Method for producing iron-based crystalline alloy

Abstract

To provide an iron-based soft magnetic alloy that possesses Bs≥1.7 T, exhibits low iron loss characteristics, and enables lamination core formation.SOLUTION: An iron-based soft magnetic alloy has a composition expressed by the formula (Fe1-mCom)100-x-ySix(B1-nCn)y, in which the composition ratios x, y, m, and n satisfy 1.0≤x≤3.0 atom%, 11.0≤y≤14.0 atom%, 0.05≤m≤0.5, and 0.0≤n≤0.3. The alloy has a metal structure composed of an α-Fe phase, with an amorphous phase of 20 vol.% or less, a saturation magnetic flux density of 1.7 T or more and 2.0 T or less, and an iron loss of 50 W / kg or less at a magnetic flux density of 1.5 T and a frequency of 1 kHz, wherein the thickness of the iron-based soft magnetic alloy is 18 μm or more and less than 40 μm.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an iron-based soft magnetic alloy and a method for manufacturing the same, and more particularly to an iron-based soft magnetic alloy applicable to various brushless DC motors and a method for manufacturing the same. [Background technology]

[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 the power electronics field, such as inductors and reactors used as electronic components. Demand is increasing for iron-based amorphous materials, which are soft magnetic materials with high magnetic permeability and low iron loss, and Fe-Si-B rapidly solidified alloy ribbons with a thickness of approximately 17 μm to 25 μm, which are made by rapidly solidifying a molten metal made primarily of iron (Fe), silicon (Si), and boron (B), such as iron-based nanocrystalline materials, as low iron loss soft magnetic materials to replace conventional silicon steel sheets (Fe-Si), 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. By applying them to the stator cores of brushless direct current (BLDC) motors, researchers are studying how to improve the motor's efficiency by reducing iron loss. 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 now accounting for approximately 60% of the world's electricity, improving motor efficiency is expected to be a direct means of achieving a carbon-free society, leading to expectations for their application 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, and 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 6 It has been disclosed that an amorphous structure could only be obtained by rapidly solidifying alloy ribbons with a thickness of approximately 17 μm 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 causes significant furnace contamination due to the volatilization of the P component during alloy melting, and therefore there are still few examples of application in the industrial field.

[0010] Non-Patent Document 2 discloses that the Fe-Si-B-P-Cu system 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 iron-based amorphous alloys. However, this iron-based nanocrystalline alloy is extremely brittle and difficult to form into laminated cores using punching and pressing methods, making it difficult to apply to the rotor cores and stator cores of BLDC motors at the mass-production level. Therefore, except for at the prototype level, there have been no examples of it being put into practical use as a core material for motors.

[0011] Patent Documents 1, 2, and 3 describe methods for producing rapidly solidified alloy ribbons with a thickness of 50 μm or more, but none of them have produced an Fe-Si-B amorphous alloy with Bs ≥ 1.7 T that 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) that are arranged substantially perpendicular to the direction of movement of the substrate and each of which has an angle of 10 to 80 degrees relative to the direction of movement, and then rapidly solidified. However, Patent Document 4 is an invention made with the aim of reducing the variation in thickness of a metal ribbon in the width direction when producing a wide rapidly spun ribbon. Furthermore, it is difficult to process a plurality of openings in the shape of an elongated parallelogram, trapezoid, or ellipse with angles of 10 to 80 degrees, and there is also the problem of high nozzle processing costs, making it difficult to use on an industrial mass production level.

[0013] Patent Document 5 discloses a method for producing 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≧1.7T, and the invention is not intended to provide a soft magnetic material for BLDC motors used to drive EVs.

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

[0015] [Patent Document 1] JP 5-329587 [Patent Document 2] Patent Publication No. 7-113151 [Patent Document 3] Patent Publication No. 8-124731 [Patent Document 4] Patent Publication No. 63-220950 [Patent Document 5] Patent Publication No. 2018-153828 [Patent Document 6] Patent Publication No. 2021-193199 [Non-patent literature]

[0016] [Non-Patent Document 1] Creation of new bulk metallic glasses / amorphous thick plates with high saturation magnetic flux density (Tohoku University, Metallic Glass Research Center) Akihiro Makino, Ken Kubota, Tono Haruta [Non-patent document 2] Latest research and development trends of "NANOMET", an ultra-low core loss, high iron content soft magnetic alloy, Journal of the Japan Society for Metals, Material, Vol. 55, No. 3 (2016) Summary of the Invention [Problem to be solved by the invention]

[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. They can also be stamped using a press like electrical steel sheets, ensuring a core space factor of 90% or more, making them suitable for use in 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 in BLDC motor cores for factory automation (FA) and air mobility.

