wound core

Abstract

The wound core is a wound core having a wound core body in which a plurality of polygonal annular directionality electromagnetic steel sheets are stacked in a side view, the directionality electromagnetic steel sheets having planar portions and curved portions alternately and continuously in a length direction, and a crystal grain size Dpx of the directionality electromagnetic steel sheets being 2W or less in at least one curved portion.

Description

Technical Field

[0001] This invention relates to wound iron cores. This application claims priority based on Japanese Patent Application No. 2020-179266, filed on October 26, 2020, the contents of which are incorporated herein by reference. Background Technology

[0002] Directional electromagnetic steel sheet contains less than 7% by mass of Si and has secondary recrystallized grains concentrated in {110}. <001> Steel sheet with a secondary recrystallization texture of orientation (Goss orientation). The magnetic properties of directional electromagnetic steel sheet are affected by the {110} direction. <001> The concentration of orientation has a significant impact. In recent years, practical directional electromagnetic steel sheets have been developed according to the principle of making the crystal... <001> The angle between the direction of rolling and the rolling direction was controlled to fall within a range of about 5°.

[0003] Directional electromagnetic steel sheets are laminated and used in transformer cores, etc., but the main magnetic properties required are high magnetic flux density and low iron loss. It is known that crystal orientation is strongly correlated with these properties, and for example, precise orientation control techniques such as those disclosed in Patent Documents 1-3 have been disclosed.

[0004] Furthermore, the influence of crystal grain size in directional electromagnetic steel sheets is well known, and patent documents 4 to 7, etc., disclose characteristics improvement techniques resulting from its control.

[0005] In addition, the manufacturing of wound iron cores has been widely known in the past, for example, by methods described in Patent Document 8: after the steel plate is rolled into a cylindrical shape, the corners are pressed in a manner that forms a certain curvature in the state of a cylindrical laminate, and after forming a roughly rectangular shape, stress is relieved and the shape is maintained by annealing.

[0006] On the other hand, as another manufacturing method for wound iron cores, patent documents 9-11 disclose a technique where the steel plate at the corner of the wound iron core is pre-bent to form a relatively small bending area with a radius of curvature of 3 mm or less, and the bent steel plate is then stacked to form the wound iron core. According to this manufacturing method, the large-scale pressing process as in the past is unnecessary; the steel plate is precisely bent to maintain the shape of the iron core, and the processing strain is concentrated only in the bending portion (corner). Therefore, the strain removal process performed using the aforementioned annealing step can be omitted, resulting in significant industrial advantages and progress in application.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2001-192785

[0010] Patent Document 2: Japanese Patent Application Publication No. 2005-240079

[0011] Patent Document 3: Japanese Patent Application Publication No. 2012-052229

[0012] Patent Document 3: Japanese Patent Application Publication No. 6-89805

[0013] Patent Document 5: Japanese Patent Application Publication No. 8-134660

[0014] Patent Document 6: Japanese Patent Application Publication No. 10-183313

[0015] Patent Document 7: International Publication No. 2019 / 131974

[0016] Patent Document 8: Japanese Patent Application Publication No. 2005-286169

[0017] Patent Document 9: Japanese Patent No. 6224468

[0018] Patent Document 10: Japanese Patent Application Publication No. 2018-148036

[0019] Patent Document 11: Australian Patent Application Publication No. 2012337260 Summary of the Invention

[0020] The problem that the invention aims to solve

[0021] The object of the present invention is to provide a wound core that is improved in a way that suppresses the efficiency degradation caused by the combination of the shape of the core and the steel plate used in a wound core manufactured by the following method: the steel plate is pre-bent in such a way that a relatively small bending area with a curvature radius of less than 5 mm is formed, and the bent steel plate is stacked to form a wound core.

[0022] Methods for solving problems

[0023] The inventors of this application conducted a detailed study on the efficiency of transformer cores manufactured by a method in which steel plates are pre-bent to form relatively small bending regions with a radius of curvature of less than 5 mm, and the bent steel plates are stacked to form a wound core. The results showed that even when using steel plates with approximately the same crystal orientation control and approximately the same magnetic flux density and iron loss measured on a single plate as raw materials, differences in core efficiency can still occur.

[0024] The causes were investigated, revealing that the efficiency differences were influenced by the crystal grain size of the raw materials. Furthermore, it was determined that the degree of the phenomenon (i.e., the difference in core efficiency) also varied depending on the size and shape of the core. Further detailed investigation suggested that the difference in the degree of iron loss degradation, particularly caused by bending, was the primary cause.

[0025] From this perspective, we studied the effects of various steel plate manufacturing conditions and core shapes on core efficiency, classifying their influence. The result was that by using steel plates manufactured under specific conditions as the raw material for cores of specific sizes and shapes, it is possible to control the core efficiency in a manner that optimally matches the magnetic properties of the steel plate raw material.

[0026] The main points of the present invention, which are made in order to achieve the above objectives, are as follows.

[0027] One embodiment of the present invention is a wound core comprising a wound core body formed by stacking multiple polygonal annular directional electromagnetic steel plates along the thickness direction in a side view.

[0028] The aforementioned directional electromagnetic steel sheet has alternating continuous planar and curved portions along its length.

[0029] The radius of curvature r of the inner surface of the aforementioned curved portion, viewed from the side, is 1 mm to 5 mm.

[0030] The aforementioned directional electromagnetic steel sheet has the following chemical composition:

[0031] It contains, by mass%:

[0032] Si: 2.0–7.0%,

[0033] The remaining portion contains Fe and impurities.

[0034] The aforementioned directional electromagnetic steel sheet has a texture oriented along a Gaussian orientation, and

[0035] In at least one of the aforementioned curved sections, the crystal grain size Dpx (mm) of the stacked directional electromagnetic steel plates is 2W or less.

[0036] Where Dpx is the average value of Dp obtained from the following equation (1),

[0037] Dc (mm) is the average grain size in the direction (hereinafter referred to as "boundary direction") extending from the boundary lines at each boundary of the aforementioned curved portion and the two aforementioned planar portions arranged in a manner that clamps the aforementioned curved portion.

[0038] Dl(mm) is the average crystal grain size at the boundary in the direction perpendicular to the boundary direction.

[0039] W (mm) is the width of the aforementioned curved portion as viewed from the side.

[0040] Furthermore, the average value of Dp is the average of the Dp on the inner surface side and the Dp on the outer surface side of one of the two planar portions, and the average of the Dp on the inner surface side and the Dp on the outer surface side of the other planar portion.

[0041] Dp=√(Dc×Dl / π) (1)

[0042] Furthermore, another embodiment of the present invention has a wound core comprising a wound core body having, in side view, a plurality of polygonal annular directional electromagnetic steel plates stacked along the thickness direction.

