Method for producing iron-based soft magnetic alloy

Abstract

Provided is a method for producing an iron-based soft magnetic alloy in a thin strip shape comprising a step for preparing a molten alloy having a predetermined composition and a rapid solidification step for rapidly solidifying the molten alloy on a cooling roll mainly composed of any one of pure copper, a copper alloy, Mo, and W, in which the iron-based soft magnetic alloy in a thin strip shape has a metal structure having an α-Fe phase as a main phase, a saturation magnetic flux density of 1.7-2.0 T, an iron loss of 15 W / kg or less at a magnetic flux density of 1.0 T and a frequency of 1 kHz, and a thickness of 18 μm or more and less than 40 μm, and wherein the rapid solidification step comprises a step in which the molten alloy is sprayed from a nozzle onto the surface of the cooling roll while rotating the cooling roll at a roll surface speed of 20-45 m / sec, the surface roughness of the cooling roll is 0.01-0.06 μm in terms of arithmetic average roughness (Ra), the nozzle is made of a material containing any one of quartz (SiO2), boron nitride (BN), silicon carbide (SiC), and alumina (Al2O3) as a main component, and the molten alloy is tapped at a pressure of 5-50 kPa.

Description

Manufacturing method of iron-based soft magnetic alloy

[0001] The present invention relates to a method for producing an iron-based soft magnetic alloy.

[0002] In recent years, the market has been demanding materials with low iron loss and high saturation magnetic flux density for various passive elements and transformers used in power electronics fields, such as inductors and reactors used as electronic components. Known soft magnetic materials with high magnetic permeability and low iron loss include iron-based amorphous materials and iron-based nanocrystalline materials, such as Fe-Si-B based rapidly solidified alloy ribbons with a thickness of approximately 17 μm to 25 μm, which are produced by rapid solidification of a molten metal made primarily of iron (Fe), silicon (Si), and boron (B). Demand for these low iron loss soft magnetic materials, which can replace conventional silicon steel sheets (Fe-Si), is increasing for use in large transformers and inductors.

[0003] In addition, the Fe-Si-B rapidly solidified alloys mentioned above have been considered for use in the stator cores of brushless direct current (BLDC) motors, taking advantage of their lower iron loss compared to silicon steel sheets. Their application to these motors is being considered to improve the efficiency of brushless direct current (BLDC) motors by reducing iron loss in the stator core. In particular, for high-speed motors exceeding 10,000 or 20,000 rpm, the operating range of soft magnetic materials is a high frequency band of 1 kHz or higher, which has been confirmed to reduce iron loss in the stator core and achieve unprecedented efficiency. Furthermore, with motors currently accounting for approximately 60% of the world's electricity, improving motor efficiency is expected to be a direct means of achieving carbon-free energy, leading to applications 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 saturation magnetic flux density of 1.6 T or less, which is lower than the 1.8 T of electrical steel sheets, which are currently used as motor core materials, and so while they can ensure the necessary motor output in high-speed motors of 10,000 rpm or more, they are difficult to apply to motors that require high torque even at low rotation speeds, such as in factory automation and air mobility. For this reason, there is a demand for iron-based soft magnetic materials that can achieve low iron loss performance comparable to that of Fe-Si-B amorphous alloys while maintaining a high saturation magnetic flux density of around 1.8 T, similar to that of electrical steel sheets.

[0005] Due to the above market demands, it is difficult for Fe-Si-B amorphous alloys, which have a maximum Bs of around 1.6T, or iron-based nanocrystalline materials (such as FINEMETR), which have a Bs of around 1.4T, to replace electrical steel sheets with a Bs of 1.8T. To date, there have been no examples of BLDC motors using Fe-Si-B rapidly solidified alloys being introduced to the market as motors for factory automation or air mobility.

[0006] Until now, BLDC motors for the above-mentioned factory automation (FA) and air mobility applications have combined a core material of magnetic steel with an anisotropic rare-earth iron-boron sintered magnet, which exhibits excellent permanent magnetic properties, to achieve high efficiency by utilizing magnetic torque. However, with magnetic steel, which has high iron loss, the input power is lost through iron loss generated in the stator core, making it impossible to achieve the motor efficiency required for BLDC motors for FA and air mobility. Therefore, there is extremely high market demand in a variety of applications for high-output, high-efficiency BLDC motors that can contribute to energy savings.

[0007] Furthermore, Fe-Si-B amorphous alloys can significantly reduce iron loss to less than one-tenth of that of electrical steel sheets, and because they also have high magnetic permeability, if they can overcome the issue of lower Bs than electrical steel sheets, they can ensure the motor output required for BLDC motors for factory automation and air mobility by achieving Bs ≥ 1.7 T. For this reason, there are extremely high expectations in the motor market worldwide for core materials that achieve low iron loss on a par with iron-based amorphous alloys, which can achieve Bs ≥ 1.7 T and can be used to replace electrical steel sheets.

[0008] The electromagnetic steel sheets used in the rotor and stator cores of BLDC motors are used as laminated cores, but existing Fe-Si-B amorphous alloys are difficult to punch due to their thin thickness of approximately 20 μm. In addition, due to the thin alloy thickness, the space factor when laminated into a core is low at less than 90%, compared to the 92% or more of electromagnetic steel sheets, making it difficult to obtain motor torque on a par with that of electromagnetic steel sheets.

[0009] In Non-Patent Document 1, Fe-Si-B amorphous alloys have been used for 10 4 ~10 6It has been disclosed that an amorphous structure could only be obtained by rapidly solidifying alloy ribbons with a thickness of approximately 17 to 22 μm at an extremely fast rapid solidification rate of 1000 K / sec, but that the addition of phosphorus (P) can reduce the rapid solidification rate and obtain iron-based amorphous alloy ribbons with a thickness of 50 μm or more. However, the addition of P not only reduces the saturation magnetic flux density Bs, but also volatilizes the P component during alloy melting, causing significant furnace contamination in P-added alloys, and therefore there are still few examples of its application in the industrial field.

[0010] Non-Patent Document 2 discloses that the Fe-Si-B-P-Cu iron-based nanocrystalline alloy "NANOMETR" is a soft magnetic material with a high saturation magnetic flux density Bs of 1.85 T and low iron loss performance comparable to that of an iron-based amorphous alloy. However, this iron-based nanocrystalline alloy is very brittle and difficult to fabricate into laminated cores using a punching press process, making it difficult to apply to the rotor cores and stator cores of BLDC motors at the mass-production level, and there have been no examples of it being put to practical use as a core material for motors except at the prototype level.

[0011] Patent Documents 1, 2, and 3 describe methods for producing rapidly solidified alloy ribbons having a thickness of 50 μm or more. However, none of these methods have produced an Fe-Si-B amorphous alloy having a Bs of 1.7 T or more, which is expected to be used in laminated cores for BLDC motors used to drive EVs. Furthermore, there have been no examples of iron-based amorphous alloys being used industrially as soft magnetic materials to replace silicon steel sheets.

[0012] Patent Document 4 discloses a method for producing a metal ribbon, in which molten metal is ejected onto a moving cooling substrate (a rotating cooling roll) from a plurality of openings (multi-hole nozzles) arranged substantially perpendicular to the direction of the substrate's movement, each of which has an angle of 10 to 80 degrees relative to the direction of the substrate's movement, and then rapidly solidified. However, the invention of Patent Document 4 is intended to reduce the thickness variation of a wide rapidly spun ribbon in the width direction. Furthermore, it is difficult to process a plurality of openings having an elongated parallelogram, trapezoid, or ellipse shape with angles of 10 to 80 degrees, and the nozzle processing costs are high, making it difficult to use in industrial mass production.

[0013] Patent Document 5 discloses a method for producing an Fe-Si-B-based amorphous alloy having a thickness of 40 μm or more, but does not disclose an alloy composition that can ensure Bs≧1.7 T, and the invention is not intended to provide a soft magnetic material for BLDC motors used to drive EVs.

