Fe-based nanocrystalline alloy thin strips and wound iron cores, and their manufacturing methods.

Abstract

This invention provides an Fe-based nanocrystalline alloy thin strip that can effectively reduce iron loss, a wound iron core using the same, and a method for manufacturing them. [Solution] The Fe-based nanocrystalline alloy thin strip has an uneven surface structure including at least one recess 1 with a depth of 3 μm or more that extends along the longitudinal direction L of the thin strip, or an uneven surface structure in which the maximum height roughness Rz in the width direction W of the thin strip is 3 μm or more, and magnetic domains are formed along the width direction W. Alternatively, the wound iron core is composed of a thin strip of Fe-based nanocrystalline alloy, and the width of the region in which the thin strip is continuous along the height direction of the wound iron core is 2.5 mm or less, and magnetic domains are formed along the height direction of the wound iron core.

Description

Technical Field

[0001] The present invention relates to Fe-based nanocrystalline alloy ribbons and wound cores, and methods for manufacturing them.

Background Art

[0002] As a type of soft magnetic material used in high-frequency transformers and choke coils, there are amorphous alloy and nanocrystalline alloy ribbons made of Fe-based alloys such as Fe-Si alloys. In these soft magnetic alloy ribbons, in addition to having high magnetic properties such as a high saturation magnetic flux density, being able to suppress low iron loss is also an important property. In such soft magnetic alloy ribbons, magnetic field annealing has been conventionally used as one means of suppressing iron loss. By magnetic field annealing, uniaxial magnetic anisotropy is imparted to the soft magnetic alloy ribbon, and the iron loss is reduced.

[0003] As another means of reducing iron loss in soft magnetic alloy ribbons, a method of forming an uneven structure on the alloy ribbon is also known. For example, Patent Document 1 discloses a form in which a plurality of laser irradiation trace arrays are formed on the surface of an Fe-based amorphous alloy ribbon in a predetermined positional relationship. In Patent Document 1, it is said that magnetic domains are subdivided by the laser irradiation trace arrays, contributing to the reduction of iron loss.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described above, performing magnetic field annealing and forming an uneven structure on a soft magnetic alloy strip independently contribute to reducing iron loss. Therefore, combining magnetic field annealing with improvements to the physical structure of the alloy strip, such as the formation of an uneven structure, may further enhance the effect of reducing iron loss. However, there is room for further investigation into what approach should be taken to combine magnetic field annealing and improvements to the physical structure while obtaining sufficiently high effects from both. In particular, when forming soft magnetic alloy strips into predetermined product shapes, such as wound iron cores, there is much room for investigation into how to combine the form of magnetic field annealing and the physical structures applied to the soft magnetic alloy strip, such as uneven structures, in relation to the product shape, in order to enhance the effect of reducing iron loss and improve the efficiency of product manufacturing.

[0006] The problem that this invention aims to solve is to provide an Fe-based nanocrystalline alloy thin strip that can effectively reduce iron loss, a wound iron core using the same, and a method for manufacturing the same. [Means for solving the problem]

[0007] To solve the above problems, the Fe-based nanocrystalline alloy thin strips and wound iron cores of the present invention, as well as the methods for manufacturing them, have the following configuration.

[0008] [1] The Fe-based nanocrystalline alloy thin strip of the present invention has an uneven surface structure including at least one recess with a depth of 3 μm or more that extends along the longitudinal direction of the thin strip, and magnetic domains are formed along the width direction that intersects the longitudinal direction.

[0009] [2] Another Fe-based nanocrystalline alloy thin strip of the present invention has an uneven surface structure in which the maximum height roughness Rz in the width direction of the thin strip is 3 μm or more, and magnetic domains are formed along the width direction.

[0010] [3] In the embodiment of [1] or [2] above, the magnetic domains are preferably divided in the width direction by the uneven structure.

[0011] [4] The wound iron core of the present invention is constructed by winding any of the Fe-based nanocrystalline alloy thin strips described in [1] to [3] above in an annular shape along the longitudinal direction.

[0012] [5] Another wound core of the present invention is a wound core composed of a thin strip of Fe-based nanocrystalline alloy, wherein the width of the region in which the thin strip is continuous along the height direction of the wound core is 2.5 mm or less, and magnetic domains are formed along the height direction of the wound core.

[0013] [6] In the embodiment described in [5] above, the height of the wound iron core is preferably 2.5 mm or less.

[0014] [7] A wound core may be formed by stacking multiple unit cores of the wound core described in [5] or [6] above along the height direction.

[0015] [8] In any one embodiment of [1] to [7] above, it is preferable that the average grain size of the crystal grains is 30 nm or less.

[0016] [9] In the method for producing a Fe-based nanocrystalline alloy thin strip of the present invention, an uneven structure is formed on the surface of a Fe-based amorphous alloy thin strip, including at least one recess with a depth of 3 μm or more that extends along the longitudinal direction of the thin strip, and the thin strip is held at a temperature of 200°C or more below the Curie point and below the Curie point while a magnetic field is applied to the thin strip in the width direction intersecting the longitudinal direction.

[0017]

[10] In another method for producing a thin strip of Fe-based nanocrystalline alloy according to the present invention, an uneven structure is formed on the surface of a thin strip of Fe-based amorphous alloy, wherein the maximum height roughness Rz in the width direction of the strip is 3 μm or more, and the strip is then held at a temperature 200°C lower than the Curie point and below the Curie point while a magnetic field is applied to the strip in the width direction.

