JP2002180134A - Method for depositing insulation film on grain oriented silicon steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a grain oriented silicon steel sheet which has extremely small iron loss by depositing a firmly adhering insulation film on a silicon steel sheet having a magnetically smooth surface. SOLUTION: A magnetically smooth grain oriented silicon steel sheet which has no forsterite based finish-annealed film is coated with a coating slution containing phosphate, free phosphoric acid, colloidal silica and an organometallic compound having a hydrophilic group or an organic bonding group and a metallic bonding group, and, baking is performed to deposit an insulation film thereon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a grain-oriented electrical steel sheet used for an iron core of a transformer and a generator, and more particularly to a grain-oriented electrical steel sheet having extremely low iron loss.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are widely used mainly as core materials for transformers and other electrical equipment.
It is important to have excellent magnetic properties such as magnetic flux density and iron loss value. In particular, it is required to reduce iron loss in order to reduce energy loss.

[0003] In order to reduce iron loss, a method for reducing the thickness of a steel sheet, a method for increasing the electrical resistance by containing effective Si in the steel sheet, and an orientation of the crystal orientation of the steel sheet effective for reducing the hysteresis loss Although there is a method of improving the heat resistance, it is known that it is effective to further apply a tension to the steel sheet. For this purpose, a coating of a material having a smaller thermal expansion coefficient than that of the steel sheet is provided.

[0004] For example, in the finish annealing step which combines the secondary recrystallization to finally align the crystal orientation and the purification of the steel sheet, the oxide on the steel sheet surface reacts with the annealing separator applied to the steel sheet surface to form forsterite as the main component. This film has a large tension applied to the steel sheet, and is effective in reducing iron loss. In order to further increase the tension, a method of overcoating a forsterite coating with a low thermal expansion coating liquid to obtain a product (oriented electrical steel sheet) has been performed.

However, in recent years, a technique for magnetically smoothing the surface of a steel sheet has been developed. For example, Japanese Patent Publication No. 52-244
No. 99 proposes a method in which after finishing annealing, surface products are removed by pickling, followed by chemical polishing or electrolytic polishing to finish the mirror surface. Japanese Patent Application Laid-Open No. 5-43943 proposes a method of removing a forsterite film and performing thermal etching in hydrogen at 1000 to 1200 ° C.

[0006] It has been found that when the surface of the steel sheet from which the forsterite coating is intentionally removed in the finish annealing step is further smoothed, a remarkable reduction in iron loss is observed. The reason iron loss is reduced by such surface treatment is that
This is because the number of pinning sites that hinder the movement of the domain wall near the surface of the steel sheet during the magnetization process is reduced.

The state of the magnetically smooth surface that reduces the hysteresis loss is not a state in which only the so-called surface roughness, which is generally expressed by Ra (center line average roughness), is reduced. It is effective that the surface state is such that it can be obtained by a crystal orientation enhancement treatment in which electrolysis is performed in a halogenated aqueous solution after removing the surface product disclosed in Japanese Patent No. 4-72920.

[0008] At present, a tension-imparting insulating coating solution applied to a grain-oriented electrical steel sheet having a forsterite film is mainly composed of a phosphate of Al or an alkaline earth metal and colloidal silica, chromic anhydride or chromate. It is often applied and baked.
The tension-imparting insulating film is formed by applying a coating solution containing an inorganic substance, such as colloidal silica, having a smaller coefficient of thermal expansion than a steel sheet at a high temperature, so that the thermal expansion between the ground iron and the insulating film at that time is performed. By utilizing the difference, tension is applied to the steel sheet at normal temperature. The formation method is described in JP-B-53-28375 and JP-B-56-52117.

The insulating coating formed by this method has a large effect of imparting tension to the steel sheet, and is effective in reducing iron loss. However, in the case of using this method, unless an insulating film having a large tension applied to a steel sheet has a stronger adhesion to a base,
There is a problem that the insulating coating peels off. That is, when the forsterite-based finish-annealed film is present on the steel sheet surface, there is no problem in the adhesion of the annealed film to the tension-imparting insulating film, but the forsterite-based finish-annealed film is removed, and particularly the mirror surface is removed. When a surface smoothing treatment such as surface treatment is performed, a tension-imparting coating liquid cannot be adhered to the surface. For this reason, the technique of magnetically smoothing the surface to reduce iron loss and the technique of reducing iron loss using a tension-imparting insulating film could not be made parallel.

