Grain-oriented electrical steel sheet and its manufacturing method

Abstract

This grain-oriented electromagnetic steel sheet comprises a base steel sheet, a glass coating formed on the base steel sheet, and a tension-imparting insulating coating formed on the glass coating, wherein: multiple linear distortion regions, which continuously or intermittently extend in a direction intersecting with a rolling direction, are present in the base steel sheet, each of the multiple linear distortion regions has a width of 210 µm or less in the rolling direction, the multiple linear distortion regions are parallel to each other, and the interval between adjoining linear distortion regions is 10 mm or less in the rolling direction; and magnetostriction λ0-pb per unit µm / m obtained when excited to 1.7 T and magnetostriction λ0-pa per unit µm / m obtained when excited to 1.7 T after having been heat-treated at 800˚ C for 4 hours satisfy 0.02 ≤ λ0-pb - λ0-pa ≤ 0.20.

Description

[Technical Field]

[0001] The present invention relates to a grain-oriented electrical steel sheet and a method for manufacturing the same. This application claims priority based on Japanese Patent Application No. 2021-053619, 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 that are primarily used as iron core materials for transformers, and therefore require magnetic properties such as high magnetization 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 perspective of energy conservation, iron loss should be as low as possible. The level of iron loss is affected by factors such as magnetic susceptibility, sheet thickness, coating tension, impurity content, electrical resistivity, crystal grain size, and magnetic domain size. Even now, when various technologies have been developed for grain-oriented electrical steel sheets, research and development into reducing iron loss continues in order to improve energy efficiency.

[0003] For example, Patent Document 1 discloses a method for producing a steel sheet by irradiating a surface of the steel sheet with a focused continuous wave laser beam while scanning the surface in a direction inclined from the rolling direction of the steel sheet, and by repeating the process while shifting the area scanned with the continuous wave laser beam at predetermined intervals. The average power of the continuous wave laser beam is represented as P (W), the scanning speed as Vc (mm / s), and 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, which satisfies the above conditions. Patent Document 1 shows that it is possible to easily reduce iron loss in both the L-direction and 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 electrical 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. It is shown that a grain-oriented electrical steel sheet with reduced iron loss can be obtained when the spot 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 range 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 electrical steel sheet in which the surface of the grain-oriented electrical 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, the irradiation beam shape is an ellipse having a long axis in the sheet width direction, the irradiation power density of the laser pulse is set below the film damage threshold of the steel sheet surface, thereby suppressing the occurrence of laser irradiation marks, and by setting the long axis length of the elliptical beam to be greater than or equal to the pulse beam irradiation interval in the sheet width direction, continuous pulse beams are superimposed on the steel sheet surface, sufficient integrated irradiation energy necessary for improving the magnetic properties is given, laser irradiation marks are suppressed, and an efficient magnetic domain control effect is obtained.

[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 electrical steel sheets used for transformer cores are required to be materials suitable for low noise and low vibration as well as low iron loss. One of the causes of noise and vibration in transformers with respect to the material is said to be the magnetostriction of the grain-oriented electrical steel sheet. The magnetostriction referred to here is the vibration observed in the rolling direction of the grain-oriented electrical steel sheet due to a slight change in the outer shape of the grain-oriented electrical steel sheet as the magnetization strength changes when the grain-oriented electrical steel sheet is excited by alternating current. The magnitude of this magnetostriction is 10 -6Although it is very small, on the order of magnitude, the magnetostriction generates vibrations in the iron core, which then propagate to external structures such as the transformer tank and become 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 there is a problem in that the closure domains formed by laser irradiation increase magnetostriction, thereby deteriorating noise characteristics.

[0008] To address this issue, for example, Patent Document 4 discloses a grain-oriented electrical steel sheet that has low iron 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: the ratio of the maximum width Wmax to the minimum width Wmin in the rolling direction on the steel sheet surface (Wmax / Wmin) is 1.2 to 2.2, the average width Wave in the rolling direction on the steel sheet surface is 80 μm to 200 μm, the 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 conventional methods.

[0009] Patent Document 5 discloses a grain-oriented electrical steel sheet in which local strain is introduced at periodic intervals in the rolling direction and in a direction transverse to the rolling direction, wherein linear closure domains are formed near the strains, and in a demagnetized state, the steel sheet has magnetic domains that extend from the closure domains in the rolling direction by a length of 1.2 mm or more in the rolling direction, and further, the magnetic domains are formed at an average of 1.8 or more per mm in a region along the closure domains, and where the line spacing of the closure domains is s (mm), the width w (mm) of the closure domains and the depth h (μm) of the closure domains 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 was 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 required in recent years. Furthermore, it was found that magnetic domain control also damages the coating formed on the surface of the steel sheet to impart insulation properties and tension to the grain-oriented electrical steel sheet, thereby reducing coating adhesion. [Prior art documents] [Patent documents]

[0011] [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 Summary of the Invention [Problem to be solved by the invention]

[0012] As described above, there has not been disclosed a grain-oriented electrical steel sheet or a manufacturing method thereof that simultaneously sufficiently improves iron loss characteristics and noise characteristics while also ensuring coating adhesion. The present invention aims to provide a grain-oriented electrical steel sheet that has excellent iron loss and noise characteristics (a large iron loss improvement rate due to magnetic domain refinement and low noise when incorporated into a transformer: an excellent balance between iron loss and noise), and a method for manufacturing the same. Preferably, the present invention aims to provide a grain-oriented electrical steel sheet that has excellent iron loss and noise characteristics, as well as excellent coating adhesion. [Means for solving the problem]

[0013] The present inventors have investigated the magnetic domain control conditions for obtaining grain-oriented electrical steel sheets with an excellent balance between iron loss and noise characteristics (iron loss / noise balance). As a result, they have found that, for magnetic domain control, a good balance between iron loss and noise can be achieved by controlling the shape of the energy beam irradiation surface, increasing the input energy, and lowering the power density. However, they have found that these steel sheets are prone to coating peeling originating from the energy beam irradiation area.

[0014] When grain-oriented electrical steel sheets are irradiated with energy beams (laser beams, electron beams, etc.), the irradiated areas are rapidly heated and cooled. As a result, residual strain is generated from the surface near the irradiated area to the interior of the steel sheet, forming a distorted area (residual strain area). Coating peeling is likely to occur starting from the energy beam irradiated area, which is thought to be caused by damage to the coating in the irradiated area as well as residual strain near the irradiated area. Taking this into consideration, the inventors attempted to adjust the energy beam irradiation conditions to a strain amount that would maintain a good balance between iron loss and noise. As a result, they found that a good balance between iron loss and noise could be achieved by adjusting the energy beam irradiation conditions to an appropriate range for the width and spacing of the distorted areas. The inventors also attempted to quantify the amount of distortion in relation to the magnitude of magnetostriction in grain-oriented electrical steel sheets irradiated with energy beams at a higher input energy and a lower power density, and found that good coating adhesion can be ensured by controlling the change in magnetostriction between before and after a specific heat treatment within a certain range. Furthermore, the inventors have conducted extensive research into the modification of the coating, focusing on the relationship between the structure of the compound phase that makes up the coating and the coating adhesion. As a result of their investigation, they have found that even better coating adhesion can be ensured by confining the MgAl2O4 phase formed in the coating to the bottom of the glass coating.

