MgO powder, MgO slurry, and their manufacturing methods, as well as manufacturing methods for grain-oriented electrical steel sheets

Abstract

This MgO powder has an MgO content of 90% or more, the mass of granular particles is 10-85% of the mass of the whole MgO powder, and if Lfave is the average particle diameter of plate-like particles and Lgave is the average particle diameter of the granular particles, Lgave / Lfave is more than 1.00.

Description

[Technical Field]

[0001] The present invention relates to an MgO powder, an MgO slurry, methods for producing them, and a method for producing a grain-oriented electrical steel sheet using them. This application claims priority based on Japanese Patent Application No. 2023-063669, filed on April 10, 2023, the contents of which are incorporated herein by reference. [Background technology]

[0002] Grain-oriented electrical steel sheets are soft magnetic materials that are primarily used as iron core materials in transformers. Therefore, grain-oriented electrical steel sheets are required to have magnetic properties, including high magnetization and low iron loss. Iron loss is the power loss consumed as thermal energy when an iron core is excited by an AC magnetic field, and from the perspective of energy conservation, iron loss should be as low as possible.

[0003] In the production of grain-oriented electrical steel sheets, a manufacturing method is generally applied in which a slab adjusted to a predetermined chemical composition is subjected to the following processes: hot rolling, hot-rolled sheet annealing, cold rolling, decarburization annealing, and finish annealing. Among these processes, in the finish annealing process, the steel sheet wound into a coil is annealed at high temperature for a long time to concentrate the crystal orientation into the Goss orientation, which is good for magnetic properties (to increase the degree of orientation concentration). During this process, an annealing separator is applied to the coil to prevent seizure.

[0004] The annealing separator applied to coils is often one primarily composed of magnesium oxide (MgO). This is because the use of an annealing separator primarily composed of MgO allows the silicon dioxide (SiO2) on the surface of the steel sheet to react with the MgO during final annealing, forming a forsterite (Mg2SiO4)-based coating (primary coating) on the surface of the steel sheet. This primary coating provides tension to the steel sheet surface and also provides insulation to the steel sheet. Using an annealing separator primarily composed of MgO not only prevents seizure during final annealing, but also improves the magnetic properties of grain-oriented electrical steel sheets.

[0005] As described above, in the production of grain-oriented electrical steel sheets, the properties of the grain-oriented electrical steel sheets can change depending on the annealing separator. Therefore, in recent years, research has been conducted on trace elements contained in magnesium oxide contained in annealing separators. Furthermore, research has been conducted not only on the content of trace elements but also on the structure of compounds containing trace element elements in magnesium oxide for annealing separators.

[0006] For example, Patent Document 1 discloses a powder for an annealing separator containing 0.04 mass % or more and 0.30 mass % or less of boron and containing magnesium oxide as a main component, characterized in that the proportion of tricoordinate boron in the boron is 70% or more and 95% or less.

[0007] Patent Document 2 discloses a method for producing a powder for an annealing separator, which comprises calcining a raw material containing either or both of magnesium hydroxide and magnesium carbonate and boron, and then adjusting the ratio of tricoordinated boron by controlling the humidity of the calcined product, in which the ratio of tricoordinated boron in the boron contained in the powder for an annealing separator is 70% or more and 95% or less.

[0008] In both Patent Documents 1 and 2, the proportion of tricoordinated boron is specified based on the findings that: 1) the purification of impurities is affected by the behavior of coating reactions at high temperatures (1100°C or higher), 2) boron in a tricoordinated form affects the behavior of coating reactions at high temperatures, and 3) boron in a tetracoordinated form not only does not contribute to the purification of impurities but also penetrates into the steel sheet during high-temperature annealing to form FeB, causing repeated bending deterioration. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2017-128772 [Patent Document 2] Japanese Patent Application Publication No. 2020-15982 Summary of the Invention [Problem to be solved by the invention]

[0010] If coarse MgO aggregates are present in the annealing separator, local volume loss may occur in the primary coating during final annealing. Local volume loss in the primary coating may cause the steel sheets to slide against each other, resulting in a change in shape across the coil. This change in shape across the coil is undesirable because it can cause the coil to buckle during annealing, resulting in a loss of yield across the coil.

[0011] In the above-mentioned Patent Documents 1 and 2, no consideration is given to changes in the shape of the coil in the width direction.

