Directional electromagnetic steel sheet and method for manufacturing the same

Abstract

This grain-oriented electrical steel sheet has a steel sheet on the surface of which a plurality of grooves extending in a direction intersecting the rolling direction and having a depth in the sheet thickness direction are formed. In a cross-section parallel to the rolling direction and parallel to the sheet thickness direction, where the groove width is defined as the distance from a groove entry portion to the opposite groove entry portion, the groove edge portion is defined as a region equivalent to the width of the groove from the entry portion of the groove on the steel sheet in the reverse direction from the center of the groove in the rolling direction, and the reference surface is defined as the surface of a region distanced further than the width of the groove from the entry portion of the groove in the reverse direction from the center of the groove in the rolling direction, there is a protrusion on the groove edge portion, said protrusion being a region with a width of 1 μm or more and a protrusion height of 1 μm or more from the reference surface, and the area ratio of Goss-oriented grains among the protrusion 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. This application claims priority based on Japanese Patent Application No. 2022-186164 filed in Japan on November 22, 2022, and incorporates the content herein by reference.

Background Art

[0002] The grain-oriented electrical steel sheet is a soft magnetic material and is mainly used as a core material for transformers. Therefore, the grain-oriented electrical steel sheet is required to have magnetic properties such as high magnetization characteristics and low iron loss. Iron loss is the power loss consumed as thermal 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 is affected by magnetic susceptibility, plate thickness, film tension, impurity amount, electrical resistivity, crystal grain size, magnetic domain width, etc. Regarding grain-oriented electrical steel sheets, even currently when various technologies have been developed, research and development to reduce iron loss are continuing in order to improve energy efficiency. As one method for reducing iron loss, a technique of performing laser irradiation has been proposed. In this technique, it is said that strain is introduced on the surface by laser irradiation, and the 180° magnetic domain width is subdivided, thereby reducing the eddy current loss, which is a part of the iron loss.

[0003] For example, Patent Document 1 discloses a process of irradiating the surface of a grain-oriented electrical steel sheet with a focused continuous-wave laser beam while scanning in a direction inclined from the rolling direction of the grain-oriented electrical steel sheet, and a process of repeating while shifting the portion where the continuous-wave laser beam is scanned at a predetermined interval. When the average power of the continuous-wave laser beam is represented as P (W), the scanning speed is represented as Vc (mm / s), and the predetermined interval is represented as PL (mm), and the input energy Ua is defined as Ua = P / (Vc×PL) (mJ / mm 2 ), when 1.0 mm ≤ PL ≤ 3.0 mm and 0.8 mJ / mm 2 ≤ Ua ≤ 2.0 mJ / mm 2 , a method for manufacturing a grain-oriented electrical steel sheet in which magnetic domains are controlled by laser beam irradiation is disclosed. In Patent Document 1, it is shown that iron loss in both the L direction and the C direction of a grain-oriented electrical steel sheet can be reduced easily and with high productivity.

[0004] However, for example, when manufacturing a wound core, since the grain-oriented electrical steel sheet is bent and formed, stress relief annealing is required. Therefore, in such a method, the stress introduced into the grain-oriented electrical steel sheet is released by stress relief annealing. Thus, the effect of magnetic domain control by laser irradiation cannot be obtained. Therefore, it has been proposed that by forming grooves on the steel sheet surface, similar to stress introduction, the 180° magnetic domain width is subdivided to reduce eddy current loss. 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 a laser beam is controlled and irradiated to form recesses with a width in the rolling direction of 0.5 mm or less and a depth of 10 μm or more. However, as described above, when grooves are formed by laser irradiation, protrusions are formed by the solidification of the melt generated by laser irradiation at the groove edges and the like. This protrusion is usually composed of fine crystal grains having a random crystal orientation other than the Goss orientation. Therefore, when 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-mentioned protrusions are removed to some extent by performing brush treatment or the like after laser irradiation. However, even if brush treatment or the like is performed, it is difficult to completely remove the protrusions because it is performed so as not to reduce the plate thickness. Such protrusions are not considered in Patent Document 2.

[0005] Regarding such a melt, for example, Patent Document 3 discloses a grain-oriented electrical steel sheet having grooves (grooves) formed on the surface and subjected to magnetic domain refinement treatment, wherein the scattered alloy layer of the groove is eroded by a Goss texture, and 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 between one end of the groove and the bottom of the groove is defined as TL, the TB / TL is 0.2 to 0.8.

[0006] However, in Patent Document 3, although the inside of the groove is mentioned, nothing is mentioned about the crystal orientation of the protrusions formed at the groove edge.

