JPH0619113B2 - Method for producing grain-oriented electrical steel sheet with extremely low iron loss - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The remarkable development of recent years that attempts to meet the extreme demands for improving the electrical and magnetic properties of grain-oriented silicon steel sheets, and especially for reducing iron loss. Efforts are gradually showing fruit, but as a serious adverse effect associated with its implementation, deterioration of properties is caused when so-called strain relief annealing is performed after processing and assembling in the use of unidirectional silicon steel sheet. It is pointed out that disadvantages arise due to the inevitable occurrence of companionship and restrictions on usage.

In this specification, regardless of whether or not a high-temperature heat history such as strain relief annealing is performed, the following will be described in relation to the results of development research on inducing a new way that can advantageously satisfy the above requirements. Describe.

As is well known, grain-oriented silicon steel sheet is a highly integrated secondary recrystallized grain of the product in {100} <001>, that is, Goss orientation, and is mainly used in transformers and other electrical equipment. It is used as an iron core, has high magnetic flux density (typically represented by B ₁₀ ) of the product as electric and magnetic characteristics, and iron loss (W
_17/50 value) is required.

This direction silicon steel sheet is manufactured through a variety of complicated processes, but numerous inventions and improvements have been added so far, and today the product with a plate thickness of 0.30 mm has a magnetic property of B ₁₀ 1.90T.
Above, W _17/50 1.05 W / Kg or less, and a product with a sheet thickness of _0.23 mm has an ultra-low iron loss unidirectional silicon steel sheet with a magnetic property of B ₁₀ 1.89 T or more and W _17/50 0.90 W / Kg or less. It is becoming manufactured.

Particularly in recent years, there has been a marked increase in demand to reduce power loss from the viewpoint of energy saving, and in Europe and the United States, when making a transformer with low loss, the amount of iron loss reduction is converted into a monetary amount and added to the transformer price.・ The “evaluation” (iron loss evaluation) system is widespread.

(Prior Art) Under such a circumstance, it has recently been possible to remove a forsterite coating on a grain-oriented silicon steel sheet or prevent the formation thereof, finish the surface of the steel sheet to be a smooth surface, and apply a tension coating to obtain a very strong iron coating. Techniques have been developed to provide low loss grain oriented silicon steel sheets.

For example, in Japanese Patent Laid-Open No. 62-1821, the forsterite undercoat on the surface of a steel sheet after finish annealing is removed, and then polished to a smooth surface of 0.4 μm or less, and further nitride, carbide or oxide is formed by a CVD method. The technique of providing a grain-oriented silicon steel sheet having extremely low iron loss by forming the tension coating film is disclosed.

In connection with this, in JP-A-62-1822, the composition of the annealing separator applied after decarburization / primary recrystallization annealing is limited so that forsterite is formed during final finishing annealing. After suppressing the reaction and removing the non-metallic substance layer on the surface of the grain-finished grain-oriented silicon steel sheet after finish annealing, by polishing treatment,
Finished to a smooth surface with an average roughness of 0.4 μm or less, then CVD
Method and ion implantation method, a tension coating of nitride, carbide or oxide is applied to provide a grain-oriented silicon steel sheet having extremely low iron loss.

Compared with the former method, the latter method does not cover the steel sheet surface with the forsterite undercoating, so Ra:
Although the pickling and polishing steps for making a smooth surface of 0.4 μm or less are greatly simplified and the cost can be reduced, the average roughness Ra: 0.4 μm or less is used for smoothing, and then the above-mentioned method is used. The magnetic properties when the tension coating is applied are inferior to the former method.

