JPH08325745A - Grain oriented silicon steel sheet with low core loss and its production - Google Patents

Abstract

PURPOSE: To provide a grain oriented silicon steel sheet having a film increased in a tension-giving effect and excellent in rust preventing property. CONSTITUTION: The tension film, having crystalline aluminum borate as a principal compound, contains alkali metal compound, silicon compound, and iron borate. This film can be obtained by applying a raw material solution, consisting of alkali-metal-elementcontaining compound, aluminum oxide precursor compound, silicon oxide precursor compound, and boric acid, to a finish-annealed grain oriented silicon steel sheet and then performing baking finish.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a unidirectional silicon steel sheet having low iron loss, excellent water resistance, and significantly less rust during storage, and a method for producing the same.

[0002]

2. Description of the Related Art One-directional silicon steel sheets are (110) [00
1) has a crystal structure with the main direction being [1] and is often used as a magnetic iron core material. In particular, a material having a small iron loss is required to reduce energy loss. As a means for reducing the iron loss of the unidirectional silicon steel sheet, the steel sheet surface after finish annealing is irradiated with a laser beam to give a local strain,
Japanese Patent Application Laid-Open No. 58-26 discloses a method for subdividing magnetic domains.
It is disclosed in Japanese Patent No. 405. Further, there is a magnetic domain refining means which does not lose its effect even after performing stress relief annealing (stress relief annealing) after iron core processing, for example, JP-A-62-861.
No. 75 publication.

On the other hand, since iron alloys containing iron and silicon have large crystal magnetic anisotropy, application of external tension causes subdivision of magnetic domains, which reduces eddy current loss which is a main factor of iron loss. You can Therefore, it is effective to apply tension to the steel sheet in order to reduce the iron loss of the unidirectional silicon steel sheet containing 5% or less of silicon, and it is effective to apply the tension up to about 1.5 kgf / mm ^2. It is known that the loss can be reduced. This tension is usually given by the film formed on the surface.

Conventionally, for unidirectional silicon steel sheets, a primary coating mainly composed of forsterite formed by a reaction between an oxide on the surface of the steel sheet and an annealing separator in the finish annealing step, and Japanese Patent Laid-Open No. 48-39338. 1.0 kgf / mm when the plate thickness is 0.23 mm, due to the two-layer film formed by baking the coating solution mainly containing colloidal silica and phosphate disclosed in Japanese Patent Publication No. Tension of about ² is applied. Therefore, in the case of these current coatings, although there is still room for iron loss improvement by applying a larger tension, increasing the applied tension by thickening the coating causes a decrease in space factor, which is not preferable.

As another method of improving the iron loss of a unidirectional silicon steel sheet, the unevenness of the steel sheet surface after finish annealing and the internal oxide layer in the vicinity of the surface are removed to perform mirror finishing.
The method of applying metal plating to the surface is Japanese Patent Publication No. 52-244.
The method of forming a tension film on the surface thereof is disclosed in, for example, Japanese Patent Publication No. 56-4150 and Japanese Patent Laid-Open No. 61-150.
-201732, Japanese Patent Publication No. 63-54767, Japanese Patent Laid-Open No. 2-213483, and the like.

In these cases as well, the greater the effect of the film to apply tension to the steel sheet, the greater the effect of improving iron loss.
From these things, a coating film which is excellent in adhesion, thin, and capable of imparting a large tension to a steel sheet has been desired.

On the other hand, the inventors have proposed a grain-oriented electrical steel sheet having aluminum borate as a main component or a composite coating of aluminum borate crystals and glassy oxide on the surface. However, in these coatings, there may be some problems in chemical stability, particularly in water resistance of the coating and rust generation, and especially for a steel sheet subjected to mirror finish, depending on the manufacturing conditions, In some cases, an oxide layer was formed at the interface with the base iron, and it was not possible to obtain a unidirectional silicon steel sheet with good characteristics.