[0043] The aforementioned directional electromagnetic steel sheet has alternating continuous planar and curved portions along its length.

[0044] The radius of curvature r of the inner surface of the aforementioned curved portion, viewed from the side, is 1 mm to 5 mm.

[0045] The aforementioned directional electromagnetic steel sheet has the following chemical composition:

[0046] It contains, by mass%:

[0047] Si: 2.0–7.0%,

[0048] The remaining portion contains Fe and impurities.

[0049] The aforementioned directional electromagnetic steel sheet has a texture oriented along a Gaussian orientation, and

[0050] In at least one of the aforementioned curved sections, the crystal grain size Dpy (mm) of the stacked directional electromagnetic steel plates is 2W or less.

[0051] Where Dpy is the average value of Dl.

[0052] Dl (mm) is the average grain size of the crystals in the direction perpendicular to the boundary direction at each boundary of the aforementioned curved portion and the two aforementioned planar portions arranged in a manner that clamps the aforementioned curved portion.

[0053] W (mm) is the width of the aforementioned curved portion as viewed from the side.

[0054] Furthermore, the average value of Dl is the average of the Dl on the inner surface side and the Dl on the outer surface side of one of the two planar portions, and the average of the Dl on the inner surface side and the Dl on the outer surface side of the other planar portion.

[0055] Furthermore, another embodiment of the present invention is a wound core comprising a wound core body formed by stacking multiple polygonal annular directional electromagnetic steel plates along the thickness direction in a side view.

[0056] The aforementioned directional electromagnetic steel sheet has alternating continuous planar and curved portions along its length.

[0057] The radius of curvature r of the inner surface of the aforementioned curved portion, viewed from the side, is 1 mm to 5 mm.

[0058] The aforementioned directional electromagnetic steel sheet has the following chemical composition:

[0059] It contains, by mass%:

[0060] Si: 2.0–7.0%,

[0061] The remaining portion contains Fe and impurities.

[0062] The aforementioned directional electromagnetic steel sheet has a texture oriented along a Gaussian orientation, and

[0063] In at least one of the aforementioned curved sections, the crystal grain size Dpz (mm) of the stacked directional electromagnetic steel plates is 2W or less.

[0064] Where Dpz is the average value of Dc.

[0065] Dc (mm) is the average crystal grain size in the boundary direction at each boundary of the aforementioned curved portion and the two aforementioned planar portions arranged in a manner that clamps the aforementioned curved portion.

[0066] W (mm) is the width of the aforementioned curved portion as viewed from the side.

[0067] Furthermore, the average value of Dc is the average of Dc on the inner surface side and Dc on the outer surface side of one of the two planar portions, and the average of Dc on the inner surface side and Dp on the outer surface side of the other planar portion.

[0068] Invention Effects

[0069] According to the present invention, in a wound iron core formed by stacking bent directional electromagnetic steel plates, efficiency degradation caused by the combination of the shape of the iron core and the steel plates used can be effectively suppressed. Attached Figure Description

[0070] Figure 1 This is a perspective view schematically illustrating one embodiment of the wound iron core of the present invention.

[0071] Figure 2 yes Figure 1 The side view of the wound iron core shown in the embodiment.

[0072] Figure 3 This is a side view schematically illustrating another embodiment of the wound iron core of the present invention.

[0073] Figure 4 This is a side view schematically showing an example of a single layer of directional electromagnetic steel sheet constituting the wound core of the present invention.

[0074] Figure 5 This is a side view schematically showing another example of a single layer of directional electromagnetic steel sheet constituting the wound core of the present invention.

[0075] Figure 6 This is a side view schematically showing an example of a bent portion of the directional electromagnetic steel sheet constituting the wound core of the present invention.

[0076] Figure 7 The figures are for illustrating the method of measuring the crystal grain size of the directional electromagnetic steel plate constituting the wound core of the present invention. (a) is a three-dimensional schematic diagram of the main part, and (b) is a cross-sectional schematic diagram of the main part.

[0077] Figure 8 This is a schematic diagram showing the dimensional parameters of the wound iron core manufactured in the embodiments and comparative examples. Detailed Implementation

[0078] The wound iron core according to one embodiment of the present invention will now be described in detail. However, the present invention is not limited to the configuration disclosed in this embodiment, and various modifications can be made without departing from the spirit of the present invention. It should be noted that the lower and upper limits of the numerical ranges described below are included within the range. Values ​​expressed as "more than" or "less than" are not included in the numerical range. Furthermore, the "%" in chemical composition refers to "mass %" unless otherwise specified.

[0079] Furthermore, the terms used in this specification that specifically describe shape, geometric conditions, and their degree, such as "parallel," "perpendicular," "identical," "right angle," etc., as well as the values ​​of length and angle, are not strictly defined and are interpreted to include the extent to which the same function can be expected.

[0080] In addition, in this specification, "directional electromagnetic steel plate" is sometimes simply referred to as "steel plate" or "electromagnetic steel plate", and "wound iron core" is simply referred to as "iron core".

[0081] The wound core of this embodiment is characterized in that it is a wound core body comprising a plurality of polygonal annular directional electromagnetic steel plates stacked along the thickness direction when viewed from the side.

[0082] The aforementioned directional electromagnetic steel sheet has alternating continuous planar and curved portions along its length.

[0083] The radius of curvature r of the inner surface of the aforementioned curved portion, viewed from the side, is 1 mm to 5 mm.

[0084] The aforementioned directional electromagnetic steel sheet has the following chemical composition:

[0085] It contains, by mass%:

[0086] Si: 2.0–7.0%,

[0087] The remaining portion contains Fe and impurities.

[0088] The aforementioned directional electromagnetic steel sheet has a texture oriented along a Gaussian orientation, and

[0089] In at least one of the aforementioned curved sections, the crystal grain size Dpx (mm) of the stacked directional electromagnetic steel plates is 2W or less.

[0090] Where Dpx(mm) is the average value of Dp(mm) obtained from the following equation (1),

[0091] Dc (mm) is the average grain size in the boundary direction at each boundary of the aforementioned curved portion and the two aforementioned planar portions arranged in a manner that clamps the aforementioned curved portion.

[0092] Dl (mm) is the average crystal grain size in the direction perpendicular to the boundary direction mentioned above.

[0093] W (mm) is the width of the aforementioned curved portion as viewed from the side.

[0094] Furthermore, the average value of Dp is the average value of the Dp on the inner surface side and the Dp on the outer surface side of one of the two aforementioned planar portions, and the average value of the Dp on the inner surface side and the Dp on the outer surface side of the other aforementioned planar portion.

