Annealing separator magnesium oxide, method for manufacturing the same and method for manufacturing grain oriented magnetic steel sheet using annealing separator magnesium oxide

Abstract

To provide annealing separator magnesium oxide capable of forming a smooth forsterite film on a surface of a grain oriented magnetic steel sheet.SOLUTION: Annealing separator magnesium oxide includes aluminum. A content of the aluminum in the magnesium oxide is 20-300 ppm; a coefficient of variation in concentration of the aluminum in the magnesium oxide is 0.25 or less; and the magnesium oxide can form a smooth forsterite film on a surface of a grain oriented magnetic steel sheet.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to magnesium oxide for an annealing separator, a method for producing the same, and a method for producing a grain-oriented electrical steel sheet using the same.

Background Art

[0002] An annealing separator aimed at enhancing the smoothness of the forsterite film in a grain-oriented electrical steel sheet is known. For example, Patent Document 1 discloses an annealing separator for a grain-oriented electrical steel sheet. The annealing separator contains Cl: 0.01 to 0.05 mass%, B: 0.05 to 0.15 mass%, CaO: 0.1 to 2 mass% and P 2 O 3 : 0.03 to 1.0 mass%, and is mainly composed of magnesia. In the magnesia, the citric acid activity is 40% CAA for 30 to 120 seconds, the specific surface area by the BET method is 8 to 50 m 2 / g, the hydration amount by ignition loss is 0.5 to 5.2 mass%, and the content of particles having a particle size of 45 μm or more is 0.1 mass% or less. Further, the annealing separator contains a water-insoluble compound having a particle size of 45 μm or more and 150 μm or less at 0.05 mass% or more and 20 mass% or less. In Patent Document 1, it is said that by using the annealing separator, a uniform and smooth forsterite film can be easily formed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, in order to form a smooth forsterite film, the content of trace elements in magnesia as an annealing separating agent, that is, magnesium oxide, is defined. However, Patent Document 1 does not describe the variation in the concentration of trace elements in magnesium oxide. Therefore, there is still room for further improvement in the technology for forming a smooth forsterite film.

[0005] An object of the present invention is to provide magnesium oxide for an annealing separating agent capable of forming a smooth forsterite film on the surface of a grain-oriented electrical steel sheet, a method for producing the same, and a method for producing a grain-oriented electrical steel sheet using the same.

Means for Solving the Problems

[0006] The present invention includes the following respective disclosures.

[0007] (First Disclosure) The first disclosure is magnesium oxide for an annealing separating agent. The magnesium oxide contains aluminum. The content of the aluminum in the magnesium oxide is 20 to 300 ppm. The coefficient of variation of the concentration of the aluminum in the magnesium oxide is 0.25 or less.

[0008] (Second Disclosure) In the second disclosure, in the first disclosure, the average size of the crystallites of the magnesium oxide is 25 to 60 nm.

[0009] (Third Disclosure) In the third disclosure, in the first disclosure or the second disclosure, the magnesium oxide further contains at least one element selected from Cl, Mn, Fe, and Cu.

[0010] (Fourth Disclosure) The fourth disclosure is a method for producing magnesium oxide for an annealing separating agent. The method for producing magnesium oxide includes a reaction step and a forming step. In the reaction step, a magnesium hydroxide raw material containing aluminum and an alkali raw material are continuously supplied to a reaction tank, respectively, while reacting the magnesium hydroxide raw material and the alkali raw material in a state where turbulent flow occurs. Then, the upper slurry of magnesium hydroxide formed by the reaction is continuously taken out from the reaction tank. The forming step is to bake the taken-out magnesium hydroxide to form magnesium oxide. The magnesium oxide contains aluminum. The content of aluminum in the magnesium oxide is 20 to 300 ppm. The coefficient of variation of the concentration of aluminum in the magnesium oxide is 0.25 or less.

[0011] (Fifth Disclosure) The fifth disclosure is a method for producing a grain-oriented electrical steel sheet. The method for producing the grain-oriented electrical steel sheet includes a coating step of applying a slurry containing magnesium oxide for an annealing separating agent to a decarburized and annealed steel sheet, and an annealing step of annealing the steel sheet coated with the slurry. The magnesium oxide contains aluminum. The content of aluminum in the magnesium oxide is 20 to 300 ppm. The coefficient of variation of the concentration of aluminum in the magnesium oxide is 0.25 or less. [Advantages of the Invention]

[0012] According to the present invention, it is possible to provide magnesium oxide for an annealing separating agent capable of forming a smooth forsterite film on the surface of a grain-oriented electrical steel sheet, a method for producing the same, and a method for producing a grain-oriented electrical steel sheet using the same. [Embodiments for Carrying Out the Invention]

[0013] Hereinafter, preferred embodiments of magnesium oxide for an annealing separating agent of the present invention, a method for producing the same, and a method for producing a grain-oriented electrical steel sheet using the same will be described.

[0014] [Magnesium Oxide for Annealing Separating Agent] The magnesium oxide for the annealing release agent of the present invention is a powder mainly composed of magnesium oxide, but may contain other trace elements. However, "containing" trace elements means containing trace elements inside and / or outside the particles of magnesium oxide. The content of magnesium oxide in the annealing release agent is at least 95% by mass or more, preferably 98% by mass or more. Therefore, the content of trace elements in the annealing release agent is less than 5% by mass, preferably less than 2% by mass. Hereinafter, the magnesium oxide for the annealing release agent is also simply referred to as magnesium oxide.

[0015] Magnesium oxide contains aluminum (Al) as a trace element. When forming a forsterite film by the reaction between the magnesium oxide for the annealing release agent and silicon dioxide on the steel plate surface, aluminum has the effect of lowering the melting point of the forsterite phase (Mg 2 SiO 4 ). Thereby, the fluidity of the forsterite phase can be improved, so that the smoothness of the appearance of the entire formed forsterite film can be improved.

