Manufacturing method for iron-based soft magnetic alloys

Abstract

The present invention provides a method for manufacturing an iron-based soft magnetic alloy that has a Bs ≥ 1.7T and low iron loss performance, making it suitable as a material for dust cores. [Solution] Composition formula (Fe 1-m Co m ) 100-x-y Si x (B 1-n C n ) y The method for producing an iron-based soft magnetic alloy comprises the steps of: preparing a molten alloy with a composition such that the composition ratios x, y, m, and n satisfy 0.5≦x≦1.5 atomic%, 11.0≦y≦13.0 atomic%, 0.05≦m≦0.5, and 0.0≦n≦0.3, respectively; and rapidly solidifying the molten alloy on a cooling roll mainly composed of pure copper, copper alloy, Mo, and W.

Description

[Technical Field]

[0001] The present invention relates to a method for producing an iron-based soft magnetic alloy, and more specifically, to a method for producing an iron-based soft magnetic alloy suitable as a material for dust cores. [Background technology]

[0002] In recent years, there has been a growing market demand for materials with low iron loss and high saturation magnetic flux density for various passive elements and transformers used in power electronics, such as inductors and reactors, which are used as electronic components. As soft magnetic powders with excellent DC superposition characteristics and low iron loss, in addition to Fe-Si-B iron-based amorphous alloy powders, Fe-Si-B-Nb-Cu iron-based nanocrystalline alloy powders are known, which are obtained by crushing Fe-Si-B amorphous alloy strips with a thickness of about 17 μm to 25 μm, produced by rapid cooling and solidification of molten metal using iron (Fe), silicon (Si), and boron (B) as the main raw materials, after appropriate crystallization heat treatment. There is increasing market demand for these powders as dust core (compacted magnetic core) powders for inductors, reactors, power conditioners, and motor cores, as they can replace Fe-Si alloy powders produced by conventional atomization methods or Fe-Si-B-Cr amorphous powders produced by the SWAP method.

[0003] In addition, the Fe-Si-B amorphous alloy powder and Fe-Si-B-Nb-Cu iron-based nanocrystalline alloy powder mentioned above are being considered as core materials for power electronics used in the several kHz to MHz (megahertz) range, taking advantage of their characteristic low iron loss compared to Fe-Si alloy powders. These alloy powders have been confirmed to suppress iron loss in the core, especially in high-frequency bands exceeding 1 MHz, resulting in unprecedentedly high efficiency. Furthermore, given that approximately 60% of the world's electricity is consumed by motors, using a dust core in the stator core of a motor reduces not only iron loss but also eddy current loss. Therefore, aside from the issue of lower magnetic flux density Bs in dust cores, this can significantly contribute to the high efficiency of motors, and as a direct means of achieving carbon-free operation, it is expected to be deployed in electric vehicles, white goods such as air conditioners, and factory automation motors.

[0004] However, the above-mentioned Fe-Si-B amorphous alloys have a Bs of ≤ 1.6T, and the Fe-Si-B-Nb-Cu iron-based nanocrystalline alloy has a Bs of ≤ 1.3T, which falls short of the existing core material Fe-Si alloy's Bs of ≥ 1.8T. Therefore, when used as a dust core, the Bs value decreases even further. Consequently, these materials have not been widely used as substitutes for Fe-Si alloy powder or pure iron powder, including in motor cores, as dust cores. There is a need for an iron-based soft magnetic powder for dust cores that can achieve both high Bs performance comparable to Fe-Si alloy powder, which is applicable to passive elements for power electronics and motor cores, and low iron loss performance comparable to Fe-Si-B amorphous alloy powder.

[0005] Given the market demands described above, Fe-Si-B amorphous alloys with a maximum Bs of around 1.6T, or iron-based nanocrystalline materials with a Bs of 1.4T or less (e.g., FINEMET®), are not suitable replacements for Fe-Si alloys with a Bs of 1.8T. To date, there have been no examples of high-Bs, low-iron-loss iron-based soft magnetic powders for dust cores being introduced to the market that can achieve low iron loss performance comparable to Fe-Si-B amorphous alloy powders.

[0006] For example, in core materials for power electronics used in the megahertz band, and core materials for EV main motors that require high-speed rotation of 20,000 rpm or more, dust cores using pure iron or Fe-Si atomized powder, which have high iron loss, generate heat in the entire passive element substrate or motor due to the iron loss generated in the core by the input power. This increases power consumption and also requires power for cooling measures. Therefore, there is an extremely high market demand for high-Bs, low-iron-loss iron-based soft magnetic powder for dust cores that can contribute to energy saving and enable high output and high efficiency, across a variety of applications.

[0007] Furthermore, if iron loss can be drastically reduced to less than 1 / 10th of that of iron-based amorphous alloys while maintaining high Bs, it is expected to have applications in various fields as a dust core. For this reason, there is extremely high market expectation for iron-based soft magnetic alloy powder for dust cores, which achieves low iron loss comparable to iron-based amorphous alloys by crushing rapidly solidified alloys obtained by the single-roll rapid quenching method, resulting in a Bs ≥ 1.7T before crushing, as an alternative to Fe-Si atomized powders, which have poor manufacturing yield and low recyclability.

[0008] Furthermore, both Fe-Si-based powders obtained by the gas atomization method and Fe-Si-B-Cr-based amorphous powders obtained by the SWAP method are spherical powders. In addition, it is difficult to create a powder particle size distribution with a two-peak particle size distribution that allows for dense packing. As a result, the powder packing rate in the dust core is 70-80 volume% in compressible molding and 50-70 volume% in injection molding. Therefore, in iron-based soft magnetic powders produced by crushing rapidly solidified alloys obtained by the single-roll rapid quenching method, a magnetic powder particle size distribution with a magnetic powder packing rate of 80 volume% or more in the dust core in compression molding and 70 volume% or more in injection molding is required to improve yield and reduce costs.

[0009] Non-patent document 1 states that Fe-Si-B amorphous alloys have conventionally been 10 4 ~10 6Amorphous structures could only be obtained in rapidly solidified alloy strips of about 17 to 22 μm in thickness at extremely fast rapid solidification rates such as K / sec. However, it has been disclosed that by adding phosphorus (P), the rapid solidification rate can be reduced, and iron-based amorphous alloy strips of 50 μm or more in thickness can be obtained. However, the addition of P not only leads to a decrease in the saturation magnetic flux density Bs, but P-added alloys also cause significant furnace contamination due to the volatilization of the P component during alloy melting, so there are still few examples of applications in industrial fields.

