Grain-oriented electrical steel sheet

Abstract

In a grain oriented electrical steel sheet, aveϕL which is an average of the angular deviation ϕ obtained from plural measurement points with spacing of 1 mm in the rolling direction L is 3.5° or less, DL10 which is a grain size at 10% by number base from largest in a case where the grain sizes DL obtained in the rolling direction L are sorted from largest to smallest is (100 - 15 × aveϕL) or less in units of mm, and aveDC which is an average of the grain size DC obtained in the transverse direction C is 50 mm or more.

Description

TECHNICAL FIELD

[0001] The present invention relates to a grain oriented electrical steel sheet.

[0002] Priority is claimed on Japanese Patent Application No. 2023-106860, filed June 29, 2023, the content of which is incorporated herein by reference.BACKGROUND ART

[0003] A grain oriented electrical steel sheet includes Si, the crystal orientation of the grains thereof closely aligns in the Goss orientation (cubic crystal {110}<001>), and the <001> orientation, which is a magnetization easy axis, is substantially aligned in the rolling direction in the steel sheet manufacturing process. Such a grain oriented electrical steel sheet is very desirable as a material for an iron core and the like of a transformer. One of important magnetic characteristics of the grain oriented electrical steel sheet is, for instance, magnetic flux density.

[0004] The magnetic flux density of the grain oriented electrical steel sheet when a predetermined magnetizing force is applied tends to increase as the degree to which the magnetization easy axes of the grains are aligned in the rolling direction of the steel sheet, that is, the orientation of the grains is higher. A magnetic flux density B 8 is generally used as an index representing the magnetic flux density. The magnetic flux density B 8 is a value of the magnetic flux density of the grain oriented electrical steel sheet excited at a magnetizing force of 800 A / m in the rolling direction. That is, the grain oriented electrical steel sheet having a larger value of the magnetic flux density B 8 is more easily magnetized with a certain magnetizing force, the magnetic flux density becomes high, and thus it is suitable for a small-sized and highly efficient transformer.

[0005] In the past, it has been proposed to control the grain growth in secondary recrystallization in order to obtain the steel sheet showing high magnetic flux density, as a method and the like. For instance, the patent documents 1 and 2 disclose a method in which the secondary recrystallization is proceeded while a thermal gradient is given to the steel sheet in a tip area of secondary recrystallized grain which is encroaching primary recrystallized grains in final annealing process.

[0006] When the secondary recrystallized grain is grown while the thermal gradient is given, the secondary recrystallized grain having the orientation close to the ideal Goss orientation is nucleated from the region where the secondary recrystallization is likely to start antecedently in the steel sheet, and the secondary recrystallized grain grows preferentially due to the thermal gradient. As a result, alignment degree to the Goss orientation increases and the magnetic flux density B 8 is improved.

[0007] However, when the secondary recrystallized grain is grown while the thermal gradient is given, the grain having the orientation close to the ideal Goss orientation may grow preferentially, but the secondary recrystallized grain may be excessively large. When the secondary recrystallized grain grows excessively, a deviation from the ideal Goss orientation increases in a tip area of growth of the secondary recrystallized grain, and the effect of improving the magnetic flux density may be restricted.

[0008] For instance, the secondary recrystallization in the steel sheet proceeds in a state of being coiled. In other words, the secondary recrystallized grain grows in a state where the steel sheet is under the condition with curvature. However, the secondary recrystallized grain while maintaining the linearity of the crystal orientation. When the secondary recrystallized grain grows larger, the deviation from the ideal Goss orientation increases in the tip area of growth of the secondary recrystallized grain due to the curvature of coil.

[0009] It is possible to represent the deviation between the actual crystal orientation and the ideal Goss orientation by a deviation angle α, a deviation angle β, and a deviation angle γ. The deviation angle α is an angle formed by the <001> direction of crystal projected on the rolled surface and the rolling direction L when viewing from the normal direction Z. The deviation angle β is an angle formed by the <001> direction of crystal projected on L cross section (cross section whose normal direction is the transverse direction) and the rolling direction L when viewing from the transverse direction C (width direction of sheet). The deviation angle γ is an angle formed by the <110> direction of crystal projected on C cross section (cross section whose normal direction is the rolling direction) and the normal direction Z when viewing from the rolling direction L.

[0010] It is known that, among these deviation angles α, β and γ, the deviation angles α and β affect the magnetic flux density. When the values of the deviation angles α and β are small, the magnetic flux density B 8 is improved.

[0011] In addition, it is known that, among the deviation angles α, β and γ, the deviation angle β affects magnetostriction. When the value of the deviation angle β is small, the magnetostriction is improved. Herein, the magnetostriction is a phenomenon in which a shape of magnetic material changes when magnetic field is applied. Since the magnetostriction causes vibration and noise, it is demanded to reduce the magnetostriction of the grain oriented electrical steel sheet utilized for a core of transformer and the like. For instance, the patent documents 3 to 5 disclose controlling the deviation angle β.Citation ListPatent Document

[0012] Patent Document 1: Japanese Unexamined Patent Application, First Publication No. S57-002839 Patent Document 2: Japanese Unexamined Patent Application, First Publication No. S61-190017 Patent Document 3: Japanese Unexamined Patent Application, First Publication No. 2001-294996 Patent Document 4: Japanese Unexamined Patent Application, First Publication No. 2005-240102 Patent Document 5: Japanese Unexamined Patent Application, First Publication No. 2015-206114 SUMMARY OF INVENTIONTechnical Problem

[0013] As described above, it has been tried to improve the magnetic flux density of the grain oriented electrical steel sheet. For instance, it has been tried to increase the alignment degree to the Goss orientation by proceeding the secondary recrystallization while the thermal gradient is given to the steel sheet, and thereby, to improve the magnetic flux density.

[0014] However, when the secondary recrystallized grain is grown while the thermal gradient is given, the secondary recrystallized grain is excessively large, and thereby, it is inevitable that the deviation from the ideal Goss orientation increases. Thus, the effect of improving the magnetic flux density may be restricted. Moreover, the magnetostriction may be deteriorated.

[0015] The present invention has been made in consideration of the above-mentioned situations. An object of the present invention is to provide a grain oriented electrical steel sheet excellent in the magnetic flux density and the magnetostriction. Specifically, an object is to provide a grain oriented electrical steel sheet excellent in both the magnetic flux density and the magnetostriction even if the technique in which the secondary recrystallization is proceeded while the thermal gradient is given to the steel sheet is applied.Solution to Problem

[0016] An aspect of the present invention employs the following. [1] A grain oriented electrical steel sheet according to an aspect of the present invention, wherein when a deviation angle from an ideal Goss orientation based on a rotation axis parallel to a normal direction Z is defined as α, when a deviation angle from the ideal Goss orientation based on a rotation axis parallel to a transverse direction C is defined as β, when a deviation angle from the ideal Goss orientation based on a rotation axis parallel to a rolling direction L is defined as γ, when a deviation angle of a crystal orientation measured at one measurement point on a sheet surface is represented as (α β γ), when an angular deviation at the measurement point is defined as ϕ = (α 2< + β 2< ) 1 / 2< , and when an average of the angular deviation ϕ obtained from plural measurement points with spacing of 1 mm in the rolling direction L is defined as aveϕ L , the aveϕ L satisfies aveϕ L ≤ 3.5°, when deviation angles of crystal orientations measured at two measurement points which are adjacent on the sheet surface and which have spacing of 1 mm are represented as (α 1 β 1 γ 1 ) and (α 2 β 2 γ 2 ), when a midpoint of two measurement points which satisfy [(α 2 - α 1 ) 2< + (β 2 - β 1 ) 2< + (γ 2 - γ 1 ) 2< ] 1 / 2< ≥ 1.0° is defined as a grain boundary GB, when a grain size in the rolling direction L obtained based on the grain boundary GB is defined as D L in units of mm, and when a grain size which is at 10% by number base from largest in a case where the grain sizes D L obtained in the rolling direction L are sorted from largest to smallest is defined as D L 10 in units of mm, the D L 10 satisfies D L 10 ≤ 100 - 15 × aveϕ L , and when a grain size in the transverse direction C obtained based on the grain boundary GB is defined as D C in units of mm, and when an average of the grain size D C obtained in the transverse direction C is defined as aveD C , the aveD C satisfies aveD C ≥ 50. Advantageous Effects of Invention

[0017] According to the above aspects of the present invention, it is possible to provide a grain oriented electrical steel sheet excellent in a magnetic flux density and a magnetostriction. Specifically, it is possible to provide the grain oriented electrical steel sheet excellent in both the magnetic flux density and the magnetostriction even if the technique in which the secondary recrystallization is proceeded while the thermal gradient is given to the steel sheet is applied.BRIEF DESCRIPTION OF DRAWINGS

[0018] [FIG. 1] A schema illustrating an instance of using spot electric heating as a local rapid heating method and illustrating an instance of arrangement of a local heating affected region in a decarburization-annealed steel sheet. [FIG. 2] A schema illustrating a distribution of Goss-oriented grains of a decarburization-annealed steel sheet. DESCRIPTION OF EMBODIMENTS

[0019] Hereinafter, a preferred embodiment of the present invention is described in detail. However, the present invention is not limited only to the configuration which is disclosed in the present embodiment, and various modifications are possible without departing from the aspect of the present invention. In addition, the limitation range as described below includes a lower limit and an upper limit thereof. However, the value represented by "more than" or "less than" does not include in the limitation range. Unless otherwise noted, "%" of the chemical composition represents "mass%".

[0020] A grain oriented electrical steel sheet (base steel sheet) according to the present embodiment, wherein when a deviation angle from an ideal Goss orientation based on a rotation axis parallel to a normal direction Z is defined as α, when a deviation angle from the ideal Goss orientation based on a rotation axis parallel to a transverse direction C is defined as β, when a deviation angle from the ideal Goss orientation based on a rotation axis parallel to a rolling direction L is defined as γ, when a deviation angle of a crystal orientation measured at one measurement point on a sheet surface is represented as (α β γ), when an angular deviation at the measurement point is defined as ϕ = (α 2< + β 2< ) 1 / 2< , and when an average of the angular deviation ϕ obtained from plural measurement points with spacing of 1 mm in the rolling direction L is defined as aveϕ L , the aveϕ L satisfies aveϕ L ≤ 3.5°.

[0021] In addition, a grain oriented electrical steel sheet (base steel sheet) according to the present embodiment, wherein when deviation angles of crystal orientations measured at two measurement points which are adjacent on the sheet surface and which have spacing of 1 mm are represented as (α 1 β 1 γ 1 ) and (α 2 β 2 γ 2 ), when a midpoint of two measurement points which satisfy [(α 2 - α 1 ) 2< + (β 2 - β 1 ) 2< + (γ 2 - γ 1 ) 2< ] 1 / 2< ≥ 1.0° is defined as a grain boundary GB, when a grain size in the rolling direction L obtained based on the grain boundary GB is defined as D L in units of mm, and when a grain size which is at 10% by number base from largest in a case where the grain sizes D L obtained in the rolling direction L are sorted from largest to smallest is defined as D L 10 in units of mm, the D L 10 satisfies D L 10 ≤ 100 - 15 × aveϕ L .

[0022] In addition, a grain oriented electrical steel sheet (base steel sheet) according to the present embodiment, wherein when a grain size in the transverse direction C obtained based on the grain boundary GB is defined as D C in units of mm, and when an average of the grain size D C obtained in the transverse direction C is defined as aveD C , the aveD C satisfies aveD C ≥ 50.

[0023] In the grain oriented electrical steel sheet according to the present embodiment, in a case where all of the above features are simultaneously satisfied, it is possible to improve both the magnetic flux density and the magnetostriction even if the technique in which the secondary recrystallization is proceeded while the thermal gradient is given to the steel sheet is applied.

[0024] In addition, in the present embodiment, the angular deviation ϕ is defined using the deviation angle α and the deviation angle β. The general angular deviation θ is often evaluated using three components: the deviation angle α, the deviation angle β, and the deviation angle γ. However, in the present embodiment, the angular deviation ϕ is defined using two components: the deviation angle α and the deviation angle β except for the deviation angle γ which does not significantly influence the magnetic flux density and the magnetostriction. It is possible to obtain the above effects by satisfying the above features using the angular deviation ϕ. On the other hand, the grain boundary and the grain size may be determined using three components: the deviation angle α, the deviation angle β, and the deviation angle γ.

[0025] The fact that the above aveφ L is 3.5° or less indicates that the angular deviation ϕ is averagely small at the measurement points along the rolling direction L. That is, it indicates that the angular deviation between the rolling direction L and the direction of the magnetization easy axis is small. As a result, the magnetic characteristics, particularly the magnetic flux density, are favorably improved. The aveϕ L is preferably 3.2° or less, more preferably 3.0° or less, and still more preferably 2.7° or less. On the other hand, since the aveϕ L is preferably as small as possible, a lower limit thereof is not particularly limited. However, since it is not easy to industrially control aveϕ L to zero, for instance, the aveϕ L may be 0.5° or more, and may be 1.0° or more.

[0026] The fact that the above D L 10 is (100 - 15 × aveϕ L ) or less in units of mm indicates that the grains do not grow coarsely in the rolling direction L. When the grains do not grow coarsely in the rolling direction L, it is possible to suppress an increase in the above deviation angles, particularly the deviation angle β. When the increase in the deviation angle β is suppressed, a decrease in the magnetic flux density is suppressed, and an increase in the magnetostriction is suppressed. When the D L 10 satisfies the above condition, the magnetic flux density and the magnetostriction are favorably improved. The D L 10 is preferably (90 - 15 × aveϕ L ) or less in units of mm, and more preferably (80 - 15 × aveϕ L ) or less in units of mm. On the other hand, since the D L 10 is preferably as small as possible, a lower limit thereof is not particularly limited. For instance, the D L 10 may be 5 mm or more, and may be 10 mm or more.

[0027] The fact that the aveD C is 50 mm or more indicates that a shape of the grain is elongated to the transverse direction C. The grain oriented electrical steel sheet according to the present embodiment is based on the premise that the technique in which the secondary recrystallization is proceeded while the thermal gradient is given to the steel sheet is applied. Thus, the secondary recrystallized grains tend to be grown coarsely. However, in the embodiment, it is suppressed to coarsely grow the grains in the rolling direction L as explained above. On the other hand, in the embodiment, it is allowed to coarsely grow the grains in the transverse direction C. In the grain oriented electrical steel sheet according to the present embodiment, since the technique in which the secondary recrystallization is proceeded while the thermal gradient is given to the steel sheet is applied, the secondary recrystallized grains tend to be grown coarsely, and the aveDc becomes 50 mm or more. The aveDc is preferably 80 mm or more, more preferably 100 mm or more, and still more preferably 200 mm or more. On the other hand, an upper limit of the aveD C is not particularly limited. For instance, the grain size in the transverse direction C may be coil width (for instance, width of 1000mm). The aveD C may be 800 mm or less, and 500 mm or less.

[0028] For the deviation angle α, the deviation angle β, the deviation angle γ, and the like explained above, a measurement line including at least 500 measurement points with 1 mm spacing on the rolled surface is arranged, and the crystal orientations may be measured. For instance, the crystal orientation may be measured by the X-ray diffraction method (Laue method). The Laue method is the method such that X-ray beam is irradiated the steel sheet with and that the diffraction spots which are transmitted or reflected are analyzed. By analyzing the diffraction spots, it is possible to identify the crystal orientation at the point irradiated with X-ray beam. Moreover, by changing the irradiated point and by analyzing the diffraction spots in plural points, it is possible to obtain the distribution of the crystal orientation based on each irradiated point. The Laue method is the preferred method for identifying the crystal orientation of the metallographic structure in which the grains are coarse.

[0029] The measurement points for the crystal orientation may be at least 500 points. It is preferable that the number of measurement points appropriately increases depending on the grain size of the secondary recrystallized grain. For instance, when the number of secondary recrystallized grains included in the measurement line is less than 10 grains in a case where the number of measurement points for identifying the crystal orientation is 500 points, it is preferable to extend the above measurement line by increasing the measurement points with 1 mm spacing so as to include 10 grains or more of the secondary recrystallized grains in the measurement line. Moreover, when it is difficult to arrange 500 measurement points in one measurement line, plural measurement lines may be arranged in order to measure the crystal orientation at the measurement points of 500 or more in total.

[0030] The crystal orientations are identified at each measurement point with 1 mm spacing on the rolled surface, and then, the deviation angle α, the deviation angle β, and the deviation angle γ are identified at each measurement point. Based on the identified deviation angles at each measurement point, the angular deviation ϕ, the aveϕ L , the grain boundary GB, the grain size D L , the D L 10, the grain size D C , and the aveD C may be obtained. Herein, the D L 10 may be obtained as the grain size which is at 10% by number base from largest in a case where the grains with the grain size D L of 2 mm or more are sorted from largest to smallest. The aveD C may be obtained as the average grain size of the grains with the grain size D C of 2 mm or more. Moreover, in a case where it is difficult to judge which grain the X-ray diffraction results come from because the irradiated region of X-ray beam spreads over two grains at the measurement point for the crystal orientation by Laue method, 0.5 mm may be respectively added to the grain size of these two grains.

[0031] In addition, the grain oriented electrical steel sheet according to the present embodiment may have the following chemical composition.

[0032] The grain oriented electrical steel sheet according to the present embodiment may contain, as a chemical composition, Si: 2.0% to 7.0% in mass percentage and the balance consisting of Fe and impurities.

[0033] In addition, this grain oriented electrical steel sheet may contain a known optional element as substitution for part of Fe for improving the magnetic characteristics. A lower limit of the optional element does not need to be limited, and the lower limit may be 0%. Moreover, an upper limit of the optional element may be a value in which the magnetic flux density or the iron loss does not significantly deteriorate. For instance, the upper limit of each optional element is described below.

[0034] The grain oriented electrical steel sheet according to the present embodiment (base steel sheet) may contain, as a chemical composition, by mass%: Si: 2.0 to 7.0%, C: 0 to 0.0050%, Mn: 0 to 1.0%, S and Se: 0 to 0.0150% in total, Al: 0 to 0.0650%, N: 0 to 0.0050%, Nb, V, Mo, Ta, and W: 0 to 0.050% in total, Cu: 0 to 0.40%, Bi: 0 to 0.010%, B: 0 to 0.080%, P: 0 to 0.50%, Ti: 0 to 0.0150%, Sn: 0 to 0.10%, Sb: 0 to 0.10%, Cr: 0 to 0.30%, Ni: 0 to 1.0%, and the balance consisting of Fe and impurities. Si: 2.0 to 7.0%

[0035] Si (silicon) is a basic element for the base steel sheet. When the Si content is less than 2.0%, the eddy-current loss cannot be sufficiently reduced, so that favorable magnetic characteristics cannot be obtained. Therefore, the Si content of the base steel sheet is 2.0% or more. The Si content is preferably 2.50% or more, and more preferably 3.0% or more. On the other hand, when the Si content is more than 7.0%, the steel sheet is embrittled, and the passability is remarkably deteriorated during manufacture, and thus the Si content of the base steel sheet is 7.0% or less. The Si content is preferably 4.50% or less, and more preferably 4.0% or less.C: 0 to 0.0050%

[0036] C (carbon) is an optional element for the base steel sheet. C is contained in a steel piece (slab), but when C excessively remains in the base steel sheet after the final annealing, favorable iron loss characteristics may not be obtained. Therefore, the C content of the base steel sheet may be 0.0050% or less. The C content is preferably 0.0040% or less, and more preferably 0.0030% or less. On the other hand, the lower limit of the C content of the base steel sheet is not particularly limited, and it may be 0%. However, since it is not industrially easy to control the C content to 0%, the C content may be more than 0% or 0.00010% or more.Mn: 0 to 1.0%

[0037] Mn (manganese) is a basic element for the base steel sheet. Although Mn is contained in the steel piece (slab), when the content is excessive, the phase of steel are transformed during secondary recrystallization annealing, the secondary recrystallization does not sufficiently proceed, and favorable magnetic characteristics cannot be obtained. Thus, the Mn content of the base steel sheet may be 1.0% or less. The Mn content is preferably 0.50% or less, and more preferably 0.20% or less. On the other hand, the lower limit of the Mn content of the base steel sheet is not particularly limited, and it may be 0%. However, since Mn forms MnS and / or MnSe which act as the inhibitor, the Mn content may be more than 0% or 0.00010% or more.S and Se: 0 to 0.0150% in total

[0038] S (sulfur) and Se (selenium) are optional elements for the base steel sheet. S and Se are contained in a steel piece (slab), but when S and Se excessively remain in the base steel sheet after the final annealing, magnetic characteristics may be adversely affected. Therefore, the total amount of S and Se of the base steel sheet may be 0.0150% or less. The total amount of S and Se is preferably 0.010% or less, and more preferably 0.0050% or less. On the other hand, the lower limit of the total amount of S and Se of the base steel sheet is not particularly limited, and it may be 0%. However, since S and Se form MnS or MnSe and have an effect as an inhibitor at the time of secondary recrystallization, the total amount of S and Se may be more than 0% or 0.00010% or more.Al: 0 to 0.0650%

[0039] Al (aluminum) (sol.Al) is an optional element for the base steel sheet. Al is contained in a steel piece (slab), but when Al excessively remains in the base steel sheet after the final annealing, magnetic characteristics may be adversely affected. Therefore, the Al content of the base steel sheet may be 0.0650% or less. The Al content is preferably 0.040% or less, and more preferably 0.035% or less. On the other hand, the lower limit of the Al content of the base steel sheet is not particularly limited, and it may be 0%. However, since Al forms AlN and has an effect as an inhibitor at the time of secondary recrystallization, the Al content may be more than 0% or 0.00010% or more. Herein, the above Al content expresses acid-soluble Al (sol.Al).N: 0 to 0.0050%

[0040] N (nitrogen) is an optional element for the base steel sheet. N is contained in a steel piece (slab), but when N excessively remains in the base steel sheet after the final annealing, magnetic characteristics may be adversely affected. Therefore, the N content of the base steel sheet may be 0.0050% or less. The N content is preferably 0.0040% or less, and more preferably 0.0030% or less. On the other hand, the lower limit of the N content of the base steel sheet is not particularly limited, and it may be 0%. However, since N forms AlN and has an effect as an inhibitor at the time of secondary recrystallization, the N content may be more than 0% or 0.00010% or more.Nb, V, Mo, Ta, and W: 0 to 0.050% in total

[0041] Nb (niobium), V (vanadium), Mo (molybdenum), Ta (tantalum), and W (tungsten) are optional elements for the base steel sheet. The Nb group element (at least one of Nb, V, Mo, Ta, and W) excessively remains in the base steel sheet, magnetic characteristics may be adversely affected. Therefore, the total amount of Nb, V, Mo, Ta, and W of the base steel sheet may be 0.050% or less. The Nb group element is preferably 0.030% or less, more preferably 0.020% or less, and still more preferably 0.010% or less. On the other hand, the total amount of Nb, V, Mo, Ta, and W of the base steel sheet is not particularly limited, and it may be 0%. However, since Nb, V, Mo, Ta, or W forms carbides, nitrides, or carbonitrides and has an effect as an inhibitor at the time of secondary recrystallization, the total amount of Nb, V, Mo, Ta, and W may be more than 0% or 0.003% or more.Cu: 0 to 0.40%

[0042] Cu (copper) is an optional element for the base steel sheet. When the Cu content exceeds 0.40%, the steel sheet may be embrittled during hot rolling. Therefore, the Cu content of the base steel sheet may be 0.40% or less. The Cu content is preferably 0.30% or less, and more preferably 0.10% or less. On the other hand, the lower limit of the Cu content is not particularly limited, and it may be 0%. However, since Cu has an effect of improving magnetic characteristics by increasing the development degree of the Goss orientation, the Cu content may be more than 0% or 0.010% or more.Bi: 0 to 0.010%

[0043] Bi (bismuth) is an optional element for the base steel sheet. When the Bi content is more than 0.010%, the coating adhesion may be deteriorated. In addition, when the purification at the time of the final annealing is insufficient and Bi remains excessively, the magnetic characteristics may be adversely affected. Therefore, the Bi content of the base steel sheet may be 0.010% or less. The Bi content is preferably 0.0050% or less, more preferably 0.0020% or less, and still more preferably 0.0010% or less. On the other hand, the lower limit of the Bi content is not particularly limited, and it may be 0%. However, since Bi has an effect of improving magnetic characteristics, the Bi content may be more than 0% or 0.00050% or more.B: 0 to 0.080%

[0044] B (boron) is an optional element for the base steel sheet. When the B content exceeds 0.080%, The dispersion (standard deviation) of the magnetic flux density may increase. Thus, the B content may be 0.080% or less. The B content is preferably 0.070% or less, and more preferably 0.060% or less. On the other hand, the lower limit of the B content is not particularly limited, and it may be 0%. However, since B forms nitrides and has an effect as an inhibitor at the time of secondary recrystallization, the B content may be more than 0% or 0.00050% or more.P: 0 to 0.50%

[0045] P (phosphorus) is an optional element for the base steel sheet. When the P content exceeds 0.50%, the workability of the steel sheet may be significantly deteriorated. Therefore, the P content of the base steel sheet may be 0.50% or less. The P content is preferably 0.30% or less, and more preferably 0.10% or less. On the other hand, the lower limit of the P content is not particularly limited, and it may be 0%. However, since P has an effect of improving the texture and improving the magnetic characteristics of the steel sheet, the P content may be more than 0% or 0.0020% or more.Ti: 0 to 0.0150%

[0046] Ti (titanium) is an optional element for the base steel sheet. When the Ti content exceeds 0.0150%, the magnetic characteristics may be significantly deteriorated. Therefore, the Ti content of the base steel sheet may be 0.0150% or less. The Ti content is preferably 0.0130% or less, and more preferably 0.010% or less. On the other hand, the lower limit of the Ti content is not particularly limited, and it may be 0%. However, since Ti forms carbides, nitrides, or carbonitrides and has an effect as an inhibitor at the time of secondary recrystallization, the Ti content may be more than 0% or 0.0020% or more.Sn: 0 to 0.10%

[0047] Sn (tin) is an optional element for the base steel sheet. When the Sn content is more than 0.10%, secondary recrystallization may become unstable, and magnetic characteristics may be adversely affected. Therefore, the Sn content of the base steel sheet may be 0.10% or less. The Sn content is preferably 0.090% or less, and more preferably 0.080% or less. On the other hand, the lower limit of the Sn content is not particularly limited, and it may be 0%. However, since Sn has an effect of improving magnetic characteristics by increasing the development degree of the Goss orientation, the Sn content may be more than 0% or 0.0050% or more.Sb: 0 to 0.10%

[0048] Sb (antimony) is an optional element for the base steel sheet. When the Sb content is more than 0.10%, magnetic characteristics may be adversely affected. Therefore, the Sb content of the base steel sheet may be 0.10% or less. The Sb content is preferably 0.090% or less, and more preferably 0.080% or less. On the other hand, the lower limit of the Sb content is not particularly limited, and it may be 0%. However, since Sb functions as an inhibitor and has an effect of stabilizing secondary recrystallization, the Sb content may be more than 0% or 0.010% or more.Cr: 0 to 0.30%

[0049] Cr (chromium) is an optional element for the base steel sheet. When the Cr content is more than 0.30%, a Cr oxide is formed, and magnetic characteristics may be adversely affected. Therefore, the Cr content of the base steel sheet may be 0.30% or less. The Cr content is preferably 0.20% or less, and more preferably 0.10% or less. On the other hand, the lower limit of the Cr content is not particularly limited, and it may be 0%. However, since Cr has an effect of improving magnetic characteristics by increasing the development degree of the Goss orientation, the Cr content may be more than 0% or 0.010% or more.Ni: 0 to 1.0%

[0050] Ni (nickel) is an optional element for the base steel sheet. When the Ni content is more than 1.0%, secondary recrystallization may become unstable. Therefore, the Ni content of the base steel sheet may be 1.0% or less. The Ni content is preferably 0.20% or less, and more preferably 0.10% or less. On the other hand, the lower limit of the Ni content is not particularly limited, and it may be 0%. However, since Ni has an effect of reducing the iron loss by increasing the electric resistance, the Ni: content may be more than 0% or 0.010% or more.

