JPH11181525A - Production of grain oriented silicon steel sheet excellent in magnetic property and film characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a grain oriented silicon steel sheet capable of giving excellent film characteristic and magnetic properties even in the case of a large sized silicon steel sheet coil and even in the case where MgO roasted in a rotary kiln is used as an essential component of a separation agent at annealing. SOLUTION: As MgO for a separation agent at annealing, MgO, prepared by roasting an Mg-element-containing raw material which forms MgO by roasting, hydrating the resultant MgO to form Mg(OH)2 having (4.0 to 15.0) m<2> /g specific surface area, 25-150 nm (c)-axis average diameter of crystallite, and 50 to 1,200 nm (a)-axis average diameter, and then roasting this Mg(OH)2 again in a rotary kiln, is used. This MgO has 40-100 sec 40%CAA value, 120-400 sec 80%CAA value, (12 to 35) m<2> /g specific surface area, and 0.7-2.8 wt.% 1 g. loss.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet used for an iron core of a transformer or a generator.
In particular, it is intended to obtain a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties by devising an annealing separator for forming a forsterite-based insulating coating.

[0002]

2. Description of the Related Art A grain-oriented electrical steel sheet is advantageous for magnetizing the direction of each crystal grain constituting the steel sheet (110) [00].
1) A steel sheet whose orientation is aligned using the secondary recrystallization phenomenon. Secondary recrystallization consists of AlN, Mn finely dispersed and precipitated in steel.
Inhibitors such as S and MnSe use the function of suppressing the growth of primary recrystallized grains, and this allows abnormal grains to grow only in nuclei with excellent crystal orientation, resulting in a product with a crystal structure consisting of grains with excellent orientation. Have gained. In general, such grain-oriented electrical steel sheets are prepared by dispersing the inhibitor finely in the steel by a hot rolling process, making the final sheet thickness by a cold rolling process and optimizing a crystal structure, and performing secondary recrystallization in final finishing annealing. At the same time, it is manufactured by forming a forsterite ceramic coating on the steel sheet surface.

[0003] This forsterite-based insulating film is formed on the surface of a grain-oriented electrical steel sheet in the manufacturing process of the grain-oriented electrical steel sheet by the following method. An electrical steel sheet cold-rolled to a desired thickness is subjected to primary recrystallization annealing (combined with decarburization annealing if necessary) at a temperature of 700 to 900 ° C. in wet hydrogen, and thereafter, an annealing separating agent containing MgO as a main component. Is applied and wound in a coil shape, and then subjected to secondary finish refining and final finish annealing for the purpose of purifying the steel sheet. At the time of this final finish annealing, the subscale containing SiO ₂ generated on the steel sheet surface by primary recrystallization annealing and the applied Mg
O 2 reacts to form an insulating film.

[0004] Such insulating coatings consist of a small amount of spinel (MgAl
_Although it may contain 2O ₄ ) or titanium nitride (TiN), it is composed of forsterite (Mg ₂ SiO ₄ ) as a main component.
Alternatively, it is called a forsterite-based coating, and determines the appearance of the product and the quality of the electrical insulation. In the case of a non-uniform coating, the production yield of the product is reduced. Furthermore, the process of forming a forsterite-based coating affects the inhibitor decomposition behavior of the steel sheet surface layer and is also involved in secondary recrystallization, so the quality of the forsterite-based coating has a considerable effect on the magnetic properties of the product. Effect. Therefore, improvement of the properties of the forsterite-based coating occupies an extremely important position as a production technique of grain-oriented electrical steel sheets.

It is known that MgO, which is one of the main components of the annealing separator as one of the raw materials for forming a forsterite film, has a great effect on the above-mentioned film formation reaction. It has been done. For example, in Japanese Patent Publication No. 41-3726, attention is focused on the primary particle size of MgO used as an annealing separator,
A method is proposed in which MgO of a type that facilitates the hydration reaction, which falls within the range of 0 to 280 mm (0.017 to 0.028 μm), is applied as a slurry, and the steel sheet is coated with substantially pure magnesium hydroxide. Have been. Also,
Japanese Patent No. 14162 discloses that MgO containing at least 70% of particles having a size of 3 μm or less obtained by calcining magnesium hydroxide having an impurity content of 0.2% or less in two stages of low temperature and high temperature is used. Has been proposed. Furthermore, Japanese Patent Publication No. 54-14566 discloses that particles having a size of
Inactive MgO containing ~ 20% has been proposed.

On the other hand, Japanese Patent Publication No. 57-45472 discloses a low-activity MgO having a predetermined purity, a specific surface area and a primary particle diameter, and having a narrow activity distribution in the evaluation of the activity by reaction with citric acid. Proposed. Japanese Patent Publication No. 56-15787 discloses a technique for controlling the total value of Ca and hydration in MgO within a predetermined range. Furthermore, JP-A-1-177376 discloses that the values of the contents of CaO and B and the value of citric acid activity in MgO to be calcined using magnesium hydroxide, magnesium carbonate and high-purity magnesium oxide as raw materials are within predetermined ranges. Controlled MgO has been proposed. Japanese Patent Publication No. 7-45322 proposes MgO ₂ in which a predetermined amount of a boron compound is added to Mg (OH) ₂ containing Cl and calcined under a high partial pressure of steam.

[0007]

Problems such as point defects (bare spots), poor adhesion, poor film formation (temper color), film pattern, white film, etc. of the film have been solved by these techniques. In recent years, the following new problems have arisen. In other words, in order to reduce the production cost of grain-oriented electrical steel sheets, the size of the coil has increased, and in order to reduce the production cost of MgO, a rotary kiln has been adopted instead of the conventional muffle furnace as its firing method. As a result of these changes in manufacturing technology, discoloration of the coating, deterioration of adhesion, and deterioration of magnetic properties have frequently occurred at the central portion in the width direction of the steel sheet.

