Grain-oriented electrical steel sheet and method for manufacturing the same

Abstract

The present application relates to a directionality electromagnetic steel sheet, which comprises: a base steel sheet; a glass coating film formed on the base steel sheet; and a tension imparting insulating coating film formed on the glass coating film. In the base steel sheet, a plurality of linear strains extending continuously or discontinuously in a direction intersecting a rolling direction are present, the interval in the rolling direction of the plurality of linear strains adjacent to each other is 10 mm or less; a closed magnetic domain is present in a region where the strain is present, the length d in the sheet thickness direction from the surface of the base steel sheet of the closed magnetic domain is 30-60 µm, the length w in the rolling direction is 200 µm or less, and the ratio m / d of the depth m from the surface of the base steel sheet at which the compressive strain in the rolling direction present in the closed magnetic domain shows a maximum value to the length d is in the range of more than 0.30 and less than 0.90.

Description

TECHNICAL FIELD

[0001] The present application relates to a grain-oriented magnetic steel sheet and a method for manufacturing the same.

[0002] This application claims priority based on Japanese Patent Application No. 2021-053620 filed on March 26, 2021, the contents of which are hereby incorporated by reference. BACKGROUND

[0003] The grain-oriented magnetic steel sheet is a soft magnetic material and is mainly used as a core material for a transformer. Therefore, the grain-oriented magnetic steel sheet is required to have high magnetization characteristics and low iron loss as magnetic characteristics.

[0004] The so-called "iron loss" is an electric power loss consumed as heat energy in the case where a core is excited in an alternating magnetic field, and from the viewpoint of energy saving, the iron loss is required to be as low as possible. The magnetic susceptibility, the sheet thickness, the coating tension, the impurity amount, the resistivity, the crystal grain diameter, the magnetic domain size, and the like affect the level of the iron loss. With respect to the grain-oriented magnetic steel sheet, even in the present day when various technologies have been developed, research and development for reducing the iron loss are being continued in order to improve the energy efficiency.

[0005] For example, Patent Literature 1 discloses a method for manufacturing a grain-oriented magnetic steel sheet in which the direction of a magnetic domain is controlled by irradiating laser light, characterized by having: a step of irradiating a continuous wave laser light, which has been condensed, while scanning in a direction inclined from a rolling direction of the grain-oriented magnetic steel sheet; and a step of repeating while shifting a portion where the continuous wave laser light is scanned by a prescribed interval. When the average power of the continuous wave laser light is represented as P (W), the speed of the scanning is represented as Vc (mm / s), the prescribed interval is represented as PL (mm), and the average irradiation energy density Ua is defined as Ua = P / (Vc x PL) (mJ / mm 2 ), 1.0 mm ≤ PL ≤ 3.0 mm, and 0.8 mJ / mm 2 ≤ Ua ≤ 2.0 mJ / mm 2 .

[0006] It is shown in Patent Literature 1 that it is easy to ensure high productivity while being able to reduce the iron loss of the grain-oriented magnetic steel sheet in both the L direction and the C direction.

[0007] In addition, Patent Literature 2 discloses a method for manufacturing a grain-oriented magnetic steel sheet in which a linear closed magnetic domain is formed approximately perpendicularly to the rolling direction of the steel sheet and at approximately constant intervals by scanning irradiation of a continuous oscillation laser beam, and the iron loss characteristics are improved.

[0008] It is shown in Patent Literature 2 that by making the laser light a TEMoo mode in which the laser intensity distribution in a cross section perpendicular to the beam propagation direction has a maximum intensity near the optical axis center, it is possible to form a linear closed magnetic domain in which the magnetic domain direction is aligned in the direction perpendicular to the rolling direction of the steel sheet.00 The mode is such that the irradiation beam has a rolling direction light concentration diameter d [mm], a laser beam scanning line speed V [mm / s], and a laser average output power P [W] in the range of 0 < d ≤ 0.2, 0.001 ≤ P / V ≤ 0.012, thereby obtaining a grain-oriented electrical steel sheet with reduced iron loss.

[0009] In addition, Patent Document 3 discloses a method for manufacturing a grain-oriented electrical steel sheet, in which a laser beam is irradiated at intervals on the surface of the grain-oriented electrical steel sheet to improve magnetic properties.

[0010] In Patent Document 3, it is shown that by making the laser a pulse oscillation Q-switched CO2laser, making the irradiation beam shape an ellipse having a long axis in the sheet width direction, and setting the irradiation power density of the laser pulse below the film damage threshold on the surface of the steel sheet, the generation of laser irradiation marks can be suppressed; and by setting the long axis length of the elliptical beam to be above the pulse beam irradiation interval in the sheet width direction, the continuous pulse beams can be overlapped on the surface of the steel sheet, the cumulative irradiation energy necessary and sufficient for magnetic property improvement can be imparted, laser irradiation marks can be suppressed, and an effective magnetic domain control effect can be obtained.

[0011] 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, and for grain-oriented electrical steel sheets used in the core of a transformer, there is a demand for materials that are suitable for low iron loss, and low noise and low vibration. As one of the causes of noise and vibration in a transformer, it can be considered that there is magnetostriction in a grain-oriented electrical steel sheet. Here, the so-called "magnetostriction" refers to the vibration of a grain-oriented electrical steel sheet that is visible in the rolling direction, caused by a slight change in the shape of a grain-oriented electrical steel sheet with the change in the strength of the magnetization when the grain-oriented electrical steel sheet is excited with alternating current; the magnitude of this magnetostriction is 10 -6 The above-described very small magnetostriction of the grade, but this magnetostriction causes the core to vibrate, which propagates to the external structure such as the tank of the transformer and becomes noise.

[0012] The laser irradiation to a grain-oriented electrical steel sheet proposed in the above-described Patent Documents 1 to 3 is effective in reducing iron loss, but there is a problem that the closed magnetic domains formed by laser irradiation increase magnetostriction, making the noise when incorporated into a transformer larger (noise characteristics deteriorate).

[0013] For such a problem, for example, Patent Document 4 discloses a grain-oriented electrical steel sheet that is low in iron loss and has small noise when incorporated into a transformer.

[0014] In Patent Literature 4, it is shown that by forming closed magnetic domain regions whose width in the rolling direction periodically changes on the surface of a steel sheet, and each of the closed magnetic domain regions satisfies conditions that the ratio (Wmax / Wmin) of the maximum width Wmax in the rolling direction on the surface of the steel sheet to the minimum width Wmin is 1.2 or more and 2.2 or less, the average width Wave in the rolling direction on the surface of the steel sheet is 80 μm or more and 250 μm or less, the maximum depth D in the sheet thickness direction is 32 μm or more, and (Wave x D) / s is 0.0007 mm or more and 0.0016 mm or less, a better balance between iron loss and noise than ever before can be achieved.

[0015] In addition, in Patent Literature 5, a grain-oriented magnetic steel sheet is disclosed which is introduced with a local strain in a direction crossing the rolling direction at periodic intervals with respect to the rolling direction; a linear closed magnetic domain portion is formed in the vicinity of the strain, and has a comb-shaped magnetic domain having a length in the rolling direction of 1.2 mm or more from the closed magnetic domain portion in a demagnetized state, and further, 1.8 or more of the magnetic domains are formed on average per 1 mm in a region along the closed magnetic domain portion, and when the linear interval s (mm) of the closed magnetic domain portion is set, the width w (mm) of the closed magnetic domain portion and the depth h (μm) in the sheet thickness direction of the closed magnetic domain portion satisfy the relations of 4 mm ≤ s ≤ 1.5 mm and hw / s ≤ 0.9 μm.

[0016] In Patent Literature 5, it is suggested that the strain introduction amount index expressed by hw / s affects the iron loss and the noise.

[0017] However, in the technologies of Patent Literatures 4 and 5, since periodicity is imparted to the width in the rolling direction of the closed magnetic domain, and the number of comb-shaped magnetic domains is controlled, it is presumed that special electron beam irradiation conditions are required, and it is difficult to obtain a high productivity.

[0018] In addition, as a technology for controlling the closed magnetic domain, for example, in Patent Literatures 6 and 7, a manufacturing method of a grain-oriented magnetic steel sheet is disclosed which provides a grain-oriented magnetic steel sheet in which a closed magnetic domain is formed without damaging a coating film, and which has extremely low transformer iron loss and BF.

[0019] In addition, in Patent Literature 8, it is shown that by forming a closed magnetic domain shape which is advantageous for reducing iron loss by utilizing the characteristics of an electron beam, a grain-oriented magnetic steel sheet is obtained which is low in iron loss in a wide range of sheet thickness.

[0020] In addition, in Patent Literature 9, a grain-oriented magnetic steel sheet for a core is disclosed which has a linear strain formed by an electron beam emitted from LaB6 in a direction of 60° to 120° with respect to the rolling direction in the plane of the steel sheet.