[0051] The base steel sheet of the grain oriented electrical steel sheet according to the present embodiment may contain impurities. Herein, the impurities correspond to elements which are contaminated during industrial manufacture of steel from ores and scrap that are used as a raw material of steel, or from environment of a manufacturing process.

[0052] The chemical composition of the base steel sheet described above may be measured by a general analysis method. For instance, the chemical composition may be measured by using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometer: inductively coupled plasma emission spectroscopy spectrometry). Herein, the acid soluble Al may be measured by ICP-AES using filtrate after heating and dissolving the sample in acid. In addition, C and S may be measured by the infrared absorption method after combustion, N may be measured by the thermal conductometric method after fusion in a current of inert gas, and O may be measured by, for instance, the non-dispersive infrared absorption method after fusion in a current of inert gas.

[0053] Herein, the chemical composition is a component of the base steel sheet. When the grain oriented electrical steel sheet, which is a measurement sample, includes an insulation coating or the like on the surface, the chemical composition is measured after removing the coating or the like by the method described below.

[0054] For instance, as a method for removing the insulation coating, the grain oriented electrical steel sheet with the coating may be immersed in hot alkaline solution. Specifically, it is possible to remove the insulation coating from the grain oriented electrical steel sheet by immersing the steel sheet in sodium hydroxide aqueous solution which includes 30 to 50 mass% of NaOH and 50 to 70 mass% of H 2 O at 80 to 90°C for 5 to 10 minutes, washing it with water, and then, drying it. Moreover, the immersing time in sodium hydroxide aqueous solution may be adjusted depending on the thickness of the insulation coating.

[0055] Moreover, as a method for removing a forsterite film (glass film), the grain oriented electrical steel sheet in which the insulation coating is removed by the above method may be immersed in hot hydrochloric acid. Specifically, it is possible to remove the forsterite film by previously investigating the preferred concentration of hydrochloric acid for removing the forsterite film to be dissolved, immersing the steel sheet in the hydrochloric acid with the above concentration (for instance, 30 to 40 mass% of HCl) at 80 to 90°C for 1 to 5 minutes, washing it with water, and then, drying it. In general, film and coating are removed by selectively using the solution, for example, the alkaline solution is used for removing the insulation coating, and the hydrochloric acid is used for removing the forsterite film.

[0056] Hereinafter, the background leading to the grain oriented electrical steel sheet according to the present embodiment will be described.

[0057] The existence frequency of practical Goss-oriented grains having small angular deviation θ and small angular deviation ϕ from the {110}<001> orientation which is the ideal Goss orientation increases as the heating rate of the primary annealing (decarburization annealing) increases. On the other hand, for the grains of the {778}<447> (≈{111}<112>) orientation, the {411 }<148> orientation, and the like which have a Σ9 coincidence site lattice relationship with the Goss orientation and tend to be encroached by Goss-oriented grains (referred to as CSL oriented grains), the existence frequency conversely decreases as the heating rate of the primary annealing increases. Therefore, it was difficult to increase the fraction of the CSL oriented grains while increasing the fraction of the practical Goss-oriented grains by the primary annealing.

[0058] In the present embodiment, it has been found for the first time that a grain oriented electrical steel sheet having exceptional quality is obtained by performing local rapid heating on a cold steel sheet to form a locally heated region, controlling annealing conditions of primary annealing (decarburization annealing), and controlling annealing conditions of secondary annealing (final annealing).

[0059] The locally heated region that forms before the primary annealing is arranged locally on the surface of the steel sheet. The crystal structure of the locally heated region includes one or both of the recrystallized structure and the recovered structure at the end of the local rapid heating. The crystal structure of a non-rapidly heated region other than the locally heated region on the sheet surface consists of a cold-deformed structure which is as-cold rolled.

[0060] In the local rapid heating, the heating rate is preferably 500 °C / sec or more, preferably 2000 °C / sec or more, and more preferably 10000 °C / sec or more. As described above, it has been found that, when the primary annealing is performed on the steel sheet after the locally heated region is formed on the surface of the steel sheet before the primary annealing, a large number of grains having the practical Goss orientation are formed in a region thermally affected by the local rapid heating (local heating affected region). In addition, it has become clear that, among the Goss-oriented grains to be formed, the fraction of the Goss-oriented grains having small angular deviation θ and small angular deviation ϕ from the ideal Goss orientation is increased, and the grain size of the Goss-oriented grains after the primary annealing is increased.

[0061] The frequency of coarse Goss-oriented grains included in the local heating affected region is higher than the frequency obtained by normal rapid heating of the entire sheet. This feature is considered to be derived from the deformed structure which includes a large amount of residual strain in the peripheral region of the locally heated region. Specifically, in a case where the local rapid heating is performed, the practical Goss-oriented grains formed in the locally heated region preferentially encroach on the non-recrystallization region that is a peripheral region and that includes a large amount of residual strain to coarsen the size during primary annealing. On the other hand, in a case where the normal heating of the entire steel sheet is performed, the initiation and growth of recrystallized grains occur uniformly in the steel sheet, and thus, coarsening explained above seems to hardly occur.

[0062] The local heating affected region having the above feature is dispersedly arranged on the surface of the steel sheet by primary annealing, and then secondary annealing is further performed. In the secondary annealing, the secondary recrystallization is proceeded while the thermal gradient is given to the steel sheet. At the time, the Goss-oriented grains formed in the local heating affected region preferentially grow during secondary annealing. A large number of Goss-oriented grains are formed in the local heating affected region, and among them, the Goss-oriented grains that are close to the ideal Goss orientation, have particularly small angular deviation θ and small angular deviation ϕ, and have a large grain size after primary annealing are included. In the secondary recrystallization, the above Goss-oriented grains among the grains grow preferentially.

[0063] Herein, since the Goss-oriented grains which act as the nucleus of the secondary recrystallization are arranged in the local heating affected region, it is not necessary to form the Goss-oriented grains by the primary annealing in a matrix region other than the local heating affected region, that is, a local heating non-affected region. Accordingly, as the heat treatment condition of the primary annealing, a mild heating condition with a low heating rate may be employed, and a primary annealing condition may be employed in which a large number of CSL oriented grains having the {111}<112> orientation and the {411 }<148> orientation, which are easily encroached, are formed in the local heating non-affected region. For instance, by controlling the heating rate of the primary annealing to 300 °C / sec or less, a large number of Goss-oriented grains close to the ideal Goss orientation and having large grain size are formed in the local heating affected region, while Goss-oriented grains are hardly formed in the local heating non-affected region, and conversely, a large number of CSL oriented grains are formed.

[0064] As described above, in the local heating affected region of the steel sheet (decarburization-annealed steel sheet) in which the local rapid heating and the primary annealing have been completed, a large number of Goss-oriented grains close to the ideal Goss orientation and having large grain size are included. On the other hand, in the matrix region (local heating non-affected region), the Goss-oriented grains having large size are hardly included, whereas a large number of CSL oriented grains that are easily encroached may be included.

[0065] When the above steel sheet (decarburization-annealed steel sheet) is subjected to secondary annealing, Goss-oriented grains that are included in the local heating affected region, are close to the ideal Goss orientation, and have large grain size initiate to grow preferentially and grow toward the local heating non-affected region.

[0066] Moreover, in the present embodiment, the secondary recrystallization is proceeded while giving the thermal gradient to the steel sheet in a tip area of secondary recrystallized grain which is encroaching primary recrystallized grains in secondary annealing. When the secondary recrystallized grains are grown using the thermal gradient, the secondary recrystallized grains having the orientation close to the ideal Goss orientation are nucleated from the area where the secondary recrystallization is likely to start antecedently in the steel sheet, and the secondary recrystallized grains grow preferentially due to the thermal gradient. As a result, the alignment degree to the Goss orientation is favorably increased. The direction to give the above thermal gradient may be the transverse direction C.

[0067] Conventionally, in a case where the secondary recrystallized grain is grown while the thermal gradient is given, the secondary recrystallized grains are excessively large, and thus, it is unavoidable that the deviation angle β deteriorates due to a coil set. Specifically, in a case where the thermal gradient during secondary recrystallization is given in the transverse direction C for instance, the secondary recrystallized Goss-oriented grains tend to grow toward an area where the temperature of steel sheet is low (toward the transverse direction C), but the secondary recrystallized grains also grow toward the rolling direction L at the time. Thus, the grain size D L in the rolling direction also becomes large. That is, in the conventional technique, the grain size D L in the rolling direction inescapably becomes large when trying to increase the magnetic flux density, and as a result, it is unavoidable that the deviation angle β is increased due to the coil set. However, in the present embodiment, since it is possible to increase the existence frequency of the secondary recrystallized grains close to the ideal Goss orientation by the above local rapid heating, it is possible to suppress the increase in the grain size D L in the rolling direction, and it is possible to suppress the deterioration of the deviation angle β due to the coil set. As explained above, in the present embodiment, the deterioration of the deviation angle β is suppressed, and thus, it is possible to obtain the steel sheet excellent in the magnetic flux density and the magnetostriction as compared with the conventional technique. In addition, in the present embodiment, the secondary recrystallized grains having the orientation close to the ideal Goss orientation are preferentially formed, and thus, it is possible to also suppress the deterioration of the deviation angle α. Therefore, it is possible to obtain the steel sheet excellent in the magnetic flux density as compared with the conventional technique.

[0068] Hereinafter, the investigations carried out by the present inventors will be described in detail.

[0069] As an aspect of the above local rapid heating, a case where spot electric heating by electric resistance heating is used will be described. In the spot electric heating, spot electrodes are arranged and contacted so as to be opposite to each other on both surfaces of the steel sheet, and a current flows between the spot electrodes to perform the spot electric heating on a region where the electrodes are held on the steel sheet. Steel having the composition indicated in Table 1 was used, and hot rolling and cold rolling were performed to obtain a cold-rolled steel sheet having a thickness of 0.22 mm. The steel sheet was subjected to the spot electric heating. The spot electric heating was performed using copper electrodes having a diameter of 3 mm under the conditions of a flowing current of 5.0 kA or less which was a range where the sheet surface was not melted, a time of current flow of 20 to 80 milliseconds, an electrode force of 50 to 150 kgf, and an electrode retention time after current flow of 0.2 seconds. On the surface of the cold-rolled steel sheet, the spot electric heating was performed by a pitch of 20 mm in the rolling direction at a position of 10 mm from an edge in the transverse direction of the cold rolled steel sheet in order to form the locally heated region. This cold-rolled steel sheet was subjected to decarburization annealing (primary annealing). In the decarburization annealing, the cold-rolled steel sheet was heated at a heating rate of 20 °C / sec and held at 830°C for 90 seconds.

[0070] FIG. 1 illustrates an instance of arrangement of the local heating affected region in the decarburization-annealed steel sheet manufactured by the above conditions. In FIG. 1, the decarburization-annealed steel sheet 1, the local heating affected regions 2, the rolling direction 21, and the width direction (transverse direction) 22 are schematically illustrated. [Table 1]CHEMICAL COMPOSITION (mass%)CSiMnSAlN0.063. 350.10.0070.0270.008

[0071] In order to prepare an observed section for Electron Back Scattering Diffraction pattern (EBSD) from the surface of a decarburization-annealed steel sheet (steel sheet after local rapid heating and after primary annealing), a surface was smoothed by mechanical polishing, and electrolytic polishing was performed to remove added strain of the surface. Thereafter, an image quality (IQ) value and a crystal orientation in a region including the locally heated region were measured by the EBSD under condition of a step of 0.5 µm. FIG. 2 is a schema illustrating a distribution of the Goss-oriented grains of the decarburization-annealed steel sheet manufactured by the above conditions.

[0072] An electrode used for spot electric heating has a circular shape, and the diameter thereof is preferably 0.5 to 10 mmϕ, and more preferably 1 to 5 mmϕ in an equivalent circle diameter. Note that, in the above description, the electrode having the circular shape is used, but in so far as the heating rate of the cold-rolled steel sheet is locally increased and Goss-oriented grains are formed and grown in this region, the electrode shape may be another shape, for instance, an elliptical shape or a linear shape.

[0073] In FIG. 2, based on the definition of the angular deviation ϕ = (α 2< + β 2< ) 1 / 2< , grains having the angular deviation ϕ of 10° or less from the ideal Goss orientation (Goss-oriented grains 14) are indicated by "∘". Further, among the grains having the angular deviation ϕ of 10° or less, grains having a coarse grain size (coarse Goss-oriented grains 15) are indicated by "⊙". Note that the coarse Goss-oriented grains 15 indicate Goss-oriented grains having a grain size of 3 times or more as compared with an average grain size.

[0074] As illustrated in FIG. 2, the decarburization-annealed steel sheet 1 manufactured by the above conditions includes the Goss-oriented grains 14 and also includes the coarse Goss-oriented grains 15. In particular, the region including the coarse Goss-oriented grains 15 corresponds to the local heating affected region 2. Note that, although a locally heated region boundary 4 and a local heating affected region boundary 5 are schematically illustrated in FIG. 2, it is not easy to identify these boundaries by microstructure observation. However, the region including the coarse Goss-oriented grains 15 can be regarded as the local heating affected region 2.

[0075] The decarburization-annealed steel sheet was further subjected to nitridation, applying an annealing separator including MgO as a main component, and then secondary annealing. The secondary annealing conditions are a hydrogen-nitrogen atmosphere, a heating rate of 15°C / hr (°C / hour), and holding at 1200°C for 20hr (hour). Moreover, in the heating stage of the final annealing, the thermal gradient of 5 °C / cm in the transverse direction was given in a border area between primary recrystallized area and secondary recrystallized area in the steel sheet.

[0076] The obtained steel sheet was subjected to macroetching to reveal grain boundaries. When a region corresponding to the local heating affected region was observed in the steel sheet after the macroetching, it was observed that plural secondary recrystallized grains grew from the region corresponding to the local heating affected region or that the secondary recrystallized grain grew from the center of the region corresponding to the local heating affected region. In addition, in the region corresponding to the local heating affected region, fine grains of 2 mm or less may or may not be observed as a vestige of the local heating affected region. Although the secondary recrystallized macrostructure may slightly change depending on the condition of the local heating, the alignment degree of the Goss orientation can be increased as compared with the case where the local heat treatment is not performed.

[0077] Moreover, the crystal orientation of the obtained steel sheet was measured by the above Laue method. In the obtained steel sheet, aveϕ L was 3.5° or less, D L 10 was (100 - 15 × aveϕ L ) or less in units of mm, and aveD C was 50 mm or more. As a result, although the thermal gradient during secondary recrystallization was given to the steel sheet, the obtained steel sheet was excellent in both the magnetic flux density and the magnetostriction.

[0078] As explained above, it was confirmed for the obtained grain oriented electrical steel sheet that the deviation between the secondary recrystallized grains and the ideal Goss orientation was extremely small. Also, it was confirmed that the angular deviation ϕ was averagely small at each measurement point along the rolling direction L, the grains did not grow coarsely in the rolling direction L, and the grains tended to become the oblate shape which was elongated to the transverse direction C and which was compressed to the rolling direction L.

[0079] Based on the above investigation, it is considered that the fact that the coarse Goss-oriented grains which are close to the ideal Goss orientation and which have the size advantage are formed in the decarburization-annealed steel sheet results in improving the crystal orientation of the secondary recrystallized grains. Also, it is considered that the fact that the locally heated regions are favorably arranged before primary annealing, the annealing conditions of primary annealing are favorably controlled, and the annealing conditions of secondly annealing are favorably controlled results in improving both the magnetic flux density and the magnetostriction.

[0080] For instance, when the above decarburization-annealed steel sheet is used, the coarse Goss-oriented grains close to the ideal Goss orientation (Goss-oriented grains having the large grain size) are preferentially grown among a large number of Goss-oriented grains in the local heating affected region during secondary recrystallization. Therefore, it is possible to obtain the steel sheet occupied by the secondary recrystallized grains close to the ideal Goss orientation without coarsening the secondary recrystallized grains. For instance, at the time when the local heating affected regions are discretely arranged on the sheet surface, if the local heating affected regions are appropriately arranged on the sheet surface, it is possible to control the size, shape, and arrangement of the grains after the secondary annealing. For instance, the Goss-oriented grain initiates to grow from one local heating affected region, the grain growth stops when the grain encounters with another Goss-oriented grain which initiates to grow from an adjacent local heating affected region, and thereby, the grain size of the Goss-oriented grains after secondary recrystallization (especially, the grain size D L in the rolling direction) can be controlled to be small in the steel sheet. In particular, as described above, in the initial stage of the secondary annealing, the Goss-oriented grains preferentially grown from the local heating affected region have the crystal orientation close to the ideal Goss orientation, and as a result, excellent magnetic flux density can be obtained even though the secondary recrystallized grain size is small. Moreover, since the grains are suppressed to grow coarsely in the rolling direction L, it is suppressed to deteriorate the deviation angle β due to the coil set, and excellent magnetostriction is obtained.

[0081] That is, in the above grain oriented electrical steel sheet, it is possible to improve the alignment degree of the Goss orientation while suppressing coarsening of the secondary recrystallized grain size (especially, the grain size D L in the rolling direction), and thus, it is possible to omit or reduce the refinement of the width of magnetic domain by applying the strain or forming the grooves. Specifically, since the effect of the magnetic domain refinement can be preferably obtained by the grain boundaries that increase as a result of the refinement of the secondary recrystallized grain size, the magnetic domain is refined without applying the conventional magnetic domain control technique. Therefore, it is possible to omit or reduce the strain which is applied into the steel sheet contrary to the conventional magnetic domain control technique, and thus, it is possible to suppress an increase in the magnetostriction. In addition, it is possible to omit forming the grooves or to reduce the depth of grooves contrary to the conventional magnetic domain control technique, and thus, it is possible to suppress a decrease in the magnetic flux density B 8 . In addition, it is possible to use the above grain oriented electrical steel sheet for utilization requiring the strain relief annealing at 800°C or higher.

[0082] Moreover, as explained above, the effect of the magnetic domain refinement can be preferably obtained by the grain boundaries that increase as a result of the refinement of the secondary recrystallized grain size (especially, the grain size D L in the rolling direction), and thereby, the grain oriented electrical steel sheet according to the present embodiment shows excellent iron loss.

[0083] Next, a preferred method for manufacturing the grain oriented electrical steel sheet according to the present embodiment will be described.

[0084] The method for manufacturing the grain oriented electrical steel sheet according to the present embodiment is not limited to the following method. The following manufacturing method is an instance for manufacturing the grain oriented electrical steel sheet according to the present embodiment.

[0085] Moreover, the processes and the quantitative conditions in each process described below are an instance employed to confirm the operability of the present embodiment, so that the present embodiment is not limited to the processes and the quantitative values. The method for manufacturing the grain oriented electrical steel sheet according to the present embodiment can employ various types of conditions as long as the conditions do not depart from the scope of the present embodiment and can achieve the object of the present embodiment.

[0086] In the method for manufacturing the grain oriented electrical steel sheet according to the present embodiment, it is possible to apply a conventional known method for manufacturing the grain oriented electrical steel sheet as fundamental processes. For instance, the conventional method for manufacturing the grain oriented electrical steel sheet includes a manufacturing method utilizing MnS and AlN as inhibitor which are formed by high temperature slab heating, a manufacturing method utilizing AlN as inhibitor which is formed by low temperature slab heating and subsequent nitridation, and the like. The method for manufacturing the grain oriented electrical steel sheet according to the present embodiment is not limited to a specific manufacturing method. Hereinafter, the method which employs the low temperature slab heating with the nitridation is explained for instance.(Casting Process)

[0087] In the casting process, a slab is made. For instance, a method for making the slab is as follow. A molten steel is made (a steel is melted). The slab is made by using the molten steel. The slab may be made by continuous casting. An ingot may be made by using the molten steel, and then, the slab may be made by blooming the ingot. A thickness of the slab is not particularly limited. The thickness of the slab may be 150 to 350 mm for instance. The thickness of the slab is preferably 220 to 280 mm. The slab with the thickness of 10 to 70 mm which is a so-called thin slab may be used. When using the thin slab, it is possible to omit a rough rolling before final rolling in the hot rolling process.

[0088] For instance, as the chemical composition, the above slab may include the following elements.C: 0.085% or less

[0089] Carbon (C) is an element effective in controlling the primary recrystallized structure in the manufacturing process. However, when the content in the final product is excessive, the magnetic characteristics are negatively affected. Thus, the C content may be 0.085% or less. The upper limit of the C content is preferably 0.075%. C is decarburized and purified in the decarburization annealing process and the final annealing process, and then, the content becomes 0.005% or less. When C is included, the lower limit of the C content may be more than 0%, and may be 0.001% from the productivity standpoint in the industrial production.Si: 2.0 to 7.0%

[0090] Silicon (Si) is an element which increases the electric resistance of the grain oriented electrical steel sheet and thereby decreases the iron loss. When the Si content is less than 2.0%, an austenite transformation occurs during the final annealing and the crystal orientation of the grain oriented electrical steel sheet is impaired. On the other hand, when the Si content is more than 7.0%, the cold workability deteriorates and the cracks tend to occur during cold rolling. The lower limit of the Si content is preferably 2.5%, and is more preferably 3.0%. The upper limit of the Si content is preferably 4.5%, and is more preferably 4.0%.Mn: 0.05 to 1.00%

[0091] Manganese (Mn) forms MnS and / or MnSe by bonding to S and / or Se, which act as the inhibitor. When Mn is included and the Mn content is 0.05 to 1.00%, the secondary recrystallization becomes stable. The nitride of the Nb group element can bear part of the function of the inhibitor. In the case, the inhibitor intensity as MnS and / or MnSe in general is controlled weakly. Thus, the upper limit of the Mn content is preferably 0.50%, and is more preferably 0.20%.At least one of S and Se: 0.003 to 0.035% in total

[0092] Sulfur (S) and Selenium (Se) form MnS and / or MnSe by bonding to Mn, which act as the inhibitor. When at least one of S and Se is included, and when the total amount of S and Se is 0.003 to 0.035%, the secondary recrystallization becomes stable. The nitride of the Nb group element can bear part of the function of the inhibitor. In the case, the inhibitor intensity as MnS and / or MnSe in general is controlled weakly. Thus, the upper limit of the total amount of S and Se is preferably 0.025%, and is more preferably 0.010%. When S and / or Se remain in the steel after the final annealing, the compound is formed, and thereby, the iron loss is deteriorated. Thus, it is preferable to reduce S and Se as much as possible by the purification during the final annealing.