[0012] The present invention has been made in view of the above-mentioned problems, and aims to provide an MgO powder, an MgO slurry, and methods for producing the same, for producing grain-oriented electrical steel sheets that exhibit minimal change in shape in the width direction, as well as a method for producing the grain-oriented electrical steel sheets. [Means for solving the problem]

[0013] The gist of the present invention is as follows. (1) An MgO powder according to one aspect of the present invention is an MgO powder containing MgO particles, The MgO powder has a Mg content of 90% or more, the mass of the MgO particles having an La / Lb ratio of less than 1.50, where La is the long axis length of the MgO particles and Lb is the short axis length of the MgO particles, is 10 to 85% of the total mass of the MgO powder; The average particle size of the MgO particles having La / Lb of 1.50 or more is defined as Lf ave and the average particle size of the MgO particles having La / Lb of less than 1.50 is Lg ave When Lg ave / Lf ave is greater than 1.00. (2) An MgO slurry according to another embodiment of the present invention contains the MgO powder described in (1) above and water. (3) A method for producing MgO powder according to another aspect of the present invention includes the steps of: A method for producing MgO powder according to (1) above, using a raw material powder containing one or more types of raw material particles selected from the group consisting of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate, When the major axis length of the raw material particle is defined as la and the minor axis length of the raw material particle is defined as lb, the mass of the raw material particles having an la / lb ratio of less than 1.50 is 10 to 85% of the mass of the entire raw material powder, and The average particle size of the raw material particles having la / lb of 1.50 or more is defined as lf ave The average particle size of the raw material particles having an Ia / Ib ratio of less than 1.50 is Ig ave When The raw material particles having the la / lb ratio of 1.50 or more and the raw material particles having the la / lb ratio of less than 1.50 are mixed together to form a mixture of 1g ave / lf ave to obtain the raw material powder, The raw material powder is heated in a temperature range of 700 to 1100°C for 5 to 120 minutes. Bake . (4) A method for producing an MgO slurry according to another embodiment of the present invention includes the steps of: A method for producing an MgO slurry according to (2) above, using a raw material powder containing one or more types of raw material particles selected from the group consisting of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate, and water, When the major axis length of the raw material particle is defined as la and the minor axis length of the raw material particle is defined as lb, the mass of the raw material particles having an la / lb ratio of less than 1.50 is 10 to 85% of the mass of the entire raw material powder, and The average particle size of the raw material particles having la / lb of 1.50 or more is defined as lf ave The average particle size of the raw material particles having an Ia / Ib ratio of less than 1.50 is Ig ave When The raw material particles having the la / lb ratio of 1.50 or more and the raw material particles having the la / lb ratio of less than 1.50 are mixed together to form a mixture of 1g ave / lf ave to obtain the raw material powder, The raw material powder is heated in a temperature range of 700 to 1100°C for 5 to 120 minutes. Baked rear, The fired raw material powder is mixed with the water. (5) A method for producing an MgO slurry according to another embodiment of the present invention includes the steps of: A method for producing an MgO slurry according to (2) above, using a raw material powder containing one or more types of raw material particles selected from the group consisting of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate, and water, When the major axis length of the raw material particle is defined as la and the minor axis length of the raw material particle is defined as lb, the mass of the raw material particles having an la / lb ratio of less than 1.50 is 10 to 85% of the mass of the entire raw material powder, and The average particle size of the raw material particles having la / lb of 1.50 or more is defined as lf ave The average particle size of the raw material particles having an Ia / Ib ratio of less than 1.50 is Ig ave When The raw material particles having the la / lb ratio of 1.50 or more are fired in a temperature range of 700 to 1100°C for 5 to 120 minutes, and the raw material particles having the la / lb ratio of less than 1.50 are fired in a temperature range of 700°C or more for 5 to 120 minutes. Baked rear, lg ave / lf ave The fired raw material particles are mixed in water so that the sintering ratio exceeds 1.00. (6) A method for producing a grain-oriented electrical steel sheet according to another embodiment of the present invention uses the MgO powder described in (1) above. (7) A method for producing a grain-oriented electrical steel sheet according to another embodiment of the present invention uses the MgO slurry described in (2) above. [Effects of the Invention]

[0014] According to the above aspect of the present invention, it is possible to provide MgO powder, MgO slurry, and methods for producing them, as well as a method for producing the oriented electromagnetic steel sheet for producing an oriented electromagnetic steel sheet with small shape change in the width direction.

Brief Description of Drawings

[0015] [Figure 1] It is a figure which shows the coil shape before and after finish annealing. [Figure 2] It is a figure for demonstrating the measuring method of the coil deformation amount in the deformation part of the coil after finish annealing.

Embodiments for Carrying Out the Invention

[0016] The MgO powder, MgO slurry, and methods for producing them, and the method for producing the oriented electromagnetic steel sheet according to the present embodiment will be specifically described below. However, the present invention is not limited to the configuration disclosed in the present embodiment, and various modifications are possible without departing from the spirit of the present invention.

