GRAIN-ORIENTED ELECTRICAL STEEL SHEET, WOUND TRANSFORMER CORE USING THE SAME, AND METHOD FOR PRODUCING WOUND CORE

Abstract

A grain-oriented electrical steel sheet for a wound transformer core. The steel sheet having a sheet thickness t, where t and an iron loss deterioration ratio obtained by subjecting the steel sheet under elliptic magnetization satisfy the following relations: (i) when t0.20 mm, the iron loss deterioration ratio is 60% or less; (ii) when 0.20 mm<t<0.27 mm, the iron loss deterioration ratio is 55% or less; and (iii) when 0.27 mmt, the iron loss deterioration ratio is 50% or less. The iron loss deterioration ratio is calculated from ((W.sub.AW.sub.B)/W.sub.B)100, where W.sub.A is iron loss under 50 Hz elliptic magnetization of 1.7 T in a rolling direction and 0.6 T in a direction orthogonal to the rolling direction, and W.sub.B is iron loss under 50 Hz alternating magnetization of 1.7 T in the rolling direction.

Claims

1. A grain-oriented electrical steel sheet used for a wound core of a transformer, the steel sheet having a sheet thickness t, wherein: the sheet thickness t and an iron loss deterioration ratio obtained when the steel sheet is subjected to elliptic magnetization satisfy the following relations: when the sheet thickness t0.20 mm, the iron loss deterioration ratio is 60% or less; when 0.20 mm<the sheet thickness t<0.27 mm, the iron loss deterioration ratio is 55% or less; and when 0.27 mmthe sheet thickness t, the iron loss deterioration ratio is 50% or less, and the iron loss deterioration ratio is defined by formula (1) below:
((W.sub.AW.sub.B)/W.sub.B)100 (1) where, in formula (1): W.sub.A is iron loss under 50 Hz elliptic magnetization of 1.7 T in a rolling direction and 0.6 T in a direction orthogonal to the rolling direction, and W.sub.B is iron loss under 50 Hz alternating magnetization of 1.7 T in the rolling direction.

2. The grain-oriented electrical steel sheet according to claim 1, wherein: the steel sheet includes: secondary recrystallized grains in the steel sheet, and a plurality of linear grooves on a surface of the steel sheet, the plurality of linear grooves extending in a direction intersecting the, rolling direction, and a width w of the grooves in the rolling direction, a depth d of the grooves, a diameter R of secondary recrystallized grains, and an average angle of the secondary recrystallized grains sheet-satisfy the relation represented by the following formula (2): [Math. 1]
Sin +4t/R+(w/a/2)(10d/t)10.sup.30.080 (2) where, in formula (2): : the average angle () of the secondary recrystallized grains, t: the thickness (mm) of the steel sheet, R: the diameter (mm) of the secondary recrystallized grains, a: spacing (mm) between the plurality of linear grooves extending in the direction intersecting the rolling direction, w: the width (m) of the grooves in the rolling direction, and d: the depth (mm) of the grooves.

3. The grain-oriented electrical steel sheet according to claim 1, wherein the steel sheet has a magnetic flux density B8 that is 1.91 T or more at a magnetizing force of 800 A/m, and the diameter R of the secondary recrystallized grains is 40 mm or more.

4. A wound core of a transformer, the wound core being formed from the grain-oriented electrical steel sheet according to claim 1.

5. A method for producing a wound core of a wound core transformer, the method allowing a building factor to be reduced, the building factor being obtained by dividing a value of iron loss of the wound core transformer by a value of iron loss of a grain-oriented electrical steel sheet used as a material of the wound core, the method comprising: winding the grain-oriented electrical steel sheet to form the wound core, wherein: a sheet thickness t of the grain-oriented electrical steel sheet and an iron loss deterioration ratio obtained when the grain-oriented electrical steel sheet is subjected to elliptic magnetization satisfy the following relations: when the sheet thickness t0.20 mm, the iron loss deterioration ratio is 60% or less; when 0.20 mm<the sheet thickness t<0.27 mm, the iron loss deterioration ratio is 55% or less; and when 0.27 mmthe sheet thickness t, the iron loss deterioration ratio is 50% or less, and the iron loss deterioration ratio is defined by formula (1) below:
((W.sub.AW.sub.B)/W.sub.B)100 (1) where, in formula (1): W.sub.A is iron loss under 50 Hz elliptic magnetization of 1.7 T in a rolling direction and 0.6 T in a direction orthogonal to the rolling direction, and W.sub.B is iron loss under 50 Hz alternating magnetization of 1.7 T in the rolling direction.