[0010] Non-patent document 2 discloses that the Fe-Si-B-P-Cu iron-based nanocrystalline alloy "NANOMET (registered trademark)" is a soft magnetic material with a high saturation magnetic flux density Bs: 1.85T and low iron loss performance comparable to iron-based amorphous alloys. However, as with non-patent document 1, this iron-based nanocrystalline alloy, being a P-added alloy, suffers from significant furnace contamination due to the volatilization of the P component during alloy melting, and requires crystallization treatment by high-speed heating. Furthermore, the thickness of the rapidly cooled alloy strip is thin, and the shape of the powder after crushing is flaky, resulting in a magnetic powder filling rate of 80% during dust core molding. Therefore, the high Bs of 1.85T cannot be utilized, and there have been no examples of its practical application as a dust core to date.

[0011] Non-patent document 3 discloses various soft magnetic properties of dust cores using Fe-Si atomized powder. The magnetic powder packing density (relative density) of the dust core is 83% for Fe-3.5Si, where the iron loss is more than 10 times that of Fe-Si-B amorphous alloys, and 81% for Fe-6.5Si, where the iron loss is about 7 times that of Fe-Si-B amorphous alloys. Although these magnetic powder packing density values ​​are higher than the 80% or less of typical dust cores using Fe-Si atomized powder, the iron loss is significantly higher than that of Fe-Si-B amorphous alloys.

[0012] Non-patent document 4 discloses various soft magnetic properties of Fe-Cr-Si-B amorphous alloy powder produced by the SWAP method and dust cores using this powder. Fe-Cr-Si-B amorphous alloy powder, like Fe-Si-B amorphous alloys, is characterized by low iron loss performance. However, the SWAP method achieves a high molten metal rapid cooling rate by finely fragmenting the molten alloy by gas atomization and then spraying it into a high-speed rotating water flow for solidification, and a step of directly water cooling the molten droplets is essential in the process of obtaining an amorphous structure. For this reason, Cr addition is essential to ensure the oxidation resistance of the molten alloy, but since Cr addition lowers the Bs of the iron-based amorphous alloy, it is not possible to obtain an iron-based soft magnetic alloy powder for dust cores that ensures Bs ≥ 1.7T while achieving low iron loss comparable to iron-based amorphous alloys.

[0013] Patent documents 1, 2, and 3 describe methods for producing rapidly cooled alloy strips with a thickness of 50 μm or more. However, none of these have realized an Fe-Si-B amorphous alloy with Bs ≥ 1.7T, which is intended for application to laminated cores for BLDC motors for EV drives. Therefore, it is not possible to obtain an iron-based soft magnetic alloy powder for dust cores that ensures Bs ≥ 1.7T before pulverization and achieves low iron loss comparable to iron-based amorphous alloys.

[0014] Patent Document 4 discloses a method for manufacturing a thin metal strip characterized by ejecting molten metal from a plurality of openings (porous nozzles) arranged almost perpendicular to the direction of movement on a moving cooling substrate (rotating cooling roll), each opening having an angle of 10 to 80° with respect to the direction of movement, and rapidly cooling and solidifying it. However, Patent Document 4 is an invention made with the aim of reducing thickness variations in the width direction of the thin metal strip when producing a wide rapidly cooled thin strip. Furthermore, it is difficult to process multiple elongated parallelogram, trapezoidal, or elliptical openings with angles of 10 to 80°, and there is a problem of high nozzle processing costs, making it difficult to use at an industrial mass production level.

[0015] Patent Document 5 discloses a method for manufacturing an Fe-Si-B-based amorphous alloy with a thickness of 40 μm or more, but does not disclose an alloy composition that can ensure Bs ≧ 1.7 T. In addition, it is not aimed at manufacturing iron-based soft magnetic alloy powder for dust cores that ensures Bs ≧ 1.7 T before pulverization and realizes low iron loss comparable to that of iron-based amorphous alloys.

[0016] Patent Document 6 describes an Fe-Si-B-based rapidly solidified alloy with a thickness of 40 μm or more and 70 μm or less, having a saturation magnetic flux density Bs ≧ 1.7 T and a coercive force Hc ≦ 200 A / m, and a method for manufacturing the same. However, due to the precipitation of 0.1 vol% or more and 10 vol% or less of α-Fe phase on the surface during the rapid solidification process, and the remaining part consisting of an amorphous structure, the pulverizability deteriorates. Therefore, it is difficult to mass-produce iron-based soft magnetic alloy powder for dust cores that ensures Bs ≧ 1.7 T and realizes low iron loss comparable to that of iron-based amorphous alloys.

Prior Art Documents

Patent Documents

[0017]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Non-Patent Documents

[0018]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0019] For Fe-Si atomized powder, if the iron loss can be significantly reduced to 1 / 10 or less of that of iron-based amorphous alloys while ensuring a high Bs, it can be used as a soft magnetic powder for dust cores applicable to inductors, reactors, power conditioners, and other core materials and motor cores for power electronics. By doing so, power consumption can be suppressed in various fields and contribute to energy conservation. However, it has been difficult to produce iron-based soft magnetic alloy powder for dust cores at a mass production level that ensures Bs ≧ 1.7T in the rapidly solidified alloy state before pulverization and realizes low iron loss at the same level as iron-based amorphous alloys.

[0020] Therefore, an object of the present invention is to provide a method for producing an iron-based soft magnetic alloy suitable as a material for dust cores by ensuring Bs ≧ 1.7T in the rapidly solidified alloy state before pulverization and realizing low iron loss at the same level as iron-based amorphous alloys.

