JP2001303258A - Magnesia for annealing and separating agent of grain oriented silicon steel sheet and method for manufacturing the same and method for manufacturing grain oriented silicon steel sheet having excellent film characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of stably improving film characteristics in particular by improving magnesia which is an essential component of an annealing and separating agent. SOLUTION: The magnesia, which is powder of 30 to 120 s in citric acid activity of 40% CAA, 8 to 50 m2/g in specific surface area by a BET method and 0.5 to 5.2 mass % in hydration rate by ignition loss and containing the ruin of a base salt and in which the powder is 20 to 90 mass % in the content of a grain size 0.2 to 0.8 μm, 7 to 40 mass % in the content of a grain size 2.5 to 5 μm and >=50 mass % in the total of the content of the grain size 0.2 to 0.8 μm and the content of the grain size 2.5 to 5 μm, is used as the essential component of the annealing and separating agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grain-oriented electrical steel sheet used for iron cores of transformers and other electric devices,
The purpose is to improve the coating properties of grain-oriented electrical steel sheets by improving the annealing separator applied during the manufacturing process.

[0002]

2. Description of the Related Art The process of producing grain-oriented electrical steel is performed by subjecting a steel slab adjusted to a predetermined composition to cold rolling after hot rolling, then to decarburizing annealing, and then to secondary recrystallization. Generally, final finish annealing is performed. Among these steps, secondary recrystallization occurs during the final finish annealing, and coarse grains having uniform axes of easy magnetization in the rolling direction are formed, resulting in excellent magnetic properties. Since this final finish annealing is performed for a long time in the state where the steel sheet is wound in a coil shape,
For the purpose of preventing seizure of the steel sheet, it is customary to apply a magnesia-based annealing separating agent as a slurry suspended in water before the annealing.

[0003] In addition to the role of such an annealing separator, this magnesia reacts with an oxide layer mainly composed of SiO ₂ generated on the steel sheet surface by primary recrystallization annealing performed prior to final finish annealing. This has the function of forming a forsterite (Mg ₂ SiO ₄ ) film. This formed forsterite film acts as a kind of binder that adheres the phosphate insulating coating to be overcoated with the iron base, acts as its own insulating film, and imparts tension to the steel sheet. Has the function of improving magnetic characteristics. Therefore, it is necessary to form a forsterite film having a uniform thickness and good adhesion to the steel sheet, and therefore, the role of the annealing separator is great.

[0004] In addition to the above, the annealing separating agent also has an effect of changing precipitate formation, growth behavior and crystal grain growth behavior of a steel sheet to affect magnetic properties. For example, if the amount of water brought in when the magnesia is slurried is too large, the steel sheet is oxidized, the magnetic properties are deteriorated, and point defects are generated in the coating. It is also known that secondary recrystallization behavior changes when impurities contained in magnesia enter a steel sheet during annealing. Therefore, it can be said that the components and the mixing ratio of the annealing separator and the quality of the powder properties are important factors that influence the magnetic properties and the coating properties of the grain-oriented electrical steel sheet.

[0005] Therefore, various methods for improving the quality of the annealing separator have been proposed. For example, Japanese Patent Publication No. 57-4
No. 5472 discloses that, while keeping powder characteristics such as impurity concentration of SO ₃ and B, specific surface area and particle diameter within a specific range, and citric acid activity distribution within a predetermined range, good A technique for stably forming a stable film is disclosed. Also, Japanese Patent No. 2665451 discloses a method of controlling the reactivity of an alkaline earth metal by changing a firing temperature and mixing the alkaline earth metals to obtain powders having different activity distributions. Have been.

[0006] Although these methods can improve the coating characteristics of the grain-oriented electrical steel sheet to some extent, since the coating is formed while being wound on the coil, the coating rises between the outer winding portion and the inner winding portion of the coil. Due to different temperature speed and atmosphere,
It was difficult to obtain a good coating over the entire length of the coil. For example, moisture in the atmosphere stays in the lower part of the inner winding part of the coil to cause a coating failure, or the upper part of the outer winding part is overheated, whereby the coating adhesion is reduced, or the outermost winding part or In several turns of the innermost part, patterns were generated as a result of being strongly influenced by the atmosphere.

As a method of improving such a situation and stabilizing the quality over the entire length of the coil, Japanese Patent Application Laid-Open No.
Japanese Patent Application Laid-Open No. 10721 and Japanese Patent Application Laid-Open No. 5-117756 disclose that formation is performed by changing the amount of oxygen per unit area after decarburizing annealing and the amount of application of an annealing separator in the longitudinal direction and width direction of the coil.