[0016] If the aluminum content in magnesium oxide is too low, it becomes difficult to lower the melting point of the forsterite phase. On the other hand, even if the aluminum content is too high, the effect of lowering the melting point tends to decrease. Therefore, the aluminum content in magnesium oxide is preferably 20 to 400 ppm. When magnesium oxide contains 20 ppm or more of aluminum, the effect of lowering the melting point of the forsterite phase is likely to occur. Thereby, the fluidity of the forsterite phase is improved, so that the forsterite film can be smoothed. When magnesium oxide contains 400 ppm or less of aluminum, a decrease in the effect of lowering the melting point of the forsterite phase due to excessive aluminum can be suppressed. Thereby, the fluidity of the forsterite phase is improved, so that the forsterite film can be smoothed. In addition, the distribution of aluminum is less likely to be uneven, and the occurrence of unevenness in the forsterite film can be suppressed. The lower limit of the aluminum content is preferably 25 ppm. The upper limit of the aluminum content is preferably 300 ppm.

[0017] As described above, the effect of lowering the melting point of the forsterite phase can vary depending on the aluminum content in magnesium oxide. That is, the smoothness of the forsterite film can vary depending on the aluminum content. Therefore, it is preferable that not only the aluminum content is within the above-mentioned predetermined range, but also the distribution of aluminum is uniform. In other words, it is preferable that not only the aluminum content is within the above-mentioned predetermined range, but also the variation in the aluminum concentration is low. Therefore, for magnesium oxide for annealing release agent, the coefficient of variation indicating the degree of variation in the aluminum concentration is preferably less than 0.30. The coefficient of variation is more preferably 0.25 or less. However, the coefficient of variation is a coefficient corresponding to the variation in the aluminum concentration contained in individual magnesium oxide particles among a plurality of magnesium oxide particles in magnesium oxide. The method for obtaining the coefficient of variation will be described later.

[0018] The magnesium oxide for the annealing release agent described above has at least an aluminum content within a predetermined numerical range, and the variation in the aluminum concentration is suppressed. Therefore, by uniformly applying the magnesium oxide for the annealing release agent onto the steel sheet, aluminum can be uniformly distributed on the steel sheet with a content within a predetermined numerical range. As a result, the melting point can be uniformly lowered throughout the forsterite phase, the fluidity can be improved, and the overall smoothness of the forsterite coating can be improved. That is, the magnesium oxide for the annealing release agent of the present invention can form a smooth forsterite coating on the surface of the grain-oriented electrical steel sheet.

[0019] The average size of the crystallites of the magnesium oxide particles is not particularly limited as long as the reactivity of the magnesium oxide can be adjusted. The average size of the crystallites is preferably 25 to 60 nm. When the average size of the crystallites is 25 nm or less, the reactivity is excessively large, and hydration occurs during the preparation of the coating slurry, or the formation of forsterite proceeds locally. When the average size of the crystallites is 60 nm or more, the reactivity of the magnesium oxide decreases, and it becomes difficult to form forsterite. The method for obtaining the average size of the crystallites will be described later.

[0020] The shape of the magnesium oxide particles is not particularly limited as long as the content of trace elements can be within a predetermined range and the variation in the concentration of trace elements can be reduced among the particles. Examples of the planar shape of the particles include polygons, rectangles, polygonal shapes, ellipses, circles, irregular shapes, and combinations thereof. The shape of the particles can be confirmed by taking a photograph at a magnification of 20,000 times using a scanning electron microscope (SEM).

[0021] The particle size distribution of magnesium oxide is not particularly limited as long as the variation in the content of trace elements and the concentration of trace elements can be reduced among particles. D10 is preferably 0.5 to 2.0 μm. D50 is preferably 1.5 to 4.0 μm. D90 is preferably 6.0 to 14 μm. The volume average diameter MV is, for example, 2.0 to 7.0 μm. In the particle size distribution of magnesium oxide, since the particle diameters are distributed in a relatively small but not too small range, the aggregation of particles in the slurry can be suppressed while enhancing the dispersibility. The method for obtaining the particle size distribution will be described later.

[0022] Magnesium oxide may contain various trace elements known to contribute to the promotion of film formation, improvement of film properties and / or improvement of magnetic properties in oriented electrical steel sheets. Such trace elements include, for example, at least one element selected from chlorine (Cl), boron (B), sodium (Na), copper (Cu), phosphorus (P), iron (Fe), manganese (Mn), titanium (Ti), and calcium (Ca), or a compound thereof.

[0023] [Method for producing magnesium oxide for annealing separator] The method for producing magnesium oxide is not particularly limited as long as it can produce magnesium oxide having the above configuration, particularly with little variation in the concentration of trace elements. Examples of the production method include the following three methods.

[0024] In the first method, an aqueous solution of a magnesium hydroxide raw material containing trace elements and an aqueous solution of an alkali raw material are continuously supplied to a reaction tank, and while reacting in a state where turbulent flow occurs, the upper layer slurry of magnesium hydroxide formed by the reaction is continuously taken out from the reaction tank. Then, the taken-out magnesium hydroxide is calcined to obtain magnesium oxide. However, the reaction may proceed while continuously supplying the aqueous solution of the trace element raw material, the aqueous solution of the magnesium hydroxide raw material, and the aqueous solution of the alkali raw material to the reaction tank, respectively.

[0025] In the second method, an aqueous solution of an alkali raw material is continuously supplied to an aqueous solution of a magnesium hydroxide raw material containing trace elements in a reaction tank, and magnesium hydroxide is synthesized by a batch reaction in a state where turbulent flow is generated. Then, the synthesized magnesium hydroxide is calcined to obtain magnesium oxide. However, the reaction may be advanced while continuously supplying an aqueous solution of a raw material of trace elements and an aqueous solution of an alkali raw material to the aqueous solution of the magnesium hydroxide raw material in the reaction tank, respectively.

