JP2001107146A - Grain-oriented silicon steel sheet extremely small in core loss and its producing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably produce a grain-oriented silicon steel sheet extremely excellent in core loss on an industrial scale, even in technology in which core loss is reduced by subjecting the surface of a steel sheet to smoothening treatment and crystal orientation emphasizing treatment and moreover depositing a tensile film thereon without damaging the adhesion of the tensile film by applying sufficient tension to the steel sheet. SOLUTION: The surface of a grain-oriented silicon steel sheet with a sheet thickness of <=0.27 mm free from forsterite films is deposited with a coating layer having the average thickness of 0.1 to 10 μm per side by vapor phase deposition in a low oxidizing atmosphere in which the total pressure is controlled to >=0.1 atmospheric pressure, and also, the oxygen partial pressure P (O2) is controlled to <0.1 atm.

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 an extremely small iron loss suitable for use as an iron core material of a transformer or a generator, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Si is contained and the crystal orientation is (110).
Grain-oriented electrical steel sheets oriented in the [001] direction or the (100) [001] direction have excellent soft magnetic properties and are therefore widely used as various iron core materials in the commercial frequency range. As a characteristic required for such a grain-oriented electrical steel sheet, it is generally important that iron loss represented by W _17/50 (W / kg), which is a loss when magnetized to 1.7 T at a frequency of 50 Hz, is low. .

In order to reduce iron loss, effective methods for reducing eddy current loss include a method of increasing electric resistance by containing Si, a method of reducing the thickness of a steel sheet, and a method of reducing a crystal grain size. There is a method, etc., on the other hand, as a method effective in reducing the hysteresis loss, there is a method of aligning the crystal orientation.

[0004] Among them, the method of increasing the electric resistance by containing Si has a limit because excessive addition of Si causes a decrease in the saturation magnetic flux density and causes an increase in the size of the iron core.
Similarly, the method of reducing the thickness of the steel sheet has a limit because it extremely increases the manufacturing cost. Further, 1.96T and 1.97T in the method of aligning the crystal orientation, and the magnetic flux density B ₈
Products have been obtained, but there is little room for further improvement.

Further, in recent years, the magnetic domain width has been artificially subdivided by a method such as locally introducing strain into the steel sheet surface by irradiating a plasma jet or a laser beam, or forming a groove in the steel sheet surface. Technology for reducing loss has been developed, and a significant iron loss reduction effect has been obtained. However,
There is a limit to the iron loss reduction effect of this technology.

On the other hand, separately from these, Japanese Patent Publication No. 52-24499
As disclosed in Japanese Unexamined Patent Publication (Kokai) No. 6-37694, it is possible to reduce the roughness of the interface between the metal surface of the steel sheet and the non-metallic coating. As disclosed in the gazette, there has been proposed a method for reducing iron loss by performing a so-called crystal orientation emphasis treatment for leaving a crystal having a specific crystal orientation on a metal surface.
However, in order to reduce iron loss with these technologies, it is essential to apply strong tension to the steel sheet.
For that purpose, it was necessary to make a tension coating exist on the steel sheet surface. In other words, in the absence of the tension coating, the steel sheet surface was smooth, and conversely, the expansion of the magnetic domain width was promoted, leading to a significant deterioration of iron loss.

As a means for solving this problem, Japanese Patent Publication No. 52-24499 mentioned above discloses a method in which the surface of a steel sheet is mirror-polished by chemical polishing or electrolytic polishing, and the surface of the steel sheet is subjected to thin metal plating to oxidize or insulate the steel sheet surface. We have proposed a method of suppressing magnetic defects due to deterioration of the steel sheet surface when coating and baking the coating.However, if the metal plating has tension, the insulating coating is easily peeled off by baking treatment. However, since the insulating coating was a normal phosphate-based non-tensile insulating coating, the effect of reducing iron loss was not so large. On the other hand, when the metal plating has no tension effect, the iron loss reduction effect is negligible, and in this case,
Even if an attempt is made to form a phosphate-based tension insulating film as the insulating film, it is difficult to improve magnetic properties because good film adhesion cannot be obtained. Therefore, this technology was never industrialized.

[0008] Japanese Patent Application Laid-Open No. 62-103374 discloses that, on the surface of a steel plate which is smoothed by polishing, various mixed oxides, borides, silicides, phosphides, sulfides and ground iron are mixed. Although a method of forming a layer and an insulating coating baking layer thereon is disclosed, this method has excellent adhesion between the steel sheet and the insulating layer, but the mirror-surface smoothing effect of the steel sheet is different from that of ground iron. Disappears due to the presence of the mixed ultrathin layer of
As expected, the effect of improving magnetic properties was not as good as expected, and it has not yet been industrialized.

