Method for producing iron-based soft magnetic alloy

Abstract

The method includes: a step for preparing a molten alloy that has a composition which is expressed by composition formula (Fe1 - mCom)100 - x - ySix(B1 - nCn)y, and in which composition ratios x, y, m, and n satisfy 1.0 atom% ≤ x ≤ 3.0 atom%, 11.0 atom% ≤ y ≤ 14.0 atom%, 0.05 ≤ m ≤ 0.5, and 0.0 ≤ n ≤ 0.3, respectively; and a rapid quenching solidification step for rapidly quenching and solidifying the molten alloy which is sprayed from a nozzle on a cooling roll that has a specific size and uses any one of pure copper, a copper alloy, Mo, and W as a main starting material. The rapid quenching solidification step includes a step for spraying the molten alloy from the nozzle onto the surface of the cooling roll while rotating the cooling roll, through which cooling water that is at not less than 5°C but less than 60°C is passed at a flow rate of not less than 0.1 m3 / min but less than 20 m3 / min, at a roll surface speed of 15 m / sec to 50 m / sec inclusive, thereby forming a thin belt-like rapidly quenched and solidified alloy that has a thickness of not less than 18 µm but less than 40 µm and has ultrafine α-Fe with an average crystal grain size of 1 nm or less as a main phase.

Description

Manufacturing method for iron-based soft magnetic alloys

[0001] This invention relates to a method for manufacturing an iron-based soft magnetic alloy, and more specifically, to a method for manufacturing an iron-based soft magnetic alloy applicable to various brushless DC motors.

[0002] In recent years, there has been a market demand for 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. Fe-Si-B rapid solidification alloy strips, approximately 17 to 25 μm thick, made by rapid solidification of molten metal using iron (Fe), silicon (Si), and boron (B) as the main raw materials, such as iron-based amorphous materials and iron-based nanocrystalline materials, are seeing increased demand in large transformers and inductors as low-iron-loss soft magnetic materials that replace conventional silicon steel sheets (Fe-Si).

[0003] In addition, the Fe-Si-B rapidly solidified alloy described above, leveraging its characteristic of low iron loss compared to silicon steel sheets, is being considered for application to the stator core of brushless direct current (BLDC) motors. This is being explored to improve the efficiency of BLDC motors by reducing iron loss in the stator core. In particular, for high-speed motors exceeding 10,000 rpm or 20,000 rpm, the operating range of the soft magnetic material is in the high-frequency band of 1 kHz or higher, which has been confirmed to suppress iron loss in the stator core and achieve unprecedented high efficiency. Furthermore, given that motors currently consume approximately 60% of the world's electricity, improving motor efficiency is expected to be a direct means of achieving carbon-free operation, and is anticipated to be applied to electric vehicles, white goods such as air conditioners, and motors for factory automation.

[0004] However, the Fe-Si-B amorphous alloys mentioned above have a saturation magnetic flux density of 1.6T or less, which is lower than the 1.8T of electrical steel sheets, an existing motor core material. Therefore, while they can secure the necessary motor output for high-speed motors rotating at 10,000 rpm or more, they are difficult to apply to motors that require high torque from low rotational speeds, such as those used in factory automation (FA) and air mobility. For this reason, there is a need for an iron-based soft magnetic material that can achieve both a high saturation magnetic flux density of around 1.8T, comparable to electrical steel sheets, and low iron loss performance comparable to Fe-Si-B amorphous alloys.

[0005] Given the market demands described above, Fe-Si-B amorphous alloys with a maximum Bs of around 1.6T, or iron-based nanocrystalline materials with a Bs of around 1.4T (e.g., FINEMET®), are not suitable replacements for electrical steel sheets with a Bs of 1.8T. To date, there have been no instances of BLDC motors using Fe-Si-B rapidly solidified alloys being introduced to the market for factory automation (FA) or air mobility applications.

[0006] BLDC motors for factory automation (FA) and air mobility have so far combined electrical steel core materials with anisotropic rare-earth iron-boron sintered magnets that exhibit excellent permanent magnet properties, and high efficiency has been achieved by utilizing magnet torque. However, with electrical steel, which has high iron loss, the input power is lost due to iron loss in the stator core, and the motor efficiency required for BLDC motors for FA and air mobility cannot be obtained. As a result, there is an extremely high market demand for high-output, high-efficiency BLDC motors that can contribute to energy saving in various applications.

[0007] Furthermore, Fe-Si-B amorphous alloys can significantly reduce iron loss to less than 1 / 10 of that of electrical steel sheets, and also have high magnetic permeability. Therefore, if the challenge of lower Bs than electrical steel sheets can be overcome, specifically by achieving Bs ≥ 1.7T, it will be possible to secure the motor output required for BLDC motors for FA and air mobility. For this reason, there is extremely high global expectation from the motor market for core materials that achieve low iron loss comparable to iron-based amorphous alloys, with a Bs ≥ 1.7T, making them viable alternatives to electrical steel sheets.

