JP3369837B2 - Low iron loss unidirectional silicon steel sheet and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a unidirectional silicon steel sheet having low iron loss, excellent water resistance and excellent rust resistance, 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,
A method for subdividing a magnetic domain by this is disclosed in Japanese Patent Laid-Open No. 58-26
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, in an iron alloy containing silicon, when an external tension is applied, the magnetic domains are subdivided, and the eddy current loss, which is the main factor of iron loss, can be reduced. Therefore,
It is effective to apply tension to the steel sheet to reduce the iron loss of the unidirectional silicon steel sheet, and it is known that the iron loss can be effectively reduced by applying the tension up to about 1.5 kgf / mm ² . 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 coating of the secondary coating formed by baking the coating liquid mainly containing colloidal silica and phosphate disclosed in Japanese Patent Publication No. Tension of about ² is applied. Therefore, in the case of these existing coatings, although there is still room for improvement of iron loss by applying a larger tension, increasing the applied tension by increasing the thickness of the coating causes a decrease in space factor, which is not preferable.

As another method for improving the iron loss of a unidirectional silicon steel sheet, the unevenness of the surface of the steel sheet after finish annealing and the internal oxide layer near the surface are removed to give a mirror finish, and the surface is made of metal. The method of plating is Japanese Patent Publication Sho 52-2
4499 discloses a method of further forming a tension film on the surface thereof, as described in JP-B-56-4150 and JP-A-61-2.
No. 01732, Japanese Examined Patent Publication No. 63-54767, and Japanese Patent Laid-Open No. 2-213483. In these cases as well, the greater the effect of the coating 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, these coatings may have some problems in chemical stability, particularly in water resistance and rust resistance of the coating.

[0007]

SUMMARY OF THE INVENTION The present invention solves these problems in the prior art and provides a unidirectional silicon steel sheet having excellent water resistance and rust resistance during storage, and a method for producing the same. The purpose is to

[0008]

According to the present invention , aluminum borate, iron borate, a silicon compound, one or two of an alkali metal compound and an alkaline earth metal compound, cerium and lanthanum are provided on the outermost surface of a steel sheet. A low iron loss unidirectional silicon steel sheet having a coating film containing one or a mixture of two or more compounds containing rare earth elements such as yttrium, terbium and praseodymium, zirconium and hafnium. Further, aluminum borate _{is, Al x B y O 3 (} x + y) / 2 (0.1 ≦ (Y / X) ≦ 5)
The gist is a low iron loss unidirectional silicon steel sheet on which the above-mentioned coating is formed, which is a crystalline aluminum borate represented by the following chemical formula.

Further, as a manufacturing method thereof, boric acid, an aluminum oxide precursor compound, one or two kinds of an alkali metal compound and an alkaline earth metal compound, and cerium are formed on the surface of the unidirectional silicon steel sheet on which the finish annealing is completed. , A lanthanum, yttrium, terbium, praseodymium or other rare earth metal element, zirconium, a suspension containing one or a mixture of two or more compounds containing hafnium is applied, dried, and then baked in a temperature range of 500 to 1350 ° C., Low iron loss unidirectional silicon steel sheet characterized by forming an oxide film, and forming a oxide film by a similar process using a suspension containing a silicon oxide precursor compound and an iron compound. The manufacturing method will be summarized.

Further, one or two of alkali metal compounds and alkaline earth metal compounds contained in the suspension, cerium, lanthanum, yttrium, terbium,
Compounds containing rare earth metal elements such as praseodymium, zirconium, and hafnium are oxides, borates, acetates, carbonates, hydroxides and alcoholates , and glass of the rare earth elements.
A gist is a method for producing a low iron loss unidirectional silicon steel sheet comprising one or more of an acid salt and one or more of oxynitrates of zirconium and hafnium .

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The unidirectional silicon steel sheet of the present invention has a coating containing aluminum borate as a main component on the outermost surface, and one or two of an alkali metal compound and an alkaline earth metal compound is formed on the coating. It contains, as a component, a seed and one or a mixture of two or more compounds containing a rare earth metal element such as cerium, lanthanum, yttrium, terbium and praseodymium, zirconium and hafnium.

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.