[0093] Here, the total amount of S and Se represents that at least one of S and Se is included and the amount thereof corresponds to the above total amount.Al: 0.010 to 0.065%

[0094] Aluminum (Al) forms (Al, Si)N by bonding to N, which acts as the inhibitor. When Al is included and the Al content is 0.010 to 0.065%, the inhibitor AlN formed by the nitridation mentioned below expands the temperature range of the secondary recrystallization, and the secondary recrystallization becomes stable especially in higher temperature range. Therefore, the Al content is 0.010 to 0.065%. The lower limit of the Al content is preferably 0.020%, and is more preferably 0.025%. The upper limit of the Al content is preferably 0.040%, and is more preferably 0.035% from the stability standpoint in the secondary recrystallization.N: 0.012% or less

[0095] Nitrogen (N) bonds to Al and acts as the inhibitor. The lower limit thereof is not limited because it is possible to include N by the nitridation in midstream of the manufacturing process. For instance, the lower limit of the N content may be more than 0% or may be 0.001%. When N is included and the N content is more than 0.012%, the blister which is a kind of defect tends to be formed in the steel sheet. The upper limit of the N content is preferably 0.010%, and is more preferably 0.009%. N is purified in the final annealing process, and then, the N content becomes 0.005% or less after the final annealing process.

[0096] The balance of the chemical composition consists of Fe and impurities. The impurities correspond to elements which are contaminated during industrial production of steel from ores and scrap that are used as a raw material of steel, or from environment of a manufacturing process. For instance, an upper limit of the impurities may be 5% in total.

[0097] In addition to solving manufacturing problems, in consideration of the influence on the magnetic characteristics and the improvement of the inhibitors function by forming compounds, the above chemical composition may include the known optional elements as substitution for part of Fe. For instance, the optional elements as substitution for part of Fe may be the following elements.Nb group element: 0.050% or less

[0098] The total amount of the Nb group element (at least one of Nb, V, Mo, Ta, and W) may be 0.050% or less. When the Nb group element (at least one of Nb, V, Mo, Ta, and W) is utilized as part of the inhibitor, and when the total amount of the Nb group element is 0.030% or less, the secondary recrystallization starts at appropriate timing, which is preferable. Moreover, the orientation of the formed secondary recrystallized grain becomes very favorable, and the microstructure is finally controlled to be favorable for the magnetization characteristics. In particular, Nb and Ta prominently shows the above effects, which is preferable. The lower limit of the total amount of the Nb group elements does not need to be limited, and the lower limit may be 0%. The lower limit is preferably 0.003%.

[0099] The total amount of the Nb group elements is more preferably 0.004 to 0.020%. The total amount is more preferably 0.005 to 0.010%.

[0100] Here, the total amount of the Nb group elements represents that at least one of Nb, V, Mo, Ta, and W is included and the amount thereof corresponds to the above total amount.

[0101] In addition, the slab may contain, as the optional element, by mass%, at least one of: Cu: 0.40% or less, Bi: 0.010% or less, B: 0.080% or less, P: 0.50% or less, Ti: 0.015% or less, Sn: 0.10% or less, Sb: 0.10% or less, Cr: 0.30% or less, and Ni: 1.00% or less.

[0102] The optional elements may be contained according to a known purpose, a lower limit of the optional elements does not need to be limited, and the lower limit may be 0%.

[0103] The chemical composition of the slab may be measured by the above analytical methods, as with the chemical composition of the grain oriented electrical steel sheet as the final product.(Hot Rolling Process)

[0104] In the hot rolling process, the slab is heated to a predetermined temperature (for instance, 1100 to 1400°C), and then, is subjected to hot rolling in order to obtain a hot rolled steel sheet. In the hot rolling process, for instance, the silicon steel material (slab) is heated in heating stage, is rough-rolled, and then, is final-rolled in order to obtain the hot rolled steel sheet with a predetermined thickness, for instance, 1.8 to 3.5 mm. After finishing the final rolling, the hot rolled steel sheet is coiled at a predetermined temperature.

[0105] In a case where of a process including the nitridation during decarburization annealing or after decarburization annealing, the inhibitor intensity as MnS is not necessarily needed, it is preferable that the slab heating temperature is 1100 to 1280°C from the productivity standpoint.(Hot-Band Annealing Process)

[0106] In the hot band annealing process, the hot rolled steel sheet after the hot rolling process is annealed under predetermined conditions (for instance, 750 to 1200°C for 30 seconds to 10 minutes) in order to obtain a hot band annealed sheet. The hot-band annealing is generally performed to control the microstructure of the steel sheet such as the recrystallization fraction, the residual strain, and the grain size by annealing the hot-rolled steel sheet after the hot rolling process and to preferably control the morphology of precipitates in the steel. For instance, in high temperature slab heating process, the above process is to finally control the morphology of precipitates such as AlN, and the conditions are controlled so that the precipitates are uniformly and finely precipitated. For instance, as the hot band annealing, the steel sheet may be heated to 1050°C to 1150°C, may be slow-cooled to an intermediate temperature (850°C to 950°C) for 50 to 150 seconds in order to appropriately precipitates A1N and the like, and thereafter, may be water-cooled.(Cold Rolling Process)

[0107] In the cold rolling process, the hot band annealed sheet after the hot band annealing process is cold-rolled once or is cold-rolled plural times (two times or more) with an annealing (intermediate annealing) (for instance, 80 to 95% of total cold reduction) in order to obtain a cold rolled steel sheet with a thickness, for instance, 0.10 to 0.50 mm. In order to improve the magnetic characteristics, for instance, an interpass temperature of the cold rolling may be approximately 100°C to 300°C.(Local Rapid Heating Process)

[0108] In the present embodiment, local rapid heating for forming the locally heated region is performed on the cold-rolled steel sheet after the cold rolling process. The rapid heating method is not particularly limited as long as the steel sheet can be locally heated. For instance, it is possible to adopt a method in which spot electrodes are arranged and contacted on both surfaces of the steel sheet and the steel sheet is heated by flowing a current in the steel sheet, a method in which the steel sheet is heated by irradiating the surface thereof with laser beam, electron beam, and the like, a method in which the steel sheet is locally heated by induction heating, a method in which the steel sheet is heated by contacting a heated piece, and the like. The size of each locally heated region may be a dotted region having a diameter of approximately 10 µm to 10 mm or a linear region having a width of approximately 10 µm to 10 mm. In addition, the electrode used for electric heating may be a circular electrode or a linear electrode as described above.

[0109] Note that regarding the size of the locally heated region, the minimum diameter and the minimum width depend on the shape of the spot electrode and the technique of reducing the focusing diameter of the laser beam or the electron beam. Although it is possible in principle to further reduce the size of the locally heated region, it is considered that the effect can be obtained when the size of the locally heated region is 1 µm or more in consideration of the fact that the nucleus of the recrystallized grain has a size of approximately 1 µm under the present conditions. From an industrial standpoint, the minimum diameter and the minimum width may be 10 µm or more. In addition, with respect to the size of the locally heated region, when the maximum diameter or the maximum width exceeds 10 mm, the area fraction of the Goss-oriented grains having relatively large angular deviation θ or angular deviation ϕ that cannot grow out of the locally heated region increases. In this case, it is difficult to obtain the effect of performing local rapid heating.

[0110] In the local rapid heating, the heating rate may be 500 °C / sec or more at a central position of the locally heated region as viewed in the thickness direction and at a thickness 1 / 5 position of the steel sheet. When the heating rate is 500 °C / sec or more at the above region, the microstructure of the locally heated region can be preferably controlled to a recovered structure or a recrystallized structure. The heating rate is preferably 2000 °C / sec or more, and more preferably 10000 °C / sec or more. On the other hand, the upper limit of the heating rate is not particularly limited, and the upper limit may be, for instance, 1000000 °C / sec.

[0111] In addition, it is preferable that the heating rate is comprehensively and inseparably controlled with the heating rate during decarburization annealing described below. For instance, in the present embodiment, although the coarse Goss-oriented grains in the local heating affected region is intended to exist after the decarburization annealing, it is difficult to achieve the above intension when the heating rate during decarburization annealing is faster than the heating rate during local rapid heating. Therefore, although depending on the degree of the value of the heating rate, the heating rate during local rapid heating is preferably equal to or more than the heating rate during decarburization annealing. A person skilled in the art can preferably control the heating rate during local rapid heating and the heating rate during decarburization annealing if a person skilled in the art understands the purpose of making the coarse Goss-oriented grains to exist in the local heating affected region after decarburization annealing.

[0112] Herein, the thickness 1 / 5 position of the steel sheet indicates a depth corresponding to 1 / 5 of the thickness of the steel sheet from the surface of the steel sheet along the thickness direction.

[0113] In addition, in the local rapid heating, the maximum attained temperature may be 700°C or more at the central position of the locally heated region as viewed in the thickness direction and at the thickness 1 / 5 position of the steel sheet. When the maximum attained temperature is 700°C or more in the above region, the microstructure of the locally heated region can be preferably controlled to the recovered structure or the recrystallized structure. The maximum attained temperature is preferably 800°C or higher, and more preferably 900°C or higher. On the other hand, the maximum attained temperature may be equal to or lower than the melting point of the steel sheet, and may be, for instance, 1400°C or lower.

[0114] In addition, in the local rapid heating, the holding time from reaching the maximum temperature until cooling to 700°C may be 0.1 seconds or more at the central position of the locally heated region as viewed in the thickness direction and at the thickness 1 / 5 position of the steel sheet. When the holding time is 0.1 seconds or more in the above region, the microstructure of the locally heated region can be preferably controlled to the recovered structure or the recrystallized structure. The holding time is preferably 0.2 seconds or more, more preferably 0.3 seconds or more, and still more preferably 0.4 seconds or more. On the other hand, the upper limit of the holding time is not particularly limited, and the upper limit may be, for instance, 10 seconds or less. The holding time from reaching the maximum temperature until cooling to 700°C has essentially affected the formation of the coarse Goss-oriented grains close to the ideal Goss orientation.

[0115] In the local rapid heating, it is important to control the above holding time in addition to the heating rate and the maximum attained temperature described above. During this holding time, it is possible to form a sub-grain structure or a recrystallized nucleus, which is advantageous for the formation of the coarse Goss-oriented grains in the locally heated region. By controlling the sub-grain structure in the locally heated region through the holding time, it is possible to preferably control the microstructure in the subsequent process.

[0116] As described above, the method of local rapid heating is not particularly limited. For instance, local rapid heating may be performed by spot electric heating, laser irradiation, or electron beam irradiation. Any local rapid heating method may be controlled so as to satisfy the heating rate, the maximum attained temperature, and the holding time described above. A person skilled in the art can combine the conditions of the local rapid heating, and thereby, can control the heating rate, maximum attained temperature, and holding time according to the purpose.

[0117] For instance, a person skilled in the art can control the heating rate and the maximum attained temperature at the central position of the locally heated region as viewed in the thickness direction and at the thickness 1 / 5 position of the steel sheet by performing thermal conductivity analysis using finite element method. Additionally, a person skilled in the art can control the above holding time by controlling conditions of heat dissipation after reaching the maximum temperature. For instance, in the case of spot electric heating, the electrode retention time after current flow may be controlled, or the shape of the spot electrode may be changed to a shape suitable for heat dissipation. In addition, in the case of laser irradiation or electron beam irradiation, the irradiation speed may be adjusted, or the shape of irradiated region may be changed to an ellipse and the like to add a gradient to the irradiation energy from the central region toward the outer edge region in irradiated region.

[0118] In general, in heating by laser irradiation, only the vicinity of the irradiated sheet surface is preferentially heated, and the inside of the steel sheet is hardly heated. In addition, since heating by laser irradiation is non-contact heating, heat dissipation after heating is fast, and it is difficult to hold the temperature. Therefore, when heating by laser irradiation is performed as the local rapid heating, in order to recover or recrystallize the cold-deformed structure in the laser-irradiated region, it is necessary to perform heating under a condition of heating not only the sheet surface but also the inside of the steel sheet and under a condition of relatively coarsening the sub-grain structure in the laser-irradiated region by slowing the cooling rate. The condition of laser irradiation for performing the local rapid heating is quite different from the condition of laser irradiation for performing the magnetic domain refinement. For instance, even if the condition of laser irradiation for performing magnetic domain refinement (usually 0.5 to 50 mJ / mm 2< ) is applied to the present embodiment, the microstructure of the locally heated region cannot be controlled in a preferable one, and the coarse Goss-oriented grains close to the ideal Goss orientation are not formed in the steel sheet after the decarburization annealing process. In addition, the situation with electron beam irradiation is the same as with laser irradiation. Even if the condition of electron beam irradiation for performing magnetic domain refinement is applied to the present embodiment, the microstructure of the locally heated region cannot be controlled in a preferable one, and the coarse Goss-oriented grains close to the ideal Goss orientation are not formed in the steel sheet after the decarburization annealing process.

[0119] Note that, even when the input power of laser irradiation or electron beam irradiation is simply increased, it is difficult to form the coarse Goss-oriented grains close to the ideal Goss orientation. For instance, when the rapid heating is performed by laser irradiation or electron beam irradiation, it is preferable to make the beam shape elliptical or control the scan speed and the like in order to secure a temperature range where the grains in the region grow after the rapid heating.

[0120] Conventionally, in an electrical steel sheet, laser irradiation and electron beam irradiation have been performed to reduce the iron loss by performing magnetic domain control on the steel sheet after secondary recrystallization. Under conditions of these laser irradiation and electron beam irradiation, since approximately 20 µm from the surface of the steel sheet is heated, heat dissipation after heating is fast. Therefore, under the conventional conditions, it is difficult to secure the holding time from reaching the maximum temperature until cooling to 700°C as described above. That is, under the conditions of conventional laser irradiation and electron beam irradiation, it may be possible to make the irradiated region act as a barrier for the growth of the secondary recrystallized grains, but it is difficult to form the coarse Goss-oriented grains having the orientation close to the ideal Goss orientation as in the present embodiment. In order to form the coarse Goss-oriented grains close to the ideal Goss orientation by laser irradiation or electron beam irradiation, it is necessary to investigate conditions of laser irradiation or electron beam irradiation as described above.

[0121] Moreover, the local heating affected regions may be appropriately arranged on the sheet surface according to the purpose. In the method for manufacturing the grain oriented electrical steel sheet according to the present embodiment, the secondary recrystallized grains is controlled so as to have the oblate shape which was elongated to the transverse direction C and which was compressed to the rolling direction L. For instance, with an increase in spacing of the local heating affected regions in the rolling direction L, the secondary recrystallized grain size tends to be coarse in the rolling direction L. In the same way, with an increase in spacing of the local heating affected regions in the transverse direction C, the secondary recrystallized grain size tends to be coarse in the transverse direction C. The arrangements of these local heating affected regions in the rolling direction L and the transverse direction C are influenced each other. For instance, when spacing in the rolling direction L increases, the secondary recrystallized grain size may become coarse in the transverse direction C even when spacing in the transverse direction C is small. Moreover, the grain growth of the secondary recrystallized grains are influenced by the steel composition, the thermal gradient in heating stage of final annealing explained below, and the like. Thus, the above oblate shape are controlled by comprehensively controlling these conditions. A person skilled in the art can appropriately combine the arrangement of the local heating affected regions and other conditions in order to control the secondary recrystallized grains to be the above oblate shape.(Decarburization Annealing Process)

[0122] In the decarburization annealing process, the cold-rolled steel sheet after the local rapid heating process is subjected to decarburization annealing (primary annealing). By this decarburization annealing, the existence frequency of the Goss-oriented grains formed in the local heating affected region is increased, the grain size of the Goss-oriented grains is increased, and the coarse Goss-oriented grains having the orientation close to the ideal Goss orientation are preferably formed. As conditions of the decarburization annealing, the heating rate may be 10 to 10000 °C / sec, the annealing temperature may be 700 to 900°C, and the annealing time may be 10 to 600 seconds. In addition, by performing decarburization annealing on the cold-rolled steel sheet, C included in the cold-rolled steel sheet is removed. In order to remove "C" included in the cold rolled steel sheet, it is preferable that the decarburization annealing is conducted in moist atmosphere.

[0123] In addition, it is effective to reduce the primary recrystallized grain size by controlling the conditions of the hot rolling and hot-band annealing described above and by decreasing the decarburization annealing temperature as necessary. The primary recrystallized grain size is not particularly limited but is preferably 8 to 30 µm.

[0124] In addition, in the present embodiment, a large number of the coarse Goss-oriented grains having the orientation close to the ideal Goss orientation are formed in the local heating affected region. Therefore, it is not necessary to form the Goss-oriented grains again by decarburization annealing. The heating rate of the decarburization annealing may be 10000 °C / sec or less as described above, but it is preferable to decrease the heating rate of the decarburization annealing in order to form {111}<112> oriented grains or {411}<148> oriented grains that are easily encroached in the matrix region (local heating non-affected region). For instance, the heating rate of the decarburization annealing is preferably 300 °C / sec or less, more preferably 200 °C / sec or less, and still more preferably 100 °C / sec or less.

[0125] In addition, the amount of oxidation caused by the decarburization annealing and the state of surface oxidized layer affect the formation of the glass film. Therefore, in the decarburization annealing, the oxidation degree (PH 2 O / PH 2 ) in the annealing atmosphere (furnace atmosphere) may be 0.01 to 0.15. Herein, the oxidation degree PH 2 O / PH 2 is defined as the ratio of water vapor partial pressure PH 2 O to hydrogen partial pressure PH 2 in the atmosphere.(Nitridation)

[0126] Nitridation is a treatment effective in the low temperature slab heating process in which the slab heating temperature is 1280°C or lower, and is an important process for controlling the inhibitor intensity in secondary recrystallization. In the nitridation, the nitrogen content of the steel sheet is made to increase to 40 to 200 ppm from starting the decarburization annealing to starting the secondary recrystallization in the final annealing. For instance, the nitridation may be a treatment of annealing the steel sheet in an atmosphere containing a gas having a nitriding ability such as ammonia, a treatment of final-annealing the decarburization annealed steel sheet being applied an annealing separator containing a powder having a nitriding ability such as MnN and the like. The nitrogen content after the nitridation is preferably 130 to 350 ppm, and more preferably 150 to 250 ppm.(Annealing Separator Applying Process)

[0127] In the annealing separator applying process, the decarburization-annealed steel sheet is applied an annealing separator to. For instance, as the annealing separator, it is possible to use an annealing separator mainly including MgO, an annealing separator mainly including Al 2 O 3 , and the like. The decarburization-annealed steel sheet after applying the annealing separator is coiled and is final-annealed in the subsequent final annealing process.(Final Annealing Process)

[0128] In the final annealing process, the decarburization annealed steel sheet after applying the annealing separator is final-annealed so that the secondary recrystallization (secondary annealing) occurs. In the process, the secondary recrystallization proceeds under conditions such that the grain growth of the primary recrystallized grain is suppressed by the inhibitor. Thereby, the grains having the {110}<001> orientation are preferentially grown, and the magnetic flux density is drastically improved.

[0129] In the final annealing, the decarburization annealed steel sheet after applying the annealing separator and being dried may be held for 10 hours or more and 60 hours or less in a temperature range of 1000°C or more and 1300°C or less. The atmosphere during final annealing may be, for instance, a nitrogen atmosphere or a mixed atmosphere of nitrogen and hydrogen.

[0130] Moreover, in the present embodiment, in the heating stage of the final annealing, the secondary recrystallization may be proceeded while giving the thermal gradient of more than 0.5 °C / cm, preferably the thermal gradient of 1.0 °C / cm or more, in a border area between primary recrystallized area and secondary recrystallized area in the steel sheet. For instance, the above thermal gradient may be given to the steel sheet in which the secondary recrystallized grains grow in progress in the temperature range of 800°C or more in the heating stage of the final annealing. The direction to give the above thermal gradient may be the transverse direction C. Moreover, the above thermal gradient may be appropriately changed depending on the steel composition. For instance, in a case of the steel composition in which the secondary recrystallized grains tend to grow preferentially, the thermal gradient may be more than 0.5 °C / cm (preferably 1.0 °C / cm or more). On the other hand, in a case of the steel composition in which the secondary recrystallized grains do not tend to grow preferentially, the thermal gradient is preferably more than 1.0 °C / cm.

[0131] The method of giving the thermal gradient is not particularly limited, and a known method may be applied. For instance, when the coiled steel sheet is heated after placing in a box type annealing furnace, the position and arrangement of the heating device and the temperature distribution in the annealing furnace may be controlled so as to make a sufficient temperature difference from upper side to lower side or from outside to inside of the coil. Alternatively, the temperature distribution may be purposely applied to the coil being subjected to the annealing by actively heating only part of the coil with arranging induction heating, high frequency heating, electric heating, and the like.

[0132] By giving the thermal gradient to the steel sheet in the heating stage of the final annealing, the secondary recrystallized grain having the ideal orientation is nucleated from the area where the secondary recrystallization is likely to start antecedently in the coil, and the secondary recrystallized grains grow preferentially due to the thermal gradient. For instance, it is possible to grow the secondary recrystallized grains throughout the entire coil.(Insulating Coating Forming Process)

[0133] A coating solution including phosphoric acid or phosphate, chromic anhydride or chromate, and colloidal silica is applied to the steel sheet after the final annealing, and is baked (for instance, 350 to 1150°C for 5 to 300 seconds) to form the insulation coating.

[0134] Through the above processes, the grain oriented electrical steel sheet according to the present embodiment can be manufactured. In the grain oriented electrical steel sheet according to the present embodiment manufactured comprehensively and inseparably by controlling each condition of each process, the deviation between the secondary recrystallized grains and the ideal Goss orientation is extremely small, the angular deviation ϕ is averagely small at each measurement point along the rolling direction L, the grains do not grow coarsely in the rolling direction L, and the grains tend to become the oblate shape which is elongated to the transverse direction C and which is compressed to the rolling direction L. Therefore, although the thermal gradient during secondary recrystallization is given to the steel sheet, the steel sheet is excellent in both the magnetic flux density and the magnetostriction.Example 1

[0135] Hereinafter, the effects of the present invention are described in detail with reference to the following examples. However, the condition in the examples is an example condition employed to confirm the operability and the effects of the present invention, so that the present invention is not limited to the example condition. The present invention can employ various types of conditions as long as the conditions do not depart from the scope of the present invention and can achieve the object of the present invention.

[0136] Using slabs having adjusted chemical composition as materials, decarburization-annealed steel sheets with chemical composition shown in Table 2A were manufactured. The chemical composition was measured by the above-mentioned methods. In Table 2, "-" indicates that the control and manufacturing conscious of content did not perform and thus, the content was not measured.

[0137] When the decarburization-annealed steel sheets were manufactured, the slabs were heated to 1150°C, and then hot-rolled to obtain the hot rolled steel sheets having the thickness of 2.6 mm. The hot rolled steel sheets were subjected to the hot band annealing in which the annealing was conducted at 1100°C and then at 900°C, and then were pickled in order to remove the surface scale. The steel sheets were cold-rolled once or cold-rolled plural times with the intermediate annealing to obtain the cold rolled steel sheets having the final thickness of 0.22 mm.

[0138] The cold-rolled steel sheets were subjected to local rapid heating under conditions shown in Tables 3 to 7. For spot electric heating, copper electrodes having a diameter of 1 mm which corresponds to contact area with the steel sheet were used, and then, the heating rate, the maximum attained temperature, the holding time from reaching the maximum temperature until cooling to 700°C (holding time above 700°C) were respectively controlled by comprehensively adjusting the electrode shape other than the contact area with the steel sheet, the electrode force, the flowing current, the time of current flow, the electrode retention time after current flow, and the like. For laser heating, fiber laser was used, focusing spot diameter of laser beam in the rolling direction (specifically, diameter including 86% of laser output) was to be 30 µm (except for Test Nos. 71 and 72), and then, the heating rate, the maximum attained temperature, the holding time above 700°C were respectively controlled by comprehensively adjusting the energy density of laser irradiation, the laser scanning speed, the shape of laser irradiated region, and the like. A person skilled in the art can combine the conditions of the local rapid heating, and thereby, can control the heating rate, the maximum attained temperature, and the holding time above 700°C according to the purpose.

[0139] Note that, in Test No. 69, the laser beam was elongated along scanning direction, and thereby, the holding time from reaching the maximum temperature until cooling to 700°C was controlled to 0.2 seconds in the local rapid heating, in order to form the coarse Goss-oriented grains having the orientation close to the ideal Goss orientation in the locally heated region. In Test No. 70, the general condition of laser irradiation for performing the magnetic domain refinement was applied. In Test No. 71, the focusing spot diameter was 0.5mm, and the energy density of laser irradiation was 2.0 J / mm 2< , in order to control the irradiated region of laser beam to be finally the grain boundary of the secondary recrystallization. In Test No. 72, the focusing spot diameter was 0.5mm, and the energy density of laser irradiation was 30.0 J / mm 2< , in order to control the irradiated region of laser beam to be finally the grain boundary of the secondary recrystallization.