[0008] Furthermore, while electrical steel sheets used for the rotor and stator cores of BLDC motors are used as laminated cores, existing Fe-Si-B amorphous alloys are difficult to punch due to their thin alloy thickness of approximately 20 μm. In addition, because of the thin alloy thickness, the space utilization ratio when laminated cores is less than 90%, compared to more than 92% for electrical steel sheets, making it difficult to obtain motor torque comparable to that of electrical steel sheets.

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

[0010] Non-patent document 2 discloses that the Fe-Si-B-P-Cu iron-based nanocrystalline alloy "NANOMET (registered trademark)" is a soft magnetic material with a high saturation magnetic flux density Bs: 1.85T and low iron loss performance comparable to iron-based amorphous alloys. However, this iron-based nanocrystalline alloy is extremely brittle and difficult to form into laminated cores by punching press processing, making it difficult to apply to rotor and stator cores of BLDC motors at a mass production level. Except for prototypes, 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 cooled alloy strips with a thickness of 50 μm or more. However, none of these have resulted in the realization of an Fe-Si-B amorphous alloy with Bs ≥ 1.7T, which is intended for application to laminated cores for BLDC motors used in electric vehicles. There are currently no examples of iron-based amorphous alloys being used industrially as a soft magnetic material to replace silicon steel sheets.

[0012] Patent Document 4 discloses a method for manufacturing a thin metal strip characterized by ejecting molten metal from a plurality of openings (porous nozzles) arranged almost perpendicular to the direction of movement on a moving cooling substrate (rotating cooling roll), each opening having an angle of 10 to 80° with respect to the direction of movement, and rapidly cooling and solidifying it. However, Patent Document 4 is an invention made with the aim of reducing thickness variations in the width direction of the thin metal strip when producing a wide rapidly cooled thin strip. Furthermore, it is difficult to process multiple elongated parallelogram, trapezoidal, or elliptical openings with angles of 10 to 80°, and there is a problem that nozzle processing costs will skyrocket, making it difficult to use at an industrial mass production level.

[0013] Patent Document 5 discloses a method for manufacturing an Fe-Si-B amorphous alloy with a thickness of 40 μm or more, but does not disclose an alloy composition that can ensure Bs ≥ 1.7T, and therefore does not aim to provide a soft magnetic material for BLDC motors for EV drives.

[0014] Patent document 6 describes an Fe-Si-B rapidly solidified alloy with a saturation magnetic flux density Bs ≥ 1.7T and coercivity Hc ≤ 200 A / m², and a thickness of 40 μm to 70 μm, as well as a method for producing the same. However, during the rapidly solidifying process, 0.1 volume% to 10 volume% of the α-Fe phase precipitates on the surface, and the remainder is an amorphous structure, which may make punching press processing difficult depending on the core shape.

[0015] Japanese Patent Publication No. 5-329587, Japanese Patent Publication No. 7-113151, Japanese Patent Publication No. 8-124731, Japanese Patent Publication No. 63-220950, Japanese Patent Publication No. 2018-153828, Japanese Patent Publication No. 2021-193199

[0016] Creation of Novel Bulk Metallic Glass / Amorphous Thick Plates with High Saturation Magnetic Flux Density (Tohoku University, Research Center for Metallic Glass) Akihiro Makino, Ken Kubota, Latest Research and Development Trends of "NANOMET," a Soft Magnetic Alloy with Ultra-Low Core Loss and High Iron Concentration, Journal of the Japan Institute of Metals, Materia, Vol. 55, No. 3 (2016)

[0017] An Fe-Si-B-based rapidly solidified alloy is expected that has a Bs≥1.7T equivalent to that of an electromagnetic steel sheet, has a low iron loss performance similar to that of an Fe-Si-B-based amorphous alloy while ensuring a saturation magnetic flux density equivalent to that of electromagnetic steel sheets widely used for transformers, various motors, etc., can be punched by pressing in the same manner as electromagnetic steel sheets, can ensure a core stacking factor of 90% or more, and can be applied as laminated cores for various motors. To ensure Bs≥1.7T, in order to increase the volume ratio of the α-Fe phase, it is necessary to lower the composition ratios of boron (B) and silicon (Si) as the alloy composition. However, when the B+Si ratio is lowered, the amorphous formation ability of the Fe-Si-B-based alloy is significantly reduced, and coarse α-Fe is non-uniformly generated during rapid solidification, so it is impossible to obtain a low iron loss performance similar to that of an Fe-Si-B-based amorphous alloy. Therefore, it has been difficult to ensure a rapid solidification rate at which coarse α-Fe is not non-uniformly generated during rapid solidification even when the B+Si ratio is lowered.

[0018] Therefore, an object of the present invention is to provide a method for producing an iron-based soft magnetic alloy capable of producing an Fe-Si-B-based rapidly solidified alloy having a high Bs of Bs≥1.7T and a low iron loss performance similar to that of an Fe-Si-B-based amorphous alloy.

