MgO powder, MgO slurry, method for producing both, and method for producing grain-oriented electrical steel sheet

Abstract

The MgO content of the MgO powder is 90% or more, the mass of the plate-shaped particles is 10-85% of the mass of the whole MgO powder, and when the average particle diameter of the plate-shaped particles is Lfave and the average particle diameter of the granular particles is Lfave, Lfave / Lfave is 1.00 or more.

Description

Technical Field

[0001] The present invention relates to MgO powder, MgO slurry, methods for producing the same, and a method for producing a grain-oriented electrical steel sheet using the same.

[0002] This application claims priority based on Japanese Patent Application No. 2023-063670 filed in Japan on April 10, 2023, and incorporates the contents herein. Background Art

[0003] Grain-oriented electrical steel sheets are soft magnetic materials primarily used as transformer core materials. Therefore, they require high magnetic properties such as high magnetization and low iron loss. Iron loss is the electrical power lost as heat when the iron core is excited by an AC magnetic field. From the perspective of energy conservation, iron loss must be kept as low as possible.

[0004] The production of grain-oriented electrical steel sheet typically involves applying a manufacturing process consisting of hot rolling, hot-rolled sheet annealing, cold rolling, decarburization annealing, and final annealing to a slab adjusted to a specified chemical composition. In the final annealing process, the coiled steel sheet is annealed at high temperature for a long period of time to align the crystals toward the Goss orientation (improve the degree of orientation) that provides excellent magnetic properties. During this process, an annealing separator is applied to prevent galling of the coil.

[0005] Annealing separators primarily composed of magnesium oxide (MgO) are commonly used as annealing separators applied to coils. This is because, during final annealing, silicon dioxide (SiO2) on the steel sheet's surface reacts with MgO, forming a forsterite (Mg2SiO4) coating (primary coating) on ​​the steel sheet's surface. This primary coating exerts tension on the steel sheet's surface and imparts insulation properties. Using an annealing separator primarily composed of MgO not only prevents galling during final annealing but also improves the magnetic properties of grain-oriented electrical steel sheets.

[0006] As described above, during the production of grain-oriented electrical steel sheets, the properties of the steel sheets can vary depending on the annealing separator. Consequently, in recent years, research has focused on the trace components contained in the magnesium oxide used as an annealing separator. Furthermore, this research not only examines the content of these trace components but also the structures of the compounds containing these trace elements in the magnesium oxide used as an annealing separator.

[0007] For example, Patent Document 1 discloses a powder for an annealing separator, characterized in that it contains 0.04 mass % to 0.30 mass % of boron, has magnesium oxide as a main component, and the proportion of tricoordinate boron in the boron is 70% to 95%.

[0008] Patent Document 2 discloses a method for producing an annealing separator powder, characterized in that a raw material containing either or both of magnesium hydroxide and magnesium carbonate and boron is calcined, and then the ratio of tricoordinate boron is adjusted by adjusting the humidity of the calcined product, so that the ratio of tricoordinate boron in the boron contained in the annealing separator powder is 70% or more and 95% or less.

[0009] Patent documents 1 and 2 both specify the proportion of tricoordinate boron based on the following insights: 1) The coating reaction behavior at high temperatures (above 1100°C) affects the purification of impurities; 2) Boron in a tricoordinate form affects the coating reaction behavior at high temperatures; 3) Boron in a tetracoordinate form not only does not contribute to the purification of impurities, but also invades the steel plate during high-temperature annealing to form Fe2B, causing deterioration due to repeated bending.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-128772

[0013] Patent Document 2: Japanese Patent Application Laid-Open No. 2020-15982 Summary of the Invention

[0014] Problems to be solved by the invention

[0015] During final annealing, the air permeability in the widthwise center of the coil is poor compared to the widthwise ends, so the primary coating may not be sufficiently formed in the widthwise center of the coil. A difference in primary coating formation between the widthwise ends and the widthwise center of the coil may result in differences in magnetic properties across the width of the grain-oriented electrical steel sheet, which is not desirable.

[0016] In the above-mentioned Patent Documents 1 and 2, the difference in primary coating formation in the width direction of the web is not considered.

[0017] The present invention has been made in view of the above-mentioned problems and has an object to provide MgO powder, MgO slurry, and methods for producing the same for producing a grain-oriented electrical steel sheet having a small difference in magnetic properties in the width direction, as well as a method for producing the grain-oriented electrical steel sheet.

[0018] Means used to solve problems

[0019] The gist of the present invention is as follows.