[0007] Further, Patent Document 4 discloses a steel sheet having a surface of a steel sheet in which grooves are formed such that the extending direction intersects the rolling direction and the depth direction is parallel to the sheet thickness direction, and there are fusion solidified products continuous in parallel with the grooves on both sides of the grooves on the surface of the steel sheet. When the height that becomes the maximum frequency in the height distribution of the height data measured at regular intervals on the surface of the steel sheet in a specific region including the grooves is defined as a virtual plane, the spatial volume of the concave portion recessed from the virtual plane is V1, and the volume of the convex portion protruding from the virtual plane is V2, the value of V2 / V1 is more than 0.10 and less than 0.80. A plurality of protrusions are formed in the specific region, and among the plurality of protrusions, the width of the protrusion closest to the groove is larger than the widths of the other protrusions. When the region where the average height in the extending direction in the height distribution is the highest is viewed in a groove longitudinal cross section including the extending direction and the sheet thickness direction, the average roughness Ra of the roughness curve forming the surface of the region is 0.30 to 2.00 μm, and the average length RSm of the roughness curve elements forming the surface of the region is 10 to 150 μm. A directional electromagnetic steel sheet is disclosed.

[0008] However, in the technique of Patent Document 4, although the crystal orientation of the protrusions in the region where the average height in the extending direction in the height distribution is the highest is defined, the crystal orientation of the protrusions in other regions is not defined. Controlling the crystal orientation is important for reducing iron loss regardless of what kind of protrusions they are, but in Patent Document 4, the examination regarding the crystal orientation of the protrusions and the reduction of iron loss has not been sufficiently made.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

[0010] 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 accordingly, the eddy current loss, which is part of the iron loss, is reduced. However, when the grooves are formed by laser irradiation, protrusions are formed due to the solidification of the melt generated by the laser irradiation at the groove edges. Since this protrusion is composed of fine crystal grains having a random crystal orientation other than the Goss orientation, when 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 protrusion is removed by brushing or the like after laser irradiation, but it is difficult to completely remove the protrusion because the brushing is performed so as not to reduce the plate thickness. In addition, when there are protrusions at the groove edges, there is also a concern that the adhesion of the coating film deteriorates. However, conventionally, sufficient examination has not been made on the coating film adhesion in the case where there are protrusions.

[0011] In view of the above, an object of the present invention is to provide a grain-oriented electrical steel sheet that realizes low iron loss by suppressing a decrease in magnetic flux density due to protrusions and an increase in hysteresis loss associated therewith, and a method for manufacturing the same, in a grain-oriented electrical steel sheet in which magnetic domain subdivision is performed by forming grooves. Another preferred object is to provide a grain-oriented electrical steel sheet that can obtain sufficient coating film adhesion even when there are protrusions. [Means for Solving the Problems]

[0012] The present inventors have studied the suppression of the increase in hysteresis loss due to protrusions. As a result, it has been found that the increase in hysteresis loss can be suppressed by controlling the crystal orientation of the protrusions formed at the groove edges so that the ratio of the Goss orientation becomes high. Further, regarding the crystal orientation of the protrusions at the groove edges, after forming grooves that form grooves on the surface of the steel sheet by laser irradiation, by grinding the surface of the steel sheet under predetermined conditions, it has been found that the ratio of the crystal orientation of the protrusions becoming the Goss orientation can be increased during subsequent annealing. It has also been found that by controlling the grinding conditions to make the surface roughness within a predetermined range, the film adhesion can be further improved.

[0013] The present invention has been made in view of the above findings. The gist of the present invention is as follows. [1] The grain-oriented electrical steel sheet according to one aspect of the present invention has a plurality of grooves formed on the surface and extending in a direction intersecting the rolling direction and having a depth in the sheet thickness direction. It is a base steel sheet of a grain-oriented electrical steel sheet In a cross-section parallel to the rolling direction and parallel to the sheet thickness direction of the steel sheet, the distance from the entrance of one groove to the entrance of the opposite groove is defined as the width of the groove. From the entrance of the groove of the steel sheet, in the rolling direction, in the direction opposite to the center of the groove, a region having the same width as the width of the groove is defined as the groove edge portion. When the surface in a region farther from the width of the groove than the width of the groove in the rolling direction from the entrance of the groove is defined as a reference surface, there are protrusions in the groove edge portion that are regions where the width is 1 μm or more and the protrusion height from the reference surface is 1 μm or more. Among the protrusions, the area ratio of Goss-oriented grains is 10% or more. [2] In the grain-oriented electrical steel sheet according to [1], the arithmetic mean roughness Ra of the surface of the groove edge portion of the steel sheet along the extending direction of the groove including the apex of the protrusion may be more than 2.0 μm and 5.0 μm or less. [3] In the grain-oriented electrical steel sheet according to [1] or [2], a forsterite film may be formed on the surface of the steel sheet. [4] In the grain-oriented electrical steel sheet according to [3], an insulating film may be formed on the surface of the forsterite film. [5] In the grain-oriented electrical steel sheet according to [1] or [2], an insulating film may be formed on the surface of the steel sheet. [6] The method for manufacturing a grain-oriented electromagnetic steel sheet according to another aspect of the present invention is the method for manufacturing a grain-oriented electromagnetic steel sheet described in [1], and includes a groove forming step of forming grooves on the surface of the steel sheet by irradiating the steel sheet with a laser, and a grinding step of grinding the surface of the steel sheet using a brush roll to which abrasive grains are fixed after the groove forming step. In the grinding step, the brush roll rotates in a direction opposite to the conveying direction of the steel sheet at a position where it contacts the steel sheet, the conveying speed of the steel sheet is 20 to 150 mpm, the rotation speed of the brush roll is 500 to 1500 rpm, the amount of reduction 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. [7] In the method for manufacturing a grain-oriented electromagnetic steel sheet described in [6], the amount of reduction of the brush roll may be 1.0 to 2.0 mm. [Advantages of the Invention]

