Annealing separator powder and method for manufacturing grain-oriented electromagnetic steel sheet using the same

Abstract

The present invention provides an annealing separator which, after being coated with the annealing separator, can maintain the shape of the roll material after annealing at a high temperature of 1000°C or more. The annealing separator used in the annealing separator contains magnesium oxide as the main component, 0.020-0.200% by mass of B, 0.030-1.000% by mass of SO3, and 0.050-1.000% by mass of P2O3, and contains 0.2-5.0% by mass of particles with a particle size of more than 45 μm and 75 μm or less, and the particles with the above particle size contain 0.002-0.020% by mass of B, less than 0.030% by mass of SO3, and less than 0.050% by mass of P2O3.

Description

Technical Field

[0001] This invention relates to a powder used in annealing release agents for manufacturing oriented electromagnetic steel sheets, specifically an annealing release agent powder that exhibits excellent shape retention of the coil after final annealing. Furthermore, it relates to a method for manufacturing oriented electromagnetic steel sheets with uniform coating and excellent magnetic properties using this annealing release agent powder. Background Technology

[0002] The manufacturing process of oriented electromagnetic steel sheets generally involves hot rolling, annealing, and cold rolling of steel billets adjusted to a specified composition, followed by recrystallization annealing and decarburization annealing, and finally annealing. In the above processes, the final annealing process requires heat treatment at temperatures above 1000°C. Therefore, to prevent the coils from sticking together, an annealing release agent with magnesium oxide powder as the main component is usually applied.

[0003] In addition to its role as an anti-sticking agent, magnesium oxide also has the function of reacting with the silica-based oxide layer formed on the surface of the steel plate during the decarburization annealing before final annealing to form a magnesium olivine film. Furthermore, after final annealing, it removes and purifies precipitates (such as AlN, MnS, MnSe, Si3N4, TiN, TiC, etc.) that control the growth of iron grains, which are known as inhibitors, from the steel plate.

[0004] To better utilize this function, for example, Patent Document 1 proposes a technique for adding trace components such as Cl, B, CaO, and P2O3 to magnesium oxide in controlled amounts, and further controlling the particle size distribution of non-water-soluble compounds added separately from these trace components.

[0005] In the final annealing process of the oriented electromagnetic steel sheet as described above, the steel sheet, wound into a coil, is placed horizontally with the hole in the center of the coil facing vertically (up and down), and annealed at a high temperature of over 1000°C. Therefore, during the heating and cooling process, a large temperature difference can easily occur within the coil, which can easily lead to shape defects such as barrel-shaped (elongated belly) or, conversely, expansion at the top and bottom (both axial directions of the coil) ends (elongated ears).

[0006] In addition, if the annealing separator with magnesium oxide as the main component shrinks due to sintering during the final annealing process, it becomes a so-called loose roll material, which will cause problems in the next roll material processing step.

[0007] As a way to avoid this loose roll material, the roll material is wound with high tension before final annealing. However, if the winding tension is too high, buckling can sometimes occur in the inner diameter portion of the roll material.

[0008] To address these issues, for example, Patent Document 2 proposes the following technology: preventing warping before final annealing by containing magnesium oxide with a particle size of 25 μm or more and less than 75 μm, and solving the problem of loose roll material treatment by setting the volume shrinkage rate of the annealing separator caused by calcination to an appropriate value.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: International Publication No. 2013 / 051270

[0012] Patent Document 2: Japanese Patent Application Publication No. 2012-177148 Summary of the Invention

[0013] However, Patent Document 1 makes no mention of the problem of the deterioration of the shape of the roll after final annealing, or what methods can be used to address this problem.

[0014] In addition, although Patent Document 2 provides solutions for the problem of flexing before final annealing and the problem of loose roll material treatment after final annealing, the problem of shape deterioration (belly elongation, ear elongation) of the roll material after final annealing still exists.

[0015] The present invention was developed in view of the above-mentioned actual situation, and its purpose is to provide an annealing separator powder suitable for use as an annealing separator, which helps to manufacture oriented electromagnetic steel sheets with excellent film uniformity and magnetic properties by eliminating the above-mentioned problems with the shape of the roll after final annealing.

[0016] The main structure of this invention is as follows.

[0017] 1. A powder for annealing separation, characterized in that it comprises magnesium oxide as the main component and contains B: 0.020% to 0.200% by mass, SO3: 0.030% to 1.000% by mass, and P2O3: 0.050% to 1.000% by mass.