[0020] (1) The MgO powder according to one embodiment of the present invention is MgO powder comprising MgO particles.

[0021] The MgO content of the MgO powder is more than 90%,

[0022] In the MgO particles, when the major axis length of the MgO particles is La and the minor axis length of the MgO particles is Lb, the mass of the MgO particles having a La / Lb ratio of 1.50 or greater accounts for 10 to 85% of the mass of the entire MgO powder.

[0023] The average particle size of the MgO particles with La / Lb of 1.50 or more is defined as Lf. ave The average particle size of the MgO particles with La / Lb less than 1.50 is set as Lg ave When Lf ave / Lg ave is 1.00 or above.

[0024] (2) The MgO slurry according to another embodiment of the present invention contains the MgO powder described in (1) above and water.

[0025] (3) Another embodiment of the present invention is a method for producing MgO powder according to the method of producing MgO powder described in (1).

[0026] The production method uses 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.

[0027] In 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 being 1.50 or greater accounts for 10 to 85% of the mass of the entire raw material powder, and

[0028] When the average particle size of the raw material particles having a la / lb of 1.50 or more is set to lf ave , the average particle size of the raw material particles with la / lb less than 1.50 is set to lg ave hour,

[0029] The raw material particles with la / lb greater than 1.50 and the raw material particles with la / lb less than 1.50 are mixed with each other. ave / lg ave The raw material powder is obtained by mixing so that the ratio becomes 1.00 or more.

[0030] The raw material powder is calcined in a temperature range of 700 to 1100° C. for 5 to 120 minutes and pulverized as needed.

[0031] (4) Another embodiment of the present invention is a method for producing MgO slurry according to the method of producing MgO slurry according to (2).

[0032] The production method uses 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.

[0033] In 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 being 1.50 or greater accounts for 10 to 85% of the mass of the entire raw material powder, and

[0034] When the average particle size of the raw material particles having a la / lb of 1.50 or more is set to lf ave , the average particle size of the raw material particles with la / lb less than 1.50 is set to lg ave hour,

[0035] The raw material particles with la / lb greater than 1.50 and the raw material particles with la / lb less than 1.50 are mixed with each other. ave / lg ave The raw material powder is obtained by mixing so that the ratio becomes 1.00 or more.

[0036] The raw material powder is calcined at a temperature range of 700 to 1100° C. for 5 to 120 minutes and then pulverized as needed.

[0037] The fired raw material powder and the water are mixed.

[0038] (5) Another embodiment of the present invention is a method for producing MgO slurry according to the method of producing MgO slurry according to (2).

[0039] The production method uses 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.

[0040] In 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 being 1.50 or greater accounts for 10 to 85% of the mass of the entire raw material powder, and

[0041] When the average particle size of the raw material particles having a la / lb of 1.50 or more is set to lf ave , the average particle size of the raw material particles with la / lb less than 1.50 is set to lg ave hour,

[0042] 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 fired in a temperature range of 700 to 1100 °C for 5 to 120 minutes, and after pulverization as needed,

[0043] with lf ave / lg ave The fired raw material particles are mixed in water in such a manner that it becomes 1.00 or more.

[0044] (6) In the method for manufacturing an oriented electromagnetic steel sheet according to another aspect of the present invention, the MgO powder described in (1) above is used.

[0045] (7) In the method for manufacturing an oriented electromagnetic steel sheet according to another aspect of the present invention, the MgO slurry described in (2) above is used.

[0046] Effects of the Invention

[0047] According to the above aspect of the present invention, it is possible to provide an MgO powder, an MgO slurry, a method for manufacturing them, and a method for manufacturing the above-oriented electromagnetic steel sheet, which are used for manufacturing an oriented electromagnetic steel sheet with small differences in magnetic properties in the width direction. Detailed Embodiment

[0048] Hereinafter, the MgO powder, the MgO slurry, the method for manufacturing them, and the method for manufacturing an oriented electromagnetic steel sheet according to the present embodiment will be specifically described. However, the present invention is not limited to the configuration disclosed in the present embodiment, and various modifications can be made without departing from the gist of the present invention.

[0049] <MgO Powder>

[0050] The MgO powder of the present embodiment is an MgO powder containing MgO particles,

[0051] The Mg amount of the MgO powder is 90% or more,

[0052] In the MgO particles, when the long axis length of the MgO particle is set as La and the short axis length of the MgO particle is set as Lb, the mass of the MgO particles with La / Lb of 1.50 or more is 10 to 85% of the total mass of the MgO powder,

[0053] The average particle diameter of the MgO particles with La / Lb of 1.50 or more is set as Lf ave , and the average particle diameter of the MgO particles with La / Lb less than 1.50 is set as Lg ave When, Lf ave / Lg ave is 1.00 or more.

