Grain-oriented electrical steel sheet and its manufacturing method

Abstract

This directional electromagnetic steel sheet comprises a base steel sheet having a prescribed chemical composition, a glass coating formed on the base steel sheet, and a tension-imparting insulation coating formed on the glass coating. A plurality of linear strains extending continuously or intermittently in a direction intersecting the rolling direction are present on the surface of the base steel sheet. The spacing p, in the rolling direction, between mutually adjacent linear strains is 3.0 to 9.0 mm, the width of the linear strains is 10-250 μm, and in an X-ray topography spectrum in the range of 1.50 mm in the rolling direction centered on the center of the linear strains, obtained from an X-ray topography image of the surface, the half width of the peak of the X-ray topography spectrum including the maximum value of the spectral intensity is 0.02 mm to 0.10 mm.

Description

[Technical field]

[0001] The present invention relates to a grain-oriented electrical steel sheet and a manufacturing method thereof. This application claims priority based on Japanese Patent Application No. 2021-053618, filed on March 26, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] Grain-oriented electrical steel sheets are soft magnetic materials and are primarily used as iron core materials for transformers, and therefore require magnetic properties such as high magnetization characteristics and low core loss. Iron loss is the power loss consumed as heat energy when an iron core is excited by an AC magnetic field, and from the viewpoint of energy saving, it is desirable to have as low iron loss as possible. The level of iron loss is affected by magnetic susceptibility, sheet thickness, coating tension, amount of impurities, electrical resistivity, crystal grain size, magnetic domain size, etc. Even now, when various technologies have been developed for grain-oriented electrical steel sheets, research and development into reducing iron loss is continuing in order to increase energy efficiency.

[0003] For example, Patent Document 1 describes a process for irradiating a surface of a grain-oriented electrical steel sheet with a focused continuous wave laser beam while scanning the surface in a direction inclined from the rolling direction of the grain-oriented electrical steel sheet, and a process for repeating the process while shifting the area scanned with the continuous wave laser beam at a predetermined interval, in which the average power of the continuous wave laser beam is represented as P (W), the scanning speed as Vc (mm / s), the predetermined interval as PL (mm), and the average irradiation energy density Ua is expressed as Ua = P / (Vc × PL) (mJ / mm 2 ), 1.0 mm ≦ PL ≦ 3.0 mm, and 0.8 mJ / mm 2 ≦Ua≦2.0mJ / mm 2 The present invention discloses a method for producing a grain-oriented electrical steel sheet in which magnetic domains are controlled by irradiation with laser light, the method being characterized by satisfying the above requirements. Patent Document 1 shows that it is possible to easily reduce iron loss in both the L direction and the C direction of a grain-oriented electrical steel sheet while ensuring high productivity.

[0004] In addition, Patent Document 2 discloses a method for manufacturing a grain-oriented electromagnetic steel sheet in which linear circulating magnetic domains are formed substantially perpendicular to the rolling direction of a steel sheet and at substantially constant intervals by scanning and irradiating a continuous oscillation laser beam, thereby improving the iron loss characteristics. In Patent Document 2, the laser has a TEM 00 mode in which the laser beam intensity distribution in a cross section perpendicular to the beam propagation direction has a maximum intensity near the optical axis center, and a directionally electromagnetic steel sheet with reduced iron loss can be obtained when the condensing diameter d [mm] of the irradiation beam in the rolling direction, the scanning linear velocity V [mm / s] of the laser beam, and the average output P [W] of the laser are in the ranges of 0 < d ≤ 0.2 and 0.001 ≤ P / V ≤ 0.012.

[0005] In addition, Patent Document 3 discloses a method for manufacturing a grain-oriented electromagnetic steel sheet in which the surface of the grain-oriented electromagnetic steel sheet is irradiated with laser beams at equal intervals to improve the magnetic properties. In Patent Document 3, the laser is a pulsed oscillation Q-switch CO2 laser, and the irradiation beam shape is an ellipse having a major axis in the sheet width direction. Further, by setting the irradiation power density of the laser pulse below the film damage threshold value of the steel sheet surface, the generation of laser irradiation marks is suppressed, and by setting the major axis length of the elliptical beam to be equal to or greater than the pulse beam irradiation interval in the sheet width direction, continuous pulse beams are superimposed on the steel sheet surface, and sufficient integrated irradiation energy necessary for improving the magnetic properties is given. It has been shown that an efficient magnetic domain control effect can be obtained by suppressing laser irradiation marks.

[0006] On the other hand, in recent years, there has been an increasing demand for reducing noise and vibration in electromagnetic application devices such as transformers. Grain-oriented electromagnetic steel sheets used for transformer cores are required to be materials suitable for low noise and low vibration as well as low iron loss. Magnetic strain in the grain-oriented electromagnetic steel sheet is said to be one of the causes of noise and vibration in transformers. The magnetic strain here refers to the vibration observed in the rolling direction of the grain-oriented electromagnetic steel sheet due to a slight change in the outer shape of the grain-oriented electromagnetic steel sheet as the magnetization strength changes when the grain-oriented electromagnetic steel sheet is excited by alternating current. The magnitude of this magnetic strain is 10 -6Although it is on the order of a very small magnitude, the magnetostriction generates vibrations in the iron core, which are transmitted to external structures such as the transformer tank and result in noise.

[0007] Laser irradiation of grain-oriented electrical steel sheets as proposed in the above-mentioned Patent Documents 1 to 3 is effective in reducing iron loss, but has the problem that the closure domains formed due to the distortion imparted by the laser irradiation increase magnetostriction, thereby degrading noise characteristics.

[0008] To address such issues, for example, Patent Document 4 discloses a grain-oriented electrical steel sheet that has low core loss and produces little noise when incorporated into a transformer. Patent Document 4 discloses that closure domain regions are formed on the steel sheet surface whose width in the rolling direction changes periodically, and that each of the closure domain regions satisfies the following conditions: a ratio (Wmax / Wmin) of the maximum width Wmax in the rolling direction on the steel sheet surface to the minimum width Wmin is 1.2 to 2.2, an average width Wave in the rolling direction on the steel sheet surface is 80 μm to 250 μm, a maximum depth D in the sheet thickness direction is 32 μm or more, and (Wave × D) / s is 0.0007 mm to 0.0016 mm, thereby achieving a better balance between iron loss and noise than before.

[0009] Patent Document 5 discloses a grain-oriented electrical steel sheet in which local strain is introduced in a direction transverse to the rolling direction at periodic intervals with respect to the rolling direction, in which linear closure domain parts are formed in the vicinity of the strain, and in a demagnetized state, the steel sheet has magnetic domains that extend from the closure domain parts in the rolling direction and have a length in the rolling direction of 1.2 mm or more, and further, the magnetic domains are formed at an average of 1.8 or more per mm in a region along the closure domain parts, and, when the line spacing of the closure domain parts is s (mm), the width w (mm) of the closure domain parts and the depth h (μm) of the closure domain parts in the sheet thickness direction satisfy the relationships 4 mm≦s≦1.5 mm and hw / s≦0.9 μm. Patent Document 5 suggests that the strain introduction index expressed in hw / s affects iron loss and noise.

[0010] However, as a result of investigations by the present inventors, it has been found that the techniques of Patent Documents 4 and 5 do not sufficiently improve noise characteristics to achieve the better iron loss / noise balance that has been demanded in recent years.

[0011] Furthermore, as other techniques for controlling closure domains, for example, Patent Documents 6 and 7 disclose manufacturing methods for grain-oriented electrical steel sheets that form closure domains without damaging the coating and provide grain-oriented electrical steel sheets with extremely low transformer iron loss and BF. Furthermore, Patent Document 8 shows that by taking advantage of the characteristics of electron beams to form a closure domain shape that is advantageous for reducing iron loss, it is possible to obtain grain-oriented electrical steel sheet with low iron loss over a wide range of sheet thicknesses. Furthermore, Patent Document 9 discloses a grain-oriented electrical steel sheet for iron cores having linear distortion formed by an electron beam emitted from LaB6 in a direction of 60° to 120° with respect to the rolling direction in the plane of the steel sheet. Furthermore, Patent Document 10 discloses a grain-oriented electrical steel sheet having excellent insulation properties and corrosion resistance, in which the area ratio of beam irradiation marks in the beam irradiation region is controlled, and a manufacturing method thereof. However, Patent Documents 6 to 10 all control closure domains to reduce iron loss, or are technologies for improving the film characteristics that arise as a result of closure domain control, and do not consider closure domain control for the purpose of achieving low noise. Therefore, it was found that the technologies in Patent Documents 6 to 10 do not sufficiently improve noise characteristics to meet the demand for a better iron loss-noise balance in recent years. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent No. 4669565 [Patent Document 2] Japanese Patent No. 4510757 [Patent Document 3] Japanese Patent No. 3361709 [Patent Document 4] Japanese Patent No. 6060988 [Patent Document 5] Japanese Patent No. 6176282 [Patent Document 6] Japanese Patent No. 6169695 [Patent Document 7] Japanese Patent No. 6245296 [Patent Document 8] International Publication No. 2014 / 068962 [Patent Document 9] Japanese Patent No. 5954421 [Patent Document 10] International Publication No. 2013 / 099272 Summary of the Invention [Problem to be solved by the invention]

[0013] As described above, conventionally, no grain-oriented electrical steel sheet or manufacturing method thereof has been disclosed that satisfactorily improves both iron loss characteristics and noise characteristics at the same time. An object of the present invention is to provide a grain-oriented electrical steel sheet that is excellent in iron loss characteristics, particularly the iron loss improvement rate before and after magnetic domain control, and noise characteristics, and a manufacturing method thereof. [Means for solving the problem]

[0014] In grain-oriented electrical steel sheets, the irradiated area is rapidly heated and cooled by irradiation with energy rays such as laser beams or electron beams. As a result, residual strain (thermal strain) occurs inside the steel sheet near the irradiated area. If this residual strain is compressive strain in the rolling direction or tensile strain in the sheet thickness direction, closure domains are generated in the area where this residual strain occurs. The formation of these closure domains generates leakage flux on the steel sheet surface, increasing the magnetostatic energy. A state in which the magnetostatic energy is high is energetically unstable. Therefore, the magnetic domain structure of the steel sheet changes to a structure that reduces leakage flux. A structure that reduces leakage flux is a state in which there are many interfaces between 180° magnetic domains parallel / antiparallel to the rolling direction, i.e., 180° magnetic domain walls, which is so-called "magnetic domain refinement." This magnetic domain refinement reduces abnormal eddy current loss, so irradiation with energy rays is advantageous for reducing iron loss. However, generally, when closure domains are formed, the degree of magnetostriction increases, and therefore noise increases when the material is incorporated in a transformer or the like. The present inventors have investigated the relationship between the irradiation conditions of a laser beam or an electron beam, etc., and the iron loss characteristics and noise characteristics. As a result, it was found that the noise characteristics can be improved by reducing the input energy of the laser beam or the electron beam, etc., but in this case, the magnetic domain control is not sufficient, and the improvement of the iron loss characteristics is not sufficient. Therefore, the inventors further investigated a method for improving the iron loss characteristics without deteriorating the noise characteristics, and found that by controlling the irradiation conditions of the laser beam or electron beam, etc., and the decarburization annealing conditions in the manufacturing process, sufficient magnetic domain refinement can be achieved even when the input energy of the laser beam or electron beam, etc. is small, and that both low iron loss and low noise can be achieved after irradiation with the laser beam or electron beam, etc.