As described above, the fortelite coating is formed at the time of final finish annealing by the reaction between the subscale containing SiO ₂ formed on the steel sheet surface after decarburizing annealing and MgO applied as an annealing separator. The timing of this reaction is important for controlling the coating and magnetic properties. For example, when the film formation reaction proceeds from a low temperature, the film has a temper color, a black pattern or a point-like defect, and the magnetic properties are deteriorated because secondary recrystallized grains having an inferior orientation grow. Conversely, when the film formation reaction proceeds at a high temperature, the film becomes a white film or poor adhesion, and the magnetic characteristics deteriorate due to poor secondary recrystallization. Therefore, it is important to control the activity of the film formation reaction, and it has been conventionally practiced to control the activity of MgO, which plays a part in the reaction. However, the reaction activity not only due Naturally activity of MgO, activity subscale containing SiO ₂ produced decarburization annealed sheet surface, and associated with the final finishing atmosphere coil layer during annealing doing.

For example, the activity of the subscale formed on the steel sheet surface by oxidation during the primary recrystallization annealing decreases as the primary recrystallization annealing temperature and the atmosphere oxidizability decrease.
Also, regarding the atmosphere between coil layers during final finish annealing,
It changes depending on the partial pressure of H ₂ O generated from the water of hydration of MgO in the annealing separator or the partial pressure of H _{2 in the} passing atmosphere. When the degree of oxidation of the atmosphere increases, the reaction is suppressed. In particular, as the size of the coil increases, the oxidizability of the atmosphere between the coil layers at the center of the coil becomes excessively high, and the tendency of occurrence of coating defects and deterioration of magnetic properties increases.

Conventionally, the coil of a grain-oriented electrical steel sheet is small, so that the change in the subscale activity due to the difference in the steel sheet composition and the change in the decarburization annealing temperature and the atmosphere oxidizing property is small. Since the activity distribution of MgO calcined in the furnace was extremely wide, it could be adequately dealt with, and the above problem did not occur. However, MgO calcined in a rotary kiln has an extremely narrow activity distribution as shown in JP-B-57-45472, which is sufficient for increasing the size of the coil and changing the activity of the surface subscale on the decarburized annealed sheet. It was not possible to cope with the problem, and the above-mentioned problems of coating defects and deterioration of magnetic properties at the central portion in the width direction of the steel sheet occurred, and became a serious problem. In addition, MgO fired in a rotary kiln has extremely excellent uniformity within the firing lot, but the short baking time causes large variations between lots. There is also the problem of doing so. The application of the above-mentioned prior art to these problems could not produce an effective effect, and a solution was needed.

Furthermore, MgO calcined in a rotary kiln
As a specific problem, when applying an annealing separator to the coil,
MgO tends to agglomerate in the slurry, causing the viscosity of the slurry to decrease, resulting in uneven application, clogging of pipes, and agglomerates adhering to the steel sheet surface, causing defects in the steel sheet, such as pressing defects. Occurred and needed a solution.

[0012] This problem is advantageously solved, and even in the case of a coil of a large magnetic steel sheet, even when MgO of rotary kiln firing is used as a main component of the annealing separator, excellent coating properties and magnetic properties can be obtained. It is an object of the present invention to disclose the technology of MgO 2 used as an annealing separator for the production of magnetic steel sheets and to propose a technique for producing excellent grain-oriented electrical steel sheets.

[0013]

SUMMARY OF THE INVENTION In order to determine the cause of the above-mentioned problems, the present inventors have investigated the use of MgO calcined in a rotary kiln.
A detailed investigation of the surface properties of showed that the surface of MgO was smooth, for example, weakly reactive with acids, extremely chemically stable and of low activity.
I thought it might be the cause of various problems. For comparison, the surface properties of MgO fired in a conventional muffle furnace were examined, and the surface was diverse and varied depending on the MgO particles.Some of the surfaces were similar to the surface properties of MgO in the rotary kiln firing described above. Intense, highly reactive with acids
There were many MgO particles.

Therefore, a method of firing MgO particles having high reactivity with an acid in a rotary kiln was considered. First, it is easy to think that it is sufficient to lower the firing temperature when firing in a rotary kiln.However, depending on the method of lowering the firing temperature, even if MgO with high surface activity is obtained, CA
The powder properties of other MgO, such as A value, Ig.loss, and specific surface area, also changed significantly, and no suitable MgO was obtained as an annealing separator for the production of grain-oriented electrical steel sheets.

From there, while diligently searching for other methods,
By increasing the size of Mg (OH) ₂ , which is the raw material for MgO firing, and optimizing the crystallite size, the surface activity of MgO can be increased without changing other powder properties of MgO much. I discovered that. Based on this discovery, we have solved various problems when using MgO by rotary kiln firing,
Further, the present invention has been completed by effectively utilizing the advantage of the rotary kiln-fired MgO, that is, the uniformity of powder characteristics.

An experiment which led to the discovery of a solution to such a problem will be described below. 3.44 wt% of Si, 0.022 wt% of Al as an inhibitor component, 0.0085 wt% of N, 0.07 wt% of Mn
Prepare 7 coils of decarburized annealed steel sheet (sheet thickness 0.22mm, sheet width 1200mm, total weight 15 ton) containing wt%, 0.016wt% Se, and 0.036wt% Sb. Describe 7
After applying various kinds of annealing separators and winding up again, final finishing annealing was performed.

