal to 40 nm and less than or equal to 300 nm, provided that the thickness of the insulating coating layer and the thickness of the outer insulating layer each meet the previously mentioned thickness ranges.

[0061] The formation of the insulating coating layers and the formation of the outer insulating layers on the outer surfaces of the pure iron particles and the iron alloy particles can each be achieved, for example, by a chemical transformation treatment. A known technique can be used for the formation of the insulating coating layer and the outer insulating layer. • Proportion of coated iron alloy powder

[0062] The proportion of coated iron alloy powder in the raw material powder can be selected according to the desired magnetic properties. For example, the proportion of coated iron alloy powder in the raw material powder is preferably more than or equal to 15% by mass and less than or equal to 40% by mass, based on 100% by mass of the raw material powder. If the proportion of coated iron alloy powder is greater than or equal to 15% by mass, the proportion of iron alloy powder with high electrical resistance can be increased. This makes it possible to reduce eddy current losses. Furthermore, increasing the proportion of coated iron alloy powder makes it easier to reduce the magnetic coercivity. If the proportion of coated iron alloy powder is less than or equal to 40% by mass, the proportion of iron alloy powder is not too high.This makes it easy to prevent excessive deformation of the coated pure iron powder, which is normally easily deformed. Consequently, damage to the insulating coating layers in the coated pure iron powder can be prevented. Furthermore, the proportion of coated pure iron powder, which is normally easily deformed, can be increased. As a result, the density of the molded part can be increased, and thus the density of the iron core can also be increased. The proportion of the coated iron alloy powder is more preferably greater than or equal to 17 wt% and less than or equal to 38 wt%, and particularly preferably greater than or equal to 20 wt% and less than or equal to 35 wt%. <metallseife>

[0063] The metal soap can increase lubricity during the forming process. Furthermore, the metal soap can prevent damage to the insulating coating layers in the coated pure iron powder. More specifically, the metal soap can reduce the stress exerted on the pure iron particles by the iron alloy particles during the forming process. One example of the form of the metal soap is a powder. The metal soap is essentially burned off in the subsequent heat treatment step. • Type

[0064] The type of metal soap can be selected appropriately depending on the temperature Td of the mold used in the forming step, which is described in detail below. More precisely, the type of metal soap is such that the difference (Tm-Td) between the melting point Tm of the metal soap and the temperature Td of the mold meets the requirement: "90 °C ≤ Tm-Td". Using a metal soap that meets the requirement "90 °C ≤ Tm-Td" allows for the production of an iron core with low core loss. This is because damage to the insulating coating layers in the coated pure iron powder during the forming step can be prevented. By preventing damage to the insulating coating layers, the insulation between the particles can be increased, thus reducing eddy current loss.By setting the temperature difference Tm-Td to greater than or equal to 90 °C, the raw material powder can be subjected to compression molding while preventing the metal soap from melting during the molding process. In other words, the raw material powder can be compression molded under conditions that allow the metal soap to maintain a specific degree of hardness. Due to the action of the metal soap, it becomes easier to reduce the stress exerted on the pure iron particles by the iron alloy particles, while simultaneously increasing lubricity during compression molding. Consequently, damage to the insulating coating layers in the coated pure iron powder can be prevented, even if the iron alloy particles deform the pure iron particles during compression molding.

[0065] The melting point Tm of the metal soap can be selected depending on the temperature Td of the mold and is preferably, for example, higher than or equal to 120 °C, more preferably higher than or equal to 150 °C, and particularly preferably higher than or equal to 200 °C. If the melting point Tm of the metal soap is higher than or equal to 120 °C, it becomes possible to increase the density of the molded part while simultaneously preventing damage to the insulating coating layers in the coated pure iron powder. Consequently, the density of the iron core can be increased. Since the melting point Tm of the metal soap is high, the temperature difference (Tm-Td) can be increased. This makes it possible to maintain a specific hardness of the metal soap during compression molding. Consequently, the effectiveness in preventing damage to the insulating coating layers in the coated pure iron powder can be enhanced.Furthermore, due to the high melting point Tm of the metal soap, the raw material powder can be press-molded at a higher temperature Td of the mold. Consequently, it becomes possible to promote the deformation of the coated pure iron powder and the iron alloy powder. As a result, it becomes possible to increase the density of the molded part.

