Grain-oriented electrical steel sheet

Abstract

This grain-oriented electrical steel sheet is provided with: a base steel sheet; a forsterite film formed on the surface of the base steel sheet; and an insulating coating film formed on the surface of the forsterite coating film, the chemical composition of the base steel sheet contains Si in an amount of 0.80-7.00% in mass%, the area ratio of crystal grains having a distance between grain boundaries of the crystal grains in the rolling direction of 3.0-13.0 mm in the surface of the base steel sheet is 70% or more, the magnetic flux density B8 generated by a magnetization force of 800 A / m is 1.88 T or more, and the thickness of the base steel sheet is 10 [mu] m or more. When the sheet thickness is t in unit mm, the frequency is 50 Hz, and the maximum magnetic flux density is 1.7 T, the iron loss W17 / 50 is 13.1 * t2-4.3 * t + 1.2 in unit W / kg or less, and the 200 Hz component LvA200 Hz of the magnetostrictive waveform is 60-78 dBA.

Description

Technical Field

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

[0002] This application claims priority based on Japanese Patent Application No. 2022-151341 filed in Japan on September 22, 2022, and the contents are incorporated herein by reference. Background Art

[0003] In recent years, electromagnetic application equipment such as transformers has been increasingly required to reduce noise and vibration. The directional electromagnetic steel sheets used in the iron core of the transformer are required to be suitable for low iron loss, low noise, and low vibration. As one of the causes of noise and vibration in the transformer, magnetostriction of the directional electromagnetic steel sheet is considered to exist. The magnetostriction mentioned here refers to the vibration observed in the rolling direction of the directional electromagnetic steel sheet caused by a slight change in the shape of the directional electromagnetic steel sheet accompanied by a change in its magnetization intensity when the directional electromagnetic steel sheet is excited by alternating current. The magnitude of this magnetostriction is 10 -6 Although the value is very small on the order of 100 Å, the magnetostriction causes the core to vibrate, which is propagated to external structures such as the transformer case and becomes noise.

[0004] The magnetostrictive properties vary depending on various factors such as the structure and state of the grain-oriented electromagnetic steel sheet, specifically the degree of crystal orientation concentration, the tension applied to the steel sheet by the insulating film, and the strain within the steel. If the magnetostrictive properties change, the noise level changes, and the noise can be reduced in some cases.

[0005] For example, in Patent Document 1, as a directional electromagnetic steel sheet that can reduce noise from components when used as a raw material for electrical components, a directional electromagnetic steel sheet is disclosed, in which the average value DLmax of the length of the grains in the rolling direction is greater than 12 mm, the film tension is less than 1 MPa, the plate thickness is less than 0.35 mm, and the steel sheet is divided into regions that divide the length of the grains in the rolling direction into four equal parts, and for the region near the grain boundary within a distance of 2 mm from the grain boundary of two regions existing on the outside thereof toward the inside of the grain, the absolute value of the intrusion angle of the crystal orientation is set to β, (the area of ​​the region near the grain boundary where β is less than 4.0°) / (the total area of ​​the region near the grain boundary) ≥ 0.50.

[0006] In addition, Patent Document 2 discloses a grain-oriented electromagnetic steel sheet having excellent magnetostrictive properties, which has a component composition comprising 3.0 to 7.0 mass % Si, 0.04 to 0.15 mass % Mn, 0.01 to 0.10 mass % Sb, and 0.01 to 0.20 mass % Sn, with the remainder consisting of Fe and unavoidable impurities, and is a grain-oriented electromagnetic steel sheet coated with an insulating film having a tensile stress of 10 MPa or more in total generated by a forsterite film, wherein the Goss orientation {110} <001> The average misorientation angle δ of the crystal orientation in the grains with the rolling direction as the rotation axis is 6° or less, and the magnetostriction λ when the compressive stress is 3.92 MPa in the rolling direction and magnetization is performed at 50 Hz and 1.7 T is p-p 1.7×10 -6 the following.

[0007] However, the above-mentioned technology cannot be said to be sufficient to improve the iron loss characteristics (reduce the iron loss). In order to reduce the iron loss, it is known that it is effective to control the magnetic domain by irradiating the surface of the grain-oriented electromagnetic steel sheet with laser or the like, but the methods of Patent Documents 1 and 2 cannot be applied to laser-irradiated materials.

[0008] As a technology for reducing iron loss and magnetostriction by laser beam irradiation, Patent Document 3 discloses a method for manufacturing a grain-oriented electromagnetic steel sheet, which comprises: generating a magnetic flux density B8 of the steel sheet at a magnetizing force of 800 A / m to be 1.92 T or more, and aligning the rolling direction and the easy magnetization axis (100) <001> When the thickness direction component of the angle deviation is set as angle β, and the total area of ​​the grains containing both the region with an absolute value of β angle of less than 0.5° and the region with an absolute value of 2° to 6° in the grains is set as the ratio of the total area of ​​the steel plate to Rs, a directional electromagnetic steel sheet with Rs of 30% to 100% is selected, and the surface of the directional electromagnetic steel sheet is irradiated with a laser beam generated by a fiber laser with an optical fiber core diameter of 5μm to 400μm approximately perpendicularly and periodically to the rolling direction of the above-mentioned directional electromagnetic steel sheet, and in a manner that the rolling direction width of the surface irradiation mark of the laser beam or the rolling direction width of the closed magnetic domain formed in the laser irradiation portion becomes 10μm to 200μm, thereby reducing the iron loss compared with before the laser beam irradiation. Patent document 3 shows that according to the above method, a directional electromagnetic steel sheet with extremely low iron loss and magnetostriction can be provided, especially in a directional electromagnetic steel sheet with a high magnetic flux density.

[0009] However, according to the research of the present inventors, it is effective to reduce the 200 Hz component of the magnetostrictive waveform when reducing transformer noise. In the technology of Patent Document 3, the 200 Hz component of the magnetostrictive waveform is not studied, and the characteristics may not be sufficient.

[0010] In addition, Patent Document 4 discloses a novel and improved method for manufacturing a grain-oriented electromagnetic steel sheet and a grain-oriented electromagnetic steel sheet manufactured by the method, wherein the method can manufacture a grain-oriented electromagnetic steel sheet with lower iron loss by rapidly increasing the temperature at a faster heating rate than before in primary recrystallization annealing. Patent Document 4 shows that the magnetic properties of the transformer can be improved and noise can be reduced by the above-mentioned technology.

[0011] However, the 200 Hz component of the magnetostrictive waveform is not studied in Patent Document 4. In addition, Patent Document 4 describes that it is assumed that the noise of the transformer will increase due to the magnetic domain control process.

[0012] Prior art literature

[0013] Patent Literature

[0014] Patent Document 1: Japanese Patent No. 6606991

[0015] Patent Document 2: Japanese Patent No. 5896112

[0016] Patent Document 3: Japanese Patent No. 4616623

[0017] Patent Document 4: International Publication No. 2019 / 181952 Summary of the invention

[0018] Problems to be solved by the invention

[0019] As described above, conventionally, among grain-oriented electrical steel sheets based on the premise of implementing magnetic domain control by laser irradiation for reducing iron loss, there has been no disclosure of a grain-oriented electrical steel sheet that reduces the 200 Hz component of the magnetostrictive waveform associated with transformer noise.

[0020] Therefore, an object of the present invention is to provide a grain-oriented electromagnetic steel sheet having low iron loss and noise, which is suitable for use in a transformer or the like.

[0021] Means for solving problems

[0022] The present inventors have studied the reduction of transformer noise and found that the transformer noise is highly correlated with the 200 Hz component of the magnetostrictive waveform and that the transformer noise can be reduced by reducing the 200 Hz component of the magnetostrictive waveform.

