Method for producing Fe-based nanocrystalline alloy powder, and Fe-based amorphous alloy

Abstract

To provide a method for producing Fe-based nanocrystal alloy powder capable of obtaining satisfactory magnetic properties by suppressing the coarsening of crystal grains and the precipitation of Fe2B crystals while generating bcc-Fe(Si) fine crystals.SOLUTION: A method for producing Fe-based nanocrystal alloy powder has a process in which Fe-based amorphous alloy powder is heat-treated under the conditions that the average temperature rising speed from 300°C to 400°C upon the temperature rising of Fe-based amorphous alloy powder is defined as TA and the average temperature rising speed from 400°C to the maximum temperature is defined as TB, TA is 2 to 10°C / min, TB is 1.5 to 8°C / min and also TA>TB.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing Fe-based nanocrystalline alloy powder and an Fe-based amorphous alloy.

Background Art

[0002] By subjecting an Fe-based amorphous alloy produced for an Fe-based nanocrystalline alloy to heat treatment, fine crystals can be precipitated in the Fe-based amorphous alloy to obtain an Fe-based nanocrystalline alloy having fine crystals. Generally, an Fe-based amorphous alloy is obtained as a thin strip-shaped Fe-based amorphous alloy (Fe-based amorphous alloy thin strip) by rapidly solidifying an alloy melt by a single roll method or the like. When forming a core of an Fe-based nanocrystalline alloy, first, the Fe-based amorphous alloy thin strip is formed into a shape such as a core. Next, heat treatment including a magnetic field is performed on the Fe-based amorphous alloy thin strip formed into the core shape to precipitate fine crystal grains in the Fe-based amorphous alloy thin strip. Thereby, a core made of an Fe-based nanocrystalline alloy thin strip having good magnetic properties can be obtained (see, for example, Patent Document 1).

[0003] Since the form of the Fe-based nanocrystalline alloy obtained by the above single roll method or the like is a thin strip, the degree of freedom in the shape of the core that can be produced is limited. That is, since the alloy thin strip is slit to a width corresponding to the desired height of the core and wound and formed in accordance with the desired inner diameter and outer diameter, its shape is limited to a toroidal shape, a racetrack shape, or the like. On the other hand, conventionally, there have been requirements for various core shapes. For this reason, if an Fe-based nanocrystalline alloy can be produced in powder form, cores having various shapes can be formed relatively easily by applying forming methods such as pressing and extrusion. Therefore, studies have been made to obtain powder also in the Fe-based nanocrystalline alloy. (See, for example, Patent Document 2)

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] When a Fe-based amorphous alloy is heat-treated to precipitate fine crystals (hereinafter also referred to as nanocrystals) to obtain a Fe-based nanocrystalline alloy, in order to obtain a nanocrystalline structure with excellent magnetic properties, it is necessary to perform rapid heating during the heat treatment. However, in the heat treatment of Fe-based amorphous alloy powder, heat generation occurs when nanocrystals precipitate in the amorphous region within the powder. During the heat treatment of Fe-based amorphous alloy powder, the heating by rapid heating and the heat generation accompanying the nanocrystallization within the powder may overlap, thereby causing an excessive temperature rise of the powder. Thus, when the temperature rise of the powder becomes excessive, the temperature of the powder exceeds the appropriate heat treatment temperature, resulting in coarsening of the crystal grains and precipitation of Fe2B crystals. As a result, Fe-based nanocrystalline alloy powder with good magnetic properties cannot be obtained. An object of the present disclosure is to provide a method for manufacturing Fe-based nanocrystalline alloy powder that suppresses coarsening of crystal grains and precipitation of Fe2B crystals while generating fine crystals and obtains Fe-based nanocrystalline alloy powder with good magnetic properties. Another object of the present disclosure is to provide a Fe-based amorphous alloy suitable for use in the method for manufacturing Fe-based nanocrystalline alloy powder of the present disclosure. [Means for Solving the Problems]