[0066] Examples of metal soaps include lithium stearate (Tm = 220 °C), barium stearate (Tm = 228 °C), and sodium stearate (Tm = 252 °C). These metal soaps can enhance the damage-preventing effect of insulating coating layers in coated pure iron powder. The type of metal soap can be selected depending on the mold temperature (Td), and examples include zinc stearate (Tm = 126 °C) and aluminum stearate (Tm = 163 °C). • Salary

[0067] The proportion of metal soap is preferably more than or equal to 0.02 wt% and less than or equal to 0.80 wt%, based on 100 wt% of the raw material powder. If the proportion of metal soap is greater than or equal to 0.02 wt%, it is easy to achieve the desired effect of improved lubricity. Consequently, the reduction of stress acting on the pure iron particles becomes significant. As a result, damage to the insulating coating layers in the coated pure iron powder can be easily prevented. If the proportion of metal soap is less than or equal to 0.80 wt%, the metal soap content is not excessive. Thus, it is possible to prevent a decrease in the metal component content in the molded part.The amount of metal soap added is more preferably more than or equal to 0.03 wt% and less than or equal to 0.70 wt%, particularly preferably more than or equal to 0.05 wt% and less than or equal to 0.60 wt%. <Weitere Komponenten>

[0068] In addition to metal soap, the raw material powder may contain a fatty acid amide, a higher fatty acid amide, an inorganic substance, a fatty acid metal salt, or the like as a lubricant. If the raw material powder contains the lubricant, its lubricity during the molding step can be improved. An example of a fatty acid amide is stearamide. An example of a higher fatty acid amide is ethylenebis(stearamide). Examples of inorganic substances include boron nitride and graphite. A fatty acid metal salt consists of a fatty acid and a metal. Examples of fatty acids include caprylic acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, nonadecanoic acid, arachidic acid, heneicosanoic acid, behenic acid, tricosanoic acid, lignoceric acid, pentacoustic acid, cerotic acid, heptacosanoic acid, and montanic acid.Examples of the metal are Mg (magnesium), Ca (calcium), Zn (zinc), Al, Ba (barium), Li (lithium), Sr (strontium), Cd (cadmium), Pb (lead), Na (sodium), and K (potassium). It is assumed that the fatty acid metal salt is limited to a material other than that used for the metal soap. The amount to be added is preferably more than or equal to 0.05 wt% and less than or equal to 0.70 wt%, more preferably more than or equal to 0.10 wt% and less than or equal to 0.60 wt%, and particularly preferably more than or equal to 0.20 wt% and less than or equal to 0.50 wt%, based on 100 wt% of the raw material powder. Like the metal soap, the lubricant is essentially burned off in the subsequent heat treatment step. [Forming step]

[0069] In the forming step, the raw material powder is subjected to compression molding to produce a shaped part. The forming part can be produced by filling the mixture into a mold that allows for the formation of a predetermined shape and then applying pressure to the raw material powder within the mold. The shape of the formed part can be selected appropriately depending on the intended shape of the magnetic core for an electromagnetic component.

[0070] An example of such a mold is one equipped with a tubular die with a through-hole, a pair of punches (an upper and a lower punch) that can be inserted into and removed from the through-hole, and a temperature control device that regulates the temperature of the upper and lower punches. The upper and lower punches are positioned opposite each other within the through-hole. Inside the mold, the upper surface of the lower punch and the inner circumferential surface of the die together form a cavity with a bottom (i.e., a molding chamber). The raw material powder is placed into this cavity. The raw material powder in the cavity is compressed by the upper and lower punches to form a columnar molded part. The molded part is then removed from the die to obtain the finished product.In cases where a tubular molded part is to be produced, the mold can additionally be equipped with a column-shaped core rod. The core rod is inserted into the interior of the upper and lower punches to form an inner circumferential surface of the molded part. In this case, the temperature control device preferably also controls the temperature of the core rod. (Printing)

