JP3379061B2 - Grain-oriented electrical steel sheet having high-tensile insulating coating and its treatment method - Google Patents

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 having a high-strength insulating coating and a method for treating the insulating coating.

[0002]

2. Description of the Related Art Generally, the surface coating of grain-oriented electrical steel sheet is
A forsterite layer called a primary coating formed during high temperature finish annealing and a phosphate coating layer formed by applying a treatment liquid containing phosphate as a main component and baking during heat flattening of a steel sheet. It is composed of two layers. These insulating coating layers are required to have electrical insulating properties, but in addition to insulating properties, various coating properties such as heat resistance, slipperiness, and adhesion are also required. Then, as one of the important characteristics of the insulating coating of the grain-oriented electrical steel sheet, there is a method of applying tension to the steel sheet to improve the magnetic characteristics of the grain-oriented electrical steel sheet.

By applying tension to the grain-oriented electrical steel sheet, the iron loss of the grain-oriented electrical steel sheet is improved, and it is one of the main causes of noise in a transformer manufactured using the grain-oriented electrical steel sheet as an iron core. It is also known to be effective in reducing magnetostriction. In addition, it takes various manufacturing steps to process the grain-oriented electrical steel sheet into an iron core such as a transformer, but when this iron core is manufactured, heat resistance, slipperiness, and adhesion are poor. It is also necessary to maintain these coating characteristics in the insulating coating of the grain-oriented electrical steel sheet, because the coating may peel off during stress relief annealing or the steel sheets may not be laminated smoothly and workability may deteriorate. .

Japanese Examined Patent Publication No. 53-28375 discloses an insulating coating solution containing a phosphate, chromate and colloidal silica of a specific composition as main components on a forsterite coating formed on the surface of a steel sheet after finish annealing. Is disclosed to form an insulating coating having a high tension on the surface of a steel sheet by coating and baking to reduce iron loss and magnetostriction of the grain-oriented electrical steel sheet.

Although various film characteristics are remarkably excellent and film tension is improved by the technique disclosed in the above-mentioned publication, since energy problems and environmental problems are recently highlighted, the efficiency of transformers is improved. And noise reduction is required. Therefore, since the grain-oriented electrical steel sheet, which is the iron core material of the transformer, is required to have further improved magnetic properties, the insulating coating having the iron loss improving effect and the magnetostriction improving effect of the grain-oriented electrical steel sheet is also further improved. There is a demand for higher tensile strength and higher performance, and various methods for improving coating properties have been proposed.

Further, in JP-A-61-41778, insulation is obtained by coating and baking an ultrafine particle colloidal silica having a particle size of 8 μm or less, a treatment liquid containing a specific ratio of primary phosphate and chromate. A method is disclosed in which the high tension of the coating is maintained and the lubricity of the coating is improved.

In the technique disclosed in the above publication, the use of ultrafine particle colloidal silica increases the specific surface area of the colloidal silica and strengthens the binding force, thereby increasing the tension imparting force to the steel sheet. To do. Although the technique disclosed in the above publication maintains high tension and further improves the lubricity of the insulating coating, the ultrafine particle colloidal silica is highly reactive and easily aggregates in the treatment liquid, or is produced. There is a problem that the cost becomes high, and an insulating coating treatment technique using colloidal silica which is stable and inexpensive in industry has been desired.

[0008]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention The present invention improves the properties of an insulating coating formed on the surface of a grain-oriented electrical steel sheet by coating and baking it in the final step of the production of grain-oriented electrical steel sheet, thereby improving various coating characteristics such as adhesion. It is an object of the present invention to obtain a grain-oriented electrical steel sheet having a high-strength coating, which is excellent in quality and is far superior to conventional ones.

[0009]

The gist of the present invention is as follows. (1) The surface has an insulating coating containing phosphate, chromate, and colloidal silica having a glass transition point (Tg point) of 950 ° C to 1200 ° C as main components, and the amount of adhesion is 2 to
A grain-oriented electrical steel sheet having a high-strength insulating coating, characterized in that it is 7 g / m ² .

(2) On the surface, phosphate, chromate and colloidal silica are the main components, and 40% or more of the total colloidal silica has a glass transition point of 950 ° C to 12 ° C.
A grain-oriented electrical steel sheet having a high-strength insulating coating having an insulating coating of colloidal silica at 00 ° C. and having an adhesion amount of ² to 7 g / m ² .