[0054] The following is a detailed description.

[0055] The MgO powder of this embodiment contains MgO particles. For example, the MgO powder of this embodiment contains 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.

[0056] MgO powder may contain impurities such as Al, B, Fe, and Si. If the content of each impurity element is 0.5 mass % or less, or the total amount is 1.0 mass % or less, the influence on the magnetic properties and coating properties of the grain-oriented electrical steel sheet is small.

[0057] Mg content in MgO powder: more than 90%

[0058] The Mg content in the MgO powder can be expressed by the left side of the following equation. A Mg content of 90% or greater in the MgO powder means that the Mg mass concentration [Mg] in a chemical analysis of the MgO powder satisfies the following equation. Chemical analysis is performed by quantitative elemental analysis using ICP-MS.

[0059] [Mg]×40 / 24≥90%

[0060] If the Mg content in the MgO powder is less than 90%, a grain-oriented electrical steel sheet with minimal variation in magnetic properties across the width cannot be obtained. Therefore, the Mg content in the MgO powder is 90% or more. The Mg content in the MgO powder is preferably 95% or more.

[0061] Mass of MgO particles with La / Lb of 1.50 or more: 10-85%

[0062] By controlling the proportion of flat and plate-like particles in the MgO particles contained in the MgO powder within a predetermined range, and by controlling 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. As a result, a sufficient primary coating can be formed even in the widthwise center portion of the coil, where primary coating is difficult to form.

[0063] In this embodiment, when the major axis length of the MgO particles contained in the MgO powder is La and the minor axis length of the MgO particles is Lb, MgO particles with a La / Lb ratio of 1.50 or greater are considered plate-like particles. Conversely, MgO particles with a La / Lb ratio of less than 1.50 are considered granular particles.

[0064] Note that, in MgO powder, MgO particles may aggregate with each other to exist as secondary particles. However, the major axis length and minor axis length mentioned here refer to the major axis length and minor axis length of primary particles of the MgO particles.

[0065] The mass of plate-like particles (MgO particles with a La / Lb ratio of 1.50 or greater) in the entire MgO powder is set to 10-85%. The mass of plate-like particles is preferably 20% or greater, more preferably 30% or greater, and preferably 40% or less.

[0066] Average particle size ratio (Lf ave / Lg ave ): 1.00 or more

[0067] When 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 the granular particles (MgO particles with La / Lb less than 1.50) is Lg ave When Lf ave / Lg ave By increasing the ratio of the average particle size of the plate-like particles to the average particle size of the granular particles, the surface contact of the MgO particles increases, and the contact frequency between the steel sheet and the primary coating can be increased. ave / Lg ave It is preferably 1.10 or more.

[0068] In addition, from the viewpoint of further reducing the change in shape in the width direction, the average particle size Lf of the plate-like particles is ave and the average particle size Lg of the granular particles ave Each of the above-mentioned diameters is preferably less than 2.000 μm, more preferably 1.500 μm or less or 1.000 μm or less, and further preferably 0.500 μm or less.

[0069] The measurement method is described below.

[0070] Using a scanning electron microscope (SEM), magnified photographs of MgO particles in MgO powder were taken. The shape of a single primary particle was profiled, and the major axis length (La) and minor axis length (Lb) of the primary particle were calculated through image analysis. This procedure was repeated for at least 50 randomly selected particles. This method identified MgO particles with a La / Lb ratio of 1.50 or greater (plate-like particles) and MgO particles with a La / Lb ratio of less than 1.50 (granular particles).

[0071] For the specific plate-like particles and granular particles, the equivalent circle diameters are calculated and their average value is calculated, thereby obtaining the average particle size (Lf ave) and the average particle diameter (Lg) of granular particles ave ).

[0072] Method for measuring the mass of granular particles

[0073] Based on the same enlarged photograph as when measuring the average particle diameter (Lf ave ) and the average particle diameter (Lg ave ) of granular particles, calculate La / Lb for more than 50 randomly selected particles, and calculate 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. By using the obtained values and Equation (1), obtain the mass % (Wf (%)) of granular particles.