[0023] In addition, if the surface of a grain-oriented electromagnetic steel sheet is irradiated with a laser in order to reduce iron loss, magnetostriction generally increases. That is, there is a trade-off between the reduction of iron loss and the reduction of magnetostriction. Therefore, in the past, when reducing magnetostriction, it was necessary to select conditions that sacrificed the effect of reducing iron loss to some extent and reduced magnetostriction by adjusting irradiation conditions such as the intensity of the laser.

[0024] However, it is difficult to further reduce both the iron loss and the magnetostriction at the same time simply by adjusting the laser irradiation conditions.

[0025] Therefore, the present inventors have studied a method of reducing magnetostriction (particularly, the 200 Hz component of the magnetostriction waveform) without impairing the iron loss by controlling the structure of a grain-oriented electrical steel sheet.

[0026] As a result, it was found that magnetostriction can be reduced without compromising iron loss by controlling the grain size (particularly the distance between grain boundaries in the rolling direction). It was also found that for such grain size control, it is effective to change the curvature of the steel sheet by performing special treatment during coiling.

[0027] The present invention has been accomplished based on the above findings. The gist of the present invention is as follows.

[0028] [1] A grain-oriented electrical steel sheet according to one embodiment of the present invention comprises: a base steel sheet; a forsterite film formed on a surface of the base steel sheet; and an insulating film formed on a surface of the forsterite film, wherein the base steel sheet has a chemical composition containing Si: 0.80 to 7.00% by mass, an area ratio of grains having a distance between grain boundaries of 3.0 mm or more and 13.0 mm or less in a rolling direction on the surface of the base steel sheet is 70% or more, a magnetic flux density B8 generated by a magnetizing force of 800 A / m is 1.88 T or more, and when the plate thickness of the base steel sheet is t in units of mm, an iron loss W17 / 50 in units of W / kg at a frequency of 50 Hz and a maximum magnetic flux density of 1.7 T is 13.1×t 2 Below -4.3×t+1.2, the 200Hz component LvA200Hz of the magnetostrictive waveform is 60~78dBA.

[0029] [2] In the grain-oriented electromagnetic steel sheet described in [1], it is also possible that: a plurality of linear strains extending in a direction intersecting the rolling direction are formed on the surface of the above-mentioned base steel sheet, and the intervals between the above-mentioned plurality of linear strains in the above-mentioned rolling direction are 3 to 10 mm.

[0030] [3] In the directional electromagnetic steel sheet described in [1] or [2], it is also possible that: in the above-mentioned base steel sheet, the area ratio of the elongated closed magnetic domains observed on the above-mentioned surface is less than 10%, and the width of the stripe-shaped main magnetic domain is less than 1.2 mm.

[0031] [4] In the grain-oriented electrical steel sheet described in [1] or [2], the magnetic flux density may be 1.92 T or more, and when the sheet thickness is 0.18 to 0.23 mm, the W17 / 50 may be 0.74 W / kg or less.

[0032] [5] In the grain-oriented electrical steel sheet described in [3], the magnetic flux density may be 1.92 T or more, and when the sheet thickness is 0.18 to 0.23 mm, the W17 / 50 may be 0.74 W / kg or less.

[0033] Effects of the Invention

[0034] According to the above aspects of the present invention, a grain-oriented electromagnetic steel sheet having low iron loss and low noise (excellent iron loss characteristics and noise characteristics) can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is an example of the observed magnetic domain pattern.

[0036] Figure 2 It is a diagram illustrating a closed magnetic domain (lancet).

[0037] Figure 3 It is a figure which shows the example of arrangement|positioning of the spacer placed between steel sheets in the coiling process.

[0038] Figure 4 This is a diagram showing an example of a method of applying an annealing separator in the coiling step. DETAILED DESCRIPTION

[0039] A grain-oriented electrical steel sheet according to one embodiment of the present invention (grain-oriented electrical steel sheet according to the present embodiment) includes a base steel sheet, a forsterite film formed on a surface of the base steel sheet, and an insulating film formed on a surface of the forsterite film.

[0040] In addition, in the grain-oriented electromagnetic steel sheet of the present embodiment, the chemical composition of the base steel sheet contains Si: 0.80-7.00% in mass %, the area ratio of grains in which the distance between grain boundaries of grains in the rolling direction in the surface of the base steel sheet is 3.0 mm or more and 13.0 mm or less is 70% or more, the magnetic flux density B8 generated by the magnetizing force of 800 A / m is 1.88 T or more, and when the plate thickness is t in mm, the iron loss W17 / 50 in W / kg at the frequency of 50 Hz and the maximum magnetic flux density of 1.7 T is 13.1×t 2 Below -4.3×t+1.2, the 200Hz component of the magnetostrictive waveform, i.e., LvA200Hz, is 60 to 78dBA.

[0041] The following will explain each one separately.

[0042] <Base Steel Plate>

[0043] (Chemical Composition)

[0044] Si: 0.80~7.00%

[0045] Si (silicon) is an element that increases the electrical resistance of grain-oriented electromagnetic steel sheets and improves iron loss characteristics. When the Si content is less than 0.80%, sufficient eddy current loss reduction effect cannot be obtained. Therefore, the Si content is set to 0.80% or more. The Si content is preferably 1.00% or more, and more preferably 1.20% or more.

[0046] On the other hand, when the Si content exceeds 7.00%, the steel sheet becomes brittle and may break during rolling. In addition, the workability of the grain-oriented electromagnetic steel sheet decreases. Therefore, the Si content is set to 7.00% or less. The Si content is preferably 6.80% or less, more preferably 6.70% or less, and further preferably 4.00% or less.

[0047] The chemical composition of the base steel sheet included in the grain-oriented electrical steel sheet of the present embodiment only needs to contain 0.80 to 7.00% of Si in terms of mass %, and the contents of other elements are not particularly limited.

[0048] However, according to the characteristics required as a grain-oriented electrical steel sheet, as components (elements) constituting the chemical composition, in addition to Si, the following elements may be contained within the ranges shown below. In this embodiment, % related to the content of each element is mass % unless otherwise specified.

[0049] C: 0.070% or less

[0050] C (carbon) is an element effective for controlling the structure of the steel sheet in the manufacturing process until the decarburization annealing process is completed. However, when the C content exceeds 0.070%, the magnetic properties of the directional electromagnetic steel sheet as a finished plate are reduced. Therefore, in the base steel sheet of the directional electromagnetic steel sheet of the present embodiment, the C content is preferably 0.070% or less. The C content is more preferably 0.050% or less, and further preferably 0.020% or less. The lower the C content, the better, but even if the C content is reduced to less than 0.0001%, the effect of the structure control is saturated, but the manufacturing cost increases. Therefore, the C content may also be 0.0001% or more.

[0051] Mn: 0.01~0.50%

[0052] Mn (manganese) is an element that combines with S to form MnS during the manufacturing process. These precipitates function as inhibitors (inhibitors of normal grain growth) and exhibit secondary recrystallization in steel. Mn is an element that further improves the hot workability of steel. When the Mn content is less than 0.01%, the above-mentioned effect cannot be fully obtained. Therefore, the Mn content is preferably 0.01% or more. The Mn content is more preferably 0.02% or more.

[0053] On the other hand, if the Mn content exceeds 0.50%, secondary recrystallization does not occur, and the magnetic properties of the steel are reduced. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet of the present 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.

[0054] N: 0.0100% or less

[0055] N (nitrogen) is an element that combines with Al in the manufacturing process to form AlN that functions as an inhibitor. When the N content exceeds 0.0100%, an excessive amount of inhibitor remains in the grain-oriented electrical steel sheet, and the magnetic properties are reduced. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet of the present embodiment, the N content is preferably 0.0100% or less. The N content is more preferably 0.0080% or less.

[0056] On the other hand, the lower limit of the N content is not particularly specified, but even if the N content is reduced to less than 0.0010%, the manufacturing cost will only increase. Therefore, the N content may be 0.0010% or more.