[0008]

DISCLOSURE OF THE INVENTION The present invention solves these problems in the prior art and has a coating film having excellent water resistance and capable of imparting a larger tensile force to a steel sheet than ever before, thereby reducing the iron content. It is an object of the present invention to provide a unidirectional silicon steel sheet that achieves damage and has significantly less rust generation during storage, and a method for manufacturing the same.

[0009]

The present invention provides a low iron loss unidirectional silicon steel sheet having a coating film containing aluminum borate and an alkali metal compound and / or an alkaline earth metal compound on the outermost surface of the steel sheet. Use as a summary. Further, the gist is a low iron loss unidirectional silicon steel sheet having a coating film containing aluminum borate, iron borate, and an alkali metal compound and / or an alkaline earth metal compound on the outermost surface of the steel sheet. In addition, aluminum borate,
A gist is a low iron loss unidirectional silicon steel sheet having a coating film containing iron borate, silicon, and an alkali metal compound and / or an alkaline earth metal compound. Further, the gist is a low iron loss unidirectional silicon steel sheet having a coating film containing aluminum borate and glass as the main components on the outermost surface of the steel sheet. Furthermore, the gist is a low iron loss unidirectional silicon steel sheet having a coating film containing aluminum borate, iron borate, and glass as the main components on the outermost surface of the steel sheet.

Here, these glass materials contain boron, silicon, an alkali metal and / or an alkaline earth metal as essential components. Further, aluminum borate is AlXBYO ₃ (X + Y) / 2 (0.
The gist is a low iron loss unidirectional silicon steel sheet on which the above-mentioned coating is formed, which is crystalline aluminum borate represented by the chemical formula 1 ≦ (Y / X) ≦ 5).

Further, as a manufacturing method thereof, the surface of the unidirectional silicon steel sheet on which finish annealing has been completed contains boric acid, an aluminum oxide precursor compound, a silicon oxide precursor compound, an alkali metal compound and / or an alkaline earth metal compound. After the suspension was applied and dried, it was baked in a temperature range of 500 to 1350 ° C. to form an oxide film, and a suspension added with an iron compound was used to form an oxide film by the same process. The gist is a method for producing a characteristic low iron loss unidirectional silicon steel sheet.

The alkali metal compound and / or alkaline earth metal compound contained in the suspension is one or two of nitrate, sulfate, borate, acetate, carbonate, chloride and hydroxide. The gist of the method for producing a low iron loss unidirectional silicon steel sheet as described above is summarized.

[0013]

The unidirectional silicon steel sheet of the present invention has a coating containing aluminum borate as a main component on the outermost surface, and contains an alkali metal compound and / or an alkaline earth metal compound as an essential component. Alternatively, the outermost surface has a coating film containing aluminum borate and glass as a main component, and the glass contains boron, silicon, an alkali metal and / or an alkaline earth metal as essential components. Is.

Conventionally, a film material having a small coefficient of thermal expansion has been selected to apply tension to a silicon steel sheet, and the stress generated during cooling due to the difference in coefficient of thermal expansion from the steel sheet has been used. However, it has been pointed out that not only the difference in thermal expansion coefficient, but also the Young's modulus of the coating material is a factor that influences the application of tension to the steel sheet.

Of the coating components of the present invention, it is presumed that aluminum borate satisfies the above requirements and brings about a large amount of tension imparted to the steel sheet. In general, Al ₂ O ₃ —B ₂ O ₃ based oxide called aluminum borate contains 9
_{Al 2 O 3 -2B 2 O 3} , 2Al 2 O 3 2 of -B ₂ O ₃
It was found that there are two equilibrium phase compounds and they are effective for applying tension to the steel sheet.

However, aluminum borate may have an intermediate composition of the two equilibrium phases or a composition in the vicinity thereof, depending on the production conditions. This is because the two equilibrium phases have the same crystal structure and the lattice constants are almost the same, so that substitution easily occurs between Al and B ion sites to form a metastable phase. There is.

