Grain-oriented electrical steel sheet and wound core

Abstract

The present invention provides a grain-oriented electrical steel sheet wherein, in a stress-strain curve obtained by a tensile test performed in accordance with metal material tensile test method (JIS Z2241:2011) and with a strain rate of 0.08 s-1, the difference εt'-εt between the strain amount εt (%) at which stress first reaches a maximum value σt and the strain amount εt' (%) at which stress next reaches a maximum value satisfies expression (1), when εA is defined by expression (2). Also provided is a wound core using said steel sheet as a material.　Expression (1) is 0<εt'-εt≤0.25*εA, and expression (2) is εA=(t / (t+2r))×100, where the thickness of the steel sheet is represented as t [mm], and the curvature radius of a bent part of the wound core is represented as r [mm] (for the steel sheet, r=0.3).

Description

Grain-oriented electrical steel sheets and wound cores

[0001] The present invention relates to a grain-oriented electrical steel sheet and a wound core.

[0002] It is known that in a wound core produced by bending a steel sheet without annealing it, iron loss can be reduced by controlling the shape of the bent portion (Patent Document 1).

[0003] Patent No. 7239089

[0004] However, in the technique described in Patent Document 1, the passage of magnetic flux is significantly hindered at the bent portion where a large amount of plastic strain is introduced, and there is room for improvement.

[0005] In view of the above problems, an object of the present disclosure is to provide a grain-oriented electrical steel sheet and a wound core that can suppress an increase in iron loss due to bending.

[0006] The gist of the present disclosure is as follows.

[0007] (1) According to the metallic material tensile test method (JIS Z2241:2011), strain rate was 0.08 s ―１ In a stress-strain curve obtained by a tensile test at 1000 rpm, the difference εt' - εt between the amount of strain εt (%) when the stress first reaches a maximum value σt and the amount of strain εt' (%) when the stress next reaches a maximum value satisfies the following formula (1), where εA is defined by the following formula (2): 0 < εt' - εt ≦ 0.25 × εA (1) εA = (t / (t + 0.6)) × 100 (2) where t [mm] is the thickness of the steel sheet.

[0008] (2) The grain-oriented electrical steel sheet according to (1) above, wherein in the stress-strain curve, the ratio TS / σt of the tensile strength TS to the first maximum value σt further satisfies the following relational expression: 1.00<TS / σt≦1.40

[0009] (3) The grain-oriented electrical steel sheet according to (1) or (2) above, wherein the ratio of the minimum value σmin among the stresses at the lower yield point to the first maximum value σt in the stress-strain curve further satisfies the following relational expression: 0.12≦σmin / σt<1.00

[0010] (4) A wound core having a wound shape formed by laminating bent steel sheets, wherein the wound core has a rectangular shape with a hollow portion at the center by having a plurality of flat portions and bent portions adjacent to the flat portions in a side view of the wound shape seen from a direction along the surface of the steel sheets, and a material sampled from the flat portions of the wound core is subjected to a tensile test at a strain rate of 0.08 s according to the Metallic Material Tensile Test Method (JIS Z2241:2011). ―１ A wound core in which, in a stress-strain curve obtained by a tensile test at 1000 rpm, the difference εt' - εt between the amount of strain εt (%) when the stress first reaches a maximum value σt and the amount of strain εt' (%) when the stress next reaches a maximum value satisfies the following equation (3), where εB is defined by the following equation (4): 0 < εt' - εt ≦ 0.25 × εB (3) εB = (t / (t + 2r)) × 100 (4) where t [mm] is the thickness of the steel plate and r [mm] is the radius of curvature of the bent portion.

[0011] (5) A wound core according to (4) above, wherein in the stress-strain curve, the ratio TS / σt of the tensile strength TS to the first maximum value σt further satisfies the following relational expression: 1.00<TS / σt≦1.40

[0012] (6) A wound core according to (4) or (5) above, wherein the ratio of the minimum value σmin among the stresses at the lower yield point to the first maximum value σt in the stress-strain curve further satisfies the following relational expression: 0.12≦σmin / σt<1.00

[0013] (7) The wound core according to (4) or (5) above, wherein the radius of curvature of the bent portion is 5 mm or less.

[0014] According to the present disclosure, a grain-oriented electrical steel sheet and a wound core are provided that are capable of suppressing an increase in iron loss due to bending.

[0015] FIG. 1 is a perspective view schematically showing an embodiment of a wound core. FIG. 2 is a side view of the wound core shown in the embodiment of FIG. 1. FIG. 3 is a side view schematically showing another embodiment of the wound core. FIG. 4 is a diagram schematically showing an example of a bent portion (curved portion) of a grain-oriented electromagnetic steel sheet. FIG. 5 is a diagram schematically showing an example of a grain-oriented electromagnetic steel sheet for one layer in a wound core body. FIG. 6 is a diagram schematically showing an example of a grain-oriented electromagnetic steel sheet for one layer in a wound core body. FIG. 7 is a characteristic diagram showing a stress-strain curve obtained by tensile testing the grain-oriented electromagnetic steel sheet material constituting the wound core according to the Tensile Testing Method for Metallic Materials (JIS Z2241:2011). FIG. 8 is a characteristic diagram showing a stress-strain curve obtained by tensile testing the grain-oriented electromagnetic steel sheet material constituting the wound core according to the Tensile Testing Method for Metallic Materials (JIS Z2241:2011). FIG. 9 is a diagram for explaining detailed dimensions of the wound core.

