Magnesium oxide for annealing separator, method for producing the same, and method for producing grain-oriented electrical steel sheet using the same

Abstract

Provided is magnesium oxide for annealing separators, which suppresses the fluctuation of the concentration of trace elements in magnesium oxide. The magnesium oxide for annealing separators contains boron. The content of the boron is 500 to 1500 ppm. The coefficient of variation of the concentration of the boron is 0.50 or less. Therefore, the fluctuation of the concentration of the boron in the magnesium oxide is suppressed.

Description

Technical Field

[0001] The present invention relates to magnesium oxide for 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] When manufacturing a grain-oriented electrical steel sheet, magnesium oxide for an annealing separator is applied to the steel sheet. The amount of trace elements contained in the magnesium oxide affects the product characteristics of the finished grain-oriented electrical steel sheet. For example, patent document 1 discloses magnesium oxide for an annealing separator, which contains 400 to 1500 ppm of boron, 1 to 650 ppm of sodium, 500 ppm or less of chlorine, and 0.10 to 0.70 mass % of sulfur calculated as SO3, and the ratio of the total molar content of chlorine and sulfur to the total molar content of boron and sodium (Cl+S) / (B+Na) is 0.50 to 0.80.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-173172 Summary of the invention

[0006] Problems to be solved by the invention

[0007] Patent Document 1 specifies the content of trace elements in magnesium oxide used as an annealing separator. However, Patent Document 1 does not describe the fluctuation of the concentration of trace elements in magnesium oxide.

[0008] An object of the present invention is to provide magnesium oxide for an annealing separator in which the variation in the concentration of trace elements in the magnesium oxide is suppressed, a method for producing the same, and a method for producing a grain-oriented electrical steel sheet using the same.

[0009] Means for solving problems

[0010] The present invention includes the following disclosures.

[0011] (First Publication)

[0012] The first disclosure is magnesium oxide for annealing separator. The magnesium oxide contains boron. The content of the boron is 500 to 1500 ppm. The coefficient of variation of the concentration of the boron is 0.50 or less.

[0013] (Second Publication)

[0014] In the second disclosure, the magnesium oxide in the first disclosure further contains sodium. The content of the sodium is 0.1 to 200 ppm. The coefficient of variation of the sodium concentration is 0.25 or less.

[0015] (3rd Publication)

[0016] In the third disclosure, the magnesium oxide in the first disclosure or the second disclosure further contains at least one element selected from the group consisting of Cl, Mn, Fe, and Cu.

[0017] (4th Publication)

[0018] The fourth disclosure is a method for producing magnesium oxide for annealing separators. The method for producing magnesium oxide includes a reaction step and a formation step. In the reaction step, a magnesium hydroxide raw material and an alkali raw material containing boron are continuously supplied to a reaction tank, and the magnesium hydroxide raw material and the alkali raw material are reacted in a turbulent state, and the upper slurry of magnesium hydroxide formed in the reaction is continuously taken out from the reaction tank. In the formation step, the taken out magnesium hydroxide is calcined to form magnesium oxide. The magnesium oxide contains boron. The content of the boron is 500 to 1500 ppm. The coefficient of variation of the concentration of the boron is less than 0.50.

[0019] (5th Publication)

[0020] The fifth disclosure is a method for producing a grain-oriented electrical steel sheet. The method for producing a grain-oriented electrical steel sheet includes: a coating step of coating a slurry containing magnesium oxide for an annealing separator on a decarburized annealed steel sheet, and an annealing step of annealing the steel sheet coated with the slurry. The magnesium oxide contains boron. The content of the boron is 500 to 1500 ppm. The coefficient of variation of the concentration of the boron is 0.50 or less.

[0021] Effects of the Invention

[0022] According to the present invention, it is possible to provide magnesium oxide for an annealing separator in which the variation in the concentration of trace elements in magnesium oxide is suppressed within a specific range, a method for producing the same, and a method for producing a grain-oriented electrical steel sheet using the same. DETAILED DESCRIPTION

[0023] Preferred embodiments of the magnesium oxide for an annealing separator, a method for producing the magnesium oxide, and a method for producing a grain-oriented electrical steel sheet using the magnesium oxide of the present invention will be described below.

[0024] [Magnesium oxide for annealing separator]

[0025] The magnesium oxide used in the annealing separator of the present invention is a powder with magnesium oxide as the main component, but may contain other trace elements. Among them, the so-called "containing" trace elements means that the trace elements are contained inside and / or outside the particles of magnesium oxide. The content of magnesium oxide in the annealing separator is at least 95% by mass, preferably 98% by mass. Therefore, the content of trace elements in the annealing separator is less than 5% by mass, preferably less than 2% by mass. The magnesium oxide used in the annealing separator is also abbreviated as magnesium oxide below.