[0057] sol.Al: 0.030% or less

[0058] Sol.Al (acid-soluble aluminum) is an element that combines with N to form AlN that functions as an inhibitor during the manufacturing process of the grain-oriented electrical steel sheet. However, when the sol.Al content of the base steel sheet exceeds 0.030%, an excessive amount of inhibitor remains in the base steel sheet, and the magnetic properties are reduced. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet of the present embodiment, the sol.Al content is preferably 0.030% or less. The sol.Al content is more preferably 0.020% or less, and even more preferably 0.015% or less. There is no particular lower limit for the sol.Al content, but even if it is reduced to less than 0.0001%, it only increases the manufacturing cost. Therefore, the sol.Al content can be 0.0001% or more.

[0059] S: 0.010% or less

[0060] S (sulfur) is an element that combines with Mn in the manufacturing process to form MnS that functions as an inhibitor. However, when the S content exceeds 0.010%, the magnetic properties are reduced due to the residual inhibitor. Therefore, in the base steel plate of the directional electromagnetic steel sheet of the present embodiment, the S content is preferably 0.010% or less. The S content in the directional electromagnetic steel sheet is preferably as low as possible. For example, less than 0.001%. However, even if the S content in the directional electromagnetic steel sheet is reduced to less than 0.0001%, the manufacturing cost will only increase. Therefore, the S content in the directional electromagnetic steel sheet can be 0.0001% or more.

[0061] The rest: Fe and impurities

[0062] The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet of the present embodiment may contain the above-mentioned elements, and the remainder may be Fe and impurities. However, for the purpose of improving magnetic properties, P, Cr, Sn, Cu, Se, Sb, and Mo may be contained within the range shown below (since they may not be contained, the lower limit is 0%). In addition, as elements other than these, even if any one or two or more of W, Nb, Ti, Ni, Bi, Co, and V are contained in a total of 1.0% or less, the effect of the grain-oriented electrical steel sheet of the present embodiment is not hindered.

[0063] Here, impurities refer to elements that are mixed from raw materials such as ores and scraps or from the manufacturing environment when the base steel sheet is industrially manufactured, and are allowed to be contained in a content that does not adversely affect the function of the grain-oriented electrical steel sheet of the present embodiment.

[0064] P: 0~0.030%

[0065] 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 in rolling workability and to suppress fracture during manufacturing. From this point of view, 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.

[0066] There is no lower limit for the P content, and the P content can be 0%, but in practical steel plates, the actual lower limit of the P content is 0.0001%. In addition, P is also an element that has the effect of improving texture and magnetic properties. In order to obtain this effect, the P content can be set to 0.001% or more, or it can be set to 0.005% or more.

[0067] Cr: 0~0.50%

[0068] Cr (chromium) is an element that contributes to an increase in the Goss orientation occupancy in the secondary recrystallization structure and improves magnetic properties. To obtain the above-mentioned effect, the Cr content is preferably 0.01% or more, more preferably 0.05% or more, and even more preferably 0.10% or more.

[0069] On the other hand, when the Cr content exceeds 0.50%, Cr oxides are formed and the magnetic properties are degraded. Therefore, the Cr content is preferably 0.50% or less. The Cr content is more preferably 0.30% or less, and even more preferably 0.15% or less.

[0070] Sn: 0~0.50%

[0071] Sn (tin) is an element that contributes to the improvement of magnetic properties by controlling the primary recrystallization structure. In order to obtain the effect of improving magnetic properties, the Sn content is preferably set to 0.01% or more. The Sn content is more preferably 0.02% or more, and further preferably 0.03% or more.

[0072] On the other hand, when 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 further preferably 0.10% or less.

[0073] Cu: 0~0.50%

[0074] Cu (copper) is an element that helps increase the Goss orientation occupancy in the secondary recrystallization structure. Cu is an optional element in the base steel sheet of the grain-oriented electrical steel sheet of this embodiment. Therefore, the lower limit of its content is 0%, but in order to obtain the above-mentioned effect, it is preferred that the Cu content is set to 0.01% or more. The Cu content is more preferably 0.02% or more, and further preferably 0.03% or more.

[0075] On the other hand, when the Cu content exceeds 0.50%, the steel sheet becomes brittle during hot rolling. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet of the present 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.

[0076] Se: 0~0.020%

[0077] Se (selenium) is an element that has the effect of improving magnetic properties. Therefore, it can also be contained. In the case of containing Se, in order to exert the effect of improving magnetic properties well, it is preferred to set the content to 0.001% or more. The Se content is more preferably 0.003% or more, and further preferably 0.006% or more.

[0078] On the other hand, when the Se content exceeds 0.020%, the adhesion of the forsterite film deteriorates. Therefore, the Se content is preferably set to 0.020% or less. The Se content is more preferably set to 0.015% or less, and further preferably set to 0.010% or less.

[0079] Sb: 0~0.50%

[0080] Sb (antimony) is an element that has the effect of improving magnetic properties. Therefore, it can also be contained. In the case of containing Sb, in order to exert the effect of improving magnetic properties well, it is preferred that the content is set to 0.005% or more. The Sb content is more preferably 0.01% or more, and further preferably 0.02% or more.

[0081] On the other hand, when the Sb content exceeds 0.50%, the adhesion of the forsterite 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 even more preferably 0.10% or less.

[0082] Mo: 0~0.10%

[0083] Mo (molybdenum) is an element that has the effect of improving magnetic properties. Therefore, it may also be contained. When Mo is contained, in order to exert the effect of improving magnetic properties well, it is preferred that the Mo content is set to 0.01% or more. The Mo content is more preferably 0.02% or more, and further preferably 0.03% or more.

[0084] 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 set to 0.10% or less. The Mo content is more preferably set to 0.08% or less, and further preferably set to 0.05% or less.

[0085] As described above, the chemical composition of the base material steel sheet of the grain-oriented electrical steel sheet of the present embodiment may be exemplified as containing the above-mentioned C, Si, Mn, N, sol.Al, and S, with the remainder being Fe and impurities, or containing the elements of C, Si, Mn, N, sol.Al, and S, and further containing one or more of P, Cr, Sn, Cu, Se, Sb, Mo, W, Nb, Ti, Ni, Bi, Co, and V, with the remainder being Fe and impurities. The total content of the above-mentioned elements W to V may be 0.05% or less.

[0086] The Si content in the chemical composition of the base steel sheet of the grain-oriented electrical steel sheet of the present embodiment is determined by the method (silicon quantitative method) specified in JIS G 1212 (1997). Specifically, when the above-mentioned chips are dissolved in acid, silicon oxide precipitates as a precipitate, so the precipitate (silicon oxide) is filtered out with filter paper, and the mass is measured to determine the Si content.

[0087] The chemical composition of the other base steel plates can be obtained by a known component analysis method. Specifically, a drill is used to generate chips from the base steel plate, the chips are collected, and the collected chips are dissolved in an acid to obtain a solution. The solution is subjected to ICP-AES to perform elemental analysis of the chemical composition.

[0088] However, for elements that are difficult to measure by ICP-AES, such as C content and S content, they can be obtained by a known high-frequency combustion method (combustion-infrared absorption method). Specifically, the above solution can be burned by high-frequency heating in an oxygen flow, and the generated carbon dioxide and sulfur dioxide can be detected to obtain C content and S content. In addition, regarding N content, it can be obtained using a known inert gas melting-thermal conductivity method.

[0089] In the grain-oriented electrical steel sheet of the present embodiment, when a forsterite film and / or an insulating film is formed on the surface, the chemical composition of the base steel sheet is measured after removing these films.

[0090] The insulating film can be 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.

[0091] In addition, the grain-oriented electrical steel sheet from which the insulating film has been removed is washed with water, and then dried with a hot air blower for less than 1 minute. The forsterite film can be removed by immersing the dried grain-oriented electrical steel sheet (grain-oriented electrical steel sheet without the insulating film) in a hydrochloric acid aqueous solution containing 30 to 40 mass % HCl at 80 to 90° C. for 1 to 10 minutes.