Several methods have conventionally been proposed as methods for forming a tension-imparting insulating film on a surface free of a forsterite-based film and on a conditioned smooth surface.
For example, the above-mentioned Japanese Patent Publication No. 52-24499 discloses a method in which metal plating is performed, and in Japanese Patent Application Laid-Open No. 6-184762, a silicon oxide thin film is formed, and then a tension-imparting coating liquid is applied and baked. I have.

Japanese Patent Publication No. Sho 56-4150 discloses a method of forming a ceramic thin film by vapor deposition, sputtering, thermal spraying, etc., and Japanese Patent Publication No. Sho 63-54767 discloses a method of ion-plating or coating a ceramic film of nitride or carbide. A method of forming by ion plantation is disclosed. Japanese Patent Publication No. 2-243770 discloses a method of directly forming a high-tension imparting ceramic coating on a steel sheet surface by a so-called sol-gel method.

Although these methods have been devised as methods for applying tension to a steel sheet having a smooth surface,
It has some problems and has not been put to practical use.
In other words, the method of coating with a thin metal plating as a base and then coating it on it does not have sufficient adhesion of the insulating film due to the uniform smoothness of the plated surface, and the method of forming a silicon oxide thin film is inferior in the effect of imparting tension. However, the effect of improving iron loss was not sufficient.

[0013] In addition, ceramic coatings made of nitrides, carbides, or a combination thereof have a significantly lower coefficient of thermal expansion than that of ground iron, so that the effect of imparting tension due to the difference in the coefficient of thermal expansion is large. There was a problem in bending adhesion between the film and the coating. Furthermore, the formation of a ceramic coating by vapor deposition, sputtering, thermal spraying, ion plating or ion plantation is expensive, and it is difficult to ensure uniformity when processing large areas in large quantities,
In the sol-gel method, a coating film can be formed by the same application and baking as in the past, but it is extremely difficult to form a uniform and beautiful film having a thickness of 0.5 μm or more, so that a large effect of imparting tension cannot be obtained. However, the expected effect of improving iron loss was not obtained.

[0014]

SUMMARY OF THE INVENTION The present invention solves these problems of the prior art and provides a manufacturing method capable of industrially producing a grain-oriented electrical steel sheet having an extremely low iron loss value at low cost. It was done for the purpose of doing.
The present inventor has conducted intensive studies on a composition for improving the adhesion of a phosphate-based insulating coating solution to a steel sheet.As a result, a specific amount of phosphoric acid was added to a primary phosphate aqueous solution as a main component of the coating solution. When an organometallic compound having a hydrophilic group or an organic bonding group and a metal bonding group is added as an adhesion improver, the adhesion between the steel sheet surface and the insulating coating is remarkably improved, and the ground iron accompanying the improvement of the reactivity of the insulating coating solution is improved. It has been found that the reaction at the interface between the film and the insulating film can be suppressed by adding a certain amount of colloidal silica to prevent an increase in hysteresis loss, and completed the present invention.

[0015]

SUMMARY OF THE INVENTION According to the present invention, a coating solution containing a phosphate as a main component is applied to a grain-oriented electrical steel sheet from which forsterite is suppressed or forsterite is removed, and tension is applied by baking. In the method for forming a mold insulating film, phosphoric acid is added in an amount of 50 to 300 parts by mass with respect to 100 parts by mass of a phosphate group of a phosphate of the liquid.
The formation of an insulating coating on a grain-oriented electrical steel sheet, comprising 0.5 to 30 parts by mass of an organic metal compound having a hydrophilic group and / or an organic binding group and a metal binding group, and 20 to 200 parts by mass of colloidal silica. Is the way.