[0074] Wf = fg × Lg ave 3 / (50 × (Lf ave 3 + Lg ave 3 )) (1)

[0075] <MgO slurry>

[0076] The MgO slurry of the present embodiment contains the above-mentioned MgO powder containing MgO particles and water. Since the MgO powder and MgO particles are as described above, the description is omitted.

[0077] The mass of the MgO powder in the MgO slurry may be set to 5 to 30%.

[0078] In the case of performing the above measurement on the MgO powder in the MgO slurry, the above measurement is performed on the MgO powder obtained by evaporating water by holding the MgO slurry in a thermostat at 80°C for a predetermined time.

[0079] <Method for manufacturing MgO powder>

[0080] Next, the method for manufacturing the above-mentioned MgO powder will be described.

[0081] The method for manufacturing the MgO powder of the present embodiment is a method for manufacturing MgO powder as follows,

[0082] In the manufacturing method, 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 is used,

[0083] In 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 being 1.50 or greater accounts for 10 to 85% of the mass of the entire raw material powder, and

[0084] When the average particle size of the raw material particles having a la / lb of 1.50 or more is set to lf ave , the average particle size of the raw material particles with la / lb less than 1.50 is set to lg ave hour,

[0085] The raw material particles with la / lb greater than 1.50 and the raw material particles with la / lb less than 1.50 are mixed with each other. ave / lg ave The raw material powder is obtained by mixing so that the ratio becomes 1.00 or more.

[0086] The raw material powder is calcined in a temperature range of 700 to 1100° C. for 5 to 120 minutes and pulverized as needed.

[0087] Raw material powder

[0088] The raw material powder includes raw material particles of one or more kinds selected from the group consisting of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate, and may contain magnesium chloride, calcium carbonate, and calcium chloride in addition to these raw material particles.

[0089] The mass of raw material pellets with la / lb of 1.50 or more: 10-85%

[0090] Among the raw material particles in the raw material powder, when the major axis length of the raw material particles is 1a and the minor axis length of the raw material particles is 1b, the mass of the raw material particles with an 1a / lb ratio of 1.50 or greater is set to 10-85% of the total mass of the raw material powder. This allows the mass of the plate-like particles in the MgO powder to be controlled within a preferred range. The mass of the raw material particles with an 1a / lb ratio of 1.50 or greater is preferably 20% or greater, more preferably 30% or greater. Furthermore, the mass of the raw material particles with an 1a / lb ratio of 1.50 or greater is preferably 40% or less.

[0091] Average particle size ratio (lf ave / lg ave ): 1.00 or more

[0092] The average particle size of the raw material particles with la / lb being 1.50 or more is 1f ave , the average particle size of the raw material particles with la / lb less than 1.50 is set to lg ave When, lf ave / lg aveis 1.00 or more. Thus, the average particle diameter of the tabular particles and the average particle diameter of the granular particles in the MgO powder can be controlled within a preferable range. lf ave / lg ave Preferably it is 1.10 or more.

[0093] In addition, from the viewpoint of further reducing the change in the shape in the width direction, the average particle diameter of the tabular particles lf ave is preferably 10.000 μm or less. Furthermore, the average particle diameter of the tabular particles lf ave and the average particle diameter of the granular particles lg ave are respectively preferably set to be less than 2.000 μm, more preferably set to be 1.500 μm or less or 1.000 μm or less, and even more preferably set to be 0.500 μm or less.

[0094] In order to control the mass and average particle diameter ratio (lf ave / lg ave ) of the raw material particles with la / lb of 1.50 or more within the above range, it is only necessary to adjust the mixing ratio of two or more kinds of raw material particles with different average particle diameters, long axis lengths and short axis lengths, etc.

[0095] It should be noted that the long axis length, short axis length and average particle diameter of the raw material powder can be measured by the same method as in the case of the above MgO powder.

[0096] Next, the raw material powder is fired in a temperature range of 700 to 1100 °C for 5 to 120 minutes. Thus, MgO powder can be obtained. After firing, if necessary, the MgO powder can also be pulverized by using a ball mill or the like. It should be noted that in these pulverization methods, the primary particles of the raw material powder are not damaged.

[0097] The firing temperature is preferably 720 °C or more, more preferably 750 °C or more. In addition, the firing temperature is preferably 1080 °C or less, more preferably 1040 °C or less. In order to preferably control the amount of Mg in the MgO powder, the firing time is 5 to 120 minutes. From the viewpoint of eliminating firing unevenness, the firing time is preferably 8 minutes or more, more preferably 10 minutes or more. On the other hand, from the economic viewpoint, the firing time is preferably 80 minutes or less, more preferably 60 minutes or less.