6. The method for producing a wound core according to claim 5, wherein: the steel sheet includes: secondary recrystallized grains in the steel sheet, and a plurality of linear grooves on a surface of the steel sheet, the plurality of linear grooves extend in a direction intersecting the rolling direction, and a width w of the grooves in the rolling direction, a depth d of the grooves, a diameter R of the secondary recrystallized grains, and an average angle of the secondary recrystallized grains satisfy the relation represented by the following formula (2): [Math. 2]
Sin +4t/R+(w/a/2)(10d/t)10.sup.30.080 (2) where, in formula (2): : the average angle () of the secondary recrystallized grains, t: the thickness (mm) of the steel sheet, R: the diameter (mm) of the secondary recrystallized grains, a: spacing (mm) between the plurality of linear grooves extending in the direction intersecting the rolling direction, w: the width (m) of the grooves in the rolling direction, and d: the depth (mm) of the grooves.

7. The method for producing a wound core according to claim 5, wherein the steel sheet used, has a magnetic flux density B8 that 1.91 T or more at a magnetizing force of 800 A/m, and the diameter R of the secondary recrystallized grains is 40 mm or more.

8. The grain-oriented electrical steel sheet according to claim 2, wherein the steel sheet has a magnetic flux density B8 that is 1.91 T or more at a magnetizing force of 800 A/m, and the diameter R of the secondary recrystallized grains is 40 mm or more.

9. A wound core of a transformer, the wound core being formed from the grain-oriented electrical steel sheet according to claim 2.

10. A wound core of a transformer, the wound core being formed from the grain-oriented electrical steel sheet according to claim 3.

11. A wound core of a transformer, the wound core being formed from the grain-oriented electrical steel sheet according to claim 8.

12. The method for producing a wound core according to claim 6, wherein the steel sheet has a magnetic flux density B8 that is 1.91 T or more at a magnetizing force of 800 A/m, and the diameter R of the secondary recrystallized grains is 40 mm or more.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0087] FIG. 1 is a schematic illustration showing an increase in iron loss of inner wound cores when the inner wound cores and an outer wound core are excited simultaneously.

[0088] FIG. 2 is a schematic illustration showing interlaminar magnetic flux transfer generated between the outer wound core and the inner wound cores.

[0089] FIG. 3 is a schematic illustration showing a lap joint portion of a wound core.

[0090] FIG. 4 is a schematic illustration showing the structure of the wound core used for examination.

[0091] FIG. 5 is a schematic illustration showing interlaminar transfer portions between the outer wound core and the inner wound cores and lap joint portions.

[0092] FIG. 6 is a schematic illustration showing the flows of magnetic flux in the lap joint portions.

[0093] FIG. 7 is a graph showing the relation between an iron loss deterioration ratio and iron loss of the interlaminar transfer portions when a 0.18 mm-thick material is subjected to elliptic magnetization.

[0094] FIG. 8 is a graph showing the relation between the iron loss deterioration ratio and iron loss of the interlaminar transfer portions when a 0.20 mm-thick material is subjected to elliptic magnetization.

[0095] FIG. 9 is a graph showing the relation between the iron loss deterioration ratio and iron loss of the interlaminar transfer portions when a 0.23 mm-thick material is subjected to elliptic magnetization.

[0096] FIG. 10 is a graph showing the relation between the iron loss deterioration ratio and iron loss of the interlaminar transfer portions when a 0.27 mm-thick material is subjected to elliptic magnetization.

[0097] FIG. 11 is a graph showing the relation between the iron loss deterioration ratio and iron loss of the interlaminar transfer portions when a 0.30 mm-thick material is subjected to elliptic magnetization.

[0098] FIG. 12 is a graph showing the relation between a parameter [Sin +4t/R+(w/a/2)(10d/t)10.sup.3] disclosed herein and the iron loss deterioration ratio.

[0099] FIG. 13 is a schematic illustration showing an example of a method for controlling an average angle of secondary recrystallized grains.

[0100] FIG. 14 shows schematic illustrations showing the structures of wound cores A to C produced in Examples.

DETAILED DESCRIPTION

[0101] The disclosed embodiments are described in detail. As described above, a grain-oriented electrical steel sheet that gives excellent transformer iron loss satisfying the following conditions is used for a wound transformer core.

[0102] The sheet thickness t of the grain-oriented electrical steel sheet (material) and an iron loss deterioration ratio obtained by subjecting steel sheets under elliptic magnetization defined by formula (1) below satisfy the following relations:

[0103] when the sheet thickness t0.20 mm, the iron loss deterioration ratio is 60% or less;

[0104] when 0.20 mm<the sheet thickness t<0.27 mm, the iron loss deterioration ratio is 55% or less; and

[0105] when 0.27 mmsheet thickness t, the iron loss deterioration ratio is 50% or less.

(The iron loss deterioration ratio under the elliptic magnetization)=((W.sub.AW.sub.B)/W.sub.B)100 (1)

[0106] In formula (1), W.sub.A is iron loss under 50 Hz elliptic magnetization of 1.7 T in an RD direction (a rolling direction) and 0.6 T in a TD direction (a direction orthogonal to the rolling direction), and W.sub.B is iron loss under 50 Hz alternating magnetization of 1.7 T in the RD direction.