[0026] In the third method, a powder of a raw material of trace elements and a powder of magnesium hydroxide are mixed and calcined to obtain magnesium oxide. However, the powder of magnesium oxide can be obtained, for example, in the first or second method, by a method of not adding a raw material of trace elements when producing magnesium hydroxide.

[0027] Conversely, when the magnesium hydroxide raw material contains an excessive amount of trace elements, a chelating agent suitable for the trace elements may be added to the magnesium hydroxide raw material.

[0028] However, examples of the magnesium hydroxide raw material include water-soluble magnesium salts or hydrates thereof, and specifically, magnesium chloride hexahydrate, magnesium chloride dihydrate, and anhydrous magnesium chloride are preferable. In addition, seawater, irrigation water, and bitter juice may be used as the magnesium hydroxide raw material.

[0029] Examples of the target raw material of trace elements, that is, the target trace element raw material, include the trace elements themselves and compounds of trace elements. Examples of the compounds of trace elements include acids, bases, and salts containing trace elements, oxides, chlorides, nitrates, sulfates, carbonates, and phosphates of trace elements. When the trace element is aluminum, examples of the aluminum compound as the aluminum raw material include aluminum chloride, aluminum nitrate, aluminum phosphate, aluminum sulfate, aluminum borate, and aluminum oxide.

[0030] Examples of the alkali raw materials include calcium hydroxide, sodium hydroxide, and potassium hydroxide. When calcining magnesium hydroxide, examples of the calcination atmosphere include air and nitrogen.

[0031] The chelating agent is not particularly limited as long as it can form a chelate complex with the target trace element raw material. When the trace element is aluminum, examples of the chelating agent include triethanolamine.

[0032] In the first method, for example, first, the target trace element raw material and the magnesium hydroxide raw material are added to deionized water to form an aqueous solution containing the target trace element raw material and the magnesium hydroxide raw material, that is, an aqueous solution of the magnesium hydroxide raw material. On the other hand, the alkali raw material is added to deionized water to form an aqueous solution containing the alkali raw material, that is, an aqueous solution of the alkali raw material. Next, the aqueous solution of the magnesium hydroxide raw material and the aqueous solution of the alkali raw material are continuously poured into the reaction tank at predetermined flow rates respectively. Then, in the reaction tank, the magnesium hydroxide raw material added with the target trace element raw material and the alkali raw material are reacted while stirring to generate turbulent flow, and the upper slurry of magnesium hydroxide formed by the reaction is continuously taken out from the reaction tank (reaction step). At this time, the aqueous solution of the magnesium hydroxide raw material and the aqueous solution of the alkali raw material are poured into the reaction tank at a flow rate such that the ratio of Mg to OH is approximately 1:2. "Approximately" means that the error in the flow rate is in the range of ±50%. At that time, if necessary, the inside of the reaction tank is maintained at a predetermined pressure and a predetermined temperature. In this way, the magnesium hydroxide added with the target trace element is synthesized by continuously reacting the magnesium hydroxide raw material added with the target trace element raw material and the alkali raw material in a state where turbulent flow is generated. If necessary, washing, filtration, and drying are performed. Then, the magnesium hydroxide added with the trace element is calcined at a predetermined temperature to obtain magnesium oxide added with the trace element (formation step).

[0033] In the second method, for example, first, the target trace element raw material and the magnesium hydroxide raw material are added to deionized water to form an aqueous solution containing the target trace element raw material and the magnesium hydroxide raw material, that is, an aqueous solution of the magnesium hydroxide raw material. On the other hand, the alkali raw material is added to deionized water to form an aqueous solution containing the alkali raw material, that is, an aqueous solution of the alkali raw material. Next, the aqueous solution of the alkali raw material is poured into the aqueous solution of the magnesium hydroxide raw material in the reaction tank at a predetermined flow rate, and in the reaction tank, the magnesium hydroxide raw material added with the target trace element raw material and the alkali raw material are reacted with each other under a state where turbulent flow is generated by stirring (reaction step). At that time, if necessary, the inside of the reaction tank is maintained at a predetermined pressure and a predetermined temperature. In this way, by reacting the magnesium hydroxide raw material added with the target trace element raw material with the alkali raw material little by little under a state where turbulent flow is generated, magnesium hydroxide added with the target trace element is synthesized. If necessary, washing, filtration, and drying are performed. Then, the magnesium hydroxide added with the trace element is fired at a predetermined temperature to obtain magnesium oxide added with the trace element (forming step).

[0034] In the third method, for example, first, the magnesium hydroxide raw material is added to deionized water to form an aqueous solution containing the magnesium hydroxide raw material, that is, an aqueous solution of the magnesium hydroxide raw material (without trace elements). On the other hand, the alkali raw material is added to deionized water to form an aqueous solution containing the alkali raw material, that is, an aqueous solution of the alkali raw material. Next, the aqueous solution of the alkali raw material is poured into the aqueous solution of the magnesium hydroxide raw material (without trace elements) in the reaction tank at a predetermined flow rate, and in the reaction tank, the magnesium hydroxide raw material and the alkali raw material are reacted with each other. At that time, while stirring if necessary, the inside of the reaction tank is maintained at a predetermined pressure and a predetermined temperature. In this way, by reacting the magnesium hydroxide raw material and the alkali raw material, magnesium hydroxide not containing trace elements is synthesized (reaction step). The powder of the magnesium hydroxide having no such trace element is mixed with the powder of the target trace element raw material. Then, the powder of the magnesium hydroxide mixed with the powder of the target trace element raw material is fired at a predetermined temperature to obtain magnesium oxide added with the trace element (forming step).

[0035] As an example of another manufacturing method, for example, there is a method using magnesium oxide obtained by firing mineral magnesite. In this manufacturing method, first, magnesium oxide obtained from mineral magnesite is hydrated to obtain magnesium hydroxide powder. Then, the third method described above is carried out using the magnesium hydroxide powder to obtain magnesium oxide.

