Grain-oriented electrical steel sheet and method for producing same

Abstract

The grain-oriented electrical steel sheet has a steel sheet in which a plurality of grooves extending in a direction intersecting the rolling direction and having a depth in the sheet thickness direction are formed on the surface, and in a cross-section parallel to the rolling direction and parallel to the sheet thickness direction, the distance from the inlet of the groove to the inlet of the opposite groove is defined as the width of the groove. A groove edge portion is defined as a region having the same width as the groove in the direction opposite the center of the groove from the inlet portion of the groove in the rolling direction of the steel plate. When a surface in a region farther than the width of the groove in a direction opposite to the center of the groove from the entrance of the groove to the rolling direction is defined as a reference surface, a protrusion, which is a region having a width of 1 [mu] m or more and a protrusion height of 1 [mu] m or more from the reference surface, is present in the groove edge. The area ratio of Goss oriented particles in the protrusions is 10% or more.

Description

Technical Field

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

[0002] This application claims priority based on Japanese Patent Application No. 2022-186164 filed on November 22, 2022, and incorporates its content herein. Background Art

[0003] A grain-oriented electrical steel sheet is a soft magnetic material and is mainly used as a core material for transformers. Therefore, high magnetization characteristics and magnetic properties such as low iron loss are required for grain-oriented electrical steel sheets. Iron loss refers to the power loss consumed as heat energy when the core is excited by an alternating magnetic field, and from the viewpoint of energy saving, it is required that the iron loss be as low as possible. The level of iron loss affects magnetic susceptibility, plate thickness, film tension, impurity content, resistivity, crystal grain size, magnetic domain width, etc. Regarding grain-oriented electrical steel sheets, in the current situation where various technologies have been developed, research and development for reducing iron loss are also continuing in order to improve energy efficiency.

[0004] As one of the methods for reducing iron loss, a technique of performing laser irradiation has been proposed. In this technique, strain is introduced into the surface by laser irradiation, and by subdividing the 180° magnetic domain width, a part of the iron loss, that is, eddy current loss, can be reduced.

[0005] For example, Patent Document 1 discloses a method for manufacturing a grain-oriented electrical steel sheet that controls magnetic domains by laser irradiation, characterized by having the following steps: irradiating the surface of the grain-oriented electrical steel sheet while scanning the focused continuous-wave laser in a direction inclined from the rolling direction of the grain-oriented electrical steel sheet; and repeating the step while staggering the part where the continuous-wave laser is scanned at a predetermined interval. When the average power of the continuous-wave laser is set to P (W), the scanning speed is set to Vc (mm / second), the predetermined interval is expressed as PL (mm), and the input energy Ua is defined as Ua = P / (Vc × PL) (mJ / mm 2 ), it satisfies 1.0 mm ≤ PL ≤ 3.0 mm and 0.8 mJ / mm 2 ≤ Ua ≤ 2.0 mJ / mm 2 .

[0006] In Patent Document 1, it is disclosed that it is possible to easily reduce the iron loss in both the L direction and the C direction of the grain-oriented electrical steel sheet while ensuring high productivity.

[0007] However, for example, in the case of manufacturing a wound core, stress relief annealing is required because the grain-oriented electrical steel sheet is bent and formed. Therefore, in such a method, the strain introduced into the grain-oriented electrical steel sheet is released by stress relief annealing. Therefore, the effect of controlling magnetic domains based on laser irradiation cannot be obtained.

[0008] Therefore, a method has been proposed to reduce eddy current loss by forming grooves on the steel sheet surface and subdividing the 180° magnetic domain width in the same way as strain introduction.

[0009] For example, Patent Document 2 discloses a method for improving the iron loss characteristics of a grain-oriented electrical steel sheet applicable to stress relief annealing, in which the stress relief annealing is performed by controlling a laser beam to irradiate and form recesses having a width in the rolling direction of 0.5 mm or less and a depth of 10 μm or more.

[0010] However, as described above, in the case of forming grooves by laser irradiation, the melt generated by laser irradiation solidifies at the groove edge portion and the like to form protrusions. This protrusion is usually composed of fine grains having a random crystal orientation other than the Goss orientation. Therefore, if there are protrusions, the magnetic flux density of the steel sheet decreases, and a part of the iron loss, i.e., the hysteresis loss, increases, and the characteristics become inferior.

[0011] The above-mentioned protrusions are removed to a certain extent by brushing treatment or the like after laser irradiation. However, even if brushing treatment or the like is performed, it is carried out in a manner that does not reduce the plate thickness, so it is difficult to completely remove the protrusions. Such protrusions are not considered in Patent Document 2.

[0012] Regarding such a melt, for example, Patent Document 3 discloses a grain-oriented electrical steel sheet in which grooves are formed on the surface to perform magnetic domain refinement treatment. When the thickness of the scattered alloy layer at the bottom of the groove is defined as TB and the thickness of the scattered alloy layer at the 1 / 2 point of the distance formed between either end of the groove and the bottom surface of the groove is defined as TL, TB / TL is 0.2 to 0.8.

[0013] However, in Patent Document 3, although the inside of the groove is mentioned, the crystal orientation of the protrusions formed at the groove edge portion is not mentioned.

[0014] In addition, a grain-oriented electromagnetic steel sheet is disclosed in Patent Document 4. The steel sheet has a steel sheet surface formed with grooves whose extending direction intersects the rolling direction and whose depth direction is parallel to the sheet thickness direction. On both sides of the grooves on the surface of the steel sheet, there are fusion solidified substances connected in parallel with the grooves. When the height that becomes the maximum degree in the height distribution of the height data measured at a constant interval on the surface of the steel sheet in a specific region including the grooves is set as a hypothetical plane, the space volume of the concave portion recessed from the hypothetical plane is set as V1, and the volume of the convex portion protruding from the hypothetical plane is set as V2, the value of V2 / V1 exceeds 0.10 and is less than 0.80. A plurality of protrusions are formed in the specific region. Among the plurality of protrusions, the width of the protrusion closest to the groove is larger than the widths of the other protrusions. When observing the region with the highest average height in the extending direction in the height distribution in a groove longitudinal section including the extending direction and the sheet thickness direction, the average roughness Ra of the roughness curve of the surface constituting the region is 0.30 to 2.00 μm, and the average length RSm of the roughness curve elements of the surface constituting the region is 10 to 150 μm.