[0018]

[11] In the method for manufacturing a wound core of the present invention, a thin strip of Fe-based amorphous alloy is wound in an annular shape to form a wound core structure, and the width of the region in which the thin strip is continuous along the height direction of the wound core structure is set to 2.5 mm or less, and the wound core structure is held at a temperature of 200°C or more below the Curie point and below the Curie point while a magnetic field is applied to the wound core structure in the height direction. [Effects of the Invention]

[0019] The Fe-based nanocrystalline alloy strip having the configuration described in [1] above has recesses along the longitudinal direction of the strip. Magnetic domains are formed along the width direction intersecting the direction in which the recesses run. This structure can be formed by forming recesses along the longitudinal direction of the strip and then applying a magnetic field in the width direction to perform magnetic field annealing, as specified in the manufacturing method described in [9] above. By applying a magnetic field in a direction intersecting the direction in which the recesses run and performing magnetic field annealing, magnetic domains develop in the direction intersecting the recesses. At this time, magnetic poles are formed on the side surfaces of the recesses, causing the magnetic domains to subdivide. This subdivision of magnetic domains reduces abnormal eddy current losses and iron losses in the alloy strip. In particular, by applying the magnetic field in the width direction of the strip, the formation of magnetic poles at the widthwise ends of the strip and on the sides of the uneven structure that occurs in a streaky manner along the longitudinal direction when manufacturing the alloy strip by the single-roll liquid quenching method can also be effectively utilized for magnetic domain subdivision. Therefore, a high effect can be obtained in reducing iron losses through magnetic domain subdivision. Furthermore, by making the depth of the recesses 3 μm or more, a particularly high effect of suppressing iron loss through the subdivision of magnetic domains can be obtained. Fe-based nanocrystalline alloy thin strips having an uneven structure including recesses with a depth of 3 μm or more can be suitably used to construct wound iron cores, as described in [4] above.

[0020] The Fe-based nanocrystalline alloy thin strip having the configuration described in [2] above has a pre-determined uneven structure in the width direction of the thin strip. Magnetic domains are formed along the width direction in which the unevenness is formed. This structure can be formed by forming unevenness in the width direction of the thin strip and then performing magnetic field annealing by applying a magnetic field in the width direction, as specified in the manufacturing method described in

[10] above. The uneven structure, which is provided with a maximum height roughness Rz of sufficient size in the width direction of the thin strip, exhibits the same effect as recesses and protrusions running along the longitudinal direction of the thin strip during magnetic field annealing performed by applying a magnetic field in the width direction. In other words, similar to the recesses of the form described in [1] above, it subdivides the magnetic domains during magnetic field annealing and effectively suppresses iron loss. The effect of suppressing iron loss by subdividing magnetic domains is particularly high when the maximum height roughness Rz in the width direction of the uneven structure is 3 μm or more. Fe-based nanocrystalline alloy thin strips having an uneven structure with a maximum height roughness Rz of 3 μm or more can also be suitably used to construct a wound iron core, as described in [4] above.

[0021] In the wound core having the configuration described in [5] above, the width of the continuous region along the height direction is limited to 2.5 mm or less. Magnetic domains are formed along this height direction. This structure can be formed by winding an alloy strip in a ring shape to form a wound core structure, limiting the width of the continuous region along the height direction to 2.5 mm or less, and then applying a magnetic field in the height direction to perform magnetic field annealing. By limiting the continuity in the height direction of the wound core and imparting uniaxial magnetic anisotropy with the height direction as the easy magnetization axis through magnetic field annealing, magnetic domains can be developed in the height direction while the magnetic domains are subdivided. In this case, by limiting the width of the continuous region of the structure in the height direction to a small width of 2.5 mm or less, a high effect can be obtained in the subdivision of magnetic domains, and as a result, iron loss can be effectively suppressed. The height direction of the wound core structure formed by winding an alloy strip corresponds to the width direction of the raw material alloy strip. In other words, magnetic field annealing, performed by applying a magnetic field in the height direction of the wound core structure, corresponds to magnetic field annealing, performed by applying a magnetic field in the width direction of the thin strip when manufacturing the alloy thin strips described in [1] and [2] above. Applying a magnetic field in the circumferential direction of the wound core structure would require special magnetic field application equipment and would likely present industrial difficulties, but applying a magnetic field in the height direction can be carried out relatively easily using general-purpose equipment. Multiple wound cores can also be stacked and used as a composite core, as in the form described in [7] above.

[0022] Here, as a method to limit the width of the continuous region along the height direction in the wound core to 2.5 mm or less, as described in [6] above, the overall height of the wound core can be limited to 2.5 mm or less. In this case, a thin alloy strip with a width of 2.5 mm or less can be wound in a ring shape to form the wound core structure. Alternatively, one or more recesses can be formed along the circumference of the wound core in the middle of the width direction, and the distance between the upper and lower edges in the height direction and the recesses, or the distance between multiple recesses, can be limited to 2.5 mm or less. In this case, as described in [1] above, a thin alloy strip with recesses extending along the longitudinal direction can be wound to form the wound core structure. Limiting the overall height of the wound core and forming recesses can be used in combination.

Brief Description of the Drawings

[0023] [Figure 1] It is a perspective view schematically showing the structure of a Fe-based nanocrystalline alloy ribbon according to an embodiment of the present invention. (a) shows a first embodiment in which a groove-shaped recess is formed on the surface, and (b) shows a second embodiment in which surface roughness is imparted. [Figure 2] It is a plan view schematically showing the domain distribution in a Fe-based nanocrystalline alloy ribbon annealed in a magnetic field. (a) shows a Fe-based nanocrystalline alloy ribbon according to the above first embodiment, and (b) shows an alloy ribbon having no concavo-convex structure on the surface. [Figure 3] It is a perspective view schematically showing (a) the structure and (b) the domain distribution of a wound iron core according to the first embodiment of the present invention. [Figure 4] It is a perspective view schematically showing (a) the structure and (b) the domain distribution of a wound iron core according to the third embodiment of the present invention [Figure 5] It is a domain observation image of the sample of Example C4. The observation field of view is 1 mm × 1 mm.

Modes for Carrying Out the Invention

[0024] Hereinafter, a Fe-based nanocrystalline alloy ribbon, a wound iron core, and a manufacturing method thereof according to an embodiment of the present invention will be described. In this specification, various characteristics refer to values at room temperature and in the atmosphere.

