Grain-oriented electrical steel sheet and method for manufacturing same

Abstract

To provide a grain-oriented electromagnetic steel sheet reduced in iron loss and magnetostriction.SOLUTION: A grain-oriented electrical steel sheet having a base coating and an insulation coating, wherein the base coating has a linear or dotted groove along a rolling direction, a groove bottom surface has an oxide film on a base iron, and the insulation coating is provided on the base coating and the groove bottom surface, and in a cross section of the steel sheet cut out in a rolling orthogonal direction, an average value of angles on the base iron side formed by a groove side wall and the rolling orthogonal direction in each groove is 30 degrees or more and 135 degrees or less, and a total of lengths of the groove bottom surfaces of all the grooves is 5% or more with respect to a length of the steel sheet in the rolling orthogonal direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] The easy axis of magnetization of iron <001> Grain-oriented electrical steel sheets, which have a crystal structure in which the orientation is highly aligned in the rolling direction of the steel sheet, are used particularly as iron core materials for power transformers. One of the characteristics strongly required for transformers is low iron loss. Transformer iron loss is closely related to the iron loss of the iron core material, and generally the lower the iron loss of the iron core material, the lower the transformer iron loss. Therefore, low iron loss is also required for the grain-oriented electrical steel sheet that is used as the iron core material.

[0003] One way to reduce iron loss in grain-oriented electrical steel sheets is to improve the anisotropy of the tension coating. Grain-oriented electrical steel sheets are usually coated with an insulating coating. In addition to ensuring insulation when stacked, this insulating coating also applies tension to the steel sheet. If the tension applied to the steel sheet is strong, the magnetic domains become more refined, resulting in lower iron loss. This also reduces the amount of magnetic domains oriented in the thickness direction, known as lancet domains, which reduces the vibration of the steel sheet, known as magnetostriction.

[0004] Based on these findings regarding the improvement of the properties of grain-oriented electrical steel sheets, the following inventions have been made. Patent Document 1 discloses a technique in which the coating tension is improved and magnetostriction can be reduced by mixing an inorganic nitride into the insulating coating raw material. Patent Document 2 discloses a technique for introducing grooves into the base steel to refine the magnetic domains and reduce iron loss. Patent Document 3 discloses a technique in which a laser is irradiated onto the surface of a steel sheet to introduce thermal strain, thereby refining magnetic domains and reducing iron loss. Patent Document 4 discloses a technique for increasing the coating tension by varying the thickness of the insulating coating in the direction perpendicular to the rolling direction. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2019-507239 [Patent Document 2] Japanese Patent Application Publication No. 2022-60749 [Patent Document 3] Patent Publication No. 2021-46592 [Patent Document 4] Japanese Patent Application Laid-Open No. 2001-303261 Summary of the Invention [Problem to be solved by the invention]

[0006] The techniques described in Patent Documents 1 to 4 have the following problems.

[0007] In Patent Document 1, the reduction of magnetostrictive vibration of grain-oriented electrical steel sheets is examined, but the most important improvement in iron loss is not sufficiently examined. In Patent Document 2, low iron loss is achieved by introducing grooves into the surface of the steel sheet. However, the steel sheet in the grooved areas is removed, which reduces the space factor and may result in inferior characteristics when processed into a transformer. The method of irradiating the steel sheet surface with a laser as described in Patent Document 3 has the drawback that the thermal strain introduced by the laser is removed by annealing, making it unsuitable for wound cores, which are generally subjected to stress relief annealing. Furthermore, the introduction of strain also increases magnetostriction, which leads to problems such as increased transformer noise. Patent Document 4 discloses a technology for improving tensile anisotropy and iron loss by locally varying the thickness of an insulating coating, but when the inventors attempted to reproduce this technology, they encountered the problem that when the base coating is removed and the steel substrate is exposed, the coating that acts as a binder disappears, making the insulating coating more susceptible to peeling. Furthermore, under these conditions, the coating is partially not bonded to the steel substrate, leaving room for improvement in the tension applied to the steel sheet.

[0008] Furthermore, with the tightening of efficiency regulations, the requirements for transformer performance are becoming stricter every year, and it is expected that these requirements will continue to improve in the future. In reality, however, improvements to the properties of grain-oriented electrical steel sheets are still in progress. [Means for solving the problem]

[0009] In light of the above background, the present inventors have conducted extensive research and developed a grain-oriented electrical steel sheet with reduced iron loss and reduced magnetostriction.