(3) C: 0.005% or less, Si:
Containing 2.5-7.0%, average crystal grain size is 1-10mm
(1) or (2) described above on the surface of the grain-oriented electrical steel sheet having a deviation of an orientation of 8 ° or less in the rolling direction on average with respect to the ideal orientation of the crystal orientation of (110) [001]. A grain-oriented electrical steel sheet having a high-strength insulating coating, characterized in that

(4) In a method of forming an insulating coating by applying a treatment liquid containing phosphate, chromate and colloidal silica to a grain-oriented electrical steel sheet as a main component, a glass transition point is 950 ° C to 1200 ° C. C, and the average particle size is 8 to 20
1 to 100 parts by weight of colloidal silica of nm
45-225 parts by weight of Al, Mg, Ca phosphate 1
At least 800 ° C. and 1000 ° C. by applying a treatment liquid containing one or more kinds and 10 to 45 parts by weight of chromate in terms of CrO _{3 with} respect to 100 parts by weight of the colloidal silica.
A method for treating a grain-oriented electrical steel sheet having a high-strength insulating coating, which comprises performing a baking treatment at a temperature of less than 1.

(5) The method for treating a grain-oriented electrical steel sheet having a high-strength insulating coating according to the above (4), wherein the colloidal silica contains 100 to 300 ppm of chlorine ions.

(6) In a method of forming an insulating coating by coating a grain-oriented electrical steel sheet with a treatment liquid containing phosphate, chromate and colloidal silica as main components, 40% or more of the total colloidal silica is used. However, the glass transition point is from 950 ° C to 1
Colloidal silica having a temperature of 200 ° C. and an average particle size of 8 to 20 nm.
A treatment liquid containing 145 to 225 parts by weight of one or more kinds of Al, Mg and Ca phosphates and 10 to 45 parts by weight of chromate in terms of CrO ₃ is applied, and the temperature is 800 ° C. or higher. A method of treating a grain-oriented electrical steel sheet having a high-strength insulating coating, which comprises performing a baking treatment at a temperature of less than 1000 ° C.

(7) C: 0.005% or less, Si:
Containing 2.5-7.0%, average crystal grain size is 1-10mm
On the surface of the grain-oriented electrical steel sheet having a deviation of an orientation of 8 ° or less in the rolling direction on the average value with respect to the ideal orientation of (110) [001], the above (4), (5) or (6) A method for treating a grain-oriented electrical steel sheet having a high-strength insulating coating, which comprises performing the treatment described in (6).

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
First, in order for the insulating coating of the grain-oriented electrical steel sheet to give tension to the steel sheet, it is necessary that there is a difference in the coefficient of thermal expansion between the steel sheet and the insulating coating. When the coefficient of thermal expansion of the insulating coating is lower than that of the steel sheet, the steel sheet receives tensile stress and compressive stress is applied to the coating because the contraction of the steel sheet when baking the insulating coating is larger than that of the insulating coating. . Therefore, the tensile stress applied to the steel sheet can be further increased by reducing the coefficient of thermal expansion of the insulating coating.

The inventors of the present invention have conducted extensive studies to reduce the coefficient of thermal expansion of the insulating coating, and as a result, in the insulating coating containing phosphate, chromate, and colloidal silica as the main components, the glass transition point of colloidal silica. Has a large influence on the thermal expansion coefficient of the insulating coating, and the glass transition temperature is from 950 ° C to 1
It has been found that the film tension can be significantly increased by applying colloidal silica at 200 ° C.

Next, the method for forming an insulating film in the present invention will be described. When the present invention is applied, the grain-oriented electrical steel sheet after finish annealing may be a normal steel sheet having a forsterite coating or a steel sheet having no forsterite coating. Whichever steel plate is used, the excess annealing separator is removed by washing with water, followed by pickling treatment with a sulfuric acid bath or the like, washing treatment with water to perform surface washing and surface activation, and then coating.

In the present invention, the glass transition point is 950.
A treatment liquid for forming an insulating film, which contains colloidal silica, phosphate and chromate as main components, is used at a temperature of ℃ to 1200 ℃. The first feature of the present invention lies in the glass transition point of this colloidal silica. That is, the glass transition point, which is a thermal property of colloidal silica, is very high, unlike the colloidal silica which has been used for the insulating coating of the conventional grain-oriented electrical steel sheet.

Usually, colloidal silica is prepared by using a sodium silicate solution and converting SiO ₂ / Na ₂ O to 6 by using an ion exchange resin.
A sol of 0 to 30 is prepared, which is then aged at a high temperature to allow the polymerization reaction to proceed, and a dilute sol produced by an ion exchange resin is gradually added to obtain a stable colloidal silica.

As described above, since colloidal silica uses sodium silicate as a raw material, it usually contains a very small amount of sodium. Various factors such as particle size, specific surface area, and type and amount of anions added during production are involved in the reactivity of colloidal silica, but the reactivity of colloidal silica also changes depending on the sodium content. However, it is known that the greater the amount of sodium contained in the colloidal silica, the higher the reactivity of the colloidal silica.