[0018] Therefore, an object of the present invention is to provide an iron-based soft magnetic alloy that satisfies Bs≧1.7T and has low core loss performance, and that can be made into a laminated core, and a method for producing the same. [Means for solving the problem]

[0019] The iron-based soft magnetic alloy according to the present invention has the composition formula (Fe 1-m Co m ) 100-x-y Si x (B 1-n C n ) y wherein the composition ratios x, y, m, and n satisfy 1.0≦x≦3.0 atomic %, 11.0≦y≦14.0 atomic %, 0.05≦m≦0.5, and 0.0≦n≦0.3, respectively; the iron-based soft magnetic alloy has a metal structure consisting of an α-Fe phase, a ratio of an amorphous phase of 20 volume % or less, 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 1.5 T and a frequency of 1 kHz of 50 W / kg or less, and a thickness of the iron-based soft magnetic alloy of 18 μm or more and less than 40 μm.

[0020] This 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.

[0021] In addition, in this iron-based soft magnetic alloy, the average crystal grain size of the α-Fe phase is preferably 5 nm or more and less than 100 nm.

[0022] The method for producing an iron-based soft magnetic alloy according to the present invention further comprises the steps of: 1-m Co m ) 100-x-y Si x (B 1-n C n ) ywherein the composition ratios x, y, m, and n satisfy the following conditions: 1.0≦x≦3.0 atomic %, 11.0≦y≦14.0 atomic %, 0.05≦m≦0.5, and 0.0≦n≦0.3, respectively; and a rapid solidification step of rapidly solidifying the molten alloy on a chill roll whose main raw material is any of pure copper, a copper alloy, Mo, and W, wherein the rapid solidification step 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 15 m / sec or more and 50 m / sec or less, the nozzle being a single-slit nozzle with the longitudinal direction of the slit arranged perpendicular to the rotation direction of the chill roll.

[0023] The nozzle material is preferably composed primarily of quartz (SiO2), boron nitride (BN), silicon carbide (SiC), or alumina (Al2O3), and the nozzle opening width is preferably 0.2 mm or more and 0.8 mm or less.

[0024] The surface roughness of the cooling roll is preferably such that the arithmetic mean roughness (Ra) is 0.01 μm or more and 0.6 μm or less.

[0025] The distance from the nozzle to the cooling roll is preferably 0.1 mm or more and 2.0 mm or less.

[0026] In this method for producing an iron-based soft magnetic alloy, it is preferable that the molten alloy be poured from the nozzle at a pressure of 5 kPa or more and 50 kPa or less. [Effects of the Invention]

[0027] According to the present invention, it is possible to provide an iron-based soft magnetic alloy having Bs≧1.7T and low core loss performance, which can be made into a laminated core, and a method for producing the same. [Brief explanation of the drawings]

[0028] [Figure 1]1(a) is a schematic diagram of an apparatus for producing an iron-based soft magnetic alloy according to one embodiment of the present invention, FIG. 1(b) is an enlarged view of the main part thereof, and FIG. 1(c) is an enlarged view of the nozzle bottom surface. [Figure 2] 1 is a powder X-ray diffraction profile of the iron-based soft magnetic alloy obtained in Example 2. [Figure 3] 1 is a powder X-ray diffraction profile of the iron-based soft magnetic alloy obtained in Example 7. [Figure 4] 1 shows X-ray diffraction profiles of the free surface (opposite to the contact surface with the chill roll) and the chill roll surface of the Fe—Si—B based rapidly solidified alloy obtained in Comparative Example 12. [Figure 5] 1 shows X-ray diffraction profiles of the free surface (opposite to the contact surface with the chill roll) and the chill roll surface of the Fe—Si—B based rapidly solidified alloy obtained in Comparative Example 13. [Figure 6] 1 is a plot of the relationship between magnetic flux density and iron loss for each operating frequency in the iron-based soft magnetic alloy obtained in Example 2. [Figure 7] 10 is a plot of the relationship between magnetic flux density and iron loss for each operating frequency in the Fe—Si—B based rapidly solidified alloy obtained in Comparative Example 12. [Figure 8] 1 shows the relationship between the operating frequency and the 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). [Figure 9] 1 is a SEM photograph of the iron-based soft magnetic alloy of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0029] The iron-based soft magnetic alloy of the present invention has iron loss that is 1 / 10 or less than 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., by using an alloy composition in which the compounding ratios of each element in the pseudo-ternary composition range of the essential elements Fe+Co, Si, and B are 1.0 atomic % to 3.0 atomic % Si, 11 atomic % to 14 atomic % B, with 5% to 50% of the Fe substituted with Co, and a portion of the B being substituted with C up to an upper limit of 30%. This has led to the invention of the present application.

[0031] [Alloy composition] By using Fe as an essential element and substituting the remainder of the above elements with Co, which is also a ferromagnetic element, for part of the 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 10% or more and 40% or less, and more preferably 15% or more and 35% or less from the viewpoint of cost-effectiveness.