[0006] Specific means for solving the above problems include the following aspects. <1> A method for manufacturing Fe-based nanocrystalline alloy powder by heat-treating Fe-based amorphous alloy powder to manufacture Fe-based nanocrystalline alloy powder, When the average heating rate of the Fe-based amorphous alloy powder from 300°C to 400°C during heating is designated as TA, and the average heating rate from 400°C to the maximum temperature is designated as TB, a method for producing an Fe-based nanocrystalline alloy powder by heat-treating the Fe-based amorphous alloy powder under the conditions that TA is 2°C / min to 10°C / min, TB is 1.5°C / min to 8°C / min, and TA > TB. <2> The method for producing an Fe-based nanocrystalline alloy powder according to <1>, which has bcc-Fe(Si) fine crystals with a crystal grain size of 100 nm or less, and the bcc-Fe(Si) fine crystals account for 50% by volume or more. <3> The method for producing an Fe-based nanocrystalline alloy powder according to <1> or <2>, wherein the composition of the Fe-based nanocrystalline alloy powder is represented by an atomic ratio of 3 to 8% of Si, 11 to 17% of B, 0.7 to 1.8% of Cu, 0.05 to 0.7% of Sn, 0 to 1.5% of Cr, 0 to 1.0% of Nb, 0 to 1.0% of Mo, and the balance consisting of Fe and impurities. <4> The method for producing an Fe-based nanocrystalline alloy powder according to any one of <1> to <3>, wherein as the Fe-based amorphous alloy powder, a powder made of an Fe-based amorphous alloy in which Cu microcrystals with a diameter of 50 nm or less are dispersed in the amorphous phase is used. <5> The Cu microcrystals are in the range of -4 pieces / nm 2 or more and -4 pieces / nm 2 or less, and the method for producing an Fe-based nanocrystalline alloy powder according to <4>. <6> An Fe-based amorphous alloy in which Cu microcrystals with a diameter of 50 nm or less are dispersed in the amorphous phase. <7> The Cu microcrystals are in the range of -4 pieces / nm 2 or more and -4 pieces / nm 2 or less, and the Fe-based amorphous alloy according to <6>. <8> The composition of the Fe-based amorphous alloy is represented by, in atomic ratio, 3 to 8% of Si, 11 to 17% of B, 0.7 to 1.8% of Cu, 0.05 to 0.7% of Sn, 0 to 1.5% of Cr, 0 to 1.0% of Nb, 0 to 1.0% of Mo, and the balance, where the balance consists of Fe and impurities. The Fe-based amorphous alloy according to <6> or <7>.

Advantages of the Invention

[0007] According to the present disclosure, a method for manufacturing Fe-based nanocrystalline alloy powder that can obtain good magnetic properties by suppressing coarsening of crystal grains and precipitation of Fe2B crystals while generating fine crystals is obtained. Further, according to the present disclosure, an Fe-based amorphous alloy suitable for use in the method for manufacturing Fe-based nanocrystalline alloy powder of the present disclosure is obtained.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0009] Hereinafter, the present disclosure will be specifically described according to the embodiments of the present disclosure, but the present disclosure is not limited by these embodiments. When describing the embodiments of the present disclosure with reference to the drawings, descriptions of overlapping components and reference numerals in the drawings may be omitted. Components denoted by the same reference numerals in the drawings mean the same components.

[0010] In the present disclosure, a numerical range indicated by using "~" indicates a range including the numerical values described before and after "~" as the lower limit value and the upper limit value, respectively. In the numerical ranges described step by step in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions. Further, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples.

[0011] In the present disclosure, the term "step" includes not only an independent step but also a step that is included in this term if the intended purpose of the step is achieved even when it cannot be clearly distinguished from other steps. In the present disclosure, the Fe-based amorphous alloy powder is a powder composed of a Fe-based amorphous alloy.

[0012] A method for producing an Fe-based nanocrystalline alloy powder according to an embodiment of the present disclosure is a method for producing an Fe-based nanocrystalline alloy powder by heat-treating an Fe-based amorphous alloy powder under the conditions that when the average heating rate from 300 °C to 400 °C during heating of the Fe-based amorphous alloy powder is TA and the average heating rate from 400 °C to the maximum temperature is TB, TA is 2 °C / min to 10 °C / min, TB is 1.5 °C / min to 8 °C / min, and TA > TB. This Fe-based amorphous alloy powder is an Fe-based amorphous alloy powder for an Fe-based nanocrystalline alloy powder produced so as to become an Fe-based nanocrystalline alloy powder by heat treatment.

