Grain-oriented electrical steel sheet and method for manufacturing same

Abstract

The present invention provides a grain-oriented electrical steel sheet 1 which has a large applied tension. The grain-oriented electrical steel sheet 1 is provided with an insulating coating film 3 that is disposed on the surface of the steel sheet. The insulating coating film 3 contains silicon and phosphorus, and in a region R1 on the surface of the grain-oriented electrical steel sheet 1, the void ratio, which is the ratio of a region R2 in which a void part is present inside the insulating coating film 3, is 50% or less. The region R1 is a region that has an X-direction length of 125 µm and a Y-direction length of 125 µm. The region R2 is a region in which, in the region R1, the ratio of the detected amount of iron to the detected amount of phosphorus is 10% or more, and the detected amount of silicon is 90% or less of the maximum value in the region R1. The detected amount of each element is determined by analyzing the region R1 using an electron probe microanalyzer.

Description

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

[0001] This invention relates to grain-oriented electrical steel sheets and a method for manufacturing the same.

[0002] Grain-oriented electrical steel sheets are used, for example, as core material for power transformers. Generally, grain-oriented electrical steel sheets consist of a steel sheet and an insulating coating formed on the surface of the steel sheet. Therefore, when grain-oriented electrical steel sheets are laminated or wound to form a core, the overlapping steel sheets are insulated from each other by the insulating coating.

[0003] Insulating coatings are typically formed by applying a coating solution containing phosphate and colloidal silica to the surface of a steel sheet and then baking it at a high temperature. The insulating coating has a lower coefficient of thermal expansion than the steel sheet. Therefore, when the temperature drops to room temperature after baking, the insulating coating imparts tension to the steel sheet, reducing iron loss.

[0004] Furthermore, in order to improve the moisture resistance of the insulating coating, hexavalent chromium compounds such as dichromate are sometimes added to the coating solution. However, in such cases, there are concerns about the environmental burden, so technologies to improve the moisture resistance of insulating coatings without adding chromium are being investigated (Patent Documents 1-4).

[0005] Japanese Patent Publication No. 2000-169972, Japanese Patent Publication No. 2000-169973, Japanese Patent Publication No. 2000-178760, International Publication No. 2018 / 079845

[0006] When the inventors of the present invention investigated grain-oriented electrical steel sheets manufactured by conventional methods, they found that the tension applied to the steel sheet by the insulating coating (also called "applied tension") was sometimes insufficient.

[0007] Furthermore, increasing the amount of insulating coating increases the applied tension. However, in that case, the volume fraction of the insulating coating in the grain-oriented electrical steel sheet increases. In other words, the space factor, which is the proportion of the steel sheet that occupies in an iron core formed by laminating or winding grain-oriented electrical steel sheets, decreases. Transformers using such an iron core may have high losses.

[0008] This invention has been made in view of the above points, and aims to provide a grain-oriented electrical steel sheet with high tension application.

[0009] The inventors diligently studied to achieve the above objective. Specifically, they observed a cross-section of an insulating film formed by a conventional method using a scanning electron microscope (SEM). As a result, they found that voids sometimes exist inside the insulating film. These voids are thought to be formed when the water in the coating liquid (insulating film) evaporates during the process of forming the insulating film by baking the coating liquid. The inventors then discovered that when voids exist inside the insulating film, the applied tension decreases by the volume of the voids, and that a good applied tension can be obtained by reducing the voids, thus completing the present invention.