[0008]

Although these methods are effective, the operation becomes complicated, and when the coil is switched to the next coil, a portion where the oxygen weight or the amount of the separating agent applied becomes abnormal occurs. In some cases, the coil may be defective, or when a coil is wound, a gap may be left at the end, resulting in poor characteristics. Therefore, all of these techniques have limitations, and the above problems have not been sufficiently solved.

Particularly, in recent years, in order to improve magnetic characteristics,
There is a tendency to use materials containing a large amount of components that are disadvantageous for forming a film such as Sb, Bi and B in steel, and even if the above method is used, a good film cannot be obtained. It was frequent that poor film formation occurred partially in the coil.
Further, in recent years, there has been a strong demand from users for ordering so-called trimless materials that do not drop the coil ends by slits, and there has been an increasing demand for producing steel sheets having no coating defects even at the coil ends.

The present invention has been made in view of the above circumstances, and obtains a uniform coating over the entire surface of a coil without using a complicated method by improving magnesia as a main component of the annealing separator. The aim is to propose a method.

[0011]

That is, the gist of the present invention is as follows. (1) citric acid activity is 30 to 120 s in 40% CAA, BET specific surface area is in the amount of hydration 0.5 to 5.2 mass% by 8~50m ² / g and a loss on ignition, the ghosts mother salt Powder having a particle size of 0.2-0.8 μm and a content of 20-90 ma.
Content of ss% and particle size of 2.5-5 μm is 7-40 mass%
And a particle size of 0.2 to 0.8 μm and a particle size of 2.5 to 5 μm.
magnesia for an annealing separator for grain-oriented electrical steel, wherein the sum of the m and the content of m is 50 mass% or more.

(2) A method for producing magnesia for an annealing separator of grain-oriented electrical steel, comprising mixing two or more kinds of powders having different particle sizes to prepare magnesia according to (1).

(3) A steel material containing Si: 1.5 to 7.0 mass% is heated and then hot-rolled and subjected to one or more cold rolling operations including intermediate annealing to finish to a final sheet thickness. In the method for producing a grain-oriented electrical steel sheet comprising a series of steps of performing a primary recrystallization annealing, then applying and drying an annealing separator slurried with water, and then performing a final finish annealing, as the annealing separator, Item 1. A method for producing a grain-oriented electrical steel sheet having excellent coating properties, characterized by using a material mainly composed of magnesia according to Item 1.

Here, the citric acid activity is determined by comparing citric acid and Mg
It is a measurement of the activity of reaction with O. Specifically,
Temperature: 30 ° C, 0.4N final reaction equivalent of MgO in 0.4N citric acid aqueous solution, ie, 40% CAA (Citric Acid Activi).
The time until the final reaction, that is, the time until the citric acid was consumed and the solution became neutral was measured while administering and stirring at ty), and the activity of MgO was evaluated at this time.

The specific surface area by the BET method is a value obtained by calculating the surface area of the powder based on the one-point gas (N ₂ ) adsorption amount of the BET method.

Further, the amount of hydration due to loss on ignition is determined by MgO
The weight loss percentage when heated to a temperature of 1000 ° C,
Mainly, the content of a trace amount of Mg (OH) ₂ contained in MgO ₂ can be estimated.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted intensive studies on a technique for obtaining a uniform coating over the entire length of the coil, and as a result, by modifying the particle size of magnesia, which is the main component of the annealing separator, It was newly found that the desired coating was obtained. Hereinafter, an experiment which led to this finding will be described.

C: 0.04 to 0.05 mass%, Si: 3.3 to 3.4 ma
ss%, Mn: 0.06-0.075 mass%, Al: 0.02-0.03mass
%, Se: 0.018 to 0.020 mass%, Sb: 0.04 to 0.05 mass%
And N: 0.007 to 0.010 mass%, the balance being substantially Fe: a silicon steel slab consisting of substantially Fe, heated at 1623 K for 18000 s, and then hot-rolled to a plate thickness of 2.2 mm;
s, and then hot-rolled at 473 K to a thickness of 0.23 mm by a Sendzimir mill to finish to a final thickness. After decarburizing annealing, Table 1 shows Nos. 1, 3, 5 and 7.
For each 100 parts by weight of various magnesia powders having powder properties (hereinafter simply referred to as powder), an annealing separator containing 5 parts by weight of titania was applied in an amount of 15 g /
m ² , hydration temperature 293 K and hydration time 24000 s,
Coated and dried.

