JP3205165B2 - Grain-oriented electrical steel sheet having a coating with excellent water resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a grain-oriented electrical steel sheet having a coating mainly composed of aluminum borate crystalline, which is excellent in tension imparting effect and water resistance.

[0002]

2. Description of the Related Art In the case of grain-oriented electrical steel sheets, when used in transformers and the like, it is common to form a coating that has the properties of an insulating material to improve iron loss and that can apply tension to the steel sheet. is there. Conventionally, JP-A-48-3933
No. 8, a phosphate-based coating was generally used as a tension-imparting coating. However, recent grain-oriented electrical steel sheets are required to have a lower iron loss and a higher space factor, and as a result, thinner films having a higher effect of imparting tension are required. I have.

[0003] Japanese Patent Application No. 4-222849 (JP-A -6-6-6)
No. 5754) and No. 4-222850 (Japanese Unexamined Patent Publication No.
No. 65755) discloses an aluminum borate crystalline film capable of giving a larger tension than the conventional one, which has a greater effect of imparting a greater tension to a grain-oriented electrical steel sheet than a conventional phosphate-based film. Things. According to this coating, iron loss can be significantly improved without deteriorating the space factor of the transformer. However, the electromagnetic steel sheet having the aluminum borate crystalline coating has a problem that the coating may be altered or deteriorated due to a reaction with moisture in the air.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a grain-oriented electrical steel sheet having a coating having good water resistance and mainly composed of crystalline aluminum borate.

[0005]

According to the present invention, there is provided a glass having excellent water resistance, comprising a crystalline portion comprising aluminum borate in an amount of 50 vol.% Or more and the remaining portion containing at least one element selected from cerium and silicon. quality or, crystalline non aluminum borate, a grain-oriented electrical steel sheet having a coating of either or both. Where the total boron in the coating,
When the amount of aluminum is 100 parts by weight in terms of metaboric acid and alumina, the amount of cerium and silicon is 0.5 to 30.
Parts by weight.

It is considered that the reason why the water resistance of the film is poor is that a moisture absorbing component is present in the film. That is, Japanese Patent Application No. 4-2
In the aluminum borate crystalline film described in No. 22849 and the like, most of the aluminum borate crystal phase is hardly soluble in water. However, in reality, a process in a non-equilibrium state is generally used. It is considered that the unreacted boron component sometimes remains. Although the form of this boron component has not been determined yet, it is considered that it exists as boron oxide. Boron oxide is unstable at room temperature and takes in water to gradually become boric acid. Therefore, it is considered that the structure other than the aluminum borate crystals in the coating is extremely easily dissolved in water, absorbs moisture in the air and generates rust on the steel plate, or elutes in water in water and causes the coating to peel off. .

[0007] Since only boron is the element to be analyzed in the coating dissolution test in water, it is clear that the component having hygroscopicity is the boron component. The inventors have studied to add a suitable additive to the coating liquid for coating to make the boric acid component in the coating excellent in water resistance. The water resistance test of the coating was performed by immersing the steel sheet after the formation of the coating in hot water for a certain period of time and examining the weight change of the steel sheet before and after that. According to the elemental analysis, a steel sheet having a large weight loss has a high boron concentration in hot water, and a small weight loss means that the coating film has little elution into the hot water. Therefore, the change in weight of the steel sheet in this test method is a good index for the water resistance of the coating.

As a result, in addition to boron and aluminum, which are the main components of the coating, one or two of silicon and cerium are selected.
Coating containing the species of elements was found to be excellent in water resistance. The mechanism by which silicon and cerium improve the water resistance of the coating is that these elements sufficiently react with the unreacted boron component to form a water-stable crystalline or glassy phase. It is thought to be.

These elements may form a solid solution in the aluminum borate crystalline material. However, there is no problem in both the coating water resistance and the coating tension unless the amount of the solid solution disturbs the crystal structure of the aluminum borate. Therefore, aluminum borate crystalline in which a small amount of these elements are dissolved is also used in the coating of the present invention.
It can be included in the aluminum borate crystalline specified to occupy 0 vol.% Or more.

The simplest way to introduce these elements into the coating is to add them as additives in the coating material. That is, when an aluminum borate crystalline film is formed on a steel sheet, a raw material sol comprising boric acid and alumina sol is applied to the steel sheet, dried, and baked at 500 to 1000 ° C. for about 1 hour or less. Is preferably added to the raw material sol in the form of a salt or sol.

The amount of the element according to the invention in the coating is 0.5
The reason for limiting to 30 parts by weight is that if it exceeds 30 parts by weight, a glossy film may not be obtained after baking, and if the amount of the element is less than 0.5 part by weight, the coating of This is because improvement in water resistance cannot be expected. When the gloss of the film is poor, it is because defects such as cracks and abnormally grown grains have occurred in the film, and this is partly due to the formation of a large amount of compounds other than aluminum borate. For example, if the amount of silicon is too large, a large amount of SiO ₂ is generated, which may cause a coating defect.