[0095] Dp=√(Dc×Dl / π) (1)

[0096] 1. Shape of the wound iron core and directional electromagnetic steel sheet

[0097] First, the shape of the wound core in this embodiment will be described. The shapes of the wound core and the directional electromagnetic steel plate described here are not particularly novel. For example, they are simply wound cores and directional electromagnetic steel plates based on the shapes of known wound cores and directional electromagnetic steel plates described in patent documents 9-11 in the background art.

[0098] Figure 1 This is a perspective view schematically illustrating one embodiment of a wound iron core. Figure 2 yes Figure 1A side view of the wound iron core shown in the embodiment. Furthermore, Figure 3 This is a side view schematically illustrating another embodiment of the wound iron core.

[0099] It should be noted that, in this embodiment, "side view" refers to the view along the width of the long strip of directional electromagnetic steel plate constituting the wound core. Figure 1 The view is taken along the Y-axis. A side view is a diagram showing the shape as identified by a side view. Figure 1 (Graph of the Y-axis direction).

[0100] The wound core of this embodiment comprises a wound core body 10 formed by stacking multiple polygonal annular (rectangular or polygonal) directional electromagnetic steel plates 1 along the thickness direction in a side view. This wound core body 10 is formed by overlapping directional electromagnetic steel plates 1 along the thickness direction, and has a polygonal stacked structure 2 in a side view. This wound core body 10 can be used directly as a wound core, or, as needed, can be equipped with known fastening tools such as cable ties to secure the overlapping multiple directional electromagnetic steel plates 1 as a single unit.

[0101] In this embodiment, there is no particular limitation on the core length of the wound core body 10. Even if the core length changes, the volume of the bend 5 remains constant, therefore the iron loss generated at the bend 5 is constant. When the core length is longer, the volume fraction of the bend 5 relative to the wound core body 10 decreases, thus its impact on iron loss degradation is also smaller. Therefore, the core length of the wound core body 10 is preferably longer. The core length of the wound core body 10 is preferably 1.5 m or more, more preferably 1.7 m or more. It should be noted that in this embodiment, the core length of the wound core body 10 refers to the circumference at the center point of the stacking direction of the wound core body 10 in a side view.

[0102] The wound core of this embodiment can also be suitably used for any of the conventionally known applications. In particular, it offers significant advantages when applied to cores for power transmission transformers where core efficiency is a problem.

[0103] like Figure 1 and 2 As shown, in the wound core body 10, the directional electromagnetic steel plate 1, in which the first flat portion 4 and the corner portion 3 alternately continue in the length direction, and the angle formed by two adjacent first flat portions 4 at each corner portion 3 is 90°, includes an overlapping portion in the thickness direction, and has a generally rectangular stacked structure 2 in side view. Furthermore, viewed in another way... Figure 1 and 2The wound core body 10 shown has an octagonal stacked structure 2. The wound core body 10 of this embodiment has an octagonal stacked structure, but the present invention is not limited to this. The wound core body can be constructed by stacking multiple polygonal annular directional electromagnetic steel plates along the thickness direction in a side view, and the directional electromagnetic steel plates have alternating continuous planar portions and curved portions in the length direction (circumferential direction).

[0104] The following description will focus on the case where the wound iron core body 10 has a generally rectangular shape with four corner portions 3.

[0105] Each corner portion 3 of the directional electromagnetic steel plate 1 has two or more curved portions 5 in a side view, and a second flat portion 4a is provided between adjacent curved portions 5, 5. Therefore, the corner portion 3 is configured to have two or more curved portions 5 and one or more second flat portions 4a. Furthermore, the sum of the curvature angles of the two curved portions 5, 5 present at a corner portion 3 is 90°.

[0106] In addition, such as Figure 3 As shown, each corner portion 3 of the directional electromagnetic steel plate 1 has three curved portions 5 in a side view, and a second flat portion 4a is provided between adjacent curved portions 5, 5, and the total bending angle of the three curved portions 5, 5, 5 at a corner portion 3 is 90°.

[0107] Furthermore, each corner portion 3 may have four or more bends. In this case, a second flat portion 4a is provided between adjacent bends 5, and the sum of the bending angles of the four or more bends 5 present at one corner portion 3 is 90°. That is, in this embodiment, each corner portion 3 is positioned between two adjacent first flat portions 4, 4 arranged at right angles, and has two or more bends 5 and one or more second flat portions 4a.

[0108] In addition, Figure 2 In the wound core body 10 shown, a bent portion 5 is disposed between the first planar portion 4 and the second planar portion 4a, but... Figure 3 In the wound core body 10 shown, bent portions 5 are respectively arranged between the first planar portion 4 and the second planar portion 4a and between the two second planar portions 4a, 4a. That is, the second planar portion 4a may also be arranged between two adjacent second planar portions 4a, 4a.

[0109] Furthermore, in Figure 2 and Figure 3 In the wound core body 10 shown, the length of the first planar portion 4 in the longitudinal direction (circumferential direction of the wound core body 10) is longer than that of the second planar portion 4a, but the lengths of the first planar portion 4 and the second planar portion 4a can also be equal.

[0110] It should be noted that in this specification, the "first planar part" and the "second planar part" are sometimes simply referred to as "planar part".

[0111] Each corner portion 3 of the directional electromagnetic steel plate 1 has two or more curved portions 5 in a side view, and the sum of the curvature angles of the curved portions at a corner portion is 90°. A second flat portion 4a is provided between adjacent curved portions 5. Therefore, the corner portion 3 is configured to have two or more curved portions 5 and one or more second flat portions 4a.

[0112] Figure 2 One implementation is that there are two curved portions 5 in one corner portion 3. Figure 3 One implementation is that there are three curved sections 5 in one corner section 3.

[0113] As shown in these examples, in this embodiment, one corner portion may be composed of two or more bend portions, but from the perspective of suppressing strain caused by deformation during processing and thus suppressing iron loss, the bending angle φ (φ1, φ2, φ3) of the bend portion 5 is preferably 60° or less, more preferably 45° or less.

[0114] It has two bends at one corner. Figure 2 In this embodiment, from the perspective of reducing iron loss, for example, φ1 = 60° and φ2 = 30° can be set, or φ1 = 45° and φ2 = 45° can be set, etc. Furthermore, it has three bends at one corner. Figure 3 In this implementation, from the perspective of reducing iron loss, φ1 = 30°, φ2 = 30°, and φ3 = 30° can be set, for example. Furthermore, from the perspective of production efficiency, it is preferable that the bending angles are equal; therefore, when there are two bends at one corner, it is preferable to set φ1 = 45° and φ2 = 45°. Moreover, when there are three bends at one corner... Figure 3 In the implementation of the method, from the perspective of reducing iron loss, it is preferred to set φ1 = 30°, φ2 = 30° and φ3 = 30°.