[0013] In one embodiment of the present disclosure, the Fe-based nanocrystalline alloy powder has bcc-Fe(Si) fine crystals (hereinafter also referred to as "bcc-Fe fine crystals" or "nanocrystals"). The bcc-Fe fine crystals of the Fe-based nanocrystalline alloy powder preferably have a crystal grain size of 100 nm or less. This bcc-Fe fine crystal preferably has an average crystal grain size of 10 to 50 nm. Further, in the Fe-based nanocrystalline alloy powder of the present disclosure, the bcc-Fe fine crystals are preferably 50% by volume or more. In the Fe-based nanocrystalline alloy powder, the portion other than the bcc-Fe fine crystals may be an amorphous phase. Here, the volume fraction of the bcc-Fe fine crystals can be calculated from the ratio of the total area of the substantially spherical structure (bcc-Fe fine crystals) observed by a transmission electron microscope (TEM) of the alloy structure of the Fe-based nanocrystalline alloy powder to the observed field area.

[0014] In one embodiment of the present disclosure, the composition of the Fe-based nanocrystalline alloy powder is preferably represented by 3 to 8% of Si, 11 to 17% of B, 0.7 to 1.8% of Cu, 0.05 to 0.7% of Sn, 0 to 1.5% of Cr, 0 to 1.0% of Nb, 0 to 1.0% of Mo, and the balance in atomic ratio. Here, the balance consists of Fe and impurities. Note that Cr, Nb, and Mo may each be 0%. When the composition of the Fe-based nanocrystalline alloy powder is this composition, the Fe-based nanocrystalline alloy powder obtained by the heat treatment method of the present disclosure can stably have a nanocrystalline structure excellent in magnetic properties. Further, in the embodiment of the present disclosure, the Fe-based amorphous alloy powder for the Fe-based nanocrystalline alloy powder and the Fe-based amorphous alloy constituting this Fe-based amorphous alloy powder preferably have the same composition.

[0015] The emergence of the nanocrystalline structure by the heat treatment method of the present disclosure requires two important elements. The first is that in the temperature range of 300°C to 400°C during heating, a phase different from the amorphous phase mainly composed of Cu and Sn that serves as the nuclei of nanocrystals (hereinafter also referred to as the "heterogeneous phase") exists at a sufficient number density. This is closely related to the amounts of Cu and Sn. The total content (atomic %) of Cu and Sn is preferably 1.2 atomic % or more, more preferably 1.3 atomic % or more. Thereby, a sufficient number density of the heterogeneous phase can be obtained. Also, when their total is 1.85 atomic % or less, coarsening of the clusters can be suppressed and a high number density can be maintained. Furthermore, the total of Cu and Sn is preferably 1.8 atomic % or less.

[0016] The second is the range of overheating in the temperature range of 400°C or higher during heating. Here, overheating means that the powder is heated above the target heat treatment temperature. In the crystallization of the amorphous phase, heat is generated by collective crystallization, which causes overheating in the temperature range of 400°C or higher. According to the manufacturing method of the present disclosure aiming at both production efficiency and magnetic properties, even when overheating occurs, the range of overheating is suppressed to about 20 to 30°C, and coarsening of crystal grains and precipitation of Fe2B crystals can be suppressed. At that time, if the thermal stability of the residual amorphous phase is high, excessive crystal grain growth can be suppressed and the non-uniformity of overheating can be tolerated, making it easier to obtain the powder for the said purpose. The improvement of the thermal stability of the residual amorphous phase is greatly related to B, Nb, Mo, and Si. Therefore, it is necessary to contain appropriate amounts of B, Si, Nb, and Mo. Accordingly, it is preferable that B is 11 atomic % or more and Si is 3 atomic % or more. Furthermore, it is more preferable that B is 13 atomic % or more and Si is 4 atomic % or more. Also, Nb and Mo are not essential elements, but it is preferable to contain at least one of Nb or Mo. When containing Nb or Mo, it is more preferable that it is 0.2 atomic % or more.

[0017] Furthermore, the amount of Fe greatly affects the saturation magnetic flux density, and a higher saturation magnetic flux density can be obtained with a higher content. Therefore, the amount of Fe is preferably 89% by weight or more, more preferably 90% by weight or more. Also, when expressed as an atomic ratio, the amount of Fe is preferably 78% or more, more preferably 80% or more.