[0017] <MgO Powder> The MgO powder according to the present embodiment is an MgO powder containing MgO particles, the Mg amount in the MgO powder is 90% or more, among the MgO particles, when the long axis length of the MgO particle is La and the short axis length of the MgO particle is Lb, the mass of the MgO particles with La / Lb less than 1.50 is 10 to 85% of the total mass of the MgO powder, the average particle size of the MgO particles with La / Lb of 1.50 or more is Lf ave and the average particle size of the MgO particles with La / Lb less than 1.50 is Lg ave when this is done, Lg ave / Lf ave is more than 1.00. This will be described in more detail below.

[0018] The MgO powder according to this embodiment contains MgO particles. The MgO powder according to this embodiment contains, for example, 50.0% or more of MgO particles. The content of MgO particles in the MgO powder is preferably 80.0% by mass or more, more preferably 90.0% by mass or more, and even more preferably 99.0% by mass.

[0019] The MgO powder may contain impurities such as Al, B, Fe, Si, etc. If the content of each impurity element is 0.5 mass% or less, or if the total content is 1.0 mass% or less, the effect on the magnetic properties or coating properties of the grain-oriented electrical steel sheet is small.

[0020] Mg content in MgO powder: 90% or more The amount of Mg in the MgO powder can be expressed by the left side of the following equation: The Mg amount in the MgO powder being 90% or more means that the Mg mass concentration [Mg] when the MgO powder is chemically analyzed satisfies the following equation: The chemical analysis is performed by quantitative analysis of elements using ICP-MS. [Mg]×40 / 24≧90%

[0021] If the Mg content in the MgO powder is less than 90%, it will be impossible to obtain a grain-oriented electrical steel sheet with minimal change in shape in the width direction. Therefore, the Mg content in the MgO powder is set to 90% or more. The Mg content in the MgO powder is preferably 95% or more.

[0022] Mass of MgO particles with La / Lb less than 1.50: 10-85% By controlling the ratio of granular particles within a predetermined range among the MgO particles contained in the MgO powder and the ratio of the average particle size of the flat, plate-like particles to the average particle size of the granular particles within a desired range, fine MgO particles that are easily sintered can be highly dispersed, thereby preventing local volume loss. Furthermore, the plate-like particles act as a framework, preventing the steel sheets from sliding against each other. As a result, deformation of the coil across the width can be prevented during final annealing.

[0023] In this embodiment, when the major axis length of an MgO particle contained in an MgO powder is La and the minor axis length of the MgO particle is Lb, MgO particles having an La / Lb ratio of less than 1.50 are considered to be granular particles, while MgO particles having an La / Lb ratio of 1.50 or more are considered to be plate-like particles. In MgO powder, MgO particles may aggregate together to form secondary particles, but the long axis length and short axis length referred to here refer to the long axis length and short axis length of the primary particle of the MgO particle.

[0024] Of the total MgO powder, the mass of granular particles (MgO particles with La / Lb less than 1.50) is 10 to 85%. The mass of granular particles is preferably 20% or more, more preferably 30% or more. The mass of granular particles is preferably 50% or less.

[0025] Ratio of average particle size (Lg ave / Lf ave ):Over 1.00 The average particle size of plate-like particles (MgO particles with La / Lb of 1.50 or more) is Lf ave The average particle size of granular particles (MgO particles with La / Lb less than 1.50) is Lg ave When Lg ave / Lf ave The Lg is set to be greater than 1.00. By increasing the ratio of the average particle size of the granular particles to the average particle size of the plate-like particles, the plate-like particles can function favorably as a framework. ave / Lf ave is preferably 1.10 or more. In addition, from the viewpoint of minimizing the change in shape in the width direction, the average particle diameter Lf ave and the average particle size of granular particles Lg ave are each preferably less than 2.000 μm, more preferably 1.500 μm or less or 1.000 μm or less, and even more preferably 0.500 μm or less.

[0026] The measurement method will be explained below. A scanning electron microscope (SEM) is used to take an enlarged photograph of the MgO particles in the MgO powder. The shape of one primary particle is traced, and the long axis length (La) and short axis length (Lb) of the primary particle are calculated through image analysis. This procedure is performed on 50 or more randomly selected particles. This allows us to identify MgO particles with an La / Lb ratio of 1.50 or more (plate-like particles) and MgO particles with an La / Lb ratio of less than 1.50 (granular particles).

[0027] The circle equivalent diameters of the identified plate-like particles and granular particles are calculated, and their average value is calculated to determine the average particle diameter of the plate-like particles (Lf ave ) and the average particle size of the granular particles (Lg ave ) is obtained.