[0010] In other words, the present invention provides the following [1] to [3]. [1] A grain-oriented electrical steel sheet comprising a steel sheet and an insulating coating disposed on the surface of the steel sheet, wherein the insulating coating contains silicon and phosphorus, and the void ratio, which is the ratio of the region R2 in which cavities exist inside the insulating coating in a region R1 on the surface of the grain-oriented electrical steel sheet, is 50% or less. However, the region R1 is a region of 125 μm in the X direction and 125 μm in the Y direction, and the region R2 is a region in the region R1 in which the ratio of the detected amount of iron to the detected amount of phosphorus is 10% or more, and the detected amount of silicon is 90% or less of the maximum value in the region R1, and the detected amount of each element is obtained by analyzing the region R1 using an electron probe microanalyzer. [2] A method for manufacturing the grain-oriented electrical steel sheet described in [1] above, wherein a coating liquid for forming the insulating film is applied to the surface of the steel sheet, and then baking is performed, wherein the coating liquid contains a phosphate, colloidal silica and a metal hydroxide, the metal hydroxide contains at least one metal element M1 selected from the group consisting of Mg, Ca, Ba and Sr, and the content of the colloidal silica in the coating liquid is such that SiO is present in proportion to 1.0 mol of the metal element of the phosphate. ２A method for producing grain-oriented electrical steel sheets, wherein the amount of metal hydroxide in the coating solution is 0.1 to 2.0 mol in terms of metal elements per 1.0 mol of metal elements in the phosphate, and the pH of the coating solution is 3 to 7. [3] A method for producing grain-oriented electrical steel sheets according to [1] above, wherein a coating solution for forming the insulating film is applied to the surface of the steel sheet, and then baking is performed, wherein the coating solution contains a phosphate, colloidal silica and a metal hydroxide, the metal hydroxide contains at least one metal element M2 selected from the group consisting of Fe, Ni, Co, Zn, Ti, V, Mn, Al, Ir, Ru, Pd and Cu, and the amount of colloidal silica in the coating solution is 0.1 to 2.0 mol in terms of metal elements per 1.0 mol of metal elements in the phosphate ２ A method for manufacturing grain-oriented electrical steel sheets, wherein the amount of metal hydroxide in the coating solution is 1.0 to 5.0 mol in terms of metal elements, the amount of metal hydroxide in the coating solution is 0.1 to 5.0 mol in terms of metal elements relative to 1.0 mol of metal elements in the phosphate, and the pH of the coating solution is 3 to 7.

[0011] According to the present invention, it is possible to provide a grain-oriented electrical steel sheet with a large applied tension.

[0012] This is a schematic plan view of a grain-oriented electrical steel sheet. This is a schematic diagram showing a grain-oriented electrical steel sheet without voids in the insulating coating. This is a schematic diagram showing a grain-oriented electrical steel sheet with voids in the insulating coating.

[0013] [Grain-oriented electrical steel sheet] The grain-oriented electrical steel sheet of this embodiment will be described below. The following description will also serve as a description of the manufacturing method of the grain-oriented electrical steel sheet. In this embodiment, the grain-oriented electrical steel sheet generally comprises a steel sheet and an insulating coating disposed on the surface of the steel sheet.

[0014] <Void Ratio> Figure 1 is a schematic plan view of a grain-oriented electrical steel sheet 1. The void ratio is the ratio of the region R2 in which a cavity 4 (not shown in Figure 1) exists inside the insulating coating 3 within a region R1 on the surface of the grain-oriented electrical steel sheet 1 (i.e., the surface of the insulating coating 3). The method for determining the void ratio will be explained below.

[0015] As shown in Figure 1, region R1 is an arbitrary region on the surface of the grain-oriented electrical steel sheet 1, and is a square region with dimensions of 125 μm in the X direction and 125 μm in the Y direction. The X direction is any one direction on the surface of the grain-oriented electrical steel sheet 1 (one direction within the plane), and the Y direction is perpendicular to the X direction.

[0016] First, using an electron probe microanalyzer (EPMA), LaB ６ Using this as the radiation source, with an acceleration voltage of 15.0 kV and an irradiation current of 5.0 × 10⁻¹⁰ －８ Under the conditions A and an irradiation time of 50.00 ms per point, the region R1 on the surface of the grain-oriented electrical steel sheet 1 (insulating coating 3) is analyzed to obtain a color map. The color map is an image that displays the magnitude of the intensity (characteristic X-ray intensity) of each element by the difference in color. For a given element, the greater the amount detected, the greater its intensity.

[0017] Figure 2A is a schematic diagram showing a grain-oriented electrical steel sheet 1 in which no voids 4 exist in the insulating coating 3, and Figure 2B is a schematic diagram showing a grain-oriented electrical steel sheet 1 in which voids 4 exist in the insulating coating 3.

[0018] The steel sheet 2 contains at least iron (Fe). The insulating coating 3 contains at least silicon (Si) and phosphorus (P). By analyzing the surface of the grain-oriented electrical steel sheet 1 (insulating coating 3) using EPMA, P contained in the insulating coating 3 can be detected. In this case, as shown in Figure 2A, if there is no cavity 4 inside the insulating coating 3, the Fe in the steel sheet 2 located below the insulating coating 3 is difficult to detect. In this case, the ratio of the amount of Fe detected to the amount of P detected (Fe / P) is, for example, less than 10%. In contrast, as shown in Figure 2B, if there is a cavity 4 inside the insulating coating 3, the Fe in the steel sheet 2 located below the insulating coating 3 is strongly detected. In this case, the Fe / P ratio increases compared to the case where there is no cavity 4 (Figure 2A), and can exceed 10%.