[0107] The iron loss in formula (1) above is measured as follows. [0108] (W.sub.A: Iron loss under 50 Hz elliptic magnetization of 1.7 T in RD direction and 0.6 T in TD direction)

[0109] W.sub.A is measured using a two-dimensional single-sheet magnetic measurement device (2D-SST) described in, for example, Non-Patent Literature 2. A grain-oriented electrical steel sheet (material) is subjected to 50 Hz sine wave excitation at a maximum magnetic flux density of 1.7 T in the RD direction and a maximum magnetic flux density of 0.6 T in the TD direction, and the difference in phase between the RD direction and the TD direction during the sine wave excitation is set to 90 to perform excitation under elliptic magnetization. The elliptic magnetization may rotate in a clockwise direction or in counterclockwise direction. It has been pointed out that the measurement value of the iron loss using a clockwise rotation direction differs from the measurement value using a counterclockwise rotation direction. Therefore, both of them are measured and averaged. Various iron loss measurement methods such as a probe method and an H coil method have been proposed, and any of these methods may be used. During excitation, the excitation voltage is feedback-controlled such that the maximum magnetic flux density in the RD direction is 1.7 T and the maximum magnetic flux density in the TD direction is 0.6 T. However, waveform control is not performed except for the moment when the magnetic flux density is maximum even though the waveform of the magnetic flux is slightly distorted from the sine wave. Preferably, the measurement sample has a size of (50 mm50 mm) or larger in consideration of the number of crystal grains contained in one sample, but this depends on the possible size for excitation of the two-dimensional single-sheet magnetic measurement device. In consideration of variations in the measurement values, it is preferable that, 30 or more samples are used for the measurement for one material and the average of the measurement values is used. [0110] (W.sub.B: Iron loss under 50 Hz alternating magnetization of 1.7 T in RD direction)

[0111] W.sub.B is measured using the same samples as those used for the above measurement under the elliptic magnetization and the same measurement device. 50 Hz sine wave excitation is performed at a maximum magnetic flux density of 1.7 T only in the RD direction. During excitation, the excitation voltage is feedback-controlled such that the maximum magnetic flux density in the RD direction is 1.7 T, and no control is performed in the TD direction.

[0112] To keep the iron loss deterioration ratio under the elliptic magnetization within the above range, it is preferable that a plurality of linear grooves extending in a direction intersecting the rolling direction are formed on the surface of the grain-oriented electrical steel sheet (material) such that the width w of the grooves in the rolling direction, the depth d of the grooves, the diameter R of secondary recrystallized grains in the steel sheet, and the average angle of the secondary recrystallized grains in the steel sheet satisfy the relation represented by formula (2) below.

[Math 3]

[0113]
Sin +4t/R+(w/a/2)(10d/t)10.sup.30.080 (2)

[0114] In formula (2),

[0115] : the average angle () of the secondary recrystallized grains,

[0116] t: the thickness (mm) of the steel sheet,

[0117] R: the diameter (mm) of the secondary recrystallized grains,

[0118] a: the spacing (mm) between the plurality of linear grooves extending in the direction intersecting the rolling direction,

[0119] w: the width (m) of the grooves in the rolling direction, and

[0120] d: the depth (mm) of the grooves.

[0121] The material properties in formula (2) above are measured as follows.

: Average Angle () of Secondary Recrystallized Grains

[0122] The angle is defined as the angle between the <100> axis of secondary recrystallized grains oriented in the rolling direction of the steel sheet and the rolling surface. The secondary recrystallization orientation of the steel sheet is measured by X-ray crystal diffraction. Since the orientations of the secondary recrystallized grains in the steel sheet vary, the measurement is performed at points set at a 10 mm RD pitch and a 10 mm TD pitch, and the data measured over a measurement area of (500 mm500 mm) or larger is averaged to determine the average angle.

R: Diameter (mm) of Secondary Recrystallized Grains

[0123] A coating on the surface of the steel sheet is removed by any chemical or electrical method, and the diameters of the secondary recrystallized grains are measured. The number of crystal grains with a size of about 1 mm.sup.2 or larger present in a measurement area with a size of (500 mm500 mm) or larger is measured by visual inspection or digital image processing, and the average area for a single secondary recrystallized grain is determined. The average area is used to compute a circle-equivalent diameter to determine the diameter of the secondary recrystallized grains.

a: Spacing (mm) Between a Plurality of Linear Grooves Extending in Direction Intersecting Rolling Direction

[0124] The spacing is defined as the spacing between linear grooves in the RD direction. When the spacings between the lines (the spacing between the grooves) are not constant, the examination is performed at five points within a longitudinal length of 500 mm, and their average is used. When the line spacing varies in the width direction of the steel sheet, their average is used.

w: Width (m) of Grooves in Rolling Direction

[0125] The surface of the steel sheet is observed under a microscope to measure the width. Since the width of a groove in the rolling direction is not always constant, observation is performed at five points or more along one linear row within a length of 100 mm in a sample, and their average is used as the groove width of the linear row in the rolling direction. Further, five or more linear rows within a longitudinal length of 500 mm in the sample are observed, and their average is used as the width w. d: Depth (mm) of Grooves

[0126] The cross section of the steel sheet at the grooves is observed under a microscope to measure the depth. Since the depth of a groove is not always constant, observation is performed at five points or more along one linear row within a length of 100 mm in a sample, and their average is used as the groove depth in the linear row. Further, five or more linear rows within a longitudinal length of 500 mm in the sample are observed, and their average is used as the depth d.