[0021] Further, Patent Literature 10 discloses a grain-oriented magnetic steel sheet having good insulation and corrosion resistance, and a method for manufacturing the same, which controls the area ratio of beam irradiation traces in a beam irradiation region.

[0022] However, there is no study on controlling the closure magnetic domain for reducing the iron loss and on the closure magnetic domain control for achieving low noise.

[0023] Prior Art Documents

[0024] Patent Literature

[0025] Patent Literature 1: Japanese Patent No. 4669565

[0026] Patent Literature 2: Japanese Patent No. 4510757

[0027] Patent Literature 3: Japanese Patent No. 3361709

[0028] Patent Literature 4: Japanese Patent No. 6060988

[0029] Patent Literature 5: Japanese Patent No. 6176282

[0030] Patent Literature 6: Japanese Patent No. 6169695

[0031] Patent Literature 7: Japanese Patent No. 6245296

[0032] Patent Literature 8: International Publication No. 2014 / 068962

[0033] Patent Literature 9: Japanese Patent No. 5954421

[0034] Patent Literature 10: International Publication No. 2013 / 099272 SUMMARY

[0035] Problems to be Solved by the Invention

[0036] As described above, the conventional grain-oriented magnetic steel sheet and the method for manufacturing the same have not been disclosed which sufficiently improve both the iron loss characteristics and the noise characteristics.

[0037] The present invention provides a grain-oriented magnetic steel sheet and a method for manufacturing the same, which have good iron loss characteristics (particularly, the improvement rate of the iron loss by energy ray irradiation) and noise characteristics.

[0038] Means for Solving the Problems

[0039] The directionality electromagnetic steel sheet is irradiated with an energy ray, and the irradiated portion is rapidly heated and rapidly cooled. As a result, a strain (residual strain) is generated in the inside of the steel sheet in the vicinity of the irradiated portion. In the case where the strain is a compressive strain in the rolling direction or a tensile strain in the sheet thickness direction, a closed magnetic domain is generated in the region where the strain is generated. The formation of this closed magnetic domain is a driving force for the 180° magnetic domain subdivision in parallel / antiparallel to the rolling direction, and thus is advantageous for low iron loss. However, generally, if a closed magnetic domain is formed, the degree of magnetostriction becomes large, and thus the noise when incorporated in a transformer becomes large (noise characteristics deteriorate).

[0040] The present inventors have investigated the relationship between the size of the closed magnetic domain and the iron loss characteristics and the noise characteristics. As a result of the investigation, it was found that, by controlling the depth of the closed magnetic domain to be within a prescribed range, it is possible to achieve both low iron loss and low noise after irradiation with an energy ray. In addition, it was found that, by controlling not only the size of the closed magnetic domain but also the state of the strain within the closed magnetic domain, it is possible to achieve a good balance between iron loss and noise. The "energy ray" referred to herein means a laser beam or an electron beam.

[0041] The present application has been made in light of the above findings. The gist of the present application is as described below.

[0042] [1] One embodiment of the present application relates to a directionality electromagnetic steel sheet including: a base steel sheet; a glass coating film formed on the base steel sheet; and a tension imparting insulating coating film formed on the glass coating film, a plurality of linear strains extending continuously or discontinuously in a direction intersecting a rolling direction being present on the base steel sheet, the interval in the rolling direction of the plurality of linear strains adjacent to each other being 10 mm or less, a closed magnetic domain being present in a region where the strain is present, the length in the sheet thickness direction of the closed magnetic domain from the surface of the base steel sheet being 30 to 60 μm, the length in the rolling direction of the closed magnetic domain being 200 μm or less, and the ratio m / d of the depth m from the surface of the base steel sheet at which the compressive strain in the rolling direction present in the closed magnetic domain shows a maximum value to the length d of the closed magnetic domain being in a range exceeding 0.30 and being less than 0.90.

[0043] [2] Another embodiment of the present application relates to a method of manufacturing a directionality electromagnetic steel sheet including a magnetic domain subdivision step of introducing a plurality of linear strains extending in a direction intersecting a rolling direction in the vicinity of the surface of a base steel sheet by irradiating the surface of a tension imparting insulating coating film with an energy ray, for a directionality electromagnetic steel sheet including the base steel sheet, a glass coating film formed on the base steel sheet, and the tension imparting insulating coating film formed on the glass coating film; in the magnetic domain subdivision step, the interval in the rolling direction of linear strains adjacent to each other among the plurality of linear strains being 10 mm or less, and the energy ray output power P in W and the interval in mm of the linear strains adjacent to each other among the plurality of linear strains being in a range of 0.1 ≤ P x interval ≤ 10.2 the energy ray irradiation cross-sectional area S, the unit defined by (P / S) is W / mm 2 The energy ray power density Ip satisfies the following equation (1), the energy ray input energy Up defined by the unit of J / mm using the energy ray output power P and the energy ray scanning speed Vs defined by the unit of mm / sec satisfies the following equation (2), and,

[0044] The diameter dl of the direction perpendicular to the beam scanning direction using the energy ray defined by the unit of pm and the diameter dc of the beam scanning direction, the beam aspect ratio defined by (dl / dc), and the dl respectively satisfy the following equation (3) and the following equation (4).

[0045] 250 ≤ Ip ≤ 5200 (1)

[0046] 0.007 < Up ≤ 0.050 (2)

[0047] 0.0010 < dl / dc < 1.0000 (3)

[0048] 10 ≤ dl < 200 (4)

[0049] Effects of the Invention

[0050] According to the above-described aspect of the present application, it is possible to provide a grain-oriented magnetic steel sheet having excellent iron loss characteristics and noise characteristics and a method for manufacturing the same. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 is a diagram showing one example of a magnetic domain contrast observed in a reflection electron image of a cross section of a steel sheet irradiated with an energy ray. DETAILED DESCRIPTION

[0052] One embodiment of the present application relates to a grain-oriented magnetic steel sheet (the grain-oriented magnetic steel sheet according to the present embodiment) including: a base steel sheet; a glass coating film formed on the base steel sheet; and a tension imparting insulating coating film formed on the glass coating film.

[0053] In addition, a plurality of linear strains (residual strains) extending continuously or discontinuously in a direction intersecting the rolling direction are formed substantially in parallel on the base steel sheet, the interval in the rolling direction of the plurality of linear strains adjacent to each other is 10 mm or less, a closure domain is present in a region where the strain is present, the length d in the sheet thickness direction from the surface of the base steel sheet of the closure domain is 30 to 60 μm, the length w in the rolling direction is 200 μm or less, and the ratio m / d of the depth m from the surface of the base steel sheet at which the compressive strain in the rolling direction present in the closure domain shows a maximum value to the length d in the sheet thickness direction of the closure domain is in a range exceeding 0.30 and less than 0.90.

[0054] Hereinafter, the grain-oriented magnetic steel sheet according to the present embodiment will be described.

[0055] < Base Steel Sheet >

[0056] (Chemical Composition)

[0057] The base steel sheet of the grain-oriented magnetic steel sheet according to the present embodiment has no particular limitation with respect to its chemical composition, and can be in a known range. For example, in order to obtain characteristics generally required for the grain-oriented magnetic steel sheet, the base steel sheet is exemplified to contain the following components as chemical components. In the present embodiment, the % of the chemical components is mass % unless otherwise specified.

[0058] C: 0.010% or less

[0059] C (carbon) is an element effective for microstructure control of the steel sheet in a process before the decarburization annealing process ends in the manufacturing process. However, if the C content of the base steel sheet of the grain-oriented magnetic steel sheet as a product sheet exceeds 0.010%, the magnetic characteristics (iron loss characteristics and magnetic flux density) can be reduced. Therefore, the C content in the base steel sheet of the grain-oriented magnetic steel sheet according to the present embodiment is preferably 0.010% or less. The C content is more preferably 0.005% or less. Although it is preferable that the C content be as low as possible, the effect of microstructure control is saturated even if the C content is reduced to less than 0.0001%, and only the manufacturing cost is increased. Therefore, the C content can be 0.0001% or more.

[0060] Si: 3.00 to 4.00%

[0061] Si (silicon) is an element for improving the electrical resistance of the grain-oriented magnetic steel sheet and improving the iron loss characteristics. When the Si content is less than 3.00%, the effect of reducing eddy current loss is not sufficient. Therefore, the Si content is preferably 3.00% or more. The Si content is more preferably 3.20% or more, and further preferably 3.50% or more.

[0062] On the other hand, if the Si content exceeds 4.00%, the grain-oriented magnetic steel sheet can be embrittled, and the sheet passing property can be significantly deteriorated. In addition, the workability of the grain-oriented magnetic steel sheet can be reduced, and the sheet can be broken during rolling. Therefore, the Si content is preferably 4.00% or less. The Si content is more preferably 3.80% or less, and further preferably 3.70% or less.