[0016] Hereinafter, several embodiments of the present invention will be described with reference to the drawings. However, these descriptions are intended to merely exemplify preferred embodiments of the present invention and are not intended to limit the present invention to such specific embodiments. In the following description, similar components will be designated by the same reference numerals.

[0017] A grain-oriented electrical steel sheet and wound core according to one embodiment of the present invention will be described in detail below. However, the present invention is not limited to the configuration disclosed in this embodiment, and various modifications are possible without departing from the spirit of the present invention. Note that the numerical ranges listed below include the lower and upper limits. Numerical values ​​indicated as "greater than" or "less than" do not include the numerical range. Furthermore, "%" in relation to chemical composition means "mass %" unless otherwise specified.

[0018] Furthermore, terms used in this specification that specify shapes, geometric conditions, and their degrees, such as "parallel," "vertical," "same," and "right angle," as well as values ​​of lengths and angles, are not to be construed as being bound by strict meanings, but rather as including a range within which similar functions can be expected.

[0019] Furthermore, in this specification, a "grain-oriented electrical steel sheet" may be simply referred to as a "steel sheet" or an "electrical steel sheet," and a "wound core" may be simply referred to as a "wound core body" or an "iron core."

[0020] (Grain-oriented electrical steel sheet) The grain-oriented electrical steel sheet according to the present invention is generally a steel sheet in which the orientation of crystal grains in the steel sheet is highly concentrated in the {110}<001> orientation, and has excellent magnetic properties in the rolling direction. An example of a preferred grain-oriented electrical steel sheet will be described below.

[0021] The chemical composition of grain-oriented electrical steel sheet is, by mass%, 2.0% to 6.0% Si, with the remainder being Fe. This chemical composition is intended to control the crystal orientation to a Goss texture concentrated in the {110}<001> orientation, thereby ensuring good magnetic properties. There are no particular restrictions on the other elements, and known elements may be included within known ranges in place of Fe. Typical content ranges for typical elements are as follows: C: 0-0.0050%, Mn: 0-1.0%, S: 0-0.0150%, Se: 0-0.0150%, Al: 0-0.0650%, N: 0-0.0050%, Cu: 0-0.40%, Bi: 0-0.010%, B: 0-0.080%, P: 0-0.50%, Ti: 0-0.0150%, Sn: 0-0.10%, Sb: 0-0.10%, Cr: 0-0.30%, Ni: 0-1.0%, Nb: 0-0.030%, V: 0-0.030%, Mo: 0-0.030%, Ta: 0 to 0.030%, W: 0 to 0.030%. These optional elements may be contained according to their purpose, so there is no need to set a lower limit, and they may not be contained substantially. Furthermore, even if these optional elements are contained as impurities, the effects of the present invention are not impaired. Note that impurities refer to elements that are unintentionally contained, and refer to elements that are mixed in from raw materials such as ore and scrap, or the manufacturing environment, during industrial production of base steel sheet.

[0022] The chemical composition of grain-oriented electrical steel sheets can be measured by a general steel analysis method. For example, it can be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Specifically, for example, a 35 mm square test piece is obtained from the center of the grain-oriented electrical steel sheet, and the test piece is measured using a Shimadzu ICPS-8100 (measuring device) or the like under conditions based on a pre-created calibration curve. C and S can be measured using a combustion-infrared absorption method, and N can be measured using an inert gas fusion-thermal conductivity method.

[0023] The above chemical composition is that of the grain-oriented electrical steel sheet. If the grain-oriented electrical steel sheet to be measured has a primary coating (glass coating, intermediate layer) or insulating coating made of oxides or the like on its surface, these are removed by a known method before measuring the chemical composition.

[0024] (Wound Core) A wound core according to one embodiment of the present invention is a wound core formed by stacking folded steel sheets. When viewed from the side of the wound core from a direction along the surface of the steel sheets, the wound core has a rectangular structure with a central hollow, including four flat portions and four corner portions adjacent to the flat portions. Here, the flat portions refer to the straight portions other than the bent portions. The radius of curvature r on the inner surface of the bent portion in side view is, for example, 1.0 mm or more and 5.0 mm or less. The grain-oriented electrical steel sheet, for example, has a chemical composition containing, by mass, 2.0 to 7.0% Si, with the remainder consisting of Fe and impurities, and has a texture oriented in the Goss orientation. For example, a grain-oriented electrical steel strip as defined in JIS C 2553:2019 can be used as the grain-oriented electrical steel sheet.

[0025] Next, the shapes of the wound core and grain-oriented electromagnetic steel sheet according to one embodiment of the present invention will be specifically described. The shapes of the wound core and grain-oriented electromagnetic steel sheet described here are not particularly new and are merely similar to the shapes of known wound cores and grain-oriented electromagnetic steel sheets. Furthermore, the numerical values ​​representing the shapes of the wound core and grain-oriented electromagnetic steel sheet are merely examples, and the wound core and grain-oriented electromagnetic steel sheet are not limited to these.

[0026] Fig. 1 is a perspective view schematically showing one embodiment of a wound core. Fig. 2 is a side view of the wound core shown in the embodiment of Fig. 1, showing a side view of the wound core. Fig. 3 is a side view schematically showing another embodiment of the wound core.

[0027] The side view refers to the winding shape of the wound core viewed from a direction along the surface of the steel sheet, and more specifically, refers to the winding shape of the wound core viewed from the axial direction of the windings of the wound core (perpendicular to the plane of the paper in FIG. 2 ). In other words, the side view refers to the view in the width direction (the Y-axis direction in FIG. 1 ) of the long grain-oriented electrical steel sheets that make up the wound core. The side view is a diagram that shows the shape as seen from the side (a diagram in the Y-axis direction in FIG. 1 ).