[0015] The present invention has been made in light of the above findings. [1] A grain-oriented electrical steel sheet according to one aspect 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, a chemical composition of the base steel plate containing 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, S: 0.010% or less, P: 0.030% or less, Cr: 0 to 0.50%, Sn: 0 to 0.50%, Cu: 0 to 0.50%, Se: 0 to 0.020%, Sb: 0 to 0.500%, Mo: 0 to 0.10%, and the balance being Fe and impurities; The base steel sheet has a plurality of linear strain regions that extend continuously or intermittently in a direction intersecting the rolling direction, the plurality of linear strain regions each having a width of 210 μm or less in the rolling direction, the plurality of linear strain regions are parallel to each other, the spacing between adjacent linear strain regions in the rolling direction is 10 mm or less, and the magnetostriction λ in μm / m when excited to 1.7 T is 0-pb and the magnetostriction λ in μm / m when magnetized up to 1.7 T after heat treatment at 800°C for 4 hours. 0-pa Grain-oriented electrical steel sheet that satisfies the following formula (1). 0.02≦λ 0-pb -λ 0-pa ≦0.20 (1) [2] In the grain-oriented electrical steel sheet according to [1], the glass coating has a structure including a main phase of Mg2SiO4 phase and an MgAl2O4 phase, and when the glass coating is divided into three regions of equal thickness in the thickness direction in a cross section in the sheet thickness direction, the regions are designated as a 1 / 3 region, a 2 / 3 region, and a 3 / 3 region from the base steel sheet side toward the tension-applying insulating coating side, and when the area fraction of the MgAl2O4 phase in the 1 / 3 region is designated as S1, the area fraction of the MgAl2O4 phase in the 2 / 3 region is designated as S2, and the area fraction of the MgAl2O4 phase in the 3 / 3 region is designated as S3, S1, S2, and S3 may satisfy the following formulas (2) to (4): S1>S2>S3 (2) (S1+S2+S3) / 3<0.50 (3) S3<0.10 (4) [3] A method for producing a grain-oriented electrical steel sheet according to another aspect of the present invention is the method for producing a grain-oriented electrical steel sheet according to [1] or [2], comprising a hot rolling step of heating a steel slab and hot rolling it to form a hot-rolled steel sheet, a hot-rolled sheet annealing step of subjecting the hot-rolled steel sheet to hot-rolled sheet annealing, a pickling step of pickling the hot-rolled steel sheet after the hot-rolled sheet annealing step, a cold rolling step of cold-rolling the hot-rolled steel sheet after the pickling step once or multiple times with annealing in between to form a cold-rolled steel sheet, a decarburization annealing step of subjecting the cold-rolled steel sheet to decarburization annealing, and applying an annealing separator mainly composed of MgO powder to both surfaces of the cold-rolled steel sheet after the decarburization annealing step, which is a base steel sheet, and drying the cold-rolled steel sheet, followed by finishing the cold-rolled steel sheet. a finish annealing step of forming a glass coating by performing finish annealing on the glass coating, a coating formation step of forming a tensioned insulating coating 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 step of irradiating the surface of the tensioned insulating coating of the grain-oriented electrical steel sheet with energy rays to form a plurality of linear strain regions in the base steel sheet, wherein in the magnetic domain refining step, the spacing in the rolling direction between adjacent linear strain regions among the plurality of linear strain regions is 10 mm or less, and 2 The unit is W / mm, defined as (P / S) using the energy ray irradiation cross section S at 2 The energy beam power density Ip at the energy beam output P satisfies the following formula (5), and 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 (6), 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, both in μm, and dl respectively satisfy the following formulas (7) and (8): 250≦Ip≦2000 (5) 0.010 <Up≦0.050 (6) 0.0010 <dl / dc<1.0000 (7) 10 <dl<200 (8) [4] In the method for producing a grain-oriented electrical steel sheet according to [3], the energy beam may be a laser beam. [5] In the method for producing a grain-oriented electrical steel sheet according to [4], the laser beam may be a fiber laser beam. [6] In the method for producing a grain-oriented electrical steel sheet according to any one of [3] to [5], the billet may contain, by mass%, C: 0.010 to 0.200%, Si: 3.00 to 4.00%, sol. Al: 0.010 to 0.040%, Mn: 0.01 to 0.50%, N: 0.020% or less, S: 0.005 to 0.040%, P: 0.030% or less, Cu: 0 to 0.50%, Cr: 0 to 0.50%, Sn: 0 to 0.50%, Se: 0 to 0.020%, Sb: 0 to 0.500%, Mo: 0 to 0.10%, and the balance being Fe and impurities. [7] In the method for producing a grain-oriented electrical steel sheet according to any one of [3] to [6], the decarburization annealing step may have a heating step and a soaking step, and the heating step may have a heating rate of 700 to 2000°C / s at 550 to 750°C and an oxygen potential of 0.0001 to 0.0100, and the soaking step may include a first soaking step in an atmosphere with an oxygen potential of 0.4 to 0.8, an annealing temperature of 800 to 900°C, and an annealing time of 100 to 500 seconds, and a second soaking step in an atmosphere with an oxygen potential of 0.1 or less, an annealing temperature of 850°C to 1000°C, and an annealing time of 5 to 100 seconds. [8] The method for producing a grain-oriented electrical steel sheet according to any one of [3] to [7] may further include a nitriding treatment step of subjecting the cold-rolled steel sheet to a nitriding treatment during or after the decarburization annealing step. [Effects 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 a good balance between iron loss and noise, and a method for manufacturing the same. Furthermore, according to a preferred aspect of the present invention, it is possible to provide a grain-oriented electrical steel sheet having a good balance between iron loss and noise and also having excellent coating adhesion. DETAILED DESCRIPTION OF THE INVENTION

[0017] A grain-oriented electrical steel sheet according to one embodiment of the present invention (grain-oriented electrical steel sheet according to the present embodiment) comprises a base steel sheet having a predetermined chemical composition, a glass coating formed on the base steel sheet, and a tension-applying insulating coating formed on the glass coating. Furthermore, the base steel sheet has a plurality of linear strain (residual strain) regions formed in approximately parallel relation, extending continuously or intermittently in a direction intersecting the rolling direction, with the width (width in the rolling direction) of each linear strain region being 210 μm or less, and the spacing between adjacent linear strain regions in the rolling direction being 10 mm or less.

[0018] The grain-oriented electrical steel sheet according to this embodiment will be described below.

[0019] <Base material steel plate> (chemical composition) The grain-oriented electrical steel sheet according to this embodiment is characterized by the strain region (linear strain region) and the structure of the compound phase in the glass coating. The base steel sheet included in the grain-oriented electrical steel sheet is not limited in chemical composition and may be within a known range. For example, in order to obtain the properties generally required of grain-oriented electrical steel sheets, it is preferable that the chemical components include the following. In this embodiment, % relating to the chemical components is % by mass unless otherwise specified.

[0020] C: 0.010% or less Carbon (C) is an element effective for controlling the structure of steel sheets in the manufacturing process up to the completion of the decarburization annealing step. However, if the C content exceeds 0.010%, the magnetic properties of the finished grain-oriented electrical steel sheet will deteriorate. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, the C content is preferably 0.010% or less. The C content is more preferably 0.005% or less. The lower the C content, the better; however, even if the C content is reduced to less than 0.0001%, the effect of structural control will saturate and the manufacturing cost will simply increase. Therefore, the C content may be 0.0001% or more.

[0021] Si: 3.00 to 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 preferably 3.00% or more. The Si content is more preferably 3.10% or more, and even more preferably 3.20% or more. On the other hand, if the Si content exceeds 4.00%, the grain-oriented electrical steel sheet becomes embrittled and the threading property deteriorates significantly. Furthermore, the workability of the grain-oriented electrical steel sheet deteriorates, and the steel sheet may break during rolling. Therefore, the Si content is preferably 4.00% or less. The Si content is more preferably 3.80% or less, and even more preferably 3.70% or less.

[0022] Mn: 0.01 to 0.50% Mn (manganese) is an element that combines with S to form MnS during the manufacturing process. These precipitates function as inhibitors (suppressors of normal grain growth) and cause secondary recrystallization in steel. Mn also improves the hot workability of steel. If the Mn content is less than 0.01%, the above-mentioned effects cannot be fully achieved. Therefore, the Mn content is preferably 0.01% or more. The Mn content is more preferably 0.02% 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 preferably 0.50% or less. The Mn content is more preferably 0.20% or less, and even more preferably 0.10% or less.

[0023] N: 0.010% or less N (nitrogen) is an element that bonds with Al during the manufacturing process to form AlN, which functions as an inhibitor. However, if the N content exceeds 0.010%, the magnetic properties will be 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 preferably 0.010% or less. The N content is more preferably 0.008% or less. On the other hand, the lower limit of the N content is not particularly specified, but reducing it to less than 0.001% would only increase the manufacturing cost, so the N content may be 0.001% or more.

[0024] sol.Al: 0.020% or less Sol-Al (acid-soluble aluminum) is an element that combines with N to form AlN, which functions as an inhibitor, during the manufacturing process of grain-oriented electrical steel sheet. However, if the sol-Al content of the base steel sheet exceeds 0.020%, the magnetic properties will be reduced due to the excess inhibitor remaining 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 preferably 0.020% or less. The sol-Al content is more preferably 0.010% or less, and even more preferably less than 0.001%. There is no particular restriction on the lower limit of the sol-Al content, but reducing it to less than 0.0001% will only increase the manufacturing cost. Therefore, the sol-Al content may be 0.0001% or more.

[0025] S: 0.010% or less S (sulfur) is an element that combines with Mn during the manufacturing process to form MnS, which functions as an inhibitor. However, if the S content exceeds 0.010%, the magnetic properties will be reduced due to the excess remaining inhibitor. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, the S content is preferably 0.010% or less. The S content in the grain-oriented electrical steel sheet is preferably as low as possible, for example, less than 0.001%. However, reducing the S content in the grain-oriented electrical steel sheet to less than 0.0001% will only increase the manufacturing cost. Therefore, the S content in the grain-oriented electrical steel sheet 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, excessive reduction in rolling workability can be prevented, and fractures during manufacturing can be suppressed. From this perspective, the P content is preferably set to 0.030% or less. The P content is more preferably set to 0.020% or less, and further preferably set to 0.010% or less. The lower limit of the P content 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 texture and magnetic properties. To achieve this effect, the P content may be set to 0.001% or more, or even 0.005% or more.

[0027] 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 elements, with the balance being Fe and impurities. However, for the purpose of improving magnetic properties, etc., it may also contain Cu, Cr, Sn, Se, Sb, and Mo in the ranges shown below. These elements may also be contained as impurities. Furthermore, even if other elements than these, such as one or more of W, Nb, Ti, Ni, Bi, 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 the manufacturing environment, when the base steel sheet is industrially manufactured, 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.

[0028] Cr: 0 to 0.50% Cr (chromium) is an element that contributes to increasing the Goss orientation occupancy rate in the secondary recrystallized structure and improves magnetic properties. To achieve this 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, resulting in a deterioration in magnetic properties. Therefore, the Cr content is preferably 0.50% or less. The Cr content is more preferably 0.30% or less, and even more preferably 0.10% or less.