[0014] Patent Document 6 discloses an Fe—Si—B based rapidly solidified alloy having a thickness of 40 μm to 70 μm, a saturation magnetic flux density Bs≧1.7 T, a coercive force Hc≦200 A / m, and a method for producing the same. However, according to this production method, an α-Fe phase of 0.1 vol % to 10 vol % is precipitated in the surface layer during the rapid solidification process, and the remainder of the rapidly solidified alloy is an amorphous structure, which may make punching press processing difficult depending on the core shape.

[0015] JP 5-329587, JP 7-113151, JP 8-124731, JP 63-220950, JP 2018-153828, JP 2021-193199

[0016] Creation of new bulk metallic glass / amorphous thick plates with high saturation magnetic flux density (Tohoku University, Metallic Glass Research Center) Akihiro Makino, Ken Kubota, Tokoshunto, Latest research and development trends of ultra-low core loss, high iron concentration soft magnetic alloy "NANOMET", Journal of the Japan Institute of Metals, Material, Vol. 55, No. 3 (2016)

[0017] Rapidly solidified Fe-Si-B alloys are expected to have low core loss performance comparable to that of Fe-Si-B amorphous alloys, which significantly improve motor efficiency while maintaining a saturation magnetic flux density equivalent to that of electrical steel sheets widely used in transformers and various motors. At the same time, they can be stamped using a press like electrical steel sheets, ensuring a core space factor of 90% or more, making them suitable for use as laminated motor cores. However, it is difficult to achieve a saturation magnetic flux density equivalent to that of electrical steel sheets with Fe-Si-B amorphous alloys. On the other hand, the rapidly solidified Fe-Si-B alloy described in Patent Document 6, which contains a mixture of amorphous and α-Fe crystalline phases, can achieve a saturation magnetic flux density Bs ≥ 1.7 T, but is difficult to stamp at press speeds comparable to that of electrical steel sheets. For this reason, it has been difficult to use them as cores for BLDC motors for factory automation (FA) and air mobility.

[0018] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for producing an iron-based soft magnetic alloy that can be easily punched while ensuring low core loss and high saturation magnetic flux density.

[0019] The object of the present invention is to provide a compound having the composition formula (Fe 1-m Co m ) 100-x-y Si x (B 1-n C n ) ywherein composition ratios x, y, m, and n satisfy the following relationships: 0.8≦x≦3.0 atomic %, 11.0≦y≦14.0 atomic %, 0.05≦m≦0.5, and 0.0≦n≦0.3, respectively, and the alloy does not contain Cu; and a rapid solidification step of rapidly solidifying the alloy molten on a chill roll made primarily of any of pure copper, a copper alloy, Mo, and W, wherein the iron-based soft magnetic alloy ribbon has a metallographic structure mainly composed of an α-Fe phase, a saturation magnetic flux density of 1.7 T or more and 2.0 T or less, an iron loss at a magnetic flux density of 1.0 T and a frequency of 1 kHz of 15 W / kg or less, and a thickness of 18 μm or more and less than 40 μm, wherein the rapid solidification step This is achieved by a method for producing an iron-based soft magnetic alloy, which includes a step of spraying the molten alloy from a nozzle onto the surface of the chill roll while rotating the chill roll at a roll surface speed of 20 m / sec or more and 45 m / sec or less, wherein the surface roughness of the chill roll is an arithmetic mean roughness (Ra) of 0.01 μm or more and 0.6 μm or less, the nozzle is made of a material containing as a main component any of quartz (SiO2), boron nitride (BN), silicon carbide (SiC), and alumina (Al2O3), and the molten alloy is poured at a pressure of 5 kPa or more and 50 kPa or less.

[0020] In this method for producing an iron-based soft magnetic alloy, the nozzle is preferably a single-slit nozzle, and is preferably arranged so that the longitudinal direction of the slit is perpendicular to the rotation direction of the chill 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 chill roll is preferably 0.1 mm or more and 2.0 mm or less.

[0021] The produced iron-based soft magnetic alloy preferably has an iron loss of 1500 W / kg or less at a magnetic flux density of 1.5 T and a frequency of 20 kHz.

[0022] The nozzle may be a strand nozzle having a plurality of holes arranged in a row perpendicular to the rotation direction of the chill 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 chill roll is preferably 0.5 mm or more and 30.0 mm or less.

[0023] When the composition ratio x satisfies 0.8≦x≦1.4 atomic %, the produced iron-based soft magnetic alloy ribbon can also be suitably used as a material for dust cores. When used as a material for dust cores, it is preferable to further include a pulverization step of pulverizing the iron-based soft magnetic alloy ribbon to an average powder particle size of 200 μm or less to form iron-based soft magnetic alloy powder.

[0024] It is preferable that the method further comprises a heat treatment step of heat treating the iron-based soft magnetic alloy powder at a constant temperature of 180°C or higher and 450°C or lower.

[0025] The iron-based soft magnetic alloy powder has a tap density of 2 g / cm 3 It is preferable that this is equal to or greater than this.

[0026] The iron-based soft magnetic alloy powder preferably has a residual magnetic flux density Bs of 1.5 T or more.

[0027] According to the present invention, it is possible to provide a method for producing an iron-based soft magnetic alloy that can be easily punched while ensuring low core loss and high saturation magnetic flux density.

[0028] 1A is a schematic diagram of a manufacturing apparatus used in a manufacturing method for an iron-based soft magnetic alloy according to a first embodiment of the present invention, (b) is an enlarged view of a main portion thereof, and (c) is an enlarged view of the nozzle bottom.

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[116] [11 1 shows the relationship between operating frequency and iron loss at a magnetic flux density of 1.5 T for Example 2, Comparative Example 12, and a commercially available electrical steel sheet (35A360 manufactured by JFE Corporation).

[0034] FIG. 1 shows an SEM photograph of the iron-based soft magnetic alloy of Example 2. (a) is a schematic diagram of a manufacturing apparatus used in a manufacturing method of an iron-based soft magnetic alloy according to a second embodiment of the present invention, (b) is an enlarged view of a main portion thereof, (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.

[0035] FIG. 1 shows a powder X-ray diffraction profile of the iron-based soft magnetic alloy obtained in Example 22. (b) is a powder X-ray diffraction profile of the iron-based soft magnetic alloy obtained in Example 27. (c) is a powder particle size distribution of the iron-based soft magnetic alloy powder obtained in Example 22. (d) is a magnetization curve of the iron-based soft magnetic alloy powder obtained in Example 27. 1 is a comparison of the magnetization curves of the iron-based soft magnetic alloy powders obtained in Examples 27 and 29. FIG. 2 is an iron loss curve of 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 22. FIG. 3 is an X-ray diffraction profile of the Fe-Si-B-based amorphous rapidly solidified alloy obtained in Comparative Example 30. FIG. 4 is a powder X-ray diffraction profile of the iron-based soft magnetic alloy obtained in Comparative Example 32. FIG. 5 is a powder particle size distribution of the Fe-Si-B-based amorphous rapidly solidified alloy powder obtained in Comparative Example 30.1 is a magnetization curve of the Fe-Si-B amorphous rapidly solidified alloy powder obtained in Comparative Example 30. 2 is a powder particle size distribution of the Fe-Si-B amorphous rapidly solidified alloy powder obtained in Comparative Example 32. 3 is an iron loss curve of the magnetic flux density and iron loss at 20 kHz in a toroidal ring-shaped dust core using the Fe-Si-B amorphous rapidly solidified alloy powder obtained in Comparative Example 30. 4 is a TEM observation photograph of the iron-based soft magnetic alloy powder of Example 22. 5 is a TEM observation photograph of the iron-based soft magnetic alloy powder of Example 2.

[0029] The iron-based soft magnetic alloy of the present invention has iron loss that is one-tenth or less of that of electromagnetic steel sheet, and has low iron loss performance that is equal to or better than that of Fe-Si-B amorphous alloys.However, by isotropically and uniformly precipitating fine crystals made of α-Fe during the rapid solidification process during manufacturing, the iron-based soft magnetic alloy has an average thickness of 18 μm or more and less than 40 μm, which allows laminated cores to be mass-produced with press punching efficiency equivalent to that of electromagnetic steel sheet, while ensuring a saturation magnetic flux density Bs of 1.7 T or more that is applicable to BLDC motors for factory automation and air mobility.