[0028] A wound core 10 according to one embodiment of the present invention comprises a wound core body that is substantially polygonal in side view. The wound core body 10 has a laminated structure in which grain-oriented electromagnetic steel sheets 1 are stacked in the thickness direction, resulting in a substantially rectangular shape in side view. The wound core body 10 may be used as a wound core as is, or may be equipped with known fasteners such as cable ties to integrally fasten the stacked grain-oriented electromagnetic steel sheets, as needed.

[0029] In this embodiment, there is no particular limit to the core length of the wound core body 10. As long as the number of bends 5 is the same, even if the core length of the wound core 10 changes, the volume of the bends 5 remains constant, and therefore the iron loss generated at the bends 5 remains constant. A longer core length reduces the volume ratio of the bends 5 to the wound core body 10, and therefore reduces the impact on iron loss degradation. Therefore, a longer core length is preferable for the wound core body 10. The core length of the wound core body 10 is preferably 1.5 m or more, and more preferably 1.7 m or more. In the present invention, the core length of the wound core body 10 refers to the circumferential length at the center point of the wound core body 10 in the lamination direction when viewed from the side. Such a wound core can be suitably used for any conventionally known application.

[0030] The iron core according to this embodiment is characterized by its substantially polygonal shape in side view. In the following explanation using figures, for simplicity of illustration and explanation, a generally-shaped substantially rectangular (quadrilateral) iron core will be described. However, iron cores of various shapes can be manufactured by changing the angle and number of bent portions 5 and the length of the flat portions 4. For example, if all bent portions 5 have an angle of 45° and the flat portions 4 are the same length, the iron core will be octagonal in side view. On the other hand, if there are six bent portions 5 with an angle of 60° and the flat portions 4 are the same length, the iron core will be hexagonal in side view.

[0031] As shown in FIGS. 1 and 2 , the wound core body 10 includes grain-oriented electrical steel sheets 1, each having alternating flat portions 4, 4 a and bent portions 5 in the longitudinal direction, stacked in the sheet thickness direction. The laminated structure 2 has a generally rectangular shape in side view and a hollow portion 15. Each corner portion 3, including the bent portions 5, has two or more bent portions 5 that are curved in side view, and the sum of the bending angles of the bent portions 5 in one corner portion 3 is, for example, 90°. The corner portion 3 has a flat portion 4 a between adjacent bent portions 5, 5, that is shorter than the flat portion 4. Therefore, the corner portion 3 has two or more bent portions 5 and one or more flat portion 4 a. In the embodiment shown in FIG. 2 , one bent portion 5 is 45°. In the embodiment shown in FIG. 3 , one bent portion 5 is 30°. The allowable angle range of the bent portions will now be described. Ideally, the angle should be the value described in the text, but in reality, it may vary due to slight variations in the mechanical properties of the steel at the bent portion, and the allowable range is set to about ±5°. In other words, the above 45° may vary within a range of 40° to 50° in an actual outer core.

[0032] As shown in these examples, the wound core of this embodiment can be configured with bent portions having various angles. However, from the viewpoint of suppressing distortion due to deformation during processing and thereby suppressing iron loss, the bending angle φ (φ1, φ2, φ3) of the bent portion 5 is preferably 60° or less, and more preferably 45° or less. The bending angle φ of the bent portions of one iron core can be configured arbitrarily. For example, φ1 = 60° and φ2 = 30°. From the viewpoint of production efficiency, it is preferable that the bending angles (bending angles) are equal. However, if the iron loss of the iron core can be reduced by reducing the number of deformation points above a certain level, a combination of different angles may be used. The design can be selected arbitrarily based on the points that are important in iron core processing.

[0033] The bent portion 5 will be described in more detail with reference to FIG. 4 . FIG. 4 is a diagram schematically illustrating an example of a bent portion (curved portion) 5 of a grain-oriented electrical steel sheet 1. The bending angle of the bent portion 5 refers to the angular difference between the straight portion on the rear side and the straight portion on the front side in the bending direction at the bent portion of the grain-oriented electrical steel sheet, and is expressed as the angle φ, which is the supplementary angle formed by two imaginary lines Lb-elongation1 and Lb-elongation2 obtained by extending the straight portions that are the surfaces of the flat portions 4, 4a on both sides of the bent portion 5 on the outer surface of the grain-oriented electrical steel sheet 1. In this case, the points where the extended lines depart from the steel sheet surface are the boundaries between the flat portions 4 and the bent portion 5 on the outer surface of the steel sheet, and in FIG. 4 , these are points F and G.

[0034] Furthermore, lines perpendicular to the outer surface of the steel plate are extended from each of points F and G, and the intersections with the inner surface of the steel plate are respectively points E and D. These points E and D are the boundaries between the flat portion 4 and the bent portion 5 on the inner surface of the steel plate.

[0035] In the present invention, the bent portion 5 is a portion of the grain-oriented electrical steel sheet 1 that is surrounded by the points D, E, F, and G in a side view of the grain-oriented electrical steel sheet 1. In Fig. 4, the steel sheet surface between points D and E, i.e., the inner surface of the bent portion 5, is shown as La, and the steel sheet surface between points F and G, i.e., the outer surface of the bent portion 5, is shown as Lb.

