Fe-co based alloy coated substrate and laminated core member

Abstract

Provided is an Fe-Co based alloy substrate with which good magnetic characteristics can be obtained while ensuring insulation and adhesion. This Fe-Co based alloy coated substrate comprises an oxide layer on at least one of a front surface and a back surface of an Fe-Co based alloy substrate, the Fe-Co based alloy coated substrate being characterized in that: when the oxide layer is formed only on the front surface or the back surface, the thickness of the oxide layer is 280-500 nm; when the oxide layer is formed on the front surface and the back surface, the thicknesses of the oxide layers on the front surface side and the back surface side are 140-500 nm; and, in a cross section in the thickness direction of the Fe-Co based alloy coated substrate, the maximum height difference of unevenness of the oxide layer at an interface between the oxide layer and the Fe-Co based alloy substrate is 300 nm or less. A laminated core member is also provided.

Description

Technical Field

[0001] The present invention relates to a Fe-Co based alloy coated substrate and a laminated core member.Related Art

[0002] Due to the growing environmental preservation awareness in recent years, attempts for electrification of automobiles and hybridization of aircraft are becoming active, and examples of elemental technologies in these attempts include increasing the output, reducing the size, and reducing the loss of electric motors. As the shape of a motor core used in these electric motors, a laminated core having a structure in which a large number of soft magnetic alloy thin plates are laminated may be used since the laminated core increases the magnetization per unit volume and is advantageous in size reduction of cores.

[0003] As a method for further reducing the size of the laminated core, it is effective to apply a soft magnetic material having high saturation magnetic flux density; as a method for further reducing the loss, it is effective to improve electrical insulation (hereinafter also simply described as insulation) between laminated single plates. For example, Patent Document 1 discloses a laminated core in which permendur (Fe-Co based alloy) single layer materials having high saturation magnetic flux density are laminated, and proposes forming a ceramic layer of magnesium oxide, zirconium oxide, aluminum oxide or the like as an insulation coating on a surface of the single layer materials.

[0004] On the other hand, since coating treatment of an insulating layer is easy, a method is also known in which an oxide layer mainly composed of Fe and Co is formed on a substrate surface by heat treatment or the like to serve as an insulating layer. Patent Document 2 describes that oxidizing annealing is performed on a plate material after a final recrystallization annealing process, an oxide layer of 0.5 µm to 10 µm is produced, and electrical insulation during lamination is ensured.Prior Art DocumentsPatent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2012-521649 Patent Document 2: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2018-529021 SUMMARY OF INVENTIONTechnical Problem

[0006] While the insulation coating of magnesium oxide or the like described in Patent Document 1 has good insulation, a separate process for performing vapor deposition or applying solution is necessary, which becomes a cause of increased man-hours. Adhesion is also required for the Fe-Co based alloy substrate serving as a material of the laminated core, so that the insulating layer does not peel off and no current flows between the laminated single plates during manufacturing of the laminated core. Neither Patent Document 1 nor Patent Document 2 discusses maintaining all of insulation, adhesion, and magnetic properties at good levels.

[0007] Accordingly, an object of the present invention is to provide a Fe-Co based alloy substrate and a laminated core member in which good magnetic properties can be achieved while insulation and adhesion are ensured.Solution to Problem

[0008] The present invention has been made in view of the above-described problems.

[0009] That is, one aspect of the present invention is a Fe-Co based alloy coated substrate having an oxide layer on at least one of a front surface and a back surface of a Fe-Co based alloy substrate. The Fe-Co based alloy coated substrate is characterized in the following. In a case where the oxide layer is formed only on the front surface or the back surface of the substrate, the oxide layer has a thickness of 280 nm to 500 nm. In a case where the oxide layer is formed on both the front surface and the back surface, the oxide layer on each of the front surface side and the back surface side has a thickness of 140 nm to 500 nm. In a cross-section in a thickness direction of the Fe-Co based alloy coated substrate, a maximum height difference of irregularities of the oxide layer at an interface between the oxide layer and the Fe-Co based alloy substrate is 300 nm or less.