[0030] As described above, the present inventors have discovered that an iron-based soft magnetic alloy can be obtained that has low iron loss performance equivalent to or better than that of an Fe-Si-B amorphous alloy, and that can be used to mass-produce laminated cores with press punching efficiency equivalent to that of electrical steel sheets, while maintaining a saturation magnetic flux density Bs≧1.7 T applicable to BLDC motors for factory automation (FA) and air mobility, etc., in an alloy composition range where the compounding ratios of each element are in the pseudo-ternary composition range of the essential elements Fe + Co, Si, and B, such that Si is 0.8 atomic % to 3.0 atomic % and B is 11 atomic % to 14 atomic %, with 5% to 50% of the Fe being substituted with Co, and where a portion of the B is substituted with C up to an upper limit of 30%. This has led to the invention.

[0031] [Alloy Composition] Fe is an essential element, and the remainder of the above elements is made up. By substituting a portion of the Fe with Co, which is also a ferromagnetic element like Fe, it is possible to ensure Bs ≥ 1.7T. However, if the substitution ratio m of Co for Fe is less than 5%, Bs ≥ 1.7T cannot be ensured. Furthermore, if the substitution ratio m of Co for Fe exceeds 50%, Bs tends to decrease. For this reason, the substitution ratio m of Co for Fe is limited to 5% or more and 50% or less. The substitution ratio m is preferably 5% or more and 30% or less, and more preferably 5% or more and 20% or less from the viewpoint of cost-effectiveness.

[0032] In the iron-based soft magnetic alloy obtained by the present invention, Si is not only an essential element for obtaining a fine structure, but also plays an important role in developing soft magnetic properties such as magnetic permeability. If the Si composition ratio x is less than 0.8 atomic percent, not only will the magnetic permeability at an applied magnetic field of 10 A / m deteriorate to 2000 or less, but it will also be difficult to maintain the core loss (core loss) at 1 kHz and 1.0 T below 15 W / kg. This reduces the high magnetic permeability and low core loss characteristics of the iron-based soft magnetic alloy of the present invention compared to electrical steel sheets. Furthermore, if the Si composition ratio x exceeds 3.0 atomic percent, the Fe content responsible for magnetization decreases, making it impossible to achieve a Bs of 1.7 T or higher. Therefore, the Si composition ratio x is set to 0.8 atomic percent or more and 3.0 atomic percent or less. The Si composition ratio x is preferably 1.0 atomic percent or more and 3.0 atomic percent or less, more preferably 1.2 atomic percent or more and 2.5 atomic percent or less, and even more preferably 1.3 atomic percent or more and 2.2 atomic percent or less.

[0033] If the B+C composition ratio y is less than 11.0 atomic percent, the iron-based soft magnetic alloy obtained by rapid solidification will have a coarse metal structure. This will not only prevent the iron loss performance of 15 W / kg or less at a magnetic flux density of 1.0 T and a frequency of 1 kHz, but will also make the iron-based soft magnetic alloy more susceptible to cracking during the stamping process, making it difficult to fabricate laminated cores. Furthermore, if the B+C composition ratio y exceeds 14.0 atomic percent, the proportion of Fe, which is responsible for magnetization, will decrease, making it impossible to achieve Bs≧1.7 T. Therefore, the B+C composition ratio y is set to 11.0 atomic percent or more and 14.0 atomic percent or less. The B+C composition ratio y is preferably set to 11.5 atomic percent or more and 13.0 atomic percent or less, and more preferably 12.0 atomic percent or more and 13.0 atomic percent or less.

[0034] By substituting a portion of B with C, the melting point of the molten alloy is lowered, the rapid solidification conditions are relaxed, and the iron-based soft magnetic alloy of the present invention is easier to produce. However, if the substitution ratio n of C to B exceeds 30%, Bs≧1.7T cannot be ensured, which is not preferable. For this reason, the substitution ratio n is limited to 30% or less. From the viewpoint of achieving both high Bs characteristics and low magnetic permeability, the substitution ratio 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, V, Ti, Mn, Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au, and Pb, but adding an additive concentration of more than 2.0 atomic % is not preferable because Bs≧1.7T cannot be obtained, and it is acceptable if the additive concentration is up to 2.0 atomic %, including the inclusion of impurities. Note that Cu does not form a solid solution in Fe, the main raw material, and adding Cu may cause the Cu dispersed in the ultrafine α-Fe structure to precipitate alone, which may interfere with the formation of the desired alloy powder, so 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 an α-Fe phase, which is isotropically precipitated without any specific orientation, as its main phase. The main phase is the phase with the largest volume fraction, preferably 50% or more, and more preferably 80% or more. The isotropically precipitated α-Fe phase has a fine crystalline structure with an average crystal grain size of less than 100 nm, and some have an ultrafine crystalline structure, which can be considered a crystalline precursor, with a crystal size of less than 1 nm. The crystal size of the α-Fe phase can be roughly determined from the half-width of the X-ray diffraction peak obtained by powder X-ray diffraction (XRD), or by observing the metallographic structure of the iron-based soft magnetic alloy using a transmission electron microscope (TEM). The volume fraction of the α-Fe phase can also be determined by the above-mentioned powder XRD or TEM. However, powder XRD is preferred because TEM observation can be difficult to distinguish from an amorphous phase when the α-Fe phase has an ultrafine crystalline structure.

[0037] However, when the molten alloy is rapidly solidified on a rotating chill roll, the iron-based soft magnetic alloy may contain amorphous phases and trace amounts of Fe-B phases in its metal structure, as long as the amounts do not adversely affect its soft magnetic properties. If the amorphous phase in the metal structure of the iron-based soft magnetic alloy exceeds 20% by volume of the entire metal structure, it becomes difficult to achieve Bs≧1.7T, so the amorphous phase content is 20% by volume or less. The amorphous phase content is preferably 10% by volume or less, and more preferably 5.0% by volume or less.

[0038] When the iron-based soft magnetic alloy obtained by the present invention is mass-produced and applied to laminated cores, it is necessary to continuously punch the iron-based soft magnetic alloy using a press to match the shape of the rotor core, stator core, etc. However, during the rapid solidification process in the production of the iron-based soft magnetic alloy, the presence of coarse α-Fe crystalline phases oriented in the (200) direction (in-plane orientation) with an average crystal grain size of 100 nm or more precipitated by heterogeneous nucleation during rapid solidification near the surface of the quench roll or free surface may serve as the starting point for cracks during punching, making punching difficult. For the reasons mentioned above, if the coarse α-Fe crystalline phase oriented in the (200) direction exceeds 10.0 volume % of the entire metal structure, cracks and chips may occur in the iron-based soft magnetic alloy during punching. Therefore, the α-Fe crystalline phase precipitated in the surface layer of the iron-based soft magnetic alloy should be 10 volume % or less, and from the viewpoint of stable punching workability, it should be 5.0 volume % or less, and more preferably 2.0 volume % or less. 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. Furthermore, as described below, when the iron-based soft magnetic alloy obtained by the present invention is pulverized and used in mass production as dust cores, if coarse α-Fe crystalline phases with an average grain size of 100 nm or more oriented in the (200) direction (in-plane orientation) precipitated by heterogeneous nucleation during the rapid solidification process during the production of the iron-based soft magnetic alloy are present near the surface of the quench roll or free surface, it may be difficult to achieve the desired low iron loss performance. To achieve 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 crystalline phase precipitated in the surface layer of the iron-based soft magnetic alloy should be 10 vol% or less. From the viewpoint of maintaining stable low iron loss performance, 5.0 vol% or less is preferred, and 2.0 vol% or less is even more preferred.

[0039] [Magnetic Properties] The saturation magnetic flux density Bs of the iron-based soft magnetic alloy of the present invention is 1.7 T or more and 2.0 T or less, either immediately after rapid solidification (as-spun) or after heat treatment from the as-spun state at a temperature of 180°C or more but less than 450°C for the purpose of distortion removal. If Bs exceeds 2.0 T, the iron loss at a magnetic flux density of 1.0 T and a frequency of 1 kHz exceeds 15 W / kg. Therefore, when used as a core for a BLDC motor for factory automation (FA) or air mobility, a clear improvement in motor efficiency compared to a core made of electrical steel sheet is not achieved. From the viewpoint of achieving both sufficient motor torque and high efficiency in the low-speed rotation range, Bs is 1.7 T or more and 2.0 T or less, preferably 1.73 T or more and 1.97 T or more, and more preferably 1.75 T or more and 1.95 T or less.