[0014] According to the above aspect of the present invention, it is possible to provide a grain-oriented electromagnetic steel sheet having a sufficiently high magnetic flux density and low iron loss, and a method for manufacturing the same. [Brief Description of the Drawings]

[0015]

Figure 1

Figure 2

[0016] A grain-oriented electromagnetic steel sheet (grain-oriented electromagnetic steel sheet according to this embodiment) and a method for manufacturing the same according to an embodiment of the present invention will be described.

[0017] [Grain-Oriented Electromagnetic Steel Sheet] As shown in FIG. 1, the grain-oriented electromagnetic steel sheet 1 according to this embodiment has a steel sheet (base steel sheet) 11 on which a plurality of grooves 21 extending in a direction intersecting the rolling direction RD and having a depth in the plate thickness direction are formed on the surface. A forsterite film or an insulating film may be formed on the surface of the steel sheet (base steel sheet). Further, the insulating film may be formed on the surface of the forsterite film. That is, the grain-oriented electrical steel sheet according to the present embodiment may be composed of only the steel sheet (base steel sheet), or may be composed of the base steel sheet and a forsterite film formed on the surface of the base steel sheet, or may be composed of the base steel sheet and an insulating film formed on the surface of the base steel sheet, or may be composed of the base steel sheet, a forsterite film formed on the surface of the base steel sheet, and an insulating film formed on the surface of the forsterite film. The forsterite film and the insulating film may be formed on one side, or may be formed on both sides. Each of these will be described below.

[0018] [Steel sheet (base steel sheet)] (Groove) As shown in FIG. 1, the steel sheet 11 has a plurality of grooves 21 formed on the surface by laser irradiation, extending in a direction intersecting the rolling direction RD and having a depth in the plate thickness direction. The steel sheet is, for example, a cold-rolled sheet. Magnetic domain control can be performed by periodically forming linear grooves in a direction intersecting the rolling direction RD. In the grain-oriented electrical steel sheet according to 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 on which a forsterite film or an insulating film is formed, the so-called base steel sheet excluding these). Here, the direction intersecting the rolling direction RD is a direction of 60 to 120° with respect to the rolling direction RD. The shape of the groove is not limited as long as the effect of magnetic domain control can be obtained, but the depth is preferably 10 to 50 μm and the width is preferably 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 at substantially constant intervals (periodically) in the rolling direction RD so that they are substantially parallel to each other. 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.

[0019] (Projection) As described above, in a grain-oriented electrical steel sheet, by forming grooves in a direction intersecting the rolling direction RD of the steel sheet, the 180-degree magnetic domain width is subdivided, and accordingly, eddy current loss, which is part of the iron loss, is reduced. However, when forming grooves by laser irradiation, protrusions are formed due to the solidification of the melt generated by the laser irradiation at the groove edges. Since this protrusion is composed of fine crystal grains having a random crystal orientation other than the Goss orientation, the presence of the protrusion reduces the magnetic flux density of the steel sheet and increases the hysteresis loss, which is part of the iron loss, resulting in inferior characteristics. Although the above protrusion is removed by brushing or the like after laser irradiation, it is difficult to completely remove the protrusion because brushing is performed so as not to reduce the plate thickness. Therefore, in the grain-oriented electrical steel sheet according to this embodiment, instead of removing the protrusion, the crystal orientation of the protrusion formed at the groove edge is controlled, and the area ratio of crystal grains (Goss orientation grains) having a crystal orientation of Goss orientation in the protrusion is set to 10% or more, thereby suppressing an increase in hysteresis loss. If the area ratio of Goss orientation 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.

[0020] Also, there is concern about deterioration of film adhesion at the portion where the protrusion exists. Therefore, in the grain-oriented electrical steel sheet according to this embodiment, it is preferable to control the roughness of the surface of the groove edge including the protrusion. Specifically, it is preferable that the arithmetic mean roughness Ra of the surface along the extending direction of the groove including the apex of the protrusion (the point where the protrusion height is maximum) is more than 2.0 μm and 5.0 μm or less. In this case, excellent film adhesion can be obtained. When Ra is 2.0 μm or less, since the surface is smooth, the effect of improving film adhesion cannot be obtained. On the other hand, when Ra exceeds 5.0 μm, since the surface is too rough, the film is likely to peel off, and the effect of improving film adhesion cannot be obtained.