[0019] Furthermore, in areas where the insulating coating 3 is completely absent (only the steel plate 2 exists), such as areas where the insulating coating 3 has peeled off from the steel plate 2, P will not be detected at all. Therefore, the detection of P means that at least the insulating coating 3 is formed, regardless of whether or not a cavity 4 exists inside the insulating coating 3.

[0020] Incidentally, as shown in Figure 2A, even if there are no cavities 4 inside the insulating coating 3, if the large amount of Fe contained in the steel plate 2 dissolves into the insulating coating 3 and forms a reaction product with the components of the insulating coating 3, Fe can be strongly detected. However, in that case, the insulating coating 3 is naturally present around the Fe, and there is also a large amount of Si present, so the amount of Si detected is high (let's assume it's 100%). In contrast, as shown in Figure 2B, when the Fe of the steel plate 2 is strongly detected due to the presence of cavities 4 in the insulating coating 3, the amount of Si detected is relatively small, and can fall below 100%, potentially to 90% or less.

[0021] Therefore, in region R1, the region where the ratio of the detected amount of Fe to the detected amount of P (Fe / P) is 10% or more, and the detected amount of Si is 90% or less of the maximum value in region R1 (maximum detected amount of Si), is defined as region R2 where a cavity 4 exists inside the insulating film 3. Furthermore, the ratio (area ratio) of region R2 to region R1 is defined as the cavity ratio.

[0022] In this embodiment, the void ratio is 50% or less. In this case, since there are few voids 4 inside the insulating coating 3, the tension (applied tension) applied to the steel plate 2 by the insulating coating 3 is large.

[0023] The void ratio may be 3-45%, 5-40%, 8-35%, or 10-30%.

[0024] In this embodiment, it is preferable that the steel sheet 2 and the insulating coating 3 are in direct contact. That is, it is preferable that the grain-oriented electrical steel sheet 1 does not have an intermediate layer (not shown) between the steel sheet 2 and the insulating coating 3. An example of an intermediate layer is a layer with a lower Fe content than the steel sheet 2 and a lower P content than the insulating coating 3.

[0025] <Steel Plate> The steel plate used in this embodiment is, for example, a secondary recrystallized plate (finish annealed plate) on which a forsterite coating is formed on the surface.

[0026] Secondary recrystallized sheets are manufactured, for example, as follows: First, a steel slab having the above-described component composition (steel composition) is obtained from molten steel produced using a conventionally known refining process, using a continuous casting method or an ingot-fraction rolling method. The steel slab is hot-rolled to obtain a hot-rolled sheet. Then, the hot-rolled sheet is annealed as needed, and then cold-rolled once or twice or more with an intermediate annealing in between to obtain a cold-rolled sheet of the final thickness. Next, the cold-rolled sheet is subjected to primary recrystallization annealing and decarburization annealing, and then an annealing separating agent mainly containing MgO is applied, followed by finish annealing (secondary recrystallization annealing) to form a forsterite coating. In this way, a secondary recrystallized sheet having a forsterite coating on the surface is obtained. Before applying the coating liquid described later, washing with water and drying may be performed to remove the residue of the annealing separating agent.

[0027] The composition of the steel sheet is not particularly limited, and examples include conventionally known compositional compositions that induce secondary recrystallization. For example, a compositional composition that produces precipitates such as AlN and MnSe as inhibitors may be used to grow secondary recrystallized grains. The properties of the steel sheet as a soft magnetic material are improved by the inclusion of Si. However, if the Si content is too high, the workability deteriorates significantly. For this reason, the Si content is preferably 2.0 to 7.0 mass%, and more preferably 3.0 to 5.0 mass%.

[0028] <Insulating Coating (Coating Liquid)> The insulating coating contains silicon (Si) and phosphorus (P). Furthermore, it is preferable that the insulating coating is substantially free of chromium (Cr). Specifically, the Cr content of the insulating coating is preferably 0.10% by mass or less, more preferably 0.05% by mass or less, and even more preferably 0.01% by mass or less. Such an insulating coating can be obtained by forming it using a coating liquid that contains phosphate and colloidal silica, and does not contain chromium compounds. The component composition of the coating liquid used to form the insulating coating will be described below.