Then, after winding the steel sheet around the coil,
After the final finish annealing and the application of the insulating tension coating, baking was performed by heat treatment at 1073 K for 60 s, also serving as flattening. Table 2 shows the results of investigations on the magnetic properties and the coating properties of the coil thus obtained.
The particle size distribution in Table 1 was 3% hexametaphosphoric acid.
After performing ultrasonic dispersion at 300 W for 180 s with an aqueous solution, measurement was performed by using a laser diffraction type particle size distribution meter.

[0020]

[Table 1]

[0021]

[Table 2]

As is clear from Table 2, the coil using powder No. 7 has a uniform coating over the entire surface.
Good results were obtained for both coating adhesion and magnetic properties.
Powder No. 1 and Powder No. 1 used to obtain Powder No. 7
Powder No. 5 which was adjusted to the same average particle size as Powder No. 7 without blending the powder, had black streaks on the upper and lower portions of the inner winding side of the coil, A point-like coating defect occurred at the outer winding end.

Although the reason why such a result is obtained is not always clear, the present inventors consider as follows. In general, the smaller the particle diameter of the powder, the higher the surface ratio or the contact area between the powders increases, and the reactivity is said to be high, but if the particle diameter is too small,
Secondary agglomeration occurs and the contact area between the steel sheet and the powder decreases, and on the contrary, the coating reactivity decreases. Further, when such agglomeration progresses, it is considered that the gap between the particles has a non-uniform distribution between the agglomerated portion and the non-agglomerated portion in the coil plate surface, and this is considered to be a pattern of the coating film.

On the other hand, when the coarse particles are mixed as in the above experiment, the secondary aggregation of the fine particles is broken, so that the contact area with the steel sheet increases, and the above-mentioned in-plane area of the plate is reduced. Since the contact unevenness between the steel sheet and the powder is eliminated and fine particles are present, the reactivity is increased. As a result, it is considered that powder No. 7 in which coarse particles and fine particles are mixed ensures high reactivity.

On the other hand, the powder No.
1 is because magnesia particles are secondary aggregated.
The area of contact with the steel sheet is reduced, the reactivity is reduced, and the powder No. In No. 5, the reactivity decreases because the contact area between the steel sheet and magnesia is reduced and the particle size is too large. In addition, the powder No. 3 is the powder No. It has an average particle size similar to that of 7, but has low contact area and low reactivity. This is presumably because, as the average particle size is reduced, the contact area with the steel sheet increases, but the secondary contact of the magnesia occurs, so that the area in contact with the steel sheet decreases and the reaction becomes difficult.

By the way, JP-A-10-88244 and JP-A-2665451 describe that magnesia having different activities determined from the time of chemical reaction is mixed. Here, the chemical activity measurement such as citric acid activity measures the ease of reaction on the magnesia surface. For example, when there is a primary particle to which a large number of crystallites are bonded, each crystallite in the primary particle has a gap, and the reaction solution in the measurement enters the inside of the primary particle. This means that the easiness of the reaction is evaluated for the surface area corresponding to the surface area. Therefore, even if the powders have the same chemical activity, the particle size distribution is various.

On the other hand, in the present invention, in addition to the chemical activity, the particle size distribution of the powder including the primary particles as described above is optimized. As this primary particle,
Single or plural powders having a form of a mother salt in which individual crystallites are aggregated may be used.

Therefore, the conventionally known method of mixing powders having different chemical activities and the method of mixing powders having different particle size distributions so that the primary particle diameter of the present invention is appropriate are as follows. It has not been clarified until now that the coating is improved by mixing a plurality of powders of different particle sizes, each having a constant chemical activity and a constant chemical activity. The present invention does not require any particular change in the activity expressed in 40% CAA, but rather controls the particle size distribution in order to control the contact area between the powder particles and between the powder and the steel sheet. It is based on a new idea.

Next, the present invention will be specifically described. That is, it is necessary to satisfy the following items as powder characteristics of magnesia. Citric acid activity (40% CAA): 30 to 120 s If the citric acid activity described above is less than 30 s, the hydration amount is too large, while if it exceeds 120 s, the reactivity is too low, and all are good coatings. No characteristics can be obtained.

When the specific surface area by 8~50m ² / g above-mentioned BET method is more than 50m ² / g,: [0030] specific surface area by the BET method:
When the hydration amount of magnesia is too large, on the other hand, when it is less than 8 m ² / g, the reactivity is too low, and no good coating properties can be obtained.