[0019] The method for producing an iron-based soft magnetic alloy according to the present invention has a composition formula (Fe 1-m Co m ) 100-x-y Si x (B 1-n C n ) yThe process comprises the steps of: preparing a molten alloy with a composition satisfying the following conditions: composition ratios x, y, m, and n are 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 rapidly solidifying the molten alloy sprayed from a nozzle on a cooling roll whose main raw material is pure copper, copper alloy, Mo, or W. The cooling roll has an outer diameter of 300 mm or more and 2000 mm or less, has a cylindrical cooling water channel formed inside through which cooling water flows axially, has an arithmetic mean surface roughness (Ra) of 0.01 μm or more and 0.6 μm or less, and a radial thickness from the surface to the cooling water channel of 5 mm or more and less than 25 mm. The rapidly solidifying process uses 0.1 m of cooling water at 5°C or more and less than 60°C. ３ / min or more 20m ３ The method includes a step of forming a thin, strip-shaped rapidly solidified alloy having a thickness of 18 μm to less than 40 μm, with ultrafine α-Fe having an average grain size of 1 nm or less as the main phase, by injecting the molten alloy from the nozzle onto the surface of the cooling roll, while rotating the cooling roll, through which water is passed at a flow rate of less than / min, at a roll surface speed of 15 m / sec to 50 m / sec.

[0020] In this method for producing an iron-based soft magnetic alloy, the nozzle is preferably made of a material mainly composed of quartz (SiO2), boron nitride (BN), silicon carbide (SiC), and alumina (Al2O3), and it is preferable to spray the molten alloy at a pressure of 5 kPa or more and 50 kPa or less.

[0021] The nozzle is preferably a single-slit nozzle, and the longitudinal direction of the slit is preferably perpendicular to the rotation direction of the cooling roll. The opening width of the slit is preferably 0.2 mm or more and 0.8 mm or less. The distance from the nozzle to the cooling roll is preferably 0.1 mm or more and 2.0 mm or less.

[0022] According to the present invention, it is possible to provide a method for producing an iron-based soft magnetic alloy that has a high Bs of Bs ≥ 1.7T and low iron loss performance comparable to that of Fe-Si-B amorphous alloys.

[0023] (a) is a schematic diagram of a manufacturing apparatus used in a method for manufacturing an iron-based soft magnetic alloy according to one embodiment of the present invention, (b) is an enlarged view of its main parts, and (c) is an enlarged view of the bottom of the nozzle. (a) is a longitudinal cross-sectional view of the cooling roll of the manufacturing apparatus shown in Figure 1, and (b) is a cross-sectional view taken along A-A in (a). This is the powder X-ray diffraction profile of the iron-based soft magnetic alloy obtained in Example 3. This is the powder X-ray diffraction profile of the iron-based soft magnetic alloy obtained in Example 6. This is the powder X-ray diffraction profile of the iron-based soft magnetic alloy obtained in Comparative Example 9. This is the powder X-ray diffraction profile of the iron-based soft magnetic alloy obtained in Comparative Example 11. This is a transmission electron microscope (TEM) photograph of the iron-based soft magnetic alloy of Example 3.

[0024] The present invention provides a method for manufacturing an iron-based soft magnetic alloy that exhibits low iron loss performance equivalent to or better than Fe-Si-B amorphous alloys, with iron loss being 1 / 10 or less compared to electrical steel sheets. Furthermore, by using ultrafine α-Fe particles of 1 nm or less as the main phase during the rapid solidification process in manufacturing, it is possible to produce an Fe-Si-B rapidly solidified alloy that can secure a saturation magnetic flux density Bs ≥ 1.7 T applicable to BLDC motors for FA and air mobility.

[0025] [Alloy Composition] Fe is the essential element, and the remaining elements mentioned above are used. By substituting a portion of Fe with Co, which is a ferromagnetic element like Fe, Bs ≥ 1.7T can be ensured. However, if the substitution rate m of Co for Fe is less than 5%, Bs ≥ 1.7T cannot be ensured. Also, if the substitution rate m of Co for Fe exceeds 50%, Bs tends to decrease. For this reason, the substitution rate m of Co for Fe is limited to 5% or more and 50% or less. The substitution rate 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.

[0026] In the iron-based soft magnetic alloy obtained by the present invention, Si is not only an essential element for obtaining a microstructure, but also plays an important role in exhibiting soft magnetic properties such as permeability. If the Si composition ratio x is less than 1.0 atomic%, not only does the permeability at an applied magnetic field of 10 A / m deteriorate to 2000 or less, but the iron loss (core loss) at 1 kHz and 1.5 T becomes 100 W / kg or more, thus diminishing the characteristics of the iron-based soft magnetic alloy of the present invention, which are high permeability and low iron loss compared to electrical steel sheets. Furthermore, if the Si composition ratio x exceeds 3.0 atomic%, the abundance of Fe, which is responsible for magnetization, decreases, and Bs ≥ 1.7 T cannot be obtained. For this reason, the Si composition ratio x is set to 1.0 atomic% or more and 3.0 atomic% or less. Preferably, the Si composition ratio x is 1.2 atomic% or more and 2.5 atomic% or less, and more preferably 1.3 atomic% or more and 2.2 atomic% or less.