Each of the seven kinds of annealing separators has an 8%
Of TiO ₂ and 2% of SnO ₂ in MgO was used, but the following seven (A) to (G) types of Mg (OH) were used for MgO.
₂ as raw material before firing
What was produced by firing at 0 ° C. for 20 minutes was used. Also, (H) ~
MgO of (J) used as a conventional example was fired in a muffle furnace.

Here, (A) is obtained by reacting ionic bitter with lime milk using Mg (OH) ₂ as a starting material.
And used as a raw material before rotary kiln firing. (B)
Is obtained by calcining Mg (OH) ₂ ((A)) in a rotary kiln at 900 ° C. for 30 minutes to obtain MgO, and hydrating the MgO in water to obtain Mg (OH) ₂ as a raw material before the rotary kiln is calcined. . For (C), Mg (OH) ₂ was recovered by administering lime milk into seawater, washing and filtering the precipitate, and this was used as a raw material before firing in the rotary kiln. (D) was prepared above
Mg (OH) ₂ ((C)) was calcined in a rotary kiln at 950 ° C. for 30 minutes to obtain MgO, and this MgO was hydrated in water to obtain Mg (O).
H) ₂ was used as the raw material before rotary kiln firing. (E)
Was administered with lime milk in brine, and the precipitate was washed and filtered to recover Mg (OH) ₂ , which was used as a raw material before rotary kiln firing. (F) is the Mg (OH) prepared above
₂ Bake ((E)) in a rotary kiln at 920 ° C for 30 minutes
O 2, and the MgO ₂ was hydrated in water to obtain Mg (OH) ₂ as a raw material before rotary kiln firing. (G) is obtained by calcining basic magnesium carbonate in a rotary kiln at 980 ° C. for 30 minutes to obtain MgO, and further hydrating the MgO in water to obtain Mg (OH) _2.
As raw materials before rotary kiln firing. (H) is
Using ion bitter as a starting material, it is reacted with lime milk to produce Mg (OH) ₂ , which is then heated at 950 ° C in a muffle furnace at 1 ° C.
It was calcined for a period of time to obtain MgO. (I) was prepared by baking basic magnesium carbonate in a rotary kiln at 980 ° C. for 30 minutes to obtain MgO. For (J), lime milk was administered into seawater, and the precipitate was washed and filtered to recover Mg (OH) ₂ , which was calcined in a muffle furnace at 950 ° C. for 1 hour to obtain MgO.

The powder properties of these MgOs and the
Table 1 shows the coating properties and magnetic properties of grain-oriented electrical steel sheets produced by applying MgO as an annealing separator.

[0020]

[Table 1]

As shown in Table 1, although the powder characteristics of any MgO are not so different, once baked MgO is further hydrated to obtain Mg (OH) ₂ and again baked in a rotary kiln.
When MgO of (B), (D), (F), and (G) is used as an annealing separator, extremely excellent magnetic properties and coating properties can be stably obtained.

The reason for obtaining the above favorable results is that the inventors have made intensive studies and found that MgO was hydrated.
Mg (OH) ₂ ungated, obtained by firing again (B), (D), (F),
It was found that the surface of MgO of (G) was highly uneven, and the surface activity was chemically high. Furthermore, as a result of the first baking, the impurity components of S, C, and Cl dissipate in the gas phase in the form of SO ₂ , CO ₂ , and Cl ₂ , resulting in the baking of MgO with excellent purity. Do you get it. Furthermore, although the application of these annealing separators to steel sheets was extremely easy, Mg
The dispersion state of O in the slurry was found to be extremely good.

In general, it has been found that MgO having a highly irregular surface and a chemically high activity can be obtained by calcining at a low temperature. Conventionally, MgO has been calcined in a muffle furnace.
Since MgO has a large sintering temperature distribution, it is known that MgO having such a high surface chemical activity exists in a certain range. On the other hand, it was fired in a rotary kiln
Since MgO had good uniformity of MgO particles, the surface activity of MgO prepared as an annealing separator for the production of grain-oriented electrical steel sheets was low. Moreover, with the rotary kiln,
MgO fired at low temperature to enhance surface activity cannot be used as MgO for an annealing separator for the production of grain-oriented electrical steel sheets because the powder properties are so different.

Therefore, the present inventors have conducted further intensive studies and have found that hexagonal plate-like particles of Mg (OH) ₂ (crystal system: hc
Coarsely increasing the size of p), that is, reducing the specific surface area of the particles and reducing the c of the crystallites constituting the Mg (OH) ₂ particles
By adjusting the shaft diameter of the shaft <001> and the shaft diameter of the a-axis <100>, the powder characteristics of the MgO 2 after firing remain almost the same.
They discovered that the surface roughness of MgO can be increased to increase the chemical activity.

As described above, the method of coarsening Mg (OH) ₂ particles before firing and adjusting the size of crystallites constituting the particles makes it possible to obtain the directionality which has been considered to be a problem inherent to MgO in rotary kiln firing. The non-uniformity of the magnetic properties and coating properties in the magnetic steel sheet coil and the variation in each coil chance are eliminated, and the excellent uniform powder characteristic of the rotary kiln enables the production of excellent grain-oriented magnetic steel sheets. Was. Furthermore, increasing the size of Mg (OH) ₂ before firing can improve the dispersibility of MgO in the annealing separator slurry and can eliminate the problems associated with the aggregation of MgO. Was.

To increase the size of Mg (OH) ₂ before sintering, it is generally sufficient to maintain Mg (OH) ₂ for low-temperature and long-time crystal growth during sintering of Mg (OH) _2. It is difficult to grow to the required size. Where Mg
As a raw material, coarse MgO obtained by firing a material containing Mg element produced from element-containing raw material or initial raw material at high temperature,
Coarse Mg (OH) easily by hydrating it
Discovered that ₂ can be generated. Where Mg
The substance containing is MgCl ₂ , basic magnesium carbonate, magnesium carbonate, Mg (OH) ₂ , and the initial raw material containing Mg element is seawater, brine, bittern, dolomite, calcareous dolomite, basic magnesium carbonate, etc. It is.