Hydration by ignition loss: 0.5 to 5.2 mass% If the hydration by ignition loss is less than 0.5 mass%, the reactivity becomes too low, while if it exceeds 5.2 mass%, it is added during finish annealing. Due to oxidation, no good film properties can be obtained.

In addition to these conditions, the following components can be contained within a predetermined range as magnesia impurities. CaO content: 0.1 to 0.8 mass% When the CaO content is less than 0.1 mass%, the coating has no irregularities and tends to peel off. On the other hand, when it exceeds 0.8 mass%, the amount of the coating formed may be insufficient.

SO ₃ content: 0.03 to 0.5 mass% B content: 0.02 to 0.2 mass% Cl content: 0.002 to 0.1 mass% F content: 0.002 to 0.1 mass% In all cases, the reactivity of magnesia is adjusted, and if both are less than the lower limit, the reactivity is low, and if the upper limit is exceeded, point-like defects may occur.

Next, when the content of particles having a particle size of 0.2 to 0.8 μm is 20 to
90 mass% and content of particle size 2.5-5 μm is 7-40 mass
% And a particle size of 0.2 to 0.8 μm and a particle size of 2.5 to 5
It is important that the sum with the content of μm is 50 mass% or more. The particle size can be measured by using a 3% aqueous solution of sodium hexamethacrylate for 3 minutes at 300 W for ultrasonic dispersion, and then using a laser diffraction type particle size distribution meter.

First, in regulating the particle size distribution of magnesia, the crystal form of magnesia is at least 20 mass%.
% Or more is a powder having a form of mother salt. For example, when magnesium hydroxide is used as the mother salt, the magnesium hydroxide is in the form of a hexagonal disk, and when this is fired, depending on the firing temperature, a large number of holes are formed, and the ends are rounded by tightening. The polyhedral structure is formed by sintering and further sintering. Here, the form of the mother salt refers to a stage before the polyhedral structure is formed. This mass of mother salt is 20 mass
If it is less than 20%, the reactivity is reduced.

The content of particles having a particle size of 0.2 to 0.8 μm is 20 ma.
less than ss%, or the content of 2.5-5 μm is 40 mass%
If the content exceeds 0.2 mm, the contact area between the steel sheet and magnesia becomes too small. On the other hand, if the content of 0.2 to 0.8 μm exceeds 90 mass% or the content of 2.5 to 5 μm becomes less than 7 mass%,
Secondary agglomeration occurs and the contact area between the steel sheet and magnesia also decreases, resulting in poor adhesion of the coating. Furthermore, 0.2 to
The content of 0.8 μm and the total content of 2.5 to 5 μm are 50
When the content is less than mass%, the reactivity is reduced due to excessively large grains, seizure of magnesia on the steel sheet due to excessively fine particles, or the steel sheet is constituted only by powder having an intermediate particle size. Failure occurs due to a decrease in the contact area with magnesia.

In order to obtain the above particle size distribution, it is recommended to blend powders having different particle sizes. That is, a method of giving a distribution to the degree of baking without mixing by batch baking or the like and keeping the particle size distribution within the above range is inevitably different in activity between large particles and small particles. Therefore, it is difficult to obtain the desired effect of the present invention. However, even in the case of batch firing, if powders having various average particle sizes can be obtained, these can be mixed and used. The mixing time is not limited as long as mixing is performed at the time of slurry immediately before coating on the steel sheet. For example, raw materials having a target particle size after firing may be mixed and fired, or may be adjusted at the slurry stage. By the above treatment, excellent magnesia for an annealing separator can be obtained.

Next, a method for producing a grain-oriented electrical steel using this magnesia-based annealing separator will be described. First, the electromagnetic steel as a material is not particularly limited as long as it is a material for grain-oriented electromagnetic steel, and a typical component composition range is as follows. First, for C, there is a method in which C is reduced at the tapping stage so that decarburization annealing is not performed, and a method in which a certain amount is secured to improve the structure and then removed by decarburization annealing. In the former, the content is set to less than 0.01 mass% in order to avoid the adverse effect of C, and in the latter, the preferred range for improving the structure is 0.01 mass% or more and less than 0.10 mass%.

Further, Si is an essential component for increasing the specific resistance of the steel sheet and reducing the iron loss. However, when the content is less than 1.5 mass% or more than 7.0 mass%, the effect of reducing the iron loss becomes weak. Therefore, the range is 1.5 to 7.0 mass%.

