JPS621822A - Production of grain oriented silicon steel sheet having thermal stability and ultra-low iron loss - Google Patents

Abstract

PURPOSE:To improve the adhesiveness and durability of a tensile coating layer on a specular surface and to obtain the titled steel sheet in a method for improving the iron loss of a grain oriented silicon steel sheet by finishing the sheet to the specular surface by specifying a separating agent for annealing to be used in the stage of finish annealing. CONSTITUTION:A hot rolled sheet of a silicon steel slab is subjected to one or two passes of cold rolling including intermediate annealing to a final sheet thickness and is then subjected to decarburization and primary recrystallization annealing. The separating agent for annealing (for example, MgO contg. >=50%>=1 kinds among Al2O3, ZrO2 and TiO2) consisting of the component compsn. to suppress the reaction for forming forsterite with the surface layer of the steel sheet essentially consisting of Si and Fe oxide is thereafter coated on the surface of the steel sheet. Such steel sheet is subjected to the final finish annealing including secondary recrystallization and purification annealing and after the non-metallic layer on the surface is removed, the surface is polished to the specular surface having <=0.4mu center line average height. The tensile film consisting of >=1 kinds among the nitrides and/or carbides of Ti, Nb, Si, V, etc., and the oxides of Al, Si, Zn, etc., is deposited by a CVD or PVD method to 0.005-5mu thickness on such surface.

Description

[Detailed Description of the Invention] (Field of Industrial Application) In recent years, remarkable efforts have been made to improve the electrical and magnetic properties of unidirectional silicon steel sheets, and in particular to meet the extreme demands of reducing iron loss. The development efforts are gradually bearing fruit, but one serious problem associated with their implementation is that when unidirectional silicon steel sheets are processed and assembled and then subjected to so-called sludge annealing, their characteristics deteriorate. It has been pointed out that the disadvantage is that it inevitably causes deterioration and limits its use.

In this specification, the following is related to the results of research and development that led to a new method that can advantageously meet the above requirements, whether or not it undergoes a high-temperature thermal process such as strain relief annealing. I will explain.

As is well known, unidirectional silicon steel sheets are products in which secondary recrystallized grains are highly concentrated in the (110) [001), or Goss, orientation, and are mainly used in transformers and other electrical equipment. When used as an iron core, the product is required to have a high magnetic flux density (represented by the B r o value) and a particularly low iron loss (represented by the Nu/S value) as electrical and magnetic properties.

This unidirectional silicon steel plate is manufactured through a wide variety of complicated processes, but numerous inventions and improvements have been made so far, and today the magnetic properties of a product with a thickness of 0.30 mm have reached Bto
l, 90T or more, W + 7ys o 1.05W/
kg or less, and the plate thickness is 0.23111! The magnetic properties of I+ products are Btol, 89T or higher, VB-ry5aO, 90
11! Unidirectional silicon steel sheets with ultra-low iron loss of less than /kg are now being manufactured.

Particularly recently, there has been a marked increase in demand for power loss reduction features from an energy-saving perspective, and in Europe and the United States, when creating a transformer with low loss, the reduction in iron loss is converted into a monetary value and added to the transformer price.・The "evaluation" (iron loss evaluation) system is becoming widespread.

(Prior art) Under these circumstances, recently, the surface of a unidirectional silicon steel plate after finish annealing is irradiated with a laser in a direction approximately perpendicular to the rolling direction to introduce local microstrain to subdivide the magnetic domains. It has been proposed to reduce iron loss (see Japanese Patent Publication No. 57-2252, Japanese Patent Publication No. 57-53419, Japanese Patent Publication No. 58-26405 and Japanese Patent Publication No. 58-26406).

This magnetic domain refining technology is effective for transformer materials for laminated core transformers that are not subjected to strain relief annealing, but for material for wound core transformers that are subjected to strain relief annealing,
There is a drawback that the local minute strain introduced by laser irradiation is released by annealing and the magnetic domain width is widened, so that the laser irradiation effect is lost.

On the other hand, earlier in Japanese Patent Publication No. 52-24499, the surface of a unidirectional silicon steel sheet after finish annealing was mirror-finished, or the mirror-finished surface was coated with thin metal plating or an insulating coating was applied thereon. A method of manufacturing a unidirectional silicon steel plate with low core loss 8 by coating and baking has been proposed.