[0092] The base steel sheet after immersion is washed with water and then dried with a hot air blower for less than 1 minute, thereby making it possible to take out the base steel sheet from the grain-oriented electrical steel sheet having the forsterite film and the insulating film.

[0093] (Microstructure)

[0094] The grain-oriented electrical steel sheet of the present embodiment has a controlled grain size in the rolling direction in its microstructure. Specifically, the area ratio of grains having a distance between grain boundaries of 3.0 mm or more and 13.0 mm or less in the rolling direction on the surface of the base steel sheet is 70% or more.

[0095] The grain boundaries that cross the rolling direction change the magnetic domain pattern. In particular, if the distance between the grain boundaries becomes shorter, the 200Hz component (sometimes referred to as LvA200Hz) of the magnetostrictive waveform decreases. This can be inferred that if the distance between the grain boundaries becomes shorter, the width of the main magnetic domain becomes narrower, thus having an effect of suppressing the closed magnetic domain (lancet) within the grain.

[0096] When the area ratio of the grains whose inter-grain boundary distance (grain boundary spacing) of the grains in the rolling direction is 3.0 mm or more and 13.0 mm or less is less than 70%, the effect of reducing LvA200Hz cannot be fully obtained. The area ratio of the grains whose inter-grain boundary spacing is 3.0 mm or more and 13.0 mm or less is preferably 75% or more, more preferably 80% or more, and further preferably 90% or more. The upper limit of the area ratio is not limited and can be 100%.

[0097] The grains whose area ratio is controlled are grains (regions) whose distance between grain boundaries is more than 3.0 mm and less than 13.0 mm because, in grains whose grain boundary spacing exceeds 13.0 mm, the magnetic domain wall spacing will not be sufficiently narrowed, and the effect of reducing LvA200 Hz is small. On the other hand, from the viewpoint of reducing LvA200 Hz, it is preferred that the grain boundary spacing is short, but the grains whose grain boundary spacing is less than 3.0 mm will hinder the movement of the magnetic domain wall, thereby possibly deteriorating the iron loss characteristics.

[0098] Figure 1 An example of a magnetic domain pattern observed in the grain-oriented electrical steel sheet according to the present embodiment is shown in FIG.

[0099] In order to obtain the above-mentioned microstructure, there is a method of irradiating the laser in a manner that the laser scanning direction is transverse to the rolling direction relative to the rolling direction of the base steel plate, but it is preferable to irradiate in a manner that does not generate fine grains on the irradiation mark. By not generating fine grains, the generation of grains whose distance between grain boundaries in the rolling direction of the surface of the base steel plate is less than 3.0 mm can be suppressed.

[0100] The average grain size in the rolling direction is preferably 3.0 to 20.0 mm.

[0101] If the average grain size is small, it is difficult to set the area ratio of grains having a distance between grain boundaries (grain boundary spacing) of 3.0 mm or more and 13.0 mm or less in the rolling direction to 70% or more, and the movement of the magnetic domain wall is hindered, so that the iron loss characteristics may be deteriorated. On the other hand, if the average grain size exceeds 20.0 mm, it is difficult to set the area ratio of grains having a distance between grain boundaries of 3.0 mm or more and 13.0 mm or less to 70% or more, and there is a concern that the noise may become larger.

[0102] The area ratio of crystal grains in which the distance between the grain boundaries of the crystal grains in the rolling direction is 3.0 mm or more and 13.0 mm or less can be obtained by the following method.

[0103] First, the distance between grain boundaries in the rolling direction is measured by observing the magnetic domains on the surface of the grain-oriented electromagnetic steel sheet using an element for observing magnetic domains. Specifically, the surface of the grain-oriented electromagnetic steel sheet is observed using a reflection electron microscope or an MO sensor using the Faraday effect to obtain an image, and the grain boundaries are determined by the direction, spacing, and contrast discontinuity of the magnetic domain walls based on the image, and the distance between the grain boundaries in the rolling direction is measured to obtain the distance.

[0104] The area ratio of the grains with a predetermined grain boundary spacing is obtained by taking an area of ​​100 mm in the width direction of the surface and 500 mm in the rolling direction as the observation range, and dividing the area of ​​the grains with a grain boundary spacing of 3.0 mm or more and 13.0 mm or less in the rolling direction by the area of ​​the measurement region in the observation range (×100 when set as a percentage). At this time, it is also possible to use a scale along the rolling direction to determine the grains that deviate from 3.0 mm or more and 13.0 mm or less, measure their areas, and subtract the area from the area of ​​the measurement region, thereby measuring the area of ​​the grains of the object (grains with a grain boundary spacing of 3.0 mm or more and 13.0 mm or less in the rolling direction).

[0105] In the above measurement, a 500 mm straight line is drawn from one end to the other end of the observation range in the rolling direction, and the number of grain boundaries intersecting the straight line is divided by the length of the straight line to measure the average grain size in the rolling direction.

[0106] The surface of the base steel plate is used to measure the area ratio. According to the above method, the measurement can be performed even if a forsterite film and an insulating film are formed on the base steel plate. Therefore, the forsterite film and the insulating film do not need to be removed during the measurement, but the measurement can be performed after removal.

[0107] In the grain-oriented electromagnetic steel sheet of this embodiment, Figure 2As shown, among the magnetic domains observed on the surface of the base steel plate, there are relatively short strip-shaped closed magnetic domains (lancets) 100 in the main magnetic domain. In the directional electromagnetic steel sheet of this embodiment, it is preferred that the area ratio of the closed magnetic domain (lancet) 100 is set to less than 10% of the whole. If the area ratio of the closed magnetic domain 100 exceeds 10%, it is difficult to obtain the specified magnetic flux density and iron loss. The lower limit of the area ratio is not limited and can be 0%.

[0108] In addition, in the directional electromagnetic steel sheet of the present embodiment, it is preferred that the width of the main magnetic domain observed on the surface as divided into stripes is less than 1.2 mm. If the width exceeds this value and becomes wider, it is easy to produce lancet 100, and it is difficult to obtain the specified magnetic flux density and iron loss. More preferably, the width of the main magnetic domain is less than 1.0 mm, and more preferably less than 0.9 mm. The width of the main magnetic domain is affected by the average grain size in the rolling direction, the intensity of the strain caused by the difference in the laser irradiation conditions, the curvature in the coil state, etc.

[0109] For the area ratio of the closed magnetic domain and the width of the main magnetic domain, the range of 100mm in the width direction and 500mm in the rolling direction of the surface of the parent steel plate is measured by a measuring device such as CMOS-MagView that utilizes the magneto-optical effect. According to this method, even electromagnetic steel plates with films can be observed for magnetic domains. Then, based on the obtained image, the area of ​​the steel plate surface of the lancet is measured to evaluate its existence ratio relative to the whole, or to measure the width of the main magnetic domain. However, the observation is carried out in a demagnetized state.

[0110] (magnetic properties)

[0111] The grain-oriented electromagnetic steel sheet of this embodiment has excellent magnetic properties by controlling the magnetic domains through laser irradiation. Specifically, the magnetic flux density B8 generated by the magnetizing force of 800 A / m is 1.88 T or more, and when the plate thickness of the base steel plate is t in mm, the iron loss W17 / 50 in W / kg at the frequency of 50 Hz and the maximum magnetic flux density of 1.7 T is 13.1×t 2 -4.3×t+1.2 or less. B8 is less than 1.88T, or W17 / 50 is greater than 13.1×t 2 At -4.3×t+1.2W / kg, it cannot be said that the magnetic properties are sufficient.

[0112] The higher B8 is, the more preferable it is. However, if the area of ​​the crystal grain is to be increased, the actual upper limit is about 1.95T, so B8 may be set to 1.95T or less.

[0113] In addition, the plate thickness t is the nominal thickness. If t=0.23 mm, W17 / 50 is 0.90 W / kg or less.

