Manufacturing method for iron-based soft magnetic alloys

Abstract

The present invention provides a method for manufacturing an iron-based soft magnetic alloy having a high Bs (Bs ≥ 1.7T) and low iron loss performance. [Solution] Composition formula (Fe 1-m Co m ) 100-x-y Si x (B 1-n C n ) y The method for producing an iron-based soft magnetic alloy comprises the steps of: preparing a molten alloy with a composition such that the composition ratios x, y, m, and n satisfy 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 cooling and solidifying the molten alloy sprayed from a nozzle on a cooling roll whose main raw material is pure copper, copper alloy, Mo, or W.

Description

[Technical Field]

[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. [Background technology]

[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 becoming increasingly popular as low-iron-loss soft magnetic materials for large transformers and inductors, replacing conventional silicon steel sheets (Fe-Si).

[0003] In addition, the Fe-Si-B rapidly solidified alloy described above, taking advantage of its low iron loss characteristics 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 rotating at speeds 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 aero 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 aero 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 rapid solidification rates such as K / sec. However, it has been disclosed that by adding phosphorus (P), the rapid solidification rate can be reduced, and iron-based amorphous alloy strips of 50 μm or more in thickness can be obtained. However, the addition of P not only leads to a decrease in the saturation magnetic flux density Bs, but P-added alloys also cause significant furnace contamination due to the volatilization of the P component during alloy melting, so there are still few examples of applications in industrial fields.

[0010] Non-patent document 2 discloses that the Fe-Si-B-P-Cu iron-based nanocrystalline alloy "NANOMET (registered trademark)" is a soft magnetic material with a high saturation magnetic flux density Bs:1.85T and low iron loss performance comparable to iron-based amorphous alloys. However, 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 of high nozzle processing costs, 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. [Prior art documents] [Patent Documents]

[0015] [Patent Document 1] Japanese Patent Publication No. 5-329587 [Patent Document 2] Japanese Patent Publication No. 7-113151 [Patent Document 3] Japanese Patent Publication No. Hei 8-124731 [Patent Document 4] Japanese Patent Publication No. 63-220950 [Patent Document 5] Japanese Patent Publication No. 2018-153828

Patent Document 6

Non-Patent Documents

[0016]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0017] An Fe-Si-B-based rapidly solidified alloy is expected to have a Bs ≥ 1.7T equivalent to that of an electromagnetic steel sheet, which can ensure a saturation magnetic flux density equivalent to that of electromagnetic steel sheets widely used for transformers and various motors, etc., while having low iron loss performance similar to that of Fe-Si-B-based amorphous alloys, enabling significant improvement in motor efficiency. At the same time, it can be punched by pressing like an electromagnetic steel sheet, ensuring a core stacking factor of 90% or more and being applicable as a laminated core 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 alloy compositions. However, when the B+Si ratio is lowered, the amorphous formation ability of the Fe-Si-B-based alloy significantly decreases, resulting in non-uniform generation of coarse α-Fe during rapid solidification. Therefore, it has been difficult to obtain low iron loss performance similar to that of Fe-Si-B-based amorphous alloys, and it has been difficult to ensure a rapid solidification rate at which coarse α-Fe does not generate non-uniformly even when the B+Si ratio is lowered.

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

Means for Solving the Problems

[0019] The method for manufacturing an iron-based soft magnetic alloy according to the present invention is represented by the composition formula (Fe 1-m Co m ) 100-x-y Si x (B 1-n C n ) y and includes a step of preparing a molten alloy having a composition in which the composition ratios x, y, m, and n satisfy 1.0 ≦ x ≦ 3.0 at%, 11.0 ≦ y ≦ 14.0 at%, 0.05 ≦ m ≦ 0.5, and 0.0 ≦ n ≦ 0.3, and a rapid solidification step of rapidly solidifying the molten alloy ejected from a nozzle on a cooling roll mainly made of any one of pure copper, copper alloy, Mo, and W. 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, the radial thickness from the surface to the cooling water channel is 5 mm or more and less than 25 mm, and 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 cooling roll at a roll surface speed of 15 m / sec or more and 50 m / sec or less, and ejecting the molten alloy 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 thickness of 18 μm or more and less than 40 μm with α-Fe as the main phase.