[0036] This figure also shows the inner surface curvature radius r in a side view of the bent portion 5. The smaller the curvature radius r, the sharper the curve of the curved portion of the bent portion 5, and the larger the curvature radius r, the gentler the curve of the curved portion of the bent portion 5.

[0037] In the wound core of the present invention, the radius of curvature r of each bent portion 5 of each grain-oriented electrical steel sheet 1 stacked in the sheet thickness direction may vary to some extent. This variation may be due to forming accuracy, or it may be due to unintended variation caused by handling during stacking. Such unintended errors can be suppressed to approximately 0.2 mm or less in current, standard industrial manufacturing. If such variation is significant, a representative value can be obtained by measuring and averaging the radius of curvature for a sufficiently large number of steel sheets. It is also possible to intentionally vary the radius of curvature for some reason, but this is not excluded by the present invention. The radius of curvature r of the bent portion 5 (the inner radius of curvature of the bent portion 5 in a side view) is preferably 1 mm or more and 5 mm or less. By setting the radius of curvature r to 1 mm or more and 5 mm or less, the building factor (BF) can be further suppressed.

[0038] There are no particular limitations on the method for measuring the radius of curvature r of the bent portion 5, and it can be measured, for example, by observing at 200x magnification using a commercially available microscope (Nikon ECLIPSE LV150). Specifically, the center of curvature A is determined from the observation results. For example, if the intersection point A is defined as the point of intersection between line segments EF and DG extended inward on the opposite side from point B, then the magnitude of the radius of curvature r corresponds to the length of line segment AC. Here, when points A and B are connected by a straight line, the intersection point C on the arc DE on the inside of the bent portion of the steel plate is defined as the point of intersection.

[0039] 5 and 6 are diagrams schematically showing an example of one layer of grain-oriented electrical steel sheet 1 in a wound core body. The grain-oriented electrical steel sheet 1 used in the example of Fig. 5 and Fig. 6 is bent to realize the wound core of this embodiment, and has two or more bent portions 5 and a flat portion 4, and forms a substantially polygonal ring in side view via joint portions 6 (gaps) that are the end faces in the longitudinal direction of one or more grain-oriented electrical steel sheets 1.

[0040] In this embodiment, it is sufficient that the wound core body 10 has a laminated structure that is generally polygonal in side view as a whole. As shown in the example of Fig. 5, one grain-oriented electromagnetic steel sheet may constitute one layer of the wound core body via one joint 6 (one grain-oriented electromagnetic steel sheet is connected via one joint 6 per turn), or as shown in the example of Fig. 6, one grain-oriented electromagnetic steel sheet 1 may constitute approximately half the circumference of the wound core, and two grain-oriented electromagnetic steel sheets 1 may constitute one layer of the wound core body via two joints 6 (two grain-oriented electromagnetic steel sheets 1 are connected to each other via two joints 6 per turn).

[0041] The thickness of the grain-oriented electrical steel sheet 1 used in this embodiment is not particularly limited and may be selected appropriately depending on the application, etc., but is usually in the range of 0.15 mm to 0.35 mm, and preferably in the range of 0.18 mm to 0.27 mm.

[0042] In the example of Fig. 5, one joint 6 of one grain-oriented electrical steel sheet that constitutes one layer of the wound core body is located in region A1 shown in Fig. 2 and Fig. 3. In the example of Fig. 6, two joints 6 of two grain-oriented electrical steel sheets that constitute one layer of the wound core body are located in regions A1 and A2 shown in Fig. 2 and Fig. 3. Note that detailed shapes and arrangements of joints 6 in region A1 or region A2 are omitted from Fig. 2 and Fig. 3.

[0043] The present inventors have thoroughly investigated the relationship between the stress-strain curve of the grain-oriented electrical steel sheet 1 constituting the wound core 10 and the iron loss of the wound core 10, and have found that iron loss decreases when the stress-strain curve satisfies certain properties. Figures 7A and 7B are characteristic diagrams showing stress-strain curves obtained by tensile testing tensile test specimens taken from the grain-oriented electrical steel sheet or wound core 10 according to the present embodiment using the metallic material tensile testing method (JIS Z2241:2011). JIS 1A test specimens were used. In Figures 7A and 7B, the vertical axis represents the nominal stress, and the horizontal axis represents the nominal strain. Furthermore, Figure 7A shows a case where the stress-strain curve satisfies the aforementioned certain properties, while Figure 7B shows a case where the stress-strain curve does not satisfy the aforementioned certain properties.

[0044] As shown in Figure 7A, in the grain-oriented electrical steel sheet and wound core 10 according to this embodiment, in the stress-strain curve obtained by tensile testing the steel sheet according to the tensile testing method for metallic materials (JIS Z2241:2011), the stress and strain increase until the stress reaches a first maximum value σt, then the stress decreases to a minimum value, after which the stress increases again and reaches a maximum value, but the increment in strain (= c) during this period is small. In other words, in the wound core 10 according to this embodiment, the yield phenomenon in which the stress reaches a minimum value and then reaches the next maximum value occurs multiple times at small intervals of strain, which is considered to indicate that deformation is progressing uniformly and overall. On the other hand, in the grain-oriented electrical steel sheet and wound core according to the comparative example shown in Figure 7B, after the stress reaches its first maximum value σt, the stress decreases to a minimum value, then increases again and reaches a maximum value, but the change in strain during this period is larger than in the example of Figure 7A. This is thought to be because deformation is more likely to concentrate in the grain-oriented electrical steel sheet and wound core according to the comparative example compared to the grain-oriented electrical steel sheet and wound core 10 according to the present embodiment shown in FIG. 7A.