[0063] Mn: 0.01 to 0.50%

[0064] Mn (manganese) is an element that forms MnS by combining with S during the manufacturing process. This precipitate functions as an inhibitor (an inhibitor of normal grain growth) and causes secondary recrystallization to occur in the steel. Mn further is an element that can improve the hot workability of the steel. When the Mn content is less than 0.01%, the above-mentioned effects cannot be sufficiently obtained. Therefore, the Mn content is preferably 0.01% or more. The Mn content is more preferably 0.02% or more.

[0065] On the other hand, if the Mn content exceeds 0.50%, secondary recrystallization does not occur, and the magnetic properties of the steel can be reduced. Therefore, in the base steel sheet of the grain-oriented magnetic steel sheet according to the present embodiment, the Mn content is preferably 0.50% or less. The Mn content is more preferably 0.20% or less, and further preferably 0.10% or less.

[0066] N: 0.010% or less

[0067] N (nitrogen) is an element that forms AlN, which functions as an inhibitor, by combining with Al during the manufacturing process. However, if the N content exceeds 0.010%, the magnetic properties are reduced due to the excess amount of inhibitors remaining in the base steel sheet. Therefore, in the base steel sheet of the grain-oriented magnetic steel sheet according to the present embodiment, the N content is preferably 0.010% or less. The N content is more preferably 0.008% or less, and further preferably 0.005% or less.

[0068] On the other hand, the lower limit value of the N content is not particularly specified, and even if it is reduced to less than 0.001%, only the manufacturing cost will increase. Therefore, the N content can be 0.001% or more.

[0069] sol. Al: 0.020% or less

[0070] sol. Al (acid-soluble aluminum) is an element that forms AlN, which functions as an inhibitor, in combination with N during the manufacturing process of the grain-oriented magnetic steel sheet. However, if the sol. Al content of the base steel sheet exceeds 0.020%, the magnetic properties can be reduced due to the excess inhibitor remaining in the base steel sheet. Therefore, the sol. Al content of the base steel sheet of the grain-oriented magnetic steel sheet according to the present embodiment is preferably 0.020% or less. The sol. Al content is more preferably 0.010% or less, and further preferably less than 0.001%. The lower limit of the sol. Al content is not particularly limited, but even if it is reduced to less than 0.0001%, only the manufacturing cost will increase. Therefore, the sol. Al content can be 0.0001% or more.

[0071] S: 0.010% or less

[0072] S (sulfur) is an element that forms MnS, which functions as an inhibitor, in combination with Mn during the manufacturing process. However, in the case where the S content exceeds 0.010%, the magnetic properties can be reduced due to the excess inhibitor remaining. Therefore, the S content of the base steel sheet of the grain-oriented magnetic steel sheet according to the present embodiment is preferably 0.010% or less. The lower the S content of the grain-oriented magnetic steel sheet is, the better. For example, it can be less than 0.001%. However, even if the S content of the grain-oriented magnetic steel sheet is reduced to less than 0.0001%, only the manufacturing cost will increase. Therefore, the S content of the grain-oriented magnetic steel sheet can be 0.0001% or more.

[0073] P: 0.030% or less

[0074] P (phosphorus) is an element that reduces the workability during rolling. By making the P content 0.030% or less, it is possible to suppress excessive reduction of the workability during rolling and to suppress breakage during manufacturing. From this viewpoint, the P content is preferably 0.030% or less. The P content is more preferably 0.020% or less, and further preferably 0.010% or less.

[0075] The lower limit of the P content can be 0%, but since the detection limit of chemical analysis is 0.0001%, the actual lower limit of the P content in a practical steel sheet is 0.0001%. In addition, P is also an element that has an effect of improving the texture and improving the magnetic properties. In order to obtain this effect, the P content can be 0.001% or more, or 0.005% or more.

[0076] Remaining portion: Fe and impurities

[0077] The chemical composition of the base steel sheet of the grain-oriented magnetic steel sheet according to the present embodiment contains the above-mentioned essential elements, and the remainder can be Fe and impurities. However, in order to improve magnetic properties and the like, further, Cu, Cr, Sn, Se, Sb, Mo can be contained in the ranges shown below as optional elements. These elements are also allowed to be contained as impurities.

[0078] In addition, as an element other than the above-mentioned elements, even if any one or two or more of, for example, W, Nb, Bi, Ti, Ni, Co, V is contained in a total of 1.0% or less, the effect of the grain-oriented magnetic steel sheet according to the present embodiment is not hindered.

[0079] Here, the so-called impurities refer to substances mixed from ores, waste materials, or manufacturing environments, and the like as raw materials at the time of industrially manufacturing the base steel sheet, and are elements allowed to be contained in a content that does not adversely affect the effect of the grain-oriented magnetic steel sheet according to the present embodiment.

[0080] Cr: 0 to 0.50%

[0081] Cr (chromium) is an element that contributes to an increase in the Goss orientation ratio in the secondary recrystallized structure, and improves magnetic properties. In order to obtain the above-mentioned effect, the Cr content is preferably 0.01% or more, more preferably 0.02% or more, and further preferably 0.03% or more.

[0082] On the other hand, in the case where the Cr content exceeds 0.50%, Cr oxides are formed, and the magnetic properties are reduced. Therefore, the Cr content is preferably 0.50% or less. The Cr content is more preferably 0.30% or less, and further preferably 0.10% or less.

[0083] Sn: 0 to 0.50%

[0084] Sn (tin) is an element that contributes to the improvement of magnetic properties through control of the primary recrystallized structure. In order 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 further preferably 0.03% or more.

[0085] On the other hand, in the case where the Sn content exceeds 0.50%, the secondary recrystallization becomes unstable, and the magnetic properties are deteriorated. Therefore, the Sn content is preferably 0.50% or less. The Sn content is more preferably 0.30% or less, and further preferably 0.10% or less.

[0086] Cu: 0 to 0.50%

[0087] Cu (copper) is an element that contributes to an increase in the Goss orientation occupancy ratio in the secondary recrystallized structure. Cu is an optional element in the base steel sheet of the grain-oriented electromagnetic steel sheet according to the present embodiment. Therefore, the lower limit of the content thereof is 0%, but in order to obtain the above-mentioned effect, the Cu content is preferably 0.01% or more. The Cu content is more preferably 0.02% or more, and further preferably 0.03% or more.

[0088] On the other hand, in the case where the Cu content exceeds 0.50%, the steel sheet is embrittled in hot rolling. Therefore, the Cu content in the base steel sheet of the grain-oriented electromagnetic steel sheet according to the present embodiment is preferably 0.50% or less. The Cu content is more preferably 0.30% or less, and further preferably 0.10% or less.

[0089] Se: 0 to 0.020%

[0090] Se (selenium) is an element that has a magnetic property improvement effect. Therefore, it can be contained. In the case where Se is contained, in order to exert the magnetic property improvement effect favorably, the Se content is preferably 0.001% or more. The Se content is more preferably 0.003% or more, and further preferably 0.006% or more.

[0091] On the other hand, if the Se content exceeds 0.020%, the adhesion of the glass coating film is deteriorated. Therefore, the Se content is preferably 0.020% or less. The Se content is more preferably 0.015% or less, and further preferably 0.010% or less.

[0092] Sb: 0 to 0.50%

[0093] Sb (antimony) is an element that has a magnetic property improvement effect. Therefore, it can be contained. In the case where Sb is contained, in order to exert the magnetic property improvement effect favorably, the Sb content is preferably 0.005% or more. The Sb content is more preferably 0.01% or more, and further preferably 0.02% or more.

[0094] On the other hand, if the Sb content exceeds 0.50%, the adhesion of the glass coating film is significantly deteriorated. Therefore, the Sb content is preferably 0.50% or less. The Sb content is more preferably 0.30% or less, and further preferably 0.10% or less.

[0095] Mo: 0 to 0.10%

[0096] Mo (molybdenum) is an element that has a magnetic property improvement effect. Therefore, it can be contained. In the case where Mo is contained, in order to exert the magnetic property improvement effect favorably, the Mo content is preferably 0.01% or more. The Mo content is more preferably 0.02% or more, and further preferably 0.03% or more.

[0097] On the other hand, if the Mo content exceeds 0.10%, there is a possibility that the cold-rolling property will deteriorate or even break. 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.

[0098] As described above, the example of the chemical composition of the base steel sheet of the grain-oriented magnetic steel sheet according to the present embodiment illustrates that the base steel sheet contains the above-mentioned essential elements, and the remainder is composed of Fe and impurities, or the base steel sheet contains the above-mentioned essential elements, and further contains one or more of the optional elements, and the remainder is composed of Fe and impurities.

[0099] As for the chemical composition of the base steel sheet of the grain-oriented magnetic steel sheet according to the present embodiment, the measurement can be performed after removing the glass coating film formed on the surface and the tension-imparting insulating coating film.