[0021] Here, in the present embodiment, as shown in FIGS. 1 and 2, in a cross-section parallel to the rolling direction RD and parallel to the plate thickness direction, the distance from the entrance portion 31 of the groove 21 (the position where the side surface of the groove that is concave with respect to the reference plane intersects the virtual line extending the reference plane) to the entrance portion 31 of the opposite groove 21 is defined as the width of the groove 21. From the entrance portion of the groove 21 of the steel plate 11 in the rolling direction RD, in the direction opposite to the center of the groove 21, a region equivalent to the width of the groove 21 is defined as the groove edge portion 41. Further, when the surface in a region farther from the groove 21 than the width of the groove 21 (that is, a region farther from the groove 21 than the groove edge portion 41) in the direction opposite to the center of the groove 21 in the rolling direction RD from the entrance portion 31 of the groove 21 is defined as the reference plane RS, in the groove edge portion 41, a region where the width at the height of the reference plane RS (the length in the direction perpendicular to the height direction (the length of the dotted line portion in FIG. 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. The area ratio of the crystal grains with the Goss orientation 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 apex of the protrusion can be controlled by a manufacturing method including a grinding process described later.

[0022] The area ratio of the crystal grains with the crystal orientation of the protrusion at the groove edge portion being the Goss orientation is obtained by the following method. First, a sample is taken from the grain-oriented electrical steel sheet to be measured so that a cross-section orthogonal to the longitudinal direction (extending direction) of the groove is exposed. At that time, the cross-section is taken to include the groove and the groove edge portion. By polishing the cross-section, a cross-section including the groove and its peripheral portion as shown in FIG. 2 is revealed, and then the cross-section is observed. A total of 10 or more cross-sections are observed, and when one or more protrusions are present at the groove edge portion, it is determined that at least one protrusion is present. When there are protrusions, the crystal orientation of the protrusions is measured by the Electron Back Scattering Diffraction Pattern (EBSD) method. Those with an angular difference of within 10° from the exact Goss orientation {110}<001> are defined as Goss orientation grains, and the area ratio of the Goss orientation grains of the protrusions is determined. When there are multiple protrusions on the observed cross-section, for each protrusion, the area ratio of the Goss orientation grains is determined, and the average value thereof is taken as the area ratio of the Goss orientation grains. The measurement conditions for EBSD are as follows. (a) Measuring device: FE-SEM "SU-70" (manufactured by Hitachi High-Tech Corporation) EBSD device "DigiView" (manufactured by TSL Solutions) (b) Magnification: 500 times (c) Step interval: 0.25 μm (d) Measurement area: 200 μm in the direction intersecting the groove longitudinal direction and 70 μm in the plate thickness direction

[0023] The arithmetic mean roughness Ra of the surface of the groove edge including the apex of the protrusion is determined by the following method. Using a laser surface roughness measuring instrument, obtain the height distribution in a range of 1000 μm in the groove extending direction and 400 μm (200 μm on each side of the groove) centered on the groove in the direction perpendicular to the groove extending 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), scanned 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. As a result of this measurement, the point with the maximum height is taken as the apex of the protrusion. Then, obtain the measurement cross-section curve of the cross-section including the plane parallel to the groove extending direction and parallel to the plate thickness direction of the steel plate and including the apex of the protrusion. Apply a low-pass filter with a cut-off value λs and a wide-pass filter with a cut-off value λc to the measurement cross-section curve to obtain a roughness curve. The arithmetic mean roughness Ra is determined from this roughness curve in accordance with JIS B 0601 (2013). At that time, the cut-off values λs and λc are determined by the type of the laser surface roughness measuring instrument and the objective lens. In this embodiment, when measuring the roughness with a magnification of 50 times for the objective lens using the VK-9700 manufactured by Keyence Corporation, λs = 0.8 μm and λc = 0.08 mm are used as the cut-off values.

[0024] (Chemical composition) The chemical composition of the base steel plate is not limited, and it may be equivalent to the base steel plate of a known grain-oriented electrical steel sheet. For example, 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% can be contained. Further, the above may be contained and the balance may be Fe and impurities. When the grain-oriented electrical steel sheet is made of the base steel plate (without a forsterite film or an insulating film), it can be said that the chemical composition of the base steel plate is the chemical composition of the grain-oriented electrical steel sheet.

[0025] The chemical composition of the base steel plate may be measured by a general analysis method for steel. For example, the chemical composition of the base steel plate may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Specifically, for example, a test piece of 35 mm square (35 mm in the rolling direction and the width direction respectively) is obtained from the central position of the base steel plate after film removal, and it can be specified by measuring under the conditions based on the calibration curve prepared in advance using an ICPS-8100 etc. (measuring device) manufactured by Shimadzu Corporation. For C and S that are difficult to measure by ICP-AES, combustion-infrared absorption method may be used, and for N, inert gas fusion-thermal conductivity method may be used for measurement. When the forsterite film and the insulating film described later are formed on the chemical composition of the base steel plate, the forsterite film and the insulating film may be removed from the grain-oriented electrical steel sheet by a known method such as pickling and then the analysis may be performed.