Means for Solving the Problems

[0021] The method for producing an iron-based soft magnetic alloy according to the present invention has a composition formula (Fe 1-m Co m ) 100-x-y Si x (B 1-n C n ) yThe process comprises the steps of: preparing a molten alloy having a composition such that the composition ratios x, y, m, and n satisfy 0.5≦x≦1.5 atomic%, 11.0≦y≦13.0 atomic%, 0.05≦m≦0.5, and 0.0≦n≦0.3, respectively; and rapidly solidifying the molten alloy on a cooling roll whose main raw material is pure copper, copper alloy, Mo, or W, wherein the rapidly solidifying process comprises the step of forming a thin strip-shaped rapidly solidified alloy having a thickness of 18 μm or more and less than 40 μm by injecting the molten alloy from a nozzle onto the surface of the cooling roll while rotating the cooling roll at a roll surface speed of 15 m / sec or more and 50 m / sec or less, and The cold-solidified alloy has a metallic structure with the α-Fe phase as the main phase, a saturation magnetic flux density of 1.7T to 2.0T, an iron loss of 15W / kg or less at a magnetic flux density of 1.0T and a frequency of 1kHz, the surface roughness of the cooling roll has an arithmetic mean roughness (Ra) of 0.01μm to 0.6μm, and the nozzle is made of a material mainly composed of quartz (SiO2), boron nitride (BN), silicon carbide (SiC), and alumina (Al2O3), and dispenses the molten alloy at a pressure of 5kPa to 50kPa.

[0022] In this method for manufacturing an iron-based soft magnetic alloy, the nozzle can be a single-slit nozzle. In this case, the longitudinal direction of the slit is arranged to be perpendicular to the rotation direction of the cooling roll, the opening width of the slit is preferably 0.2 mm or more and 0.8 mm or less, and the distance from the nozzle to the cooling roll is preferably 0.1 mm or more and 2.0 mm or less.

[0023] Alternatively, the nozzle can be a strand nozzle in which a plurality of holes are arranged in a row perpendicular to the rotation direction of the cooling roll. In this case, the diameter of the holes is preferably 0.6 mm or more and 1.3 mm or less, and the distance from the nozzle to the cooling roll is preferably 0.5 mm or more and 30.0 mm or less.

[0024] The thin, strip-shaped rapidly solidified alloy preferably has a magnetic permeability of 2000 or more at a magnetic flux density of 1.0 T and a frequency of 1 kHz.

[0025] Furthermore, the method for producing the iron-based soft magnetic alloy preferably further comprises a grinding step of grinding the thin strip-shaped rapidly solidified alloy to an average powder particle size of 200 μm or less to form an iron-based soft magnetic alloy powder. Furthermore, it is preferable to further comprise a heat treatment step of heat treating the iron-based soft magnetic alloy powder at a constant temperature of 180°C to 450°C.

[0026] The aforementioned iron-based soft magnetic alloy powder has a tap density of 2 g / cm³. 3 It is preferable that the above conditions are met.

[0027] The iron-based soft magnetic alloy powder preferably has a residual magnetic flux density Bs of 1.5T or higher. [Effects of the Invention]

[0028] According to the present invention, it is possible to provide a method for producing an iron-based soft magnetic alloy suitable as a dust core material by ensuring a Bs of ≥ 1.7T comparable to that of Fe-Si alloys in the rapidly solidified alloy state before pulverization, while achieving low iron loss at a level equivalent to that of iron-based amorphous alloys. [Brief explanation of the drawing]

[0029] [Figure 1] (a) is a schematic diagram of a manufacturing apparatus used in a method for manufacturing an iron-based soft magnetic alloy according to one embodiment of the present invention, (b) is an enlarged view of its main parts, (c) is an enlarged view of the bottom of a slit nozzle, and (d) is an enlarged view of the bottom of a strand nozzle. [Figure 2] This is the powder X-ray diffraction profile of the iron-based soft magnetic alloy obtained in Example 2. [Figure 3] This is the powder X-ray diffraction profile of the iron-based soft magnetic alloy obtained in Example 7. [Figure 4] This is the particle size distribution of the iron-based soft magnetic alloy powder obtained in Example 2. [Figure 5] This is the particle size distribution of the iron-based soft magnetic alloy powder obtained in Example 7. [Figure 6] This is the magnetization curve of the iron-based soft magnetic alloy powder obtained in Example 2. [Figure 7] This is the magnetization curve of the iron-based soft magnetic alloy powder obtained in Example 7. [Figure 8] This shows a comparison of the magnetization curves of the iron-based soft magnetic alloy powders obtained in Example 7 and Example 9. [Figure 9] This is the iron loss curve for the magnetic flux density and iron loss at 20 kHz in a toroidal ring-shaped dust core using the iron-based soft magnetic alloy powder obtained in Example 2. [Figure 10] This is the X-ray diffraction profile of the Fe-Si-B amorphous quenched solidified alloy obtained in Comparative Example 10. [Figure 11] This is the powder X-ray diffraction profile of the iron-based soft magnetic alloy obtained in Comparative Example 12. [Figure 12] This is the particle size distribution of the Fe-Si-B amorphous quenched solidified alloy powder obtained in Comparative Example 10. [Figure 13] This is the magnetization curve of the Fe-Si-B amorphous quenched solidified alloy powder obtained in Comparative Example 10. [Figure 14] This is the particle size distribution of the Fe-Si-B amorphous quenched solidified alloy powder obtained in Comparative Example 12. [Figure 15] This is the iron loss curve for the magnetic flux density and iron loss at 20 kHz in a toroidal ring-shaped dust core using Fe-Si-B amorphous quenched solidified alloy powder obtained in Comparative Example 10. [Figure 16] This is a TEM observation image of the iron-based soft magnetic alloy powder from Example 2. [Modes for carrying out the invention]

[0030] The inventors of the present invention have come up with the present invention by finding that, in the pseudo-ternary composition range of the essential elements Fe+Co, Si, and B, the blending ratio of each element is set to 0.5 atomic% to 1.5 atomic%, B to 11 atomic% to 13 atomic%, and the remainder Fe, with 5% to 50% of Fe replaced by Co, and a portion of B replaced by C up to 30%, and in this alloy composition range, it is possible to obtain a rapidly solidified alloy with excellent pulverability while maintaining a saturation magnetic flux density Bs of 1.7T or higher before pulverization, similar to that of Fe-Si alloys.

[0031] [Alloy composition] Fe is the essential element, and the remaining elements mentioned above are used. By substituting a portion of Fe with Co, which is also a ferromagnetic element like Fe, a Bs of ≥ 1.7T before grinding can be ensured. However, if the substitution rate of Co for Fe m is less than 5%, a Fe-B phase with low magnetization precipitates along with α-Fe, making it impossible to ensure Bs of ≥ 1.7T. If the substitution rate of Co for Fe m exceeds 50%, Bs tends to decrease. For this reason, the substitution rate of Co for Fe m is limited to 5% or more and 50% or less. The substitution rate m is preferably 5% or more and 30% or less, and more preferably 5% or more and 20% or less from a cost-effectiveness viewpoint.

