Method for manufacturing Fe-Co-based coated alloy substrate, Fe-Co-based coated alloy substrate, and laminated core member

Abstract

Provided are: a method for manufacturing an Fe-Co-based alloy substrate equipped with a surface film having high electrical insulation properties on the substrate surface, the method maintaining workability of the Fe-Co-based alloy substrate; an Fe-Co-based alloy substrate; and a laminated core member. The method for manufacturing an Fe-Co-based alloy substrate comprises: a step for coating a surface of an Fe-Co-based alloy substrate with a magnesium hydroxide solution to form a liquid film; and a heat treatment step for heat treating the coated substrate at a temperature of 300-480°C with a heating retention time set so as to satisfy the conditional expression "T × H / 1000 ≤ 12.5" (where T is the heating retention time [min] and H is the heating temperature [°C]), and forming a film of magnesium oxide having a thickness of 0.4-2.0 µm on the surface of the Fe-Co-based alloy substrate.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an Fe-Co-based coated alloy substrate, an Fe-Co-based coated alloy substrate, and a laminated core member.

Background Art

[0002] In recent years, from the perspective of global environmental protection, the electrification of the automotive and aircraft fields has been actively studied, and further higher output, miniaturization, and higher efficiency of the rotating machines to be installed have been required. To improve the performance of such rotating machines, it is necessary to improve the saturation magnetic flux density and iron loss characteristics of the magnetic members used as the magnetic core materials of the rotating machines. As a general magnetic member for rotating machines, an Fe-approximately 3 mass% Si-based alloy called non-oriented electrical steel sheet is used. However, as a magnetic member capable of obtaining a higher saturation magnetic flux density, an Fe-Co-based alloy called Permendur has been known for a long time.

[0003] Here, as a magnetic member for a rotating machine, it is common to process the above non-oriented electrical steel sheet or Permendur substrate into a member shape and laminate them integrally. However, in order to reduce iron loss, it is necessary to improve the electrical insulation (hereinafter, also simply referred to as insulation) between the laminated substrates. For example, Patent Document 1 discloses a laminated core member in which Fe-Co-based alloy substrates are laminated, and it has been proposed to form a surface film of magnesium oxide, zirconium oxide, or aluminum oxide that becomes an insulating film on the substrate surface.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The laminated core member for a rotating machine formed by laminating an Fe-Co alloy base material coated with the surface film disclosed in Patent Document 1 described above is also excellent in electrical insulation between the laminated base materials and is effective for improving the performance of the rotating machine. On the other hand, when the heat treatment conditions for forming the surface film are not optimized, due to embrittlement caused by normalization of the Fe-Co alloy base material, the workability during processing into a component shape using press punching or the like and the handleability of the base material are impaired. Also, when the film thickness of the surface film is thin, there is a concern that high electrical insulation cannot be obtained. Therefore, an object of the present invention is to provide a method for manufacturing an Fe-Co coated alloy base material that maintains the workability of the Fe-Co alloy base material and has high electrical insulation on the surface of the base material, an Fe-Co coated alloy base material, and a laminated core member.

Means for Solving the Problems

[0006] The present inventors investigated the relationship between the heat treatment conditions, workability, and the film thickness and electrical insulation of the surface when forming a surface film of magnesium oxide (hereinafter also referred to as MgO) on the surface of an Fe-Co alloy base material. As a result, it was found that by simply optimizing the heat treatment conditions and the film thickness of the MgO film, the workability of the Fe-Co coated alloy base material is not significantly impaired and high electrical insulation can be obtained, leading to the present invention.

[0007] That is, one aspect of the present invention is a method for manufacturing an Fe-Co coated alloy base material, comprising a step of applying a magnesium hydroxide solution to the surface of an Fe-Co alloy base material to form a liquid film, and heat-treating the coated base material at a temperature of 300°C or higher and 480°C or lower, and setting the heating holding time so as to satisfy the following conditional formula (1), thereby forming a magnesium oxide film with a film thickness of 0.4 to 2.0 μm on the surface of the Fe-Co alloy base material. Conditional formula (1): T×H / 1000 ≦ 12.5 Here, T is the heating holding time [min], and H is the heating temperature [°C].