Further, as a conventional method of not forming a forsterite coating, there is a method of considering the components of the annealing separator used before the final finish annealing. That is, JP-A-53-22113
Japanese Unexamined Patent Publication No. 55-89423 discloses a method of applying an annealing separator composed of hydrous silicate mineral powder and fine particle alumina to a decarburized / primary recrystallization annealed plate having a thickness of 4 μm or less. A method of applying an annealing separator containing Al ₂ O ₃ as a main component and further containing an Sr or Ba compound to a charcoal / primary recrystallization annealed plate, and Japanese Patent Laid-Open No. 59-96278 discloses Al ₂ O ₃ Each of them discloses a method of applying an annealing separator containing, as a main component, inactive MgO. However, since all of these methods use Al ₂ O ₃ as a main component, Al ₂ O ₃ locally adheres to the surface of the steel sheet after final finish annealing, and a great deal of labor is required to remove it. Not only does it have an average roughness of 0.
The magnetic properties after smoothing the surface to 4 μm or less were the same as when the forsterite film was formed and then the film was removed, but the magnetic properties when the tension film was subsequently applied. Is inferior.

(Problems to be solved by the invention) Therefore, it is an object of the present invention to realize magnetic characteristics equivalent to those of a method of forming a forsterite film and then removing the film even by a method of not forming the forsterite film. Is.

(Means for Solving Problems) The inventors of the present invention formed a forsterite film after smoothing the surface, removed the film, then smoothed the surface to Ra: 0.3 μm, and deposited TiN to a plate thickness of 0.23. mm and a 0.23 mm thick plate with TiN deposited with Ra: 0.3 μm smoothed by suppressing the formation of forsterite coating. Chemically polish the base metal surface of the steel plate of each sample. Further, several stages of polishing were performed, and changes in magnetic properties and average roughness when a tension film was applied at each polishing stage were examined. The result, as a function of the polishing thickness from the original ground metal surface,
As shown in the figure, in the forsterite film removal method, good magnetic properties are obtained as the average roughness of the steel plate surface becomes 0.4 μm or less, whereas in the forsterite film formation suppression method, the steel plate surface roughness is reduced. Saga Ra: 0.4 μm
However, the magnetic characteristics are not improved, and polishing with a thickness of 5 μm or more is required to obtain good magnetic characteristics. However, polishing a base metal substrate requires a great deal of labor and cost, and is extremely difficult to carry out on an industrial scale.

In the method of making the surface of the steel sheet subjected to final finish annealing smooth and applying a tension coating on it, the inventors
It has been newly found that the magnetic properties after applying the tension coating become extremely excellent by making the oxygen basis weight of the decarburized / primary recrystallization annealed plate extremely low and sufficiently performing the decarburization. However, at this time, it was also found that it is necessary to use MgO as a main component as an annealing separator applied to the steel sheet after decarburization / primary recrystallization annealing, and obtained the beginning of the present invention.

That is, according to the present invention, a hot-rolled sheet obtained by hot-rolling a silicon steel slab is cold-rolled once or twice with intermediate annealing to obtain a final sheet thickness, and then decarburized. After performing the secondary recrystallization annealing, after applying the annealing separation agent and subsequent final finishing annealing including secondary recrystallization annealing and purification annealing, after removing the non-metallic substance layer on the steel sheet surface, the average roughness Ra at 0.
Finished to a smooth surface of 4 μm or less, and CVD on this surface
In the method for producing a grain-oriented electrical steel sheet on which a tension coating of metal or ceramic is formed by a metal ion method, an ion plating method or an ion implantation method, the amount of oxide on the surface layer of the steel sheet after decarburization and primary recrystallization annealing is set to oxygen The weight per unit surface is 0.3 g / m ² or less, the carbon content in the steel sheet is 0.003 wt% or less, and the separating agent containing MgO as the main component is used as the annealing separating agent. It is a method of manufacturing a low-oriented electrical steel sheet.