[0026] (Plate thickness) The plate thickness of the base steel plate of the grain-oriented electrical steel sheet according to this embodiment is not limited, but from the viewpoint of reducing eddy current loss, it is preferably, for example, 0.15 to 0.35 mm because a thinner plate thickness results in lower eddy current loss.

[0027] [Forsterite coating] In the grain-oriented electrical steel sheet according to this embodiment, a forsterite coating may be formed on the surface of the steel plate serving as the base steel plate. The forsterite coating is an inorganic coating mainly composed of magnesium silicate. The forsterite coating is formed by the reaction of the annealing release agent containing magnesia (MgO) applied to the surface of the base steel plate with the components on the surface of the base steel plate during finish annealing, and has a composition derived from the components of the annealing release agent and the base steel plate (more specifically, a composition mainly composed of Mg2SiO4). On the other hand, when an annealing release agent mainly composed of Al2O3 is used during finish annealing, the forsterite coating may not be formed in some cases.

[0028] [Insulating coating] In the grain-oriented electrical steel sheet according to this embodiment, an insulating coating may be formed on the surface of the base steel plate or on the surface of the forsterite coating. The insulating coating reduces eddy current loss by imparting electrical insulation to the grain-oriented electrical steel sheet, thereby reducing the iron loss of the grain-oriented electrical steel sheet. The insulating coating has a function of applying tension to the grain-oriented electrical steel sheet. By applying tension to the grain-oriented electrical steel sheet to facilitate magnetic wall movement in the grain-oriented electrical steel sheet, the iron loss of the grain-oriented electrical steel sheet can be reduced. In addition, according to the insulating coating, various properties such as corrosion resistance, heat resistance, and slidability can be obtained in addition to the electrical insulation as described above. In the grain-oriented electrical steel sheet according to this embodiment, the insulating coating may be a known coating formed, for example, by applying a coating solution mainly composed of phosphate and colloidal silica to the surface of the forsterite coating and baking it.

[0029] [Manufacturing method] The grain-oriented electrical steel sheet according to this embodiment can achieve the above-described effects as long as it has the above characteristics regardless of the manufacturing method. However, a manufacturing method including the following steps is preferable because it enables stable manufacturing. (I) A hot rolling step of heating a slab and hot rolling it to obtain a hot-rolled sheet. (II) A hot-rolled sheet annealing step of annealing the hot-rolled sheet after the hot rolling step. (III) A cold rolling step of pickling the hot-rolled sheet after the hot-rolled sheet annealing step and cold rolling it to obtain a steel sheet (cold-rolled sheet). (IV) A groove forming step of forming grooves on the surface by irradiating the steel sheet with a laser. (V) A grinding step of grinding the surface of the steel sheet after the groove forming step using a brush roll with abrasive grains fixed thereto. (VI) A decarburizing annealing step of performing decarburizing annealing on the steel sheet after the grinding step. (VII) A finish annealing step of applying an annealing release agent to the steel sheet after the decarburizing annealing step and performing finish annealing. Further, the manufacturing method of the grain-oriented electrical steel sheet according to this embodiment may further include any one or both of the following steps. (VIII) A nitriding treatment step of increasing the nitrogen content of the steel sheet after the decarburizing annealing step. (IX) An insulating film forming step of forming an insulating film on the surface of the steel sheet after the finish annealing step (or on the surface of the forsterite film formed on the surface of the steel sheet).

[0030] Among these, the manufacturing method of the grain-oriented electrical steel sheet according to this embodiment is characterized by the groove forming step and the grinding step. On the other hand, the hot rolling step, the hot-rolled sheet annealing step, the cold rolling step, the decarburizing annealing step, the nitriding treatment step, the finish annealing step, and the insulating film forming step are not particularly limited and can be performed under known conditions. Hereinafter, preferable conditions will be described. Even for the conditions not described, they can be performed under known conditions.

[0031] [Hot Rolling Step] In the hot rolling process, a slab having a predetermined chemical composition (a chemical composition corresponding to the chemical composition of the base steel plate of the grain-oriented electrical steel sheet according to the present embodiment) is heated and hot rolled into a hot rolled sheet. The conditions are not limited, but for example, the heating temperature is 1050 to 1400 °C.

[0032] The chemical composition of the slab to be subjected to hot rolling may be determined in consideration of the change in chemical composition in each step according to the chemical composition desired to obtain as the grain-oriented electrical steel sheet. For example, when obtaining the chemical composition of the base steel plate of the grain-oriented electrical steel sheet according to the above-described preferred present embodiment, it is preferable to use a slab having the following chemical composition. 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% can be contained. Further, it may contain the above and the balance may be Fe and impurities.

[0033] The method for obtaining the slab is not limited. For example, molten steel having a predetermined chemical composition may be melted and produced using the molten steel. The slab may be produced by a continuous casting method, or an ingot may be produced using the molten steel and the ingot may be subjected to block rolling to produce the slab. Further, the slab may be produced by other methods. The thickness of the slab is not particularly limited, but for example, it is 150 to 350 mm. The thickness of the slab is preferably 220 to 280 mm. A so-called thin slab having a thickness of 10 to 70 mm may also be used.