[0025] [Fe-based nanocrystalline alloy ribbon and its manufacturing method] The Fe-based nanocrystalline alloy ribbon according to an embodiment of the present invention is configured as a ribbon of a soft magnetic Fe-based alloy containing nanocrystals The component composition of the Fe-based alloy is not particularly limited, but examples of the Fe-based alloy that becomes a nanocrystalline alloy having good soft magnetic properties include Fe-Si-based alloys, particularly Fe-Si-B-Nb-Cu alloys.

[0026] <First Embodiment> The Fe-based nanocrystalline alloy thin strip (hereinafter sometimes simply referred to as an alloy thin strip or thin strip) according to the first embodiment of the present invention has an uneven surface structure, as shown in Figure 1(a). The uneven structure is formed to include at least one recess 1 extending along the longitudinal direction L of the alloy thin strip. The recess 1 has a depth (d) of 3 μm or more. Furthermore, in the Fe-based nanocrystalline alloy thin strip, magnetic domains are formed along the width direction W, as shown in Figure 2(a).

[0027] Here, the longitudinal direction L of the Fe-based nanocrystalline alloy strip refers to the direction along the long side of the elongated strip of alloy, and corresponds to the casting direction, which is the direction of rotation of the roll when manufacturing the alloy strip by the single-roll liquid quenching method, as described later. The width direction W is the direction along the short side that intersects the longitudinal direction L in the alloy strip, and is typically perpendicular to the longitudinal direction L. When a recess 1 extends along the longitudinal direction L, it means that it extends parallel to the longitudinal direction L. Furthermore, when a magnetic domain is formed along the width direction W, it means that an elongated magnetic domain is formed with its long axis parallel to the width direction W. In this specification, when a recessed or uneven structure or magnetic domain is described as being along or parallel to a certain direction, it includes not only strictly parallel states but also a range of error of approximately ±10°.

[0028] The Fe-based nanocrystalline alloy ribbon according to this embodiment can be manufactured by the following method. First, an Fe-based amorphous alloy ribbon having the same composition as the soft magnetic Fe-based alloy to be manufactured is produced. For this production, the single-roll melt spinning method can be preferably used. That is, an alloy melt having a predetermined component composition is discharged onto the surface of a rapidly rotating copper roll and quenched and solidified, whereby an amorphous alloy ribbon can be obtained. Next, an uneven structure including at least one recess 1 with a depth of 3 μm or more is formed along the longitudinal direction L of the obtained alloy ribbon. The formation of the recess 1 can be performed by laser processing, machining, etching, or the like. From the viewpoint of controllability with respect to the shape of the recess 1, including the depth, it is most preferable to use laser processing. The recess 1 may be formed as a continuous structure along the longitudinal direction L, or may be formed as a structure in which a plurality of discontinuous concave structures such as dot-like depressions are arranged along the longitudinal direction L, but a continuous structure is preferred. Further, it is preferable that the recess 1 is formed over the entire longitudinal direction of the alloy ribbon except for regions where it cannot be unavoidably formed.

[0029] Next, the amorphous alloy ribbon with the uneven structure is annealed in a magnetic field. As annealing in a magnetic field, as shown in Fig. 1(a), while applying a magnetic field H in the width direction W of the ribbon, the ribbon is held at a heat treatment temperature that is 200 °C lower than the Curie point (Tc) or higher and lower than the Curie point (maintained at a temperature T satisfying Tc - 200 °C ≤ T < Tc). Preferably, a heat treatment temperature that is 10 °C lower than the Curie point or lower is employed. The annealing in a magnetic field is preferably performed in an inert atmosphere such as an Ar atmosphere. Examples of the intensity of the magnetic field H can be 0.01 to 1 T.

[0030] Magnetic field annealing may be performed after crystallization heat treatment of the alloy strip, as appropriate. Crystallization heat treatment is a process of heating the alloy strip without applying a magnetic field, and promotes the formation of nanocrystalline alloys by crystallization of amorphous alloys. Preferably, the treatment temperature for crystallization heat treatment is 450 to 600°C, and the heating rate to the heat treatment temperature is 0.1 to 20°C / min. It is also preferable to perform the heat treatment in an inert atmosphere such as an Ar atmosphere.

[0031] By annealing in a magnetic field, uniaxial magnetic anisotropy can be imparted, with the direction of the applied magnetic field H, i.e., the width direction W, as the easy magnetization axis. In this case, as shown in Figure 2(a), the magnetic domain structure of the alloy strip changes. In Figure 2(a), adjacent, mutually antiparallel magnetic domains are shown in different colors. Each magnetic domain develops along the direction in which the magnetic field H is applied. That is, each magnetic domain is formed along the width direction W, and its easy magnetization axis is oriented in the width direction W. For comparison, Figure 2(b) shows the distribution of magnetic domains when annealing in a magnetic field is performed on a flat alloy strip without a surface irregularity, by applying a magnetic field H in the width direction W. Compared to this case, the magnetic domains are subdivided by providing an irregularity on the surface. That is, the width of the magnetic domains along the longitudinal direction L of the alloy strip is reduced. The subdivision of magnetic domains is achieved by applying a magnetic field H in a direction intersecting the recess 1, which forms magnetic poles on the side surface 11 (side wall surface of the groove) of the recess 1. In addition to being subdivided along the longitudinal direction L of the alloy thin strip, the magnetic domains are also physically divided in the width direction W of the alloy thin strip by the recesses 1. This subdivision of the magnetic domains allows for minimizing abnormal current losses associated with domain wall movement when an AC magnetic field is applied. As a result, iron losses in the Fe-based nanocrystalline alloy thin strip can be kept to a minimum.

