JP3406801B2 - Method for producing low iron loss unidirectional silicon steel sheet - Google Patents

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 used for an iron core or the like of a transformer, in particular, having a good adhesion of an insulating coating on the surface and excellent iron loss characteristics. Of the manufacturing method of.

[0002]

2. Description of the Related Art One-directional silicon steel sheets are (100) [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. 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 the iron loss can be effectively reduced by applying the tension up to about 1.5 kgf / mm ^2. It is known that this can be reduced. This tension is usually applied by a film formed on the surface.

To date, the inventors of the present invention have disclosed in Japanese Patent Laid-Open No. 6-657.
54, JP-A-6-65755 and the like, a method for forming a new oxide film by applying a fine particle dispersion containing alumina sol and boric acid, drying and gelling, and baking, and the resulting aluminum oxide. -We have proposed boron oxide composite coatings and aluminum borate high-strength coatings. It has been found that this coating can give a steel sheet a tension as high as 1.5 to 2 times that of a conventional coating and, as a result, the magnetic properties of the steel sheet can be improved.

In recent years, in order to further reduce iron loss,
The forsterite film formed by reacting with the annealing separator during the finish annealing is removed, or annealing is performed under the condition that this film is not formed, and the surface of the unidirectional silicon steel sheet is smoothed, or Further attempts have been made to obtain mirror-finished steel sheets. In this case as well, a coating on the surface is required to secure the insulation between the steel sheets, but as described above, the greater the tension from the coating, the greater the iron loss reduction effect.

However, in the case of a unidirectional silicon steel sheet having a smooth surface, the adhesiveness of the insulating coating on the surface is significantly reduced as compared with the conventional silicon steel sheet. This is because in the case of conventional silicon steel sheets, an inorganic coating mainly composed of forsterite is formed on the surface, and this and the insulating coating normally adhered without any problem, but on the smooth metal surface. This is because it is difficult to directly form the insulating coating. Therefore, from the viewpoint of the adhesiveness of the insulating coating, it can be said that the solution becomes more difficult as the iron loss is pursued to improve the smoothness of the surface.

Several techniques have been proposed to overcome this problem. The main point is to interpose an inorganic layer at the surface of the steel sheet, that is, at the interface between the steel sheet and the insulating coating, as in the current steel. Japanese Patent Laid-Open No. 3-1
In JP 30376, a gel thin film of silicon oxide, antimony oxide, zircon oxide or the like having a thickness of 0.1 to 0.5 μm is formed on a smoothed unidirectional silicon steel sheet surface by a sol-gel method. A technique for forming an insulating coating made of magnesium phosphate-colloidal silica on the above is disclosed. Further, in Japanese Unexamined Patent Publication No. 5-287544, a composite oxide of aluminum oxide generated by a reaction in a baking step and another oxide, an iron-aluminum composite oxide,
Alternatively, a technique of forming an aluminum oxide film on the surface with a silicon-aluminum composite oxide interposed is disclosed. Further, Japanese Patent Laid-Open No. 8-283956 discloses that
An aluminum borate insulating coating is formed on the surface by using silicon oxide, a composite oxide of silicon oxide and another oxide, an iron-silicon composite oxide, or an iron-boron composite oxide generated in the baking step as an interface layer. The technology is disclosed.

Among these, an intermediate layer is formed at the same time in the step of baking the outermost aluminum oxide film or aluminum borate film disclosed in JP-A-5-287544 or JP-A-8-283956. The method is an excellent method for easily obtaining a coating having good adhesion without increasing the number of steps. However, when comparing the magnetic properties, the method of simultaneously forming the intermediate layer in the baking step may not obtain good iron loss and magnetic flux density when baking is performed under conditions other than relatively limited conditions. I understand. Further, the technique disclosed in Japanese Patent Laid-Open No. 3-130376 shows good adhesion to a film having a not so high film tension such as phosphate-colloidal silica, but a high tensile film such as aluminum borate. However, peeling from the interface between the intermediate layer and the steel sheet occurs.

According to a study by the inventors, the disclosed method of coating and drying may not provide sufficient adhesion at the interface between the intermediate layer and the steel sheet, and 0.1 to 0.
It was concluded that the thickness of 5 μm was too thick for the intermediate layer.

[0009]

SUMMARY OF THE INVENTION The present invention solves the problems of the prior art as described above, and it is preferable to form an intermediate layer of a specific compound in advance on the smoothed steel plate surface. It is an object of the present invention to provide a method for producing a unidirectional silicon steel sheet having an adhesive high-strength insulating coating and achieving a significantly low iron loss.