[0026] Magnesium oxide contains boron (B) as a trace element. When a forsterite film is formed by the reaction of magnesium oxide used as an annealing separator with silicon dioxide on the surface of the steel sheet, boron has the effect of promoting the formation of the forsterite film. In addition, when magnesium oxide is formed by calcining magnesium hydroxide, when the holding temperature during calcination is set to about 1200 to 1300°C, boron has the effect of lowering the melting point of the substance to be calcined.

[0027] The content of boron in magnesium oxide is 500 to 1500 ppm. By containing 500 ppm or more of boron, magnesium oxide can fully form a forsterite film. By containing 1500 ppm or less of boron, magnesium oxide can suppress the excessive formation of a forsterite film and the generation of unevenness. As the lower limit of the content of boron, 700 ppm is preferred. As the upper limit of the content of boron, 1200 ppm is preferred.

[0028] The coefficient of variation of the boron concentration in magnesium oxide is 0.50 or less from the viewpoint of suppressing the fluctuation of the boron content in magnesium oxide used as an annealing separator. From the viewpoint of further suppressing the fluctuation, the coefficient of variation is preferably 0.40 or less. The coefficient of variation is a coefficient corresponding to the fluctuation of the boron concentration contained in individual magnesium oxide particles among a plurality of magnesium oxide particles in magnesium oxide. The method for calculating the coefficient of variation will be described later.

[0029] According to the present invention, since the fluctuation of the content of boron, one of the trace elements, in magnesium oxide used as an annealing separator is suppressed, a predetermined amount of boron can be uniformly distributed in the steel sheet by uniformly applying magnesium oxide to the steel sheet. As a result, fluctuations in the magnetic properties of the finished grain-oriented electrical steel sheet can be suppressed.

[0030] As for the particle size and shape of the magnesium oxide particles, there is no particular limitation as long as the fluctuation of the concentration of trace elements can be made small between particles. As the particle size, for example, 0.02 to 5 μm can be listed. As for the lower limit of the particle size, from the viewpoint of making it difficult for the particles to agglomerate in the slurry, 0.05 μm is preferred. As for the upper limit of the particle size, from the viewpoint of making the particles uniformly dispersed in the slurry, 1 μm is more preferred. As for the planar shape of the particles, for example, polygonal, rectangular, polygonal, elliptical, circular, amorphous, and combinations thereof can be listed.

[0031] As for the particle size distribution of magnesium oxide, there is no particular limitation as long as the fluctuation of the concentration of trace elements can be minimized between 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 can be, for example, 2.0 to 7.0 μm. By achieving a particle size distribution within the above range, the aggregation of particles in the slurry is suppressed and the dispersibility is improved.

[0032] Magnesium oxide may contain other trace elements other than magnesium oxide and boron (B). As such other trace elements, sodium (Na) can be cited, for example. When magnesium oxide containing sodium as a trace element is used to form a forsterite film, sodium has the effect of adjusting the formation rate of the forsterite film.

[0033] The sodium content in magnesium oxide is preferably 0.1 to 200 ppm. By containing 0.1 ppm or more of sodium, magnesium oxide can increase the rate of formation of the forsterite film. By containing 200 ppm or less of sodium, magnesium oxide can reduce the rate of formation of the forsterite film and suppress excessive formation. The lower limit of the sodium content is preferably 0.5 ppm. The upper limit of the sodium content is preferably 150 ppm.

[0034] The coefficient of variation of the sodium concentration in magnesium oxide is preferably 0.25 or less from the viewpoint of suppressing the fluctuation of the sodium content in magnesium oxide used as an annealing separator. From the viewpoint of further suppressing the fluctuation, the coefficient of variation is more preferably 0.20 or less. The coefficient of variation is a coefficient corresponding to the fluctuation of the sodium concentration contained in individual magnesium oxide particles among a plurality of magnesium oxide particles in magnesium oxide. The method for calculating the coefficient of variation will be described later.

[0035] Examples of other trace elements other than magnesium oxide and boron (B) include aluminum (Al). When a forsterite film is formed using magnesium oxide containing aluminum as a trace element, aluminum has an effect of promoting the formation of the forsterite film.

[0036] The aluminum content in magnesium oxide is preferably 20 to 400 ppm. By containing more than 20 ppm of aluminum, magnesium oxide can fully form a forsterite film. By containing less than 400 ppm of aluminum, magnesium oxide can suppress the excessive formation of a forsterite film and the generation of unevenness. As the lower limit of the aluminum content, 25 ppm is preferred. The upper limit of the aluminum content is preferably 300 ppm.