When the composition ratio for forming such a metastable phase is expressed by AlxByO ₃ (x + y) / 2,
It was found that 0.1 ≦ (y / x) ≦ 5, and
It was confirmed that there is no problem in any of these cases and that the tension can be effectively applied. Among these, 0.1 ≦ (y / x) ≦ 2 is preferable, and 0.2 ≦ (y / x) ≦ 1 is more preferable as a composition particularly effective for imparting tension.

These aluminum borates usually have a crystallite size of several mm to several tens of mm or more regardless of the composition, and are preferably crystalline in order to give a large tension. On the other hand, when aluminum borate does not have sufficient crystallinity and is in a state close to glassy, the tension applied to the steel sheet is lower than that in the case of being crystalline, but compared with conventional coatings. Since a much larger tension can be applied, it can be used without any particular problem as an embodiment of the present invention.

The inclusion of an alkali metal compound and / or an alkaline earth metal compound in the outermost coating of the unidirectional silicon steel sheet of the present invention has succeeded in significantly reducing the occurrence of rust during storage. This is because when the steel sheet is exposed to a moist environment, alkali metal and / or alkaline earth metal in the coating dissolves little by little, and rust is generated by boric acid or an acid added as a sol stabilizer. It is speculated that this is because the action is weakened.

The content of the alkali metal and / or alkaline earth metal compound in the coating may be extremely small, and if the weight ratio of the alkali metal and / or alkaline earth metal element to the entire coating is 10% or less, it is sufficient. Be effective. On the other hand, if the content of the alkali metal and / or alkaline earth metal compound is too large, the elution of the components in a moist atmosphere becomes severe, which is not preferable.

Therefore, in order to effectively obtain a rust suppressing effect, the content of the alkali metal and / or alkaline earth metal element is 0.5 to 10 wt% with respect to the entire coating.
% Is suitable, and particularly good results are obtained at 1 to 8 wt%.

Further, the outermost coating of the unidirectional silicon steel sheet of the present invention should also contain, as a main component, a glassy substance containing boron, silicon, an alkali metal and / or an alkaline earth metal as essential components. You can This is because boric acid and a silicon oxide precursor, an alkali metal and / or
Alkaline earth metal compounds, which are formed by the reaction of silicon, etc. in steel plate components, but are thought to often exist in the form of a matrix in the film. It reduces the microscopic pores that can be seen in the.

It is estimated that this effect has the effect of alleviating the problem of interfacial oxidation that occurs during baking. Further, by reducing the fine pores, the stability of the coating film can be increased, and the corrosion resistance, especially the water resistance can be remarkably improved. At this time, it is presumed that silicon contributes to the formation of glass, and the amount thereof should be 30 wt% or less (not including 0) of the coating as SiO ₂ .

The essential components other than the aluminum borate crystals in the coating are boron, silicon, alkali metal and / or alkaline earth metal, but even if other components are mixed in, other than that, it is unidirectional. It doesn't matter. Further, it does not matter whether the structure of these components is glassy or crystalline. These may be unavoidably mixed with other components in the coating film, impurities, or the like, or may be intentionally added to the coating solution.

As the component, a transition metal element is generally used, but in addition thereto, there are a glass-forming oxide element, a modifying oxide element and the like. Some elements, such as Fe, have the effect of increasing the chemical stability of the entire coating by mixing in the glass phase that may be present in the coating. Therefore, when added to the coating solution, the characteristics of the coating are positively affected. Can be improved.

The outermost coating of the unidirectional silicon steel sheet of the present invention may contain aluminum borate and glass as main components, but the main component here is 50% in volume ratio with respect to the entire coating. Points to the above. A more preferable content ratio is 70% or more as a volume ratio to the entire coating film.

Components other than the main component in the coating film are not particularly limited, but are generally crystalline compounds such as transition metals. In particular, the inclusion of a crystalline iron compound can significantly enhance the chemical stability of the coating.