[0015] The present invention has been made in view of the above findings. [1] A grain-oriented electrical steel sheet according to one embodiment of the present invention comprises a base steel sheet, a glass coating formed on the base steel sheet, and a tension-applying insulating coating formed on the glass coating, wherein the base steel sheet contains, by mass%, C: 0.010% or less, Si: 3.00 to 4.00%, Mn: 0.01 to 0.50%, N: 0.010% or less, Sol.Al: 0.020% or less, P: 0.030% or less, S: 0.010% or less, Sn: 0 to 0.50%, The base steel sheet has a chemical composition of Cu: 0-0.50%, Cr: 0-0.50%, Se: 0-0.020%, Sb: 0-0.500%, Mo: 0-0.10%, and the balance: Fe and impurities. A plurality of linear strains extending continuously or intermittently in a direction intersecting with a rolling direction are present on a surface of the base steel sheet, and a distance p between adjacent linear strains in the rolling direction is 3.0-9.0 mm, and a width of the linear strain is 10- 200 μm, and in an X-ray topography spectrum obtained from an X-ray topography image of the surface in a range of 1.50 mm in the rolling direction centered on the linear strain, the half-width of a peak in the X-ray topography spectrum containing the maximum value of the spectral intensity is 0.02 mm or more and 0.10 mm or less. [2] The grain-oriented electrical steel sheet according to [1] is characterized in that an X-ray beam is irradiated to an area of ​​3.0 mm in the rolling direction centered on the linear distortion on the surface, and the minimum value of the X-ray reflection intensity of the (310) plane is determined by I min The background intensity is I0, and an X-ray beam is irradiated to an area of ​​3.0 mm in the rolling direction centered on the linear distortion on the back surface, and the minimum value of the X-ray reflection intensity of the diffraction surface (310) is taken as J. min , when the background intensity is J0, the above I min , I0, J min The J0 may satisfy the following formula (2): 0.02 ≦ |J0-J min | / |I0-I min | ≦ 1.00 (2) [3] In the grain-oriented electrical steel sheet according to [1] or [2], the chemical composition of the base steel sheet may include either or both of Sn: 0.01-0.50% and Cu: 0.05-0.50%. [4] A method for producing a grain-oriented electrical steel sheet according to another embodiment of the present invention is a method for producing a grain-oriented electrical steel sheet according to [1] or [2], comprising the steps of: C: 0.010 to 0.200%, Si: 3.00 to 4.00%, Mn: 0.01 to 0.50%, N: 0.020% or less, Sol.Al: 0.010 to 0.040%, P: 0.030% or less, S: 0.005 to 0.040%, Sn: 0 to 0.50%, Cu: 0 to 0.5 The present invention relates to a hot rolling process in which a steel slab having a chemical composition of 0%, Bi: 0-0.020%, Cr: 0-0.50%, Se: 0-0.020%, Sb: 0-0.500%, Mo: 0-0.10%, and the balance: Fe and impurities is heated and then hot rolled to obtain a hot rolled steel sheet; a hot rolled sheet annealing process in which the hot rolled steel sheet is annealed; and a hot rolled sheet annealing process in which the hot rolled steel sheet after the hot rolled sheet annealing process is cold rolled once or multiple times with intermediate annealing in between to obtain a hot rolled steel sheet. a finish annealing process in which an annealing separator mainly composed of MgO is applied to front and back surfaces of the cold-rolled steel sheet after the decarburization annealing process, which is a base steel sheet, and then dried and finish annealed to form a glass coating; a coating formation process in which a tensioned insulating coating is formed on the glass coating to obtain a grain-oriented electrical steel sheet comprising the base steel sheet, the glass coating formed on the base steel sheet, and the tensioned insulating coating formed on the glass coating; and a magnetic domain refining process in which an energy beam is irradiated onto a surface of the tensioned insulating coating of the grain-oriented electrical steel sheet to impart a plurality of linear strains to the base steel sheet, 2 The unit is W / mm2, defined as (P / S) using the energy ray irradiation cross section S at 2the energy beam power density Ip at the energy beam output satisfies the following formula (3), the energy beam input energy Up in the unit of J / mm defined as (P / Vs) using the energy beam output P and the energy beam scanning speed Vs in the unit of mm / sec satisfies the following formula (4), and the beam aspect ratio defined as (dl / dc) using the diameter dl of the energy beam in the direction perpendicular to the beam scanning direction and the diameter dc of the energy beam in the beam scanning direction in the unit of μm, and the dl satisfies the following formulas (5) and (6), respectively, and in the decarburization annealing step, the heating rate S1 in a first temperature range of 550 to 750°C is 500°C / sec or more and the heating rate S2 in a second temperature range of 750 to 800°C is 800°C / sec or more, or the heating rate S2 in the second temperature range is 50°C / sec or more and the atmospheric dew point in the second temperature range is -50°C to 20°C. 250≦Ip≦2000 (3) 0.005 <Up≦0.050 (4) 0.001 <dl / dc<1.000 (5) 10≦dl<200 (6) [5] The method for producing a grain-oriented electrical steel sheet according to [4] may further include, between the decarburization annealing step and the finish annealing step, a nitriding treatment step of subjecting the cold-rolled steel sheet to a nitriding treatment. [6] In the method for producing a grain-oriented electrical steel sheet according to [4] or [5], the chemical composition of the steel billet may include either or both of Sn: 0.01-0.50% and Cu: 0.05-0.50%. Effect of the Invention

[0016] According to the above aspects of the present invention, it is possible to provide a grain-oriented electrical steel sheet having excellent core loss characteristics and noise characteristics, and a manufacturing method thereof. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 illustrates the measurement geometry of X-ray topography. [Diagram 2] FIG. 1 is a diagram showing an example of image data of X-ray topography. [Diagram 3] FIG. 1 is a diagram showing an example of a distribution curve (line profile) of reflected diffracted X-ray intensity. [Figure 4] FIG. 1 is a diagram illustrating dynamic diffraction due to multiple scattering in X-ray diffraction. [Diagram 5] FIG. 1 is a diagram illustrating kinematic diffraction and dynamic diffraction in X-ray diffraction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] A grain-oriented electrical steel sheet according to one embodiment of the present invention (grain-oriented electrical steel sheet according to this embodiment) comprises a base steel sheet having a predetermined chemical composition, a glass coating formed on the base steel sheet, and a tension-imparting insulating coating formed on the glass coating. In addition, on the surface of the base steel plate, multiple linear strains (thermal strains) are formed that extend continuously or intermittently and are approximately parallel to each other in a direction intersecting the rolling direction, more specifically in a direction that forms an angle (φ) of 60 to 120° with respect to the rolling direction, and the spacing (p) between adjacent multiple linear strains in the rolling direction is 3.0 to 9.0 mm, and the width (length in the direction perpendicular to the extension direction) of each of the multiple linear strains measured by X-ray topography is 10 to 250 μm. Furthermore, in the grain-oriented electrical steel sheet according to this embodiment, in an X-ray topography spectrum obtained from an X-ray topography image of the surface in a range of 1.50 mm in the rolling direction centered on the linear distortion (a range of ±0.75 mm in the rolling direction from the linear distortion), the half-width of the peak in the X-ray topography spectrum containing the maximum value of the spectral intensity is 0.02 mm or more and 0.10 mm or less.

[0019] Hereinafter, the grain-oriented electrical steel sheet according to this embodiment will be described.

[0020] <Base material steel plate> (chemical composition) The grain-oriented electrical steel sheet according to this embodiment is characterized by the state of linear distortion, and the base steel sheet of the grain-oriented electrical steel sheet is not limited in terms of its chemical composition. However, in order to obtain the characteristics generally required for grain-oriented electrical steel sheets, the following ranges are set. In this embodiment, % relating to the content of each element is mass % unless otherwise specified.

[0021] C: 0.010% or less C (carbon) is an element effective for controlling the structure of the steel sheet in the process up to the completion of the decarburization annealing process in the manufacturing process. However, if the C content exceeds 0.010%, the magnetic properties (iron loss properties and magnetic flux density) of the finished grain-oriented electrical steel sheet are reduced. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, the C content is set to 0.010% or less. The C content is preferably 0.005% or less. The lower the C content, the more preferable it is, but even if the C content is reduced to less than 0.0001%, the effect of controlling the structure is saturated and the manufacturing cost is simply increased. Therefore, the C content may be set to 0.0001% or more.

[0022] Si: 3.00-4.00% Silicon (Si) is an element that increases the electrical resistance of grain-oriented electrical steel sheets and improves their core loss characteristics. If the Si content is less than 3.00%, a sufficient eddy current loss reduction effect cannot be obtained. Therefore, the Si content is set to 3.00% or more. The Si content is preferably 3.20% or more, and more preferably 3.50% or more. On the other hand, if the Si content exceeds 4.00%, the grain-oriented electrical steel sheet becomes embrittled and the sheet passing property is significantly deteriorated. In addition, the workability of the grain-oriented electrical steel sheet is deteriorated, and the steel sheet may break during rolling. For this reason, the Si content is set to 4.00% or less. The Si content is preferably 3.80% or less, and more preferably 3.70% or less. Some of the Si contained in the steel pieces such as slabs may be consumed in the formation of a glass coating mainly composed of Mg2SiO4, so the Si content in the grain-oriented electrical steel sheet may be reduced compared to that at the time of tapping.

[0023] Mn: 0.01 to 0.50% Mn (manganese) is an element that combines with S to form MnS during the manufacturing process. This precipitate functions as an inhibitor (a suppressor of normal grain growth) and causes secondary recrystallization in steel. Mn is also an element that improves the hot workability of steel. If the Mn content is less than 0.01%, the above-mentioned effects cannot be fully obtained. Therefore, the Mn content is set to 0.01% or more. The Mn content is preferably 0.02% or more, more preferably 0.05% or more. On the other hand, if the Mn content exceeds 0.50%, secondary recrystallization does not occur and the magnetic properties of the steel deteriorate. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, the Mn content is set to 0.50% or less. The Mn content is preferably 0.20% or less, and more preferably 0.10% or less.