[0037] The coefficient of variation of the aluminum concentration in magnesium oxide is preferably 0.40 or less from the viewpoint of suppressing the fluctuation of the aluminum content in magnesium oxide used as an annealing separator. From the viewpoint of further suppressing the fluctuation, the coefficient of variation is more preferably 0.30 or less. The coefficient of variation is a coefficient corresponding to the fluctuation of the aluminum concentration contained in individual magnesium oxide particles among a plurality of magnesium oxide particles in magnesium oxide. The method for calculating the coefficient of variation will be described later.

[0038] Magnesium oxide may contain various trace elements known to contribute to promoting film formation, improving film properties and / or improving magnetic properties of grain-oriented electrical steel sheets. Examples of such trace elements include at least one element or compound thereof selected from chlorine (Cl), copper (Cu), phosphorus (P), iron (Fe), manganese (Mn), titanium (Ti), and calcium (Ca). For example, chlorine is an element that promotes the formation of forsterite film. Copper is an element that improves the film properties and magnetic properties of grain-oriented electrical steel sheets. Phosphorus is an element that promotes the formation of forsterite film.

[0039] [Method for producing magnesium oxide for annealing separator]

[0040] As a method for manufacturing magnesium oxide, there is no particular restriction as long as it is possible to manufacture magnesium oxide with the above-mentioned composition, especially with small fluctuations in the concentration of trace elements. As its manufacturing method, for example, the following three methods can be listed. The first method is to add the raw material of the target trace element to the magnesium hydroxide raw material, so that the alkali raw material continuously reacts with the magnesium hydroxide raw material to synthesize magnesium hydroxide, and the magnesium hydroxide is calcined to obtain a method of magnesium oxide. The second method is to synthesize magnesium hydroxide by an intermittent reaction by adding the raw material of the target trace element and the magnesium hydroxide raw material to the alkali raw material at the same time, and the magnesium hydroxide is calcined to obtain magnesium oxide. The third method is a method of mixing and calcining the powder of the raw material of the target trace element and the powder of magnesium hydroxide to obtain magnesium oxide. In addition, when the magnesium hydroxide raw material contains trace elements excessively, a chelating agent suitable for the trace elements can be added to the magnesium hydroxide raw material.

[0041] Among them, as the raw material of magnesium hydroxide, for example, water-soluble magnesium salts or hydrates thereof can be listed, and specifically, magnesium chloride hexahydrate, magnesium chloride dihydrate, and magnesium chloride anhydrate are preferred. In addition, as the raw material of magnesium hydroxide, seawater, salt water (swamp water), and bittern can be used.

[0042] As the raw material of the target trace element, i.e. the target trace element raw material, for example, trace elements themselves and trace element compounds can be listed. As trace element compounds, for example, acids, alkalis and their salts, oxides, chlorides, nitrates, sulfates, carbonates and phosphates containing trace elements can be listed. In the case where the trace element is boron, as the boron raw material, i.e. the compound of boron, for example, boric acid, alkali metal borate, ammonium borate, alkali metal metaborate system and boron oxide can be listed. As alkali metal borate, for example, magnesium borate, calcium borate and sodium borate can be listed. In the case where the trace element is sodium, as the sodium raw material, i.e. the compound of sodium, for example, sodium chloride, sodium nitrate, sodium phosphate, sodium sulfate and sodium borate can be listed. In the case where the trace element is aluminum, as the aluminum raw material, i.e. the compound of aluminum, for example, aluminum chloride, aluminum nitrate, aluminum phosphate, aluminum sulfate, aluminum borate and aluminum oxide can be listed.

[0043] Examples of the alkali raw material include calcium hydroxide, sodium hydroxide, potassium hydroxide, and ammonia. In addition, when magnesium hydroxide is calcined, examples of the calcination atmosphere include air and nitrogen.

[0044] As a chelating agent, there is no particular limitation as long as it can form a chelate complex with the target trace element raw material. When the trace element is boron, as a chelating agent, for example, 1,2-ethylene glycol can be listed. When the trace element is aluminum, as a chelating agent, for example, triethanolamine can be listed.

