JPH04308093A - Silicon steel sheet having electrolytic-treated insulating film and its production - Google Patents

Abstract

PURPOSE:To inexpensively produce a silicon steel sheet excellent in insulating property and punchability by forming an insulating film consisting of specific amounts of chromium oxide and specific amounts of at least one kind among Al oxide, Zr oxide, etc., on a silicon steel sheet. CONSTITUTION:An electrolytic-treated insulating film consisting of chromium hydrated oxide and/or chromium oxide and at least one kind among Al oxide, Si oxide, Ti oxide, and Zr oxide is formed on the surface of a silicon steel sheet. The amount of chromium hydrated oxide and/or chromium oxide is regulated to 5-50mg/m<2> expressed in terms of chromium, and further, the total amount of at least one kind among Al oxide, Si oxide, Ti oxide, and Zr oxide is regulated, expressed in terms of Al, Si, Ti, and Zr, to a value 0.1-10 times the amount of chromium hydrated oxide and/or chromium oxide expressed in terms of chromium. By this method, the silicon steel sheet having the insulating film excellent in heat resistance, corrosion resistance, and adhesive strength of coating can be produced easily and inexpensively.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an electromagnetic steel sheet having an electrolytically treated insulating coating excellent in insulation, punchability, heat resistance, corrosion resistance, weldability and paint adhesion, and a method for manufacturing the same.

0002

2. Description of the Related Art Electrical steel sheets are widely used as iron core materials for electrical equipment such as motors and transformers. An insulating coating is usually formed on the surface of the electromagnetic steel sheet used as such an iron core material in order to reduce eddy current loss. This insulating coating is required to have excellent punchability, heat resistance, corrosion resistance, weldability, and paint adhesion as well as insulation.

Insulating coatings for electrical steel sheets are broadly classified into inorganic coatings, inorganic/organic coatings, and organic coatings, and many proposals have been made regarding these insulating coatings, but none of them have the above-mentioned performance. There is nothing that can satisfy all of them.

[0004] An inorganic insulating coating is produced by applying a treatment solution containing at least one of a phosphate compound, a chromate compound, and an oxide sol onto the surface of an electrical steel sheet, and then
It is formed by baking at a relatively high temperature of 00 to 600°C.

[0005] The inorganic/organic insulating coating is produced by applying a mixed treatment solution of an inorganic aqueous solution consisting of at least one of a phosphate compound, a chromate compound, and an oxide sol, and an aqueous organic resin onto the surface of an electrical steel sheet. It is formed by applying the coating to a surface and then baking it, and has been widely put into practical use as an insulating coating with excellent punching properties.

[0006] Organic coatings are formed by applying an organic coating onto the surface of an electrical steel sheet and then baking it. It is often formed as a so-called varnish treatment before and after processing. In some cases, the organic coating may be formed after the coating of the electrical steel sheet on which the above-mentioned inorganic coating or inorganic/organic coating has been formed is removed by grinding with a grinder or the like.

[0007]

[Problems to be Solved by the Invention] Although inorganic insulating coatings have excellent heat resistance and weldability, they are hard and brittle and therefore have poor punchability. Therefore, especially when the coating is thick, the coating may peel off or be damaged from the surface of the steel sheet during punching. Then, the coating powder generated by such peeling or breakage becomes clogged between the punch and the tie of the punching die, and as a result, burrs are generated.

Inorganic/organic insulating coatings solve the above-mentioned drawbacks of inorganic insulating coatings and have excellent punchability. However, on the other hand, since the organic resin is contained, a decrease in heat resistance and weldability is unavoidable. Magnetic steel sheets for iron cores are often subjected to strain relief annealing during or after forming into iron cores in order to remove generated processing strains and improve magnetic properties. For such strain relief annealing, the electrical steel sheet is heated at a temperature of approximately 700 to 800°C. At this time,
As mentioned above, the inorganic/organic insulating coating has low heat resistance, so the organic resin in the coating is thermally decomposed and a part of it is gasified. As a result, the coating becomes porous, and its insulation, adhesion, and corrosion resistance are significantly reduced. In addition, during welding, the organic resin in the coating is thermally decomposed due to welding heat, and part of it is gasified, resulting in a blowhole in the weld bead and a decrease in weld strength. .

