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

Abstract

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. Provided is magnesium oxide for an annealing separation agent, said magnesium oxide being capable of forming a smooth forsterite film on the surface of a grain-oriented electrical steel sheet. The magnesium oxide for the annealing separator contains aluminum. The content of the aluminum in the magnesium oxide is 20-300 ppm. The coefficient of variation in the concentration of the aluminum in the magnesium oxide is 0.25 or less. The magnesium oxide can form a smooth forsterite coating film on the surface of the grain-oriented electrical steel sheet.

Description

[0001] This application is a divisional application of a Chinese patent application with the application number 202410438998.7, the application date of April 12, 2024, and the invention title of "Magnesium Oxide for Annealing Release Agent, Its Manufacturing Method, and Manufacturing Method of Grain-Oriented Electrical Steel Sheet Using the Same". Technical Field

[0002] The present invention relates to magnesium oxide for an annealing release agent, a manufacturing method thereof, and a manufacturing method of a grain-oriented electrical steel sheet using the same. Background Art

[0003] An annealing release agent for improving the smoothness of the forsterite film in a grain-oriented electrical steel sheet is known. For example, an annealing release agent for a grain-oriented electrical steel sheet is disclosed in Patent Document 1. This annealing release agent contains Cl: 0.01 to 0.05% by mass, B: 0.05 to 0.15% by mass, CaO: 0.1 to 2% by mass, and P 2 O 3 : 0.03 to 1.0% by mass, with magnesium oxide as the main body. For this magnesium oxide, the citric acid activity is 30 to 120 seconds in 40% CAA, the specific surface area obtained by the BET method is 8 to 50 m 2 / g, the hydration amount obtained by ignition loss is 0.5 to 5.2% by mass, and the content of particles with a particle size of 45 μm or more is 0.1% by mass or less. Further, this annealing release agent contains 0.05% by mass or more and 20% by mass or less of a water-insoluble compound with a particle size of 45 μm or more and 150 μm or less. In Patent Document 1, it is considered that by using this annealing release agent, a uniform and smooth forsterite film can be easily formed.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: International Publication No. 2013 / 051270 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] In Patent Document 1, in order to form a smooth forsterite film, the content of trace elements in the magnesium oxide of the annealing release agent, that is, in the magnesium oxide, is specified. However, in Patent Document 1, there is no description of the fluctuation of the concentration of trace elements in the magnesium oxide. Therefore, there is room for further improvement in the technology for forming a smooth forsterite film.

[0009] 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 an oriented electromagnetic steel sheet, a method for manufacturing the same, and a method for manufacturing an oriented electromagnetic steel sheet using the same.

[0010] Means for Solving the Problems

[0011] The present invention includes the following disclosures.

[0012] (First Disclosure)

[0013] 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.

[0014] (Second Disclosure)

[0015] In the second disclosure, the average size of the microcrystals of the magnesium oxide in the first disclosure is 25 to 60 nm.

[0016] (Third Disclosure)

[0017] In the third disclosure, the magnesium oxide in the first disclosure or the second disclosure further contains at least one element selected from Cl, Mn, Fe, and Cu.

[0018] (Fourth Disclosure)

[0019] The fourth disclosure is a method for manufacturing magnesium oxide for an annealing separating agent. The method for manufacturing the magnesium oxide includes a reaction step and a forming step. In the reaction step, while continuously supplying a magnesium hydroxide raw material containing aluminum and an alkali raw material to a reaction tank, the magnesium hydroxide raw material and the alkali raw material are reacted in a state of generating turbulence. Then, the upper slurry of magnesium hydroxide formed during the reaction is continuously taken out from the reaction tank. In the forming step, the taken-out magnesium hydroxide is fired to form magnesium oxide. 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.

[0020] (Fifth Disclosure)

[0021] The fifth disclosure is a method for manufacturing an oriented electromagnetic steel sheet. The method for manufacturing the oriented electromagnetic steel sheet includes: a coating step of coating a slurry containing magnesium oxide for an annealing separating agent on a decarburized 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 the aluminum in the magnesium oxide is 0.25 or less.

[0022] Effects of the Invention

[0023] According to the present invention, it is possible to provide magnesia for an annealing release agent that can form a smooth forsterite film on the surface of an oriented electrical steel sheet, a method for manufacturing the same, and a method for manufacturing an oriented electrical steel sheet using the same. Detailed embodiments

[0024] Hereinafter, preferred embodiments of the magnesia for an annealing release agent, a method for manufacturing the same, and a method for manufacturing an oriented electrical steel sheet using the same according to the present invention will be described.

[0025] [Magnesia for annealing release agent]

[0026] The magnesia for an annealing release agent of the present invention is a powder having magnesia as a main component, but may contain other trace elements. Here, the term "containing" trace elements means containing trace elements inside and / or outside the particles of magnesia. The content of magnesia 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 magnesia for an annealing release agent will also be abbreviated as magnesia.

[0027] Magnesia contains aluminum (Al) as a trace element. When a forsterite film is formed by the reaction of magnesia for an annealing release agent with silica on the surface of a steel sheet, 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, and thus the smoothness of the overall appearance of the formed forsterite film can be improved.