[0127] A method for producing a grain-oriented electrical steel sheet satisfying the above relations is described. Any method other than the following method may be used provided that formula (2) is satisfied by controlling each parameters, and no particular limitation is imposed on the production method.

[0128] The average angle of the secondary recrystallized grains can be controlled by controlling the primary recrystallization texture or using, for example, a coil set for finishing annealing. For example, when finishing annealing is performed under conditions having the coil set as shown in FIG. 13, the <001> orientations within the crystal grains in such state are uniformly aligned. Then flattening annealing is performed, and the coil is flattened. In this state, the <001> orientation within each crystal grain is inclined to the sheet thickness direction depending on the coil set used for the finishing annealing, and the angle increases. Specifically, the smaller the coil set, the larger the angle after the flattening annealing. With excessively larger angle, the magnetic flux density B8 of the material decreases, and hysteresis loss deteriorates. Therefore, the angle is preferably 5 or less.

[0129] The diameter (mm) of the secondary recrystallized grains can be controlled by controlling the amount of Goss grains present in the primary recrystallized grains. For example, by increasing the final reduction ratio in cold rolling or increasing friction during rolling to thereby increase the amount of shear strain introduced before primary recrystallization of grains, the amount of the Goss grains in the primary recrystallized grains can be increased. Further, the amount of the Goss grains present in the primary recrystallized grains can be controlled also by controlling the heating-up rate during primary recrystallization annealing. The Goss grains in the primary recrystallized grains serve as secondary recrystallization nuclei during finishing annealing. Therefore, the larger the amount of the Goss grains, the larger the amount of secondary recrystallized grains, and which results in smaller diameter of the secondary recrystallized grains.

[0130] Examples of a method for forming a plurality of grooves extending in a direction intersecting the rolling direction and used to obtain the magnetic domain refining effect include existing techniques such as (i) an etching method including applying a resist ink to portions of a cold-rolled sheet other than portions in which grooves are to be formed, subjecting the resulting sheet to electropolishing to form grooves, and then removing the resist ink, (ii) a magnetic domain refining technique including applying a load of 882 to 2156 MPa (90 to 220 kgf/mm.sup.2) to a finishing-annealed steel sheet to form grooves with a depth of 5 m or more in a base steel and subjecting the resulting steel sheet to heat treatment at a temperature of 750 C. or higher, and (iii) a method in which grooves are formed by irradiation with a high-energy density laser beam before or after primary recrystallization or secondary recrystallization. In the disclosed embodiments, any of these groove formation methods may be applied. A production issue with the method including applying a load is control of the wear of a gear type roll. A production issue with the groove formation method using irradiation with a high-energy density laser beam is removal of molten iron. It is therefore preferable to form grooves by subjecting a cold-rolled sheet to electrolytic etching.

[0131] A specific production method is described using the groove formation by electrolytic etching of a cold-rolled sheet as an example. The width of the grooves in the rolling direction can be controlled by controlling the width of portions not coated with the resist ink. By controlling the spreading of the resist ink or controlling a pattern on a resist ink applying roll, linear grooves having a constant width in the width direction of the steel sheet can be formed. The depth of the grooves can be controlled by the conditions for subsequent electrolytic etching. Specifically, the depth of the grooves is controlled by adjusting the electrolytic etching time or current density.

[0132] No particular limitation is imposed on the width of the grooves in the rolling direction provided that formula (2) above is satisfied. However, excessively narrower width induces magnetic poles coupling, leading to an insufficient magnetic domain refining effect. Excessively wider width, to the contrary, reduces the magnetic flux density B8 of the steel sheet. Therefore, the width is preferably from 40 m to 250 m inclusive. No particular limitation is imposed on the depth of the grooves provided that formula (2) above is satisfied. However, excessively small depth leads to an insufficient magnetic domain refining effect. Excessively larger depth reduces the magnetic flux density B8 of the steel sheet. Therefore, the depth is preferably from 10 m or more and about or less of the sheet thickness inclusive.

[0133] As for the spacing of the plurality of grooves extending in the direction intersecting the rolling direction, the spacing between the grooves formed can be controlled during their production process using any of the above methods. Excessively larger spacing between the grooves reduces the magnetic domain refining effect obtained by the grooves. Therefore, the spacing between the grooves is preferably 10 mm or less.

[0134] No particular limitation is imposed on the sheet thickness of the grain-oriented electrical steel sheet of the disclosure. From the viewpoint of manufacturability, onset stability of secondary recrystallization, etc. the sheet thickness is preferably 0.15 mm or more and furthermore 0.18 mm or more. From the viewpoint of reducing eddy-current loss etc., the sheet thickness is preferably 0.35 mm or less and further more preferably 0.30 mm or less.