Further, Japanese Patent Publication No. 2-243770 discloses a method of forming a ceramic film by a sol-gel method. However, this method has a problem that a sufficient tension is applied because of poor adhesion to a steel sheet. No effect could be exerted on the steel sheet.

In addition, Japanese Patent Publication No. 56-4150 discloses that the surface of a steel sheet is subjected to chemical line polishing or electrolytic polishing to obtain a center line average roughness Ra.
A method of forming a ceramic thin film on a smooth surface of 0.4 μm or less and further forming a ceramic thin film thereon is disclosed.However, since the method of forming a ceramic thin film having good adhesion is chemical vapor deposition or vacuum vapor deposition, mass production in equipment is required. It is difficult and the deposition rate is slow, so it is not suitable for industrial production and has not yet been industrialized.

In addition, Japanese Patent Application Laid-Open Nos. 3-47957 and 3-294465.
No. 3-294466, No. 3-294467, No. 3-294468
Nos. 3-294469 and 3-294470,
Japanese Patent Application Laid-Open No. 10-245667 discloses a method of forming a coating of an oxide or a silicide on a smoothed ground iron surface or a metal plating surface thereon by a low-pressure plasma spraying method. Each of these methods discloses a method of forming a tensile film of a material, nitride, or carbide, but as described later, these methods can secure an industrial film forming speed, but can form a film by adhering droplets. Because of this, a dense film cannot be formed, and the formed surface is rough, easily peels off by friction, and the adhesion between the steel plate or plated surface and the plasma sprayed oxide or silicide film is not sufficient. The magnetic properties described above were not obtained, and large-scale decompression equipment was required.

[0012]

As described above, recent trends in the technology for reducing iron loss of grain-oriented electrical steel sheets are to smooth the surface of the steel sheet during and after finish annealing or to perform crystal orientation emphasis treatment. After that, it is indispensable to form a tension coating on the steel sheet surface. As a result, the film did not peel off, and as a result, tension could not be applied, and the effect of improving the magnetic properties could not be expected. Therefore, various measures have been taken to ensure the adhesion of the tension coating. However, if the adhesion is good, the magnetic smoothing effect on the steel sheet surface is lost, and the magnetic properties also deteriorate. Therefore, none of them has been industrially commercialized by such technology.

[0013] Further, the film formation by the gas phase is usually performed in a vacuum atmosphere, and not only the film formation speed is slow but also the installation of a vacuum chamber is indispensable. It was difficult. Furthermore, when the crystal orientation enhancement treatment is applied to the steel sheet surface, the adhesion of the tension coating is somewhat lessened than in the case of the smoothing treatment, but it is still far from the original adhesion, and the tension action is applied to the steel sheet. Because of insufficient transmission, a satisfactory iron loss reduction effect was not obtained.

[0014] The present invention advantageously solves the above-mentioned problems, and performs a smoothing process or a crystal orientation emphasizing process on the surface of a steel sheet, and further imparts tension to the steel sheet with a tension coating to greatly reduce iron loss. Even in the case of reducing the strength, an advantageous method of manufacturing a grain-oriented electrical steel sheet that can apply sufficient tension to the steel sheet without impairing the adhesion of the tension coating is extremely small, and the iron loss obtained by this method is extremely small. The purpose is to propose with a grain-oriented electrical steel sheet.

[0015]

The development of the present invention will be elucidated below. Now, the present inventors have conducted a thorough study on the cause of peeling of the low-pressure plasma sprayed material or the ordinary plasma sprayed material described above, and found that a) the coating is not a dense single layer but derived from droplets during spraying. Has a structure in which granular coatings are sequentially adhered and have voids between grains. B) Therefore, the coating is broken from the coating voids, or the coating is oxidized on the steel sheet surface through the voids. It has been clarified that the above-mentioned granular coating is promoted due to peeling or surface irregularities.

The formation of voids between individual grains is due to a structure in which flat particles, which are smashed with semi-molten droplets on the surface of the steel sheet and are sequentially fixed, are piled up. It is considered that the formation of the joint causes a decrease in strength, and that irregularities derived from individual grains remain on the outermost surface. Further, it is considered that the oxidation of the steel sheet surface through the intergranular voids accelerates the peeling of the particles. In order to solve this problem, it is considered sufficient to deposit the coating in a gaseous state.However, the conventionally known vacuum evaporation method and gas phase synthesis method require a large-scale vacuum tank, Industrialization is extremely difficult due to disadvantages such as extremely low speed.