When a film having good gloss cannot be obtained due to the conditions for forming the film, the content of the element can be reduced to such an extent that the water resistance is not deteriorated. However, when the total amount of boron and aluminum contained in the coating is 100 parts by weight in terms of metaboric acid and alumina, if the total content of at least one of cerium and silicon is less than 1 part by weight, the water resistance of the coating is reduced. No improvement in sex can be expected. The reason that the aluminum borate crystal is limited to 50 vol.% Or more is because the presence of aluminum borate crystal is a factor of the effect of imparting tension to the coating, and if the aluminum borate crystal content is less than 50 vol. This is because no effect can be expected and the superiority over the existing phosphate-based coating is lost.

[0013] For example, aluminum borate crystalline 4
When the volume is 0 vol.%, The effect of imparting tension to the steel sheet by the coating film is almost 40% when the aluminum borate crystalline is 100%. In practice, the coating components other than the crystalline aluminum borate also have some tensioning effect, so that the tensioning effect as a whole coating is somewhat higher than 40%. But,
In order to obtain a film utilizing the effect of imparting high tension of aluminum borate crystalline, it is necessary that the aluminum borate crystalline is 50 vol.% Or more.

The crystalline aluminum borate in this case is:
As described above, silicon, also contain minor amounts dissolved the aluminum borate in a range that does not alter the structure of the boron <br/> aluminum one or two cerium. Aluminum borate crystalline 50
In order to determine whether or not it is vol.% or more, the crystal phase is identified using a means such as electron beam diffraction. According to this, when the crystalline aluminum borate is less than about 50 vol.% Of the coating, the coating cannot be expected to have high tensile strength. The element contained in the present invention does not affect the film tension and the iron loss of the steel sheet as long as the content is within the range of the present invention. Therefore, the water resistance of the aluminum borate crystalline coating can be improved without impairing the effect of the coating. The coating according to the present invention is applicable not only to grain-oriented electrical steel sheets but also to non-oriented electrical steel sheets.

[0015]

EXAMPLES (Example 1 ) Metaboric acid, alumina sol and nitrate having the composition shown in Table 1 were sufficiently distilled water-distilled into a finish-annealed magnetic steel sheet (sheet thickness 0.22 mm) having a forsterite film. The sol produced by dispersing and dissolving was applied and dried. This was baked at 900 ° C. for 10 minutes in a nitrogen atmosphere having a hydrogen concentration of 25%. At this time, the cross section of the coating formed on the steel
Observation with a scanning electron microscope confirmed that 50 vol.% Or more of the aluminum borate crystalline of the coating was formed.

The sample thus obtained was immersed in hot water, and the weight loss of the steel sheet was examined. Furthermore, the film tension also evaluated rows that have a conjunction, the film tension is 1.0 kgf / mm ² or more
The obtained one was rated good in tension. As a result, Table 1
As shown in the figure, the weight loss of the steel sheet after the hot water test was
It is improved by a single or combined addition of arm.

[0017]

[Table 1]

(Example 2 ) Metaboric acid, alumina sol, nitrate, silica sol or tetraethoxysilane was distilled from the finish-annealed electrical steel sheet (sheet thickness 0.22 mm) having a forsterite film with the composition shown in Table 2. A sol prepared by sufficiently dispersing and dissolving in water was applied and dried. This was baked at 850 ° C. for 15 minutes in a nitrogen atmosphere having a hydrogen concentration of 20%. As in Example 1 , 50 vol.% Of aluminum borate crystalline
It was confirmed that the above was formed.

The sample thus obtained was immersed in hot water, and the weight loss of the steel sheet was examined. The film tension was also evaluated according to Example 1. As a result, Table 2
Weight loss of the steel sheet after the hot water test as shown in is improved by alone or combined addition of silica sol or tetraethoxysilane (TEOS).

[0020]

[Table 2]

[0021]

According to the present invention, it is possible to obtain a grain-oriented electrical steel sheet having a coating with high tensile strength and excellent water resistance.

──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Shuichi Yamazaki 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (56) References JP-A-6-65754 (JP, A) JP-A-56-81681 (JP, A) JP-A-54-143737 (JP, A) JP-A-52-153825 (JP, A) JP-B-39-24034 (JP, B1) (58) Int.Cl. ⁷ , DB name) C23C 22/00-22/86

Claims (1)

(57) [Claims] The method according to claim 1 Crystalline portion consisting aluminum borate and 50 vol.% Or more, cerium the rest, at least one element from among silicon, or glassy excellent in water resistance, crystal other than aluminum borate of quality, any one
A grain-oriented electrical steel sheet having a coating consisting of one or both . Here, when the total amount of boron and aluminum in the coating is 100 parts by weight in terms of metaboric acid and alumina , the existing amounts of cerium and silicon are 0.5 to 30 parts by weight.