Among them, iron borate is replaced with aluminum borate,
By containing it as a main component in the coating as in the case of vitreous, it is possible to obtain a good coating having a large effect on both imparting large tension to the steel sheet and chemical stability of the coating. Iron borate includes Fe ₃ BO ₅ , Fe ₃ BO ₆ , and FeB.
O ₃ , FeB ₂ O ₄ , FeB ₄ O _7, etc. Fe and B ratio,
There are several types of crystalline compounds depending on the oxidation state of Fe. The iron borate of the present invention may be any one of these, but the iron borate most suitable for the purpose of the present invention is Fe ₃ BO ₅ .

The content ratio of aluminum borate and / or iron borate, which is the main component of the coating, to the vitreous material is such that aluminum borate and / or iron borate can be mixed with the vitreous material from the viewpoint that a larger coating tension can be obtained. The volume ratio with respect to the combined total is 60% or more, preferably 80% or more.

Further, in order to obtain the effect of improving the water resistance by vitreous material, the preferable amount of vitreous material is 5% or more in terms of volume ratio to the total amount of aluminum borate and / or iron borate and the vitreous material, It is preferably 10% or more. At this time, iron borate may be Fe ₃ BO ₅ in an amount of 20 wt% or less (not including 0) of the coating,
Particularly, if it is 5 to 15 wt%, sufficient water resistance is secured and good results are obtained.

As an embodiment of the low iron loss unidirectional silicon steel sheet of the present invention, the outermost surface of the steel sheet has the above-mentioned coating, but the secondary recrystallization is completed for the base steel sheet on which the coating is formed. If it does, there is no particular limitation. Generally, a steel sheet generally used as a base material is a steel sheet having a forsterite primary coating formed during finish annealing (secondary recrystallization annealing), and the primary coating is removed by a method such as pickling. Then, the steel sheet with the exposed metal surface, or the steel sheet whose surface is further flattened by polishing or the like, is subjected to finish annealing (secondary recrystallization annealing) under the condition that a primary coating is not formed,
It is a steel plate having a metal surface exposed, or a steel plate having a further flattened surface.

The coating of the unidirectional silicon steel sheet of the present invention is preferably as thin as possible depending on the purpose because the space factor decreases if it is too thick. preferable. It is more preferably 2% or less. Further, from the viewpoint of applying tension, if the thickness is extremely thin, a sufficient effect cannot be obtained, and 0.1 μm is preferable.

Next, a method for suitably manufacturing the unidirectional silicon steel sheet of the present invention will be described below. A suspension (slurry) containing an alkali metal compound and / or an alkaline earth metal compound in boric acid, an aluminum oxide precursor compound, and a silicon oxide precursor compound is prepared. Boric acid is H ₃ B
Orthoboric acid represented by O ₃ is the most preferable from the viewpoints of workability and price, but metaboric acid represented by HBO ₂ and B ₂
Boric oxide represented by O ₃ or a mixture thereof can also be used.

Aluminum oxide precursor compounds include aluminum oxide and Al ₂ O ₃ such as boehmite.
-Indicates aluminum oxide hydrate, aluminum hydroxide, etc. expressed by mH ₂ O. Also, various aluminum salts such as aluminum nitrate and aluminum chloride are preferably used.

The silicon oxide precursor compound is also a generic term for compounds that similarly become silicon oxide after baking, and hydrates of silicon oxide, silicon oxyhydroxide, various silicon compounds and the like are preferably used. Most of the alkali metal compounds and alkaline earth metal compounds can be used without any problem,
Soluble compounds such as alkali hydroxide, alkali nitrate, alkali chloride, or alkaline earth nitrates, chlorides, and sulfates are particularly preferably used.

The iron source of iron borate in the coating film may be secured by adding an iron compound to the coating solution, or may be supplied from a steel plate during coating baking. In this case, the iron compound can be used without any problem as long as it is a compound that becomes iron oxide after baking. For example, iron oxide, Fe ₂ O
Not only iron oxide hydroxide and iron hydroxide such as ₃ · aH ₂ O, but also various iron compounds such as iron nitrate, iron chloride and sulfate can be preferably used. Above all, even if the iron compound is soluble in the dispersion medium or the iron compound is insoluble in the dispersion medium, compound particles having a fine particle size after dispersion are particularly preferably used. The preferable particle diameter is 1 μm or less, more preferably 0.5 μm or less.