Among the coating components of the present invention, aluminum borate satisfies the above requirements and is presumed to bring about a large amount of tension to the steel sheet. The present inventors have previously generally the Al ₂ O ₃ -B ₂ O ₃ based oxide called aluminum _{borate, 9Al 2 O 3 -2B 2 O} 3, 2Al 2 O 3
-B ₂ 2 two equilibrium phases compound of O ₃ is present, it was found to be effective in tensioning of 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.

[0015] As the composition ratio for forming such a metastable phase, when expressed in _{Al x B y O 3 (x} + y) / 2, 0.1 ≦
It was found that (y / x) ≦ 5, and it was confirmed that there was no problem in any of these cases and the tension could be effectively applied. Among these, 0.1 ≦ (y / x) ≦ 2 is preferable as a composition particularly effective for imparting tension,
More preferably, the composition range is 0.2 ≦ (y / x) ≦ 1. Usually, these aluminum borates often have a crystallite size of several nm to several tens of nm or more regardless of the composition, and are preferably crystalline in order to give a large tension.

In the coating on the outermost surface of the unidirectional silicon steel sheet of the present invention, one or two of an alkali metal compound and an alkaline earth metal compound, and a rare earth metal element such as cerium, lanthanum, yttrium, terbium, praseodymium, By containing one or a mixture of two or more of the compounds containing zirconium and hafnium, we succeeded in significantly reducing rust generation during storage.

The content of the alkali metal and / or alkaline earth metal compound in the coating may be small, and the weight ratio of the alkali metal and / or alkaline earth metal to the entire coating in terms of element is 10% or less. 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 the rust suppressing effect, the content of the alkali metal and / or the alkaline earth metal is 0.1 to 10 wt% with respect to the entire coating in terms of element.
Particularly, good results are obtained at 0.3 to 8 wt%.

If a rare earth metal element such as cerium, lanthanum, yttrium, terbium or praseodymium, or an element such as zirconium or hafnium is present, 800
At a high temperature of ℃ or more, these metal ions are in a high oxidation state, and when the temperature is lowered, the iron atoms on the surface of the iron plate are oxidized to form an oxide film of iron, which has the effect of preventing further oxidation.

Further, a sulfur compound is present in the vicinity of the surface of iron, and in a wet atmosphere, it starts to melt and generate H ₂ S, which may cause rust on the surface. The presence of rare earth elements such as cerium, lanthanum, yttrium, terbium, praseodymium, and elements such as zirconium and hafnium forms a sparingly soluble sulfide, fixing the sulfur content and reducing rust generation even in a wet atmosphere.

Although different from the present invention, the fact that cerium forms sulfur and sulfide in the applied coating is as follows.
There is a description in JP-A-60-2674. As the content in the coating, the polymerization ratio with respect to the entire coating is 0.001.
The effect is exhibited in the range of wt% to 10 wt%. On the contrary, when the amount of the compound such as cerium, lanthanum, yttrium, zirconium, hafnium, terbium, praseodymium added is too large, the adhesion of the coating is adversely affected.

Therefore, in order to effectively obtain the rust inhibiting effect, the content of the cerium, lanthanum, yttrium, zirconium, hafnium, terbium, praseodymium, etc. is 0.001 to 0.001 based on the total amount of the film. 10
wt% is suitable, and particularly 0.01 to 2 wt% gives good results. Furthermore, the simultaneous addition of an alkali metal and / or alkaline earth metal compound and its addition has a remarkable effect on adhesion and rust resistance.

Further, in the outermost coating of the unidirectional silicon steel sheet of the present invention, boron, silicon, alkali metal and / or alkaline earth metal, cerium, lanthanum,
A glassy material containing, as a component, one or a mixture of two or more compounds containing a rare earth metal element such as yttrium, terbium, praseodymium, zirconium or hafnium can also be contained as a component.

This is because boric acid and a silicon oxide precursor in the coating solution, an alkali metal and / or an alkaline earth metal compound, a rare earth metal element such as cerium, lanthanum, yttrium, terbium and praseodymium, zirconium and hafnium. One or a mixture of two or more of the compounds containing it, which is formed by the reaction of the steel sheet component silicon, etc., but it is thought that it often exists as a matrix-like phase in the coating, and the aluminum borate component is It reduces the microscopic pores and other particles that are found in the main coating.

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 is 10 wt% of the coating as SiO _2.
% Or less (including 0 wt%) is preferable. If the amount added is more than this range, the film tension tends to be low, which is not preferable.