[0010] Grain-oriented electrical steel sheets are usually manufactured by creating a crystalline structure with a highly oriented {0110} {001} orientation, known as the Goss orientation, and then applying an insulating coating, such as a silica-based glass coating.

[0011] Here, there are two known methods for controlling the iron loss of grain-oriented electrical steel sheets: sharpening the grain orientation and magnetic domain refinement. Known methods for magnetic domain refinement include reducing the grain size, introducing grooves, introducing thermal strain, and applying tension.

[0012] Among these methods, reducing the grain size has the problem of deteriorating the crystal orientation, introducing grooves has the problem of reducing the magnetic flux density, and introducing thermal strain has the problem of increasing magnetostriction.On the other hand, tensioning is generally achieved by forming a base coat and an insulating coat on the grain-oriented electrical steel sheet, and the degree of impact of the improvement is greater than with other methods.

[0013] One known method for increasing the tension of a coating is to increase the coating weight. However, increasing the coating weight of the base coating is difficult. This is because the formation of the base coating occurs during finish annealing, which is the most important process that determines the magnetic properties of grain-oriented electrical steel sheet. Therefore, it is necessary to increase the coating weight of the base coating while controlling secondary recrystallization during finish annealing. On the other hand, insulating coatings are formed on steel sheets that have undergone secondary recrystallization and do not involve the creation of a crystalline structure, making it easier to adjust the coating weight than primer coatings. For example, by increasing the amount of coating solution applied, the thickness of the insulating coating can be increased, which in turn makes it easier to increase the tension. However, increasing the thickness of the insulating coating leads to a decrease in the space factor when the steel sheets are stacked, resulting in a deterioration of transformer characteristics.

[0014] In view of the above-mentioned circumstances regarding iron loss and tension, the present invention aims to reduce iron loss and magnetostriction without increasing the thickness of the insulating coating. The inventors have newly discovered that by providing grooves in the base coating below the insulating coating and forming an oxide film on the bottom of the grooves, it is possible to improve the properties related to iron loss and magnetostriction without increasing the thickness of the insulating coating (i.e., without reducing the space factor when laminated into a transformer core) and without deteriorating the coating releasability. Note that the coating releasability in this specification can be evaluated by the method described in the Examples.

[0015] The gist and configuration of the present invention are as follows. [1] A grain-oriented electrical steel sheet having a base coating and an insulating coating, the undercoating has linear or dot-like grooves along the rolling direction; The bottom surface of the groove has an oxide film on the steel substrate, an insulating coating on the undercoating and on the bottom surface of the groove; A grain-oriented electrical steel sheet in which, in a cross section of the steel sheet cut in the direction perpendicular to the rolling direction, the average angle formed by the groove side wall and the direction perpendicular to the rolling direction in each groove on the base steel side is 30 degrees or more and 135 degrees or less, and the total length of the groove bottom surfaces of all grooves is 5% or more of the length of the steel sheet in the direction perpendicular to the rolling direction. [2] A method for manufacturing a grain-oriented electrical steel sheet according to [1], The hot-rolled steel sheet is subjected to cold rolling once or twice or more times with intermediate annealing to obtain a cold-rolled steel sheet of the final thickness. The cold-rolled steel sheet is subjected to primary recrystallization annealing including decarburization, then coated with an annealing separator, and subjected to finish annealing to obtain a steel sheet having a base coating on the steel sheet surface; the method comprises removing the base coating on the surface of the steel sheet along the rolling direction to form grooves having groove bottoms where the base steel is exposed, then annealing the steel sheet to form an oxide film on the groove bottoms, and then forming an insulating coating. Manufacturing method for grain-oriented electrical steel sheets. [Effects of the Invention]

[0016] According to the present invention, a grain-oriented electrical steel sheet having improved core loss and magnetostriction properties is provided, along with a manufacturing method thereof. The present invention makes it possible to achieve the above improvements without increasing the thickness of the insulating coating (i.e., without reducing the space factor when laminated as a transformer core) and without deteriorating the peelability of the insulating coating. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram of a cross section of a grain-oriented electrical steel sheet of the present invention cut in a direction perpendicular to the rolling direction. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be specifically described below.