A slurry is prepared by dispersing these raw materials in a dispersion medium. Water is most suitable as the dispersion medium, but an organic solvent or a mixture thereof can be used unless there is any particular problem in other steps. By using a so-called sol fine particle dispersion system as an aluminum oxide precursor and a silicon oxide precursor in this slurry, a thin and uniform coating having good adhesion may be obtained. This is particularly remarkable in the case where a non-metallic substance does not exist on the surface and a film is directly formed on the metal surface. In this case, the fine particle dispersed sol described above or a sol containing a soluble component is preferably used. If the particle size of the sol used is too small, cracks during drying, peeling, etc., tend to occur,
Since it becomes difficult to form a film having a predetermined thickness, it is preferably 10
It is at least nm, more preferably at least 15 nm.

When a sol solution is used as the coating liquid, the above-mentioned boehmite sol and / or alumina sol is used as the aluminum oxide precursor for workability,
Alternatively, it is particularly preferably used in terms of price. on the other hand,
As the silicon oxide precursor sol, various ones can be used, but silica sol represented by the chemical formula SiO ₂ · nH ₂ O or SiO _p (OH) _q and / or colloidal silica can be used because of its workability and cost. It is preferably used from the point.

Above all, Si is used as the silicon oxide precursor sol.
An alkyl silicate represented by the formula (OC _z H2 _{z + 1} ) ₄ and / or a hydrolyzate thereof is preferably used. Alkyl silicate is one kind of metal alkoxide, but its hydrolysis is relatively slow, and stable properties can be obtained as a precursor.

Alkyl silicate usually forms a hydroxide of silicon or a hydrate of silicon oxide by hydrolysis. However, in the case of forming a certain kind of film, this kind of hydrolyzate is used rather than using the alkyl silicate as it is. There are cases in which it is preferable to use a degradation product. In such a case, the precursor sol after hydrolysis is preferably used.

For this, (1) a method of preliminarily hydrolyzing and then mixing with other components, (2) hydrolysis in parallel with mixing with other components, and aging if necessary,
There are no particular problems in the present invention.

Among the preferred alkyl silicate compounds, those having a fast hydrolysis rate and a small number of carbon atoms z are preferable, and z ≦ 3 is preferable. However, methyl silicate with z = 1 is a methyl alcohol produced by hydrolysis. Ethyl silicate of z = 2 is particularly preferably used because it is harmful.

When using a precursor sol of silicon oxide or aluminum oxide, it is possible to disperse it in a dispersion medium, especially water, as in the case of the above-mentioned slurry. In order to obtain particularly good dispersibility, pH adjustment of the coating solution by addition of acid, alkali and the like is a method often used, and can be carried out in the present invention without any trouble. Further, there is no problem in adding an extremely small amount of a surfactant or the like to improve the coating property on the steel sheet.

The obtained slurry is applied to the surface of the unidirectional silicon steel sheet which has been subjected to finish annealing by a conventionally known method such as a coater such as a roll coater, a dipping method, spraying or electrophoresis.

The finish-annealed steel sheet herein means (1) a steel sheet having a forsterite primary coating formed on its surface by finish-annealing by a conventionally known method.
(2) A steel sheet obtained by immersing an acid in the primary coating and an incidentally formed internal oxide layer, (3) a steel sheet obtained by subjecting the steel sheet obtained in (2) above to flattening annealing in hydrogen, Alternatively, a steel plate that has been subjected to polishing such as chemical polishing and electrolytic polishing, (4) an conventionally known annealing separator to which a trace amount of an additive such as an alumina powder or the like which is inert to film formation, or a chloride is added,
It refers to a steel sheet or the like that has been finish annealed under conditions that do not produce a primary coating.