[0024] N: 0.010% or less N (nitrogen) is an element that combines with Al in the manufacturing process to form AlN, which functions as an inhibitor. However, if the N content exceeds 0.010%, the magnetic properties are reduced due to the inhibitor remaining in excess in the base steel sheet. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, the N content is set to 0.010% or less. The N content is preferably 0.008% or less, more preferably 0.005% or less. On the other hand, the lower limit of the N content is not particularly specified, but reducing it to less than 0.0001% would only increase the manufacturing cost, and therefore the N content may be set to 0.0001% or more.

[0025] Sol.Al: 0.020% or less Sol.Al (acid-soluble aluminum) is an element that bonds with N in the manufacturing process to form AlN, which functions as an inhibitor. However, if the Sol.Al content of the base steel sheet exceeds 0.020%, the magnetic properties are reduced due to the inhibitor remaining in excess in the base steel sheet. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, the Sol.Al content is 0.020% or less. It is preferable that the Sol.Al content in the grain-oriented electrical steel sheet is as low as possible. For example, the Sol.Al content is 0.010% or less, or less than 0.001%, and may be 0%. On the other hand, the lower limit of the sol.Al content is not particularly specified, but reducing it to less than 0.0001% would only increase the production cost, so the sol.Al content may be 0.0001% or more.

[0026] P:0.030% or less P (phosphorus) is an element that reduces workability in rolling. By setting the P content to 0.030% or less, it is possible to prevent the rolling workability from being excessively reduced, and to prevent breakage during manufacturing. From this viewpoint, the P content is set to 0.030% or less. The P content is preferably 0.020% or less, and more preferably 0.010% or less. The lower limit of the P content is not limited and may include 0%, but since the detection limit of chemical analysis is 0.0001%, the substantial lower limit of the P content in practical steel sheets is 0.0001%. P is also an element that has the effect of improving the texture and magnetic properties. To obtain this effect, the P content may be 0.001% or more, or may be 0.005% or more.

[0027] S: 0.010% or less S (sulfur) is an element that combines with Mn in the manufacturing process to form MnS, which functions as an inhibitor. However, if the S content exceeds 0.010%, the magnetic properties are reduced due to the excessive remaining inhibitor. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, the S content is set to 0.010% or less. It is preferable that the S content in the grain-oriented electrical steel sheet is as low as possible. For example, it is less than 0.0001%, and may be 0%. However, even if the S content in the base steel sheet of the grain-oriented electrical steel sheet is reduced to less than 0.0001%, the manufacturing cost will only increase. Therefore, the S content may be 0.0001% or more.

[0028] Remainder: Fe and impurities The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment may contain the above-mentioned essential elements, with the balance being Fe and impurities. However, for the purpose of improving magnetic properties, etc., optional elements such as Sn, Cu, Cr, Se, Sb, and Mo may also be contained in the ranges shown below. These elements are also allowed to be contained as impurities. Furthermore, even if other elements than these, such as one or more of W, Nb, Bi, Ti, Ni, Co, and V are contained in a total amount of 1.0% or less, this does not impair the effects of the grain-oriented electrical steel sheet according to this embodiment. Here, impurities refer to elements that are mixed in from raw materials such as ore or scrap, or from the manufacturing environment, during industrial production of the base steel sheet, and are permissible to be contained in amounts that do not adversely affect the function of the grain-oriented electrical steel sheet according to this embodiment.

[0029] Sn: 0 to 0.50% Sn (tin) is an element that increases the Goss orientation and is effective for refining secondary recrystallized grains. If the secondary recrystallized grains are small, a sufficient iron loss improvement effect can be obtained even with a small input energy when performing magnetic domain refinement. In order to obtain the above effect, the Sn content is preferably 0.01% or more. The Sn content is more preferably 0.02% or more, and further preferably 0.03% or more. However, there is a concern that the occupancy rate of the Goss orientation in the secondary recrystallized structure decreases when Sn is contained. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, when Sn is contained, it is preferable to contain it simultaneously with Cu, which will be described later. On the other hand, if the Sn content exceeds 0.50%, the secondary recrystallization becomes unstable and the magnetic properties deteriorate. Therefore, even if Sn is contained, the Sn content is set to 0.50% or less. The Sn content is preferably 0.30% or less, and more preferably 0.20% or less.

[0030] Cu: 0-0.50% Cu (copper) is an element that contributes to increasing the Goss orientation occupancy rate in the secondary recrystallized structure. In order to obtain the above effect, the Cu content is preferably 0.05% or more. The Cu content is more preferably 0.06% or more, and further preferably 0.07% or more. On the other hand, if the Cu content exceeds 0.50%, the steel sheet becomes embrittled during hot rolling. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, even if Cu is contained, the Cu content is set to 0.50% or less. The Cu content is preferably 0.30% or less, and more preferably 0.20% or less.

[0031] Cr: 0~0.50% Cr (chromium) is an element that improves magnetic properties. Although the reason is unclear, it is believed to have the effect of improving magnetic properties by contributing to an increase in the Goss orientation occupancy rate in the secondary recrystallized structure. In order to obtain the above effect, the Cr content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more. On the other hand, if the Cr content exceeds 0.50%, Cr oxides are formed and the magnetic properties deteriorate. Therefore, even if Cr is contained, the Cr content is set to 0.50% or less. The Cr content is preferably 0.30% or less, and more preferably 0.10% or less.

[0032] Se: 0 to 0.020% Se (selenium) is an element that has a magnetic property improving effect. Therefore, it may be contained. When Se is contained, in order to exhibit a good magnetic property improving effect, it is preferable that the Se content is 0.001% or more. The Se content is more preferably 0.003% or more, and further preferably 0.006% or more. On the other hand, if the Se content exceeds 0.020%, the adhesion of the glass coating deteriorates. Therefore, even if Se is contained, the Se content is set to 0.020% or less. The Se content is preferably 0.015% or less, and more preferably 0.010% or less.

[0033] Sb: 0 to 0.500% Sb (antimony) is an element that has a magnetic property improving effect. Therefore, it may be contained. When Sb is contained, the content is preferably 0.005% or more in order to exhibit a good magnetic property improving effect. The Sb content is more preferably 0.010% or more, and further preferably 0.020% or more. On the other hand, if the Sb content exceeds 0.500%, the adhesion of the glass coating is significantly deteriorated. Therefore, even if Sb is contained, the Sb content is set to 0.500% or less. The Sb content is preferably 0.300% or less, and more preferably 0.100% or less.

[0034] Mo: 0 to 0.10% Mo (molybdenum) is an element that has a magnetic property improving effect. Therefore, it may be contained. When Mo is contained, it is preferable that the Mo content is 0.01% or more in order to effectively exhibit the magnetic property improving effect. The Mo content is more preferably 0.02% or more, and further preferably 0.03% or more. On the other hand, if the Mo content exceeds 0.10%, the cold rolling property deteriorates and may lead to fracture. Therefore, even if Mo is contained, the Mo content is set to 0.10% or less. The Mo content is preferably 0.08% or less, and more preferably 0.05% or less.

[0035] As described above, the chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment may, for example, contain the essential elements described above with the balance consisting of Fe and impurities, or contain the essential elements described above and further contain one or more optional elements with the balance consisting of Fe and impurities.

[0036] The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment can be measured after removing the glass coating and tension-applying insulating coating formed on the surface. Specifically, the tension-applying insulating coating is removed by immersing the grain-oriented electrical steel sheet in an aqueous sodium hydroxide solution at 80 to 90°C containing 30 to 50 mass% NaOH and 50 to 70 mass% H2O for 7 to 10 minutes. The grain-oriented electrical steel sheet from which the tension-applying insulating coating has been removed is washed with water, and after washing, it is dried for slightly less than 1 minute with a hot air blower. The dried grain-oriented electrical steel sheet (a grain-oriented electrical steel sheet not provided with a tension-applying insulating coating) is immersed for 1 to 10 minutes in an aqueous hydrochloric acid solution at 80 to 90°C containing 30 to 40 mass% HCl, to remove the glass coating. The base steel sheet after immersion is washed with water, and after washing, it is dried for slightly less than 1 minute with a hot air blower. Through the above steps, a base steel sheet can be taken out from the grain-oriented electrical steel sheet. The chemical composition of such a base steel plate is determined by a known compositional analysis method. Specifically, a drill is used to generate chips from the base steel plate, the chips are collected, and the collected chips are dissolved in acid to obtain a solution. ICP-AES is performed on the solution to perform elemental analysis of the chemical composition. Here, the Si content in the chemical composition of the base steel plate is determined by the method (silicon determination method) specified in JIS G 1212 (1997). Specifically, when the above-mentioned cutting chips are dissolved in acid, silicon oxide is precipitated, and this precipitate (silicon oxide) is filtered out with filter paper and the mass is measured to determine the Si content. The C content and S content are determined by the well-known high-frequency combustion method (combustion-infrared absorption method). Specifically, the above-mentioned solution is combusted in an oxygen stream by high-frequency heating, and the generated carbon dioxide and sulfur dioxide are detected to determine the C content and S content. The N content is determined using the well-known inert gas fusion-thermal conductivity method.

[0037] (Linear distortion) In the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, there are a plurality of linear strains (thermal strains) near the surface, which are residual strains formed by irradiation with energy rays such as laser beams and electron beams. These linear strains extend continuously or intermittently in a direction (a direction intersecting the rolling direction) at an angle φ of 60 to 120° with respect to the rolling direction. The strains may be continuous and linear, or may be intermittently in one direction (for example, dotted lines). The distortion (residual distortion) formed by such irradiation of energy rays is compressive distortion in the rolling direction and tensile distortion in the thickness direction, and it is known that a region magnetized in the thickness direction, called a closure domain, is formed in the distorted part and below it in the thickness direction. When the size of the closure domain is equal to or larger than a certain size, the 180° domain width is subdivided, eddy current loss is reduced, and iron loss is reduced. On the other hand, when the size of the closure domain becomes large, magnetostriction when excited by AC increases, and noise in the transformer becomes evident.