[0032] As described above, in this embodiment, a nanocrystalline alloy strip is obtained by forming an uneven structure on the surface of an amorphous alloy strip and then performing magnetic field annealing. By combining the formation of the uneven structure and magnetic field annealing in this way, a high effect in reducing iron loss can be obtained. In particular, by setting the direction in which the recesses 1 run to the longitudinal direction L of the alloy strip and the direction in which the magnetic field H is applied during magnetic field annealing to the width direction W, a high iron loss suppression effect can be obtained. As described above, the subdivision of magnetic domains is achieved by the formation of magnetic poles on the side surface 11 of the recesses 1, but by setting the direction of the recesses 1 to the longitudinal direction L and the direction in which the magnetic field H is applied to the width direction W, in addition to the formation of magnetic poles on the side surface 11, the formation of magnetic poles at the widthwise ends of the alloy strip (the edges on both sides in the widthwise direction of the alloy strip), and the formation of magnetic poles on the side surface of the uneven structure that occurs during the manufacturing of the alloy strip, as will be described later in the second embodiment, can also contribute to the subdivision of magnetic domains. Furthermore, by applying a magnetic field H during magnetic field annealing and setting the direction in which the magnetic domains develop to the width direction W of the alloy strip, it is possible to improve the convenience of manufacturing for many products produced using Fe-based nanocrystalline alloy strips. For example, when manufacturing a wound core by winding an alloy strip in a ring shape along its longitudinal direction L, the width direction W of the alloy strip corresponds to the height (thickness) direction of the core. Applying a magnetic field in the height direction of the core is simpler than applying a magnetic field in the circumferential direction of the core, which corresponds to the longitudinal direction L of the alloy strip. Note that in Patent Document 1, as shown in Figures 3 and 8, the laser irradiation marks are formed along the width direction of the alloy strip or a direction close to it. Also, magnetic field annealing is not performed.

[0033] Furthermore, in this embodiment, the depth of the recess 1 provided along the longitudinal direction L of the alloy strip is set to 3 μm or more. This further enhances the effect of reducing iron loss by refining the magnetic domains. More preferably, the depth of the recess 1 is 5 μm or more, or 10 μm or more. There is no particular upper limit set for the depth of the recess 1.

[0034] The number of recesses 1 is not particularly limited, as long as there is one or more. When only one recess 1 is provided, it is preferable that the recess 1 be located in the center of the width direction of the alloy strip. The spacing between recesses 1, that is, the distance between multiple adjacent recesses 1, and the distance along the width direction W between the edges on both sides in the width direction and the recess 1, is not particularly limited, but it is preferable to be 1 to 10 mm or less. The recesses 1 may be provided on only one side of the alloy strip or on both sides. The dimensions of the alloy strip are not particularly specified, but a form with a thickness of 20 to 30 μm or less and a width of 60 mm or less can be suitably exemplified.

[0035] As described above, in manufacturing the Fe-based nanocrystalline alloy thin strip according to this embodiment, the nanocrystalline alloy structure is formed by subjecting the amorphous alloy thin strip, which has the recess 1, to appropriate crystallization heat treatment followed by magnetic field annealing. The smaller the grain size of the crystal grains contained in the nanocrystalline alloy, the higher the soft magnetic properties obtained. For example, it is preferable that the average grain size of the nanocrystalline alloy thin strip is 30 nm or less, and more preferably 20 nm or less. The grain size can be controlled by the conditions of the crystallization heat treatment, etc.

[0036] As described above, the Fe-based nanocrystalline alloy thin strip according to this embodiment exhibits excellent iron loss reduction. For example, when using an Fe-Si-B-Nb-Cu alloy, the iron loss (Pcv) at an applied magnetic field of 0.1 T and a frequency of 10 kHz can be suppressed to 0.6 W / kg or less. Furthermore, while it is generally difficult to achieve both increased saturation magnetic flux density and reduced iron loss in soft magnetic materials, the Fe-based nanocrystalline alloy thin strip according to this embodiment makes it easier to achieve both high saturation magnetic flux density and low iron loss. For example, when using an Fe-Si-B-Nb-Cu alloy, the ratio Pcv / Bs of iron loss (Pcv, unit: W / kg) to saturation magnetic flux density (Bs, unit: T) measured under the above conditions can be suppressed to less than 0.50, and even less than 0.40.

[0037] In the Fe-based nanocrystalline alloy thin strip according to the first embodiment of the present invention described above, a recess 1 is provided along the longitudinal direction L as an uneven structure, and magnetic domains are formed along the width direction W. By providing a sufficient difference in unevenness along the width direction W of the alloy thin strip with the recess 1, a high effect of suppressing iron loss can be obtained. Not limited to the recess 1 along the longitudinal direction L, if an uneven structure that provides a sufficient difference in unevenness along the width direction W is provided on the surface of the alloy thin strip, iron loss suppression can be achieved by annealing in a magnetic field by applying a magnetic field H along the width direction W. As an example of providing an uneven structure other than the recess 1, the Fe-based nanocrystalline alloy thin strip according to the second embodiment of the present invention will be described below.

[0038] <Second Embodiment> The Fe-based nanocrystalline alloy thin strip according to the second embodiment of the present invention has an uneven structure on its surface in which the maximum height roughness Rz in the width direction W of the alloy thin strip is 3 μm or more, instead of the uneven structure including the recess 1 along the longitudinal direction L of the alloy thin strip in the first embodiment described above. Furthermore, magnetic domains are formed along the width direction W of the alloy thin strip.

[0039] An uneven surface structure can be imparted as surface roughness to the surface of an Fe-based nanocrystalline alloy thin strip. For example, as shown in Figure 1(b), the surface of the alloy thin strip may have height differences along the width direction W. Here, areas with higher and lower surface heights extend along the longitudinal direction L of the alloy thin strip, forming mountain-like areas 21 and valley-like areas 22 along the longitudinal direction L. In this structure, the height difference between the highest point of the peak 21 and the lowest point of the valley 22 on a straight line crossing the surface of the alloy thin strip along the width direction W is the maximum height roughness Rz. Thus, an uneven surface structure with peaks 21 and / or valleys 22 extending along the longitudinal direction L of the alloy thin strip is easily formed as a streaky structure along the longitudinal direction L corresponding to the rotation direction of the roll when forming the alloy thin strip by the single-roll liquid quenching method.