[0071] The mold pressure is preferably greater than or equal to 500 MPa. With a mold pressure greater than or equal to 500 MPa, it is easy to produce a molded part with a high density. The mold pressure is even more preferably greater than or equal to 800 MPa, more preferably greater than or equal to 950 MPa, more preferably greater than or equal to 1100 MPa, and more preferably greater than or equal to 1250 MPa. The upper limit of the mold pressure is preferably, for example, less than or equal to 3000 MPa. With a mold pressure less than or equal to 3000 MPa, damage to the insulating coating layers can be prevented. Furthermore, the service life of the mold is not affected as significantly. The mold pressure is preferably less than or equal to 2500 MPa, and more preferably less than or equal to 2000 MPa. (Temperature of the mold)

[0072] The temperature Td of the mold is such that the difference (Tm-Td) between the melting point Tm of the metal soap and the temperature Td of the mold can meet the requirement: "90 °C ≤ Tm-Td". If the requirement that the difference (Tm-Td) be greater than or equal to 90 °C is met, it becomes possible to produce an iron core with low core loss, as previously mentioned. The difference (Tm-Td) is preferably greater than or equal to 100 °C, more preferably greater than or equal to 120 °C, more preferably greater than or equal to 140 °C, and more preferably greater than or equal to 150 °C.

[0073] The mold temperature Td is preferably less than or equal to 130 °C. If the mold temperature Td is less than or equal to 130 °C, an excessive rise in the mold temperature Td can be prevented. Thus, excessive deformation of the coated pure iron powder and the iron alloy powder can be easily prevented. Consequently, it is easy to prevent damage to the insulating coating layers in the coated pure iron powder caused by the metal soap. The mold temperature Td is preferably higher than or equal to room temperature (ambient temperature). If the mold temperature Td is equal to the ambient temperature, molding can be carried out under high pressure due to the addition of the metal soap. Thus, it becomes easy to produce a molded part with a high density. The mold temperature Td is preferably higher than or equal to 60 °C.If the mold temperature Td is preferably higher than or equal to 60 °C, it becomes easy to deform the coated pure iron powder and the iron alloy powder. This makes it easy to produce a molded article with an even higher density. The mold temperature Td is preferably higher than or equal to 80 °C and lower than or equal to 120 °C. The mold temperature Td is a preset temperature for the temperature control device in the mold immediately before the raw material powder is added. The preset temperature is equal to the temperature of a raw material powder contact area (for example, the inner circumferential surface of the die, a pressing surface of the upper punch and the lower punch) in the mold immediately before the raw material powder is added. Therefore, the temperature of the raw material powder contact area can be set to the mold temperature Td.A commercially available non-contact thermometer can be used to measure the temperature of the raw material powder contact section.

[0074] The lubricant can be applied to the raw material powder contact area in the mold. The lubricant applied to this contact area reduces friction with the powders. Furthermore, it facilitates the production of a high-density molded part. Examples of lubricant materials include those mentioned in the "Other Components" section regarding the raw material powder mentioned earlier. [Heat treatment step]

[0075] In the heat treatment step, the molded part undergoes heat treatment to eliminate deformations that occurred in the coated pure iron powder and in the iron alloy powder during the molding step.

[0076] The heat treatment atmosphere to be used is one with an oxygen concentration of more than 0 ppm by volume and less than or equal to 10,000 ppm by volume, preferably more than or equal to 100 ppm by volume and less than or equal to 5,000 ppm by volume, and particularly preferably more than or equal to 200 ppm by volume and less than or equal to 1,000 ppm by volume. The heat treatment temperature is preferably greater than or equal to 400 °C and less than or equal to 1,000 °C. The heat treatment temperature is preferably greater than or equal to 450 °C, and particularly preferably greater than or equal to 500 °C. The heat treatment temperature is preferably less than or equal to 900 °C, and particularly preferably less than or equal to 800 °C.The residence time is preferably greater than or equal to 10 minutes and less than or equal to 60 minutes, more preferably greater than or equal to 10 minutes and less than or equal to 30 minutes, and more preferably greater than or equal to 10 minutes and less than or equal to 15 minutes. When the molded part is heat-treated under these conditions, the deformations in the coated pure iron powder and the iron alloy powder can be sufficiently eliminated. As a result, the hysteresis loss can be reduced. Accordingly, it becomes easy to produce an iron core with low core loss. [Application]