The components other than aluminum borate in the coating include boron, alkali metal and / or alkaline earth metal, one of rare earth metal elements such as cerium, lanthanum, yttrium, terbium, praseodymium, zirconium and hafnium, or Although it is a mixture of two or more kinds, there is no problem even if other components are mixed in addition to this. These other mixed components may be unavoidably mixed with other components in the coating film, impurities, etc., or may be intentionally added to the coating liquid.

As the component, a transition metal element is generally used, but in addition, a glass forming oxide element and the like are also included. Among them, 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. Addition to the coating solution positively affects the characteristics of the coating. Can be improved.

Iron borate includes Fe ₃ BO ₅ and Fe ₃ BO.
₆ , FeBO ₃ , FeB ₂ O ₄ , FeB ₄ O _7, etc. There are several kinds of crystalline compounds depending on the ratio of Fe to B and the oxidation state of Fe. The iron borate of the present invention is not particularly problematic in any of these.

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 film, but the base material steel sheet on which the coating film is formed completes the secondary recrystallization. If it does, there is no particular limitation. Usually, a steel sheet generally used as a base material is a steel sheet having a forsterite primary coating formed during finish annealing (secondary crystal annealing), and the primary coating is removed by a method such as pickling. , A steel sheet having an exposed metal surface, or a steel sheet having the surface further flattened by polishing or the like, and a steel sheet having a metal surface exposed by performing finish annealing (secondary recrystallization annealing) under the condition that a primary coating is not formed Alternatively, it is a steel plate whose surface is further flattened.

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 film is extremely thin, a sufficient effect cannot be obtained, and about 0.1 μm is preferable.

Next, a method for suitably manufacturing the unidirectional silicon steel sheet of the present invention will be described below. Boric acid, an aluminum oxide precursor compound, an alkali metal compound and / or an alkaline earth metal compound in a silicon oxide precursor compound, a rare earth metal element such as cerium, lanthanum, yttrium, terbium, praseodymium, zirconium,
A suspension (slurry) containing one or more compounds containing hafnium is prepared.

As the boric acid, orthoboric acid represented by H ₃ BO ₃ is most preferable from the viewpoints of workability and cost, but HB
Metaboric acid represented by O ₂ , boron oxide represented by B ₂ O ₃ , or a mixture thereof can also be used.
The aluminum oxide precursor compound includes not only aluminum oxide, but also aluminum oxide hydrate such as boehmite represented by Al ₂ O ₃ .mH ₂ O, aluminum hydroxide and the like. Various aluminum salts including aluminum nitrate are also 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 hydroxides, alkali nitrates, or alkaline earth nitrates are particularly preferably used.

The compound containing a rare earth metal element such as cerium, lanthanum, yttrium, terbium and praseodymium, zirconium and hafnium is preferably a soluble compound such as hydroxide, nitrate (oxynitrate in the case of zirconium and hafnium) and alcoholate. 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 can be preferably used. Among them, especially iron compounds soluble in the dispersion medium,
Alternatively, even if the iron compound is insoluble in the dispersion medium, compound particles having a fine particle shape after dispersion are particularly preferably used. The preferable particle size is 1 μm or less, more preferably 0.
It is 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 a particular problem in other steps. Of these slurries, a thin and uniform coating having good adhesion may be obtained by using a so-called sol fine particle dispersion system as the aluminum oxide precursor and the silicon oxide precursor.

This is particularly remarkable when a non-metal 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. The particle diameter of the sol used is preferably 10 nm or more, more preferably 15 nm or more, because if it is too small, cracking and peeling during drying easily occur and it becomes difficult to form a film having a predetermined thickness.

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,
Although various kinds of silicon oxide precursor sols can be used, SiO ₂ · nH ₂ O, or SiOp (OH) q
Silica sol and / or colloidal silica represented by the following chemical formula are also preferably used in terms of workability and cost.

Above all, Si is used as the silicon oxide precursor sol.
An alkyl silicate of the formula (OC _z H _{2z + 1} ) ₄ ,
And / or a hydrolyzate thereof is preferably used. Alkyl silicate is one kind of metal alkoxide,
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. There are several methods such as (1) pre-hydrolysis and then mixing with other ingredients, (2) parallel hydrolysis while mixing with other ingredients, and adding aging if necessary. However, in the present invention, any of these is not particularly problematic.

