JPH09272982A - Low core los grain oriented silicon steel sheet and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a silicon steel sheet desirable in core loss and corrosion resistance by forming a coating film composed of a primary layer having specified Young's modulus and thermal expansion coefficient and a secondary layer contg. aluminum phosphoric acid on a silicon steel sheet. SOLUTION: The Young's modulus of a primary layer is regulated to >=100GPa, and the difference in linear thermal expansion coefficients between a steel sheet and the primary layer is regulated to 2×10<-6> . It is preferable that, in the primary layer, aluminum borate is present by >=50% per the whole body of the layer and iron compounds are present by 0.1 to 20% expressed in terms of Fe2 O3 per aluminum borate. In the secondary layer, aluminum phosphate by 50 to 70% expressed in terms of aluminum diphosphate, silicon oxide by 20 to 50% and chromium compounds by 0.5 to 10% expressed in terms of chromium trioxide are preferably present. The surface of a steel sheet is coated with the compositional soln. of the primary layer, which is dried, and baking is executed at 400 to 1000 deg.C. The compositional soln. of the secondary layer is applied thereto, which is dried, and baking is executed at 400 to 1000 deg.C. The primary layer imparts tension to the steel sheet, and the secondary layer imparts corrosion resistance thereto.

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 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 Magnetic steel sheets are required to have a low iron loss because they are used in electric equipment utilizing magnetism, and for this reason, development has been carried out to reduce magnetic loss. In particular, grain-oriented electrical steel sheets in which the axis of easy magnetization is aligned with the rolling direction have low iron loss and are widely used in equipment such as transformers that require low iron loss.

This grain-oriented electrical steel sheet has a characteristic that iron loss further decreases when tension is applied in the rolling direction, which is the axis of easy magnetization of the steel sheet. Therefore, as disclosed in Japanese Patent Publication No. 53-28375, the steel sheet surface There has been proposed a method of applying an inorganic coating material of aluminum phosphate-silicon oxide-chromium oxide and baking it, and applying tension to the steel sheet due to the difference in thermal expansion from the steel sheet to improve iron loss.

The tension coating that gives tension has a greater effect of giving tension as the absolute value of the coefficient of linear thermal expansion becomes smaller. Therefore, a coating made of a material having low thermal expansion and high Young's modulus can be formed on the grain-oriented electrical steel sheet. desirable. Although various compounds can be considered as such a compound, the method of forming a coating film by the baking method has a problem that baking must be performed at a high temperature.

On the other hand, Japanese Unexamined Patent Publication No. 61-201732 proposes a method of forming a coating film of TiN or the like, which is difficult to form by a coating and baking method, by a vapor phase method to greatly improve iron loss. The film formation by the vapor phase method is effective even for a film composition that requires a high baking temperature under normal film forming conditions.
It has an advantage that it can be performed while keeping the surface of the steel sheet at a relatively low temperature, but it requires a vacuum system and requires a long processing time, which causes a big problem in terms of cost.

On the other hand, recently, as disclosed in Japanese Patent Laid-Open No. 4-222850, a method of forming a tension film on the surface of a steel sheet at a relatively low temperature by using a sol-gel method has been disclosed. According to this, it is possible to form aluminum borate having a lower thermal expansion property and a higher Young's modulus, which are superior to those of the aluminum phosphate-silicon oxide-chromium oxide composite coating, by a normal coating baking method, and the grain-oriented electrical steel sheet having this coating is formed. Is low iron loss,
Good magnetic properties can be obtained.

However, the electrical steel sheet thus obtained may be inferior in corrosion resistance to a steel sheet having an aluminum phosphate-silicon oxide-chromium oxide composite coating, and if left to stand in high humidity, rusting occurs. Sometimes caused.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to obtain, by a simple method, a grain-oriented electrical steel sheet having a coating film which is more effective in imparting tension than conventional coating films and which is excellent in rust resistance. It is what

[0009]

DISCLOSURE OF THE INVENTION The present invention is provided on a steel plate surface,
It has a coating consisting of a first layer with a Young's modulus of 100 GPa or more and a linear thermal expansion coefficient difference of 2 × 10 ^-6 or more with a steel sheet, and a second layer containing aluminum phosphate, and has low iron loss and water resistance. The present invention relates to a grain-oriented electrical steel sheet that has excellent properties and has extremely little rust generation during storage. Further, the gist is that the first layer of the coating contains aluminum borate.