[0098] The firing atmosphere is preferably an air atmosphere or a nitrogen atmosphere. Atmospheres other than these are economically disadvantageous and thus not preferred.

[0099] <Method for manufacturing MgO slurry>

[0100] The MgO slurry manufacturing method of this embodiment includes a method of mixing raw material powder with water and a method of mixing two or more raw material particles in water. The difference between these two methods is whether the two or more raw material particles are mixed before or simultaneously with the water.

[0101] In the method of mixing raw material powder with water, MgO slurry is obtained by mixing the raw material powder with water.

[0102] More specifically, the method for producing MgO slurry is as follows:

[0103] The production method uses 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.

[0104] In 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 being 1.50 or greater accounts for 10 to 85% of the mass of the entire raw material powder, and

[0105] When the average particle size of the raw material particles having a la / lb of 1.50 or more is set to lf ave , the average particle size of the raw material particles with la / lb less than 1.50 is set to lg ave hour,

[0106] The raw material particles with la / lb greater than 1.50 and the raw material particles with la / lb less than 1.50 are mixed with each other. ave / lg ave The raw material powder is obtained by mixing so that the ratio becomes 1.00 or more.

[0107] The raw material powder is calcined at a temperature range of 700 to 1100° C. for 5 to 120 minutes and then pulverized as needed.

[0108] The fired raw material powder and the water are mixed.

[0109] In the method of mixing two or more kinds of raw material particles in water, two or more kinds of raw material particles are mixed in water, and the raw material powders after mixing are mixed so as to achieve the above-mentioned ratio of mass and average particle size, thereby obtaining MgO slurry.

[0110] More specifically, the method for producing MgO slurry is as follows:

[0111] The production method uses 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.

[0112] In 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 being 1.50 or greater accounts for 10 to 85% of the mass of the entire raw material powder, and

[0113] When the average particle size of the raw material particles having a la / lb of 1.50 or more is set to lf ave , the average particle size of the raw material particles with la / lb less than 1.50 is set to lg ave hour,

[0114] The raw material particles having la / lb of 1.50 or more and the raw material particles having la / lb of less than 1.50 are fired at a temperature range of 700 to 1100° C. for 5 to 120 minutes, respectively, and crushed as needed.

[0115] lf ave / lg ave The fired raw material pellets are mixed in water so that the ratio becomes 1.00 or more.

[0116] <Method for Manufacturing Grain-Oriented Electrical Steel Sheet>

[0117] In the method for manufacturing a grain-oriented electrical steel sheet according to this embodiment, the aforementioned MgO powder is used as an annealing separator. The method for manufacturing a grain-oriented electrical steel sheet according to this 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 a final annealing step in which an annealing separator containing the aforementioned MgO powder is applied to the cold-rolled sheet after the decarburization annealing step, the sheet is dried, and then final annealed. This manufacturing method using the MgO powder or MgO slurry according to this embodiment enables the manufacture of grain-oriented electrical steel sheets with minimal variation in magnetic properties across the width.

[0118] In the present embodiment, as an annealing separator applied before final annealing, an annealing separator prepared by mixing the MgO powder of the present embodiment described above with water to prepare an MgO slurry is used.

[0119] In the above-mentioned production method, regarding the chemical composition of the slab and the conditions of each step, except for the annealing separator used, known production conditions for grain-oriented electrical steel sheets can be applied.

[0120] Example

[0121] Next, the effects of one embodiment of the present invention will be further specifically described using examples. However, the conditions in the examples are merely examples of conditions employed to confirm the feasibility and effects of the present invention, and the present invention is not limited to these examples. Various conditions may be employed within the scope of the present invention as long as they do not deviate from the spirit of the present invention and achieve the purpose of the present invention.

[0122] (Example 1)

[0123] The average particle size, major axis length la of primary particles, minor axis length lb of primary particles, average aspect ratio (la / lb), particle size ratio (lf ave / lg ave ) are calcined at a temperature range of 700-1100°C for 5-120 minutes and then pulverized to obtain MgO particles 1 and MgO particles 2. MgO particles 1 and MgO particles 2 are mixed with water to obtain an annealing separator (aqueous slurry).

[0124] It should be noted that the average particle diameters and the like of the MgO particles 1 and MgO particles 2 are not shown in the table.

[0125] The MgO powder obtained by evaporating water in the annealing separator obtained by the above method was used to identify MgO particles (plate-like particles) having an La / Lb of 1.50 or more and MgO particles (granular particles) having an La / Lb of less than 1.50, and their contents, average aspect ratios, average particle sizes, and particle size ratios (Lf ave / Lg ave ).