[0034] [Hot rolled sheet annealing process] 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 it becomes possible to realize good magnetic properties. In the hot-rolled sheet annealing process of this embodiment, the hot-rolled sheet manufactured through the hot rolling process may be annealed according to a known method. The means for heating the hot-rolled sheet during annealing is not particularly limited, and a known heating method can be adopted. Also, the annealing conditions are not particularly limited, but for example, annealing can be performed on the hot-rolled sheet in a temperature range of 900 to 1200 °C for 10 seconds to 5 minutes.

[0035] [Cold rolling process] In the cold rolling process, the hot-rolled sheet after the hot-rolled sheet annealing process is pickled and cold-rolled to obtain a cold-rolled sheet. The cold rolling may be a single-pass (a series without intermediate annealing) cold rolling, or before the final pass of the cold rolling process, the cold rolling may be interrupted and at least one or two or more intermediate annealings may be performed, and multiple cold rollings with intermediate annealings interposed may be performed. For the conditions of cold rolling, follow a known method. For example, the final reduction ratio can be within the range of 80% or more and 95% or less. The final reduction ratio is the cumulative reduction ratio of cold rolling, and when intermediate annealing is performed, it is the cumulative reduction ratio of cold rolling after the final intermediate annealing. When performing intermediate annealing, for example, hold 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. Also, pickling can be performed under known conditions.

[0036] [Groove forming process] In the groove forming process, grooves are formed on the surface of the cold-rolled sheet (the steel sheet after cold rolling) by irradiating with a laser. A method of forming grooves is preferred in which the laser is scanned and irradiated while moving in the direction of forming the grooves (the direction intersecting the rolling direction) to melt a part of the steel sheet surface and removing the melt from the surface. Examples of the method for removing the melt from the surface include blowing assist gas. Also, the laser irradiation is preferably performed a plurality of times while moving in the width direction so that the grooves are arranged substantially parallel at a certain interval (for example, 1 to 10 mm) in the rolling direction. Although the laser irradiation conditions are not limited, in order to form grooves with a predetermined shape (for example, a depth of 10 to 50 μm and a groove width of 10 to 200 μm), the laser output is 200 to 3000 W, the condensing spot diameter in the rolling direction of the laser (that is, the diameter including 86% of the laser output) is 10 to 1000 μm, the condensing spot diameter in the plate width direction of the laser (that is, the diameter including 86% of the laser output) is 10 to 1000 μm, and the laser scanning speed is preferably 5 to 50 m / s. By forming grooves on the surface of the cold-rolled sheet (which becomes the base steel sheet), the magnetic domain width is refined and the magnetic properties are improved.

[0037] <Grinding process> In the grinding process, the surface of the steel sheet after the groove forming process is ground using a brush roll with abrasive grains fixed thereto. By performing grinding under appropriate conditions, it is possible to impart strain to the protrusions formed at the groove edges while avoiding a reduction in the plate thickness (a part of the protrusions is removed by grinding, but a part remains). The protrusions with strain applied have an increased driving force for recrystallization, and primary recrystallization and grain growth occur in the subsequent decarburizing annealing process, making them easily eaten away in the Goss orientation during finish annealing. Therefore, the protrusions with strain applied undergo secondary recrystallization during finish annealing and the area ratio of Goss-oriented grains increases (if there is random recrystallization without strain application, the area ratio of Goss-oriented grains is usually less than 5%, but by passing through the grinding process, it becomes 10% or more). In order to apply appropriate strain, while moving the steel sheet at a conveying speed of 20 to 150 meter / minutes (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. The rotational speed of the brush roll is 500 to 1500 rpm, the reduction amount of the brush roll is 1.0 to 5.0 mm, the grain size of the abrasive grains is #60 to #400, and grinding is performed under the condition that the diameter of the brush roll is 200 to 500 mm. If the conveying speed (line speed) of the steel sheet is less than 20 mpm, the grinding amount is too large and the plate thickness will decrease. On the other hand, if it exceeds 150 mpm, the amount of strain applied by grinding is not sufficient and the area ratio of Goss-oriented grains does not increase. Also, 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 too large, resulting in a decrease in the plate thickness. When the press-down amount of the brush roll is less 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 too large, resulting in a decrease in the plate thickness. When the grain size of the abrasive grains is less than #60, the grinding amount is too large, resulting in a decrease in the plate thickness. 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. When the diameter of the brush roll is less than 200 mm, the grinding amount is too large, resulting in a decrease in the plate thickness. 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. Also, preferably, the conveyance speed of the steel sheet is 20 - 150 mpm, the rotational speed of the brush roll is 500 - 1000 rpm, the press-down amount of the brush roll is 1.0 - 4.0 mm, the grain size of the abrasive grains is #100 - 400, and the diameter of the brush roll is 200 - 500 mm. More preferably, the press-down amount of the brush roll is 1.0 - 2.0 mm. By setting the press-down amount in such a range, the roughness Ra of the longitudinal section of the groove including the apex of the protrusion can be made to be in the range of more than 2.0 μm and 5.0 μm or less.