[0032] In the iron-based soft magnetic alloy obtained by the present invention, Si is not only an essential element for obtaining a microstructure, but also plays an important role in exhibiting soft magnetic properties such as permeability. If the Si composition ratio x is less than 0.5 atomic%, not only does the permeability at an applied magnetic field of 10 A / m deteriorate to less than 2000, but the iron loss (core loss) at 1 kHz and 1.0 T exceeds 15 W / kg, thus diminishing the characteristics of the iron-based soft magnetic alloy of the present invention, which are high permeability and low iron loss. Furthermore, if the Si composition ratio x exceeds 1.5 atomic%, the ability to form amorphous material in the rapidly solidified alloy increases, and the pulverability of the rapidly solidified alloy decreases. As a result, iron-based soft magnetic alloy powder with an average powder particle size of 10 μm to 200 μm cannot be obtained in the pulverization process. Moreover, if the Si composition ratio x is too high, the abundance of Fe, which is responsible for magnetization, decreases, making it impossible to obtain Bs ≥ 1.7 T. For this reason, the Si composition ratio x should be between 0.5 atomic% and 1.5 atomic%. The Si composition ratio x is preferably 0.8 atomic% to 1.4 atomic%, and more preferably 1.0 atomic% to 1.3 atomic%.

[0033] If the composition ratio y of B+C is less than 11.0 atomic%, the metallic structure of the iron-based soft magnetic alloy obtained by rapid solidification becomes coarser, making it impossible to secure low iron loss performance of 15 W / kg or less at a magnetic flux density of 1.0 T and a frequency of 1 kHz. Furthermore, if the composition ratio y of B+C exceeds 13.0 atomic%, the ability to form amorphous material in the rapidly solidified alloy increases, and the pulverability of the rapidly solidified alloy decreases. As a result, not only is it impossible to obtain iron-based soft magnetic alloy powder with an average powder particle size of 10 μm to 200 μm in the pulverization process, but the proportion of Fe, which is responsible for magnetization, decreases, making it impossible to obtain a Bs ≥ 1.7 T of the rapidly solidified alloy before pulverization. For this reason, the composition ratio y of B+C is between 11.0 atomic% and 13.0 atomic%. Preferably, the composition ratio y of B+C is between 11.5 atomic% and 13.0 atomic%, and more preferably between 12.0 atomic% and 13.0 atomic%.

[0034] Substituting a portion of B with C lowers the melting point of the molten alloy, relaxing the rapid solidification conditions and making it easier to produce the iron-based soft magnetic alloy of the present invention. However, if the substitution rate n of C for B exceeds 30%, it is undesirable because it is not possible to ensure that the Bs of the rapidly solidified alloy before pulverization is ≥ 1.7T. For this reason, the substitution rate n is limited to 30% or less. From the viewpoint of achieving both high Bs characteristics and low permeability, the substitution rate n is preferably 20% or less, and more preferably 15% or less.

[0035] In the iron-based soft magnetic alloy obtained by the present invention, it is possible to add one or more additive elements selected from the group consisting of Al, Si, V, Ti, Mn, Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au, and Pb. However, if the additive concentration exceeds 2.0 atomic%, it is undesirable because the Bs≧1.7T of the rapidly solidified alloy before grinding cannot be obtained. It is acceptable if the additive concentration, including impurities, is within 2.0 atomic%. Furthermore, Cu does not solidify in Fe, the main raw material, and if Cu is added, the Cu dispersed in the ultrafine α-Fe structure may precipitate on its own, potentially hindering the formation of the desired alloy powder. Therefore, the iron-based soft magnetic alloy of the present invention does not contain Cu.

[0036] [Metal structure] The iron-based soft magnetic alloy obtained by the present invention is characterized by having a main phase of α-Fe that precipitates isotropically without orientation in a specific direction. The main phase is the phase with the largest volume ratio, preferably 50% or more, and more preferably 80% or more. The isotropically precipitated α-Fe phase has a fine crystalline structure with an average grain size of less than 100 nm, and there are also ultrafine crystalline structures that can be called crystal precursors with a crystal size of less than 1 nm. The crystal size of the α-Fe phase can be roughly determined from the full width at half maximum of the X-ray diffraction peak obtained by powder X-ray diffraction (XRD), or it can also be determined by observing the metallic structure of the iron-based rapidly solidified alloy using a transmission electron microscope (TEM).

[0037] However, when the molten alloy is rapidly cooled and solidified on a rotating cooling roll, if amorphous phase and trace amounts of Fe-B phase are present in the microstructure of the resulting iron-based soft magnetic alloy, this is acceptable as long as the amount does not adversely affect the soft magnetic properties. If the amorphous phase in the microstructure of the iron-based soft magnetic alloy powder exceeds 20 volume%, it becomes difficult to obtain Bs≧1.7T, so the amorphous phase content is 20 volume% or less. Preferably, the amorphous phase content is 10 volume% or less, and more preferably 5.0 volume% or less.

[0038] When the iron-based soft magnetic alloy obtained by the present invention is crushed and mass-produced as a dust core, if coarse α-Fe crystal phases with an average grain size of 100 nm or more, oriented in the (200) direction (in-plane orientation) and precipitated by non-uniform nucleation during the rapid solidification process in the manufacturing of the iron-based soft magnetic alloy, are present near the surface of the rapid-cooled roll surface or free surface, it may be difficult to obtain the desired low iron loss performance. In order to obtain low iron loss performance of 15 W / kg or less at a magnetic flux density of 1.0 T and a frequency of 1 kHz, the α-Fe crystal phase precipitated on the surface of the iron-based soft magnetic alloy should preferably be 10 volume% or less, and from the viewpoint of stably maintaining low iron loss performance, 5.0 volume% or less is preferable, and 2.0 volume% or less is even more preferable. In the present invention, the surface layer refers to a depth from the surface of the iron-based soft magnetic alloy that is within 10% of the thickness of the iron-based soft magnetic alloy.