[0028] Method for measuring the mass of granular particles Average particle size of plate-like particles (Lf ave ) and the average particle size of granular particles (Lg ave From the same enlarged photograph as when measuring the La / Lb ratio, the La / Lb of 50 or more randomly selected particles is calculated, and the number frequency ff (%) of MgO particles (plate-like particles) with an La / Lb ratio of 1.50 or more and the number frequency fg (%) of MgO particles (granular particles) with an La / Lb ratio of less than 1.50 are calculated. The mass percentage (Wg (%)) of the granular particles is calculated using the obtained values and equation (1).

[0029] Wg=ff×Lf ave 3 / (50×(Lf ave 3 +Lg ave 3 )) …(1)

[0030] <MgOスラリー> The MgO slurry according to this embodiment contains water and an MgO powder containing the above-described MgO particles. The MgO powder and MgO particles have been described above, so further description will be omitted. The mass of the MgO powder in the MgO slurry may be 5 to 30%.

[0031] When performing the above-described measurement on the MgO powder in the MgO slurry, the above-described measurement is performed on the MgO powder obtained by evaporating moisture by holding the MgO slurry in a thermostatic bath at 80°C for a predetermined time.

[0032] <Method for producing MgO powder> Next, the method for producing the MgO powder described above will be explained. The method for producing MgO powder according to the present embodiment is a method for producing MgO powder using a raw material powder containing one or more raw material particles selected from the group consisting of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate, Among the raw material particles, when the major axis length of the raw material particles is la and the minor axis length of the raw material particles is lb, the mass of the raw material particles with la / lb less than 1.5 is 10 to 85% of the total mass of the raw material powder, and the average particle size of the raw material particles with la / lb of 1.50 or more is lf ave and the average particle size of the raw material particles with la / lb less than 1.50 is lg ave When the raw material particles with la / lb of 1.50 or more and the raw material particles with la / lb less than 1.50 are mixed so that lg ave / lf ave exceeds 1.00 to obtain the raw material powder, the raw material powder is fired in a temperature range of 700 to 1100°C for 5 to 120 minutes and pulverized as necessary.

[0033] Raw material powder The raw material powder contains one or more raw material particles selected from the group consisting of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate. In addition to these raw material particles, magnesium chloride, calcium carbonate, and calcium chloride may also be included.

[0034] Mass of raw material particles with la / lb less than 1.50: 10 - 85% When the major axis length of the raw material particles in the raw material powder is taken as la and the minor axis length of the raw material particle is taken as lb, the mass of raw material particles having an la / lb ratio of less than 1.50 is 10 to 85% of the total mass of the raw material powder. This allows the mass of granular particles in the MgO powder to be controlled within a preferred range. The mass of raw material particles having an la / lb ratio of less than 1.50 is preferably 20% or more, more preferably 30% or more. Furthermore, the mass of raw material particles having an la / lb ratio of less than 1.50 is preferably 40% or less.

[0035] Ratio of average particle size (lg ave / lf ave ):Over 1.00 The average particle size of raw material particles with la / lb of 1.50 or more is defined as lf ave The average particle size of raw material particles with la / lb less than 1.50 is lg ave When this is done, lg ave / lf ave is set to be greater than 1.00. This makes it possible to control the average particle size of the plate-like particles and the average particle size of the granular particles in the MgO powder within a preferred range. ave / lf ave is preferably 1.10 or more. In addition, from the viewpoint of minimizing the change in shape in the width direction, the average particle diameter lf of the plate-like particles is ave It is preferable that the average particle diameter lf of the plate-like particles is 10,000 μm or less. ave and the average particle size of granular particles lg ave are each preferably less than 2.000 μm, more preferably 1.500 μm or less or 1.000 μm or less, and even more preferably 0.500 μm or less.

[0036] The mass and average particle size ratio of raw material particles with Ia / Ib less than 1.50 (Ig ave / lf ave ) can be controlled within the above range by adjusting the mixing ratio of two or more types of raw material particles that differ in average particle size, major axis length, minor axis length, etc. The major axis length, minor axis length, and average particle size of the raw material powder may be measured by the same method as that for the MgO powder described above.

[0037] Next, the raw material powder is fired in a temperature range of 700 to 1100 °C. Thereby, MgO powder can be obtained. After firing, the MgO powder may be pulverized by a method using a ball mill or the like as necessary. In these pulverization methods, the primary particles of the raw material powder are not broken. The firing temperature is preferably 720 °C or higher, more preferably 750 °C or higher. Also, the firing temperature is preferably 1080 °C or lower, more preferably 1040 °C or lower. The firing time is set to 5 to 120 minutes in order to preferably control the amount of Mg in the MgO powder. From the viewpoint of eliminating firing unevenness, the firing time is preferably 8 minutes or longer, more preferably 10 minutes or longer. On the other hand, from the viewpoint of economy, the firing time is preferably 80 minutes or shorter, more preferably 60 minutes or shorter. However, when only the raw material particles with la / lb less than 1.50 are fired, they may be fired at a temperature exceeding 1100 °C.