[0029] 《Phosphates》 The coating solution contains phosphates. As a result, the insulating film obtained has excellent adhesion to steel plates. Phosphates contain metallic elements such as magnesium (Mg), aluminum (Al), calcium (Ca), strontium (Sr), barium (Ba), zinc (Zn), manganese (Mn), and selenium (Se). Among these, phosphates containing at least one metallic element selected from the group consisting of Mg, Al, Ca, Sr, Ba, and Zn are preferred. Specific examples of phosphates include magnesium phosphate, aluminum phosphate, calcium phosphate, strontium phosphate, barium phosphate, zinc phosphate, manganese phosphate, and selenium phosphate. These may be used individually or in combination of two or more. Hereinafter, for example, magnesium phosphate may be written as "Mg phosphate," and the same applies to other phosphates. As for phosphates, monophosphates (biphosphates) are readily available and preferred.

[0030] The Colloidal Silica coating solution further contains colloidal silica. By adding an appropriate amount of colloidal silica to the phosphate, the number of voids in the resulting insulating film is reduced. This is presumed to be because, together with the metal hydroxide described later, the coating solution has an appropriate component composition, which promotes the formation of a good insulating film and suppresses the formation of voids.

[0031] Specifically, the colloidal silica content is such that SiO is present in proportion to 1.0 mol of the metal element in the phosphate. ２In terms of conversion, this is 1.0 to 5.0 mol, and may also be 1.5 to 4.5 mol, or 2.0 to 4.0 mol.

[0032] 《Metal Hydroxides》 The coating solution further contains metal hydroxides (hydroxide salts). The metal hydroxide contains at least one metal element M1 selected from the group consisting of magnesium (Mg), calcium (Ca), barium (Ba), and strontium (Sr), or at least one metal element M2 selected from the group consisting of iron (Fe), nickel (Ni), cobalt (Co), zinc (Zn), titanium (Ti), vanadium (V), manganese (Mn), aluminum (Al), iridium (Ir), ruthenium (Ru), palladium (Pd), and copper (Cu).

[0033] The metal element M2 is preferably at least one selected from the group consisting of Fe, Ni, Co, Zn, Ti, V, Mn, Al, Ir, Ru, and Pd.

[0034] Specific examples of metal hydroxides include magnesium(II) hydroxide, calcium(II) hydroxide, barium(II) hydroxide, strontium(II) hydroxide, iron(II) hydroxide, iron(III) hydroxide, nickel(II) hydroxide, cobalt(II) hydroxide, cobalt(III) hydroxide, zinc(II) hydroxide, titanium(III) hydroxide, vanadium(II) hydroxide, manganese(II) hydroxide, aluminum(III) hydroxide, iridium(III) hydroxide, ruthenium(II) hydroxide, and palladium(II) hydroxide. In the following text, for example, magnesium(II) hydroxide may be written as "Mg hydroxide," and the same applies to other metal hydroxides.

[0035] Hereinafter, for convenience, metal hydroxides containing metal element M1 may be referred to as "metal hydroxide 1," and metal hydroxides containing metal element M2 may be referred to as "metal hydroxide 2."

[0036] By using a coating liquid containing an appropriate amount of such metal hydroxide (metal hydroxide 1 or metal hydroxide 2), the moisture absorption resistance of the insulating film is improved. At this time, if the amount of the metal hydroxide is too small or too large, the effect of moisture absorption resistance cannot be sufficiently obtained.

[0037] And by using metal hydroxide 1 or metal hydroxide 2, the formation of voids is suppressed. The reason for this is not clear, but it is presumed as follows. First, the metal element (metal atom) of the metal hydroxide becomes the metal center during baking (especially pre-baking described later) and forms a complex with water, phosphate ions, etc. At this time, metal element M1 and metal element M2 form an octahedral complex with six coordination. By forming such a complex, a three-dimensional network is formed inside the insulating film, and the local concentration of water is suppressed. That is, water is dispersed. As a result, during baking (especially full baking described later), the large amount of water escaping from the inside of the insulating film is suppressed, and the formation of voids inside the insulating film is suppressed.

