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

Abstract

This MgO powder contains 90% or more of MgO, wherein plate-like particles constitute 10-85% of the total mass of the MgO powder, and Lfave / Lgave is 1.00 or more, where Lfave is the average particle diameter of the plate-like particles and Lgave is the average particle diameter of granular particles.

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. 2023-063670, 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] During finish annealing, the atmosphere in the center of the coil in the width direction is poorer than that in the ends in the width direction, so the primary coating may not be sufficiently formed in the center of the coil in the width direction. If there is a difference in the formation of the primary coating between the ends and the center of the coil in the width direction, this may cause a difference in the magnetic properties of the grain-oriented electrical steel sheet in the width direction, which is not preferable.

[0011] The above-mentioned Patent Documents 1 and 2 do not take into consideration the difference in the formation of the primary coating in the width direction of the coil.

[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 with small differences in magnetic properties 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 an MgO content of 90% or more, the mass of the MgO particles having an La / Lb ratio of 1.50 or more, 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 The average particle size of the MgO particles having La / Lb of less than 1.50 is defined as Lg ave When Lf ave / Lg ave is 1.00 or greater. (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 1.50 or more accounts for 10 to 85% of the mass of the entire raw material powder, and The average particle size of the raw material particles having the la / lb ratio 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 by lf ave / lg ave The raw material powder is obtained by mixing the raw material powder so that the value of the raw material powder is 1.00 or more. 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 1.50 or more accounts for 10 to 85% of the mass of the entire raw material powder, and The average particle size of the raw material particles having the la / lb ratio 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 by lf ave / lg aveThe raw material powder is obtained by mixing the raw material powder so that the value of the raw material powder is 1.00 or more. 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 1.50 or more accounts for 10 to 85% of the mass of the entire raw material powder, and The average particle size of the raw material particles having the la / lb ratio 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 each heated in a temperature range of 700 to 1100°C for 5 to 120 minutes. Baked rear, lf ave / lg ave The raw material particles after firing are mixed in water so that the sintering ratio is 1.00 or more. (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 an MgO powder, an MgO slurry, and methods for producing the same, for producing grain-oriented electrical steel sheets having small differences in magnetic properties in the width direction, as well as a method for producing the grain-oriented electrical steel sheets. DETAILED DESCRIPTION OF THE INVENTION

[0015] The MgO powder, MgO slurry, and their manufacturing methods according to this embodiment, as well as the manufacturing method of the grain-oriented electrical steel sheet, will be specifically described below. However, the present invention is not limited only to the configurations disclosed in this embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0016] <MgO powder> The MgO powder according to this embodiment is a MgO powder containing MgO particles, the MgO powder has a Mg content of 90% or more, among the MgO particles, when the major axis length of the MgO particle is La and the minor axis length of the MgO particle is Lb, the mass of the MgO particles with La / Lb being 1.50 or more is 10 to 85% of the total mass of the MgO powder, the average particle size of the MgO particles with La / Lb being 1.50 or more is Lf ave and the average particle size of the MgO particles with La / Lb being less than 1.50 is Lg ave when, ave Lf ave / Lg is 1.00 or more.

[0017] 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.

[0018] The MgO powder may contain impurities such as Al, B, Fe, and Si. If the content of each impurity element is 0.5% by mass or less, or the total amount is 1.0% by mass or less, the influence on the magnetic properties or film properties of the grain-oriented electrical steel sheet is small.

[0019] Mg content in the 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%

[0020] 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 small differences in magnetic properties 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.

[0021] Mass of MgO particles with La / Lb of 1.50 or more: 10 to 85% By controlling the ratio of flat, plate-like particles within a predetermined range among the MgO particles contained in the MgO powder and the ratio of the average particle size of the plate-like particles to the average particle size of the granular particles within a desired range, the frequency of contact between the annealing separator and the steel sheet can be increased, and as a result, a primary coating can be sufficiently formed even in the widthwise central portion of the coil, where the primary coating is difficult to form.

[0022] 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 1.50 or more are considered to be plate-like particles, while MgO particles having an La / Lb ratio of less than 1.50 are considered to be granular 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.

[0023] The mass of plate-like particles (MgO particles with La / Lb of 1.50 or more) of the entire MgO powder is 10 to 85%. The mass of the plate-like particles is preferably 20% or more, more preferably 30% or more. The mass of the plate-like particles is preferably 40% or less.