[0008] Another aspect of the present invention is an Fe-Co-based coated alloy substrate having a magnesium oxide film formed on the surface of an Fe-Co-based alloy substrate, wherein the total film thickness of the magnesium oxide film is 0.4 to 2.0 μm, and a test piece with a short side of 10 mm and a long side of 25 mm is taken from the coated alloy substrate, and when a 90-degree bending test is repeatedly performed, the number of bending times until fracture occurs is 3 or more, which is an Fe-Co-based coated alloy substrate.

[0009] Another aspect of the present invention is a laminated core member in which the above-described Fe-Co-based coated alloy substrates are laminated.

Advantages of the Invention

[0010] According to the present invention, it is possible to obtain an Fe-Co-based coated alloy substrate having high electrical insulation on the substrate surface while maintaining workability, and a high-performance laminated core member.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0012] First, in the present invention, an Fe-Co-based alloy substrate is used as a magnetic member used as a core material of a rotating machine. The Fe-Co-based alloy substrate of the present invention refers to a strip (coil) or a rectangular thin plate (sheet). And the plate thickness of the Fe-Co-based alloy substrate of the present invention can be, for example, 0.5 m m or less. A preferable plate thickness is 0.25 mm or less. Here, the Fe-Co-based alloy in the present invention refers to an alloy material in which Fe + Co is 95% or more by mass and contains 25 to 60% of Co. The lower limit of the preferable Co amount is 40%. Thereby, a high magnetic flux density can be exhibited.

[0013] Next, elements that may be contained in the Fe-Co alloy of the present invention will be described. In order to improve the magnetic properties and cold workability of the Fe-Co alloy of the present invention, one or more elements of V, Si, Mn, Al, Zr, B, Ni, Ta, Nb, W, Ti, Mo, and Cr may be contained in a total amount of up to 5.0% by mass. For example, in the case of V, it is preferably contained in an amount of 1.0 to 3.0%. In addition, as inevitable impurity elements, for example, C, S, P, and O may be mentioned, and it is preferable to set the upper limit of each of them to 0.1%, for example.

[0014] In the manufacturing method of the present invention, first, in order to form a film made of magnesium oxide (hereinafter also referred to as MgO) on the surface of the Fe-Co alloy base material, a step of applying a solution containing magnesium hydroxide (hereinafter also referred to as Mg(OH)2) to form a liquid film (coating step) is performed. The reason for selecting MgO for the surface film is that MgO is excellent in electrical insulation and thermal stability and tends to have a lower hardness compared to other oxide layers. Further, when magnetic annealing is performed to obtain desired magnetic properties, the surface film is exposed to a temperature of about 850°C in a hydrogen atmosphere, for example, but MgO is hardly reduced by hydrogen and also has excellent weld resistance between the base materials.

[0015] In the present invention, as a coating liquid for forming the film made of MgO described above, a Mg(OH)₂ solution (hereinafter also referred to as slurry) in which a powder of Mg(OH)₂ serving as a precursor of MgO is used as a solute and dispersed in a solvent is used. By using this slurry as the coating liquid, the slurry can be uniformly coated on the surface of the substrate with a stable film thickness. Since Mg(OH)₂ used as the solute of the slurry thermally decomposes into MgO by heating, an MgO film can be easily formed. Here, magnesium carbonate (MgCO₃) can also be used as a precursor other than Mg(OH)₂. In addition, the solvent of the slurry can be water, an amphoteric solvent such as alcohol, and an organic solvent. As a method of coating the slurry on a metal substrate, roll coating in which the slurry is applied to the substrate with a roller, dip coating in which the substrate is immersed in the slurry and then pulled up, screen printing, etc. can be used. In addition, in order to improve the wettability between the substrate and the slurry, before coating the slurry, degreasing treatment of the substrate surface by immersion in an alkaline solution or the like, or discharge treatment may be performed.