[0015] However, in the technology of Patent Document 4, the crystal orientation of the protrusions in the region with the highest average height in the extending direction in the height distribution is specified, but the crystal orientation of the protrusions in the regions other than this is not specified. Although how to control the crystal orientation of the protrusions is important for reducing iron loss, the research on the crystal orientation of the protrusions and the reduction of iron loss is not sufficiently carried out in Patent Document 4.

[0016] Prior Art Documents

[0017] Patent Documents

[0018] Patent Document 1: Japanese Patent No. 4669565 Gazette

[0019] Patent Document 2: Japanese Patent Application Laid-Open No. 6-57335 Gazette

[0020] Patent Document 3: Japanese Patent No. 6405378 Gazette

[0021] Patent Document 4: Japanese Patent No. 6569803 Gazette Summary of the Invention

[0022] Problems to be Solved by the Invention

[0023] As described above, in a grain-oriented electrical steel sheet, by forming grooves substantially parallel to the width direction of the steel sheet, the 180-degree magnetic domain width is subdivided, and along with this, the eddy current loss, which is part of the iron loss, is reduced. However, in the case where the above grooves are formed by laser irradiation, a protrusion is formed by the solidification of the melt generated by the laser irradiation at the groove edge portion. This protrusion is generally composed of fine grains having a random crystal orientation other than the Goss orientation. Therefore, if the protrusion exists, the magnetic flux density of the steel sheet decreases, and the hysteresis loss, which is part of the iron loss, increases, resulting in inferior characteristics. The above protrusion is removed by brushing treatment after laser irradiation, etc. However, in order to perform the brushing treatment without reducing the plate thickness, it is difficult to completely remove the protrusion.

[0024] In addition, in the case where a protrusion exists at the groove edge portion, the adhesion of the coating film may deteriorate. However, in the past, sufficient research has not been conducted on the adhesion of the coating film when there is a protrusion.

[0025] In view of the above circumstances, an object of the present invention is to provide a grain-oriented electrical steel sheet and a method for manufacturing the same, which is a grain-oriented electrical steel sheet in which magnetic domains are subdivided by forming grooves, and in which low iron loss is achieved by suppressing a decrease in magnetic flux density caused by protrusions and an increase in hysteresis loss accompanying this.

[0026] Another preferred object of the present invention is to provide a grain-oriented electrical steel sheet that can obtain sufficient adhesion of the coating film even in the case where there is a protrusion.

[0027] Means for Solving the Problem

[0028] The present inventors have studied suppressing an increase in hysteresis loss caused by protrusions.

[0029] As a result, it has been found that by controlling the crystal orientation of the protrusion formed at the groove edge portion so that the proportion of the Goss orientation becomes higher, an increase in hysteresis loss can be suppressed.

[0030] In addition, it has been found that regarding the crystal orientation of the protrusion at the groove edge portion, after forming a groove for forming a groove on the surface of the steel sheet by laser irradiation, the surface of the steel sheet is ground under specified conditions, whereby at the subsequent annealing, the proportion of the crystal orientation of the protrusion becoming the Goss orientation can be increased.

[0031] It has also been found that if the surface roughness is controlled within a specified range by controlling the grinding conditions, the adhesion of the coating film can be further improved.

[0032] The present invention has been completed in view of the above findings. The gist of the present invention is as follows.

[0033] [1]An oriented electrical steel sheet according to one embodiment of the present invention has a steel sheet with a plurality of grooves formed on the surface, the grooves extending in a direction crossing the rolling direction and having a depth in the plate thickness direction. In a cross-section parallel to the rolling direction and parallel to the plate thickness direction of the above-mentioned steel sheet, the distance from the inlet portion of the groove to the inlet portion of the opposite groove is defined as the width of the groove, and a region equal to the width of the groove in the direction opposite to the center of the groove from the inlet portion of the groove of the above-mentioned steel sheet in the rolling direction is defined as the groove edge portion. When the surface in the region farther from the width of the groove than the groove width in the direction opposite to the center of the groove from the inlet portion of the groove in the rolling direction is defined as the reference surface, there is a protrusion in the groove edge portion, where the width of the protrusion is 1 μm or more and the protrusion height from the reference surface is 1 μm or more, and the area ratio of Goss-oriented grains in the above-mentioned protrusion is 10% or more.

[0034] [2]In the oriented electrical steel sheet described in [1], it is also possible that the arithmetic mean roughness Ra of the surface of the groove edge portion of the above-mentioned steel sheet along the extending direction of the groove including the vertex of the above-mentioned protrusion exceeds 2.0 μm and is 5.0 μm or less.

[0035] [3]In the oriented electrical steel sheet described in [1] or [2], a forsterite coating may be formed on the above-mentioned surface of the steel sheet.

[0036] [4]In the oriented electrical steel sheet described in [3], an insulating coating may be formed on the surface of the above-mentioned forsterite coating.

[0037] [5]In the oriented electrical steel sheet described in [1] or [2], an insulating coating may be formed on the above-mentioned surface of the steel sheet.

[0038] [6]A method for manufacturing an oriented electrical steel sheet according to another embodiment of the present invention is the method for manufacturing the oriented electrical steel sheet described in [1], which includes: a groove forming step of forming grooves on the surface by irradiating the steel sheet with a laser; and a grinding step of grinding the surface of the above-mentioned steel sheet using a brush roll fixed with abrasive grains after the above-mentioned groove forming step. In the above-mentioned grinding step, the above-mentioned brush roll rotates in a direction opposite to the conveying direction of the above-mentioned steel sheet at the position where it abuts against the above-mentioned steel sheet. The conveying speed of the above-mentioned steel sheet is 20 to 150 mpm, the rotational speed of the above-mentioned brush roll is 500 to 1500 rpm, the pressing amount of the above-mentioned brush roll is 1.0 to 5.0 mm, the grain size of the above-mentioned abrasive grains is #60 to #400, and the diameter of the above-mentioned brush roll is 200 to 500 mm.