[0040] While conventional electrical steel sheets, iron-based amorphous alloys, and iron-based nanocrystalline alloys exhibit a tendency for their iron loss values ​​at each operating frequency to increase with increasing magnetic flux density, the iron-based soft magnetic alloy of the present invention exhibits a highly unique magnetic property in that its iron loss values ​​at each operating frequency show a clear tendency toward saturation with increasing magnetic flux density. In particular, the iron loss value at a high frequency of 20 kHz at a magnetic flux density of 1.5 T is 1500 W / kg or less, potentially significantly reducing the iron loss problematic in ultra-high-speed rotating motors (e.g., 50,000 rpm or more) and transformers for voltage step-up units. If the iron loss value at a magnetic flux density of 1.5 T at a frequency of 20 kHz is too high (e.g., 2000 W / kg or more), the iron loss becomes comparable to that of iron-based amorphous alloys and iron-based nanocrystalline alloys. Therefore, the iron loss value at a magnetic flux density of 1.5 T at a frequency of 20 kHz is preferably 1500 W / kg or less, more preferably 1300 W / kg or less, and even more preferably 1000 W / kg or less.

[0041] [First embodiment] A method for producing an iron-based soft magnetic alloy according to a first embodiment of the present invention includes a step of preparing a molten alloy having the above-described composition, and a rapid solidification step of rapidly solidifying the prepared molten alloy.

[0042] Fig. 1(a) is a schematic diagram of a single-roll molten metal quenching apparatus used in a method for producing an iron-based soft magnetic alloy according to a first embodiment of the present invention, Fig. 1(b) is an enlarged view of a nozzle, and Fig. 1(c) is an enlarged view of the nozzle bottom. The single-roll molten metal quenching apparatus 1 shown in Fig. 1 comprises a melting furnace 2, a molten metal storage vessel 5, and a cooling roll 8.

[0043] The melting furnace 2 supplies molten alloy 3, obtained by melting raw materials using high-frequency induction heating, to a molten alloy storage container 5 by rotating a tilting shaft 4. The molten alloy storage container 5 is equipped with a nozzle 6 at its bottom, and further heats the molten alloy 3 using a heating coil (not shown). The molten alloy 3 is then ejected onto the surface (outer periphery) of a chill roll 8 through a slit 7 formed at the bottom end of the nozzle 6. Cooling water is supplied to the chill roll 8, which rapidly cools the molten alloy that comes into contact with its surface, forming a thin ribbon of rapidly solidified alloy 9. The material of the nozzle 6 can be appropriately selected from materials primarily composed of, for example, quartz (SiO2), boron nitride (BN), silicon carbide (SiC), or alumina (Al2O3).

[0044] The nozzle 6 is a single-slit nozzle with a single slit 7 formed therein, and the longitudinal direction of the slit 7 is arranged so that it is perpendicular to the rotation direction of the chill roll 8 (i.e., parallel to the rotation axis of the chill roll 8). The width W1 of the slit 7 serves to adjust the tapping rate of the molten alloy 3 supplied to the chill roll 8. If the slit width W1 is too small, slit processing becomes difficult and the slit 7 is likely to be blocked by the molten alloy. On the other hand, if the slit width W1 is too large, the tapping rate becomes too high, preventing heat removal by the chill roll 8 in time, causing the rapidly solidified alloy to stick to the chill roll 8 and making it difficult to maintain stable rapid solidification of the molten alloy. Therefore, the slit width W1 is 0.2 mm or more and 0.8 mm or less. The slit width W1 is preferably 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.

[0045] The molten metal supplied to the surface of the chill roll 8 becomes a thin ribbon of rapidly solidified alloy 9 as the chill roll 8 rotates, and is then peeled off from the chill roll 8. If the roll surface speed of the chill roll 8 is less than 20 m / sec, the rapidly solidified alloy will have an excessive thickness of 40 μm or more. This may result in the presence of more than 10.0 volume % of α-Fe crystalline phases oriented in the (200) direction and having an average grain size of 100 nm or more, precipitated by heterogeneous nucleation during rapid solidification, near the chill roll surface or free surface of the ribbon of iron-based soft magnetic alloy. This may make the iron-based soft magnetic alloy more susceptible to cracking or chipping during punching. On the other hand, if the surface speed of the chill roll 8 exceeds 45 m / sec, the ribbon of iron-based soft magnetic alloy will be too thin, making it difficult to ensure a core space factor of 90% or more when it is formed into a laminated core. For this reason, the surface speed of the chill roll 8 is 20 m / sec or more and 45 m / sec or less, more preferably 25 m / sec or more and 40 m / sec or less.

[0046] 1(a), if the distance d from the tip of the nozzle 6 to the surface of the chill roll 8 is too small, the quenched alloy may stick to the chill roll 8, preventing stable rapid solidification of the molten alloy 3. If the distance d is too large, a puddle may not form on the surface of the chill roll 8, preventing rapid solidification of the molten alloy 3. Therefore, the 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.

[0047] In producing the ribbon-shaped rapidly solidified alloy 9, the adhesion of the molten alloy 3 to the outer surface of the chill roll 8 is important, but this adhesion of the molten alloy is largely dependent on the surface roughness of the chill roll 8. If the surface roughness of the chill roll 8 is too small, the molten alloy 3 will slide on the surface of the chill roll 8, making it difficult to cool it sufficiently, while if the surface roughness of the chill roll 8 is too large, the quenched alloy may stick to the chill roll 8. For this reason, the arithmetic mean roughness (Ra) of the surface of the chill roll 8 is 0.01 μm or more and 0.6 μm or less, preferably 0.05 μm or more and 0.55 μm or less, and more preferably 0.1 μm or more and 0.5 μm or less.

[0048] The chill roll 8 is preferably formed from a material whose main ingredient is pure copper, a copper alloy, molybdenum (Mo), or tungsten (W), thereby providing excellent thermal conductivity and durability. The term "main ingredient" refers to a material that accounts for 50% or more by weight. The surface of the chill roll 8 may be plated with chromium, nickel, or an alloy thereof, which increases the heat resistance and hardness of the chill roll 8 surface and prevents melting or deterioration of the roll surface during rapid solidification.

[0049] The diameter of the chill roll 8 is, for example, 200 to 20,000 mm. Water cooling of the chill roll 8 is not necessarily required if the continuous rapid solidification time is short, such as 10 seconds or less, but if the continuous rapid solidification time is 10 seconds or longer, it is preferable to run cooling water through the inside of the chill roll 8 to suppress the temperature rise on the surface of the chill roll 8. The water cooling capacity of the chill roll 8 is preferably adjusted appropriately depending on the latent heat of solidification per unit time and the melt pouring rate.

[0050] [Heat Treatment] In a preferred embodiment, the iron-based soft magnetic alloy is heat-treated at a constant temperature of 180°C to 450°C after rapid solidification or punching press, thereby enabling strain removal in the iron-based soft magnetic alloy and further improving magnetic permeability. Heat treatment temperatures below 180°C reduce the strain removal effect, while temperatures above 450°C tend to increase iron loss due to grain growth of the α-Fe that constitutes the iron-based soft magnetic alloy. The heat treatment temperature is preferably 200°C to 400°C, more preferably 200°C to 350°C. The heat treatment is preferably performed in a vacuum or inert gas atmosphere, but heat treatment in air is also acceptable as long as it is below 350°C.

[0051] The heat treatment may be performed in a state where a plurality of ribbons of iron-based soft magnetic alloy are superimposed and adhered together. An adhesive resin may be applied to the adhesion surfaces of the superimposed ribbons of iron-based soft magnetic alloy, and a thermocompression bonding process may be performed within the above-mentioned heat treatment temperature range, thereby forming a multilayer bonded iron-based soft magnetic alloy simultaneously with the heat treatment.

[0052] [Examples of the First Embodiment] The first embodiment of the present invention will be described in more detail below with reference to examples, although the present invention is not limited to the following examples.