[0018] Hereinafter, the manufacturing method of the Fe-based nanocrystalline alloy powder according to one embodiment of the present disclosure will be described in the order of steps. In the present disclosure, when manufacturing an Fe-based nanocrystalline alloy powder, first, an Fe-based amorphous alloy powder for the Fe-based nanocrystalline alloy powder is manufactured. Next, the Fe-based nanocrystalline alloy powder is manufactured by heat-treating the Fe-based amorphous alloy powder. This follows the method of first manufacturing an Fe-based amorphous alloy and then heat-treating the Fe-based amorphous alloy to manufacture an Fe-based nanocrystalline alloy when manufacturing an Fe-based nanocrystalline alloy.

[0019] First, the Fe-based amorphous alloy powder used in this embodiment will be described. The Fe-based amorphous alloy powder used in this embodiment is a powder composed of an Fe-based amorphous alloy and can be obtained by rapidly solidifying an alloy melt by an atomization method or the like. At this time, the alloy melt is adjusted to the alloy composition for obtaining the target Fe-based nanocrystalline alloy powder.

[0020] <Alloy melt> The alloy melt is prepared by blending each element source such as pure iron, ferroboron, and ferrosilicon so as to have the desired alloy composition and heating and melting it to the alloy melting point in an induction heating furnace or the like. Thereby, an alloy melt having the alloy composition of the target Fe-based nanocrystalline alloy powder can be obtained.

[0021] <Atomization method> As a method for manufacturing an Fe-based amorphous alloy powder, there is an atomization method in which a medium such as gas or water is collided with an alloy melt at high speed to pulverize it. Also, the Fe-based amorphous alloy powder of this embodiment can be manufactured using the atomization method. For example, an atomization method using a manufacturing apparatus (jet atomization apparatus) described in Japanese Patent Application Laid-Open No. 2017-155341 or the like can be used. Various atomization methods are known, and the manufacturing conditions can be appropriately selected from known manufacturing techniques to obtain an Fe-based amorphous alloy.

[0022] In addition, in the present embodiment, for example, it is preferable to produce Fe-based amorphous alloy powder using a metal powder manufacturing apparatus described in International Publication No. 2019 / 49865. The Fe-based amorphous alloy powder of the present embodiment is obtained by rapidly solidifying an alloy melt. Therefore, after pulverizing the alloy melt, it is necessary to rapidly solidify and cool the pulverized fine powder (alloy melt). Thus, it is preferable to employ water or a solvent with high cooling capacity and spray the water or solvent with high cooling capacity onto the pulverized fine powder (alloy melt), or immerse the pulverized fine powder (alloy melt) into the water or solvent with high cooling capacity. The metal powder manufacturing apparatus described in International Publication No. 2019 / 49865 uses a swirling water flow and is suitable for rapidly solidifying an alloy melt.

[0023] <Fe-based amorphous alloy, and Fe-based amorphous alloy powder> The Fe-based amorphous alloy powder in the present disclosure is an alloy powder having an amorphous phase. The Fe-based amorphous alloy constituting the alloy powder having the amorphous phase preferably has nanoscale Cu microcrystals present in the amorphous phase. Note that the nanoscale Cu microcrystals have a diameter of 50 nm or less. Preferably, the diameter is 30 nm or less, more preferably 20 nm or less. Also, it is preferable that the diameter is 1 nm or more, more preferably 5 nm or more. In addition, the Cu microcrystals are -4 pieces / nm 2 or more and 6×10 -4 pieces / nm 2 or less and are preferably dispersed and present in the amorphous phase. The presence of these Cu microcrystals helps to produce bcc-Fe fine crystals by heat treatment and helps to obtain an Fe-based nanocrystalline alloy powder with good magnetic properties. In addition, in the Fe-based amorphous alloy constituting the Fe-based amorphous alloy powder of the present disclosure, it is preferable that portions other than the Cu microcrystals are amorphous phases. That is, an Fe-based amorphous alloy in which Cu microcrystals having a diameter of 50 nm or less are dispersed in the amorphous phase is suitable as the Fe-based amorphous alloy constituting the Fe-based amorphous alloy powder for the Fe-based nanocrystalline alloy powder of the present disclosure.