[0018] It contains 0.2% to 5.0% by mass particles with a diameter greater than 45 μm and less than 75 μm.

[0019] The particles with a diameter greater than 45 μm and less than 75 μm contain more than 0.002% B by mass and less than 0.020% by mass, less than 0.030% sulfur by mass (equivalent to SO3), and less than 0.050% phosphorus by mass (equivalent to P2O3).

[0020] 2. The annealing separator powder according to claim 1 above, wherein the sodium (Na) contained in the particles with a particle size of more than 45 μm and less than 75 μm is less than 0.010% by mass.

[0021] 3. The annealing separator powder according to 1 or 2 above, wherein the purity of the magnesium oxide is 95% by mass or more.

[0022] 4. A method for manufacturing an orientation-oriented electromagnetic steel sheet, characterized in that the steel billet for the orientation-oriented electromagnetic steel sheet is subjected to hot rolling and cold rolling, followed by recrystallization annealing and decarburization annealing, then coated with an annealing separating agent and subjected to final annealing, wherein the annealing separating agent powder described in any one of 1 to 3 above is used in the annealing separating agent.

[0023] 5. The method for manufacturing the oriented electromagnetic steel sheet according to 4 above, wherein the thickness of the steel sheet is 0.05 mm to 0.20 mm.

[0024] According to the present invention, annealing separator powder can be obtained inexpensively, which has excellent coating reactivity and can be used to manufacture oriented electromagnetic steel sheets with good coating quality, while the final annealed coil has good shape and can achieve a high manufacturing yield.

[0025] In addition, the present invention can provide a method for manufacturing oriented electromagnetic steel sheets with good coating quality by using powder with annealing separating agent. Attached Figure Description

[0026] Figure 1 These are schematic diagrams illustrating the ear elongation shape of the roll material after final annealing. (a) is a view of the roll material from the side, and (b) is a view of the roll material from above.

[0027] Figure 2 These are schematic diagrams illustrating the web elongation shape of the roll material after final annealing. (a) is a view of the roll material from the side, and (b) is a view of the roll material from above. Detailed Implementation

[0028] The experimental results from which this invention was derived are described below.

[0029] First, prepare the sample as follows.

[0030] As the starting material, high-purity ultrafine magnesium oxide 2000A produced by Ube Material Industries, Ltd. via gas-phase polymerization was used. This magnesium oxide has extremely high purity, with MgO accounting for 99.98% by mass.

[0031] The starting material was hydrated with pure water to obtain magnesium hydroxide slurry.

[0032] Next, the magnesium hydroxide slurry was pressed using a filter press to obtain magnesium hydroxide filter cake. Boric acid (H3BO3), magnesium sulfate (MgSO4), and diammonium phosphate ((NH4)2HPO4) were added to the magnesium hydroxide slurry to adjust the amount of trace components in the calcined magnesium oxide.

[0033] It should be noted that the amount of this trace component can be adjusted not only by adjusting the amount added to the slurry, but also by appropriately adjusting the degree of washing of the magnesium hydroxide filter cake, the calcination temperature, etc.

[0034] 400g of the obtained magnesium hydroxide filter cake was placed in an alumina crucible and calcined in air for 60 minutes at 700°C in an electric furnace (Marusho Electric SPX1518T-17). The calcined product was cooled directly in the furnace and then pulverized. After pulverization, the particle size of the obtained powder was adjusted using a sieve to prepare magnesium oxide for this experiment.

[0035] The properties of the magnesium oxide thus obtained are shown in Table 1. It should be noted that in the table, "Particle size (mass%)" indicates the percentage by mass of the sieved powder that passed through a sieve of a specified mesh size. Therefore, 100.0% by mass means that all passed. The same applies to Tables 2, 4, and 5 below.

[0036]

[0037] The magnesium oxide with particle size adjusted as shown in Table 1 was mixed in the proportions shown in Table 2. Then, as shown in Table 2, powders for annealing separation agents with different particle size distributions and trace component amounts were obtained.