[0024] Ratio of average particle size (Lf ave / Lg ave ): 1.00 or more 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 Lf ave / Lg ave The Lf is set to 1.00 or more. By increasing the ratio of the average particle size of the plate-like particles to the average particle size of the granular particles, the contact between the MgO particles and the primary coating increases, which increases the frequency of contact between the steel sheet and the primary coating. ave / Lg 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.

[0025] 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).

[0026] 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.

[0027] Method for measuring the mass of granular particles Average particle size of plate-like particles (Lf ave) and the average particle size (Lg of the granular particles ave ) From the same magnified photograph as when measured, the La / Lb of 50 or more particles randomly selected is calculated, and the number frequency ff (%) of MgO particles (plate-like particles) with La / Lb of 1.50 or more and the number frequency fg (%) of MgO particles (granular particles) with La / Lb less than 1.50 are calculated. By using the obtained values and Equation (1), the mass% (Wf (%)) of the granular particles is obtained.

[0028] Wf = fg × Lg ave 3 / (50 × (Lf ave 3 + Lg ave 3 )) …(1)

[0029] <MgO slurry> The MgO slurry according to this embodiment contains MgO powder containing the above-described MgO particles and water. Since the MgO powder and the MgO particles have been described above, the description thereof will be omitted. The mass of the MgO powder in the MgO slurry may be 5 to 30%.

[0030] When performing the above measurement on the MgO powder in the MgO slurry, the above 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.

[0031] <Method for producing MgO powder> Next, the method for producing the above-described MgO powder will be described. The method for producing MgO powder according to this 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 of 1.50 or more is 10 to 85% of the total mass of the raw material powder, and The average particle size of the raw material particles having the la / lb ratio 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 by lf ave / lg ave The raw material powder is obtained by mixing the raw material powder so that the value of the raw material powder is 1.00 or more. The raw material powder is fired in a temperature range of 700 to 1100° C. for 5 to 120 minutes, and then pulverized as necessary.

[0032] Raw material powder The raw material powder contains one or more types of raw material particles selected from the group consisting of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate. In addition to these raw material particles, the raw material powder may also contain magnesium chloride, calcium carbonate, and calcium chloride.

[0033] Mass of raw material particles with Ia / lb of 1.50 or more: 10 to 85% When the major axis length of the raw material particles in the raw material powder is defined as la and the minor axis length of the raw material particle is defined as lb, the mass of raw material particles having an la / lb ratio of 1.50 or more is 10 to 85% of the total mass of the raw material powder. This allows the mass of plate-like particles in the MgO powder to be controlled within a preferred range. The mass of raw material particles having an la / lb ratio of 1.50 or more is preferably 20% or more, more preferably 30% or more. Furthermore, the mass of raw material particles having an la / lb ratio of 1.50 or more is preferably 40% or less.

[0034] Ratio of average particle size (lf ave / lg ave ): 1.00 or more 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 ave / lg aveis set to 1.00 or more. 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 / lg 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 Furthermore, the average particle size lf of the plate-like particles is preferably 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.

[0035] The mass and average particle size ratio of raw material particles with Ia / Ib of 1.50 or more (lf ave / lg 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 for the MgO powder described above.

[0036] Next, the raw material powder is fired at a temperature range of 700 to 1100°C for 5 to 120 minutes. This allows MgO powder to be obtained. After firing, the MgO powder may be pulverized using a ball mill or other method, if necessary. Note that these pulverization methods do not destroy the primary particles of the raw material powder. The firing temperature is preferably 720°C or higher, more preferably 750°C or higher. The firing temperature is also preferably 1080°C or lower, more preferably 1040°C or lower. The firing time is 5 to 120 minutes to suitably control the Mg content 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.

[0037] The firing atmosphere is preferably an air atmosphere or a nitrogen atmosphere. Atmospheres other than these are not preferable because they are economically disadvantageous.

[0038] <Method for producing MgO slurry> The method for producing MgO slurry according to this embodiment includes a method of mixing 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 whether the mixing of two or more types of raw material particles is performed before mixing with water or together with mixing with water.