[0077] The method for producing an iron core according to the embodiment can be suitably used in the production of an iron core provided in various electromagnetic components (for example, a choke, a transformer, a motor, a choke coil, an antenna, an injector, an ignition coil). The raw material powder (raw material powder for the iron core) according to the embodiment can suitably be used as raw material for an iron core. [Functional effect]

[0078] According to the method for producing an iron core as described in the embodiment, if the melting point Tm of the metal soap is set to 90 °C or higher, and the temperature Td of the mold is set to greater than or equal to 90 °C, the raw material powder can be press-molded while preventing the metal soap from melting and maintaining a specific degree of hardness of the metal soap during the forming step. Due to the effect of the metal soap, it is easy to reduce the stress exerted on the pure iron particles by the iron alloy particles and simultaneously increase lubricity during press-molding. Consequently, damage to the insulating coating layers in the coated pure iron powder can be prevented, even if the iron alloy particles deform the pure iron particles during press-molding.As a result of preventing damage to the insulating coating layers, the insulation between the particles can be improved. This improved insulation, in turn, reduces eddy current loss. Consequently, it is possible to produce an iron core with low iron loss (core loss). <<Testbeispiel 1> >

[0079] Iron core samples were produced and the density and magnetic properties of each sample were evaluated. [Samples No. 1 to 11]

[0080] The iron cores of samples No. 1 to 11 were produced in the same way as in the previously mentioned process for producing an iron core, that is, by the process with a manufacturing step, a forming step and a heat treatment step, in that order. [Manufacturing step]

[0081] Raw material powders were produced, each containing a coated pure iron powder, a coated iron alloy powder, and a metal soap. Each of the raw material powders of samples 1 to 4 and 6 to 11, with the exception of sample 5, additionally contained a lubricant other than a metal soap, as described below. Coated pure iron powders were produced, consisting of: a multitude of pure iron particles, insulating coating layers, each covering the outer circumferences of the pure iron particles, and outer insulating layers, each covering the outer circumferences of the insulating coating layers. The pure iron particles consisted of pure iron (purity: greater than or equal to 99 wt%; the remainder consisted of unavoidable impurities). The mean particle diameter (D50) of the pure iron particles was 55 µm.Coated iron alloy powders were produced, consisting of: a multitude of iron alloy particles formed from an iron alloy, insulating coating layers covering the outer circumferences of the iron alloy particles, and outer insulating layers covering the outer circumferences of the insulating coating layers. The mean particle diameter (D50) of the iron alloy particles was 60 µm.

[0082] The iron alloy powder for the samples was prepared with each type having a chemical composition represented by one of the type symbols a to c and a specific Vickers hardness, as shown in Table 1. The type symbols a to c, shown in the column for chemical compositions in Table 1, are as follows. Each of the Vickers hardness values ​​in Table 1 was determined by embedding the iron alloy particles in a resin, subsequently milling the resin to expose the iron alloy particles forming the iron alloy powder, and then measuring the exposed iron alloy particles (a mean of the measured values ​​with respect to n = 10).

[0083] Type symbol a: 9.5 wt% Si, 5.5 wt% Al, the remainder consisted of Fe and unavoidable impurities.

[0084] Type symbol by mass: 6.5 wt% Si, the remainder consisted of Fe and unavoidable impurities.

[0085] Type symbol c: 3.5 wt% Si, the remainder consisted of Fe and unavoidable impurities.

[0086] An insulating coating layer of iron phosphate was formed on the outer circumference of each pure iron and iron alloy particle, and an outer insulating layer, containing Si-O as its main component, was formed on the outer circumference of the insulating coating layer. The thickness of both the insulating coating layer and the outer insulating layer was approximately 100 nm. The insulating coating layer was formed by bonding (phosphating). The outer insulating layer was formed by chemical transformation treatment.