[0038] At this time, if the amount of the metal hydroxide is too small, this action effect cannot be fully exerted. On the other hand, if the amount of the metal hydroxide is too large, the amount of metal atoms relative to phosphate ions and water becomes excessive, and the metal atoms are more likely to bond with phosphate ions in a ratio of 1:1 or 2:3 rather than forming a complex with six coordination, forming a phosphate. In that case, the action of dispersing water decreases, and the formation of voids is not suppressed.

[0039] Therefore, the content of metal hydroxide 1 is 0.1 to 2.0 mol in terms of metal element with respect to 1.0 mol of the metal element of the phosphate, and may be 0.4 to 1.7 mol, or may be 0.8 to 1.3 mol.

[0040] The content of metal hydroxide 2 is 0.1 to 5.0 mol in terms of metal element with respect to 1.0 mol of the metal element of the phosphate, and may be 0.8 to 4.2 mol, or may be 1.5 to 3.5 mol.

[0041] 《pH of the coating solution》 The pH of the coating solution should be in the range of 3 to 7. This controls the dissociation state of the phosphate ion protons, disperses water in the insulating film, and suppresses the formation of cavities. The pH of the coating solution may also be 4 to 6. The pH of the coating solution is measured using a pH meter and the glass electrode method. Water is a possible solvent for the coating solution, but an aqueous solution of orthophosphoric acid may also be used because it is easier to adjust the pH of the coating solution. The pH of the coating solution is adjusted by, for example, the amount of colloidal silica added, the amount of metal hydroxide added in the form of an aqueous solution, and the amount of aqueous solution of orthophosphoric acid added.

[0042] The change in the properties of the insulating film due to the pH of the coating solution is thought to be due to a change in the protonation state of the phosphate ion. More specifically, it is speculated as follows: When the pH of the coating solution is in the range of 3 to 7, the most common state of phosphate ions is when two of its oxygen atoms are protonated. In this state, the number of sites on which phosphate ions can coordinate to metal atoms is limited. When the pH of the coating solution is greater than 7, deprotonation of the phosphate ion proceeds. In this case, the phosphate ion has multiple coordination sites and therefore polydentately coordinates to the metal atom. As a result, the number of phosphate ions coordinating to the metal atom decreases, and the formation of a three-dimensional network is inhibited. Conversely, when the pH of the coating solution is less than 3, the phosphate ion exists in a completely protonated state. In this state, it is difficult for the phosphate ion to coordinate to the metal atom, and even if coordination is possible, the coordination bond angle is limited by the hydrogen bonded to the oxygen atom. As a result, the degree of freedom of the three-dimensional network structure decreases, water disperses less easily, and cavities are more likely to form.

[0043] 《Application and Baking of Coating Liquid》 When forming an insulating film using a coating liquid, the coating liquid is applied to the surface of the steel plate, and then baking is performed. Planar annealing, which also serves as baking, may be performed. The method of applying the coating liquid is not particularly limited, and one example is to apply it using a roll coater.

[0044] The conditions for baking (main baking) are as follows: The baking temperature is preferably 600 to 1000°C, more preferably 700 to 950°C, and even more preferably 800 to 900°C. The baking atmosphere is preferably an inert gas atmosphere such as a nitrogen gas atmosphere. The baking time is preferably 1 to 300 seconds, more preferably 5 to 200 seconds, and more preferably 10 to 100 seconds.

[0045] Pre-baking may be performed before the main baking. The conditions for pre-baking are as follows: the baking temperature is preferably 200 to 600°C, and more preferably 300 to 500°C. The baking atmosphere is preferably an atmospheric atmosphere. The baking time is preferably 5 to 100 seconds, and more preferably 10 to 40 seconds.

[0046] The insulating coating is formed on both sides of a steel plate, for example. The amount of insulating coating applied (per side) is, for example, 1.0 to 10.0 g / m². ２ The concentration is 2.0 to 8.0 g / m². ２ It may also be 3.0 to 6.0 g / m ２ That's fine.

[0047] After forming the insulating film, magnetic domain subdivision may be performed. Examples of methods for magnetic domain subdivision include forming grooves in the steel plate; using laser irradiation, plasma jet irradiation, or electron beam irradiation; and so on.

[0048] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples described below.

[0049] [Test 1] <Manufacturing of grain-oriented electrical steel sheet> A finish-annealed secondary recrystallized sheet with a thickness of 0.22 mm was prepared as the steel sheet. Since it had been finish-annealed, a forsterite coating had formed on its surface.