[0027] If the composition ratio y of B+C is less than 11.0 atomic%, the metallic structure of the iron-based soft magnetic alloy obtained by rapid cooling of the molten metal becomes coarser. This makes it impossible to secure low iron loss performance of 50 W / kg or less at a magnetic flux density of 1.5 T and a frequency of 1 kHz. Furthermore, cracks easily occur in the iron-based soft magnetic alloy during the stamping process, making it difficult to form laminated cores. Also, if the composition ratio y of B+C exceeds 14.0 atomic%, the abundance of Fe, which is responsible for magnetization, decreases, making it impossible to obtain Bs ≥ 1.7 T. For this reason, the composition ratio y of B+C is between 11.0 atomic% and 14.0 atomic%. Preferably, the composition ratio y of B+C is between 11.5 atomic% and 13.5 atomic%, and more preferably between 12.0 atomic% and 13.5 atomic%.

[0028] Substituting a portion of B with C lowers the melting point of the molten alloy, relaxes the rapid cooling conditions for the molten metal, and makes it easier to produce Fe-Si-B rapidly solidified alloys using the manufacturing method of the present invention. However, if the substitution rate n of C for B exceeds 30%, it is not desirable because Bs ≥ 1.7T cannot be ensured. For this reason, the substitution rate n is limited to 30% or less. From the viewpoint of achieving both high Bs characteristics and low magnetic permeability, the substitution rate n is preferably 20% or less, and more preferably 15% or less.

[0029] In the iron-based soft magnetic alloy (Fe-Si-B rapidly solidified alloy) obtained by the present invention, it is possible to add one or more additive elements selected from the group consisting of Al, Si, V, Ti, Mn, Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au, and Pb. However, if the additive concentration exceeds 2.0 atomic%, Bs≧1.7T cannot be obtained, which is undesirable. It is acceptable if the additive concentration, including impurities, is within 2.0 atomic%. Furthermore, Cu does not solidify in Fe, the main raw material, and if Cu is added, the Cu dispersed in the ultrafine α-Fe structure may precipitate on its own, potentially hindering the formation of the desired alloy structure. Therefore, the iron-based soft magnetic alloy of the present invention does not contain Cu.

[0030] [Metal structure] The iron-based soft magnetic alloy obtained by the present invention is characterized by having α-Fe as the main phase, which precipitates isotropically without orientation in a specific direction. The main phase is the phase with the largest volume ratio, preferably 50% or more, and more preferably 80% or more. The isotropically precipitated α-Fe crystalline phase is an ultrafine crystal with an average grain size of 1 nm or less. The average grain size of the α-Fe phase can be determined by the full width at half maximum of the X-ray diffraction beak obtained by powder X-ray diffraction (XRD) as described later, or by transmission electron microscopy (TEM).

[0031] However, when rapidly cooling and solidifying the molten alloy on a rotating cooling roll, if amorphous phases are present in the microstructure of the resulting iron-based soft magnetic alloy, this is acceptable as long as it does not adversely affect the soft magnetic properties. If the amorphous phase in the microstructure of the iron-based soft magnetic alloy exceeds 20 volume%, it becomes difficult to obtain Bs≧1.7T, so the amorphous phase content is 20 volume% or less. Preferably, the amorphous phase content is 10 volume% or less, and more preferably 5.0 volume% or less.

[0032] [Magnetic Properties] The saturation magnetic flux density Bs of the iron-based soft magnetic alloy obtained by the present invention is 1.7T to 2.0T in the state immediately after rapid solidification (as-spun), or after heat treatment at a temperature of 180°C to less than 450°C for the purpose of removing strain from the as-spun state. If Bs exceeds 2.0T, the iron loss at a magnetic flux density of 1.5T and a frequency of 1kHz exceeds 50W / kg, so when applied to the core of a BLDC motor for FA and air mobility, a clear improvement in motor efficiency cannot be obtained compared to a core made of electromagnetic steel sheet. From the viewpoint of achieving both sufficient motor torque and high efficiency in the low-speed rotation range, Bs is 1.7T to 2.0T, preferably 1.73T to 1.97T, and more preferably 1.75T to 1.95T.

[0033] Furthermore, while existing electrical steel sheets, iron-based amorphous alloys, and iron-based nanocrystalline alloys tend to show an increase in iron loss values ​​at each operating frequency with increasing magnetic flux density, the iron-based soft magnetic alloy of the present invention exhibits an extremely unique magnetic property in which the iron loss values ​​at each operating frequency show a clear saturation tendency with increasing magnetic flux density. In particular, the iron loss value at a magnetic flux density of 1.5T at a frequency of 20kHz, which is in the high-frequency range, is 1500W / kg or less, which has the potential to significantly reduce iron loss, a problem in ultra-high-speed rotating motors of 50,000 rpm or more and transformers in boost-up units. If the iron loss value at a magnetic flux density of 1.5T at a frequency of 20kHz is too high (for example, 2000W / kg or more), the iron loss will be at the same level as that of iron-based amorphous alloys and iron-based nanocrystalline alloys. Therefore, the iron loss value at a magnetic flux density of 1.5T at a frequency of 20kHz is preferably 1500W / kg or less, more preferably 1300W / kg or less, and even more preferably 1000W / kg or less.