[0009] Organic coatings have a problem in that the adhesion of the coating to the surface of the steel plate is poor, and therefore coating unevenness and repellency are likely to occur due to the cleanliness of the steel plate surface before coating.

On the other hand, the formation of the above-mentioned insulating film has been conventionally
This is done by the so-called coating and baking method, which consists of applying a treatment liquid onto the surface of an electrical steel sheet and then baking it. However, the conventional coating/baking method has many problems in actual operation, such as the following. In other words, a squeeze roll or three-roll coater is normally used as a means to continuously apply a treatment liquid to an electromagnetic steel strip running at high speed. In order to form a thin coating film of uniform thickness, it is necessary to delicately adjust conditions such as the nip thickness between the roll and the steel strip or the roll, and the peripheral speed ratio of the rolls. Therefore, each time the width or thickness of the steel strip changes, the above conditions must be set, which requires a lot of time.

[0011] Furthermore, continuous application of the treatment liquid causes wear of the roll, which changes the surface shape and quality of the roll, resulting in changes in the amount of treatment liquid applied to the steel strip and the appearance of the coating film. Therefore, it is necessary to periodically replace the rolls, which requires a great deal of effort.

Furthermore, the treatment liquid applied to the surface of the steel strip foams between the roll and the steel plate or between the rolls, causing the foam to become entangled in the coating film. As a result, when the paint film is baked, the water in the paint film rapidly evaporates, producing minute pinholes in the paint film, resulting in quality defects such as reduced corrosion resistance.

[0013] Therefore, the object of the present invention is to solve the above-mentioned problems and provide an electrical steel sheet that is easy to manufacture and inexpensive, having an insulating coating with excellent insulation properties, punchability, heat resistance, corrosion resistance, and paint adhesion. and its manufacturing method.

[0014]

[Means for Solving the Problems] The present inventors have conducted extensive research in order to solve the above-mentioned problems. As a result, a predetermined amount of chromium hydrated oxide and/or chromium oxide and a predetermined amount of Al oxide, Si oxide, Ti oxide, and Zr oxide are present on at least one surface of the electrical steel sheet. If an insulating film consisting of at least one of these is formed by cathodic electrolytic treatment, it is possible to easily and inexpensively produce an electrical steel sheet having an insulating film with excellent insulation, punchability, heat resistance, corrosion resistance, and paint adhesion. I found out that.

[0015] This invention was made based on the above-mentioned knowledge.
An electrolytically treated insulating film consisting of chromium hydrate oxide and/or chromium oxide and at least one of Al oxide, Si oxide, Ti oxide and Zr oxide is formed on one surface. , the amount of the chromium hydrated oxide and/or chromium oxide is 5 to 50% in terms of chromium.
mg/m2, and the total amount of at least one of the Al oxide, Si oxide, Ti oxide and Zr oxide is within the range of the chromium hydrated oxide in terms of Al, Si, Ti and Zr. The amount of chromium oxide and/or chromium oxide is within the range of 0.1 to 10 times the chromium equivalent amount.

[0016]

[Operation] In the present invention, chromium hydrated oxide and/or chromium oxide, Al oxide, S
In the insulating film made of at least one of i oxide, Ti oxide and Zr oxide, the chromium hydrated oxide and/or the chromium oxide has non-electrical conductivity,
And Al oxide, Si oxide, Ti oxide and Z
Since at least one of the r-oxides has heat resistance and non-electrical conductivity, it imparts high insulation, heat resistance, and corrosion resistance to the electrical steel sheet. Therefore, even if heat treatment such as strain relief annealing is performed and most of the hydrated chromium oxide in the coating is transformed into chromium oxide, the insulation and corrosion resistance will not deteriorate.

As mentioned above, in order to form a film by the conventional coating and baking method, baking treatment at a relatively high temperature of 300 to 600° C. is required. Therefore, since the coating is hardened while the steel plate is thermally expanded, a large internal stress exists in the coating at room temperature. As a result, during the punching process, the coating peels off or breaks from the surface of the steel plate, and the resulting coating powder gets stuck between the punch and the tie of the punching die, causing burrs. On the other hand, in the present invention, about 40 to 6
Since the film is formed at a low temperature of 0°C, the internal stress in the film is small, and it has excellent adhesion, which is a characteristic of electrolytic treatment. Punching properties are good.