[0024] In Fe-based nanocrystalline alloy powders, as a method for refining the crystal grain size of nanocrystals contained in the alloy after heat treatment, there is a method of precipitating finer bcc-Fe fine crystals in the amorphous phase obtained by rapidly solidifying a molten alloy. However, in the case of an alloy ribbon with a uniform thickness, uniform heat treatment is easy, but in the case of alloy powders, it is difficult to control the degree of crystallization progress due to variations in the powder volume (powder particle size). Particularly in the case of large-diameter powders where the cooling rate tends to be slow, the nanocrystals coarsen due to excessive crystallization progress, or phases that significantly deteriorate the magnetic properties, such as the precipitation of Fe-B-based compounds, precipitate, making it not easy to apply.

[0025] However, in the case of an Fe-based amorphous alloy powder composed of an Fe-based amorphous alloy in which nanoscale Cu microcrystals are present according to the present disclosure, during the heat treatment process, the Cu microcrystals present before the heat treatment serve as nucleation sites for bcc-Fe fine crystals and have the effect of increasing the generation probability of bcc-Fe fine crystals. On the other hand, when the generation probability of bcc-Fe fine crystals increases, the number density of bcc-Fe fine crystals increases, and as a result, the average crystal grain size of the fine crystals decreases. When the average crystal grain size of bcc-Fe fine crystals decreases, the magnetic permeability increases due to the effect of random magnetic anisotropy, and low loss is easily achieved.

[0026] In addition, since the fine crystals of Cu that exist before the heat treatment play the role of nucleation sites for the bcc-Fe fine crystals during the heat treatment process, heat generation occurs gradually when the bcc-Fe fine crystals gradually precipitate at 300°C or higher, which can suppress a rapid temperature rise of the entire powder to be heat-treated and prevent coarsening of the bcc-Fe fine crystals.

[0027] <Heat treatment> In this embodiment, an Fe-based amorphous alloy powder is heat-treated to produce an Fe-based nanocrystalline alloy powder. The furnace used for the heat treatment can be a continuous furnace or a stationary furnace as long as the desired temperature can be obtained. When using a continuous furnace, the powder may be placed in a container (for example, ceramics) that does not react with the Fe-based amorphous alloy, and conveyed in and out of a furnace with a continuously set temperature by a continuous conveying device. Also, as shown in JP-A-2018-204072, the powder may be continuously introduced into the heat treatment furnace. In the case of a stationary furnace, the powder placed in a container that does not react with the Fe-based amorphous alloy can be continuously heated by raising the temperature according to a temperature control program.

[0028] In any case, in order to suppress oxidation of the powder, it is desirable to have an inert atmosphere in which an inert gas such as argon or nitrogen is enclosed or introduced. In this case, in addition to the method of making the entire inside of the furnace an inert atmosphere, methods such as filling and enclosing or introducing an inert gas into the powder container are also acceptable.

[0029] In the heat treatment of this embodiment, during the temperature rise, the average temperature rise rate TA from 300°C to 400°C, which is the temperature range in which precipitation and growth of bcc-Fe fine crystals occur in the amorphous phase and Cu precipitates, is set to 2°C / min to 10°C / min.

[0030] When the average heating rate TA is slower than 2 °C / min, the number density of the bcc-Fe fine crystals precipitated in the amorphous phase is insufficient, resulting in coarse crystals and deteriorating magnetic properties. Also, although fine crystals of Cu are precipitated, since the temperature rise is gentle, the size of each fine crystal of Cu becomes coarse. For this reason, a state of fine and dispersed Cu fine crystals that can serve as nuclei for the bcc-Fe fine crystals cannot be obtained, and as a result, it causes the nano-crystalline particles to become coarse. Therefore, the average heating rate TA should be 2 °C / min or more. Preferably, it is 3 °C / min or more.

[0031] When the average heating rate TA exceeds 10 °C / min, the temperature rises rapidly due to the heat generation when the bcc-Fe fine crystals precipitate in the amorphous phase. As a result, the temperature of the powder rises rapidly, and the powder temperature may greatly exceed 400 °C, or it may cause variations in the precipitation of bcc-Fe fine crystals for powders with different particle sizes. Therefore, the average heating rate TA should be 10 °C / min or less. Also, preferably, it is 9.8 °C / min or less.