[0039] [7]In the method for manufacturing an oriented electrical steel sheet described in [6], the pressing amount of the above-mentioned brush roll may be 1.0 to 2.0 mm.

[0040] Advantages of the Invention

[0041] According to the above method of the present invention, it is possible to provide a grain-oriented electrical steel sheet with a sufficiently high magnetic flux density and low iron loss, and a method for manufacturing the same. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a diagram showing an example of the formation state of the grooves of the grain-oriented electrical steel sheet of the present embodiment.

[0043] Figure 2 It is a schematic view of observing the grooves and their surroundings of the grain-oriented electrical steel sheet of the present embodiment in a cross-section orthogonal to the extending direction of the grooves. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] A grain-oriented electrical steel sheet (the grain-oriented electrical steel sheet of the present embodiment) and a method for manufacturing the same according to an embodiment of the present invention will be described.

[0045] <Grain-oriented electrical steel sheet>

[0046] As Figure 1 shown, the grain-oriented electrical steel sheet 1 of the present embodiment has, on the surface, a steel sheet (base steel sheet) 11 in which a plurality of grooves 21 extending in a direction crossing the rolling direction RD and having a depth in the plate thickness direction are formed.

[0047] A forsterite coating film or an insulating coating film may be formed on the surface of the steel sheet (base steel sheet). Further, the insulating coating film may be formed on the surface of the forsterite coating film.

[0048] That is, the grain-oriented electrical steel sheet of the present embodiment may not only include the case of the steel sheet (base steel sheet), but may also include the case of including the forsterite coating film formed on the surface of the base steel sheet, may include the case of including the insulating coating film formed on the surface of the base steel sheet, or may include the case of including the forsterite coating film formed on the surface of the base steel sheet and the insulating coating film formed on the surface of the forsterite coating film.

[0049] The forsterite coating film and the insulating coating film may be formed on one side or both sides.

[0050] The following will be described separately.

[0051] [Steel sheet (base steel sheet)]

[0052] (Grooves)

[0053] As Figure 1 shown, the steel sheet 11 has, on the surface, a plurality of grooves 21 formed by laser irradiation, extending in a direction crossing the rolling direction RD and having a depth in the plate thickness direction. The steel sheet is, for example, a cold-rolled sheet.

[0054] Magnetic domain control can be carried out by periodically forming linear grooves in a direction crossing the rolling direction RD. In the grain-oriented electrical steel sheet of the present embodiment, in order to obtain this effect, grooves are formed on the surface of the steel sheet (in the grain-oriented electrical steel sheet formed with a forsterite coating and an insulating coating, the so-called base steel sheet other than these).

[0055] Here, the direction crossing the rolling direction RD is a direction of 60 to 120° with respect to the rolling direction RD.

[0056] Regarding the shape of the grooves, there is no limitation as long as the effect of magnetic domain control can be obtained. Preferably, the depth is 10 to 50 μm and the width is 10 to 200 μm. Among the plurality of grooves, the interval in the rolling direction RD between adjacent grooves is preferably 1 to 20 mm. The plurality of grooves are preferably formed to be substantially parallel to each other at substantially constant intervals (periodically) in the rolling direction RD. The groove interval is the distance from the center in the width direction of one groove to the center in the width direction of the adjacent groove.

[0057] (Projection)

[0058] As described above, in the grain-oriented electrical steel sheet, by forming grooves in a direction crossing the rolling direction RD of the steel sheet, the 180-degree magnetic domain width is subdivided. Along with this, the eddy current loss, which is part of the iron loss, is reduced. However, in the case of forming grooves by laser irradiation, a projection is formed by the solidification of the melt generated by laser irradiation at the groove edge portion. This projection is usually composed of fine grains having a random crystal orientation other than the Goss orientation. Therefore, if the projection exists, the magnetic flux density of the steel sheet decreases, and the hysteresis loss, which is part of the iron loss, increases, resulting in inferior characteristics. The above-mentioned projection is removed by brushing treatment or the like after laser irradiation. However, in order to perform the brushing treatment without reducing the plate thickness, it is difficult to completely remove the projection.

[0059] Therefore, in the grain-oriented electrical steel sheet of the present embodiment, instead of removing the projection, the crystal orientation of the projection formed at the groove edge portion is controlled so that the area ratio of the grains having the Goss orientation (Goss-oriented grains) in the projection is 10% or more, thereby suppressing the increase in the hysteresis loss. When the area ratio of the Goss-oriented grains is less than 10%, the magnetic flux density of the steel sheet decreases, and the hysteresis loss, which is part of the iron loss, increases.

[0060] In addition, in the portion where the projection exists, the coating adhesion may deteriorate. Therefore, in the grain-oriented electrical steel sheet of the present embodiment, it is preferable to control the surface roughness of the groove edge portion including the projection.

[0061] Specifically, it is preferable that the arithmetic mean roughness Ra of the surface of the groove along the extending direction, which includes the vertex of the protrusion (the point where the protrusion height is the maximum), is more than 2.0 μm and 5.0 μm or less. At this time, excellent film adhesion can be obtained.

[0062] When Ra is 2.0 μm or less, the surface is smooth, so the effect of improving film adhesion cannot be obtained. On the other hand, when Ra exceeds 5.0 μm, the surface is too rough, so the film is likely to peel off, and the effect of improving film adhesion cannot be obtained.