[0114] B8 and W17 / 50 are achieved by controlling the texture, magnetic domain and other fine regions by controlling the manufacturing method including laser irradiation, but there are many factors that change the magnetic properties, and it is not easy to measure. Therefore, the grain-oriented electrical steel sheet of this embodiment is defined by the values ​​of B8 and W17 / 50.

[0115] As for magnetic properties, B8 is preferably 1.92 T or more. In addition, as for iron loss, W17 / 50 is preferably 0.74 W / kg or less when the plate thickness (t) is in the range of 0.18 to 0.23 mm.

[0116] For B8 and W17 / 50, test pieces having a size of 100 mm in the width direction and 500 mm in the rolling direction were cut out from grain-oriented electrical steel sheets and measured by a single sheet magnetic property measurement method (Single Sheet Tester: SST) in accordance with JIS C 2556:2015.

[0117] (Noise characteristics)

[0118] The 200Hz component of the magnetostrictive waveform of the directional electromagnetic steel sheet of this embodiment, i.e., LvA200Hz, is 60 to 78dBA. As a result, when used as a material for a transformer, the noise of the transformer can be reduced. When LvA200Hz exceeds 78dB, the noise reduction effect is small. On the other hand, it is not easy to make LvA200Hz less than 60dBA while ensuring the prescribed magnetic properties, so LvA200Hz is set to 60dBA or more.

[0119] LvA200 Hz is determined by measuring the expansion and contraction of a steel plate using a vibration measuring instrument using laser Doppler in accordance with IEC standard IEC 606404-17ED1.

[0120] During the measurement, a 50 Hz magnetic field was applied from the outside to cause expansion and contraction of the steel sheet. After obtaining the expansion and contraction of the length with respect to time as a magnetostrictive waveform, the waveform was subjected to frequency analysis and separated into 100 Hz and 200 Hz components for evaluation.

[0121] As a result of magnetic domain control, the grain-oriented electrical steel sheet of the present embodiment has the above-mentioned B8 and W17 / 50, and LvA200Hz is 60 to 78 dBA. That is, the grain-oriented electrical steel sheet of the present embodiment is a magnetic domain controlled material.

[0122] There is no limitation on the method of controlling the magnetic domains. For example, it is preferred to control the magnetic domains by laser irradiation under the conditions described below. In this case, a plurality of linear strains extending in a direction intersecting the rolling direction are formed on the surface of the base steel plate, and the intervals in the rolling direction of the plurality of linear strains are 3 to 10 mm. Therefore, the intervals in the rolling direction of the plurality of linear strains are preferably 3 to 10 mm.

[0123] The interval between linear strains in the rolling direction refers to the distance in the rolling direction from the center of a linear strain in the width direction to the center of an adjacent linear strain in the width direction.

[0124] In addition, from the viewpoint of contributing to the improvement of iron loss characteristics, the width of the linear strain in the rolling direction is preferably 250 μm or less. The linear shape includes a straight line shape which is a continuous line shape and a dotted line shape which is a discontinuous line shape.

[0125] The presence of linear strain can be analyzed using residual strain measurement technology based on X-ray diffraction (e.g. K. Iwata, et al, j. Appl. Phys. 117.17A910 (2015)). In addition, if energy line irradiation marks can be confirmed on the surface of the steel plate, the irradiation marks can also be directly judged as strain.

[0126] In addition, for the observed linear strain, a certain distance L of at least L>5mm can be set in the rolling direction, the number of strain roots n present therein is counted, and L / n is used as the interval of the linear strain in the rolling direction. The width of the linear strain in the rolling direction is the value obtained by averaging the widths of the n roots measured.

[0127] (plate thickness)

[0128] The plate thickness of the base steel plate of the grain-oriented electromagnetic steel plate of the present embodiment is not limited, but is preferably 0.17 to 0.30 mm in consideration of application to an iron core of a transformer requiring low iron loss and low noise.

[0129] The thinner the plate thickness, the more the eddy current loss can be reduced, and good iron loss can be obtained, so the upper limit of the preferred plate thickness of the base steel plate is 0.30 mm. On the other hand, in order to manufacture a base steel plate below 0.17 mm, special equipment is required, and the manufacturing cost increases, which is not preferred in terms of production. Therefore, the lower limit of the industrially preferred plate thickness is 0.17 mm. Preferably, it is 0.18 to 0.23 mm.

[0130] <Forsterite film>

[0131] The grain-oriented electrical steel sheet of the present embodiment has a forsterite film (sometimes also referred to as a glass film) formed on the surface of the base steel sheet. The forsterite film may be any known film. Generally, it is an inorganic film mainly composed of magnesium silicate.

[0132] The forsterite film is formed by the reaction of an annealing separator containing magnesium oxide (MgO) applied to the surface of the base steel plate during the final annealing with the components on the surface of the base steel plate, and has a composition derived from the annealing separator and the components of the base steel plate, and is formed by a structure containing (50 area % or more) Mg2SiO4 phase and MgAl2O4 phase as the main phase. In addition to these phases, precipitates of about 1% or less are sometimes contained.

[0133] <Insulation film>

[0134] In the grain-oriented electrical steel sheet of the present embodiment, an insulating film (tension-applying insulating film) is formed on the surface of the forsterite film. The insulating film may be any known film used in the technical field.

[0135] The insulating film reduces eddy current loss by imparting electrical insulation to the oriented electromagnetic steel sheet, thereby improving the iron loss characteristics of the oriented electromagnetic steel sheet (reducing iron loss). In addition, according to the insulating film, in addition to the electrical insulation as described above, various characteristics such as corrosion resistance, heat resistance, and sliding properties can also be obtained. Furthermore, the insulating film has the function of imparting tension to the oriented electromagnetic steel sheet. By imparting tension to the oriented electromagnetic steel sheet, the movement of the magnetic domain wall in the oriented electromagnetic steel sheet becomes easier, and the iron loss of the oriented electromagnetic steel sheet can be reduced (improving the iron loss characteristics). The insulating film is formed, for example, by applying a coating liquid mainly composed of metal phosphate and silicon dioxide to the surface of the forsterite film and baking it.

[0136] <Manufacturing method>

[0137] The grain-oriented electrical steel sheet of the present embodiment can be produced by a production method including the following steps.

[0138] (i) A hot rolling process of hot-rolling a steel slab having a predetermined chemical composition to obtain a hot-rolled sheet (hot-rolled steel sheet)

[0139] (ii) a cold rolling step of cold-rolling the hot-rolled sheet to obtain a cold-rolled sheet (cold-rolled steel sheet);

[0140] (iii) a decarburization annealing step of decarburizing the cold rolled sheet

[0141] (iv) a final annealing step of applying an annealing separator containing MgO to the cold rolled sheet after the decarburization annealing step, and then winding the sheet into a coil and performing a final annealing step.

[0142] (v) an insulating film forming step of forming an insulating film on the surface of the cold-rolled sheet after the final annealing to obtain a grain-oriented electrical steel sheet

[0143] (vi) a laser irradiation step of irradiating the grain-oriented electrical steel sheet having the insulating film with laser light

[0144] Furthermore, the method for producing the grain-oriented electrical steel sheet according to the present embodiment may further include the following steps.

[0145] (I) Hot rolled sheet annealing step of annealing the hot rolled sheet

[0146] (II) Nitriding treatment step for increasing the nitrogen content of the cold-rolled sheet

[0147] The method for producing a grain-oriented electrical steel sheet according to the present embodiment is characterized by the above-mentioned (iv) final annealing step and (vi) laser irradiation step. Preferred conditions in these steps are described below. In other steps, known conditions for producing a grain-oriented electrical steel sheet can be applied.

[0148] Each process is described.

[0149] (Hot rolling process)

[0150] In the hot rolling process, a steel slab or other steel billet is heated and then hot rolled to obtain a hot rolled sheet. The heating temperature of the steel billet is not particularly limited, but is preferably within a range of 1100 to 1450°C.