[0087] The metal soaps used in the raw material powders of the samples were Li-st (lithium stearate), Na-st (sodium stearate), and Ba-st (barium stearate), as shown in Table 1. The melting points Tm of the metal soaps are shown in Table 1. Each raw material powder of samples 1 to 4 and 6 to 11, with the exception of sample 5, additionally contained EBS (ethylenebis(stearamide)) as a lubricant other than the metal soap.

[0088] The proportions of the coated iron alloy powder, the metal soap and the lubricant other than metal soap in the raw material powder of each sample were those amounts shown in Table 1, based on 100 mass % of the raw material powder, and the remainder of the raw material powder of each sample was the coated pure iron powder. [Forming step]

[0089] Each of the raw material powders was placed in a mold and then pressed to produce an annular (outer diameter: 34 mm, inner diameter: 20 mm, thickness: 5 mm) molded part. The mold consisted of a die, an upper and lower punch, a core rod, and a temperature control device. The die had a cylindrical through-hole. The upper and lower punches were cylindrical with an annular pressing surface and were inserted into and removed from the through-hole in the die. The core rod was cylindrical, forming the inner circumference of the molded part, and was inserted into and removed from the inside of the upper and lower punches. The temperature control device regulated the mold temperature.The compression molding process was carried out under atmospheric conditions at a mold temperature Td, as shown in Table 1, and under a mold pressure of 1,500 MPa. The mold temperature Td was a temperature measured on the part of the die in contact with the raw material powder (for example, the inner circumferential surface of the die, a pressing surface of the upper punch and the lower punch) using a thermocouple immediately before the raw material powder was poured in. [Heat treatment step]

[0090] The molded part was heat-treated to produce an iron core. The heat treatment was carried out in a nitrogen atmosphere at a temperature of 700 °C with a residence time of 15 minutes. [Samples No. 101 to 111]

[0091] Iron cores of samples No. 101 to 111 were prepared in the same manner as for the preparation of the samples mentioned below, except that the points mentioned below were different, as shown in Table 1.

[0092] Sample No. 101 differed from Sample No. 1 in that no metal soap was contained in Sample No. 101.

[0093] Sample No. 102 differed from Sample No. 1 in that the metal soap used in Sample No. 102 was Zn-st (zinc stearate).

[0094] Sample No. 103 differed from sample No. 1 in that the metal soap used in sample No. 103 was Al-st (aluminum stearate).

[0095] Specimen No. 104 differed from Specimen No. 3 in that the temperature Td of the mold used for Specimen No. 104 was higher than that used for Specimen No. 3.

[0096] Sample No. 105 differed from sample No. 8 in that sample No. 105 did not contain any metal soap.

[0097] Sample No. 106 differed from sample No. 9 in that sample No. 106 did not contain any metal soap.

[0098] Sample No. 107 differed from sample No. 8 in that the content of coated iron alloy powder in sample No. 107 was lower than in sample No. 8 and no metal soap was contained in sample No. 107.

[0099] Sample No. 108 differed from sample No. 9 in that the content of coated iron alloy powder in sample No. 108 was greater than in sample No. 9 and no metal soap was contained in sample No. 108.

[0100] Sample No. 109 differed from sample No. 10 in that sample No. 109 did not contain any metal soap.

[0101] Sample No. 110 differed from sample No. 11 in that sample No. 110 did not contain any metal soap.

[0102] Sample No. 111 differed from Sample No. 1 in that the iron alloy in the coated iron alloy powder of Sample No. 111 had a chemical composition represented by the type symbol d, as mentioned below, the Vickers hardness of Sample No. 111 was lower than that of Sample No. 1, and Sample No. 111 did not contain any metal soap.

[0103] Type symbol d: 3.0 wt% Si, the remainder consisted of Fe and unavoidable impurities. [Density]

[0104] The density (g / cm³) 3 The viscosity of the iron core of each sample was measured. The density was measured using an Archimedes method. The results are shown in Table 1. [Magnetic properties]

[0105] The magnetic properties of an iron core from each sample were measured as follows. A copper wire was wound around a ring-shaped iron core from each sample to create a measuring element (a primary winding coil: 300 turns, a secondary winding coil: 20 turns). An iron loss W1 / 20k (a hysteresis loss + an eddy current loss) at an excited magnetic flux density Bm of 0.1 T and a measurement frequency of 20 kHz was determined using the measuring element and an AC-BH curve recorder (Riken Denshi Co., Ltd., BHU-60). The results for the iron losses W1 / 20k and the results for the eddy current losses W1e / 20k are presented together in Table 1.