[0034] [Method for producing an iron-based crystalline alloy] The method for producing an iron-based crystalline alloy of the present invention comprises the steps of preparing a molten alloy having the above composition and a rapid cooling and solidification step of rapidly cooling and solidifying the prepared molten alloy.

[0035] FIG. 1(a) is a schematic configuration diagram of a single-roll melt quenching apparatus used in a method for producing an iron-based soft magnetic alloy according to an 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 bottom surface of the nozzle. The single-roll melt quenching apparatus 1 shown in FIG. 1 includes a melting furnace 2, a molten metal storage container 5, and a cooling roll 8.

[0036] The melting furnace 2 supplies the alloy melt 3 obtained by melting the raw materials by high-frequency induction heating to the molten metal storage container 5 by rotating the tilting shaft 4. The molten metal storage container 5 has a nozzle 6 at the bottom, and further heats the alloy melt 3 by a heating coil (not shown), and ejects the alloy melt 3 from the slit 7 formed at the lower end of the nozzle 6 onto the surface (outer peripheral surface) of the cooling roll 8. The cooling roll 8 is supplied with cooling water inside, so as to rapidly cool the alloy melt contacting the surface and form a thin strip-shaped rapidly solidified alloy 9. The material of the nozzle 6 can be appropriately selected from those mainly composed of, for example, any one of quartz (SiO2), boron nitride (BN), silicon carbide (SiC), and alumina (Al2O3).

[0037] The nozzle 6 is a single slit nozzle in which a single slit 7 is formed, and the longitudinal direction of the slit 7 is arranged so as to be orthogonal to the rotation direction of the cooling roll 8 (that is, parallel to the rotation axis of the cooling roll 8). The width W1 of the slit 7 serves to adjust the molten metal discharge rate of the alloy melt 3 supplied to the cooling roll 8. If the slit width W1 is too small, slit processing tends to be difficult, and furthermore, the slit 7 is likely to be blocked by the molten metal. On the other hand, if the slit width W1 is too large, the discharge rate becomes too high and heat extraction by the cooling roll 8 is insufficient, and the rapidly solidified alloy adheres to the cooling roll 8, making it difficult to continue stable melt rapid solidification. 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.

[0038] Instead of the slit nozzle shown in Fig. 1(c), the nozzle 6 may be a strand nozzle in which a plurality of holes are arranged in a row so as to be orthogonal to the rotation direction of the cooling roll 8 (i.e., parallel to the rotation axis of the cooling roll 8). The diameter of each hole of the strand nozzle is 0.6 mm or more and 1.3 mm or less, preferably 0.7 mm or more and 1.2 mm or less, and more preferably 0.7 mm or more and 1.1 mm or less. When the diameter of the hole is less than 0.6 mm, the amount of molten metal discharged per hole is small, so the temperature at the tip of the nozzle 6 may decrease and the discharge of molten metal may not be able to be continued. On the other hand, when the diameter of the hole exceeds 1.3 mm, the amount of molten metal discharged per hole becomes too large, so the rapid solidification of the molten metal becomes incomplete, and there is a possibility that coarse α-Fe that causes a decrease in magnetic properties may precipitate. Also, if the interval between each hole is too small, the molten metal discharged from each hole may come into contact with each other and the rapid solidification of the molten metal may become incomplete, and there is a possibility that coarse α-Fe precipitation that causes a decrease in magnetic properties may occur. Therefore, it is preferably 1.0 mm or more, more preferably 3.0 mm or more, and still more preferably 5.0 mm or more. The interval between each hole is preferably 20 mm or less from the viewpoints of the production efficiency of the rapidly solidified alloy and prevention of temperature decrease at the tip of the nozzle. Note that the shape of the opening of the nozzle 6 can be other shapes such as a single hole.

[0039] The molten metal supplied to the surface of the cooling roll 8 becomes a thin strip of rapidly solidified alloy 9 due to the rotation of the cooling roll 8 and is peeled off from the cooling roll 8. If the surface speed of the cooling roll 8 is less than 15 m / sec, the rapidly solidified alloy becomes excessively thick, exceeding 40 μm. This may result in the α-Fe crystalline phase, which precipitates due to heterogeneous nucleation during rapid solidification and has an average grain size of 100 nm or more oriented in the (200) direction, exceeding 10.0 volume percent near the surface of the rapidly solidified roll surface or free surface of the iron-based soft magnetic alloy strip. As a result, it becomes impossible to maintain a low iron loss level equivalent to that of Fe-Si-B amorphous alloys. On the other hand, if the surface speed of the cooling roll 8 exceeds 50 m / sec, the thickness of the iron-based soft magnetic alloy strip becomes less than 18 μm. This increases the rapid cooling rate of the molten metal, causing the amorphous phase to become dominant instead of the α-Fe crystalline phase, making it difficult to ensure Bs ≥ 1.7T. Therefore, the surface speed of the cooling roll 8 is 15 m / sec to 50 m / sec, preferably 20 m / sec to 45 m / sec, and more preferably 25 m / sec to 40 m / sec. This makes it possible to obtain a thin, strip-shaped rapidly solidified alloy with a thickness of 18 μm to less than 40 μm.