[0038] The firing atmosphere is preferably an air atmosphere or a nitrogen atmosphere. Atmospheres other than these are not preferable because they are economically disadvantageous.

[0039] <Method for producing MgO slurry> The method for producing the MgO slurry according to the present embodiment includes a method of mixing the raw material powder and water and a method of mixing two or more types of raw material particles in water. The difference between these two methods is only the point of whether the mixing of two or more types of raw material particles is performed before the mixing with water or together with the mixing with water.

[0040] In the method of mixing the raw material powder and water, the MgO slurry is obtained by mixing the raw material powder described above and water. More specifically, it is a method for producing an MgO slurry using a raw material powder containing one or more raw material particles selected from the group consisting of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate, and water. When the major axis length of the raw material particle is defined as la and the minor axis length of the raw material particle is defined as lb, the mass of the raw material particles having an la / lb ratio of less than 1.50 is 10 to 85% of the mass of the entire raw material powder, and The average particle size of the raw material particles having la / lb of 1.50 or more is defined as lf ave The average particle size of the raw material particles having an Ia / Ib ratio of less than 1.50 is Ig ave When The raw material particles having the la / lb ratio of 1.50 or more and the raw material particles having the la / lb ratio of less than 1.50 are mixed together to form a mixture of 1g ave / lf ave to obtain the raw material powder, The raw material powder is fired at a temperature range of 700 to 1100°C for 5 to 120 minutes, pulverized as necessary, and then The fired raw material powder is mixed with the water.

[0041] In the method of mixing two or more types of raw material particles in water, two or more types of raw material particles are mixed in water so that the mixed raw material powder has the above-mentioned mass and average particle size ratios, thereby obtaining MgO slurry. More specifically, the present invention relates to a method for producing an MgO slurry using water and a raw material powder containing one or more types of raw material particles selected from the group consisting of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate, When the major axis length of the raw material particle is defined as la and the minor axis length of the raw material particle is defined as lb, the mass of the raw material particles having an la / lb ratio of less than 1.50 is 10 to 85% of the mass of the entire raw material powder, and The average particle size of the raw material particles having la / lb of 1.50 or more is defined as lf ave The average particle size of the raw material particles having an Ia / Ib ratio of less than 1.50 is Ig ave When The raw material particles having an Ia / Ib ratio of 1.50 or more are fired in a temperature range of 700 to 1100°C for 5 to 120 minutes, and the raw material particles having an Ia / Ib ratio of less than 1.50 are fired in a temperature range of 700°C or more for 5 to 120 minutes, and each is crushed as necessary, and then: lg ave / lf ave The fired raw material particles are mixed in water so that the sintering ratio exceeds 1.00.

[0042] <Method of manufacturing grain-oriented electrical steel sheets> In the manufacturing method of grain-oriented electrical steel sheet according to the present embodiment, the above-mentioned MgO powder is used as an annealing separator. The manufacturing method of grain-oriented electrical steel sheet according to the present embodiment includes, for example, a hot rolling step in which a slab is hot-rolled to obtain a hot-rolled sheet, a hot-rolled sheet annealing step in which the hot-rolled sheet is annealed, a cold-rolling step in which the hot-rolled sheet after the hot-rolled sheet annealing step is cold-rolled to obtain a cold-rolled sheet, a decarburization annealing step in which the cold-rolled sheet is decarburized and annealed, and a finish annealing step in which an annealing separator containing the MgO powder is applied to the cold-rolled sheet after the decarburization annealing step, dried, and then finish annealed. This manufacturing method using the MgO powder or MgO slurry according to the present embodiment makes it possible to manufacture grain-oriented electrical steel sheet with small differences in magnetic properties in the width direction.

[0043] In this embodiment, the annealing separator to be applied before finish annealing is an annealing separator prepared by mixing the MgO powder according to the embodiment described above with water to form an MgO slurry. In the above manufacturing method, the chemical composition of the slab and the conditions of each step can be the same as those for manufacturing known grain-oriented electrical steel sheets, except for the annealing separator used. [Example]

[0044] Next, the effects of one embodiment of the present invention will be explained in more detail using examples, but the conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to these examples. Various conditions can be adopted in the present invention as long as they do not deviate from the gist of the present invention and the object of the present invention is achieved.

[0045] Example 1 The average particle size, the long axis length of the primary particle Ia, the short axis length of the primary particle Ib, the average aspect ratio (Ia / Ib), and the particle size ratio (Ig) are listed in Table 1. ave / lf ave The raw material particles having the above composition were fired at a temperature range of 700 to 1100°C for 5 to 120 minutes and pulverized to obtain MgO particles 1 and MgO particles 2. The MgO particles 1 and MgO particles 2 were mixed with water to obtain an annealing separator (aqueous slurry). The average particle size of MgO particles 1 and MgO particles 2 is not shown in the table.