[0029] Sn: 0 to 0.50% Sn (tin) is an element that contributes to improving magnetic properties by controlling the primary recrystallization structure. To obtain the effect of improving magnetic properties, the Sn content is preferably 0.01% or more. The Sn content is more preferably 0.02% or more, and even more preferably 0.03% or more. On the other hand, if the Sn content exceeds 0.50%, secondary recrystallization becomes unstable and magnetic properties deteriorate. Therefore, the Sn content is preferably 0.50% or less. The Sn content is more preferably 0.30% or less, and even more preferably 0.10% or less.

[0030] Cu: 0 to 0.50% Cu (copper) is an element that contributes to increasing the Goss orientation occupancy rate in the secondary recrystallized structure. Cu is an optional element in the base steel sheet according to this embodiment. Therefore, the lower limit of its content is 0%, but in order to obtain the above-mentioned effects, the Cu content is preferably 0.01% or more. The Cu content is more preferably 0.02% or more, and even more preferably 0.03% 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, the Cu content is preferably 0.50% or less. The Cu content is more preferably 0.30% or less, and even more preferably 0.10% or less.

[0031] Se: 0 to 0.020% Se (selenium) is an element that has the effect of improving magnetic properties. Therefore, it may be contained. When Se is contained, the content is preferably 0.001% or more in order to effectively exhibit the effect of improving magnetic properties. The Se content is preferably 0.003% or more, and more preferably 0.006% or more. On the other hand, if the Se content exceeds 0.020%, the adhesion of the glass coating deteriorates. Therefore, the Se content is preferably 0.020% or less. The Se content is more preferably 0.015% or less, and even more preferably 0.010% or less.

[0032] Sb: 0 to 0.500% Sb (antimony) is an element that has the effect of improving magnetic properties. Therefore, it may be contained. When Sb is contained, the content is preferably 0.005% or more in order to effectively exhibit the effect of improving magnetic properties. The Sb content is more preferably 0.010% or more, and even more preferably 0.020% or more. On the other hand, if the Sb content exceeds 0.500%, the adhesion of the glass coating significantly deteriorates. Therefore, the Sb content is preferably 0.500% or less. The Sb content is more preferably 0.300% or less, and even more preferably 0.100% or less.

[0033] Mo: 0 to 0.10% Mo (molybdenum) is an element that has the effect of improving magnetic properties. Therefore, it may be contained. When Mo is contained, the Mo content is preferably 0.01% or more in order to effectively exhibit the effect of improving magnetic properties. The Mo content is more preferably 0.02% or more, and even more preferably 0.03% or more. On the other hand, if the Mo content exceeds 0.10%, the cold rolling property deteriorates and there is a possibility of fracture. Therefore, the Mo content is preferably 0.10% or less. The Mo content is more preferably 0.08% or less, and further preferably 0.05% or less.

[0034] As described above, the chemical composition of the base steel sheet of the grain-oriented electrical steel sheet in this embodiment may, for example, contain the above-mentioned essential elements with the balance consisting of Fe and impurities, or may contain the above-mentioned essential elements and further contain one or more optional elements with the balance consisting of Fe and impurities.

[0035] 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 containing 30 to 50 mass % of NaOH and 50 to 70 mass % of H2O at 80 to 90°C 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 then dried for just under one minute with a hot air blower. The dried grain-oriented electrical steel sheet (grain-oriented electrical steel sheet without the tension-applying insulating coating) is immersed in an aqueous hydrochloric acid solution containing 30 to 40 mass% HCl at 80 to 90°C for one to ten minutes to remove the glass coating. After immersion, the base steel plate is rinsed with water and then dried with a hot air blower for just under one minute. Through the above steps, the 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 elemental analysis method. Specifically, chips are generated from the base steel plate using a drill, the chips are collected, and the collected chips are dissolved in acid to obtain a solution. The solution is subjected to ICP-AES 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 chips are dissolved in acid, silicon oxide is precipitated, and this precipitate (silicon oxide) is filtered out with filter paper and its mass is measured to determine the Si content. The carbon and sulfur contents are determined by the well-known high-frequency combustion method (combustion-infrared absorption method). Specifically, the above solution is combusted in an oxygen stream by high-frequency heating, and the generated carbon dioxide and sulfur dioxide are detected to determine the carbon and sulfur contents. The N content is determined using the well-known inert gas fusion-thermal conductivity method.

[0036] (distortion area) The base steel sheet included in the grain-oriented electrical steel sheet according to this embodiment has a plurality of linear strain regions (residual strain regions) formed by energy beam irradiation. These multiple linear strain regions extend in a direction intersecting the rolling direction on the surface of the base steel sheet, and are parallel to each other (a deviation of about 5° is allowed in actual manufacturing), have a width of 210 μm or less in the rolling direction, and adjacent linear strain regions are formed at intervals of 10 mm or less in the rolling direction. By configuring the strain regions as described above, a good balance between iron loss and noise is obtained. The location of strain can be analyzed using residual strain measurement technology using X-ray diffraction (e.g., K. Iwata, et.al., J. Appl. Phys. 117. 17A910 (2015)). In addition, if energy beam irradiation marks can be confirmed on the steel sheet surface, the irradiation marks can be directly judged as the strain area.

[0037] Furthermore, when this strain (residual strain) is compressive strain in the rolling direction and tensile strain in the thickness direction, it is known that a region magnetized in the thickness direction, called a closure domain, is formed in the region where the strain exists (distortion region).

[0038] In this embodiment, "extending in a direction intersecting the rolling direction" means that the extension direction of the strained regions is within a range of a deviation angle of 30° from the direction perpendicular to the rolling direction. If the angle is outside this range, the 180° magnetic domain refinement effect of the steel sheet is reduced, and a sufficient iron loss reduction effect cannot be obtained. The strain region may be continuous and linear, or may extend intermittently in one direction (e.g., in a dotted line), but from the viewpoint of improving iron loss, it is preferable that it be continuous. The linear strain region is formed by irradiating with an energy beam. The type of energy beam is not particularly limited, but a laser or an electron beam, which are generally in practical use, are preferred. When irradiating with an electron beam, the atmosphere during electron beam irradiation must be kept at a vacuum level below a certain value, which may increase production costs. Furthermore, if the spacing between adjacent linear strain regions in the rolling direction exceeds 10 mm, the magnetic domain refinement effect of the 180° magnetic domains is reduced, resulting in insufficient iron loss improvement. Therefore, the spacing between adjacent linear strain regions in the rolling direction is set to 10 mm or less. It is preferable that the spacing between the multiple linear strain regions be approximately equal. Although narrowing the irradiation pitch generally reduces iron loss, if the pitch is too narrow, the magnetic domain refinement effect saturates and eddy current loss hardly decreases, while hysteresis loss due to distortion increases significantly, worsening iron loss. Furthermore, noise characteristics may deteriorate. Therefore, it is preferable that the distance between adjacent linear distortion regions in the rolling direction be 3 mm or more. Here, the interval between adjacent strain regions in the rolling direction is the distance between the center of a linear strain region and the center of an adjacent linear strain region in the rolling direction. The length of the strain in the sheet width direction is not limited, but it is preferable that the 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 sufficient that the major axis (length along the width direction) d0 of the energy beam irradiated area and the length along the width direction d1 of the energy beam non-irradiated area sandwiched between two energy beam irradiated areas satisfy d1≦3×d0. d0 may be in the range of 50 μm or more and 50 mm or less.

[0039] Furthermore, if the proportion of the strained region on the surface of the base steel sheet becomes excessively large, the strain of the entire base steel sheet increases, the total hysteresis loss increases, iron loss deteriorates, and noise characteristics deteriorate. Therefore, the width of the strained region is set to 210 μm or less. It is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less.

[0040] In the grain-oriented electrical steel sheet according to this embodiment, the state related to distortion is further defined by the amount of change in magnetostriction when a specific heat treatment is performed. Specifically, the magnetostriction λ when excited up to 1.7 T is 0-pb and magnetostriction λ when excited to 1.7 T after heat treatment at 800°C for 4 hours. 0-pa and satisfy the following formula (1). 0.02≦λ 0-pb -λ 0-pa ≦0.20 (μm / m) (1) When the above formula (1) is satisfied, a good balance between iron loss and noise can be ensured. This formula is thought to be a formula that basically evaluates the strain introduced into the base steel sheet by energy beam irradiation, taking into account not only the amount of strain but also the distribution of strain, and even the state of the lattice defects that make up the strain. By releasing the strain through heat treatment at 800°C for 4 hours, and keeping the strain within the range of formula (1) in relation to magnetostriction, it is possible to achieve a good balance between iron loss and noise. If the change in magnetostriction before and after heat treatment is less than 0.02 μm / m, it means that either an appropriate amount of strain was not introduced at the time of energy beam irradiation, or the heat treatment has created a strain state in which strain release is difficult. In this case, a good balance between iron loss and noise cannot be obtained. On the other hand, if the change in magnetostriction before and after heat treatment is more than 0.20 μm / m, it means that an excessive amount of strain was introduced at the time of energy beam irradiation, or the heat treatment has created a strain state in which strain release is too easy. In this case, too, a good balance between iron loss and noise cannot be obtained.

[0041] <Glass coating> In the grain-oriented electrical steel sheet according to this embodiment, a glass coating is formed on the surface of the base steel sheet. The glass coating is an inorganic coating whose main component is magnesium silicate. It is formed during finish annealing by a reaction between the surface components of the base steel sheet and an annealing separator containing magnesia (MgO) applied to the surface of the base steel sheet. Its composition is derived from the components of the annealing separator and the base steel sheet, and it has a structure containing the Mg2SiO4 phase (50% or more by area) as the main phase and the MgAl2O4 phase. In addition to these phases, precipitates of approximately 1% or less may be present.