[0106] As shown in Table 1, samples 1 to 11, each meeting the requirement that the difference (Tm-Td) between the melting point Tm of the metal soap and the temperature Td of the mold was greater than or equal to 90 °C, exhibited low eddy current losses and low iron losses (low core losses). Furthermore, samples 1 to 11 exhibited high densities.

[0107] A comparison between samples 1 to 7 and samples 101 to 104, between sample 8 and sample 105, between sample 9 and sample 106, between sample 10 and sample 109, and between sample 11 and sample 110 showed that the eddy current loss can be reduced if the requirement is met that the previously mentioned temperature difference (Tm-Td) is greater than or equal to 90 °C. Thus, it was shown that the iron loss can be reduced. Sample 8 and sample 107 were compared. Sample 8 contained a higher proportion of coated iron alloy powder than sample 107. Therefore, it was more likely that the electrical resistance in sample 8 would be increased. However, in sample 8, it was likely that the pure iron particles were deformed to increase the eddy current loss. Nevertheless, it was shown that in sample no.8. The eddy current loss was reduced to a lower value than in sample no. 107. Thus, it was shown that iron loss can be reduced. A comparison was made between sample no. 9 and sample no. 108. Sample no. 9 contained a smaller quantity of the coated iron alloy powder than sample no. 108. Therefore, in sample no. 9, the pure iron particles were less likely to deform in order to reduce eddy current loss. However, in sample no. 9, the specific electrical resistivity was less likely to increase. Nevertheless, it could be shown that the eddy current loss was reduced in sample no. 9. That is, it was shown that iron loss can be reduced. A comparison was made between samples no. 1 to 7 and sample no. 111. In each of samples no. 1 to 7, the Vickers hardness of the iron alloy particles was higher than that of sample no. 111.Thus, in each of samples 1 to 7, it was likely that the pure iron particles were deformed to increase the eddy current loss. Nevertheless, it could be shown that in each of samples 1 to 7, the eddy current loss could be reduced to a lower value than in sample 111. That is, it was shown that the iron loss can be reduced.

[0108] The results from samples 1 to 3 showed that the eddy current loss tended to decrease with increasing difference (Tm-Td). The results from samples 1, 4, and 5 showed that the metal soap could be used effectively to reduce the eddy current loss, even when added in small quantities. Furthermore, it was shown that the metal soap was effective in reducing the eddy current loss even when no other lubricant was present. The results from samples 1, 6, and 7 showed that when the requirement "90 °C ≤ difference (Tm-Td)" was met, the eddy current loss was also reduced when Na-st, Ba-st, and Li-st were used as metal soaps. Accordingly, in samples 1, 6, and 7, the following results were obtained:In samples 102 and 103, where Zn-st and Al-st were used, although the eddy current loss was not reduced, it was expected that the eddy current loss would decrease by fulfilling the requirement: “90 °C ≤ difference (Tm-Td)”, even if the metal soap used was Zn-st or Al-st. From the results of samples 1, 8, and 9, it was shown that an increase in electrical resistance was more likely to increase with an increase in the content of coated iron alloy powder. However, it was more likely that the coated pure iron particles would deform, and the eddy current loss would increase with an increasing amount of coated iron alloy powder. Nevertheless, the effect of reducing the eddy current loss was shown to be significant. From the results of samples 1, 8, and 9, it was shown that the eddy current loss was significantly reduced.In studies 1, 10, and 11, it was shown that the pure iron particles were more likely to deform, and that the eddy current loss was more likely to increase with increasing Vickers hardness of the iron alloy particles. Nevertheless, it was shown that the eddy current loss decreased.