In general, when baking coarsened Mg (OH) ₂ particles, the sinterability of the MgO particles increases, and it becomes difficult to obtain MgO having proper characteristics. In contrast, Mg (OH) ₂
By adjusting the size of the crystallites that make up the particles, MgO
It has been found that the sinterability of the particles can be controlled and that proper characteristics can be easily obtained.

This is because the crystallites in the Mg (OH) ₂ particles have different crystal orientations, so that the orientation of MgO generated during sintering differs for each crystallite, and the sintering rate is suppressed. is there. In contrast, the size of the Mg (OH) ₂ particles is large,
In addition, when the crystallite size is large, the sintering reaction of MgO easily proceeds in the Mg (OH) ₂ particles, and it becomes difficult to control the characteristics of MgO.

Further, by firing at a high temperature of 850 ° C. or more, components such as Cl, SO ₃ and CO ₂ dissipate in the gas phase,
The high purity is suitable as MgO for the annealing separator for the production of grain-oriented electrical steel sheets.
H) It has been found that by containing an appropriate amount in ₂ , it is possible to obtain more suitable MgO for an annealing separator.

The present invention has been made without much effort based on such a finding, and its gist is described below. That is, after the slab for grain-oriented electrical steel sheet is made to have a final thickness by hot rolling and subsequent cold rolling, a primary recrystallization annealing is performed, and then an annealing separator containing MgO as a main component is applied to the steel sheet surface. In the method for producing a grain-oriented electrical steel sheet, which is wound in a coil shape and then subjected to final finish annealing, the following MgO for the annealing separator is used as the MgO for the annealing separator. Manufacturing method of electrical steel sheet. The Mg-containing material or a material containing Mg produced from the initial material is calcined to obtain MgO, and the MgO is hydrated to have a specific surface area of 4.0 to 15.0 m ² / g, a crystallite c-axis average diameter of 25 to 150 nm, a
An axis average diameter 50~1200nm of Mg (OH) _2, the Mg (OH) ₂ obtained by re-sintering in a rotary kiln, is 40% CAA value of 40
~ 100 seconds, 80% CAA value 120 ~ 400 seconds, specific surface area 12 ~
MgO (first invention) having 35 m ^{2 /} g and an Ig.loss of 0.7 to 2.8 wt%. In the first invention, a Mg-containing material or a material containing Mg produced from an initial material is heated to a high temperature of 850 ° C. or more. For producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties, characterized by hydrating MgO having a content of S, C, and Cl of 0.4 wt% or less, respectively, by baking at a temperature of 2 wt.
Invention), wherein in the first invention or the second invention, one or more of seawater, brine, bittern, and basic magnesium carbonate are used as the initial material containing the Mg element. And a method for producing a grain-oriented electrical steel sheet having excellent film properties (third invention), wherein the first invention or the second invention
In the present invention, when re-burning Mg (OH) ₂ in a rotary kiln, firing in a rotary kiln having a temperature uniformity in the circumferential direction of the rotary kiln of 10 ° C. or more, or a maximum value of a time change of temperature at a fixed point in the rotary kiln, is performed. It is characterized by using MgO with expanded activity distribution by changing one or more of the following: changing to 20 ° C / h or more, or mixing MgO calcined at different set temperatures in a rotary kiln. A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties (fourth invention). In the first invention, the second invention or the fourth invention, in the stage before refiring in a rotary kiln,
By adding a substance containing Ca and / or Cl,
0.10-1.0 wt% of Ca as content in MgO after re-firing,
A fifth aspect of the present invention is a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties, characterized by using MgO 2 in which Cl is adjusted to 0.01 to 0.08 wt%.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the constitutional requirements and the reasons for limiting the method for producing a grain-oriented electrical steel sheet according to the present invention will be described. The grain-oriented electrical steel sheet of the present invention is generally known C,
Steel containing inhibitor components such as Si, Mn and commonly known Al, S, Se, Sb, B, etc., is subjected to hot rolling and subsequent cold rolling to a final thickness, and then subjected to primary recrystallization annealing. It is manufactured by a series of well-known manufacturing processes in which an annealing separator is applied to the surface of a steel sheet, wound into a coil, and subjected to final finish annealing.

Here, the present invention is characterized in that MgO, which is a main component of the annealing separator applied to the steel sheet surface after the primary recrystallization annealing, uses MgO obtained under particularly limited production conditions. Thereby, a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties can be obtained.

[0033] That is, MgO for annealing separator used in this invention is a MgO powder obtained by firing Mg (OH) ₂ in a rotary kiln, the Mg (OH) ₂ prior to firing by a rotary kiln, the It is essential to control the size especially strictly. This size is controlled by the specific surface area of Mg (OH) ₂ , and it is necessary to suppress this value as low as 4.0 to 15.0 m ² / g, that is, it is necessary to increase the size. Here, when the specific surface area of Mg (OH) ₂ is smaller than 4.0 m ² / g, the sinterability of the generated MgO increases, and it becomes difficult to obtain the desired MgO characteristics at the time of firing, and conversely, 15 m ² / g Exceeds Mg (OH) ₂
Becomes too small, the surface activity of MgO after firing decreases, and the magnetic properties and coating properties of the grain-oriented electrical steel sheet become inhomogeneous in the coil and the quality deteriorates for each coil chance.