[0016] In the present invention, after coating, a heat treatment step is carried out in which the substrate coated with the slurry is heat-treated by setting the heating holding time so as to satisfy a temperature of 300 °C or higher and 480 °C or lower and the conditional formula "T×H / 1000 ≤ 12.5 (where T is the heating holding time [min] and H is the heating temperature [°C])." to form an MgO film on the substrate. When the heat treatment step is carried out at an insufficient heat treatment temperature and heating holding time, the applied Mg(OH)₂ solution does not completely turn into an MgO film, and Mg(OH)₂ remains wholly or partially, raising concerns about a decrease in electrical insulation and impaired adhesion to the substrate. Conversely, at excessive heat treatment temperatures and times, even if a complete MgO film is obtained, there is a concern that the regularization of the Fe-Co alloy substrate progresses and the workability of the Fe-Co alloy substrate is impaired. Therefore, in the present invention, the substrate coated with the slurry is heat-treated by setting the heating holding time so as to satisfy a temperature of 300 °C or higher and 480 °C or lower and the conditional formula "T×H / 1000 ≤ 12.5 (where T is the heating holding time [min] and H is the heating temperature [°C])." As a result, an Fe-Co-based coated alloy substrate excellent in the workability of the substrate and the electrical insulation of the surface can be obtained.

[0017] Even if the above conditional formula "T×H / 1000≤12.5 (where T is the heating retention time [min] and H is the heating temperature [°C])" is satisfied, when the heat treatment temperature is less than 300°C, a complete MgO film cannot be obtained, and Mg(OH)₂ remains entirely or partially. Also, when the heat treatment temperature exceeds 480°C, or even if the heat treatment temperature satisfies 300°C or more and 480°C or less, when the conditional formula "T×H / 1000" exceeds 12.5, the normalization of the Fe-Co alloy substrate progresses, and the workability of the Fe-Co alloy substrate tends to be impaired. Incidentally, the lower limit of the preferable heat treatment temperature is 350°C, more preferably 400°C. Also, the upper limit of the preferable heat treatment temperature is 450°C. Further, it is preferable to set the conditional formula in the range of "2.0≤T×H / 1000≤12.5", and more preferably in the range of "2.0≤T×H / 1000≤5.0". For example, when the baking temperature is 450°C and the heat treatment time is set to 10 minutes, T×H / 1000 becomes 4.5, which is within the scope of the present invention.

[0018] The atmosphere during the heat treatment in the production method of the present invention is preferably an inert gas atmosphere or a vacuum atmosphere. This is to prevent the deterioration of the soft magnetic properties of the Fe-Co alloy substrate due to excessive oxidation of the Fe-Co alloy substrate when baking is performed in the air. This atmosphere can be appropriately selected according to the equipment available, desired properties, etc. For example, when it is desired to improve productivity, it is preferable to use an inert gas atmosphere that enables more improvement in productivity by continuous processing while passing the plate, and when it is difficult to introduce an inert gas atmosphere device or when it is desired to suppress costs, it is preferable to use a vacuum atmosphere. Examples of the inert gas atmosphere include a nitrogen gas atmosphere and an Ar gas atmosphere.

[0019] In the present invention, after applying (coating) a slurry on the surface of a Fe-Co alloy substrate, a heat treatment is performed to form a MgO film, but a drying step of evaporating the solvent may be provided before the heat treatment. Since the drying step can be carried out at a low temperature near the boiling point of the solvent, the slurry can be quickly dried, and dripping, which causes uneven film thickness, can be suppressed. Further, since the drying step can be carried out at a low temperature, there is also an advantage that the liquid film can be made into a dry film in the atmosphere.

