JP2592740B2 - Ultra-low iron loss unidirectional electrical steel sheet and method of manufacturing the same - Google Patents

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 extremely low iron loss and a method for producing the same.

[0002]

2. Description of the Related Art In the production of a grain-oriented electrical steel sheet, it is important to reduce iron loss from the viewpoint of energy saving. As methods for reducing iron loss, in addition to conventionally known metallurgical methods such as increasing magnetic flux density, increasing specific resistance, and reducing thickness, Japanese Patent Application Laid-Open Nos. 55-18566 and 551-1
No. 17218, magnetic domain subdivision technology disclosed in JP-A-49-96920, and JP-A-53-14 / 1979.
For example, there is a mirror finishing process disclosed in Japanese Patent No. 4419 and the like.
In addition, Japanese Patent Laid-Open Publication No.
There is a method of applying a minute strain to a steel plate having a mirror surface as disclosed in JP-A-43115 to subdivide magnetic domains. However, this method has a drawback that it is not useful as a material for a wound iron core transformer requiring strain relief annealing because the magnetic domain segmentation effect is lost by annealing.

[0003]

The present invention has a large iron loss reducing effect as compared with the above-mentioned method, and can obtain an unprecedented ultra-low iron loss material. It is an object of the present invention to provide a unidirectional magnetic steel sheet which has a high value of use as a material for a wound iron core transformer and requires extremely low iron loss, and a method for manufacturing the same.

[0004]

SUMMARY OF THE INVENTION The present invention removes the surface film of a finish-annealed grain-oriented electrical steel sheet having a linear or dot-like groove having a certain depth and width, thereby reducing the surface roughness. After forming the above-mentioned grooves on the surface of a mirror-finished surface with an average roughness of 0.4 μm or less or a finish-annealed grain-oriented electrical steel sheet having a mirror surface with an average roughness of 0.4 μm or less, a tension insulating coating The purpose of the present invention is to obtain a grain-oriented electrical steel sheet having extremely low iron loss. Therefore, the application is not limited to the wound iron core transformer, and a sufficient effect can be expected with a stacked iron core transformer. That is, the present invention is intended to reduce surface roughness and form grooves.
Ultra-low iron loss unlike before
The aim is to obtain a grain-oriented electrical steel sheet.

Hereinafter, the present invention will be described in detail. In the present invention
Material used develops Goss orientation by secondary recrystallization method
It is not something that is particular about the manufacturing method
Absent. Common processes are converters, electric furnaces, vacuum melting furnaces, etc.
Smelting and refining, adjusting the ingredients and adding the inhibitor
After adding a few elements etc., continuous casting or normal casting
After casting into a mold, the slab is formed by slab rolling. Slab
Is usually 3.0 mm or less in thickness by hot rolling under known conditions.
Coil. Alternatively, the molten steel is directly quenched and solidified,
The plate does not change the essence of the present invention. So
After hot-rolled sheet is annealed or pickled without annealing
You. In the case of a single cold rolling process, roll to the final thickness as it is
I do. In the case of the twice cold rolling step,
The final thickness is obtained by rolling twice. Then decarburized annealing and necessary
Nitriding treatment, apply an annealing separator and finish annealing
You. MgO is usually used as an annealing separator, and
TiO to help the formation of lusterite coating_TwoAddition of etc.
Sometimes. B-based compounds, Sb-based compounds,
The proper addition of Na, K-based compounds, etc. is the essence of the present invention.
Does not affect Also, Al _TwoO_Three, SiO_TwoEtc.
A blunt separating agent may be used.

In the present invention, it is more convenient not to form a forsterite film, but in the present invention, the presence or absence of a forsterite film does not matter. In grain-oriented electrical steel sheets,
It is important that the orientation of the secondary recrystallized grains is high. Finish annealing for secondary recrystallization is performed under known conditions.
This is performed at a temperature of 200 ° C. for about 20 hours. In the production of normal grain-oriented electrical steel sheets, there are a product in which an annealing separator is washed off after finish annealing to produce a product, and a product in which a coating is applied on the forsterite film and shape correction annealing is performed.

[0007] The steel sheet treated in such a process is subjected to magnetic domain control to withstand strain relief annealing by a known method. As a magnetic domain control method, for example, there is a groove forming method by a mechanical method disclosed in JP-A-61-1117218.
There is a method disclosed in Japanese Patent Application Laid-Open No. 0-255926, in which the insulating film is locally removed by laser irradiation, and then the base iron is dissolved with an acid to form a groove. In addition, a method of forming a concave portion having a constant depth by laser irradiation may be used, or a known method may be used as long as it is a magnetic domain control method that can withstand strain relief annealing.