Next, in order to stabilize the excellent characteristics of MgO, it is necessary to optimize the size of the crystallites constituting the Mg (OH) ₂ particles. If the size of this crystallite is small, MgO generated during firing inside Mg (OH) ₂ particles will be composed of a large number of MgO with different crystal orientations, and the sintering rate of MgO will decrease, so the characteristics of MgO Control becomes easy. For this purpose, it is necessary that the average diameter of the crystallite of Mg (OH) ₂ be 25 to 150 nm on the c-axis and 50 to 1200 nm on the a-axis. If less than this range, MgO
Sintering is suppressed, and the desired powder characteristics cannot be obtained.
If it is larger than this range, the sintering of MgO proceeds rapidly, so that it is difficult to obtain desired properties of MgO.
Therefore, it is adjusted to the above range.

[0035] Note that the c shaft diameter and a shaft diameter of the Mg (OH) ₂ of the crystallites, the <001> direction and <100> direction of the shaft diameter of the single crystal constituting the Mg (OH) ₂ particles This is measured by excluding the contribution of the device-specific spread in the spread of the X-ray diffraction peak width.

MgO The Mg (OH) ₂ before the final firing is obtained by hydrating MgO obtained by firing a material containing an Mg element.

Here, the substance containing the Mg element is defined as Mg (OH) formed by adding lime milk or the like to bitterness, seawater, brine, dolomite water, etc. generated in the process of manufacturing salt or the like as an initial raw material. ₂ ) MgCl ₂ , basic magnesium carbonate, magnesium carbonate, and other substances that produce MgO 2 upon firing. Among them, it is desirable to use seawater, brine, bittern, or basic magnesium carbonate as the initial raw material because of its good quality and purity.

MgO obtained by calcining a substance containing a Mg element preferably contains S, C, and Cl as impurities in a content of 0.4% or less, respectively, and is calcined at a temperature of 850 ° C. or more. This makes it possible to effectively reduce the impurity components in MgO obtained by hydration and re-firing in the next step, and to reduce the grain orientation of the grain-oriented electrical steel sheet caused by excessive inclusion of these impurities in MgO. It is possible to prevent the occurrence of point-like coating defects.

Next, the purity of Mg (OH) ₂ before the final calcination is very good in the method of the present invention, so that the content of trace elements may be reduced to below an appropriate amount. It is preferable to add an effective trace component-containing substance to the intermediate substance from the raw material to before the final firing by the rotary kiln in order to improve the magnetic properties and coating properties of the grain-oriented electrical steel sheet. Components that are preferably adjusted include Ca, Cl,
B and S are 0.10 to 1.0 wt% and 0.01% respectively in MgO.
It is preferable to adjust the thickness within the range of 0.08 wt%, 0.04 to 0.5 wt%, and 0.01 to 0.4 wt% for stabilizing the film properties.
Of these, Ca and Cl are particularly important trace elements for obtaining good film properties.

The Mg (OH) ₂ thus produced is finally produced using a rotary kiln. Here, the rotary kiln is a general term for furnaces that fire while moving the object to be fired while the hearth rotates, but this enables MgO to be fired uniformly and produces extremely excellent grain-oriented electrical steel sheets. It becomes possible.

Conditions such as the firing temperature and time of MgO are adjusted so that the obtained MgO satisfies the following powder characteristics. 40%
And 80% CAA value for 40 to 100 seconds and 120 to 40 seconds, respectively.
For 0 second, the specific surface area value is 12 to 35 g / m ² , and the Ig.loss value is 0.7 to 2.8 wt%.

Here, CAA (Citric Acid Activity) measures the reaction activity of citric acid and MgO.
A 40% or 80% final reaction equivalent of MgO is administered to a 0.4N aqueous citric acid solution at 30 ° C and stirred and the time until the final reaction is reached (the time until the solution becomes neutral due to consumption of citric acid). )
Is measured and evaluated in this time. When each CAA value is less than the lower limit, the magnetic properties of the grain-oriented electrical steel sheet deteriorate, and many point-like coating defects occur in the coating of the steel sheet, and conversely, each CAA value exceeds the upper limit. As a result, the magnetic properties are similarly deteriorated, and the adhesion of the film is also deteriorated. Therefore,
It is necessary to control within the above range.

The specific surface area can be determined by a general measurement such as the BET method in which the surface area of a powder is determined based on the amount of gas adsorbed at one point or at multiple points. The specific surface area is 12 to 35 g / m ^2. It is necessary to control within the range. When the specific surface area is less than 12 g / m ² , the coating becomes white and the adhesion is deteriorated. Conversely, if it exceeds 35 g / m ² , many point-like film defects will be generated in the film.

Further, the value of Ig.loss is 0.7 to 2.8 wt%
It is necessary to adjust to the range. Ig.loss is Mg
The percentage of weight loss when O is heated to 1000 ° C.
A small amount of Mg mainly contained in MgO due to this Ig.loss
The (OH) ₂ content can be estimated. Traces in MgO
Mg (OH) ₂ needs to be present in a small amount in order to promote the film formation reaction, but if it is present in excess, it causes point-like film defects, so it is necessary to control it to the above range.

In order to enhance the effects of the present invention, in addition to the above-mentioned constituent requirements, it is preferable to expand the MgO activity distribution, which is effective for improving the coating characteristics and magnetic characteristics of the grain-oriented electrical steel sheet. It is. For this purpose, when re-firing MgO in a rotary kiln, the uniformity of the firing time may be reduced. Therefore, first, a method of mixing MgO fired at different set temperatures of the rotary kiln, and second, Baking in a rotary kiln with a temperature uniformity of 10 ° C. or more in the circumferential direction of the rotary kiln;
Any one or more of the methods of changing the maximum amount of time change of the temperature at a fixed point in the rotary kiln over time to 20 ° C. or more is more advantageously adapted, whereby Mg
The activity distribution of O 2 can be expanded, and the magnetic properties and coating properties of the grain-oriented electrical steel sheet can be further improved.