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 to.

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 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 steel sheet that has been subjected to finish annealing as used herein means (1) a steel sheet on which a forsterite primary coating is formed on the surface by performing finish annealing by a conventionally known method, (2) a primary coating and incidental The steel sheet obtained by immersing and removing the internal oxide layer formed on the steel sheet in (3), the steel sheet obtained in (2) above, which has been flattened and annealed in hydrogen, or the polishing such as chemical polishing and electrolytic polishing. Steel plate,
(4) Applying a conventionally known annealing separator containing a trace amount of additives such as alumina powder, which is inactive to form a film,
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 the temperature exceeds 1350 ° C, it is not economical but not particularly disadvantageous, and more preferably 1250 ° C.
It is the following. The present invention will be described below based on examples, but the present invention is not limited to these examples.

[0045]

EXAMPLES (Example 1) Commercially available boric acid reagents, iron nitrate _{(Fe (NO 3) 3 ·} 9H 2
O), potassium nitrate (KNO ₃ ), cerium nitrate (Ce)
(NO ₃ ) ₃ ) · 6H ₂ O) is dissolved in ion-exchanged water, ethyl silicate is added, and the mixture is stirred. In addition to this, boehmite sol (average particle size: 10 to 100 nm; mixture of plate-like particles and feather-like particles, powder-like particles used: 78% in terms of aluminum oxide, feather-like particles in terms of aluminum oxide) Of 10% was used as a slurry.) To prepare a mixed sol.

The amounts of additives are shown in Table 1. The added solid content at this time is 10 to 15 wt%. This is Si 3.2
% Contained in 0.2 mm thick finish-annealed unidirectional silicon steel sheet (with forsterite primary coating) so that the coating weight after baking is 4 g / m ^2, and after drying, H ₂ 850 in N ₂ atmosphere containing 3 vol%
An oxide film was formed on the surface by baking at 1 ° C for 1 minute.

[0047] Chemical analysis, X-rays diffraction, the result of such an electron microscopic observation, the resulting coating aluminum borate crystalline _{(2Al 2 O 3 · B 2} O 3 or 9Al ₂ O ₃ · 2B,
₂ O ₃ ) and vitreous. Two
A winding test was conducted around a 0 mmφ cylinder so that the angle was 180 degrees, and the adhesion of the coating film evaluated from the peeling condition was very good.

The water resistance of the coating film was evaluated by immersing the coated steel sheet in 100 ml of boiling water for 10 minutes and then changing the weight before and after the immersion. The results are both 50 cm
^The change in weight was less than 5 mg per ² steel plates. Further, as shown in Table 1, the rust resistance was very good, showing rust resistance for 48 hours or longer in an atmosphere at a temperature of 80 ° C. and a humidity of 98%. In Table 1, the elements other than the numeral 17 are examples of the present invention.

Comparative Example 1 A sol was prepared without adding potassium nitrate and cerium nitrate in Example 1. All other conditions were the same as in Example 1. The addition conditions and the like are shown in Table 1 (No. 17). In the rust resistance test, rust occurred after 8 hours.

[0050]

[Table 1]

[0051]

[Table 2]

Example 2 Commercial boric acid reagent, boehmite sol (average particle size: 50 n)
m), ethyl silicate, iron nitrate, potassium nitrate, cerium nitrate in the proportions shown in Table 2 in ion-exchanged water,
A sol was prepared. The sol preparation conditions are the same as in Example 1. This was applied to a 0.2 mm-thickness unidirectional silicon steel sheet containing 3.2 wt% of Si, aluminum oxide applied as an annealing separator, and subjected to mirror finishing at the same time as secondary recrystallization. After coating and drying so that the coating weight becomes 4 g / m ² , it is 850 in an N ₂ atmosphere containing 3 vol% of H _2.
An oxide film was formed on the surface by baking at 1 ° C for 1 minute.

[0053] Chemical analysis, X-rays diffraction, the result of such an electron microscopic observation, the resulting coating aluminum borate crystalline _{(2Al 2 O 3 · B 2} O 3 or 9Al ₂ O ₃ · 2B,
₂ O ₃ ) and vitreous. In addition, a small amount of potassium and cerium components were present in the glass. The adhesion, water resistance, and rust resistance of the coating film evaluated in the same manner as in Example 1 are as shown in Table 1.
It was at the same level as, and was extremely good. In Table 2, elements other than number 8 are examples of the present invention.