[0045] Compared to the present embodiment shown in Figure 7A, the grain-oriented electrical steel sheet and wound core 10 according to the comparative example have stress-strain curves like those in Figure 7B, possibly due to the following four factors: 1) There is significant surface unevenness due to an oxide film formed on the surface layer of the steel sheet during the manufacturing process of the grain-oriented electrical steel sheet. 2) With regard to the α, β, and γ angles, which are the orientations of the crystal grains in the Goss orientation, which is the parent orientation of the grain-oriented electrical steel sheet, the deformation mode is limited when the γ angle dispersion is large. 3) Dislocations are fixed by the solute C and N in the steel of the grain-oriented electrical steel sheet, so the amount of mobile dislocations is small. 4) There are many inclusions in the steel of the grain-oriented electrical steel sheet.

[0046] The tensile test specimens for the wound core 10 are taken from the flat surface of the wound core 10. In this case, the shape of the tensile test specimens that can be taken is limited by the core dimensions, but this is not a problem. The specimens are cut out using an end mill for milling. The cutting direction is parallel to the X direction in the tensile test, and the specimens are taken from the flat surface of the wound core 10. After cutting out the tensile test specimens, the tensile test must be performed without heat treatment. In other words, no annealing is performed to remove distortion from the cut specimens. Test specimens for plate tensile tests can be JIS 1A, JIS 1B, JIS 5, JIS 13B, etc. Tensile tests are performed in accordance with the Metallic Materials Tensile Test Method (JIS Z2241:2011). The strain rate in the tensile test is defined as v / s, which is the tensile rate v (mm / s) divided by the gauge length s mm of the tensile test specimen. Specifically, in this disclosure, the strain rate is 0.08 s －1 The tensile test environment is set at a room temperature of 20 to 30°C where the test machine is located, and the tensile test specimen is not heated or cooled.

[0047] In the tensile test, a material (tensile test piece) taken from the grain-oriented electromagnetic steel sheet or the flat portion 4 of the wound core 10 is subjected to a tensile test, and the value of the difference c (= εt' - εt), the TS value, the σt value, and the σmin value are evaluated from the measured nominal stress-nominal strain curve.

[0048] The grain-oriented electrical steel sheet according to this embodiment has a strain rate of 0.08 s according to the tensile test method for metallic materials (JIS Z2241:2011). ―１ In a stress-strain curve obtained by a tensile test at σt, the following property (1) is satisfied: (1) The difference εt' - εt between the amount of strain εt (%) when the stress first reaches a maximum value σt and the amount of strain εt' (%) when the stress next reaches a maximum value, satisfies the following formula (1) when εA is defined by the following formula (2): 0 < εt' - εt ≦ 0.25 × εA (1) εA = (t / (t + 0.6)) × 100 (2) where t [mm] is the thickness of the steel plate.

[0049] In addition, in the wound core 10 according to this embodiment shown in FIG. 7A, a material sampled from the flat portion 4 of the wound core 10 was subjected to a tensile test at a strain rate of 0.08 s―１ In a stress-strain curve obtained by a tensile test at σt, the following property (1)' is satisfied. (1)' The difference c (=εt' - εt) between the amount of strain εt (%) when the stress first reaches its maximum value σt and the amount of strain εt' (%) when the stress next reaches its maximum value satisfies the following formula (3) when εB is defined by the following formula (4): 0 < εt' - εt ≦ 0.25 × εB (3) εB = (t / (t + 2r)) × 100 (4) where the thickness of the steel plate is t [mm] and the radius of curvature of the bent portion 5 is r [mm].

[0050] In properties (1) and (1)', the difference c (= εt' - εt) between the strain εt at the time when the first maximum stress value occurs and the strain εt' at the time when the next maximum stress value occurs can be considered to be the degree of deformation concentration that occurs during bending in iron core manufacturing. In other words, the larger the difference c, the greater the degree of deformation concentration, and the more localized the deformation progresses. Here, εA and εB are values ​​corresponding to the equivalent plastic strain at the outermost periphery of the curvature of the bent portion 5. If the difference c is 0.25 times or less than εA and εB, the adverse effect on magnetic properties during bending in iron core manufacturing is reduced. The upper limit of the difference c (= εt' - εt) is preferably 0.20 times εA and εB, and more preferably 0.15 times εA and εB.

[0051] Furthermore, the grain-oriented electrical steel sheet or wound iron core 10 according to this embodiment shown in FIG. 7A further satisfies the following property (2) in the stress-strain curve. (2) The ratio TS / σt of the tensile strength TS to the first maximum value σt satisfies the following relational expression: 1.00<TS / σt≦1.40 When the first maximum value σt is smaller than the tensile strength TS, tensile strain is introduced more uniformly at the deformed location, work hardening occurs, and deformation concentration is less likely to occur. The lower limit of TS / σt is preferably 1.1 or more, more preferably 1.15 or more, and the upper limit is preferably 1.3 or less, more preferably 1.25 or less, in order to make it less likely for work hardening to occur and to minimize the occurrence of undesirable deformation concentration.

[0052] Furthermore, the grain-oriented electrical steel sheet or wound iron core 10 according to this embodiment shown in FIG. 7A further satisfies the following property (3) in the stress-strain curve. (3) The ratio of the minimum value σmin among the stresses at the lower yield point to the first maximum value σt satisfies the following relational expression: 0.12≦σmin / σt<1.00. As the ratio σmin / σt becomes smaller, the concentration of local deformation at the deformed location decreases. On the other hand, if the ratio becomes too small, the deformed location expands from a local area to a wide area. In other words, the lower limit of σmin / σt is preferably 0.40 or more, more preferably 0.50 or more, and the upper limit is preferably 0.90 or less, more preferably 0.80 or less.