The thus-prepared MgO for an annealing separator according to the present invention is mixed with a known additive for an annealing separator such as TiO ₂ , SrSO ₄ , and SnO ₂ to obtain a directional electromagnetic material before final finishing. It is applied to a steel sheet. As a method of application, a conventionally known method such as a method of coating and drying after forming into a slurry or an electrostatic coating can be used. The coated steel sheet is wound into a coil,
It is subjected to final finish annealing. In the final finish annealing, secondary recrystallization, film formation, and purification of impurity components in steel are performed, and the basic characteristics of grain-oriented electrical steel products are obtained here. Thereafter, after removing the unreacted annealing separating agent, an insulating coating is applied and baked to serve as a flattening anneal as necessary, thereby obtaining a product.

A large number of grooves may be formed on the surface of the grain-oriented electromagnetic steel sheet in a direction transverse to the longitudinal direction of the coil for magnetic domain subdivision, and laser or plasma jet may be applied to the steel sheet surface after the final finish annealing. A magnetic domain refinement process by irradiation and distortion application or a magnetic domain refinement process by application of grooves with a projection roll may be performed.

[0048]

EXAMPLES (Example 1) 0.0011 wt% of C, 3.23 wt% of S
i, 0.07 wt% Mn, 0.018 wt% Se, 0.021 wt% Al,
The steel sheet contains 0.040 wt% of Sb and 0.008 wt% of N, and the rest consists of unavoidable impurities and iron and has a thickness of 0.22 mm, a width of 1000 mm, and a total weight of 15 tons after decarburization annealing. Prepare 10 coils of steel plate with a large number of grooves in the width direction with a width of 100 μm and a depth of 20 μm as a surface treatment, and 10 types of (K) to (T)
An annealing separator containing MgO as a main component was applied, wound up again, and then subjected to final finish annealing.

At this time, the annealing separator was 8% Ti
A mixture of O ₂ , 3% SnO ₂ and 2% Sr (OH) ₂ .7H ₂ O in MgO was used. MgO is described below.
Mg (OH) ₂ of types (K) to (S) were used as raw materials before firing, and all were manufactured using a rotary kiln while changing the firing temperature and time. As the MgO of (T), a material fired in a muffle furnace was used as a conventional example.

Here, (K) to (R) are obtained by reacting seawater as a starting material with lime milk to obtain Mg (OH).
Sample No. ₂ was prepared and subjected to MgO calcination by a first rotary kiln and subsequent rehydration, followed by second recalcination of MgO by a rotary kiln to obtain MgO for an annealing separator. Among them, (K) to (N) are Mg (O) containing low S, C, Cl (0.2 to 1.5%) by adjusting the purity, reaction rate and time of lime milk.
H) creating a _{2, (O) ~ (R} ) is MgSO _4, MgCO ₃ and MgCl
₂ of the above any one or two added to MgO before rehydration high S, made C, Cl-containing (1.0 ~4.8%) Mg and (OH) _2. The conditions for the first rotary kiln firing were as follows: (K) and (O) were at 800 ° C for 30 minutes, and (L)
(P) is 850 ° C for 20 minutes, (M) and (Q) are 850 ° C for 30 minutes, (N) and (R) are 900 ° C for 15 minutes.
And calcined for minutes. Table 2 shows the contents of impurities S, C, and Cl in MgO after the first firing.

[0051]

[Table 2]

The MgO was hydrated to obtain Mg (OH) ₂ ,
At this time, it takes a long time for each Mg (OH) _{2 to} have a specific surface area of 5.3 to 8.5 m ² / g and a c-axis average axis diameter as a crystallite.
The crystal was grown to a crystal having a diameter of 35 to 48 nm and an average a-axis diameter of 88 to 260 nm. Thereafter, each Mg (OH) ₂ is heated at 950 ° C. in a rotary kiln.
Then, the second baking was performed for 20 minutes in a furnace to obtain final MgO.

The MgO of (S) is the same as the initial Mg of (L) described above.
(OH) ₂ in a rotary kiln at 950 ° C
The firing was performed only once for 20 minutes to obtain the final MgO 2. Furthermore, MgO of (T) was used as Mg (OH) ₂ after rehydration of (L), and calcined in a muffle furnace at 950 ° C. for 90 minutes in a furnace.
MgO.

The final finish annealing conditions are as follows: up to 800 ° C.
N ₂ atmosphere, a mixed atmosphere of up to 800 to 1050 ° C. 25% of the N ₂ and 75% H _2, carried out in an H ₂ atmosphere until soaking 5 hours at up to from 1,050 to 1,150 ° C. and 1150 ° C., The temperature was lowered to 800 ° C. by forcible cooling in H ₂ , and a heat cycle and atmosphere in which 800 ° C. or less was cooled by N ₂ was employed. After the final finish annealing, after removing unreacted annealing segregation, a tension coat composed of 50% colloidal silica and magnesium phosphate was applied and baked to obtain a product.

From each product, a test piece of Epstein size was cut out from the whole in the sheet width direction along the rolling direction, subjected to strain relief annealing at 800 ° C. for 3 hours, and then the iron loss value W _{17 at} a magnetic flux density of 1.7 T was obtained. _{/ 50} and magnetic flux density B ₈ were measured. Further, the film appearance and the film adhesion at the center of the product sheet width where the film characteristics were the poorest were investigated. The film adhesion was evaluated by wrapping a steel sheet of the product around the cylinder and using the minimum diameter of the cylinder from which the film did not peel off. Table 3 shows the results of these investigations.