[0032] The maximum temperature of the heat treatment is preferably above the temperature at which the first (initially, the low-temperature side) exothermic peak (the exothermic peak due to the precipitation of bcc-Fe fine crystals) appears and below the temperature at which the second (high-temperature side) exothermic peak (the exothermic peak due to the precipitation of coarse crystals) appears when the Fe-based amorphous alloy is measured by a differential scanning calorimeter (DSC) (heating rate 20 °C / min). At this time, when heat-treating a large amount of alloy powder in one batch, it is effective to set the maximum temperature to about ±30 °C of the first exothermic peak in consideration of the heating rate and heat generation.

[0033] The average heating rate TB from 400 °C to the maximum temperature shall be 1.5 °C / min to 8 °C / min. When the average heating rate TB is slower than 1.5 °C / min, the time to reach the maximum temperature becomes longer, which causes the nanocrystalline particles to coarsen. When the average heating rate TB exceeds 8 °C / min, the temperature rises rapidly due to the heat generated during the precipitation of bcc-Fe fine crystals in the amorphous phase. As a result, the desired maximum temperature is exceeded, and phases such as coarsening of nanocrystals or precipitation of Fe-B-based compounds that greatly deteriorate magnetic properties are precipitated. Preferably, it is 2 °C / min or more, and more preferably 3 °C / min or more. Also, preferably, it is 7 °C / min or less, and more preferably 6 °C / min or less. Further, when reaching the maximum temperature, it is preferable that the heating rate is gentle so that the temperature of the powder becomes uniform. The average heating rate TB is preferably 30% to 70% of the average heating rate TA, and more preferably 40% to 60%.

[0034] Therefore, in the heat treatment of the present disclosure, when the average heating rate from 300 °C to 400 °C during heating of the Fe-based amorphous alloy powder is TA, and the average heating rate from 400 °C to the maximum temperature is TB, TA is set to 2 °C / min to 10 °C / min, TB is set to 1.5 °C / min to 8 °C / min, and TA > TB.

[0035] When performing the above heat treatment, it may be a step of holding at the maximum temperature. At this time, the holding time at the maximum temperature may be a sufficiently short time with respect to the heating time. For example, it may be 5 minutes to 15 minutes. Although it is possible to gradually cool the alloy powder in the furnace after reaching the maximum temperature, it may be carried out quickly to shorten the time to the next step. At this time, it can also be taken out of the furnace together with the container and exposed to an inert atmosphere outside the furnace for cooling.

Examples

[0036] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Each elemental source such as pure iron, ferroboron, and ferrosilicon was blended so as to obtain the alloy composition shown in Table 1, and the alloy melt heated and melted in an induction heating furnace was obtained. The alloy melt was atomized and rapidly solidified using the rapid solidification device (jet atomizer) described in International Publication No. 2019 / 49865 to obtain Fe-based amorphous alloy powder. The estimated temperature of the frame jet was 1300 to 1600 °C, and the swirling flow velocity was approximately 160 m / s.

[0037]

Table 1

[0038] In order to confirm the particle size of the obtained Fe-based amorphous alloy powder and determine the maximum temperature during heat treatment, particle size distribution measurement and DSC measurement were carried out. For the particle size distribution, d10 = 10.0 μm, d50 = 24.4 μm, and d90 = 49.8 μm were obtained using a particle size distribution measuring device (MT3000) manufactured by Microtrac·Bell. Also, for the DSC measurement, a device (EXTRA6000) manufactured by Hitachi High-Tech was used, and the measurement was carried out with a measured powder amount of 30 to 40 mg, a temperature range of 200 to 750 °C, and a heating rate of 20 °C / min. The maximum temperature during heat treatment was determined from the first peak at 408 °C and the second peak at 534 °C of the obtained profile.

[0039] A container (made of stainless steel and aluminum) that does not react with the Fe-based amorphous alloy was prepared, the Fe-based amorphous alloy powder was placed in the container, and a thermocouple was inserted into the center of the inserted powder to measure the temperature of the powder. The container was heated in advance at a temperature higher than the target heating temperature, and gas was released in advance by heating from deposits such as surface moisture. The container filled with the Fe-based amorphous alloy powder was installed so as to be located in the soaking zone in the furnace for heat treatment, and an inert gas was allowed to flow in. The flow rate of the inert gas was adjusted so that the oxygen concentration was 0.1% or less.