[0038] As a result of the inventors' investigations, it was found that by controlling the width of the distortion formed on the surface and the state of introduction of distortion in the plate thickness direction, iron loss can be reduced (iron loss characteristics are improved) and the noise problem can be prevented from becoming apparent (noise characteristics are improved). As mentioned above, the closure domains formed with the formation of residual distortion are the driving force for 180° magnetic domain refinement, which is advantageous for reducing iron loss, but the closure domains increase the degree of magnetostriction, which causes a problem of increased noise (deterioration of noise characteristics) when incorporated into a transformer. Conventionally, measures to suppress the deterioration of noise characteristics have been taken, such as increasing the irradiation pitch of the energy beam or reducing the input energy of the energy beam. However, such measures were merely a means of improving noise characteristics by sacrificing to some extent the iron loss improvement effect of energy beam irradiation, based on the premise that there is a trade-off between iron loss characteristics and noise characteristics. In response to this, the inventors have conducted research and found that by introducing strain into grain-oriented electrical steel sheets that forms closure domain regions that are shallow from the surface (localized in the surface layer), it is possible to improve iron loss characteristics while suppressing deterioration of noise characteristics. In other words, the inventors have found that controlling the spatial distribution of strain is important from the viewpoint of simultaneously reducing iron loss and noise. The spatial distribution of strain can be identified by using an X-ray diffraction analysis technique known as X-ray topography.

[0039] Details will be described later, but in areas where distortion is particularly strong, for example in areas irradiated with energy rays where the input energy is particularly high, the lattice is so disordered that the diffraction phenomenon itself does not occur (highly distorted areas). In such areas, diffraction does not occur in X-ray topography, so the X-ray topography image appears white. Therefore, the X-ray topography spectrum obtained from the image shows low intensity (low pixel value). On the other hand, if a region where residual strain has been introduced (a region with a relatively low dislocation density) exists, even though the diffraction phenomenon does occur, the X-ray topography image will turn black. Therefore, the X-ray topography spectrum obtained from the image will show high intensity (high pixel value). The residual strain region where this diffraction phenomenon occurs has a magnetic domain refinement effect (iron loss improvement effect), while the crystal lattice itself is not damaged. Therefore, the adverse effect on noise is limited. Therefore, in order to achieve both excellent core loss characteristics and excellent noise characteristics, it is important to introduce an appropriate amount of residual strain region in which the diffraction phenomenon occurs.

[0040] In the grain-oriented electrical steel sheet according to this embodiment, in order to achieve both excellent iron loss characteristics and excellent noise characteristics, the width of each of the multiple linear distortions measured by X-ray topography is 10 to 250 μm, and in an X-ray topography spectrum obtained from an X-ray topography image of the surface in a range of 1.50 mm in the rolling direction centered on the linear distortion, the half-width of the peak in the X-ray topography spectrum containing the maximum value of the spectral intensity is 0.02 mm or more and 0.10 mm or less. If the width of the linear distortion is less than 10 μm, the effect of improving iron loss cannot be obtained. In addition, it is industrially difficult to make the beam diameter less than 10 μm. Therefore, the width of the distortion is set to 10 μm or more. The width of the distortion is preferably 50 μm or more. On the other hand, if the width of the distortion exceeds 250 μm, the volume of the closure domain formed by the distortion increases, and the degree of magnetostriction increases. Therefore, the width of the distortion is set to 250 μm or less. The width of the distortion is preferably 200 μm or less, and more preferably 150 μm or less. Furthermore, if the half-width of the peak in the X-ray topography spectrum is less than 0.02 mm, the range of strain introduction is small, and no iron loss improvement effect can be obtained. On the other hand, if the half-width exceeds 0.10 mm, excessive strain is introduced, and no noise characteristic improvement effect can be obtained. The half-width of the peak in the X-ray topography spectrum is preferably in the range of 0.03 mm to 0.08 mm, and more preferably in the range of 0.03 mm to 0.06 mm. The half-width of the peak in the X-ray topography spectrum is affected by the crystal orientation of the base material. Therefore, to obtain a specified half-width, it is necessary to increase the sharpness of the crystal orientation of the Goss orientation, for example by increasing the temperature rise rate in the decarburization annealing, as described later. If the sharpness of the crystal orientation of the Goss orientation is poor, when strain-introducing magnetic domain control is performed, the half-width exceeds 0.10 mm, and the effect of improving noise characteristics cannot be obtained.

[0041] The width of the linear distortion is measured using X-ray topography (XRT) (for example, Rigaku's XRTmicron X-ray topography imaging system) by the following method. The target of the X-ray source is Cu, and the voltage and current are 40 kV and 30 mA, respectively. The CCD resolution in the detector is Binning 1×1 (5.4 μm). The CCD viewing size is 17 mm×13.5 mm (3326 pixels×2540 pixels), and the digital resolution is 16 bits (65536 gradations). First, an X-ray beam is irradiated onto a steel plate sample so as to satisfy the Bragg diffraction condition, and the diffracted X-ray beam is exposed to a detector (CCD camera) to collect mapping data of the diffracted X-ray intensity. The diffracted X-ray intensity is converted into color density, and the X-ray scan area is displayed as a color density distribution image. This results in an X-ray topography image (mapping data of the diffracted X-ray intensity). The higher the diffracted X-ray intensity, the darker the color density of the X-ray topography image tends to be (negative display). In addition, the measurement position may be adjusted to maximize the intensity by rocking curve measurement. Specifically, a curve is swept with the X-ray incidence angle θs (°) on the horizontal axis and the diffracted X-ray intensity on the vertical axis, and the θs at which the strongest intensity is obtained is selected. max (°). However, in the present invention, θs(°)=θs max The X-ray topography image is taken at a position of +~0.09 (corresponding to the use of the same technique as the weak beam method in dark-field image observation with a transmission electron microscope (TEM)). For example, the peak position of the rocking curve is at an X-ray incidence angle θs (°) = 32.8343° and an X-ray emission angle θd = 83.5257°, ​​while the X-ray topography shooting position may be θs = 32.9200° and θd = 83.4400°. Figure 2 shows an example of an X-ray topography image. For the measurement, for example, a sample of 50 mm in the width direction (TD) and 150 mm in the rolling direction (RD) is taken from a grain-oriented electrical steel sheet, and an X-ray beam (Cu Kα radiation) is irradiated onto the surface of the sample so as to satisfy the Bragg diffraction condition for the desired diffraction plane (hkl), and the intensity of the reflected diffracted X-rays is measured with a high-resolution CCD camera or the like to create a mapping image of the diffracted X-ray intensity (see Figure 1). In this case, a TDI (Time Delay Integration) scan is not performed, and a still image of the diffraction image is taken with the sample stationary (Snap Shot). Each pixel of the CCD camera is exposed to the diffracted X-rays from each position on the sample and charges are accumulated, so the sample is scanned and the exposure charges at each position are read out to create mapping data of the diffracted X-ray intensity. The condition in which the RD axis direction (rolling direction) of the sample is parallel to the incident and reflected directions of the X-ray beam is called the g=222 measurement condition or the diffraction plane (222) condition. On the other hand, the condition in which the TD axis of the sample is parallel to the incident and reflected directions of the X-ray beam is called the g=310 measurement condition or the diffraction plane (310) condition. In this embodiment, unless otherwise specified, the measurement condition is the diffraction plane (310) condition. From this mapping image, multiple linear areas extending at approximately equal intervals in a direction with an angle φ of 60 to 120° with respect to the rolling direction of the steel plate and having an intensity lower than the average value of the X-ray diffraction intensity of the entire mapping data (areas that appear white due to low color density) are determined to be linear distortions introduced by the energy beam.

[0042] The width of the linear distortion and the half-width of the peak of the X-ray topography spectrum are obtained by the following method. That is, the position of the linear distortion with the lowest intensity on the X-ray topography image obtained by the above method is defined as the center position of the distortion. Color density data (pixel value) is obtained on a line connecting two desired points so that a range of 1.50 mm in the rolling direction (a range of ±0.75 mm in the rolling direction centered on the linear distortion) is targeted. This is plotted as shown in FIG. 3 with the horizontal axis representing the measurement position and the vertical axis representing the pixel value, thereby obtaining a distribution curve (line profile) of the reflected diffracted X-ray intensity (this curve is called the X-ray topography spectrum. The pixel value on the vertical axis corresponds to the reflected diffracted X-ray intensity). In this line profile, the maximum reflection intensity is I max , the background intensity is I0, and I max The peak in the X-ray topography spectrum containing (I max In the continuous curve range including |I max The length connecting the two points where -I0| / 2 is defined as the half-width. From the viewpoint of removing noise in the spectrum, measurements may be taken at the same position several times and the sum of the measurements may be used. The X-ray topography spectrum may be approximated as a continuous curve by fitting processing. A continuous curve range where the reflection intensity is smaller than I0 and includes the center position of the distortion is defined as linear distortion. The reflection intensity in the linear distortion region is defined as Iz. The width of the distortion is defined as the length connecting the two points where Iz=0 in the direction parallel to the rolling direction of the steel sheet sample.

[0043] In general, the intensity of diffracted X-rays is stronger as the distortion of the crystal lattice increases, and weakens as the distortion decreases, reaching a constant value when the distortion is zero (extinction effect). In a crystal lattice with very small distortion, as shown in Figure 4, the traveling wave in the X-ray incident direction and the diffracted wave scattered at the diffraction surface undergo multiple interference (multiple scattering), and then the propagating wave in the diffraction direction emerges from the crystal surface as a reflected diffracted X-ray (dynamic diffraction). This multiple interference within the crystal occurs at the diffraction surface where a uniform and constant lattice plane spacing is continuously formed, and the wavelength of the diffracted wave at that time corresponds to the diffraction plane spacing formed by the undistorted crystal lattice. On the other hand, in places where there are localized areas with large distortion, multiple interference does not occur because a uniform and constant lattice plane spacing is not formed, and instead, a diffracted wave is generated that is scattered only once locally at a wavelength corresponding to the distorted lattice plane spacing (see Figure 5). The wavelength of the diffracted wave generated in this locally distorted region is different from the wavelength of the diffracted wave due to multiple scattering in the non-distorted region, so the diffracted wave generated in the locally distorted region travels through the crystal without being caught up in the multiple scattering in the non-distorted region and emerges as a reflected diffracted X-ray from the crystal surface (kinematic diffraction). In general, the intensity of diffracted X-rays is stronger in kinematic diffraction than in dynamic diffraction (extinction effect). In addition, the spectral intensity is stronger in areas where a lot of distortion has been introduced locally due to kinematic diffraction (for example, the maximum value is I max On the other hand, in areas with little distortion (base material), the spectral intensity remains constant due to the extinction effect (for example, I o In addition, in areas where the crystal lattice is disordered due to excessive local distortion, Bragg diffraction does not occur, and the spectral intensity is weak (for example, the minimum value is I min (Assuming that.)