[0010] Preferably, a lower limit of the thickness of the oxide layer on each of the front surface side and the back surface side is 250 nm.

[0011] Another aspect of the present invention is a laminated core member in which the Fe-Co based alloy coated substrate is laminated.Effects of Invention

[0012] According to the present invention, a Fe-Co based alloy coated substrate in which good magnetic properties can be achieved while insulation and adhesion are ensured, as well as a high-performance laminated core member, can be obtained.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 includes scanning transmission electron microscope (STEM) images and elemental mapping images showing a cross-section of a sample of the present inventive example. FIG. 2 includes STEM images and elemental mapping images showing a cross-section of a sample of a comparative example. FIG. 3 includes photographs showing a corrosion resistance test result of the present inventive example and a comparative example. DESCRIPTION OF THE EMBODIMENTS

[0014] A Fe-Co based alloy substrate of the present invention refers to one (coil) of a strip shape, one (sheet) of a rectangular shape, or a thin plate of a part shape. The Fe-Co based alloy substrate of the present invention may have a plate thickness of, for example, 0.5 mm or less, preferably 0.25 mm or less. Here, the Fe-Co based alloy in the present invention refers to an alloy material containing 95% by mass or more of Fe+Co and containing 25% to 60% by mass of Co. The lower limit of Co content is preferably 40%. Accordingly, high magnetic flux density can be exhibited.

[0015] Next, elements that may be contained in the Fe-Co based alloy substrate of the present invention will be described. In order to improve magnetic properties or cold workability, the Fe-Co based alloy of the present invention may contain, in addition to 1.70% to 2.10% by mass of V and 0.01% to 0.40% by mass of Mn, one or two or more elements selected from Si, Al, Zr, B, Ni, Ta, Nb, W, Ti, Mo, and Cr in a total amount of up to 2.5% by mass. In addition, examples of impurity elements that are inevitably contained include C, S, P, and O, and the upper limit of each of these elements is preferably, for example, 0.1%.

[0016] The Fe-Co based alloy coated substrate of the present invention has an oxide layer on at least one of a front surface and a back surface of the Fe-Co based alloy substrate having the composition described above. The present invention is characterized in the following: in the case where the oxide layer is formed on either the front surface or the back surface of the substrate, the oxide layer has a thickness of 280 nm to 500 nm; in the case where the oxide layer is formed on both the front surface and back surface of the substrate, the oxide layer on each of the front surface side and the back surface side has a thickness within the range of 140 nm to 500 nm. By providing this oxide layer, the minimum thickness necessary for ensuring insulation of the Fe-Co based alloy substrate of the present invention is achieved, thereby not impairing magnetic properties. In addition, since the oxide layer that has a larger lattice constant than the Fe-Co based alloy is formed on the substrate surface, slight tensile stress is applied to the substrate surface, and DC magnetic properties of the Fe-Co alloy having positive magnetostriction tend to be improved. In the case where the oxide layer has a thickness of 280 nm or less (when the oxide layer is formed on only one side of the substrate) 140 nm or less (when the oxide layer is formed on both sides (front surface and back surface) of the substrate), the thickness of the oxide layer is insufficient, and there is a possibility that current may flow between laminated single plates in the laminated core and iron loss may deteriorate. In the case where the oxide layer has a thickness of more than 500 nm, there is a risk that a difference in thermal expansion coefficient between the Fe-Co alloy substrate and the oxide layer may increase, adhesion may significantly decrease, and the oxide layer may peel off during core manufacturing. Furthermore, when the oxide layer has a thickness of more than 500 nm, due to an increase in the oxide layer that is not ferromagnetic, the magnetic flux density tends to decrease. Here, in the present embodiment, a reason why the preferable lower limit of the thickness differs between the case where the oxide layer is formed on only one side (either front surface or back surface) of the substrate and the case where the oxide layer is formed on both sides is that the Fe-Co based alloy coated substrate of the present invention is assumed to be applied to a laminated core. That is, when the Fe-Co based alloy coated substrates having the oxide layer on both sides are laminated, the thickness of the oxide layer between the coated substrates is a total thickness obtained by adding the thickness of the oxide layer on the back surface of the substrate and the thickness of the oxide layer on the front surface of the substrate. Hence, the coated substrate having the oxide layer on both sides of the substrate may have a thinner oxide layer than the coated substrate having the oxide layer on only one side. In the coated substrate having the oxide layer on only one side of the substrate, the lower limit of the thickness of the oxide layer is preferably 300 nm, more preferably 310 nm. In the coated substrate having the oxide layer on both sides of the substrate, the lower limit of the thickness of the oxide layer is preferably 150 nm, more preferably 160 nm, even more preferably 180 nm, 200 nm, or 220 nm. The upper limit of the thickness of the oxide layer is preferably 400 nm, more preferably 350 nm.