Further, in such a steel sheet, the second layer of the coating film contains, in addition to aluminum phosphate, silicon oxide and a chromium compound, and each of them is 50 to 70% by weight of aluminum diphosphate with respect to the entire second layer. 20 to 50 with silicon oxide
%, And the content of chromium trioxide is 0.5 to 10%.

Further, the first layer contains an iron compound in addition to aluminum borate, and the proportion of the entire first layer is 50% or more by weight of aluminum borate, and the iron compound converted to Fe ₂ O ₃ is aluminum borate. To 0.1 to 20
% Existence exists.

Further, the gist is that the aluminum borate of the first layer is crystalline and is 50% or more by weight ratio with respect to the entire first layer. Further, the gist is a method of forming the first layer, the second layer or the second layer, and the first layer in this order in such a steel sheet with the baking temperature of the coating film set to 400 to 1000 ° C.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
In the present invention, the layer that realizes the function of the tension film (called the first layer) and the layer that expresses the function against the rust resistance of the film and other external environments (called the second layer) are provided. Form separately. The Young's modulus of the first layer of the film responsible for the development of tension is 10
By setting the linear thermal expansion coefficient difference to the steel plate to be 0 GPa or more and 2 × 10 ⁻⁶ or more, sufficient tension for obtaining a steel plate with low iron loss can be obtained.

Since the tension caused by the coating film is generated by the difference in thermal expansion between the steel sheet and the coating film after baking, its magnitude is proportional to the product of the Young's modulus of the coating film and the linear thermal expansion coefficient difference between the steel sheet and the coating film. Therefore, the greater the difference between the Young's modulus of the coating and the linear thermal expansion coefficient of the steel sheet, the greater the tension applied by the coating to the steel sheet.

As a result of examination by the inventors, the Young's modulus is 10
When the linear thermal expansion coefficient difference from the steel plate is 0 GPa or more and 2 × 10 ⁻⁶ or more, a coating film that gives sufficient tension for improving iron loss can be realized. As such a compound, various compounds such as mullite, cordierite and aluminum borate can be applied. Among them, aluminum borate is most suitable from the viewpoint of production conditions.

Although the amorphous aluminum borate phase is sufficient for generating tension in the form of the compound constituting the coating in the first layer, crystalline aluminum borate is required for generating larger tension. Is desirable. The component system called aluminum borate includes Al ₄ B
_{There are 2} O ₉ and Al ₁₈ B ₄ O ₃₃ , and in reality, a mixed system or aluminum borate in a metastable state is produced, but any of these crystal systems can be used as the tension applying layer.

If the proportion of the aluminum borate phase in the tension imparting layer is 50 wt% or more, a sufficient tension imparting effect can be expected, and more desirably, the proportion of the aluminum borate phase is 70 wt% or more. Further, the proportion of the crystalline aluminum borate phase in the tension-applying layer is 50%.
If it is at least wt%, a sufficient tension imparting effect can be expected, and more desirably, the proportion of the crystalline aluminum borate phase is 80 wt%.
That is all.

When an iron compound is introduced into the first layer, the water resistance of the aluminum borate layer can be improved, but it is particularly preferable to use iron borate as the iron compound. Iron borate is Fe ₃ B
Although various forms such as O ₅ , FeBO ₃ , Fe ₃ BO ₆ and amorphous can be adopted, there is no particular limitation.

If the amount of the iron compound is too small, there is no effect on the water resistance, and if it is too large, the tension-imparting ability of the first layer deteriorates. Therefore, the amount of iron compound is calculated by converting the amount of iron into Fe ₂ O _3. Good results are obtained when the compound is 0.1 to 20 wt% with respect to aluminum borate, and particularly good results are obtained in the range of 1 to 5 wt%. To identify the aluminum borate phase and the iron compound phase, a transmission electron microscope, X-ray diffraction, or XPS can be used.

In order to determine the amount of the compound in the coating film, the results of a transmission image and an electron diffraction image by a transmission electron microscope are used.
In such a method, a crystalline iron compound such as iron borate corresponding to the amount of iron added may not be found in the first layer. It is thought that this is because the iron compound exists in an amorphous state, but even in such a case, regarding the rust resistance,
The effect of adding the iron compound in the coating is sufficiently obtained.

Since the first layer is intended to apply tension to the steel sheet, if the thickness is too thin, the tension applied to the steel sheet will not be sufficient, and if it is too thick, a large tension will be obtained. Good results are obtained when the thickness of the first layer coating on both sides of the steel sheet is combined to be 0.5 to 2% of that of the steel sheet, since this leads to a reduction in the product ratio and is not desirable.