[0019] The grain-oriented electrical steel sheet of the present invention is a grain-oriented electrical steel sheet having a base coating and an insulating coating, wherein the base coating has linear or dot-like grooves along the rolling direction, the bottom surfaces of the grooves have an oxide film on the base steel, and the base coating and the bottom surfaces of the grooves have insulating coatings on them, and in a cross section of the steel sheet cut in a direction perpendicular to the rolling direction, the average angle between the groove sidewalls and the direction perpendicular to the rolling in each groove on the base steel side is 30 degrees or more and 135 degrees or less, and the total length of the groove bottoms of all grooves is 5% or more of the length of the steel sheet in the direction perpendicular to the rolling direction.

[0020] The grain-oriented electrical steel sheet of the present invention is not particularly limited in its composition, as long as the base coating and insulating coating have the above-mentioned shapes. The composition of the hot-rolled steel sheet used to produce the grain-oriented electrical steel sheet is also not limited, and can be a composition that causes secondary recrystallization, and may be a system that uses an inhibitor to grow secondary recrystallized grains, or a system that does not use an inhibitor (inhibitor-less system).

[0021] When an inhibitor is used, if the inhibitor is an AlN-based inhibitor, the steel material may contain appropriate amounts of Al and N, or if the inhibitor is an MnS- or MnSe-based inhibitor, the steel material may contain appropriate amounts of Mn, Se and / or S. In this case, the contents of Al, N, S and Se in the steel material are preferably 0.008 to 0.08 mass% Al, 0.004 to 0.012 mass% N, 0.004 to 0.03 mass% S and 0.001 to 0.03 mass% Se, respectively.

[0022] Si is an element that is effective in improving the properties of a soft magnetic material when contained in a steel sheet, and is therefore preferably contained in the steel material. In order to avoid deterioration of workability and difficulty in manufacturing, the Si content is preferably 7.0 mass% or less, and more preferably 5.0 mass% or less. On the other hand, in order to fully obtain the effects of containing Si, the Si content is preferably 2.0 mass% or more.

[0023] In addition to Si, elements that can be contained in the steel material include the following. C: 0.08% by mass or less C is an effective element for improving the structure of hot-rolled steel sheets, but if the content exceeds 0.08 mass%, it becomes difficult to reduce the C content to 50 mass ppm or less, at which point magnetic aging does not occur, during the manufacturing process. Therefore, the C content is preferably 0.08 mass% or less. Note that there is no need to set a lower limit for the C content because secondary recrystallization is possible even in materials that do not contain C, but from the viewpoint of improving the structure of hot-rolled steel sheets, a C content of 0.01 mass% or more is preferable.

[0024] Mn:0.005~1.0% by mass Mn is an effective element for improving hot workability, but if the content is less than 0.005% by mass, the effect of adding it is poor. On the other hand, if the Mn content exceeds 1.0% by mass, the magnetic flux density of the finished sheet decreases. Therefore, the Mn content is preferably in the range of 0.005 to 1.0% by mass. More preferably, the Mn content is 0.010% by mass or more. Furthermore, the Mn content is more preferably 0.10% by mass or less.

[0025] O: 0.0020% by mass or less If the O content exceeds 0.0020 mass%, it decomposes the inhibitor and causes the secondary recrystallization to become unstable, so the O content in the steel material is preferably 0.0020 mass% or less, and more preferably 0.0015 mass% or less. On the other hand, the O content may be 0 mass%.

[0026] In addition to the above basic components, one or more elements selected from the following elements may be appropriately contained in the steel material as magnetic property improving components (optional added components). Ni: 1.50% by mass or less, Sn: 1.50% by mass or less, Sb: 1.50% by mass or less, Cu: 3.0% by mass or less, P: 0.50% by mass or less, Mo: 0.10% by mass or less, and Cr: 1.50% by mass. In order to obtain the effects of containing these elements, it is preferable to set the content to Ni: 0.01 mass% or more, Sn: 0.001 mass% or more, Sb: 0.005 mass% or more, Cu: 0.03 mass% or more, P: 0.01 mass% or more, Mo: 0.001 mass% or more, and Cr: 0.01 mass% or more.

[0027] When the above elements are contained, the effect of improving the magnetic properties can be fully expected. On the other hand, in order to avoid inhibiting the development of secondary recrystallized grains, it is preferable that the contents of the elements be within the above-mentioned ranges.