[0063] Here, in the present embodiment, as Figure 1 , Figure 2 shown, in a cross-section parallel to the rolling direction RD and parallel to the plate thickness direction, the distance from the inlet portion 31 of the groove 21 (the position where the side surface of the groove, which is concave with respect to the reference plane, intersects the imaginary line extending the reference plane) to the inlet portion 31 of the opposite groove 21 is defined as the width of the groove 21, and the region equal to the width of the groove 21 in the direction opposite to the center of the groove 21 from the inlet portion of the groove 21 of the steel plate 11 in the rolling direction RD is defined as the groove edge portion 41. In addition, when the surface of the region (i.e., the region farther from the groove 21 than the groove edge portion 41) that is away from the groove 21 by the width of the groove 21 from the inlet portion 31 of the groove 21 in the rolling direction RD is defined as the reference plane RS, in the groove edge portion 41, the region where the width of the reference plane RS height (the length in the direction perpendicular to the height direction (the length of the dotted line portion in Figure 2 ) is 1 μm or more and the protrusion height from the reference plane RS is 1 μm or more is defined as the protrusion 101.

[0064] The area ratio of the Goss-oriented grains of the protrusion 101 can be increased by a manufacturing method including a grinding process described later. The Ra of the groove edge portion including the vertex of the protrusion can be controlled by a manufacturing method including a grinding process described later.

[0065] The area ratio of the grains with the crystal orientation of the protrusion in the groove edge portion becoming the Goss orientation is obtained by the following method.

[0066] First, a sample is collected from the grain-oriented electrical steel sheet to be measured so that a cross-section orthogonal to the length direction (extending direction) of the groove is exposed. At this time, the collection is performed so as to include the groove and the groove edge portion in the cross-section.

[0067] After polishing the cross-section to expose the cross-section including the groove and its peripheral portion as shown in Figure 2 , the cross-section is observed. When observing a total of 10 or more cross-sections, if there is one or more protrusions in the groove edge portion, it is determined that at least one protrusion exists.

[0068] In addition, in the case where protrusions exist, the crystal orientation of the protrusions is measured by the Electron Back Scattering Diffraction Pattern (EBSD) method. Grains with an orientation difference of within 10° from the correct Goss orientation {110}<001> are defined as Goss-oriented grains, and the area ratio of the Goss-oriented grains of the protrusions is determined. In the case where multiple protrusions exist in the observed cross-section, for each protrusion, the area ratio of the Goss-oriented grains is determined, and their average value is used as the area ratio of the Goss-oriented grains.

[0069] The measurement conditions for EBSD are as described below.

[0070] (a) Measuring device: FE-SEM "SU-70" (manufactured by Hitachi High-Technologies Corporation)

[0071] EBSD device "DigiView" (manufactured by TSL Solutions)

[0072] (b) Magnification: 500 times

[0073] (c) Step interval: 0.25 μm

[0074] (d) Measurement area: 200 μm in the direction intersecting the groove length direction × 70 μm in the plate thickness direction

[0075] The arithmetic mean roughness Ra of the surface of the groove edge portion including the vertex of the protrusion is obtained by the following method.

[0076] Using a laser surface roughness measuring instrument, a height distribution is obtained within a range of 1000 μm in the groove extension direction and 400 μm (200 μm on each side of the groove) centered on the groove in the direction orthogonal to the groove extension direction on the steel plate surface. In this measurement, the laser spot diameter is set to 0.40 μm or less (for example, 0.40 μm), scanning is performed in steps of 0.30 μm or less (for example, 0.30 μm), the measurement accuracy in the height direction is set to 0.10 μm or less, and the magnification of the objective lens is set to 50 times.

[0077] As a result of this measurement, the point with the maximum height is taken as the vertex of the protrusion. Then, a measurement cross-section curve of a cross-section including the vertex of the protrusion and a plane parallel to the groove extension direction and parallel to the plate thickness direction of the steel plate is obtained. A low-pass filter with a cut-off value λs and a wide-pass filter with a cut-off value λc are applied to the measurement cross-section curve to obtain a roughness curve. The arithmetic mean roughness Ra is obtained from this roughness curve according to JIS B 0601 (2013).

[0078] At this time, the cut-off values λs and λc are determined by the model of the laser surface roughness meter and the objective lens. In the present embodiment, as the cut-off values when measuring the surface roughness with the objective lens magnification set to 50 times using the VK-9700 manufactured by KEYENCE Corporation, λs = 0.8 μm and λc = 0.08 mm are used.

[0079] (Chemical composition)

[0080] The chemical composition of the base metal steel sheet is not limited as long as it is equivalent to the base metal steel sheet of a known grain-oriented electrical steel sheet. For example, it may contain, by mass%, Si: 2.5 to 4.5%, Mn: 0.01 to 0.15%, C: 0 to 0.085%, acid-soluble Al: 0 to 0.065%, N: 0 to 0.012%, Cr: 0 to 0.30%, Cu: 0 to 0.40%, P: 0 to 0.50%, Sn: 0 to 0.30%, Sb: 0 to 0.30%, Ni: 0 to 1.000%, S: 0 to 0.015%, Se: 0 to 0.015%, Bi: 0 to 0.02%. In addition, the above may be contained, and the balance is Fe and impurities.

[0081] When the grain-oriented electrical steel sheet is composed of a base metal steel sheet (without a forsterite coating and an insulating coating), it can be said that the chemical composition of the base metal steel sheet is the chemical composition of the grain-oriented electrical steel sheet.

[0082] The chemical composition of the base metal steel sheet can be determined by general analysis methods for steel. For example, the chemical composition of the base metal steel sheet can be determined using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Specifically, for example, a test piece with a size of 35 mm square (35 mm in the rolling direction and the width direction respectively) can be taken from the central position of the base metal steel sheet after removing the coating, and using an ICPS-8100 manufactured by Shimadzu Corporation, etc. (measurement device), it can be specified by measuring under the conditions based on a pre-made standard curve. C and S, which are difficult to measure by ICP-AES, can be measured using combustion-infrared absorption method, and N can be measured using inert gas fusion-thermal conductivity method. When the magnesium olivine coating and the insulating coating are formed on the base metal steel sheet, the chemical composition of the base metal steel sheet can be analyzed after removing the magnesium olivine coating and the insulating coating from the grain-oriented electrical steel sheet by a known method such as pickling.

[0083] (Thickness)

[0084] The thickness of the base metal steel sheet of the grain-oriented electrical steel sheet in the present embodiment is not limited, but from the viewpoint of reducing eddy current loss, when the thickness is relatively thin, for example, it is preferably 0.15 to 0.35 mm.