[0020] Here, the film thickness of the MgO film formed on the surface of the Fe-Co alloy substrate of the present invention is 0.4 to 2.0 μm. There is a correlation between the film thickness of the MgO film and the electrical insulation of the surface. By optimizing the film thickness in combination with the MgO conversion of the surface film, the electrical insulation of the surface can be enhanced. That is, when the film thickness of the MgO film formed on the substrate surface is less than 0.4 μm, in the MgO layer (the sum of the MgO film formed on the upper substrate + the MgO film formed on the lower substrate) formed between the soft magnetic members of the laminated core member (hereinafter, also referred to as the laminated core member for a rotating machine) obtained by laminating the Fe-Co coated alloy substrates, high electrical insulation cannot be obtained. Further, when the film thickness of the MgO film exceeds 2.0 μm, high electrical insulation can be obtained, but there is a concern that the workability is impaired when punching the part shape from the substrate by pressing or the like, and the productivity of the Fe-Co coated alloy substrate decreases. The lower limit of the preferred film thickness of the MgO film is 0.5 μm, and the upper limit of the preferred film thickness of the MgO film is 1.0 μm. In addition, the "film thickness of the MgO film formed on the surface of the substrate" in the present invention indicates the total film thickness obtained by summing the film thicknesses of the MgO films formed on both sides of the substrate. Specifically, for example, when a 0.2-μm MgO film is formed on the surface of the substrate and a 0.2-μm MgO film is formed on the back surface of the substrate, or when a 0.4-μm MgO film is formed on the surface of the substrate and no MgO film is formed on the back surface, it is also within the scope of the present invention. Preferably, MgO films are formed on both sides of the substrate. Also, when MgO films are formed on both sides of the substrate, the film thickness of the MgO film formed on one side is 0.2 mm or more. Further, it is preferable to manage the film thickness with significant figures up to the second decimal place, and the more preferred film thickness of the MgO film formed on one side is 0.40 μm or more. When the film thickness of MgO formed on one side is 0.40 μm or more and the total film thickness of the front and back surfaces is 0.60 μm or more, 6 a sheet resistance (electrical insulation) of 9.0×10

[0021] In addition, since the Fe-Co-based coated alloy substrate obtained by the manufacturing method of the present invention can suppress the normalization of the Fe-Co alloy substrate, it exhibits good workability with the number of bending cycles until fracture occurring being 3 or more times in a 90-degree bending test. FIGS. 1 and 2 show schematic diagrams of the 90-degree bending test apparatus of the present embodiment. FIG. 2 is a schematic diagram seen from the A direction of FIG. 1. In the 90-degree bending test in the present embodiment, a test piece 1 with a short side of 10 mm and a long side of 25 mm is clamped at right angles to the long side direction (rolling direction) with clamp jigs 2a and 2b having a chamfer width of 0.1 mm or less at the edge portion, and repeated bending at 90 degrees is performed to measure the number of bending cycles for every 90 degrees until the test piece breaks. Note that the number of bending cycles defined in the present invention is an average value. Specifically, two test pieces may be collected and measured, and the average of the obtained results may be taken. Also, the number of bending cycles is counted when the test piece is bent and when the bent test piece is returned. For example, when performing a bending test in the order of b1 (bending) → b2 (returning) → b3 (bending in the opposite direction to b1) → b4 (returning) in FIG. 2, if the test piece breaks during b4, the number of bending cycles is counted as 4 times.

[0022] The laminated core member for a rotating machine using the above-described Fe-Co-based coated alloy substrate can achieve high performance of the rotating machine due to the increase in the high magnetic flux density of the substrate and the reduction in iron loss due to the high electrical insulation of the surface. When actually manufacturing the laminated core member for a rotating machine, a plurality of substrates of the present invention are laminated. At this time, when the MgO layer is formed on both sides (front and back) of the substrate, the thickness of the MgO layer formed between the substrates is the sum of the thickness of the back-side MgO film formed on the upper substrate and the thickness of the front-side MgO film formed on the lower substrate during lamination. For example, in the case of laminating substrates each having an MgO film with a thickness of 0.2 μm on both sides, the thickness of the MgO layer formed between the substrates is 0.4 μm.