In view of the above findings, various film forming methods were examined. According to the thermal plasma evaporation method and the thermal plasma flash evaporation method, the coating material can be deposited in a plasma state, which is a kind of gaseous state, and the atmosphere can be easily removed. It is possible to work at atmospheric pressure or a slightly reduced pressure atmosphere, and at the same time, it is possible to form a dense coating layer with a high vapor deposition rate and a small porosity, so that the above disadvantages can be advantageously overcome. There was found.

Therefore, the present inventors further conducted research on applying this deposit to grain-oriented electrical steel sheets. As a result, the present inventors applied the above-mentioned means to a steel sheet having a thickness of 0.27 mm or less and reduced the deposition thickness to 0.1% per side. By applying a magnetic domain refining treatment before or after vapor deposition, preferably before or after evaporation, a coating layer having a porosity of 10% or less and having a smooth surface can be formed, and as a result, good coating adhesion can be obtained. It has been found that the iron loss can be obtained and a large reduction in iron loss can be achieved. In addition, at this time, the adhesion is further improved by increasing the temperature of the electromagnetic steel material at the time of vapor deposition to 200 ° C or higher, or by subjecting the steel sheet to a heat treatment at a temperature of 200 ° C or higher after the vapor deposition. It has been found that the use of a fine powder having a particle size of 5 μm or less reduces unevenness on the surface of the steel sheet and can further improve the adhesion. The present invention is based on the above findings.

That is, the gist of the present invention is as follows. 1. The thickness of the grain-oriented electrical steel sheet, which suppresses the formation of forsterite or removes the generated forsterite: 0.27 mm or less, has a total pressure of 0.1 atm or more and an oxygen partial pressure P (O ₂ ) of 0.1 atm. The average thickness per side is 0.1μm or more and 10μm by vapor deposition in a low oxidizing atmosphere of less than
A method for producing a grain-oriented electrical steel sheet having extremely small iron loss, comprising forming the following coating layer.

2. 2. The method for producing a grain-oriented electrical steel sheet according to the above item 1, wherein the vapor phase deposition is thermal plasma deposition.

3. 2. The method for producing a grain-oriented electrical steel sheet according to the above 1, wherein the temperature of the electrical steel material during vapor deposition is set to 200 ° C. or higher.

4. 2. The method for producing a grain-oriented electrical steel sheet according to the above 1, wherein the steel sheet is subjected to a heat treatment at a temperature of 200 ° C. or higher after the vapor phase deposition.

5. 5. The method for producing a grain-oriented electrical steel sheet according to any one of the above items 1 to 4, wherein a fine powder having an average particle size of 5 μm or less is used as a vapor deposition material.

6. The method for producing a grain-oriented electrical steel sheet according to any one of the above 1 to 5, wherein a surface of the steel sheet is subjected to a smoothing treatment or a crystal orientation emphasis treatment before vapor deposition.

[7] 7. The method for producing a grain-oriented electrical steel sheet according to any one of the above items 1 to 6, wherein a magnetic domain refining treatment is performed before or after the vapor deposition.

8. After vapor deposition, a tension coating and / or
Or an insulating film is formed.
The method for producing a grain-oriented electrical steel sheet according to any one of the above.

9. 9. The method for producing a grain-oriented electrical steel sheet according to any one of the above items 1 to 8, wherein the low oxidizing atmosphere is a mixed atmosphere of nitrogen and hydrogen.

10. A grain-oriented electrical steel sheet having a coating thickness of 0.27 mm or less having a coating layer formed by vapor deposition on the surface of a steel sheet from which forsterite has been suppressed or the generated forsterite has been removed. The layer is made of a material having a porosity of 10% or less and a coefficient of thermal expansion smaller than that of iron. The thickness of the layer satisfies an average thickness per side of 0.1 μm or more and 10 μm or less, and the surface has a center line average roughness. 0.5μm with Ra
A grain-oriented electrical steel sheet having extremely small iron loss, characterized by having a smooth surface of less than.

11. The grain-oriented electrical steel sheet according to the above item 10, which has been subjected to a magnetic domain refinement treatment before or after the vapor deposition.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. The use of a steel sheet with a thickness of 0.27 mm or less, for which the formation of forsterite has been suppressed or forsterite has been removed, is required to improve the denseness of the vapor deposition (thermal plasma deposition) coating layer obtained at a relatively high pressure near atmospheric pressure. It is important to obtain low iron loss by utilizing the tension. Here, as the grain-oriented electrical steel sheet to be used, the sheet thickness was limited to 0.27 mm or less, but the reason is that when the sheet thickness exceeds 0.27 mm, the effect of applying tension by the coating is not sufficiently exhibited. It is.