[0036] Here, the meanings of the terms related to the firing of a magnesium hydroxide sample used in this specification are as follows. "Heating-up time" means the time from room temperature to the target maximum temperature when firing the sample. "Holding temperature" means the target maximum temperature when firing the sample, also referred to as the firing temperature. "Holding time" means the time to maintain the holding temperature when firing the sample. "Cooling-down time" means the time from the holding temperature to room temperature after the holding time has elapsed when firing the sample. Note that cooling includes not only active cooling using a cooling means but also gentle cooling such as natural cooling.

[0037] <Firing conditions> Magnesium oxide can be controlled by adjusting the final firing conditions for obtaining magnesium oxide and the trace elements contained in the precursor subjected to the final firing. The firing conditions include heating-up time, holding temperature, holding time, and cooling-down time.

[0038] As the conditions for obtaining magnesium oxide, for example, the heating-up time is preferably 0.5 to 3 hours, more preferably 1 to 2 hours. The holding temperature is preferably 600°C to 1300°C, more preferably 700°C to 1200°C. The holding time is preferably 0.1 to 15 hours, more preferably 0.2 to 13 hours. The cooling-down time is preferably 0.1 to 6 hours, more preferably 0.2 to 5 hours.

[0039] If the heating time, holding time, and cooling time are shorter than the above ranges, the firing of magnesium hydroxide may not be completed, or the reactivity of magnesium oxide during the formation of the forsterite film may be too high, making it difficult to form forsterite uniformly. On the other hand, if the heating time, holding time, and cooling time are longer than the above ranges, the reactivity of magnesium oxide becomes too low, making it difficult to form forsterite.

[0040] Boron contained in magnesium oxide has the effect of lowering the melting point of the substance to be fired when the holding temperature during firing is about 1200 - 1300°C. The content of boron contained in magnesium oxide is preferably 0.05 - 0.15% by mass. When magnesium oxide having a boron content within such a numerical range is used as an annealing separator, the properties of the forsterite film can be improved, and the magnetic properties and insulation properties of the grain-oriented electrical steel sheet can be made good.

[0041] The content of sodium contained in magnesium oxide is preferably 0.1 - 200 ppm. When magnesium oxide having a sodium content within such a numerical range is used as an annealing separator, the properties of the forsterite film can be improved, and the magnetic properties and insulation properties of the grain-oriented electrical steel sheet can be made good.

[0042] <Firing atmosphere> The atmosphere during firing can be nitrogen or air. It is only necessary that heat is evenly applied to the substance to be fired. The substance to be fired may be uniformly stirred during firing. As an apparatus for performing such firing, for example, a rotary kiln can be mentioned.

[0043] <Control of the content of trace elements in magnesium oxide> The content of trace elements in magnesium oxide can be controlled as follows. First, measure the content of trace elements contained in the raw materials for manufacturing magnesium oxide. Then, based on the results, add or remove trace elements in the raw materials or intermediate products so that the content of trace elements in magnesium oxide reaches the desired content. Examples of raw materials include magnesium raw materials, mineral magnesite, and alkalis reacted with magnesium raw materials. Examples of intermediate products include magnesium hydroxide.

[0044] The method for adding trace elements is not particularly limited. For example, a method of mixing a compound containing the trace element to be restricted into the raw materials or intermediate products can be mentioned. The mixing method can be wet or dry. Note that the intermediate products include the above-mentioned precursors.

[0045] The method for removing trace elements is not particularly limited. Examples of such methods include a method of washing the raw materials or intermediate products, and a method of adding a chelating agent to the target trace element. A specific example of washing is water washing.

[0046] After mixing intermediate products with different compositions to adjust the excess or deficiency of trace elements, final firing can be performed to obtain magnesium oxide in which the content of trace elements reaches the desired content. Alternatively, magnesium oxide after final firing with different compositions can be mixed to adjust the excess or deficiency of trace elements to obtain magnesium oxide in which the content of trace elements reaches the desired content.

[0047] In the manufacturing process of magnesium oxide, various additives known to function to improve film properties and magnetic properties may be effectively added. Examples of such additives include copper (Cu), phosphorus (P), manganese (Mn), titanium (Ti), calcium (Ca), and their compounds.

[0048] <Control of Particle Size Distribution (D10, D50, D90, MV) of Magnesium Oxide> The particle size distribution of magnesium oxide can be controlled by the following method. One of the methods is to adjust at least one of the reaction temperature, reaction rate, and stirring conditions when synthesizing magnesium hydroxide by reacting a magnesium raw material and an alkali raw material. Another method is to pulverize the precursor before the final firing. Another method is to control the firing conditions of magnesium hydroxide. Another method is to re-fire or pulverize the magnesium oxide after the final firing.

[0049] Under the above conditions, magnesium oxide for an annealing separating agent is manufactured. Since this magnesium oxide has the above-described predetermined configuration, variations in the content of trace elements in the magnesium oxide can be suppressed.

[0050] [Method for manufacturing a grain-oriented electrical steel sheet using magnesium oxide for an annealing separating agent] Next, a method for manufacturing a grain-oriented electrical steel sheet using the magnesium oxide for an annealing separating agent described above will be explained. The manufacturing method includes a coating step of applying a slurry containing the above-described magnesium oxide to a decarburized and annealed steel sheet, and a high-temperature annealing step of annealing the steel sheet coated with magnesium oxide.

[0051] <Coating step> The above-described magnesium oxide is uniformly dispersed in a liquid to form a slurry containing magnesium oxide. The liquid is, for example, water. At this time, the slurry is formed at a low temperature such as 5°C so that the magnesium oxide does not hydrate.

[0052] The concentration of magnesium oxide is, for example, 5 to 30% by mass. The lower limit of the concentration of magnesium oxide is preferably 7% by mass from the viewpoint of facilitating uniform coating of the slurry on the steel sheet. The upper limit of the concentration of the annealing separating agent is preferably 25% by mass from the viewpoint of making the viscosity of the slurry easy to coat.