[0040] The uneven structure in this second embodiment, like the uneven structure in the first embodiment, shares the commonality of having irregularities along the width direction W of the alloy thin strip, thereby interrupting the continuity of the metallic material in the width direction W. Therefore, in the second embodiment, as in the first embodiment, by applying a magnetic field H in the width direction W to an amorphous alloy thin strip with an uneven structure on its surface, and performing magnetic field annealing at a temperature 200°C lower than the Curie point and below the Curie point, a structure in which subdivided magnetic domains are formed along the width direction W can be obtained. Just as the formation of magnetic poles on the side surface 11 of the recess 1 in the first embodiment contributes to the subdivision of magnetic domains, in the second embodiment, the formation of magnetic poles on the side surface of the uneven structure, that is, on the surfaces located on both sides in the width direction of the peaks 21 and / or valleys 22, contributes to the subdivision of magnetic domains. The subdivision of magnetic domains reduces abnormal eddy current losses in the alloy thin strip, and a high effect is obtained in suppressing iron loss. The effect can be particularly enhanced by setting the maximum height roughness Rz in the width direction W of the uneven structure to 3 μm or more. More preferably, Rz should be 5 μm or more. There is no particular upper limit to Rz. It is preferable that the peaks 21 and / or valleys 22 that give the uneven structure are formed over the entire longitudinal direction of the alloy strip, except for regions where they cannot be formed inevitably. The uneven structure may also have height differences in the longitudinal direction L of the alloy strip, but it is preferable that the maximum height roughness Rz in the longitudinal direction L is smaller than the maximum height roughness Rz in the width direction W.

[0041] Regarding the second embodiment, we will omit the explanation of the configurations common to the first embodiment described above. However, the mechanisms, preferred structures, and preferred physical properties mentioned above for the first embodiment also apply to the second embodiment. Either the uneven structure formed by recesses in the first embodiment or the uneven structure formed by surface roughness in the second embodiment may be adopted, but the first embodiment is superior in that it is easier to control the position and depth of the recess formation. On the other hand, the second embodiment is superior in versatility because it can be applied to uneven structures formed in various forms, such as using the striated structure formed during the manufacturing of the alloy strip as the uneven structure. An uneven structure having both the recesses of the first embodiment and the surface roughness of the second embodiment may be formed. For example, an embodiment can be considered in which grooves are further formed along the longitudinal direction L on the surface of an alloy strip in which the maximum height roughness Rz in the width direction W is 3 μm or more.

[0042] [Wound iron core and method for manufacturing the same] The wound core according to an embodiment of the present invention is composed of Fe-based nanocrystalline alloy strips. Multiple layers of alloy strips are wound in a ring shape to form a wound core (toroidal core). Similar to the Fe-based nanocrystalline alloy strips described above, the component composition of the Fe-based alloy constituting the wound core is not particularly limited, but Fe-Si alloys, especially Fe-Si-B-Nb-Cu alloys, can be cited.

[0043] <First and Second Embodiments> The wound core according to the first embodiment of the present invention is composed of an Fe-based nanocrystalline alloy thin strip according to the first embodiment of the present invention described above, that is, an Fe-based nanocrystalline alloy thin strip having an uneven structure including at least one recess 1 extending along the longitudinal direction L. Furthermore, the wound core according to the second embodiment of the present invention is composed of an Fe-based nanocrystalline alloy thin strip according to the second embodiment of the present invention described above, that is, an Fe-based nanocrystalline alloy thin strip having an uneven structure in which the maximum height roughness Rz in the width direction W is 3 μm or more.

[0044] As shown in Figure 3(a) for a representative example of the structure of the wound core according to the first embodiment, the wound cores according to the first and second embodiments are constructed by winding a thin strip of Fe-based nanocrystalline alloy having a predetermined uneven structure in a multi-layered annular shape along the longitudinal direction L. The width direction W of the alloy strip is oriented in the height direction of the wound core. As shown in Figure 3(b), magnetic domains are formed along the height direction of the wound core corresponding to the width direction W. Unlike the wound core according to the third embodiment, which will be described later, the height dimension of the wound core as a whole is not particularly limited in the first and second embodiments.

[0045] The wound cores according to the first and second embodiments can be manufactured by the following method. First, as described above, for the first embodiment, a thin strip of Fe-based amorphous alloy is prepared, which has an uneven structure including recesses with a depth of 3 μm or more, and for the second embodiment, an uneven structure with a maximum height roughness Rz in the width direction W of 3 μm or more. Then, the amorphous alloy strip is wound along the longitudinal direction L to form a wound core structure. Next, the wound core structure is annealed in a magnetic field while applying a magnetic field H in the height direction. Crystallization heat treatment may be performed before annealing in a magnetic field as appropriate. The conditions for annealing in a magnetic field and crystallization annealing should be the same as those described above for the manufacturing method of the Fe-based nanocrystalline alloy strip.

[0046] After appropriate crystallization heat treatment, the structure of the alloy strip constituting the wound core is transformed into a nanocrystalline alloy by annealing in a magnetic field, which was originally amorphous. Furthermore, as shown in Figure 3(b), magnetic domains are formed along the height direction of the wound core, which is the direction in which the magnetic field H is applied. In the wound cores according to the first and second embodiments, an uneven structure is formed along the width direction W of the alloy strip, i.e., the height direction of the wound core. As explained above regarding the properties of the Fe-based nanocrystalline alloy strip, the magnetic domains are subdivided, and abnormal current losses due to magnetic domain wall movement when an AC magnetic field is applied can be kept to a minimum. As a result, iron losses can be kept to a minimum in the wound core. In the wound core, applying a magnetic field in the height direction differs from applying a magnetic field in the circumferential direction, and can be easily carried out using a general-purpose magnetic field application device. Therefore, the wound cores according to these first and second embodiments also have excellent manufacturing efficiency.