[0151] The hot rolling conditions are not particularly limited and may be appropriately set based on the required properties. The thickness of the hot-rolled sheet obtained by hot rolling is preferably within a range of 2.0 to 3.0 mm, for example.

[0152] The chemical composition of the steel slab may be set within a preferred range in order to obtain the chemical composition of the above-mentioned base steel plate in consideration of the manufacturing steps after the hot rolling step (in consideration of changes in the chemical composition in each step).

[0153] (Hot rolled sheet annealing process)

[0154] The hot rolled sheet annealing process is a process for annealing the hot rolled sheet manufactured by the hot rolling process. By performing such an annealing treatment, recrystallization occurs in the steel sheet structure, and good magnetic properties can be achieved. Therefore, it can also be performed.

[0155] When annealing the hot-rolled sheet, the hot-rolled sheet manufactured by the hot rolling process can be annealed according to a known method. There is no particular limitation on the annealing conditions. For example, the hot-rolled sheet can be annealed in a temperature range of 900 to 1200°C for 10 seconds to 5 minutes. There is no particular limitation on the means for heating the hot-rolled sheet during annealing. A known heating method can be used. It can also be set as a two-stage annealing in which the annealing temperature is changed midway.

[0156] (Cold rolling process)

[0157] In the cold rolling process, the hot rolled sheet after the hot rolled sheet annealing process is subjected to cold rolling including multiple passes to obtain a cold rolled sheet. The cold rolling may be a single cold rolling (a series of cold rolling without intermediate annealing), or the cold rolling may be interrupted before the final pass of the cold rolling process, and intermediate annealing may be performed at least once or twice, or multiple cold rollings may be performed with intermediate annealing.

[0158] When performing intermediate annealing, it is preferably maintained at a temperature of 1000 to 1200° C. for 5 to 180 seconds. The annealing atmosphere is not particularly limited. In consideration of the manufacturing cost, the number of intermediate annealing is preferably within 3 times.

[0159] In the cold rolling process, the hot rolled sheet is cold rolled according to a known method to obtain a cold rolled sheet. For example, the final reduction ratio can be set within the range of 80 to 95%. By setting the final reduction ratio to 80 to 95%, {110} <001> The orientation has a high concentration of Goss nuclei in the rolling direction and can suppress the destabilization of the secondary recrystallization.

[0160] The final reduction ratio refers to the cumulative reduction ratio of cold rolling, and when intermediate annealing is performed, it refers to the cumulative reduction ratio of cold rolling after the final intermediate annealing.

[0161] In addition, before the cold rolling step, the surface of the hot-rolled sheet may be pickled under known conditions.

[0162] (Decarburization annealing process)

[0163] In the decarburization annealing process, the cold rolled sheet is subjected to decarburization annealing. In the decarburization annealing, the cold rolled sheet is subjected to primary recrystallization, and the C that will cause adverse effects on magnetic properties is removed from the steel sheet. In addition, in the decarburization annealing process, in order to make the secondary recrystallization grains obtained during the final annealing described later become fine, the Goss nucleus is increased. If it is considered that the grain boundary itself has the function as a magnetic pole (the generation site of leakage flux), then by the refinement of the secondary recrystallization grains, the static magnetoelectric energy of the system as a whole is improved. That is, the driving force of the magnetic domain segmentation becomes high.

[0164] The conditions for decarburization annealing can be within a known range, and for example, the conditions of maintaining the annealing temperature at 750 to 900°C for 10 to 600 seconds in a wet hydrogen and nitrogen atmosphere can be exemplified. In terms of the control of the average grain size taking into account the balance between iron loss and noise, the decarburization annealing temperature is most suitable at about 835 to 845°C.

[0165] (Nitriding process)

[0166] In the nitriding step, the nitrogen content of the steel sheet is increased. The nitriding step may be performed at any one or more times during the decarburization annealing step, between the decarburization annealing step and the final annealing step, or during the temperature increase process of the final annealing step until the start of secondary recrystallization.

[0167] Examples of methods for increasing the nitrogen content of a steel sheet include: a method of controlling the nitrogen content of the steel sheet by annealing in an atmosphere containing a gas having nitriding ability; and a method of adding a powder having nitriding ability such as MnN to an annealing separator during the temperature rise process of the final annealing step.

[0168] (Final annealing process)

[0169] In the final annealing step, a predetermined annealing separator is applied to one or both sides of the cold-rolled sheet obtained in the decarburization annealing step or further subjected to nitriding treatment, and then the sheet is wound into a coil and subjected to final annealing.

[0170] When manufacturing the grain-oriented electrical steel sheet of this embodiment, a certain curvature is given to the steel sheet (steel strip) when coiling it into a coil, thereby controlling the distance between grain boundaries in the rolling direction and increasing the area ratio of grains with a distance between grain boundaries of 3.0 to 13.0 mm.

[0171] There are the following two methods for imparting curvature.

[0172] (a) When coiling, spacers are placed between the steel sheets.

[0173] (b) The coating amount of the annealing separator is periodically changed.

[0174] (a) and (b) are described below.

[0175] Even if (a) or (b) is not performed, the steel sheet is given a curvature when it is made into a coil. In addition, a larger curvature is given to the inner side of the coil than to the outer side. However, in the conventional coiling, even on the inner side of the coil with a relatively large curvature, it is not possible to give the steel sheet a sufficient curvature to obtain the grain-oriented electromagnetic steel sheet of the present embodiment.

[0176] (a) Place spacers between steel plates

[0177] In this method, if Figure 3 As shown, when a steel sheet 1 is coiled into a coil, ceramic round rods are periodically inserted perpendicularly to the coiling direction as spacers 2, so that the curvature of the steel sheet changes periodically. The steel sheet is bent in a manner that the spacers 2 adjacent to the steel sheet in the rolling direction are alternately contacted with the front, back, front, back, etc., thereby imparting curvature.

[0178] If the curvature is small, the area ratio of the grains with a distance between grain boundaries of 3.0 to 13.0 mm cannot be sufficiently increased. On the other hand, if the curvature is too large, the preferred crystal orientation cannot be obtained, and the magnetic properties deteriorate. In order to obtain the specified curvature, the diameter (φ) of the spacer 2 (ceramic round rod) is set to 3 to 20 mm, and the distance (φ) of the spacer 2 relative to the rolling direction of the steel plate 1 is set to 1.25 mm. Figure 3 (L1 in the figure) is set to 15~100mm.

[0179] (b) Periodically changing the amount of annealing separator applied

[0180] In this method, Figure 4 As shown, by changing the coating amount (thickness) of the annealing separator 3, the steel sheet is made to have a corrugated shape along the rolling direction.

[0181] In order to impart a certain curvature, the steel sheet 1 is rolled at a period of 15 to 100 mm ( Figure 4 L2 in the middle), wave height ( Figure 4 In h), the annealing separator 3 is applied (arranged) in a manner varying by 3 to 20 mm.

[0182] An annealing separator is applied to the cold-rolled sheet for the purpose of preventing adhesion between the inside and outside of the coil and forming a forsterite film.

[0183] In the method for manufacturing the grain-oriented electrical steel sheet of the present embodiment, an annealing separator having MgO as the main component (e.g., containing 80% by mass or more) is used as the annealing separator to be applied. By using an annealing separator having MgO as the main component, a forsterite film can be formed on the surface of the base steel sheet. In the case where MgO is not the main component, a primary film (forsterite film) cannot be formed. This is because the forsterite film is a Mg2SiO4 or MgAl2O4 compound and lacks the Mg required for the formation reaction.

[0184] The annealing separator may further contain TiO 2. By containing TiO 2, the effect of suppressing the formation of the glass film can be obtained. The content of TiO 2 is, for example, 0 to 10% by mass.

[0185] The annealing separator can be mixed with water to form a slurry and applied to the steel plate.