[0044] In the grain-oriented electrical steel sheet according to this embodiment, the extension direction of the multiple linear distortions on the surface of the base steel sheet is within a range of a deviation angle of 30° with respect to the direction perpendicular to the rolling direction. In other words, the multiple linear distortions extend continuously or intermittently in a direction at an angle φ of 60 to 120° with respect to the rolling direction. If the angle is outside this range, the 180° magnetic domain refinement effect of the steel sheet decreases, and a sufficient iron loss reduction effect cannot be obtained. In addition, the interval between adjacent linear residual strains in the rolling direction is 3.0 to 9.0 mm. If the interval in the rolling direction exceeds 9.0 mm, the effect of refining the 180° magnetic domain decreases, so the iron loss improvement effect is insufficient. On the other hand, narrowing the interval between the linear residual strains (narrowing the irradiation pitch) tends to reduce the iron loss, but if it is below a certain threshold, the total hysteresis loss increases, and the iron loss may deteriorate, and the noise characteristics may deteriorate. Therefore, the interval between adjacent residual strains in the rolling direction is 3.0 mm or more. It is preferable that the linear residual strains are approximately parallel and the intervals between them are approximately equal. The length of the residual strain in the sheet width direction is not limited, but it is preferable that the residual strain is formed from one end of the base steel sheet in the width direction to the other end. In the case of discontinuous (intermittent) energy beam irradiation, when the energy beam is irradiated onto the steel sheet at a specific pitch in the width direction, it is preferable that the major axis (length along the width direction) d0 of the energy beam irradiation portion and the length d1 along the width direction of the energy beam non-irradiation section sandwiched between two energy beam irradiation portions satisfy d1≦3×d0. d0 may be in the range of 50 μm or more and 50 mm or less.

[0045] The spacing between adjacent linear thermal distortions (the distance from the center of a linear distortion to the center of an adjacent linear distortion in the rolling direction) can be measured by identifying the positions of the distortions using X-ray topography under the conditions described above.

[0046] In addition, in the grain-oriented electrical steel sheet according to this embodiment, an X-ray beam is irradiated to an area of ​​3.0 mm in the rolling direction centered on the linear distortion on the surface, and the minimum value of the X-ray reflection intensity of the (310) plane is set to I min The background intensity is I0, and the X-ray beam is irradiated over an area of ​​3.0 mm in the rolling direction centered on the linear distortion on the back surface. The minimum X-ray reflection intensity of the diffraction surface (310) is taken as J. min , when the background intensity is J0, the above I min , I0, J min It is preferable that J0 satisfies the following formula (2), in which case the iron loss characteristics and noise characteristics are further improved. 0.02≦|J0-J min | / |I0-I min | ≦ 1.00 (2) By satisfying equation (2), the strain distribution becomes more favorable for noise characteristics. min | / |I0-I min Satisfying | means that the amount of closure domains near the back surface is smaller than the amount of closure domains near the front surface. Although the reason is not clear, the strain in the back surface layer of the strain-introduced surface may also have an effect on improving iron loss, and |J0-J min | / |I0-I min It is believed that this effect can be obtained if | is 0.02 or more. On the other hand, although the cause is unclear, |J0-J min | / |I0-I min If | exceeds 1.00, that is, if the amount of closure domains on the back surface exceeds the amount of closure domains on the front surface, the noise characteristics tend to deteriorate. min | / |I0-I min It is believed that by setting | to 1.00 or less, more preferable iron loss characteristics and noise characteristics can be obtained.

[0047] The X-ray reflection intensity of the diffraction surface (310) within a range of 3.0 mm (±1.5 mm) in the rolling direction centered on the linear distortion on the front and back surfaces is determined by the following method. That is, if it is the surface, an X-ray topography image (strain distribution image) is obtained under the above-mentioned conditions. On the obtained image, a point with distortion is selected, and from there, point A at +0.075 mm and point B at -0.075 mm are connected with straight lines parallel to the rolling direction (RD direction). Color density data (pixel values) are obtained for the line connecting A and B. This is plotted with the horizontal axis representing the measurement position and the vertical axis representing the pixel value (diffraction intensity) to obtain a distribution curve (line profile) of the reflected diffracted X-ray intensity. The diffraction intensity at the position where the diffraction intensity at point A is the average of the diffraction intensity at point B is defined as I0. The diffraction intensity at the position where the diffraction intensity is the lowest is defined as I min Let us assume that. In the case of the back surface, the diffraction intensity at the position where the diffraction intensity at the start point and the end point of the line is averaged is defined as J0, and the diffraction intensity at the position where the diffraction intensity is the lowest is defined as J. min Let us assume that.

[0048] <Glass coating> In the grain-oriented electrical steel sheet according to the present embodiment, a glass coating is formed on the surface of the base steel sheet. The glass coating may be formed on only one side of the base steel sheet, but is preferably formed on both sides. The glass coating is an inorganic coating mainly composed of magnesium silicate. The glass coating is formed by the reaction of an annealing separator containing magnesia (MgO) applied to the surface of the base steel sheet with the surface components of the base steel sheet during finish annealing, and has a composition derived from the components of the annealing separator and the base steel sheet (more specifically, a composition mainly composed of Mg2SiO4).

[0049] <Tensioned insulating coating> In the grain-oriented electrical steel sheet according to this embodiment, a tension-applying insulating coating is formed on the surface of the glass coating. The tension-applying insulating coating may be formed on only one side, but is preferably formed on both sides. The tensioned insulating coating imparts electrical insulation to the grain-oriented electrical steel sheet, thereby reducing eddy current loss and improving the core loss of the grain-oriented electrical steel sheet. In addition to the electrical insulation described above, the tensioned insulating coating also provides various other properties such as corrosion resistance, heat resistance, and slipperiness. Furthermore, the tension-applying insulating coating has a function of applying tension to the grain-oriented electrical steel sheet. By applying tension to the grain-oriented electrical steel sheet, it is possible to facilitate domain wall motion in the grain-oriented electrical steel sheet, thereby improving the iron loss of the grain-oriented electrical steel sheet. The tension-applying insulating coating may be a known coating formed, for example, by applying a coating liquid containing phosphate and colloidal silica as main components to the surface of the glass coating and baking it.

[0050] <Base steel plate thickness: 0.17~0.30mm> The thickness of the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment is not limited, but is preferably 0.17 to 0.30 mm in consideration of application to the iron core of a transformer, which requires low noise and low vibration as well as low iron loss. The thinner the thickness, the more effective it is to reduce eddy current loss, and the better the iron loss, so the base steel sheet is more preferably 0.23 mm or less, and even more preferably 0.20 mm or less. Special equipment is required to manufacture a base steel sheet of less than 0.17 mm, which is undesirable in terms of production, such as increasing manufacturing costs. Therefore, the industrially preferable thickness is 0.17 mm or more. More preferably, it is 0.18 mm or more.

[0051] <Manufacturing method> The grain-oriented electrical steel sheet according to this embodiment can be manufactured by a manufacturing method including the following steps. (i) a hot rolling process in which a steel slab having a chemical composition, in mass%, consisting of C: 0.010-0.200%, Si: 3.00-4.00%, Mn: 0.01-0.50%, N: 0.020% or less, Sol.Al: 0.010-0.040%, P: 0.030% or less, S: 0.005-0.040%, Sn: 0-0.50%, Cu: 0-0.50%, Bi: 0-0.020%, Cr: 0-0.50%, Se: 0-0.020%, Sb: 0-0.500%, Mo: 0-0.10%, and the balance: Fe and impurities is heated and then hot rolled to obtain a hot rolled steel sheet; (ii) a hot-rolled sheet annealing step of subjecting the hot-rolled steel sheet to hot-rolled sheet annealing; (iii) a cold rolling step of performing cold rolling once or multiple times with intermediate annealing on the hot-rolled steel sheet after the hot-rolled sheet annealing step to obtain a cold-rolled steel sheet; (iv) a decarburization annealing step of subjecting the cold-rolled steel sheet to decarburization annealing; (v) a finish annealing process in which an annealing separator mainly composed of MgO is applied to the front and back surfaces of the cold-rolled steel sheet after the decarburization annealing process, which is the base steel sheet, and then dried and finish annealed to form a glass coating; (vi) a coating formation step of forming a tensioned insulating coating on the glass coating to obtain a grain-oriented electrical steel sheet including the base steel sheet, the glass coating formed on the base steel sheet, and the tensioned insulating coating formed on the glass coating; and (vii) a magnetic domain refining step of irradiating a surface of the tension-applying insulating coating of the grain-oriented electrical steel sheet with an energy beam to impart a plurality of linear strains to the base steel sheet. These steps will be described in detail below. In the following description, unless conditions are specified for each step, each step can be carried out under known conditions as appropriate.

[0052] <Hot rolling process> In the hot rolling process, a steel slab or other steel piece having a chemical composition containing, for example, in mass%, C: 0.010-0.200%, Si: 3.00-4.00%, Mn: 0.01-0.50%, N: 0.020% or less, Sol.Al: 0.010-0.040%, P: 0.030% or less, S: 0.005-0.040%, Sn: 0-0.50%, Cu: 0-0.50%, Bi: 0-0.020%, Cr: 0-0.50%, Se: 0-0.020%, Sb: 0-0.500%, Mo: 0-0.10%, and the balance being Fe and impurities, is heated and then hot rolled to obtain a hot-rolled steel sheet. The heating temperature of the steel slab is not particularly limited, but is preferably within the range of 1100-1450°C. The heating temperature is more preferably 1300 to 1400°C. The hot rolling conditions are not particularly limited and may be appropriately set based on the desired properties. The thickness of the hot rolled steel sheet obtained by hot rolling is preferably within a range of, for example, 2.0 mm to 3.0 mm. The reason why the chemical composition of the steel slab is set within the above range is to obtain the above-mentioned chemical composition of the base steel sheet, taking into consideration the following manufacturing process.

[0053] <Hot-rolled sheet annealing process> The hot-rolled steel sheet annealing process is a process of annealing the hot-rolled steel sheet manufactured through the hot rolling process. By carrying out such annealing treatment, recrystallization occurs in the steel sheet structure, making it possible to realize good magnetic properties. In the hot-rolled steel sheet annealing process of this embodiment, the hot-rolled steel sheet manufactured through the hot rolling process may be annealed according to a known method. The means for heating the hot-rolled steel sheet during annealing is not particularly limited, and known heating methods can be adopted. The annealing conditions are also not particularly limited, but for example, the hot-rolled steel sheet may be annealed in a temperature range of 900 to 1200°C for 10 seconds to 5 minutes.