[0038]

[0039] Next, an electromagnetic steel sheet containing C: 0.045 wt%, Si: 3.25 wt%, Mn: 0.070 wt%, Al: 80 mass ppm, N: 40 mass ppm, and S: 20 mass ppm was hot-rolled from a slab heated to 1200°C to produce a 2.0 mm thick hot-rolled sheet, which was then wound into a coil. This hot-rolled sheet coil was then subjected to hot-rolled annealing at 1000°C for 30 seconds to remove the oxide scale from the steel surface. Next, cold rolling was performed to produce a final cold-rolled sheet with a thickness of 0.23 mm. Subsequently, after performing decarburization annealing on the cold-rolled sheet at a homogenization temperature of 850°C for 60 seconds, which also serves as recrystallization annealing, the annealing separating agent shown in Table 2 was coated as powder onto the slurry and then wound into a roll. The slurry was heated to 1200°C in a mixed atmosphere of 75 vol% nitrogen and 25 vol% hydrogen at a heating rate of 25°C / h, and held at 1200°C for 20 hours in a 100 vol% hydrogen atmosphere to perform final annealing. Then, smoothing annealing was performed to prepare the sample.

[0040] The uniformity of the film appearance, the film adhesion, and the shape of the roll after final annealing of the samples obtained in this way were investigated.

[0041] In this experiment, the uniformity of the film appearance was assessed by visual inspection. Areas with different hues accounting for less than 20% of the total surface area were considered uniform, while areas with different hues accounting for more than 20% were considered non-uniform.

[0042] For coating adhesion, the sample was rolled 280 mm in the rolling direction and sheared 30 mm in the right-angle direction. After stress relief annealing in a nitrogen atmosphere at 820°C for 3 hours, the steel plate was pressed onto a round bar with various inner diameters (5 mm units) and the minimum diameter (mm) that did not produce coating peeling was measured.

[0043] Regarding the shape of the roll material after final annealing (hereinafter referred to as "annealing"), after cooling the roll material to room temperature, the various deformation modes of the roll material are determined according to... Figure 1 (Ear elongation shape) or Figure 2 (Abdominal elongation shape) Determine the amount of deformation before and after annealing. Specifically, such as... Figure 1 (b) Figure 2 (b) As described, the radius (r) of the inscribed circle of the outer periphery of the coil before annealing and the radius (R) of the inscribed circle of the outer periphery of the coil after annealing are measured, and the value of the deformation (Rr) is calculated and evaluated accordingly. If this value is less than 20 mm, it is evaluated as good.

[0044] It should be explained that Figure 1 These are schematic diagrams illustrating the ear elongation shape of the annealed roll material. (a) is a side view of the roll material, and (b) is a top view of the roll material. Additionally, Figure 2 These are schematic diagrams illustrating the web elongation shape of the rolled material after annealing. (a) is a view of the rolled material from the side, and (b) is a view of the rolled material from above. In both diagrams, dashed lines represent the shape before annealing, and solid lines represent the shape after annealing. It should be noted that since the hollow portion of the rolled material does not deform significantly before and after annealing, in (a), only dashed lines are used to represent its outline, which is hidden from view from the side, and in (b), its outline is omitted for ease of explanation of the deformation (Rr).

[0045] Table 3 shows the powder No. of the annealing separator used in the experiment and its trace components (transcribed from Table 2), the characteristics (mass ratio and trace components) of particles with a particle size ranging from more than 45 μm to less than 75 μm (hereinafter also referred to as "particles larger than 45 μm and smaller than 75 μm"), the shape of the roll after annealing, the uniformity of the coating appearance, and the coating adhesion. It should be noted that the "mass ratio" in the above and table refers to the mass ratio of particles larger than 45 μm and smaller than 75 μm relative to the total mass of the annealing separator powder.

[0046] As shown in Table 3, when the amounts of trace components B, SO3, and P2O3 in the annealing separator powder deviate from the scope of this invention (No. 3-1, 3-3, 3-5), even if the mass ratio of particles larger than 45 μm and smaller than 75 μm and the amount of trace components are within the scope of this invention, the appearance of the film becomes uneven or the adhesion of the film deteriorates. Furthermore, when the mass ratio of particles larger than 45 μm and smaller than 75 μm is excessive (No. 3-5), pitting occurs on the appearance of the film. On the other hand, when the amounts of trace components B, SO3, and P2O3 contained in particles larger than 45 μm and smaller than 75 μm deviate from the scope of this invention (No. 3-2, 3-6), even if the composition of the annealing separator powder and the mass ratio of particles larger than 45 μm and smaller than 75 μm are within the scope of this invention, the shape of the annealed roll becomes poor.