[0028] If the content of aluminum in magnesia is too small, it is difficult to produce the effect of lowering the melting point of the forsterite phase. On the other hand, even if the content of aluminum is too large, the effect of lowering the melting point is likely to decrease. Therefore, the content of aluminum in magnesia is preferably 20 to 400 ppm. When magnesia contains 20 ppm or more of aluminum, the effect of lowering the melting point of the forsterite phase is likely to occur. Thereby, since the fluidity of the forsterite phase is improved, the forsterite film can be made smooth. When magnesia contains 400 ppm or less of aluminum, it is possible to suppress the decrease in the effect of lowering the melting point of the forsterite phase caused by excessive aluminum. Thereby, since the fluidity of the forsterite phase is improved, the forsterite film can be made smooth. In addition, the distribution of aluminum is less likely to become uneven, and the generation of unevenness in the forsterite film can be suppressed. As the lower limit of the content of aluminum, 25 ppm is preferred. The upper limit of the content of aluminum is preferably 300 ppm.

[0029] As described above, the effect of lowering the melting point of the forsterite phase may vary depending on the aluminum content in magnesium oxide. That is, the smoothness of the forsterite film may vary depending on the aluminum content. Therefore, it is preferable that not only the aluminum content is within the above-specified range, but also the aluminum is uniformly distributed. In other words, it is preferable that not only the aluminum content is within the above-specified range, but also the fluctuation of the aluminum concentration is low. Therefore, for magnesium oxide used as an annealing release agent, the coefficient of variation indicating the degree of fluctuation of the aluminum concentration is preferably less than 0.30. The coefficient of variation is more preferably 0.25 or less. Here, 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 obtaining the coefficient of variation will be described later.

[0030] Regarding the magnesium oxide for the above annealing release agent, at least the aluminum content is within a specified numerical range, and the fluctuation of its aluminum concentration is suppressed. Therefore, by uniformly coating the magnesium oxide for the annealing release agent on a steel sheet, aluminum can be uniformly distributed on the steel sheet in an amount within a specified numerical range. As a result, the melting point of the entire forsterite phase decreases uniformly, the fluidity increases, 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 an oriented electrical steel sheet.

[0031] Regarding the average size of the microcrystals of the magnesium oxide particles, there is no particular limitation as long as the reactivity of the magnesium oxide can be adjusted. As the average size of the microcrystals, 25 to 60 nm is preferable. If the average size of the microcrystals is 25 nm or less, the reactivity is too high, and hydration occurs during the preparation of the coating slurry, or the formation of forsterite proceeds locally. If the average size of the microcrystals 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 microcrystals will be described later.

[0032] Regarding the shape of the magnesium oxide particles, there is no particular limitation as long as the content of trace elements can be within a specified range and the fluctuation of the concentration of trace elements among the particles is small. As the planar shape of the particles, for example, polygons, rectangles, polygonal shapes, ellipses, circles, amorphous shapes, and combinations thereof can be cited. 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).

[0033] Regarding the particle size distribution of magnesium oxide, there is no particular limitation as long as the fluctuations in the content of trace elements and the concentration of trace elements are small 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 can be, for example, 2.0 to 7.0 μm. In the particle size distribution of magnesium oxide, since the particle diameter is distributed in a relatively small but not overly small range, the aggregation of particles in the slurry is suppressed and the dispersibility is improved at the same time. The method for obtaining the particle size distribution will be described later.

[0034] Magnesium oxide may contain various trace elements known to contribute to promoting the formation of a coating film on an oriented electromagnetic steel sheet, improving the coating film properties, and / or improving the magnetic properties. Examples of such trace elements include at least one or more elements selected from chlorine (Cl), boron (B), sodium (Na), copper (Cu), phosphorus (P), iron (Fe), manganese (Mn), titanium (Ti), and calcium (Ca), or their compounds.

[0035] [Method for manufacturing magnesium oxide for annealing release agent]

[0036] As a method for manufacturing magnesium oxide, there is no particular limitation as long as it can manufacture magnesium oxide having the above-described constitution, particularly with small fluctuations in the concentration of trace elements. Examples of the manufacturing method include the following three methods.

[0037] 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 while reacting them in a turbulent state, and at the same time, the upper slurry of magnesium hydroxide formed during the reaction is continuously taken out from the reaction tank. Then, the taken-out magnesium hydroxide is calcined to obtain magnesium oxide. Among them, an aqueous solution of a raw material of a trace element, an aqueous solution of a magnesium hydroxide raw material, and an aqueous solution of an alkali raw material can be continuously supplied to the reaction tank separately while reacting.

[0038] 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 while synthesizing magnesium hydroxide through an intermittent reaction in a turbulent state. Then, the synthesized magnesium hydroxide is calcined to obtain magnesium oxide. Among them, an aqueous solution of a raw material of a trace element and an aqueous solution of an alkali raw material can be continuously supplied to the aqueous solution of the magnesium hydroxide raw material in the reaction tank separately while reacting.