Then, colloidal silica is added to and mixed with a solution containing phosphate and chromate as a main component to prepare an insulating coating treatment liquid, which is then applied to a steel sheet and baked to form the insulating coating. , Because it is better to use highly reactive colloidal silica to form a strong coating,
In the past, it was usual to use colloidal silica with a high sodium content.

However, when the sodium content of the colloidal silica is high, the glass transition temperature tends to be lowered, and the glass transition temperature of colloidal silica usually used for the insulating coating of grain-oriented electrical steel sheet is lower than 900 ° C. It is normal.

The present inventors also examined the anion added during the production of colloidal silica, and found that the colloidal silica using chloride ion had good reactivity with phosphate. It was

Next, the reasons for limitation of the present invention will be described. First, a feature of the present invention is that an insulating coating is formed of phosphate, chromate, and colloidal silica having a glass transition point of 950 to 1200 ° C. By setting the glass transition point of colloidal silica to 950 to 1200 ° C., a significantly higher tension than before is applied to the steel sheet during baking of the coating. When the glass transition point of colloidal silica is less than 950 ° C., high tension cannot be obtained, and therefore it is limited. On the other hand, if the temperature exceeds 1200 ° C., the reaction between the phosphate or chromate and the colloidal silica is poor, and the insulating coating is cracked to reduce the adhesiveness of the coating.

The amount of insulating film of the product is 2.5 to 7.0 g / m ²
Is. If it is less than 2.5 g / m ^2, it is difficult to obtain high tension, and the insulation and corrosion resistance are also reduced, resulting in 7.0 g / m ²
If it exceeds, the space factor will decrease and it will be limited.

Next, the reasons for limiting the manufacturing method of the present invention will be described. First, the mixing ratio of the colloidal silica and the phosphate used in the present invention is 10 in terms of solid content.
0 to 5 parts by weight of Al, Mg, Ca phosphate 145-
225 parts by weight are compounded. If it is less than 145 parts by weight, the tension effect cannot be sufficiently exhibited. On the other hand, if the content exceeds 225 parts by weight, the excess phosphoric acid content causes the so-called sticking property that is seized during annealing, and thus is limited.

The mixing ratio of the chromate is 10 to 45 parts by weight in terms of CrO _{3 based} on 100 parts by weight of colloidal silica in terms of solid content. If the amount is less than 10 parts by weight, the ability to fix the phosphoric acid component is not sufficient, resulting in poor sticking property, and if the amount exceeds 45 parts by weight, the treatment liquid tends to gel, which is a limitation.

Next, the baking temperature of the insulating coating in the present invention is 800 ° C. or more and less than 1000 ° C. If the baking temperature is less than 800 ° C, sufficient tension will not be exerted, and
If it exceeds 1000 ° C., the coating film is cracked, and the insulating property is deteriorated.

Next, the chloride ion contained in the colloidal silica solution is preferably 100 to 300 ppm.
If the chlorine ion content is less than 100 ppm, the reactivity improving effect is low, and if it exceeds 300 ppm, the corrosion resistance of the insulating coating formed tends to be reduced, so that it is limited.

The colloidal silica used in the present invention is
It is also possible to use it by mixing with ordinary colloidal silica having a glass transition point of about 900 ° C. In this case, the mixing ratio of the colloidal silica used in the present invention needs to be 40% or more of the total amount of the colloidal silica. This is because if the blending ratio is less than 40%, the effect of the present invention cannot be obtained.

Incidentally, the above-mentioned insulating film treatment is carried out by the method described in JP-A-7-26.
It contains C: 0.005% or less and Si: 2.5 to 7.0% produced by using the technique disclosed in Japanese Patent No. 8567, has an average crystal grain size of 1 to 10 mm, and has a crystal orientation. (1
10) The effect of further reducing the iron loss can be obtained by applying it to a grain-oriented electrical steel sheet having an average deviation of 8 ° or less in the rolling direction with respect to the ideal orientation of [001].