The preferred present invention is the above-described method for forming an insulating film on a grain-oriented electrical steel sheet, which comprises smoothing the surface of the grain-oriented electrical steel sheet before applying a coating liquid.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS It was considered important to enhance the reactivity of a coating solution in order to improve the adhesion between an insulating coating and the surface of a steel sheet. A coating solution was prepared by mixing free phosphoric acid (non-phosphate) with the coating solution containing the phosphoric acid. Then, 4.0 g / m ^{2 was} applied per one side to a smoothed magnetic steel sheet produced and processed by the following method using a grooved rubber roll, while changing the composition of the coating liquid.
Baking was performed at 50 ° C. to obtain an electromagnetic steel sheet to which the insulating coating was firmly adhered.

That is, a cold-rolled steel sheet (final sheet thickness: 0.23 mm) containing 3% by mass of Si is decarburized, subjected to primary recrystallization annealing, and then coated with an annealing separator mainly composed of magnesia.
Perform final annealing including secondary recrystallization process and purification process, further wash with sulfuric acid to remove forsterite on the surface, and then perform electropolishing in a phosphoric acid-chromic acid bath to magnetically smooth the surface. A steel plate was used.

FIG. 1 shows an example in an aqueous solution of aluminum phosphate monobasic.
Phosphate groups (PO _Four) 100 parts by mass
And 100 parts by mass of colloidal silica
Visually determine the base iron coverage of the coating liquid when added
This is the result. If the amount of phosphoric acid is less than 50 parts by mass,
The insulation coating peeled off after baking and did not even adhere
On the other hand, when the amount is 50 parts by mass or more, the effect of improving the adhesion of the insulating film is not obtained.
Appearance and almost 100% coverage could be obtained. Co
Of free phosphoric acid in the plating solution
It is thought to have increased and developed strong adhesion in the film formation process.
Can be However, when adding over 350 parts by mass,
Is an etching pattern called a wetting pattern on the insulation coating
Appeared. This is because the surface of the iron base is partially etched by phosphoric acid.
It is presumed to be a phenomenon that occurred due to
Damaged. The preferred addition amount is 150 to 250 parts by mass.
It is.

FIG. 2 shows an example in an aqueous solution of magnesium monophosphate.
Phosphate groups (PO _Four) 100 parts by mass
On the other hand, add 200 parts by mass of phosphoric acid, and
Iron loss W when the amount of idal silica was changed_17/50Measuring values
It is a fixed result. No colloidal silica added
In this case, phosphoric acid is added because iron loss value deterioration is particularly large.
When the colloidal silica is used in an amount of 20 to 200 parts by mass.
Or 50-150 parts by weight at the same time
is there.

Section SE of magnetic steel sheet on which insulating film is formed
When M observation was performed, internal oxidation occurred in the ground iron portion in contact with the insulating coating, a silica layer was formed inside the ground iron, and the smooth surface that had been smooth before the application of the coating liquid was significantly disturbed. When thin film X-ray diffraction was performed, it was also found that iron phosphate was formed. Colloidal silica is added to the phosphate-containing coating solution to lower the coefficient of thermal expansion by forming an insulating film, thereby improving the effect of imparting tension to the steel sheet. However, when colloidal silica is added to the coating solution of the present invention, If the addition amount is less than 20 parts by mass, the effect of improving the adhesion is obtained, but the iron loss value is degraded.

However, when colloidal silica was added in an amount of 20 parts by mass or more, a very thin layer was formed outward from the base iron while the interface was kept smooth. The addition of colloidal silica changes the oxidation behavior of the interface between the insulating coating and the ground iron,
It seems to have the effect of suppressing internal oxidation. Although the identity and formation mechanism of this layer is not clear, it is presumed that it is formed outside of the base iron and plays a role of a binder without losing magnetic smoothness, contributing to the improvement of adhesion. . When more than 200 parts by mass of colloidal silica was added, powdering occurred and the appearance of the insulating coating was also poor.

The third feature of the present invention is that the coating liquid
The point is that an organic metal compound having a hydrophilic group and / or an organic bonding group and further having a metal bonding group is added. Here, it is presumed that the metal bonding group chemically bonds to the steel plate or the very thin forming layer and contributes to the adhesion of the insulating film.
Further, it is presumed that the organic bonding group and the hydrophilic group also chemically act on the insulating film and contribute to the adhesion.