[0186] After being wound into a coil, final annealing is performed, for example, in an atmosphere containing hydrogen and nitrogen, by raising the temperature to 1150 to 1250° C. and maintaining the temperature in this range for 10 to 60 hours.

[0187] (Insulation film forming process)

[0188] In the insulating film forming step, an insulating film (tension-applying insulating film) is formed on one or both sides of the cold-rolled sheet after final annealing. The conditions for forming the insulating film are not particularly limited, and a known insulating film treatment liquid may be used, and the treatment liquid may be applied and dried by a known method. By forming an insulating film on the surface of the steel sheet, the magnetic properties of the grain-oriented electrical steel sheet can be further improved.

[0189] The surface of the steel sheet on which the insulating film is formed may be a surface that has been subjected to any pretreatment such as degreasing with alkali or pickling with hydrochloric acid, sulfuric acid, phosphoric acid, etc. before applying the treatment liquid, or may be a surface that has been subjected to final annealing without undergoing such pretreatment.

[0190] The insulating film formed on the surface of the steel plate is not particularly limited as long as it can be used as an insulating film of a grain-oriented electromagnetic steel plate, and a known insulating film can be used. As such an insulating film, for example, a film with phosphate and colloidal silica as the main components can be cited. In addition, a composite insulating film with an inorganic substance as the main component and also containing an organic substance can be cited. Here, the composite insulating film is, for example, an insulating film with at least one of inorganic substances such as metal chromate, metal phosphate or colloidal silica, Zr compound, Ti compound as the main component, and fine organic resin particles dispersed therein. In particular, from the perspective of reducing the environmental load during manufacturing, which has been in increasing demand in recent years, an insulating film using a metal phosphate, a coupling agent of Zr or Ti, or their carbonates and ammonium salts as the starting material is sometimes used.

[0191] (Laser irradiation process)

[0192] In the laser irradiation step, the grain-oriented electromagnetic steel sheet on which the insulating film is formed is irradiated with a laser beam to perform magnetic domain control, thereby improving the magnetic properties.

[0193] As the laser irradiation conditions, for example, the laser input energy Ua is set to 1.0 to 4.0 mJ / mm 2 , set the laser power density Ip to 500~4000W / mm 2In addition, the laser beam is irradiated in a manner extending in a direction intersecting the rolling direction (for example, a direction of 60 to 120 degrees relative to the rolling direction) (preferably from one end of the steel plate in the width direction to the other end), and irradiated multiple times (preferably over the entire length of the steel plate) in a manner such that the interval PL in the rolling direction is 3 to 10 mm and the respective irradiation directions are approximately parallel.

[0194] When Ua is less than 1.0mJ / mm 2 Or Ip is less than 500W / mm 2 On the other hand, when Ua exceeds 4.0 mJ / mm 2 Or Ip exceeds 4000W / mm 2 When the noise characteristics are deteriorated. This is believed to be due to the generation of a large number of closed magnetic domains. Ip is preferably 2000W / mm 2 the following.

[0195] Example

[0196] Hereinafter, the grain-oriented electrical steel sheet of the present invention will be specifically described by way of examples. The examples described below are merely examples, and the grain-oriented electrical steel sheet of the present invention is not limited to the examples described below.

[0197] <Example 1>

[0198] A steel billet containing C: 0.055%, Si: 0.86-3.15%, Mn: 0.14%, S: 0.007%, sol.Al: 0.027%, Cr: 0.12%, N: 0.0075% and the remainder containing Fe and impurities is heated to 1150°C and then hot-rolled to produce a hot-rolled plate with a thickness of 2.3 mm.

[0199] Next, the hot-rolled sheet was subjected to hot-rolled sheet annealing. In the hot-rolled sheet annealing, the sheet was heated to 1120°C and maintained for 180 seconds, then cooled to 900°C and maintained at the same temperature for 120 seconds, and then rapidly cooled using 100°C hot water.

[0200] Then, after pickling, the steel sheet was cold-rolled to obtain a cold-rolled sheet with a thickness of 0.23 mm.

[0201] Next, the cold-rolled sheet (steel sheet) was subjected to decarburization annealing in which the sheet was heated to the temperature listed in Table 1 in a wet hydrogen and nitrogen atmosphere and held for 150 seconds.

[0202] After decarburization annealing, the cold-rolled sheet was heated to 750° C. in an atmosphere composed of N2: 25% and H2: 75% to which NH3 was added, and maintained at this temperature for 30 seconds, thereby performing a nitriding treatment to increase the N content of the steel sheet to 180 ppm.

[0203] After the nitriding treatment, a known annealing separator containing MgO and TiO2 as the main components and Na, B, Cl, etc. is applied, and a final annealing is performed at 1200°C for 20 hours. At this time, the steel sheets are made into a corrugated shape by arranging the spacers between the steel sheets at a certain interval, and the steel sheets are coiled into a coil shape, and then the final annealing is performed. The diameter of the spacer (ceramic rod) and the interval of the arrangement are shown in Table 1. After the final annealing, a forsterite film is formed on the surface.

[0204] After the final annealing, a coating liquid mainly composed of chromic anhydride and aluminum phosphate is applied to the surface of the steel sheet (a steel sheet having a forsterite film formed on the surface of the base steel sheet) and baked annealing is performed to form an insulating film.

[0205] Then, the surface of the steel sheet with the insulating film formed thereon was irradiated with a laser beam to perform magnetic domain segmentation (magnetic domain control). At this time, the laser input energy and laser power density are shown in Table 1. The scanning direction of the laser beam (the extension direction of the irradiation mark) was 90° relative to the rolling direction, and the interval in the rolling direction of adjacent laser beam irradiation positions (the interval in the rolling direction of multiple linear strains) was 4 mm.

[0206] For the steel plate after magnetic domain control (directional electromagnetic steel plate), the chemical composition, the ratio of grains with a distance between grain boundaries in the rolling direction of 3.0 to 13.0 mm, the area ratio of the lancet, the width of the striped main magnetic domain, the magnetic properties (B8 and W17 / 50) and the value of LvA200Hz are obtained by the above method. The magnetic domain observation at this time is carried out in a demagnetized state. In addition, the average particle size in the rolling direction of the surface and the width of the linear strain formed in the rolling direction at 4 mm intervals over the entire area of ​​the steel plate in the rolling direction (the average of multiple linear strains) are also obtained.

[0207] The results are shown in Table 1.

[0208] The contents of the various elements, except for Si, which is not shown in the table, are 0.014-0.055% C, 0.001-0.007% S, 0.011-0.027% sol.Al, and 0.0049-0.0075% N. The Mn and Cr contents do not show significant changes compared to the slab stage.

[0209]

[0210] As can be seen from Table 1, in the present invention example, the area ratio of the grains whose distance between the grain boundaries of the grains in the rolling direction of the surface of the base steel plate is 3.0 mm or more and 13.0 mm or less is 70% or more, the magnetic flux density B8 generated by the magnetizing force of 800 A / m is 1.88 T or more, and W17 / 50 is 13.1×t in W / kg.2 -4.3×t+1.2 or less, LvA200Hz is 60 to 78 dBA. No fine grains are generated on the irradiation marks.

[0211] On the other hand, in the comparative examples, one or more of the above-mentioned factors are out of the scope of the present invention, and the iron loss and the noise cannot be sufficiently reduced at the same time.

[0212] For example, in No. 12, although the decarburization annealing temperature is slightly lower, the Ip is 1100W / mm 2 , but the average grain size is as small as 2.8 mm, and the area ratio of grains whose inter-grain boundary distance in the rolling direction is 3.0 mm or more and 13.0 mm or less is small. In addition, B8 is low, iron loss is high, and LvA200Hz is high.

[0213] In No. 13, the decarburization annealing temperature was slightly high, the average grain size was large to 20.2 mm, and accordingly, the area ratio of grains having a distance between grain boundaries in the rolling direction of 3.0 mm or more and 13.0 mm or less was small. As a result, LvA200 Hz was high.