[0028] The remainder other than the above-mentioned components is inevitable impurities mixed in during the manufacturing process and Fe. That is, in the steel material of the present invention, the remainder other than the above-mentioned components is Fe and inevitable impurities. On the other hand, in grain-oriented electrical steel sheets, C is decarburized during primary recrystallization annealing, and Al, N, S, and Se are purified during final annealing, so that in the steel sheet (product sheet) after final annealing, Al is reduced to 0.01 mass% or less, and C, N, S, and Se are all reduced to 0.005 mass% or less. There is no change in the proportions of the other elements (Si, Mn, Ni, Sn, Sb, Cu, P, Mo, and Cr) in the steel sheet before and after final annealing.

[0029] The hot-rolled steel sheet is not particularly limited, and may be one obtained by heating a steel material and subjecting it to hot rolling. For example, one may include a hot-rolled steel sheet obtained by casting a steel slab and then subjecting it to hot rolling immediately with or without heating. The hot-rolled steel sheet may have the chemical composition described above for the steel material. To improve the properties as a soft magnetic material, it is preferable to contain Si. The Si content is preferably 7.0 mass% or less, more preferably 5.0 mass% or less, and preferably 2.0 mass% or more.

[0030] In the manufacturing process of the grain-oriented electrical steel sheet of the present invention, a hot-rolled steel sheet is cold-rolled once or twice or more times with intermediate annealing to obtain a cold-rolled steel sheet of a final thickness, and the cold-rolled steel sheet is then subjected to primary recrystallization annealing including decarburization. In order to improve the magnetic properties, the hot-rolled steel sheet may be cold-rolled after the hot-rolled sheet annealing.

[0031] After cold rolling the hot-rolled steel sheet, it is subjected to decarburization annealing, which creates a primary recrystallization structure necessary for secondary recrystallization grain growth. The conditions for hot rolling, cold rolling, any intermediate annealing, and primary recrystallization annealing are not particularly limited.

[0032] An annealing separator is applied to a decarburized annealed steel sheet, and then finish annealing is performed to cause secondary recrystallization. The composition and amount of the annealing separator to be applied are not particularly limited, as long as it does not inhibit secondary recrystallization and can form a base coating that acts as a binder for the insulating coating.

[0033] In the grain-oriented electrical steel sheet of the present invention, the base coating not only acts as a binder for the insulating coating, but also plays a role in efficiently purifying unnecessary inhibitor components during finish annealing and in regulating the amount of gas infiltration from the steel sheet surface, thereby improving the magnetic properties.

[0034] After finish annealing, the base coating on the surface of the steel sheet is removed along the rolling direction to form grooves having bottom surfaces that expose the base steel. The grooves may be linear (continuous) or dotted (discontinuous) along the rolling direction.

[0035] After finish annealing and before the formation of the grooves, it is preferable to remove the residue of the annealing separator adhering to the surface of the steel sheet by means of pickling, brushing, or the like.

[0036] The grooves are preferably formed by removing only the base coating and not removing the surface of the base steel. The method for forming the grooves is not particularly limited, and examples include a method of grinding the steel sheet in the rolling direction with abrasive paper, for example, using a roll passing strip with abrasive paper attached. The grooves can also be formed by using a roll passing strip with protrusions, or by chemical treatment, grinding the base coating with a laser, etc. The method for forming the grooves can be selected depending on the shape of the grooves, which will be described later.

[0037] After the grooves are formed, the steel sheet is annealed to form an oxide film on the exposed steel substrate at the bottom of the grooves. Annealing conditions such as time, temperature, and atmosphere are not particularly limited as long as an oxide film can be formed. The oxide film acts as a binder between the insulating coating and the steel substrate at the bottom of the grooves from which the base coating has been removed.

[0038] After annealing the steel sheet, an insulating coating is formed on the base coating and on the bottom surface of the groove. At the bottom surface of the groove, the insulating coating is formed on the oxide film on the steel substrate. The composition of the insulating coating is not particularly limited as long as it ensures insulation and can impart tension to the steel sheet, and may be organic or inorganic.

[0039] The insulating coating can be formed by tension coating, for example, inorganic coating containing silica, ceramic coating by physical vapor deposition, chemical vapor deposition, or the like.