The addition amount of the organometallic compound may be small since it only needs to act on the interface between the ground iron and the insulating coating.
It is preferably 0 parts by mass, particularly preferably 5 to 15 parts by mass.
When the amount is less than 0.5 part by mass, there is no effect of improving the adhesion of the insulating film, and when the amount exceeds 30 parts by mass, the film formation of the coating liquid is adversely affected, and it becomes difficult to form the film in a short time.

The organometallic compound used in the present invention is methane,
Hydrocarbons such as linear hydrocarbons such as ethane, propane and butane, and alicyclic hydrocarbons such as cyclohexane,
The skeleton is made of a compound in which one or more metals such as l, Fe, Si, Ti, and Zr are bonded together (single metal) or two or more, but is not limited to those exemplified as a matter of course. The organometallic compound of the present invention has a hydrophilic group and / or an organic bonding group and a metal bonding group in addition to the above skeleton.
It also includes those in which the skeleton hydrocarbon also serves as an organic bonding group.

Examples of the metal binding group include an alkoxy group which produces an MO--Fe type metal bond by hydrolysis such as a methoxy group and an ethoxy group, a hydrolyzable group thereof, an acyl group such as an acetoxy group, and a methoxycarbonyl group. Examples include a halogen atom such as a lower alkoxycarbonyl group and a chlorine atom. Here, M is a metal in the organometallic compound, and is one or more of Al, Fe, Si, Ti, and Zr described above. However, since Si can form a stable bond as described later, preferable.

Examples of the hydrophilic group include an amino group, a carboxyl group, a hydroxyl group, a carbonyl group and a sulfo group.

As the organic bonding group, a vinyl group, an epoxy group, a methacryl group, a methacryloxy group, a mercapto group,
Examples include organic groups other than simple alkyl groups such as ureido groups and glycidoxy groups, and halogen atoms such as chlorine atoms.

Preferred organometallic compounds are the organosilicon compounds known as silane coupling agents, or oligomers thereof. Specifically, vinyltrichlorosilane, vinyltris (β-methoxyethoxy) silane, vinyltriethoxysilane, vinyltrimethoxysilane, γ-
(Methacryloyloxypropyl) trimethoxysilane and other organic bonding group-containing organometallic compounds, β- (3,4
-Epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidyloxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane, γ-aminopropyl Examples include hydrophilic group-containing organometallic compounds such as triethoxysilane and γ-mercaptopropyltrimethoxysilane.
Preferred is γ-aminopropyltriethoxysilane,
γ-glycidyloxypropyltrimethoxysilane.

The grain-oriented electrical steel sheet to which the coating solution of the present invention is applied is one after the formation of forsterite has been suppressed or after the finish annealing for removing forsterite. As a metal surface after finish annealing, it is effective to use a ground iron surface that simply removes an inorganic coating such as forsterite, but it is more effective to further smooth the surface from the viewpoint of lowering iron loss value. It is valid. For example,
The surface roughness is preferably minimized by thermal etching, chemical polishing, or the like, and the surface is preferably mirror-finished or a graining-like surface obtained by crystal orientation enhancement treatment by electrolysis in an aqueous halide solution. .

Hereinafter, the component composition of the magnetic steel sheet of the present invention will be described. As a component of the magnetic steel sheet, Si is 1.5 to
It is desirable to make it contain 7.0 mass%. That is, S
i is an effective component for increasing the electrical resistance of the product and reducing the iron loss, but when the Si content exceeds 7.0% by mass, the hardness increases, and the production and processing tend to be difficult. . S
If the i content is less than 1.5% by mass, transformation occurs during the final finish annealing, and a stable secondary recrystallized structure cannot be obtained.