[0054] <Cold rolling process> In the cold rolling process, the hot rolled steel sheet after the hot rolled sheet annealing process is subjected to cold rolling including multiple passes to obtain a cold rolled steel sheet having a thickness of 0.17 to 0.30 mm. The cold rolling may be a single cold rolling (a series of cold rolling without intermediate annealing) or may be multiple cold rollings with intermediate annealing by interrupting the cold rolling and performing at least one or two or more intermediate annealings before the final pass of the cold rolling process. When intermediate annealing is performed, it is preferable to hold the steel sheet at a temperature of 1000 to 1200° C. for 5 to 180 seconds. The annealing atmosphere is not particularly limited. In consideration of the manufacturing cost, it is preferable to perform intermediate annealing three times or less. Furthermore, before the cold rolling step, the surface of the hot-rolled steel sheet may be subjected to pickling under known conditions.

[0055] In the cold rolling step of this embodiment, the hot rolled steel sheet may be cold rolled according to a known method to obtain a cold rolled steel sheet. For example, the final rolling reduction may be in the range of 80% to 95%. When the final rolling reduction is less than 80%, the {110} <001> It is undesirable that Goss nuclei having a high degree of integration in the rolling direction cannot be obtained. On the other hand, if the final reduction exceeds 95%, it is undesirable that the secondary recrystallization becomes unstable in the subsequent finish annealing process. By keeping the final reduction within the above range, it is possible to obtain the {110} <001> It is possible to obtain Goss nuclei with a high degree of orientation in the rolling direction, and to suppress the instability of secondary recrystallization. The final rolling reduction is the cumulative rolling reduction of cold rolling, and in the case where intermediate annealing is performed, it is the cumulative rolling reduction of cold rolling after final intermediate annealing.

[0056] <Decarburization annealing process> In the decarburization annealing process, the obtained cold-rolled steel sheet is subjected to decarburization annealing, which causes primary recrystallization of the cold-rolled steel sheet and removes C, which has a negative effect on the magnetic properties, from the steel sheet. The decarburization annealing process increases the number of Goss nuclei and refines the secondary recrystallized grains obtained during the finish annealing process described below. Considering that the grain boundaries themselves function as magnetic poles (sites where leakage magnetic flux is generated), the refinement of secondary recrystallized grains increases the magnetostatic energy of the entire system. In other words, the driving force for magnetic domain refinement becomes high, making it possible to achieve both low iron loss and low noise without relying on the introduction of excessive closure domains. In the manufacturing method of the grain-oriented electrical steel sheet according to the present embodiment, in order to increase the Goss nuclei, the heating rate in the temperature range of 550 to 750°C (first temperature range) is increased during heating for decarburization annealing, and the residence time in the temperature range is shortened. Specifically, if the heating rate in the first temperature range is less than 500°C / sec, the increase in Goss nuclei is insufficient. Therefore, the heating rate in the temperature range of 550 to 750°C is set to 500°C / sec or more. There is no upper limit to the heating rate, but if the heating rate exceeds 2000°C / sec, there is a concern that the load on the device will become too high. Therefore, the heating rate in the temperature range of 550 to 750°C may be set to 2000°C / sec or less. By performing decarburization annealing under such conditions, the sharpness of the crystal orientation after secondary recrystallization approaches the ideal Goss orientation. In other words, a secondary recrystallized structure with a relatively small crystal orientation dispersion is obtained. By introducing strain into such a structure under the conditions described below, it becomes possible to achieve both low iron loss and low noise.

[0057] However, when the steel sheet is heated in the temperature range of 550 to 750°C at a heating rate of 500°C / sec or more, the oxide film formed on the steel sheet surface in this temperature range is mostly SiO2. This is because SiO2 has the fastest formation rate compared to other oxide films. Since SiO2 has the effect of suppressing decarburization, it is preferable from the viewpoint of promoting decarburization that the amount of SiO2 film formation is not excessive. In the manufacturing method for grain-oriented electrical steel sheet according to this embodiment, even when heating is performed in the temperature range of 550 to 750°C at a heating rate of 500°C / sec or more, it is possible to prevent the SiO2 generated in the temperature range of 550 to 750°C from becoming thicker by increasing the heating rate in the temperature range of 750 to 800°C (second temperature range) or by increasing the heating rate in the temperature range of 750 to 800°C while controlling the dew point atmosphere. Specifically, when only the heating rate is controlled, the heating rate in the temperature range of 750 to 800°C is set to 800°C / sec or more. If the heating rate is less than 800°C / sec, the growth of SiO2 (thickening of the oxide film) cannot be sufficiently suppressed. The heating rate in the temperature range of 750 to 800°C is preferably 1000°C / sec or more. There is no upper limit to the heating rate, but if the heating rate exceeds 2000°C / sec, there is a concern that the load on the device will become too high. Therefore, the heating rate in the temperature range of 750 to 800°C may be set to 2000°C / sec or less. In addition, when simultaneously controlling the temperature rise rate and the atmospheric dew point in the temperature range of 750 to 800°C (second temperature range), from the viewpoint of suppressing the growth of SiO2, the atmospheric dew point is set to -50 to 20°C and the temperature rise rate is set to 50°C / sec or more. If the atmospheric dew point is more than 20°C or the temperature rise rate is less than 50°C / sec, the growth of SiO2 cannot be sufficiently suppressed. On the other hand, the lower the atmospheric dew point, the more preferable it is. Therefore, no lower limit is particularly set, but in order to achieve less than -50°C, special equipment is required, which is not industrially preferable. Therefore, the lower limit of the atmospheric dew point may be set to -50°C. The atmosphere in the first temperature range is not particularly limited, and known conditions can be applied.

[0058] <Nitriding process> A nitriding treatment may be carried out between the decarburization annealing step and the finish annealing step described below. In the nitriding process, for example, the cold-rolled steel sheet after the decarburization annealing process is maintained at about 700 to 850°C in a nitriding atmosphere (an atmosphere containing hydrogen, nitrogen, and ammonia or other gases having nitriding ability). Here, it is preferable to perform the nitriding process on the steel sheet so that the N content of the cold-rolled steel sheet is 40 to 1000 ppm by mass. If the N content of the cold-rolled steel sheet after the nitriding process is less than 40 ppm, AlN does not precipitate sufficiently in the cold-rolled steel sheet, and AlN may not function as an inhibitor. Therefore, when AlN is used as an inhibitor, it is preferable that the N content of the cold-rolled steel sheet after the nitriding process is 40 ppm or more. On the other hand, if the N content of the cold-rolled steel sheet exceeds 1000 ppm, excess AlN remains in the steel sheet even after secondary recrystallization is completed in the finish annealing. Such AlN causes iron loss deterioration. For this reason, it is preferable that the N content of the cold-rolled steel sheet after the nitriding treatment is 1000 ppm or less.

[0059] <Finish annealing process> In the final annealing process, a predetermined annealing separator is applied to one or both sides of the cold-rolled steel sheet obtained in the decarburization annealing process or further subjected to nitriding treatment, and then the cold-rolled steel sheet is subjected to final annealing. The final annealing is generally performed for a long time while the steel sheet is wound in a coil shape. Therefore, prior to the final annealing, an annealing separator is applied to the cold-rolled steel sheet and dried in order to prevent seizure between the inside and outside of the coil winding. The annealing separator to be applied is one that contains MgO as its main component (e.g., 80% or more by weight). By using an annealing separator that contains MgO as its main component, a glass coating can be formed on the surface of the base steel sheet. If MgO is not the main component, the primary coating (glass coating) will not be formed. This is because the primary coating is an Mg2SiO4 or MgAl2O4 compound, and there is a shortage of Mg, which is necessary for the formation reaction. The finish annealing may be performed, for example, in an atmospheric gas containing hydrogen and nitrogen by raising the temperature to 1150 to 1250° C. and annealing at that temperature for 10 to 60 hours.

[0060] <Film formation process> In the coating formation step, a tensioned insulating coating is formed on one or both sides of the cold-rolled steel sheet after the finish annealing. The conditions for forming the tensioned insulating coating are not particularly limited, and a known insulating coating treatment liquid may be used, and the treatment liquid may be applied and dried by a known method. By forming a tensioned insulating coating on the steel sheet surface, it is possible to further improve the magnetic properties of the grain-oriented electrical steel sheet. The surface of the steel sheet on which the insulating coating (tension-imparting insulating coating) is formed may be a surface that has been subjected to any pretreatment, such as a degreasing treatment with an alkali or the like, or an acid pickling treatment with hydrochloric acid, sulfuric acid, phosphoric acid or the like, before the treatment liquid is applied, or the surface may be as it is after finish annealing without being subjected to such pretreatment. The insulating coating formed on the surface of the steel sheet is not particularly limited as long as it is used as an insulating coating for oriented electrical steel sheets, and a known insulating coating can be used. Examples of such insulating coatings include coatings mainly composed of phosphate and colloidal silica. Examples of composite insulating coatings include inorganic substances and further containing organic substances. Here, the composite insulating coating is, for example, an insulating coating mainly composed of at least one of inorganic substances such as metal chromate salts, metal phosphate salts, colloidal silica, Zr compounds, and Ti compounds, in which fine organic resin particles are dispersed. In particular, from the viewpoint of reducing the environmental load during production, which has become increasingly necessary in recent years, insulating coatings using metal phosphate salts, Zr or Ti coupling agents, or carbonates or ammonium salts thereof as starting materials may be used.

[0061] <Magnetic domain refining process> In the magnetic domain refinement process, an energy beam such as a laser beam or an electron beam is irradiated onto the surface of the tensioned insulating coating to introduce multiple linear strains extending in a direction at an angle φ of 60 to 120° with respect to the rolling direction near the surface of the base steel sheet (from the surface to the inside of the steel sheet). In the magnetic domain refinement process, multiple linear strains (thermal strains caused by rapid heating by energy beam irradiation and subsequent rapid cooling) are formed at predetermined intervals in the rolling direction, and the intervals (i.e., the interval (p) between adjacent strains) are 3.0 to 9.0 mm in the rolling direction. If the interval p in the rolling direction of a plurality of linear strains exceeds 9.0 mm, the iron loss improvement effect will be insufficient. Examples of the energy beam include a laser beam and an electron beam. The laser beam may be a continuous wave laser or a pulsed laser. Examples of the type of laser beam include a fiber laser, a YAG laser, or a CO2 laser. The electron beam may be a continuous beam or an intermittent beam.