[0020] In this method for manufacturing an iron-based soft magnetic alloy, the nozzle is preferably made of a material mainly composed of any one of quartz (SiO₂), boron nitride (BN), silicon carbide (SiC), and alumina (Al₂O₃), and it is preferable to eject 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. [Effects of the Invention]

[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. [Brief explanation of the drawing]

[0023] [Figure 1] (a) is a schematic diagram of a manufacturing apparatus used in a method for manufacturing an iron-based soft magnetic alloy according to one embodiment of the present invention, (b) is an enlarged view of its main parts, and (c) is an enlarged view of the bottom surface of the nozzle. [Figure 2] (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 AA of (a). [Figure 3] This is the powder X-ray diffraction profile of the iron-based soft magnetic alloy obtained in Example 3. [Figure 4] This is the powder X-ray diffraction profile of the iron-based soft magnetic alloy obtained in Example 6. [Figure 5] This is the powder X-ray diffraction profile of the iron-based soft magnetic alloy obtained in Comparative Example 9. [Figure 6] This is the powder X-ray diffraction profile of the iron-based soft magnetic alloy obtained in Comparative Example 11. [Figure 7] This is a transmission electron microscope (TEM) image of the iron-based soft magnetic alloy of Example 3. [Modes for carrying out the invention]

[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] By using Fe as an essential element and occupying the remaining elements as described above, and substituting a portion of Fe with Co, which is also a ferromagnetic element like Fe, a Bs of ≥ 1.7T can be ensured. However, if the substitution rate m of Co for Fe is less than 5%, a Bs of ≥ 1.7T cannot be ensured. Furthermore, 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 a cost-effectiveness viewpoint.

[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 microstructure 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 phase is 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 voltage boosting 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] [Manufacturing method for iron-based crystalline alloys] The present invention provides a method for producing an iron-based crystalline alloy, comprising the steps of preparing a molten alloy having the above composition and rapidly solidifying the prepared molten alloy.

[0035] Figure 1(a) is a schematic diagram of a single-roll molten metal rapid cooling apparatus used in a method for manufacturing an iron-based soft magnetic alloy according to one embodiment of the present invention, Figure 1(b) is an enlarged view of the nozzle, and Figure 1(c) is an enlarged view of the nozzle bottom surface. The single-roll molten metal rapid cooling apparatus 1 shown in Figure 1 comprises a melting furnace 2, a molten metal storage container 5, and a cooling roll 8.

[0036] The melting furnace 2 supplies molten alloy 3, which has been melted by high-frequency induction heating, to the storage container 5 by the rotation of the tilting shaft 4. The storage container 5 is equipped with a nozzle 6 at its bottom, and the molten alloy 3 is further heated by a heating coil (not shown), and the molten alloy 3 is ejected from a slit 7 formed at the lower end of the nozzle 6 onto the surface (outer surface) of the cooling roll 8. The cooling roll 8 rapidly cools the molten alloy in contact with its surface by supplying cooling water to its interior, forming a thin strip of rapidly solidified alloy 9. The material of the nozzle 6 can be appropriately selected from, for example, materials mainly composed of quartz (SiO2), boron nitride (BN), silicon carbide (SiC), and alumina (Al2O3).

[0037] The nozzle 6 is a single-slit nozzle with a single slit 7 formed therein, and the longitudinal direction of the slit 7 is positioned perpendicular to the rotation direction of the cooling roll 8 (i.e., parallel to the rotation axis of the cooling roll 8). The width W1 of the slit 7 plays a role in adjusting the pouring rate of the molten alloy 3 supplied to the cooling roll 8. If the slit width W1 is too small, slitting becomes difficult, and the slit 7 is more likely to become blocked by the molten metal. On the other hand, if the slit width W1 is too large, the pouring rate becomes too high, and the cooling roll 8 cannot keep up with the heat dissipation, causing the rapidly solidified alloy to stick to the cooling roll 8 and making it difficult to continue stable rapid solidification of the molten metal. Therefore, the slit width W1 is 0.2 mm or more and 0.8 mm or less. Preferably, the slit width W1 is 0.3 mm or more and 0.7 mm or less, and more preferably 0.3 mm or more and 0.6 mm or less.