[0140] In the tables, "Not performed" of heating method of local rapid heating indicates that the local rapid heating was not performed. "Linear or Dotted" of local heating condition indicates the shape of the locally heated region on the surface of the cold-rolled steel sheet, and "Spacing in rolling direction" and "Spacing in width direction" of local heating condition indicates the spacing in the rolling direction and the transverse direction in which the locally heated regions were arranged on the surface of the cold-rolled steel sheet. The locally heated regions were uniformly arranged at even spacing in the rolling direction and the transverse direction. Herein, when the locally heated regions were arranged on the surface of the cold rolled steel sheet, the locally heated regions were arranged so that the distribution was not uneven.

[0141] Moreover, in the tables, "edge 10" of spacing in width direction of local heating condition of local rapid heating indicates that the locally heated regions were formed only at a position of 10 mm from an edge in the width direction of the cold rolled steel sheet.

[0142] The cold-rolled steel sheets after the local rapid heating were subjected to decarburization annealing under the conditions shown in Tables 3 to 7. Herein, in the decarburization annealing, the oxidation degree (PH 2 O / PH 2 ) in the annealing atmosphere (furnace atmosphere) was 0.13.

[0143] The manufactured decarburization-annealed steel sheet was subjected to nitridation at 750°C in nitrogen-hydrogen-ammonia atmosphere, and the nitrogen content of the steel sheet was to be 220 ppm. Thereafter, the annealing separator including MgO as a main component was applied and the final annealing was performed.

[0144] In the heating stage of the final annealing, the steel sheet was heated to 1000°C at 15°C / hr (°C / hour) in a mixed atmosphere of hydrogen and nitrogen, heated to 1200°C at heating rates shown in Tables 3 to 7. Moreover, in the heating stage of the final annealing, the thermal gradient in the transverse direction C shown in Tables 3 to 7 was given to the border area between primary recrystallized area and secondary recrystallized area in the steel sheet in the temperature range of 800°C or more. Herein, in Tables 3 to 7, "< 1.0" of thermal gradient of heating stage of final annealing indicates that the thermal gradient was not substantially controlled in the heating stage. After the heating stage of the final annealing, the steel sheet was held at 1200°C - 20hr (hour) in a hydrogen atmosphere.

[0145] For the steel sheet after the final annealing, the coating solution for forming insulation coating which mainly included the phosphate and the colloidal silica and which included the chromic anhydride as necessary was applied and baked to form the insulating coating.

[0146] For the manufactured grain oriented electrical steel sheet, the chemical composition of the base steel sheet, the aveϕ L which was the average of the angular deviation ϕ, the D L 10 which was the grain size at 10% by number base of the grain sizes D L , and the aveD C which was the average of the grain size D C were measured by the above-mentioned methods. The results are indicated in Tables 7 to 13. In Table 13, "-" indicates that the control and manufacturing conscious of content did not perform and thus, the content was not measured. Moreover, for the manufactured grain oriented electrical steel sheet, various features were evaluated. The evaluation results are shown in Tables 7 to 12.

[0147] The magnetic characteristics of the grain oriented electrical steel sheet were measured based on the single sheet tester (SST) method regulated by JIS C 2556: 2015.

[0148] The samples of 20 sheets with a size of 100 mm × 500 mm for the single sheet tester were taken from the obtained grain oriented electrical steel sheets, and then, the single sheet test was performed. As the magnetic characteristics, the magnetic flux density B 8 (T) in the rolling direction of the steel sheet was measured under the condition such that the steel sheet was excited at 800 A / m. When the magnetic flux density B 8 was 1.945T or more, it was judged to as acceptable. Moreover, for reference, the iron loss W 17 / 50 (W / kg) which was defined as the power loss per unit weight (1 kg) of the steel sheet was measured under the conditions of 50 Hz of AC frequency and 1.7 T of excited magnetic flux density.

[0149] In addition, as the magnetic characteristics, the magnetostriction λp-p@1.7T (difference between the minimum and the maximum of magnetostriction at 1.7 T) generated in the steel sheet was measured under the conditions of 50 Hz of AC frequency and 1.7 T of excited magnetic flux density. Specifically, using the maximum length L max and the minimum length L min of the test piece (steel sheet) under the above excitation condition and using the length L 0 of the test piece under 0T of the magnetic flux density, the magnetostriction λp-p@1.7T was calculated based on λp-p@1.7T = (L max - L min ) ÷ L 0 .

[0150] Based on the values of the magnetic characteristics, the magnetostriction velocity level at 1.7 T was calculated. The magnetostrictive waveform with cycles of two or more and the waveform obtained at a sampling frequency of 6.4 kHz were fourier-transformed, the magnetostriction λ at each frequency (fi) (0 to 3.2 kHz) was obtained, and thereby, the magnetostriction velocity level Lva (unit: dB) was calculated using a following expression 1. The magnetostriction velocity level Lva composed of 200 Hz was evaluated.

[0151] Herein, ρ : Density of air (kg / m 3< ) c : Speed of sound (m / s) P 0 : Minimum pressure which human can hear sound of 1kHz (Pa), fi : Frequency (Hz) λ(fi) : Magnetostriction at each frequency converted into Fourier α(fi) : A-weighting at frequency fi π : Pi (the ratio of the circumference of a circle to its diameter)

[0152] In order to obtain Lva@ 1.7T, the following values were substituted. ρ = 1.185 (kg / m 3< ) c = 346.3 (m / s) P 0 = 2 × 10 -5< (Pa)

[0153] When the magnetic flux density B 8 was 1.945T or more and the magnetostriction velocity level Lva @ 1.7T was 41 dB or less, both the magnetic flux density and the magnetostriction were judged to be acceptable.

[0154] In the grain oriented electrical steel sheets which were the inventive examples among Nos. 1 to 98, the aveϕ L , the D L 10, and the aveD C were favorably controlled. These inventive examples showed excellent magnetic flux density and magnetostriction. Also, these inventive examples also showed excellent iron loss.

[0155] On the other hand, in grain oriented electrical steel sheets which were the comparative examples among Nos. 1 to 98, the aveϕ L , the D L 10, or the aveD C was not favorably controlled. In these comparative examples, excellent magnetic flux density or magnetostriction was not obtained as the grain oriented electrical steel sheet. [Table 3]No.STEEL TYPEMANUFACTURING CONDITIONSTOTALLOCAL RAPID HEATINGDECARBURIZATION ANNEALINGFINAL ANNEALINGCOLD REDUCTION OF COLD ROLLINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONHEATING RATEANNEALING TEMPERATUREANNEALING TIMEHEATING STAGELINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONHEATING RATETHERMAL GRADIENT%°C / sec°Csecmmmm°C / sec°Csec°C / hr°C / cm1A91.5SPOT ELECTRIC50009000.3DOTTED160301008509010<1.02A91.5SPOT ELECTRIC50009000.3DOTTED120301008509010<1.03A91.5SPOT ELECTRIC50009000.3DOTTED100301008509010<1.04A91.5SPOT ELECTRIC50009000.3DOTTED80301008509010<1.05A91.5SPOT ELECTRIC50009000.3DOTTED60301008509010< 1.06A91.5SPOT ELECTRIC50009000.3DOTTED50301008509010<1.07A91.5SPOT ELECTRIC50009000.3DOTTED30301008509010<1.08A91.5SPOT ELECTRIC50009000.3DOTTED15301008509010<1.09A91.5SPOT ELECTRIC50009000.3DOTTED160EDGE 101008509010510A91.5SPOT ELECTRIC50009000.3DOTTED120EDGE 101008509010511A91.5SPOT ELECTRIC50009000.3DOTTED100EDGE 101008509010512A91.5SPOT ELECTRIC50009000.3DOTTED80EDGE 101008509010513A91.5SPOT ELECTRIC50009000.3DOTTED60EDGE 101008509010514A91.5SPOT ELECTRIC50009000.3DOTTED30EDGE 101008509010515A91.5SPOT ELECTRIC50009000.3DOTTED15EDGE 101008509010516A91.5SPOT ELECTRIC50009000.3DOTTED100EDGE 1010085090101.017A91.5SPOT ELECTRIC50009000.3DOTTED100EDGE 101008509010318A91.5SPOT ELECTRIC50009000.3DOTTED100EDGE 101008509010519A91.5SPOT ELECTRIC50009000.3DOTTED100EDGE 101008509010720A91.5SPOT ELECTRIC50009000.3DOTTED100EDGE 10100850901010 [Table 4] No.STEEL TYPEMANUFACTURING CONDITIONSTOTAL COLD REDUCTION OF COLD ROLLINGLOCAL RAPID HEATINGDECARBURIZATION ANNEALINGFINAL ANNEALINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONHEATING RATEANNEALING TEMPERATUREANNEALING TIMEHEATING STAGELINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONHEATING RATETHERMAL GRADIENT%°C / sec°Csecmmmm°C / sec°Csec°C / hr°C / cm21A91.5SPOT ELECTRIC50009000.3DOTTED1001001008509010<1.022A91.5SPOT ELECTRIC50009000.3DOTTED10010010085090101.023A91.5SPOT ELECTRIC50009000.3DOTTED1001001008509010324A91.5SPOT ELECTRIC50009000.3DOTTED1001001008509010525A91.5SPOT ELECTRIC50009000.3DOTTED30301008509010< 1.026A91.5SPOT ELECTRIC50009000.3DOTTED30301008509010527A91.5SPOT ELECTRIC50009000.3DOTTED100301008509010<1.028A91.5SPOT ELECTRIC50009000.3DOTTED100301008509010529A91.5SPOT ELECTRIC50009000.3DOTTED100301008509010530A91.5SPOT ELECTRIC50009000.3DOTTED100501008509010531A91.5SPOT ELECTRIC50009000.3DOTTED1001001008509010532A91.5SPOT ELECTRIC50009000.3DOTTED100EDGE 101008509010533A91.5NOT PERFORMED------1008509010<1.034A91.5NOT PERFORMED------10085090101.035A91.5NOT PERFORMED------1008509010336A91.5NOT PERFORMED------1008509010537A91.5NOT PERFORMED------1008509010738A91.5NOT PERFORMED------10085090101039A91.5NOT PERFORMED------100850905<1.040A91.5NOT PERFORMED------100850901<1.0 [Table 5] No.STEEL TYPEMANUFACTURING CONDITIONSTOTAL COLD REDUCTION OF COLD ROLLINGLOCAL RAPID HEATINGDECARBURIZATION ANNEALINGFINAL ANNEALINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONHEATING RATEANNEALING TEMPERATUREANNEALING TIMEHEATING STAGELINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONHEATING RATETHERMAL GRADIENT%°C / sec°Csecmmmm°C / sec°Csec°C / hr°C / cm41A91.5SPOT ELECTRIC50009000.3DOTTED100EDGE 1010085090101.042B91.5SPOT ELECTRIC50009000.3DOTTED100EDGE 1010085090101.043A91.5SPOT ELECTRIC5009000.3DOTTED100100100008309010544A91.5SPOT ELECTRIC5009000.3DOTTED10010020008309010545A91.5SPOT ELECTRIC5009000.3DOTTED1001005008309010546A91.5SPOT ELECTRIC5009000.3DOTTED1001003008309010547A91.5SPOT ELECTRIC5009000.3DOTTED1001001008309010548A91.5SPOT ELECTRIC20009000.3DOTTED100100100008309010549A91.5SPOT ELECTRIC20009000.3DOTTED10010020008309010550A91.5SPOT ELECTRIC20009000.3DOTTED1001005008309010551A91.5SPOT ELECTRIC20009000.3DOTTED1001003008309010552A91.5SPOT ELECTRIC20009000.3DOTTED1001001008309010553A91.5SPOT ELECTRIC50009000.3DOTTED100100100008309010554A91.5SPOT ELECTRIC50009000.3DOTTED10010020008309010555A91.5SPOT ELECTRIC50009000.3DOTTED1001005008309010556A91.5SPOT ELECTRIC50009000.3DOTTED1001003008309010557A91.5SPOT ELECTRIC50009000.3DOTTED1001001008309010558A91.5SPOT ELECTRIC100009000.3DOTTED100100100008309010559A91.5SPOT ELECTRIC100009000.3DOTTED10010020008309010560A91.5SPOT ELECTRIC100009000.3DOTTED10010050083090105 [Table 6] No.STEEL TYPEMANUFACTURING CONDITIONSTOTAL COLD REDUCTION OF COLD ROLLINGLOCAL RAPID HEATINGDECARBURIZATION ANNEALINGFINAL ANNEALINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONHEATING RATEANNEALING TEMPERATUREANNEALING TIMEHEATING STAGELINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONHEATING RATETHERMAL GRADIENT%°C / sec°Csecmmmm°C / sec°Csec°C / hr°C / cm61A91.5SPOT ELECTRIC100009000.3DOTTED1001003008309010562A91.5SPOT ELECTRIC100009000.3DOTTED1001001008309010563A91.5SPOT ELECTRIC50009000.3DOTTED1001001008509010<1.064A91.5SPOT ELECTRIC100009000.3DOTTED1001001008309010565A90.4SPOT ELECTRIC5008000.3DOTTED501003008509010466A90.4SPOT ELECTRIC5008000.2DOTTED501003008509010467A90.4SPOT ELECTRIC5008000.1DOTTED501003008509010468A90.4SPOT ELECTRIC5008000.03DOTTED501003008509010469A91.5LASER20008000.2SHORT LINEAR20EDGE 103008309010470A91.5LASER<2000<200<0.03SHORT LINEAR20EDGE 103008309010471A91.5LASER5000800<0.03SHORT LINEAR20EDGE 103008309010472A91.5LASER7000800<0.03SHORT LINEAR20EDGE 103008309010473A90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010374B90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010375C90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010376D90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010377E90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010378F90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010379G90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010380H90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 1010085090103 [Table 7] No.STEEL TYPEMANUFACTURING CONDITIONSTOTAL COLD REDUCTION OF COLD ROLLINGLOCAL RAPID HEATINGDECARBURIZATION ANNEALINGFINAL ANNEALINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONHEATING RATEANNEALING TEMPERATUREANNEALING TIMEHEATING STAGELINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONHEAT ING RATETHERMAL GRADIENT%°C / sec°Csecmmmm°C / sec°Csec°C / hr°C / cm81I90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010382J90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010383K90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010384L90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010385M90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010386N90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010387O90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010388P90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010389Q90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010390R90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010391S90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010392T90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010393U90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010394V90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010395W90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010396X90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010397Y90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010398Z90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 1010085090103 [Table 8] No.STEEL TYPEMANUFACTURING RESULTSEVALUATION RESULTSNOTEaveΦ L VALUE OF (100 - 15 × aveΦ L )D L 10aveD C MAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50MAGNETOSTRICTION Lva200Hz @1.7Tunit: °mmmmTW / kgdB1A3.94147221.9320.82146.1COMPARATIVE EXAMPLE2A3.84351221.9350.80845.9COMPARATIVE EXAMPLE3A3.74553211.9390.79145.7COMPARATIVE EXAMPLE4A3.64646211.9410.78542.2COMPARATIVE EXAMPLE5A3.54738211.9430.77742.0COMPARATIVE EXAMPLE6A3.54835211.9440.77241.9COMPARATIVE EXAMPLE7A3.45027211.9470.74141.7COMPARATIVE EXAMPLE8A3.35122211.9490.71741.6COMPARATIVE EXAMPLE9A2.563794101.9670.81843.5COMPARATIVE EXAMPLE10A2.365643691.9700.78240.4INVENTIVE EXAMPLE11A2.267553411.9740.75739.3INVENTIVE EXAMPLE12A2.168473111.9760.73637.3INVENTIVE EXAMPLE13A2.169382811.9790.71735.5INVENTIVE EXAMPLE14A2.069252231.9810.68933.0INVENTIVE EXAMPLE15A2.070191891.9830.67431.8INVENTIVE EXAMPLE16A3.548521501.9440.81442.2COMPARATIVE EXAMPLE17A2.661542511.9660.77540.0INVENTIVE EXAMPLE18A2.267553411.9740.75739.3INVENTIVE EXAMPLE19A1.873595271.9840.74439.1INVENTIVE EXAMPLE20A2.070608871.9800.76140.2INVENTIVE EXAMPLE [Table 9] No.STEEL TYPEMANUFACTURING RESULTS"EVALUATION RESULTSNOTEaveΦ L VALUE OF (100 - 15 × aveΦ L )D L 10aveD C MAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50MAGNETOSTRICTION Lva200Hz @1.7Tunit: °mmmmTW / kgdB21A3.84347241.9360.80042.9COMPARATIVE EXAMPLE22A3.64649551.9410.80942.5COMPARATIVE EXAMPLE23A2.95652911.9590.77739.9INVENTIVE EXAMPLE24A2.759531251.9640.76439.4INVENT IVE EXAMPLE25A3.45027211.9470.74141.7COMPARATIVE EXAMPLE26A3.35030261.9480.74041.7COMPARATIVE EXAMPLE27A3.74553211.9390.79145.7COMPARATIVE EXAMPLE28A2.95656731.9590.77640.8INVENTIVE EXAMPLE29A2.95656731.9590.77640.8INVENTIVE EXAMPLE30A2.95754901.9600.77140.8INVENTIVE EXAMPLE31A2.759531251.9640.76439.4INVENTIVE EXAMPLE32A2.365553411.9740.75239.3INVENTIVE EXAMPLE33A4.63137221.9150.83145.3COMPARATIVE EXAMPLE34A4.434431261.9200.82644.9COMPARATIVE EXAMPLE35A3.449542301.9460.81943.2COMPARATIVE EXAMPLE36A3.055663231.9570.79742.4COMPARATIVE EXAMPLE37A2.661834501.9670.80741.8COMPARATIVE EXAMPLE38A2.8591076551.9630.83542.0COMPARATIVE EXAMPLE39A4.04051301.9300.81644.3COMPARATIVE EXAMPLE40A3.64660351.9410.81443.5COMPARATIVE EXAMPLE [Table 10] No.STEEL TYPEMANUFACTURING RESULTSEVALUATION RESULTSNOTEaveΦ L VALUE OF (100 - 15 × aveΦ L )D L 10aveD C MAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50MAGNETOSTRICTION Lva200Hz @1.7Tunit: °mmmmTW / kgdB41A3.548521501.9440.81443.3COMPARATIVE EXAMPLE42B2.858551711.9620.76739.0INVENTIVE EXAMPLE43A3.84327501.9360.82838.9COMPARATIVE EXAMPLE44A3.64636891.9410.81839.5COMPARATIVE EXAMPLE45A3.648401031.9440.81239.7COMPARATIVE EXAMPLE46A3.154421081.9550.79038.1INVENTIVE EXAMPLE47A3.056451181.9580.78438.0INVENTIVE EXAMPLE48A3.74532571.9390.82239.1COMPARATIVE EXAMPLE49A3.05540921.9560.78837.5INVENTIVE EXAMPLE50A3.056441061.9580.78437.8INVENTIVE EXAMPLE51A2.957451101.9600.78037.7INVENTIVE EXAMPLE52A2.858481201.9620.77637.9INVENTIVE EXAMPLE53A3.05540711.9560.78837.5INVENTIVE EXAMPLE54A3.056471011.9580.78438.3INVENTIVE EXAMPLE55A2.957501131.9600.78038.5INVENTIVE EXAMPLE56A2.859511171.9630.77438.2INVENTIVE EXAMPLE57A2.760541261.9650.77038.3INVENTIVE EXAMPLE58A3.05653931.9580.78439.4INVENTIVE EXAMPLE59A2.859581181.9630.77439.4INVENTIVE EXAMPLE60A2.760591251.9650.77039.1INVENTIVE EXAMPLE [Table 11] No.STEEL TYPEMANUFACTURING RESULTSEVALUATION RESULTSNOTEaveΦ L VALUE OF (100 - 15 × aveΦ L )D L 10aveD C MAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50MAGNETOSTRICTION Lva200Hz @1.7Tunit: °mmmmTW / kgdB61A2.661591281.9680.76438.6INVENTIVE EXAMPLE62A2.563591341.9700.76038.3INVENTIVE EXAMPLE63A3.84347241.9360.80042.9COMPARATIVE EXAMPLE64A2.563591341.9700.76038.3INVENT IVE EXAMPLE65A3.153321021.9540.77236.4INVENTIVE EXAMPLE66A3.252441291.9520.78036.7INVENTIVE EXAMPLE67A3.351481831.9500.79036.9INVENTIVE EXAMPLE68A3.646562671.9430.81442.0COMPARATIVE EXAMPLE69A2.168212231.9800.68032.3INVENTIVE EXAMPLE70A3.252632971.9510.79644.8COMPARATIVE EXAMPLE71A3.351582751.9500.78343.5COMPARATIVE EXAMPLE72A3.449552581.9480.76842.8COMPARATIVE EXAMPLE73A2.168281781.9760.68033.4INVENTIVE EXAMPLE74B1.381332111.9980.63630.3INVENTIVE EXAMPLE75C2.069291861.9780.67633.2INVENTIVE EXAMPLE76D2.169271811.9770.67833.1INVENTIVE EXAMPLE77E2.267281801.9740.68433.7INVENTIVE EXAMPLE78F1.774301961.9870.65831.8INVENTIVE EXAMPLE79G1.480312071.9960.64030.5INVENTIVE EXAMPLE80H1.677312051.9910.65031.2INVENTIVE EXAMPLE [Table 12] No.STEEL TYPEMANUFACTURING RESULTSEVALUATION RESULTSNOTEaveΦ L VALUE OF (100 - 15 × aveΦ L )D L 10aveD C MAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50MAGNETOSTRICTION Lva200Hz @1.7Tunit: °mmmmTW / kgdB81I1.774291891.9860.66031.8INVENTIVE EXAMPLE82J2.069281841.9780.67633.1INVENTIVE EXAMPLE83K1.380332041.9970.63830.6INVENTIVE EXAMPLE84L1.774291891.9860.66031.8INVENTIVE EXAMPLE85M1.677312021.9910.65031.4INVENTIVE EXAMPLE86N1.380322061.9970.63830.4INVENTIVE EXAMPLE87O1.971291881.9810.67032.7INVENTIVE EXAMPLE88P2.070281821.9790.67432.9INVENTIVE EXAMPLE89Q2.168271751.9760.68033.3INVENTIVE EXAMPLE90R2.267271711.9740.68433.6INVENTIVE EXAMPLE91S1.775302001.9880.65631.7INVENTIVE EXAMPLE92T2.069291841.9780.67633.1INVENTIVE EXAMPLE93U2.268281791.9750.68233.5INVENTIVE EXAMPLE94V2.168281811.9760.68033.3INVENTIVE EXAMPLE95W2.169281761.9770.67833.3INVENTIVE EXAMPLE96X2.069291821.9780.67633.2INVENTIVE EXAMPLE97Y1.677321961.9910.65031.4INVENTIVE EXAMPLE98Z2.365261731.9710.69034.0INVENTIVE EXAMPLE INDUSTRIAL APPLICABILITY

[0156] According to the above aspects of the present invention, it is possible to provide a grain oriented electrical steel sheet excellent in both the magnetic flux density and the magnetostriction even if the technique in which the secondary recrystallization is proceeded while the thermal gradient is given to the steel sheet is applied. Accordingly, the present invention has significant industrial applicability.REFERENCE SIGNS LIST

[0157] 1Decarburization-Annealed Steel sheet 2Local heating affected region 3Local heating non-affected region (matrix region) 4Locally heated region boundary 5Local heating affected region boundary 14Goss-oriented grain 15Coarse Goss-oriented grain 21Rolling direction 22Width direction (transverse direction)

Examples

example 1

[0135]Hereinafter, the effects of the present invention are described in detail with reference to the following examples. However, the condition in the examples is an example condition employed to confirm the operability and the effects of the present invention, so that the present invention is not limited to the example condition. The present invention can employ various types of conditions as long as the conditions do not depart from the scope of the present invention and can achieve the object of the present invention.

[0136]Using slabs having adjusted chemical composition as materials, decarburization-annealed steel sheets with chemical composition shown in Table 2A were manufactured. The chemical composition was measured by the above-mentioned methods. In Table 2, "-" indicates that the control and manufacturing conscious of content did not perform and thus, the content was not measured.

[0137]When the decarburization-annealed steel sheets were manufactured, the slabs were heated...

TECHNICAL FIELD

[0001] The present invention relates to a grain oriented electrical steel sheet.

[0002] Priority is claimed on Japanese Patent Application No. 2023-106860, filed June 29, 2023, the content of which is incorporated herein by reference.BACKGROUND ART

[0003] A grain oriented electrical steel sheet includes Si, the crystal orientation of the grains thereof closely aligns in the Goss orientation (cubic crystal {110}<001>), and the <001> orientation, which is a magnetization easy axis, is substantially aligned in the rolling direction in the steel sheet manufacturing process. Such a grain oriented electrical steel sheet is very desirable as a material for an iron core and the like of a transformer. One of important magnetic characteristics of the grain oriented electrical steel sheet is, for instance, magnetic flux density.