[0040] In Figure 1(a), if the distance d from the tip of the single-slit nozzle 6 to the surface of the cooling roll 8 is too small, the rapidly cooled alloy may stick to the cooling roll 8, making it impossible to continue stable rapid cooling and solidification of the molten alloy 3. On the other hand, if the distance is too large, a paddle may not form on the surface of the cooling roll 8, making it impossible to perform rapid cooling and solidification of the molten alloy 3. For this reason, the above distance d is 0.1 mm or more and 2.0 mm or less, preferably 0.1 mm or more and 1.5 mm or less, and more preferably 0.15 mm or more and 1.0 mm or less.

[0041] When the nozzle 6 is a strand nozzle, if the distance d from the tip of the nozzle 6 to the surface of the cooling roll 8 is too small or too large, the same problems as in the case of the single-slit nozzle described above will occur. For this reason, when the nozzle 6 is a strand nozzle, the above distance d is 0.5 mm or more and 30.0 mm or less, preferably 1.0 mm or more and 20.0 mm or less, and more preferably 2.0 mm or more and 10.0 mm or less.

[0042] In the production of a thin strip of rapidly solidified alloy 9, the adhesion of the molten alloy 3 to the outer surface of the cooling roll 8 is important, but this adhesion largely depends on the surface roughness of the cooling roll 8. If the surface roughness of the cooling roll 8 is too low, the molten alloy 3 will slide on the surface of the cooling roll 8, making sufficient cooling difficult. On the other hand, if the surface roughness of the cooling roll 8 is too high, the rapidly solidified alloy may stick to the cooling roll 8. For this reason, the arithmetic mean roughness (Ra) on the surface of the cooling roll 8 is preferably between 0.01 μm and 0.6 μm, more preferably between 0.05 μm and 0.55 μm, and more preferably between 0.1 μm and 0.5 μm.

[0043] The cooling roll 8 is preferably formed from a material primarily composed of pure copper, copper alloy, molybdenum (Mo), or tungsten (W) to ensure excellent thermal conductivity and durability. "Primary material" means that it accounts for 50% or more of the material by weight. The surface of the cooling roll 8 may be plated with chromium, nickel, or an alloy thereof. This increases the heat resistance and hardness of the cooling roll 8 surface, suppressing melting and deterioration of the roll surface during rapid solidification.

[0044] The outer diameter of the cooling roll 8 is between 300 mm and 2000 mm. If the outer diameter is less than 300 mm, the maximum distance (i.e., 1 / 4 of the circumference of the cooling roll 8) from the molten metal ejected from the nozzle 6 to the surface of the cooling roll 8 until it separates from the cooling roll 8 becomes too short, preventing the molten metal from undergoing sufficient rapid cooling on the cooling roll 8. As a result, the amount of α-Fe crystal phase with an average grain size of 100 nm or more, oriented in the (200) direction and precipitated by heterogeneous nucleation during rapid solidification, may exceed 10.0 volume percent near the surface of the rapidly cooled roll surface or free surface of the iron-based soft magnetic alloy thin strip, making it impossible to maintain a low iron loss level equivalent to that of Fe-Si-B amorphous alloys. On the other hand, if the outer diameter of the cooling roll 8 exceeds 2000 mm, the distance over which the molten metal detaches from the cooling roll 8 becomes too long, causing the molten metal to be cooled too rapidly on the cooling roll 8. This increases the rapid cooling rate of the molten metal, resulting in the amorphous phase becoming dominant instead of the α-Fe crystalline phase, making it difficult to ensure Bs ≥ 1.7T. The outer diameter of the cooling roll 8 is preferably between 500 mm and 2000 mm, and more preferably between 500 mm and 1600 mm, taking into consideration the manufacturing cost of the cooling roll 8.

[0045] Figure 2(a) is a longitudinal cross-sectional view of the cooling roll 8, and Figure 2(b) is a cross-sectional view taken along line A-A in Figure 2(a). As shown in Figure 2, a cylindrical cooling water channel 81 is formed inside the cooling roll 8. Cooling water supplied from an inlet 83 formed on one end of the rotating shaft 82 of the cooling roll 8 spreads radially along the communication passage 84, is introduced into one end of the cooling water channel 81, flows along the axial direction of the cooling roll 8, then merges at the other end of the cooling water channel 81, and is discharged from an outlet 85 formed on the other end of the rotating shaft 82.