[0038] The nozzle 6 may be a strand nozzle in which multiple holes are arranged in a row perpendicular to the rotation direction of the cooling roll 8 (i.e., parallel to the rotation axis of the cooling roll 8), instead of the slit nozzle shown in Figure 1(c). The diameter of each hole in the strand nozzle is 0.6 mm or more and 1.3 mm or less, preferably 0.7 mm or more and 1.2 mm or less, and more preferably 0.7 mm or more and 1.1 mm or less. If the diameter of the holes is less than 0.6 mm, the amount of molten metal dispensed per hole is small, which may cause the temperature at the tip of the nozzle 6 to drop and make it impossible to continue dispensing the molten metal. On the other hand, if the diameter of the holes exceeds 1.3 mm, the amount of molten metal dispensed per hole becomes too large, which may result in incomplete rapid cooling of the molten metal and the precipitation of coarse α-Fe, which leads to a decrease in magnetic properties. Furthermore, if the spacing between the holes is too small, the molten metal coming out of each hole may come into contact with each other, resulting in incomplete rapid cooling of the molten metal and the possibility of coarse α-Fe precipitation that leads to a decrease in magnetic properties. Therefore, a spacing of 1.0 mm or more is preferable, 3.0 mm or more is more preferable, and 5.0 mm or more is even preferable. From the viewpoint of production efficiency of the rapidly solidified alloy and prevention of a drop in nozzle tip temperature, the spacing between the holes is preferably 20 mm or less. Note that the shape of the opening of the nozzle 6 can also be other shapes, such as a single hole.

[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% 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 rapidly cool and solidify the molten alloy 3. For this reason, the above distance d is 0.1 mm or more and 2.0 mm or less, preferably 0.1 mm or more and 1.5 mm or less, and more preferably 0.15 mm or more and 1.0 mm or less.

[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%, 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 account 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 AA of 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 rotation 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 rotation 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%, so it will not be possible to maintain a low iron loss level equivalent to that of an Fe-Si-B amorphous alloy. 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 flow rate is less than 0.1 m³ / 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 Less than / min is preferable, 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 (e.g., between 23°C and 30°C) and 60°C.

[0049] [Heat treatment] The present invention's method for producing an iron-based soft magnetic alloy may further include a heat treatment step in which the 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 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, iron loss tends to increase due to the crystal grain growth of α-Fe constituting the iron-based soft magnetic alloy. The above heat treatment temperature is preferably between 200°C and 400°C, and more preferably between 200°C and 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 the temperature is 350°C or lower.

[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 zirconium 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 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 ratios of the amorphous phase, calculated from the powder X-ray diffraction results, are 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 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 the 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] [Table 1]

[0060] [Table 2]

[0061] [Table 3]

[0062] [Table 4] [Explanation of Symbols]

[0063] l Single-roll molten metal rapid cooling device 2 Melting furnace 3. Molten alloy 4 Tilt axis 5. Hot water storage container 1. Hot water nozzle 7 slits 8 Cooling Rolls 9 Rapidly solidified alloys

Claims

1. Composition formula (Fe 1-m Co m ) 100-x-y Si x (B 1-n C n ) y It is expressed as follows, where the composition ratios x, y, m, and n are, 1.0≦x≦3.0 atomic%, 11.0≦y≦14.0 atomic%, 0.05≦m≦0.5、 0.0 ≤ n ≤ 0.3 The process of preparing a molten alloy with a composition that satisfies the following conditions, The system comprises a rapid cooling and solidification step in which the molten alloy sprayed from a nozzle is rapidly cooled and solidified on a cooling roll that uses pure copper, copper alloy, Mo, and W as the main raw materials, 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 has a radial thickness from the surface to the cooling water channel of 5 mm or more and less than 25 mm. The rapid solidification process is such that cooling water at a temperature of 5°C or higher and lower than 60°C is passed at a flow rate of 0.1 m ３ / min or higher and lower than 20 m ３ / min while rotating the cooling roll through which the cooling water is passed at a roll surface speed of 15 m / sec or higher and 50 m / sec or lower, and spraying the molten alloy from the nozzle onto the surface of the cooling roll, thereby forming a thin strip-shaped rapidly solidified alloy having a thickness of 18 μm or more and less than 40 μm and having ultrafine α-Fe with an average crystal grain size of 1 nm or less as the main phase. A method for producing an iron-based soft magnetic alloy comprising this process.

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