[0085] [Forsterite coating film]

[0086] In the grain-oriented electrical steel sheet of the present embodiment, a forsterite coating film may also be formed on the surface of the steel sheet that serves as the base material steel sheet.

[0087] The forsterite coating film is an inorganic coating film mainly composed of magnesium silicate. The forsterite coating film is formed by the reaction of an annealing release agent containing magnesium oxide (MgO) coated on the surface of the base material steel sheet with the components on the surface of the base material steel sheet during final annealing, and has a composition derived from the components of the annealing release agent and the base material steel sheet (more specifically, a composition mainly composed of Mg2SiO4).

[0088] On the other hand, in the case of using an annealing release agent mainly composed of Al2O3 during final annealing, the forsterite coating film may not be formed sometimes.

[0089] [Insulating coating film]

[0090] In the grain-oriented electrical steel sheet of the present embodiment, an insulating coating film may also be formed on the surface of the base material steel sheet or the surface of the forsterite coating film.

[0091] The insulating coating film reduces eddy current loss by imparting electrical insulation to the grain-oriented electrical steel sheet, and reduces the iron loss of the grain-oriented electrical steel sheet. The insulating coating film has a function of imparting tension to the grain-oriented electrical steel sheet. By imparting tension to the grain-oriented electrical steel sheet, the movement of magnetic domain walls in the grain-oriented electrical steel sheet becomes easier, and the iron loss of the grain-oriented electrical steel sheet can be reduced.

[0092] In addition, due to the insulating coating film, various properties such as corrosion resistance, heat resistance, and slidability can be obtained in addition to the electrical insulation as described above.

[0093] In the grain-oriented electrical steel sheet of the present embodiment, the insulating coating film may be, for example, a known coating film formed by coating a coating solution mainly composed of phosphate and colloidal silica on the surface of the forsterite coating film and baking it.

[0094] [Manufacturing method]

[0095] The grain-oriented electrical steel sheet of the present embodiment can achieve its effects as long as it has the above-mentioned characteristics regardless of the manufacturing method, but it can be stably manufactured as long as it is a manufacturing method including the following processes, and thus is preferred.

[0096] (I) A hot rolling process in which a slab is heated and hot rolled to form a hot rolled sheet;

[0097] (II) A hot rolled sheet annealing process in which the hot rolled sheet after the hot rolling process is annealed;

[0098] (III) A cold rolling process of pickling and cold rolling the hot-rolled sheet after the annealing process of the hot-rolled sheet to form a steel sheet (cold-rolled sheet);

[0099] (IV) A groove forming process of forming grooves on the surface by irradiating the steel sheet with a laser;

[0100] (V) A grinding process of grinding the surface of the steel sheet after the groove forming process with a brush roll fixed with abrasive grains;

[0101] (VI) A decarburizing annealing process of performing decarburizing annealing on the steel sheet after the grinding process; and

[0102] (VII) A final annealing process of coating an annealing release agent on the steel sheet after the decarburizing annealing process and performing final annealing.

[0103] In addition, the method for manufacturing an oriented electrical steel sheet according to the present embodiment may further include any one or both of the following processes.

[0104] (VIII) A nitriding treatment process of increasing the nitrogen content of the steel sheet after the decarburizing annealing process; and

[0105] (IX) An insulating film forming process of forming an insulating film on the surface of the steel sheet after the final annealing process (or on the surface of the forsterite coating film formed on the surface of the steel sheet).

[0106] Among them, the method for manufacturing an oriented electrical steel sheet according to the present embodiment is characterized by the groove forming process and the grinding process. On the other hand, the hot rolling process, the hot-rolled sheet annealing process, the cold rolling process, the decarburizing annealing process, the nitriding treatment process, the final annealing process, and the insulating film forming process are not particularly limited and can be carried out under known conditions.

[0107] Hereinafter, preferred conditions will be described. For the conditions not described, they can also be carried out under known conditions.

[0108] [Hot Rolling Process]

[0109] In the hot rolling process, a slab having a specified chemical composition (the chemical composition corresponding to the chemical composition of the base steel sheet of the oriented electrical steel sheet according to the present embodiment) is heated and hot rolled to form a hot-rolled sheet.

[0110] The conditions are not limited. For example, the heating temperature is 1050 to 1400 °C.

[0111] The chemical composition of the slab to be hot rolled can be determined as long as it is considered in accordance with the chemical composition desired to obtain an oriented electrical steel sheet and the changes in the chemical composition in each process.

[0112] For example, in the case of obtaining the chemical composition of the base steel sheet of the preferred oriented electromagnetic steel sheet of the present embodiment, it is preferable to use a slab having the following chemical composition.

[0113] It may contain, by mass%, Si: 2.5 to 4.5%, Mn: 0.01 to 0.15%, C: 0.02 to 0.10%, acid-soluble Al: 0 to 0.065%, N: 0.002 to 0.030%, Cr: 0 to 0.30%, Cu: 0 to 0.40%, P: 0 to 0.50%, Sn: 0 to 0.30%, Sb: 0 to 0.30%, Ni: 0 to 1.000%, S: 0.001 to 0.050%, Se: 0 to 0.050%, Bi: 0 to 0.02%. In addition, the above may also be contained, and the balance is Fe and impurities.

[0114] The method for obtaining the slab is not limited. For example, molten steel having a prescribed chemical composition is melted and used to manufacture it. The slab can be manufactured by continuous casting, or an ingot can be manufactured using molten steel, and the ingot can be subjected to blooming rolling to manufacture the slab. In addition, the slab can also be manufactured by other methods.

[0115] The thickness of the slab is not particularly limited. For example, it is 150 to 350 mm. The thickness of the slab is preferably 220 to 280 mm. It is also possible to use a so-called thin slab having a thickness of 10 to 70 mm.

[0116] [Hot-rolled sheet annealing process]

[0117] In the hot-rolled sheet annealing process, the hot-rolled sheet after the hot-rolling process is annealed. By performing such an annealing treatment, recrystallization occurs in the steel sheet structure, and good magnetic properties can be achieved.