Example

[0023] (Example 1) As an alloy substrate, a cold-rolled material (alloy substrate sheet) of an Fe-Co-based alloy shown in Table 1 was prepared. Subsequently, after performing degreasing treatment, water washing, and hot air drying on the prepared substrate with an alkaline solution, a coating process was carried out to form a liquid film of the slurry on both surfaces of the substrate by dip coating, in which the substrate was immersed in a slurry in which Mg(OH)2 particles as a solute were dispersed in water as a solvent and then pulled up. The pulling-up speed of the dip coating was fixed at 1.2 mm / s. The substrate with the formed liquid film was treated in the air at a temperature of 110 °C for a holding time of 5 min, and a drying process was carried out to dry the liquid film once. After drying the liquid film, as a heat treatment process, the substrate was further heat-treated in a nitrogen gas atmosphere at a heat treatment temperature of 400 to 600 °C for a holding time of 5 to 60 min, and an Fe-Co-based coated alloy substrate having an MgO film with a thickness of 0.75 μm on both surfaces of the substrate was obtained. The MgO conversion of the surface film after heat treatment was determined by using the X-ray diffraction method (line source CoKα) from the presence or absence of diffraction peaks of the (101) plane of Mg(OH)2 and the (200) plane of MgO, and the quality of the substrate workability was discriminated by the 90-degree bending test method. Here, in the 90-degree bending test, a test piece with a short side of 10 mm and a long side of 25 mm was clamped with a metal clamping jig (fillet width of 0.1 mm or less) at a right angle to the long side direction (rolling direction), and repeated bending at 90 degrees was carried out, and the number of bending times per 90 degrees until the test piece broke was evaluated. In addition, in the 90-degree bending test, two test pieces were collected under each heat treatment condition for testing, and the heat treatment conditions showing an average number of bending times of 3 or more were judged to be good. The results are shown in Table 2 (the value of "temperature × time" in Table 2 indicates T×H / 1000).

[0024]

Table 1

[0025]

Table 2

[0026] From the results in Table 2, for Nos. 2 to 4, 6, and 7 which are the Fe-Co-based coated alloy substrates of the present invention examples, from the disappearance of the diffraction peak on the (101) plane of Mg(OH)2 and the detection of the diffraction peak on the (200) plane of MgO, complete MgO conversion of the surface film was confirmed. Furthermore, it was confirmed that the number of 90-degree bends was 3 to 5 times and good workability of the Fe-Co alloy substrate was also obtained. Note that for Condition No. 1 which is a comparative example deviating from the provisions of the present invention, the liquid film after dip coating remains in a dried state. While the number of bends is 4.5 times showing good workability, the diffraction peak on the (101) plane of Mg(OH)2 remains (the diffraction peak on the (200) plane of MgO is not detected), and it was found that the heat treatment conditions are insufficient. Also, for Conditions No. 5, 8 to 17 which are comparative examples, the disappearance of the diffraction peak on the (101) plane of Mg(OH)2 and the detection of the diffraction peak on the (200) plane of MgO were confirmed. However, the number of 90-degree bends was 1 to 2.5 times, and a significant decrease in workability presumably affected by the regularization of the Fe-Co alloy substrate was observed, and the heat treatment conditions were unsuitable.

[0027] (Example 2) An alloy substrate sheet of the Fe-Co-based alloy shown in Table 3 was prepared. Similar to Example 1, after subjecting the prepared substrate to degreasing treatment with an alkaline solution, water washing, and hot air drying, the substrate was immersed in a slurry in which Mg(OH)2 particles as a solute were dispersed in water as a solvent and then pulled up, and a liquid film of the slurry was formed on both surfaces of the substrate by dip coating. The pulling-up speed of the dip coating was adjusted within the range of 0.02 to 1.20 mm / s so that the film thickness of the liquid film to be coated would vary respectively. After drying the liquid film, the substrate was further subjected to a heat treatment in a nitrogen gas atmosphere at a heat treatment temperature of 400°C or higher (maximum reaching temperature 417°C) with a holding time of about 10 minutes. The value of Conditional Formula (1) is approximately 4.1. The film thickness of the surface film (MgO) after heat treatment was measured using a transmission electron microscope (TEM) by fabricating a film test piece for film thickness measurement from a cross-section in the substrate thickness direction perpendicular to the rolling direction of the substrate using a focused ion beam apparatus (FIB-SEM). Also, the electrical insulation of the surface film (MgO) after heat treatment was determined by measuring the sheet resistance (surface resistivity) of the surface using the four-terminal method with a specific resistance measuring machine. The results are shown in Table 4. Here, the film thickness shown in Table 4 indicates the film thickness formed on one side of the substrate. In reality, since MgO films are formed on both surfaces of the substrate, the total film thickness obtained by adding the film thickness on the front surface side and the back surface side of the substrate is approximately twice the film thickness described in Table 4.