[0050] After washing and drying the surface of the steel sheet, a coating solution containing phosphate, colloidal silica, and metal hydroxide shown in Table 1 below was applied using a roll coater. As the phosphate, primary phosphates were all used. As the colloidal silica, Snowtex 30 manufactured by Nissan Chemical Industries, Ltd. was used. As the metal hydroxide containing metal element M1, calcium hydroxide (II) was used. As the metal hydroxide containing metal element M2, nickel hydroxide (II) was used. As the solvent of the coating solution, an orthophosphoric acid aqueous solution (concentration: 85% by mass) was used.

[0051] Note that the content of colloidal silica shown in Table 1 below (unit: mol) is the content in terms of SiO ２ conversion with respect to 1.0 mol of the metal element of the phosphate (hereinafter the same). Also, the content of the metal hydroxide shown in Table 1 below (unit: mol) is the content in terms of the metal element with respect to 1.0 mol of the metal element of the phosphate (hereinafter the same).

[0052] Then, baking was carried out. More specifically, after preliminary baking (baking temperature: 400 °C, baking time: 20 seconds) in an air atmosphere, main baking (baking temperature: 840 °C, baking time: 20 seconds) was carried out in a 100% by volume nitrogen atmosphere.

[0053] Thus, a grain-oriented electrical steel sheet with an insulating film formed on the surface of the steel sheet (adhesion amount per side: 5.0 g / m ２ ) was obtained.

[0054] 〈Porosity〉 For the obtained grain-oriented electrical steel sheet, analysis using EPMA was carried out, and the porosity (unit: %) was determined by the method described above. The results are shown in Table 1 below.

[0055] <Applied Tension> A test specimen (280 mm in the rolling direction, 30 mm in the direction perpendicular to the rolling direction) was taken from the obtained grain-oriented electrical steel sheet. To remove the insulating coating on one side, the test specimen, with the other side protected, was immersed in a sodium hydroxide aqueous solution (concentration: 20 mass%) heated to 110°C for 10 minutes. The amount of warpage of the test specimen with the insulating coating removed from one side was determined, and with a measurement length of 250 mm and a steel sheet Young's modulus of 132 GPa, the tension applied by the insulating coating to the steel sheet (applied tension) was calculated based on the following formula (I). The results are shown in Table 1 below. Applied tension [MPa] = Steel sheet Young's modulus [GPA] × Sheet thickness [mm] × Warpage [mm] ÷ (Measurement length [mm]) ２ ×10 ３ ... (I) The applied tension is preferably, for example, 6.0 MPa or more.

[0056] <Moisture Resistance> Three test pieces (50 mm x 50 mm) were taken from the obtained grain-oriented electrical steel sheet. The three test pieces were immersed in distilled water at 100°C for 5 minutes and boiled, and the amount of phosphorus (P) eluted (unit: μg / 150 cm) was analyzed using ICP emission spectrometry. ２ The following was determined: The lower the amount of phosphorus (P) eluted, the less soluble the insulating coating is in water, and the better its moisture resistance. ２ If the following conditions are met, select "A", and the P elution amount is 220 μg / 150 cm². ２ If the result was "great," it was marked with "B" in Table 1 below.

[0057]

[0058] <Summary of Evaluation Results> As shown in Table 1 above, it was found that when the void ratio is 50% or less, a greater tension can be obtained compared to when the void ratio is greater than 50%. Note that in the cases where the colloidal silica content is outside the range of 1.0 to 5.0 mol (A1 to A6, A25 to A30, A55 to A60) and in the cases where the pH of the coating solution is outside the range of 3 to 7 (A61, A67 to A70, A76 to A78), the void ratio was greater than 50%.

[0059] [Test 2] The coating liquid shown in Table 2 below was applied to the surface of the steel sheet. Otherwise, the process was carried out in the same manner as in Test 1, to form an insulating film, and a grain-oriented electrical steel sheet was obtained. The void ratio, applied tension, and P elution amount (moisture resistance) were then determined. The results are shown in Table 2 below.

[0060]

[0061] <Summary of Evaluation Results> As shown in Table 2 above, it was found that when the void ratio is 50% or less, a greater tension can be applied compared to when the void ratio is greater than 50%. In addition, in the cases where the content of metal hydroxide 1 (metal element M1) is outside the range of 0.1 to 2.0 mol (B1, B5 to B8), and in the cases where the content of metal hydroxide 2 (metal element M2) is outside the range of 0.1 to 5.0 mol (B9, B16), the void ratio was greater than 50%, and the moisture resistance was also "B".