[0053] Furthermore, in the wound core 10 according to this embodiment, although there is no restriction on the radius of curvature of the bent portion 5, the effect is particularly large when the radius of curvature of the bent portion 5 is 5 mm or less.

[0054] On the other hand, the stress-strain curve shown in Figure 7B does not satisfy the above-mentioned properties (1) to (3), and iron loss cannot be suppressed. More specifically, for example, in the stress-strain curve shown in Figure 7B, the first maximum value σt is the maximum value of stress. When a wound core is formed using a steel sheet having such a stress-strain curve, iron loss cannot be effectively suppressed.

[0055] When many materials for tensile testing are taken from an iron core, it is desirable that as many of them as possible satisfy the above properties (1) to (3). However, in order to achieve the desired effect, it is sufficient that any one of the tensile test specimens taken from the flat surface of the steel plate of an iron core made by laminating folded steel plates (for example, about 100 to 1000 sheets) satisfies at least property (1) of the above properties.

[0056] By satisfying at least property (1) among properties (1) to (3), deformation concentration during bending of the bent portion 5 is less likely to occur, and the deformation of the steel sheet becomes more uniform. As a result, it has been found that the deterioration of iron loss due to bending deformation can be suppressed. Although the mechanism itself is not completely clear at this time, based on the results of intensive research by the inventors, it can be inferred that the more uniform deformation of the steel sheet makes it easier for magnetic flux to pass through the steel sheet, thereby reducing iron loss. However, it should be noted that this is merely one hypothesis at this time to theoretically support the empirical rule discovered by the inventors as a result of intensive research. It is hoped that the academically correct mechanism will be clarified in the future.

[0057] For example, when attention is paid to the strain in the region of any one of the bent portions 5 in the cross section along the winding direction, in the steel sheet having the stress-strain curve shown in Fig. 7B, regions of locally high strain occur in multiple locations in the region of the bent portion 5. This is thought to be because, during bending, the steel sheet is suddenly deformed in these local regions, causing the regions of high strain to separate, resulting in the generation of the locally high strain regions.

[0058] On the other hand, in the steel sheet having the stress-strain curve shown in Fig. 7A, by satisfying at least property (1) among the above-mentioned properties (1) to (3), the steel sheet gradually deforms during bending, making it difficult for stress to concentrate in the region of the bent portion 5, and the strain is distributed relatively uniformly throughout the bent portion. This is thought to suppress deterioration of iron loss.

[0059] In particular, this embodiment is particularly effective in the case of a wound core 10 formed so that the radius of curvature on the inside of the bend 5 is 5 mm or less. In a bend 5 with such a small radius of curvature, the difference εt' - εt between the amount of strain εt (%) when the stress first reaches a maximum value σt and the amount of strain εt' (%) when the stress next reaches a maximum value in the stress-strain curve of the steel sheet used is 0.25 times or less the equivalent plastic strain εA at the outermost periphery of the curvature of the bend 5. As a result, it is thought that localized concentration of deformation is less likely to occur because the deformation is widely dispersed over more locations. Of the above-mentioned properties (1) to (3), satisfying at least property (1) can suppress localized concentration of deformation even in a bend 5 with a small radius of curvature, and as a result, is thought to be effective in suppressing deterioration of iron loss.

[0060] Next, a method for manufacturing a grain-oriented electrical steel sheet according to the present invention will be described. The method for manufacturing a grain-oriented electrical steel sheet can basically employ conditions similar to those of conventionally known methods for manufacturing grain-oriented electrical steel sheets. A preferred example of the manufacturing method involves, for example, heating a slab having 0.04 to 0.1 mass% C and the other chemical composition of the grain-oriented electrical steel sheet to 1000°C or higher and hot-rolling it, followed by annealing the hot-rolled sheet as needed, followed by cold-rolling once or twice or more times with intermediate annealing in between to produce a cold-rolled steel sheet. The cold-rolled steel sheet is then heated to 700 to 900°C in a wet hydrogen-inert gas atmosphere for decarburization annealing, optionally followed by nitriding annealing as needed, applying an annealing separator, and then finish-annealing at 1000°C or higher. An insulating coating is then formed at about 900°C, followed by planarization annealing at about 500°C. Furthermore, the shot blasting temperature is optimally controlled, and the temperature and tension are appropriately controlled in the subsequent additional annealing step.

[0061] For grain-oriented electrical steel sheets according to the present invention, the shot blasting temperature is first controlled, and the temperature range is from 70°C to 1000°C. Preferably, the shot blasting temperature range is from 185°C to 970°C. More preferably, the shot blasting temperature range is from 500°C to 780°C. By controlling the temperature in this manner, grain-oriented electrical steel sheets that satisfy properties (1) and (1)' can be produced, and uniform deformation during tensile testing can be achieved. By controlling the temperature in this manner, it is possible to obtain steel sheets that exhibit a stress-strain curve that conforms to the present application, with residual strain particularly in the surface layer of the steel sheet.

[0062] Next, the control of the additional annealing step will be described. The temperature and tension are controlled, and the temperature range is 50°C or higher and 660°C or lower. By controlling the temperature in this manner, it is possible to appropriately control the ratio of TS to σt, and it is possible to produce a grain-oriented electrical steel sheet that satisfies property (2).