[0039] In the third method, a powder of a raw material of a trace element and a powder of magnesium hydroxide are mixed and calcined to obtain magnesium oxide. Among them, regarding the powder of magnesium oxide, for example, it can be obtained by a method in which no raw material of a trace element is added when magnesium hydroxide is generated in the first or second method.

[0040] Conversely, in the case where trace elements are excessively contained in the magnesium hydroxide raw material, a chelating agent suitable for the trace element can be added to the magnesium hydroxide raw material.

[0041] Among them, as the magnesium hydroxide raw material, for example, water-soluble magnesium salts or their hydrates can be cited. Specifically, magnesium chloride hexahydrate, magnesium chloride dihydrate, and anhydrous magnesium chloride are preferred. In addition, as the magnesium hydroxide raw material, seawater, brine (irrigation water), and bittern can be used.

[0042] As the raw material of the target trace element, that is, the target trace element raw material, for example, the trace element itself and compounds of the trace element can be cited. As the compounds of the trace element, for example, acids, bases, and their salts containing the trace element, oxides, chlorides, nitrates, sulfates, carbonates, and phosphates of the trace element can be cited. In the case where the trace element is aluminum, as the aluminum raw material, that is, the compound of aluminum, for example, aluminum chloride, aluminum nitrate, aluminum phosphate, aluminum sulfate, aluminum borate, and aluminum oxide can be cited.

[0043] As the base raw material, for example, calcium hydroxide, sodium hydroxide, and potassium hydroxide can be cited. It should be noted that when magnesium hydroxide is calcined, as the calcination atmosphere, for example, air and nitrogen can be cited.

[0044] As the chelating agent, as long as it can form a chelate complex with the target trace element raw material, there is no particular limitation. In the case where the trace element is aluminum, as the chelating agent, for example, triethanolamine can be cited.

[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, an aqueous solution of 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 alkali raw material. Secondly, the aqueous solution of magnesium hydroxide raw material and the aqueous solution of alkali raw material are 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 react in a turbulent state caused by stirring, and at the same time, the upper slurry of magnesium hydroxide formed during the reaction is continuously taken out from the reaction tank (reaction step). At this time, the aqueous solution of magnesium hydroxide raw material and the aqueous solution of alkali raw material are injected into the reaction tank at a flow rate such that the ratio of Mg to OH is approximately 1:2. The term "approximately" means that the error of the flow rate is in the range of ±50%. At this time, if necessary, the inside of the reaction tank is maintained at a specified pressure and a specified temperature. In this way, by continuously reacting the magnesium hydroxide raw material and the alkali raw material added with the target trace element raw material in a turbulent state, magnesium hydroxide added with the target trace element is synthesized. If necessary, washing, filtration, and drying are carried out. Then, the magnesium hydroxide added with the trace element is calcined at a specified temperature to obtain magnesium oxide added with the trace element (forming step).

[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, that is, an aqueous solution of 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 alkali raw material. Secondly, the aqueous solution of alkali raw material is injected into the aqueous solution of magnesium hydroxide raw material in the reaction tank at a specified flow rate. In the reaction tank, the magnesium hydroxide raw material and the alkali raw material added with the target trace element raw material react in a turbulent state caused by stirring (reaction step). At this time, if necessary, the inside of the reaction tank is maintained at a specified pressure and a specified temperature. In this way, by reacting the alkali raw material little by little with the magnesium hydroxide raw material added with the target trace element raw material in a turbulent state, magnesium hydroxide added with the target trace element is synthesized. If necessary, washing, filtration, and drying are carried out. Then, the magnesium hydroxide added with the trace element is calcined at a specified temperature to obtain magnesium oxide added with the trace element (forming step).

[0047] In the third method, for example, first, a 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 magnesium hydroxide raw material (without trace elements). On the other hand, an alkali raw material is added to deionized water to form an aqueous solution containing the alkali raw material, that is, an aqueous solution of alkali raw material. Secondly, the aqueous solution of alkali raw material is injected into the aqueous solution of magnesium hydroxide raw material (without trace elements) in the reaction tank at a specified flow rate, and in the reaction tank, the magnesium hydroxide raw material and the alkali raw material are made to react. At this time, stirring is carried out as required, and at the same time, the inside of the reaction tank is maintained at a specified pressure and a specified temperature. In this way, by reacting the magnesium hydroxide raw material and the alkali raw material, magnesium hydroxide without trace elements is synthesized (reaction step). The powder of the target trace element raw material is mixed into the powder of this magnesium hydroxide without trace elements. Then, the powder of magnesium hydroxide mixed with the powder of the target trace element raw material is fired at a specified temperature to obtain magnesium oxide added with trace elements (forming step).

[0048] As an example of another manufacturing method, for example, a method using magnesium oxide obtained by firing the mineral magnesite can be cited. This manufacturing method is to first hydrate the magnesium oxide obtained from the mineral magnesite to obtain a powder of magnesium hydroxide, and secondly, use this powder of magnesium hydroxide to carry out the above-mentioned third method to obtain magnesium oxide.