[0062] [Test 3] The coating solution shown in Table 3 below was applied to the surface of the steel sheet. The metal hydroxide used in the coating solution was one of the following: magnesium(II) hydroxide, calcium(II) hydroxide, barium(II) hydroxide, strontium(II) hydroxide, iron(II) hydroxide, iron(III) hydroxide, nickel(II) hydroxide, cobalt(II) hydroxide, cobalt(III) hydroxide, zinc(II) hydroxide, titanium(III) hydroxide, vanadium(II) hydroxide, manganese(II) hydroxide, aluminum(III) hydroxide, iridium(III) hydroxide, ruthenium(II) hydroxide, palladium(II) hydroxide, lanthanum(II) hydroxide, praseodymium(II) hydroxide, potassium(I) hydroxide, or sodium(I). Otherwise, as in Test 1, baking was performed to form an insulating film, obtaining a grain-oriented electrical steel sheet, and the void ratio, applied tension, and P elution amount (moisture resistance) were determined. The results are shown in Table 3 below.

[0063]

[0064] <Summary of Evaluation Results> As shown in Table 3 above, it was found that when the void ratio is 50% or less, a greater tension can be obtained compared to when the void ratio is greater than 50%. In addition, in the cases where La hydroxide, Pr hydroxide, K hydroxide, or Sodium hydroxide was used as the metal hydroxide in the coating solution (C18-C21, C39-C42, C60-C63, C81-C84, C102-C105, C123-C126), the void ratio was greater than 50%, and the hygroscopicity was "B". Furthermore, in the cases where the pH of the coating solution was outside the range of 3-7 (C144, C162), the void ratio was greater than 50%.

[0065] 1: Grain-oriented electrical steel sheet 2: Steel sheet 3: Insulating coating 4: Cavity

Claims

1. A grain-oriented electrical steel sheet comprising a steel sheet and an insulating coating disposed on the surface of the steel sheet, wherein the insulating coating contains silicon and phosphorus, and the void ratio, which is the ratio of regions R2 in which cavities exist within the insulating coating in a region R1 on the surface of the grain-oriented electrical steel sheet, is 50% or less. However, region R1 is a region of 125 μm in the X direction and 125 μm in the Y direction, and region R2 is a region in region R1 in which the ratio of the detected amount of iron to the detected amount of phosphorus is 10% or more, and the detected amount of silicon is 90% or less of the maximum value in region R1, and the detected amount of each element is obtained by analyzing region R1 using an electron probe microanalyzer.

2. A method for manufacturing a grain-oriented electrical steel sheet according to claim 1, comprising: applying a coating liquid for forming the insulating film onto the surface of the steel sheet, and then baking it; the coating liquid containing a phosphate, colloidal silica, and a metal hydroxide; the metal hydroxide containing at least one metal element M1 selected from the group consisting of Mg, Ca, Ba, and Sr; and the content of the colloidal silica in the coating liquid being SiO2 per 1.0 mol of the metal element in the phosphate. ２ A method for manufacturing grain-oriented electrical steel sheets, wherein the amount of metal hydroxide in the coating solution is 1.0 to 5.0 mol in terms of conversion, the amount of metal hydroxide in the coating solution is 0.1 to 2.0 mol in terms of metal element relative to 1.0 mol of metal element in the phosphate, and the pH of the coating solution is 3 to 7.

3. A method for manufacturing a grain-oriented electrical steel sheet according to claim 1, comprising: applying a coating liquid for forming the insulating film onto the surface of the steel sheet, and then baking it; the coating liquid containing a phosphate, colloidal silica, and a metal hydroxide; the metal hydroxide containing at least one metal element M2 selected from the group consisting of Fe, Ni, Co, Zn, Ti, V, Mn, Al, Ir, Ru, Pd, and Cu; and the content of the colloidal silica in the coating liquid being SiO2 per 1.0 mol of the metal element in the phosphate. ２ A method for manufacturing grain-oriented electrical steel sheets, wherein the amount of metal hydroxide in the coating solution is 1.0 to 5.0 mol in terms of metal elements, the amount of metal hydroxide in the coating solution is 0.1 to 5.0 mol in terms of metal elements relative to 1.0 mol of metal elements in the phosphate, and the pH of the coating solution is 3 to 7.

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