[0032] In 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 1.0 atomic percent, not only will the magnetic permeability at an applied magnetic field of 10 A / m deteriorate to 2000 or less, but the core loss at 1 kHz and 1.5 T will be 100 W / kg or more. This will diminish 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 abundance ratio of Fe, which is responsible for magnetization, will decrease, making it impossible to achieve Bs≧1.7 T. For this reason, the Si composition ratio x is set to 1.0 atomic percent or more and 3.0 atomic percent or less. The Si composition ratio x is preferably 1.2 atomic percent or more and 2.5 atomic percent or less, and 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 50 W / kg or less at a magnetic flux density of 1.5 T and a frequency of 1 kHz, but 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 11.5 atomic percent or more and 13.5 atomic percent or less, and more preferably 12.0 atomic percent or more and 13.5 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%, it is not possible to ensure Bs≧1.7T, 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 of the present invention, it is possible to add one or more additive elements selected from the group consisting of Al, Si, V, Ti, Mn, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au, and Pb. However, if the additive concentration exceeds 2.0 atomic %, Bs≧1.7T cannot be obtained, which is not preferable, and the addition of up to 2.0 atomic % is permissible, including the presence as an impurity.

[0036] [Metal structure] The iron-based soft magnetic alloy of the present invention is characterized by being composed of an α-Fe phase that precipitates isotropically without being oriented in a specific direction. The fine α-Fe crystalline phase that precipitates isotropically throughout the iron-based soft magnetic alloy has a fine crystalline structure with an average crystal grain size of 5 nm or more and less than 100 nm. The average crystal grain size of the α-Fe phase can be determined from the half-width of the X-ray diffraction peak by powder X-ray diffraction (XRD) as described below.

[0037] However, even if an amorphous phase is present in the metal structure of the iron-based soft magnetic alloy obtained when the molten alloy is rapidly solidified on a rotating chill roll, this is acceptable as long as the amount does not adversely affect the 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 of the present invention is mass-produced for use in laminated cores, it is necessary to continuously punch the iron-based soft magnetic alloy using a press to match the shape of a rotor core, stator core, etc. However, during the rapid solidification process in the production of the iron-based soft magnetic alloy, 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 near the surface of the quench roll or free surface during rapid solidification may become 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 vol% 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 vol% or less, and from the viewpoint of stable punching workability, it should be 5.0 vol% or less, preferably 2.0 vol% 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 a range of 10% of the thickness of the iron-based soft magnetic alloy.

[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 1.5 T and a frequency of 1 kHz exceeds 50 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 is not achieved compared to a core made of electrical steel sheet. 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 existing electrical steel sheets, iron-based amorphous alloys, and iron-based nanocrystalline alloys tend to exhibit increasing iron loss values ​​at each operating frequency with increasing magnetic flux density, the iron-based soft magnetic alloy of the present invention exhibits extremely unique magnetic properties in that its iron loss value at each operating frequency clearly tends to saturate with increasing magnetic flux density. In particular, the iron loss value at a magnetic flux density of 1.5 T at a frequency of 20 kHz, which is a high frequency range, is 1500 W / kg or less, potentially significantly reducing the iron loss that is problematic in ultra-high-speed rotating motors (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] [Method of manufacturing iron-based crystalline alloy] The iron-based soft magnetic alloy of the present invention is produced by a method for producing an iron-based crystalline alloy, which includes a step of preparing a molten alloy having the above-described composition, and a 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 one embodiment of the present invention, Fig. 1(b) is an enlarged view of the 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 metal storage container 5 by rotating a tilting shaft 4. The molten metal 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 containing, for example, quartz (SiO2), boron nitride (BN), silicon carbide (SiC), and alumina (Al2O3) as its main component.

[0044] The nozzle 6 is a single-slit nozzle with a single slit 7 formed therein. 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. This causes the rapidly solidified alloy to stick to the chill roll 8, 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 surface speed of the chill roll 8 is less than 15 m / sec, the rapidly solidified alloy will have an excessive thickness of 40 μm or more. This may result in the iron-based soft magnetic alloy ribbon having an α-Fe crystalline phase oriented in the (200) direction and an average crystal grain size of 100 nm or more, which is precipitated by heterogeneous nucleation during rapid solidification, near the surface of the chill roll or the free surface, exceeding 10.0 volume %. 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 50 m / sec, the thickness of the iron-based soft magnetic alloy ribbon will be 18 μm or less, making it difficult to ensure a core space factor of 90% or more when it is made into a laminated core. Therefore, 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.