[0046] The radial thickness T from the surface of the cooling roll 8 to the cooling water channel 81 is 5 mm or more and less than 25 mm. If the thickness T is less than 5 mm, the cooling roll 8 is more likely to deform due to the centrifugal force caused by the rotation of the cooling roll 8, and there is a risk that the surface (outer surface) of the cooling roll 8 and the tip of the nozzle 6 may come into contact. On the other hand, if the thickness of the cooling roll 8 is 25 mm or more, the heat capacity of the cooling roll 8 increases, and the heat removal effect of the cooling water on the molten alloy decreases, so the rapid cooling rate of the molten metal decreases, and there is a risk that the α-Fe crystal phase with an average grain size of 100 nm or more, oriented in the (200) direction and precipitated by heterogeneous nucleation during rapid solidification, will exceed 10.0 volume% near the surface of the rapidly cooled roll surface or free surface of the Fe-Si-B iron-based soft magnetic alloy thin strip, so it will not be possible to maintain a low iron loss level equivalent to that of Fe-Si-B amorphous alloys. The thickness T is preferably 5 mm or more and less than 23 mm, and more preferably 7 mm or more and less than 20 mm, considering the balance between the strength and heat dissipation capacity of the cooling roll 8.

[0047] The amount of cooling water flowing inside the cooling roll 8 is 0.1 m³. ３ / min or more 20m ３ The cooling water volume is less than / min. ３ If the rate is less than / min, the molten metal supplied from the nozzle 6 to the surface of the cooling roll 8 cannot be sufficiently cooled, the surface temperature of the cooling roll 8 rises, the roll surface melts locally, the Fe-Si-B iron-based soft magnetic alloy strip adheres to the surface of the cooling roll, and rapid cooling of the molten metal cannot be continued. On the other hand, 20m ３ If the flow rate exceeds 0.3 m³ / min, water leakage is likely to occur from the rotary joint that supplies cooling water to the inside of the cooling roll 8, which may prevent the rapid cooling of the molten metal from continuing. The flow rate of the cooling water supplied to the cooling roll 8 is 0.3 m³ / min. ３ / min or more 15m ３ Preferably less than / min, and 0.4m ３ / min or more 10m ３ Less than / min is preferable.

[0048] To ensure a stable rapid cooling rate of the molten alloy from the time it is ejected onto the surface of the cooling roll 8 until it peels off, the cooling water temperature should be between 5°C and 60°C. To prevent condensation on the cooling roll 8, the cooling water temperature should preferably be between room temperature (for example, between 23°C and 30°C) and 60°C.

[0049] [Heat Treatment] The method for producing the iron-based soft magnetic alloy of the present invention may further include a heat treatment step in which the thin strip-shaped rapidly solidified alloy obtained by the rapid solidification step is heat-treated at a constant temperature of 180°C to 450°C. This makes it possible to remove the strain generated in the iron-based soft magnetic alloy powder due to the stress during pulverization, and further improves the magnetic permeability. If the heat treatment temperature is below 180°C, the effect of strain removal is reduced, while if it exceeds 450°C, the iron loss tends to increase due to the crystal grain growth of α-Fe that constitutes the iron-based soft magnetic alloy. The above heat treatment temperature is preferably 200°C to 400°C, and more preferably 200°C to 350°C. The above heat treatment is preferably carried out in a vacuum or inert gas atmosphere, but heat treatment in air is also acceptable as long as it is below 350°C.

[0050] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples.

[0051] 100 kg of raw materials containing elements B, C, Co, and Fe with a purity of 99.5% or higher were placed in an alumina crucible (melting furnace) and melted by high-frequency induction heating to form a molten alloy. 50 kg of this molten alloy was poured into an alumina storage container with an inner diameter of 200 mm and a height of 400 mm, equipped with a single-slit nozzle made of BN at the bottom. The slit width and length of the nozzle are as shown in Table 1.

[0052] Subsequently, the 50 kg of molten alloy was further heated by energizing the high-frequency heating coils installed around the hot water storage container. After the molten metal temperature reached approximately 100°C above the melting point of the alloy composition, the alumina molten metal stopper placed above the nozzle was withdrawn, and the molten alloy was ejected from the nozzle onto the cooling roll surface directly below. The cooling roll was made of chromium zirconite copper, and its outer diameter and thickness, as well as the gap between the nozzle and the cooling roll surface, are shown in Table 1. The injection pressure of the molten alloy from the nozzle, the roll surface velocity of the cooling roll, the thickness of the cooling roll (radial distance from the roll surface to the cooling water channel), the amount of cooling water in the roll, the temperature of the cooling water in the roll, and the arithmetic mean roughness (Ra) of the roll surface of the cooling roll are shown in Table 2.