[0039] [Magnetic properties] The iron-based soft magnetic alloy powder obtained by the present invention is characterized by having a saturation magnetic flux density Bs of 1.7T or higher before grinding. However, if Bs exceeds 2.0T, the iron loss at a magnetic flux density of 1.5T and a frequency of 1kHz exceeds 50W / kg, so a clear improvement in efficiency cannot be obtained compared to a dust core using Fe-Si atomized powder. In order to obtain stable energy-saving performance from the commercial frequency band of 60Hz to the megahertz band, the Bs of the rapidly solidified alloy before grinding must be between 1.7T and 2.0T, preferably between 1.73T and 1.97T, and more preferably between 1.75T and 1.95T.

[0040] When the iron-based soft magnetic alloy powder obtained by the present invention is used to manufacture a dust core having high Bs and low iron loss performance, it is effective for the Bs to be 1.5T or higher when the powder is ground to an average particle size of 200 μm or less. The Bs of the iron-based soft magnetic alloy powder is preferably 1.55T or higher, and more preferably 1.6T or higher.

[0041] Furthermore, while existing Fe-Si atomized powders, iron-based amorphous alloy powders, and iron-based nanocrystalline alloy powders tend to show an increase in iron loss values ​​at each operating frequency as the magnetic flux density increases, the iron-based soft magnetic alloy obtained by the present invention exhibits an extremely unique magnetic property in which the iron loss values ​​at each operating frequency show a clear saturation tendency as the magnetic flux density increases. In particular, the iron loss value at a magnetic flux density of 1.5T at a high frequency of 20kHz is 1500W / kg or less, which has the potential to significantly reduce iron loss, a problem in reactors and ultra-high-speed rotating motors operating in the tens of kHz to tens of MHz bands. If the iron loss value at a magnetic flux density of 1.5T at a frequency of 20kHz is too high (for example, 2000W / kg or more), the iron loss will be at the same level as that of iron-based amorphous alloys and iron-based nanocrystalline alloys. Therefore, the iron loss value at a magnetic flux density of 1.5T at a frequency of 20kHz is preferably 1500W / kg or less, more preferably 1300W / kg or less, and even more preferably 1000W / kg or less.

[0042] [Manufacturing method for iron-based crystalline alloys] The present invention provides a method for producing an iron-based soft magnetic alloy, comprising the steps of preparing a molten alloy having the above composition and rapidly cooling and solidifying the prepared molten alloy. Furthermore, by including a grinding step of grinding the obtained iron-based soft magnetic alloy, an iron-based soft magnetic alloy powder can be formed.

[0043] Figure 1(a) is a schematic diagram of a single-roll molten metal rapid cooling apparatus used in a method for manufacturing an iron-based soft magnetic alloy according to one embodiment of the present invention, Figure 1(b) is an enlarged view of the nozzle, and Figure 1(c) is an enlarged view of the nozzle bottom surface. The single-roll molten metal rapid cooling apparatus 1 shown in Figures 1(a) to (c) comprises a melting furnace 2, a molten metal storage container 5, and a cooling roll 8.

[0044] The melting furnace 2 supplies molten alloy 3, which has been melted by high-frequency induction heating, to the storage container 5 by the rotation of the tilting shaft 4. The storage container 5 is equipped with a nozzle 6 at its bottom, and the molten alloy 3 is further heated by a heating coil (not shown), and the molten alloy 3 is ejected from a slit 7 formed at the lower end of the nozzle 6 onto the surface (outer surface) of the cooling roll 8. The cooling roll 8 rapidly cools the molten alloy in contact with its surface by supplying cooling water to its interior, forming a thin strip of rapidly solidified alloy 9. The material of the nozzle 6 can be appropriately selected from, for example, materials mainly composed of quartz (SiO2), boron nitride (BN), silicon carbide (SiC), and alumina (Al2O3).

[0045] The nozzle 6 is a single-slit nozzle with a single slit 7 formed therein, and the longitudinal direction of the slit 7 is positioned perpendicular to the rotation direction of the cooling roll 8 (i.e., parallel to the rotation axis of the cooling roll 8). The width W1 of the slit 7 plays a role in adjusting the pouring rate of the molten alloy 3 supplied to the cooling roll 8. If the slit width W1 is too small, slitting becomes difficult, and the slit 7 is more likely to become blocked by the molten metal. On the other hand, if the slit width W1 is too large, the pouring rate becomes too high, and the cooling roll 8 cannot keep up with the heat dissipation, causing the rapidly solidified alloy to stick to the cooling roll 8 and making it difficult to continue stable rapid solidification of the molten metal. Therefore, the slit width W1 is 0.2 mm or more and 0.8 mm or less. Preferably, the slit width W1 is 0.3 mm or more and 0.7 mm or less, and more preferably 0.3 mm or more and 0.6 mm or less.

[0046] The nozzle 6 may be a strand nozzle as shown in Figure 1(d) instead of the slit nozzle shown in Figure 1(c). In the strand nozzle shown in Figure 1(d), a plurality of holes 7a are arranged in a row perpendicular to the rotation direction of the cooling roll 8 (i.e., parallel to the rotation axis of the cooling roll 8). The diameter of each hole 7a in the strand nozzle is 0.6 mm or more and 1.3 mm or less, preferably 0.7 mm or more and 1.2 mm or less, and more preferably 0.7 mm or more and 1.1 mm or less. If the diameter of the hole 7a is less than 0.6 mm, the amount of molten metal dispensed per hole is small, which may cause the temperature at the tip of the nozzle 6 to drop and make it impossible to continue dispensing the molten metal. On the other hand, if the diameter of the hole 7a exceeds 1.3 mm, the amount of molten metal dispensed per hole becomes too large, which may result in incomplete rapid cooling of the molten metal and the precipitation of coarse α-Fe, which leads to a decrease in magnetic properties. Furthermore, if the spacing between each hole 7a is too small, the molten metal coming out of each hole 7a may come into contact with each other, resulting in incomplete rapid cooling of the molten metal and the possibility of coarse α-Fe precipitation that leads to a decrease in magnetic properties. Therefore, a spacing of 1.0 mm or more is preferable, 3.0 mm or more is more preferable, and 5.0 mm or more is even preferable. From the viewpoint of production efficiency of the rapidly solidified alloy and prevention of a drop in nozzle tip temperature, the spacing between each hole 7a is preferably 20 mm or less. Note that the shape of the opening of the nozzle 6 can also be other shapes, such as a single hole.