[0063] Furthermore, the tension condition in the additional annealing step is in the range of 2.0 MPa to 10.5 MPa. By controlling the tension in this manner, the ratio of σmin to σt can be appropriately controlled, and a grain-oriented electrical steel sheet satisfying property (3) can be manufactured.

[0064] In addition, in this embodiment, the wound core made of grain-oriented electromagnetic steel sheets having the above-described configuration is formed by stacking grain-oriented electromagnetic steel sheets 1 that have been individually bent in layers and assembling them into a wound shape, and multiple grain-oriented electromagnetic steel sheets 1 are connected to each other via at least one joint per turn.

[0065] An apparatus that enables the manufacture of a wound core involving the bending of steel sheets as described above may include a bending processing unit that individually bends grain-oriented electromagnetic steel sheets, and may also include an assembly unit that stacks the bent grain-oriented electromagnetic steel sheets in layers and assembles them into a wound shape, thereby forming a wound core that includes a portion where grain-oriented electromagnetic steel sheets, each having a series of alternating flat portions and curved portions in the longitudinal direction, are stacked in the sheet thickness direction.

[0066] The grain-oriented electrical steel sheet is fed to the bending section by being unwound at a predetermined conveying speed from a steel sheet supply section that holds a hoop material formed by winding the grain-oriented electrical steel sheet into a roll. The grain-oriented electrical steel sheet thus fed is cut to an appropriate size in the bending section and then individually bent in small batches, such as one by one.

[0067] In the grain-oriented electrical steel sheet obtained in this manner, the radius of curvature of the bent portion caused by the bending process is extremely small, and therefore the processing strain imparted to the grain-oriented electrical steel sheet by the bending process is extremely small.Thus, while it is expected that the density of the processing strain will be large, if the volume affected by the processing strain can be reduced, the annealing step can be omitted.

[0068] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiment that has substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibits similar effects is included within the technical scope of the present disclosure.

[0069] The present disclosure will be specifically described below using examples. Note that the conditions in the examples are examples adopted to confirm the feasibility and effects of the present disclosure, and the present disclosure is not limited to the conditions in the examples. Various conditions may be adopted in the present disclosure as long as they do not deviate from the gist of the disclosure and the purpose is achieved.

[0070] Table 1 shows the chemical composition in mass % of the slabs used to manufacture the grain-oriented electrical steel sheets 1 that make up the wound core 10. In this example, two types of steel, type A and type B, shown in Table 1, were used.

[0071]

[0072] Table 2 also shows the chemical composition in mass % of the grain-oriented electrical steel sheet 1 that constitutes the wound core 10 in the final product state.

[0073]

[0074] Tables 3-1, 3-2, 3-3, and 3-4 show the manufacturing process conditions and properties (B8, material iron loss) of manufactured steel sheets Nos. A1 to A20 and B1 to B19.

[0075]

[0076]

[0077]

[0078]

[0079] A wound core was then produced from the steel sheets shown in Table 3. Detailed dimensions of the wound core are shown in Figure 8 and Table 4. In Table 4, L1, L2, L3, and L4 represent the distance between opposing inner surfaces in the X-axis direction in hollow portion 15 of the wound core, the distance between opposing inner surfaces in the Z-axis direction in hollow portion 15 of the wound core, the thickness of the steel sheets of the wound core in the lamination direction, and the width of the wound core in the Y-axis direction, respectively. Also in Table 4, r represents the radius of curvature on the inner surface side of bent portion 5, φ represents the bending angle of bent portion 5, and L5 represents the distance between bent portions (the length of the flat portion between bent portions).

[0080]

[0081] The iron loss of the wound cores was then evaluated, and the results are shown in Tables 5-1, 5-2, 5-3, and 5-4 below.

[0082]

[0083]

[0084]

[0085]

[0086] In the evaluation of Table 5, each characteristic was measured by the above-mentioned method. In addition, in the evaluation of Table 5, iron loss at 50 Hz and a magnetic flux density of 1.7 T was measured by the excitation current method.

[0087] In the evaluations in Table 5, examples with an iron loss ratio (= iron core iron loss / material iron loss) of less than 1.25 are considered to be invention examples, and comparative examples with an iron loss ratio of 1.25 or greater are considered to be comparison examples. As shown in Table 5, all invention examples satisfied the above properties (1) and (1)'. Regarding property (2), the invention examples of Experiments Nos. 7, 8, 13, 14, 17, 23, 24, 26, 28, 29, 30, 33, 36, and 37 did not satisfy property (2), but had good iron loss ratios of less than 1.25. Regarding property (3), the invention examples of Experiments Nos. 17, 22, 28, 29, and 37 did not satisfy property (3), but had good iron loss ratios of less than 1.25.

[0088] Furthermore, the iron loss of a wound core made by mixing the grain-oriented electrical steel sheets according to the present example and the grain-oriented electrical steel sheets of the comparative example was evaluated. The results are shown in Table 6 below. In the evaluation in Table 6, each characteristic was measured using the method described above. In addition, the iron loss at 50 Hz and a magnetic flux density of 1.7 T was measured using the excitation current method.