[0045] 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, the magnesium hydroxide raw material aqueous solution. On the other hand, the alkali raw material is added to the deionized water to form an aqueous solution containing the alkali raw material, that is, the alkali raw material aqueous solution. Secondly, the magnesium hydroxide raw material aqueous solution and the alkali raw material aqueous solution are respectively continuously injected into the reaction tank at a specified flow rate. Then, in the reaction tank, the magnesium hydroxide raw material and the alkali raw material added with the target trace element raw material are reacted in a state of turbulence caused by stirring, and the upper slurry of magnesium hydroxide formed in the reaction is continuously taken out from the reaction tank (reaction process). At this time, the magnesium hydroxide raw material aqueous solution and the alkali raw material aqueous solution are injected into the reaction tank at a flow rate at which the ratio of Mg to OH is approximately 1:2. The so-called "approximately" means that the error of the flow rate is within the range of ±50%. At this time, the reaction tank is maintained at a specified pressure and a specified temperature as needed. In this way, magnesium hydroxide raw material added with target trace element raw material and alkali raw material are continuously reacted under turbulent state, thereby synthesizing magnesium hydroxide added with target trace element. If necessary, it is washed with water, filtered and dried. Then, the magnesium hydroxide added with trace element is calcined at a predetermined temperature to obtain magnesium oxide added with trace element (forming process).

[0046] 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, i.e., a magnesium hydroxide raw material aqueous solution. On the other hand, an alkali raw material is added to the deionized water to form an aqueous solution containing the alkali raw material, i.e., an alkali raw material aqueous solution. Secondly, the alkali raw material aqueous solution is added to the magnesium hydroxide raw material aqueous solution in the reaction tank at a specified 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 under a state of turbulence caused by stirring (reaction process). At this time, as required, the reaction tank is maintained at a specified pressure and a specified temperature. In this way, by reacting the alkali raw material with the magnesium hydroxide raw material added with the target trace element raw material little by little under a state of turbulence, magnesium hydroxide added with the target trace element is synthesized. As required, water washing, filtering, and drying are performed. Then, the magnesium hydroxide added with the trace element is calcined at a specified temperature to obtain magnesium oxide added with the trace element (formation process).

[0047] In the third method, for example, first, magnesium hydroxide raw material is added to deionized water to form an aqueous solution containing magnesium hydroxide raw material, i.e., magnesium hydroxide raw material aqueous solution (without trace elements). On the other hand, alkali raw material is added to deionized water to form an aqueous solution containing alkali raw material, i.e., alkali raw material aqueous solution. Secondly, in the magnesium hydroxide raw material aqueous solution (without trace elements) in the reaction tank, the alkali raw material aqueous solution is injected at a specified flow rate, and the magnesium hydroxide raw material and the alkali raw material are reacted in the reaction tank. At this time, stirring is performed as needed, and the reaction tank is maintained at a specified pressure and a specified temperature. In this way, magnesium hydroxide without trace elements is synthesized by reacting the magnesium hydroxide raw material with the alkali raw material (reaction process). The powder of the target trace element raw material is mixed in the powder of the magnesium hydroxide without trace elements. Then, the magnesium hydroxide mixed with the target trace element raw material is calcined at a specified temperature to obtain magnesium oxide added with trace elements (formation process).

[0048] As another example of a production method, for example, a method using magnesium oxide obtained by calcining the mineral magnesite can be cited. This production method is firstly to hydrate the magnesium oxide obtained from the mineral magnesite to obtain a powder of magnesium hydroxide, and then, using the powder of magnesium hydroxide, the above-mentioned third method is implemented to obtain magnesium oxide.

[0049] Here, the meanings of the terms used in this specification and related to the calcination of the sample of magnesium hydroxide are as follows. "Heating time" means the time from room temperature to the target maximum temperature when the sample is calcined. "Holding temperature" means the target maximum temperature when the sample is calcined. It is also called the calcination temperature. "Holding time" means the time to maintain the holding temperature when the sample is calcined. "Cooling time" means the time from the holding temperature to the room temperature after the holding time when the sample is calcined. It should be noted that cooling includes slow cooling such as cooling in addition to active cooling using cooling means.

[0050] <Firing conditions>

[0051] The magnesium oxide can be controlled by adjusting the final calcination conditions when obtaining the magnesium oxide and the trace elements contained in the precursor used for the final calcination. The calcination conditions include the heating time, the holding temperature, the holding time and the cooling time.

[0052] As conditions for obtaining magnesium oxide, for example, the heating 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 time is preferably 0.1 to 6 hours, more preferably 0.2 to 5 hours.

[0053] If the heating time, holding time, and cooling time are shorter than the above ranges, the calcination of magnesium hydroxide is not completed, or the reactivity of magnesium oxide is too high when the forsterite film is formed, so it is difficult to uniformly form forsterite. On the other hand, if the heating time, holding time, and cooling time are longer than the above ranges, the reactivity of magnesium oxide is excessively reduced, so it becomes difficult to form forsterite.