The crystal orientation can be further improved by adding 0.006% by mass or more of Al as an inhibitor element in the initial steel. The upper limit is 0.06% by mass. If the upper limit is exceeded, degradation of crystal orientation starts again. Nitrogen has the same effect, and the upper limit is preferably 100 ppm from the occurrence of blistering defects. Although the lower limit of the nitrogen content is not particularly specified, it is economically difficult to reduce the nitrogen content to less than 20 ppm on an industrial scale, and 20 ppm is preferred.

It is also effective to add a step of performing a nitrogen increasing treatment after the primary recrystallization annealing. When the nitrogen increasing treatment is not performed, 0.02 to 0.2% by mass of Mn is contained in the initial steel in order to precipitate MnSe and MnS as sub-inhibitors.
And Se and / or S are 0.01 to
It is important to contain 0.06% by mass. If the respective contents are too small, the amount of precipitates for secondary recrystallization will be too small, and if too large, it will be difficult to form a solid solution before hot rolling. When performing the nitrogen increasing treatment, Mn is not necessarily added, but it is preferable to add as appropriate for the purpose of improving the ductility of the steel sheet.

In the steel, besides the above-mentioned elements, B, Bi,
Sb, Mo, Te, Sn, P, Ge, As, Nb, N
An element selected from i, Cr, Ti, Cu, Pb, Zn and In can be contained alone or in a composite of about 0.0005 to 2.0% by mass.

Further, impurities such as C, S and N all have a harmful effect on magnetic properties and particularly deteriorate iron loss, so that C: 0.003% by mass or less and S: 0.
It is preferable to reduce the content to 002% by mass or less and N: 0.002% by mass or less.

Next, the preferred conditions and the reasons for the method for producing an electromagnetic steel sheet of the present invention will be described. After the steel adjusted to the predetermined component is usually subjected to slab heating, it is turned into a hot-rolled coil by hot rolling.
Any of a high temperature of 0 ° C. or higher and a low temperature of 1250 ° C. or lower may be used. In recent years, a method of performing direct hot rolling after continuous casting without performing slab heating has been developed. However, the method of the present invention can also be applied to a steel sheet by this method.

The hot-rolled steel sheet is subjected to hot-rolled sheet annealing as necessary, and a final cold-rolled sheet is obtained by performing one cold rolling or a plurality of rolling steps including intermediate annealing. These rollings may be those subjected to so-called warm rolling aiming at dynamic aging or inter-pass aging aiming at static aging.

The steel sheet after the final cold rolling is subjected to primary recrystallization annealing also serving as decarburization annealing, and is subjected to secondary recrystallization treatment by final finish annealing to obtain a directionality. When performing final finish annealing, usually apply an annealing separator after primary recrystallization annealing,
Although an oxide film is thereby formed, the composition of the annealing separator can be adjusted to suppress the formation of an oxide film on the steel sheet surface.

Even if the steel sheet thus obtained is irradiated with a laser or plasma flame for the purpose of further reducing iron loss, and the magnetic domains are subdivided, there is no problem in the adhesion of the insulating film. Absent. Also, at any stage of the production process of the grain-oriented electrical steel sheet of the present invention, for magnetic domain refinement, etching or forming grooves at regular intervals on the surface with tooth-shaped rolls is also effective as a means for further reducing iron loss. It is.

[0040]

EXAMPLES (Examples 1 to 4, Comparative Examples 1 to 6) A cold-rolled steel sheet (final sheet thickness: 0.23 mm) containing 3% by mass of Si was decarburized and subjected to primary recrystallization annealing. Using an annealing separator containing 0.3% by mass of lead chloride to suppress the formation of a forsterite film, form grooves for subdividing magnetic domains, and then recrystallize the grain-oriented electrical steel sheet. I got

Colloidal silica, phosphoric acid, an ethoxy group as a metal binding group and an amino group as a hydrophilic group were added to an aqueous solution obtained by adding 15 parts by weight of potassium dichromate to 100 parts by weight of magnesium phosphate having a phosphate group. The aminopropylethoxysilane was mixed at a ratio shown in Table 1 to prepare a coating solution. The liquid was applied to the above steel sheet with a roll coater and baked at 800 ° C. to form a coating having a thickness of about 4.0 g / m ² .