[0049] Here, the meanings of the terms related to the firing of the 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. It is also called 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 when firing the sample. It should be noted that cooling includes not only active cooling using cooling means but also slow cooling such as natural cooling.

[0050] <Firing conditions>

[0051] For magnesium oxide, it can be controlled by adjusting the conditions of the final firing when obtaining magnesium oxide and the trace elements contained in the precursor supplied for the final firing. The firing conditions include heating-up time, holding temperature, holding time, and cooling-down time.

[0052] As the conditions for obtaining magnesium oxide, for example, the heating-up time is preferably 0.5 hour to 3 hours, more preferably 1 hour 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 hour to 15 hours, more preferably 0.2 hour to 13 hours. The cooling-down time is preferably 0.1 hour to 6 hours, more preferably 0.2 hour to 5 hours.

[0053] If the heating time, holding time, and cooling time are shorter than the above ranges, the firing of magnesium hydroxide is not completed, or the reactivity of magnesium oxide during the formation of the forsterite film is too high, making it 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, making it difficult to form forsterite.

[0054] Boron contained in magnesium oxide has the effect of lowering the melting point of the material 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 with a boron content within such a numerical range is used as an annealing separator, the characteristics of the forsterite film can be improved, and the magnetic and insulating characteristics of the grain-oriented electrical steel sheet can be made good.

[0055] The content of sodium contained in magnesium oxide is preferably 0.1 - 200 ppm. When magnesium oxide with a sodium content within such a numerical range is used as an annealing separator, the characteristics of the forsterite film can be improved, and the magnetic and insulating characteristics of the grain-oriented electrical steel sheet can be made good.

[0056] <Firing atmosphere>

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

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

[0059] The control of the content of trace elements in magnesium oxide can be carried out as follows. First, measure the content of trace elements contained in the raw materials for manufacturing magnesium oxide. Then, based on this result, add or remove trace elements in the raw materials and intermediate products so that the content of trace elements contained in magnesium oxide becomes the required content. As raw materials, for example, magnesium raw materials, the mineral magnesite, and alkalis that react with magnesium raw materials can be cited. As intermediate products, for example, magnesium hydroxide can be cited.

[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 the raw materials and intermediate products can be cited. The mixing method can be wet or dry. It should be noted that the above-mentioned precursors are included in the intermediate products.

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

[0062] After mixing intermediate products with different compositions to adjust the excess and deficiency of trace elements, final firing is carried out to obtain magnesium oxide in which the content of trace elements becomes the required content. Alternatively, by mixing magnesium oxide after final firing with different compositions and adjusting the excess and deficiency of trace elements, magnesium oxide in which the content of trace elements becomes the required content can also be obtained.

[0063] In the manufacturing process of magnesium oxide, various additives known to have the effect of improving film properties and magnetic properties can be effectively added. As such additives, for example, copper (Cu), phosphorus (P), manganese (Mn), titanium (Ti), calcium (Ca), and their compounds can be cited.

[0064] <Control of particle size distribution (D10, D50, D90, MV) of magnesium oxide>

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

[0066] One method is to adjust at least one of the reaction temperature, reaction rate, and stirring conditions when reacting a magnesium raw material and an alkali raw material to synthesize magnesium hydroxide. Another method is to crush the precursor before 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 final firing.

[0067] Using the above conditions, magnesium oxide for an annealing release agent is manufactured. Since the magnesium oxide has the above-described constitution, fluctuations in the content of trace elements in the magnesium oxide can be suppressed.

[0068] [Manufacturing method of grain-oriented electrical steel sheet using magnesium oxide for annealing release agent]

[0069] Next, a manufacturing method of a grain-oriented electrical steel sheet using the above-described magnesium oxide for an annealing release agent will be described. The manufacturing method includes: a coating step of coating a slurry containing the above-described magnesium oxide on a decarburized annealed steel sheet; and a high-temperature annealing step of annealing the steel sheet coated with magnesium oxide.

[0070] <Coating step>

[0071] The above-described magnesium oxide is uniformly dispersed in a liquid to form a slurry containing magnesium oxide. As the liquid, for example, water can be cited. At this time, the slurry is formed at a low temperature of 5°C in such a manner that magnesium oxide does not hydrate.

[0072] The concentration of magnesium oxide may be, for example, 5 to 30% by mass. From the viewpoint of easily and uniformly coating the slurry on the steel sheet, the lower limit of the concentration of magnesium oxide is preferably 7% by mass. From the viewpoint of achieving a viscosity suitable for easy coating of the slurry, the upper limit of the concentration of the annealing release agent is preferably 25% by mass.

[0073] The viscosity of the slurry at 5°C may be, 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] Using a roll coating device or a spraying device, the slurry is continuously coated on the decarburized annealed steel sheet. Among them, the slurry is coated at a low temperature of 5°C in such a manner that magnesium oxide does not hydrate. At this time, since magnesium oxide having the above-described configuration is used and the slurry containing the magnesium oxide is uniformly coated on the steel sheet, fluctuations in the content of trace elements in the coated slurry can be suppressed. Then, the coated slurry is dried, for example, at a temperature of about 300 to 500°C.