[0054] The boron contained in the 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 to 1300°C. The content of boron contained in the magnesium oxide is preferably 0.05 to 0.15% by mass. When the magnesium oxide having a boron content in 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 improved.

[0055] The sodium content in magnesium oxide is preferably 0.1 to 200 ppm. When magnesium oxide having a sodium content in this 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 improved.

[0056] <Firing atmosphere>

[0057] The atmosphere during firing can be nitrogen or air. It is sufficient as long as the material to be fired is heated uniformly. The material to be fired can be stirred uniformly during firing. As an apparatus for performing such firing, for example, a rotary kiln can be cited.

[0058] <Control of trace element content in magnesium oxide>

[0059] The control of the content of trace elements in magnesium oxide can be carried out as described below. First, the content of trace elements contained in the raw materials for the manufacture of magnesium oxide is measured. Then, based on the result, the trace elements are added to or removed from the raw materials or intermediate products in such a way that the content of trace elements contained in magnesium oxide becomes the desired content. As raw materials, for example, magnesium raw materials, mineral magnesite, and alkalis reacting with magnesium raw materials can be listed. As intermediate products, for example, magnesium hydroxide can be listed.

[0060] There is no particular limitation on the method of adding trace elements. For example, a method of mixing a compound containing the trace element to be restricted in a raw material or an intermediate product can be cited. The mixing method can be wet or dry. It should be noted that the intermediate product contains the above-mentioned precursor.

[0061] There is no particular limitation on the method for removing trace elements. For example, the method includes washing the raw materials and intermediate products, and adding a chelating agent to the target trace element. As a specific example of washing, water washing can be cited.

[0062] By mixing intermediate products of different compositions to adjust the excess and deficiency (over-deficit) of trace elements and then performing final calcination, magnesium oxide having a desired content of trace elements can be obtained. Alternatively, by mixing magnesium oxides of different compositions after final calcination and adjusting the excess and deficiency of trace elements, magnesium oxide having a desired content of trace elements can also be obtained.

[0063] In the manufacturing process of magnesium oxide, various additives known to improve film properties and magnetic properties can be effectively added. Examples of such additives include copper (Cu), phosphorus (P), aluminum (Al), manganese (Mn), titanium (Ti), calcium (Ca), and compounds thereof.

[0064] <Control of Magnesium Oxide Particle Size Distribution (D10, D50, D90, MV)>

[0065] The particle size distribution of magnesium oxide can be controlled by the following method.

[0066] One method is to adjust at least one of the reaction temperature, reaction rate, and stirring conditions when reacting the magnesium raw material and the alkali raw material to synthesize magnesium hydroxide. Another method is to crush the precursor before the final firing. Another method is to control the firing conditions of magnesium hydroxide. Another method is to re-fire or crush the magnesium oxide after the final firing.

[0067] The above-mentioned conditions are used to produce magnesium oxide for annealing separators. Since the magnesium oxide has the above-mentioned predetermined structure, the fluctuation of the content of trace elements in the magnesium oxide can be suppressed.

[0068] [Method for producing grain-oriented electrical steel sheet using magnesium oxide for annealing separator]

[0069] Next, a method for producing a grain-oriented electrical steel sheet using the above-mentioned magnesium oxide for annealing separator is described. The method comprises: a coating step of coating a slurry containing the above-mentioned magnesium oxide on a decarburized annealed steel sheet; and a high temperature annealing step of annealing the steel sheet coated with the magnesium oxide.

[0070] <Coating process>

[0071] The magnesium oxide is uniformly dispersed in a liquid to form a slurry containing the magnesium oxide. The liquid may be water, for example. At this time, the slurry is formed at a low temperature of 5° C. so that the magnesium oxide is not hydrated.

[0072] The concentration of magnesium oxide can be, for example, 5 to 30% by mass. From the viewpoint of making it easy to evenly apply the slurry to the steel sheet, the lower limit of the concentration of magnesium oxide is preferably 7% by mass. From the viewpoint of making the viscosity of the slurry easy to apply, the upper limit of the concentration of the annealing separator is preferably 25% by mass.

[0073] The viscosity of the slurry at 5° C. is, for example, 2.2 to 5.2 mPa·s. From the viewpoint of ensuring a sufficient coating amount, the lower limit of the viscosity of the slurry at 5° C. is preferably 2.6 mPa·s. From the viewpoint of easy coating of the slurry, the upper limit of the viscosity of the slurry at 5° C. is preferably 4.6 mPa·s.