In addition to C and Si, an inhibitor component is added. AlN, MnS, MnSe and the like are well known as inhibitors, but any of these may be used,
Further, two or more of these may be combined. When MnS and / or MnSe is used for the inhibitor, Mn is set to 0.03 to 0.3.
50 mass%, S and Se are contained in a total range of 0.01 to 0.03 mass%. When AlN is used as an inhibitor j, the Al content is set to 0.005 to 0.04 mass% and the N content is set to 30 to 120 ppm. In any case, if the ratio is lower than these ranges, the effect does not work as an inhibitor, and if the ratio is higher, the secondary recrystallization becomes unstable.

In addition to these main inhibitor components, Cu, Sn, Cr,
One or more of Sb, Ge, Mo, Te, Mo, Te, Bi, B, P, and V can be used.

As a concentration effective for the function as an inhibitor, the auxiliary inhibitor component is 0.01 ma in total amount.
It is ss% or more and 0.8 mass% or less. Each of these inhibitors can be used alone or in combination. In particular,
According to the present invention, good characteristics can be obtained even if a component which is disadvantageous for forming a film is added.

After these materials are hot-rolled by a known method, cold rolling is performed once or a plurality of times with intermediate annealing to obtain a final sheet thickness. Further, if necessary, the hot rolled sheet can be annealed before cold rolling. Next, after cold rolling, primary recrystallization annealing is performed, and a final finish annealing is performed after applying an annealing separating agent.

The main component of the annealing separator is preferably 60 ma
It is important to use the above-mentioned magnesia according to the present invention for ss% or more. Additives can also be used for this. Additives include Ti, Cr, Mn, Sr, Fe, Ni,
Oxides, hydroxides, sulfates, nitrates, sulfides, chlorides and the like of Cu, Sb, B, Sn, Al, Tl and Mg are used. Since the amount of chlorine added has a large effect on film formation with a slight amount of chlorine, a preferable range is 0.01 to 0.10 in terms of chlorine.
Parts by weight. That is, if the amount is less than 0.01 part by weight, there is no effect. If the amount is more than 0.10 part by weight, the coating peels off like a scale, resulting in poor adhesion.

As for oxides, hydroxides, sulfates, nitrates and sulfides, the effect is manifested by adding a larger amount than chlorides.
Parts by weight. If the amount is less than this range, there is no effect, and if it exceeds 20 parts by weight, the amount is excessively increased, and the coating and the magnetic properties are rather poor.

Further, since the magnesia of the present invention has an effect of making the contact between the steel sheet and the powder uniform, it can be used for the production of a steel sheet having a metallic luster by suppressing the formation of a forsterite film. is there. At this time, one or more of chlorides and calcium compounds are added to magnesia 10
0.5 to 20 parts by weight of chloride or 10 to 60 parts by weight of calcium compound is used based on 0 parts by weight. If chlorine in the annealing separator is present in a large amount, it has a function of peeling off the forsterite film. However, if it is less than this range, there is no effect, and if it exceeds this range, the magnetic properties are impaired. The calcium compound has a function of suppressing the formation of forsterite itself, and has no effect if it is less than this range, and impairs magnetic properties if it exceeds this range.

The amount of the annealed separating agent applied is 6 to 20 g / m ² on both sides, and the hydration temperature is about 277 to 313 K.
Normal conditions are sufficient. After the application of the annealing separator, final finishing annealing is performed. The final finish annealing may be performed by a known method.
After these series of treatments, a tension coating is applied and flattening annealing is performed to finish the product. By such a processing step, it is possible to obtain a grain-oriented electrical steel sheet with a high yield without a coil shape defect.

[0048]

EXAMPLES Example 1 C: 0.05-0.07 mass%, Si: 3.2-3.5 mass%, Mn: 0.
06-0.075 mass%, Al: 0.02-0.03 mass%, Se: 0.018
~ 0.021 mass%, Sb: 0.02 ~ 0.03mass%, Bi: 0.002 ~
Containing 0.005 mass% and N: 0.007 to 0.009 mass%,
The rest is a steel slab consisting essentially of Fe for 1800s at 1623K.
After heating, hot-rolled to a thickness of 2.2 mm, and then 1173
After performing hot-rolled sheet annealing at 60 Ks for 60 s, sandwich intermediate annealing at 1273 K for 60 s, and use a tandem mill to reduce the thickness to 0.23 mm.
It was cold-rolled at 3K and finished to the final thickness. Then, after the steel sheet was decarburized and annealed, the powder no. An annealed separating agent in which 7.2 mass% of titanium oxide and 2.7 mass% of strontium sulfate were added to various magnesia having powder characteristics of 7, 8, and 9, respectively, was applied in an amount of 13 g / m ^{2 on} both sides and water. Sum temperature:
293 K and hydration time: hydrated at 2400 sec, applied and dried.