[0126] In the test numbers that meet the preferred conditions, the mass of the MgO particles with a MgO content of 90% or more and a La / Lb ratio of 1.50 or more accounts for 10-85% of the total mass of the MgO powder. ave / Lg ave is 1.00 or above.

[0127] Next, the cold-rolled steel sheets after primary recrystallization annealing were coated with the aforementioned annealing separator. For all test numbers, the cold-rolled steel sheets coated with the annealing separator were sintered at 300°C for 30 seconds to dry the annealing separator. After sintering, a final annealing treatment was performed. For the final annealing treatment, all test numbers were held at 1200°C for 20 hours.

[0128] Through the above manufacturing process, a grain-oriented electrical steel sheet having a base steel sheet and a glass coating of a composite oxide such as forsterite (containing Mg2SiO4) was produced. Ten or more samples measuring 60 mm in width and 300 mm in length were collected from the same longitudinal position of the resulting grain-oriented electrical steel sheet. A magnetic field of 800 A / m was applied to each sample using single-plate magnetic measurement (SST). The magnetic flux density B8 was determined, and the difference between the sample with the lowest magnetic flux density and the sample with the highest magnetic flux density was calculated to obtain the widthwise magnetic nonuniformity (T).

[0129] When the obtained widthwise magnetic variation (T) is less than 0.015T, the grain-oriented electrical steel sheet is judged as acceptable, as having a small variation in magnetic properties in the width direction. On the other hand, when the obtained widthwise magnetic variation (T) is 0.015T or greater, the grain-oriented electrical steel sheet is judged as unacceptable, as having a large variation in magnetic properties in the width direction.

[0130] Table 1 shows the test results.

[0131] In Test Nos. 1 and 2, the average aspect ratio of the MgO raw material particles was less than 1.50, so the MgO particles having a La / Lb of 1.50 or more were insufficient, and the magnetic unevenness in the width direction of the grain-oriented electrical steel sheet became 0.015 T or more.

[0132] In Test No. 6, the amount of MgO raw material particles having a large aspect ratio was small, so MgO particles having a La / Lb of 1.50 or greater were insufficient, and the magnetic unevenness in the width direction of the grain-oriented electrical steel sheet became 0.015 T or greater.

[0133] In Test No. 7, the blending amount of MgO raw material particles having a large aspect ratio was large, so MgO particles having La / Lb of 1.50 or greater were excessive, and the magnetic nonuniformity in the width direction of the grain-oriented electrical steel sheet became 0.015 T or greater.

[0134] 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 the MgO particles with La / Lb of 1.50 or more were ave / Lg ave Within the preferred range, the magnetic nonuniformity in the width direction of the grain-oriented electrical steel sheet becomes less than 0.015T.

[0135] In particular, in test numbers 8 to 11, the magnetic variations in the width direction of the grain-oriented electrical steel sheets were 0.010 T or less. This is considered to be because, in these test numbers, Lf ave / Lg aveSince the ratio is 1.10 or more, the adhesion state of the annealing separator is further improved.

[0136]

[0137] (Example 2)

[0138] MgO raw material particles 1 shown in Table 2 were calcined under the conditions described in Table 2 to obtain MgO particles 1. MgO raw material particles 2 shown in Table 3 were calcined under the conditions described in Table 3 to obtain MgO particles 2. MgO particles 1 and 2 were mixed in the amounts described in Table 2 and Table 3, respectively, to obtain the MgO powder described in Table 4. The obtained MgO powder was mixed with water to obtain an annealing separator (aqueous slurry).

[0139] The MgO powder obtained by evaporating water in the annealing separator obtained by the above method was used to identify MgO particles (plate-like particles) having an La / Lb of 1.50 or more and MgO particles (granular particles) having an La / Lb of less than 1.50, and their contents, average aspect ratios, average particle sizes, and particle size ratios (Lf ave / Lg ave ).

[0140] Next, the cold-rolled steel sheets after primary recrystallization annealing were coated with the aforementioned annealing separator. For all test numbers, the cold-rolled steel sheets coated with the annealing separator were sintered at 300°C for 30 seconds to dry the annealing separator. After sintering, a final annealing treatment was performed. For the final annealing treatment, all test numbers were held at 1200°C for 20 hours.

[0141] Through the above-described manufacturing steps, a grain-oriented electrical steel sheet having a base steel sheet and a glass coating of a composite oxide such as forsterite (containing Mg2SiO4) is manufactured.