[0042] The area (area ratio) occupied by each phase is determined from the oxide composition obtained by observing the cross section of the glass coating through its thickness using an energy dispersive X-ray analyzer attached to a scanning electron microscope. Mg, Al, and O are present, and the area with an Al concentration of 5% or more is considered to be the MgAl2O4 phase, and the area with a Si concentration of 5% or more is considered to be the Mg2SiO4 phase.

[0043] In the grain-oriented electrical steel sheet according to the present embodiment, it is preferable that the compound phase constituting the glass coating has a predetermined structure. Specifically, when the glass coating is divided into three regions of equal thickness in the thickness direction in a cross section of the grain-oriented electrical steel sheet, and the regions are designated as 1 / 3 region, 2 / 3 region, and 3 / 3 region from the base steel sheet side toward the steel sheet surface, and the area fraction of the MgAl2O4 phase in the 1 / 3 region is designated as S1, the area fraction of the MgAl2O4 phase in the 2 / 3 region is designated as S2, and the area fraction of the MgAl2O4 phase in the 3 / 3 region is designated as S3, it is preferable that the following formulas (2) to (4) are satisfied: In cross-sectional observation, the tip of the glass coating is observed to have severe irregularities and isolated island-like regions. In this embodiment, a sufficient length of at least 20 mm is observed in a direction parallel to the steel sheet surface, and the total thickness of the glass coating is determined by the distance between the position of the glass coating that penetrates deepest into the base steel sheet and the outermost surface of the steel sheet in the sheet thickness direction at which the glass coating is present. Furthermore, in calculating the area fraction of the MgAl2O4 phase in each region, the total area of ​​each region, which serves as the denominator, is the "glass coating region," including the island-like regions. That is, in the 1 / 3 region, which is the tip of the glass coating, the "glass coating region" tends to have severe irregularities and isolated island-like regions. Although a considerable amount of Fe phase is present in the same thickness range, the Fe phase region is not included in the area (total area) which serves as the denominator in calculating the area fraction of the MgAl2O4 phase. Therefore, the total area of ​​the 1 / 3 region is generally smaller than the total area of ​​the 2 / 3 region or the 3 / 3 region. S1>S2>S3 (2) (S1+S2+S3) / 3<0.50 (3) S3<0.10 (4) When formulas (2) to (4) are satisfied, it indicates that the MgAl2O4 phase, which is a mixed phase, is unevenly distributed on the base steel sheet side in the glass coating.

[0044] In the first-third region, the MgAl2O4 phase is a compound phase that improves the adhesion of the coating. One-third of the glass coating is the region that is bonded to the base steel sheet. The interface between the glass coating and the base steel sheet has a complex, uneven shape, commonly referred to as a "root." This shape firmly bonds the glass coating to the base steel sheet through the so-called anchor effect. For this reason, even if a certain amount of MgAl2O4 phase is mixed in this region, cracks that could become the starting point for coating peeling are unlikely to occur. Therefore, it is preferable that the MgAl2O4 phase is unevenly distributed in the 1 / 3 region of the glass coating. From the viewpoint of adhesion, it is preferable that the MgAl2O4 phase is unevenly distributed as close to the base steel sheet as possible even in the 1 / 3 region, and it can be said that one of the most preferable forms is one in which the MgAl2O4 phase is unevenly distributed only at the interface between the glass coating and the base steel sheet.

[0045] On the other hand, in the 3 / 3 region, the formation of the MgAl2O4 phase is a compound phase that should be avoided. If the MgAl2O4 phase is present in the 3 / 3 region of the glass coating, the MgAl2O4 phase will become the starting point for crack initiation, significantly reducing coating adhesion. Therefore, S3 is preferably < 0.10, more preferably < 0.05, and most preferably S3 = 0. Furthermore, if the proportion of the MgAl2O4 phase in the total is 0.50 or more, starting points for peeling will occur between the MgAl2O4 phase and the Mg2SiO4 phase. Therefore, the area fraction of the MgAl2O4 phase in the glass coating, (S1 + S2 + S3) / 3, is preferably less than 0.50, and more preferably 0.30 or less.

[0046] By having this type of morphology for the primary coating, it is possible to obtain better coating adhesion while maintaining a good balance between iron loss and noise in steel sheets with the aforementioned distortion (magnetostriction change due to heat treatment).The reason for this is not clear, but it is thought to be as follows. The grain-oriented electrical steel sheet according to this embodiment achieves a good balance between iron loss and noise under irradiation conditions, typically involving high input energy and low power density, but it also tends to peel off from the laser-irradiated area. This suggests that the strain generated in the grain-oriented electrical steel sheet according to this embodiment differs from the typical strain distribution. Therefore, when stress acts on the grain-oriented electrical steel sheet, higher peeling stress than conventional methods is expected to act at the interface between the base steel sheet and the glass coating in the strained region. This peeling stress is thought to be alleviated by the uneven distribution of the MgAl2O4 phase in the glass coating toward the base steel sheet. It is unclear whether this alleviation is due to the stress generated by the uneven distribution of the heterogeneous phase alleviating the peeling stress caused by residual strain, or whether the uneven distribution of the heterogeneous phase itself has strong resistance to the peeling stress. However, considering that the coating adhesion improvement effect of the uneven distribution of the MgAl2O4 phase specified in this embodiment is significantly effective in the magnetic domain control material having the strain shown in this embodiment, this combination is thought to have a particularly favorable interaction. Furthermore, it is possible that not only the energy beam irradiation conditions but also the uneven distribution of the MgAl2O4 phase in the glass coating itself has a qualitative effect on the distortion in the energy beam irradiated area, resulting in a more favorable balance between iron loss and noise. We look forward to future detailed analysis to clarify the effect that the interaction between distortion and glass coating morphology has on the balance between iron loss and noise or adhesion.

[0047] The grain-oriented electrical steel sheet according to this embodiment achieves a good balance between iron loss and noise under irradiation conditions, typically energy beam irradiation, with a higher input energy and a lower power density, and still provides sufficient coating adhesion. Specifically, when the grain-oriented electrical steel sheet is wrapped around a round bar with a diameter of 20 mm and bent back, the coating remaining area ratio is 90 to 100%. This coating remaining area ratio is an index that indicates the quality of coating adhesion. Preferably, the coating remaining area ratio is 95% or more.

[0048] The remaining coating area percentage is evaluated by a bending adhesion test. An 80 mm x 80 mm flat test piece taken from a coated grain-oriented electrical steel sheet is wrapped around a 20 mm diameter round bar and flattened. The area of ​​the coating (glass coating and / or tensile insulation coating) that has not peeled off from the electrical steel sheet is measured, and the remaining coating area percentage (%) is defined as the unpeeled area divided by the area of ​​the steel sheet. For example, a transparent film with a 1 mm grid can be placed on the test piece to measure the area where the coating has not peeled off.

[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 tensioned insulating coating imparts electrical insulation to the grain-oriented electrical steel sheet, thereby reducing eddy current loss and improving the iron loss of the grain-oriented electrical steel sheet. In addition to the electrical insulation properties mentioned above, the tensioned insulating coating also provides various other properties such as corrosion resistance, heat resistance, and slip resistance. Furthermore, the tension-applying insulating coating has the function of applying tension to the grain-oriented electrical steel sheet. Applying tension to the grain-oriented electrical steel sheet facilitates 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 by, for example, applying a coating liquid containing metal phosphate and silica as its main components to the surface of the glass coating and baking it.

[0050] <Base steel plate thickness: 0.17 to 0.30 mm> 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 when considering application to transformer cores, which require low noise and vibration in addition to low iron loss. The thinner the sheet thickness, the greater the effect of reducing eddy current loss and the better the iron loss, so the preferred upper limit of the thickness of the base steel sheet is 0.30 mm. However, special equipment is required to manufacture a base steel sheet with a thickness of less than 0.17 mm, which is undesirable from a production standpoint, such as increasing manufacturing costs. Therefore, the industrially preferred lower limit of the thickness is 0.17 mm.

[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 the billet is heated and hot-rolled into a hot-rolled steel sheet; (ii) a hot-rolled sheet annealing step of annealing the hot-rolled steel sheet; (iii) a pickling step of pickling the hot-rolled steel sheet after the hot-rolled sheet annealing step; (iv) a cold rolling step in which the hot-rolled steel sheet after the pickling step is cold-rolled once or multiple times (two or more times) with annealing interposed therebetween to obtain a cold-rolled steel sheet; (v) a decarburization annealing step of subjecting the cold-rolled steel sheet to decarburization annealing; (vi) a finish annealing process in which an annealing separator mainly composed of MgO powder is applied to the front and back surfaces of the cold-rolled steel sheet that has been subjected to the decarburization annealing process, which is the base steel sheet, and then dried and subjected to finish annealing to form a glass coating; (vii) a coating formation step of forming a tensioned insulating coating 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; (viii) a magnetic domain refining step of irradiating the surface of the tension-applying insulating coating of the grain-oriented electrical steel sheet with an energy beam to form a plurality of linear strain regions in the base steel sheet. The method for producing a grain-oriented electrical steel sheet according to this embodiment is characterized by the conditions in the magnetic domain refinement step, which control the state of strain, and the conditions in the decarburization annealing step, which control the morphology of the MgAlO phase in the glass coating. These steps will be described in detail below. In the following description, unless conditions for each step are specified, each step can be carried out by appropriately applying known conditions.