[0047]

[0048] The reasons for limiting the various constituent elements of the present invention will be explained below.

[0049] [Powder for annealing separator]

[0050] The annealing separator powder targeted in this invention has magnesium oxide as its main component (main body). Here, "main component" means containing 50% by mass or more. If the magnesium oxide content is less than 50% by mass, the amount of magnesium olivine film formed by the reaction of the internal silica formed during decarburization annealing with the magnesium oxide in the annealing separator will be insufficient. The proportion of magnesium oxide is preferably 60% by mass or more, and more preferably 80% by mass or more.

[0051] In this invention, in order to improve the uniformity of the coating appearance and the adhesion of the coating, the contents of B, SO3 and P2O3 in the annealing separator powder are respectively: B: 0.020% to 0.200% by mass, SO3: 0.030% to 1.000% by mass, and P2O3: 0.050% to 1.000% by mass.

[0052] If the B content is less than 0.020% by mass, the film formation becomes insufficient, and the film thickness becomes too thin. On the other hand, if it is more than 0.200% by mass, B penetrates into the steel plate and causes embrittlement. The lower limit of the B content in the annealing separator powder is preferably 0.025% by mass or more. In addition, the upper limit of this B content is preferably 0.180% by mass or less.

[0053] The B content can be determined by dissolving the powder of the test object in acid and then performing ICP emission spectroscopy analysis.

[0054] If the SO3 content is less than 0.030% by mass, the film formation becomes insufficient, which is therefore undesirable. On the other hand, if it is more than 1.000% by mass, excessive film formation occurs, resulting in over-formed areas in a dotted pattern, and the film appearance becomes unsatisfactory. The lower limit of the SO3 content in the annealing separating agent powder is preferably 0.034% by mass or more. Furthermore, the upper limit of this SO3 content is preferably 0.700% by mass or less.

[0055] The SO3 content can be determined by dissolving the powder of the test object in acid and performing ICP emission spectroscopy analysis to measure the S content and then converting it into SO3 content.

[0056] If the P2O3 content is less than 0.050% by mass, the film-forming reaction shifts to the high-temperature side, thereby deteriorating the film adhesion. On the other hand, if it is more than 1.000% by mass, the film-forming reaction shifts to the low-temperature side, affecting secondary recrystallization and leading to poor magnetism. The lower limit of the P2O3 content in the annealing separator powder is preferably 0.060% by mass or more. Furthermore, the upper limit of this P2O3 content is preferably 0.800% by mass or less.

[0057] The P2O3 content can be determined by dissolving the powder of the test object in acid and performing ICP emission spectroscopy analysis to determine the P content and then converting it into the P2O3 content.

[0058] To maintain the shape of the annealed roll material, the powder used as the annealing separator needs to contain 0.2% to 5.0% by mass of particles with a particle size greater than 45 μm and less than 75 μm. The lower limit of the proportion of these particles in the powder is preferably 0.5% by mass or more, and the upper limit is preferably 3.0% by mass or less.

[0059] Since the distance between steel sheets wound into rolls after being coated with annealing release agent is approximately 30–40 μm, particles with a diameter exceeding 45 μm are required to support this distance. On the other hand, if the particle size is greater than 75 μm, the particles will indent the surface of the annealed steel sheet, creating indentations. Therefore, the proportion of particles with a diameter exceeding 75 μm in the annealing release agent powder is preferably 2.00% by mass or less.

[0060] Furthermore, if the proportion of particles with a diameter exceeding 45 μm but less than 75 μm is less than 0.2% by mass, the roll shape cannot be adequately maintained. On the other hand, if it exceeds 5.0% by mass, the pitting on the film surface becomes more pronounced, which is therefore undesirable.

[0061] Particles larger than 45 μm but smaller than 75 μm are preferably magnesium oxide. This is because the particle size can change significantly due to the reaction of sintering aids and annealing separating agents, but the particle size change caused by annealing is small for magnesium oxide.

[0062] In this invention, it is essential that particles larger than 45 μm and smaller than 75 μm contain more than 0.002% by mass and less than 0.020% by mass of boron, less than 0.030% by mass of sulfur (equivalent to SO3), and less than 0.050% by mass of phosphorus (equivalent to P2O3).