[0010]

The present invention provides (a) silicon and aluminum on the surface of a unidirectional silicon steel sheet on which primary recrystallization has been completed.
Metal alkoxides of nickel and iron and their hydrolyzable organisms
One or both, or colloidal silica, colloid
Alumina, boehmite sol, iron hydroxide colloid or
Is the method of applying these mixtures to the steel plate surface, (b) before
A method of heat-treating the coating material obtained by the method (a),
(C) Aluminum, iron nitrates, sulfates, chlorides
Heat treatment after immersing in one of the treatment liquids to treat the surface
By either method, pre-oxidized silicon, aluminum oxide, one or a mixture of two or more of iron oxide, 及
And one or both of complex oxides of one or more of these oxides
A method for producing a low iron loss unidirectional silicon steel sheet, which comprises forming an aluminum borate coating film on the surface of the intermediate layer after forming the intermediate layer. The gist is a method for producing a low iron loss unidirectional silicon steel sheet, wherein the intermediate layer has a thickness of 0.001 μm or more and less than 0.1 μm.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The production method of the present invention comprises, in advance, one or more mixtures of silicon oxide, aluminum oxide and iron oxide, and / or two or more of these oxides, on the surface of the unidirectional silicon steel sheet that has been subjected to finish annealing. An intermediate layer made of a complex oxide is formed. Conventionally, as the intermediate layer, SiO ₂ , titanium oxide, antimony oxide, zircon oxide, SiZrO
₄ , or iron-aluminum-based, silicon-aluminum-based, iron-silicon-based, iron-boron-based composite oxides produced in the baking process have been proposed, but an aluminum borate coating is formed on the surface with good adhesion. In order to obtain good magnetic properties and a low iron loss value, one or a mixture of two or more of silicon oxide, aluminum oxide and iron oxide disclosed in the present invention, and / or 2 of these oxides. An intermediate layer composed of one or more kinds of composite oxides is preferable, and particularly, silicon oxide and / or a composite oxide of silicon oxide and aluminum oxide is preferable.

[0012] us describe the method for forming these intermediate layers Nitsu. The first method is a method in which a metal alkoxide of silicon, aluminum, iron and / or a hydrolysis product thereof, colloidal silica, colloidal alumina, boehmite sol, iron hydroxide colloid or a mixture thereof is applied to the surface of a steel sheet. is there. The application method may be any method such as dipping or spraying. When a colloid or a sol is used, an intermediate layer having good adhesion, which withstands the high tension of the aluminum borate coating film, can be obtained by using a fine particle having a low water content and good crystallinity. Further, by setting the particle size of the fine particles to about 30 nm or less, preferably 20 nm or less, a thin and uniform intermediate layer can be formed, which is more advantageous for adhesion.

Further, by heat-treating this coating material, the adhesion can be further improved. It is desirable to change the temperature of the heat treatment depending on what is applied. Usually, when the temperature at which the hydroxide decomposes to become an oxide is t, the heat treatment temperature T is set to t <T ≦ t + 200 ° C. good. If the heat treatment temperature is too low, the oxide is not completely oxidized, resulting in lack of stability and the steel sheet may rust. Conversely, if it is too high, it is not economical. In the case of this method, there is a method of directly applying the intended component as the intermediate layer, but there is also a method of reacting the components in the steel sheet, such as iron and silicon, with the applied component to form the intermediate layer having a desired composition.
In this case, there is a high possibility that higher adhesiveness will be obtained at the interface between the intermediate layer and the steel sheet.

The second method is aluminum, iron nitrate,
In this method, the surface is treated by immersing it in a sulfate or chloride and then heat-treated. By using these compounds, the effect of activating the steel sheet surface by the contained acid can be expected. As for the temperature of the heat treatment, when the decomposition temperature of the metal salt is t, the above-mentioned heat treatment temperature conditions can be applied as they are. In order to form a thin and uniform intermediate layer and also to prevent the smoothed / mirror-finished steel plate surface from being overactivated and roughened, it is preferable that the concentration of the treatment liquid used in this method is low. The preferred concentration is 0.
1 mol / l (liter) or less, more preferably 0.05 mo
It is less than l / l (liter). Of course, there is no problem even if the intermediate layer is formed by using a treatment liquid obtained by mixing the first treatment liquid and the second treatment liquid.

This intermediate layer has a thickness of 0.001 μm or more and 0.1 or more.
A thickness of less than μm is particularly effective for adhesion. Particularly, it is particularly effective when only the coating process is performed in the first method and the sufficient heat treatment is not performed. A thickness of less than 0.1 μm is a limit thickness for ensuring flexibility / flexibility of the intermediate layer coating, and is a limit that can withstand bending peeling. The thickness is preferably 0.08 μm or less. On the other hand, if the intermediate layer is too thin, the effect of improving the adhesiveness cannot be obtained, so 0.001 μm or more is necessary, preferably 0.005 μm or more, and particularly preferably 0.01 μm or more.