However, this method of improving iron loss through mirror finishing cannot be adopted from a process perspective, as it does not contribute enough to reducing iron loss despite the significant increase in cost. Furthermore, it has not been adopted in the current manufacturing process because it has problems with adhesion to the steel plate during long-time strain relief annealing at a high temperature of 600° C. or higher.

Japanese Patent Publication No. 56-4150 also proposes a method in which a steel plate surface is mirror-finished and then an oxide-based ceramic thin film is vapor-deposited. However, this method also has 60
If high-temperature annealing is performed at a temperature of 0° C. or higher, the steel sheet and the ceramic layer will separate, so it cannot be used in actual manufacturing processes.

(Problems to be Solved by the Invention) The inventors have sought to more advantageously bring out the effectiveness of improving iron loss through mirror finishing, which outweighs the disadvantage of increased costs, especially from the perspective of today's development of energy-saving materials. We believe that it is essential to overcome the problems of adhesion and durability of the insulating layer without deteriorating the properties, especially during high-temperature treatment, and based on this basic understanding, we have developed a fundamental method for processing steel sheets after mirror finishing. This invention was arrived at after extensive reexamination.

Here, unidirectional silicon steel sheets subjected to final finish annealing are usually coated with an annealing separator mainly composed of MgO at the time of the preceding decarburization and primary recrystallization annealing. On the surface of the steel sheet, a so-called forsterite base film is formed, which originates mainly from the reaction between Si oxide and MgO during decarburization and primary recrystallization annealing. When aiming to improve iron loss through the above-mentioned mirror finish, it is clear that removal by pickling is quite troublesome and results in roughening of the steel plate surface, making mirror finishing operations difficult. It became.

(Means for solving the problem) As a result of the above study, while we were considering the simple removal of the forsterite film, we focused on the method of suppressing its formation, which was more advantageous, and conducted repeated experiments. We have established an advantageous manufacturing method for thermally stable, ultra-low core loss unidirectional silicon steel sheets based on mirror finish using the following procedure.

A hot rolled sheet obtained by hot rolling a silicon-containing steel slab is cold rolled once or twice with intermediate annealing to achieve the final thickness, and then subjected to decarburization and primary recrystallization annealing. After that, the following 2
Applying an annealing separator having a composition that suppresses the forsterite formation reaction between the surface layer of the steel sheet and the surface layer mainly composed of Si oxide during the final annealing including the next recrystallization and purification annealing; After removing the non-metallic material layer on the surface of grain-oriented silicon steel sheet, polishing treatment reduces the centerline average roughness to 0.4.
Ti, Nb, Si, V
, Cr, Al, B, Ni, Co, Mo, W, Zr.

Nitride and/or carbide of Hf, Mn, and Ta and AI.

Si, Zn, Ti, Zr, Sn, Fe, Ni,
Thermal stability, characterized by the combination of depositing an ultra-thin tension film with a film thickness of 0.005 to 5 μm, consisting of at least one selected from oxides of Cu, W and Mg. , a method for producing an ultra-low core loss unidirectional silicon steel sheet (first invention).

A hot rolled sheet obtained by hot rolling a silicon-containing steel slab is cold rolled once or twice with intermediate annealing to achieve the final thickness, and then subjected to decarburization and primary recrystallization annealing. After that, the following 2
Applying an annealing separator with a composition that suppresses the forsterite production reaction between the surface layer of the steel sheet mainly consisting of S1 oxide during final finish annealing including secondary recrystallization and purification annealing; After removing the non-metallic material layer on the surface of grain-oriented silicon steel sheet, polishing process reduces the centerline average roughness to 0.4μ.
Ti, Nb, Si,
V, Cr, Al, B, Ni, Co, Mo
, W, Zr, Hf.

Nitride and/or carbide of Mn and Ta and Al, S
i.

Depositing an ultra-thin tension film with a thickness of 0.005 to 5 μm consisting of at least one selected from oxides of Zn, Ti, Zr, Sn, Fe, and Mg, and on this tension film. A method for producing a highly insulating, thermally stable, ultra-low core loss unidirectional silicon steel sheet, which is characterized by: applying an insulating coated baked layer to the unidirectional silicon steel sheet, and combining the following steps. (Second invention).