[0004] The magnetic flux density of the grain oriented electrical steel sheet when a predetermined magnetizing force is applied tends to increase as the degree to which the magnetization easy axes of the grains are aligned in the rolling direction of the steel sheet, that is, the orientation of the grains is higher. A magnetic flux density B 8 is generally used as an index representing the magnetic flux density. The magnetic flux density B 8 is a value of the magnetic flux density of the grain oriented electrical steel sheet excited at a magnetizing force of 800 A / m in the rolling direction. That is, the grain oriented electrical steel sheet having a larger value of the magnetic flux density B 8 is more easily magnetized with a certain magnetizing force, the magnetic flux density becomes high, and thus it is suitable for a small-sized and highly efficient transformer.

[0005] In the past, it has been proposed to control the grain growth in secondary recrystallization in order to obtain the steel sheet showing high magnetic flux density, as a method and the like. For instance, the patent documents 1 and 2 disclose a method in which the secondary recrystallization is proceeded while a thermal gradient is given to the steel sheet in a tip area of secondary recrystallized grain which is encroaching primary recrystallized grains in final annealing process.

[0006] When the secondary recrystallized grain is grown while the thermal gradient is given, the secondary recrystallized grain having the orientation close to the ideal Goss orientation is nucleated from the region where the secondary recrystallization is likely to start antecedently in the steel sheet, and the secondary recrystallized grain grows preferentially due to the thermal gradient. As a result, alignment degree to the Goss orientation increases and the magnetic flux density B 8 is improved.

[0007] However, when the secondary recrystallized grain is grown while the thermal gradient is given, the grain having the orientation close to the ideal Goss orientation may grow preferentially, but the secondary recrystallized grain may be excessively large. When the secondary recrystallized grain grows excessively, a deviation from the ideal Goss orientation increases in a tip area of growth of the secondary recrystallized grain, and the effect of improving the magnetic flux density may be restricted.

[0008] For instance, the secondary recrystallization in the steel sheet proceeds in a state of being coiled. In other words, the secondary recrystallized grain grows in a state where the steel sheet is under the condition with curvature. However, the secondary recrystallized grain while maintaining the linearity of the crystal orientation. When the secondary recrystallized grain grows larger, the deviation from the ideal Goss orientation increases in the tip area of growth of the secondary recrystallized grain due to the curvature of coil.

[0009] It is possible to represent the deviation between the actual crystal orientation and the ideal Goss orientation by a deviation angle α, a deviation angle β, and a deviation angle γ. The deviation angle α is an angle formed by the <001> direction of crystal projected on the rolled surface and the rolling direction L when viewing from the normal direction Z. The deviation angle β is an angle formed by the <001> direction of crystal projected on L cross section (cross section whose normal direction is the transverse direction) and the rolling direction L when viewing from the transverse direction C (width direction of sheet). The deviation angle γ is an angle formed by the <110> direction of crystal projected on C cross section (cross section whose normal direction is the rolling direction) and the normal direction Z when viewing from the rolling direction L.

[0010] It is known that, among these deviation angles α, β and γ, the deviation angles α and β affect the magnetic flux density. When the values of the deviation angles α and β are small, the magnetic flux density B 8 is improved.

[0011] In addition, it is known that, among the deviation angles α, β and γ, the deviation angle β affects magnetostriction. When the value of the deviation angle β is small, the magnetostriction is improved. Herein, the magnetostriction is a phenomenon in which a shape of magnetic material changes when magnetic field is applied. Since the magnetostriction causes vibration and noise, it is demanded to reduce the magnetostriction of the grain oriented electrical steel sheet utilized for a core of transformer and the like. For instance, the patent documents 3 to 5 disclose controlling the deviation angle β.Citation ListPatent Document

[0012] Patent Document 1: Japanese Unexamined Patent Application, First Publication No. S57-002839 Patent Document 2: Japanese Unexamined Patent Application, First Publication No. S61-190017 Patent Document 3: Japanese Unexamined Patent Application, First Publication No. 2001-294996 Patent Document 4: Japanese Unexamined Patent Application, First Publication No. 2005-240102 Patent Document 5: Japanese Unexamined Patent Application, First Publication No. 2015-206114 SUMMARY OF INVENTIONTechnical Problem

[0013] As described above, it has been tried to improve the magnetic flux density of the grain oriented electrical steel sheet. For instance, it has been tried to increase the alignment degree to the Goss orientation by proceeding the secondary recrystallization while the thermal gradient is given to the steel sheet, and thereby, to improve the magnetic flux density.

[0014] However, when the secondary recrystallized grain is grown while the thermal gradient is given, the secondary recrystallized grain is excessively large, and thereby, it is inevitable that the deviation from the ideal Goss orientation increases. Thus, the effect of improving the magnetic flux density may be restricted. Moreover, the magnetostriction may be deteriorated.

[0015] The present invention has been made in consideration of the above-mentioned situations. An object of the present invention is to provide a grain oriented electrical steel sheet excellent in the magnetic flux density and the magnetostriction. Specifically, an object is to provide a grain oriented electrical steel sheet excellent in both the magnetic flux density and the magnetostriction even if the technique in which the secondary recrystallization is proceeded while the thermal gradient is given to the steel sheet is applied.Solution to Problem

[0016] An aspect of the present invention employs the following. [1] A grain oriented electrical steel sheet according to an aspect of the present invention, wherein when a deviation angle from an ideal Goss orientation based on a rotation axis parallel to a normal direction Z is defined as α, when a deviation angle from the ideal Goss orientation based on a rotation axis parallel to a transverse direction C is defined as β, when a deviation angle from the ideal Goss orientation based on a rotation axis parallel to a rolling direction L is defined as γ, when a deviation angle of a crystal orientation measured at one measurement point on a sheet surface is represented as (α β γ), when an angular deviation at the measurement point is defined as ϕ = (α 2< + β 2< ) 1 / 2< , and when an average of the angular deviation ϕ obtained from plural measurement points with spacing of 1 mm in the rolling direction L is defined as aveϕ L , the aveϕ L satisfies aveϕ L ≤ 3.5°, when deviation angles of crystal orientations measured at two measurement points which are adjacent on the sheet surface and which have spacing of 1 mm are represented as (α 1 β 1 γ 1 ) and (α 2 β 2 γ 2 ), when a midpoint of two measurement points which satisfy [(α 2 - α 1 ) 2< + (β 2 - β 1 ) 2< + (γ 2 - γ 1 ) 2< ] 1 / 2< ≥ 1.0° is defined as a grain boundary GB, when a grain size in the rolling direction L obtained based on the grain boundary GB is defined as D L in units of mm, and when a grain size which is at 10% by number base from largest in a case where the grain sizes D L obtained in the rolling direction L are sorted from largest to smallest is defined as D L 10 in units of mm, the D L 10 satisfies D L 10 ≤ 100 - 15 × aveϕ L , and when a grain size in the transverse direction C obtained based on the grain boundary GB is defined as D C in units of mm, and when an average of the grain size D C obtained in the transverse direction C is defined as aveD C , the aveD C satisfies aveD C ≥ 50. Advantageous Effects of Invention

[0017] According to the above aspects of the present invention, it is possible to provide a grain oriented electrical steel sheet excellent in a magnetic flux density and a magnetostriction. Specifically, it is possible to provide the grain oriented electrical steel sheet excellent in both the magnetic flux density and the magnetostriction even if the technique in which the secondary recrystallization is proceeded while the thermal gradient is given to the steel sheet is applied.BRIEF DESCRIPTION OF DRAWINGS

[0018] [FIG. 1] A schema illustrating an instance of using spot electric heating as a local rapid heating method and illustrating an instance of arrangement of a local heating affected region in a decarburization-annealed steel sheet. [FIG. 2] A schema illustrating a distribution of Goss-oriented grains of a decarburization-annealed steel sheet. DESCRIPTION OF EMBODIMENTS

[0019] Hereinafter, a preferred embodiment of the present invention is described in detail. However, the present invention is not limited only to the configuration which is disclosed in the present embodiment, and various modifications are possible without departing from the aspect of the present invention. In addition, the limitation range as described below includes a lower limit and an upper limit thereof. However, the value represented by "more than" or "less than" does not include in the limitation range. Unless otherwise noted, "%" of the chemical composition represents "mass%".

[0020] A grain oriented electrical steel sheet (base steel sheet) according to the present embodiment, wherein when a deviation angle from an ideal Goss orientation based on a rotation axis parallel to a normal direction Z is defined as α, when a deviation angle from the ideal Goss orientation based on a rotation axis parallel to a transverse direction C is defined as β, when a deviation angle from the ideal Goss orientation based on a rotation axis parallel to a rolling direction L is defined as γ, when a deviation angle of a crystal orientation measured at one measurement point on a sheet surface is represented as (α β γ), when an angular deviation at the measurement point is defined as ϕ = (α 2< + β 2< ) 1 / 2< , and when an average of the angular deviation ϕ obtained from plural measurement points with spacing of 1 mm in the rolling direction L is defined as aveϕ L , the aveϕ L satisfies aveϕ L ≤ 3.5°.

[0021] In addition, a grain oriented electrical steel sheet (base steel sheet) according to the present embodiment, wherein when deviation angles of crystal orientations measured at two measurement points which are adjacent on the sheet surface and which have spacing of 1 mm are represented as (α 1 β 1 γ 1 ) and (α 2 β 2 γ 2 ), when a midpoint of two measurement points which satisfy [(α 2 - α 1 ) 2< + (β 2 - β 1 ) 2< + (γ 2 - γ 1 ) 2< ] 1 / 2< ≥ 1.0° is defined as a grain boundary GB, when a grain size in the rolling direction L obtained based on the grain boundary GB is defined as D L in units of mm, and when a grain size which is at 10% by number base from largest in a case where the grain sizes D L obtained in the rolling direction L are sorted from largest to smallest is defined as D L 10 in units of mm, the D L 10 satisfies D L 10 ≤ 100 - 15 × aveϕ L .

[0022] In addition, a grain oriented electrical steel sheet (base steel sheet) according to the present embodiment, wherein when a grain size in the transverse direction C obtained based on the grain boundary GB is defined as D C in units of mm, and when an average of the grain size D C obtained in the transverse direction C is defined as aveD C , the aveD C satisfies aveD C ≥ 50.

[0023] In the grain oriented electrical steel sheet according to the present embodiment, in a case where all of the above features are simultaneously satisfied, it is possible to improve both the magnetic flux density and the magnetostriction even if the technique in which the secondary recrystallization is proceeded while the thermal gradient is given to the steel sheet is applied.

[0024] In addition, in the present embodiment, the angular deviation ϕ is defined using the deviation angle α and the deviation angle β. The general angular deviation θ is often evaluated using three components: the deviation angle α, the deviation angle β, and the deviation angle γ. However, in the present embodiment, the angular deviation ϕ is defined using two components: the deviation angle α and the deviation angle β except for the deviation angle γ which does not significantly influence the magnetic flux density and the magnetostriction. It is possible to obtain the above effects by satisfying the above features using the angular deviation ϕ. On the other hand, the grain boundary and the grain size may be determined using three components: the deviation angle α, the deviation angle β, and the deviation angle γ.

[0025] The fact that the above aveφ L is 3.5° or less indicates that the angular deviation ϕ is averagely small at the measurement points along the rolling direction L. That is, it indicates that the angular deviation between the rolling direction L and the direction of the magnetization easy axis is small. As a result, the magnetic characteristics, particularly the magnetic flux density, are favorably improved. The aveϕ L is preferably 3.2° or less, more preferably 3.0° or less, and still more preferably 2.7° or less. On the other hand, since the aveϕ L is preferably as small as possible, a lower limit thereof is not particularly limited. However, since it is not easy to industrially control aveϕ L to zero, for instance, the aveϕ L may be 0.5° or more, and may be 1.0° or more.

[0026] The fact that the above D L 10 is (100 - 15 × aveϕ L ) or less in units of mm indicates that the grains do not grow coarsely in the rolling direction L. When the grains do not grow coarsely in the rolling direction L, it is possible to suppress an increase in the above deviation angles, particularly the deviation angle β. When the increase in the deviation angle β is suppressed, a decrease in the magnetic flux density is suppressed, and an increase in the magnetostriction is suppressed. When the D L 10 satisfies the above condition, the magnetic flux density and the magnetostriction are favorably improved. The D L 10 is preferably (90 - 15 × aveϕ L ) or less in units of mm, and more preferably (80 - 15 × aveϕ L ) or less in units of mm. On the other hand, since the D L 10 is preferably as small as possible, a lower limit thereof is not particularly limited. For instance, the D L 10 may be 5 mm or more, and may be 10 mm or more.

[0027] The fact that the aveD C is 50 mm or more indicates that a shape of the grain is elongated to the transverse direction C. The grain oriented electrical steel sheet according to the present embodiment is based on the premise that the technique in which the secondary recrystallization is proceeded while the thermal gradient is given to the steel sheet is applied. Thus, the secondary recrystallized grains tend to be grown coarsely. However, in the embodiment, it is suppressed to coarsely grow the grains in the rolling direction L as explained above. On the other hand, in the embodiment, it is allowed to coarsely grow the grains in the transverse direction C. In the grain oriented electrical steel sheet according to the present embodiment, since the technique in which the secondary recrystallization is proceeded while the thermal gradient is given to the steel sheet is applied, the secondary recrystallized grains tend to be grown coarsely, and the aveDc becomes 50 mm or more. The aveDc is preferably 80 mm or more, more preferably 100 mm or more, and still more preferably 200 mm or more. On the other hand, an upper limit of the aveD C is not particularly limited. For instance, the grain size in the transverse direction C may be coil width (for instance, width of 1000mm). The aveD C may be 800 mm or less, and 500 mm or less.

[0028] For the deviation angle α, the deviation angle β, the deviation angle γ, and the like explained above, a measurement line including at least 500 measurement points with 1 mm spacing on the rolled surface is arranged, and the crystal orientations may be measured. For instance, the crystal orientation may be measured by the X-ray diffraction method (Laue method). The Laue method is the method such that X-ray beam is irradiated the steel sheet with and that the diffraction spots which are transmitted or reflected are analyzed. By analyzing the diffraction spots, it is possible to identify the crystal orientation at the point irradiated with X-ray beam. Moreover, by changing the irradiated point and by analyzing the diffraction spots in plural points, it is possible to obtain the distribution of the crystal orientation based on each irradiated point. The Laue method is the preferred method for identifying the crystal orientation of the metallographic structure in which the grains are coarse.

[0029] The measurement points for the crystal orientation may be at least 500 points. It is preferable that the number of measurement points appropriately increases depending on the grain size of the secondary recrystallized grain. For instance, when the number of secondary recrystallized grains included in the measurement line is less than 10 grains in a case where the number of measurement points for identifying the crystal orientation is 500 points, it is preferable to extend the above measurement line by increasing the measurement points with 1 mm spacing so as to include 10 grains or more of the secondary recrystallized grains in the measurement line. Moreover, when it is difficult to arrange 500 measurement points in one measurement line, plural measurement lines may be arranged in order to measure the crystal orientation at the measurement points of 500 or more in total.

[0030] The crystal orientations are identified at each measurement point with 1 mm spacing on the rolled surface, and then, the deviation angle α, the deviation angle β, and the deviation angle γ are identified at each measurement point. Based on the identified deviation angles at each measurement point, the angular deviation ϕ, the aveϕ L , the grain boundary GB, the grain size D L , the D L 10, the grain size D C , and the aveD C may be obtained. Herein, the D L 10 may be obtained as the grain size which is at 10% by number base from largest in a case where the grains with the grain size D L of 2 mm or more are sorted from largest to smallest. The aveD C may be obtained as the average grain size of the grains with the grain size D C of 2 mm or more. Moreover, in a case where it is difficult to judge which grain the X-ray diffraction results come from because the irradiated region of X-ray beam spreads over two grains at the measurement point for the crystal orientation by Laue method, 0.5 mm may be respectively added to the grain size of these two grains.

[0031] In addition, the grain oriented electrical steel sheet according to the present embodiment may have the following chemical composition.

[0032] The grain oriented electrical steel sheet according to the present embodiment may contain, as a chemical composition, Si: 2.0% to 7.0% in mass percentage and the balance consisting of Fe and impurities.

[0033] In addition, this grain oriented electrical steel sheet may contain a known optional element as substitution for part of Fe for improving the magnetic characteristics. A lower limit of the optional element does not need to be limited, and the lower limit may be 0%. Moreover, an upper limit of the optional element may be a value in which the magnetic flux density or the iron loss does not significantly deteriorate. For instance, the upper limit of each optional element is described below.

[0034] The grain oriented electrical steel sheet according to the present embodiment (base steel sheet) may contain, as a chemical composition, by mass%: Si: 2.0 to 7.0%, C: 0 to 0.0050%, Mn: 0 to 1.0%, S and Se: 0 to 0.0150% in total, Al: 0 to 0.0650%, N: 0 to 0.0050%, Nb, V, Mo, Ta, and W: 0 to 0.050% in total, Cu: 0 to 0.40%, Bi: 0 to 0.010%, B: 0 to 0.080%, P: 0 to 0.50%, Ti: 0 to 0.0150%, Sn: 0 to 0.10%, Sb: 0 to 0.10%, Cr: 0 to 0.30%, Ni: 0 to 1.0%, and the balance consisting of Fe and impurities. Si: 2.0 to 7.0%

[0035] Si (silicon) is a basic element for the base steel sheet. When the Si content is less than 2.0%, the eddy-current loss cannot be sufficiently reduced, so that favorable magnetic characteristics cannot be obtained. Therefore, the Si content of the base steel sheet is 2.0% or more. The Si content is preferably 2.50% or more, and more preferably 3.0% or more. On the other hand, when the Si content is more than 7.0%, the steel sheet is embrittled, and the passability is remarkably deteriorated during manufacture, and thus the Si content of the base steel sheet is 7.0% or less. The Si content is preferably 4.50% or less, and more preferably 4.0% or less.C: 0 to 0.0050%

[0036] C (carbon) is an optional element for the base steel sheet. C is contained in a steel piece (slab), but when C excessively remains in the base steel sheet after the final annealing, favorable iron loss characteristics may not be obtained. Therefore, the C content of the base steel sheet may be 0.0050% or less. The C content is preferably 0.0040% or less, and more preferably 0.0030% or less. On the other hand, the lower limit of the C content of the base steel sheet is not particularly limited, and it may be 0%. However, since it is not industrially easy to control the C content to 0%, the C content may be more than 0% or 0.00010% or more.Mn: 0 to 1.0%

[0037] Mn (manganese) is a basic element for the base steel sheet. Although Mn is contained in the steel piece (slab), when the content is excessive, the phase of steel are transformed during secondary recrystallization annealing, the secondary recrystallization does not sufficiently proceed, and favorable magnetic characteristics cannot be obtained. Thus, the Mn content of the base steel sheet may be 1.0% or less. The Mn content is preferably 0.50% or less, and more preferably 0.20% or less. On the other hand, the lower limit of the Mn content of the base steel sheet is not particularly limited, and it may be 0%. However, since Mn forms MnS and / or MnSe which act as the inhibitor, the Mn content may be more than 0% or 0.00010% or more.S and Se: 0 to 0.0150% in total

[0038] S (sulfur) and Se (selenium) are optional elements for the base steel sheet. S and Se are contained in a steel piece (slab), but when S and Se excessively remain in the base steel sheet after the final annealing, magnetic characteristics may be adversely affected. Therefore, the total amount of S and Se of the base steel sheet may be 0.0150% or less. The total amount of S and Se is preferably 0.010% or less, and more preferably 0.0050% or less. On the other hand, the lower limit of the total amount of S and Se of the base steel sheet is not particularly limited, and it may be 0%. However, since S and Se form MnS or MnSe and have an effect as an inhibitor at the time of secondary recrystallization, the total amount of S and Se may be more than 0% or 0.00010% or more.Al: 0 to 0.0650%

[0039] Al (aluminum) (sol.Al) is an optional element for the base steel sheet. Al is contained in a steel piece (slab), but when Al excessively remains in the base steel sheet after the final annealing, magnetic characteristics may be adversely affected. Therefore, the Al content of the base steel sheet may be 0.0650% or less. The Al content is preferably 0.040% or less, and more preferably 0.035% or less. On the other hand, the lower limit of the Al content of the base steel sheet is not particularly limited, and it may be 0%. However, since Al forms AlN and has an effect as an inhibitor at the time of secondary recrystallization, the Al content may be more than 0% or 0.00010% or more. Herein, the above Al content expresses acid-soluble Al (sol.Al).N: 0 to 0.0050%

[0040] N (nitrogen) is an optional element for the base steel sheet. N is contained in a steel piece (slab), but when N excessively remains in the base steel sheet after the final annealing, magnetic characteristics may be adversely affected. Therefore, the N content of the base steel sheet may be 0.0050% or less. The N content is preferably 0.0040% or less, and more preferably 0.0030% or less. On the other hand, the lower limit of the N content of the base steel sheet is not particularly limited, and it may be 0%. However, since N forms AlN and has an effect as an inhibitor at the time of secondary recrystallization, the N content may be more than 0% or 0.00010% or more.Nb, V, Mo, Ta, and W: 0 to 0.050% in total

[0041] Nb (niobium), V (vanadium), Mo (molybdenum), Ta (tantalum), and W (tungsten) are optional elements for the base steel sheet. The Nb group element (at least one of Nb, V, Mo, Ta, and W) excessively remains in the base steel sheet, magnetic characteristics may be adversely affected. Therefore, the total amount of Nb, V, Mo, Ta, and W of the base steel sheet may be 0.050% or less. The Nb group element is preferably 0.030% or less, more preferably 0.020% or less, and still more preferably 0.010% or less. On the other hand, the total amount of Nb, V, Mo, Ta, and W of the base steel sheet is not particularly limited, and it may be 0%. However, since Nb, V, Mo, Ta, or W forms carbides, nitrides, or carbonitrides and has an effect as an inhibitor at the time of secondary recrystallization, the total amount of Nb, V, Mo, Ta, and W may be more than 0% or 0.003% or more.Cu: 0 to 0.40%

[0042] Cu (copper) is an optional element for the base steel sheet. When the Cu content exceeds 0.40%, the steel sheet may be embrittled during hot rolling. Therefore, the Cu content of the base steel sheet may be 0.40% or less. The Cu content is preferably 0.30% or less, and more preferably 0.10% or less. On the other hand, the lower limit of the Cu content is not particularly limited, and it may be 0%. However, since Cu has an effect of improving magnetic characteristics by increasing the development degree of the Goss orientation, the Cu content may be more than 0% or 0.010% or more.Bi: 0 to 0.010%

[0043] Bi (bismuth) is an optional element for the base steel sheet. When the Bi content is more than 0.010%, the coating adhesion may be deteriorated. In addition, when the purification at the time of the final annealing is insufficient and Bi remains excessively, the magnetic characteristics may be adversely affected. Therefore, the Bi content of the base steel sheet may be 0.010% or less. The Bi content is preferably 0.0050% or less, more preferably 0.0020% or less, and still more preferably 0.0010% or less. On the other hand, the lower limit of the Bi content is not particularly limited, and it may be 0%. However, since Bi has an effect of improving magnetic characteristics, the Bi content may be more than 0% or 0.00050% or more.B: 0 to 0.080%

[0044] B (boron) is an optional element for the base steel sheet. When the B content exceeds 0.080%, The dispersion (standard deviation) of the magnetic flux density may increase. Thus, the B content may be 0.080% or less. The B content is preferably 0.070% or less, and more preferably 0.060% or less. On the other hand, the lower limit of the B content is not particularly limited, and it may be 0%. However, since B forms nitrides and has an effect as an inhibitor at the time of secondary recrystallization, the B content may be more than 0% or 0.00050% or more.P: 0 to 0.50%

[0045] P (phosphorus) is an optional element for the base steel sheet. When the P content exceeds 0.50%, the workability of the steel sheet may be significantly deteriorated. Therefore, the P content of the base steel sheet may be 0.50% or less. The P content is preferably 0.30% or less, and more preferably 0.10% or less. On the other hand, the lower limit of the P content is not particularly limited, and it may be 0%. However, since P has an effect of improving the texture and improving the magnetic characteristics of the steel sheet, the P content may be more than 0% or 0.0020% or more.Ti: 0 to 0.0150%

[0046] Ti (titanium) is an optional element for the base steel sheet. When the Ti content exceeds 0.0150%, the magnetic characteristics may be significantly deteriorated. Therefore, the Ti content of the base steel sheet may be 0.0150% or less. The Ti content is preferably 0.0130% or less, and more preferably 0.010% or less. On the other hand, the lower limit of the Ti content is not particularly limited, and it may be 0%. However, since Ti forms carbides, nitrides, or carbonitrides and has an effect as an inhibitor at the time of secondary recrystallization, the Ti content may be more than 0% or 0.0020% or more.Sn: 0 to 0.10%

[0047] Sn (tin) is an optional element for the base steel sheet. When the Sn content is more than 0.10%, secondary recrystallization may become unstable, and magnetic characteristics may be adversely affected. Therefore, the Sn content of the base steel sheet may be 0.10% or less. The Sn content is preferably 0.090% or less, and more preferably 0.080% or less. On the other hand, the lower limit of the Sn content is not particularly limited, and it may be 0%. However, since Sn has an effect of improving magnetic characteristics by increasing the development degree of the Goss orientation, the Sn content may be more than 0% or 0.0050% or more.Sb: 0 to 0.10%

[0048] Sb (antimony) is an optional element for the base steel sheet. When the Sb content is more than 0.10%, magnetic characteristics may be adversely affected. Therefore, the Sb content of the base steel sheet may be 0.10% or less. The Sb content is preferably 0.090% or less, and more preferably 0.080% or less. On the other hand, the lower limit of the Sb content is not particularly limited, and it may be 0%. However, since Sb functions as an inhibitor and has an effect of stabilizing secondary recrystallization, the Sb content may be more than 0% or 0.010% or more.Cr: 0 to 0.30%

[0049] Cr (chromium) is an optional element for the base steel sheet. When the Cr content is more than 0.30%, a Cr oxide is formed, and magnetic characteristics may be adversely affected. Therefore, the Cr content of the base steel sheet may be 0.30% or less. The Cr content is preferably 0.20% or less, and more preferably 0.10% or less. On the other hand, the lower limit of the Cr content is not particularly limited, and it may be 0%. However, since Cr has an effect of improving magnetic characteristics by increasing the development degree of the Goss orientation, the Cr content may be more than 0% or 0.010% or more.Ni: 0 to 1.0%

[0050] Ni (nickel) is an optional element for the base steel sheet. When the Ni content is more than 1.0%, secondary recrystallization may become unstable. Therefore, the Ni content of the base steel sheet may be 1.0% or less. The Ni content is preferably 0.20% or less, and more preferably 0.10% or less. On the other hand, the lower limit of the Ni content is not particularly limited, and it may be 0%. However, since Ni has an effect of reducing the iron loss by increasing the electric resistance, the Ni: content may be more than 0% or 0.010% or more.