[0074] The slurry is continuously applied to the decarburized annealed steel sheet using a roller coating device or a spray coating device. The slurry is applied at a low temperature of 5°C so that the magnesium oxide is not hydrated. At this time, since the magnesium oxide having the above-mentioned structure is used, the slurry containing the magnesium oxide is evenly applied to the steel sheet, thereby suppressing the fluctuation of the content of trace elements in the applied slurry. Then, the applied slurry is dried at a temperature of about 300 to 500°C, for example.

[0075] <High temperature annealing process>

[0076] The above slurry is applied, thereby annealing the steel sheet coated with magnesium oxide. As the annealing conditions, for example, 1000-1200°C and 10-20 hours can be listed. Thus, a forsterite film is formed on the surface of the steel sheet, and then, a known prescribed treatment is performed as needed to form a grain-oriented electromagnetic steel sheet using the above annealing separator.

[0077] In the method for producing a grain-oriented electrical steel sheet of the present invention, since it has the above-mentioned predetermined structure, by uniformly applying magnesium oxide on the steel sheet, a forsterite film which suppresses the fluctuation of the content of trace elements can be formed on the steel sheet. Thus, a grain-oriented electrical steel sheet with improved magnetic properties can be obtained.

[0078] It should be noted that the magnesium oxide for annealing separator of the present invention, the production method thereof, and the production method of a grain-oriented electrical steel sheet using the same are not limited to the above-mentioned embodiment and the examples described below, and can be appropriately combined, substituted, and modified within the scope of the purpose and spirit of the present invention.

[0079] <Measurement method, test method>

[0080] Various measurement methods and test methods are as follows.

[0081] 1. Concentration of trace elements and their mean, standard deviation and coefficient of variation

[0082] The concentration of trace elements, their average value, standard deviation and coefficient of variation were determined by the following method.

[0083] (1) Prepare magnesium oxide (powder) to be measured.

[0084] (2) The magnesium oxide was molded into pellets of 4 mm in length and 4 mm in width to prepare samples.

[0085] (3) The sample was placed in D-SIMS (Dynamic Secondary Ion Mass Spectrometry) PHI ADEPT-1010 manufactured by ULVAC-PHI Co., Ltd. Then, under the condition of a primary acceleration voltage of 5.0 kV, the concentration of trace elements at 250 measurement points in the depth direction from the surface of the sample to a depth of about 5 μm was measured.

[0086] (4) Based on the trace element concentrations measured at 250 points, the average value (μ) and the standard deviation (σ) of the trace element concentrations were determined.

[0087] (5) Calculate the coefficient of variation based on standard deviation (σ) / mean value (μ).

[0088] It should be noted that the concentration of trace elements at each measurement point of D-SIMS is not necessarily the concentration of trace elements for each particle. The measurement points exist every 5μm / 250=0.02μm, and the measurement interval is roughly smaller than the particle size of magnesium oxide. Therefore, the concentration of trace elements at each measurement point can be approximated to be a more detailed concentration of trace elements than for each particle.

[0089] 2. Content of trace elements

[0090] The content of trace elements was determined by the following method. 0.5 g of the sample to be measured was dissolved in 5 ml of 30% HNO3 solution, and then the volume was fixed to 100 ml with ultrapure water to prepare a test solution. The test solution was measured using a luminescence spectrophotometer SPS3520-DD (manufactured by Hitachi High-Tech Co., Ltd.) using the calibration line method to obtain the content of trace elements.

[0091] 3. Particle size distribution

[0092] The particle size distribution is measured using a particle size distribution measuring device MT3300EXI I (manufactured by Microtrac BEL Co., Ltd.). First, the particle size distribution measuring device is filled with ethanol and the solvent is circulated. An appropriate amount of the sample of the measurement object is added thereto and it is confirmed that it falls within an appropriate range. Then, after the solvent containing the sample is circulated for 1 minute, the particle size distribution is measured. The measurement time is 30 seconds.

[0093] Example

[0094] The present invention is further described below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples and Comparative Examples.

[0095] (1) About the sample

[0096] The samples of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were produced as follows.