Here, regarding the component composition of the annealing separator that should suppress the forsterite production reaction, Al2O3, 2rO7゜Ti
It is preferable to mix at least 50% of at least one selected from O□, etc. with MgO, and in this case, the function of absorbing the inhibitor transferred to the annealing separator during purification annealing is maintained. MgO and the like are also suitable insofar as they are suitable.

The explanation will proceed according to specific experiments that led to the success of each of the above inventions.

C0,048% by weight (hereinafter simply expressed as %), Si3.
44%, MnQ, 060%, Seo, 022%, S
b O, 025% and M.

Continuously cast silicon steel slab containing 35% O.
After heating at ℃ for 4 hours, hot rolling was carried out.2. It was made into a hot-rolled sheet with a thickness of 0 mm.

After that, after equalization annealing at 900℃ for 3 minutes, at 950℃ for 3 minutes.
Cold rolled twice with intermediate annealing for 0.2 min.
The final cold rolled sheet was 3+nm thick.

After that, after decarburization and next crystal annealing in a wet hydrogen atmosphere at 820℃, apply an annealing separator mainly composed of MgO to the steel plate surface, ■A120
After applying an annealing separator consisting of No. 3 (70%) and MgO (30%), secondary recrystallization annealing was performed at 850°C for 50 hours and purification annealing at 1200°C in saturated hydrogen for 5 hours. did.

Thereafter, since a forsterite film was formed in the annealing separator (2), the forsterite film was removed by pickling in a 50-100% H2SO4 solution, and then chemical polishing and electrolytic polishing were performed to give a mirror finish.

On the other hand, with the annealing separator (2), since no forsterite film was formed, it could be subjected to chemical polishing and electrolytic polishing after being lightly pickled in 10% H2SO.

Then, using an ion plating device, the film thickness was 0°5.
TiN ion plating was performed at μm.

Following the above ion plating, a coating treatment (formation of an insulating coated baked layer) was performed using a coating liquid containing phosphate and colloidal silica as main components.

The experimental results of the magnetic properties and adhesion of the products at this time are summarized in Table 1.

As is clear from Table 1, a forsterite film was once formed by final finish annealing using the usual M g O coating in (■), and then the forsterite film was removed by strong pickling treatment, followed by chemical polishing and electrolytic polishing. The magnetic properties of the resulting product sheet were approximately 0.04 W/kg inferior in iron loss to those treated similarly using the annealing separator (2).

In the case of (2) in which no forsterite film is formed, the element surface of the steel plate is lightly pickled, so there is less roughness, and it is thought that the decrease in iron loss is more remarkable than in the case (2) under the same polishing conditions.

In other words, by suppressing the formation of forsterite during final finish annealing, the subsequent process of reducing super iron loss will become significantly easier, and at the same time, a significant improvement in magnetic properties can be expected.

(Function) The improvement in magnetic properties described above is achieved by creating an ultra-thin tension film with improved adhesion under conditions where the surface of the steel sheet is mirror-finished after final annealing, resulting in an unparalleled ultra-low core loss. be done.

Since the action of plastic microstrain is not used here, there is no problem with thermal stability, and the electrical and magnetic properties are not affected by high-temperature thermal processes such as strain relief annealing. .

The centerline average roughness of the finished surface must be mirror-like with Ra≦0.4 μm, and when Ra>0.4 μm,
Because the surface is rough, sufficient iron loss reduction cannot be expected.

Next, the thickness of the tension insulating film is suitable in the range of 0.005 to 5 μm; if it is less than 0.005 μm, it will not be able to contribute to providing the necessary tension, while if it exceeds 5 μm, the cost will increase. At the same time, disadvantages arise in terms of space factor and adhesion.

This strong adhesion through the mixed phase of the tension coating on the mirror-finished surface is advantageously achieved by either CVD, ion plating or ion implantation.

Next, a more detailed explanation will be given including the general manufacturing process of the unidirectional silicon steel sheet.

The starting material is a conventionally known unidirectional silicon steel material composition, for example, ■C: 0. Old ~ 0.060%, Si: 2.50 ~ 4.5
%, Mn: 0.04-0.2%, Mo+0.003-0
．． 1%, sb:o, 005~0.2%, S or S
0.005 to 0.05% in total of one or two types of e.
Composition containing ■C: 0.01-0.08%, Si: 2.0-4.0
%, Sol Al: 0.005-0.06%, S: 0
．． 005-0.05%, N: 0.001-0.01%,
Sn: 0.01-0.5%, Cu: 0.01-0.3%
, Mn: 0.01-0.2% composition ■C: 0.
01-0.06%, Si:2.0-4.0%, S:0.
005~0, 05%, Boo, 0003~0.00
40%, N: 0.001-0.01%, Mn: 0.01
It is applicable in compositions containing up to 0.2%.