The second layer mainly provides the steel sheet with corrosion resistance. Better results are obtained when the second layer is a layer containing not only aluminum phosphate but also silicon oxide and chromium oxide, and the same components as those in JP-B-53-28375 can be used for this.

As disclosed in JP-B-53-28375, this coating has 4 to 16% by weight of colloidal silica and 3% of aluminum phosphate in terms of aluminum diphosphate.
It is obtained by applying, drying and baking a coating solution containing -24% by weight and chromic anhydride 0.2-4.5% by weight.

Since the tension is applied to the first layer, the thickness of the second layer can be made smaller than that of the first layer. However, if the second layer is too thin, the rust preventive property becomes insufficient, and if the second layer is thick, a high rust preventive property is obtained, but this is not preferable because it causes a decrease in space factor. Under these conditions, the thickness of the second layer is preferably 0.1 μm or more.

Next, a method for suitably manufacturing the electromagnetic steel sheet of the present invention will be described. The coating of aluminum borate for the first layer can be obtained by preparing a coating liquid containing a boron component and an aluminum component, coating the coating liquid on a steel plate, drying and baking the coating liquid. Here, boric acid is preferably used as the boron component because it is easy to obtain an aqueous solution, and the form of boric acid may be any of orthoboric acid, metaboric acid, boron oxide, etc. From the viewpoint of workability, orthoboric acid is suitable.

Good results are obtained by using an aluminum oxide precursor as the aluminum component. The aluminum oxide precursor refers to not only aluminum oxide but also aluminum oxide hydrate represented by boehmite, aluminum hydroxide and the like. Further, aluminum salts such as aluminum nitrate and aluminum chloride can also be used.

Regarding the iron compound in the first layer, it is preferable to introduce the iron compound in the form of a sol or salt into the coating liquid for the first layer. As the sol of the iron compound, iron hydroxide or FeOO
Water-soluble iron nitrate or the like is preferably used as the salt represented by H and the salt, but the iron source is not particularly limited thereto.

The second layer coating can also be obtained by preparing a coating solution containing the above components, and applying, drying and baking the coating solution. The coating solution for obtaining aluminum phosphate or a coating film containing silicon oxide and chromium oxide in addition to aluminum phosphate is preferably obtained by dissolving aluminum phosphate or a silicon oxide precursor and chromic anhydride in water. . Here, the silicon oxide precursor refers to a substance that becomes silicon oxide after baking the coating, and includes a hydrate of silicon oxide, silicon oxyhydroxide, and various silicon compounds.

The reason for limiting these amounts is that when aluminum phosphate is more than 70 wt% as aluminum diphosphate, the second layer coating tends to become cloudy, and when it is less than 50 wt%, the adhesion of the second layer coating is sufficient. This is because it cannot be obtained. Further, when the content of silicon oxide is less than 20 wt%, the appearance of the second layer coating is not good, and when it is more than 50 wt%, the adhesion of the second layer coating cannot be sufficiently obtained. Further, if the chromium compound is less than 0.5 wt% of chromium trioxide, sufficient corrosion resistance of the coating cannot be obtained, and if it exceeds 10 wt%, the appearance of the second layer coating is impaired.

The structure of the first layer and the second layer on the steel sheet can be in any order of steel sheet / first layer / second layer or steel sheet / second layer / first layer. Good results can be obtained by forming the coating film in the order of steel plate / first layer / second layer in order to efficiently apply tension and thin the rust preventive layer of the second layer.

The steel sheet here is a finish-annealed electromagnetic steel sheet, which is (1) finish-annealed by a conventionally known method, and the surface is finish-annealed mainly forsterite (referred to as a primary coating). ) Formed steel plate,
(2) A steel sheet in which the primary coating and the incidentally formed internal oxide layer are immersed and removed in acid, (3) a steel sheet obtained by subjecting the steel sheet obtained in (2) above to flattening annealing in hydrogen, or A steel sheet that has been subjected to polishing such as chemical electropolishing, (4) an alumina powder that is inert to film formation, or a conventionally known annealing separator to which a trace amount of additives such as chlorides has been added to form a primary coating. A steel sheet that has been subjected to finish annealing under conditions that do not generate

In order to form a coating film having a two-layer structure, the raw material liquids of the first layer (a layer containing aluminum borate) and the second layer (a layer containing aluminum phosphate) are applied respectively. A process is required. The baking temperature of the film for producing aluminum borate or aluminum phosphate in the film after coating and drying is preferably 400 to 1000 ° C. for both the first layer and the second layer, and particularly good results are obtained at 700 to 900 ° C. can get.