[0115] Reference Figure 6 The curved portion 5 will be described in more detail. Figure 6This diagram schematically illustrates an example of a curved portion (curved section) of a directional electromagnetic steel sheet. The bending angle of the curved portion 5 refers to the angle difference between the straight section on the rear side and the straight section on the front side of the curved portion 5 in the bending direction. It is expressed as the supplementary angle φ formed by extending the straight sections of the plane portions 4 and 4a on both sides of the curved portion 5 at the outer surface of the directional electromagnetic steel sheet 1. At this point, the point where the extended straight lines detach from the steel sheet surface is the boundary between the plane portions 4 and 4a on the outer surface of the steel sheet and the curved portion 5. Figure 6 In the middle, points F and G are points F and G respectively.

[0116] Furthermore, straight lines perpendicular to the outer surface of the steel plate are extended from points F and G respectively, and their intersections with the inner surface of the steel plate are designated as points E and D. These points E and D are the boundaries between the planar portions 4 and 4a and the curved portion 5 on the inner surface of the steel plate.

[0117] Furthermore, in this embodiment, the so-called curved portion 5 is the part of the directional electromagnetic steel plate 1 enclosed by the aforementioned points D, E, F, and G, viewed from the side. Figure 6 In the diagram, the inner surface of the steel plate between point D and point E, i.e., the curved part 5, is denoted as La, and the outer surface of the steel plate between point F and point G, i.e., the curved part 5, is denoted as Lb.

[0118] also, Figure 6 The diagram shows the radius of curvature r (hereinafter also simply referred to as radius of curvature r) of the inner surface of the curved portion 5 in a side view. The radius of curvature r of the curved portion 5 is obtained by approximating the above-mentioned La with an arc passing through points E and D. The smaller the radius of curvature r, the steeper the curvature of the curved portion 5; the larger the radius of curvature r, the gentler the curvature of the curved portion 5.

[0119] In the wound core of this embodiment, the radius of curvature r at each bend 5 of the directional electromagnetic steel plates 1 stacked along the thickness direction can vary to a certain extent. This variation may be due to variations in forming accuracy, or unintentional variations caused by operations during stacking. Such unintentional errors can be suppressed to about 0.2 mm or less in conventional industrial manufacturing. In cases of large variations, a representative value can be obtained by measuring the radius of curvature of a sufficiently large number of steel plates and averaging them. Furthermore, intentional variations for some reason are also considered, but this embodiment does not exclude such variations.

[0120] Furthermore, there are no particular limitations on the method for measuring the radius of curvature r of the inner surface of the curved portion 5, but it can be measured, for example, by observing it at 200x magnification using a commercially available microscope (Nikon ECLIPSE LV150). Specifically, the radius of curvature r is determined from the observation results. Figure 6 The curvature center point A is shown as in the diagram, but as a method of calculation, for example, if the intersection point obtained by extending line segments EF and DG inwards to the opposite side of point B is defined as A, then the size of the inner surface curvature radius r is equivalent to the length of line segment AC. Here, when connecting point A and point B with a straight line, the intersection point with the arc DE on the inner surface of the curved portion 5 is set as point C.

[0121] In this embodiment, by manufacturing a wound core using a specific directional electromagnetic steel sheet with the inner surface curvature radius r of the bent portion 5 set to a range of 1 mm to 5 mm and the crystal grain size described below controlled, the efficiency of the wound core can be optimized to match the magnetic properties. The inner surface curvature radius r of the bent portion 5 is preferably 3 mm or less. In this case, the effects of this embodiment are more significantly realized.

[0122] Furthermore, it is most preferred that all the bends within the core satisfy the inner surface curvature radius r specified in this embodiment. In the case where there are bends in the wound core that satisfy the inner surface curvature radius r of this embodiment and bends that do not satisfy the inner surface curvature radius r of this embodiment, it is preferred that at least half of the bends satisfy the inner surface curvature radius r specified in this embodiment.

[0123] Figure 4 and Figure 5 This is a schematic diagram illustrating an example of a directional electromagnetic steel sheet 1 wound in one layer within the core body 10. (See diagram below.) Figure 4 and Figure 5 As shown in the example, the directional electromagnetic steel plate 1 used in this embodiment is a bent steel plate with a corner portion 3 consisting of two or more bends 5 and a first flat portion 4. A roughly rectangular ring is formed in the side view through the end face, i.e., the joint portion 6, in the length direction of one or more directional electromagnetic steel plates 1.

[0124] In this embodiment, the wound core body 10 only needs to have a generally rectangular stacked structure 2 when viewed from the side as a whole. It can be as follows: Figure 4 As shown in the example, a single layer of directional electromagnetic steel sheet 1 is formed by a single joint 6 to form the core body 10 (i.e., each roll is connected by a single joint 6 to form a single directional electromagnetic steel sheet 1). Figure 5As shown in the example, one directional electromagnetic steel plate 1 constitutes about half a turn of the core, and two directional electromagnetic steel plates 1 constitute one layer of the core body 10 through two joints 6 (i.e., each roll connects the two directional electromagnetic steel plates 1 to each other through two joints 6).

[0125] The thickness of the directional electromagnetic steel plate 1 used in this embodiment is not particularly limited. It can be appropriately selected according to the application, etc., but it is usually in the range of 0.15mm to 0.35mm, preferably in the range of 0.18mm to 0.23mm.

[0126] 2. Composition of directional electromagnetic steel plates

[0127] Next, the configuration of the directional electromagnetic steel plate 1 constituting the wound core body 10 will be described. In this embodiment, the crystal grain size of the planar portions 4 and 4a adjacent to the bent portion 5 of the adjacently stacked directional electromagnetic steel plates, and the arrangement position of the directional electromagnetic steel plates within the core in which the crystal grain size is controlled, are characterized.

[0128] (1) Crystal grain size of the planar portion adjacent to the curved portion

[0129] In this embodiment, the directional electromagnetic steel plate 1 constituting the wound core is controlled, at least in a portion of the corner portion, in such a way that the grain size of the stacked steel plates decreases. If the grain size near the bend 5 becomes coarse, the effect of avoiding efficiency degradation in the core having the core shape of this embodiment will not be exhibited. In other words, it means that efficiency degradation can be easily suppressed by arranging grain boundaries near the bend 5.

[0130] The mechanism behind this phenomenon is not clear, but it can be considered as follows.