Next, the hot-rolled sheet undergoes uniform annealing at 800 to 1100°C.
One-time cold rolling method, in which the final plate thickness is reached by two cold rolling steps, or two-step cold rolling method, in which intermediate annealing from 850°C to 1050 t is interposed, and further cold rolling is performed.In the latter case, the initial rolling reduction is is 50
% to about 80%, the final rolling reduction is about 50% to 85%, and the final cold rolled plate thickness is 0.15 mm to 0.35 mm.

After the final cold rolling, the steel plate finished to the product thickness is subjected to decarburization and primary recrystallization annealing in wet hydrogen at 750°C to 850°C after surface degreasing.

Thereafter, an annealing separator is applied to the surface of the steel plate according to the method already described.

After that, secondary recrystallization annealing is performed, but this step is (100)
This is done to sufficiently develop secondary recrystallized grains with <001> orientation, and is usually box annealed immediately at 1000°C.
This is done by raising the temperature to a higher temperature and maintaining it at that temperature.

In this case, in the (100) <001> direction, two highly aligned
In order to develop the next recrystallized grain structure,
It is more advantageous to carry out retention annealing at a low temperature of 0°C, and in addition, for example, 0.5 to b heat annealing may be used.

Purification annealing after secondary recrystallization annealing is carried out at 1100°C in hydrogen hydrogen.
It is necessary to perform annealing for 1 to 20 hours to achieve purification of the steel sheet.

Next, the nonmetallic substances on the surface after this purification annealing are removed by known chemical removal methods such as pickling, mechanical removal methods such as cutting and grinding, or a combination thereof.

After this removal treatment, the steel plate surface can be easily made into a mirror-like state, that is, with a center line average roughness of 0.4 μm or less, by chemical polishing such as chemical polishing or electrolytic polishing, mechanical polishing such as buffing, or a combination thereof. can be finished.

Thereafter, it is necessary to form an extremely thin tension coating of 0.005 to 5 μm on the surface of the mirror-like steel plate by CVD, ion plating, or ion implantation. .

Konotoki's CVD, ion plating, or ion implantation equipment may be any conventionally known method.

As ultra-thin tension coatings made by these methods, for example, T
iN, TiC, VN, VC, NbN, NbC, S
i, N,, SiC.

(:r2N, Cr3C,,AIN, A14C,BN
, NiC, CoC, CoN.

Mo2C, WC, iS2N, ZrN, ZrC, Hf
N, HfC, Mn2C, TaC.

TaN, Al2O3, Sin. , ZnO, Tin.

, ZrO2,5n02゜Fe2O3, Nip, Cub
, MgO, etc. are suitable.

Furthermore, after forming an ultra-thin tension film by CVD, ion plating or ion implantation, it is possible to apply and bake an insulating film whose main components are phosphate and colloidal silica over this.
This is naturally necessary in the use of large-capacity transformers of up to 10,000 KVA, and conventionally known methods may be used to form this insulating coated and baked layer.

The silicon steel plate treated as described above can be subjected to flattening heat treatment.

(Example) Example 1 (::Q, 046%, Si: 3.42%, Mn: 0.
064%, Mo: 0.025%, Se: 0.021%,
A hot-rolled sheet containing 0.025% Sb was heated at 900°C for 3
After homogenization annealing for 2 minutes, intermediate annealing at 950℃ is performed for 2 minutes.
Cold rolling was performed twice to obtain a final cold rolled sheet with a thickness of 0.23+nm.

Then, after decarburization annealing in wet hydrogen at 820℃, A1
After applying an annealing separator consisting of 203 (75%) and MgO (25%), secondary recrystallization annealing was performed at 850°C for 50 hours, and purification annealing was performed at 1200°C for 8 hours in dry hydrogen.

After that, it was lightly pickled, and then chemically polished in 3% HF and 820□ solution to give it a mirror finish to a center line average roughness of Rag, 05 μm.