[0018] Furthermore, by at least one of Al oxide, Si oxide, Ti oxide, and Zr oxide,
Improves paint adhesion of insulation coating. In this way, the paint adhesion of the insulating coating is improved by at least one of Al oxide, Si oxide, Ti oxide, and Zr oxide.
This is presumed to be due to the presence of granular protrusions on the surface of the coating, which act as an anchor effect for the paint.

Chromium hydrated oxide and/or in the insulation coating
Or the content of chromium oxide is 5 to 5 in terms of chromium.
It should be within the range of 0mg/m2. If the content of chromium hydrated oxide and/or chromium oxide is less than 5 mg/m2 in terms of chromium, sufficient corrosion resistance and insulation cannot be obtained. On the other hand, its content is 5% in terms of chromium.
If it exceeds 0 mg/m2, punching performance deteriorates.

[0020] Al oxide, Si oxide,
The total content of at least one of Ti oxide and Zr oxide is calculated based on Al, Si, Ti, and Zr.
In terms of conversion, the amount of chromium hydrated oxide and/or chromium oxide should be within the range of 0.1 to 10 times the amount of chromium equivalent. The reason is as follows. That is, each of the above-mentioned oxides does not itself contribute to the electrolytic deposition reaction, but exists dispersedly in the electrolytically deposited chromium hydrated oxide and/or chromium oxide layer. Therefore, the hydrated chromium oxide and/or the chromium oxide act as a binder that fixes at least one of the above-mentioned oxides. As a result, the content of at least one of the above-mentioned oxides is 10 times the amount of chromium hydrated oxide and/or at least one of the chromium oxides in terms of Al, Si, Ti, and Zr. If it exceeds the range, the above-mentioned oxides will easily peel off, and the effect will be reduced. On the other hand, if the content is less than 0.1 times, the above effects cannot be obtained.

Next, a method for manufacturing the electrical steel sheet of the present invention will be described. The above-mentioned insulating coating formed on at least one surface of the electrical steel sheet contains at least one of chromic anhydride and chromate group, and at least one of Al oxide, Si oxide, Ti oxide, and Zr oxide. It is formed by subjecting an electrical steel sheet to cathodic electrolytic treatment in an electrolytic treatment solution containing one of the above.

It is desirable that the surface of the electrical steel sheet to be subjected to the above-mentioned electrolytic treatment is clean, and if necessary, the electrical steel sheet is spray-cleaned or electrolytically cleaned in advance with an alkaline aqueous solution or an acid aqueous solution.

The composition of the electrolytic treatment solution includes at least one of chromic anhydride and chromate group, ie, chromic anhydride, ammonium chromate, ammonium dichromate, sodium chromate, sodium dichromate, and A.
It is not particularly limited as long as it contains at least one of L oxide, Si oxide, Ti oxide, and Zr oxide. In addition, electrical conduction aids such as sodium sulfate and p-containing agents such as boric acid may be added to the electrolytic treatment solution as aids.
H buffer may be added.

[0024] Al oxide added to the electrolytic treatment solution;
At least one of the Si oxide, Ti oxide, and Zr oxide is preferably in the form of an oxide sol or fine particle oxide powder, particularly in the form of an aqueous oxide sol with a particle size of 50 mμ or less. However, it is effective in terms of dispersion stability in the electrolytic treatment solution and uniform dispersibility in the film.

The pH value of the electrolytic treatment solution is preferably within the range of 1 to 5. When the pH value is less than 1, the efficiency of precipitation of hydrated chromium oxide and/or chromium oxide is low. On the other hand, when the pH value exceeds 5, the adhesion of the hydrated chromium oxide and/or chromium oxide to the steel plate decreases. When using an aqueous oxide sol, good dispersion stability is exhibited within the pH value range of 1 to 5.

[0026] The cathodic electrolytic conditions may be the usual electrolytic conditions for forming a chromate film using a steel plate as a cathode. Note that before and after the cathodic electrolytic treatment, the electrical steel sheet may be subjected to an anodic electrolytic treatment using the steel sheet as an anode in order to adjust the amount of hydrated chromium oxide and/or chromium oxide. The temperature of the electrolytic treatment solution is preferably within the range of 40 to 60°C,
The cathode current density is preferably in the range of 5 to 80 A/dm2, and the anodic current density in the case of anodic electrolytic treatment is preferably in the range of 0.1 to 20 A/dm2.