[0131] In the core of this embodiment, the macroscopic strain (deformation) caused by bending is confined to a very narrow region, namely the bending portion 5. However, if the microscopic strain is considered as the crystal structure inside the steel plate, it is believed that dislocations formed at the bending portion 5 also move and extend to the outer side of the bending portion 5, namely the planar portions 4, 4a. It is believed that in the directional electromagnetic steel plate with a grain size of several millimeters, which is envisioned as the raw material in the core of this embodiment, grain boundaries act as strong barriers to dislocation movement, and the movement of dislocations is confined to a single grain that can be considered approximately a single crystal. That is, it is believed that dislocations will not be generated beyond the grain adjacent to the grain boundary. It is known that lattice defects such as dislocations generally cause significant deterioration of iron loss. Therefore, by refining the grain size near the bending portion, the grain boundaries function as barriers to the movement of dislocations towards the planar portions (dislocation disappearance sites), thereby enabling the region where dislocations exist to remain extremely close to the bending portion 5. It is believed that this can suppress the reduction of core efficiency. The mechanism of action of this embodiment is believed to be a special phenomenon in the iron core of a specific shape that is the object of this embodiment, which has not been considered to date, but can be explained in accordance with the insights obtained by the inventors of this invention.

[0132] In this embodiment, the crystal grain size is measured as follows.

[0133] The thickness of the steel plate stack of the wound core body 10 is set to T (equivalent to...). Figure 8 When “L3” is shown, a total of five directional electromagnetic steel plates, including the innermost surface of the region containing the corner portion, are extracted from the innermost surface of the wound core body 10 at positions where the innermost layers are stacked at every T / 4. For each extracted steel plate, if the surface of the steel plate has a primary coating (glass coating, interlayer), insulating coating, etc., formed of oxides, etc., they are removed by known methods, such as… Figure 7 As shown in (a), the crystal structure of the inner and outer side surfaces of the steel sheet is observed visually. Then, at the boundary line B where the curved and flat portions of each surface are approximately straight, the grain size in the direction of the boundary (the direction in which the boundary line B extends (the rolling right-angle direction of the directional electromagnetic steel sheet)) and the grain size in the direction perpendicular to the boundary (the boundary perpendicular direction (the rolling direction of the directional electromagnetic steel sheet)) are measured as follows.

[0134] Particle size Dc (mm) in the boundary direction, for example... Figure 7 As shown in the schematic diagram of (a), when the length of the boundary line B (equivalent to the width of the directional electromagnetic steel plate 1 constituting the iron core) is set to Lc and the number of grain boundaries intersecting with the boundary line B is set to Nc, it is obtained by the following formula (2).

[0135] Dc=Lc / (Nc+1) (2)

[0136] Furthermore, regarding the grain size Dl (mm) in the direction perpendicular to the boundary (the direction perpendicular to the boundary direction), in the extension direction of the boundary line B (the boundary direction), at the five locations other than the ends where Lc is divided into 6 sections, the distance from the boundary line B of one curved section 5 and the first planar section 4 as the starting point to the point where a line extending perpendicularly to the boundary line B along the region of the first planar section 4 initially intersects the grain boundary is set as Dl1 to Dl5 in the first planar section 4. Similarly, the distance from the boundary line B of one curved section 5 and the second planar section (the planar section within the corner) 4a as the starting point to the point where a line extending perpendicularly to the boundary line B along the region of the second planar section 4a initially intersects the grain boundary or the boundary line B of another curved section 5 adjacent to the second planar section 4a is set as Dl1 to Dl5 in the second planar section. The same procedure is performed for the other curved section 5 to determine Dl1 to Dl5 in both the first planar section 4 and the second planar section 4a. Then, using the average distances of these Dl1 to Dl5, the particle size Dl in the direction perpendicular to the boundary is calculated.

[0137] Then, the equivalent circle crystal grain size Dp (mm) of the first planar portion 4 and the second planar portion 4a adjacent to the curved portion 5 is obtained by the following formula (1).

[0138] Dp=√(Dc×Dl / π) (1)

[0139] Furthermore, such as Figure 7 As shown in the schematic diagram of (b), the crystal grain size on the inner surface side of the second planar portion 4a is labeled with the subscript ii, and the crystal grain size on the outer surface side is labeled with the subscript io. The crystal grain size on the inner surface side of the first planar portion 4 is labeled with the subscript oi, and the crystal grain size on the outer surface side is labeled with the subscript oo. In this way, for a curved portion 5, 12 crystal grain sizes (Dcii, Dcio, Dcoi, Dcoo, Dlii, Dlio, Dloi, Dloo, Dpii, Dpio, Dpoi, Dpoo) are determined as (Dc, Dl, Dp) - (ii, io, oi, oo). Then, for two or more crystal grain sizes present at each corner (e.g., at...) Figure 2 The wound iron core body 10 shown has two units, in Figure 3 In the winding core body 10 shown, there are 3 bent portions 5. The above 12 crystal grain sizes are averaged, and 12 crystal grain sizes such as (Dc, Dl, Dp)-(ii, io, oi, oo) are determined for each corner portion.

[0140] It should be noted that, generally speaking, directional electromagnetic steel sheets have crystal grain sizes of several millimeters, which are very large compared to the thickness of the steel sheet. Therefore, in most cases, a single grain appears columnar in cross-section, penetrating from one surface (e.g., the inner surface side in this embodiment) to the other surface (e.g., the outer surface side in this embodiment). Therefore, although the crystal grain sizes measured on the inner and outer surface sides are approximately the same as described above, since in reality there may be fine grains remaining on the surface that do not penetrate the thickness of the sheet, in this embodiment, the crystal grain size is measured on both sides of the steel sheet, and the average value is used to define the wound core of this embodiment.

[0141] In this embodiment, the crystal grain size is defined by comparing it with the width W (mm) of the bent portion 5. In this embodiment, the width W of the bent portion 5 is set to the inner surface La of the bent portion 5 (refer to...). Figure 6 The length of the bending section 5 (length in the bending direction) and the outer surface Lb of the bending section 5 (refer to) Figure 6 The average length (length in the bending direction) of ).

[0142] In one embodiment of this invention, the average value of Dp-(ii, io, oi, oo) is set to Dpx (mm) in at least one corner portion 3, where Dpx ≤ 2W. This specification corresponds to the basic characteristics of the mechanism described above. By satisfying this specification, the grain boundary can function as an obstacle to the movement of dislocations generated at the bend portion 5 toward the first plane portion 4 and the second plane portion 4a, resulting in the effect of this embodiment. The upper limit of Dpx is twice W because dislocations generated at the bend portion 5 can only move up to about twice the size of the deformed area, and even if Dpx exceeds 2W, it is unlikely to become an obstacle to dislocation movement. Preferably, Dpx ≤ W. Furthermore, it is undoubtedly preferable that Dpx ≤ 2W be satisfied in all four corner portions present in the wound core body 10.