[0053] 100 kg of raw materials containing B, C, Co, and Fe with a purity of 99.5% or higher was placed in an alumina crucible (melting furnace) and melted by high-frequency induction heating to form a molten alloy, resulting in the alloy compositions shown in Examples 1-11 and Comparative Examples 12-17 in Table 1 below. 50 kg of this molten alloy was poured into an alumina storage vessel with an inner diameter of 200 mm and a height of 400 mm, equipped with a single-slit BN nozzle at the bottom. The nozzle slit width and length are shown in Table 1.

[0054] The 50 kg of molten alloy was then further heated by passing electricity through a high-frequency heating coil installed around the molten alloy storage vessel. After the temperature of the molten alloy reached a temperature approximately 100°C higher than the melting point of the alloy composition, the alumina molten alloy stopper located above the nozzle was removed, and the molten alloy was sprayed from the nozzle onto the surface of the chill roll directly below. The chill roll was made of chromium zirconium copper and had an outer diameter of 600 mm and a width of 200 mm. The gap between the nozzle and the chill roll surface was as shown in Table 1. The spray pressure of the molten alloy from the nozzle, the roll surface speed of the chill roll, and the arithmetic mean roughness (Ra) of the chill roll surface were as shown in Table 2.

[0055] The molten alloy ejected onto the surface of the chill roll formed a puddle on the surface of the chill roll and was rapidly solidified at the interface between the puddle and the chill roll, thereby obtaining a ribbon-shaped rapidly solidified alloy (in the examples, an iron-based soft magnetic alloy) having the average thickness and average width shown in Table 3. The obtained rapidly solidified alloy was subjected to a 10-time punching test using a 1 mm diameter punch, and it was confirmed whether or not cracks occurred in the iron-based soft magnetic alloy during the test. The results are shown in Table 3.

[0056] The rapidly solidified alloys were subjected to structural evaluation by powder X-ray diffraction (XRD). It was found that the rapidly solidified alloys made of the iron-based soft magnetic alloy ribbons of Examples 1 to 11 all had a metallic structure in which the α-Fe phase precipitated isotropically without being oriented in a specific direction. The volume ratio of the amorphous phase calculated from the powder X-ray diffraction results is shown in Table 3.

[0057] As representative examples, X-ray diffraction profiles evaluated from the free surface side of the ribbon-shaped iron-based soft magnetic alloy for Example 2 and Example 7 are shown in Figures 2 and 3, respectively. In both Figures 2 and 3, the main peak of α-Fe, (110), and the secondary peak, (200), were confirmed, and both were diffraction peaks with wide half-widths, confirming the presence of a fine metal structure consisting of an isotropically precipitated α-Fe crystalline phase.

[0058] Of the iron-based soft magnetic alloys of Examples 1-11, all except Example 10 were measured immediately after rapid solidification, and Example 10 was measured after heat treatment. The results of measuring the saturation magnetic flux density Bs, core loss (core loss) and permeability (μ) at a magnetic flux density of 1.5 T at 1 kHz, and core loss (core loss) at a magnetic flux density of 1.5 T at 20 kHz are shown in Table 4. Table 5 also shows the results of measuring core loss (core loss) and permeability (μ) at a magnetic flux density of 1.0 T at 1 kHz, and core loss (core loss) at a magnetic flux density of 1.0 T at 20 kHz. Bs measurements were performed using a Toei Industrial Co., Ltd. vibration-type sample magnetometer, and μ and core loss measurements were performed using an Iwasaki Electric Co., Ltd. BH analyzer equipped with an SST unit (single sheet magnetic property tester). As a representative example showing the relationship between magnetic flux density and core loss, a plot of the iron-based soft magnetic alloy of Example 2 at each operating frequency is shown in Figure 6.

[0059] On the other hand, powder X-ray diffraction (XRD) analysis of the Fe-Si-B rapidly solidified alloys of Comparative Examples 12-15 revealed that the amorphous phase was dominant. As representative examples, X-ray diffraction profiles evaluated from the free surface side of the rapidly solidified alloy ribbons for Comparative Examples 12 and 13 are shown in Figures 4 and 5, respectively. As shown in Figure 4, Comparative Example 12 had an amorphous single-phase structure. Furthermore, as shown in Figure 5, Comparative Example 13 was found to have a structure in which the amorphous phase, which was the main phase, was mixed with an α-Fe phase with in-plane orientation due to heterogeneous nucleation in the surface layer. The volume fraction of the amorphous phase calculated from the powder X-ray diffraction results is shown in Table 3.

[0060] As in Examples 1-11, for Comparative Examples 12-15, the saturation magnetic flux density Bs, the core loss and permeability (μ) at a magnetic flux density of 1.5 T at 1 kHz, and the core loss at a magnetic flux density of 1.5 T at 20 kHz were measured, and the results are shown in Table 4. Furthermore, the core loss and permeability (μ) at a magnetic flux density of 1.0 T at 1 kHz, and the core loss at a magnetic flux density of 1.0 T at 20 kHz were measured, and the results are shown in Table 5. Furthermore, as a representative example of a comparative example showing the relationship between magnetic flux density and core loss, a plot of the iron-based soft magnetic alloy of Comparative Example 12 for each operating frequency is shown in FIG.

[0061] The rapidly solidified alloy of Comparative Example 16 was Si-free and had a slow roll surface speed of 10 m / sec, resulting in a coarse metal structure with an average crystal grain size of 100 nm or more, making it impossible to punch. In Comparative Example 17, the slit width was as wide as 0.9 mm, which increased the rate at which the molten metal was supplied from the single slit to the surface of the rapidly solidified roll, resulting in an average thickness of 40 μm or more, as shown in Table 3, and the punching test results were unacceptable.

[0062] The relationship between the operating frequency and the iron loss at a magnetic flux density of 1.5 T for each of Example 2, Comparative Example 12, and a commercially available electrical steel sheet (35A360 manufactured by JFE Corporation) is shown in Figure 8. Also, an SEM photograph of the iron-based soft magnetic alloy of Example 2 is shown in Figure 9.

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[0067]

[0068] [Second embodiment] According to the method for producing an iron-based soft magnetic alloy according to the first embodiment of the present invention, it is possible to produce an iron-based soft magnetic alloy that can be easily punched while ensuring low iron loss and high saturation magnetic flux density, and it is possible to mass-produce laminated cores with press punching efficiency equivalent to that of electromagnetic steel sheets. However, by adjusting the composition ratio x in the composition of the molten alloy according to the first embodiment to a narrower range, it is possible to obtain an iron-based soft magnetic alloy that is suitable not only for producing laminated cores but also for producing dust cores.

[0069] The method for producing an iron-based soft magnetic alloy according to the second embodiment of the present invention includes, in addition to the steps of preparing a molten alloy and the rapid solidification step of rapidly solidifying the prepared molten alloy, a crushing step of crushing the obtained iron-based soft magnetic alloy, thereby forming an iron-based soft magnetic alloy powder.

[0070] In the second embodiment, if the Si composition ratio x of the molten alloy exceeds 1.4 atomic percent, the amorphous formation ability of the rapidly solidified alloy increases and the pulverizability of the rapidly solidified alloy decreases, making it difficult to obtain an iron-based soft magnetic alloy powder with an average powder particle size of 10 μm to 200 μm. Therefore, the Si composition ratio x is set to 0.8 atomic percent to 1.4 atomic percent. The Si composition ratio x is preferably 1.0 atomic percent to 1.3 atomic percent.

[0071] When mass-producing dust cores using the manufacturing method of the second embodiment, if coarse α-Fe crystalline phases with an average grain size of 100 nm or more and oriented in the (200) direction (in-plane orientation) precipitated by heterogeneous nucleation during the rapid solidification process are present near the surface of the quench roll or the free surface, it may be difficult to achieve the desired low core loss performance. To achieve low core loss performance, i.e., an iron loss of 15 W / kg or less at a magnetic flux density of 1.0 T and a frequency of 1 kHz, the α-Fe crystalline phase precipitated in the surface layer of the iron-based soft magnetic alloy should be 10 vol% or less. From the viewpoint of maintaining stable low core loss performance, 5.0 vol% or less is preferred, and 2.0 vol% or less is even more preferred. In this invention, the "surface layer" refers to a depth from the surface of the iron-based soft magnetic alloy that is 10% of the thickness of the iron-based soft magnetic alloy.