[0053] The viscosity of the slurry at 5° C. is, for example, 2.2 to 5.2 mPa·s. The lower limit of the viscosity of the slurry at 5° C. is preferably 2.6 mPa·s from the viewpoint of ensuring a sufficient amount of coating. The upper limit of the viscosity of the slurry at 5° C. is preferably 4.6 mPa·s from the viewpoint of facilitating coating of the slurry.

[0054] The slurry is continuously applied to the decarburized annealed steel sheet using a roll coating device or a spray device. However, the slurry is applied at a low temperature such as 5°C so that the magnesium oxide does not hydrate. Since the magnesium oxide having the above-mentioned configuration is used at this time, the slurry containing the magnesium oxide is uniformly applied to the steel sheet, thereby suppressing the variation in the content of trace elements in the applied slurry. Thereafter, the applied slurry is dried at a temperature of, for example, about 300 to 500°C.

[0055] <High-temperature annealing process> The steel sheet coated with the above-mentioned slurry and thus coated with magnesium oxide is annealed. Annealing conditions include, for example, 1000 to 1200°C and 10 to 20 hours. As a result, a forsterite film is formed on the surface of the steel sheet, and then, by carrying out a known predetermined treatment as necessary, a grain-oriented electrical steel sheet using the above-mentioned annealing separator is formed.

[0056] Since the method for producing a grain-oriented electrical steel sheet of the present invention has the above-mentioned specific configuration, it is possible to form a forsterite coating on the steel sheet with reduced variation in the contents of trace elements by uniformly applying magnesium oxide on the steel sheet, thereby obtaining a grain-oriented electrical steel sheet with improved magnetic properties.

[0057] The magnesium oxide for an annealing separator of the present invention, its manufacturing method, and its manufacturing method for a grain-oriented electrical steel sheet using the same are not limited to the above-mentioned embodiment or the examples described later, and may be appropriately combined, substituted, or modified without departing from the object and spirit of the present invention.

[0058] <Measurement and test methods> The various measurement and test methods are as follows:

[0059] 1. Concentration of trace elements, their average values, standard deviations and coefficients of variation The concentrations of trace elements, their average values, standard deviations and coefficients of variation were determined by the following methods. (1) Magnesium oxide (powder) to be measured was prepared. (2) The magnesium oxide was formed into a pellet measuring 4 mm in length and 4 mm in width to prepare a sample. (3) The sample was set in a D-SIMS (Dynamic Secondary Ion Mass Spectrometry) PHI ADEPT-1010 manufactured by ULVAC-PHI, Inc. Then, the concentration of trace elements was measured at 250 measurement points in the depth direction from the surface of the sample to a depth of about 5 μm under the condition of a primary acceleration voltage of 5.0 kV. (4) Based on the measured concentrations of trace elements at 250 points, the average (μ) and standard deviation (σ) of the concentrations of trace elements were calculated. (5) The coefficient of variation was calculated by dividing the standard deviation (σ) by the mean value (μ). It should be noted that the concentration of trace elements at each measurement point of the D-SIMS does not necessarily represent the concentration of the trace elements in each individual particle. Measurement points are located every 5μm / 250=0.02μm, and the measurement interval is generally smaller than the particle diameter of magnesium oxide. Therefore, the concentration of trace elements at each measurement point can be approximated to a more precise concentration of the trace elements than that of each individual particle.

[0060] 2. Trace element content The trace element content was determined by the following method. 0.5 g of the sample to be measured was dissolved in 30% HNO 3 After dissolving in 5 ml of solution, the test solution was adjusted to 100 ml with ultrapure water to obtain the test solution. The test solution was measured using an emission spectrometer SPS3520-DD (Hitachi High-Tech Science Corporation) by the calibration curve method to obtain the trace element content.

[0061] 3. Average crystallite size The average crystallite size was determined by the following method. (1) Magnesium oxide (powder) to be measured was prepared. (2) The magnesium oxide was placed in a powder X-ray diffractometer (Malvern Panalytical X-ray diffractometer Empyrean) and powder X-ray diffraction measurements were performed to obtain diffraction data under the following measurement conditions: X-ray output: 45 kV, 40 mA, scanning speed: 40 degrees / min, step width: 0.02 degrees, X-ray: CuKα radiation. (3) Based on the diffraction data, the components were identified, and the average crystallite size was calculated from the half-width of the peak assigned to the (200) plane of magnesium oxide. The integrated powder X-ray analysis software HighScore Plus was used as the XRD analysis software. The average crystallite size was calculated using the diffraction peak assigned to the (200) plane of magnesium oxide according to the Scherrer formula below. L(200)=(K λ) / (β cosθ) (L: average crystallite size, λ: 1.542 Å (CuKα), θ: Bragg diffraction angle, β: half-width, K: 0.94) The diffraction peak attributable to the (200) plane of magnesium oxide is observed at 2θ=42.80° to 42.90°.

[0062] 4.Particle size distribution The particle size distribution was measured using a particle size distribution analyzer MT3300EXII (manufactured by Microtrack Bell Co., Ltd.). First, the particle size distribution analyzer was filled with ethanol and the solvent was circulated. An appropriate amount of the sample to be measured was added thereto, and it was confirmed that it was within the appropriate range. After that, the solvent containing the sample was circulated for 1 minute, and then the particle size distribution was measured. The measurement time was 30 seconds.

[0063] 5.Coating properties 3.5 g of magnesium oxide to be evaluated was suspended in 30 ml of water at 5°C to obtain a slurry. The obtained slurry was applied to a steel plate measuring 150 mm in length, 80 mm in width, and 0.5 mm in thickness, homogenized through a rubber roll, and then fired to bake the magnesium oxide. The film properties of the magnesium oxide film on the steel plate, namely, gloss, adhesion, and smoothness, were evaluated visually.

Example

[0064] The present invention will be further described below with reference to examples and comparative examples. However, the present invention is not limited to these examples and comparative examples.