[0097] [Example 1]

[0098] 386g of magnesium chloride hexahydrate, 0.80g of boric acid and 3.0g of sodium chloride are dissolved in deionized water to obtain an aqueous solution of 1.9L. The aqueous solution and 1.7L of sodium hydroxide aqueous solution of 2mol / L are respectively injected into a container of overflow capacity 220mL at normal pressure and 25°C, so that it is continuously reacted to obtain magnesium hydroxide slurry. A propeller with a diameter of 2.5cm is used in the reaction to stir at a rotation speed of 450rpm. Secondly, the temperature of the aqueous solution is set to 45°C, and heat treatment is performed for 5.0 hours under the stirring condition of 350rpm. Then, the magnesium hydroxide slurry treated above is filtered to obtain a filter cake. Wash twice with pure water 25 times by weight relative to the solid content of the obtained filter cake, and dry for 12 hours at 105°C to obtain magnesium hydroxide. The magnesium hydroxide is calcined at 900°C for 1 hour to obtain magnesium oxide. The particle size distribution of the magnesium oxide was such that D10 was 1.0 μm, D50 was 2.9 μm, D90 was 10 μm, and the volume mean diameter MV was 5.0 μm.

[0099] [Example 2]

[0100] 386g of magnesium chloride hexahydrate, 0.75g of boric acid and 2.5g of sodium chloride were dissolved in deionized water to obtain an aqueous solution of 1.9L. 1.7L of a 2mol / L sodium hydroxide aqueous solution was injected into the aqueous solution at a speed of 100mL / min at normal pressure and 25°C to obtain a magnesium hydroxide slurry. A propeller with a diameter of 2.5cm was used in the reaction to stir at a rotation speed of 600rpm. Secondly, the temperature of the aqueous solution was set to 40°C and heat treated for 5.0 hours under a stirring condition of 400rpm. Furthermore, the magnesium hydroxide slurry treated above was filtered to obtain a filter cake. The solid content of the obtained filter cake was washed twice with pure water 25 times by weight, and magnesium hydroxide was obtained by drying at 105°C for 12 hours. The magnesium hydroxide was calcined at 900°C for 1 hour to obtain magnesium oxide. The particle size distribution of the magnesium oxide was as follows: D10 was 1.1 μm, D50 was 3.2 μm, D90 was 12 μm, and the volume mean diameter MV was 5.3 μm.

[0101] [Comparative Example 1]

[0102] 386g of magnesium chloride hexahydrate, 0.50g of boric acid and 3.0g of sodium chloride were dissolved in deionized water to obtain an aqueous solution of 1.9L. 1.7L of a 2mol / L sodium hydroxide aqueous solution was injected into the aqueous solution at a speed of 170mL / min at normal pressure and 25°C to obtain a magnesium hydroxide slurry. A propeller with a diameter of 2.5cm was used in the reaction to stir at a rotation speed of 450rpm. Secondly, the temperature of the aqueous solution was set to 40°C and heat treated for 5.0 hours under a stirring condition of 400rpm. Furthermore, the magnesium hydroxide slurry treated above was filtered to obtain a filter cake. The solid content of the obtained filter cake was washed twice with pure water 25 times by weight, and magnesium hydroxide was obtained by drying at 105°C for 12 hours. The magnesium hydroxide was calcined at 850°C for 1 hour to obtain magnesium oxide. The particle size distribution of the magnesium oxide was as follows: D10 was 0.9 μm, D50 was 2.6 μm, D90 was 9.8 μm, and the volume mean diameter MV was 5.0 μm.

[0103] [Comparative Example 2]

[0104] 386g of magnesium chloride hexahydrate is dissolved in deionized water to obtain an aqueous solution of 1.9L. The aqueous solution and 1.7L of a 2mol / L sodium hydroxide aqueous solution are respectively injected into a container with an overflow capacity of 220mL at normal pressure and 25°C, so that it reacts continuously to obtain a magnesium hydroxide slurry. A propeller with a diameter of 2.5cm is used in the reaction to stir at a rotation speed of 400rpm. Secondly, the temperature of the aqueous solution is set to 40°C, and heat treatment is performed for 5.0 hours under the stirring condition of 350rpm. Furthermore, the magnesium hydroxide slurry treated above is filtered to obtain a filter cake. Wash twice with pure water 25 times by weight relative to the solid content of the obtained filter cake, and dry for 12 hours at 105°C to obtain magnesium hydroxide. Boric acid and sodium chloride of the reagent are mixed in the magnesium hydroxide, and calcined for 1 hour at 950°C to obtain magnesium oxide. The particle size distribution of the magnesium oxide was as follows: D10 was 1.3 μm, D50 was 3.4 μm, D90 was 11 μm, and the volume mean diameter MV was 5.5 μm.

[0105] (2) About the evaluation items

[0106] For the magnesium oxides of Example 1, Example 2, Comparative Example 1 and Comparative Example 2, the average value, standard deviation and coefficient of variation of the concentration of trace elements and the content of the trace elements were evaluated.