[0039] In the method of mixing raw material powder and water, MgO slurry is obtained by mixing the above-mentioned raw material powder and water. More specifically, it is a method for producing 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, 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 of 1.50 or more 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 When the average particle size of the raw material particles with la / lb less than 1.50 is lg ave Then, The raw material powder is obtained by mixing the raw material particles with la / lb of 1.50 or more and the raw material particles with la / lb less than 1.50 so that ave lf ave / lg is 1.00 or more, The raw material powder is fired in a temperature range of 700 to 1100 °C for 5 to 120 minutes, pulverized as necessary, and then The fired raw material powder and the water are mixed.

[0040] 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 1.50 or more accounts for 10 to 85% of the mass of the entire raw material powder, and The average particle size of the raw material particles having the la / lb ratio 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 and the raw material particles having an Ia / Ib ratio of less than 1.50 are each fired in a temperature range of 700 to 1100°C for 5 to 120 minutes, and then crushed as necessary, lf ave / lg ave The raw material particles after firing are mixed in water so that the sintering ratio is 1.00 or more.

[0041] <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.

[0042] 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]

[0043] 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.

[0044] 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 (Ib) are listed in Table 1. ave / lg 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.

[0045] 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 (Lf ave / Lg ave ) was obtained. In the test number that satisfies the preferable conditions, the amount of MgO is 90% or more, the mass of MgO particles with La / Lb of 1.50 or more is 10 to 85% of the mass of the total MgO powder, and Lf ave / Lg ave was 1.00 or higher.

[0046] 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.

[0047] 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). Ten or more samples, each measuring 60 mm in the width direction and 300 mm in the length direction, were taken from the same longitudinal position on the resulting grain-oriented electrical steel sheet. A magnetic field of 800 A / m was applied to each sample using single sheet magnetic testing (SST) to determine the magnetic flux density B8. The difference between the sample with the lowest magnetic flux density and the sample with the highest magnetic flux density was calculated to determine the magnetic unevenness across the width (T).

[0048] When the obtained width direction magnetic unevenness (T) was less than 0.015 T, the grain-oriented electrical steel sheet was judged to have a small difference in magnetic properties in the width direction and to have passed the test. On the other hand, when the obtained width direction magnetic unevenness (T) was 0.015 T or more, the grain-oriented electrical steel sheet was judged to have a large difference in magnetic properties in the width direction and to have passed the test.

[0049] Table 1 shows the test results.

[0050] In test numbers 1 and 2, the average aspect ratio of all MgO raw material particles was less than 1.50, so there was a shortage of MgO particles with an La / Lb of 1.50 or more, and the magnetic unevenness in the width direction of the grain-oriented electrical steel sheet was 0.015T or more.

[0051] In test number 6, the amount of MgO raw material particles with a large aspect ratio was small, resulting in a shortage of MgO particles with an La / Lb of 1.50 or more, and the magnetic unevenness in the width direction of the grain-oriented electrical steel sheet was 0.015T or more. In test number 7, the amount of MgO raw material particles with a large aspect ratio was large, resulting in an excess of MgO particles with an La / Lb of 1.50 or more, and the magnetic unevenness in the width direction of the grain-oriented electrical steel sheet was 0.015T or more.

[0052] In test numbers 3 to 5, 8 to 11, and 13 to 18, 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 Lf of MgO particles with La / Lb of 1.50 or more were ave / Lg ave Since this was within the preferred range, the magnetic unevenness in the width direction of the grain-oriented electrical steel sheet was less than 0.015T.

[0053] In particular, in test numbers 8 to 11, the magnetic unevenness in the width direction of the grain-oriented electrical steel sheets was 0.010 T or less. ave / Lg ave This is thought to be because the adhesion state of the annealing separator was improved since the value of the annealing separator was 1.10 or more.

[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 (Lf ave / Lg 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 magnetic unevenness in the width direction (T) was measured for the obtained grain-oriented electrical steel sheet in the same manner as in Example 1. Table 4 shows the test results.

[0059] In test numbers 19, 21, 23, and 24, 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 0.015 T or more.

[0060] In test numbers 20 and 22, the sintering conditions for the MgO raw material particles were not within the preferred range, which resulted in a decrease in the aspect ratio of the plate-shaped MgO particles, which led to deformation of the plate-shaped particles due to sintering, and a shortage of MgO particles with an La / Lb ratio of 1.50 or more. As a result, the magnetic unevenness in the width direction of the grain-oriented electrical steel sheet was 0.015 T or more.