[0051] The base steel sheet of the grain oriented electrical steel sheet according to the present embodiment may contain impurities. Herein, the impurities correspond to elements which are contaminated during industrial manufacture of steel from ores and scrap that are used as a raw material of steel, or from environment of a manufacturing process.

[0052] The chemical composition of the base steel sheet described above may be measured by a general analysis method. For instance, the chemical composition may be measured by using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometer: inductively coupled plasma emission spectroscopy spectrometry). Herein, the acid soluble Al may be measured by ICP-AES using filtrate after heating and dissolving the sample in acid. In addition, C and S may be measured by the infrared absorption method after combustion, N may be measured by the thermal conductometric method after fusion in a current of inert gas, and O may be measured by, for instance, the non-dispersive infrared absorption method after fusion in a current of inert gas.

[0053] Herein, the chemical composition is a component of the base steel sheet. When the grain oriented electrical steel sheet, which is a measurement sample, includes an insulation coating or the like on the surface, the chemical composition is measured after removing the coating or the like by the method described below.

[0054] For instance, as a method for removing the insulation coating, the grain oriented electrical steel sheet with the coating may be immersed in hot alkaline solution. Specifically, it is possible to remove the insulation coating from the grain oriented electrical steel sheet by immersing the steel sheet in sodium hydroxide aqueous solution which includes 30 to 50 mass% of NaOH and 50 to 70 mass% of H 2 O at 80 to 90°C for 5 to 10 minutes, washing it with water, and then, drying it. Moreover, the immersing time in sodium hydroxide aqueous solution may be adjusted depending on the thickness of the insulation coating.

[0055] Moreover, as a method for removing a forsterite film (glass film), the grain oriented electrical steel sheet in which the insulation coating is removed by the above method may be immersed in hot hydrochloric acid. Specifically, it is possible to remove the forsterite film by previously investigating the preferred concentration of hydrochloric acid for removing the forsterite film to be dissolved, immersing the steel sheet in the hydrochloric acid with the above concentration (for instance, 30 to 40 mass% of HCl) at 80 to 90°C for 1 to 5 minutes, washing it with water, and then, drying it. In general, film and coating are removed by selectively using the solution, for example, the alkaline solution is used for removing the insulation coating, and the hydrochloric acid is used for removing the forsterite film.

[0056] Hereinafter, the background leading to the grain oriented electrical steel sheet according to the present embodiment will be described.

[0057] The existence frequency of practical Goss-oriented grains having small angular deviation θ and small angular deviation ϕ from the {110}<001> orientation which is the ideal Goss orientation increases as the heating rate of the primary annealing (decarburization annealing) increases. On the other hand, for the grains of the {778}<447> (≈{111}<112>) orientation, the {411 }<148> orientation, and the like which have a Σ9 coincidence site lattice relationship with the Goss orientation and tend to be encroached by Goss-oriented grains (referred to as CSL oriented grains), the existence frequency conversely decreases as the heating rate of the primary annealing increases. Therefore, it was difficult to increase the fraction of the CSL oriented grains while increasing the fraction of the practical Goss-oriented grains by the primary annealing.

[0058] In the present embodiment, it has been found for the first time that a grain oriented electrical steel sheet having exceptional quality is obtained by performing local rapid heating on a cold steel sheet to form a locally heated region, controlling annealing conditions of primary annealing (decarburization annealing), and controlling annealing conditions of secondary annealing (final annealing).

[0059] The locally heated region that forms before the primary annealing is arranged locally on the surface of the steel sheet. The crystal structure of the locally heated region includes one or both of the recrystallized structure and the recovered structure at the end of the local rapid heating. The crystal structure of a non-rapidly heated region other than the locally heated region on the sheet surface consists of a cold-deformed structure which is as-cold rolled.

[0060] In the local rapid heating, the heating rate is preferably 500 °C / sec or more, preferably 2000 °C / sec or more, and more preferably 10000 °C / sec or more. As described above, it has been found that, when the primary annealing is performed on the steel sheet after the locally heated region is formed on the surface of the steel sheet before the primary annealing, a large number of grains having the practical Goss orientation are formed in a region thermally affected by the local rapid heating (local heating affected region). In addition, it has become clear that, among the Goss-oriented grains to be formed, the fraction of the Goss-oriented grains having small angular deviation θ and small angular deviation ϕ from the ideal Goss orientation is increased, and the grain size of the Goss-oriented grains after the primary annealing is increased.

[0061] The frequency of coarse Goss-oriented grains included in the local heating affected region is higher than the frequency obtained by normal rapid heating of the entire sheet. This feature is considered to be derived from the deformed structure which includes a large amount of residual strain in the peripheral region of the locally heated region. Specifically, in a case where the local rapid heating is performed, the practical Goss-oriented grains formed in the locally heated region preferentially encroach on the non-recrystallization region that is a peripheral region and that includes a large amount of residual strain to coarsen the size during primary annealing. On the other hand, in a case where the normal heating of the entire steel sheet is performed, the initiation and growth of recrystallized grains occur uniformly in the steel sheet, and thus, coarsening explained above seems to hardly occur.

[0062] The local heating affected region having the above feature is dispersedly arranged on the surface of the steel sheet by primary annealing, and then secondary annealing is further performed. In the secondary annealing, the secondary recrystallization is proceeded while the thermal gradient is given to the steel sheet. At the time, the Goss-oriented grains formed in the local heating affected region preferentially grow during secondary annealing. A large number of Goss-oriented grains are formed in the local heating affected region, and among them, the Goss-oriented grains that are close to the ideal Goss orientation, have particularly small angular deviation θ and small angular deviation ϕ, and have a large grain size after primary annealing are included. In the secondary recrystallization, the above Goss-oriented grains among the grains grow preferentially.

[0063] Herein, since the Goss-oriented grains which act as the nucleus of the secondary recrystallization are arranged in the local heating affected region, it is not necessary to form the Goss-oriented grains by the primary annealing in a matrix region other than the local heating affected region, that is, a local heating non-affected region. Accordingly, as the heat treatment condition of the primary annealing, a mild heating condition with a low heating rate may be employed, and a primary annealing condition may be employed in which a large number of CSL oriented grains having the {111}<112> orientation and the {411 }<148> orientation, which are easily encroached, are formed in the local heating non-affected region. For instance, by controlling the heating rate of the primary annealing to 300 °C / sec or less, a large number of Goss-oriented grains close to the ideal Goss orientation and having large grain size are formed in the local heating affected region, while Goss-oriented grains are hardly formed in the local heating non-affected region, and conversely, a large number of CSL oriented grains are formed.

[0064] As described above, in the local heating affected region of the steel sheet (decarburization-annealed steel sheet) in which the local rapid heating and the primary annealing have been completed, a large number of Goss-oriented grains close to the ideal Goss orientation and having large grain size are included. On the other hand, in the matrix region (local heating non-affected region), the Goss-oriented grains having large size are hardly included, whereas a large number of CSL oriented grains that are easily encroached may be included.

[0065] When the above steel sheet (decarburization-annealed steel sheet) is subjected to secondary annealing, Goss-oriented grains that are included in the local heating affected region, are close to the ideal Goss orientation, and have large grain size initiate to grow preferentially and grow toward the local heating non-affected region.

[0066] Moreover, in the present embodiment, the secondary recrystallization is proceeded while giving the thermal gradient to the steel sheet in a tip area of secondary recrystallized grain which is encroaching primary recrystallized grains in secondary annealing. When the secondary recrystallized grains are grown using the thermal gradient, the secondary recrystallized grains having the orientation close to the ideal Goss orientation are nucleated from the area where the secondary recrystallization is likely to start antecedently in the steel sheet, and the secondary recrystallized grains grow preferentially due to the thermal gradient. As a result, the alignment degree to the Goss orientation is favorably increased. The direction to give the above thermal gradient may be the transverse direction C.

[0067] Conventionally, in a case where the secondary recrystallized grain is grown while the thermal gradient is given, the secondary recrystallized grains are excessively large, and thus, it is unavoidable that the deviation angle β deteriorates due to a coil set. Specifically, in a case where the thermal gradient during secondary recrystallization is given in the transverse direction C for instance, the secondary recrystallized Goss-oriented grains tend to grow toward an area where the temperature of steel sheet is low (toward the transverse direction C), but the secondary recrystallized grains also grow toward the rolling direction L at the time. Thus, the grain size D L in the rolling direction also becomes large. That is, in the conventional technique, the grain size D L in the rolling direction inescapably becomes large when trying to increase the magnetic flux density, and as a result, it is unavoidable that the deviation angle β is increased due to the coil set. However, in the present embodiment, since it is possible to increase the existence frequency of the secondary recrystallized grains close to the ideal Goss orientation by the above local rapid heating, it is possible to suppress the increase in the grain size D L in the rolling direction, and it is possible to suppress the deterioration of the deviation angle β due to the coil set. As explained above, in the present embodiment, the deterioration of the deviation angle β is suppressed, and thus, it is possible to obtain the steel sheet excellent in the magnetic flux density and the magnetostriction as compared with the conventional technique. In addition, in the present embodiment, the secondary recrystallized grains having the orientation close to the ideal Goss orientation are preferentially formed, and thus, it is possible to also suppress the deterioration of the deviation angle α. Therefore, it is possible to obtain the steel sheet excellent in the magnetic flux density as compared with the conventional technique.

[0068] Hereinafter, the investigations carried out by the present inventors will be described in detail.

[0069] As an aspect of the above local rapid heating, a case where spot electric heating by electric resistance heating is used will be described. In the spot electric heating, spot electrodes are arranged and contacted so as to be opposite to each other on both surfaces of the steel sheet, and a current flows between the spot electrodes to perform the spot electric heating on a region where the electrodes are held on the steel sheet. Steel having the composition indicated in Table 1 was used, and hot rolling and cold rolling were performed to obtain a cold-rolled steel sheet having a thickness of 0.22 mm. The steel sheet was subjected to the spot electric heating. The spot electric heating was performed using copper electrodes having a diameter of 3 mm under the conditions of a flowing current of 5.0 kA or less which was a range where the sheet surface was not melted, a time of current flow of 20 to 80 milliseconds, an electrode force of 50 to 150 kgf, and an electrode retention time after current flow of 0.2 seconds. On the surface of the cold-rolled steel sheet, the spot electric heating was performed by a pitch of 20 mm in the rolling direction at a position of 10 mm from an edge in the transverse direction of the cold rolled steel sheet in order to form the locally heated region. This cold-rolled steel sheet was subjected to decarburization annealing (primary annealing). In the decarburization annealing, the cold-rolled steel sheet was heated at a heating rate of 20 °C / sec and held at 830°C for 90 seconds.

[0070] FIG. 1 illustrates an instance of arrangement of the local heating affected region in the decarburization-annealed steel sheet manufactured by the above conditions. In FIG. 1, the decarburization-annealed steel sheet 1, the local heating affected regions 2, the rolling direction 21, and the width direction (transverse direction) 22 are schematically illustrated. [Table 1]CHEMICAL COMPOSITION (mass%)CSiMnSAlN0.063. 350.10.0070.0270.008

[0071] In order to prepare an observed section for Electron Back Scattering Diffraction pattern (EBSD) from the surface of a decarburization-annealed steel sheet (steel sheet after local rapid heating and after primary annealing), a surface was smoothed by mechanical polishing, and electrolytic polishing was performed to remove added strain of the surface. Thereafter, an image quality (IQ) value and a crystal orientation in a region including the locally heated region were measured by the EBSD under condition of a step of 0.5 µm. FIG. 2 is a schema illustrating a distribution of the Goss-oriented grains of the decarburization-annealed steel sheet manufactured by the above conditions.

[0072] An electrode used for spot electric heating has a circular shape, and the diameter thereof is preferably 0.5 to 10 mmϕ, and more preferably 1 to 5 mmϕ in an equivalent circle diameter. Note that, in the above description, the electrode having the circular shape is used, but in so far as the heating rate of the cold-rolled steel sheet is locally increased and Goss-oriented grains are formed and grown in this region, the electrode shape may be another shape, for instance, an elliptical shape or a linear shape.

[0073] In FIG. 2, based on the definition of the angular deviation ϕ = (α 2< + β 2< ) 1 / 2< , grains having the angular deviation ϕ of 10° or less from the ideal Goss orientation (Goss-oriented grains 14) are indicated by "∘". Further, among the grains having the angular deviation ϕ of 10° or less, grains having a coarse grain size (coarse Goss-oriented grains 15) are indicated by "⊙". Note that the coarse Goss-oriented grains 15 indicate Goss-oriented grains having a grain size of 3 times or more as compared with an average grain size.

[0074] As illustrated in FIG. 2, the decarburization-annealed steel sheet 1 manufactured by the above conditions includes the Goss-oriented grains 14 and also includes the coarse Goss-oriented grains 15. In particular, the region including the coarse Goss-oriented grains 15 corresponds to the local heating affected region 2. Note that, although a locally heated region boundary 4 and a local heating affected region boundary 5 are schematically illustrated in FIG. 2, it is not easy to identify these boundaries by microstructure observation. However, the region including the coarse Goss-oriented grains 15 can be regarded as the local heating affected region 2.

[0075] The decarburization-annealed steel sheet was further subjected to nitridation, applying an annealing separator including MgO as a main component, and then secondary annealing. The secondary annealing conditions are a hydrogen-nitrogen atmosphere, a heating rate of 15°C / hr (°C / hour), and holding at 1200°C for 20hr (hour). Moreover, in the heating stage of the final annealing, the thermal gradient of 5 °C / cm in the transverse direction was given in a border area between primary recrystallized area and secondary recrystallized area in the steel sheet.

[0076] The obtained steel sheet was subjected to macroetching to reveal grain boundaries. When a region corresponding to the local heating affected region was observed in the steel sheet after the macroetching, it was observed that plural secondary recrystallized grains grew from the region corresponding to the local heating affected region or that the secondary recrystallized grain grew from the center of the region corresponding to the local heating affected region. In addition, in the region corresponding to the local heating affected region, fine grains of 2 mm or less may or may not be observed as a vestige of the local heating affected region. Although the secondary recrystallized macrostructure may slightly change depending on the condition of the local heating, the alignment degree of the Goss orientation can be increased as compared with the case where the local heat treatment is not performed.

[0077] Moreover, the crystal orientation of the obtained steel sheet was measured by the above Laue method. In the obtained steel sheet, aveϕ L was 3.5° or less, D L 10 was (100 - 15 × aveϕ L ) or less in units of mm, and aveD C was 50 mm or more. As a result, although the thermal gradient during secondary recrystallization was given to the steel sheet, the obtained steel sheet was excellent in both the magnetic flux density and the magnetostriction.

[0078] As explained above, it was confirmed for the obtained grain oriented electrical steel sheet that the deviation between the secondary recrystallized grains and the ideal Goss orientation was extremely small. Also, it was confirmed that the angular deviation ϕ was averagely small at each measurement point along the rolling direction L, the grains did not grow coarsely in the rolling direction L, and the grains tended to become the oblate shape which was elongated to the transverse direction C and which was compressed to the rolling direction L.

[0079] Based on the above investigation, it is considered that the fact that the coarse Goss-oriented grains which are close to the ideal Goss orientation and which have the size advantage are formed in the decarburization-annealed steel sheet results in improving the crystal orientation of the secondary recrystallized grains. Also, it is considered that the fact that the locally heated regions are favorably arranged before primary annealing, the annealing conditions of primary annealing are favorably controlled, and the annealing conditions of secondly annealing are favorably controlled results in improving both the magnetic flux density and the magnetostriction.

[0080] For instance, when the above decarburization-annealed steel sheet is used, the coarse Goss-oriented grains close to the ideal Goss orientation (Goss-oriented grains having the large grain size) are preferentially grown among a large number of Goss-oriented grains in the local heating affected region during secondary recrystallization. Therefore, it is possible to obtain the steel sheet occupied by the secondary recrystallized grains close to the ideal Goss orientation without coarsening the secondary recrystallized grains. For instance, at the time when the local heating affected regions are discretely arranged on the sheet surface, if the local heating affected regions are appropriately arranged on the sheet surface, it is possible to control the size, shape, and arrangement of the grains after the secondary annealing. For instance, the Goss-oriented grain initiates to grow from one local heating affected region, the grain growth stops when the grain encounters with another Goss-oriented grain which initiates to grow from an adjacent local heating affected region, and thereby, the grain size of the Goss-oriented grains after secondary recrystallization (especially, the grain size D L in the rolling direction) can be controlled to be small in the steel sheet. In particular, as described above, in the initial stage of the secondary annealing, the Goss-oriented grains preferentially grown from the local heating affected region have the crystal orientation close to the ideal Goss orientation, and as a result, excellent magnetic flux density can be obtained even though the secondary recrystallized grain size is small. Moreover, since the grains are suppressed to grow coarsely in the rolling direction L, it is suppressed to deteriorate the deviation angle β due to the coil set, and excellent magnetostriction is obtained.

[0081] That is, in the above grain oriented electrical steel sheet, it is possible to improve the alignment degree of the Goss orientation while suppressing coarsening of the secondary recrystallized grain size (especially, the grain size D L in the rolling direction), and thus, it is possible to omit or reduce the refinement of the width of magnetic domain by applying the strain or forming the grooves. Specifically, since the effect of the magnetic domain refinement can be preferably obtained by the grain boundaries that increase as a result of the refinement of the secondary recrystallized grain size, the magnetic domain is refined without applying the conventional magnetic domain control technique. Therefore, it is possible to omit or reduce the strain which is applied into the steel sheet contrary to the conventional magnetic domain control technique, and thus, it is possible to suppress an increase in the magnetostriction. In addition, it is possible to omit forming the grooves or to reduce the depth of grooves contrary to the conventional magnetic domain control technique, and thus, it is possible to suppress a decrease in the magnetic flux density B 8 . In addition, it is possible to use the above grain oriented electrical steel sheet for utilization requiring the strain relief annealing at 800°C or higher.

[0082] Moreover, as explained above, the effect of the magnetic domain refinement can be preferably obtained by the grain boundaries that increase as a result of the refinement of the secondary recrystallized grain size (especially, the grain size D L in the rolling direction), and thereby, the grain oriented electrical steel sheet according to the present embodiment shows excellent iron loss.

[0083] Next, a preferred method for manufacturing the grain oriented electrical steel sheet according to the present embodiment will be described.

[0084] The method for manufacturing the grain oriented electrical steel sheet according to the present embodiment is not limited to the following method. The following manufacturing method is an instance for manufacturing the grain oriented electrical steel sheet according to the present embodiment.

[0085] Moreover, the processes and the quantitative conditions in each process described below are an instance employed to confirm the operability of the present embodiment, so that the present embodiment is not limited to the processes and the quantitative values. The method for manufacturing the grain oriented electrical steel sheet according to the present embodiment can employ various types of conditions as long as the conditions do not depart from the scope of the present embodiment and can achieve the object of the present embodiment.

[0086] In the method for manufacturing the grain oriented electrical steel sheet according to the present embodiment, it is possible to apply a conventional known method for manufacturing the grain oriented electrical steel sheet as fundamental processes. For instance, the conventional method for manufacturing the grain oriented electrical steel sheet includes a manufacturing method utilizing MnS and AlN as inhibitor which are formed by high temperature slab heating, a manufacturing method utilizing AlN as inhibitor which is formed by low temperature slab heating and subsequent nitridation, and the like. The method for manufacturing the grain oriented electrical steel sheet according to the present embodiment is not limited to a specific manufacturing method. Hereinafter, the method which employs the low temperature slab heating with the nitridation is explained for instance.(Casting Process)

[0087] In the casting process, a slab is made. For instance, a method for making the slab is as follow. A molten steel is made (a steel is melted). The slab is made by using the molten steel. The slab may be made by continuous casting. An ingot may be made by using the molten steel, and then, the slab may be made by blooming the ingot. A thickness of the slab is not particularly limited. The thickness of the slab may be 150 to 350 mm for instance. The thickness of the slab is preferably 220 to 280 mm. The slab with the thickness of 10 to 70 mm which is a so-called thin slab may be used. When using the thin slab, it is possible to omit a rough rolling before final rolling in the hot rolling process.

[0088] For instance, as the chemical composition, the above slab may include the following elements.C: 0.085% or less

[0089] Carbon (C) is an element effective in controlling the primary recrystallized structure in the manufacturing process. However, when the content in the final product is excessive, the magnetic characteristics are negatively affected. Thus, the C content may be 0.085% or less. The upper limit of the C content is preferably 0.075%. C is decarburized and purified in the decarburization annealing process and the final annealing process, and then, the content becomes 0.005% or less. When C is included, the lower limit of the C content may be more than 0%, and may be 0.001% from the productivity standpoint in the industrial production.Si: 2.0 to 7.0%

[0090] Silicon (Si) is an element which increases the electric resistance of the grain oriented electrical steel sheet and thereby decreases the iron loss. When the Si content is less than 2.0%, an austenite transformation occurs during the final annealing and the crystal orientation of the grain oriented electrical steel sheet is impaired. On the other hand, when the Si content is more than 7.0%, the cold workability deteriorates and the cracks tend to occur during cold rolling. The lower limit of the Si content is preferably 2.5%, and is more preferably 3.0%. The upper limit of the Si content is preferably 4.5%, and is more preferably 4.0%.Mn: 0.05 to 1.00%

[0091] Manganese (Mn) forms MnS and / or MnSe by bonding to S and / or Se, which act as the inhibitor. When Mn is included and the Mn content is 0.05 to 1.00%, the secondary recrystallization becomes stable. The nitride of the Nb group element can bear part of the function of the inhibitor. In the case, the inhibitor intensity as MnS and / or MnSe in general is controlled weakly. Thus, the upper limit of the Mn content is preferably 0.50%, and is more preferably 0.20%.At least one of S and Se: 0.003 to 0.035% in total

[0092] Sulfur (S) and Selenium (Se) form MnS and / or MnSe by bonding to Mn, which act as the inhibitor. When at least one of S and Se is included, and when the total amount of S and Se is 0.003 to 0.035%, the secondary recrystallization becomes stable. The nitride of the Nb group element can bear part of the function of the inhibitor. In the case, the inhibitor intensity as MnS and / or MnSe in general is controlled weakly. Thus, the upper limit of the total amount of S and Se is preferably 0.025%, and is more preferably 0.010%. When S and / or Se remain in the steel after the final annealing, the compound is formed, and thereby, the iron loss is deteriorated. Thus, it is preferable to reduce S and Se as much as possible by the purification during the final annealing.

[0093] Here, the total amount of S and Se represents that at least one of S and Se is included and the amount thereof corresponds to the above total amount.Al: 0.010 to 0.065%

[0094] Aluminum (Al) forms (Al, Si)N by bonding to N, which acts as the inhibitor. When Al is included and the Al content is 0.010 to 0.065%, the inhibitor AlN formed by the nitridation mentioned below expands the temperature range of the secondary recrystallization, and the secondary recrystallization becomes stable especially in higher temperature range. Therefore, the Al content is 0.010 to 0.065%. The lower limit of the Al content is preferably 0.020%, and is more preferably 0.025%. The upper limit of the Al content is preferably 0.040%, and is more preferably 0.035% from the stability standpoint in the secondary recrystallization.N: 0.012% or less

[0095] Nitrogen (N) bonds to Al and acts as the inhibitor. The lower limit thereof is not limited because it is possible to include N by the nitridation in midstream of the manufacturing process. For instance, the lower limit of the N content may be more than 0% or may be 0.001%. When N is included and the N content is more than 0.012%, the blister which is a kind of defect tends to be formed in the steel sheet. The upper limit of the N content is preferably 0.010%, and is more preferably 0.009%. N is purified in the final annealing process, and then, the N content becomes 0.005% or less after the final annealing process.