[0135] In the method for producing the grain-oriented electrical steel sheet of the disclosure used for a wound core of a transformer, no limitation is imposed on the matters not directly related to the above properties. However, a recommended preferred component composition and some points of the production method of the disclosure other than the points described above are described.

[0136] An inhibitor may be used in the disclosed embodiments. Using, for example, an AlN-based inhibitor, appropriate amounts of Al and N may be added. Using a MnS.MnSe-based inhibitor is used, appropriate amounts of Mn and Se and/or S may be added. Obviously, the both inhibitors may be used in combination. Contents of Al, N, S, and Se, in such case, may be Al: 0.01 to 0.065% by mass, N: 0.005 to 0.012% by mass, S: 0.005 to 0.03% by mass, and Se: 0.005 to 0.03% by mass.

[0137] The disclosure may be applied also to a grain-oriented electrical steel sheet in which the contents of Al, N, S, and Se are limited, i.e., no inhibitor is used. The amounts of Al, N, S, and Se in such case may be limited to Al: 100 mass ppm or less, N: 50 mass ppm or less, S: 50 mass ppm or less, and Se: 50 mass ppm or less.

[0138] Other basic components and optional components are as follows.

C: 0.08% by Mass or Less

[0139] The content of C exceeding 0.08% by mass is difficult to reduce to 50 mass ppm or less at which magnetic aging does not occur during the production process. Therefore, the C content may be 0.08% by mass or less. The lower limit is not provided because secondary recrystallization may occur even in a material containing no C.

Si: 2.0 to 8.0% by Mass

[0140] Si is an element effective in increasing the electric resistance of steel and reducing iron loss. However, when the content of Si is less than 2.0% by mass, the effect of reducing the iron loss is insufficient. The content of Si exceeding 8.0% by mass significantly deteriorates workability, and reduces the magnetic flux density. Therefore, the Si content is preferably within the range of 2.0 to 8.0% by mass.

Mn: 0.005 to 1.0% by Mass

[0141] Mn is an element necessary for improving hot workability. However, the Mn content being less than 0.005% by mass, the effect of Mn added is small. The Mn content exceeding 1.0% by mass reduces the magnetic flux density of a product sheet. Therefore, the Mn content is preferably within the range of 0.005 to 1.0% by mass.

[0142] In addition to the above basic components, the following elements may be appropriately added as components improving the magnetic properties.

[0143] At least one selected from Ni: 0.03 to 1.50% by mass, Sn: 0.01 to 1.50% by mass, Sb: 0.005 to 1.50% by mass, Cu: 0.03 to 3.0% by mass, P: 0.03 to 0.50% by mass, Mo: 0.005 to 0.10% by mass, and Cr: 0.03 to 1.50% by mass.

[0144] Ni is an element useful to improve the texture of a hot-rolled sheet to thereby improve its magnetic properties. However, the content being less than 0.03% by mass, the effect of improving the magnetic properties is small. The content exceeding 1.50% by mass, secondary recrystallization becomes unstable, deteriorating the magnetic properties. Therefore, the amount of Ni is within the range of preferably 0.03 to 1.50% by mass.

[0145] Sn, Sb, Cu, P, Cr, and Mo are elements useful to improve the magnetic properties. However, if their contents are lower than their lower limits of the components described above, the effect of improving the magnetic properties is small. The contents exceeding the upper limits of the components described above inhibit the growth of the secondary recrystallized grains. It is therefore preferable that the contents of these components are within the respective ranges described above. The remainder other than the above components is Fe and inevitable impurities mixed during the production process.

[0146] The steel having a component composition adjusted to the above appropriate component composition may be subjected to a standard ingot making process or a standard continuous casting process to form a slab, or a thin cast piece having a thickness of 100 mm or less may be produced by direct continuous casting process. The slab is heated using a common method and then hot-rolled. However, the slab may be subjected directly to hot-rolling without heating after casting. The thin cast piece may be hot-rolled or may be subjected to the subsequent process without the hot-rolling. Then the hot-rolled sheet is optionally annealed and then subjected to cold rolling once or subjected to cold rolling twice or more including process annealing to obtain a final sheet thickness. Then the product is subjected to decarburization annealing and finishing annealing. Then an insulating tension coating is applied, and flattening annealing is performed. In the course of the above process, grooves are formed by electrolytic etching after the cold rolling or formed at some point after the cold rolling by applying a load using a gear type roll or by irradiation with a laser beam. In the composition of the steel product, the C content is reduced to 50 ppm or less by the decarburization annealing, and the contents of Al, N, S, and Se are reduced to the level of inevitable impurities by purification in the finishing annealing.

[0147] The characteristics of the three-phase three-legged excitation-type wound core transformer have been described in the present specification. However, the disclosed embodiments are also suitable for wound core transformers having other joint portion structures such as three-phase five-legged cores and single-phase excitation-type cores.