[0063] If boron content is less than 0.002% by mass, the film-forming ability becomes too low. Therefore, thin, dotted areas of the film are produced. On the other hand, if it is 0.020% by mass or more, the particles undergo self-sintering and shrink during annealing, failing to maintain the roll shape. Similarly, when SO3 content is 0.030% by mass or more and / or P2O3 content is 0.050% by mass or more, the particles also shrink due to self-sintering, thus failing to maintain the roll shape well.

[0064] It should be noted that there is no particular limit to the lower limit content of sulfur and phosphorus, but in industry, sulfur is preferably 0.0001% by mass or more when converted to SO3, and phosphorus is preferably 0.0005% by mass or more when converted to P2O3.

[0065] The contents of boron, SO3 (or sulfur), and P2O3 (or phosphorus) can be determined in the same way as those in the powder of the annealing separating agent by dissolving the powder of the particle of the test object in acid and performing ICP emission spectroscopy analysis on each of the elements B, S, and P.

[0066] When analyzing annealing separator powder in a mixed state, particles larger than 45 μm and smaller than 75 μm are removed for analysis by wet sieving. It is preferable to use a JIS sieve with a diameter of 200 mm and a height of 45 mm as described in JIS Z 8801.

[0067] It should be noted that, in this invention, particles larger than 45 μm and smaller than 75 μm refer to particles that pass through a 200-mesh sieve as described in JIS Z8801 but do not pass through a 330-mesh sieve.

[0068] In addition, the above sieving was carried out using the Viblette (registered trademark) VBL automatic wet sieve manufactured by Hosokawa Micron Corporation under the following conditions: sieve powder amount of 100g, water spray volume of 5L / min, water spray rotation speed of 200rpm, running time of 10min, and power frequency of 60Hz.

[0069] <Method for manufacturing powder for annealing separating agent>

[0070] The manufacturing method of the annealing separating agent powder of the present invention is not particularly limited, but it is usually made of magnesium oxide produced by calcining raw materials as the main component. Examples of raw materials include magnesium hydroxide, magnesium carbonate, and magnesium chloride.

[0071] The amounts of B, SO3, and P2O3 mentioned above can be adjusted by including borates, sulfates, and phosphates in the raw materials before calcination, such as magnesium oxide. In this case, when using Na salts, sodium remains in the magnesium oxide. Like B, SO3, and P2O3, sodium promotes the self-sintering of particles during annealing; therefore, the sodium (Na) content in particles larger than 45 μm and smaller than 75 μm is preferably less than 0.010% by mass. It should be noted that this sodium (Na) content can be 0% by mass. The Na content can be determined by dissolving the particles of the test object in acid and performing ICP emission spectroscopy analysis.

[0072] In addition to MgO, the magnesium oxide used in this invention may also contain B, SO3, P2O3, and Na, and may also contain Cl, CaO, SiO2, Fe2O3, Al2O3, and unavoidable impurities.

[0073] It should be noted that the purity of magnesium oxide (MgO content in magnesium oxide) is preferably 95% by mass or more, and more preferably 98% by mass or more.

[0074] Therefore, the content of components other than MgO in the above-mentioned magnesium oxide is preferably 5% by mass or less, more preferably 2% by mass or less.

[0075] In addition, the boron (B), sulfur and phosphorus content contained in the particles larger than 45 μm and smaller than 75 μm also includes B, SO3 and P2O3 in the magnesium oxide mentioned above.

[0076] In addition to magnesium oxide, the powder used as an annealing separating agent may also contain reaction aids such as titanium oxide and strontium hydroxide. It can also be mixed with other annealing separating agent powders to form an annealing separating agent and then coated onto the roll material.

[0077] [Manufacturing method of oriented electromagnetic steel sheet]

[0078] In this invention, the steel sheet being considered is not particularly limited to any type of oriented electromagnetic steel sheet having a coating primarily composed of magnesium olivine on its surface. Typically, such oriented electromagnetic steel sheets are manufactured by the following operations: hot rolling a silicon-containing steel billet using a known method, cold rolling it to the final sheet thickness in one pass or multiple passes with intermediate annealing, followed by a recrystallization annealing and a decarburization annealing, and then coating it with an annealing separating agent followed by a final annealing.