[0143] As another embodiment, the feature is that, in at least one corner portion 3, the average value of Dl-(ii, io, oi, oo) is set to Dpy (mm), where Dpy ≤ 2W. This specification, considering the mechanism described above, corresponds to the following feature: in particular, grain boundaries existing in a manner intersecting the directions toward the first plane portion 4 and the second plane portion 4a (directions perpendicular to the boundary direction in the curved portion 5) are more likely to act as barriers to dislocation movement toward each plane portion compared to grain boundaries existing parallel to the directions toward the first plane portion 4 and the second plane portion 4a (directions perpendicular to the boundary of the curved portion). By satisfying this specification, dislocation movement toward the plane portion region can be sufficiently suppressed. Preferably, Dpy ≤ W. Furthermore, it is undoubtedly preferable that Dpy ≤ 2W is satisfied in all four corner portions present in the wound core body 10.

[0144] In another embodiment, the average value of Dc-(ii, io, oi, oo) is set to Dpz (mm) in at least one corner portion 3, where Dpz ≤ 2·W. This specification corresponds to the feature that even grain boundaries existing parallel to the direction toward the first plane portion 4 and the second plane portion 4a (the direction perpendicular to the boundary of the bend) readily function as disappearance sites for dislocations moving toward the first plane portion 4 and the second plane portion 4a. By satisfying this specification, the movement of dislocations toward the plane portion region can be sufficiently suppressed. Preferably, Dpz ≤ W. Furthermore, it is undoubtedly preferable that Dpz ≤ 2W is satisfied in all four corner portions present in the wound core body 10.

[0145] (2) Directional electromagnetic steel sheet

[0146] As described above, in the directional electromagnetic steel plate 1 used in this embodiment, the mother steel plate is one in which the grain orientation is highly concentrated in {110}. <001> Oriented steel sheets have excellent magnetic properties in the rolling direction.

[0147] In this embodiment, the mother steel plate can be a known directional electromagnetic steel plate. Hereinafter, an example of a preferred mother steel plate will be described.

[0148] The chemical composition of the mother steel plate, by mass percent, contains 2.0%–6.0% Si, with the remainder being Fe and impurities. This chemical composition is designed to control the crystal orientation to concentrate in {110}. <001> The oriented Gaussian texture ensures good magnetic properties. There are no particular limitations on other elements, but in this embodiment, in addition to Si, Fe, and impurities, elements within a range that do not hinder the effects of the invention may be included. For example, instead of a portion of Fe, the following elements are permitted to be included within the following ranges. Representative optional element ranges are described below.

[0149] C: 0~0.0050%

[0150] Mn: 0~1.0%

[0151] S: 0~0.0150%

[0152] Se: 0~0.0150%

[0153] Al: 0~0.0650%

[0154] N: 0~0.0050%

[0155] Cu: 0–0.40%

[0156] Bi: 0~0.010%

[0157] B: 0~0.080%

[0158] P: 0–0.50%

[0159] Ti: 0~0.0150%

[0160] Sn: 0-0.10%

[0161] Sb: 0~0.10%

[0162] Cr: 0–0.30%

[0163] Ni: 0-1.0%

[0164] Nb: 0~0.030%

[0165] V: 0~0.030%

[0166] Mo: 0–0.030%

[0167] Ta: 0~0.030%

[0168] W: 0–0.030%.

[0169] These optional elements only need to be included according to their purpose, so there is no need to limit the lower limit value, and they can be substantially absent. Furthermore, even if these optional elements are included as impurities, it will not impair the effect of this embodiment. In addition, setting the C content to 0% in practical steel plates is difficult in manufacturing, so the C content can also be set to more than 0%. It should also be noted that impurities refer to elements unintentionally present, meaning elements that are mixed in from the ore, waste, or manufacturing environment used as raw materials during the industrial manufacture of the mother steel plate. The upper limit of the total impurity content can be, for example, 5%.

[0170] The chemical composition of the base steel plate can be determined using general analytical methods for steel. For example, the chemical composition of the base steel plate can be determined using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Specifically, for example, it can be determined by taking a 35 mm square test piece from the center of the base steel plate after the coating has been removed, and measuring it using a Shimadzu ICPS-8100 or similar measuring device, based on pre-prepared calibration lines. Furthermore, C and S can be determined using the combustion-infrared absorption method, and N can be determined using the inert gas melting-thermal conductivity method.

[0171] It should be noted that the above-mentioned chemical composition refers to the composition of the directional electromagnetic steel plate 1, which serves as the mother steel plate. When the directional electromagnetic steel plate 1, which is used as the test sample, has a primary coating (glass coating, intermediate layer), an insulating coating, etc., formed from oxides or the like on its surface, these are removed using known methods before the chemical composition is determined.

[0172] (3) Manufacturing method of directional electromagnetic steel sheet

[0173] The manufacturing method of directional electromagnetic steel sheet is not particularly limited, but by precisely controlling the manufacturing conditions as described later, the grain size of the steel sheet can be produced. By using directional electromagnetic steel sheet with such a desired grain size and manufacturing a wound core using the preferred processing conditions described later, a wound core capable of suppressing the deterioration of core efficiency can be obtained. As a preferred specific example of the manufacturing method, for example, firstly, a slab with C set to 0.04 to 0.1% by mass and having the above-described chemical composition of directional electromagnetic steel sheet is heated to 1000°C or higher for hot rolling, and then wound at 400 to 850°C. The hot-rolled sheet is then annealed as needed. The annealing conditions of the hot-rolled sheet are not particularly limited, but from the viewpoint of precipitate control, the annealing temperature can be set to 800 to 1200°C and the annealing time to 10 to 1000 seconds. Next, a cold-rolled steel sheet is obtained by one cold rolling or two or more cold rollings with intermediate annealing. From the perspective of texture control, the cold rolling ratio can be set to 80-99% at this point. The cold-rolled steel sheet is then decarburized and annealed, for example, in a moist hydrogen-inert gas atmosphere to 700-900°C, and further nitrided if necessary. Afterward, an annealing separating agent is applied to the annealed steel sheet, and it is then annealed at a maximum temperature of 1000-1200°C for 40-90 hours, forming an insulating film at approximately 900°C. Among these conditions, decarburization annealing and final annealing, in particular, affect the grain size of the steel sheet. Therefore, when manufacturing wound cores, it is preferable to use directional electromagnetic steel sheets manufactured within the above-mentioned conditions.

[0174] Furthermore, even steel sheets that have undergone a process known as "magnetic domain control" during the steel sheet manufacturing process can enjoy the effects of this embodiment.