[0038] [Decarburization annealing process] In the decarburization annealing process, decarburization annealing is performed on the steel sheet after the grinding process. In this decarburization annealing, carbon that has an adverse effect on the magnetic properties is removed (decarburized) from the steel sheet, and the steel sheet undergoes primary recrystallization. The decarburization annealing conditions are not limited, but it can be set to heat at 700 - 900 °C and hold for 1 - 3 minutes.

[0039] [Nitriding treatment process] After the decarburization annealing process and before the finish annealing process, nitriding treatment may be performed to increase the nitrogen content of the grain-oriented electrical steel sheet. The nitriding treatment may be performed by a known method. For example, by annealing in an atmosphere containing a nitriding gas such as ammonia, nitrogen is introduced into the steel. Thereby, an inhibitor for secondary recrystallization can be formed by nitridation.

[0040] [Finish Annealing Process] In the finish annealing process, an annealing release agent is applied to the steel sheet after the decarburization annealing process, and finish annealing is performed. Since the finish annealing is performed after the steel sheet is wound into a coil, an annealing release agent is applied so that the steel sheet does not adhere during the finish annealing. Generally, an annealing release agent mainly composed of MgO or Al2O3 is used. After applying such an annealing release agent, finish annealing is performed. For example, when an annealing release agent containing MgO is used, a layer of forsterite (Mg2SiO4) film is formed. When an annealing release agent mainly composed of Al2O3 is used, a forsterite film may not be formed. In addition, in the finish annealing process, by heating to the annealing temperature, the primary recrystallized grains obtained in the decarburization annealing process are secondary recrystallized to obtain grains aligned in the Goss orientation, and by holding at the annealing temperature for a predetermined time, impurities (N, S, etc.) that have an adverse effect on magnetic properties are removed (purified). In the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment, in the steel sheet to be subjected to decarburization annealing, the driving force for recrystallization is enhanced by the strain introduced in the grinding process, primary recrystallization and grain growth occur in the decarburization annealing process, and it becomes a state in which it is easily nibbled in the Goss orientation during finish annealing. Therefore, in the protrusion, the area ratio of the grains having the Goss orientation increases. The conditions for finish annealing are not limited, but examples include heating to 1100 to 1300 °C and holding for 20 to 24 hours.

[0041] [Insulating Film Forming Process] In the insulating film forming process, an insulating film is formed on the steel sheet after the finish annealing process (on the surface of the forsterite film when a forsterite film is formed on the surface of the steel sheet by finish annealing). For example, the insulating film can be formed by applying a coating solution containing phosphoric acid or phosphate, colloidal silica, and anhydrous chromic acid or chromate to a steel sheet after finish annealing (including the case having a forsterite film), and baking and drying at 300 to 950 °C for 10 seconds or more. Through these steps, a grain-oriented electrical steel sheet provided with a base steel sheet and, if necessary, a forsterite film and / or an insulating film can be obtained.

Example

[0042] 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%, with the balance being Fe and impurities, was subjected to a hot rolling process to obtain a hot-rolled sheet with a thickness of 2.6 mm. This hot-rolled sheet was heated to 1000 °C and held for 1 minute for hot-rolled sheet annealing. 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 obtain a steel sheet (cold-rolled sheet) with a thickness of 0.23 mm. This steel sheet was subjected to laser irradiation under the conditions of a laser output of 1500 W, a spot diameter in the rolling direction of the laser of 40 μm, a spot diameter in the sheet width direction of the laser of 40 μm, and a scanning speed of 45 m / s to form grooves extending in a direction 90° with respect to the rolling direction on the surface, with a width of 40 μm and a depth of 30 μm. Further, a plurality of these grooves were formed in parallel at intervals of 5 mm in the rolling direction. The surface of the steel sheet with grooves formed thereon was ground under the conditions shown in Table 1 using a brush roll rotating in a direction opposite to the conveying direction of the steel sheet. After grinding, decarburization annealing was performed under the conditions of heating to 800 °C and holding for 2 minutes. An annealing separation agent mainly composed of magnesia (MgO) was applied to the steel sheet after decarburization annealing, and finish annealing was carried out under the conditions of heating to 1200 °C and holding for 20 hours. As a result, a grain-oriented electrical steel sheet with a forsterite film formed on the surface of the steel sheet (base metal steel sheet) was obtained. An insulating film was formed by applying a coating solution containing colloidal silica and phosphate to the obtained grain-oriented electrical steel sheet and performing heat treatment under the conditions of heating to 850 °C and holding for 1 minute.

[0043] When the chemical composition of the base metal steel sheet of the obtained grain-oriented electrical steel sheet was determined, by mass fraction, 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, and the balance was composed of Fe and impurities.

[0044] From the obtained grain-oriented electrical steel sheet, the area ratio of the Goss-oriented grains of the protrusions was determined by the EBSD method in the above-described manner. Also, in the above-described manner, a measurement cross-sectional curve of a cross-section including a plane parallel to the extending direction of the groove and parallel to the thickness direction of the steel sheet and including the apex of the protrusion was obtained, and the arithmetic mean roughness Ra was determined according to JIS B 0601 (2013) from the roughness curve obtained from this measurement cross-sectional curve. The results are shown in Table 1.