The reason why the baking temperature is limited to this range is as follows.
This is because if the baking temperature is too low, the desired compound cannot be obtained, or a long time baking is required for the formation of the compound, and if the baking temperature is too high, there is no particular problem but the efficiency deteriorates. Is.

There is no limitation on the method of applying the coating liquid, as long as the coating amount can be controlled with good controllability. Therefore, a roll coater method, a brush coating method, a spray method or the like can be applied, and the coating method is not limited. The present invention will be described below based on examples, but the present invention is not limited to these examples.

[0035]

【Example】

Example 1 Commercially available boric acid (industrial grade H ₃ BO ₃ ),
Using boehmite sol (average particle size 100 nm) as a raw material Table 1
The composition of the grain-oriented electrical steel sheet (Si having a composition ratio of
Is applied to a steel plate having a thickness of 3.1% and a thickness of 0.2 mm) so that one side of the steel plate has a thickness of 3 μm after baking, and baking is performed at 1000 ° C. for 5 minutes in a nitrogen atmosphere containing hydrogen.
The first layer was formed.

[Table 1]

When this coating was analyzed by X-ray diffraction,
Aluminum borate (Al ₄ B ₂ O ₉ ) was produced.
Further observation of this coating with a transmission electron microscope revealed that 80 wt% or more of the coating was aluminum borate crystals (Al ₄ B
₂ O ₉ ). It was confirmed from the results of XPS and chemical analysis that an amorphous mixture of aluminum borate and boron oxide constituted the first layer coating in addition to the aluminum borate crystals.

On this, coating solutions having the compositions shown in Table 2 were prepared and coated at various coating amounts (indicated as the second layer coating amount in the table), and then 800 in a nitrogen atmosphere containing hydrogen. 5 at ℃
It was baked for a minute. It was confirmed by X-ray diffraction that the second layer after baking was composed of silicon oxide and amorphous, and from the result of chemical analysis, the second layer was 63 wt% as aluminum diphosphate and 30 wt% as silicon oxide (SiO ₂ ). It was confirmed that the amount of chromium oxide (Cr ₂ O ₃ ) was 7 wt%.

[0038]

[Table 2]

Table 3 shows the rust resistance and iron loss of the magnetic steel sheet having the coating film thus obtained. Rust resistance is 5
It was left in an atmosphere of 0 ° C and 91RH% (relative humidity) for 1 week and evaluated by the weight change before and after that, but when rust occurred, a weight increase (a positive value in the table) was observed. It was judged that the smaller the number, the better the rust resistance.

[0040]

[Table 3]

As is clear from Table 3, a steel sheet having a two-layer structure of a first layer coating containing aluminum borate and a second layer coating containing aluminum phosphate is better than a steel sheet having only an aluminum phosphate coating. It is obvious that the iron loss is excellent, and the rust resistance is remarkably improved as compared with the steel sheet having the coating consisting of only the aluminum borate coating. If the thickness of the aluminum phosphate coating of the second layer is sufficient, the rust resistance is improved, and particularly at a thickness of 0.1 μm or more, the improvement effect is remarkable.

Example 2 As in Example 1, commercially available boric acid (industrial grade H ₃ BO ₃ ) and boehmite sol (average particle size 100 nm) were used as raw materials, and the composition ratios shown in Table 4 were used. A sol liquid prepared by adding a certain amount of iron nitrate was used as a coating liquid. The amount of iron nitrate added is as shown in Table 6, and it is assumed that aluminum borate (Al ₄ B ₂ O ₉ ) is produced from the composition of Table 4 by the total consumption of aluminum.
The amount of iron in terms of Fe ₂ O _{3 with} respect to this amount is shown in% by weight.

A grain-oriented electrical steel sheet having a primary coating finish-annealed (containing 3.1% Si, sheet thickness 0.2 mm)
Was baked to a mirror-finished plate, the coating solution was baked to a thickness of 3 μm, and baked in a nitrogen atmosphere containing hydrogen at 1000 ° C. for 5 minutes.

When the coating of the first layer obtained here was analyzed by X-ray diffraction, aluminum borate (Al ₄ B ₂ O ₉ ) and iron borate (Fe ₃ B) were found when the amount of iron nitrate added was large.
It was confirmed that it consisted of O ₅ ). When the amount of iron nitrate added was small, the presence of iron nitrate could not be confirmed by X-ray diffraction.