[0040] A temperature control program was set in a temperature control device for controlling the heating of a furnace, and heat treatment was carried out. The heating was carried out continuously, but when approaching the target temperature, the heating rate was automatically reduced by the temperature control program. Therefore, alloy powder was put into a powder container in advance, a thermocouple was inserted to measure the temperature, and the program was applied so as to obtain a predetermined heating rate. The heat treatment temperature conditions of the examples and comparative examples are shown in Table 2.

[0041]

Table 2

[0042] Fe-based nanocrystalline alloy powders of Examples 1 and 2 and Comparative Examples 1 and 2 were produced under the heat treatment conditions described in Table 2. As evaluations of the powders of Examples 1 and 2 and Comparative Examples 1 and 2, the following evaluations were carried out. The evaluation results are shown in Table 3. <Saturation magnetic flux density> The saturation magnetic flux density (Ms) of each of the powders of Examples 1 and 2 and Comparative Examples 1 and 2 was measured using a vibrating sample type magnetometer (VSM) device (BHV-35). Each 0.25 to 0.30 g of powder was weighed and packed into a resin capsule to make a sample. The measurement magnetic field was measured in the range of -10,000 to 10,000 Oe.

[0043] <Core loss> 5 wt% of silicone resin was added to each of the powders of Examples 1 and 2 and Comparative Examples 1 and 2, and molded at a molding pressure of 1 t / cm 2 to produce a ring core having an outer diameter of 13.5 mm, an inner diameter of 7.50 mm, and a thickness of 2.5 mm. A sample in which a primary winding copper wire and a secondary winding copper wire each having a diameter of 0.25 mm were wound 18 times around the produced ring core (magnetic core) was measured using a B-H analyzer (SY-8218) under the conditions of a measured magnetic flux density Bm = 20 and a frequency f = 3000 kHz to obtain the core loss P.

[0044]

Table 3

[0045] As shown in Table 3, Examples 1 and 2 have a saturation magnetic flux density (Ms) equivalent to that of the comparative examples, showing a high value of 160 emu / g or more. Also, in Examples 1 and 2, the core loss P is significantly reduced compared to the comparative examples. Thus, according to this example, Fe-based nanocrystalline alloy powders with good magnetic properties were obtained.

[0046] Regarding the Fe-based nanocrystalline alloy powders of Examples 1 and 2 and Comparative Examples 1 and 2, the cross-section (internal) was observed with a transmission electron microscope to obtain a transmission electron microscope observation image (TEM image). Fig. 1 shows the TEM image of Example 1. In the Fe-based nanocrystalline alloy powder of Example 1, bcc-Fe fine crystals are developed throughout the area. The diameter of the bcc-Fe fine crystals is about 30 nm, and it has a structure with the characteristics of a structure having good magnetic properties. Note that Example 2 also had a similar structure.

[0047] In the Fe-based nanocrystalline alloy powders of Examples 1 and 2, regarding the Fe-based amorphous alloy powder before heat treatment, the cross-section (internal) was observed with a transmission electron microscope to obtain a transmission electron microscope observation image (TEM image). This Fe-based amorphous alloy powder is a powder obtained by atomization and corresponds to the structure after rapid solidification by atomization. That is, the TEM image of this Fe-based amorphous alloy powder is also the TEM image of the Fe-based amorphous alloy. Fig. 2 shows the TEM image of the Fe-based amorphous alloy of this example. Also, Fig. 3 shows a schematic diagram processed from the TEM image of Fig. 2.