[0075] <High-temperature annealing process>

[0076] By coating the above-described slurry, the steel sheet coated with magnesium oxide is annealed. As the annealing conditions, for example, 1000 to 1200°C and 10 to 20 hours can be cited. Thereby, a forsterite film is formed on the surface of the steel sheet, and then, if necessary, a known prescribed treatment is performed to form an oriented electrical steel sheet using the above-described annealing release agent.

[0077] In the method for manufacturing an oriented electrical steel sheet of the present invention, since it has the above-described configuration, by uniformly coating magnesium oxide on the steel sheet, a forsterite film in which fluctuations in the content of trace elements are suppressed can be formed on the steel sheet. Thereby, an oriented electrical steel sheet having improved magnetic properties can be obtained.

[0078] It should be noted that the magnesium oxide for the annealing release agent of the present invention, its manufacturing method, and the manufacturing method of the oriented electrical steel sheet using the same are not limited to the above-described embodiments and the examples described later, and can be appropriately combined, substituted, and changed within the scope not departing from the object and gist of the present invention.

[0079] <Measurement methods, test methods>

[0080] Regarding various measurement methods and test methods, they are as described below.

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

[0082] For the concentration of trace elements, its average value, standard deviation, and coefficient of variation, the following methods are used to obtain them.

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

[0084] (2) Mold the magnesium oxide into pellets with a length of 4 mm × width of 4 mm to prepare a sample.

[0085] (3) Set the sample on the D-SIMS (Dynamic Secondary Ion Mass Spectrometry) PHI ADEPT-1010 manufactured by ULVAC-PHI. Then, under the condition that the primary acceleration voltage is 5.0 kV, measure the concentration of trace elements at 250 measurement points in the depth direction from the surface of the sample to a depth of approximately 5 μm.

[0086] (4) Based on the measured concentration of trace elements at 250 points, calculate the average value (μ) and standard deviation (σ) of the concentration of trace elements.

[0087] (5) Calculate the coefficient of variation according to the standard deviation (σ) / average value (μ).

[0088] It should be noted that the concentration of trace elements at each measurement point of D-SIMS may not necessarily be regarded as the concentration of trace elements in each individual particle. The measurement points are present every 5 μm / 250 = 0.02 μm, and its measurement interval is approximately smaller than the particle size of magnesium oxide. Therefore, the concentration of trace elements at each measurement point can be approximated as the concentration of trace elements that is more detailed than each individual particle.

[0089] 2. Content of trace elements

[0090] For the content of trace elements, the following method is used to obtain it. Dissolve 0.5 g of the sample to be measured in 5 ml of 30% HNO 3 solution, and then make up the volume to 100 ml with ultrapure water to prepare a test solution. Measure the test solution using the emission spectroscopic analysis device SPS3520-DD (manufactured by Hitachi High-Technologies Corporation) by the calibration curve method to obtain the content of trace elements.

[0091] 3. Average size of microcrystals

[0092] For the average size of microcrystals, the following method is used to obtain it.

[0093] (1) Prepare magnesium oxide (powder) to be measured.

[0094] (2) The magnesium oxide was placed in a powder X-ray diffractometer (X-ray diffractometer Empyrean manufactured by Malvern Panalytical), and powder X-ray diffraction was measured to obtain diffraction data. Among them, the measurement conditions were set as X-ray output: 45 kV, 40 mA, scanning speed: 40 degrees / minute, step width: 0.02 degrees, X-ray: CuKα ray.

[0095] (3) Based on the diffraction data, the constituent components were identified, and at the same time, the average size of the microcrystals was obtained from the full width at half maximum of the peak attributed to the (200) plane of magnesium oxide. Among them, the XRD analysis software used was the integrated powder X-ray analysis software HighScorePlus. Among them, the average size of the microcrystals was obtained using the diffraction peak attributed to the (200) plane of magnesium oxide and calculated using the following Scherrer formula.

[0096] L(200) = (K·λ) / (β·cosθ)

[0097] (L: average size of microcrystals, λ: (CuKα), θ: Bragg diffraction angle, β: full width at half maximum, K: 0.94)

[0098] It should be noted that the diffraction peak attributed to the (200) plane of magnesium oxide was observed around 2θ = 42.80° - 42.90°.

[0099] 4. Particle size distribution

[0100] The particle size distribution was measured using a particle size distribution measuring device MT3300EXII (manufactured by Microtrac BEL Co., Ltd.). First, the inside of the particle size distribution measuring device was filled with ethanol and the solvent was circulated. An appropriate amount of the sample to be measured was added thereto and confirmed to fall within an appropriate range. Then, after circulating the solvent containing the sample for 1 minute, the particle size distribution was measured. The measurement time was 30 seconds.

[0101] 5. Film properties

[0102] 3.5 g of the magnesium oxide to be evaluated was suspended in 30 ml of water at 5 °C to obtain a slurry. The obtained slurry was coated on a steel plate with a length of 150 mm, a width of 80 mm, and a thickness of 0.5 mm, homogenized by a rubber roller, and then sintered to obtain sintered magnesium oxide. The film properties of the magnesium oxide film on the steel plate, namely, gloss, adhesion, and smoothness, were evaluated visually.