[0062] Also, as described above, in order to obtain a grain-oriented electromagnetic steel sheet that achieves both low iron loss and low noise, in the magnetic domain refinement step, an energy beam is irradiated from above the tension insulating film to introduce strain into the base steel sheet and form a reflux magnetic domain with a shallow depth from the surface. Specifically, using the laser output P in units of W and the laser irradiation cross-sectional area S in units of mm 2 The laser beam is irradiated so that the laser power density Ip defined by P / S satisfies the following formula (3), and the laser input energy Up defined by (P / Vs) using the laser output P and the laser scanning speed Vs in units of mm / second satisfies the following formula (4). 250 ≤ Ip ≤ 2000 Formula (3) 0.005 < Up ≤ 0.050 Formula (4) If Ip is less than 250, sufficient energy is not input, and the magnetic domain refinement effect (iron loss improvement effect) cannot be obtained. Therefore, Ip is 250 or more. Ip is preferably 500 or more. On the other hand, when Ip exceeds 2000, excess thermal strain is introduced beyond the magnetic domain refinement effect, deteriorating the noise characteristics. Therefore, Ip is 2000 or less. Ip is preferably 1750 or less, more preferably 1500 or less. Also, if Up is 0.005 or less, the irradiation effect cannot be sufficiently obtained and the iron loss cannot be sufficiently improved. Therefore, Up is more than 0.005. On the other hand, when Up exceeds 0.050, the noise characteristics deteriorate. Therefore, Up is 0.050 or less. Although a laser beam has been described here as a specific example, the same applies when using other energy beam means such as an electron beam.

[0063] Furthermore, in the manufacturing method of the grain-oriented electrical steel sheet according to this embodiment, when irradiating the energy beam, the beam aspect ratio defined as (dl / dc) using the diameter dl of the energy beam in the direction perpendicular to the beam scan direction (scanning direction) and the diameter dc of the energy beam in the beam scan direction, in units of μm, is controlled so as to satisfy the following equation (5). 0.001 <dl / dc<1.000 (5) If the beam aspect ratio is 0.001 or less, heat extraction occurs during beam irradiation, the input energy efficiency decreases, and sufficient magnetic domain refinement effect (iron loss improvement effect) cannot be obtained. Therefore, the beam aspect ratio is set to be more than 0.001. On the other hand, if the beam aspect ratio is 1.000 or more, the heat extraction associated with the beam irradiation does not occur, but instead, residual stress occurs, and the noise reduction effect cannot be obtained. Therefore, the beam aspect ratio is less than 1.000. The beam aspect ratio is preferably less than 0.050, more preferably less than 0.005.

[0064] Moreover, the diameter dl of the energy beam in the direction perpendicular to the beam scanning direction (unit: μm) is set to satisfy the following formula (6). 10≦dl<200 (6) It is industrially difficult to produce a beam with dl of less than 10. Therefore, dl is 10 or more. On the other hand, if dl is 200 or more, the magnetic domain refining effect is exceeded and excess thermal strain is introduced, deteriorating noise characteristics. Therefore, dl is less than 200. dl is preferably less than 150, and more preferably less than 100.

[0065] In the manufacturing method of the grain-oriented electrical steel sheet according to the present embodiment, as described above, an energy beam with a relatively strong Ip is irradiated with a small beam aspect ratio. Such irradiation is not usually performed because a small beam aspect ratio leads to dispersion of the irradiation energy, which is thought to reduce the effect of increasing Ip. However, the present inventors conducted an investigation based on the new knowledge that control of the spatial distribution of strain is important from the viewpoint of simultaneously reducing iron loss and noise, and as a result, discovered for the first time that the above-mentioned irradiation conditions are preferable. EXAMPLES

[0066] As shown in Table 1, steel pieces having different chemical compositions were prepared for each steel number (A to G). Next, grain-oriented electrical steel sheets (Test Nos. 1 to 28) were manufactured using each steel piece. Specifically, steels B, E, and F were heated to a temperature in the range of 1100 to 1200°C, and then hot-rolled to produce hot-rolled steel sheets having a thickness of 2.3±0.3 mm. Steel billets A, C, D, and G were heated to a temperature in the range of 1300 to 1400°C, and then hot-rolled to produce hot-rolled steel sheets having a thickness of 2.3±0.3 mm. Next, the obtained hot-rolled steel sheet was subjected to hot-rolled sheet annealing. Specifically, the hot-rolled steel sheet was annealed under the conditions of an annealing temperature of 1000 to 1200° C. and a holding time of 10 to 200 seconds. Next, the surface scale was removed from the hot-rolled and annealed hot-rolled steel sheet by pickling or the like, and then cold rolling was performed once or twice with annealing in between to produce a cold-rolled steel sheet having a base thickness of 0.19 to 0.23 mm. The obtained cold-rolled steel sheets were subjected to decarburization annealing under the conditions shown in Table 2. The soaking process of the decarburization annealing was carried out at a temperature of 800 to 840°C for 100 to 150 seconds. The degree of oxidation (PH2O / PH2) was controlled to 0.3 to 0.5. Tests Nos. 2, 5, 6, 9, 10, 14, 16, 18, 23, 26, and 27 using steels B, E, and F were further subjected to nitriding treatment. Next, the cold-rolled steel sheet was subjected to a finish annealing process. Specifically, an annealing separator containing magnesium oxide (MgO) as a main component (weight fraction of 80% or more) was applied to the surface of the cold-rolled steel sheet. Next, the cold-rolled steel sheet coated with the annealing separator was annealed at 1000 to 1300° C. to produce a steel sheet having a glass coating on the base steel sheet. Next, a coating formation step was carried out on this steel sheet. Specifically, an insulating coating formation liquid mainly containing colloidal silica and phosphate was applied to the surface of the steel sheet (more specifically, the surface of the glass coating, which is the primary coating), and heat-treated (baked). As a result, a grain-oriented electrical steel sheet was obtained that included a base steel sheet, a glass coating formed on the base steel sheet, and a tension-applying insulating coating formed on the glass coating.

[0067] [Table 1]

[0068] [Table 2]

[0069] [Analysis of the chemical composition of base steel plate] The chemical composition of the base steel sheet of each test number of grain-oriented electrical steel sheets before magnetic domain refinement obtained in the above manner was determined by the following method. First, the tension-applying insulating coating was removed from the grain-oriented electrical steel sheet of each test number. Specifically, the grain-oriented electrical steel sheet was immersed for 7 to 10 minutes in an aqueous sodium hydroxide solution containing 30 to 50 mass% NaOH and 50 to 70 mass% H2O at 80 to 90°C. After immersion, the grain-oriented electrical steel sheet (the grain-oriented electrical steel sheet from which the tension-applying insulating coating was removed) was washed with water. After washing with water, it was dried for just under 1 minute with a hot air blower. Next, the glass coating was removed from the grain-oriented electrical steel sheet not provided with a tension-applying insulating coating. Specifically, the grain-oriented electrical steel sheet was immersed for 1 to 10 minutes in an aqueous hydrochloric acid solution containing 30 to 40 mass% HCl and at 80 to 90°C. This removed the glass coating from the base steel sheet. The base steel sheet after immersion was washed with water. After washing with water, it was dried for just under 1 minute with a hot air blower. Through the above steps, the base steel sheet was removed from the grain-oriented electrical steel sheet. The chemical composition of the removed base steel plate was determined by a known compositional analysis method. Specifically, cutting chips were generated from the base steel plate using a drill, and the cutting chips were collected. The collected cutting chips were dissolved in acid to obtain a solution. ICP-AES was performed on the solution to perform elemental analysis of the chemical composition. The Si in the chemical composition of the base steel plate was determined by the method (silicon quantification method) specified in JIS G 1212 (1997). Specifically, when the above-mentioned cutting chips were dissolved in acid, silicon oxide precipitated. This precipitate (silicon oxide) was filtered out with filter paper, and the mass was measured to determine the Si content. The C content and S content were determined by a known high-frequency combustion method (combustion-infrared absorption method). Specifically, the above-mentioned solution was burned by high-frequency heating in an oxygen stream, and the generated carbon dioxide and sulfur dioxide were detected to determine the C content and S content. The N content was determined by a known inert gas fusion-thermal conductivity method. The chemical composition of the base steel sheet was determined by the above analytical methods. The results are shown in Table 3.

[0070] [Table 3]

[0071] Although not shown in the table, in order to evaluate the iron loss improvement rate, the iron loss of the grain-oriented electrical steel sheet of each test number was evaluated before magnetic domain refinement. A sample of 60 mm width x 300 mm length, including the center position of the sheet width, was taken from the grain-oriented electrical steel sheet of each test number. The length direction of the sample was parallel to the rolling direction. The taken samples were held at 800°C for 2 hours in a nitrogen atmosphere with a dew point below 0°C to remove any distortion that had been introduced when the samples were taken. Using this sample, the iron loss W when the frequency is 50Hz and the maximum magnetic flux density is 1.7T 17 / 50 (W / kg) was measured.

[0072] Thereafter, for the grain-oriented electrical steel sheets of each test number, magnetic domain refinement was performed by irradiating the surface of the grain-oriented electrical steel sheets with energy rays using a continuous wave laser or an intermittent wave laser under the conditions shown in Tables 4 and 5. Evaluation tests of noise characteristics and magnetic properties were performed on the grain-oriented electrical steel sheets after magnetic domain refinement.

[0073] [Noise characteristics evaluation] The magnetostriction of the sample having a width of 60 mm and a length of 300 mm that had been subjected to the magnetic domain control was measured by an AC magnetostriction measurement method using a magnetostriction measurement device that was equipped with a laser Doppler vibrometer, an excitation coil, an excitation power supply, a magnetic flux detection coil, an amplifier, and an oscilloscope. Specifically, an AC magnetic field was applied to the sample so that the maximum magnetic flux density in the rolling direction was 1.7 T. The change in length of the sample due to expansion and contraction of the magnetic domains was measured with a laser Doppler vibrometer to obtain a magnetostriction signal. The obtained magnetostriction signal was subjected to Fourier analysis to obtain the amplitude Cn of each frequency component fn (n is a natural number equal to or greater than 1) of the magnetostriction signal. The A correction coefficient αn of each frequency component fn was used to obtain the magnetostriction rate level LVA (dB) given by the following equation. LVA=20×Log(√(Σ(ρc×2π×fn×αn×Cn / √2) 2 ) / Pe0) Here, ρc is the specific acoustic resistance, and ρc = 400. Pe0 is the minimum audible sound pressure, and Pe0 = 2 × 10 -5 (Pa) was used. The A correction coefficient αn was the value listed in Table 2 of JIS C 1509-1 (2005). Based on the obtained magnetostrictive rate level (LVA), the noise characteristics were evaluated according to the following criteria. If the magnetostrictive rate level was less than 60 dBA, it was judged to have "excellent noise characteristics." If it was less than 50 dBA, it was judged to have particularly excellent noise characteristics. If the magnetostrictive rate level was 60 dBA or more, it was judged to have "inadequate noise characteristics." The results are shown in Table 5.