[0017] In the Fe-Co based alloy coated substrate of the present invention, in the case where the oxide layer is formed on both the front surface and back surface of the substrate, it is more preferable that the lower limit of the thickness of the oxide layer on each of the front surface side and the back surface side is 250 nm. By this configuration, the Fe-Co based alloy substrate can be coated with a stable oxide layer, and it is possible to further enhance an effect of suppressing corrosion that may occur during storage of materials or the like. From the above viewpoint, the lower limit of the thickness of the oxide layer is more preferably 280 nm, even more preferably 300 nm or more. A laminated core member obtained by laminating the Fe-Co based alloy coated substrate described above has good magnetic properties.

[0018] The Fe-Co based alloy coated substrate of the present invention is also characterized in that a maximum height difference of irregularities at an interface between the oxide layer and the substrate is 300 nm or less in a cross-section in a thickness direction of the substrate. By having this requirement, the Fe-Co based alloy coated substrate of the present invention tends to have improved adhesion between the oxide layer and the substrate. In the case where the maximum height difference of irregularities at the interface between the oxide layer and the substrate exceeds 300 nm, nonuniform stress occurs between the oxide layer and the substrate, and the adhesion of the oxide layer tends to decrease. The thickness of the oxide layer and the maximum height difference of irregularities at the interface between the oxide layer and the substrate in the present invention can be measured by using, for example, elemental mapping by a field emission transmission electron microscope (FE-TEM) and a length measurement function of an FE-TEM analysis tool. The adhesion in the present invention can be measured by conducting a cross-cut test specified in, for example, JIS K 5400 (1990) or JIS K 5600.

[0019] Next, an example of a manufacturing method will be described in which the Fe-Co based alloy substrate of the present invention can be obtained. In the manufacturing method according to the present invention, first, cold rolling is performed on an intermediate material, the intermediate material having the Fe-Co based alloy composition described above, having been subjected to rapid cooling treatment from an ordering temperature of around 730 °C or higher and having been disordered. For this intermediate material, a hot rolled material, or a strip-shaped material obtained by performing preliminary cold rolling on a hot rolled material, can be used. In the case where the intermediate material has an oxide layer formed on a surface, the oxide layer may be, for example, mechanically or chemically removed. Subsequently, in the manufacturing method according to the present invention, in order to obtain a desired plate thickness, cold rolling is performed on the intermediate material to obtain a cold rolled material having a plate thickness of 0.5 mm or less. Then, magnetic annealing is performed to obtain a sufficiently coarse recrystallized grain structure, thereby obtaining a Fe-Co based alloy substrate having good magnetic properties. Before and after magnetic annealing, machining to obtain a part shape may be performed by press punching, wire cutting, laser processing or the like.

[0020] In the manufacturing method according to the present invention, oxidation heat treatment is applied to an annealed material that has been subjected to the magnetic annealing described above, so that a thickness of 200 nm to 500 nm is obtained and the maximum height difference of irregularities at the interface between the oxide layer and the substrate is 300 nm or less in the cross-section in the thickness direction. Here, the thickness of the oxide layer or the maximum height difference of irregularities can be controlled mainly by adjusting the heating temperature and heating time of the oxidation heat treatment. In order to form the oxide layer of a desired thickness, an oxygen partial pressure may be adjusted. For example, by performing heat treatment at 450 °C for 0.5 to 4 hours in an atmospheric atmosphere, it is possible to obtain a Fe-Co based alloy coated substrate having the oxide layer specified in the present invention.Examples