[0047] <Third Embodiment> As shown in Figure 4(a), the wound core according to the third embodiment of the present invention has a height (thickness) t of 2.5 mm or less. This limits the width of the region in which the alloy strip is continuous along the height direction (thickness direction) of the wound core to 2.5 mm or less. Furthermore, as shown in Figure 4(b), magnetic domains are formed along the height direction in the wound core. Unlike the wound cores according to the first and second embodiments described above, the wound core according to the third embodiment does not require the alloy strip constituting the wound core to have a specific uneven structure, and can be composed of Fe-based nanocrystalline alloy strips of any structure, including those substantially without an uneven structure.

[0048] The wound core according to the third embodiment can be manufactured by the following method. First, an Fe-based amorphous alloy thin strip is prepared in the same manner as described above for the Fe-based nanocrystalline alloy thin strips according to the first and second embodiments. However, it is not necessary to provide a specific uneven structure on the alloy thin strip. Next, the obtained alloy thin strip is wound in a multi-layered annular shape along the longitudinal direction to form a wound core structure. In this case, an alloy thin strip with a width of less than 2.5 mm is used, and the height t of the wound core structure is set to 2.5 mm or less, thereby limiting the width of the region in which the alloy thin strip is continuous along the height direction of the wound core structure to 2.5 mm or less. Next, the wound core structure is subjected to magnetic field annealing. For magnetic field annealing, as shown in Figure 4(a), a magnetic field H is applied in the height direction of the wound core structure, and the alloy thin strip is held at a heat treatment temperature of 200°C or more below the Curie point and below the Curie point. Crystallization heat treatment may be performed as appropriate before magnetic field annealing. Suitable conditions for crystallization heat treatment and magnetic field annealing can be the same as those listed above for the Fe-based nanocrystalline alloy thin strips according to the first and second embodiments.

[0049] After appropriate crystallization heat treatment and subsequent annealing in a magnetic field, the amorphous structure of the alloy strip constituting the wound core is transformed into a nanocrystalline alloy. Furthermore, as shown in Figure 4(b), magnetic domains are formed along the height direction of the wound core, which is the direction in which the magnetic field H is applied. In this third embodiment of the wound core, the height t is limited to a small value, and magnetic poles are formed at the height-direction ends of the alloy strip, thereby subdividing the magnetic domains. This subdivision of magnetic domains reduces abnormal current losses associated with domain wall movement when an alternating magnetic field is applied. As a result, iron losses in the Fe-based nanocrystalline alloy strip can be reduced.

[0050] The height direction of the wound core corresponds to the width direction W of the alloy strip, and limiting the height t of the wound core is similar to the first and second embodiments described above, in that it utilizes the magnetic poles at the ends of the alloy strip, by creating irregularities along the width direction W of the alloy strip, i.e., the height direction of the wound core, through the formation of recesses or the imparting of surface roughness, thereby utilizing the magnetic poles on the sides of the irregular structure. Therefore, limiting the height t of the wound core and then applying a magnetic field H in the height direction to perform magnetic field annealing corresponds to creating irregularities along the width direction W of the alloy strip and then applying a magnetic field H in that width direction W to perform magnetic field annealing. In this third embodiment of the wound core, as described for the Fe-based nanocrystalline alloy strip in the first and second embodiments, the continuity of the magnetic metal portion in the height direction is limited, which, along with the contribution of magnetic pole formation at the ends in the height direction, effectively realizes the subdivision of magnetic domains and provides a high effect in reducing iron loss. Furthermore, as described above, applying a magnetic field in the height direction of the wound core can be easily done, and combined with the fact that there is no need to provide a specific uneven structure in the alloy strip, the wound core according to the third embodiment is particularly efficient in terms of manufacturing.

[0051] In the wound core according to the third embodiment, limiting the height t to 2.5 mm or less is particularly effective in suppressing iron loss due to the subdivision of magnetic domains. More preferably, the height t of the wound core is 2.0 mm or less. In the wound core according to the third embodiment, it is sufficient that the width of the region in which the alloy strip is continuous along the height direction of the wound core is limited to 2.5 mm or less. Limiting the overall height t of the wound core to 2.5 mm or less is a simple means to achieve this, but other means can also be considered. For example, an annular recess along the circumferential direction can be formed in the middle of the height direction of the wound core. The distance between the upper and lower edges in the height direction and the recess, and between multiple recesses, should be 2.5 mm or less. It is preferable that the recess be formed along the longitudinal direction of the alloy strip before forming the wound core structure. In this case, it is preferable that the depth of the recess be 3 μm or more. Limiting the overall height t of the wound core and forming a recess along the circumferential direction can be done in combination. Furthermore, a composite wound core may be constructed by stacking multiple wound cores along the height direction, using a wound core with a height t of 2.5 mm or less, and a wound core with a width of 2.5 mm or less in the height direction as a unit core. In this case as well, the effect of suppressing iron loss by refining the magnetic domains can be obtained in the same way as described above. Other desirable physical properties and metallic structure that the wound core according to the third embodiment should have are the same as those described in detail above for the Fe-based nanocrystalline alloy thin strips according to the first and second embodiments. [Examples]

[0052] The present invention will be described in more detail below using examples. However, the present invention is not limited to these examples.

[0053] [Sample preparation] Three types of wound cores were prepared as samples: groove formation, roughening, and core height restriction. The groove formation sample corresponds to the first embodiment described above and is a wound core composed of an Fe-based nanocrystalline alloy strip with groove-like recesses formed along the longitudinal direction of the alloy strip. The roughening sample corresponds to the second embodiment described above and is a wound core composed of an Fe-based nanocrystalline alloy strip with a surface roughness having a predetermined maximum height roughness Rz in the width direction. The core height restriction sample corresponds to the third embodiment described above and is a wound core with its height dimension restricted.