[0096] The balance of the chemical composition consists of Fe and impurities. The impurities correspond to elements which are contaminated during industrial production of steel from ores and scrap that are used as a raw material of steel, or from environment of a manufacturing process. For instance, an upper limit of the impurities may be 5% in total.

[0097] In addition to solving manufacturing problems, in consideration of the influence on the magnetic characteristics and the improvement of the inhibitors function by forming compounds, the above chemical composition may include the known optional elements as substitution for part of Fe. For instance, the optional elements as substitution for part of Fe may be the following elements.Nb group element: 0.050% or less

[0098] The total amount of the Nb group element (at least one of Nb, V, Mo, Ta, and W) may be 0.050% or less. When the Nb group element (at least one of Nb, V, Mo, Ta, and W) is utilized as part of the inhibitor, and when the total amount of the Nb group element is 0.030% or less, the secondary recrystallization starts at appropriate timing, which is preferable. Moreover, the orientation of the formed secondary recrystallized grain becomes very favorable, and the microstructure is finally controlled to be favorable for the magnetization characteristics. In particular, Nb and Ta prominently shows the above effects, which is preferable. The lower limit of the total amount of the Nb group elements does not need to be limited, and the lower limit may be 0%. The lower limit is preferably 0.003%.

[0099] The total amount of the Nb group elements is more preferably 0.004 to 0.020%. The total amount is more preferably 0.005 to 0.010%.

[0100] Here, the total amount of the Nb group elements represents that at least one of Nb, V, Mo, Ta, and W is included and the amount thereof corresponds to the above total amount.

[0101] In addition, the slab may contain, as the optional element, by mass%, at least one of: Cu: 0.40% or less, Bi: 0.010% or less, B: 0.080% or less, P: 0.50% or less, Ti: 0.015% or less, Sn: 0.10% or less, Sb: 0.10% or less, Cr: 0.30% or less, and Ni: 1.00% or less.

[0102] The optional elements may be contained according to a known purpose, a lower limit of the optional elements does not need to be limited, and the lower limit may be 0%.

[0103] The chemical composition of the slab may be measured by the above analytical methods, as with the chemical composition of the grain oriented electrical steel sheet as the final product.(Hot Rolling Process)

[0104] In the hot rolling process, the slab is heated to a predetermined temperature (for instance, 1100 to 1400°C), and then, is subjected to hot rolling in order to obtain a hot rolled steel sheet. In the hot rolling process, for instance, the silicon steel material (slab) is heated in heating stage, is rough-rolled, and then, is final-rolled in order to obtain the hot rolled steel sheet with a predetermined thickness, for instance, 1.8 to 3.5 mm. After finishing the final rolling, the hot rolled steel sheet is coiled at a predetermined temperature.

[0105] In a case where of a process including the nitridation during decarburization annealing or after decarburization annealing, the inhibitor intensity as MnS is not necessarily needed, it is preferable that the slab heating temperature is 1100 to 1280°C from the productivity standpoint.(Hot-Band Annealing Process)

[0106] In the hot band annealing process, the hot rolled steel sheet after the hot rolling process is annealed under predetermined conditions (for instance, 750 to 1200°C for 30 seconds to 10 minutes) in order to obtain a hot band annealed sheet. The hot-band annealing is generally performed to control the microstructure of the steel sheet such as the recrystallization fraction, the residual strain, and the grain size by annealing the hot-rolled steel sheet after the hot rolling process and to preferably control the morphology of precipitates in the steel. For instance, in high temperature slab heating process, the above process is to finally control the morphology of precipitates such as AlN, and the conditions are controlled so that the precipitates are uniformly and finely precipitated. For instance, as the hot band annealing, the steel sheet may be heated to 1050°C to 1150°C, may be slow-cooled to an intermediate temperature (850°C to 950°C) for 50 to 150 seconds in order to appropriately precipitates A1N and the like, and thereafter, may be water-cooled.(Cold Rolling Process)

[0107] In the cold rolling process, the hot band annealed sheet after the hot band annealing process is cold-rolled once or is cold-rolled plural times (two times or more) with an annealing (intermediate annealing) (for instance, 80 to 95% of total cold reduction) in order to obtain a cold rolled steel sheet with a thickness, for instance, 0.10 to 0.50 mm. In order to improve the magnetic characteristics, for instance, an interpass temperature of the cold rolling may be approximately 100°C to 300°C.(Local Rapid Heating Process)

[0108] In the present embodiment, local rapid heating for forming the locally heated region is performed on the cold-rolled steel sheet after the cold rolling process. The rapid heating method is not particularly limited as long as the steel sheet can be locally heated. For instance, it is possible to adopt a method in which spot electrodes are arranged and contacted on both surfaces of the steel sheet and the steel sheet is heated by flowing a current in the steel sheet, a method in which the steel sheet is heated by irradiating the surface thereof with laser beam, electron beam, and the like, a method in which the steel sheet is locally heated by induction heating, a method in which the steel sheet is heated by contacting a heated piece, and the like. The size of each locally heated region may be a dotted region having a diameter of approximately 10 µm to 10 mm or a linear region having a width of approximately 10 µm to 10 mm. In addition, the electrode used for electric heating may be a circular electrode or a linear electrode as described above.

[0109] Note that regarding the size of the locally heated region, the minimum diameter and the minimum width depend on the shape of the spot electrode and the technique of reducing the focusing diameter of the laser beam or the electron beam. Although it is possible in principle to further reduce the size of the locally heated region, it is considered that the effect can be obtained when the size of the locally heated region is 1 µm or more in consideration of the fact that the nucleus of the recrystallized grain has a size of approximately 1 µm under the present conditions. From an industrial standpoint, the minimum diameter and the minimum width may be 10 µm or more. In addition, with respect to the size of the locally heated region, when the maximum diameter or the maximum width exceeds 10 mm, the area fraction of the Goss-oriented grains having relatively large angular deviation θ or angular deviation ϕ that cannot grow out of the locally heated region increases. In this case, it is difficult to obtain the effect of performing local rapid heating.

[0110] In the local rapid heating, the heating rate may be 500 °C / sec or more at a central position of the locally heated region as viewed in the thickness direction and at a thickness 1 / 5 position of the steel sheet. When the heating rate is 500 °C / sec or more at the above region, the microstructure of the locally heated region can be preferably controlled to a recovered structure or a recrystallized structure. The heating rate is preferably 2000 °C / sec or more, and more preferably 10000 °C / sec or more. On the other hand, the upper limit of the heating rate is not particularly limited, and the upper limit may be, for instance, 1000000 °C / sec.

[0111] In addition, it is preferable that the heating rate is comprehensively and inseparably controlled with the heating rate during decarburization annealing described below. For instance, in the present embodiment, although the coarse Goss-oriented grains in the local heating affected region is intended to exist after the decarburization annealing, it is difficult to achieve the above intension when the heating rate during decarburization annealing is faster than the heating rate during local rapid heating. Therefore, although depending on the degree of the value of the heating rate, the heating rate during local rapid heating is preferably equal to or more than the heating rate during decarburization annealing. A person skilled in the art can preferably control the heating rate during local rapid heating and the heating rate during decarburization annealing if a person skilled in the art understands the purpose of making the coarse Goss-oriented grains to exist in the local heating affected region after decarburization annealing.

[0112] Herein, the thickness 1 / 5 position of the steel sheet indicates a depth corresponding to 1 / 5 of the thickness of the steel sheet from the surface of the steel sheet along the thickness direction.

[0113] In addition, in the local rapid heating, the maximum attained temperature may be 700°C or more at the central position of the locally heated region as viewed in the thickness direction and at the thickness 1 / 5 position of the steel sheet. When the maximum attained temperature is 700°C or more in the above region, the microstructure of the locally heated region can be preferably controlled to the recovered structure or the recrystallized structure. The maximum attained temperature is preferably 800°C or higher, and more preferably 900°C or higher. On the other hand, the maximum attained temperature may be equal to or lower than the melting point of the steel sheet, and may be, for instance, 1400°C or lower.

[0114] In addition, in the local rapid heating, the holding time from reaching the maximum temperature until cooling to 700°C may be 0.1 seconds or more at the central position of the locally heated region as viewed in the thickness direction and at the thickness 1 / 5 position of the steel sheet. When the holding time is 0.1 seconds or more in the above region, the microstructure of the locally heated region can be preferably controlled to the recovered structure or the recrystallized structure. The holding time is preferably 0.2 seconds or more, more preferably 0.3 seconds or more, and still more preferably 0.4 seconds or more. On the other hand, the upper limit of the holding time is not particularly limited, and the upper limit may be, for instance, 10 seconds or less. The holding time from reaching the maximum temperature until cooling to 700°C has essentially affected the formation of the coarse Goss-oriented grains close to the ideal Goss orientation.

[0115] In the local rapid heating, it is important to control the above holding time in addition to the heating rate and the maximum attained temperature described above. During this holding time, it is possible to form a sub-grain structure or a recrystallized nucleus, which is advantageous for the formation of the coarse Goss-oriented grains in the locally heated region. By controlling the sub-grain structure in the locally heated region through the holding time, it is possible to preferably control the microstructure in the subsequent process.

[0116] As described above, the method of local rapid heating is not particularly limited. For instance, local rapid heating may be performed by spot electric heating, laser irradiation, or electron beam irradiation. Any local rapid heating method may be controlled so as to satisfy the heating rate, the maximum attained temperature, and the holding time described above. A person skilled in the art can combine the conditions of the local rapid heating, and thereby, can control the heating rate, maximum attained temperature, and holding time according to the purpose.

[0117] For instance, a person skilled in the art can control the heating rate and the maximum attained temperature at the central position of the locally heated region as viewed in the thickness direction and at the thickness 1 / 5 position of the steel sheet by performing thermal conductivity analysis using finite element method. Additionally, a person skilled in the art can control the above holding time by controlling conditions of heat dissipation after reaching the maximum temperature. For instance, in the case of spot electric heating, the electrode retention time after current flow may be controlled, or the shape of the spot electrode may be changed to a shape suitable for heat dissipation. In addition, in the case of laser irradiation or electron beam irradiation, the irradiation speed may be adjusted, or the shape of irradiated region may be changed to an ellipse and the like to add a gradient to the irradiation energy from the central region toward the outer edge region in irradiated region.

[0118] In general, in heating by laser irradiation, only the vicinity of the irradiated sheet surface is preferentially heated, and the inside of the steel sheet is hardly heated. In addition, since heating by laser irradiation is non-contact heating, heat dissipation after heating is fast, and it is difficult to hold the temperature. Therefore, when heating by laser irradiation is performed as the local rapid heating, in order to recover or recrystallize the cold-deformed structure in the laser-irradiated region, it is necessary to perform heating under a condition of heating not only the sheet surface but also the inside of the steel sheet and under a condition of relatively coarsening the sub-grain structure in the laser-irradiated region by slowing the cooling rate. The condition of laser irradiation for performing the local rapid heating is quite different from the condition of laser irradiation for performing the magnetic domain refinement. For instance, even if the condition of laser irradiation for performing magnetic domain refinement (usually 0.5 to 50 mJ / mm 2< ) is applied to the present embodiment, the microstructure of the locally heated region cannot be controlled in a preferable one, and the coarse Goss-oriented grains close to the ideal Goss orientation are not formed in the steel sheet after the decarburization annealing process. In addition, the situation with electron beam irradiation is the same as with laser irradiation. Even if the condition of electron beam irradiation for performing magnetic domain refinement is applied to the present embodiment, the microstructure of the locally heated region cannot be controlled in a preferable one, and the coarse Goss-oriented grains close to the ideal Goss orientation are not formed in the steel sheet after the decarburization annealing process.

[0119] Note that, even when the input power of laser irradiation or electron beam irradiation is simply increased, it is difficult to form the coarse Goss-oriented grains close to the ideal Goss orientation. For instance, when the rapid heating is performed by laser irradiation or electron beam irradiation, it is preferable to make the beam shape elliptical or control the scan speed and the like in order to secure a temperature range where the grains in the region grow after the rapid heating.

[0120] Conventionally, in an electrical steel sheet, laser irradiation and electron beam irradiation have been performed to reduce the iron loss by performing magnetic domain control on the steel sheet after secondary recrystallization. Under conditions of these laser irradiation and electron beam irradiation, since approximately 20 µm from the surface of the steel sheet is heated, heat dissipation after heating is fast. Therefore, under the conventional conditions, it is difficult to secure the holding time from reaching the maximum temperature until cooling to 700°C as described above. That is, under the conditions of conventional laser irradiation and electron beam irradiation, it may be possible to make the irradiated region act as a barrier for the growth of the secondary recrystallized grains, but it is difficult to form the coarse Goss-oriented grains having the orientation close to the ideal Goss orientation as in the present embodiment. In order to form the coarse Goss-oriented grains close to the ideal Goss orientation by laser irradiation or electron beam irradiation, it is necessary to investigate conditions of laser irradiation or electron beam irradiation as described above.

[0121] Moreover, the local heating affected regions may be appropriately arranged on the sheet surface according to the purpose. In the method for manufacturing the grain oriented electrical steel sheet according to the present embodiment, the secondary recrystallized grains is controlled so as to have the oblate shape which was elongated to the transverse direction C and which was compressed to the rolling direction L. For instance, with an increase in spacing of the local heating affected regions in the rolling direction L, the secondary recrystallized grain size tends to be coarse in the rolling direction L. In the same way, with an increase in spacing of the local heating affected regions in the transverse direction C, the secondary recrystallized grain size tends to be coarse in the transverse direction C. The arrangements of these local heating affected regions in the rolling direction L and the transverse direction C are influenced each other. For instance, when spacing in the rolling direction L increases, the secondary recrystallized grain size may become coarse in the transverse direction C even when spacing in the transverse direction C is small. Moreover, the grain growth of the secondary recrystallized grains are influenced by the steel composition, the thermal gradient in heating stage of final annealing explained below, and the like. Thus, the above oblate shape are controlled by comprehensively controlling these conditions. A person skilled in the art can appropriately combine the arrangement of the local heating affected regions and other conditions in order to control the secondary recrystallized grains to be the above oblate shape.(Decarburization Annealing Process)

[0122] In the decarburization annealing process, the cold-rolled steel sheet after the local rapid heating process is subjected to decarburization annealing (primary annealing). By this decarburization annealing, the existence frequency of the Goss-oriented grains formed in the local heating affected region is increased, the grain size of the Goss-oriented grains is increased, and the coarse Goss-oriented grains having the orientation close to the ideal Goss orientation are preferably formed. As conditions of the decarburization annealing, the heating rate may be 10 to 10000 °C / sec, the annealing temperature may be 700 to 900°C, and the annealing time may be 10 to 600 seconds. In addition, by performing decarburization annealing on the cold-rolled steel sheet, C included in the cold-rolled steel sheet is removed. In order to remove "C" included in the cold rolled steel sheet, it is preferable that the decarburization annealing is conducted in moist atmosphere.

[0123] In addition, it is effective to reduce the primary recrystallized grain size by controlling the conditions of the hot rolling and hot-band annealing described above and by decreasing the decarburization annealing temperature as necessary. The primary recrystallized grain size is not particularly limited but is preferably 8 to 30 µm.

[0124] In addition, in the present embodiment, a large number of the coarse Goss-oriented grains having the orientation close to the ideal Goss orientation are formed in the local heating affected region. Therefore, it is not necessary to form the Goss-oriented grains again by decarburization annealing. The heating rate of the decarburization annealing may be 10000 °C / sec or less as described above, but it is preferable to decrease the heating rate of the decarburization annealing in order to form {111}<112> oriented grains or {411}<148> oriented grains that are easily encroached in the matrix region (local heating non-affected region). For instance, the heating rate of the decarburization annealing is preferably 300 °C / sec or less, more preferably 200 °C / sec or less, and still more preferably 100 °C / sec or less.

[0125] In addition, the amount of oxidation caused by the decarburization annealing and the state of surface oxidized layer affect the formation of the glass film. Therefore, in the decarburization annealing, the oxidation degree (PH 2 O / PH 2 ) in the annealing atmosphere (furnace atmosphere) may be 0.01 to 0.15. Herein, the oxidation degree PH 2 O / PH 2 is defined as the ratio of water vapor partial pressure PH 2 O to hydrogen partial pressure PH 2 in the atmosphere.(Nitridation)

[0126] Nitridation is a treatment effective in the low temperature slab heating process in which the slab heating temperature is 1280°C or lower, and is an important process for controlling the inhibitor intensity in secondary recrystallization. In the nitridation, the nitrogen content of the steel sheet is made to increase to 40 to 200 ppm from starting the decarburization annealing to starting the secondary recrystallization in the final annealing. For instance, the nitridation may be a treatment of annealing the steel sheet in an atmosphere containing a gas having a nitriding ability such as ammonia, a treatment of final-annealing the decarburization annealed steel sheet being applied an annealing separator containing a powder having a nitriding ability such as MnN and the like. The nitrogen content after the nitridation is preferably 130 to 350 ppm, and more preferably 150 to 250 ppm.(Annealing Separator Applying Process)

[0127] In the annealing separator applying process, the decarburization-annealed steel sheet is applied an annealing separator to. For instance, as the annealing separator, it is possible to use an annealing separator mainly including MgO, an annealing separator mainly including Al 2 O 3 , and the like. The decarburization-annealed steel sheet after applying the annealing separator is coiled and is final-annealed in the subsequent final annealing process.(Final Annealing Process)

[0128] In the final annealing process, the decarburization annealed steel sheet after applying the annealing separator is final-annealed so that the secondary recrystallization (secondary annealing) occurs. In the process, the secondary recrystallization proceeds under conditions such that the grain growth of the primary recrystallized grain is suppressed by the inhibitor. Thereby, the grains having the {110}<001> orientation are preferentially grown, and the magnetic flux density is drastically improved.

[0129] In the final annealing, the decarburization annealed steel sheet after applying the annealing separator and being dried may be held for 10 hours or more and 60 hours or less in a temperature range of 1000°C or more and 1300°C or less. The atmosphere during final annealing may be, for instance, a nitrogen atmosphere or a mixed atmosphere of nitrogen and hydrogen.

[0130] Moreover, in the present embodiment, in the heating stage of the final annealing, the secondary recrystallization may be proceeded while giving the thermal gradient of more than 0.5 °C / cm, preferably the thermal gradient of 1.0 °C / cm or more, in a border area between primary recrystallized area and secondary recrystallized area in the steel sheet. For instance, the above thermal gradient may be given to the steel sheet in which the secondary recrystallized grains grow in progress in the temperature range of 800°C or more in the heating stage of the final annealing. The direction to give the above thermal gradient may be the transverse direction C. Moreover, the above thermal gradient may be appropriately changed depending on the steel composition. For instance, in a case of the steel composition in which the secondary recrystallized grains tend to grow preferentially, the thermal gradient may be more than 0.5 °C / cm (preferably 1.0 °C / cm or more). On the other hand, in a case of the steel composition in which the secondary recrystallized grains do not tend to grow preferentially, the thermal gradient is preferably more than 1.0 °C / cm.

[0131] The method of giving the thermal gradient is not particularly limited, and a known method may be applied. For instance, when the coiled steel sheet is heated after placing in a box type annealing furnace, the position and arrangement of the heating device and the temperature distribution in the annealing furnace may be controlled so as to make a sufficient temperature difference from upper side to lower side or from outside to inside of the coil. Alternatively, the temperature distribution may be purposely applied to the coil being subjected to the annealing by actively heating only part of the coil with arranging induction heating, high frequency heating, electric heating, and the like.

[0132] By giving the thermal gradient to the steel sheet in the heating stage of the final annealing, the secondary recrystallized grain having the ideal orientation is nucleated from the area where the secondary recrystallization is likely to start antecedently in the coil, and the secondary recrystallized grains grow preferentially due to the thermal gradient. For instance, it is possible to grow the secondary recrystallized grains throughout the entire coil.(Insulating Coating Forming Process)

[0133] A coating solution including phosphoric acid or phosphate, chromic anhydride or chromate, and colloidal silica is applied to the steel sheet after the final annealing, and is baked (for instance, 350 to 1150°C for 5 to 300 seconds) to form the insulation coating.

[0134] Through the above processes, the grain oriented electrical steel sheet according to the present embodiment can be manufactured. In the grain oriented electrical steel sheet according to the present embodiment manufactured comprehensively and inseparably by controlling each condition of each process, the deviation between the secondary recrystallized grains and the ideal Goss orientation is extremely small, the angular deviation ϕ is averagely small at each measurement point along the rolling direction L, the grains do not grow coarsely in the rolling direction L, and the grains tend to become the oblate shape which is elongated to the transverse direction C and which is compressed to the rolling direction L. Therefore, although the thermal gradient during secondary recrystallization is given to the steel sheet, the steel sheet is excellent in both the magnetic flux density and the magnetostriction.Example 1

[0135] Hereinafter, the effects of the present invention are described in detail with reference to the following examples. However, the condition in the examples is an example condition employed to confirm the operability and the effects of the present invention, so that the present invention is not limited to the example condition. The present invention can employ various types of conditions as long as the conditions do not depart from the scope of the present invention and can achieve the object of the present invention.

[0136] Using slabs having adjusted chemical composition as materials, decarburization-annealed steel sheets with chemical composition shown in Table 2A were manufactured. The chemical composition was measured by the above-mentioned methods. In Table 2, "-" indicates that the control and manufacturing conscious of content did not perform and thus, the content was not measured.

[0137] When the decarburization-annealed steel sheets were manufactured, the slabs were heated to 1150°C, and then hot-rolled to obtain the hot rolled steel sheets having the thickness of 2.6 mm. The hot rolled steel sheets were subjected to the hot band annealing in which the annealing was conducted at 1100°C and then at 900°C, and then were pickled in order to remove the surface scale. The steel sheets were cold-rolled once or cold-rolled plural times with the intermediate annealing to obtain the cold rolled steel sheets having the final thickness of 0.22 mm.

[0138] The cold-rolled steel sheets were subjected to local rapid heating under conditions shown in Tables 3 to 7. For spot electric heating, copper electrodes having a diameter of 1 mm which corresponds to contact area with the steel sheet were used, and then, the heating rate, the maximum attained temperature, the holding time from reaching the maximum temperature until cooling to 700°C (holding time above 700°C) were respectively controlled by comprehensively adjusting the electrode shape other than the contact area with the steel sheet, the electrode force, the flowing current, the time of current flow, the electrode retention time after current flow, and the like. For laser heating, fiber laser was used, focusing spot diameter of laser beam in the rolling direction (specifically, diameter including 86% of laser output) was to be 30 µm (except for Test Nos. 71 and 72), and then, the heating rate, the maximum attained temperature, the holding time above 700°C were respectively controlled by comprehensively adjusting the energy density of laser irradiation, the laser scanning speed, the shape of laser irradiated region, and the like. A person skilled in the art can combine the conditions of the local rapid heating, and thereby, can control the heating rate, the maximum attained temperature, and the holding time above 700°C according to the purpose.

[0139] Note that, in Test No. 69, the laser beam was elongated along scanning direction, and thereby, the holding time from reaching the maximum temperature until cooling to 700°C was controlled to 0.2 seconds in the local rapid heating, in order to form the coarse Goss-oriented grains having the orientation close to the ideal Goss orientation in the locally heated region. In Test No. 70, the general condition of laser irradiation for performing the magnetic domain refinement was applied. In Test No. 71, the focusing spot diameter was 0.5mm, and the energy density of laser irradiation was 2.0 J / mm 2< , in order to control the irradiated region of laser beam to be finally the grain boundary of the secondary recrystallization. In Test No. 72, the focusing spot diameter was 0.5mm, and the energy density of laser irradiation was 30.0 J / mm 2< , in order to control the irradiated region of laser beam to be finally the grain boundary of the secondary recrystallization.

[0140] In the tables, "Not performed" of heating method of local rapid heating indicates that the local rapid heating was not performed. "Linear or Dotted" of local heating condition indicates the shape of the locally heated region on the surface of the cold-rolled steel sheet, and "Spacing in rolling direction" and "Spacing in width direction" of local heating condition indicates the spacing in the rolling direction and the transverse direction in which the locally heated regions were arranged on the surface of the cold-rolled steel sheet. The locally heated regions were uniformly arranged at even spacing in the rolling direction and the transverse direction. Herein, when the locally heated regions were arranged on the surface of the cold rolled steel sheet, the locally heated regions were arranged so that the distribution was not uneven.

[0141] Moreover, in the tables, "edge 10" of spacing in width direction of local heating condition of local rapid heating indicates that the locally heated regions were formed only at a position of 10 mm from an edge in the width direction of the cold rolled steel sheet.