After the coated steel sheet is dried, 500 to 1350
An oxide film is formed on the surface by baking at ° C. The atmosphere during baking is an inert gas atmosphere such as nitrogen,
A reducing atmosphere such as a nitrogen-hydrogen mixed atmosphere is preferable, and an atmosphere containing air or oxygen may undesirably oxidize the steel sheet.

There is no particular limitation on the dew point of the atmospheric gas. When the baking temperature is less than 500 ° C., the applied precursor may not become an oxide, and since the baking temperature is low, sufficient tension is not expressed, which is not preferable. on the other hand,
When it exceeds 1350 ° C., it is not economical although it is not particularly disadvantageous, and more preferably 1250 ° C. or less.

The present invention will be described below based on examples, but the present invention is not limited to such examples.

[0049]

【Example】

Example 1 Commercially available boric acid reagent, aluminum oxide powder (average particle size:
0.4 μm), silicon oxide powder, and sodium hydroxide are shown in Table 1.
The mixture was mixed in the proportion shown in, and distilled water was added to this to prepare a slurry. This has a thickness of 0.2% containing 3.2% of Si.
A 2 mm finish-annealed unidirectional silicon steel sheet (with a forsterite primary coating) was applied so that the coating weight after baking was 4 g / m ^2, and after drying, 3 vol of H ₂ was applied.
% 1000 ° C. in a N ₂ atmosphere containing, to form an oxide film on the surface by baking for 5 minutes.

From the results of chemical analysis, X-ray diffraction, electron microscope observation, etc., the obtained coating film was crystalline aluminum borate (2Al ₂ O ₃ .B ₂ O ₃ or 9Al ₂ O ₃ .2B ₂
It was found that the content of O ₃ ) and glass was 80% or more by volume, and some unreacted silicon oxide was also contained. In addition, a small amount of sodium component was present in the glass. The angle is 18 around a 20mmφ cylinder.
The winding test was carried out so that it was 0 degree, and the adhesion of the coating film evaluated from the peeling condition was very good.

The water resistance of the coating is as follows:
The sample was immersed in 100 ml of boiling distilled water as it was for 10 minutes, and the weight change before and after the immersion was evaluated. The result was a weight change of less than 5 mg per 50 cm ² of steel sheet for both compositions. A slight elution of sodium component was observed in boiling distilled water. The storage rust resistance was evaluated by keeping it in an atmosphere of 50 ° C. and 91% RH for 1 week, and then increasing the weight and visually observing the surface state. The weight increase before and after the rust resistance test is
Both compositions had less than 3 mg per 50 cm ² steel sheet, and no rust was observed by visual observation.
The applied tension to the steel sheet calculated from the bending of the sheet after removing the coating on one surface and the magnetic properties are shown in Table 1. From the results in Table 1, it can be seen that the grain-oriented silicon steel sheets having significantly low iron loss are obtained.

[0052]

[Table 1]

Example 2 Commercial boric acid reagent, boehmite sol (average particle size: 100)
nm), colloidal silica (average particle size: 15 nm), and calcium oxide were mixed in the proportions shown in Table 2, and distilled water was added to this to prepare a mixed sol. This was coated with 3.2% Si and aluminum oxide was applied as an annealing separator,
Subsequent to recrystallization, it was applied to a 0.2 mm thick unidirectional silicon steel sheet that had been mirror-finished at the same time so that the coating weight after baking was 4 g / m ^2, and after drying it contained 10 vol% of H _2. N
_An oxide film was formed on the surface by baking in a ₂ atmosphere at 850 ° C. for 3 minutes.

From the results of chemical analysis, X-ray diffraction, electron microscope observation, etc., the obtained coating film was crystalline aluminum borate (2Al ₂ O ₃ .B ₂ O ₃ or 9Al ₂ O ₃ .2B ₂
It was found that the content of O ₃ ) and glass was 80% or more by volume. Also, a small amount of calcium component was present in the glass.