[0056]

[Table 3] As shown in Table 3, the MgO symbols (L) according to the present invention,
When (M), (N), (P), (Q), and (R) are made of MgO for annealing separator, grain-oriented electrical steel sheets with excellent coating properties and excellent magnetic properties Can be manufactured stably.

(Example 2) 0.05% by weight of C and 3.25% by weight of S
i, containing 0.08 wt% of Mn, 0.0012 wt% of B, 0.008 wt% of N, and the balance consisting of unavoidable impurities and iron with a thickness of 0.35 m
m, 1000mm wide, 15 tons gross weight cold rolled steel coil at 830 ° C as P (H ₂ O) / P (H ₂ ) in a 0.50 oxidizing atmosphere at a soaking temperature of 2 minutes for continuous decarburization annealing , An annealing separator consisting of MgO of (U) to (X) shown below and 4% of TiO ₂ , 3% of SnO ₂ and 2% of Sr (OH) _{2 respectively} added to the surface of each steel sheet The application chance was changed by 4 coils each time, and MgO was newly fired at each application opportunity, applied to the surface of the steel sheet and wound into a coil, and then subjected to final finish annealing at 1200 ° C. for 5 hours. A tension coating was applied and baked to serve as a flattening anneal to obtain a product. Table 4 shows the magnetic properties and coating properties of these products.

MgO of symbol (U): Mg (OH) ₂ produced by pouring lime milk into seawater is calcined at 900 ° C. to obtain S content, C content and Cl content of 0.15% and 0.05%, respectively. , 0.25% after confirming that the specific surface area
Mg (OH) _{2 with} 29.3 m ² / g, c-axis average axis diameter of 19 nm and a-axis average of 43 nm
Was manufactured and baked again in a rotary kiln at 940 ° C. for 30 minutes, and was 40% CAA value; 78 seconds, 80% CAA value;
Second, specific surface area: 17 m ^{2 /} g, Ig.loss: 0.84% (comparative example).

MgO of the symbol (V): Mg (OH) ₂ formed by adding lime milk to ion bitter is calcined at 900 ° C. to obtain an S content,
The C content and the Cl content are 0.32%, 0.15%, and 0.1%, respectively.
After confirming that it is 22%, it is further hydrated to give a specific surface area of 7.5 m ² / g, a c-axis average axis diameter of 44 nm, and an a-axis average of 148 nm.
Produce Mg (OH) ₂ and again use a rotary kiln at 940 ° C, 30
Min fired MgO, 40% CAA value; 79%, 80% CAA
Value: 282 seconds, specific surface area: 17 m ^{2 /} g, Ig.loss: 0.83%
(Invention example).

MgO of the symbol (W): Mg (OH) ₂ obtained by hydration under the same conditions as the symbol (V) was calcined again in a rotary kiln at 940 ° C. for 30 minutes. OH) ₂ is divided into three parts, and the furnace is kept at 900 ° C for 40 minutes, at 930 ° C for 30 minutes,
MgO mixed with MgO 2 baked at each condition for 15 minutes in an oven at 40 ° C., 40% CAA value; 73 seconds, 80% CAA value; 36
5 seconds, specific surface area: 17 m ^{2 /} g, Ig.loss: 0.95% (invention example).

MgO of symbol (U): Mg (OH) ₂ obtained by hydration under the same conditions as symbol (V) was calcined again with a rotary kiln. At this time, the set temperature of the rotary kiln was 930 ° C. MgO which was periodically fluctuated in the range of 30 ° C at the upper and lower limits at 10 minute intervals around the center, and calcined for 30 minutes as an in-furnace time, 40% CAA value; 68 seconds, 80% CAA value; 372 seconds, Specific surface area: 17 m ^{2 /} g, Ig.loss: 0.94% (Example).

[0062]

[Table 4]

As shown in Table 4, the Mg according to the present invention
When O (symbols (V) to (X)) was used, a good product was obtained with extremely stable coating characteristics and magnetic characteristics. In addition, MgO of the symbol (X) gave the best results.

Example 3 0.04 wt% of C and 3.09 wt% of S
i, containing 0.07 wt% of Mn, 0.020 wt% of Se, and 0.025 wt% of Sb, and the balance consisting of unavoidable impurities and iron, 2.4 m thick
m, hot-rolled steel coil 2 with a width of 1000 mm and a total weight of 15 tons
The book is subjected to hot-rolled sheet annealing at 950 ° C for 1 minute, cold-rolled to an intermediate sheet thickness of 0.55 mm, further subjected to intermediate annealing at 950 ° C for 1 minute, and then cooled to a final sheet thickness of 0.20 mm. Rolled. After this,
After subjecting to continuous decarburization annealing at 840 ° C as P (H ₂ O) / P (H ₂ ) in an oxidizing atmosphere of 0.60 for 2 minutes at a soaking temperature, the surface of each steel coil is shown below with (Y) and 1.5% TiO _{2 in} MgO of (Z)
And an annealing separator containing 2% SrSO ₄ and wound into a coil, then subjected to a final finish annealing at 1200 ° C for 5 hours, and then a tension coating is applied and baked for flattening annealing. And Table 5 shows the magnetic properties and coating properties of these products.