[0100] Specifically, the tension-imparting insulating coating film is removed by immersing the grain-oriented magnetic steel sheet in a sodium hydroxide aqueous solution containing NaOH: 30 to 50 mass% and H2O: 50 to 70 mass% at 80 to 90°C for 7 to 10 minutes. The grain-oriented magnetic steel sheet from which the tension-imparting insulating coating film is removed is subjected to water washing, and then dried for less than 1 minute using a warm air blower. The glass coating film is removed by immersing the dried grain-oriented magnetic steel sheet (grain-oriented magnetic steel sheet not provided with the tension-imparting insulating coating film) in a hydrochloric acid aqueous solution containing HCl: 30 to 40 mass% at 80 to 90°C for 1 to 10 minutes. The base steel sheet after the immersion is subjected to water washing, and then dried for less than 1 minute using a warm air blower.

[0101] Through the above procedure, the base steel sheet can be taken out from the grain-oriented magnetic steel sheet.

[0102] The chemical composition of such a base steel sheet is obtained using a known component analysis method. Specifically, a drill bit is used to generate a cut powder from the base steel sheet, the cut powder is collected, and the collected cut powder is dissolved in an acid to obtain a solution. The solution is subjected to ICP-AES, and elemental analysis of the chemical composition is performed.

[0103] Here, as for Si in the chemical composition of the base steel sheet, the Si content is obtained by a method (silicon quantitative method) specified in JIS G 1212 (1997). Specifically, if the above-mentioned cut powder is dissolved in an acid, silicon oxide is precipitated in the form of a precipitate, and therefore, the precipitate (silicon oxide) is obtained by filtration using filter paper, the mass is measured, and the Si content is obtained.

[0104] As for the C content and the S content, a known high-frequency combustion method (combustion-infrared absorption method) is used. Specifically, the above-mentioned solution is combusted using high-frequency heating in an oxygen stream, and the generated carbon dioxide and sulfur dioxide are detected, and the C content and the S content are obtained.

[0105] The N content was measured using a known inert gas fusion-thermal conductivity method.

[0106] (strain and closure magnetic domain)

[0107] For the base steel sheet of the grain-oriented electrical steel sheet according to the present embodiment, a plurality of linear strains (residual strains) formed by irradiation of energy rays exist in the vicinity of the surface. The positions of the strains can be analyzed using a residual strain measurement technique using X-ray diffraction by irradiating X-rays to the surface of the steel sheet.

[0108] The plurality of linear strains extend in a direction intersecting the rolling direction, and each of the strains is substantially parallel, and adjacent linear strains are formed at an interval of 10 mm or less in the rolling direction (a distance from the center of a linear strain to the center of an adjacent linear strain in the rolling direction).

[0109] In addition, in the case where the strain is particularly a compressive strain in the rolling direction and a tensile strain in the sheet thickness direction, it is known that a region magnetized in the sheet thickness direction, which is called a "closure magnetic domain", is formed in a region where the strain exists (a region where the strain exists when viewed from the surface of the steel sheet). When the size of the closure magnetic domain is a predetermined size or more, the 180° magnetic domain width is subdivided, the eddy current loss is reduced, and the iron loss is reduced. On the other hand, if the closure magnetic domain size becomes large, the magnetostriction when excited by alternating current becomes large, and the noise of the transformer is significantly present.

[0110] As a result of the research by the present inventors, it was found that, regarding the size of the closure magnetic domain formed and present in the region where the strain exists, in the case where the length d in the sheet thickness direction from the surface of the base steel sheet is 30 to 60 μm and the length w in the rolling direction is 200 μm or less, the iron loss is reduced, and the significant presence of the noise problem is suppressed.

[0111] In addition, the present inventors have newly found that, by controlling the strain distribution in the closure magnetic domain, further noise reduction can be achieved. That is, it was found that, in the case where the ratio m / d of the depth m from the surface of the base steel sheet at which the compressive strain in the rolling direction present in the closure magnetic domain shows a maximum value to the length d described above is in the range of more than 0.30 and less than 0.90, further noise reduction can be achieved.

[0112] In the present embodiment, the expression "extending in a direction intersecting the rolling direction" means that the extension direction of the linear strain is within a range of 30° or less from a direction at a right angle to the rolling direction (i.e., within a range of 60 to 120° from the rolling direction) in terms of a deviation angle. If the angle range is deviated, the 180° magnetic domain of the steel sheet is less subdivided, and sufficient iron loss reduction effect is not obtained.

[0113] The strain can exist continuously in a straight line or discontinuously in one direction (e.g., in a dashed line).

[0114] In addition, if the interval of the plurality of linear strains in the rolling direction exceeds 10 mm, the domain refinement effect of the 180° magnetic domains decreases, and thus the iron loss improvement effect is insufficient. Therefore, the interval of each of the plurality of linear strains in the rolling direction is 10 mm or less. The interval of the plurality of linear strains is preferably substantially equal.

[0115] Although the iron loss decreases when the irradiation interval is reduced (the interval of the plurality of linear strains is reduced), if it is reduced below a threshold value, the total hysteresis loss increases, the iron loss deteriorates, and the noise characteristics deteriorate. Therefore, the interval of each of the plurality of linear strains in the rolling direction is preferably 3 mm or more.

[0116] The length of the strain in the plate width direction is not limited, and is preferably formed from one end to the other end of the width direction of the base steel plate. In the case where the energy ray irradiation is performed discontinuously (intermittently), when the energy ray irradiation is performed on the steel plate at a certain interval in the width direction, the length (length in the width direction) d00 of the energy ray irradiation portion and the length d01 of the energy ray non-irradiation interval sandwiched by the two energy ray irradiation portions in the width direction satisfy d01≤3×d00. The d00 can be in the range of 50 μm or more and 50 mm or less.

[0117] In addition, as described above, the closure magnetic domain formed with the strain is a driving force for the refinement of the 180° magnetic domains, and thus is advantageous for low iron loss. However, there is a problem in that the degree of magnetostriction increases and the noise increases due to the closure magnetic domain.

[0118] In the past, in the case where the deterioration of the noise characteristics is suppressed, measures such as increasing the energy ray irradiation interval or reducing the energy ray input energy are taken. However, such measures are means for improving the noise characteristics at the expense of the iron loss improvement effect by the energy ray irradiation, on the premise that the iron loss characteristics and the noise characteristics are in a trade-off relationship.

[0119] In contrast, the present inventors have found that, by forming a shallow (localized in the surface layer) closure magnetic domain region from the surface in the grain-oriented magnetic steel sheet, the deterioration of the noise characteristics can be suppressed and the iron loss characteristics can be improved. Specifically, it has been found that, by making the length d of the closure magnetic domain in the plate thickness direction present in the region where the strain is formed 60 μm or less, the deterioration of the noise characteristics can be suppressed and the iron loss characteristics can be improved. Therefore, the length d of the closure magnetic domain in the plate thickness direction from the surface of the base steel plate is set to 60 μm or less.

[0120] On the other hand, when the length d of the closed magnetic domain in the sheet thickness direction is less than 30 μm, an improvement effect on the iron loss is not obtained. Therefore, the length d is set to 30 μm or more.

[0121] Further, when the length w of the closed magnetic domain in the rolling direction of the base material steel sheet exceeds 200 μm, the volume of the closed magnetic domain increases, and the degree of magnetostriction becomes large. Therefore, the length w of the closed magnetic domain is set to 200 μm or less. The length w of the closed magnetic domain is preferably 150 μm or less, and more preferably 100 μm or less. On the other hand, the length w of the closed magnetic domain in the rolling direction of the base material steel sheet is preferably 50 μm or more.

[0122] Further, the ratio m / d of the depth m from the surface of the base material steel sheet at which the compressive strain in the rolling direction existing in the closed magnetic domain shows a maximum value to the length d described above is set to a range exceeding 0.30 and being less than 0.90. Although the reason why further low noise is achieved by the control of m / d is not clear, it is presumed that, in the case where m / d is 0.90 or more, since the depth at which the compressive strain in the rolling direction exists in the closed magnetic domain is large, the closed magnetic domain becomes more stabilized, and the external magnetic field required for the disappearance of the closed magnetic domain becomes larger, and thus the higher harmonic component of the magnetostriction waveform becomes large, and the noise becomes larger. Therefore, m / d is set to be less than 0.90. On the other hand, the range of m / d being 0.30 or less is difficult to achieve in the range of the conditions of laser or electron beam irradiation in practical operation. Therefore, m / d is set to exceed 0.30.

[0123] Evaluation of the size of the closed magnetic domain (length in the sheet thickness direction, length in the rolling direction) is performed by observing a reflection electron image of the inclined directionality electromagnetic steel sheet in a scanning electron microscope.