Further observation of this coating with a transmission electron microscope revealed that 70% by weight or more of the coating was aluminum borate crystals (A
l ₄ B ₂ O ₉ ). From the results of XPS and chemical analysis, it was confirmed from the results of XPS and chemical analysis that an amorphous mixture of aluminum borate, boron oxide and iron borate constituted the film other than the aluminum borate crystals.

On this, a coating solution having the composition shown in Table 5 was prepared, and after baking, it was applied so as to have a thickness of 0.2 μm, and baked at 800 ° C. for 5 minutes in a nitrogen atmosphere containing hydrogen. I went. It was confirmed by X-ray diffraction that the second layer after baking was composed of silicon oxide and glass, and the result of chemical analysis showed that the second layer was aluminum diphosphate.
It was confirmed that 6 wt%, 37 wt% silicon oxide (SiO ₂ ) and 7 wt% chromium oxide (Cr ₂ O ₃ ).

Table 6 shows the rust resistance and iron loss of the magnetic steel sheet having the coating film thus obtained. Rust resistance is 5
The sample was left in an atmosphere of 0 ° C and 91RH% for 1 week and evaluated by the weight change before and after that, but when rust occurred, a weight increase (a positive value in the table) was observed. It was judged that the rust property was good.

[0048]

[Table 4]

[Table 5]

[0049]

[Table 6]

As is clear from Table 6, it is clear that in the steel sheet having a two-layer structure of aluminum phosphate coating, the rust resistance is further improved when the iron compound is added to the aluminum borate coating. It is clear that both excellent iron loss and rust resistance are achieved when the amount of the Fe ₂ O ₃ equivalent iron compound in the aluminum borate coating is in the range of 0.1 to 20% by weight. Is.

[0051]

According to the present invention, it is possible to obtain a grain-oriented electrical steel sheet which has a coating film having a larger tension imparting effect than that of the conventional method, remarkably reduces iron loss and is excellent in rust resistance.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yukihiro Yamamoto 1618 Ida, Nakahara-ku, Kawasaki City Nippon Steel Corp. Technology Development Division

Claims (8)

[Claims] 1. A coating comprising two layers, a first layer having a Young's modulus of 100 GPa or more and a linear thermal expansion coefficient difference of 2 × 10 ⁻⁶ or more with the steel sheet, and a second layer containing aluminum phosphate. A low iron loss grain-oriented electrical steel sheet. 2. The low iron loss unidirectional electrical steel sheet according to claim 1, wherein the first layer contains aluminum borate. 3. The low iron loss unidirectional electrical steel sheet according to claim 1 or 2, wherein the second layer contains silicon oxide and a chromium compound in addition to aluminum phosphate. 4. The aluminum diphosphate, the silicon oxide, and the chromium compound contained in the second layer are 50 to 70% of aluminum diphosphate and 50% to 70% of silicon oxide, respectively, with respect to the entire weight of the second layer. The low iron loss unidirectional electrical steel sheet according to any one of claims 1 to 3, wherein the content is 20 to 50% and the content of chromium trioxide is 0.5 to 10%. 5. The iron layer according to claim 1, wherein the first layer contains an iron compound in addition to aluminum borate, and the proportion of the entire first layer is 50% or more by weight of aluminum borate and Fe.
The low iron loss unidirectional electrical steel sheet according to any one of claims 1 to 4, wherein the iron compound calculated as ₂ O ₃ is present in an amount of 0.1 to 20% with respect to aluminum borate. 6. The method according to any one of claims 1 to 5, wherein the aluminum borate in the first layer is 50% or more by weight of the entire first layer as a crystalline material. Low iron loss unidirectional electrical steel sheet. 7. The method according to claim 1, wherein a coating solution having the composition as a first layer is prepared, coated and dried on a steel plate, and
After baking at 00 to 1000 ° C., a coating solution having the composition as the second layer is prepared, coated and dried to give 400
The method for producing a low iron loss grain-oriented electrical steel sheet according to any one of claims 1 to 6, wherein baking is performed at 〜1000 ° C. 8. The method according to claim 1, wherein a coating solution having the composition as a second layer is prepared on the steel sheet, coated and dried, and
After baking at 00 to 1000 ° C., a coating solution having the composition as the first layer is prepared, coated and dried to give 400
The method for producing a low iron loss grain-oriented electrical steel sheet according to any one of claims 1 to 6, wherein baking is performed at 〜1000 ° C.