[0175] As described above, the characteristic of the directional electromagnetic steel sheet 1 used in this embodiment, namely the crystal grain size, is preferably adjusted, for example, by the highest reaching temperature and time of the finished product annealing. By reducing the average crystal grain size of the steel sheet as a whole and setting each crystal grain size to 2W or less as described above, even if the bend 5 is formed at any position during the manufacturing of the wound core, it is expected that the aforementioned Dpx, etc., will be 2W or less. Alternatively, in order to manufacture a wound core with small crystal grains arranged near the bend 5, it is also effective to control the bending position of the steel sheet in a way that the area with small crystal grains is arranged near the bend 5. In this method, it is also possible to manufacture a steel sheet in which the growth of secondary recrystallization grains is locally suppressed by known methods such as locally changing the state of the annealing separating agent during the steel sheet manufacturing process, and to select the part with fine grains for bending.

[0176] 3. Manufacturing method of wound iron core

[0177] The method for manufacturing the wound core in this embodiment is not particularly limited as long as it can manufacture the wound core of this embodiment described above. For example, the method for manufacturing a wound core according to known methods described in patent documents 9-11 in the background art can be used. In particular, the method using the UNICORE (https: / / www.aemcores.com.au / technology / unicore / ) manufacturing apparatus from AEM UNICORE Corporation is considered optimal.

[0178] It should be noted that, from the perspective of precisely controlling Dpx, Dpy, and Dpz, it is preferable to control the shape of the punch and die used during processing, as well as the amount of temperature rise in the steel sheet caused by processing heat. Specifically, the radius of curvature of the punch used is set to r. p (mm), Set the radius of curvature of the die to r. d In the case of (mm), it is preferable to use r p / r d The temperature is set within the range of 2.0 to 10.0. Furthermore, when the temperature rise of the steel sheet caused by processing heat is set to ΔT, ΔT is preferably suppressed to below 4.8°C. If ΔT is too large, even if a steel sheet with an appropriate grain size is used as raw material, the grain size may become coarse, reducing the core efficiency of the wound core. There are no particular limitations on the cooling method, but for example, the steel sheet temperature can be adjusted by blowing a refrigerant such as liquid nitrogen during or immediately after processing.

[0179] Alternatively, heat treatment can be performed as needed using known methods. Furthermore, the resulting wound core body 10 can be used directly as a wound core, but it can also be further manufactured by fixing multiple overlapping directional electromagnetic steel plates 1 together using known fastening tools such as cable ties.

[0180] This embodiment is not limited to the above-described embodiment. The above-described embodiment is illustrative, and any embodiment that has essentially the same structure and performs the same effect as the technical concept described in the claims of this invention, regardless of the method, is included within the technical scope of this invention.

[0181] Example

[0182] The technical content of the present invention will be further described below while listing embodiments of the invention. The conditions in the embodiments shown below are examples of conditions adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to these examples of conditions. Furthermore, various conditions can be adopted in the present invention as long as they do not depart from the spirit of the present invention and achieve the purpose of the present invention.

[0183] (Directional electromagnetic steel sheet)

[0184] Using slabs with the chemical composition shown in Table 1 (mass %), the remainder other than those shown is Fe, as raw materials, a final product (product plate) with the chemical composition shown in Table 2 (mass %) is manufactured. The resulting steel plate has a width of 1200 mm.

[0185] In Tables 1 and 2, “-” indicates elements for which no conscious content control or manufacturing process was carried out and for which no content determination was performed. Furthermore, “<0.002” and “<0.004” indicate elements for which conscious content control or manufacturing process was carried out and for which content determination was performed, but for which a sufficient determination value (below the detection limit) was not obtained as a reliable measure of accuracy.

[0186] [Table 1]

[0187]

[0188] [Table 2]

[0189]

[0190] In addition, the details of the steel plate manufacturing process and conditions are shown in Table 3.

[0191] Specifically, hot rolling, hot-rolled plate annealing, and cold rolling were performed. For some steel plates, cold-rolled steel plates after decarburization annealing were subjected to nitriding treatment (nitriding annealing) in a mixed atmosphere of hydrogen, nitrogen, and ammonia.

[0192] Then, an annealing separating agent with MgO as the main component was applied, and the finished product was annealed. On the primary coating formed on the surface of the finished annealed steel plate, an insulating coating solution containing chromium and phosphate as the main components was applied, and the coating was heat-treated to form an insulating coating.

[0193] At this point, by adjusting the cold rolling rate or the annealing time of the finished product, steel sheets with controlled crystal grain size are manufactured. Details of the manufactured steel sheets are shown in Table 3.

[0194] [Table 3]

[0195]

[0196] (Iron core)

[0197] Using various steel plates as raw materials, manufacture products with the features shown in Table 4 and... Figure 8 The iron cores No. a to f are shown in the diagram. It should be noted that L1 is the distance between the innermost parallel directional electromagnetic steel plates 1 of the wound iron core in a plane section parallel to the X-axis and including the center CL (distance between the inner surface side plane portions); L2 is the distance between the innermost parallel directional electromagnetic steel plates 1 of the wound iron core in a longitudinal section parallel to the Z-axis and including the center CL (distance between the inner surface side plane portions); L3 is the stacking thickness of the wound iron core in a plane section parallel to the X-axis and including the center CL (thickness in the stacking direction); L4 is the width of the stacked steel plates of the wound iron core in a plane section parallel to the X-axis and including the center CL; and L5 is the distance between the innermost adjacent plane portions of the wound iron core arranged at right angles (distance between curved portions). In other words, L5 is the length in the longitudinal direction of the shortest plane portion 4a among the plane portions 4 and 4a of the innermost directional electromagnetic steel plates. r is the radius of curvature (mm) of the curved portion on the inner surface side of the wound iron core, and φ is the bending angle (°) of the curved portion on the inner surface side of the wound iron core. The roughly rectangular iron cores No.a to f have the following structure: the planar portion on the inner surface side is divided at a distance of L1 at approximately the center of L1, and two iron cores with a shape roughly resembling a "ko" are joined together.

[0198] The core of core No. f is a cylindrical core (Japanese: トランココア) manufactured using a method commonly used for wound cores: steel sheets are rolled into a cylindrical shape, and the corners are pressed in a cylindrical laminated state to achieve a certain curvature, forming a roughly rectangular shape. The shape is then maintained by annealing. Therefore, the radius of curvature of the bent portion varies considerably depending on the lamination position of the steel sheets. Furthermore, in Table 4, the radius of curvature r (mm) of core No. f increases as it becomes more outer, reaching 6 mm at the innermost circumference and approximately 85 mm at the outermost circumference (referred to as "-" in Table 4).

[0199] [Table 4]

[0200]

[0201] (Evaluation Method)

[0202] (1) Magnetic properties of directional electromagnetic steel sheets

[0203] The magnetic properties of directional electromagnetic steel sheets are determined based on the Single Sheet Tester (SST) method specified in JIS C 2556:2015.