Thereafter, ion plating was performed for 3 minutes at an ionization voltage of 10 KV to form a TiN tension film with a thickness of 0.5 μm.

Next, an insulating coated and baked layer containing phosphate and colloidal silica as main components was formed, and then strain relief annealing was performed at 80°C for 2 hours.

The magnetic properties and adhesion of the product at that time were as follows.

Magnetic properties ILo=1.90T, Wuzso=0.68
W/kg Adhesion 180° with bending diameter 30+n+n
It did not peel off even when bent, and the adhesion was good.

Example 2 coo, 061%, Si: 3.38%, Mn: 0.0
80%, A1: 0.025%, S: 0.029%, N:
A hot-rolled sheet containing 0.0068% was uniformly annealed at 1150°C for 3 minutes and then rapidly cooled, and then warm-rolled at 300°C to obtain a final cold-rolled sheet with a thickness of 0.23mm.

After decarburization annealing in wet hydrogen at 850°C, the surface is coated with Al2.
O3 (40%), ZrO2 (30%), Mg0 (30%
) from 850℃ to 115℃ after applying an annealing separator consisting of
After secondary recrystallization by raising the temperature to 0°C at a rate of 8°C/hr, 1
Purification annealing was performed in dry hydrogen at 200° C. for 8 hours.

After that, it was lightly pickled, and then chemically polished in 3% HF and 820□ solution to give it a mirror finish with a center line average roughness of 3 μm.

After that, nitrogen ions were implanted using the ion implantation method at an ion acceleration voltage of 60 KV for 250 minutes to form a film with a thickness of 1
．． An ultra-thin tension film made of Si3N with a thickness of 2 μm was formed, and then an insulating coating and baking layer containing phosphate and colloidal silica as main components was formed, followed by strain relief annealing at 800°C for 2 hours. I did it.

The magnetic properties and adhesion of the product at that time were as follows.

Magnetic properties B, o=1,947. W+7. =so=0.
65111/kg Adhesion 18 at bending diameter 30mm
Even when bent by 0°, it could not be peeled off, and the adhesion was good.

Example 3 C: 0.043%, Si: 3.46%, Mn: 0.06
0%, Mo: 0.026%, Se: 0.023%, Sb
: A hot-rolled sheet containing 0.025% was uniformly annealed at 900°C for 3 minutes, then cold-rolled twice with intermediate annealing at 950°C, and finally cold-rolled to a thickness of 0.20mj. It was made into a board.

After that, after decarburization annealing in wet hydrogen at 800℃, A
After applying an annealing separator consisting of 12O3 (70%) and MgO (30%), secondary recrystallization annealing was performed at 850°C for 50 hours, and purification annealing in dry hydrogen was performed at 1180°C for 100 hours.

After that, it was lightly pickled, then 3% HF...! : Chemically polished in H20□ solution to a mirror surface with a center line average roughness of Rag, 05 μm.

Thereafter, an extremely thin tension film of TiC was formed with a film thickness of 0.4 μm using the CVD method.

The magnetic properties and adhesion of the product at that time were as follows.

Magnetic properties B+o=1.9LT, Wu7so=0.69
W/kg Adhesion The adhesion was good as it could not be peeled off even when bent by 1&0° with a bending diameter of 30 mm.

Example 4 c:o, 044%, Si: 3.36%, Mn: 0.0
66%, Mo: 0.027%, Se: 0.021%, s
b: (Hot rolled sheet containing 1,025% (2,2mff1
After uniform annealing at 900°C for 3 minutes, cold rolling was performed twice with intermediate annealing at 950°C to reduce the thickness to 0.23mm.
A thick final cold-rolled sheet was obtained.

After that, after decarburization annealing in wet hydrogen at 820℃, A
120z (75%) and MgO (20%), Zr0z
After applying an annealing separator mainly composed of (5%) 85
Secondary recrystallization annealing was performed at 0° C. for 50 hours and purification annealing was performed at 1200° C. for 8 hours in dry hydrogen.

Thereafter, the oxide film on the surface of the steel plate was removed by light pickling, and then electrolytically polished to a mirror finish. After that, CVD (
(no mark in Table 4), ion plating (○ mark in Table 4)
and ion implantation (marked with Δ in Table 4) to form thin films of various nitrides, carbides, and oxides (
1.0-1.5 μm thick).