[0061] In test numbers 25 and 26, the average aspect ratio of the raw material particles was less than 1.50, resulting in a shortage of MgO particles with an La / Lb ratio of 1.50 or more. As a result, the magnetic unevenness in the width direction of the grain-oriented electrical steel sheet was 0.015T or more.

[0062] In test numbers 27 and 28, the content of MgO particles with a large aspect ratio was outside the preferred range, and therefore the desired amount of MgO particles with an La / Lb ratio of less than 1.50 could not be obtained. As a result, the magnetic unevenness in the width direction of the grain-oriented electrical steel sheet was 0.015 T or more.

[0063] In test numbers 29 and 30, the particle size ratio of the two types of MgO particles was within the preferred range, and the content was also appropriate, so the magnetic unevenness in the width direction of the grain-oriented electrical steel sheet was less than 0.015T.

[0064] In particular, in test number 30, the magnetic unevenness in the width direction of the grain-oriented electrical steel sheet was 0.010T or less. ave / Lg ave This is thought to be because the adhesion state of the annealing separator was improved since the value of the annealing separator was 1.10 or more.

[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 (Lf ave / Lg 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 magnetic unevenness in the width direction (T) was measured for the obtained grain-oriented electrical steel sheet in the same manner as in Example 1. Table 7 shows the test results.

[0072] In test numbers 35 and 37, the firing conditions for the MgO raw material particles were not within the preferred range, resulting in residual raw material and an MgO content of 90% or less in the fired MgO powder. As a result, the magnetic unevenness in the width direction of the grain-oriented electrical steel sheet was 0.015T or more.

[0073] In test number 36, the sintering conditions for the MgO raw material powder were not within the preferred conditions, and the sintering conditions for the MgO raw material particles were not within the preferred conditions, which resulted in a decrease in the aspect ratio of the plate-like MgO particles, which led to deformation of the plate-like particles due to sintering, and a shortage of MgO particles with an La / Lb ratio of 1.50 or more. As a result, the magnetic unevenness in the width direction of the grain-oriented electrical steel sheet was 0.015 T or more.

[0074] In test numbers 38 and 39, the average aspect ratio of all MgO raw material particles was less than 1.50, so the grain-oriented electrical steel sheets lacking MgO particles with an La / Lb of 1.50 or more had width-direction magnetic unevenness of 0.015 T or more.

[0075] In test numbers 40 and 41, the content of MgO particles with a large aspect ratio was outside the preferred range, and therefore the magnetic unevenness in the width direction of the grain-oriented electrical steel sheet was 0.015T or more.

[0076] In test numbers 42 and 43, the particle size ratio of the two types of MgO particles was within the preferred range, and the content was also appropriate, so the magnetic unevenness in the width direction of the grain-oriented electrical steel sheet was less than 0.015T.

[0077] In particular, in test number 43, the magnetic unevenness in the width direction of the grain-oriented electrical steel sheet was 0.010T or less. ave / Lg ave This is thought to be because the adhesion state of the annealing separator was improved since the value of the annealing separator was 1.10 or more. [Table 5]

[0078] [Table 6]

[0079] [Table 7] [Industrial Applicability]

[0080] 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 grain-oriented electrical steel sheets having small differences in magnetic properties in the width direction, as well as a method for producing the grain-oriented electrical steel sheets.

Claims

1. An MgO powder comprising MgO particles, The MgO powder has an MgO content of 90% or more, the mass of the MgO particles having an La / Lb ratio of 1.50 or more, where La is the long axis length of the MgO particle and Lb is the short axis length 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 The average particle size of the MgO particles having La / Lb of less than 1.50 is defined as Lg ａｖｅ When this is done, Lf ａｖｅ / Lg ａｖｅ The MgO powder is characterized in that:

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 1.50 or more accounts for 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 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 lf ａｖｅ / lg 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 1.50 or more accounts for 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 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 lf ａｖｅ / lg 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 1.50 or more accounts for 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 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 Ia / Ib ratio of 1.50 or more and the raw material particles having an Ia / Ib ratio of less than 1.50 are each fired in a temperature range of 700 to 1100°C for 5 to 120 minutes, and then lf ａｖｅ / lg ａｖｅ and mixing the fired raw material particles in water so that the MgO slurry has a viscosity of 1.00 or more.

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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