[0040] In the present invention, the grooves in the cross section of the steel plate cut in the direction perpendicular to the rolling direction have an average angle (hereinafter also referred to as the "groove angle") on the base steel side formed by the groove side wall and the direction perpendicular to the rolling direction in each groove of 30 degrees or more and 135 degrees or less, and the ratio (hereinafter also referred to as the "groove length ratio") of the total length of the groove bottom surfaces of all grooves to the length of the steel plate in the direction perpendicular to the rolling direction (i.e., the length in the plate width direction) of 5% or more. The groove angle and groove length ratio can be determined by the method described in the Examples, by observing at least 1 cm in the sheet width direction on a cross section of a steel sheet cut out in a direction perpendicular to the rolling direction.

[0041] FIG. 1 is a schematic diagram of a cross section of a grain-oriented electrical steel sheet of the present invention cut in a direction perpendicular to the rolling direction. The bottom surface of the groove has an oxide film (not shown) on the substrate steel. The rolling direction is normal to the paper. In FIG. 1, θ1, θ2, θ3, and θ4, which are angles measured from the substrate steel side of the groove sidewall with respect to the direction perpendicular to the rolling direction, correspond to the groove angles. In the case of FIG. 1, the average value of the groove angles corresponds to the average value of θ1, θ2, θ3, and θ4. If the average groove angle is less than 30 degrees, the grooves will become flat and will not exhibit the effect of improving tension, and if it exceeds 135 degrees, the insulating coating liquid will have difficulty penetrating into the grooves, causing the coating to peel off and reducing insulation properties. Therefore, the average groove angle is 30 degrees or more and 135 degrees or less, preferably 45 degrees or more and preferably 120 degrees or less.

[0042] It is preferable that all grooves in the cross section of the steel plate have a groove angle of 30 degrees or more and 135 degrees or less, but grooves with an angle of less than 30 degrees or more than 135 degrees may exist as long as the effects of the present invention are not impaired.

[0043] In the present invention, the ratio (groove length ratio) of the sum of the lengths of the groove bottoms of all grooves in a cross section of a steel sheet cut in a direction perpendicular to the rolling direction to the length of the steel sheet in the direction perpendicular to the rolling direction (i.e., the length in the width direction) is 5% or more. The groove length ratio is preferably 10% or more in order to further increase the iron loss reduction effect. Furthermore, the groove length ratio can be 80% or less, and preferably 60% or less, in order to increase the difference in cross-sectional area of ​​the insulating coating in the rolling direction and the direction perpendicular to the rolling direction in order to impart tensile anisotropy to the insulating coating.

[0044] In the schematic diagram of FIG. 1, a predetermined length of the steel plate in the direction perpendicular to the rolling direction is represented by L, and the lengths of the groove bottom surfaces of the grooves are represented by l1 and l2. In the case of FIG. 1, the groove length ratio can be calculated by (l1 + l2) / L × 100(%).

[0045] It is preferable that all grooves observed in the cross section of the steel sheet have a groove angle of 30 degrees or more and 135 degrees or less, but grooves with an angle of less than 30 degrees or more than 135 degrees may be present as long as the effects of the present invention are not impaired.

[0046] The grooves may be linear (continuous) or dotted (discontinuous) along the rolling direction, with a linear shape being preferred from the viewpoint of uniforming the tension of the insulating coating along the rolling direction. Furthermore, the angle of the groove can be adjusted by, for example, adjusting the shape of the abrasive grains in the abrasive paper or adjusting the irradiation diameter and incident angle of the laser used to form the grooves, and the length ratio of the groove can be adjusted by adjusting the grinding length in the direction perpendicular to the rolling direction and the grinding cycle.

[0047] The process for forming the insulating coating is not particularly limited. The steel sheet on which the insulating coating is formed may be used as a product as is, or the steel sheet on which the insulating coating is formed may be subjected to stress relief annealing, or may be subjected to laser irradiation or magnetic domain refinement treatment by further forming grooves that reach the base steel.

[0048] The grain-oriented electrical steel sheet of the present invention can be used in a transformer. The method for manufacturing the transformer is not particularly limited. For example, the grain-oriented electrical steel sheet of the present invention may be laminated to form a stacked core, or may be wound to form a wound core. The grain-oriented electrical steel sheet of the present invention can be applied regardless of whether it has been subjected to stress relief annealing, its shape, or its type, such as Unicore or Trancocore. [Example]

[0049] Next, the present invention will be specifically described based on examples. The following examples show preferred examples of the present invention, and the present invention is not limited by these examples. The embodiments of the present invention can be appropriately modified within the scope of the invention, and all such modifications are included in the technical scope of the present invention.