[0079] Here, in this invention, the powder used as the annealing separating agent is the following powder: with magnesium oxide as the main component, containing B: 0.020% to 0.200% by mass, SO3: 0.030% to 2.000% by mass, P2O3: 0.050% to 1.000% by mass, and further containing 0.2% to 5.0% by mass of particles larger than 45 μm and smaller than 75 μm, wherein the particles larger than 45 μm and smaller than 75 μm contain more than 0.002% by mass and less than 0.020% by mass of boron (B), less than 0.030% by mass of sulfur (equivalent to SO3), and less than 0.050% by mass of phosphorus (equivalent to P2O3).

[0080] Alternatively, depending on the requirements, the sodium (Na) content in the particles exceeding 45 μm and below 75 μm can be made to be less than 0.010% by mass, and the purity of MgO in the magnesium oxide powder can be 95% by mass or more.

[0081] Furthermore, thinner steel sheets improve (reduce) iron loss, which is preferable; however, thinner steel sheets can easily lead to deterioration of the shape of the annealed coil. In such cases, the annealing separator of the present invention is preferred. It is particularly preferred when applied to thin steel sheets with a thickness of 0.20 mm or less, compared to conventionally known annealing separators. It should be noted that the lower limit of this sheet thickness is approximately 0.05 mm.

[0082] Example

[0083] Using basic magnesium carbonate (MgCO3)4Mg(OH)2·xH2O manufactured by Fujifilm and Kojun Pharmaceutical Co., Ltd. as the starting material, the starting material was slurried with pure water. Boric acid (H3BO3), magnesium sulfate (MgSO4), and disodium hydrogen phosphate (Na2HPO4·12H2O) were then added to the slurry to adjust the amount of trace components in the calcined magnesium oxide. The adjustment was made appropriately based on the amount added to the slurry, the calcination temperature, and the degree of water washing of the filter cake. The slurry was pressed using a filter press to obtain a filter cake. Next, the filter cake was placed in an alumina crucible and calcined in air in a box furnace at the temperature listed in Table 4 for 20 minutes. After calcination, it was pulverized, and the particle size was adjusted using a sieve to prepare powdered raw materials 4-1 to 4-10 for annealing separation agents.

[0084] Magnesium chloride hexahydrate manufactured by NACALAI TESQUE, INC. was dissolved in pure water maintained at 25°C to prepare a saturated aqueous solution. This solution was then reacted with sodium hydroxide to obtain magnesium hydroxide. The resulting magnesium hydroxide was filtered and washed with water. The residual sodium (Na) content in the magnesium hydroxide was adjusted by varying the washing time. This magnesium hydroxide was then added back to pure water to prepare a magnesium hydroxide slurry. Boric acid (H3BO3), magnesium sulfate (MgSO4), and diammonium phosphate ((NH4)2HPO4) were added to this slurry to adjust the amount of trace components in the calcined magnesium oxide. This adjustment can be made appropriately based on the amount added to the slurry, the calcination temperature, and the degree of washing of the magnesium hydroxide filter cake. The slurry was pressed using a filter press to obtain a filter cake. Next, the filter cake was placed in an alumina crucible and calcined in air in a box furnace at the temperatures listed in Table 4 for 20 minutes. After calcination, the cake was pulverized and the particle size was adjusted using a sieve to prepare powdered raw materials 4-11 to 4-16 for annealing separation agents.

[0085]

[0086] The annealing separator powder raw materials 4-1 to 4-16, as adjusted as described above, are mixed as shown in Table 5 to obtain annealing separator powders 5-1 to 5-28 with various particle size distributions and compositions.

[0087]

[0088] Next, a steel billet containing C: 0.06 wt%, Si: 2.95 wt%, Mn: 0.07 wt%, S: 0.015 wt%, Sb: 0.015 wt%, and Cr: 0.03 wt%, with the remainder being Fe and unavoidable impurities, is heated at 1350°C for 40 minutes and then hot-rolled to a plate thickness of 2.6 mm. It is then subjected to hot-rolled annealing at 900°C for 60 seconds, followed by intermediate annealing at 1050°C for 60 seconds. The plate is cold-rolled to a final thickness of 0.20 mm. After decarburization annealing, which also serves as recrystallization annealing, the powders (5-1 to 5-28) listed in Table 5 are coated as annealing separating agents. The heating rate is set to 25 °C / h up to 1200 °C, and the atmosphere is set to a mixed atmosphere of 75 vol% nitrogen and 25 vol% hydrogen. The plate is then held at 1200 °C in a 100 vol% hydrogen atmosphere for 20 h to perform final annealing, followed by smoothing annealing.