[0089] In Experiments 51 to 54, in the wound core of Core No. a-2 shown in Table 4, Steel Plate No. A13 was used on the inside of the wound core, and Steel Plate No. A2 was used on the outside of the wound core. The thicknesses of Steel Plates No. A2 and A13 were both 0.23 mm. As shown in Experiment No. 40 in Tables 5-2 and 5-4, Steel Plate No. A2 is a comparative steel sheet and does not satisfy the above-mentioned property (1). On the other hand, as shown in Experiment No. 16 in Tables 5-1 and 5-3, Steel Plate No. A13 is an example steel sheet and satisfies the above-mentioned property (1). In Experiment No. 51, Steel Plate No. A13 made up the inner 5% of the thickness in the steel sheet lamination direction (L3 shown in FIG. 8 ), and Steel Plate No. A2 made up the outer 95%. In Experiment No. 52, the inner 20% of the thickness in the steel sheet stacking direction was steel plate No. A13, and the outer 80% was steel plate No. A2. In Experiment No. 53, the inner 50% of the thickness in the steel sheet stacking direction was steel plate No. A13, and the outer 50% was steel plate No. A2. In Experiment No. 54, the inner 95% of the thickness in the steel sheet stacking direction was steel plate No. A13, and the outer 5% was steel plate No. A2.

[0090] In Experiments Nos. 55 to 58, in the wound core of Core No. a-3 shown in Table 4, Steel Plate No. A17 was used on the inside of the wound core, and Steel Plate No. A3 was used on the outside. The thicknesses of Steel Plates No. A3 and A17 were both 0.20 mm. As shown in Experiment No. 41 in Tables 5-2 and 5-4, Steel Plate No. A3 is a comparative steel plate and does not satisfy the above-mentioned property (1). On the other hand, as shown in Experiment No. 20 in Tables 5-1 and 5-3, Steel Plate No. A17 is an example steel plate and satisfies the above-mentioned property (1). In Experiment No. 55, Steel Plate No. A17 made up the inner 5% of the thickness in the steel plate lamination direction (L3 shown in FIG. 8 ), and Steel Plate No. A3 made up the outer 95%. In Experiment No. 56, the inner 20% of the thickness in the steel sheet stacking direction was steel plate No. A17, and the outer 80% was steel plate No. A3. In Experiment No. 57, the inner 50% of the thickness in the steel sheet stacking direction was steel plate No. A17, and the outer 50% was steel plate No. A3. In Experiment No. 58, the inner 95% of the thickness in the steel sheet stacking direction was steel plate No. A17, and the outer 5% was steel plate No. A3.

[0091] As is clear from Experiments No. 51 to 58, even when a wound core was constructed by mixing the steel sheets according to the Examples with the steel sheets according to the Comparative Examples, the iron loss ratio (= iron core iron loss / material iron loss) was less than 1.25. In particular, according to Experiments No. 51 and No. 55, even when the steel sheets according to the Examples accounted for 5% of the thickness in the lamination direction, the iron loss ratio was favorable at less than 1.25.

[0092]

[0093] DESCRIPTION OF SYMBOLS 1 Grain-oriented electrical steel sheet 2 Laminated structure 3 Corner portion 4, 4a Flat portion 5 Bent portion 6 Joint portion 10 Wound core

Claims

1. According to the metallic material tensile test method (JIS Z2241:2011), strain rate was 0.08 s ―１ In a stress-strain curve obtained by a tensile test at 1000 rpm, the difference εt' - εt between the amount of strain εt (%) when the stress first reaches a maximum value σt and the amount of strain εt' (%) when the stress next reaches a maximum value satisfies the following formula (1), where εA is defined by the following formula (2): 0 < εt' - εt ≦ 0.25 × εA (1) εA = (t / (t + 0.6)) × 100 (2) where t [mm] is the thickness of the steel sheet.

2. The grain-oriented electrical steel sheet according to claim 1, wherein the ratio TS / σt of the tensile strength TS to the first maximum value σt in the stress-strain curve further satisfies the following relationship: 1.00<TS / σt≦1.40 3. The grain-oriented electrical steel sheet according to claim 1 or 2, wherein the ratio of the minimum value σmin among the stresses at the lower yield point to the first maximum value σt in the stress-strain curve further satisfies the following relational expression: 0.12≦σmin / σt<1.00 4. A wound core formed by laminating bent steel sheets, wherein the wound core has a rectangular shape with a hollow at the center, in a side view of the wound shape seen from the direction along the surface of the steel sheets, by having a plurality of flat portions and bent portions adjacent to the flat portions, and wherein a material sampled from the flat portions of the wound core is subjected to a tensile test at a strain rate of 0.08 s according to the Metallic Material Tensile Test Method (JIS Z2241:2011). ―１ A wound core in which, in a stress-strain curve obtained by a tensile test at 1000 rpm, the difference εt' - εt between the amount of strain εt (%) when the stress first reaches a maximum value σt and the amount of strain εt' (%) when the stress next reaches a maximum value satisfies the following equation (3), where εB is defined by the following equation (4): 0 < εt' - εt ≦ 0.25 × εB (3) εB = (t / (t + 2r)) × 100 (4) where t [mm] is the thickness of the steel plate and r [mm] is the radius of curvature of the bent portion.

5. A wound core according to claim 4, wherein the ratio TS / σt of the tensile strength TS to the first maximum value σt in the stress-strain curve further satisfies the following relationship: 1.00<TS / σt≦1.40 6. A wound core according to claim 4 or 5, wherein the ratio of the minimum value σmin among the stresses at the lower yield point to the first maximum value σt in the stress-strain curve further satisfies the following relational expression: 0.12≦σmin / σt<1.00 7. A wound core according to claim 4 or 5, wherein the radius of curvature of the bent portion is 5 mm or less.

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