[0124] Specifically, regarding the directionality electromagnetic steel sheet having a residual strain and a closed magnetic domain, a cross section perpendicular to the sheet width direction (sheet thickness direction cross section) is obtained, and processing strain on the surface of the cross section is removed using an argon ion beam. At the time of obtaining the cross section perpendicular to the sheet width direction, the cross section is cut out in a manner that the deviation angle from the {110} crystal plane of iron is less than 1° around the ND axis (sample surface vertical direction). Thereafter, an electron beam is irradiated to the obtained cross section in a scanning electron microscope, and a reflection electron image is obtained. The analysis sample is inclined by 45 degrees to 80 degrees or so in advance. In the case where a magnetic domain exists in the analysis sample, depending on the magnetization direction inside the magnetic domain, the incident electron and the reflection electron are subjected to orbit change inside the sample by the Lorentz force, and thus contrast by the magnetic domain is generated in the reflection electron image. The closed magnetic domain is judged from the contrast, and the size thereof is taken as the size of the closed magnetic domain.

[0125] A method of judging the closed magnetic domain from the contrast is described. Figure 1An example of a reflected electron image, showing the location of the irradiating energy rays, in a direction parallel to the plate thickness and rolling direction. For example... Figure 1 As shown, inside a steel plate directly below which energy rays were irradiated, the following was observed in the reflected electron image: there are areas where a striped pattern with contrast is observed. Figure 1 The region SPR is enclosed by white and black dashed lines. The magnetic domain structure in this region differs from its surroundings due to the residual strain introduced by energy ray irradiation. In this embodiment, it is as follows (e.g.) Figure 1 The region (enclosed by a dashed line) in the rolling direction where the pixel intensity varies with an amplitude of more than 0.4% of the average pixel intensity (with visible stripe pattern contrast) at 2-10 μm intervals is defined as a closed magnetic domain, and its size is taken as the size of the closed magnetic domain. Here, the average pixel intensity refers to the average pixel intensity within the region where the stripe pattern is observed.

[0126] Regarding the strain within the closed magnetic domains, after obtaining a cross-section perpendicular to the width direction (thickness direction section), it is evaluated by mapping using electron backscatter diffraction (EBSD). When obtaining strain using EBSD, the strain value is converted by saving the EBSD image at high resolution and measuring the displacement between the images. For example, the EBSD image is saved at 956×956 pixels for strain calculation. The method of converting displacement between EBSD images into strain is well-known in the paper and can be calculated using commercially available software such as CrossCourt4 from BLG Vantage. Thus, the depth from the steel plate surface where the compressive strain in the rolling direction shows its maximum value is calculated.

[0127] <Glass Coating>

[0128] In the directional electromagnetic steel sheet of this embodiment, a glass coating is formed on the surface of the base steel sheet.

[0129] The glass coating is an inorganic coating with magnesium silicate as the main component. The glass coating is formed during the final annealing process by reacting an annealing separating agent containing magnesium oxide (MgO) applied to the surface of the base steel sheet with the components on the surface of the base steel sheet. The glass coating has a composition derived from both the annealing separating agent and the base steel sheet (more specifically, a composition with Mg2SiO4 as the main component).

[0130] <Tension imparts insulating coating>

[0131] In the directional electromagnetic steel plate of this embodiment, a tension-insulating coating is formed on the surface of the glass coating.

[0132] The tension-imparting insulating coating imparts electrical insulation to the grain-oriented magnetic steel sheet, thereby reducing eddy current loss and improving the iron loss of the grain-oriented magnetic steel sheet. In addition, according to the tension-imparting insulating coating, in addition to the electrical insulation as described above, various properties such as corrosion resistance, heat resistance, smoothness, and the like can be obtained.

[0133] Further, the tension-imparting insulating coating has a function of imparting tension to the grain-oriented magnetic steel sheet. By imparting tension to the grain-oriented magnetic steel sheet, movement of magnetic domain walls in the grain-oriented magnetic steel sheet becomes easy, whereby the iron loss of the grain-oriented magnetic steel sheet can be improved.

[0134] The tension-imparting insulating coating may, for example, be a publicly known coating film formed by applying a coating liquid containing metal phosphate and silica as main components to the surface of a glass coating film and baking.

[0135] <Thickness of the base steel sheet: 0.17 to 0.30 mm>

[0136] The thickness of the base steel sheet of the grain-oriented magnetic steel sheet according to the present embodiment is not limited, and in consideration of application to the core of a transformer that requires low iron loss and simultaneously requires low noise and low vibration, the thickness is preferably 0.17 to 0.30 mm. The thinner the thickness, the more the effect of reduction in eddy current loss can be enjoyed, and a good iron loss can be obtained, and therefore the upper limit of the preferred thickness of the base steel sheet is 0.30 mm. However, for manufacturing a base steel sheet of less than 0.17 mm, special equipment is required, and production is not preferred in terms of increased manufacturing cost and the like. Therefore, the lower limit of the thickness industrially preferred is 0.17 mm.

[0137] <Manufacturing method>

[0138] The grain-oriented magnetic steel sheet according to the present embodiment can be manufactured by a manufacturing method including the following steps.

[0139] (i) a hot-rolling step of heating a steel billet containing, in mass %, C: 0.01 to 0.20 %, Si: 3.0 to 4.0 %, 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 0.50 %, and Mo: 0 to 0.10 %, with the remainder being Fe and impurities, and then hot-rolling to obtain a hot-rolled steel sheet;

[0140] (ii) a hot-rolled sheet annealing step of annealing the hot-rolled steel sheet to obtain a hot-rolled annealed steel sheet;

[0141] (iii) a cold rolling process of subjecting the hot-rolled and annealed steel sheet to cold rolling once or to cold rolling a plurality of times with interposed annealing to obtain a cold-rolled steel sheet;

[0142] (iv) a decarburization annealing process of subjecting the cold-rolled steel sheet to decarburization annealing to obtain a decarburization annealed steel sheet;

[0143] (v) a final annealing process of subjecting the decarburization annealed steel sheet to final annealing after applying an annealing separator to the surface of the decarburization annealed steel sheet to obtain a final annealed steel sheet;

[0144] (vi) an insulating film forming process of forming a tension imparting insulating film on the surface of the final annealed steel sheet;

[0145] (vii) a magnetic domain refinement process of introducing linear thermal strain to the surface of the tension imparting insulating film by energy ray irradiation.

[0146] Hereinafter, these processes will be described in detail. In the following description, in cases where certain conditions in each process are not described, publicly known conditions can be appropriately applied to each process.

[0147] <Hot rolling process>

[0148] In the hot rolling process, a hot-rolled steel sheet is obtained by, for example, subjecting a steel slab such as a slab formed of C: 0.01 to 0.20%, Si: 3.0 to 4.0%, 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 0.50%, and Mo: 0 to 0.10%, the remainder: Fe and impurities, in mass%, to heating and then subjecting to hot rolling. The heating temperature of the steel slab is preferably in the range of 1100 to 1450°C. The heating temperature is more preferably 1300 to 1400°C.

[0149] The hot rolling conditions are not particularly limited and can be appropriately set based on the required characteristics. The thickness of the hot-rolled steel sheet is preferably in the range of 2.0 mm or more and 3.0 mm or less, for example.

[0150] <Hot-rolled sheet annealing process>

[0151] The hot-rolled sheet annealing process is a process of annealing the hot-rolled steel sheet manufactured through the hot rolling process to form a hot-rolled and annealed steel sheet. By subjecting to such annealing treatment, recrystallization is generated in the steel sheet structure, and good magnetic characteristics can be achieved.

[0152] In the annealing process of the hot-rolled sheet according to the present embodiment, the hot-rolled steel sheet manufactured through the hot-rolling process is annealed according to a known method to form a hot-rolled annealed steel sheet. The method of heating the hot-rolled steel sheet at the time of annealing is not particularly limited, and a known heating method can be used. Also, the annealing conditions are not particularly limited, and for example, the hot-rolled steel sheet can be annealed at a temperature ranging from 900 to 1200°C for 10 seconds to 5 minutes.

[0153] < Cold-rolling process >

[0154] In the cold-rolling process, the hot-rolled annealed steel sheet after the annealing of the hot-rolled sheet is subjected to cold-rolling including a plurality of passes to obtain a cold-rolled steel sheet having a sheet thickness of 0.17 to 0.30 mm. The cold-rolling can be performed once (a series of cold-rolling without interposed annealing), or the cold-rolling can be interrupted before the final pass of the cold-rolling process, and at least once or more than twice of interposed annealing can be performed, and the cold-rolling with interposed annealing can be performed a plurality of times.

[0155] When the interposed annealing is performed, it is preferable to maintain the temperature at 1000 to 1200°C for 5 to 180 seconds. The annealing atmosphere is not particularly limited. The number of times of interposed annealing is preferably 3 or less in consideration of manufacturing costs.

[0156] Also, pickling can be performed on the surface of the hot-rolled annealed steel sheet before the cold-rolling process.