MgO of symbol (Y): Mg (OH) ₂ formed by adding lime milk to ion bitter is calcined at 950 ° C. to obtain a Ca content,
S content, C content, Cl content are 0.05wt%, 0.
After confirming that the content is 15 wt%, 0.08 wt%, and 0.003 wt%, Mg (OH) having a specific surface area of 8.7 m ² / g, a c-axis average axis diameter of 32 nm, and an a-axis average axis diameter of 480 nm is further hydrated. ₂ was manufactured and MgO 2 was calcined again at 930 ° C. for 20 minutes in a rotary kiln.
% CAA value; 65 seconds, 80% CAA value; 235 seconds, specific surface area;
12.5 m ^{2 /} g, Ig.loss: 0.97%, Ca content 0.05 wt%, S content 0.07 wt%, C content 0.03 as trace components
wt% and a Cl content of 0.002 wt% were obtained.

MgO of symbol (Z): Mg (OH) ₂ formed by adding lime milk to ion bitter is calcined at 950 ° C.
S content, C content, Cl content are 0.05wt%, 0.
15 wt%, 0.08 wt%, 0.003 After confirming that a wt%, after the CaO and MgCl ₂ was added in a small amount to this, the specific surface area by further hydrated 10.5 m ² / g, c-axis average axis diameter 28nm, a
Mg (OH) ₂ having an average shaft diameter of 450 nm was produced, and again MgO 2 baked in a rotary kiln at 930 ° C. for 20 minutes, 40% CAA value;
63%, 80% CAA value; 220 seconds, specific surface area: 13.2 m ² / g,
Ig.loss; 0.96%, Ca content as trace component
The values of 0.35 wt%, S content 0.07 wt%, C content 0.03 wt%, and Cl content 0.05 wt% were obtained.

[0067]

[Table 5]

As shown in Table 5, the Mg according to the present invention
In the case of using O (symbols (Y) and (Z)), a good product is obtained in both film properties and magnetic properties. Of MgO after re-firing
In MgO (symbol (Z)) with adjusted Ca and Cl contents, excellent products are obtained.

(Example 4) 0.04 wt% of C and 2.95 wt% of Si
%, 0.005 wt% of Nb and 0.02% of Sb as inhibitor components
After heating eight steel slabs containing 0 wt% and the rest unavoidable impurities and iron to 1200 ° C, total weight 20 tons, thickness
A 2.2 mm hot-rolled steel coil was used. At 950 ° C, 1
After hot-rolled sheet annealing for 0.3 minutes and cold-rolling to a sheet thickness of 0.34 mm, soak at 840 ° C as P (H ₂ O) / P (H ₂ ) in a 0.55 oxidizing atmosphere for 2 minutes Decarburization annealing was performed. Thereafter, the MgO of each of (A) to (H) used in the experimental example was applied to the surface of each steel coil.
And 3.5% of TiO ₂ and 2.0% of SnO ₂ were added to the annealing separator, wound into a coil, and then subjected to a final finish annealing at 1150 ° C. for 5 hours. The coating was applied and baked to produce the product. The magnetic and film properties of these products are shown in Table 6, together with the properties of MgO _{2 and} the properties of the intermediate product Mg (OH) ₂ before final firing.

[0070]

[Table 6]

When MgO (symbols (B), (D), (F), (G)) according to the present invention shown in Table 6 is used,
Good characteristics are obtained in both the film characteristics and the magnetic characteristics.

[0072]

As described in detail above, if a grain-oriented electrical steel sheet is manufactured using MgO for an annealing separator, which is a feature of the present invention, a grain-oriented electrical steel sheet having extremely excellent magnetic properties and coating properties can be obtained. Electromagnetic steel sheets can be stably manufactured.

Claims (5)

[Claims] 1. A slab for a grain-oriented electrical steel sheet is subjected to a hot rolling and a subsequent cold-rolling rolling step to a final sheet thickness, then subjected to a primary recrystallization annealing, and then to an annealing separator containing MgO as a main component on the surface of the steel sheet. In the method for producing a grain-oriented electrical steel sheet that is coated and then wound into a coil and subjected to final finish annealing, the following MgO is used as the MgO for the annealing separating agent. An excellent method for producing grain-oriented electrical steel sheets. The Mg element-containing material or a material containing Mg produced from the initial material is calcined to obtain MgO, and this MgO is hydrated to have a specific surface area of 4.0 to 15.0 m ² / g, a crystallite c-axis average diameter of 25 to 150 nm, Mg (O-axis average diameter 50-1200nm)
H) ₂ , and the Mg (OH) ₂ was recalcined in a rotary kiln to obtain a 40% CAA value of 40 to 100 seconds and an 80% CAA value of 120 to 400 seconds.
Second, the specific surface area is 12~35m ² /g,Ig.loss is 0.7 ~2.8 wt%
MgO. 2. A magnesium-containing material or a material containing Mg produced from an initial material is calcined at a high temperature of 850 ° C. or more to form S,
2. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein MgO having a content of C and Cl of 0.4 wt% or less is hydrated. 3. The magnetic property and coating according to claim 1, wherein one or more of seawater, brine, bitter, and basic magnesium carbonate are used as the initial raw material containing the Mg element. A method for producing grain-oriented electrical steel sheets with excellent properties. 4. When re-firing Mg (OH) ₂ in a rotary kiln, the rotary kiln should be fired in a rotary kiln having a temperature uniformity of 10 ° C. or more in the circumferential direction of the rotary kiln, or the maximum time change in temperature at a fixed point in the rotary kiln. Use MgO with an extended activity distribution by changing the value to at least 20 ° C / h or mixing MgO calcined at different set temperatures in a rotary kiln. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties according to claim 1 or 2. 5. In a stage before recalcination in a rotary kiln, by adding a substance containing Ca and / or Cl, Ca as a content in MgO after recalcination is 0.10 to 1.10.
The method for producing a grain-oriented electrical steel sheet according to claim 1, 2, or 4, wherein MgO adjusted to 0 wt% and Cl to 0.01 to 0.08 wt% is used.