[0142] The cold-rolled steel sheets after the local rapid heating were subjected to decarburization annealing under the conditions shown in Tables 3 to 7. Herein, in the decarburization annealing, the oxidation degree (PH 2 O / PH 2 ) in the annealing atmosphere (furnace atmosphere) was 0.13.

[0143] The manufactured decarburization-annealed steel sheet was subjected to nitridation at 750°C in nitrogen-hydrogen-ammonia atmosphere, and the nitrogen content of the steel sheet was to be 220 ppm. Thereafter, the annealing separator including MgO as a main component was applied and the final annealing was performed.

[0144] In the heating stage of the final annealing, the steel sheet was heated to 1000°C at 15°C / hr (°C / hour) in a mixed atmosphere of hydrogen and nitrogen, heated to 1200°C at heating rates shown in Tables 3 to 7. Moreover, in the heating stage of the final annealing, the thermal gradient in the transverse direction C shown in Tables 3 to 7 was given to the border area between primary recrystallized area and secondary recrystallized area in the steel sheet in the temperature range of 800°C or more. Herein, in Tables 3 to 7, "< 1.0" of thermal gradient of heating stage of final annealing indicates that the thermal gradient was not substantially controlled in the heating stage. After the heating stage of the final annealing, the steel sheet was held at 1200°C - 20hr (hour) in a hydrogen atmosphere.

[0145] For the steel sheet after the final annealing, the coating solution for forming insulation coating which mainly included the phosphate and the colloidal silica and which included the chromic anhydride as necessary was applied and baked to form the insulating coating.

[0146] For the manufactured grain oriented electrical steel sheet, the chemical composition of the base steel sheet, the aveϕ L which was the average of the angular deviation ϕ, the D L 10 which was the grain size at 10% by number base of the grain sizes D L , and the aveD C which was the average of the grain size D C were measured by the above-mentioned methods. The results are indicated in Tables 7 to 13. In Table 13, "-" indicates that the control and manufacturing conscious of content did not perform and thus, the content was not measured. Moreover, for the manufactured grain oriented electrical steel sheet, various features were evaluated. The evaluation results are shown in Tables 7 to 12.

[0147] The magnetic characteristics of the grain oriented electrical steel sheet were measured based on the single sheet tester (SST) method regulated by JIS C 2556: 2015.

[0148] The samples of 20 sheets with a size of 100 mm × 500 mm for the single sheet tester were taken from the obtained grain oriented electrical steel sheets, and then, the single sheet test was performed. As the magnetic characteristics, the magnetic flux density B 8 (T) in the rolling direction of the steel sheet was measured under the condition such that the steel sheet was excited at 800 A / m. When the magnetic flux density B 8 was 1.945T or more, it was judged to as acceptable. Moreover, for reference, the iron loss W 17 / 50 (W / kg) which was defined as the power loss per unit weight (1 kg) of the steel sheet was measured under the conditions of 50 Hz of AC frequency and 1.7 T of excited magnetic flux density.

[0149] In addition, as the magnetic characteristics, the magnetostriction λp-p@1.7T (difference between the minimum and the maximum of magnetostriction at 1.7 T) generated in the steel sheet was measured under the conditions of 50 Hz of AC frequency and 1.7 T of excited magnetic flux density. Specifically, using the maximum length L max and the minimum length L min of the test piece (steel sheet) under the above excitation condition and using the length L 0 of the test piece under 0T of the magnetic flux density, the magnetostriction λp-p@1.7T was calculated based on λp-p@1.7T = (L max - L min ) ÷ L 0 .

[0150] Based on the values of the magnetic characteristics, the magnetostriction velocity level at 1.7 T was calculated. The magnetostrictive waveform with cycles of two or more and the waveform obtained at a sampling frequency of 6.4 kHz were fourier-transformed, the magnetostriction λ at each frequency (fi) (0 to 3.2 kHz) was obtained, and thereby, the magnetostriction velocity level Lva (unit: dB) was calculated using a following expression 1. The magnetostriction velocity level Lva composed of 200 Hz was evaluated.

[0151] Herein, ρ : Density of air (kg / m 3< ) c : Speed of sound (m / s) P 0 : Minimum pressure which human can hear sound of 1kHz (Pa), fi : Frequency (Hz) λ(fi) : Magnetostriction at each frequency converted into Fourier α(fi) : A-weighting at frequency fi π : Pi (the ratio of the circumference of a circle to its diameter)

[0152] In order to obtain Lva@ 1.7T, the following values were substituted. ρ = 1.185 (kg / m 3< ) c = 346.3 (m / s) P 0 = 2 × 10 -5< (Pa)

[0153] When the magnetic flux density B 8 was 1.945T or more and the magnetostriction velocity level Lva @ 1.7T was 41 dB or less, both the magnetic flux density and the magnetostriction were judged to be acceptable.

[0154] In the grain oriented electrical steel sheets which were the inventive examples among Nos. 1 to 98, the aveϕ L , the D L 10, and the aveD C were favorably controlled. These inventive examples showed excellent magnetic flux density and magnetostriction. Also, these inventive examples also showed excellent iron loss.

[0155] On the other hand, in grain oriented electrical steel sheets which were the comparative examples among Nos. 1 to 98, the aveϕ L , the D L 10, or the aveD C was not favorably controlled. In these comparative examples, excellent magnetic flux density or magnetostriction was not obtained as the grain oriented electrical steel sheet. [Table 3]No.STEEL TYPEMANUFACTURING CONDITIONSTOTALLOCAL RAPID HEATINGDECARBURIZATION ANNEALINGFINAL ANNEALINGCOLD REDUCTION OF COLD ROLLINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONHEATING RATEANNEALING TEMPERATUREANNEALING TIMEHEATING STAGELINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONHEATING RATETHERMAL GRADIENT%°C / sec°Csecmmmm°C / sec°Csec°C / hr°C / cm1A91.5SPOT ELECTRIC50009000.3DOTTED160301008509010<1.02A91.5SPOT ELECTRIC50009000.3DOTTED120301008509010<1.03A91.5SPOT ELECTRIC50009000.3DOTTED100301008509010<1.04A91.5SPOT ELECTRIC50009000.3DOTTED80301008509010<1.05A91.5SPOT ELECTRIC50009000.3DOTTED60301008509010< 1.06A91.5SPOT ELECTRIC50009000.3DOTTED50301008509010<1.07A91.5SPOT ELECTRIC50009000.3DOTTED30301008509010<1.08A91.5SPOT ELECTRIC50009000.3DOTTED15301008509010<1.09A91.5SPOT ELECTRIC50009000.3DOTTED160EDGE 101008509010510A91.5SPOT ELECTRIC50009000.3DOTTED120EDGE 101008509010511A91.5SPOT ELECTRIC50009000.3DOTTED100EDGE 101008509010512A91.5SPOT ELECTRIC50009000.3DOTTED80EDGE 101008509010513A91.5SPOT ELECTRIC50009000.3DOTTED60EDGE 101008509010514A91.5SPOT ELECTRIC50009000.3DOTTED30EDGE 101008509010515A91.5SPOT ELECTRIC50009000.3DOTTED15EDGE 101008509010516A91.5SPOT ELECTRIC50009000.3DOTTED100EDGE 1010085090101.017A91.5SPOT ELECTRIC50009000.3DOTTED100EDGE 101008509010318A91.5SPOT ELECTRIC50009000.3DOTTED100EDGE 101008509010519A91.5SPOT ELECTRIC50009000.3DOTTED100EDGE 101008509010720A91.5SPOT ELECTRIC50009000.3DOTTED100EDGE 10100850901010 [Table 4] No.STEEL TYPEMANUFACTURING CONDITIONSTOTAL COLD REDUCTION OF COLD ROLLINGLOCAL RAPID HEATINGDECARBURIZATION ANNEALINGFINAL ANNEALINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONHEATING RATEANNEALING TEMPERATUREANNEALING TIMEHEATING STAGELINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONHEATING RATETHERMAL GRADIENT%°C / sec°Csecmmmm°C / sec°Csec°C / hr°C / cm21A91.5SPOT ELECTRIC50009000.3DOTTED1001001008509010<1.022A91.5SPOT ELECTRIC50009000.3DOTTED10010010085090101.023A91.5SPOT ELECTRIC50009000.3DOTTED1001001008509010324A91.5SPOT ELECTRIC50009000.3DOTTED1001001008509010525A91.5SPOT ELECTRIC50009000.3DOTTED30301008509010< 1.026A91.5SPOT ELECTRIC50009000.3DOTTED30301008509010527A91.5SPOT ELECTRIC50009000.3DOTTED100301008509010<1.028A91.5SPOT ELECTRIC50009000.3DOTTED100301008509010529A91.5SPOT ELECTRIC50009000.3DOTTED100301008509010530A91.5SPOT ELECTRIC50009000.3DOTTED100501008509010531A91.5SPOT ELECTRIC50009000.3DOTTED1001001008509010532A91.5SPOT ELECTRIC50009000.3DOTTED100EDGE 101008509010533A91.5NOT PERFORMED------1008509010<1.034A91.5NOT PERFORMED------10085090101.035A91.5NOT PERFORMED------1008509010336A91.5NOT PERFORMED------1008509010537A91.5NOT PERFORMED------1008509010738A91.5NOT PERFORMED------10085090101039A91.5NOT PERFORMED------100850905<1.040A91.5NOT PERFORMED------100850901<1.0 [Table 5] No.STEEL TYPEMANUFACTURING CONDITIONSTOTAL COLD REDUCTION OF COLD ROLLINGLOCAL RAPID HEATINGDECARBURIZATION ANNEALINGFINAL ANNEALINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONHEATING RATEANNEALING TEMPERATUREANNEALING TIMEHEATING STAGELINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONHEATING RATETHERMAL GRADIENT%°C / sec°Csecmmmm°C / sec°Csec°C / hr°C / cm41A91.5SPOT ELECTRIC50009000.3DOTTED100EDGE 1010085090101.042B91.5SPOT ELECTRIC50009000.3DOTTED100EDGE 1010085090101.043A91.5SPOT ELECTRIC5009000.3DOTTED100100100008309010544A91.5SPOT ELECTRIC5009000.3DOTTED10010020008309010545A91.5SPOT ELECTRIC5009000.3DOTTED1001005008309010546A91.5SPOT ELECTRIC5009000.3DOTTED1001003008309010547A91.5SPOT ELECTRIC5009000.3DOTTED1001001008309010548A91.5SPOT ELECTRIC20009000.3DOTTED100100100008309010549A91.5SPOT ELECTRIC20009000.3DOTTED10010020008309010550A91.5SPOT ELECTRIC20009000.3DOTTED1001005008309010551A91.5SPOT ELECTRIC20009000.3DOTTED1001003008309010552A91.5SPOT ELECTRIC20009000.3DOTTED1001001008309010553A91.5SPOT ELECTRIC50009000.3DOTTED100100100008309010554A91.5SPOT ELECTRIC50009000.3DOTTED10010020008309010555A91.5SPOT ELECTRIC50009000.3DOTTED1001005008309010556A91.5SPOT ELECTRIC50009000.3DOTTED1001003008309010557A91.5SPOT ELECTRIC50009000.3DOTTED1001001008309010558A91.5SPOT ELECTRIC100009000.3DOTTED100100100008309010559A91.5SPOT ELECTRIC100009000.3DOTTED10010020008309010560A91.5SPOT ELECTRIC100009000.3DOTTED10010050083090105 [Table 6] No.STEEL TYPEMANUFACTURING CONDITIONSTOTAL COLD REDUCTION OF COLD ROLLINGLOCAL RAPID HEATINGDECARBURIZATION ANNEALINGFINAL ANNEALINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONHEATING RATEANNEALING TEMPERATUREANNEALING TIMEHEATING STAGELINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONHEATING RATETHERMAL GRADIENT%°C / sec°Csecmmmm°C / sec°Csec°C / hr°C / cm61A91.5SPOT ELECTRIC100009000.3DOTTED1001003008309010562A91.5SPOT ELECTRIC100009000.3DOTTED1001001008309010563A91.5SPOT ELECTRIC50009000.3DOTTED1001001008509010<1.064A91.5SPOT ELECTRIC100009000.3DOTTED1001001008309010565A90.4SPOT ELECTRIC5008000.3DOTTED501003008509010466A90.4SPOT ELECTRIC5008000.2DOTTED501003008509010467A90.4SPOT ELECTRIC5008000.1DOTTED501003008509010468A90.4SPOT ELECTRIC5008000.03DOTTED501003008509010469A91.5LASER20008000.2SHORT LINEAR20EDGE 103008309010470A91.5LASER<2000<200<0.03SHORT LINEAR20EDGE 103008309010471A91.5LASER5000800<0.03SHORT LINEAR20EDGE 103008309010472A91.5LASER7000800<0.03SHORT LINEAR20EDGE 103008309010473A90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010374B90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010375C90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010376D90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010377E90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010378F90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010379G90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010380H90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 1010085090103 [Table 7] No.STEEL TYPEMANUFACTURING CONDITIONSTOTAL COLD REDUCTION OF COLD ROLLINGLOCAL RAPID HEATINGDECARBURIZATION ANNEALINGFINAL ANNEALINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONHEATING RATEANNEALING TEMPERATUREANNEALING TIMEHEATING STAGELINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONHEAT ING RATETHERMAL GRADIENT%°C / sec°Csecmmmm°C / sec°Csec°C / hr°C / cm81I90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010382J90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010383K90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010384L90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010385M90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010386N90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010387O90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010388P90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010389Q90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010390R90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010391S90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010392T90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010393U90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010394V90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010395W90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010396X90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010397Y90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 101008509010398Z90.4SPOT ELECTRIC100009000.3DOTTED20EDGE 1010085090103 [Table 8] No.STEEL TYPEMANUFACTURING RESULTSEVALUATION RESULTSNOTEaveΦ L VALUE OF (100 - 15 × aveΦ L )D L 10aveD C MAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50MAGNETOSTRICTION Lva200Hz @1.7Tunit: °mmmmTW / kgdB1A3.94147221.9320.82146.1COMPARATIVE EXAMPLE2A3.84351221.9350.80845.9COMPARATIVE EXAMPLE3A3.74553211.9390.79145.7COMPARATIVE EXAMPLE4A3.64646211.9410.78542.2COMPARATIVE EXAMPLE5A3.54738211.9430.77742.0COMPARATIVE EXAMPLE6A3.54835211.9440.77241.9COMPARATIVE EXAMPLE7A3.45027211.9470.74141.7COMPARATIVE EXAMPLE8A3.35122211.9490.71741.6COMPARATIVE EXAMPLE9A2.563794101.9670.81843.5COMPARATIVE EXAMPLE10A2.365643691.9700.78240.4INVENTIVE EXAMPLE11A2.267553411.9740.75739.3INVENTIVE EXAMPLE12A2.168473111.9760.73637.3INVENTIVE EXAMPLE13A2.169382811.9790.71735.5INVENTIVE EXAMPLE14A2.069252231.9810.68933.0INVENTIVE EXAMPLE15A2.070191891.9830.67431.8INVENTIVE EXAMPLE16A3.548521501.9440.81442.2COMPARATIVE EXAMPLE17A2.661542511.9660.77540.0INVENTIVE EXAMPLE18A2.267553411.9740.75739.3INVENTIVE EXAMPLE19A1.873595271.9840.74439.1INVENTIVE EXAMPLE20A2.070608871.9800.76140.2INVENTIVE EXAMPLE [Table 9] No.STEEL TYPEMANUFACTURING RESULTS"EVALUATION RESULTSNOTEaveΦ L VALUE OF (100 - 15 × aveΦ L )D L 10aveD C MAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50MAGNETOSTRICTION Lva200Hz @1.7Tunit: °mmmmTW / kgdB21A3.84347241.9360.80042.9COMPARATIVE EXAMPLE22A3.64649551.9410.80942.5COMPARATIVE EXAMPLE23A2.95652911.9590.77739.9INVENTIVE EXAMPLE24A2.759531251.9640.76439.4INVENT IVE EXAMPLE25A3.45027211.9470.74141.7COMPARATIVE EXAMPLE26A3.35030261.9480.74041.7COMPARATIVE EXAMPLE27A3.74553211.9390.79145.7COMPARATIVE EXAMPLE28A2.95656731.9590.77640.8INVENTIVE EXAMPLE29A2.95656731.9590.77640.8INVENTIVE EXAMPLE30A2.95754901.9600.77140.8INVENTIVE EXAMPLE31A2.759531251.9640.76439.4INVENTIVE EXAMPLE32A2.365553411.9740.75239.3INVENTIVE EXAMPLE33A4.63137221.9150.83145.3COMPARATIVE EXAMPLE34A4.434431261.9200.82644.9COMPARATIVE EXAMPLE35A3.449542301.9460.81943.2COMPARATIVE EXAMPLE36A3.055663231.9570.79742.4COMPARATIVE EXAMPLE37A2.661834501.9670.80741.8COMPARATIVE EXAMPLE38A2.8591076551.9630.83542.0COMPARATIVE EXAMPLE39A4.04051301.9300.81644.3COMPARATIVE EXAMPLE40A3.64660351.9410.81443.5COMPARATIVE EXAMPLE [Table 10] No.STEEL TYPEMANUFACTURING RESULTSEVALUATION RESULTSNOTEaveΦ L VALUE OF (100 - 15 × aveΦ L )D L 10aveD C MAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50MAGNETOSTRICTION Lva200Hz @1.7Tunit: °mmmmTW / kgdB41A3.548521501.9440.81443.3COMPARATIVE EXAMPLE42B2.858551711.9620.76739.0INVENTIVE EXAMPLE43A3.84327501.9360.82838.9COMPARATIVE EXAMPLE44A3.64636891.9410.81839.5COMPARATIVE EXAMPLE45A3.648401031.9440.81239.7COMPARATIVE EXAMPLE46A3.154421081.9550.79038.1INVENTIVE EXAMPLE47A3.056451181.9580.78438.0INVENTIVE EXAMPLE48A3.74532571.9390.82239.1COMPARATIVE EXAMPLE49A3.05540921.9560.78837.5INVENTIVE EXAMPLE50A3.056441061.9580.78437.8INVENTIVE EXAMPLE51A2.957451101.9600.78037.7INVENTIVE EXAMPLE52A2.858481201.9620.77637.9INVENTIVE EXAMPLE53A3.05540711.9560.78837.5INVENTIVE EXAMPLE54A3.056471011.9580.78438.3INVENTIVE EXAMPLE55A2.957501131.9600.78038.5INVENTIVE EXAMPLE56A2.859511171.9630.77438.2INVENTIVE EXAMPLE57A2.760541261.9650.77038.3INVENTIVE EXAMPLE58A3.05653931.9580.78439.4INVENTIVE EXAMPLE59A2.859581181.9630.77439.4INVENTIVE EXAMPLE60A2.760591251.9650.77039.1INVENTIVE EXAMPLE [Table 11] No.STEEL TYPEMANUFACTURING RESULTSEVALUATION RESULTSNOTEaveΦ L VALUE OF (100 - 15 × aveΦ L )D L 10aveD C MAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50MAGNETOSTRICTION Lva200Hz @1.7Tunit: °mmmmTW / kgdB61A2.661591281.9680.76438.6INVENTIVE EXAMPLE62A2.563591341.9700.76038.3INVENTIVE EXAMPLE63A3.84347241.9360.80042.9COMPARATIVE EXAMPLE64A2.563591341.9700.76038.3INVENT IVE EXAMPLE65A3.153321021.9540.77236.4INVENTIVE EXAMPLE66A3.252441291.9520.78036.7INVENTIVE EXAMPLE67A3.351481831.9500.79036.9INVENTIVE EXAMPLE68A3.646562671.9430.81442.0COMPARATIVE EXAMPLE69A2.168212231.9800.68032.3INVENTIVE EXAMPLE70A3.252632971.9510.79644.8COMPARATIVE EXAMPLE71A3.351582751.9500.78343.5COMPARATIVE EXAMPLE72A3.449552581.9480.76842.8COMPARATIVE EXAMPLE73A2.168281781.9760.68033.4INVENTIVE EXAMPLE74B1.381332111.9980.63630.3INVENTIVE EXAMPLE75C2.069291861.9780.67633.2INVENTIVE EXAMPLE76D2.169271811.9770.67833.1INVENTIVE EXAMPLE77E2.267281801.9740.68433.7INVENTIVE EXAMPLE78F1.774301961.9870.65831.8INVENTIVE EXAMPLE79G1.480312071.9960.64030.5INVENTIVE EXAMPLE80H1.677312051.9910.65031.2INVENTIVE EXAMPLE [Table 12] No.STEEL TYPEMANUFACTURING RESULTSEVALUATION RESULTSNOTEaveΦ L VALUE OF (100 - 15 × aveΦ L )D L 10aveD C MAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50MAGNETOSTRICTION Lva200Hz @1.7Tunit: °mmmmTW / kgdB81I1.774291891.9860.66031.8INVENTIVE EXAMPLE82J2.069281841.9780.67633.1INVENTIVE EXAMPLE83K1.380332041.9970.63830.6INVENTIVE EXAMPLE84L1.774291891.9860.66031.8INVENTIVE EXAMPLE85M1.677312021.9910.65031.4INVENTIVE EXAMPLE86N1.380322061.9970.63830.4INVENTIVE EXAMPLE87O1.971291881.9810.67032.7INVENTIVE EXAMPLE88P2.070281821.9790.67432.9INVENTIVE EXAMPLE89Q2.168271751.9760.68033.3INVENTIVE EXAMPLE90R2.267271711.9740.68433.6INVENTIVE EXAMPLE91S1.775302001.9880.65631.7INVENTIVE EXAMPLE92T2.069291841.9780.67633.1INVENTIVE EXAMPLE93U2.268281791.9750.68233.5INVENTIVE EXAMPLE94V2.168281811.9760.68033.3INVENTIVE EXAMPLE95W2.169281761.9770.67833.3INVENTIVE EXAMPLE96X2.069291821.9780.67633.2INVENTIVE EXAMPLE97Y1.677321961.9910.65031.4INVENTIVE EXAMPLE98Z2.365261731.9710.69034.0INVENTIVE EXAMPLE INDUSTRIAL APPLICABILITY

[0156] According to the above aspects of the present invention, it is possible to provide a grain oriented electrical steel sheet excellent in both the magnetic flux density and the magnetostriction even if the technique in which the secondary recrystallization is proceeded while the thermal gradient is given to the steel sheet is applied. Accordingly, the present invention has significant industrial applicability.REFERENCE SIGNS LIST

[0157] 1Decarburization-Annealed Steel sheet 2Local heating affected region 3Local heating non-affected region (matrix region) 4Locally heated region boundary 5Local heating affected region boundary 14Goss-oriented grain 15Coarse Goss-oriented grain 21Rolling direction 22Width direction (transverse direction)

Examples

example 1

[0135]Hereinafter, the effects of the present invention are described in detail with reference to the following examples. However, the condition in the examples is an example condition employed to confirm the operability and the effects of the present invention, so that the present invention is not limited to the example condition. The present invention can employ various types of conditions as long as the conditions do not depart from the scope of the present invention and can achieve the object of the present invention.

[0136]Using slabs having adjusted chemical composition as materials, decarburization-annealed steel sheets with chemical composition shown in Table 2A were manufactured. The chemical composition was measured by the above-mentioned methods. In Table 2, "-" indicates that the control and manufacturing conscious of content did not perform and thus, the content was not measured.

[0137]When the decarburization-annealed steel sheets were manufactured, the slabs were heated...

Claims

1. A grain oriented electrical steel sheet, wherein when a deviation angle from an ideal Goss orientation based on a rotation axis parallel to a normal direction Z is defined as α, when a deviation angle from the ideal Goss orientation based on a rotation axis parallel to a transverse direction C is defined as β, when a deviation angle from the ideal Goss orientation based on a rotation axis parallel to a rolling direction L is defined as y, when a deviation angle of a crystal orientation measured at one measurement point on a sheet surface is represented as (α β γ), when an angular deviation at the measurement point is defined as ϕ = (α2 + β2)1 / 2, and when an average of the angular deviation ϕ obtained from plural measurement points with spacing of 1 mm in the rolling direction L is defined as aveϕL, the aveϕL satisfies aveϕL ≤ 3.5°, when deviation angles of crystal orientations measured at two measurement points which are adjacent on the sheet surface and which have spacing of 1 mm are represented as (α1 β1 γ1) and (α2 β2 γ2), when a midpoint of two measurement points which satisfy [(α2 - α1)2 + (β2 - β1)2 + (γ2 - γ1)2]1 / 2 ≥ 1.0° is defined as a grain boundary GB, when a grain size in the rolling direction L obtained based on the grain boundary GB is defined as DL in units of mm, and when a grain size which is at 10% by number base from largest in a case where the grain sizes DL obtained in the rolling direction L are sorted from largest to smallest is defined as DL10 in units of mm, the DL10 satisfies DL10 ≤ 100 - 15 × aveϕL, and when a grain size in the transverse direction C obtained based on the grain boundary GB is defined as DC in units of mm, and when an average of the grain size DC obtained in the transverse direction C is defined as aveDC, the aveDC satisfies aveDC ≥ 50.

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