[0047] The molten metal supplied to the surface of the cooling roll 8 becomes a thin strip of rapidly solidified alloy 9 due to the rotation of the cooling roll 8 and is peeled off from the cooling roll 8. If the surface speed of the cooling roll 8 is less than 15 m / sec, the rapidly solidified alloy becomes excessively thick, exceeding 40 μm, which may result in more than 10.0 volume% of α-Fe crystal phases with an average grain size of 100 nm or more, oriented in the (200) direction and precipitated near the surface of the rapidly solidified roll surface or free surface of the iron-based soft magnetic alloy strip due to heterogeneous nucleation during rapid solidification. On the other hand, if the surface speed of the cooling roll 8 exceeds 50 m / sec, the thickness of the iron-based soft magnetic alloy strip becomes less than 18 μm, and the pulverability of the rapidly solidified alloy strip is significantly reduced. In either case, it becomes difficult to obtain the desired alloy powder in subsequent processes. For this reason, the surface speed of the cooling roll 8 is 15 m / sec or more and 50 m / sec or less, preferably 20 m / sec or more and 45 m / sec or less, and more preferably 25 m / sec or more and 40 m / sec or less. This makes it possible to form a thin, strip-shaped rapid-solidified alloy having a desired rapid-solidification alloy structure with a thickness of 18 μm or more and less than 40 μm, and exhibiting excellent pulverability.

[0048] In Figure 1(a), if the distance d from the tip of the nozzle 6, which consists of a single slit, to the surface of the cooling roll 8 is too small, the rapidly cooled alloy may stick to the cooling roll 8, making it impossible to continue stable rapid cooling and solidification of the molten alloy 3. On the other hand, if the distance is too large, a paddle may not form on the surface of the cooling roll 8, making it impossible to rapidly cool and solidify the molten alloy 3. For this reason, the above distance d is 0.1 mm or more and 2.0 mm or less, preferably 0.1 mm or more and 1.5 mm or less, and more preferably 0.15 mm or more and 1.0 mm or less.

[0049] Even when the nozzle 6 is a strand nozzle, if the distance d from the tip of the nozzle 6 to the surface of the cooling roll 8 in Figure 1(a) is too small or too large, the same problems as in the case of the single-slit nozzle described above will occur. For this reason, when the nozzle 6 is a strand nozzle, the above distance d is 0.5 mm or more and 30.0 mm or less, preferably 1.0 mm or more and 20.0 mm or less, and more preferably 2.0 mm or more and 10.0 mm or less.

[0050] In the production of a thin strip of rapidly solidified alloy 9, the adhesion of the molten alloy 3 to the outer surface of the cooling roll 8 is important, but this adhesion largely depends on the surface roughness of the cooling roll 8. If the surface roughness of the cooling roll 8 is too low, the molten alloy 3 will slide on the surface of the cooling roll 8, making sufficient cooling difficult. On the other hand, if the surface roughness of the cooling roll 8 is too high, the rapidly solidified alloy may stick to the cooling roll 8. For this reason, the arithmetic mean roughness (Ra) on the surface of the cooling roll 8 is preferably between 0.01 μm and 0.6 μm, more preferably between 0.05 μm and 0.55 μm, and more preferably between 0.1 μm and 0.5 μm.

[0051] The cooling roll 8 is preferably formed from a material primarily composed of pure copper, copper alloy, molybdenum (Mo), or tungsten (W) to ensure excellent thermal conductivity and durability. "Primary material" means that it accounts for 50% or more of the material by weight. The surface of the cooling roll 8 may be plated with chromium, nickel, or an alloy thereof. This increases the heat resistance and hardness of the cooling roll 8 surface, suppressing melting and deterioration of the roll surface during rapid solidification.

[0052] The diameter of the cooling roll 8 is, for example, 200 to 20,000 mm. Water cooling is not necessarily required for the cooling roll 8 if the continuous rapid cooling and solidification time is short, such as 10 seconds or less. However, if the continuous rapid cooling and solidification time exceeds 10 seconds, it is preferable to circulate cooling water inside the cooling roll 8 to suppress the temperature rise of the surface of the cooling roll 8. The water cooling capacity of the cooling roll 8 is preferably adjusted appropriately according to the latent heat of solidification per unit time and the molten metal output rate.

[0053] [Crush] As described above, the method for producing the iron-based soft magnetic alloy of the present invention may include a grinding step for grinding the obtained iron-based soft magnetic alloy. The grinding method involves selecting various grinding devices such as ball mills, feather mills, pin disc mills, and jet mills as appropriate, depending on the dust core molding method. For example, in the case of general compression molding using a thermosetting resin as a binder, a high magnetic powder filling rate can be obtained by grinding to an average powder particle size of 70 μm to 200 μm using a feather mill or pin disc mill. The average powder particle size is preferably 100 μm to 180 μm, and more preferably 100 μm to 140 μm. On the other hand, in injection molding, since a thermoplastic resin is generally used as a binder, a high magnetic powder filling rate can be obtained by grinding to an average powder particle size of 10 μm or more and 100 μm or less using a pin disc mill or jet mill. In this case, the average powder particle size is preferably 20 μm to 80 μm, and more preferably 30 μm to 70 μm.

[0054] The tap density of the iron-based soft magnetic alloy powder obtained by the grinding process is 2 g / cm³. 3 The above is preferable. Tap density is measured in accordance with the "Method for Measuring Tap Density of Metal Powder" specified in JIS Z 2512:2012. There is no particular upper limit to the tap density, but a tap density of 6 g / cm³ is preferable. 3 If the density exceeds 6 g / cm³, the fluidity of the powder within the cavity of the press mold decreases significantly in the case of compression molding, and a high molding density cannot be obtained. 3 The following are preferable.