[0072] The iron-based soft magnetic alloy powder obtained by the manufacturing method of the second embodiment is characterized by a saturation magnetic flux density Bs of 1.7 T or more before pulverization. If Bs exceeds 2.0 T, the iron loss at a magnetic flux density of 1.5 T and a frequency of 1 kHz exceeds 50 W / kg, and no clear improvement in efficiency is achieved compared to dust cores using Fe-Si atomized powder. To achieve stable energy-saving performance from the 60 Hz commercial frequency band to the megahertz band, the Bs of the rapidly solidified alloy before pulverization must be 1.7 T or more and 2.0 T or less, with 1.73 T or more and 1.97 T being preferred, and 1.75 T or more and 1.95 T being even more preferred.

[0073] When the iron-based soft magnetic alloy powder obtained by the manufacturing method of the second embodiment is used to manufacture a dust core having high Bs and low iron loss performance, it is effective that the powder has a Bs of 1.5 T or more when pulverized to an average powder particle size of 200 μm or less. The Bs of the iron-based soft magnetic alloy powder is preferably 1.55 T or more, and more preferably 1.6 T or more.

[0074] While the iron loss values ​​of existing Fe-Si atomized powders, iron-based amorphous alloy powders, and iron-based nanocrystalline alloy powders tend to increase with increasing magnetic flux density at each operating frequency, the iron-based soft magnetic alloy obtained by this embodiment exhibits extremely unique magnetic properties in that the iron loss values ​​at each operating frequency clearly tend to saturate with increasing magnetic flux density. In particular, the iron loss value at a high frequency of 20 kHz and a magnetic flux density of 1.5 T is 1500 W / kg or less, which may significantly reduce the iron loss that is a problem in reactors and ultra-high-speed rotation motors operating in the range of several tens of kHz to several tens of MHz. If the iron loss value at a frequency of 20 kHz and a magnetic flux density of 1.5 T is too high (for example, 2000 W / kg or more), the iron loss will be at the same level as that of an iron-based amorphous alloy and an iron-based nanocrystalline alloy. Therefore, the iron loss value at a frequency of 20 kHz and a magnetic flux density of 1.5 T is preferably 1500 W / kg or less, more preferably 1300 W / kg or less, and even more preferably 1000 W / kg or less.

[0075] 10(a) is a schematic diagram of a single-roll molten metal quenching apparatus used in a method for producing an iron-based soft magnetic alloy according to a second embodiment of the present invention, (b) is an enlarged view of a main portion thereof, (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. The single-roll molten metal quenching apparatus 1 shown in Figures 10(a) to 10(c) has the same configuration as the single-roll molten metal quenching apparatus 1 shown in Figures 1(a) to 1(c), and therefore description thereof will be omitted.

[0076] The slit nozzle 6 shown in Figures 10(a)-(c) may be replaced by a strand nozzle shown in Figure 10(d). In the strand nozzle shown in Figure 10(d), multiple holes 7a are arranged in a row perpendicular to the rotation direction of the chill roll 8 (i.e., parallel to the rotation axis of the chill roll 8). The diameter of each hole 7a of the strand nozzle is 0.6 mm to 1.3 mm, preferably 0.7 mm to 1.2 mm, and more preferably 0.7 mm to 1.1 mm. If the diameter of the holes 7a is less than 0.6 mm, the amount of molten metal tapped per hole is small, which may result in a drop in the temperature at the tip of the nozzle 6 and the inability to continue tapping. On the other hand, if the diameter of the holes 7a is greater than 1.3 mm, the amount of molten metal tapped per hole becomes too large, which may result in incomplete quenching of the molten metal and the precipitation of coarse α-Fe, which may deteriorate the magnetic properties. Furthermore, if the spacing between the holes 7a is too small, the molten metal coming out of the holes 7a may come into contact with each other, resulting in incomplete quenching of the molten metal and the precipitation of coarse α-Fe particles that deteriorate the magnetic properties. Therefore, the spacing between the holes 7a is preferably 1.0 mm or more, more preferably 3.0 mm or more, and even more preferably 5.0 mm or more. From the viewpoints of production efficiency of the rapidly solidified alloy and prevention of a decrease in the temperature at the nozzle tip, the spacing between the holes 7a is preferably 20 mm or less. The opening of the nozzle 6 may have other shapes, such as a single hole.

[0077] When the nozzle 6 is a strand nozzle, if the distance d from the tip of the nozzle 6 to the surface of the chill roll 8 in Figure 10(a) is too small or too large, the same problems as in the case of the single slit nozzle described above will occur. Therefore, when the nozzle 6 is a strand nozzle, the 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.

[0078] [Pulverization Step] As described above, the manufacturing method of the iron-based soft magnetic alloy according to the second embodiment of the present invention includes a pulverization step of pulverizing the obtained iron-based soft magnetic alloy. The pulverization method uses various pulverization devices, such as a ball mill, feather mill, pin-disk mill, or jet mill, appropriately selected depending on the molding method of the dust core. For example, in the case of typical compression molding using a thermosetting resin as a binder, a high magnetic powder packing ratio can be achieved by pulverizing the powder to an average powder particle size of 70 μm to 200 μm using a feather mill or pin-disk 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, since injection molding generally uses a thermoplastic resin as a binder, a high magnetic powder packing ratio can be achieved by pulverizing the powder to an average powder particle size of 10 μm to 100 μm using a pin-disk 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.

[0079] The tap density of the iron-based soft magnetic alloy powder obtained by the pulverization process was 2 g / cm 3 The tap density is measured in accordance with "Metal powder - Tap density measurement method" specified in JIS Z 2512:2012. There is no particular upper limit to the tap density, but a tap density of 6 g / cm or more is preferred. 3 If the density exceeds 6 g / cm, the flowability of the powder in the cavity of the press die is significantly reduced in the case of compression molding, and a high molding density cannot be obtained. 3 The following is preferred:

[0080] [Heat Treatment] The manufacturing method of the second embodiment can also 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 or higher and 450°C or lower. This allows for the removal of strain caused by the stress during pulverization, thereby improving the iron loss and magnetic permeability of the iron-based soft magnetic alloy powder. Heat treatment can be performed using various heat treatment furnaces, such as a batch furnace or a hoop belt furnace. Known methods for completing the strain-relief heat treatment in a short time (several seconds to several tens of seconds) without increasing the heat capacity of the powder due to contact (accumulation) between pulverized powder particles can be used (see, for example, Japanese Patent No. 6857392). The heat treatment temperature is preferably 200°C or higher but lower than 400°C, more preferably 200°C or higher but lower than 350°C. Additionally, the heat treatment is preferably performed in a vacuum or inert gas atmosphere, but heat treatment in air is also acceptable as long as the temperature is lower than 350°C.

[0081] [Examples of the Second Embodiment] The second embodiment of the present invention will be described in more detail below with reference to examples, although the present invention is not limited to the following examples.

[0082] 100 kg of raw materials containing B, C, Co, and Fe with a purity of 99.5% or higher was placed in an alumina crucible (melting furnace) and melted by high-frequency induction heating to form a molten alloy, resulting in the alloy compositions shown in Examples 21-29 and Comparative Examples 30-36 in Table 6 below. 50 kg of this molten alloy was poured into an alumina storage vessel with an inner diameter of 200 mm and a height of 400 mm, equipped at the bottom with a BN slit nozzle (Examples 21-24, Examples 27-29, Comparative Examples 30-32, and Comparative Examples 34 and 35) or a strand nozzle (Examples 25-26, Comparative Examples 33 and 36). The slit width and length of the slit nozzle, as well as the diameter, hole spacing, and number of holes in the strand nozzle, are shown in Table 6.