[0142] The width direction magnetic unevenness (T) of the obtained grain-oriented electrical steel sheet was obtained by the same method as in Example 1.

[0143] Table 4 shows the test results.

[0144] In Test Nos. 19, 21, 23, and 24, the sintering conditions for the MgO raw material particles deviated from the optimal conditions, resulting in residual raw material and a Mg content of 90% or less in the sintered MgO powder. As a result, the magnetic nonuniformity in the width direction of the grain-oriented electrical steel sheet became 0.015T or more.

[0145] In Tests 20 and 22, the sintering conditions for the MgO raw material particles deviated from the optimal conditions, resulting in a reduced aspect ratio of the plate-shaped MgO particles. This led to a further increase in deformation due to sintering of the plate-shaped particles, and a shortage of MgO particles with an La / Lb ratio of 1.50 or greater. Consequently, the magnetic field variation in the grain-oriented electrical steel sheet in the width direction exceeded 0.015 T.

[0146] In Test Nos. 25 and 26, the average aspect ratio of the raw material particles was less than 1.50, so there was a shortage of MgO particles with a La / Lb ratio of 1.50 or more. As a result, the magnetic nonuniformity in the width direction of the grain-oriented electrical steel sheet became 0.015 T or more.

[0147] In Test Nos. 27 and 28, the content of MgO particles with a large aspect ratio was outside the preferred range, so the desired amount of MgO particles with a La / Lb ratio of less than 1.50 was not obtained. As a result, the magnetic nonuniformity in the width direction of the grain-oriented electrical steel sheet became 0.015 T or more.

[0148] In test numbers 29 and 30, the particle size ratio of the two types of MgO particles was within the preferred range and their contents were also appropriate, so the magnetic nonuniformity in the width direction of the grain-oriented electrical steel sheet was less than 0.015T.

[0149] In particular, in test number 30, the magnetic variation in the width direction of the grain-oriented electrical steel sheet was 0.010 T or less. It is considered that in this test number, Lf ave / Lg ave Since the ratio is 1.10 or more, the adhesion state of the annealing separator is further improved.

[0150]

[0151]

[0152]

[0153] (Example 3)

[0154] MgO raw material particles 1 and MgO raw material particles 2 shown in Tables 5 and 6 were mixed in the amounts shown in Tables 5 and 6 to obtain raw material powders. The obtained raw material powders were calcined under the conditions shown in Table 7. Thus, the MgO powder shown in Table 7 was obtained. The obtained MgO powder was mixed with water to obtain an annealing separator (aqueous slurry).

[0155] The MgO powder obtained by evaporating water in the annealing separator obtained by the above method was used to identify MgO particles (plate-like particles) having an La / Lb of 1.50 or more and MgO particles (granular particles) having an La / Lb of less than 1.50, and their contents, average aspect ratios, average particle sizes, and particle size ratios (Lf ave / Lg ave ).

[0156] Next, the cold-rolled steel sheets after primary recrystallization annealing were coated with the aforementioned annealing separator. For all test numbers, the cold-rolled steel sheets coated with the annealing separator were sintered at 300°C for 30 seconds to dry the annealing separator. After sintering, a final annealing treatment was performed. For the final annealing treatment, all test numbers were held at 1200°C for 20 hours.

[0157] Through the above-described manufacturing steps, a grain-oriented electrical steel sheet having a base steel sheet and a glass coating of a composite oxide such as forsterite (containing Mg2SiO4) is manufactured.

[0158] The width direction magnetic unevenness (T) of the obtained grain-oriented electrical steel sheet was obtained by the same method as in Example 1.

[0159] Table 7 shows the test results.

[0160] In Test Nos. 35 and 37, the sintering conditions of the MgO raw material particles deviated from the optimal conditions, so the raw material remained and the MgO content of the sintered MgO powder was 90% or less. As a result, the magnetic nonuniformity in the width direction of the grain-oriented electrical steel sheet became 0.015T or more.

[0161] In Test No. 36, the sintering conditions for the MgO raw material powder deviated from the optimal conditions, and the sintering conditions for the MgO raw material particles deviated from the optimal conditions. This reduced the aspect ratio of the plate-shaped MgO particles, and deformation due to sintering of the plate-shaped particles progressed, resulting in a shortage of MgO particles with an La / Lb ratio of 1.50 or greater. As a result, the magnetic field unevenness in the width direction of the grain-oriented electrical steel sheet exceeded 0.015T.