Examples

[0148] Cold-finished grain-oriented electrical steel sheets having a thickness of 0.18 to 0.30 mm were produced at different reduction ratios and different heating-up rates for primary recrystallization annealing. During the process, electrolytic etching was performed after cold rolling under various conditions to form grooves, and grain-oriented electrical steel sheets having material properties shown in Table 3 were obtained. These electrical steel sheets were subjected to two-dimensional magnetic measurement by the method described in the present description to thereby measure their iron loss deterioration ratio under elliptic magnetization. Transformer wound cores A to C having core shapes shown in FIG. 14 were produced using each of the above materials. As for the core A, a single-phase winding was formed, and iron loss under single-phase excitation at 50 Hz and 1.7 T was measured. As for the cores B and C, a three-phase winding was formed, and iron loss under three-phase excitation at 50 Hz and 1.7 T was measured. The wound core A shown in FIG. 14 has a shape with a stacked thickness of 22.5 mm, a steel sheet width of 100 mm, seven step laps, and a single step lap length of 8 mm. The wound core B has a shape with a stacked thickness of 20 mm, a steel sheet width of 100 mm, seven step laps, and a single step lap length of 5 mm. The wound core C has a shape with a stacked thickness of 30 mm, a steel sheet width of 120 mm, seven step laps, and a single step lap length of 8 mm. In grain-oriented electrical steel sheets in which the iron loss deterioration ratio under elliptic magnetization satisfies the range of the disclosure, the BF for each of the core shapes was smaller than those in Comparative Examples. In particular, when a grain-oriented electrical steel sheet in which the magnetic flux density B8 at a magnetizing force of 800 A/m was equal to or larger than 1.91 T and the diameter R of the secondary recrystallized grains was equal to or larger than 40 mm was used, the material iron loss was small, the BF was small, and the iron loss of the transformer was very small.