Further, the atmosphere must be a low oxidizing atmosphere such as an inert gas or a reducing gas in order to prevent deterioration of adhesion and iron loss due to oxidation of the steel sheet surface. Specifically, it is important that the oxygen partial pressure P (O ₂ ) in the atmosphere be less than 0.1 atm. As the atmosphere gas, a gas containing no carbon is preferable, and a nitrogen gas containing hydrogen is suitable industrially. Further, regarding the pressure, it is industrially difficult to make the pressure less than 0.1 atm.
Atmospheric pressure. More preferably, 0.8 atm or more is recommended. Note that the upper limit is not particularly defined, but an atmospheric pressure or a slightly pressurized atmosphere is convenient for maintaining a low oxidation atmosphere.

Next, the thickness of the coating layer formed by vapor deposition is 0.1
If it is less than μm, not only is it not possible to expect a sufficient effect of applying tension, but also it becomes difficult to stably cover the steel sheet surface for insulation and corrosion resistance, so the lower limit was set to 0.1 μm. on the other hand,
When the thickness exceeds 10 μm, the deterioration of iron loss, deterioration of coating adhesion and deterioration of surface smoothness due to a decrease in space factor are introduced, so the upper limit was set to 10 μm.

Further, the adhesion of the deposited film can be increased by setting the temperature of the electromagnetic steel material to 200 ° C. or higher during the vapor deposition or heating the steel sheet to a temperature of 200 ° C. or higher after the vapor deposition. This is probably due to the effect that impurities in the atmosphere present in a small amount between the steel sheet and the vapor deposition layer are taken into the steel sheet or the vapor deposition layer by diffusion.

Further, it is desirable to use a powder having an average particle diameter of 5 μm or less as a starting material for vapor deposition. That is, this allows the deposited material to be stably formed in a complete vapor state as a dense and strong coating layer, and the obtained coating layer has a porosity of 10% or less and a surface roughness of a center line. This is because the coating can be effectively prevented from falling off as a smooth surface having an average roughness Ra of less than 0.5 μm. Here, the components of the coating layer are not particularly limited, but chalcogenides, silicides, borides, carbides, nitrides, and the like containing any oxide are advantageously suited.

It is advantageous to perform a smoothing treatment or a crystal orientation emphasis treatment on the surface of the steel sheet before vapor deposition to reduce iron loss. If necessary, a tension film or an insulating film can be further formed after the vapor deposition. Further, it is advantageous to perform a magnetic domain refining treatment before or after the vapor deposition, whereby the effect of imparting tension by the coating is more effectively exerted.

[0036]

Example 1 A linear groove was formed in the width direction of a steel sheet for subdividing magnetic domains, and then secondary recrystallized. The average roughness of the steel sheet surface is 0.10μm with a mixture of sulfuric acid and chromic acid.
Smoothing processing was performed until the degree reached. Then, while heating the steel sheet to 300 ° C, 0.9 atm (nitrogen 75% + hydrogen)
In a mixed atmosphere of (25%), Al ₂ O ₃ having an average particle diameter of 2 μm was vapor-phase deposited as a starting material so as to have a coating thickness of 5 μm per side as a starting material. The oxygen partial pressure P (O ₂ ) in this atmosphere was 0.01 atm or less. The porosity (calculated from the bulk density with respect to the theoretical density) of the coating layer on the surface of the obtained steel sheet was 4%, and the surface roughness Ra was 0.22 μm.

With respect to the steel sheet thus obtained, the adhesion of the tensile coating (the minimum cylinder diameter at which no peeling of the coating is observed when the steel sheet is wound around the cylinder: indicated by the minimum bending peeling diameter) and the magnetic properties of the steel sheet are shown. When checking, minimum bending peel diameter _{= 20 mm, B 8 = l.902} T, the iron loss W _17/50 = 0.59 W / kg
Met.