[0107] (3) Evaluation results

[0108] (a) Embodiment 1

[0109] The average concentration of boron (B) as a trace element is 3.12×1020 Atom / cm 3 The standard deviation of boron concentration is 0.484×10 20 Atom / cm 3 Therefore, the coefficient of variation σ / μ of the boron concentration was 0.155, which was 0.50 or less. The boron content was 1078 ppm, which was within the range of 500 to 1500 ppm.

[0110] The average value of the concentration of sodium (Na) as a trace element is 13.0×10 17 Atom / cm 3 The standard deviation of sodium concentration is 7.79×10 16 Atom / cm 3 Therefore, the coefficient of variation σ / μ of the sodium concentration is 0.0598, which is 0.25 or less. The sodium content is 22 ppm, which is within the range of 0.1 to 200 ppm.

[0111] (b) Embodiment 2

[0112] The average concentration μ of boron (B), a trace element, is 3.59×10 20 Atom / cm 3 The standard deviation of boron concentration is 1.39×10 20 Atom / cm 3 Therefore, the coefficient of variation σ / μ of the boron concentration was 0.386, which was 0.50 or less. The boron content was 980 ppm, which was within the range of 500 to 1500 ppm.

[0113] The average value of the concentration of sodium (Na) as a trace element is 9.92×10 17 Atom / cm 3 The standard deviation of sodium concentration is 19.0×10 16 Atom / cm 3 Therefore, the coefficient of variation σ / μ of the sodium concentration is 0.191, which is 0.25 or less. The sodium content is 8 ppm, which is within the range of 0.1 to 200 ppm.

[0114] (c) Comparative Example 1

[0115] The average value of the concentration of boron (B) as a trace element is 1.46×10 20 Atom / cm 3 The standard deviation of boron concentration is 0.276×10 20 Atom / cm 3 Therefore, the coefficient of variation σ / μ of the boron concentration was 0.190, which was 0.50 or less. The boron content was 650 ppm, which was within the range of 500 to 1500 ppm.

[0116] The average value of the concentration of sodium (Na) as a trace element is 25.2×10 17 Atom / cm 3 The standard deviation of sodium concentration is 67.0×10 16 Atom / cm 3 Therefore, the coefficient of variation σ / μ of the sodium concentration was 0.266, which exceeded 0.25. The sodium content was 19 ppm, which was within the range of 0.1 to 200 ppm.

[0117] (d) Comparative Example 2

[0118] The average value of the concentration of boron (B) as a trace element is 0.303×10 20 Atom / cm 3 The standard deviation of boron concentration is 0.288×10 20 Atom / cm 3 Therefore, the coefficient of variation σ / μ of the boron concentration was 0.951, exceeding 0.50. The boron content was 540 ppm, which was within the range of 500 to 1500 ppm.

[0119] The average value of the concentration of sodium (Na) as a trace element is 2.30×10 17 Atom / cm 3 The standard deviation of sodium concentration is 3.99×10 16 Atom / cm 3 Therefore, the coefficient of variation σ / μ of the sodium concentration was 0.173, which was 0.25 or less. The sodium content was 26 ppm, which was within the range of 0.1 to 200 ppm.

[0120] The results of (a) to (d) above are summarized in Table 1.

[0121]

Table 1

[0122]

[0123] From the above data, it can be seen that the content of trace elements in the magnesium oxide used as an annealing separator of the present invention is within a specified numerical range, and the fluctuation of its content is suppressed. Therefore, by uniformly applying the magnesium oxide used as an annealing separator on the steel plate, the trace elements can be evenly distributed on the steel plate. Thus, a forsterite film with good film properties can be obtained. Therefore, the magnetic properties of the oriented electromagnetic steel sheet manufactured using the magnesium oxide used as an annealing separator can be improved.

Claims

1. Magnesium oxide for annealing separator, wherein: Contains boron and sodium, wherein the boron content is 980-1500 ppm, and the coefficient of variation of the boron concentration is 0.50 or less; the sodium content is 8-200 ppm, and the coefficient of variation of the sodium concentration is 0.25 or less.

2. The magnesium oxide for annealing separator according to claim 1, further comprising at least one element selected from the group consisting of Cl, Mn, Fe, and Cu.

3. A method for manufacturing a grain-oriented electromagnetic steel sheet, comprising: A coating step of coating a slurry containing magnesium oxide for an annealing separator on the decarburized annealed steel sheet, and An annealing step of annealing the steel sheet coated with the slurry; The magnesium oxide contains boron and sodium. The boron content is 980 to 1500 ppm, and the coefficient of variation of the boron concentration is 0.50 or less. The sodium content is 8 to 200 ppm, and the coefficient of variation of the sodium concentration is 0.25 or less.

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