The adhesion of the coating film evaluated in the same manner as in Example 1,
The water resistance and rust resistance were at the same level as in Example 1 and were extremely good. After the water resistance test, a slight elution of calcium component was observed in boiling distilled water. Table 2 shows the tension applied to the steel sheet and the magnetic properties. From the results shown in Table 2, it can be seen that unidirectional silicon steel sheets having significantly low iron loss were obtained.

[0056]

[Table 2]

Example 3 Table 3 shows metaboric acid prepared by drying a commercially available boric acid reagent at 120 ° C., boehmite powder (average particle size: 50 nm), colloidal silica (average particle size: 15 nm), FeOOH powder, and sodium nitrate. The mixture was mixed in the proportion shown in, and distilled water was added to this to prepare a mixed sol. Here, the addition amount of iron nitrate and sodium nitrate is 0.01 to 0.05 wt% with respect to the sol.
The sol was adjusted so as to be%.

This was made to have a thickness of 0.
A 2 mm finish-annealed unidirectional silicon steel sheet (with a forsterite primary coating) was applied so that the coating weight after baking was 4 g / m ^2, and after drying, 3 vol of H ₂ was applied.
%, An oxide film was formed on the surface by baking at 900 ° C. for 1 minute in an N ₂ atmosphere.

From the results of chemical analysis, X-ray diffraction, electron microscope observation, etc., the obtained coating film was crystalline aluminum borate (2Al ₂ O ₃ .B ₂ O ₃ or 9Al ₂ O ₃ .2B ₂
It was found that it contained 80% by volume or more of O ₃ ), glass, and iron borate (Fe ₃ BO ₅ ). No iron compound was detected other than iron borate, and the amount of iron borate in the coating was 6 to 13 wt%. Also, a small amount of calcium component was present in the glass.

The adhesion of the coating film evaluated in the same manner as in Example 1,
The rust resistance was at the same level as in Examples 1 and 2, and was extremely good. The water resistance of the coating exceeded that of Examples 1 and 2, and the weight change was less than 1 mg per 50 cm ² of steel plate. After the water resistance test, a slight elution of sodium component was observed in boiling distilled water. Table 3 shows the tension applied to the steel sheet and the magnetic properties. From the results in Table 3, it can be seen that the grain-oriented silicon steel sheets having extremely low iron loss are obtained.

[0061]

[Table 3]

Example 4 Commercial boric acid reagent, boehmite sol (average particle size: 50 n
m), ethyl silicate, and potassium nitrate were mixed in the proportions shown in Table 4 (however, ethyl silicate is converted to the oxide finally obtained), and distilled water was added to this to prepare a mixed sol.

This was baked on a 0.2 mm thick unidirectional silicon steel plate containing 3.2% of Si, coated with aluminum oxide as an annealing separator, and subjected to mirror finishing at the same time as secondary recrystallization. After coating so as to have a coating weight of 4 g / m ² , drying and then 8 in an N ₂ atmosphere containing 3 vol% of H _2.
An oxide film was formed on the surface by baking at 50 ° C. for 1 minute.

From the results of chemical analysis, X-ray diffraction, electron microscope observation, etc., the obtained coating film was crystalline aluminum borate (2Al ₂ O ₃ .B ₂ O ₃ or 9Al ₂ O ₃ .2B ₂
It was found that the content of O ₃ ) and glass was 80% or more by volume. Also, a small amount of potassium component was present in the glass.

The adhesion of the coating film evaluated in the same manner as in Example 1,
The water resistance and rust resistance were at the same level as in Examples 1 to 3 and were extremely good. After the water resistance test, a slight elution of potassium component was observed in boiling distilled water. Table 4 shows the tension applied to the steel sheet and the magnetic properties. From the results in Table 4, it can be seen that the grain-oriented silicon steel sheets having extremely low iron loss are obtained.