[0083] The 50 kg of molten alloy was then further heated by passing current through a high-frequency heating coil installed around the molten alloy storage vessel. After the temperature of the molten alloy reached a temperature approximately 100°C higher than the melting point of the alloy composition, the alumina molten alloy stopper located above the nozzle was removed, and the molten alloy was sprayed from the nozzle onto the surface of the chill roll directly below. The chill roll was made of chromium zirconium copper and had an outer diameter of 600 mm and a width of 200 mm. The gap between the nozzle and the chill roll surface was as shown in Table 6. The spray pressure of the molten alloy from the nozzle, the roll surface speed of the chill roll, and the arithmetic mean roughness (Ra) of the chill roll surface were as shown in Table 7.

[0084] The molten alloy ejected onto the surface of the chill roll formed a puddle on the surface of the chill roll and was rapidly solidified at the interface between the puddle and the chill roll, producing a ribbon-shaped rapidly solidified alloy having the average thickness and average width shown in Table 8. When the obtained rapidly solidified alloys were subjected to structural evaluation by powder X-ray diffraction (XRD), it was found that the iron-based soft magnetic alloys of Examples 21 to 29 all had a metal structure in which the α-Fe phase precipitated isotropically without being oriented in a specific direction.

[0085] As representative examples, X-ray diffraction profiles of iron-based soft magnetic alloy powders for Examples 22 and 27 are shown in FIGS. 11 and 12, respectively. In both FIGS. 11 and 12, the main α-Fe peak (110) and the secondary α-Fe peak (200) are observed. Both peaks have broad half-widths, confirming a fine metal structure composed of an isotropically precipitated α-Fe crystalline phase. A transmission electron microscope (TEM) photograph of Example 22 is shown in FIG. 25. The metal structure of Example 22 shown in FIG. 25 was an extremely fine metal structure composed of α-Fe crystalline precursors with sizes of 1 nm or less. Furthermore, a transmission electron microscope (TEM) photograph of Example 2 of the first embodiment is shown in FIG. 26. The metal structure of Example 2 shown in FIG. 26 was also an extremely fine metal structure composed of α-Fe crystalline precursors with sizes of 1 nm or less.

[0086] The saturation magnetic flux density Bs, core loss (core loss) and magnetic permeability (μ) at a magnetic flux density of 1.0 T at 1 kHz, and core loss at a magnetic flux density of 1.5 T at 20 kHz were measured for the rapidly solidified alloys obtained in Examples 21-29 before pulverization, and the results are shown in Table 9. Bs was measured using a vibration-type sample magnetometer manufactured by Toei Kogyo. Magnetic permeability μ and core loss were measured using an Iwasaki Electric BH analyzer equipped with an SST unit (single sheet magnetic property tester).

[0087] The rapidly solidified alloys obtained in Examples 21-29 were then coarsely pulverized to a few mm or less using a feather mill, followed by fine pulverization using a pin-disk mill. The average pulverized powder particle size (D50), tap density, and Bs after fine pulverization are shown in Table 10. The particle size distributions of the pulverized powders for Examples 22 and 27 are shown in Figures 13 and 14, respectively. The magnetization curves of the pulverized powders for Examples 22 and 27 are shown in Figures 15 and 16, respectively.

[0088] The pulverized powders obtained in Examples 26 and 27 were heat-treated at 260°C for 15 seconds using a method similar to that described in Japanese Patent No. 6,857,392, to obtain the heat-treated pulverized powders of Examples 28 and 29. Figure 17 compares the magnetization curves of the pulverized powders of Examples 27 and 29. As shown in Figure 17, the heat treatment relieves the strain imparted to the rapidly solidified alloy by pulverization, improving the magnetic permeability μ that had decreased due to pulverization, accelerating the rise of the initial magnetization curve, and overall improving the magnetization for each applied magnetic field.

[0089] In Example 22, 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. 2 A toroidal ring with an outer diameter of 37 mm, an inner diameter of 17 mm, and a height of 6 mm was fabricated using a molding pressure of 1000 MPa. This toroidal ring was thermally cured (heat treated) at 180°C for 1 hour, and the surface of the toroidal ring was insulated by coating it with an acrylic paint. The soft magnetic properties were then evaluated using an Iwasaki Electric BH analyzer. Figure 18 shows the iron loss curve of the magnetic flux density and iron loss at 20 kHz for the toroidal ring-shaped dust core.

[0090] On the other hand, powder X-ray diffraction (XRD) analysis of the rapidly solidified Fe-Si-B alloys of Comparative Examples 30 and 33 revealed that the amorphous phase was dominant. Furthermore, similar to Examples 21-29, Comparative Examples 31 and 32 had metal structures in which the α-Fe phase precipitated isotropically without orientation in a specific direction. Comparative Example 34 had a structure consisting of the α-Fe phase, and Comparative Example 36 had a structure in which the α-Fe phase and amorphous phases were mixed. However, XRD analysis of Comparative Example 34 revealed that the peak intensity of the α-Fe (200) was higher than that of the α-Fe (110), indicating that the α-Fe was in-plane oriented perpendicular to the thickness direction of the rapidly solidified alloy ribbon. In Comparative Example 35, the surface speed of the chill roll was slow, so the molten metal was not sufficiently quenched on the chill roll, resulting in oxidation of the surface of the rapidly solidified alloy, resulting in an alloy composed of α-Fe and iron-based oxides. As representative examples, powder X-ray diffraction profiles of the rapidly solidified alloy ribbons of Comparative Examples 30 and 32 are shown in Figures 19 and 20. As shown in FIGS. 19 and 20, Comparative Example 30 had an amorphous single-phase structure, and Comparative Example 32 had an α-Fe single-phase structure.

[0091] As in Examples 21-29, the saturation magnetic flux density Bs of the rapidly solidified alloys before pulverization obtained for Comparative Examples 30-36, the core loss (core loss) and magnetic permeability (μ) at a magnetic flux density of 1.0 T at 1 kHz, and the core loss at a magnetic flux density of 1.5 T at 20 kHz were measured. The results are shown in Table 9.

[0092] The rapidly solidified alloys obtained in Comparative Examples 30-36 were then coarsely pulverized to a few mm or less using a feather mill, followed by fine pulverization using a pin-disk mill. The average pulverized powder particle size (D50), tap density, and Bs after fine pulverization are shown in Table 10. The particle size distribution of the Fe-Si-B amorphous rapidly solidified alloy powder obtained in Comparative Example 30 is shown in Figure 21, and the magnetization curve is shown in Figure 22. The particle size distribution of the (Fe,Co)-Si-B rapidly solidified alloy powder obtained in Comparative Example 32 is shown in Figure 23. Comparative Example 32, which has a high concentration of Si and B, has an α-Fe precursor structure similar to Examples 21-29. However, like Comparative Example 30, which has an amorphous structure, it contains more than 30% coarse particles of 250 μm or larger even after fine pulverization using a pin-disk mill, demonstrating significantly poor pulverizability. Furthermore, Comparative Example 34 exhibited coarsening of the α-Fe phase, resulting in a significant increase in iron loss. In Comparative Example 36, the amorphous phase was contained, which significantly reduced the pulverization, but in Comparative Example 35, iron-based oxides were formed in the surface layer of the rapidly solidified alloy, so pulverization using a pin mill was abandoned.

[0093] For Comparative Example 30, a toroidal ring was produced from the obtained iron-based soft magnetic alloy powder, heat-cured, and then insulated, and the soft magnetic properties were evaluated, as in Example 22. Fig. 24 shows the iron loss curve of the magnetic flux density and iron loss at 20 kHz for the toroidal ring-shaped dust core.

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[0098]

[0099] In addition to Fe-Si-B iron-based amorphous alloy powder, other soft magnetic powders with excellent DC bias characteristics and low core loss are known. These include Fe-Si-B-Nb-Cu iron-based nanocrystalline alloy powders, which are obtained by crushing Fe-Si-B amorphous alloy ribbons with a thickness of approximately 17 to 25 μm, which are produced by rapid solidification of a melt made primarily from iron (Fe), silicon (Si), and boron (B), after appropriate crystallization heat treatment. There is increasing market demand for this powder as a dust core (powder magnetic core) powder to replace Fe-Si alloy powder produced by the conventional atomization method or Fe-Si-B-Cr amorphous powder produced by the SWAP method, for use in inductors, reactors, power conditioners, motor cores, etc.