[0027] Next, the present invention will be explained in more detail by way of Examples and in comparison with Comparative Examples.

[Example] Si was added to 0.4 wt. Thickness containing 0.5%
An electrical steel sheet of mm 2 was degreased by a known method and then pickled to clean both surfaces. Next, cathodic electrolytic treatment was performed under the treatment conditions (A) to (D) shown below to form an insulating film on both surfaces of the electrical steel sheet, thus obtaining steel sheet No. 1 of the present invention. 1 to 4 were prepared.

(A) Treatment electrolytic treatment solution: Sodium dichromate: 30g/l Chromic anhydride: 5g/l silica sol
:50g/l (solid content 20%)
Treatment temperature: 45℃ Treatment method: 10A/dm2 using a steel plate as a cathode
After electrolysis for 1.4 seconds at a current density of , it was immediately washed with water and dried.

(B) Treatment electrolytic treatment solution: Chromic anhydride: 60
g/l Sodium dichromate: 10g/l Titania sol: 30g/l (solid content 10%) Treatment temperature: 45℃ Treatment method: 50A/dm2 using a steel plate as a cathode
After electrolysis for 0.8 seconds at a current density of , immediately washed with water and dried.

(C) Treatment electrolytic treatment solution: Sodium dichromate: 30 g/l
Sodium sulfate: 10g/l boric acid
:20g/l alumina sol
: 50g/l (solid content 20%) Treatment temperature: 45℃ Treatment method: 20A/dm2 using a steel plate as a cathode
After electrolysis for 1.4 seconds at a current density of , it was immediately washed with water and dried.

(D) Treatment electrolytic treatment solution: Ammonium dichromate: 20g/l
Boric acid: 20g/l
Silica sol: 30g/l (
Solid content 20%) Zirconia sol:
10g/l (solid content 10%) Processing temperature:
45℃ Treatment method: 30A/dm2 using a steel plate as a cathode
After electrolysis for 1.4 seconds at a current density of , it was immediately washed with water and dried.

For comparison, with respect to the above-mentioned electrical steel sheet,
Comparative steel plate No. 1 was prepared by the following treatments E and F.
1 and 2 were prepared. (E) Treatment coating liquid: Magnesium monophosphate: 150
g/l calcium dichromate: 20 g/l silica sol: 25 g/l
(Solid content 20%) Boric acid
: 15 g/l Processing method: The above coating liquid is applied onto the surface of an electrical steel sheet using a 3-roll coater, and then baked in a baking furnace to reach a plate temperature of 450°C. .3μ
An inorganic insulating film with a thickness of m was formed.

(F) Treatment coating liquid: Magnesium dichromate: 130
g/l boric acid:
25 g/l ethylene glycol: 25 g
/l Acrylic resin emulsion: 30 g/l (
Processing method: The above coating liquid is applied onto the surface of an electrical steel sheet using a 3-roll coater, and then this is heated in a baking furnace to reach a board temperature of 290°C.
A baking treatment was performed at 0.3° C. to form an inorganic/organic insulating film with a thickness of 0.3 μm.

[0034] Cr, Al, Si, T
The contents of i and Zr were investigated by quantitative analysis using a fluorescent X-ray analyzer (FX) or an X-ray microanalyzer (EPMA). Furthermore, the punchability, weldability, paint adhesion, interlayer insulation resistance before and after strain relief annealing, and corrosion resistance of each of the steel sheets of the present invention and comparative steel sheets were examined by the methods described below. Note that strain relief annealing was performed by heating the test piece at a temperature of 750° C. for 2 hours in a nitrogen atmosphere.

(1) Punching property test The burr height of the blank was examined when the specimen was continuously punched under the following conditions, and evaluation was made based on this. Punching shape: Round shape with a diameter of 10 mm, Number of punchings: 200,000 times, Mold material: SKD-11, Punching oil: Used.