[0157] In the cold-rolling process, the hot-rolled annealed steel sheet is cold-rolled according to a known method to form a cold-rolled steel sheet. For example, the final reduction ratio can be in the range of 80 to 95%. In the case where the final reduction ratio is less than 80%, the possibility of obtaining a Goss nucleus having a high degree of aggregation in the rolling direction in the {110} <001> orientation becomes high, and thus is not preferable. On the other hand, in the case where the final reduction ratio exceeds 95%, the possibility of destabilization of secondary recrystallization in the final annealing process as a subsequent process becomes high, and thus is not preferable. By making the final reduction ratio in the above range, it is possible to obtain a Goss nucleus having a high degree of aggregation in the rolling direction in the {110} <001> orientation, while it is possible to suppress the destabilization of secondary recrystallization.

[0158] The final reduction ratio refers to the cumulative reduction ratio of cold-rolling, and in the case where interposed annealing is performed, the cumulative reduction ratio of cold-rolling after the final interposed annealing.

[0159] < Decarburization annealing process >

[0160] In the decarburization annealing step, the obtained cold-rolled steel sheet is subjected to decarburization annealing to form a decarburization annealed steel sheet. In the decarburization annealing, as long as the cold-rolled steel sheet is once recrystallized and C, which adversely affects magnetic properties, is removed from the steel sheet, the decarburization annealing conditions are not limited, and for example, the degree of oxidation (PH2O / PH2) in the annealing atmosphere (furnace atmosphere) is set to 0.3 to 0.6, and the annealing temperature is set to 800 to 900°C, and the holding time is set to 10 to 600 seconds.

[0161] < Nitriding treatment step >

[0162] The nitriding treatment can also be performed between the decarburization annealing step and a final annealing step described later.

[0163] In the nitriding treatment step, for example, the decarburization annealed steel sheet is maintained at 700 to 850°C in a nitriding treatment atmosphere (an atmosphere containing hydrogen, nitrogen, ammonia, and the like, which have a nitriding ability). Here, the nitriding treatment is preferably performed so that the N content of the decarburization annealed steel sheet after the nitriding treatment step is 40 to 1000 ppm on a mass basis. When the N content of the decarburization annealed steel sheet after the nitriding treatment is less than 40 ppm, there is a possibility that AlN is not sufficiently precipitated in the decarburization annealed steel sheet, and AlN does not function as an inhibitor. Therefore, when AlN is used as an inhibitor, the N content of the decarburization annealed steel sheet after the nitriding treatment is preferably 40 ppm or more.

[0164] On the other hand, when the N content of the decarburization annealed steel sheet exceeds 1000 ppm, AlN is excessively present in the steel sheet after the secondary recrystallization ends in the final annealing. Such AlN becomes a cause of deterioration of iron loss. Therefore, the N content of the decarburization annealed steel sheet after the nitriding treatment step is preferably 1000 ppm or less.

[0165] < Final annealing step >

[0166] In the final annealing step, the decarburization annealed steel sheet obtained in the decarburization annealing step or further subjected to the nitriding treatment is subjected to final annealing after being coated with a prescribed annealing separator. The final annealing is generally performed for a long time in a state in which the steel sheet is wound in a coiled shape. Therefore, before the final annealing, the annealing separator is coated on the decarburization annealed steel sheet and dried in order to prevent the inside and the outside of the coil of the coiled shape from being burned.

[0167] As the coating annealing separator, an annealing separator mainly composed of MgO (for example, containing 80 mass% or more) is used. By using an annealing separator mainly composed of MgO, a glass coating film can be formed on the surface of the base steel sheet. In the case where MgO is not the main component, a primary coating film (glass coating film) is not formed. The reason is that, since the primary coating film is a Mg2SiO4or MgAl2O4compound, Mg necessary for the reaction for formation is lacking.

[0168] The final annealing is performed, for example, under the conditions of heating to 1150 to 1250°C in an atmosphere gas containing hydrogen and nitrogen, and annealing for 10 to 60 hours.

[0169] <Insulating Coating Film Forming Step>

[0170] In the insulating coating film forming step, a tension imparting insulating coating film is formed on one side or both sides of the cold-rolled steel sheet after the final annealing. The forming conditions of the tension imparting insulating coating film are not particularly limited, and a publicly known insulating coating treatment liquid is used, and the coating and drying of the treatment liquid are performed by a publicly known method. By forming the tension imparting insulating coating film on the surface of the steel sheet, the magnetic characteristics of the grain-oriented electromagnetic steel sheet can be further improved.

[0171] The surface of the steel sheet on which the tension imparting insulating coating film is to be formed can be a surface on which any of a degreasing treatment using an alkali or the like, or an acid pickling treatment using hydrochloric acid, sulfuric acid, phosphoric acid, or the like, or the like has been performed before the coating treatment liquid is applied, or can be a surface as it is after the final annealing without performing these pretreatments.

[0172] The insulating coating film formed on the surface of the steel sheet is not particularly limited as long as it is a coating film that can be used as an insulating coating film of a grain-oriented electromagnetic steel sheet, and a publicly known insulating coating film can be used. As such an insulating coating film, for example, a composite insulating coating film mainly composed of an inorganic substance and further containing an organic substance can be cited. Here, the composite insulating coating film is, for example, an insulating coating film mainly composed of at least any one of inorganic substances such as a chromic acid metal salt, a phosphoric acid metal salt, or colloidal silica, a Zr compound, a Ti compound, and the like, and dispersed with fine organic resin particles. In particular, from the viewpoint of reducing the environmental burden at the time of production, which has been increasingly demanded in recent years, it is preferable to use an insulating coating film using a phosphoric acid metal salt or a coupling agent of Zr or Ti, or a carbonate or an ammonium salt thereof as a starting material.

[0173] <Magnetic Domain Refinement Step>

[0174] In the magnetic domain subdivision process, a plurality of linear strains extending in a direction intersecting the rolling direction are introduced near the surface of the base material steel sheet (from the surface to the inside of the steel sheet) by irradiating an energy ray (laser beam or electron beam) on the surface of the tension-imparting insulating coating. In the magnetic domain subdivision process, a plurality of linear strains (thermal strains resulting from rapid heating by irradiation of the energy ray and subsequent rapid cooling) are formed at a prescribed interval in the rolling direction, and the interval (i.e., the interval of adjacent linear strains) is 10 mm or less in the rolling direction.

[0175] If the interval of the plurality of linear strains in the rolling direction exceeds 10 mm, the iron loss improvement effect is insufficient. Therefore, the energy ray is irradiated at 10 mm or less in each of the rolling directions to form the strains.

[0176] The energy ray can be continuous wave irradiation or pulsed irradiation. Examples of the laser beam include a fiber laser, a YAG laser, or a CO2 laser. The electron beam can be a continuous beam or a discontinuous beam.

[0177] In addition, as described above, in order to obtain a grain-oriented electromagnetic steel sheet that balances low iron loss and low noise, strains are introduced into the base material steel sheet to form closed magnetic domains having a shallow depth from the surface.

[0178] Specifically, the energy ray is irradiated in such a manner that the energy ray output power P in W and the energy ray irradiation cross-sectional area S in mm2 are used, the energy ray power density Ip defined by P / S satisfies the following equation (1), and the energy ray input energy Up in J / mm defined by P / Vs is satisfied using the energy ray output power P and the energy ray scanning speed Vs in mm / sec. 2

[0179] 250 ≤ Ip ≤ 5200 Equation (1)

[0180] 0.007 < Up ≤ 0.050 Equation (2)

[0181] If Ip is less than 250, the irradiation effect cannot be sufficiently obtained, and the iron loss cannot be sufficiently improved. Therefore, Ip is 250 or more. On the other hand, if Ip exceeds 5200, the depth of the closed magnetic domains becomes large, and the noise characteristics deteriorate. Therefore, Ip is 5200 or less. Ip is preferably 2000 or less, more preferably 1750 or less, and further preferably 1500 or less. In this case, the noise characteristics are more excellent.

[0182] ​Further, when Up is 0.007 or less, the irradiation effect cannot be sufficiently obtained, and the iron loss cannot be sufficiently improved. Therefore, Up is more than 0.007. On the other hand, if Up exceeds 0.050, the depth of the closed magnetic domain becomes large, and the noise characteristics deteriorate. Therefore, Up is 0.050 or less.

[0183] Further, in the method of manufacturing the grain-oriented magnetic steel sheet according to the present embodiment, when the energy rays are irradiated, the beam aspect ratio defined by (dl / dc) is controlled to satisfy the following equation (5) using dl, which is the diameter in the direction perpendicular to the beam scanning direction of the energy rays, in units of pm, and dc, which is the diameter in the beam scanning direction, in units of pm.

[0184] 0.0010 < dl / dc < 1.0000 (5)

[0185] When the beam aspect ratio is 0.0010 or less, heat is emitted with the beam irradiation, the input efficiency of the input energy decreases, and a sufficient magnetic domain subdivision effect (iron loss improvement effect) cannot be obtained. Therefore, the beam aspect ratio is more than 0.0010.

[0186] On the other hand, when the beam aspect ratio is 1.0000 or more, the volume in which the residual stress exists increases, and the low noise characteristics become a disadvantage. Therefore, the beam aspect ratio is less than 1.0000. The beam aspect ratio is preferably less than 0.0500, and more preferably less than 0.0050.