[0008] A feature of the present invention is that the surface of a steel sheet formed with grooves by the above method has a mirror surface having a roughness less than a certain critical value, and furthermore, a coating which imparts a specific range of tension to the surface. The point is to apply. Here, the mirror surface means one having a roughness average roughness of 0.4 μm or less. One known method for obtaining a mirror surface is electrolytic polishing. This is to remove the insulating coating or oxide on the steel sheet surface with acid etc.
For example, it can be obtained by electropolishing in an electrolytic solution of phosphoric acid and chromic anhydride. A method of chemically obtaining a mirror surface is also known. For example, there is a method of using a liquid obtained by adding a small amount of hydrofluoric acid to a hydrogen peroxide solution. In addition, when using dilute sulfuric acid, dilute nitric acid, or dilute hydrochloric acid, a surface with low roughness can be obtained. In addition, it can also be obtained by an annealing separator applied before the finish annealing or the finish annealing atmosphere conditions.

In the present invention, a similar effect can be obtained by forming the above-described groove after obtaining a mirror surface by the above method. Next, a method for imparting tension to a steel sheet will be described. It is well known that applying tension in the rolling direction of a grain-oriented electrical steel sheet reduces iron loss. Currently commercial products are provided by the tension created by the difference in the expansion coefficients of the steel sheet and the surface coating. In the present invention, as a tension coating solution, for example, a solution containing chromic anhydride-aluminum phosphate as a main component described in JP-B-53-28375, or a chromic anhydride-magnesium phosphate described in JP-B-56-52117. By applying and baking a liquid containing as a main component a steel plate, tension can be imparted. This tension was further increased by repeating the number of times of coating and baking, and a new finding was obtained that iron loss characteristics were significantly improved. This will be further described below based on experimental results.

FIG. 1 shows a sheet thickness of 0.16 containing 3.2% of Si.
mm, the magnetic flux density B _8: from 90 to 22 in which the grain-oriented electrical steel sheet 1.94T shown in JP-A-61-117218
The magnetic domain was controlled by forming a groove in the steel sheet with a load of 0 kg / m ² and heat-treating at a temperature of 750 ° C. or more (in this experiment, the groove depth was 13 μm, the width was 50 μm, and the width was 75 μm in the rolling direction).
° groove interval in the direction of 5mm, strain relief annealing 850 ° C × 2 hours),
It shows the iron loss characteristics after baking a coating solution containing chromic anhydride-aluminum phosphate as a main component at 820 ° C. after removing the surface coating and adjusting the smoothness of the steel sheet surface by chemical polishing. From the figure, the average roughness is 0.4 μm
It can be seen that a very low iron loss is obtained below.

FIG. 2 shows the relationship between the number of application and baking of the coating liquid and the iron loss. The material used was one subjected to magnetic domain control under the same conditions as in FIG. The average roughness of the steel sheet surface after the removal of the coating was adjusted to 0.1 μm or less by chemical polishing. This steel sheet was dipped in 10% diluted sulfuric acid aqueous solution for a short time, washed with water and dried, then coated with a solution containing chromic anhydride-aluminum phosphate as a main component at 3 g / m ² per side, and dried, and then dried at 820 ° C.
Annealing was performed for 30 seconds, and then magnetic measurement was performed. Next, the coating and the heat treatment were further repeated, and a magnetic measurement was performed. From the figure, if you repeat the coating baking process,
It turns out that iron loss is improved more.

FIG. 3 shows the relationship between the number of coating baking treatments and the tension applied to the steel sheet. The tension was obtained by calculating the bending amount of the steel sheet after removing the insulating coating on one side of the steel sheet with acid. It can be seen that the tension increases as the number of printing operations increases. It can be said that this tension brings about a further improvement in iron loss and achieves ultra-low iron loss. As the coating liquid, a known liquid such as a liquid mainly containing chromic anhydride-aluminum phosphate or a liquid mainly containing chromic anhydride-magnesium phosphate can be used. A thin metal plating may be applied to the steel sheet in order to enhance the adhesion to the steel sheet.

Next, the reasons for limitation of the present invention will be described. S
i is an element effective for reducing iron loss, and the upper limit is 4.5.
%. If it exceeds 4.5%, there is a problem such as brittleness in the ordinary secondary recrystallization method, and the production becomes difficult. As shown in FIG. 1, an extremely low iron loss cannot be obtained unless the surface roughness of the steel sheet is 0.4 μm or less. The depth, width and spacing of the grooves formed in the steel sheet are disclosed in Japanese Patent Publication No. Sho 62-53579. According to this, when the depth of the groove formed in the steel plate exceeds 5 μm, there is an effect of magnetic domain control, and when the width of the groove exceeds 300 μm, the margin of improvement in iron loss is reduced. The groove spacing is 2
15 mm, preferably 3 to 8 mm, 4 mm in the rolling direction
The direction is 5 to 90 °, preferably 70 to 90 °.