[0046] The annealing separator thus obtained was used to evaporate the water content by the above-mentioned method to obtain MgO powder. MgO particles (plate-like particles) with an La / Lb ratio of 1.50 or more and MgO particles (granular particles) with an La / Lb ratio of less than 1.50 were identified, and their content, average aspect ratio, average particle size, particle size ratio (Lg ave / Lf ave ) was obtained. In the test number that satisfies the preferable conditions, the amount of Mg is 90% or more, the mass of MgO particles with La / Lb less than 1.50 is 10 to 85% of the mass of the entire MgO powder, and Lg ave / Lf ave was over 1.00.

[0047] Next, the above-mentioned annealing separator was applied to the cold-rolled steel sheet after primary recrystallization annealing. For all test numbers, the cold-rolled steel sheet with the annealing separator applied to its surface was baked at 300°C for 30 seconds to dry the annealing separator. After the bake treatment, a final annealing treatment was performed. For all test numbers, the final annealing treatment was performed by holding the steel sheet at 1200°C for 20 hours.

[0048] Using the above manufacturing process, grain-oriented electrical steel sheets were produced, each comprising a base steel sheet and a glass coating containing a composite oxide such as forsterite (Mg2SiO4). The coil deformation (mm) of the grain-oriented electrical steel sheet was then measured by measuring the height from the bottom end of the coil, where the deformation was greatest, to the top end of the region where deformation of 1% or more occurred in the outer or inner circumferential direction, relative to the diameter at the center of the width direction. Specifically, the coil deformation (mm) of the grain-oriented electrical steel sheet was measured at the position shown in Figure 2 for cross section A (Figure 2) of the coil, which was deformed from the coil before finish annealing shown in Figure 1(a) to the shape shown in Figure 1(b) by finish annealing.

[0049] If the coil deformation of the obtained grain-oriented electrical steel sheet was less than 70 mm, it was judged to be a grain-oriented electrical steel sheet with small shape change in the width direction and to pass.If the coil deformation of the obtained grain-oriented electrical steel sheet was 70 mm or more, it was judged to be a grain-oriented electrical steel sheet with large shape change in the width direction and to fail.

[0050] In Test Nos. 1 and 2, the average aspect ratio of all MgO raw material particles was 1.50 or more, which resulted in a shortage of MgO particles with an La / Lb ratio of less than 1.50. As a result, loosening of the coil occurred, and the coil deformation of the grain-oriented electrical steel sheet reached 70 mm or more. In addition, in test number 12, the particle size ratio of the MgO raw material particles (lg ave / lf ave ) was 1.00 or less, the coil loosened, and the coil deformation of the grain-oriented electrical steel sheet exceeded 70 mm.

[0051] In test number 6, the amount of MgO raw material particles with a small aspect ratio was small, resulting in a shortage of MgO particles with an La / Lb of less than 1.50, and the coil deformation of the grain-oriented electrical steel sheet was 70 mm or more. In test number 7, the amount of MgO raw material particles with a small aspect ratio was large, resulting in an excess of MgO particles with an La / Lb of less than 1.50, and the coil deformation of the grain-oriented electrical steel sheet was 70 mm or more.

[0052] In test numbers 3 to 5, 8 to 11, and 13 to 19, the average aspect ratios of the two types of MgO raw material particles were within the preferred range, and their particle size ratios and contents were also appropriate. Therefore, the mass and Lg of MgO particles with La / Lb of less than 1.50 were ave / Lf ave was within the preferred range, the coil deformation of the grain-oriented electrical steel sheet was less than 70 mm.

[0053] In particular, in test numbers 8 to 11, the particle size ratio of the MgO raw material particles (lg ave / lf ave ) was higher, so Lg ave / Lf ave was 1.10 or more, making the steel plate less likely to slip, and the coil deformation was reduced to 20 mm or less.

[0054] [Table 1]

[0055] Example 2 MgO particles 1 were obtained by firing MgO raw material particles 1 shown in Table 2 under the conditions described in Table 2. MgO particles 2 were obtained by firing MgO raw material particles 2 shown in Table 3 under the conditions described in Table 3. MgO particles 1 and MgO particles 2 were mixed in the amounts described in Tables 2 and 3, respectively, to obtain MgO powder described in Table 4. The obtained MgO powder was mixed with water to obtain an annealing separator (aqueous slurry).

[0056] The annealing separator thus obtained was used to evaporate the water content by the above-mentioned method to obtain MgO powder. MgO particles (plate-like particles) with an La / Lb ratio of 1.50 or more and MgO particles (granular particles) with an La / Lb ratio of less than 1.50 were identified, and their content, average aspect ratio, average particle size, particle size ratio (Lg ave / Lf ave ) was obtained.