(2) Weldability A plurality of laminated electrical steel sheets were TIG welded under the following conditions and evaluated based on the maximum welding speed at which no blowholes were generated at the bead. Core tightening pressure: 60Kg/cm2 Welding current: 100A

(3) Paint adhesion test A 30 μm thick cationic electrodeposition coating of epoxy paint was applied to the surface of the test piece, and then this was immersed in boiling water for 2 hours to confirm the application of such treatment. The peeled area of the coating film was examined when the test piece was subjected to a cross-cut tape test, and evaluation was made based on this.

(4) Interlayer insulation resistance value: Examined based on JIS C 2550 Method 2. (5) After leaving the corrosion resistance test piece in a constant temperature and humidity test chamber at a temperature of 50°C and a relative humidity of 80% for 20 days, the rusted area of the test piece (
%) and was evaluated based on this.

Table 1 shows the composition of the insulating coating of each of the steel sheets of the present invention and comparative steel sheets, as well as the above-mentioned examination of punchability, weldability, paint adhesion, interlayer insulation resistance before and after strain relief annealing, and corrosion resistance. Show the results.

[0040]

[Table 1]

As is clear from Table 1, comparative steel sheet No. 1 has an inorganic insulating coating formed by the conventional coating and baking method.
Sample No. 1 had poor punchability, paint adhesion, interlayer insulation resistance after strain relief annealing, and corrosion resistance. Comparative steel sheet No. 1 has an inorganic/organic insulating coating formed by conventional coating and baking methods. Sample No. 2 had poor weldability, paint adhesion, interlayer insulation resistance after strain relief annealing, and corrosion resistance.

On the other hand, steel sheet No. of the present invention. Nos. 1 to 4 are excellent in punchability, weldability, paint adhesion, interlayer insulation resistance before and after strain relief annealing, and corrosion resistance, and the thickness of the insulation coating is uniform across the width and length of the steel plate. Met.

[0043]

[Effects of the Invention] As described above, according to the present invention,
Electrical steel sheets with insulating coatings that have excellent insulation, punchability, heat resistance, corrosion resistance, and paint adhesion can be manufactured easily and inexpensively, and even if the steel sheets are subjected to heat treatment such as strain relief annealing, The heat does not deteriorate insulation properties, corrosion resistance, paint adhesion, etc. Furthermore, for the formation of an insulating coating on electromagnetic steel strips running at high speed,
There is no need to periodically replace the rolls due to wear, unlike the conventional coating/baking method using a squeeze roll or 3-roll coater, and it is easy to create a thin insulating coating with a uniform thickness in the longitudinal and width directions. Many industrially useful effects are brought about, such as being able to be formed in a short time and economically.

Claims (3)

[Claims] Claim 1: On at least one surface of an electrical steel sheet, chromium hydrated oxide and/or chromium oxide and A
An electrolytically treated insulating film consisting of at least one of chromium oxide, Si oxide, Ti oxide and Zr oxide is formed, and the amount of the chromium hydrated oxide and/or chromium oxide is 5 to 50 mg/m2 in terms of
and the total amount of at least one of the Al oxide, Si oxide, Ti oxide and Zr oxide is within the range of the chromium hydrated oxide and/or in terms of Al, Si, Ti and Zr. Or an electromagnetic steel sheet having an electrolytically treated insulating coating, characterized in that the amount of chromium oxide is in the range of 0.1 to 10 times the amount of chromium equivalent. 2. In an electrolytic treatment solution containing at least one of chromic anhydride and chromate group, and at least one of Al oxide, Si oxide, Ti oxide, and Zr oxide, an electrical steel sheet is treated. is subjected to cathodic electrolysis treatment to coat at least one surface of the electrical steel sheet with chromium hydrated oxide and/or chromium oxide in an amount within the range of 5 to 50 mg/m2 in terms of chromium, and the total amount thereof. ,
0 of the chromium equivalent amount of the chromium hydrated oxide and/or chromium oxide in terms of Al, Si, Ti and Zr.
．． Al oxide, Si oxide, within the range of 1 to 10 times
A method for manufacturing an electrical steel sheet having an electrolytically treated insulating film, the method comprising forming an insulating film comprising at least one of Ti oxide and Zr oxide. 3. The method according to claim 2, wherein the pH value of the electrolytic treatment solution is within the range of 1 to 5.