Results of searching for the baking temperature of the tension insulating film (sheet thickness 0.15 mm, adhesion amount 3 g / m ² , baking process twice)
Is shown in FIG. According to this, it is found that the temperature is higher than 750 ° C. to 950 ° C., preferably 800 to 900 ° C. 750 ° C
If the temperature is lower than 950 ° C. or more than 950 ° C., sufficient tension cannot be obtained. When the number of times of coating baking is repeated two or more times, the tension increases, and the effect of reducing iron loss is large. But the tension is 1.0kg
/ Mm ^2, a considerable effect can be expected even once.

[0015]

Embodiments will be described below. Example 1 A point-like groove having a depth of 12 μm, a diameter of 50 μm, and a distance between points of 0.2 mm was formed at 90 ° with respect to the rolling direction on the surface of a steel plate of a steel plate.
High magnetic flux density unidirectional electrical steel sheet (A) having a thickness of 0.15 mm and containing 3.2% Si formed at intervals of 5 mm in the direction,
(B) was prepared.

The surface coating of the sample (A) was removed with hydrofluoric acid, and Ra was adjusted to 0.1 μm or less by electrolytic polishing.
Next, after immersion in 5% dilute sulfuric acid, a coating solution containing chromic anhydride + aluminum phosphate + colloidal silica as a main component was applied, and annealing was performed at 800 ° C. for 30 seconds.
Then, coating under the same conditions and annealing at 820 ° C. for 30 seconds were repeated twice. Sample B was coated and 820 ° C
Annealing for 30 seconds was performed once. FIG. 4 shows cross-sectional photographs of the coatings of the samples (A) and (B). The boundary between the ground iron and the coating of the sample (A) is smoother than that of the sample (B).

The magnetic properties are as follows. Sample (A) Sample _{(B) B 8 1.91T B 8} 1.91T W 13/50 0.23w / kg W 13/50 0.35w / kg Sample (A) showed a very low iron loss value.

Example 2 C: 0.054%, Si: 3.3%, Mn: 0.14
%, S: 0.007%, acid-soluble Al: 0.030%,
N: 0.0075%, Cr: 0.10%, Sn: 0.0
5%, the ingot consisting of the balance Fe and inevitable impurities is 115
After heating to 0 ° C., it was hot-rolled to a thickness of 1.6 mm. This hot-rolled sheet was annealed at 1100 ° C., pickled, and cold-rolled to a thickness of 0.16 mm. Next, after decarburizing annealing was performed at 830 ° C. in a wet hydrogen nitrogen atmosphere, nitriding was performed at 750 ° C. with hydrogen, nitrogen,
The test was performed in an ammonia mixed gas. Then the annealing separator Mg
O was applied and finish annealing at 1200 ° C. was performed to complete secondary recrystallization.

Samples A and B having substantially uniform magnetic properties were selected from the obtained samples, and a 14 μm-thick sample was formed using a toothed roll.
m, a groove with a width of 50 μm in the direction of 75 ° with respect to the rolling direction.
mm. Next, annealing was performed at 850 ° C. × 2 hours. Next, after removing the surface coating of the sample A with an acid, Ra was adjusted to 0.1 μm with a mixed solution of a hydrogen peroxide solution and hydrofluoric acid.
(Plate thickness reduced 10 μm) or less. Then sample A,
B Coating solution containing chromic anhydride, aluminum phosphate and colloidal silica as main components at 3 g / m ² per side
Apply, 820 ℃ × 30 seconds tension coating,
The magnetism was measured. Further, the same tension coating was repeated, and the magnetic measurement was performed. Table 1 shows the results.

[0020]

[Table 1]

Sample A had an extremely low iron loss compared to Sample B. Example 3 C: 0.056%, Si: 3.6%, Mn: 0.09
%, S: 0.007%, acid-soluble Al: 0.029%,
N: 0.0078%, Cr: 0.08%, Sn: 0.0
4%, 115 ingot consisting of Fe and unavoidable impurities
After heating to 0 ° C., the sheet was hot-rolled to a thickness of 1.4 mm. After annealing this hot-rolled sheet at 1100 ° C., it was pickled and 0.14 mm
Cold rolled thick. Next, after decarburizing annealing was performed at 830 ° C. in a wet hydrogen nitrogen atmosphere, nitriding was performed at 750 ° C. in a mixed gas of hydrogen, nitrogen, and ammonia to reduce the [N] amount of the steel sheet to 2%.
It was set to 00 ppm.

Next, Al ₂ O ₃ as an annealing separating agent was dissolved in alcohol and applied, followed by finish annealing at 1200 ° C. for 20 hours. Then, in the state of washing and drying, no forsterite was formed on the surface of the steel sheet, and the surface roughness was Ra = 0.3 μm. Next, a groove having a depth of 12 μm and a width of 50 μm was formed in the same state as in Example 2 using a toothed roll. Then, it is dipped in 10% dilute sulfuric acid for a short time, washed with water and dried, and coated with a coating solution containing chromic anhydride, aluminum phosphate and colloidal silica as main components at 3 g / m ² on one side, and subjected to annealing at 880 ° C. for 30 seconds. And performed magnetic measurements. Further, the same coating baking treatment was repeated, and the magnetism was measured. Table 2 shows the results.