[0021] A cold rolling material having a Fe-Co based alloy composition shown in Table 1 was prepared, subjected to cold rolling multiple times to obtain a cold rolled material having a thickness of 0.2 mm, followed by being subjected to magnetic annealing at 850 °C for 3 hours in a hydrogen atmosphere to obtain an annealed material (Fe-Co based alloy substrate) of Fe-Co based alloy. Thereafter, oxidation heat treatment was performed under the conditions shown in Table 2 to obtain Fe-Co based alloy coated substrates of the present inventive examples and comparative examples in which an oxide layer is formed on the front and back surfaces of the substrate. For each sample obtained, the oxide layer was observed, and adhesion, insulation, and DC magnetic properties were evaluated. [Table 1](% by mass)CSiMnCoVResidue0.0030.050.0448.981.91Fe and unavoidable impurities [Table 2] Sample No.Oxidation treatment temperature [°C]Oxidation treatment time [h]Remarks14501Present inventive example24502Present inventive example34503Present inventive example113502Comparative example124002Comparative example135002Comparative example

[0022] For observation of the oxide layer, a surface of a sample was protected with a C film. The sample was processed into a film-like cross-sectional test piece parallel to a width direction from the outermost surface of the test piece using focused ion beam scanning electron microscopy (FIB-SEM), and STEM observation was performed with an FE-TEM. Elemental mapping of each of O, Fe, Co, and V was also performed, and the results are shown in FIG. 1. The lower side in each image is the Fe-Co based alloy substrate side. The thickness of the oxide layer and the maximum height difference of irregularities at the interface between the oxide layer and the substrate were measured using a length measurement function of an FE-TEM analysis tool. For evaluation of adhesion, a cross-cut test specified in JIS K 5400 (1990) was conducted and the presence or absence of peeling of the insulating layer was confirmed. For evaluation of insulation, the evaluation was determined by measuring the sheet resistance (surface resistivity) of the surface using a four-probe method by a specific resistance measuring instrument. The measurement results of the oxide layer thickness, maximum height difference of irregularities at the interface between the oxide layer and the substrate, presence or absence of film peeling, and sheet resistance are shown in Table 3. The "maximum height difference of irregularities" in Table 3 indicates the maximum height difference of irregularities at the interface between the oxide layer and the substrate. All the measurement results in Table 3 are for the oxide layer on the substrate surface side. In actual samples, the oxide layer was also formed on the back surface of the substrate, and the thickness thereof and the maximum height difference of irregularities were approximately equivalent to those on the front surface side. [Table 3]Sample No.Oxide layer thickness [nm]Maximum height difference of irregularities [nm]Film peelingSheet resistance [Ω / sq.]124587No1.90×10 -3< 231688No5.38×10 -3< 3315149No5.58×10 -3< 113618No1.93×10 -3< 1210643No2.15×10 -3< 13935405Yes7.74×10 -3<

[0023] DC magnetic properties were measured using a sample obtained by cutting a cold rolled material having a thickness of 0.2 mm into 110 mm in a rolling direction and 25 mm in a direction perpendicular to rolling, followed by subjecting the cold rolled material to magnetic annealing at 850 °C for 3 hours in a hydrogen atmosphere. Thereafter, the same sample was subjected to oxidation heat treatment under the conditions shown in Table 2, and then measured for DC magnetic properties again. The change rates of coercivity, maximum magnetic permeability, and magnetic flux density before and after the oxidation heat treatment were measured, and the results are shown in Table 4. [Table 4]Sample No.Change rate (%) of magnetic properties before and after oxidation heat treatmentCoercivityMaximum magnetic permeabilityMagnetic flux density B20001-5.0%+15%+0.1%2-4.7%+20%+0.2%3+1.0%+17%+0.2%11-3.8%+3%±0.0%12-1.9%±0%+0.1%13+1.7%+9%-0.4%