[0187] Further, dl, which is the diameter in the direction perpendicular to the beam scanning direction of the energy rays, in units of pm, satisfies the following equation (6).

[0188] 10 < dl < 200 (6)

[0189] In the energy rays such as laser light or electron rays, it is industrially difficult to reduce the beam diameter to less than 10 pm. Therefore, dl is 10 or more.

[0190] On the other hand, if dl is 200 or more, the magnetic domain subdivision effect is exceeded, the remaining thermal strain is introduced, and thus the noise characteristics deteriorate. Therefore, dl is less than 200. dl is preferably less than 150, and more preferably less than 100.

[0191] In the method of manufacturing the grain-oriented magnetic steel sheet according to the present embodiment, as described above, the energy rays of Ip, which is relatively strong, are irradiated in a state in which the beam aspect ratio is small. Such irradiation is not generally performed. This is because it is considered that reducing the beam aspect ratio relates to dispersing the irradiation energy, and the effect of increasing Ip can be reduced.

[0192] However, the inventors have found, as a result of their research based on the new insight that the spatial distribution of strain is important in terms of simultaneously reducing iron loss and noise, that the above-described irradiation conditions are preferable.

[0193] Example

[0194] A slab containing 3.0 mass% Si (a steel slab containing, in mass%, C: 0.03%, Si: 3.0%, sol. Al: 0.040%, Mn: 0.05%, N: 0.005%, S: 0.005%, P: 0.01%, with the remainder including Fe and impurities) was subjected to a hot rolling process. Specifically, after heating the slab to 1350°C, the slab was subjected to hot rolling, and a hot-rolled steel sheet having a sheet thickness of 2.3 mm was produced.

[0195] The hot-rolled steel sheet after the hot rolling process was subjected to a hot-rolled sheet annealing process at an annealing temperature of 900 to 1200°C, with a holding time of 10 to 300 seconds.

[0196] Subsequently, one cold rolling, or a plurality of cold rollings with intermediate annealing interposed, was performed, and a cold-rolled steel sheet having a thickness of 0.17 to 0.30 mm was obtained.

[0197] The cold-rolled steel sheet was subjected to decarburization annealing under conditions of 800 to 850°C for 100 to 200 seconds. The decarburization annealing atmosphere was a well-known wet atmosphere containing hydrogen and nitrogen.

[0198] After the decarburization annealing, for Steel Sheets No. 4, 6, and 13, nitriding treatment was performed in a well-known nitriding treatment atmosphere (an atmosphere containing hydrogen, nitrogen, and ammonia, or the like, having a nitriding capacity) at 700 to 850°C for 10 to 60 seconds, in a manner such that the N content after the nitriding treatment of the decarburization-annealed steel sheet was 40 to 1000 ppm.

[0199] After the nitriding treatment of Steel Sheets No. 4, 6, and 13, in addition thereto, after the decarburization annealing, an annealing release agent mainly composed of magnesium oxide (MgO) was applied to the surface of the steel sheet, and final annealing was performed. The final annealing temperature in the final annealing was 1200°C, and the holding time at the final annealing temperature was 20 hours.

[0200] After the cooling of the final annealing, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface (glass coating film) of the steel sheet (directional electromagnetic steel sheet), and baking was performed, and a tension-imparting insulating coating film was formed.

[0201] Through the above process, a directional electromagnetic steel sheet of each Steel Sheet No. was produced.

[0202] [Analysis of the Chemical Composition of the Base Steel Sheet]

[0203] The chemical composition of the base steel sheet of each steel sheet No. before the magnetic domain subdivision of the grain-oriented magnetic steel sheet obtained using the above-mentioned points was obtained by the following method. First, the tension imparting insulating coating was removed from the grain-oriented magnetic steel sheet of each steel sheet No. Specifically, the grain-oriented magnetic steel sheet was immersed in a sodium hydroxide aqueous solution containing NaOH: 30 to 50 mass% and H2O: 50 to 70 mass% at 80 to 90°C for 7 to 10 minutes. The immersed grain-oriented magnetic steel sheet (grain-oriented magnetic steel sheet from which the tension imparting insulating coating was removed) was subjected to water washing. After the water washing, drying was performed using a hair dryer for less than 1 minute.

[0204] Next, the glass coating was removed from the grain-oriented magnetic steel sheet not having the tension imparting insulating coating. Specifically, the grain-oriented magnetic steel sheet was immersed in a hydrochloric acid aqueous solution containing HCl: 30 to 40 mass% at 80 to 90°C for 1 to 10 minutes. Thus, the glass coating was removed from the base steel sheet. The immersed base steel sheet was subjected to water washing. After the water washing, drying was performed using a hair dryer for less than 1 minute.

[0205] The base steel sheet was taken out from the grain-oriented magnetic steel sheet by the above procedure.

[0206] The chemical composition of the taken-out base steel sheet was obtained using a known composition analysis method. Specifically, a drill was used to generate a cut powder from the base steel sheet, and the cut powder was collected. The collected cut powder was dissolved in an acid to obtain a solution. The solution was subjected to ICP-AES, and elemental analysis of the chemical composition was performed. As for Si in the chemical composition of the base steel sheet, it was obtained by a method (silicon quantitative method) prescribed in JIS G 1212 (1997). Specifically, if the above-mentioned cut powder is dissolved in an acid, silicon oxide is precipitated as a precipitate. The precipitate (silicon oxide) was obtained by filtration using filter paper, and the mass was measured to obtain the Si content. As for the C content and the S content, they were obtained using a known high-frequency combustion method (combustion-infrared absorption method). Specifically, the above-mentioned solution was combusted using high-frequency heating in an oxygen stream, and the generated carbon dioxide and sulfur dioxide were detected to obtain the C content and the S content. As for the N content, a known inert gas melting-thermal conductivity method was used. The chemical composition of the base steel sheet was obtained by the above analysis method. The chemical composition of the steel sheet (base steel sheet) of each steel sheet No. was C: 0.001%, Si: 3.0%, sol. Al: less than 0.001%, Mn: 0.05%, N: 0.002%, S: less than 0.001%, P: 0.01%, and the remainder: Fe and impurities in mass%.

[0207] [Evaluation of Magnetic Properties]

[0208] Although not shown in the table, in order to evaluate the iron loss improvement rate, the iron loss before the magnetic domain subdivision was evaluated. From each steel sheet No. of the grain-oriented electromagnetic steel sheet, a sample of width 60 mm x length 300 mm including the central position of the plate width was taken. The length direction of the sample was parallel to the rolling direction. The sample taken was subjected to strain removal by being held at 800°C for 2 hours under a nitrogen atmosphere at dew point 0°C or lower.

[0209] Using this sample, the iron loss W 17 / 50 (W / kg) was measured at a frequency of 50 Hz and a maximum magnetic flux density of 1.7 T in accordance with JIS C2556 (2015).

[0210] After that, by using an optical fiber laser or an electron beam on each steel sheet No. of the grain-oriented electromagnetic steel sheet, laser irradiation or electron beam irradiation was performed on the steel sheet surface under the conditions shown in Table 1, whereby magnetic domain subdivision was performed, and while investigating the closed magnetic domain size, evaluation experiments of the noise characteristics and the magnetic characteristics were performed. The laser irradiation was performed in an atmospheric atmosphere, and the electron beam irradiation was performed in a vacuum (vacuum degree: 0.2 Pa).

[0211] Table 1

[0212]

[0213] [Closed magnetic domain distribution of energy ray-processed steel sheet]

[0214] The closed magnetic domain size of the cross section in the sheet thickness direction of each grain-oriented electromagnetic steel sheet evaluated according to the above points was observed by reflection electron image observation in a scanning electron microscope. Regarding the grain-oriented electromagnetic steel sheet having residual strain and closed magnetic domains, after obtaining a cross section perpendicular to the plate width direction (cross section in the sheet thickness direction), the machining strain on the surface of the cross section was removed using an argon ion beam with an acceleration voltage of 1 kV. When the cross section perpendicular to the plate width direction was obtained, the cross section was cut out in a manner so that the deviation angle from the {110} crystal face of iron was less than 1° around the ND axis (direction perpendicular to the sample surface). By tilting the sample by 70 degrees in the scanning electron microscope and irradiating the cross section with electron rays, a reflection electron image was obtained. The acceleration voltage of the electron rays was set to 20 kV. The evaluation results are shown in Table 2.

[0215] [Evaluation of strain in closed magnetic domain]

[0216] As for the strain in the closed magnetic domain (residual strain), after obtaining a cross section in the plate thickness direction, mapping measurement was performed by using an electron backscatter diffraction method (EBSD), whereby evaluation was performed. An electron beam was irradiated to a sample tilted at 70 degrees, and an EBSD image was obtained. The EBSD image was saved at 956 x 956 pixels, and was used for strain calculation. Strain calculation was performed using CrossCourt4 software of BLG Vantage Co. Thereby, the depth from the surface of the steel sheet at which the rolling direction compressive strain showed a maximum value was calculated.