[0054] As a common raw material for the three samples, alloy strips prepared by the single-roll liquid quenching method were used. The alloy strips consisted of the following four types of alloys, with alloy 1 being the primary alloy used, as indicated by the alloy composition in atomic percent. The thickness of each alloy strip was 18 μm. ·Alloy 1:Fe74.5-Si13.5-B8-Nb3-Cu1 Curie point: 572°C ·Alloy 2:Fe73.5-Si14.5-B8-Nb3-Cu1 Curie point: 567°C ·Alloy 3:Fe72-Si16-B8-Nb3-Cu1 Curie point: 565°C ·Alloy 4:Fe70-Si18-B8-Nb3-Cu1 Curie point: 555°C

[0055] For the grooved samples, a groove-like recess with a predetermined depth was formed along the longitudinal direction of a 10 mm wide alloy strip, with one recess positioned in the center of the width direction. Groove formation was mainly performed by laser processing, but for some samples, it was performed by machining or etching. For laser processing, a femtosecond laser was used to form a recess with a width of 10 μm. The depth of the recess was adjusted by the laser intensity. For machining, a diamond pen was pressed against the surface of the alloy strip to form the recess. The depth of the recess was controlled by the pressure applied to the diamond pen. Etching was performed by photoetching. In all cases, the recess was formed on the free surface of the alloy strip (the surface that was not in contact with the roll during rapid cooling), and the maximum height roughness Rz in the width direction outside the area where the recess was formed was less than 0.5 μm.

[0056] For the roughening test, a 10 mm wide alloy strip was used, with surface roughness applied to its surface to achieve a predetermined maximum height roughness Rz in the width direction. Surface roughness and Rz adjustment were performed by adjusting manufacturing conditions such as roll peripheral speed and differential pressure during rapid cooling of the strip. Rz was measured using a white light interferometer.

[0057] For the core height limiting sample, alloy strips without any uneven structure were used as the raw material for the wound core. In this process, multiple alloy strips of different widths were prepared to vary the height of the wound core.

[0058] For all three types of samples, the alloy strip prepared above was wound in an annular shape along its longitudinal direction to create a wound core structure. The outer diameter of the wound core structure was 28 mmφ, and the inner diameter was 20 mmφ. The height of the wound core structure was 10 mm for the grooved and roughened samples, and as shown in Table 1 for the core height-limited samples.

[0059] Next, crystallization heat treatment and magnetic field annealing were performed on the wound cores of the three samples. For the crystallization heat treatment, the alloy strip was heated to 570°C at a heating rate of 5°C / min and held at 570°C for 1 hour. For the magnetic field annealing, the wound core was held for 60 minutes at the holding temperature shown in Table 1, while applying a magnetic field in the height direction in a magnetic field with a magnetic flux density of 0.1 T. The crystallization heat treatment and magnetic field annealing were performed consecutively in an Ar atmosphere, after which the samples were allowed to cool. In this way, three types of wound core samples were prepared. In addition, for each sample, a thin strip sample was also prepared in which the crystallization heat treatment and magnetic field annealing were performed under the same conditions as above, before processing into a wound core structure. The direction of application of the magnetic field was in the width direction of the thin strip.

[0060] [Evaluation Method] The following evaluations were performed on each sample prepared as described above. Each evaluation was conducted at room temperature.

[0061] (1) Evaluation of grain size For each thin strip sample, the grain size was evaluated using X-ray diffraction. The average grain size was calculated from the width of the peak corresponding to the (110) plane of the body-centered cubic structure (α phase) of Fe in the obtained diffraction pattern.

[0062] (2) Evaluation of magnetic properties For each coiled iron core sample, the saturation magnetic flux density and iron loss were measured. For the saturation magnetic flux density (Bs), a BH curve was obtained at a maximum magnetic field Hm = 800 A / m using a DC magnetization characteristic tester, and the value of the magnetic flux density at H = 800 A / m was recorded as the saturation magnetic flux density (Bs). For iron loss, AC BH measurements were performed and evaluated at an applied magnetic flux density of 0.1 T and a frequency of 10 kHz. Furthermore, the ratio Pcv / Bs of the obtained iron loss (Pcv, unit: W / kg) to the saturation magnetic flux density (Bs, unit: T) was calculated. If Pcv / Bs is less than 0.50, it can be considered that both high saturation magnetic flux density and low iron loss have been achieved.

[0063] (3) Confirmation of the distribution of magnetic domains As a representative example, magnetic domain observation was performed on the sample of Example C4, which was configured as a roughness-impregnating sample. Magnetic domain observation was performed on a thin strip-shaped sample using a Kerr effect microscope.

[0064] [Test Results] Table 1 shows the composition and manufacturing conditions of each example and comparative example, as well as the results of the evaluation of their magnetic properties. The grain size for all samples was between 14.0 nm and 14.5 nm.

[0065] [Table 1]

[0066] In Table 1, among the samples using alloy 1, groups A, C, and D are groove-formed samples, group B is a roughened sample, and group E is a core height-limited sample. For Comparative Example 0, an unprocessed alloy strip was used in which neither groove-like recesses nor roughening was applied, and the height of the wound core was set to 10 mm, the same as the other groove-formed and roughened samples.

[0067] In each of the above samples, for each example in groups A to D, the depth of the recesses in the grooved samples or the maximum height roughness Rz in the width direction in the roughened samples is 3 μm or more in the alloy thin strip, and furthermore, a magnetic field is applied in the width direction, and the samples are annealed in a magnetic field at a temperature of 200°C lower than the Curie point but below the Curie point. In addition, for examples E1 and E2, the height of the wound core in the core height-restricted samples is 2.5 mm or less, and furthermore, a magnetic field is applied in the height direction, and the samples are annealed in a magnetic field at a temperature of 200°C lower than the Curie point but below the Curie point. In each of these examples, the ratio of iron loss to saturation magnetic flux density Pcv / Bs is less than 0.50, demonstrating that high saturation magnetic flux density and low iron loss are achieved simultaneously. For these samples, it is considered that subdivided magnetic domains are formed along the width direction of the alloy thin strip and along the height direction of the wound core after magnetic field annealing. In addition, Figure 5 shows the magnetic domain observation image of the sample from Example C4, and it can be seen that the magnetic domains have developed along the horizontal direction of the image, which corresponds to the width direction, and that the magnetic domains have been subdivided along the longitudinal direction, which corresponds to the vertical direction of the image.