[0033]

EXAMPLES Next, examples will be described. [Example 1] Width 7 cm x length 300 cm from the same coil after final finish annealing of a grain-oriented electrical steel sheet having a thickness of 0.23 mm
The sample was cut out, and the annealing separator remaining on the surface was removed by washing with water and light pickling to leave a glass film, and then strain relief annealing was performed. Next, after preparing a phosphate solution with the compounding ratio shown in Table 1, the colloidal silica shown in Table 2 was used to apply an insulating coating solution having the composition shown in Table 3 so that the coating amount was 4 g / m ^2. After coating and baking, the coating properties and magnetic properties were evaluated. The results are shown in Table 4.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

[0037]

[Table 4]

Example 2 Using the technique disclosed in Japanese Patent Laid-Open No. 7-268567, a molten steel containing 3.25% Si was cast, and after heating the slab, hot rolling was performed.
The hot-rolled plate was annealed at 00 ° C. for 5 minutes and then cold-rolled to 0.
22mm thick. This steel sheet was heated to 850 ° C. at a heating rate of 400 ° C./second, decarburized and annealed, an annealing separator was applied, and 1200 ° C. × 20 hours of finish annealing were performed. The same operation as in Example 1 was performed from the same coil thus obtained, which had an average grain size of 7.5 mm and a crystal orientation of 6.5 ° on the average from the ideal orientation of (110) [001]. Then, using the phosphate solution of Table 1 and the colloidal silica of Table 2, an insulating film treatment solution having the composition shown in Table 5 was applied to the steel sheet at a coating amount of 4 g / m ² and baked, and then the film was formed. The properties and magnetic properties were evaluated. The results are shown in Table 6.

[0039]

[Table 5]

[0040]

[Table 6]

As a result of this test, the glass transition point was 950 ° C.
The insulating coating agent using colloidal silica at 1 to 1200 ° C. had a higher tensile strength and an excellent adhesiveness as compared with the comparative example, and the effect of improving the magnetic properties was good.

[0042]

According to the present invention, it is possible to obtain a grain-oriented electrical steel sheet having a large film tension applied to the surface of the steel sheet, good adhesion of the iron core material in the production of a transformer, and good magnetic characteristics.

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Claims (7)

(57) [Claims] 1. An insulating coating comprising, on its surface, a phosphate, a chromate, and a colloidal silica having a glass transition point (Tg point) of 950 ° C. to 1200 ° C. as a main component, and the amount of adhesion is 2 A grain-oriented electrical steel sheet having a high-strength insulating coating, characterized in that it is about 7 g / m ² . 2. The surface is mainly composed of phosphate, chromate and colloidal silica, and 40% or more of all colloidal silica has a glass transition point of 950 ° C. to 1200 ° C.
1. A grain-oriented electrical steel sheet having a high-strength insulating coating, characterized in that it has an insulating coating that is colloidal silica and has an adhesion amount of ² to 7 g / m ² . 3. C: 0.005% or less, Si: 2.5-
7.0%, the average crystal grain size is 1 to 10 mm,
The coating according to claim 1 or 2 is applied to the surface of a grain-oriented electrical steel sheet having an average deviation of 8 ° or less in the rolling direction from the ideal orientation of (110) [001]. A grain-oriented electrical steel sheet having a high-strength insulating coating. 4. A method of forming an insulating coating by applying a treatment liquid containing phosphate, chromate and colloidal silica as a main component to a grain-oriented electrical steel sheet, which has a glass transition point of 95.
145 to 100 parts by weight of colloidal silica having an average particle diameter of 8 to 20 nm at 0 to 1200 ° C.
Treatment containing 225 parts by weight of one or more kinds of phosphates of Al, Mg and Ca and 10 to 45 parts by weight of chromate in terms of CrO _{3 with} respect to 100 parts by weight of the colloidal silica. A method for treating a grain-oriented electrical steel sheet having a high-strength insulating coating, which comprises applying a liquid and performing a baking treatment at a temperature of 800 ° C or higher and lower than 1000 ° C. 5. The colloidal silica has a chloride ion content of 10
The method for treating a grain-oriented electrical steel sheet having a high-strength insulating coating according to claim 4, wherein the content is 0 to 300 ppm. 6. A method of forming an insulating coating by applying a treatment liquid containing phosphate, chromate and colloidal silica as main components to a grain-oriented electrical steel sheet, wherein 40% or more of all colloidal silica is contained. , Glass transition point from 950 ° C to 1200
145 ° C. and an average particle size of 8 to 20 nm, which is 145 with respect to 100 parts by weight of the total colloidal silica.
225 parts by weight of Al, Mg, and one or more phosphorus acid salts of Ca, CrO ₃ treatment liquid was applied containing a chromic acid salt of 10 to 45 parts by weight in terms, 800 ° C. or higher 10
A method of treating a grain-oriented electrical steel sheet having a high-strength insulating coating, which comprises performing a baking treatment at a temperature of less than 00 ° C. 7. C: 0.005% or less, Si: 2.5-
7.0%, the average crystal grain size is 1 to 10 mm,
The treatment according to claim 4, 5 or 6 is performed on the surface of a grain-oriented electrical steel sheet having a deviation of an orientation of 8 ° or less in the rolling direction as an average value with respect to the ideal orientation of (110) [001] crystal orientation. A method for treating a grain-oriented electrical steel sheet having a high-strength insulating coating.