[0052] <Chemical composition of steel billets> The chemical composition of the steel slab to be subjected to the heating step is not limited, but in order to obtain the properties generally required of a grain-oriented electrical steel sheet, it is preferable that the chemical components contain the following. In the following description, unless otherwise specified, the notation "%" represents "mass %." The steel slab is, for example, a slab.

[0053] C: 0.010 to 0.200% C (carbon) is an element that has an effect of improving magnetic flux density. However, if the C content of a steel slab exceeds 0.200%, the steel undergoes a phase transformation during secondary recrystallization annealing (i.e., finish annealing), and secondary recrystallization does not proceed sufficiently, making it difficult to obtain good magnetic flux density and iron loss characteristics. Therefore, it is preferable that the C content of the steel slab be 0.200% or less. The lower the C content, the better for reducing iron loss. From the viewpoint of reducing iron loss, the C content is more preferably 0.150% or less, and even more preferably 0.100% or less. On the other hand, if the C content of the steel slab is less than 0.010%, the effect of improving the magnetic flux density cannot be obtained. Therefore, the C content of the steel slab is set to 0.010% or more. The C content is preferably 0.040% or more, and more preferably 0.060% or more.

[0054] Si: 3.00 to 4.00% Silicon (Si) is an extremely effective element for increasing the electrical resistance (resistivity) of steel and reducing eddy current loss, which constitutes part of iron loss. If the Si content of a steel slab is less than 3.00%, the steel undergoes phase transformation during secondary recrystallization annealing, preventing sufficient secondary recrystallization and resulting in poor magnetic flux density and iron loss characteristics. Therefore, the Si content of a steel slab is preferably 3.00% or more. The Si content of a steel slab is more preferably 3.10% or more, and even more preferably 3.20% or more. On the other hand, if the Si content exceeds 4.00%, the steel sheet becomes embrittled and the sheet passing property during the manufacturing process deteriorates significantly. Therefore, the Si content of the steel billet is preferably 4.00% or less. The Si content of the steel billet is more preferably 3.80% or less, and further preferably 3.60% or less.

[0055] sol.Al: 0.010~0.040% Sol-Al (acid-soluble aluminum) is a constituent element of a major inhibitor among compounds called inhibitors that affect secondary recrystallization in grain-oriented electrical steel sheets, and is an essential element in the base steel sheet according to this embodiment from the viewpoint of secondary recrystallization occurrence. If the sol-Al content of the steel slab is less than 0.010%, AlN, which functions as an inhibitor, is not sufficiently generated, secondary recrystallization becomes insufficient, and iron loss characteristics do not improve. Therefore, the sol-Al content of the steel slab is preferably 0.010% or more. The sol-Al content is more preferably 0.015% or more, and even more preferably 0.020%. On the other hand, if the sol. Al content exceeds 0.040%, the embrittlement of the steel sheet becomes significant. Therefore, the sol. Al content of the steel slab is preferably 0.040% or less. The sol. Al content is more preferably 0.035% or less, and even more preferably 0.030% or less.

[0056] Mn: 0.01 to 0.50% Mn (manganese) is an important element that forms MnS, one of the main inhibitors. If the Mn content of a steel slab is less than 0.01%, the absolute amount of MnS required to cause secondary recrystallization is insufficient. Therefore, the Mn content of a steel slab is preferably 0.01% or more. The Mn content is more preferably 0.03% or more, and even more preferably 0.06% or more. On the other hand, if the Mn content of the steel slab exceeds 0.50%, the steel undergoes a phase transformation during secondary recrystallization annealing, secondary recrystallization does not proceed sufficiently, and good magnetic flux density and iron loss characteristics cannot be obtained. Therefore, the Mn content of the steel slab is set to 0.50% or less. The Mn content is more preferably 0.40% or less, and even more preferably 0.30% or less.

[0057] N: 0.020% or less N (nitrogen) is an element that reacts with the acid-soluble Al to form AlN, which functions as an inhibitor. If the N content of a steel slab exceeds 0.020%, blisters (voids) will form in the steel sheet during cold rolling, and the strength will increase, resulting in poor sheet threadability during production. Therefore, the N content of the steel slab is preferably 0.020% or less. The N content is more preferably 0.015% or less, and even more preferably 0.010% or less. If AlN is not used as an inhibitor, the lower limit of the N content may include 0%. However, since the detection limit of chemical analysis is 0.0001%, the lower limit of the N content in practical steel sheets is essentially 0.0001%. On the other hand, in order to bond with Al to form AlN, which functions as an inhibitor, the N content of the steel slab is preferably 0.001% or more, and more preferably 0.005% or more.

[0058] S: 0.005 to 0.040% S (sulfur) is an important element that reacts with the above-mentioned Mn to form MnS, an inhibitor. If the S content of the steel slab is less than 0.005%, a sufficient inhibitor effect cannot be obtained. Therefore, the S content of the steel slab is preferably 0.005% or more. The S content is more preferably 0.010% or more, and even more preferably 0.020% or more. On the other hand, if the S content of the steel slab exceeds 0.040%, it causes hot embrittlement, making hot rolling extremely difficult. Therefore, the S content of the steel slab is preferably 0.040% or less. The S content is more preferably 0.035% or less, and even more preferably 0.030% or less.

[0059] 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, excessive reduction in rolling workability can be prevented, and fractures during manufacturing can be suppressed. From this perspective, the P content is preferably set to 0.030% or less. The P content is more preferably set to 0.020% or less, and further preferably set to 0.010% or less. The lower limit of the P content 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 texture and magnetic properties. To achieve this effect, the P content may be set to 0.001% or more, or even 0.005% or more.

[0060] Remainder: Fe and impurities The chemical composition of the steel billet used to manufacture the grain-oriented electrical steel sheet according to this embodiment basically contains the above-mentioned elements, with the balance being Fe and impurities. However, for the purpose of improving magnetic properties, etc., the billet may further contain Cu, Cr, Sn, Se, Sb, and Mo in the ranges shown below. Here, impurities refer to elements that are mixed in from raw materials such as ore or scrap, or the manufacturing environment, when the base steel sheet is industrially manufactured, 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.

[0061] Cu: 0 to 0.50% Copper (Cu) is an element that contributes to increasing the Goss orientation occupancy rate in the secondary recrystallized structure and also contributes to improving the adhesion of the glass coating. To achieve the above effects, the Cu content is preferably 0.02% or more. The Cu content is more preferably 0.03% or more. On the other hand, if the Cu content exceeds 0.50%, the steel sheet becomes embrittled during hot rolling. Therefore, the Cu content of the steel slab is preferably 0.50% or less. The Cu content is more preferably 0.30% or less, and even more preferably 0.10% or less.

[0062] Cr: 0 to 0.50% Cr (chromium), like Sn and Cu described below, is an element that contributes to increasing the Goss orientation occupancy rate in the secondary recrystallized structure, thereby improving magnetic properties and glass coating adhesion. To achieve the above effects, the Cr content is preferably 0.02% or more, and more preferably 0.03% or more. On the other hand, if the Cr content exceeds 0.50%, Cr oxides are formed, resulting in a deterioration in magnetic properties. Therefore, the Cr content is preferably 0.50% or less. The Cr content is more preferably 0.30% or less, and even more preferably 0.10% or less.

[0063] Sn: 0 to 0.50% Sn (tin) is an element that has the effect of improving magnetic properties. Therefore, it may be contained. When Sn is contained, the content is preferably 0.005% or more to effectively exhibit the effect of improving magnetic properties. In consideration of achieving both magnetic properties and coating adhesion, the Sn content is preferably 0.02% or more, and more preferably 0.03% or more. On the other hand, if the Sn content exceeds 0.50%, the adhesion of the glass coating significantly deteriorates. Therefore, the Sb content is preferably 0.50% or less. The Sn content is more preferably 0.30% or less, and even more preferably 0.10% or less.

[0064] Se: 0 to 0.020% Se (selenium) is an element that has the effect of improving magnetic properties. Therefore, it may be contained. When Se is contained, the content is preferably 0.001% or more to effectively exhibit the effect of improving magnetic properties. In consideration of achieving both magnetic properties and coating adhesion, the Se content is more preferably 0.003% or more, and even more preferably 0.006% or more. On the other hand, if the Se content exceeds 0.020%, the glass coating will deteriorate significantly. Therefore, the upper limit of the Se content is preferably set to 0.020%. The Se content is more preferably 0.015% or less, and even more preferably 0.010% or less.

[0065] Sb: 0 to 0.500% Sb (antimony) is an element that has the effect of improving magnetic properties. Therefore, it may be contained. When Sb is contained, the content is preferably 0.001% or more to effectively exhibit the effect of improving magnetic properties. In consideration of achieving both magnetic properties and coating adhesion, the Sb content is more preferably 0.005% or more, and even more preferably 0.010% or more. On the other hand, if the Sb content exceeds 0.500%, the glass coating deteriorates significantly. Therefore, the upper limit of the Sb content is preferably set to 0.500%. The Sb content is more preferably 0.300% or less, and even more preferably 0.100% or less.