[0217] [Noise characteristic evaluation]

[0218] A sample having a width of 100 mm x length of 500 mm was used from each of the grain-oriented electrical steel sheets. The length direction of the sample corresponded to the rolling direction RD, and the width direction corresponded to the sheet width direction TD.

[0219] Magnetostriction was measured by an alternating current magnetostriction measurement method using a magnetostriction measurement device for the sample. The magnetostriction measurement device was a device provided with a laser Doppler vibrometer, an excitation coil, an excitation power source, a magnetic flux detection coil, an amplifier, and an oscilloscope.

[0220] Specifically, an alternating current magnetic field was applied to the sample in such a manner that the maximum magnetic flux density in the rolling direction was 1.7 T. The change in the length of the sample caused by the expansion and contraction of the magnetic domain was measured using the laser Doppler vibrometer, and a magnetostriction signal was obtained. The obtained magnetostriction signal was subjected to Fourier analysis, and the amplitude Cn of each frequency component fn (n is a natural number of 1 or more) of the magnetostriction signal was calculated. Using an A correction coefficient an of each frequency component fn, a magnetostriction velocity level LVA (dB) represented by the following formula was calculated.

[0221]

[0222] Here, pc is the specific acoustic impedance, pc = 400. Pe0 is the minimum audible sound pressure, and Pe0 = 2 x 10 -5 (Pa) was used. The A correction coefficient an used the value described in Table 2 of JIS C 1509-1 (2005).

[0223] Based on the obtained magnetostriction velocity level (LVA), the noise characteristic was evaluated according to the following criteria. When the magnetostriction velocity level was less than 60 dBA, it was determined that the noise characteristic was good.

[0224] The results are shown in Table 2.

[0225] [Magnetic characteristic evaluation]

[0226] A sample of width 60 mm x length 300 mm including the center of the plate width was taken from each of the grain-oriented electrical steel sheets No. The length direction of the sample was parallel to the rolling direction. The sample taken was held at 800°C for 2 hours under a nitrogen atmosphere having a dew point of 0°C or less, and the strain introduced at the time of taking the sample was removed.

[0227] Using this sample, the magnetic flux density (T) was found by the single sheet tester (SST) test according to JIS C2556 (2015). Specifically, a magnetic field of 800 A / m was applied to the sample, and the magnetic flux density (T) was found.

[0228] Further, using the above sample, the iron loss W 17 / 50 (W / kg) was measured at a frequency of 50 Hz and a maximum magnetic flux density of 1.7 T according to JIS C2556 (2015).

[0229] The measurement results are shown in Table 2.

[0230] Here, the improvement rate (%) of the iron loss before and after the energy ray irradiation was defined as 100 x the difference in the iron loss before and after the energy ray irradiation / the iron loss before the energy ray irradiation, and the iron loss improvement rate of 5.0% or more was set as acceptable. The measurement results of the iron loss improvement rate are shown together in Table 2.

[0231]

[0232] As can be seen from Tables 1 to 2, in the present application examples, the ratio (m / d) of the depth m from the surface of the base material steel sheet at which the maximum value of the size (d and w) of the closure domain and the compression strain in the rolling direction existing in the closure domain is shown, and d is within the range of the present application. As a result, the magnetic properties are good, the improvement rate of the iron loss is also high, and the noise properties are also good.

[0233] On the other hand, in the comparative examples, the size of the closure domain or m / d is outside the range of the present application. As a result, at least one of the iron loss improvement rate or the noise properties is poor.

[0234] In Steel Sheet No. 1, the energy ray input energy Up is low, and in Steel Sheet No. 14, the energy ray power density Ip is low, and the length in the plate thickness direction of the closure domain is insufficient. As a result, the iron loss improvement rate is less than 5.0%.

[0235] In Steel Sheet No. 9, although the energy ray input energy Up is large, the energy ray power density Ip is low, and therefore, the length in the plate thickness direction of the closure domain is insufficient. As a result, the iron loss improvement rate is less than 5.0%.

[0236] In Steel Sheet No. 15, the energy ray power density Ip is low, and m / d is large. As a result, the noise properties are poor.

[0237] In Steel Sheet No. 19, the length of the closed magnetic domain in the sheet thickness direction is too long because the energy ray input energy Up is too large. As a result, the noise characteristic is disadvantageous.

[0238] In Steel Sheet No. 21, the length of the closed magnetic domain in the sheet thickness direction is too long because the energy ray power density Ip is too high. As a result, the noise characteristic is disadvantageous.

[0239] In Steel Sheet No. 23, the interval of the adjacent linear strains in the rolling direction exceeds 10 mm. As a result, the iron loss improvement rate is less than 5.0%.

[0240] In Steel Sheet No. 25, the length of the closed magnetic domain in the sheet thickness direction is too long because the energy ray input energy Up is small and the energy ray power density Ip is high. As a result, the noise characteristic is disadvantageous.

[0241] In Steel Sheet No. 26, the length of the energy ray irradiation trace in the rolling direction is too long, and the length of the closed magnetic domain in the rolling direction exceeds 200 μm. As a result, the noise characteristic is disadvantageous.

[0242] In Steel Sheet No. 28, the aspect ratio of the energy ray irradiation trace is too small, and sufficient energy ray irradiation effect is not obtained under the influence of the heat dissipation, and the length of the closed magnetic domain in the sheet thickness direction is insufficient. As a result, the iron loss improvement rate is less than 5.0%.

[0243] In Steel Sheet No. 29, the aspect ratio of the energy ray irradiation trace is too large, and the length of the closed magnetic domain in the sheet thickness direction is too long. As a result, the noise characteristic is disadvantageous.

[0244] Industrial Applicability

[0245] According to the present application, a grain-oriented electromagnetic steel sheet having good iron loss characteristics and noise characteristics and a method for manufacturing the same can be provided. Therefore, the industrial applicability is high.

[0246] Explanation of Symbols

[0247] ND Sheet surface normal direction

[0248] TD Sheet width direction

[0249] RD Rolling direction

[0250] S Surface

[0251] SPR Region where a striped pattern is observed

[0252] EIrD Energy ray irradiation direction

Claims

1. A grain-oriented electrical steel sheet characterized by, Possessing: a base steel sheet; a glass clad layer formed on the base steel sheet; and a tension-imparting insulating clad layer formed on the glass clad layer, a plurality of linear strains extending continuously or discontinuously in a direction intersecting a rolling direction are present in the base steel sheet, a pitch in the rolling direction of the plurality of linear strains adjacent to each other is 10 mm or less, a closed magnetic domain is present in a region where the strain is present, a length d in a sheet thickness direction from a surface of the base steel sheet of the closed magnetic domain is 30 to 60 µm, a length w in the rolling direction is 200 µm or less, a ratio m / d of a depth m from the base steel sheet surface at which the compression strain in the rolling direction present within the closed magnetic domain shows a maximum value to the length d is in a range exceeding 0.30 and less than 0.90, a chemical composition of the base steel sheet contains, in mass %, C: 0.010% or less, Si: 3.00 to 4.00%, Mn: 0.01 to 0.50%, N: 0.010% or less, sol. Al: 0.020% or less, 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 0.50%, Mo: 0 to 0.10%, and the remainder: Fe and impurities.

2. The method of producing a grain-oriented magnetic steel sheet according to claim 1, characterized by including a magnetic domain subdivision process, the magnetic domain subdivision process imparts, to a grain-oriented electrical steel sheet provided with a base steel sheet, a glass clad layer formed on the base steel sheet, and a tension-imparting insulating clad layer formed on the glass clad layer, a plurality of linear strains extending in a direction intersecting a rolling direction in a surface vicinity of the base steel sheet by irradiating an energy ray to a surface of the tension-imparting insulating clad layer, in the magnetic domain subdivision process, a pitch in the rolling direction of linear strains adjacent to each other in the plurality of linear strains is 10 mm or less, The energy ray output power P is in units of W, and the energy ray irradiation cross-sectional area S is in units of mm 2 The energy ray output power P is in units of W, and the energy ray irradiation cross-sectional area S is in units of mm 2 The energy ray power density Ip defined by P / S satisfies the following equation (1), an energy ray input energy Up defined in J / mm using an energy ray output power P and an energy ray scanning speed Vs in mm / sec satisfies the following equation (2), and a beam aspect ratio defined using a diameter dl in a direction perpendicular to a beam scanning direction of the energy ray in µm and a diameter dc in the beam scanning direction, and the dl respectively satisfy the following equation (3) and the following equation (4), 250 ≤ Ip ≤ 5200 (1) 0.007 < Up ≤ 0.050 (2) 0.0010 < dl / dc < 1.0000 (3) 0.0010 < dl < 1.0000 (4) 10≤dl＜200 (4)。

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