[0024] From the results of FIG. 1 and Table 3, it can be confirmed that the thickness or form (maximum height difference of irregularities) of the oxide layer differs depending on the heating temperature and heating time of the oxidation heat treatment. Samples 1 to 3 and 11 to 12 in which the maximum height difference of irregularities at the interface between the oxide layer and the substrate was 300 nm or less exhibited good adhesion and no film peeling. Sample 13 in which the maximum height difference of irregularities at the interface between the oxide layer and the substrate exceeded 300 nm exhibited poor adhesion and the occurrence of film peeling. When the oxide layer has poor adhesion, there is a possibility that the insulating layer may peel off during manufacturing of the laminated core, current may flow between the laminated single plates and iron loss may deteriorate, which is thus unfavorable.

[0025] Regarding sheet resistance, samples No. 2, No. 3, and No. 13 showed excellent values, indicating that good insulation was exhibited. While sample No. 1 had smaller sheet resistance than samples No. 2 and No. 3, in actual use as a laminated core, since the oxide layer is formed on both surfaces of the substrate, the thickness is defined by adding the thickness on the front surface side and the thickness on the back surface side of the substrate. Hence, the thickness of the oxide layer of sample No. 1 also becomes approximately twice (about 490 nm) in the use as a laminated core, indicating that sufficient insulation was exhibited. On the other hand, in samples No. 11 and No. 12 being comparative examples, since the oxide layer was excessively thin, even if the thickness is doubled assuming lamination, the thickness of the oxide layer of sample No. 1 was not reached, thus indicating that sufficient insulation could not be exhibited. According to Table 4, samples 1 to 3 in which the oxide layer fell in the range of the present inventive examples exhibited improved DC magnetic properties. In the DC magnetic properties of a soft magnetic material, lower coercivity, higher maximum magnetic permeability and higher magnetic flux density are better. In the present inventive examples 1 to 3, it can be confirmed that a significant improvement occurred particularly in maximum magnetic permeability.

[0026] Next, corrosion resistance of samples No. 1 to No. 3 and No. 11 to No. 13 was evaluated. A temperature and humidity acceleration test (85 °C / 85% RH) was conducted on each sample after oxidation heat treatment. Data photographs at time points when 0 h, 560 h, and 760 h elapsed are shown in FIG. 3. At the time point of 560 h, while spot corrosion occurred in samples No. 1, No. 11, and No. 12, samples No. 2, No. 3, and No. 13 having an oxide layer thickness of 250 nm or more exhibited almost no spot corrosion, and can be confirmed to exhibit good corrosion resistance. Samples No. 2, No. 3, and No. 13 also exhibited almost no spot corrosion at the time point of 760 h, and can be confirmed to exhibit very good corrosion resistance. From the above results, it is confirmed that the Fe-Co based alloy coated substrates of the present inventive examples had better insulation, adhesion, and magnetic properties than the Fe-Co based alloy coated substrates of comparative examples. Particularly, it is confirmed that the present inventive examples No. 2 and No. 3 having an oxide layer thickness of 250 nm or more were excellent in corrosion resistance as well.

Claims

1. A Fe-Co based alloy coated substrate, having an oxide layer on at least one of a front surface and a back surface of a Fe-Co based alloy substrate, characterized in that, in a case where the oxide layer is formed only on the front surface or the back surface, the oxide layer has a thickness of 280 nm to 500 nm; in a case where the oxide layer is formed on both the front surface and the back surface, the oxide layer on each of the front surface side and the back surface side has a thickness of 140 nm to 500 nm; and in a cross-section in a thickness direction of the Fe-Co based alloy coated substrate, a maximum height difference of irregularities of the oxide layer at an interface between the oxide layer and the Fe-Co based alloy substrate is 300 nm or less.

2. The Fe-Co based alloy coated substrate as claimed in claim 1, wherein in the case where the oxide layer is formed on both the front surface and the back surface, a lower limit of the thickness of the oxide layer on each of the front surface side and the back surface side is 250 nm.

3. A laminated core member, in which the Fe-Co based alloy coated substrate as claimed in claim 1 or 2 is laminated.

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