TABLE-US-00003 TABLE 3 Linear grooves a: Spacing between a plurality of Material properties linear grooves : Average extending in w: Width angle of t: Steel R: Secondary direction of grooves secondary sheet recrystallized intersecting in rolling d: Depth Iron loss recrystallized thickness grain diameter rolling direction of grooves Disclosed deterioration Condition grains () (mm) (mm) direction (mm) (m) (mm) parameter*.sup.1 ratio*.sup.2 (%) 1 2.3 0.18 24 3 200 0.023 0.130 42 2 2.2 0.18 22 4 200 0.022 0.114 43 3 2.1 0.18 23 4 180 0.018 0.100 48 4 2.3 0.18 21 5 150 0.018 0.096 50 5 2.2 0.18 20 5 150 0.015 0.092 52 6 2.1 0.18 21 5 120 0.015 0.085 56 7 2.6 0.18 24 5 100 0.014 0.086 58 8 2.3 0.18 22 5 80 0.015 0.082 59 9 2.1 0.18 26 5 80 0.015 0.074 63 10 1.8 0.18 28 5 50 0.015 0.063 67 11 1.7 0.18 44 3 120 0.022 0.081 58 12 1.6 0.18 51 3 180 0.022 0.094 49 13 1.3 0.18 38 3 150 0.022 0.085 55 14 1.7 0.18 57 5 150 0.015 0.060 68 15 2.4 0.20 17 3 160 0.025 0.136 40 16 2.3 0.20 18 3 160 0.025 0.132 42 17 2.2 0.20 17 3 140 0.022 0.122 43 18 2.3 0.20 20 4 140 0.022 0.107 44 19 2.1 0.20 19 4 120 0.020 0.100 45 20 2.2 0.20 21 4 120 0.015 0.092 51 21 2.3 0.20 22 5 100 0.017 0.089 54 22 2.0 0.20 20 5 90 0.015 0.084 59 23 1.8 0.20 21 5 70 0.015 0.077 63 24 1.8 0.20 24 5 70 0.015 0.072 67 25 1.4 0.20 42 3 150 0.025 0.088 49 26 1.8 0.20 64 3 180 0.022 0.091 45 27 1.2 0.20 36 3 150 0.022 0.082 55 28 1.3 0.20 54 5 90 0.015 0.047 75 29 2.5 0.23 18 3 180 0.025 0.141 38 30 2.2 0.23 21 3 150 0.025 0.121 42 31 2.3 0.23 19 3 150 0.018 0.116 43 32 2.2 0.23 18 4 120 0.021 0.109 46 33 2.5 0.23 21 4 120 0.019 0.105 47 34 2.4 0.23 22 4 100 0.020 0.099 48 35 2.0 0.23 24 3 80 0.025 0.094 53 36 1.8 0.23 26 3 80 0.020 0.083 54 37 1.7 0.23 28 3 80 0.017 0.076 57 38 1.7 0.23 28 4 80 0.018 0.074 62 39 1.9 0.23 49 3 150 0.025 0.090 50 40 1.8 0.23 75 3 200 0.022 0.089 49 41 1.7 0.23 38 3 170 0.022 0.092 47 42 1.8 0.23 62 4 90 0.02 0.060 62 43 2.3 0.27 17 3 150 0.027 0.139 32 44 2.1 0.27 21 3 120 0.026 0.115 37 45 2.2 0.27 22 3 120 0.020 0.108 39 46 2.2 0.27 23 4 100 0.019 0.098 42 47 2.3 0.27 24 4 80 0.018 0.095 43 48 2.0 0.27 25 4 80 0.020 0.089 44 49 1.7 0.27 27 3 80 0.020 0.084 48 50 1.7 0.27 29 3 80 0.020 0.081 49 51 1.8 0.27 27 5 60 0.017 0.077 52 52 1.6 0.27 26 5 60 0.018 0.075 54 53 1.7 0.27 45 3 120 0.029 0.084 48 54 1.3 0.27 68 3 150 0.032 0.080 49 55 1.6 0.27 37 3 150 0.025 0.090 43 56 1.8 0.27 58 4 120 0.024 0.069 54 57 2.1 0.30 16 4 200 0.032 0.149 28 58 2.0 0.30 17 3 180 0.028 0.145 32 59 1.8 0.30 15 4 180 0.025 0.138 34 60 2.2 0.30 20 4 150 0.027 0.122 38 61 2.1 0.30 23 4 150 0.022 0.108 41 62 1.9 0.30 31 4 120 0.025 0.090 45 63 1.8 0.30 28 3 100 0.021 0.091 47 64 1.7 0.30 32 3 80 0.024 0.082 49 65 1.8 0.30 35 5 80 0.025 0.075 52 66 1.8 0.30 37 6 80 0.025 0.072 55 67 1.5 0.30 49 3 150 0.033 0.090 41 68 1.6 0.30 62 3 180 0.035 0.097 44 69 1.7 0.30 34 3 150 0.032 0.103 40 70 1.9 0.30 63 5 120 0.027 0.067 53 Material magnetic properties Material Core A Core B Core C iron loss Transformer Transformer Transformer W17/50 iron loss iron loss iron loss Condition B8(T) (W/kg) (W/kg) BF (W/kg) BF (W/kg) BF Remarks 1 1.87 0.65 0.66 1.02 0.85 1.31 0.93 1.43 Inventive Example 2 1.86 0.67 0.68 1.01 0.88 1.31 0.96 1.43 Inventive Example 3 1.88 0.65 0.66 1.02 0.86 1.32 0.92 1.42 Inventive Example 4 1.87 0.68 0.69 1.01 0.90 1.33 0.97 1.43 Inventive Example 5 1.87 0.68 0.69 1.01 0.90 1.33 0.97 1.42 Inventive Example 6 1.87 0.68 0.69 1.02 0.90 1.33 0.97 1.43 Inventive Example 7 1.86 0.70 0.71 1.02 0.93 1.33 0.99 1.41 Inventive Example 8 1.88 0.68 0.69 1.01 0.90 1.33 0.97 1.42 Inventive Example 9 1.88 0.67 0.70 1.05 0.93 1.39 1.00 1.49 Comparative Example 10 1.88 0.67 0.70 1.05 0.94 1.40 1.01 1.50 Comparative Example 11 1.91 0.60 0.61 1.01 0.79 1.32 0.85 1.41 Inventive Example (particularly preferable) 12 1.92 0.59 0.58 0.99 0.77 1.31 0.84 1.42 Inventive Example (particularly preferable) 13 1.89 0.64 0.64 1.00 0.83 1.30 0.91 1.42 