[0066]

[Table 4]

[0067]

EFFECTS OF THE INVENTION According to the present invention, by virtue of having a glass containing a specific component and a coating film containing aluminum borate as a main component on the surface, the coating film is excellent in water resistance and rust resistance, and its tension imparting effect. Provided is a unidirectional silicon steel sheet with significantly improved iron loss, and a method for producing the same. In particular, it shows good characteristics for both steel sheets having a primary coating that has been conventionally used and mirror-finished steel sheets for the purpose of significantly reducing iron loss, and has an industrial effect from the viewpoint of versatility. It is enormous.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Misao Hashimoto 1618 Ida, Nakahara-ku, Kawasaki City Nippon Steel Corp. Advanced Technology Research Laboratories

Claims (13)

[Claims] 1. A low iron loss unidirectional silicon steel sheet having a coating film containing aluminum borate, an alkali metal compound and / or an alkaline earth metal compound on the outermost surface of the steel sheet. 2. A low iron loss unidirectional silicon steel sheet having a coating film containing aluminum borate, a silicon compound, an alkali metal compound and / or an alkaline earth metal compound on the outermost surface of the steel sheet. 3. A low iron loss unidirectional silicon steel sheet having a coating film containing aluminum borate, iron borate, a silicon compound, and an alkali metal compound and / or an alkaline earth metal compound on the outermost surface of the steel sheet. 4. A low iron loss unidirectional silicon steel sheet having an aluminum borate and a coating film mainly composed of glass on the outermost surface of the steel sheet. However, it is assumed that the glassy material contains boron, silicon, an alkali metal and / or an alkaline earth metal as essential components. 5. A low iron loss unidirectional silicon steel sheet having a coating film containing aluminum borate, iron borate, and glass as the main components on the outermost surface of the steel sheet. However, in the glass,
Boron, silicon, an alkali metal and / or an alkaline earth metal are contained as essential components. 6. Aluminum borate is AlXBYO ₃
The crystalline aluminum borate represented by the chemical formula: (X + Y) / 2 (0.1 ≦ (Y / X) ≦ 5).
6. The low iron loss unidirectional silicon steel sheet according to any one of 1 to 5. 7. The content of the alkali metal compound and / or the alkaline earth metal compound is
Or 10wt% of coating as alkaline earth metal element in total
% Or less (not including 0), the low iron loss unidirectional silicon steel sheet according to any one of claims 1 to 6. 8. The low iron loss unidirectional silicon steel sheet according to claim 1, wherein the content of iron borate is 20 wt% or less (not including 0) of the coating film. 9. The low iron loss unidirectional silicon steel sheet according to claim 1, wherein the content of the silicon compound is 30 wt% or less (not including 0) of the total coating as SiO ₂ . 10. A suspension containing boric acid, an aluminum oxide precursor compound, an alkali metal compound and / or an alkaline earth metal compound is applied to the surface of the unidirectional silicon steel sheet on which finish annealing has been completed, and after drying, 500 to A method for producing a low iron loss unidirectional silicon steel sheet, comprising baking at a temperature range of 1350 ° C. to form an oxide film. 11. A suspension containing boric acid, an aluminum oxide precursor compound, a silicon oxide precursor compound, an alkali metal compound and / or an alkaline earth metal compound is applied to the surface of the unidirectional silicon steel sheet on which finish annealing has been completed. A method for producing a low iron loss unidirectional silicon steel sheet, which comprises baking after drying in a temperature range of 500 to 1350 ° C. to form an oxide film. 12. A suspension containing boric acid, an aluminum oxide precursor compound, a silicon oxide precursor compound, an iron compound, an alkali metal compound and / or an alkaline earth metal compound on the surface of a unidirectional silicon steel sheet that has undergone finish annealing. A method for producing a low iron loss unidirectional silicon steel sheet, which comprises applying a liquid, drying the product, and baking it in a temperature range of 500 to 1350 ° C. to form an oxide film. 13. The alkali metal compound and / or alkaline earth metal compound comprises one or more of nitrates, sulfates, borates, acetates, carbonates, chlorides and hydroxides. 13. The method for producing a low iron loss unidirectional silicon steel sheet according to any one of 1 to 12.