[0057] Next, the above-mentioned annealing separator was applied to the cold-rolled steel sheet after primary recrystallization annealing. For all test numbers, the cold-rolled steel sheet with the annealing separator applied to its surface was baked at 300°C for 30 seconds to dry the annealing separator. After the bake treatment, a final annealing treatment was performed. For all test numbers, the final annealing treatment was performed by holding the steel sheet at 1200°C for 20 hours.

[0058] Through the above manufacturing process, a grain-oriented electrical steel sheet having a base steel sheet and a glass coating containing a composite oxide such as forsterite (Mg2SiO4) was manufactured. The coil deformation of the obtained grain-oriented electrical steel sheet was measured in the same manner as in Example 1. Table 4 shows the test results.

[0059] In test numbers 20, 22, 24, and 25, the firing conditions for the MgO raw material particles were not within the preferred range, resulting in residual raw material and a Mg content of 90% or less in the MgO powder after firing. As a result, the magnetic unevenness in the width direction of the grain-oriented electrical steel sheet was 0.015T or more.

[0060] In test number 23, the firing conditions for MgO raw material particles 2 with a large average aspect ratio (la / lb) were not within the preferred conditions, resulting in coarsening of the particles and resulting in the average particle size of the plate-like particles becoming too large.

[0061] In test numbers 26 and 27, the average aspect ratio of all raw material particles was 1.50 or more, which resulted in a shortage of MgO particles with an La / Lb ratio of less than 1.50. As a result, the coil deformation of the grain-oriented electrical steel sheet was 70 mm or more.

[0062] In test numbers 28 and 29, the content of MgO, which has a small aspect ratio, was outside the preferred range, and therefore the coil deformation of the grain-oriented electrical steel sheet was 70 mm or more.

[0063] In test numbers 30 and 31, the particle size ratio of the two types of MgO particles was within the preferred range, and the content thereof was also appropriate, so the coil deformation of the grain-oriented electrical steel sheet was less than 70 mm.

[0064] In particular, in test number 31, the particle size ratio (Lg ave / Lf ave ) was 1.10 or more, the steel sheet was less likely to slip, and the coil deformation amount was 20 mm or less.

[0065] [Table 2]

[0066] [Table 3]

[0067] [Table 4]

[0068] Example 3 A raw material powder was obtained by mixing MgO raw material particles 1 and MgO raw material particles 2 shown in Tables 5 and 6 in the blending amounts shown in Tables 5 and 6. The obtained raw material powder was fired under the conditions shown in Table 7. As a result, the MgO powder shown in Table 7 was obtained. The obtained MgO powder was mixed with water to obtain an annealing separator (aqueous slurry).

[0069] The annealing separator thus obtained was used to evaporate the water content by the above-mentioned method to obtain MgO powder. MgO particles (plate-like particles) with an La / Lb ratio of 1.50 or more and MgO particles (granular particles) with an La / Lb ratio of less than 1.50 were identified, and their content, average aspect ratio, average particle size, particle size ratio (Lg ave / Lf ave ) was obtained.

[0070] Next, the above-mentioned annealing separator was applied to the cold-rolled steel sheet after primary recrystallization annealing. For all test numbers, the cold-rolled steel sheet with the annealing separator applied to its surface was baked at 300°C for 30 seconds to dry the annealing separator. After the bake treatment, a final annealing treatment was performed. For all test numbers, the final annealing treatment was performed by holding the steel sheet at 1200°C for 20 hours.

[0071] Through the above manufacturing process, a grain-oriented electrical steel sheet having a base steel sheet and a glass coating containing a composite oxide such as forsterite (Mg2SiO4) was manufactured. The coil deformation of the obtained grain-oriented electrical steel sheet was measured in the same manner as in Example 1. Table 7 shows the test results.

[0072] In test numbers 36 and 38, the firing conditions for the MgO raw material powder were not within the preferred conditions, so the raw material remained.

[0073] In test number 37, the sintering conditions for the MgO raw material powder were not within the preferred range, resulting in a decrease in plate-like particles and an excessive increase in the content of granular particles. As a result, the coil deformation of the grain-oriented electrical steel sheet exceeded 70 mm.

[0074] In test numbers 39 and 40, the average aspect ratio of all MgO raw material particles was 1.50 or more, so there was a shortage of MgO particles with an La / Lb ratio of less than 1.50. As a result, the coil deformation of the grain-oriented electrical steel sheet was 70 mm or more.

[0075] In test numbers 41 and 42, the content of the MgO raw material particles with a small aspect ratio was outside the preferred range, and therefore the coil deformation of the grain-oriented electrical steel sheet was 70 mm or more.