[0065] (1) Regarding the samples The samples of Examples 1 to 5 and Comparative Examples 1 to 3 were manufactured as follows.

[0066] [Example 1] 386 g of magnesium chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) and 0.05 g of aluminum chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) were dissolved in 1.9 L of deionized water to obtain an aqueous solution with 1 mol / L of magnesium and 1.1×10 -4 mol / L of aluminum. At normal pressure and 25°C, 1.9 L of this aqueous solution and 1.7 L of a 2 mol / L aqueous sodium hydroxide solution were respectively poured into a container with an overflow capacity of 220 mL and continuously reacted to obtain a magnesium hydroxide slurry. During the reaction, a screw propeller with a diameter of 2.5 cm was used and stirring was performed at a rotational speed of 450 rpm. Next, the temperature of the aqueous solution was set to 45°C and heat treatment was performed for 5.0 hours under stirring conditions of 400 rpm. Further, the magnesium hydroxide slurry that had undergone the above treatment was filtered to obtain a cake. The obtained cake was washed twice with 25 times the weight of pure water based on the solid content, and dried at 105°C for 12 hours to obtain magnesium hydroxide. This magnesium hydroxide was fired at 700°C for 0.5 hours to obtain magnesium oxide. When the particle size distribution of the obtained magnesium oxide was measured, D10 was 1.0 μm, D50 was 2.0 μm, and D90 was 8.0 μm.

[0067] [Example 2] 386 g of magnesium chloride hexahydrate (Wako Pure Chemical Industries) and 0.35 g of aluminum chloride hexahydrate (Wako Pure Chemical Industries) were dissolved in 1.9 L of deionized water to obtain an aqueous solution with 1 mol / L of magnesium and 7.6×10 -4 mol / L of aluminum. At normal pressure and 25 °C, 1.7 L of a 2 mol / L aqueous sodium hydroxide solution was added dropwise to 1.9 L of this aqueous solution at a rate of 170 mL / min to obtain a magnesium hydroxide slurry. During the reaction, a screw propeller with a diameter of 2.5 cm was used and stirring was carried out at a rotational speed of 500 rpm. Next, the temperature of the aqueous solution was set to 40 °C and heat treatment was carried out for 5.0 hours under stirring conditions of 400 rpm. Further, the magnesium hydroxide slurry that had been subjected to the above treatment was filtered to obtain a cake. The obtained cake was washed twice with 25 times the weight of pure water based on the solid content, and dried at 105 °C for 12 hours to obtain magnesium hydroxide. This magnesium hydroxide was calcined at 900 °C for 5 hours to obtain magnesium oxide. When the particle size distribution of the obtained magnesium oxide was measured, D10 was 1.5 μm, D50 was 3.0 μm, and D90 was 12 μm.

[0068] [Example 3] 386 g of magnesium chloride hexahydrate (Wako Pure Chemical Industries) and 0.1 g of aluminum chloride hexahydrate (Wako Pure Chemical Industries) were dissolved in 1.9 L of deionized water to obtain an aqueous solution with 1 mol / L of magnesium and 2.2×10 -4An aqueous solution of mol / L was obtained. At normal pressure and 25 °C, 1.9 L of this aqueous solution and 1.7 L of a 2 mol / L aqueous sodium hydroxide solution were respectively poured into a container with an overflow capacity of 220 mL, and reacted continuously to obtain a magnesium hydroxide slurry. During the reaction, a screw propeller with a diameter of 2.5 cm was used and stirring was carried out at a rotation speed of 500 rpm. Next, the temperature of the aqueous solution was set to 40 °C, and heat treatment was carried out for 5.5 hours under stirring conditions of 350 rpm. Furthermore, the magnesium hydroxide slurry was filtered to obtain a cake. The obtained cake was washed twice with 25 times the weight of pure water based on the solid content, and dried at 105 °C for 12 hours to obtain magnesium hydroxide. This magnesium hydroxide was calcined at 900 °C for 1 hour to obtain magnesium oxide. When the particle size distribution of the obtained magnesium oxide was measured, D10 was 0.6 μm, D50 was 1.6 μm, and D90 was 6.0 μm.

[0069] [Example 4] 386 g of magnesium chloride hexahydrate (Wako Pure Chemical Industries) and 0.1 g of aluminum chloride hexahydrate (Wako Pure Chemical Industries) were dissolved in 1.9 L of deionized water to obtain an aqueous solution with 1 mol / L of magnesium and 2.2×10 -4 mol / L. At normal pressure and 25 °C, 1.7 L of a 2 mol / L aqueous sodium hydroxide solution was poured into 1.9 L of this aqueous solution at a rate of 170 mL / min to obtain a magnesium hydroxide slurry. During the reaction, a screw propeller with a diameter of 2.5 cm was used and stirring was carried out at a rotation speed of 500 rpm. Next, the temperature of the water bath was set to 40 °C, and heat treatment was carried out for 5.5 hours under stirring conditions of 350 rpm. Furthermore, the magnesium hydroxide slurry that had undergone the above treatment was filtered to obtain a cake. The obtained cake was washed twice with 25 times the weight of pure water based on the solid content, and dried at 105 °C for 12 hours to obtain magnesium hydroxide. This magnesium hydroxide was calcined at 800 °C for 1 hour to obtain magnesium oxide. When the particle size distribution of the obtained magnesium oxide was measured, D10 was 1.4 μm, D50 was 3.2 μm, and D90 was 13 μm.