[0214] In No. 16, the laser input energy Ua is relatively high, 4.1 mJ / mm 2 , As a result, LvA200Hz is high.

[0215] The laser input energy Ua in No.17 is also relatively high, at 4.4 mJ / mm 2 , As a result, LvA200Hz is high.

[0216] In No. 19, the diameter of the spacer and the interval between the spacers were not within the preferred range, so the average grain size was as large as 21.2 mm, and the area ratio of the grains whose inter-grain boundary distance in the rolling direction was 3.0 mm or more and 13.0 mm or less was small. As a result, LvA200 Hz was high.

[0217] In No.20, the laser power density Ip is as low as 200W / m 2 The area ratio of the grains whose inter-grain boundary distance in the rolling direction is 3.0 mm or more and 13.0 mm or less is small. As a result, the iron loss is high.

[0218] <Example 2>

[0219] A steel billet containing C: 0.070%, Si: 3.08-3.24%, Mn: 0.09%, S: 0.006%, sol.Al: 0.026%, Cr: 0.11%, N: 0.0076%, and the remainder containing Fe and impurities is heated to 1140°C and hot-rolled to produce a hot-rolled plate with a thickness of 2.4 mm.

[0220] Next, the hot-rolled sheet was subjected to hot-rolled sheet annealing. In the hot-rolled sheet annealing, the sheet was heated to 1120°C and maintained for 180 seconds, then cooled to 900°C and maintained at the same temperature for 120 seconds, and then rapidly cooled using 100°C hot water.

[0221] Then, after pickling, the steel sheet was cold-rolled to obtain a cold-rolled sheet with a thickness of 0.23 mm.

[0222] Next, the cold-rolled sheet (steel sheet) was subjected to decarburization annealing in which the sheet was heated to the temperature listed in Table 2 in a wet hydrogen and nitrogen atmosphere and held for 150 seconds.

[0223] After decarburization annealing, a known annealing separator containing MgO and TiO2 as main components and Na, B, Cl, etc. is applied, and a final annealing is performed at 1200°C for 20 hours. Figure 4 As shown in Table 2, the annealing separator is distributed between the steel sheets in a manner that the thickness varies at a certain interval, and then the steel sheets are coiled into a coil shape and subjected to final annealing. The annealing separator is applied by varying the thickness in a manner that the steel sheet becomes a wave shape in which the wave height varies in the wave period (rolling direction) shown in Table 2. After the final annealing, a forsterite film is formed on the surface.

[0224] After the final annealing, a coating liquid mainly composed of chromic anhydride and aluminum phosphate is applied to the surface of the steel sheet (a steel sheet having a forsterite film formed on the surface of the base steel sheet) and baked annealing is performed to form an insulating film.

[0225] Then, the surface of the steel sheet with the insulating film formed thereon was irradiated with a laser beam to perform magnetic domain segmentation (magnetic domain control). At this time, the laser input energy and laser power density are shown in Table 2. The scanning direction of the laser beam (the extension direction of the irradiation mark) was set to be 90° relative to the rolling direction, and the interval in the rolling direction between the irradiation positions of adjacent laser beams was 4 mm.

[0226]

[0227] For the steel sheet after magnetic domain control (directional electromagnetic steel sheet), the chemical composition, the ratio of grains with a distance between grain boundaries in the rolling direction of 3.0 to 13.0 mm, the area ratio of the lancet, the width of the striped main magnetic domain, the magnetic properties (B8 and W17 / 50) and the value of LvA200Hz are obtained by the above method. The magnetic domain observation is carried out in a demagnetized state. In addition, the average grain size in the rolling direction on the surface and the width of multiple linear strains formed at intervals of 4 mm in the rolling direction (the average of multiple linear strains) are also obtained.

[0228] The results are shown in Table 2.

[0229] The contents of the various elements, except for Si, which is not shown in the table, are 0.016-0.070% C, 0.001-0.006% S, 0.010-0.026% sol.Al, and 0.0051-0.0076% N. The Mn and Cr contents do not show significant changes compared to the slab stage.

[0230] As can be seen from Table 2, in the present invention example, the area ratio of grains whose distance between grain boundaries in the rolling direction of the surface of the base steel plate is 3.0 mm or more and 13.0 mm or less is 70% or more, the magnetic flux density B8 generated by the magnetizing force of 800 A / m is 1.88 T or more, and W17 / 50 is 13.1 × t in W / kg. 2 -4.3×t+1.2 or less, LvA200Hz is 60 to 78 dBA. Here, the laser was irradiated in a direction transverse to the rolling direction of the steel sheet, but fine grains were not generated in the irradiation marks.

[0231] On the other hand, in the comparative examples, one or more of the above-mentioned factors are out of the scope of the present invention, and the iron loss and the noise cannot be sufficiently reduced at the same time.

[0232] In No. 24, the decarburization annealing temperature is slightly low, and even if the laser power density is in the preferred range, the area ratio of the grains whose inter-grain boundary distance in the rolling direction is 3.0 mm or more and 13.0 mm or less is small. In addition, B8 is low, LvA200Hz is high, and W17 / 50 is high.

[0233] In No. 25, the decarburization annealing temperature is slightly high, the average grain size is large, and the area ratio of grains whose inter-grain boundary distance in the rolling direction is 3.0 to 13.0 mm is low. As a result, LvA200Hz is high. In addition, W17 / 50 is high.

[0234] In No. 26 and No. 27, the laser input energy is large, and as a result, LvA200Hz is high and W17 / 50 is high.

[0235] In No. 28, the wave period is large, so the average grain size is large, and the area ratio of grains whose distance between grain boundaries in the rolling direction is 3.0 mm or more and 13.0 mm or less is small. As a result, LvA200 Hz is high.

[0236] Explanation of symbols

[0237] 100: Lancet (closed magnetic domain)

[0238] 1: Steel plate

[0239] 2: Spacer

[0240] 3: Annealing separator

[0241] L1: The distance between the spacers

[0242] L2: Cycle

[0243] h: wave height

Claims

1. A directional electromagnetic steel sheet, characterized in that: It has: Base steel plate; a forsterite film formed on the surface of the base steel plate; and an insulating film formed on the surface of the forsterite film, The chemical composition of the base steel plate contains Si in mass %: 0.80-7.00%, The area ratio of the grains in which the distance between the grain boundaries of the grains in the rolling direction is 3.0 mm or more and 13.0 mm or less on the surface of the base steel plate is 70% or more, The magnetic flux density B8 generated by the magnetizing force of 800A / m is above 1.88T. When the plate thickness of the base steel plate is expressed in mm as t, the iron loss W17 / 50 at a frequency of 50 Hz and a maximum magnetic flux density of 1.7 T is expressed in W / kg as 13.1×t 2 -4.3×t+1.2 or less, The 200Hz component LvA200Hz of the magnetostrictive waveform is 60~78dBA.

2. The grain-oriented electrical steel sheet according to claim 1, characterized in that: A plurality of linear strains extending in a direction intersecting a rolling direction are formed on the surface of the base steel plate, and an interval between the plurality of linear strains in the rolling direction is 3 to 10 mm.

3. The grain-oriented electrical steel sheet according to claim 1 or 2, characterized in that: In the base steel plate, the area ratio of the elongated closed magnetic domains observed on the surface is 10% or less, and the width of the stripe-shaped main magnetic domain is 1.2 mm or less.

4. The grain-oriented electrical steel sheet according to claim 1 or 2, characterized in that: The magnetic flux density is greater than or equal to 1.92 T, and when the plate thickness is 0.18 to 0.23 mm, the W17 / 50 is less than or equal to 0.74 W / kg.

5. The grain-oriented electromagnetic steel sheet according to claim 3, characterized in that: The magnetic flux density is greater than or equal to 1.92 T, and when the plate thickness is 0.18 to 0.23 mm, the W17 / 50 is less than or equal to 0.74 W / kg.

Images