[0055] [Heat treatment] The present invention's method for producing an iron-based soft magnetic alloy may further include a heat treatment step in which the obtained iron-based soft magnetic alloy powder is heat-treated at a constant temperature of 180°C to 450°C. This makes it possible to remove the strain generated in the iron-based soft magnetic alloy powder due to stress during grinding, and is expected to improve the iron loss and permeability of the iron-based soft magnetic alloy powder. Various heat treatment furnaces, such as batch furnaces and hoop belt furnaces, can be used for the heat treatment, and known methods can be used in which the strain-removing heat treatment is completed in a short time of a few seconds to tens of seconds without increasing the heat capacity of the powder due to contact (accumulation) between the ground powder particles (see, for example, Japanese Patent No. 6857392). The heat treatment temperature is preferably 200°C to less than 400°C, and more preferably 200°C to less than 350°C. In addition, the above heat treatment is preferably carried out in a vacuum or inert gas atmosphere, but heat treatment in air is also acceptable as long as the temperature is below 350°C.

[0056] [Examples] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples.

[0057] 100 kg of raw materials, each containing elements B, C, Co, and Fe with a purity of 99.5% or higher, were placed in an alumina crucible (melting furnace) and melted by high-frequency induction heating to form a molten alloy. 50 kg of this molten alloy was poured into an alumina storage container with an inner diameter of 200 mm and a height of 400 mm, equipped with a BN slit nozzle (Examples 1-4, 7-9, Comparative Examples 10-12 and 14, 15) or a strand nozzle (Examples 5-6, 13, 16) at the bottom. The slit width and length of the slit nozzles, or the diameter of each hole, the spacing between holes, and the number of holes in the strand nozzles are as shown in Table 1.

[0058] Subsequently, the 50 kg of molten alloy was further heated by energizing the high-frequency heating coils installed around the hot water storage container. After the molten alloy temperature reached approximately 100°C above the melting point of the alloy composition, the alumina molten metal stopper placed above the nozzle was withdrawn, and the molten alloy was ejected from the nozzle onto the cooling roll surface directly below. The cooling roll was made of chromium zirconite copper, with an outer diameter of 600 mm and a width of 200 mm. The gap between the nozzle and the cooling roll surface is shown in Table 1. The injection pressure of the molten alloy from the nozzle, the surface velocity of the cooling roll, and the arithmetic mean roughness (Ra) of the cooling roll surface are shown in Table 2.

[0059] The molten alloy ejected onto the surface of the cooling roll formed a puddle on the surface of the cooling roll, and rapidly solidified at the interface between the puddle and the cooling roll, thereby producing a thin, strip-shaped rapidly solidified alloy with the average thickness and width shown in Table 3. Microstructure evaluation of the obtained rapidly solidified alloys was performed by powder X-ray diffraction (XRD), and it was found that all of the iron-based soft magnetic alloys in Examples 1-9 had a metallic structure in which the α-Fe phase precipitated isotropically without being oriented in any particular direction.

[0060] As representative examples, the X-ray diffraction profiles of iron-based soft magnetic alloy powders for Example 2 and Example 7 are shown in Figures 2 and 3, respectively. In both Figures 2 and 3, diffraction peaks at (110), the main peak of α-Fe, and (200), the secondary peak, were confirmed. Since both are diffraction peaks with broad full widths at half maximum, it was confirmed that the microstructure consists of a fine metallic structure composed of isotropically precipitated α-Fe crystalline phases. Furthermore, a transmission electron microscope (TEM) image of Example 2 is shown in Figure 16. The metallic structure of Example 2 shown in Figure 16 was an extremely fine metallic structure consisting of α-Fe crystalline precursors of 1 nm or less.

[0061] Table 4 shows the results of measuring the saturation magnetic flux density Bs, iron loss (core loss), and permeability (μ) at a magnetic flux density of 1.0T at 1kHz, and the iron loss at a magnetic flux density of 1.5T at 20kHz, for the rapidly solidified alloys obtained in Examples 1-9 before pulverization. Bs was measured using a vibrating sample magnetometer manufactured by Toei Kogyo. Permeability μ and iron loss were measured using an SST unit (single-plate magnetic property tester) attached to a BH analyzer manufactured by Iwasaki Tsushinki.

[0062] Next, the rapidly solidified alloys obtained in Examples 1-9 were coarsely ground to a few millimeters or less using a feather mill, and then finely ground using a pin disc mill. The average particle size (D50), tap density, and Bs after fine grinding are shown in Table 5. The particle size distribution of the ground powder for Examples 2 and 7 is shown in Figures 4 and 5, respectively. The magnetization curves of the ground powder for Examples 2 and 7 are shown in Figures 6 and 7, respectively.

[0063] Furthermore, the pulverized powders obtained in Examples 6 and 7 were heat-treated at 260°C for 15 seconds using the same method as described in the aforementioned Japanese Patent Publication No. 6857392, to obtain the heat-treated pulverized powders of Examples 8 and 9. Figure 8 shows a comparison of the magnetization curves of the pulverized powders of Examples 7 and 9. As shown in Figure 8, it can be seen that by performing heat treatment, the strain imparted to the rapidly solidified alloy by pulverization is relieved, improving the permeability μ which was reduced by pulverization, resulting in a faster rise of the initial magnetization curve, and in addition, the magnetization for each applied magnetic field is improved overall.

[0064] In Example 2, 2% by mass of thermosetting epoxy resin was added to the obtained iron-based soft magnetic alloy powder and kneaded to prepare a compound for compression molding, which was then molded at 12 ton / cm². 2A toroidal ring with an outer diameter of 37 mm, an inner diameter of 17 mm, and a height of 6 mm was fabricated using the molding pressure specified. This toroidal ring was heat-cured (heat-treated) at 180°C for 1 hour, and after coating the surface of the toroidal ring with acrylic paint for insulation, its soft magnetic properties were evaluated using an Iwasaki Communication Equipment BH analyzer. Figure 9 shows the magnetic flux density and iron loss curve at 20 kHz in the toroidal ring-shaped dust core.

[0065] On the other hand, evaluation by powder X-ray diffraction (XRD) revealed that the Fe-Si-B rapidly solidified alloys of Comparative Examples 10 and 11 were predominantly amorphous. Comparative Examples 12 and 13, like Examples 1-9, had a microstructure in which the α-Fe phase was precipitated isotropically without orientation in any particular direction. Comparative Example 14 had a microstructure consisting of the α-Fe phase, and Comparative Example 16 had a microstructure in which the α-Fe phase and amorphous material were mixed. However, XRD analysis of Comparative Example 14 showed that the peak intensity of α-Fe(200) was higher than that of α-Fe(110), indicating that α-Fe was oriented in-plane perpendicular to the thickness direction of the rapidly solidified alloy strip. In Comparative Example 15, because the surface velocity of the cooling roll was slow, the molten metal was not sufficiently rapidly cooled on the cooling roll, and the surface of the rapidly solidified alloy oxidized, resulting in an alloy consisting of α-Fe and iron-based oxides. As representative examples, the powder X-ray diffraction profiles of the rapidly solidified alloy strips of Comparative Examples 10 and 12 are shown in Figures 10 and 11. As shown in Figures 10 and 11, Comparative Example 10 had an amorphous single-phase structure, and Comparative Example 12 had an α-Fe single-phase structure.