[0118] In the hot-rolled sheet annealing process of the present embodiment, the hot-rolled sheet manufactured through the hot-rolling process may be annealed according to a known method. The method for heating the hot-rolled sheet during annealing is not particularly limited, and a known heating method can be adopted. In addition, the annealing conditions are not particularly limited. For example, the hot-rolled sheet can be annealed in a temperature range of 900 to 1200 °C for 10 seconds to 5 minutes.

[0119] [Cold-rolling process]

[0120] In the cold-rolling process, the hot-rolled sheet after the hot-rolled sheet annealing process is pickled and cold-rolled to form a cold-rolled sheet. The cold-rolling can be single-pass (a series of cold-rolling without intermediate annealing), or intermediate annealing can be performed at least once or two or more times by interrupting the cold-rolling before the final pass of the cold-rolling process, and multi-pass cold-rolling with intermediate annealing can be performed.

[0121] It can be carried out according to the conditions of cold rolling and known methods. For example, the final reduction ratio can be set within the range of 80% or more and 95% or less.

[0122] The final reduction ratio is the cumulative reduction ratio of cold rolling. In the case of intermediate annealing, it is the cumulative reduction ratio of cold rolling after the final intermediate annealing.

[0123] When performing intermediate annealing, for example, it is held at a temperature of 1000 to 1200 °C for 5 to 180 seconds. The annealing atmosphere is not particularly limited. Considering the manufacturing cost, the number of intermediate annealings is preferably within 3 times.

[0124] In addition, pickling can also be carried out under known conditions.

[0125] [Groove forming process]

[0126] In the groove forming process, grooves are formed on the surface by irradiating a cold-rolled sheet (cold-rolled steel sheet) with a laser. It is preferable to irradiate the laser while scanning in the direction of groove formation (the direction intersecting the rolling direction) to melt a part of the steel sheet surface and remove the molten material from the surface, thereby forming grooves. As a method for removing the molten material from the surface, spraying of auxiliary gas, etc. can be cited.

[0127] In addition, the laser irradiation is preferably carried out while moving the laser multiple times in the width direction in such a manner that the grooves are arranged substantially parallel to each other at a constant interval (for example, 1 to 10 mm) in the rolling direction.

[0128] The laser irradiation conditions are not limited, but in order to form grooves with a specified shape (for example, a depth of 10 to 50 μm and a groove width of 10 to 200 μm), it is preferable to set the laser output to 200 to 3000 W, set the condensing spot diameter of the laser in the rolling direction (i.e., the diameter including 86% of the laser output) to 10 to 1000 μm, set the condensing spot diameter of the laser in the plate width direction (i.e., the diameter including 86% of the laser output) to 10 to 1000 μm, and set the laser scanning speed to 5 to 50 m / second.

[0129] By forming grooves on the surface of the cold-rolled sheet (the base steel sheet), the magnetic domain width is subdivided and the magnetic properties are improved.

[0130] [Grinding process]

[0131] In the grinding process, a brush roll fixed with abrasive grains is used to grind the surface of the steel sheet after the groove forming process. By grinding under appropriate conditions, it is possible to avoid a reduction in the plate thickness and impart strain to the protrusions formed at the groove edge (a part of the protrusions is removed by grinding, but a part remains). The driving force for recrystallization of the strained protrusions increases, and primary recrystallization and grain growth occur in the subsequent decarburizing annealing process, making it easy for the Goss orientation to be nibbled at during the final annealing. Therefore, the strained protrusions undergo secondary recrystallization during the final annealing, and the area ratio of Goss-oriented grains increases (if random recrystallization occurs without the imparting of strain, the area ratio of Goss-oriented grains is usually less than 5%, but after the grinding process, it becomes 10% or more).

[0132] To impart appropriate strain, while moving the steel sheet at a conveying speed of 20 to 150 meters per minute (meter / mimutes (mpm)), a brush roll that rotates in a direction opposite to the conveying direction of the steel sheet at the position where it contacts the steel sheet is used, and grinding is carried out under the conditions that the rotational speed of the brush roll is 500 to 1500 rpm, the pressing amount of the brush roll is 1.0 to 5.0 mm, the grain size of the abrasive grains is #60 to #400, and the diameter of the brush roll is 200 to 500 mm.

[0133] When the conveying speed (linear speed) of the steel sheet is lower than 20 mpm, the grinding amount is excessive, so the plate thickness decreases. On the other hand, when it exceeds 150 mpm, the amount of strain imparted by grinding is insufficient, and the area ratio of Goss-oriented grains does not increase.

[0134] In addition, when the rotational speed of the brush roll is less than 500 rpm, the amount of strain imparted by grinding is insufficient, and the area ratio of Goss-oriented grains does not increase. On the other hand, when it exceeds 1500 rpm, the grinding amount is excessive, so the plate thickness decreases.

[0135] When the pressing amount of the brush roll is lower than 1.0 mm, the amount of strain imparted by grinding is insufficient, and the area ratio of Goss-oriented grains does not increase. On the other hand, when it exceeds 5.0 mm, the grinding amount is excessive, so the plate thickness decreases.

[0136] When the grain size of the abrasive grains is less than #60, the grinding amount is excessive, so the plate thickness decreases. On the other hand, when it exceeds #400, the amount of strain imparted by grinding is insufficient, and the area ratio of Goss-oriented grains does not increase.

[0137] When the diameter of the brush roll is less than 200 mm, the grinding amount is excessive, so the plate thickness decreases. On the other hand, when it exceeds 500 mm, the amount of strain imparted by grinding is insufficient, and the area ratio of Goss-oriented grains does not increase.

[0138] In addition, the conveying speed of the steel plate is preferably 20 to 150 mpm, the rotational speed of the brush roll is 500 to 1000 rpm, the amount of roll pressure of the brush roll is 1.0 to 4.0 mm, the grain size of the abrasive grains is #100 to 400, and the diameter of the brush roll is 200 to 500 mm.