[0103] Examples

[0104] Examples and comparative examples are listed below to further illustrate the present invention. However, the present invention is not limited to these examples and comparative examples.

[0105] (1) Regarding the samples

[0106] The specimens of Examples 1 to 5 and Comparative Examples 1 to 3 were produced as described below.

[0107] [Example 1]

[0108] 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 containing 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 injected into a container with an overflow capacity of 220 mL, and the reaction was continuously carried out to obtain a magnesium hydroxide slurry. A propeller with a diameter of 2.5 cm was used in the reaction, and stirring was carried out at a rotational speed of 450 rpm. Next, the temperature of the aqueous solution was set to 45°C, and heat treatment was carried out for 5.0 hours under stirring conditions of 400 rpm. Furthermore, the magnesium hydroxide slurry that had undergone the above treatment was filtered to obtain a cake. The cake was washed twice with pure water 25 times the weight of the solid component of the obtained cake, and dried at 105°C for 12 hours to obtain magnesium hydroxide. The magnesium hydroxide was calcined at 700°C for 0.5 hour to obtain magnesium oxide. The particle size distribution of the obtained magnesium oxide was measured, and the results were D10 = 1.0 μm, D50 = 2.0 μm, and D90 = 8.0 μm.

[0109] [Example 2]

[0110] 386 g of magnesium chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) and 0.35 g of aluminum chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) were dissolved in 1.9 L of deionized water to obtain an aqueous solution containing 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 injected into 1.9 L of this aqueous solution at a rate of 170 mL / min to obtain a magnesium hydroxide slurry. A propeller with a diameter of 2.5 cm was used in the reaction, 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. Furthermore, the magnesium hydroxide slurry that had undergone the above treatment was filtered to obtain a cake. The cake was washed twice with pure water 25 times the weight of the solid component of the obtained cake, and dried at 105°C for 12 hours to obtain magnesium hydroxide. The magnesium hydroxide was calcined at 900°C for 5 hours to obtain magnesium oxide. The particle size distribution of the obtained magnesium oxide was measured, and the results were D10 = 1.5 μm, D50 = 3.0 μm, and D90 = 12 μm.

[0111] [Example 3]

[0112] Dissolve 386 g of magnesium chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) and 0.1 g of aluminum chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) 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 of aluminum. At normal pressure and 25 °C, inject 1.9 L of this aqueous solution and 1.7 L of 2 mol / L sodium hydroxide aqueous solution into a container with an overflow capacity of 220 mL, and continuously react them to obtain a magnesium hydroxide slurry. During the reaction, a propeller with a diameter of 2.5 cm is used and stirred at a rotational speed of 500 rpm. Next, set the temperature of the aqueous solution to 40 °C and perform heat treatment for 5.5 hours under stirring conditions of 350 rpm. Furthermore, filter the magnesium hydroxide slurry to obtain a filter cake. Wash the filter cake twice with pure water 25 times the weight of the solid component of the obtained filter cake, and dry it at 105 °C for 12 hours to obtain magnesium hydroxide. Burn the obtained magnesium hydroxide at 900 °C for 1 hour to obtain magnesium oxide. Measure the particle size distribution of the obtained magnesium oxide, and the results show that D10 is 0.6 μm, D50 is 1.6 μm, and D90 is 6.0 μm.

[0113] [Example 4]

[0114] Dissolve 386 g of magnesium chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) and 0.1 g of aluminum chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) 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 of aluminum. At normal pressure and 25 °C, inject 1.7 L of 2 mol / L sodium hydroxide aqueous solution 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 propeller with a diameter of 2.5 cm is used and stirred at a rotational speed of 500 rpm. Next, set the temperature of the water bath to 40 °C and perform heat treatment for 5.5 hours under stirring conditions of 350 rpm. Furthermore, filter the magnesium hydroxide slurry that has undergone the above treatment to obtain a filter cake. Wash the filter cake twice with pure water 25 times the weight of the solid component of the obtained filter cake, and dry it at 105 °C for 12 hours to obtain magnesium hydroxide. Burn the obtained magnesium hydroxide at 800 °C for 1 hour to obtain magnesium oxide. Measure the particle size distribution of the obtained magnesium oxide, and the results show that D10 is 1.4 μm, D50 is 3.2 μm, and D90 is 13 μm.

[0115] [Example 5]

[0116] Dissolve 386 g of magnesium chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) in 1.9 L of deionized water to obtain an aqueous solution of magnesium at 1 mol / L. At normal pressure and 25 °C, inject 1.7 L of 2 mol / L sodium hydroxide aqueous solution into 1.9 L of this aqueous solution at a rate of 170 mL / min to obtain a magnesium hydroxide slurry. A propeller with a diameter of 2.5 cm was used in the reaction and stirred 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. Furthermore, the magnesium hydroxide slurry that had undergone the above treatment was filtered to obtain a filter cake. The filter cake was washed twice with pure water 25 times the weight of the solid component of the obtained filter cake, 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. The particle size distribution of the obtained magnesium oxide was measured, and the results were D10 = 1.9 μm, D50 = 4.0 μm, and D90 = 14 μm.