[0023]

[Table 2]

Example 4 C: 0.080%, Si: 3.5%, Mn: 0.075
%, S: 0.025%, acid-soluble Al: 0.035%,
N: 0.0080%, Sn: 0.13%, Cu: 0.0
135% steel ingot consisting of 7%, balance Fe and unavoidable impurities
After heating to 0 ° C., it was hot-rolled to a thickness of 2.3 mm. Then, after hot-rolled sheet annealing was performed at 1000 ° C., it was pickled, and 1.35 mm
Cold rolled until Next, annealing was performed at 1120 ° C. in the former stage and 90 in the latter stage.
After performing at a temperature of 0 ° C., put into 100 ° C. hot water and cool,
Next, it was pickled and cold rolled to 0.17 mm. Next, the cold-rolled sheet is degreased, and a 2% aqueous sodium hydroxide solution is applied,
Decarburization annealing was performed at 850 ° C.

Next, an MgO slurry was applied and 1200
Finish annealing was performed at a temperature of ° C. Then after washing and drying,
Using a toothed roll, grooves having a depth of 15 μm and a width of 50 μm were formed at intervals of 5 mm in a direction at 75 ° to the rolling direction. Next, after annealing at 800 ° C., the average roughness of the surface after immersion in 5% sulfuric acid was about 0.2 μm. Then, a coating solution containing chromic anhydride, aluminum phosphate, and colloidal silica as main components was applied in an amount of 3 g / m3 per side.
^2. After performing tension coating at 820 ° C. for 30 seconds under annealing conditions, application and annealing under the same conditions were repeated. The magnetic properties were as follows: iron loss W _{13/5 0} = 0.28 w / kg, showing a very low iron loss value.

[0026]

Industrial Applicability According to the present invention, there is a wide range of applications as various iron core materials, and in particular, a unidirectional electrical steel sheet with extremely low iron loss, which is highly useful as a material for wound iron core transformers requiring strain relief annealing. Is provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the average roughness of a steel sheet surface and iron loss.

FIG. 2 is a diagram showing a relationship between the number of times of coating and baking of a coating liquid and iron loss.

FIG. 3 is a diagram showing the relationship between the number of times of coating and baking of a coating liquid and the film tension.

FIG. 4 is a photograph showing a cross section of a coating before removing the coating and a cross section of the coating after coating after removing the coating.

FIG. 5 is a diagram showing the relationship between coating baking temperature and film tension.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Shuichi Yamazaki 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Corporation Technology Development Division (72) Inventor Yoshiyuki Ushigami 20-1 Shintomi, Futtsu City, Chiba Prefecture New (56) References JP-A-2-30740 (JP, A) JP-A-61-117218 (JP, A) JP-A-60-255926 (JP, A) 62-290844 (JP, A)

Claims (5)

(57) [Claims] 1. A linear or dot-like groove having a surface iron surface Ra of 0.4 μm or less and a depth of more than 5 μm and a width of 300 μm or less in the steel sheet at 45 to 90 ° with respect to the rolling direction. , And the iron loss of the steel sheet surface coated with a tension insulating coating is W13 / 50: 0.34 w /
Ultra-low iron loss unidirectional electrical steel sheet containing 4.5 kg or less of Si and 4.5% or less. 2. A linear or dot-like groove having a surface iron surface Ra of 0.4 μm or less and a depth of more than 5 μm and a width of 300 μm or less 45-90 ° with respect to the rolling direction. Ultra-low iron loss containing 4.5% or less of Si, characterized in that a finish-annealed unidirectional electrical steel sheet formed at an interval of 2 to 15 mm in the direction of 張力 is subjected to a tension coating treatment in a temperature range of more than 750 ° C to 950 ° C. Manufacturing method of unidirectional electrical steel sheet. 3. The method for producing an ultra-low iron loss unidirectional magnetic steel sheet according to claim 2, wherein the tension coating treatment is repeated twice or more in a temperature range of more than 750 ° C. to 950 ° C. 4. An ultra-low iron loss unidirectional electrical steel sheet according to claim 2, wherein a tension of more than 1.0 kg / mm ² is applied by a tension coating treatment in a temperature range of more than 750 ° C. to 950 ° C. Manufacturing method. 5. The ultra-low iron loss according to claim 2, wherein a liquid mainly composed of chromic anhydride-aluminum phosphate-colloidal silica is used as the tension coating liquid. Manufacturing method of grain-oriented electrical steel sheet.