[0162] In test numbers 38 and 39, the average aspect ratio of the MgO raw material particles was less than 1.50. Therefore, the grain-oriented electrical steel sheet having insufficient MgO particles and a La / Lb ratio of 1.50 or more had a magnetic nonuniformity in the width direction of 0.015 T or more.

[0163] In test numbers 40 and 41, the content of MgO particles having a large aspect ratio was outside the preferred range, so the magnetic nonuniformity in the width direction of the grain-oriented electrical steel sheet became 0.015 T or more.

[0164] In test numbers 42 and 43, the particle size ratio of the two types of MgO particles was within the preferred range and their contents were also appropriate, so the magnetic nonuniformity in the width direction of the grain-oriented electrical steel sheet was less than 0.015T.

[0165] In particular, in test number 43, the magnetic variation in the width direction of the grain-oriented electrical steel sheet was 0.010 T or less. ave / Lg ave Since the ratio is 1.10 or more, the adhesion state of the annealing separator is further improved.

[0166]

[0167]

[0168]

[0169] Industrial applicability

[0170] According to the above aspects of the present invention, it is possible to provide MgO powder and MgO slurry for producing a grain-oriented electrical steel sheet having a small difference in magnetic properties in the width direction, and methods for producing the same, as well as a method for producing the grain-oriented electrical steel sheet.

Claims

1. A MgO powder, characterized in that: It is MgO powder containing MgO particles, The MgO content of the MgO powder is more than 90%, In the MgO particles, when the major axis length of the MgO particles is La and the minor axis length of the MgO particles is Lb, the mass of the MgO particles having a La / Lb ratio of 1.50 or greater accounts for 10 to 85% of the mass of the entire MgO powder. The average particle size of the MgO particles with La / Lb of 1.50 or more is defined as Lf. ave The average particle size of the MgO particles with La / Lb less than 1.50 is set as Lg ave When Lf ave / Lg ave is 1.00 or above.

2. A MgO slurry, characterized in that: Contains the MgO powder according to claim 1 and water.

3. A method for producing MgO powder, characterized in that: This is the method for producing the MgO powder according to claim 1, The production method uses 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. In 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 being 1.50 or greater accounts for 10 to 85% of the mass of the entire raw material powder, and When the average particle size of the raw material particles having a la / lb of 1.50 or more is set to lf ave , the average particle size of the raw material particles with la / lb less than 1.50 is set to lg ave hour, The raw material particles with la / lb greater than 1.50 and the raw material particles with la / lb less than 1.50 are mixed with each other. ave / lg ave The raw material powder is obtained by mixing so that the ratio becomes 1.00 or more. The raw material powder is calcined in a temperature range of 700 to 1100° C. for 5 to 120 minutes and pulverized as needed.

4. A method for producing MgO slurry, characterized in that: This is the method for producing the MgO slurry according to claim 2, The production method uses 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. In 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 being 1.50 or greater accounts for 10 to 85% of the mass of the entire raw material powder, and When the average particle size of the raw material particles having a la / lb of 1.50 or more is set to lf ave , the average particle size of the raw material particles with la / lb less than 1.50 is set to lg ave hour, The raw material particles with la / lb greater than 1.50 and the raw material particles with la / lb less than 1.50 are mixed with each other. ave / lg ave The raw material powder is obtained by mixing so that the ratio becomes 1.00 or more. The raw material powder is calcined at a temperature range of 700 to 1100° C. for 5 to 120 minutes and then pulverized as needed. The fired raw material powder and the water are mixed.

5. A method for producing MgO slurry, characterized in that: This is the method for producing the MgO slurry according to claim 2, The production method uses 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. In 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 being 1.50 or greater accounts for 10 to 85% of the mass of the entire raw material powder, and When the average particle size of the raw material particles having a la / lb of 1.50 or more is set to lf ave , the average particle size of the raw material particles with la / lb less than 1.50 is set to lg ave hour, The raw material particles having la / lb of 1.50 or more and the raw material particles having la / lb of less than 1.50 are fired at a temperature range of 700 to 1100° C. for 5 to 120 minutes, respectively, and crushed as needed. lf ave / lg ave The fired raw material pellets are mixed in water so that the ratio becomes 1.00 or more.

6. A method for manufacturing a grain-oriented electrical steel sheet, characterized in that: The MgO powder according to claim 1 is used.

7. A method for manufacturing a grain-oriented electrical steel sheet, characterized in that: The MgO slurry according to claim 2 is used.

Images