[0070] [Example 5] 386 g of magnesium chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) was dissolved in 1.9 L of deionized water to obtain an aqueous solution of 1 mol / L magnesium. At normal pressure and 25 °C, 1.7 L of a 2 mol / L aqueous sodium hydroxide solution was added dropwise to 1.9 L of this aqueous solution at a rate of 170 mL / min to obtain a magnesium hydroxide slurry. During the reaction, a screw propeller with a diameter of 2.5 cm was used and stirring was carried out at a rotational speed of 500 rpm. Next, the temperature of the aqueous solution was set to 40 °C and heat treatment was carried out for 5.5 hours under stirring conditions of 350 rpm. Further, the treated magnesium hydroxide slurry was filtered to obtain a cake. The obtained cake was washed twice with 25 times the weight of pure water based on the solid content and dried at 105 °C for 12 hours to obtain magnesium hydroxide. 0.3 g of aluminum chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) was mixed with 110 g of this magnesium hydroxide and calcined at 1000 °C for 3 hours to obtain magnesium oxide. When the particle size distribution of the obtained magnesium oxide was measured, D10 was 1.9 μm, D50 was 4.0 μm, and D90 was 14 μm.

[0071] [Comparative Example 1] 386 g of magnesium chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) was dissolved in 1.9 L of deionized water to obtain an aqueous solution of 1 mol / L magnesium. At normal pressure and 25 °C, 1.9 L of this aqueous solution and 1.7 L of a 2 mol / L aqueous sodium hydroxide solution were respectively added dropwise to a container with an overflow capacity of 220 mL and reacted continuously to obtain a magnesium hydroxide slurry. During the reaction, a screw propeller with a diameter of 2.5 cm was used and stirring was carried out at a rotational speed of 400 rpm. Next, the temperature of the aqueous solution was set to 40 °C and heat treatment was carried out for 5.0 hours under stirring conditions of 350 rpm. Further, the treated magnesium hydroxide slurry was filtered to obtain a cake. The obtained cake was washed twice with 25 times the weight of pure water based on the solid content and dried at 105 °C for 12 hours to obtain magnesium hydroxide. 0.05 g of aluminum chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) was mixed with 110 g of this magnesium hydroxide and calcined at 800 °C for 1.5 hours to obtain magnesium oxide. When the particle size distribution of the obtained magnesium oxide was measured, D10 was 2.0 μm, D50 was 3.8 μm, and D90 was 13 μm.

[0072] [Comparative Example 2] 386 g of magnesium chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) and 0.05 g of aluminum chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) were dissolved in 1.9 L of deionized water to obtain an aqueous solution with 1 mol / L of magnesium and 1.1×10 -4 mol / L of aluminum. At normal pressure and 25°C, 1.9 L of this aqueous solution and 1.7 L of a 2 mol / L aqueous sodium hydroxide solution were respectively poured into a container with an overflow volume of 220 mL and continuously reacted to obtain a magnesium hydroxide slurry. During the reaction, a screw propeller with a diameter of 2.5 cm was used and stirring was carried out at a rotation speed of 400 rpm. Next, the temperature of the water bath was set to 40°C and heat treatment was carried out for 5.5 hours under stirring conditions of 350 rpm. Furthermore, the treated magnesium hydroxide slurry was filtered to obtain a cake. The obtained cake was washed twice with 25 times the weight of pure water based on the solid content and dried at 105°C for 12 hours to obtain magnesium hydroxide. This magnesium hydroxide was calcined at 1000°C for 3.0 hours to obtain magnesium oxide. When the particle size distribution of the obtained magnesium oxide was measured, D10 was 0.8 μm, D50 was 1.8 μm, and D90 was 10 μm.

[0073] [Comparative Example 3] 386 g of magnesium chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) was dissolved in 1.9 L of deionized water to obtain an aqueous solution of magnesium at 1 mol / L. At normal pressure and 25 °C, 1.9 L of this aqueous solution and 1.7 L of a 2 mol / L aqueous sodium hydroxide solution were each poured into a container with an overflow capacity of 220 mL and continuously reacted to obtain a magnesium hydroxide slurry. During the reaction, a screw propeller with a diameter of 2.5 cm was used and stirring was carried out at a rotation speed of 400 rpm. Next, the temperature of the aqueous solution was set to 40 °C and heat treatment was carried out for 5.0 hours under stirring conditions of 350 rpm. Further, the magnesium hydroxide slurry that had undergone the above treatment was filtered to obtain a cake. The obtained cake was washed twice with 25 times the weight of pure water based on the solid content, and dried at 105 °C for 12 hours to obtain magnesium hydroxide. 0.8 g of aluminum chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) was mixed with 110 g of this magnesium hydroxide and calcined at 900 °C for 2.0 hours to obtain magnesium oxide. When the particle size distribution of the obtained magnesium oxide was measured, D10 was 1.8 μm, D50 was 3.8 μm, and D90 was 14 μm.

[0074] The production conditions of Examples 1 to 5 and Comparative Examples 1 to 3 described above were summarized in Table 1.

Table 1

[0075] (2) Regarding the evaluation items Regarding the magnesium oxides of Examples 1 to 5 and Comparative Examples 1 to 3, the average size of the crystallites, the coefficient of variation of the aluminum concentration, the aluminum content, and the film properties of the magnesium oxide film, that is, gloss, adhesion, and smoothness, were evaluated.

[0076] (3) Regarding the evaluation results (a) Example 1 The aluminum content of the completed magnesium oxide was 25 ppm. The coefficient of variation of the aluminum concentration determined from the measurement of the aluminum concentration in magnesium oxide using D-SIMS was 0.10. The average size of the crystallites of magnesium oxide measured by X-ray diffraction was 20 nm. Among the film properties, regarding gloss, the film was non-uniform and had no gloss. Regarding adhesion, the film was slightly non-uniform but there were no peeling sites. Regarding smoothness, the smoothness of the film surface was good. Overall, it was in a good state.

[0077] (b) Example 2 The aluminum content of the completed magnesium oxide was 298 ppm. The coefficient of variation of the aluminum concentration determined from the measurement of the aluminum concentration in magnesium oxide using D-SIMS was 0.25. The average size of the crystallites of magnesium oxide measured by X-ray diffraction was 65 nm. Among the film properties, regarding gloss, the film was slightly non-uniform but had gloss. Regarding adhesion, the film was non-uniform and had pinhole-like peeling sites. Regarding smoothness, the smoothness of the film surface was good. Overall, it was in a good state.