The film adhesion and iron loss W _{17/50 of the} obtained steel sheet
The value was evaluated by the following method. Table 1 summarizes the liquid composition and the evaluation results.

[Table 1] The iron loss was measured by measuring a loss [W _17/50 (W / kg)] when magnetized to 1.7 T at a frequency of 50 Hz. The adhesion of the coating was evaluated by wrapping the sample around a round bar having various diameters and the minimum diameter (mm) at which the coating did not peel off. The appearance was visually observed.

As is clear from Table 1, Samples 2, 8,
Since _Nos . 9 and 10 are compatible with the coating liquid composition of the present invention, they show excellent appearance, coating adhesion (minimum bending peel diameter), and iron loss W _17/50 value. On the other hand, the addition amount of phosphoric acid, colloidal silica, or an organometallic compound having a metal binding group is not compatible with the composition of the present invention. That is, Samples 1, 3 to 7 have poor adhesion and appearance, and have poor magnetic properties. Has deteriorated.

(Examples 5 to 8, Comparative Examples 7 to 12) Cold rolled steel sheet containing 3% by mass of Si (final sheet thickness: 0.23 mm)
After forming etching grooves at intervals of 5 mm for subdividing magnetic domains, decarburizing and performing primary recrystallization annealing, an annealing separator containing magnesia as a main component and containing 0.3% by mass of lead chloride is applied, and final finish annealing is performed. I got a board. Further, as an additional treatment, a smoothing treatment as a crystal orientation enhancement treatment by electrolysis in an aqueous sodium chloride solution was performed to magnetically smooth the surface.

In an aqueous solution containing 100 parts by mass of a phosphate group and 10 parts by mass of chromic acid, colloidal silica, phosphoric acid, and a glycide having a methoxy group as a metal binding group and a glycidoxy group as an organic binding group. A coating solution prepared by mixing xypropyltrimethoxysilane was applied to the above steel plate and baked at 850 ° C. to form a coating having a thickness of about 5.0 g / m ² . The appearance, adhesion and magnetic properties of the magnetic steel sheet were evaluated, and the evaluation results are shown together with the liquid composition in Table 2.

[Table 2]

As is clear from Table 2, Samples 12, 1
Nos. 6, 19 and 20 are suitable for the coating liquid composition of the present invention, and thus have excellent appearance, film adhesion and iron loss _{W17 / 50} value. In contrast, phosphoric acid and colloidal silica,
Samples 11, 13 to 15, 1 and 1 in which the amount of the organometallic compound having a metal binding group is not compatible with the composition of the present invention.
In Nos. 7 and 18, the insulating film was not formed well or the magnetic properties were deteriorated.

[0047]

According to the method of the present invention, it is possible to form an insulating coating having good adhesion on the surface of a smooth grain-oriented electrical steel sheet having no finish-annealed coating, and to significantly reduce iron loss. Can be produced on an industrial scale at low cost. The obtained steel sheet can be suitably used as a core material of a transformer or the like.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of phosphoric acid added to a coating solution and the coverage of the coating solution on a steel plate.

FIG. 2 is a graph showing the relationship between the amount of colloidal silica added to a coating solution and the iron loss value of a steel sheet on which an insulating film has been formed.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Mitsumasa Kurosawa 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. EA01 EA06 EA07 EB11 4K033 RA04 TA04 TA08 5E041 AA02 BC08 CA02 HB14

Claims (2)

[Claims] 1. A method for forming a tension-imparting insulating film by applying and baking a coating solution containing phosphate as a main component to a grain-oriented electrical steel sheet in which forsterite formation is suppressed or forsterite is removed. ,
50 to 350 parts by mass of phosphoric acid, 0.5 to 30 parts by mass of an organometallic compound having a hydrophilic group or an organic binding group and a metal binding group, based on 100 parts by mass of the phosphate group of the phosphate of the solution. And 20 to 200 parts by mass of colloidal silica. 2. The method for forming an insulating coating on a grain-oriented electrical steel sheet according to claim 1, wherein the surface of the grain-oriented electrical steel sheet is smoothed before applying the coating liquid.