In order to form an intermediate layer of this thickness, the concentration of the treatment liquid is made low in the case of the first method, or in the case of a colloid or sol solution, fine particles as already mentioned. It is good to utilize. Similarly, the second method can be realized by reducing the concentration of the treatment liquid .

A smoothed / mirror-finished steel sheet which has been subjected to finish annealing and which forms an intermediate layer means (1) a forsterite film formed in the finish annealing step and an interfacial oxide layer which is additionally formed. Steel plate removed by immersing in acid, (2) Steel plate obtained by flattening and annealing the steel plate obtained in (1) above in hydrogen, or steel plate subjected to polishing such as chemical polishing and electrolytic polishing, (3) Film formation Alumina powder that is inactive against, or using a conventionally known annealing separator with addition of a trace amount of additives such as chloride, a steel sheet that has been subjected to finish annealing under the condition that a forsterite annealed film is not formed. Point to.

In the manufacturing method of the present invention, the aluminum borate high-strength coating is formed on the surface of the intermediate layer formed as described above. The method of forming the coating film can be obtained by applying a conventionally known boron oxide precursor compound or aluminum oxide precursor compound to the surface of the steel sheet as a starting material, and baking / solidifying to form an oxide. In a particularly preferred embodiment, a coating solution containing boric acid and boehmite is applied to a steel sheet surface having a smoothing / mirror-finished intermediate layer after finishing annealing is completed, and is applied at a predetermined temperature in an atmosphere of controlled oxygen potential. Obtained by baking. The boehmite to be used is not particularly limited, but by using a mixture of relatively good crystallinity and poor crystallinity, it is possible to obtain a film with good adhesion to the steel sheet and good tension. . In addition, when the ratio of boric acid to boehmite is a total of 100 in terms of weight ratio of respective oxides, the total amount is more than 12 to 40% boric acid, 60 to 8%.
When boehmite of less than 8% is used, an aluminum borate coating film excellent in various properties can be obtained. Further, the coating solution may contain a small amount of additives in addition to boric acid and boehmite sol. Additives that are often used are silicon oxide precursor compounds, transition metal compounds, alkali / alkaline earth metal compounds, rare earth element compounds, acids such as inorganic acids and organic acids, ammonia, etc., depending on the purpose. It can be added in an amount.

The coating solution is applied on the surface of the steel sheet on which the intermediate layer is formed.
Coating is performed by a conventionally known method such as a coater such as a roll coater, a dipping method, a spraying method, or an electrophoresis method. As the coating method, an optimum method can be selected depending on the liquid properties. The coating thickness is such that the coating thickness on one surface after baking does not exceed 2% of the steel plate thickness. When the coating film exceeds 2% of the steel plate thickness, it is a region where the effect of reducing iron loss by applying tension is almost constant and saturated,
On the contrary, the thick coating reduces the space factor.

The coated steel sheet is dried to cause gelation, and finally, it is baked and solidified in a reducing atmosphere containing an inert gas or hydrogen at 500 to 1200 ° C. to mainly contain aluminum borate. The oxide insulating film is formed. Baking in an oxidizing atmosphere is not preferable because the steel sheet may be oxidized. The smoothed / mirror-finished steel sheet is sensitive to atmospheric oxidation, and if the interface is slightly damaged by oxidation and unevenness occurs,
It is desirable to set the conditions with particular care, because a remarkable deterioration of the characteristics will occur. The inventors' studies have shown that generally good results can be obtained when the oxygen potential is P H ₂ O / P H ₂ ≦ 0.2. When the baking temperature is lower than 500 ° C., the decomposition of boehmite in the gel is insufficient and the gel does not become an oxide, and there is a high possibility that the coating will lack stability. Further, if it exceeds 1200 ° C, it is not economical although there is no particular inconvenience. Especially preferred is 600-
The temperature range is 1000 ° C., and within this range, a steel sheet having a coating excellent in almost all properties including adhesion and tension can be obtained.

In the method for producing a unidirectional silicon steel sheet according to the present invention, the insulating / tensioning film on the surface is formed after the intermediate layer is formed. However, the finally obtained film is not necessarily two layers. It doesn't have to be separate. When the insulating coating is baked, the components of the intermediate layer may be diffused to the insulating coating side or the components of the insulating coating may be diffused to the intermediate layer side. The same applies when a reaction layer is formed at the interface between the intermediate layer and the insulating coating. Rather, diffusion of such components or formation of a reaction layer is highly likely to improve the adhesion between the intermediate layer and the insulating coating.