[0068] In Comparative Example 0 and Examples / Comparative Examples A and B, the presence or absence of a surface irregularity structure in the alloy strip, and the size of the irregularities (depth of the depressions and maximum height roughness Rz), differ from one another. In addition, in Example / Comparative Example E, the height of the wound core differs from one another. Comparative Example 0 uses an unprocessed alloy strip without a surface irregularity structure, and the maximum height roughness Rz in the width direction across the entire surface is less than 3 μm. In Comparative Examples A1, A2 and Comparative Examples B1-B3, the depth of the depressions in the grooved strip, or the maximum height roughness Rz in the width direction in the roughened strip, is less than 3 μm. In addition, in Comparative Examples E1-E3, the height of the wound core exceeds 2.5 mm. In all of these samples, the ratio of iron loss to saturation magnetic flux density Pcv / Bs is 0.50 or higher. It is thought that the continuous metallic structure over a wide area along the width direction of the strip and the height direction of the wound core prevented sufficient subdivision of magnetic domains, resulting in insufficient iron loss suppression.

[0069] In the Examples / Comparative Examples C group, the holding temperatures during magnetic field annealing differed from one another. In Comparative Example C3, the holding temperature exceeded the Curie point. In Comparative Example C2, the holding temperature was approximately the same as the Curie point. In these samples, the ratio of iron loss to saturation magnetic flux density, Pcv / Bs, was 0.50 or higher. On the other hand, in Comparative Example C1, the holding temperature was more than 200°C lower than the Curie point, and in this sample as well, the ratio of iron loss to saturation magnetic flux density, Pcv / Bs, was 0.50 or higher. In both cases, it is considered that magnetic anisotropy was not effectively imparted during magnetic field annealing, and therefore the subdivision of magnetic domains was not effectively achieved.

[0070] Among the various groove-forming samples using alloy 1, Example A3 and Examples D1 and D2 differ in the means used to form groove-shaped recesses. However, in all cases, the ratio of iron loss to saturation magnetic flux density, Pcv / Bs, was reduced to a similar degree, indicating that iron loss was effectively reduced.

[0071] The above descriptions all involved samples using alloy 1, but the F group of examples / comparative examples uses different alloys. In all cases, in Examples F1 to F3, where a recess of 3 μm or more in depth was formed, a magnetic field was applied in the width direction of the thin strip, and magnetic field annealing was performed at a temperature 200°C lower than the Curie point but below the Curie point, the ratio of iron loss to saturation magnetic flux density Pcv / Bs was less than 0.50, indicating that the reduction of iron loss was effectively achieved. In Comparative Examples F1 to F3, which used the above alloys, magnetic field annealing was not performed, and in these samples, the ratio Pcv / Bs was 0.50 or higher. From this, it is confirmed that the reduction of iron loss cannot be fully achieved by the effects of alloy composition or recess formation alone, and that magnetic field annealing performed at a temperature 200°C lower than the Curie point but below the Curie point, with a magnetic field applied in the width direction, is necessary. In comparative example F4, the ratio of iron loss to saturation magnetic flux density Pcv / Bs is 0.50 or higher, corresponding to the holding temperature being approximately the same as the Curie point.

[0072] The embodiments and examples of the present invention have been described above. The present invention is not particularly limited to these embodiments and examples, and various modifications are possible. [Explanation of symbols]

[0073] 1 recess 11 Side part 21 mountains 22 Valley d Depth of the recess t Height of the wound iron core H magnetic field Longitudinal direction of the L alloy thin strip W alloy thin strip width direction

Claims

1. The surface has an uneven structure including at least one recess with a depth of 3 μm or more that extends along the longitudinal direction of the thin strip. A thin strip of Fe-based nanocrystalline alloy in which magnetic domains are formed along the width direction intersecting the longitudinal direction.

2. The surface has an uneven structure in which the maximum height roughness Rz in the width direction of the thin band is 3 μm or more. A thin strip of Fe-based nanocrystalline alloy in which magnetic domains are formed along the width direction.

3. The Fe-based nanocrystalline alloy thin strip according to claim 1 or claim 2, wherein the magnetic domains are divided in the width direction by the uneven structure.

4. A wound iron core comprising an Fe-based nanocrystalline alloy thin strip according to claim 1 or claim 2, wound in an annular shape along the longitudinal direction.

5. This is a wound iron core composed of thin strips of Fe-based nanocrystalline alloy. The width of the region in which the thin band is continuous along the height direction of the wound iron core is 2.5 mm or less. A wound core in which magnetic domains are formed along the height direction of the wound core.

6. The wound iron core according to claim 5, wherein the height is 2.5 mm or less.

7. A wound core comprising a wound core according to claim 5 or claim 6, wherein a plurality of the unit cores are stacked along the height direction.

8. A thin Fe-based nanocrystalline alloy strip according to claim 1 or claim 2, or a wound iron core according to claim 5 or claim 6, wherein the average grain size of the crystal grains is 30 nm or less.

9. A surface is formed on a thin strip of Fe-based amorphous alloy, including at least one recess with a depth of 3 μm or more that extends along the longitudinal direction of the strip, A method for producing an Fe-based nanocrystalline alloy thin strip, comprising applying a magnetic field to the thin strip in the width direction intersecting the longitudinal direction, and maintaining it at a temperature 200°C or higher below the Curie point and below the Curie point.

10. A surface is formed on a thin strip of Fe-based amorphous alloy, with a maximum height roughness Rz in the width direction of the strip being 3 μm or more. A method for producing an Fe-based nanocrystalline alloy thin band, comprising applying a magnetic field to the thin band in the width direction and maintaining it at a temperature 200°C or higher below the Curie point and below the Curie point.

11. A thin strip of Fe-based amorphous alloy is wound in a ring shape to form a wound iron core structure, The width of the region in which the thin band is continuous along the height direction of the wound core structure is set to 2.5 mm or less, A method for manufacturing a wound iron core, comprising applying a magnetic field to the wound iron core structure in the height direction and maintaining it at a temperature 200°C or higher below the Curie point and below the Curie point.

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