[0050] Example 1 A steel slab containing the components shown in Steel A in Table 1, with the balance being Fe and unavoidable impurities, was produced by continuous casting, heated at 1420°C, and then hot-rolled to a hot-rolled steel sheet with a thickness of 2.3 mm, which was then annealed at 900°C for 10 seconds and then cold-rolled to a cold-rolled steel sheet with a thickness of 0.22 mm.

[0051] The cold-rolled steel sheets underwent primary recrystallization annealing at an oxidation degree of PH2O / PH2 = 0.32 and a temperature of 850°C for 120 seconds. An annealing separator primarily composed of MgO was then applied, followed by finish annealing for the purpose of secondary recrystallization and the formation of a forsterite film as a base film. The finish annealing was performed by heating the sheet to 1200°C at a rate of 20°C per hour in a nitrogen atmosphere, holding it at 1200°C for 10 hours, and then cooling it to room temperature at a rate of 20°C per hour. After finish annealing, continuous grooves were formed in the forsterite surface by pressing abrasive paper (#600, #800, #1000) against the steel sheet surface with a force of 0.17 MPa or 0.32 MPa while sliding the steel sheet in the rolling direction. For comparison, a sample without grooves was also prepared. SEM confirmed that the forsterite in the polished area was completely removed in the sample polished with a 0.32 MPa abrasive paper pressing force, exposing the steel substrate at the bottom of the grooves. On the other hand, the forsterite coating remained at the bottom of the grooves in the sample polished with a 0.17 MPa abrasive paper, and the steel substrate was not exposed. The condition of the abrasive paper was adjusted by changing the type of abrasive paper, adjusting the abrasive grain shape by sliding the abrasive paper multiple times in advance, and partially removing the abrasive grains, thereby adjusting the groove angle and groove length ratio of each sample.

[0052] Samples with exposed steel substrate at the bottom of the grooves (samples polished with a force of 0.32 MPa) were annealed to form an oxide film on the exposed steel substrate surface. The annealing conditions were 850°C, oxidation degree PH2O / PH2 = 0.43, and annealing time 15 seconds. All samples were then coated with a coating solution consisting primarily of phosphoric acid and silica, and annealed in a nitrogen atmosphere at 800°C for 15 seconds to bake on the insulating coating.

[0053] The samples thus prepared were subjected to cross-sectional observation, surface observation, iron loss measurement, and coating tension measurement.

[0054] (Cross-section observation) The cross-section observation was performed by observing a 1 cm area in the sheet width direction (C direction) of a steel sheet cross section (C cross section) cut in the direction orthogonal to the rolling direction using an SEM. The angle formed by the line connecting the start and end points of the polished groove bottom surface and the unpolished surface with the direction orthogonal to the rolling direction was determined through SEM observation, and the average value was calculated as the groove angle. The total length of the groove bottom surface within a 1 cm field of view in the C direction was then calculated, and the ratio to the length of that field in the direction orthogonal to the rolling direction, i.e., 1 cm, was calculated to obtain the groove length ratio.

[0055] (Surface observation) The surface of the steel sheet was observed with an SEM to check whether the base coating was exposed at the bottom of the grooves.

[0056] (iron loss measurement) A test piece with a width of 100 mm and a length of 280 mm was prepared from each sample, and an AC SST test was performed. The iron loss W 17 / 50 The difference between the maximum and minimum values ​​of the magnetostriction waveform, λp-p, was also measured.

[0057] (Coating tension measurement) The coating tension was measured by peeling off the insulating coating from one side and measuring the warpage and weight change of the steel sheet. 2 Normalization was carried out so that The peelability of the coating was evaluated by winding the test piece after the magnetic measurement around round rods of different diameters in order from the largest diameter to the smallest diameter, and recording the largest diameter at which the coating peeled off.

[0058] The results are shown in Table 2.

[0059] [Table 1]

[0060] [Table 2]

[0061] As shown in Table 2, the inventive examples had lower iron loss and magnetostriction than the comparative examples, which was favorable. Furthermore, the comparative examples under conditions 34 to 37, in which annealing was not performed despite the steel substrate being exposed after the formation of the primer coating, exhibited particularly poor properties. This was because the insulating coating was not directly bonded to the steel substrate, and therefore sufficient tension of the insulating coating was not imparted to the steel sheet.