[0204] As a magnetic property, the magnetic flux density B8(T) in the rolling direction of the steel plate under excitation of 800 A / m and the iron loss of the steel plate under AC frequency of 50 Hz and excitation magnetic flux density of 1.7 T were measured.

[0205] (2) Grain size in the iron core

[0206] The 12 crystal grain sizes (Dcii, Dcio, Dcoi, Dcoo, Dlii, Dlio, Dloi, Dloo, Dpii, Dpio, Dpoi, Dpoo) were determined by observing the two surfaces of the steel plate extracted from the core as described above.

[0207] (3) Efficiency of the iron core

[0208] For the iron core made from each steel plate as raw material, the no-load loss is calculated, and the building factor (BF) is obtained by comparing it with the magnetic properties of the steel plate calculated in (1). Here, BF refers to the value obtained by dividing the iron loss value of the wound iron core by the iron loss value of the raw material of the wound iron core, namely the directional electromagnetic steel plate. The smaller the BF, the lower the iron loss of the wound iron core relative to the raw material steel plate. It should be noted that in this embodiment, a BF of 1.15 or less is considered to suppress the deterioration of iron loss efficiency.

[0209] The efficiency of various cores manufactured using steel plates with different domain widths was evaluated. The results are shown in Table 5. It should be noted that "r" in Table 5... p / r d "" indicates the radius of curvature r of the punch used in the machining of the iron core. p (mm) and the radius of curvature r of the die d The ratio (mm) indicates the temperature rise of the steel plate (°C) caused by heat generated during processing.

[0210] It has been learned that even when using the same type of steel, the efficiency of the iron core can be improved by appropriately controlling the crystal grain size.

[0211] [Table 5]

[0212]

[0213] The above results show that the wound core of the present invention has the characteristic of low iron loss because the crystal grain sizes Dpx, Dpy and Dpz of the stacked directional electromagnetic steel plates are all below 2W.

[0214] Industrial availability

[0215] According to the present invention, in a wound iron core formed by stacking bent steel plates, the efficiency deterioration of the iron core can be effectively suppressed.

[0216] Explanation of symbols

[0217] 1 Directional Electromagnetic Steel Sheet

[0218] 2-layer structure

[0219] 3 corners

[0220] 4. First planar portion (planar portion)

[0221] 4a Second planar portion (planar portion)

[0222] 5. Bending section

[0223] 6 joints

[0224] 10-winding iron core body

Claims

1. A wound iron core, characterized in that, It is a wound core having a body composed of multiple polygonal ring-shaped directional electromagnetic steel plates stacked along the thickness direction when viewed from the side. The directional electromagnetic steel plate is continuously interspersed with flat and curved portions along its length, i.e., along the circumference of the wound iron core body. The radius of curvature r of the inner surface of the curved portion, viewed from the side, is 1 mm to 5 mm. The directional electromagnetic steel sheet has the following chemical composition: It contains, by mass%: Si: 2.0–7.0%, The remaining portion contains Fe and impurities. The directional electromagnetic steel sheet has a texture oriented along a Gaussian orientation, and In at least one of the aforementioned curved portions, the crystal grain size Dpx of the stacked directional electromagnetic steel plates, measured in mm, is 2W or less. Wherein, Dpx in mm is the average value of Dp in mm obtained by the following formula (1). Dc, in mm, is the average grain size in the direction of the boundary line extending from each boundary of the curved portion and the two planar portions arranged in a manner that clamps the curved portion. It is calculated by the following formula (2) when the length of the boundary line is set to Lc and the number of grain boundaries intersecting the boundary line is set to Nc. Dl, expressed in mm, represents the average crystal grain size at the boundary in the direction perpendicular to the direction in which the boundary line extends. W, in mm, represents the width of the curved portion as seen from the side. Furthermore, the average value of Dp is the average of the Dp on the inner surface side and the Dp on the outer surface side of one of the two planar portions, and the average of the Dp on the inner surface side and the Dp on the outer surface side of the other planar portion. Dp = √(Dc × Dl / π) (1) Dc = Lc / (Nc + 1) (2).

2. A wound iron core, characterized in that, It is a wound core having a body composed of multiple polygonal ring-shaped directional electromagnetic steel plates stacked along the thickness direction when viewed from the side. The directional electromagnetic steel sheet is continuously interspersed with flat and curved portions along its length, i.e., along the circumference of the wound iron core body. The radius of curvature r of the inner surface of the curved portion, viewed from the side, is 1 mm to 5 mm. The directional electromagnetic steel sheet has the following chemical composition: It contains, by mass%: Si: 2.0–7.0%, The remaining portion contains Fe and impurities. The directional electromagnetic steel sheet has a texture oriented along a Gaussian orientation, and In at least one of the curved portions, the crystal grain size Dpy of the stacked directional electromagnetic steel plates, expressed in mm, is 2W or less. Where Dpy is the average value of Dl. Dl, measured in mm, represents the average grain size at each boundary of the curved portion and the two planar portions arranged in a manner that clamps the curved portion, in a direction perpendicular to the direction in which the boundary lines extend. W, in mm, represents the width of the curved portion as seen from the side. Furthermore, the average value of Dl is the average of the Dl on the inner surface side and the Dl on the outer surface side of one of the two planar portions, and the Dl on the inner surface side and the Dl on the outer surface side of the other planar portion.

3. A wound iron core, characterized in that, It is a wound core having a body composed of multiple polygonal ring-shaped directional electromagnetic steel plates stacked along the thickness direction when viewed from the side. The directional electromagnetic steel sheet is continuously interspersed with flat and curved portions along its length, i.e., along the circumference of the wound iron core body. The radius of curvature r of the inner surface of the curved portion, viewed from the side, is 1 mm to 5 mm. The directional electromagnetic steel sheet has the following chemical composition: It contains, by mass%: Si: 2.0–7.0%, The remaining portion contains Fe and impurities. The directional electromagnetic steel sheet has a texture oriented along a Gaussian orientation, and In at least one of the aforementioned curved portions, the crystal grain size Dpz (in mm) of the stacked directional electromagnetic steel plates is 2W or less. Where Dpz is the average value of Dc. Dc, in mm, is the average grain size in the direction of the boundary line extending from each boundary of the curved portion and the two planar portions arranged in a manner that clamps the curved portion. It is calculated by the following formula (2) when the length of the boundary line is set to Lc and the number of grain boundaries intersecting the boundary line is set to Nc. W, in mm, represents the width of the curved portion as seen from the side. Furthermore, the average value of Dc is the average of the Dc and Dc of the inner surface side of one of the two planar portions and the Dp of the inner surface side of the other planar portion. Dc = Lc / (Nc + 1) (2).

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