[0117] [Comparative Example 1]

[0118] Dissolve 386 g of magnesium chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) 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 2 mol / L sodium hydroxide aqueous solution were respectively injected into a container with an overflow capacity of 220 mL, and reacted continuously to obtain a magnesium hydroxide slurry. A propeller with a diameter of 2.5 cm was used in the reaction and stirred 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. Furthermore, the magnesium hydroxide slurry that had undergone the above treatment was filtered to obtain a filter cake. The filter cake was washed twice with pure water 25 times the weight of the solid component of the obtained filter cake, 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. The particle size distribution of the obtained magnesium oxide was measured, and the results were D10 = 2.0 μm, D50 = 3.8 μm, and D90 = 13 μm.

[0119] [Comparative Example 2]

[0120] Dissolve 386 g of magnesium chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) and 0.05 g of aluminum chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) in 1.9 L of deionized water to obtain an aqueous solution of magnesium at 1 mol / L and aluminum at 1.1×10 -4An aqueous solution of mol / L. At normal pressure and 25 °C, 1.9 L of this aqueous solution and 1.7 L of a 2 mol / L sodium hydroxide aqueous solution were respectively injected into a container with an overflow capacity of 220 mL, and the reaction was continuously carried out to obtain a magnesium hydroxide slurry. A propeller with a diameter of 2.5 cm was used in the reaction, 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 magnesium hydroxide slurry that had undergone the above treatment was filtered to obtain a filter cake. The filter cake was washed twice with pure water 25 times the weight of the solid component of the obtained filter cake, and magnesium hydroxide was obtained by drying at 105 °C for 12 hours. This magnesium hydroxide was calcined at 1000 °C for 3.0 hours to obtain magnesium oxide. The particle size distribution of the obtained magnesium oxide was measured, and the results were D10 = 0.8 μm, D50 = 1.8 μm, and D90 = 10 μm.

[0121] [Comparative Example 3]

[0122] Dissolve 386 g of magnesium chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) in 1.9 L of deionized water to obtain an aqueous solution with a magnesium concentration of 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 sodium hydroxide aqueous solution were respectively injected into a container with an overflow capacity of 220 mL, and the reaction was continuously carried out to obtain a magnesium hydroxide slurry. A propeller with a diameter of 2.5 cm was used in the reaction, 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. Furthermore, the magnesium hydroxide slurry that had undergone the above treatment was filtered to obtain a filter cake. The filter cake was washed twice with pure water 25 times the weight of the solid component of the obtained filter cake, and magnesium hydroxide was obtained by drying at 105 °C for 12 hours. 0.8 g of aluminum chloride hexahydrate (Wako Pure Chemical Industries, Ltd.) was mixed into 110 g of this magnesium hydroxide, and it was calcined at 900 °C for 2.0 hours to obtain magnesium oxide. The particle size distribution of the obtained magnesium oxide was measured, and the results were D10 = 1.8 μm, D50 = 3.8 μm, and D90 = 14 μm.

[0123] The manufacturing conditions of the above Examples 1 - 5 and Comparative Examples 1 - 3 are summarized in Table 1.

[0124]

Table 1

[0125]

[0126]

[0127] (2) Regarding the evaluation items

[0128] For the magnesium oxides of Examples 1 to 5 and Comparative Examples 1 to 3, the average size of the microcrystals, the coefficient of variation of the aluminum concentration, the aluminum content, and the film properties of the magnesium oxide film, namely, gloss, adhesion, and smoothness, were evaluated.

[0129] (3) Regarding the evaluation results

[0130] (a) Example 1

[0131] The aluminum content of the completed magnesium oxide was 25 ppm. The coefficient of variation of the aluminum concentration determined by measuring the aluminum concentration in the magnesium oxide using D-SIMS was 0.10. The average size of the microcrystals of the magnesium oxide measured by X-ray diffraction was 20 nm. Among the film properties, regarding gloss, the film was in a non-uniform and dull state. Regarding adhesion, the film was slightly non-uniform but had no peeling sites. Regarding smoothness, the surface of the film had good smoothness. Overall, it was in a good state.

[0132] (b) Example 2

[0133] The aluminum content of the completed magnesium oxide was 298 ppm. The coefficient of variation of the aluminum concentration determined by measuring the aluminum concentration in the magnesium oxide using D-SIMS was 0.25. The average size of the microcrystals of the magnesium oxide measured by X-ray diffraction was 65 nm. Among the film properties, regarding gloss, the film was slightly non-uniform but shiny. Regarding adhesion, the film was non-uniform and had pinhole-like peeling sites. Regarding smoothness, the surface of the film had good smoothness. Overall, it was in a good state.