[0139] More preferably, the amount of roll pressure of the brush roll is 1.0 to 2.0 mm. By setting the amount of roll pressure in this way, the surface roughness Ra of the groove longitudinal section including the apex of the protrusion can be in the range of more than 2.0 μm and 5.0 μm or less.

[0140] [Decarburizing annealing process]

[0141] In the decarburizing annealing process, the steel plate after the grinding process is subjected to decarburizing annealing. In this decarburizing annealing, carbon that has an adverse effect on magnetic properties is removed (decarburized) from the steel plate, and the steel plate undergoes primary recrystallization.

[0142] The decarburizing annealing conditions are not limited, and can be set to conditions of heating to 700 to 900 °C and holding for 1 to 3 minutes.

[0143] [Nitriding treatment process]

[0144] After the decarburizing annealing process and before the final annealing process, a nitriding treatment can be performed to increase the nitrogen content of the grain-oriented electrical steel sheet. The nitriding treatment can be carried out by a known method. For example, by annealing in an atmosphere containing a gas having nitriding ability such as ammonia, nitrogen is introduced into the steel. Thereby, an inhibitor for secondary recrystallization can be formed by nitriding.

[0145] [Final annealing process]

[0146] In the final annealing process, an annealing parting agent is applied to the steel plate after the decarburizing annealing process, and final annealing is performed.

[0147] Since the final annealing is performed after the steel plate is wound into a coil, the annealing parting agent is applied in such a way that the steel plate is not baked during the final annealing. Generally, an annealing parting agent mainly containing MgO and Al2O3 is used. After applying such an annealing parting agent, final annealing is performed. For example, if an annealing parting agent containing MgO is used, a layer with a forsterite (Mg2SiO4) coating film is formed. In the case of using an annealing parting agent mainly composed of Al2O3, a forsterite coating film may not be formed.

[0148] In addition, in the final annealing process, by heating to the annealing temperature, the primary recrystallized grains obtained in the decarburizing annealing process are secondary recrystallized to obtain grains that are consistent in the Goss orientation, and by holding at the annealing temperature for a specified time, impurities (N, S, etc.) that have an adverse effect on magnetic properties are removed (purified).

[0149] In the method for manufacturing the grain-oriented electrical steel sheet according to the present embodiment, in the steel sheet to be subjected to decarburizing annealing, the driving force for recrystallization is increased by the strain introduced in the grinding process, primary recrystallization and grain growth occur in the decarburizing annealing process, and it becomes a state in which it is easily eaten by Goss orientation during final annealing. Therefore, in the projections, the area ratio of the grains having Goss orientation is increased.

[0150] The conditions for final annealing are not limited, and conditions such as heating to 1100 to 1300 °C and holding for 20 to 24 hours can be exemplified.

[0151] [Insulating film forming process]

[0152] In the insulating film forming process, an insulating film is formed on the steel sheet after the final annealing process (the surface of the forsterite film in the case where a forsterite film is formed on the surface of the steel sheet by final annealing).

[0153] For example, the insulating film can be formed by coating a coating solution containing phosphoric acid or phosphate, colloidal silica, and anhydrous chromic acid or chromate on the steel sheet after final annealing (including the case having a forsterite film), and baking and drying at 300 to 950 °C for 10 seconds or more.

[0154] Through these processes, a base steel sheet is provided, and if necessary, a grain-oriented electrical steel sheet having a forsterite film and / or an insulating film can be obtained.

[0155] Examples

[0156] A slab having a chemical composition containing, by mass fraction, Si: 3.3%, C: 0.060%, acid-soluble Al: 0.028%, N: 0.008%, Mn: 0.12%, Cr: 0.05%, Cu: 0.04%, P: 0.01%, Sn: 0.02%, Ni: 0.005%, S: 0.007%, and the balance including Fe and impurities was subjected to a hot rolling process to produce a hot-rolled sheet having a thickness of 2.6 mm.

[0157] The hot-rolled sheet was heated to 1000 °C and subjected to hot-rolled sheet annealing under the condition of holding for 1 minute.

[0158] The hot-rolled sheet after hot-rolled sheet annealing was pickled and cold-rolled under the condition that the final reduction ratio was 91% to produce a steel sheet (cold-rolled sheet) having a thickness of 0.23 mm.

[0159] The steel plate was irradiated with a laser under the conditions of a laser output of 1500 W, a condensing spot diameter of 40 μm in the rolling direction of the laser, a condensing spot diameter of 40 μm in the plate width direction of the laser, and a scanning speed of 45 m / second, thereby forming grooves on the surface that extend in a direction perpendicular to the rolling direction, have a width of 40 μm, and a depth of 30 μm. In addition, a plurality of these grooves were formed in parallel at intervals of 5 mm in the rolling direction.

[0160] A brush roll rotating in a direction opposite to the conveying direction of the steel plate was used to grind the surface of the steel plate with grooves under the conditions shown in Table 1.

[0161] After grinding, it was heated to 800 °C and decarburization annealing was carried out under the condition of holding for 2 minutes.

[0162] An annealing parting agent mainly composed of magnesium oxide (MgO) was coated on the steel plate after decarburization annealing, and it was heated to 1200 °C and final annealing was carried out under the condition of holding for 20 hours. As a result, an oriented electrical steel sheet with a forsterite coating film formed on the surface of the steel plate (base steel plate) was obtained.

[0163] A coating solution containing colloidal silica and phosphate was coated on the obtained oriented electrical steel sheet, and heat treatment was carried out under the condition of heating to 850 °C and holding for 1 minute, thereby forming an insulating coating film.

[0164] The chemical composition of the base steel plate of the obtained oriented electrical steel sheet was determined. As a result, it contained Si: 3.3%, C: 0.001% or less, acid-soluble Al: 0.004% or less, N: 0.001% or less, Mn: 0.12%, Cr: 0.05%, Cu: 0.04%, P: 0.01%, Sn: 0.02%, Ni: 0.005%, S: 0.001% or less by mass fraction, and the balance contained Fe and impurities.

[0165] From the obtained oriented electrical steel sheet, in accordance with the above-mentioned procedure, the area ratio of the protruding Goss-oriented grains was determined by the EBSD method.