Next, the steel sheet was wound into a coil and subjected to final finish annealing. Thereafter, an insulating coating was applied and baked at 1123 K for 60 s to also serve as heat flattening, and then magnetic domain refinement was performed by plasma irradiation. As shown in Table 3, the results of an examination of the coating properties of the steel sheet thus obtained show that excellent coating properties can be obtained by using magnesia according to the present invention as the main component of the annealing separator.

[0050]

[Table 3]

Example 2 C: 0.05-0.07 mass%, Si: 3.2-3.5 mass%, Mn: 0.
06-0.075 mass%, Se: 0.018-0.021 mass% and S
b: A steel slab containing 0.02 to 0.03 mass%, with the remainder substantially consisting of Fe, heated at 1623 K for 1800 s and then hot-rolled.
After 2 mm in thickness, hot-rolled sheet annealing at 1173 K for 60 s is performed, then intermediate annealing at 1273 K for 60 s is sandwiched, and cold-rolled at 393 K to 0.35 mm thickness using a tandem rolling mill. Finished thick. And after decarburizing annealing the steel sheet, the powder of Table 1
No. Various magnesia having powder characteristics of 10, 11 and 12 were mixed with an annealing separator containing 2.9 mass% of magnesium chloride, respectively. An application amount: 13 g / m ² , a hydration temperature: 293 K,
Hydration time: hydrated at 2400 s, applied and dried.

Next, the steel sheet was wound into a coil and subjected to final finish annealing. Thereafter, an insulating coating was applied and baked at 1123 K for 60 s to serve as heat flattening. The results of an examination of the coating properties of the steel sheet thus obtained are shown in Table 4. As shown in Table 4, it can be seen that the use of magnesia according to the present invention as the main component of the annealing separator makes it possible to obtain a steel sheet having a metallic luster on the entire surface of the coil. .

[0053]

[Table 4]

[0054]

By using the magnesia of the present invention as a main component of the annealing separator, especially the coating characteristics of the grain-oriented electrical steel sheet to which the annealing separator is applied can be stably improved.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01F 1/16 H01F 1/16 B (72) Inventor Atsuto Honda 1-chome, Mizushima Kawasaki-dori, Kurashiki City, Okayama Prefecture (Without address) Mizushima Steel Works, Kawasaki Steel Corporation (72) Inventor Michio Komatsubara 1-chome, Mizushima Kawasaki-dori, Kurashiki-shi, Okayama Prefecture BB10 CA16 CA18 CA32 CA33 CA36 DA02 DA11 EA17 EB02 EB11 4K033 RA04 SA01 TA02 5E041 AA02 BC01 CA02 HB05 HB07 HB11 HB14 NN05

Claims (3)

[Claims] 1. A citric acid activity of 30 to 120 at 40% CAA.
a powder having a specific surface area of 8 to 50 m ² / g according to the BET method and a hydration amount of 0.5 to 5.2 mass% due to loss on ignition, and containing a form of a mother salt; The content of 0.8 μm is 20 to 90 mass% and the content of particle size 2.5 to 5 μm is 7
Content and particle size of up to 40 mass% and particle size of 0.2 to 0.8 μm
A magnesia for an annealing separator for grain-oriented electrical steel, the sum of the content of which is 2.5 to 5 μm and which is 50 mass% or more. 2. A method for producing magnesia for an annealing separator of grain-oriented electrical steel, comprising mixing two or more kinds of powders having different particle sizes to prepare the magnesia according to claim 1. 3. A steel material containing Si: 1.5 to 7.0 mass% is heated and then hot-rolled and subjected to one or more cold rollings including intermediate annealing to finish to a final sheet thickness and then to a primary material. After performing recrystallization annealing, and then applying and drying an annealing separating agent slurried with water, in a method for producing a grain-oriented electrical steel sheet comprising a series of steps of performing final finish annealing, the method according to claim 1, wherein A method for producing a grain-oriented electrical steel sheet having excellent coating properties, characterized by using the one containing magnesia as a main component as described in (1).