After that, the surface of the sample treated with these treatments was treated with an insulating coating mainly composed of phosphate and colloidal silica.
Strain relief annealing was performed at 0°C for 3 hours. The magnetic properties of the products at that time are summarized in Table 2.

Example 5 coo, 039%, Si: 3.26%, Mn: 0.0
62%, B: 0.029%, S: 0.032%, Cu
: A silicon steel slab containing 0.12% was heated at 1320° C. for 6 hours and then hot rolled to obtain a 2.2 mm thick hot rolled plate. After that, homogenization annealing was performed at 950°C for 2 minutes, and then 950°C
Cold rolling was performed twice with intermediate annealing at 0.2 °C.
The final cold-rolled sheet had a thickness of 3+n+n.

After that, after primary recrystallization annealing that also served as decarburization in wet hydrogen at 840°C, Al2O, (60%) and ZrO□ (3
%).

After applying an annealing separator mainly composed of Mg0 (37%), the temperature was raised from 850°C to 1050°C at a rate of 5°C/hr for secondary recrystallization, and then it was heated at 1200°C for 10 hours in dry hydrogen. Purification annealing was performed.

Thereafter, the oxide film on the surface of the steel plate was removed by pickling, and then electrolytically polished to a mirror-like finish.

After that, TiN (3.5 μm
After forming a tensile film with a thickness of 1.5 mm, an insulating coated and baked layer containing phosphate and colloidal silica as main components was formed, and strain relief annealing was performed at 800° C. for 3 hours.

The magnetic properties and adhesion of the product at that time were as follows.

Magnetic properties B 1o=1.93T, II + t7s
o=0゜691'i/kg Adhesion Bending diameter 30
+nm, the adhesiveness was good and could not be peeled off even when bent by 180°.

(Effects of the Invention) According to the first invention, an appropriate manufacturing method for ultra-low iron loss unidirectional silicon steel sheet that is advantageously suitable for use where strain relief annealing is applied is established, and according to the second invention, Further insulation enhancement is added.

Claims (1)

[Claims] 1. A hot rolled sheet obtained by hot rolling a silicon-containing steel slab.
After performing cold rolling twice or intermediate annealing to reach the final thickness, decarburization and primary recrystallization annealing are performed, followed by final finish annealing including secondary recrystallization and purification annealing. Applying an annealing separator with a composition that suppresses the forsterite formation reaction between the surface layer of the steel sheet mainly consisting of Si and Fe oxides to the finish annealed grain-oriented silicon steel sheet. After removing the non-metallic layer, the center line average roughness was reduced to 0.0 by polishing.
Finish to a mirror-like state of 4 μm or less. Ti
, Nb, Si, V, Cr, Al, B, Ni, Co, Mo
, W, Zr, Hf, Mn and Ta nitrides and/or carbides, and Al, Si, Zn, Ti, Zr, Sn, Fe
, consisting of at least one kind selected from oxides of Ni, Cu, W and Mg, characterized in that it is a combination of depositing an ultra-thin tension film with a film thickness of 0.005 to 5 μm, A method for producing thermally stable, ultra-low core loss unidirectional silicon steel sheets. 2. 1 to a hot rolled plate obtained by hot rolling a silicon-containing steel slab
After performing cold rolling twice or intermediate annealing to reach the final thickness, decarburization and primary recrystallization annealing are performed, followed by final finish annealing including secondary recrystallization and purification annealing. Applying an annealing separator with a composition that suppresses the forsterite production reaction between the surface layer of the steel sheet and the steel sheet surface layer, which is mainly composed of Si and Fe oxides, to the grain-oriented silicon steel sheet that has been finish annealed. After removing the non-metallic material layer, the centerline average roughness is reduced to 0 by polishing.
．． Finish to a mirror-like state of 4 μm or less. Ti
, Nb, Si, V, Cr, Al, B, Ni, Co, Mo
, W, Zr, Hf, Mn and Ta nitrides and/or carbides, and Al, Si, Zn, Ti, Zr, Sn, Fe
, depositing an ultra-thin tension film with a thickness of 0.005 to 5 μm, which is made of at least one kind selected from oxides of Ni, Cu, W, and Mg, and having an insulating property on this tension film. A method for producing a highly insulating, thermally stable, ultra-low core loss unidirectional silicon steel sheet, which is characterized by depositing coated and baked layers in a stacked manner, and forming a bond of the following.