Comparative Example 2 A sol was prepared without adding potassium nitrate and cerium nitrate in Example 2. All other conditions were the same as in Example 2. The addition conditions and the like are shown in Table 2 (No. 8). In the rust resistance test, rust occurred in 5 hours.

[0055]

[Table 3]

[0056]

[Table 4]

[0057]

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.

Front page continued (72) Inventor Shuichi Yamazaki 20-1 Shintomi, Futtsu City Nippon Steel Co., Ltd. Technology Development Headquarters (72) Inventor Masao Sakashita 1618 Ida, Nakahara-ku, Kawasaki City Nippon Steel Corporation Technology Development Division (56) Reference JP-A-7-228977 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 22/00-22/86 C22C 38/00 303 H01F 1/16

Claims (9)

(57) [Claims] 1. An aluminum borate on the outermost surface of a steel sheet,
Iron borate, silicon compounds, one or two of alkali metal compounds and alkaline earth metal compounds, and one or two of compounds containing rare earth elements such as cerium, lanthanum, yttrium, terbium, praseodymium, zirconium, and hafnium. A low iron loss unidirectional silicon steel sheet having a coating containing a mixture of one or more kinds. Wherein aluminum borate is, Al _x B _y O
The low iron loss unidirectional silicon steel sheet according to claim 1, which is a crystalline aluminum borate represented by a chemical formula of _{3 (x + y) / 2} (0.1 ≦ (Y / X) ≦ 5). 3. A content of one or more of an alkali metal compound and an alkaline earth metal compound and one or more of a rare earth element such as cerium, lanthanum, yttrium, terbium, praseodymium, zirconium and hafnium. Is 0.1 wt% or more and 10 wt% or less in total, the low iron loss unidirectional silicon steel sheet according to claim 1 . 4. The low iron loss unidirectional silicon steel sheet according to claim 1 , wherein the content of iron borate is 6 wt% or less. 5. The low iron loss unidirectional silicon steel sheet according to claim 1, wherein the content of the silicon compound is 10 wt% or less in total as SiO ₂ . 6. A boric acid, an aluminum oxide precursor compound, and one or two kinds of an alkali metal compound and an alkaline earth metal compound, on the surface of the unidirectional silicon steel sheet,
A suspension containing one or a mixture of two or more compounds containing rare earth elements such as cerium, lanthanum, yttrium, terbium, praseodymium, zirconium and hafnium is applied, dried, and baked in a temperature range of 500 to 1350 ° C. for oxidation. A method for producing a low iron loss unidirectional silicon steel sheet, which comprises forming a material coating. 7. A boric acid, an aluminum oxide precursor compound, a silicon oxide precursor compound, one or two of an alkali metal compound and an alkaline earth metal compound, and cerium on a surface of a unidirectional silicon steel sheet. Rare earth elements such as lanthanum, yttrium, terbium, praseodymium,
After applying a suspension containing one or a mixture of two or more compounds containing zirconium and hafnium, and drying,
A method for producing a low iron loss unidirectional silicon steel sheet, which comprises baking at a temperature range of 1350 ° C. to form an oxide film. 8. One or two kinds of boric acid, an aluminum oxide precursor compound, a silicon oxide precursor compound, an iron compound, an alkali metal compound and an alkaline earth metal compound on the surface of the unidirectional silicon steel sheet. And a suspension containing one or a mixture of two or more compounds containing rare earth elements such as cerium, lanthanum, yttrium, terbium, praseodymium, zirconium, hafnium, etc., dried, and baked in a temperature range of 500 to 1350 ° C. A method for producing a low iron loss unidirectional silicon steel sheet, which comprises forming an oxide film. And one or two of 9. alkali metal compounds and alkaline earth metal compounds, cerium, lanthanum, yttrium, terbium, rare earth elements such as praseodymium, zirconium, compounds containing hafnium oxide, boric acid Salts, acetates, carbonates, hydroxides and alcoholates , nitrates of said rare earth elements, and zirconium
The method for producing a low iron loss unidirectional silicon steel sheet according to any one of claims 6 to 8 , which comprises one or more of oxynitrates of aluminum and hafnium .