Inventive Example 14 1.92 0.63 0.67 1.07 0.91 1.45 0.98 1.55 Comparative Example 15 1.87 0.68 0.69 1.01 0.88 1.29 0.99 1.45 Inventive Example 16 1.87 0.67 0.68 1.01 0.86 1.29 0.97 1.45 Inventive Example 17 1.88 0.69 0.70 1.02 0.88 1.28 1.01 1.46 Inventive Example 18 1.88 0.70 0.71 1.01 0.90 1.28 1.02 1.46 Inventive Example 19 1.89 0.71 0.72 1.01 0.91 1.28 1.03 1.45 Inventive Example 20 1.88 0.70 0.71 1.01 0.90 1.28 1.03 1.47 Inventive Example 21 1.88 0.71 0.71 1.00 0.92 1.29 1.04 1.46 Inventive Example 22 1.88 0.71 0.72 1.01 0.92 1.30 1.04 1.46 Inventive Example 23 1.89 0.71 0.75 1.06 0.98 1.38 1.08 1.52 Comparative Example 24 1.89 0.71 0.75 1.06 0.99 1.39 1.08 1.52 Comparative Example 25 1.91 0.65 0.66 1.01 0.83 1.27 0.94 1.45 Inventive Example (particularly preferable) 26 1.92 0.63 0.63 1.00 0.80 1.27 0.92 1.46 Inventive Example (particularly preferable) 27 1.90 0.66 0.67 1.01 0.84 1.28 0.96 1.46 Inventive Example 28 1.92 0.66 0.71 1.08 0.92 1.39 1.05 1.59 Comparative Example 29 1.86 0.74 0.75 1.01 0.94 1.27 1.09 1.47 Inventive Example 30 1.87 0.75 0.76 1.01 0.95 1.26 1.10 1.47 Inventive Example 31 1.87 0.75 0.75 1.00 0.95 1.26 1.10 1.47 Inventive Example 32 1.88 0.76 0.77 1.01 0.96 1.26 1.12 1.48 Inventive Example 33 1.87 0.76 0.77 1.01 0.97 1.27 1.12 1.48 Inventive Example 34 1.87 0.77 0.78 1.01 0.98 1.27 1.14 1.48 Inventive Example 35 1.88 0.74 0.75 1.01 0.93 1.26 1.09 1.47 Inventive Example 36 1.88 0.73 0.74 1.02 0.93 1.28 1.08 1.48 Inventive Example 37 1.89 0.74 0.78 1.05 1.00 1.35 1.14 1.54 Comparative Example 38 1.90 0.75 0.79 1.05 1.01 1.35 1.16 1.55 Comparative Example 39 1.92 0.69 0.69 1.00 0.87 1.26 1.02 1.48 Inventive Example (particularly preferable) 40 1.93 0.68 0.69 1.01 0.85 1.25 1.00 1.47 Inventive Example (particularly preferable) 41 1.90 0.72 0.73 1.01 0.91 1.26 1.06 1.47 Inventive Example 42 1.92 0.68 0.73 1.08 0.97 1.42 1.10 1.62 Comparative Example 43 1.88 0.83 0.83 1.00 1.03 1.24 1.21 1.46 Inventive Example 44 1.89 0.82 0.83 1.01 1.02 1.24 1.21 1.47 Inventive Example 45 1.89 0.81 0.81 1.00 1.01 1.25 1.18 1.46 Inventive Example 46 1.88 0.83 0.83 1.01 1.03 1.24 1.22 1.47 Inventive Example 47 1.89 0.83 0.83 1.01 1.04 1.25 1.22 1.47 Inventive Example 48 1.89 0.84 0.85 1.01 1.04 1.24 1.23 1.47 Inventive Example 49 1.89 0.85 0.86 1.01 1.06 1.25 1.25 1.47 Inventive Example 50 1.89 0.84 0.85 1.02 1.05 1.25 1.23 1.47 Inventive Example 51 1.89 0.85 0.90 1.06 1.12 1.32 1.33 1.56 Comparative Example 52 1.89 0.82 0.87 1.06 1.09 1.33 1.28 1.56 Comparative Example 53 1.92 0.77 0.77 1.00 0.96 1.25 1.12 1.46 Inventive Example (particularly preferable) 54 1.93 0.75 0.75 1.00 0.94 1.25 1.10 1.47 Inventive Example (particularly preferable) 55 1.90 0.80 0.81 1.01 0.99 1.24 1.17 1.46 Inventive Example 56 1.93 0.77 0.85 1.10 1.06 1.38 1.25 1.62 Comparative Example 57 1.90 0.91 0.91 1.00 1.11 1.22 1.34 1.47 Inventive Example 58 1.90 0.93 0.93 1.01 1.13 1.21 1.38 1.48 Inventive Example 59 1.90 0.92 0.92 1.00 1.13 1.23 1.37 1.49 Inventive Example 60 1.89 0.92 0.92 1.00 1.12 1.22 1.37 1.49 Inventive Example 61 1.90 0.92 0.93 1.01 1.12 1.22 1.36 1.48 Inventive Example 62 1.90 0.93 0.93 1.00 1.13 1.22 1.39 1.49 Inventive Example 63 1.90 0.94 0.95 1.01 1.16 1.23 1.40 1.49 Inventive Example 64 1.90 0.95 0.96 1.01 1.17 1.23 1.42 1.49 Inventive Example 65 1.90 0.96 1.01 1.05 1.24 1.29 1.51 1.57 Comparative Example 66 1.90 0.97 1.03 1.06 1.25 1.29 1.53 1.58 Comparative Example 67 1.93 0.85 0.85 1.00 1.05 1.23 1.25 1.47 Inventive Example (particularly preferable) 68 1.92 0.86 0.87 1.01 1.05 1.22 1.27 1.48 Inventive Example (particularly preferable) 69 1.90 0.91 0.91 1.00 1.12 1.23 1.34 1.47 Inventive Example 70 1.94 0.86 0.96 1.12 1.16 1.35 1.43 1.66 Comparative Example *.sup.1Sin + 4t/R + (W/a/2) (10d/t) 10.sup.3: underlines indicate that disclosed parameter is not satisfied. *.sup.2Iron loss deterioration ratio under elliptic magnetization: underlined values are outside the range of the disclosure.