[0074] [Magnetic property evaluation] The magnetic properties were evaluated in terms of the iron loss improvement rate in order to evaluate the iron loss improvement effect due to magnetic domain control. Using a sample with a width of 60 mm and a length of 300 mm that had been subjected to the above magnetic domain control, the iron loss W 17 / 50 (W / kg) was measured. And the iron loss measured here is W 17 / 50 (W / kg) and the iron loss measured before domain control W 17 / 50 Using this, the iron loss improvement rate (%) was calculated as [(iron loss before magnetic domain control - iron loss after magnetic domain control) x 100] / iron loss before magnetic domain control. An iron loss improvement rate of 5% or more was judged to have an "iron loss improvement effect," and an iron loss improvement rate of 10% or more was judged to have a "great iron loss improvement effect." However, for materials whose iron loss after magnetic domain control exceeded 0.85 W / kg, it was determined that the materials had "insufficient magnetic properties" regardless of the improvement rate of magnetic domain control. Additionally, the magnetic flux density (T) was determined by a single sheet magnetic property test (SST test) using this sample. Specifically, a magnetic field of 800 A / m was applied to the sample to determine the magnetic flux density (T). The results are shown in Table 5.

[0075] In this evaluation, only those that had "iron loss improvement effect" and "excellent noise characteristics" were considered to pass, i.e., inventive examples, in which at least one of the magnetic properties and noise characteristics was "insufficient noise characteristics" or "insufficient magnetic characteristics," the product was classified as a "comparative example."

[0076] [Table 4]

[0077] [Table 5]

[0078] As can be seen from Tables 1 to 5, Test Nos. 1 to 12, 21, and 24 to 28, which are examples of the invention, have excellent magnetic properties and noise properties. That is, "iron loss improvement rate is 5% or more," "iron loss after magnetic domain control is 0.85 W / kg or less," and "magnetostriction rate level is less than 60 dBA." For Test Nos. 5 to 11 and Test No. 21, the iron loss improvement rate exceeded 10% and the magnetostriction rate level was less than 50 dBA, which were particularly good characteristics. This was because the laser irradiation conditions Ip and Up were within a more preferable control range. In Test Nos. 1 to 4 and Test No. 12, the laser irradiation conditions Ip and Up were both outside the preferred or more preferred ranges, but were within the ranges of the present invention, and therefore the effects of the invention could be enjoyed.

[0079] In contrast, Test Nos. 13 to 20, 22, and 23 were comparative examples, and at least one of the magnetic properties and noise properties was poor. In the case of Test No. 13, the temperature increase step of the decarburization annealing was outside the range of the present invention. That is, in Test No. 13, the orientation sharpness of the Goss grains in the secondary recrystallized structure was insufficient. Therefore, even though the strain introduction conditions were within the range of the present invention, the half-width of the X-ray topography spectrum was outside the range of the present invention, and the noise characteristics were poor. In test No. 14, decarburization was insufficient. As a result, the iron loss exceeded 0.85 W / kg even after domain control, and the iron loss improvement rate was also low. In test No. 15, the interval of the linear distortion exceeded 9.0 mm. As a result, the interval of the distortion was wider, and the frequency of secondary recrystallized grains without magnetic domain control increased. As a result, the magnetic domain control effect was insufficient, and the iron loss improvement rate did not reach 5%. In test No. 16, the interval between the linear strains was less than 3.0 mm. The excessive strain introduced resulted in poor noise characteristics. In Test Nos. 17 to 20, the strain application conditions were outside the range of the present invention. Test No. 17 had a small Ip, and Test No. 20 had a small Up, so the magnetic domain refinement effect was not obtained, the half-width of the X-ray topography spectrum was outside the range of the present invention, and the iron loss improvement rate did not reach 5%. Test No. 18 had a large Ip, and Test No. 19 had a large Up, so the half-width of the X-ray topography spectrum was outside the range of the present invention, and the noise characteristics were poor. In Test No. 22, the beam aspect ratio exceeded 1.000, so the half-width of the X-ray topography spectrum was outside the range of the present invention, and the desired noise reduction effect was not obtained. In test No. 23, the diameter dl in the direction perpendicular to the beam scanning direction was 200 μm or more, so the width of the distortion became large, and excess thermal distortion was introduced, so that the noise reduction effect was not obtained. [Industrial Applicability]

[0080] INDUSTRIAL APPLICABILITY The present invention provides a grain-oriented electrical steel sheet having excellent iron loss characteristics and noise characteristics, and a manufacturing method thereof, and has high industrial applicability.

Claims

1. A base steel plate; A glass coating formed on the base steel sheet; a tension-applying insulating coating formed on the glass coating; Equipped with The base steel plate comprises, in mass%, C: 0.010% or less, Si: 3.00-4.00%, Mn: 0.01 to 0.50%, N: 0.010% or less, Sol. Al: 0.020% or less, P: 0.030% or less, S: 0.010% or less, Sn: 0 to 0.50%, Cu: 0 to 0.50%, Cr: 0 to 0.50%, Se: 0 to 0.020%, Sb: 0 to 0.500%, Mo: 0 to 0.10%, The balance is Fe and impurities, A plurality of linear strains extending continuously or intermittently in a direction intersecting with the rolling direction are present on the surface of the base steel sheet, The interval p between the adjacent linear strains in the rolling direction is 3.0 to 9.0 mm; The width of the linear distortion is 10 to 200 μm, In an X-ray topography spectrum obtained from an X-ray topography image of the surface in a range of 1.50 mm in the rolling direction centered on the linear strain, the half-width of a peak in the X-ray topography spectrum including a maximum value of the spectrum intensity is 0.02 mm or more and 0.10 mm or less. A directional electrical steel sheet.

2. An X-ray beam is irradiated to an area of ​​3.0 mm in the rolling direction centered on the linear distortion on the surface, and the minimum value of the X-ray reflection intensity of the (310) plane is defined as I ｍｉｎ , background intensity I ０ The X-ray beam was irradiated to a range of 3.0 mm in the rolling direction centered on the linear distortion on the back surface, and the minimum value of the X-ray reflection intensity of the diffraction surface (310) was defined as J ｍｉｎ , background intensity J ０ When the above I ｍｉｎ , the above I ０ , said J. ｍｉｎ , said J. ０ satisfies the following formula (2): The grain-oriented electrical steel sheet according to claim 1 . 0.02 ≦ |J ０ -J ｍｉｎ | / |I ０ -I ｍｉｎ | ≦ 1.00 (2)

3. The chemical composition of the base steel plate is Contains either or both of Sn: 0.01 to 0.50% and Cu: 0.05 to 0.50%; The grain-oriented electrical steel sheet according to claim 1 or 2.

4. A method for producing the grain-oriented electrical steel sheet according to claim 1 or 2, A hot rolling process in which a steel slab having a chemical composition consisting of, in mass%, C: 0.010 to 0.200%, Si: 3.00 to 4.00%, Mn: 0.01 to 0.50%, N: 0.020% or less, Sol. Al: 0.010 to 0.040%, P: 0.030% or less, S: 0.005 to 0.040%, Sn: 0 to 0.50%, Cu: 0 to 0.50%, Bi: 0 to 0.020%, Cr: 0 to 0.50%, Se: 0 to 0.020%, Sb: 0 to 0.500%, Mo: 0 to 0.10%, and the balance: Fe and impurities is heated and then hot rolled to obtain a hot-rolled steel sheet; A hot-rolled sheet annealing process for subjecting the hot-rolled steel sheet to hot-rolled sheet annealing; A cold rolling process in which the hot-rolled steel sheet after the hot-rolled sheet annealing process is subjected to cold rolling once or multiple times with intermediate annealing to obtain a cold-rolled steel sheet; a decarburization annealing step of subjecting the cold-rolled steel sheet to decarburization annealing; A finish annealing process in which an annealing separator mainly composed of MgO is applied to the front and back surfaces of the cold-rolled steel sheet after the decarburization annealing process, which is the base steel sheet, and then dried and finish annealed to form a glass coating; a coating formation process for forming a tension-applied insulating coating on the glass coating to obtain a grain-oriented electrical steel sheet including the base steel sheet, the glass coating formed on the base steel sheet, and the tension-applied insulating coating formed on the glass coating; a magnetic domain refining step of irradiating a surface of the tension-applying insulating coating of the grain-oriented electrical steel sheet with an energy beam to impart a plurality of linear strains to the base steel sheet; having In the magnetic domain refining step, Among the plurality of linear strains, the interval between adjacent linear strains in the rolling direction is 3.0 to 9.0 mm; Energy beam output P in W and mm ２ The unit is W / mm2, which is defined as (P / S) using the energy beam irradiation cross-sectional area S at ２ The energy beam power density Ip at satisfies the following formula (3): Using the energy beam output P and the energy beam scanning speed Vs in the unit of mm / sec, the energy beam input energy Up in the unit of J / mm defined as (P / Vs) satisfies the following formula (4), The beam aspect ratio defined by (dl / dc) using a diameter dl of the energy beam in a direction perpendicular to the beam scanning direction and a diameter dc of the energy beam in the beam scanning direction, both in the unit of μm, and the dl satisfy the following formula (5) and the following formula (6), respectively: In the decarburization annealing step, The heating rate S1 in the first temperature range of 550 to 750 ° C. is 500 ° C. / sec or more, The heating rate S2 in the second temperature range of 750 to 800 ° C. is 800 ° C. / sec or more, or the heating rate S2 in the second temperature range is 50 ° C. / sec or more and the atmospheric dew point in the second temperature range is −50 ° C. to 20 ° C.; A method for producing a grain-oriented electrical steel sheet comprising the steps of: 250≦Ip≦2000 (3) 0.005<Up≦0.050 (4) 0.001<dl / dc<1.000 (5) 10≦dl<200 (6)

5. Between the decarburization annealing step and the finish annealing step, a nitriding treatment step is further included in which the cold-rolled steel sheet is subjected to a nitriding treatment. The method for producing a grain-oriented electrical steel sheet according to claim 4 .

6. The chemical composition of the steel piece is Contains either or both of Sn: 0.01 to 0.50% and Cu: 0.05 to 0.50%; The method for producing a grain-oriented electrical steel sheet according to claim 4 or 5.

Images