[0066] Mo: 0 to 0.10% Mo (molybdenum) is an element that has the effect of improving magnetic properties. Therefore, it may be contained. When Mo is contained, the Mo content is preferably 0.01% or more in order to effectively exhibit the effect of improving magnetic properties. The Mo content is more preferably 0.02% or more, and even more preferably 0.03% or more. On the other hand, if the Mo content exceeds 0.10%, the cold rolling property deteriorates and there is a possibility of fracture. Therefore, the Mo content is preferably 0.10% or less. The Mo content is more preferably 0.08% or less, and further preferably 0.05% or less.

[0067] <Hot rolling process> In the hot rolling process, a steel slab having a predetermined chemical composition is heated and then hot rolled to obtain a hot-rolled steel sheet. The heating temperature of the steel slab is preferably within a range of 1100 to 1450°C, and 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 is preferably within the range of 2.0 mm to 3.0 mm, for example.

[0068] <Hot-rolled sheet annealing process> The hot-rolled steel sheet annealing process is a process in which a hot-rolled steel sheet manufactured through a hot-rolling process is annealed to produce a hot-rolled annealed steel sheet. By performing such annealing treatment, recrystallization occurs in the steel sheet structure, making it possible to achieve good magnetic properties. In the hot-rolled steel sheet annealing step according to this embodiment, a hot-rolled steel sheet manufactured through a hot rolling step is annealed according to a known method to obtain a hot-rolled annealed steel sheet. 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 can be annealed in a temperature range of 900 to 1200°C for 10 seconds to 5 minutes.

[0069] <Cold rolling process> In the cold rolling process, the hot-rolled and annealed steel sheet after the hot-rolled sheet annealing is subjected to cold rolling including multiple passes to obtain a cold-rolled steel sheet with 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 rolling passes with intermediate annealing between them, with the cold rolling interrupted and at least one or two or more intermediate annealings performed before the final pass of the cold rolling process. When intermediate annealing is performed, it is preferably performed for 5 seconds or more and 180 seconds or less at a temperature of 1000 to 1200° C. The annealing atmosphere is not particularly limited. In consideration of production costs, the number of times intermediate annealing is performed is preferably three or less. Furthermore, before the cold rolling step, the surface of the hot-rolled annealed steel sheet may be subjected to pickling.

[0070] In the cold rolling step according to the present embodiment, the hot-rolled annealed 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 because it is highly likely that Goss nuclei with a high degree of orientation accumulation in the rolling direction cannot be obtained. On the other hand, if the final reduction exceeds 95%, it is undesirable because it is highly likely that secondary recrystallization will become unstable in the subsequent finish annealing process. By keeping the final reduction within the above range, it is possible to obtain Goss nuclei with a high degree of orientation accumulation in the rolling direction. <001> This method can obtain Goss nuclei with a high degree of orientation in the rolling direction, and can also 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.

[0071] <Decarburization annealing process> The decarburization annealing process is an important process for controlling the state of the MgAl2O4 phase in the glass coating. To achieve the above-mentioned state of the MgAl2O4 phase, the decarburization annealing process, which includes a heating process and a soaking process, must include a first soaking process in the heating process, in which the heating rate from 550 to 750°C is 700 to 2000°C / s and the oxygen potential is 0.0001 to 0.0100, and the soaking process is in an atmosphere with an oxygen potential of 0.4 to 0.8, an annealing temperature of 800 to 900°C, and an annealing time of 100 to 500 seconds, and a second soaking process in an atmosphere with an oxygen potential of 0.1 or less, an annealing temperature of 850 to 1000°C, and an annealing time of 5 to 100 seconds. The second soaking step (second heat treatment) may be carried out after the temperature is lowered once after the first soaking step (first heat treatment), or may be carried out continuously after the first heat treatment without lowering the temperature.

[0072] The reason why the state of the MgAl2O4 phase in the glass coating becomes as desirable as described above when decarburization annealing is performed within the above range is not clear, but is thought to be as follows. The glass coating is formed by a reaction between MgO, which is applied as an annealing separator to the surface of the steel sheet before final annealing, and the Si contained in the base steel sheet. As the reaction progresses with the progress of final annealing, the interface between the glass coating and the base steel sheet progresses into the base steel sheet, and eventually the tip of the glass coating on the base steel sheet side develops to exhibit the complex uneven shape resembling the "root" mentioned above. During this process, the MgAl2O4 phase is formed by a reaction between MgO and Al in the base steel sheet. This reaction is believed to occur via two major pathways. One is a direct reaction between MgO in the annealing separator and Al supplied from the base steel sheet. The other is a reaction in which MgO in the annealing separator first reacts with Si from the base steel sheet to form the Mg2SiO4 phase, and then reacts with Al to transform into the MgAl2O4 phase. In the former case, the MgAl2O4 phase is thought to form relatively early in the glass coating formation process. In the latter case, however, Mg and O are initially fixed as oxides with Si, so the formation of the MgAl2O4 phase is thought to occur relatively late in the glass coating formation process. Considering that the final formation of a glass coating primarily composed of the Mg2SiO4 phase occurs as the oxidized region progresses into the base steel sheet, the MgAl2O4 phase formed relatively early is thought to be left behind on the surface side of the glass coating. Conversely, the MgAl2O4 phase, which is formed at a relatively late stage, is thought to be positioned on the interface side between the glass coating and the base steel sheet. Considering these factors, it can be inferred that creating a situation in which the MgO present on the surface of the base steel sheet reacts preferentially with Si during final annealing is preferable for keeping the MgAl2O4 phase formed in the glass coating on the base steel sheet side. The decarburization annealing conditions of this embodiment are considered to be conditions that allow a sufficient amount of SiO2 to form on the surface of the steel sheet after the decarburization annealing process. In other words, if the surface of the steel sheet after the decarburization annealing process is covered with a sufficient amount of SiO2, when an annealing separator mainly composed of MgO is further applied to that surface and the reaction of the annealing separator is initiated by finish annealing, the MgO will preferentially form the Mg2SiO4 phase in the early stages of the reaction. As a result, the presence of the MgAl2O4 phase in the glass coating will be favorable. Conversely, if the above decarburization annealing conditions are not met, there will not be a sufficient amount of SiO2 on the surface of the steel sheet after the decarburization annealing process. Therefore, when the reaction of the annealing separator is initiated by finish annealing, the MgO will react directly with the Al-containing base steel sheet in the early stages of the reaction to form the MgAl2O4 phase. As a result, the presence of the MgAl2O4 phase in the glass coating will be unfavorable.

[0073] By undergoing the above thermal history in the decarburization annealing process, the glass coating that is subsequently formed on the surface of the base steel sheet takes on a favorable form, and by controlling the magnetic domains under appropriate laser processing conditions, it is possible to manufacture grain-oriented electrical steel sheets that have a good balance between iron loss and noise and better coating adhesion.

[0074] <Nitriding process> Nitriding treatment may be carried out during or after the decarburization annealing step and before the finish annealing step described below. In the nitriding process, for example, the cold-rolled steel sheet after the soaking step in the decarburization annealing process is maintained at approximately 700 to 850°C in a nitriding atmosphere (an atmosphere containing hydrogen, nitrogen, and a nitriding gas such as ammonia). Nitriding is preferably performed 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 nitriding is less than 40 ppm, AlN may 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, the N content of the cold-rolled steel sheet after nitriding is preferably 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 during finish annealing. Such AlN causes deterioration of iron loss. Therefore, it is preferable that the N content of the cold-rolled steel sheet after nitriding treatment be 1000 ppm or less.

[0075] <Finishing annealing process> In the final annealing process, a predetermined annealing separator is applied to the cold-rolled steel sheet obtained in the decarburization annealing process or that has further been subjected to nitriding treatment, and then the cold-rolled steel sheet is subjected to final annealing. Final annealing is generally performed for a long period of time while the steel sheet is wound into a coil. 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 (for example, 80% by mass or more). 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 carried out, for example, in an atmospheric gas containing hydrogen and nitrogen, by raising the temperature to 1150 to 1250° C. and annealing for 10 to 60 hours.

[0076] <Insulating film formation process> In the insulating coating formation step, a tensioned insulating coating is formed on one or both sides of the cold-rolled steel sheet after finish annealing. The conditions for forming the tensioned insulating coating are not particularly limited, and a known insulating coating treatment solution may be used, and the treatment solution may be applied and dried by a known method. Forming a tensioned insulating coating on the steel sheet surface can further improve the magnetic properties of the grain-oriented electrical steel sheet. The surface of the steel sheet on which the insulating coating (tensioned insulating coating) is formed may be a surface that has been subjected to any pretreatment, such as degreasing treatment with an alkali or pickling treatment with hydrochloric acid, sulfuric acid, phosphoric acid, or the like, before the treatment liquid is applied, or the surface may be left as is after finish annealing without being subjected to these pretreatments. The tension-applying insulating coating formed on the surface of the glass coating (formed on the base steel sheet via the glass coating) is not particularly limited as long as it is suitable for use as an insulating coating for grain-oriented electrical steel sheets, and any known insulating coating can be used. Examples of such insulating coatings include composite insulating coatings primarily containing an inorganic material and an organic material. Here, a composite insulating coating is an insulating coating primarily containing at least one inorganic material, such as a metal chromate salt, a metal phosphate salt, colloidal silica, a Zr compound, or a Ti compound, with fine organic resin particles dispersed therein. In particular, from the perspective of reducing the environmental impact during production, which has become increasingly important in recent years, insulating coatings using metal phosphate salts, Zr or Ti coupling agents, or their carbonates or ammonium salts as starting materials are preferred.