[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. For this reason, 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, copper alloy, molybdenum (Mo), or tungsten (W), thereby providing excellent thermal conductivity and durability. The main ingredient means that the main ingredient accounts for 50% or more by weight. The surface of the chill roll 8 may be plated with chromium, nickel, or an alloy of these, 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. If the continuous rapid solidification time is short, such as 10 seconds or less, the chill roll 8 does not necessarily need to be water-cooled. However, 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 a temperature rise on the surface of the chill roll 8. It is preferable to adjust the water-cooling capacity of the chill roll 8 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] In addition, the heat treatment may be performed in a state where a plurality of iron-based soft magnetic alloy ribbons are superposed and adhered to each other. An adhesive resin may be applied to the adhesion surfaces of the plurality of superposed iron-based soft magnetic alloy ribbons, and a thermocompression bonding treatment 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] 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, so as to obtain the alloy compositions shown in Examples 1-11 and Comparative Examples 12-15 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 is 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 are 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 microstructural evaluation by powder X-ray diffraction (XRD). It was found that the iron-based soft magnetic alloys 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 fraction 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 iron-based soft magnetic alloy ribbons for Example 2 and Example 7 are shown in Figures 2 and 3, respectively. In both Figures 2 and 3, a diffraction peak of (110), which is the main peak of α-Fe, and a diffraction peak of (200), which is the secondary peak, were confirmed, and both were diffraction peaks with wide half-widths, confirming 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 after heat treatment. The saturation magnetic flux density Bs, core loss (core loss) and magnetic permeability (μ) at a magnetic flux density of 1.5 T at 1 kHz, and core loss at a magnetic flux density of 1.5 T at 20 kHz were measured, and the results are shown in Table 4. Bs was measured using a vibration-type sample magnetometer manufactured by Toei Kogyo, and μ and core loss were measured using an Iwasaki Electric 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 (core loss) and magnetic 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. In addition, 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.

[0063] [Table 1]

[0064] [Table 2]

[0065] [Table 3]

[0066] [Table 4] [Explanation of symbols]

[0067] l Single roll molten metal quenching equipment 2 Melting furnace 3 Molten alloy 4 Tilt axis 5 Hot water container 6. Water outlet nozzle 7 Slit 8. Cooling roll 9 Rapidly solidified alloys

Claims

1. In iron-based soft magnetic alloys, the composition formula (Fe 1-m Co m ) 100-x-y Si x (B 1-n C n ) y where the composition ratios x, y, m, and n are expressed as follows: 1.0≦x≦3.0 atomic%, 11.0≦y≦14.0 atomic%, 0.05≦m≦0.5、 0.0≦n≦0.3 and It has a metal structure consisting of an α-Fe phase, The ratio of the amorphous phase is 20% by volume or less, The saturation magnetic flux density is 1.7T or more and 2.0T or less, The iron loss at a magnetic flux density of 1.5T and a frequency of 1kHz is 50W / kg or less. The thickness of the iron-based soft magnetic alloy is 18 μm or more and less than 40 μm.

2. 2. The iron-based soft magnetic alloy according to claim 1, which 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.

3. 2. The iron-based soft magnetic alloy according to claim 1, wherein the average crystal grain size of the α-Fe phase is 5 nm or more and less than 100 nm.

4. Composition formula (Fe 1-m Co m ) 100-x-y Si x (B 1-n C n ) y where the composition ratios x, y, m, and n are expressed as follows: 1.0≦x≦3.0 atomic%, 11.0≦y≦14.0 atomic%, 0.05≦m≦0.5、 0.0≦n≦0.3 preparing a molten alloy having a composition that satisfies the above; a rapid solidification step of rapidly solidifying the molten alloy on a chill roll whose main raw material is any one of pure copper, copper alloy, Mo, and W, the rapid solidification step includes a step of injecting the molten alloy from a nozzle onto the surface of the chill roll while rotating the chill roll at a roll surface speed of 15 m / sec or more and 50 m / sec or less, A method for producing an iron-based soft magnetic alloy, wherein the nozzle is a single-slit nozzle, and the longitudinal direction of the slit is arranged perpendicular to the rotation direction of the cooling roll.

5. The nozzle is made of a material containing one of quartz (SiO2), boron nitride (BN), silicon carbide (SiC), and alumina (Al2O3) as a main component, 5. The method for producing an iron-based soft magnetic alloy according to claim 4, wherein the nozzle opening width is 0.2 mm or more and 0.8 mm or less.

6. 5. The method for producing an iron-based soft magnetic alloy according to claim 4, 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.

7. 5. The method for producing an iron-based soft magnetic alloy according to claim 4, wherein the distance from the nozzle to the chill roll is 0.1 mm or more and 2.0 mm or less.

8. The method for producing an iron-based soft magnetic alloy according to claim 4, wherein the molten alloy is poured from the nozzle at a pressure of 5 kPa or more and 50 kPa or less.

9. An iron core having a space factor of 90% or more obtained by laminating a plurality of layers of the iron-based soft magnetic alloy according to claim 1.

Images