[0053] The molten alloy ejected onto the surface of the cooling roll formed a puddle (molten metal pool) on the surface of the cooling roll. Rapid cooling and solidification occurred at the interface between the puddle and the cooling roll, yielding a thin, strip-shaped Fe-Si-B rapidly solidified alloy with the average thickness and width shown in Table 3.

[0054] Powder X-ray diffraction (XRD) analysis was performed on the obtained Fe-Si-B rapidly solidified alloys. It was found that all of the iron-based soft magnetic alloys in Examples 1-8 had a metallic structure in which the α-Fe phase precipitated isotropically without orientation in any particular direction. The volume ratio of the amorphous phase calculated from the powder X-ray diffraction results is shown in Table 3.

[0055] As representative examples, the powder X-ray diffraction profiles for Example 3 and Example 6 are shown in Figures 3 and 4, respectively. In both Figures 3 and 4, diffraction peaks at (110), the main peak of α-Fe, and (200), the secondary peak, were confirmed. Since both are diffraction peaks with broad full widths at half maximum, it was confirmed that the microstructure consists of a fine metallic structure composed of an isotropically precipitated α-Fe crystalline phase. A transmission electron microscope (TEM) image of Example 3 is shown in Figure 7. The metallic structure of Example 3 shown in Figure 7 was an extremely fine metallic structure with an average grain size of 1 nm or less.

[0056] Table 4 shows the results of measuring the saturation magnetic flux density Bs, iron loss (core loss) and permeability (μ) at a magnetic flux density of 1.5T at 2kHz, and iron loss at a magnetic flux density of 1.5T at 20kHz for the rapidly solidified alloys of Examples 1-8. Bs was measured using a vibrating sample magnetometer manufactured by Toei Kogyo, and μ and iron loss were measured using an SST unit (single-plate magnetic property tester) attached to a BH analyzer manufactured by Iwasaki Tsushinki.

[0057] On the other hand, evaluation of the rapidly solidified alloys of Comparative Examples 9 and 12 by powder X-ray diffraction (XRD) revealed diffraction peaks with α-Fe(200) as the main peak, indicating a crystalline structure containing coarse α-Fe, which is oriented in-plane within the rapidly solidified alloy strip due to heterogeneous nucleation caused by insufficient rapid cooling of the molten metal. As representative examples, the powder X-ray diffraction profiles of the rapidly solidified alloy strips for Comparative Examples 9 and 12 are shown in Figures 5 and 6, respectively. The volume ratio of the amorphous phase calculated from the powder X-ray diffraction results is shown in Table 3. Comparative Examples 10 and 11 were unable to form rapidly solidified alloy strips.

[0058] Table 4 shows the results of measuring the saturation magnetic flux density Bs, iron loss (core loss) and permeability (μ) at a magnetic flux density of 1.5T at 2kHz, and iron loss at a magnetic flux density of 1.5T at 20kHz for Comparative Examples 9 and 12, similar to Examples 1-8.

[0059]

[0060]

[0061]

[0062]

[0063] 1. Single-roll molten metal rapid cooling device 2. Melting furnace 3. Molten alloy 4. Tilting shaft 5. Storage container 6. Dispensing nozzle 7. Slit 8. Cooling roll 9. Rapidly solidified alloy

Claims

1. An alloy melt having a composition represented by (Fe 1-m Co m ), 100-x-y Si x (B 1-n ) C n ) y is prepared, where the composition ratios x, y, m, and n respectively satisfy 1.0 ≤ x ≤ 3.0 atomic %, 11.0 ≤ y ≤ 14.0 atomic %, 0.05 ≤ m ≤ 0.5, and 0.0 ≤ n ≤ 0.

3. The method includes a rapid solidification step of rapidly solidifying the alloy melt ejected from a nozzle on a cooling roll having any one of pure copper, a copper alloy, Mo, and W as a main raw material. The cooling roll has an outer diameter of 300 mm or more and 2000 mm or less, a cylindrical cooling water channel through which cooling water flows in the axial direction is formed inside, the arithmetic mean roughness (Ra) of the surface is 0.01 μm or more and 0.6 μm or less, and the radial thickness from the surface to the cooling water channel is 5 mm or more and less than 25 mm. The rapid solidification step includes rotating the cooling roll through which cooling water at 5°C or more and less than 60°C is passed at a flow rate of 0.1 m ３ / min or more and less than 20 m ３ / min while rotating the surface of the cooling roll at a roll surface speed of 15 m / sec or more and 50 m / sec or less, and ejecting the alloy melt from the nozzle onto the surface of the cooling roll to form a thin strip-shaped rapidly solidified alloy having an average crystal grain size of 1 nm or less and a main phase of ultrafine α-Fe and a thickness of 18 μm or more and less than 40 μm. A method for producing an iron-based soft magnetic alloy.

2. The method for producing an iron-based soft magnetic alloy according to claim 1, wherein the nozzle is made of a material mainly composed of quartz (SiO2), boron nitride (BN), silicon carbide (SiC), and alumina (Al2O3), and the molten alloy is sprayed at a pressure of 5 kPa or more and 50 kPa or less.

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

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