[0077] <Magnetic domain refining process> In the magnetic domain refinement process, an energy beam is irradiated onto the surface of the tension-applying insulating coating to introduce multiple linear strains extending in a direction intersecting the rolling direction onto the surface of the base steel sheet. In the magnetic domain refinement process, regions (distortion regions) are formed in the base steel sheet at predetermined intervals in the rolling direction, where multiple substantially parallel linear strains (thermal strains caused by rapid heating due to energy beam irradiation and subsequent rapid cooling) exist, and the intervals (i.e., the intervals between adjacent distortion regions) are 10 mm or less in the rolling direction. If the interval between the multiple linear strain regions in the rolling direction exceeds 10 mm, the iron loss improvement effect will be insufficient. Therefore, the energy beam is irradiated in the rolling direction at intervals of 10 mm or less to form strain (residual strain). The type of energy beam is not particularly limited, and a laser or electron beam, which are generally in practical use, can be used. When laser irradiation is applied, the laser beam may be a continuous wave laser or a pulsed laser, but a continuous wave laser is preferred. Furthermore, between a laser beam and an electron beam, a laser beam is preferred. This is because the electron beam irradiation process requires a vacuum environment, which increases production costs. Therefore, in this embodiment, a magnetic domain refining process is performed using a laser beam. The laser beam is, for example, a fiber laser beam.

[0078] Also, as described above, in order to obtain a grain-oriented electromagnetic steel sheet that achieves both low iron loss and low noise and has excellent film adhesion, strain is introduced into the base steel sheet. Specifically, using the energy beam output P per unit W and the energy beam irradiation cross-sectional area S per unit mm 2 the energy beam power density Ip defined by P / S satisfies the following formula (5), and the energy beam input energy Up per unit J / mm defined by P / Vs using the energy beam output P and the energy beam scanning speed Vs per unit mm / second irradiates the energy beam so as to satisfy the following formula (6).

[0079] 250 ≦ Ip ≦ 2000 Formula (5) 0.01 < Up ≦ 0.05 Formula (6)

[0080] When 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, when Up is less than 0.010, the irradiation effect cannot be sufficiently obtained and the iron loss is not improved. On the other hand, when Up exceeds 0.050, the noise characteristics deteriorate.

[0081] Furthermore, in the method for manufacturing a grain-oriented electromagnetic steel sheet according to the present embodiment, when irradiating the energy beam, using the diameter dl in the direction perpendicular to the beam scanning direction (scanning direction) per unit μm of the energy beam and the diameter dc in the beam scanning direction, the beam aspect ratio defined by (dl / dc) is controlled to satisfy the following formula (7).

[0082] 0.0010 < dl / dc < 1.0000 (7)

[0083] If the beam aspect ratio is 0.0010 or less, heat is extracted during beam irradiation, the input energy efficiency decreases, and a sufficient magnetic domain refinement effect (iron loss improvement effect) cannot be obtained. Therefore, the beam aspect ratio is set to be greater than 0.0010. On the other hand, if the beam aspect ratio is 1.0000 or more, heat dissipation due to 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 1.0000. The beam aspect ratio is preferably less than 0.0500, more preferably less than 0.0050.

[0084] Moreover, the diameter dl of the energy beam in the direction perpendicular to the beam scanning direction in the unit of μm is set to satisfy the following formula (8).

[0085] 10 <dl<200 (8)

[0086] It is difficult to reduce the beam diameter to 10 μm or less with a general laser light source, so dl is greater than 10. 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.

[0087] In the manufacturing method of the grain-oriented electrical steel sheet according to this embodiment, as described above, a relatively strong Ip energy beam is irradiated with a small beam aspect ratio. This type of 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 research based on the new knowledge that controlling the spatial distribution of strain is important from the viewpoint of simultaneously reducing iron loss and noise, and as a result, they discovered for the first time that the above irradiation conditions are preferable. [Example]

[0088] A slab having the chemical composition shown in Table 1 is manufactured. This slab is subjected to a hot rolling process. Specifically, the slab is heated to 1350°C, and then hot rolling is performed on the slab to manufacture a hot-rolled steel sheet having a thickness of 2.3 mm. The hot-rolled steel sheet after the hot rolling step is subjected to a hot-rolled sheet annealing step at an annealing temperature of 900 to 1200°C for a holding time of 10 to 300 seconds. Thereafter, the steel sheet is subjected to multiple cold rolling processes to obtain a cold-rolled steel sheet having a thickness of 0.17 to 0.27 mm. This cold-rolled steel sheet is subjected to decarburization annealing under the conditions shown in Tables 2A and 2B. After decarburization annealing, Test Nos. 11, 13, and 15 are held at 700 to 850°C for 10 to 60 seconds in a known nitriding atmosphere (an atmosphere containing hydrogen, nitrogen, and a gas having nitriding ability such as ammonia) so that the N content of the cold-rolled steel sheet after decarburization annealing becomes 40 ppm or more and 1000 ppm or less. After nitriding for Test Nos. 11, 13, and 15, and after decarburization annealing for the others, an annealing separator mainly composed of magnesium oxide (MgO) was applied to the steel sheet surface, and then a finish annealing process was carried out. The finish annealing temperature in the finish annealing process was 1200°C, and the holding time at the finish annealing temperature was 20 hours. An insulating coating agent mainly consisting of colloidal silica and phosphate is applied to the surface (on the glass coating) of the steel sheet (grain-oriented electrical steel sheet) after cooling in the final annealing process, and then baked to form a tension-applying insulating coating. Grain-oriented electrical steel sheets of each test number are manufactured through the above process.

[0089] [Table 1]

[0090] [Table 2A]

[0091] [Table 2B]

[0092] [Analysis of the chemical composition of base steel plate] The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet of each test number obtained in the above manner before magnetic domain refinement is determined by the following method. First, the tension-applying insulating coating is removed from the grain-oriented electrical steel sheet of each test number. Specifically, the grain-oriented electrical steel sheet is immersed for 7 to 10 minutes in an aqueous sodium hydroxide solution containing 30 to 50 mass% NaOH and 50 to 70 mass% HO at 80 to 90°C. After immersion, the grain-oriented electrical steel sheet (grain-oriented electrical steel sheet from which the tension-applying insulating coating has been removed) is washed with water. After washing, it is dried for just under 1 minute using a hot air blower. Next, the glass coating is removed from the grain-oriented electrical steel sheet that does not have a tension-applying insulating coating. Specifically, the grain-oriented electrical steel sheet is immersed in an aqueous hydrochloric acid solution containing 30 to 40 mass% HCl at 80 to 90°C for 1 to 10 minutes. This removes the glass coating from the base steel sheet. After immersion, the base steel sheet is rinsed with water. After rinsing, it is dried with a hot air blower for just under 1 minute. Through these steps, the base steel sheet is removed from the grain-oriented electrical steel sheet. The chemical composition of the removed base steel plate is determined using a well-known elemental analysis method. Specifically, chips are generated from the base steel plate using a drill and collected. The collected chips are dissolved in acid to obtain a solution. The solution is subjected to ICP-AES for elemental analysis of the chemical composition. The silicon content in the chemical composition of the base steel plate is determined using the method specified in JIS G 1212:1997 (silicon determination method). Specifically, when the above-mentioned chips are dissolved in acid, silicon oxide precipitates. This precipitate (silicon oxide) is filtered through filter paper and its mass is measured to determine the silicon content. The carbon content and sulfur content are determined using a well-known high-frequency combustion method (combustion-infrared absorption method). Specifically, the above-mentioned solution is combusted by high-frequency heating in an oxygen stream, and the carbon dioxide and sulfur dioxide generated are detected to determine the carbon content and sulfur content. The nitrogen content is determined using a well-known inert gas fusion-thermal conductivity method. The chemical composition of the base steel plate is determined using the above analytical methods. The chemical composition of the steel plate (base steel plate) for each test number is shown in Table 3. In Table 3, "-" indicates that the content of the corresponding element is below the detection limit.

[0093] [Magnetic property evaluation] Although not shown in the table, a sample measuring 60 mm wide x 300 mm long was taken from each grain-oriented electrical steel sheet of each test number, including the center position of the sheet width. The length of the sample was parallel to the rolling direction. The taken sample was held at 800°C for 2 hours in a nitrogen atmosphere with a dew point below 0°C to remove any strain introduced when the sample was taken. Using this sample, the magnetic flux density (T) is determined by a single sheet magnetic property test (SST test) in accordance with JIS C2556 (2015). Specifically, a magnetic field of 800 A / m is applied to the sample to determine the magnetic flux density (T). Furthermore, using the above sample, the iron loss W when the frequency was 50Hz and the maximum magnetic flux density was 1.7T in accordance with JIS C2556 (2015) was measured. 17 / 50 Measure (W / kg).

[0094] [Table 3]

[0095] Furthermore, for the grain-oriented electrical steel sheets (after forming the tensioned insulating coating) of each test number obtained, magnetic domain refinement is performed by irradiating the steel sheet surface with energy rays using a laser (fiber laser or pulse laser) or electron beam under the conditions shown in Tables 4A and 4B, and then evaluation tests for noise characteristics and magnetic properties are carried out. Furthermore, after measuring the total thickness of the glass coating using the method described above, the area fractions S1, S2, and S3 of the MgAl2O4 phase in each region are also measured.