[0062] <Example 2> A steel slab containing the components shown in Steel B in Table 1, with the remainder being Fe and unavoidable impurities, was produced by continuous casting, heated at 1420°C, and then hot-rolled to a hot-rolled sheet with a thickness of 2.3 mm, which was then annealed at 900°C for 10 seconds. This was then cold-rolled to an intermediate thickness of 1.1 mm, and intermediate annealed at 1070°C for 30 seconds with an oxidation degree of PH2O / PH2 = 0.32. This was then cold-rolled again to produce a cold-rolled steel sheet with a thickness of 0.22 mm.

[0063] The cold-rolled steel sheets underwent primary recrystallization annealing at an oxidation degree of PH2O / PH2 = 0.32 and a temperature of 850°C for 120 seconds. An annealing separator primarily composed of MgO was then applied, followed by finish annealing for the purpose of secondary recrystallization and the formation of a forsterite film as a base film. The finish annealing was performed by heating the sheet to 1200°C at a rate of 20°C per hour in a nitrogen atmosphere, holding it at 1200°C for 10 hours, and then cooling it to room temperature at a rate of 20°C per hour.

[0064] After finish annealing, continuous grooves were formed in the forsterite surface by pressing abrasive paper (#800) against the steel sheet surface at a force of 0.15 MPa or 0.29 MPa while sliding the steel sheet in the rolling direction. For comparison, a sample without grooves was also prepared. SEM confirmed that the forsterite in the polished area was completely removed in the sample where the abrasive paper was pressed against the surface at 0.29 MPa, and the steel substrate was exposed at the bottom of the grooves. On the other hand, in the sample polished with a force of 0.15 MPa, a forsterite coating remained at the bottom of the grooves, and the steel substrate was not exposed. The groove angle and groove length ratio of each sample were adjusted using the same method as in Example 1.

[0065] Samples with groove bottoms that exposed the steel substrate (samples polished with a force of 0.29 MPa) were annealed to form an oxide film on the exposed steel substrate surface. The annealing conditions were 850°C, oxidation degree PH2O / PH2 = 0.48, and annealing time 15 seconds. All steel sheets were then coated with a coating solution consisting mainly of phosphoric acid and silica. The coating amount was 4 g / m2 after baking. 2After coating, the insulating coating was baked by annealing in a nitrogen atmosphere at 800°C for 15 seconds. The samples thus prepared were subjected to cross-sectional observation, surface observation, magnetic measurement, and coating tension measurement in the same manner as in Example 1. The results are shown in Table 3.

[0066] [Table 3]

[0067] As shown in Table 3, the inventive examples had lower iron loss and magnetostriction than the comparative examples, which was favorable. [Industrial Applicability]

[0068] According to the present invention, a grain-oriented electrical steel sheet having reduced core loss and reduced magnetostriction is provided together with a method for manufacturing the same.

Claims

1. A grain-oriented electrical steel sheet having a base coating and an insulating coating, the undercoating has linear or dot-like grooves along the rolling direction; The bottom surface of the groove has an oxide film on the steel substrate, an insulating coating on the undercoating and on the bottom surface of the groove; A grain-oriented electrical steel sheet, in which, in a cross section of the steel sheet cut out in a direction perpendicular to the rolling direction, the average angle formed by the groove side wall in each groove and the direction perpendicular to the rolling direction on the base steel side is 30 degrees or more and 135 degrees or less, and the total length of the groove bottom surfaces of all grooves is 5% or more of the length of the steel sheet in the direction perpendicular to the rolling direction.

2. The method for producing the grain-oriented electrical steel sheet according to claim 1, The hot-rolled steel sheet is subjected to cold rolling once or twice or more times with intermediate annealing to obtain a cold-rolled steel sheet of a final thickness; The cold-rolled steel sheet is subjected to primary recrystallization annealing including decarburization, then coated with an annealing separator, and subjected to finish annealing to obtain a steel sheet having a base coating on the steel sheet surface; The method includes removing the base coating on the surface of the steel sheet along the rolling direction to form grooves having groove bottoms where the base steel is exposed, followed by annealing to form oxide films on the groove bottoms, and then forming an insulating coating. Manufacturing method for grain-oriented electrical steel sheets.

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