[0078] (c) Example 3 The aluminum content of the completed magnesium oxide was 123 ppm. The coefficient of variation of the aluminum concentration determined from the measurement of the aluminum concentration in magnesium oxide using D-SIMS was 0.09. The average size of the crystallites of magnesium oxide measured by X-ray diffraction was 25 nm. Among the film properties, regarding gloss, the film was uniform and had very good gloss. Regarding adhesion, the film was uniform and there were no peeling sites. Regarding smoothness, the smoothness of the film surface was very good. Overall, it was in a very good state.

[0079] (d) Example 4 The aluminum content of the completed magnesium oxide was 100 ppm. The coefficient of variation of the aluminum concentration determined from the measurement of the aluminum concentration in magnesium oxide using D-SIMS was 0.20. The average size of the crystallites of magnesium oxide measured by X-ray diffraction was 20 nm. Among the film properties, regarding the gloss, the film was slightly non-uniform but had gloss. Regarding the adhesion, the film was uniform and there was no peeling site. Regarding the smoothness, the smoothness of the film surface was good. Overall, it was in a very good state.

[0080] (e) Example 5 The aluminum content of the completed magnesium oxide was 292 ppm. The coefficient of variation of the aluminum concentration determined from the measurement of the aluminum concentration in magnesium oxide using D-SIMS was 0.25. The average size of the crystallites of magnesium oxide measured by X-ray diffraction was 60 nm. Among the film properties, regarding the gloss, the film was slightly non-uniform but had gloss. Regarding the adhesion, the film was slightly non-uniform but there was no peeling site. Regarding the smoothness, the smoothness of the film surface was very good. Overall, it was in a very good state.

[0081] (f) Comparative Example 1 The aluminum content of the completed magnesium oxide was 35 ppm. The coefficient of variation of the aluminum concentration determined from the measurement of the aluminum concentration in magnesium oxide using D-SIMS was 0.30. The average size of the crystallites of magnesium oxide measured by X-ray diffraction was 60 nm. Among the film properties, regarding the gloss, the film was non-uniform and part of the underlying steel plate was exposed. Regarding the adhesion, the film was non-uniform and there were pinhole-like peeling sites. Regarding the smoothness, the smoothness of the film surface was good. Overall, it was in a poor state.

[0082] (g) Comparative Example 2 The aluminum content of the completed magnesium oxide was 15 ppm. The coefficient of variation of the aluminum concentration determined from the measurement of the aluminum concentration in magnesium oxide using D-SIMS was 0.20. The average size of the crystallites of magnesium oxide measured by X-ray diffraction was 60 nm. Among the film properties, regarding gloss, the film was non-uniform and had no gloss. Regarding adhesion, the film was non-uniform and there were obvious peeling sites. Regarding smoothness, the smoothness of the film surface was poor. Overall, it was in a defective state.

[0083] (h) Comparative Example 3 The aluminum content of the completed magnesium oxide was 620 ppm. The coefficient of variation of the aluminum concentration determined from the measurement of the aluminum concentration in magnesium oxide using D-SIMS was 0.32. The average size of the crystallites of magnesium oxide measured by X-ray diffraction was 40 nm. Among the film properties, regarding gloss, the film was non-uniform and had no gloss. Regarding adhesion, the film was non-uniform and there were obvious peeling sites. Regarding smoothness, the smoothness of the film surface was very poor. Overall, it was in a very defective state.

[0084] The evaluation results of the above Examples 1 to 5 and Comparative Examples 1 to 3 were summarized in Table 2.

Table 2

[0085] As can be seen from the above data, the magnesium oxide for the annealing release agent of the present invention has at least the aluminum content within a predetermined numerical range, and the variation in the aluminum concentration is suppressed. Therefore, by uniformly applying the magnesium oxide for the annealing release agent on the steel sheet, aluminum can be uniformly distributed on the steel sheet with a content within a predetermined numerical range. Thereby, in the entire forsterite phase, uniformly, the melting point decreases, the fluidity improves, and the overall smoothness of the forsterite film can be improved. That is, the magnesium oxide for the annealing release agent of the present invention can form a smooth forsterite film on the surface of the grain-oriented electrical steel sheet. Therefore, the magnetic properties of the grain-oriented electrical steel sheet manufactured using the magnesium oxide for the annealing release agent can be improved.

Claims

1. The aluminum content is 20 to 300 ppm, and the coefficient of variation of the concentration of the aluminum is 0.25 or less, magnesium oxide for annealing release agent.

2. The average size of the crystallites is 25 to 60 mm, Magnesium oxide for annealing release agent according to Claim 1.

3. Further containing at least one element selected from Cl, Mn, Fe, and Cu, Magnesium oxide for annealing release agent according to Claim 1.

4. A method for producing magnesium oxide for annealing release agent, comprising: a reaction step of continuously supplying a magnesium hydroxide raw material containing aluminum and an alkali raw material to a reaction tank, reacting the magnesium hydroxide raw material and the alkali raw material while generating turbulent flow, and continuously taking out the upper slurry of magnesium hydroxide formed by the reaction from the reaction tank; a forming step of firing the taken-out magnesium hydroxide to form magnesium oxide; and the aluminum content in the magnesium oxide is 20 to 300 ppm, the coefficient of variation of the concentration of the aluminum in the magnesium oxide is 0.25 or less. A method for producing magnesium oxide for annealing release agent.

5. A method for producing a grain-oriented electrical steel sheet, comprising: a coating step of coating a slurry containing magnesium oxide for annealing release agent on a decarburized annealed steel sheet; an annealing step of annealing the steel sheet coated with the slurry; and the aluminum content in the magnesium oxide is 20 to 300 ppm, the coefficient of variation of the concentration of the aluminum in the magnesium oxide is 0.25 or less, A method for producing a grain-oriented electrical steel sheet.

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