[0096] [Table 4A]

[0097] [Table 4B]

[0098] [Noise characteristics and magnetostriction evaluation] A sample of 100 mm wide x 500 mm long is taken from each grain-oriented electrical steel sheet. The length direction of the sample corresponds to the rolling direction RD, and the width direction corresponds to the sheet width direction TD. The magnetostriction of the sample is measured by AC magnetostriction measurement using a magnetostriction measurement device that includes 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 is applied to the sample so that the maximum magnetic flux density is 1.7 T in the rolling direction and the frequency is 50 Hz. The change in sample length due to expansion and contraction of the magnetic domains is measured using a laser Doppler vibrometer to obtain a magnetostriction signal. The obtained magnetostriction signal is subjected to Fourier analysis to determine the amplitude Cn of each frequency component fn (n is a natural number greater than or equal to 1) of the magnetostriction signal. The A correction coefficient αn for each frequency component fn is used to determine the magnetostriction velocity level LVA (dB) as shown in 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) is used. The A correction coefficient αn uses the values ​​listed in Table 2 of JIS C 1509-1 (2005). Based on the obtained magnetostriction velocity level (LVA), noise characteristics are evaluated in accordance with the following criteria: If the magnetostriction velocity level is less than 60 dBA, it is judged to have excellent noise characteristics.

[0099] Furthermore, the magnetostriction λ 0-p Specifically, λ (μm / m) is calculated from the length Lp (μm) of the test piece (steel plate) when the magnetic flux density is 1.7 T under the above excitation conditions and the length L0 (m) of the test piece when the magnetic flux density is 0 T. 0-p =(Lp-L0) / L0. Furthermore, for steel sheets that were heat treated at 800°C for 4 hours, the magnetostriction λ was measured at a frequency of 50Hz and a maximum magnetic flux density of 1.7T. 0-p (μm / m) and measure the magnetostriction before heat treatment as λ 0-pb , the magnetostriction after heat treatment is λ 0-paAs, λ 0-pb -λ 0-pa Ask for. The results are shown in Tables 5A, 5B, 6A and 6B.

[0100] [Magnetic property evaluation] A sample measuring 60 mm wide and 300 mm long is taken from each grain-oriented electrical steel sheet of each test number, including the center position of the sheet width. The length of the sample is parallel to the rolling direction. The taken sample is held at 800°C for 2 hours in a nitrogen atmosphere with a dew point below 0°C to remove any strain introduced when the sample was taken. Using this sample, the magnetic flux density (T) is determined by a single sheet magnetic property test (SST test) in accordance with JIS C2556 (2015). Specifically, a magnetic field of 800 A / m is applied to the sample to determine the magnetic flux density (T). Furthermore, using the above sample, the iron loss W when the frequency was 50Hz and the maximum magnetic flux density was 1.7T in accordance with JIS C2556 (2015) was measured. 17 / 50 (W / kg) is measured. When the iron loss improvement rate is 5.0% or more, it is judged that the iron loss improvement rate is excellent. The measurement results are shown in Tables 6A and 6B.

[0101] [Coating adhesion] The coating adhesion (remaining coating area ratio) of grain-oriented electrical steel sheets was measured using the method described above. If the remaining coating area ratio was 50% or more, the coating adhesion was judged to be fair (evaluated as ◯), and if it was 90% or more, the coating adhesion was judged to be excellent (evaluated as ⊚). The evaluation results are shown in Tables 6A and 6B.

[0102] [Table 5A]

[0103] [Table 5B]

[0104] [Table 6A]

[0105] [Table 6B]

[0106] As can be seen from Tables 1 to 6B, the strain region is preferably present, and λ 0-pb -λ 0-pa In the steel sheet (invention example) where λ is within the range of the present invention, a good balance between iron loss and noise is ensured. 0-pb -λ 0-pa However, in steel sheets that can ensure a good balance between iron loss and noise within the range of the present invention, when the area ratio of the MgAl2O4 phase in the glass coating in each region satisfies a preferred relationship, the remaining coating area ratio is sufficiently high and good adhesion can be achieved. On the other hand, λ 0-pb -λ 0-pa However, for steel sheets that are outside the range of the present invention and do not have a good balance between iron loss and noise, the effect of the area ratio of the MgAl2O4 phase in the glass coating on the remaining coating area ratio is not clear. [Industrial Applicability]

[0107] According to the present invention, it is possible to provide a grain-oriented electrical steel sheet having a good balance between iron loss and noise, and a method for manufacturing the same. Furthermore, according to a preferred embodiment of the present invention, it is possible to provide a grain-oriented electrical steel sheet having a good balance between iron loss and noise and also having excellent coating adhesion, which 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 has a chemical composition containing 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, S: 0.010% or less, P: 0.030% or less, Cr: 0 to 0.50%, Sn: 0 to 0.50%, Cu: 0 to 0.50%, Se: 0 to 0.020%, Sb: 0 to 0.500%, Mo: 0 to 0.10%, and the balance being Fe and impurities; The base steel sheet has a plurality of linear strain regions extending continuously or intermittently in a direction intersecting the rolling direction, Each of the plurality of linear strain regions has a width in the rolling direction of 210 μm or less, The plurality of linear strain regions are parallel to each other, and the interval between adjacent linear strain regions in the rolling direction is 10 mm or less; Magnetostriction λ in μm / m when excited up to 1.7 T 0-pb and the magnetostriction λ in μm / m when excited to 1.7 T after heat treatment at 800°C for 4 hours. 0-pa satisfies the following formula (1): Grain-oriented electrical steel sheet characterized by: 0.02≦λ 0-pb -l 0-pa ≦0.20・・・・(1)

2. The glass coating is a main phase of Mg ２ SiO ４ phase and MgAl ２ O ４ and a structure including In the cross section in the thickness direction, the glass coating is divided into three regions of equal thickness in the thickness direction, and each region is designated as a 1 / 3 region, a 2 / 3 region, and a 3 / 3 region from the base steel sheet side toward the tension-applied insulating coating side. ２ O ４ The area ratio of the phase is S1, and the area ratio of the MgAl ２ O ４ The area ratio of the phase is S2, and the MgAl ２ O ４ When the area ratio of the phase is S3, The grain-oriented electrical steel sheet according to claim 1, characterized in that the S1, S2, and S3 satisfy the following formulas (2) to (4). S1>S2>S3...(2) (S1+S2+S3) / 3<0.50 (3) S3<0.10...(4)

3. A method for producing the grain-oriented electrical steel sheet according to claim 1 or 2, a hot rolling process in which the steel billet is heated and hot-rolled into a hot-rolled steel sheet; a hot-rolled sheet annealing step of annealing the hot-rolled steel sheet; a pickling step of pickling the hot-rolled steel sheet after the hot-rolled sheet annealing step; A cold rolling process in which the hot-rolled steel sheet after the pickling process is subjected to cold rolling once or multiple times with annealing therebetween 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 containing MgO powder as a main component is applied to the front and back surfaces of the cold-rolled steel sheet that has been subjected to the decarburization annealing process, which is the base steel sheet, and then dried, followed by finish annealing to form a glass coating; 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; 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 form a plurality of linear strain regions in the base steel sheet; and In the magnetic domain refining step, Among the plurality of linear strain regions, the interval between adjacent linear strain regions in the rolling direction is 10 mm or less, Energy beam output P in W and mm ２ The unit 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 (5): Using the energy beam output P and the energy beam scanning speed Vs in units of mm / sec, the energy beam input energy Up in units of J / mm defined as P / Vs satisfies the following formula (6), A 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 formulas (7) and (8), respectively: A method for producing a grain-oriented electrical steel sheet. 250≦Ip≦2000 (5) 0.010<Up≦0.050 (6) 0.0010<dl / dc<1.0000 (7) 10<dl<200 (8)

4. The method for producing a grain-oriented electrical steel sheet according to claim 3, wherein the energy beam is a laser beam.

5. The method for producing a grain-oriented electrical steel sheet according to claim 4, wherein the laser beam is a fiber laser beam.

6. the steel slab contains, in mass%, C: 0.010 to 0.200%, Si: 3.00 to 4.00%, sol. Al: 0.010 to 0.040%, Mn: 0.01 to 0.50%, N: 0.020% or less, S: 0.005 to 0.040%, P: 0.030% or less, Cu: 0 to 0.50%, Cr: 0 to 0.50%, Sn: 0 to 0.50%, Se: 0 to 0.020%, Sb: 0 to 0.500%, Mo: 0 to 0.10%, and the balance consisting of Fe and impurities. The method for producing the grain-oriented electrical steel sheet according to any one of claims 3 to 5.

7. the decarburization annealing step includes a temperature rising step and a soaking step, In the temperature rising process, the temperature rising rate in the range of 550 to 750°C is set to 700 to 2000°C / sec, and the oxygen potential is set to 0.0001 to 0.0100, The soaking step includes a first soaking step in which the annealing temperature is 800 to 900°C and the annealing time is 100 to 500 seconds in an atmosphere having an oxygen potential of 0.4 to 0.8, and a second soaking step in which the annealing temperature is 850 to 1000°C and the annealing time is 5 to 100 seconds in an atmosphere having an oxygen potential of 0.1 or less. The method for producing a grain-oriented electrical steel sheet according to any one of claims 3 to 6.

8. The method further includes a nitriding treatment step of subjecting the cold-rolled steel sheet to a nitriding treatment during or after the decarburization annealing step. The method for producing a grain-oriented electrical steel sheet according to any one of claims 3 to 7.

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