[0066] Similar to Examples 1-9, Table 4 shows the results of measuring the saturation magnetic flux density Bs, iron loss (core loss) and permeability (μ) at a magnetic flux density of 1.0T at 1kHz, and iron loss at a magnetic flux density of 1.5T at 20kHz for Comparative Examples 10-16, before pulverization. Bs was measured using a vibrating sample magnetometer manufactured by Toei Kogyo. Permeability μ and iron loss were measured using an SST unit (single-plate magnetic property tester) attached to a BH analyzer manufactured by Iwasaki Tsushinki.

[0067] Next, the rapidly solidified alloys obtained in Comparative Examples 10-16 were coarsely ground to a few millimeters or less using a feather mill, and then finely ground using a pin disc mill. The average particle size (D50), tap density, and Bs after fine grinding are shown in Table 5. The particle size distribution of the Fe-Si-B amorphous rapidly solidified alloy powder obtained in Comparative Example 10 is shown in Figure 12, and the magnetization curve is shown in Figure 13. The particle size distribution of the (Fe,Co)-Si-B rapidly solidified alloy powder obtained in Comparative Example 12 is shown in Figure 14. Comparative Example 12, which has high Si and B concentrations, has an α-Fe precursor structure similar to Examples 1-9, but like Comparative Example 10, which has an amorphous structure, it still contains more than 30% coarse powder of 250 μm or larger even after fine grinding with a pin disc mill, indicating significantly poor grindability. In addition, the structure consisting of the α-Fe phase in Comparative Example 14 was coarser, resulting in a significant increase in iron loss. Comparative Example 16 showed a significant decrease in pulverization due to the presence of an amorphous phase, while in Comparative Example 15, pulverization by pin milling was abandoned because iron-based oxides had formed on the surface layer of the rapidly solidified alloy.

[0068] For Comparative Example 10, a toroidal ring was fabricated from the obtained iron-based soft magnetic alloy powder, heat-cured, and then insulated before evaluating its soft magnetic properties, similar to Example 2. Figure 15 shows the magnetic flux density and iron loss curves at 20 kHz in the toroidal ring-shaped dust core.

[0069] [Table 1]

[0070] [Table 2]

[0071] [Table 3]

[0072] [Table 4]

[0073] [Table 5] [Explanation of Symbols]

[0074] l Single-roll molten metal rapid cooling device 2 Melting furnace 3. Molten alloy 4 Tilt axis 5. Hot water storage container 6. Hot water nozzle 7 slits 8 Cooling Rolls 9 Rapidly solidified alloys

Claims

1. Composition formula (Fe 1-m Co m ) 100-x-y Si x (B 1-n C n ) y It is expressed as follows, where the composition ratios x, y, m, and n are, 0.5≦x≦1.5 atomic%, 11.0≦y≦13.0 atomic%, 0.05≦m≦0.5、 0.0 ≤ n ≤ 0.3 The process of preparing a molten alloy with a composition that satisfies the following conditions, The system comprises a rapid cooling and solidification step in which the molten alloy is rapidly cooled and solidified on a cooling roll that uses pure copper, copper alloy, Mo, and W as the main raw materials, The rapid solidification step comprises a step of forming a thin strip of rapidly solidified alloy with a thickness of 18 μm or more and less than 40 μm by injecting the molten alloy from a nozzle onto the surface of the cooling roll while rotating the cooling roll at a roll surface speed of 15 m / sec or more and 50 m / sec or less. The aforementioned thin, strip-shaped rapidly solidified alloy has a metallic structure with an α-Fe phase as the main phase, a saturation magnetic flux density of 1.7T to 2.0T, and an iron loss of 15W / kg or less at a magnetic flux density of 1.0T and a frequency of 1kHz. The surface roughness of the cooling roll is such that the arithmetic mean roughness (Ra) is 0.01 μm or more and 0.6 μm or less. The nozzle is made of a material mainly composed of quartz (SiO2), boron nitride (BN), silicon carbide (SiC), and alumina (Al2O3), and the method for manufacturing an iron-based soft magnetic alloy involves dispensing the molten alloy at a pressure of 5 kPa to 50 kPa.

2. The nozzle is a single-slit nozzle, and the longitudinal direction of the slit is arranged to be perpendicular to the rotation direction of the cooling roll. The opening width of the slit is 0.2 mm or more and 0.8 mm or less. The method for manufacturing an iron-based soft magnetic alloy according to claim 1, wherein the distance from the nozzle to the cooling roll is 0.1 mm or more and 2.0 mm or less.

3. The nozzle is a strand nozzle in which a plurality of holes are arranged in a row perpendicular to the rotation direction of the cooling roll, The diameter of the hole is 0.6 mm or more and 1.3 mm or less. A method for manufacturing an iron-based soft magnetic alloy according to claim 1, wherein the distance from the nozzle to the cooling roll is 0.5 mm or more and 30.0 mm or less.

4. The method for producing an iron-based soft magnetic alloy according to claim 1, further comprising a grinding step of grinding the thin strip-shaped rapidly solidified alloy to an average powder particle size of 200 μm or less to form an iron-based soft magnetic alloy powder.

5. The method for producing an iron-based soft magnetic alloy according to claim 4, further comprising a heat treatment step of heat-treating the iron-based soft magnetic alloy powder at a constant temperature of 180°C to 450°C.

6. The aforementioned iron-based soft magnetic alloy powder has a tap density of 2 g / cm³. 3 The method for producing an iron-based soft magnetic alloy according to claim 4.

7. The method for producing an iron-based soft magnetic alloy according to claim 4, wherein the iron-based soft magnetic alloy powder has a residual magnetic flux density Bs of 1.5T or more.

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