The unidirectional electrical steel sheet to which the present invention is applied has been put into practical use in the past or manufactured by the technology already disclosed, and is a steel sheet having particularly excellent magnetic properties.

[0023]

EXAMPLES The present invention will be described below based on examples.
Finishing annealing was performed using alumina as an annealing separator, and the surface was mirror finished to give a unidirectional silicon steel sheet (Si content: 3.2).
%, Thickness: 0.2 mm) An intermediate layer having the components shown in Table 1 was formed on the surface. The outline of the forming method is also shown. A fine particle dispersion containing boric acid and boehmite sol as main components was applied to this steel sheet, and the coating thickness after baking was about 2 μm per side.
was coated by a roll coater so that the m, after a drying and gelation step, containing final H ₂ 75 vol% N ₂
The film was baked in an atmosphere at 800 to 850 ° C. for about 30 seconds to form an aluminum borate film.

Table 1 shows the adhesion and magnetic properties of the insulating coating of the obtained grain-oriented silicon steel sheet. The components of the intermediate layer were measured by X-ray diffraction, infrared spectroscopy, etc., and the thickness was measured by observing the weight change before and after the formation of the intermediate layer and directly observing the cross section of the steel sheet with a microscope. The adhesion of the aluminum borate coating film was evaluated by measuring the diameter of the column where peeling occurred by conducting a winding test around a column having a predetermined diameter so that the angle was 180 °. Passes if φ20 or less, exceeds φ20 to φ3
0 is a caution, and φ30 or more is a fail level. The magnetic property was an average value of 10 test pieces. In the comprehensive evaluation, the adhesion and magnetic properties are comprehensively considered, and ◎ and ○ are pass levels, △ is somehow usable but caution is required, and × is fail.

From Table 1, it can be seen that when the intermediate layer is formed by the method of the present invention, the adhesion of the insulating coating is excellent and good magnetic properties are obtained. Particularly, in the case of the intermediate layer having a thickness of 0.08 μm or less, extremely good adhesion is obtained.

On the other hand, in the comparative example carried out based on the conventional technique, the intermediate layer component is different from that of the present invention, so that a remarkable poor adhesion is caused or the magnetic properties are deteriorated. It is also found that when the intermediate layer is formed at the same time as the step of baking the aluminum borate coating film, even if the composition of the intermediate layer is the same as that of the invention of the present application, the adhesiveness is significantly deteriorated and the magnetic properties are lowered.

Therefore, in order to form an insulating coating on a smoothed / mirror-finished steel sheet with good adhesion and obtain good magnetic properties, it is necessary to previously form an intermediate layer of predetermined components. In addition, further improvement can be expected by forming this intermediate layer within a predetermined thickness range.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

The manufacturing method of the present invention aims to obtain an excellent magnetic property by forming an insulating coating having high tension on the surface of a smoothed / mirror-finished unidirectional silicon steel sheet with good adhesion. The magnetic properties of the obtained unidirectional silicon steel sheet are unprecedented. Further, the manufacturing method of the present invention,
The process is the same as the conventional process except that the process of forming the intermediate layer is added, and since the conventional process can be used as it is in terms of equipment, the industrial effect is great from the viewpoint of versatility and mass productivity.

Continuation of the front page (56) Reference JP-A-7-278833 (JP, A) JP-A-8-285956 (JP, A) JP-A-6-184762 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) C23C 22/00-22/86 C23C 28/04 H01F 1/16 C21D 9/46 501

Claims (2)

(57) [Claims] 1. A surface of a unidirectional silicon steel sheet on which secondary recrystallization has been completed: (a) a metal alkoxide of silicon, aluminum or iron.
One or both of sid and its hydrolyzable organism, or
Colloidal silica, colloidal alumina, boehmite
Steel, iron hydroxide colloid or a mixture of these
Method of applying on surface, (b) Obtained by the method of (a) above
Method of heat treatment of coating material, (c) Aluminum, iron glass
Surface soaked in treatment solution of acid salt, sulfate or chloride
After processing, by any method of heat treating, pre-oxidized silicon, aluminum oxide, one or a mixture of two or more of iron oxide, and from one or both of two or more composite oxides of these oxides Is formed, and then an aluminum borate coating is formed on the surface of the intermediate layer, the method for producing a low iron loss unidirectional silicon steel sheet. 2. A silicon oxide, aluminum oxide, one or more of a mixture of iron oxide, and 2 of these oxides
The method for producing a low iron loss unidirectional silicon steel sheet according to claim 1, wherein the thickness of the intermediate layer made of one or both of at least one kind of complex oxide is 0.001 μm or more and less than 0.1 μm. .