[0048] As shown in Figs. 2 and 3, in the Fe-based amorphous alloy constituting the Fe-based amorphous alloy powder of this example, Cu microcrystals are dispersed. The round forms in this figure are the Cu microcrystals. That this is Cu was confirmed by SEM energy dispersive X-ray analysis (SEM-EDX) analysis. These Cu microcrystals have a diameter of about 10 nm, and when calculated from the TEM image, they are dispersed at a density of about 3×10 -4 pieces / nm 2 The density of these Cu microcrystals was confirmed by checking the number of Cu microcrystals that can be confirmed from the TEM image, and the number per area (pieces / nm2 ) was used. The conditions for obtaining the TEM image were an acceleration voltage of 200.0 kV and a magnification of 600,000 times, and the apparatus used was JEM-2800 manufactured by JEOL Ltd. By heat-treating the Fe-based amorphous alloy powder composed of the Fe-based amorphous alloy in which these Cu microcrystals are present with the heat treatment method of the present disclosure, Fe-based nanocrystalline alloy powder having good magnetic properties was obtained. That is, the Fe-based amorphous alloy in which Cu microcrystals having a diameter of 50 nm or less are dispersed and present in the amorphous phase is an alloy suitable as the Fe-based amorphous alloy powder for producing Fe-based nanocrystalline alloy powder having good magnetic properties.

Claims

1. A method for manufacturing an Fe-based nanocrystalline alloy powder by heat-treating an Fe-based amorphous alloy powder to produce an Fe-based nanocrystalline alloy powder, When the average heating rate from 300 °C to 400 °C during heating of the Fe-based amorphous alloy powder is TA and the average heating rate from 400 °C to the maximum temperature is TB, by heat-treating the Fe-based amorphous alloy powder under the conditions that TA is 2 °C / min or more and 10 °C / min or less, TB is 1.5 °C / min or more and 8 °C / min or less, and TA > TB, An Fe-based nanocrystalline alloy powder having bcc-Fe(Si) fine crystals with a crystal grain size of 100 nm or less and the bcc-Fe(Si) fine crystals being 50% by volume or more is produced, The composition of the Fe-based nanocrystalline alloy powder is, in atomic ratio, Si of 3% or more and 8% or less, B of 11% or more and 17% or less, Cu of 0.7% or more and 1.8% or less, Sn of 0.05% or more and 0.7% or less, Cr of 0% or more and 1.5% or less (excluding 0%), Mo of 0% or more and 1.0% or less (excluding 0%), and the balance, where the balance consists of Fe and impurities, a method for manufacturing an Fe-based nanocrystalline alloy powder.

2. The crystal grain size is observed by a transmission electron microscope (TEM) for the alloy structure of the Fe-based nanocrystalline alloy powder, The volume % is calculated from the ratio to the observed field area by summing the areas of the substantially spherical structures (bcc-Fe fine crystals) observed by a transmission electron microscope (TEM) for the alloy structure of the Fe-based nanocrystalline alloy powder, the method for manufacturing an Fe-based nanocrystalline alloy powder according to Claim 1.

3. As the Fe-based amorphous alloy powder, a powder composed of an Fe-based amorphous alloy in which Cu microcrystals with a diameter of 1 nm or more and 50 nm or less are dispersed in the amorphous phase is used, the method for manufacturing an Fe-based nanocrystalline alloy powder according to Claim 1 or 2.

4. The Cu microcrystals are confirmed by SEM-EDX, the method for manufacturing an Fe-based nanocrystalline alloy powder according to Claim 3.

5. The Cu microcrystals are 1×10 －４more than 0 pieces / nm² and 6×10 －４ The method for producing an Fe-based nanocrystalline alloy powder according to claim 3 or 4, which exists in the range of not more than 0 pieces / nm².

6. The method for producing an Fe-based nanocrystalline alloy powder according to any one of claims 1 to 5, wherein the heat treatment is performed under an inert atmosphere.

7. Fine crystals of Cu having a diameter of 1 nm or more and 50 nm or less are dispersed and present in the amorphous phase. The fine crystals of Cu exist in the range of 1×10⁻⁴ pieces / nm² or more and 6×10⁻⁴ pieces / nm² or less. The composition is represented by an atomic ratio of 3% or more and 8% or less of Si, 11% or more and 17% or less of B, 0.7% or more and 1.8% or less of Cu, 0.05% or more and 0.7% or less of Sn, 0% or more and 1.5% or less (excluding 0%) of Cr, 0% or more and 1.0% or less (excluding 0%) of Mo, and the balance. The balance consists of Fe and impurities, and it is an Fe-based amorphous alloy.

8. The Fe-based amorphous alloy according to claim 7, wherein the fine crystals of Cu are confirmed by SEM-EDX.

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