[0089] The magnetic flux density, repeated bending characteristics, uniformity of film appearance and film adhesion of the obtained samples were investigated, as well as the shape of the roll and the roll cutting ratio after final annealing.

[0090] Magnetic flux density and repeated bending characteristics were determined using the method of JIS C 2550 (2000). Here, magnetic flux density is expressed as the magnetic flux density when excited at 800 A / m.

[0091] It should be noted that, regarding repeated bending characteristics, as shown in Table 6, annealing separator powder 5-1 showed 2 times, annealing separator powder 5-26 showed 1 time, and all others showed values ​​of more than 10 times, which is good.

[0092] For the uniformity of the coating appearance, by visual inspection, areas with different hues accounting for less than 20% of the total surface area are evaluated as uniform, while those exceeding 20% ​​are evaluated as non-uniform. For the coating adhesion, the sample is cut 280 mm along the rolling direction and 30 mm at the right angle to the rolling direction, then subjected to stress-relief annealing at 820°C in a nitrogen atmosphere for 3 hours. The steel plate is then pressed onto round bars with various inner diameters (5 mm units), and the minimum diameter (mm) that does not produce peeling is measured. If it is below 40 mm, it is evaluated as good.

[0093] Regarding the shape of the annealed roll material, after the roll material cools to room temperature, as follows: Figure 1 (b) Figure 2 (b) The radius (r) (mm) of the inscribed circle of the outer periphery of the roll before annealing and the radius (R) (mm) of the inscribed circle of the outer periphery of the roll after annealing are measured from the diagram observed above, and the value of (Rr) (mm) is calculated. If the value of (Rr) (mm) is 20 mm or less, it is evaluated as good.

[0094] Table 6 shows the composition (mass ratio and trace component amount) of the annealing separating agent powder and its trace components, the composition of particles larger than 45 μm and smaller than 75 μm, the shape of the roll after annealing, the roll cutting ratio, the uniformity of the coating appearance, the coating adhesion, the magnetic flux density, and the number of repeated bending cycles used in the experiment.

[0095]

[0096] As shown in Table 6, when the trace component amount of the annealing separator powder is outside the scope of the invention, the magnetic flux density deteriorates, the appearance of the film becomes uneven, or the adhesion of the film deteriorates. Furthermore, when the mass proportion of powder exceeding 45 μm but below 75 μm is high, pitting occurs. When the trace component amount of powder exceeding 45 μm but below 75 μm exceeds the scope of the invention or the mass proportion of such powder is too low, the shape of the annealed roll becomes poor. As a result, the roll cutting ratio (i.e., the proportion of waste due to poor shape) becomes greater than 1.0% by mass, thereby increasing manufacturing costs.

[0097] It should be noted that when the amount of Na in powders with a diameter greater than 45 μm and less than 75 μm is less than 0.010% by mass, the shape becomes better after annealing.

Claims

1. A powder for an annealing separator, characterized by, having magnesium oxide as a main component and containing B: 0.020 mass% to 0.200 mass%, SO3: 0.030 mass% to 1.000 mass%, and P2O3: 0.050 mass% to 1.000 mass%, particles of magnesium oxide having a particle size of more than 45 μm and 75 μm or less, the particles of magnesium oxide having a particle size of more than 45 μm and 75 μm or less contain B: 0.002 mass% or more and less than 0.020 mass%, SO3: less than 0.030 mass%, and P2O3: less than 0.050 mass% with respect to the mass of the particles having a particle size of more than 45 μm and 75 μm or less.

2. The annealing separator powder according to claim 1, wherein, sodium Na contained in the particles of magnesium oxide having a particle size of more than 45 μm and 75 μm or less is 0.010 mass% or less with respect to the mass of the particles having a particle size of more than 45 μm and 75 μm or less.

3. The annealing separator powder according to claim 1 or 2, wherein, the purity of the magnesium oxide is 95 mass% or more.

4. A method of manufacturing an oriented electromagnetic steel sheet, characterized by, a steel slab for an oriented electromagnetic steel sheet is subjected to hot rolling and cold rolling, and then subjected to final annealing after recrystallization annealing and decarburization annealing, and coating of an annealing separator, the annealing separator for use in the annealing separator contains the powder for an annealing separator according to any one of claims 1 to 3.

5. The method of producing an oriented electromagnetic steel sheet according to claim 4, wherein the thickness of the steel sheet is 0.05 mm to 0.20 mm.

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