[0134] (c) Example 3

[0135] The aluminum content of the completed magnesium oxide was 123 ppm. The coefficient of variation of the aluminum concentration determined by measuring the aluminum concentration in the magnesium oxide using D-SIMS was 0.09. The average size of the microcrystals of the magnesium oxide measured by X-ray diffraction was 25 nm. Among the film properties, regarding gloss, the film was uniform and particularly shiny. Regarding adhesion, the film was uniform and had no peeling sites. Regarding smoothness, the surface of the film had very good smoothness. Overall, it was in a very good state.

[0136] (d) Example 4

[0137] The aluminum content of the completed magnesium oxide is 100 ppm. The coefficient of variation of the aluminum concentration determined by measuring the aluminum concentration in magnesium oxide using D-SIMS is 0.20. The average size of the magnesium oxide microcrystals measured by X-ray diffraction is 20 nm. In terms of film properties, regarding gloss, the film is slightly uneven but shiny. Regarding adhesion, the film is uniform and there are no peeling sites. Regarding smoothness, the smoothness of the film surface is good. Overall, it is in a very good state.

[0138] (e) Example 5

[0139] The aluminum content of the completed magnesium oxide is 292 ppm. The coefficient of variation of the aluminum concentration determined by measuring the aluminum concentration in magnesium oxide using D-SIMS is 0.25. The average size of the magnesium oxide microcrystals measured by X-ray diffraction is 60 nm. In terms of film properties, regarding gloss, the film is slightly uneven but shiny. Regarding adhesion, the film is slightly uneven but there are no peeling sites. Regarding smoothness, the smoothness of the film surface is very good. Overall, it is in a very good state.

[0140] (f) Comparative Example 1

[0141] The aluminum content of the completed magnesium oxide is 35 ppm. The coefficient of variation of the aluminum concentration determined by measuring the aluminum concentration in magnesium oxide using D-SIMS is 0.30. The average size of the magnesium oxide microcrystals measured by X-ray diffraction is 60 nm. In terms of film properties, regarding gloss, the film is uneven and part of the base steel plate is exposed. Regarding adhesion, the film is uneven and there are pinhole-like peeling sites. Regarding smoothness, the smoothness of the film surface is good. Overall, it is in a poor state.

[0142] (g) Comparative Example 2

[0143] The aluminum content of the completed magnesium oxide is 15 ppm. The coefficient of variation of the aluminum concentration determined by measuring the aluminum concentration in magnesium oxide using D-SIMS is 0.20. The average size of the magnesium oxide microcrystals measured by X-ray diffraction is 60 nm. In terms of film properties, regarding gloss, the film is uneven and dull. Regarding adhesion, the film is uneven and there are obvious peeling sites. Regarding smoothness, the smoothness of the film surface is poor. Overall, it is in a poor state.

[0144] (h) Comparative Example 3

[0145] The aluminum content of the completed magnesium oxide is 620 ppm. The coefficient of variation of the aluminum concentration determined by measuring the aluminum concentration in magnesium oxide using D-SIMS is 0.32. The average size of the microcrystals of magnesium oxide measured by X-ray diffraction is 40 nm. In terms of film properties, regarding gloss, the film is in a non-uniform and dull state. Regarding adhesion, the film is in a non-uniform state with obvious peeling sites. Regarding smoothness, the smoothness of the film surface is very poor. Overall, it is in a very poor state.

[0146] The evaluation results of the above Examples 1 to 5 and Comparative Examples 1 to 3 are summarized in Table 2.

[0147]

Table 2

[0148]

[0149] Among them, the meanings represented by gloss, adhesion, and smoothness in the table are as described below.

[0150] · Gloss

[0151] ◎: The film is uniform and particularly shiny.

[0152] 〇: The film is slightly non-uniform but shiny.

[0153] △: The film is non-uniform and dull.

[0154] ×: The film is non-uniform and a part of the base steel plate is exposed.

[0155] · Adhesion

[0156] ◎: The film is uniform and there are no peeling sites.

[0157] ○: The film is slightly non-uniform but there are no peeling sites.

[0158] △: The film is non-uniform and there are pinhole-like peeling sites.

[0159] ×: The film is non-uniform and there are obvious peeling sites.

[0160] · Smoothness

[0161] ◎: The smoothness of the film surface is very good.

[0162] ○: The smoothness of the film surface is good.

[0163] △: The smoothness of the film surface is poor.

[0164] ×: The smoothness of the film surface is very poor.

[0165] From the above data, it can be seen that for the magnesium oxide used in the annealing parting agent of the present invention, the aluminum content is at least within a specified numerical range, and the fluctuation of the aluminum concentration is suppressed. Therefore, by uniformly coating the magnesium oxide for the annealing parting agent on the steel sheet, aluminum can be uniformly distributed on the steel sheet within a specified numerical range. As a result, the melting point of the entire forsterite phase is uniformly reduced, the fluidity is improved, and the overall smoothness of the forsterite film can be enhanced. That is, the magnesium oxide for the annealing parting 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 parting agent can be improved.

Claims

1. Magnesium oxide for annealing separator, wherein: The aluminum content is 20 to 300 ppm, and the coefficient of variation of the aluminum concentration is 0.25 or less.

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