Example 2 Using a separating agent containing 0.3 wt% of PbCl ₂ in MgO as an annealing separating agent, the formation of a forsterite film was suppressed, and the separation in the width direction of the steel sheet was performed in order to refine the magnetic domains. By performing secondary recrystallization while forming linear fine grains at an appropriate interval, a grain-oriented electrical steel sheet having a thickness of 0.25 mm was produced. Next, this steel sheet was subjected to high-frequency + direct current hybrid thermal plasma evaporation in an Ar atmosphere at 1.05 atm, and SiO ₂ having an average particle size of 1.6 μm was used as a starting material in a vapor phase such that the coating thickness per side was 0.8 μm. Evaporated. Then, a tension coating solution containing 60% colloidal silica and 40% magnesium phosphate as the main component is applied to the steel sheet surface,
Baked at 800 ° C. The oxygen partial pressure P (O ₂ ) in this atmosphere was 0.012 atm. The porosity of the coating layer on the surface of the obtained steel sheet was 6%, and the surface roughness Ra was 0.35 μm.

With respect to the steel sheet thus obtained, the adhesion of the tension coating and the magnetic properties of the steel sheet were examined. The minimum bending peel diameter was 25 mm, B ₈ = 1.920 T, and the iron loss W _17/50 =
It was 0.63 W / kg.

Comparative Example 1 A linear groove was formed in the width direction of the steel sheet for subdividing the magnetic domain, and then the secondary recrystallization was performed. The forsterite film of the grain-oriented electrical steel sheet having a thickness of 0.22 mm was pickled. Removed, and the average roughness of the steel sheet surface is 0.10μm with a mixture of sulfuric acid and chromic acid.
Smoothing processing was performed until the degree reached. Then, while heating the steel plate to 300 ° C, 0.9 atm (nitrogen 75% + hydrogen)
In a mixed atmosphere of 25%), Al ₂ O ₃ having an average particle size of 7 μm was formed as a starting material in the form of droplets by a usual plasma spraying method, and was thermally sprayed and fixed so as to have a coating thickness of 5 μm per side. .

With respect to the steel sheet thus obtained, the adhesion of the tension coating and the magnetic properties of the steel sheet were examined. The minimum peeling diameter = 60 mm, B ₈ = 1.888 T, and the iron loss W _17/50 =
It was 0.77 W / kg. The porosity of the coating layer on the surface of the obtained steel sheet was 29%, and the surface roughness Ra was 1.4 μm.

[0042]

As described above, according to the present invention, a grain-oriented electrical steel sheet having excellent adhesion of a tension film and capable of applying a sufficient tension to a steel sheet, and thus having significantly reduced iron loss as compared with the prior art. Can be obtained stably on an industrial scale.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mitsumasa Kurosawa 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. Chome (without address) Kawasaki Steel Corporation Mizushima Works F-term (reference) 4K030 BA43 BA44 CA02 DA02 DA08 FA01 JA01 LA26 4K033 AA02 PA01 PA03 PA10 PA12 RA04 TA04

Claims (11)

[Claims] 1. A sheet thickness of 0.27 mm in which forsterite formation is suppressed or generated forsterite is removed.
On the surface of the following grain-oriented electrical steel sheet, the average thickness per side was 0.1% by vapor phase deposition in a low oxidizing atmosphere where the total pressure was 0.1 atm or more and the oxygen partial pressure P (O ₂ ) was less than 0.1 atm. μm
A method for producing a grain-oriented electrical steel sheet having extremely small iron loss, comprising forming a coating layer having a thickness of 10 μm or more. 2. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the vapor phase deposition is thermal plasma deposition. 3. The temperature of an electromagnetic steel material during vapor deposition
The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the temperature is 200 ° C or higher. 4. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein after the vapor deposition, the steel sheet is subjected to a heat treatment at a temperature of 200 ° C. or higher. 5. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein a fine powder having an average particle size of 5 μm or less is used as a vapor deposition material. 6. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the surface of the steel sheet is subjected to a smoothing treatment or a crystal orientation enhancement treatment before the vapor deposition. 7. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein a magnetic domain refining treatment is performed before or after the vapor deposition. 8. The method according to claim 1, further comprising forming a tension coating and / or an insulating coating after the vapor deposition.
The method for producing a grain-oriented electrical steel sheet according to any one of the above. 9. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the low oxidizing atmosphere is a mixed atmosphere of nitrogen and hydrogen. 10. A grain-oriented electrical steel sheet having a thickness of 0.27 mm or less having a coating layer formed by vapor deposition on the surface of a steel sheet from which forsterite has been suppressed or the generated forsterite has been removed. The layer is made of a material having a porosity of 10% or less and a coefficient of thermal expansion smaller than that of iron. 0.5μm with Ra
A grain-oriented electrical steel sheet having extremely small iron loss, characterized by having a smooth surface of less than. 11. The grain-oriented electrical steel sheet according to claim 10, which has been subjected to a magnetic domain refining treatment before or after the vapor deposition.