[0028]

Table 3

[0029] From the results in Table 4, it was found that Conditions Nos. 24 to 26 of the present invention examples, where the film thickness on one side is 0.40 μm or more, have high sheet resistance (electrical insulation). Note that for Nos. 24 to 26, the film thickness of MgO formed on one side is 0.40 μm or more, and the total film thickness of the front and back surfaces is 0.60 μm or more. On the other hand, for Invention Examples Nos. 22 and 23, where the film thickness on one side is less than 0.40 μm, a slight improvement in electrical insulation was observed compared to No. 18, which is a substrate without an MgO film on the surface. Also, for Comparative Example Conditions Nos. 19 to 21, there was no significant difference from the sheet resistance of No. 18, which is a substrate without an MgO film on the surface, and they did not show high electrical insulation. In this embodiment, each sample was a single coated alloy base material sheet. However, when actually used as a laminated core member for a rotating machine, it goes through a process of laminating multiple alloy base material sheets. Since the MgO layer existing between the laminated base materials has a thickness that is the sum of the MgO layer formed on the upper base material and the MgO layer formed on the lower base material, if laminated using an alloy base material sheet with an MgO film having a thickness of 0.2 μm or more on one side (total film thickness of 0.4 μm or more) on both sides of the base material as in Conditions No. 22 and 23 of the present invention example, the total thickness of the MgO layer existing between the base materials during lamination will be 0.40 μm or more, and good electrical insulation can be expected. And if the film thickness is as in Conditions No. 24 to 26 of the present invention example, even when the MgO film is formed only on one side, it can have a high sheet resistance (electrical insulation). From the above, since the Fe-Co-based coated alloy base material obtained by the manufacturing method of the present invention has good workability and high electrical insulation, it can contribute to improving the manufacturability of the laminated core member and the high performance of the rotating machine.

[0030] [Table 4] [Explanation of Reference Signs]

[0031] 1 Coated base material 2a, 2b Clamping jig

Claims

1. A coating step of forming a liquid film by applying a magnesium hydroxide solution onto the surface of an Fe—Co alloy base material having a thickness of 0.5 mm or less; A heat treatment step of performing heat treatment by setting a heating retention time so that the base material after coating is heated and retained at a temperature of 300° C. or higher and 480° C. or lower and satisfies the following conditional expression (1), and forming a magnesium oxide film having a film thickness of 0.4 to 2.0 μm on the surface of the Fe—Co alloy base material. A method for manufacturing an Fe—Co based coated alloy base material, characterized by comprising: Conditional expression (1): T×H / 1000 ≦ 12.5 Here, T is the heating retention time [min], and H is the heating temperature [° C.].

2. An Fe—Co based coated alloy base material having a magnesium oxide film formed on the surface of an Fe—Co alloy base material having a thickness of 0.5 mm or less, The film thickness of the magnesium oxide film is 0.4 to 2.0 μm, When a test piece having a short side of 10 mm and a long side of 25 mm is taken from the coated alloy base material and the 90-degree bending test is repeatedly performed, the number of bending times until fracture occurs is 3 or more. Fe—Co based coated alloy base material.

3. A laminated core member in which the Fe—Co based coated alloy base materials according to Claim 2 are laminated.

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