[0109] It is understood that the present invention is not limited to the disclosed exemplary embodiments, but is defined by the attached claims and is intended to include all modifications within the scope and meaning of the claims.< / metallseife>

Claims

[1] Method for producing an iron core, comprising: a step for the preparation of a raw material powder comprising a coated pure iron powder formed from a variety of pure iron particles, each having an insulating coating layer, a coated iron alloy powder formed from a variety of iron alloy particles, each having an insulating coating layer, and a metal soap; a step towards the production of a molded part by compression molding of the raw material powder filled into a mold; and a step to carry out a heat treatment of the molded part in order to eliminate deformations in the coated pure iron powder and in the coated iron alloy powder, wherein a difference Tm-Td between a melting point Tm of the metal soap and a temperature Td of the mold in the step to produce the molded part is greater than or equal to 90 °C, the temperature Td of the mold is equal to the temperature of a raw material powder contact section of the mold immediately before the raw material powder is poured in, a proportion of metal soap in the raw material powder is greater than or equal to 0.02% by mass and less than or equal to 0.80% by mass, Each of the iron alloy particles contains at least one additional element, selected from Si and Al, the insulating coating layer contains a phosphoric acid compound which contains a phosphate salt as its main component, the metal soap contains at least one substance selected from the group consisting of lithium stearate, barium stearate, sodium stearate, zinc stearate and aluminium stearate, a forming pressure of the compression molding process is greater than or equal to 500 MPa and less than or equal to 3000 MPa, the temperature Td of the mold is higher than or equal to 60 °C and lower than or equal to 130 °C and The step involves carrying out a heat treatment of the molded part in an atmosphere with an oxygen concentration greater than 0 volume ppm and less than or equal to 10,000 volume ppm at a temperature greater than or equal to 400 °C and less than or equal to 1,000 °C and with a residence time greater than or equal to 10 minutes and less than or equal to 60 minutes. [2] Method for producing an iron core according to claim 1, wherein the melting point Tm of the metal soap is greater than or equal to 200 °C and less than or equal to 252 °C. [3] Method for producing an iron core according to claim 1 or 2, wherein the Vickers hardness of the iron alloy particles is greater than or equal to 200 HV and less than or equal to 1000 HV. [4] Method for producing an iron core according to claim 1, wherein a Vickers hardness of the iron alloy particles greater than or equal to 200 HV and less than or equal to 1000 HV, the melting point Tm of the metal soap is higher than or equal to 200 °C and lower than or equal to 252 °C, and The temperature Td of the mold is higher than or equal to 60 °C and lower than or equal to 130 °C. [5] Method for producing an iron core according to any one of claims 1 to 4, wherein a proportion of the coated iron alloy powder in the raw material powder is greater than or equal to 15 wt% and less than or equal to 40 wt%. [6] Method for producing an iron core according to any one of claims 1 to 5, wherein the thickness of both the insulating coating layer in the coated pure iron powder and the insulating coating layer in the coated iron alloy powder is greater than or equal to 30 nm and less than or equal to 300 nm. [7] Raw material powder for an iron core, comprising: a coated pure iron powder formed from a multitude of pure iron particles, each having an insulating coating layer; a coated iron alloy powder formed from a multitude of iron alloy particles, each having an insulating coating layer; and a metal soap having a melting point Tm greater than or equal to 200 °C, wherein the thickness of the insulating coating layer in the coated pure iron powder is greater than or equal to 30 nm and less than or equal to 300 nm, a Vickers hardness of the iron alloy particles greater than or equal to 200 HV and less than or equal to 1000 HV, a proportion of the coated iron alloy powder greater than or equal to 15 wt% and less than or equal to 40 wt%, and a proportion of the metal soap greater than or equal to 0.02 mass-% and less than or equal to 0.80 mass-%, Each of the iron alloy particles contains at least one additional element, selected from Si and Al, the insulating coating layer contains a phosphoric acid compound which contains a phosphate salt as its main component, the metal soap contains at least one substance selected from the group consisting of lithium stearate, barium stearate, sodium stearate, zinc stearate and aluminum stearate, the coated pure iron powder and / or the coated iron alloy powder has a double-layer structure consisting of both an insulating coating layer and an insulating outer layer formed on an outer perimeter of the insulating coating layer, and The insulating outer layer contains a silica compound containing Si and O as its main components.