[0076] In test numbers 43 and 44, the particle size ratio of the two types of MgO particles was within the preferred range, and the content thereof was also appropriate, so the coil deformation of the grain-oriented electrical steel sheet was less than 70 mm.

[0077] In particular, in test number 44, the particle size ratio (Lg ave / Lf ave ) was 1.10 or more, the steel sheet was less likely to slip, and the coil deformation amount was 20 mm or less.

[0078] [Table 5]

[0079] [Table 6]

[0080] [Table 7] [Industrial Applicability]

[0081] According to the above aspects of the present invention, it is possible to provide an MgO powder, an MgO slurry, and methods for producing the same, for producing a grain-oriented electrical steel sheet that exhibits little change in shape in the width direction, as well as a method for producing the grain-oriented electrical steel sheet.

Claims

1. An MgO powder comprising MgO particles, The MgO powder has a Mg content of 90% or more, the mass of the MgO particles having an La / Lb ratio of less than 1.50, where La is the length of the major axis of the MgO particle and Lb is the length of the minor axis of the MgO particle, is 10 to 85% of the total mass of the MgO powder; The average particle size of the MgO particles having La / Lb of 1.50 or more is defined as Lf ａｖｅ and the average particle size of the MgO particles having La / Lb of less than 1.50 is Lg ａｖｅ When this is done, Lg ａｖｅ / Lf ａｖｅ The MgO powder characterized in that the MgO content is greater than 1.

00.

2. An MgO slurry comprising the MgO powder according to claim 1 and water.

3. 2. A method for producing an MgO powder according to claim 1, wherein a raw material powder containing one or more types of raw material particles selected from the group consisting of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate is used, When the major axis length of the raw material particle is defined as la and the minor axis length of the raw material particle is defined as lb, the mass of the raw material particles having an la / lb ratio of less than 1.50 is 10 to 85% of the mass of the entire raw material powder, and The average particle size of the raw material particles having an 1a / 1b ratio of 1.50 or more is defined as 1f ａｖｅ and the average particle size of the raw material particles having an 1a / 1b ratio of less than 1.50 is 1g ａｖｅ When The raw material particles having the la / lb ratio of 1.50 or more and the raw material particles having the la / lb ratio of less than 1.50 are mixed together by 1g ａｖｅ / lf ａｖｅ to obtain the raw material powder, The method for producing MgO powder is characterized by firing the raw material powder at a temperature in the range of 700 to 1100°C for 5 to 120 minutes.

4. 3. The method for producing an MgO slurry according to claim 2, wherein water and a raw material powder containing one or more types of raw material particles selected from the group consisting of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate are used, When the major axis length of the raw material particle is defined as la and the minor axis length of the raw material particle is defined as lb, the mass of the raw material particles having an la / lb ratio of less than 1.50 is 10 to 85% of the mass of the entire raw material powder, and The average particle size of the raw material particles having an 1a / 1b ratio of 1.50 or more is defined as 1f ａｖｅ and the average particle size of the raw material particles having an 1a / 1b ratio of less than 1.50 is 1g ａｖｅ When The raw material particles having the la / lb ratio of 1.50 or more and the raw material particles having the la / lb ratio of less than 1.50 are mixed together by 1g ａｖｅ / lf ａｖｅ to obtain the raw material powder, The raw material powder is fired at a temperature range of 700 to 1100°C for 5 to 120 minutes, A method for producing an MgO slurry, comprising mixing the fired raw material powder with water.

5. 3. The method for producing an MgO slurry according to claim 2, wherein water and a raw material powder containing one or more types of raw material particles selected from the group consisting of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate are used, When the major axis length of the raw material particle is defined as la and the minor axis length of the raw material particle is defined as lb, the mass of the raw material particles having an la / lb ratio of less than 1.50 is 10 to 85% of the mass of the entire raw material powder, and The average particle size of the raw material particles having an 1a / 1b ratio of 1.50 or more is defined as 1f ａｖｅ and the average particle size of the raw material particles having an 1a / 1b ratio of less than 1.50 is 1g ａｖｅ When The raw material particles having an l / lb ratio of 1.50 or more are fired in a temperature range of 700 to 1100°C for 5 to 120 minutes, and the raw material particles having an l / lb ratio of less than 1.50 are fired in a temperature range of 700°C or more for 5 to 120 minutes, and then lg ａｖｅ / lf ａｖｅ and mixing the fired raw material particles in water so that the MgO slurry has a viscosity of more than 1.

00.

6. A method for producing a grain-oriented electrical steel sheet, comprising using the MgO powder according to claim 1.

7. A method for producing a grain-oriented electrical steel sheet, comprising using the MgO slurry according to claim 2.

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