[0045] Also, a sample with a width of 60 mm and a rolling direction 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 sample in accordance with JIS C2556 (2015), and the iron loss W17 / 50 at a frequency of 50 Hz and a maximum magnetic flux density of 1.7 T was measured. Also, the magnetic flux density B8 generated when magnetized at 800 A / m was measured. The results are shown in Table 1. It was determined that if B8 was 1.88 T or more and W17 / 50 was 0.750 W / kg or less, it had excellent magnetic properties.

[0046] Also, the adhesion of the insulating film (film adhesion) of the obtained grain-oriented electrical steel sheet was evaluated by the following method. A test piece with dimensions of plate thickness × 80 mm × 80 mm was cut out from a portion including the groove edge of the obtained grain-oriented electrical steel sheet, and this test piece was wound around a round bar with a diameter of 20 mm and then flattened. The surface of the test piece after being flattened was observed, the area of the insulating film that had not peeled off from the steel sheet was measured with respect to the area of the bent portion, and the film remaining area ratio (%) was calculated. The insulating film adhesion of the test piece with a film remaining area ratio of 95% or more was evaluated as "excellent", the insulating film adhesion of the test piece with a film remaining area ratio of 90% or more and less than 95% was evaluated as "good", and the insulating film adhesion of the test piece with a film remaining area ratio of less than 90% was evaluated as "poor".

[0047]

Table 1

[0048] As can be seen from Table 1, when the area ratio of the Goss-oriented grains of the protrusions (protrusion parts) 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). Also, although all had sufficient film adhesion, when Ra was within a preferable range, the film adhesion was particularly excellent (Inventive Examples 7 to 10). On the other hand, as shown in Comparative Examples (1 to 6), when the grinding conditions such as the conveyance speed, the rotation speed of the brush roll, the rolling reduction, the abrasive grain size, and the diameter of the brush roll are not within a preferable range, there are no protrusions or the area ratio of the Goss-oriented grains of the protrusions becomes low, B8 becomes low, and W17 / 50 becomes high.

Industrial Applicability

[0049] According to 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. Therefore, the industrial applicability is high.

Explanation of Reference Numerals

[0050] 1 Grain-oriented electrical steel sheet 11 Steel sheet (base steel sheet) 21 grooves 31 inlet part 41 groove edge part 101 protrusion RD rolling direction TD sheet width direction RS reference plane

Claims

1. It has a steel plate which is a base material steel plate of a grain-oriented electrical steel sheet in which a plurality of grooves extending in a direction intersecting the rolling direction are formed on the surface and the depth is in the sheet thickness direction, In a cross-section parallel to the rolling direction and parallel to the sheet thickness direction, the distance from the entrance of one groove to the entrance of the opposite groove is defined as the width of the groove. From the entrance of the groove of the steel plate, in the rolling direction, in the direction opposite to the center of the groove, a region having the same width as the width of the groove is defined as the groove edge portion. When the surface in the region farther from the width of the groove than the groove edge portion from the entrance of the groove in the rolling direction and in the direction opposite to the center of the groove is defined as the reference surface, There are protrusions in the groove edge portion, which are regions where the width is 1 μm or more and the protrusion height from the reference surface is 1 μm or more, Among the protrusions, the area ratio of the Goss orientation grains is 10% or more, A grain-oriented electrical steel sheet characterized by the above.

2. The arithmetic mean roughness Ra of the surface along the extending direction of the groove including the apex of the protrusion in the groove edge portion of the steel plate is more than 2.0 μm and 5.0 μm or less, The grain-oriented electrical steel sheet according to claim 1, characterized by the above.

3. A forsterite film is formed on the surface of the steel plate, The grain-oriented electrical steel sheet according to claim 1 or 2, characterized by the above.

4. An insulating film is formed on the surface of the forsterite film, The grain-oriented electrical steel sheet according to claim 3, characterized by the above.

5. An insulating film is formed on the surface of the steel plate, The grain-oriented electrical steel sheet according to claim 1 or 2, characterized by the above.

6. A method for manufacturing the grain-oriented electrical steel sheet according to claim 1, A groove forming step of forming grooves on the surface by irradiating the steel plate with a laser, After the groove forming step, a grinding step of grinding the surface of the steel plate using a brush roll with abrasive grains fixed thereon, Including, In the grinding step, The brush roll rotates in a direction opposite to the conveyance direction of the steel plate at the position where it contacts the steel plate, The conveyance speed of the steel plate is 20 to 150 mpm, The rotational speed of the brush roll is 500 to 1500 rpm, The amount of press-down 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, A method for manufacturing a grain-oriented electrical steel sheet, characterized by the above.

7. The amount of press-down of the brush roll is 1.0 to 2.0 mm, The method for manufacturing a grain-oriented electrical steel sheet according to claim 6, characterized by the above.

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