[0166] In addition, in accordance with the above-mentioned procedure, a measurement cross-sectional curve of a cross-section including the vertex of the protrusion and a plane parallel to the extending direction of the groove and parallel to the plate thickness direction of the steel plate was obtained, and the arithmetic mean roughness Ra was determined in accordance with JIS B 0601 (2013) based on the roughness curve obtained from this measurement cross-sectional curve.

[0167] The results are shown in Table 1.

[0168] In addition, a specimen with a width of 60 mm and a rolling direction length of 300 mm was taken from the obtained grain-oriented electrical steel sheet, and a single-sheet magnetic property test (SST test) was carried out on this specimen in accordance with JIS C2556 (2015). The iron loss W17 / 50 was measured when the frequency was set to 50 Hz and the maximum magnetic flux density was set to 1.7 T. In addition, the magnetic flux density B8 generated when magnetized at 800 A / m was measured.

[0169] The results are shown in Table 1.

[0170] If B8 is 1.88 T or more and W17 / 50 is 0.750 W / kg or less, it is judged to have excellent magnetic properties.

[0171] In addition, the adhesion of the insulating coating film (coating film adhesion) of the obtained grain-oriented electrical steel sheet was evaluated by the following method.

[0172] A test piece with a thickness × 80 mm × 80 mm was cut out from the part of the obtained grain-oriented electrical steel sheet including the slot edge portion, and this test piece was wound around a round bar with a diameter of 20 mm, and then extended flatly.

[0173] The surface of the test piece after being extended flatly was observed, the area of the insulating coating film that did not peel off from the steel sheet with respect to the area of the bent portion was measured, and the coating film remaining area ratio (%) was calculated.

[0174] The adhesion of the insulating coating film of the test piece with a coating film remaining area ratio of 95% or more was evaluated as "excellent", the adhesion of the insulating coating film of the test piece with a coating film remaining area ratio of 90% or more and less than 95% was evaluated as "good", and the adhesion of the insulating coating film of the test piece with a coating film remaining area ratio of less than 90% was evaluated as "poor".

[0175]

[0176] As can be seen from Table 1, if the area ratio of Goss-oriented grains of the protrusion (protrusion part) is 10% or more, a grain-oriented electrical steel sheet with high B8 and low W17 / 50 can be obtained (Inventive Examples 1 to 10). In addition, they all have sufficient coating film adhesion, but if Ra is within the preferred range, the coating film adhesion is particularly excellent (Inventive Examples 7 to 10).

[0177] On the other hand, as shown in the Comparative Examples (1 to 6), when the grinding conditions such as the conveying speed, the rotational speed of the brush roll, the reduction amount, the abrasive grain size, and the diameter of the brush roll do not fall within the preferred range, there is no protrusion, or the area ratio of Goss-oriented grains of the protrusion becomes low, B8 is low and W17 / 50 becomes high.

[0178] Industrial Applicability

[0179] According to the present invention, it is possible to provide a grain-oriented electrical steel sheet having a sufficiently high magnetic flux density and low iron loss, and a method for manufacturing the same. Therefore, the industrial applicability is high.

[0180] Description of Reference Numerals

[0181] 1 Grain-oriented electrical steel sheet

[0182] 11 Steel sheet (base steel sheet)

[0183] 21 Groove

[0184] 31 Inlet portion

[0185] 41 Groove edge portion

[0186] 101 Projection

[0187] RD Rolling direction

[0188] TD Sheet width direction

[0189] RS Reference plane

Claims

1. An oriented electromagnetic steel sheet, characterized in that, There is a steel plate with a plurality of grooves formed on the surface, extending in a direction crossing the rolling direction and having a depth in the plate thickness direction. In a cross-section parallel to the rolling direction and parallel to the plate thickness direction, the distance from the inlet portion of the groove to the inlet portion of the opposite groove is defined as the width of the groove, and the region having the same width as the groove in the direction opposite to the center of the groove from the inlet portion of the groove of the steel plate in the rolling direction is defined as the groove edge portion. When the surface in the region farther from the width of the groove than the width of the groove in the direction opposite to the center of the groove from the inlet portion of the groove in the rolling direction is defined as the reference surface, There is a protrusion, i.e., a region having a width of 1 μm or more and a protrusion height from the reference surface of 1 μm or more, in the groove edge portion. The area ratio of Goss-oriented grains in the protrusion is 10% or more.

2. The oriented electromagnetic steel sheet according to claim 1, wherein, The arithmetic mean roughness Ra of the surface of the groove edge portion of the steel plate along the extending direction of the groove including the vertex of the protrusion exceeds 2.0 μm and is 5.0 μm or less.

3. The oriented electromagnetic steel sheet according to claim 1 or 2, characterized in that, A forsterite coating film is formed on the surface of the steel plate.

4. The oriented electromagnetic steel sheet according to claim 3, characterized in that, An insulating coating film is formed on the surface of the forsterite coating film.

5. The oriented electromagnetic steel sheet according to claim 1 or 2, characterized in that, An insulating coating film is formed on the surface of the steel plate.

6. A method for manufacturing an oriented electromagnetic steel sheet, which is the method for manufacturing the oriented electromagnetic steel sheet according to claim 1, characterized in that, It includes: A groove forming process for forming grooves on the surface by irradiating the steel plate with a laser. And A grinding process for grinding the surface of the steel plate with a brush roll fixed with abrasive grains after the groove forming process. In the grinding process, The brush roll rotates in a direction opposite to the conveying direction of the steel plate at the position where it abuts against the steel plate. The conveying speed of the steel plate is 20 to 150 mpm. The rotational speed of the brush roll is 500 to 1500 rpm. The pressing amount of the brush roll is 1.0 to 5.0 mm. The grain size of the abrasive grains is #60 to #400. The diameter of the brush roll is 200 to 500 mm.

7. The manufacturing method of the oriented electromagnetic steel sheet according to claim 6, characterized in that, The pressing amount of the brush roll is 1.0 to 2.0 mm.

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