[0100] In addition, the Fe-Si-B amorphous alloy powder and Fe-Si-B-Nb-Cu iron-based nanocrystalline alloy powder, which feature lower core loss than Fe-Si alloy powder, are being considered as core materials for power electronics operating in the several kHz to megahertz (MHz) range. These alloy powders have been shown to reduce core loss, particularly at high frequencies above 1 MHz, achieving unprecedented efficiency. Furthermore, with motors accounting for approximately 60% of the world's electricity, using dust cores in motor stator cores reduces not only core loss but also eddy current loss, significantly contributing to high motor efficiency (apart from the issue of low magnetic flux density Bs). As a direct means of achieving carbon-free energy, they are expected to be used in electric vehicles, white goods such as air conditioners, and factory automation motors.

[0101] However, the above-mentioned Fe-Si-B amorphous alloy has a Bs ≦ 1.6 T, and the Fe-Si-B-Nb-Cu iron-based nanocrystalline alloy has a Bs ≦ 1.3 T, which is lower than the Bs ≧ 1.8 T of the Fe-Si alloy, which is the existing core material, and therefore the Bs drops even further when used as a dust core. For this reason, it has not been widely used as a dust core substitute for Fe-Si alloy powder or pure iron powder, including for motor cores. There is a demand for an iron-based soft magnetic powder for dust cores that can achieve low iron loss performance comparable to that of Fe-Si-B amorphous alloy powder while maintaining high Bs performance comparable to that of Fe-Si alloy powder, which can be used for everything from passive elements in power electronics to motor cores.

[0102] Due to the above market demands, it is difficult for Fe-Si-B amorphous alloys, which have a maximum Bs of about 1.6 T, or iron-based nanocrystalline materials (such as FINEMET (registered trademark)), with a Bs of about 1.4 T or less, to replace Fe-Si alloys with a Bs of 1.8 T or more. For this reason, there have been no examples to date of a high-Bs, low-iron-loss iron-based soft magnetic powder for dust cores that is capable of achieving both low iron loss performance and high Bs on a par with Fe-Si-B amorphous alloy powders.

[0103] For example, in core materials for power electronics used in the megahertz band, or core materials for EV main motors that require high-speed rotation of over 20,000 rpm, dust cores made with pure iron or Fe-Si atomized powder, which have high iron loss, heat is generated in the core due to the iron loss generated in the core when power is input, which not only increases power consumption but also requires electricity for cooling.For this reason, there is extremely high market demand in a variety of applications for high-Bs, low-iron-loss iron-based soft magnetic powder for dust cores that can achieve high output and high efficiency and contribute to energy savings.

[0104] Furthermore, if it is possible to significantly reduce iron loss to less than one-tenth of that of iron-based amorphous alloys while maintaining high Bs, it is expected that this powder will be used in a variety of fields as a dust core.For this reason, there are extremely high expectations from the market for iron-based soft magnetic alloy powder for dust cores that achieves low iron loss on the same level as iron-based amorphous alloys, with Bs ≥ 1.7T before crushing, by crushing rapidly solidified alloys obtained by the single-roll quenching method, as an alternative to Fe-Si atomized powder, which has poor manufacturing yield and low recyclability.

[0105] In addition, both the Fe-Si powder obtained by gas atomization and the Fe-Si-B-Cr amorphous powder obtained by the SWAP method are spherical powders, and it is difficult to create a powder particle size distribution with a bimodal particle size distribution that allows for close packing, so the powder filling rate in the dust core is 70 to 80 volume percent for compression molding and 50 to 70 volume percent for injection molding. For this reason, in order to improve yield and achieve low costs, iron-based soft magnetic powders produced by pulverizing rapidly solidified alloys obtained by the single-roll quenching method require a magnetic powder particle size distribution with a magnetic powder filling rate in the dust core of 80 volume percent or more for compression molding and 70 volume percent or more for injection molding.

[0106] If it is possible to significantly reduce the iron loss of Fe-Si atomized powder to less than one-tenth of that of iron-based amorphous alloys while maintaining a high Bs, it can be used as a soft magnetic powder for dust cores that can be applied to core materials for inductors, reactors, power conditioners, and other power electronics, as well as motor cores, thereby reducing power consumption and contributing to energy conservation in a variety of fields.

[0107] According to the manufacturing method of the iron-based soft magnetic alloy of the second embodiment, it is possible to ensure Bs≧1.7T, which is comparable to that of Fe-Si alloys, in the rapidly solidified alloy state before pulverization, and also to realize low iron loss at the same level as that of iron-based amorphous alloys, thereby making it possible to mass-produce iron-based soft magnetic alloys suitable as materials for dust cores.

[0108] 1. Single roll molten metal quenching device 2. Melting furnace 3. Molten alloy 4. Tilting shaft 5. Melt storage container 6. Melt outlet nozzle 7. Slit 8. Cooling roll 9. Rapidly solidified alloy

Claims

1. Composition formula (Fe 1-m Co m ) 100-x-y Si x (B 1-n C n ) y and wherein composition ratios x, y, m, and n satisfy the following respectively: 0.8≦x≦3.0 atomic %, 11.0≦y≦14.0 atomic %, 0.05≦m≦0.5, 0.0≦n≦0.3, and the composition does not contain Cu; and a rapid solidification step of rapidly solidifying the molten alloy on a chill roll made primarily of pure copper, a copper alloy, Mo, or W, wherein the method for producing a ribbon of an iron-based soft magnetic alloy has a metallographic structure mainly composed of an α-Fe phase, a saturation magnetic flux density of 1.7 T or more and 2.0 T or less, an iron loss of 15 W / kg or less at a magnetic flux density of 1.0 T and a frequency of 1 kHz, and a thickness of 18 μm or more and less than 40 μm, The rapid solidification process includes a step of spraying the molten alloy from a nozzle onto the surface of the chill roll while rotating the chill roll at a roll surface speed of 20 m / sec or more and 45 m / sec or less, the surface roughness of the chill roll being an arithmetic mean roughness (Ra) of 0.01 μm or more and 0.6 μm or less, the nozzle being made of a material containing as a main component any of quartz (SiO2), boron nitride (BN), silicon carbide (SiC) and alumina (Al2O3), and discharging the molten alloy at a pressure of 5 kPa or more and 50 kPa or less.

2. A method for producing an iron-based soft magnetic alloy as set forth in claim 1, wherein the nozzle is a single-slit nozzle, and is arranged so that the longitudinal direction of the slit is perpendicular to the rotation direction of the chill roll, the opening width of the slit is 0.2 mm or more and 0.8 mm or less, and the distance from the nozzle to the chill roll is 0.1 mm or more and 2.0 mm or less.

3. A method for producing an iron-based soft magnetic alloy according to claim 1, wherein the iron loss at a magnetic flux density of 1.5 T and a frequency of 20 kHz is 1500 W / kg or less.

4. A method for producing an iron-based soft magnetic alloy as set forth in claim 1, wherein the nozzle is a strand nozzle having a plurality of holes arranged in a row perpendicular to the direction of rotation of the chill roll, the diameter of the holes is 0.6 mm or more and 1.3 mm or less, and the distance from the nozzle to the chill roll is 0.5 mm or more and 30.0 mm or less.

5. A method for producing an iron-based soft magnetic alloy according to claim 1, wherein the composition ratio x satisfies 0.8≦x≦1.4 atomic percent.

6. The method for producing an iron-based soft magnetic alloy according to claim 5, further comprising a pulverization step of pulverizing the ribbon-shaped iron-based soft magnetic alloy to an average powder particle size of 200 μm or less to form iron-based soft magnetic alloy powder.

7. The method for producing an iron-based soft magnetic alloy according to claim 6, further comprising a heat treatment step of heat treating the iron-based soft magnetic alloy powder at a constant temperature of 180°C or higher and 450°C or lower.

8. The iron-based soft magnetic alloy powder has a tap density of 2 g / cm 3 The method for producing an iron-based soft magnetic alloy according to claim 6, wherein the above-mentioned steps are carried out.

9. The method for producing an iron-based soft magnetic alloy according to claim 6, wherein the iron-based soft magnetic alloy powder has a residual magnetic flux density Bs of 1.5 T or more.

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