Moreover, in the implementation, the silicon steel slab contains C: 0.010 wt% or less, Si: 2.0
wt% or less, acid-soluble Al: 0.010 to 0.060 wt% and Tota
l N: 0.003 to 0.010 wt% is contained, and rolling before decarburization and primary recrystallization annealing uses a smooth roll to reduce the average roughness of the steel sheet surface to Ra of 0.2 μm or less. The smooth surface finish is due to the rolling treatment, and the reduction of the oxygen basis weight is reduced before decarburization and primary recrystallization annealing.
e, Co, Ni, Mn and Cd are plated with one or more selected from the group of 0.5 g / m ² or more and less than 20 g / m ² and the oxygen basis weight is reduced. It is advantageous to carry out by grinding the surface layer of the steel sheet after decarburization and primary recrystallization annealing.

Here, the oxygen basis weight of the oxide of the steel sheet surface layer after decarburization / primary recrystallization annealing is the oxygen content of the sample obtained by removing the inside of the steel sheet, that is, the steel sheet surface layer with a thickness of 20 μm or more from the oxygen content analyzed on both sides of the steel sheet. It is a value obtained by calculating the oxygen amount per unit area of the front and back surfaces of the steel sheet based on the subtracted value.

In addition to the methods described above, decarburization / reduction of oxygen and carbon in the steel sheet surface layer after decarburization / primary recrystallization annealing
This can be achieved by adjusting the degree of oxidation of the atmosphere in the primary recrystallization annealing, the annealing temperature and the annealing time, and it is also possible to combine the above-mentioned methods including the method.

Next, the description will proceed according to the concrete experiments that have led to the success of each invention.

C: 0.045 wt% (hereinafter simply referred to as%), Si 3.35%, M
n 0.065%, Se 0.020%, Sb 0.025% and Mo 0.01
A continuous cast slab of silicon steel containing 2% was heated at 1320 ° C. for 4 hours and then hot rolled into a hot rolled sheet having a thickness of 2.0 mm. Then 90
After homogenizing annealing at 0 ° C. for 3 minutes, cold rolling was performed twice with intermediate annealing at 950 ° C. for 3 minutes to obtain a final cold-rolled sheet having a thickness of 0.03 mm.

After that, when performing decarburization and primary recrystallization annealing in a wet hydrogen atmosphere at 820 ° C, the dew point and annealing time in the wet hydrogen atmosphere were changed to change the carbon content in the steel to 0.001% to 0.008%, steel sheet. The oxygen amount in the surface layer was changed from 0.1 g / m ^{2 to} 0.5 g / m ² .

Each of the above decarburized and primary recrystallization annealed steel sheets is divided into two parts, one is applied with an annealing separator containing MgO as the main component, and the other is Al ₂ O ₃ (70%) and MgO (30%). After the annealing separator composed of and was applied, secondary recrystallization annealing was carried out at 850 ° C. for 50 hours and purification annealing was carried out at 1200 ° C. in dry hydrogen for 5 hours.

In the above, forsterite coating was not formed on all the steel sheets in which the oxygen basis weight of the steel sheet surface layer after decarburization / primary recrystallization annealing was set to 0.3 g / m ² or less per one surface, and 10 The surface oxide could be removed by a light pickling treatment in a% H ₂ SO ₄ solution. However, if the oxygen basis weight of the surface layer of the steel sheet after decarburization / primary recrystallization annealing exceeds 0.3 g / m ² per side, 10% H ₂
The surface oxide could not be removed by the light pickling treatment in SO ₄ solution, and the subsequent experiments were stopped.

Next, with respect to the sample from which the oxide on the surface of the steel sheet could be removed by the light pickling treatment, the iron ground surface was polished by 2.0 μm from the surface layer by chemical polishing and electrolytic polishing.
A smooth surface condition of 0.3 μm was obtained.

After that, ion plating was performed. The magnetic properties of the products at this time are summarized in Tables 1 and 2.

From the table, it can be seen that the carbon content and the oxygen basis weight of the steel plate surface layer are in the range according to the present invention, and by using the annealing separator having MgO as the main component, good magnetic properties can be obtained. It was

(Operation) The above-mentioned improvement of magnetic properties is due to the fact that MgO is the main component under the control of the oxygen basis weight of the oxide of the surface layer of the steel sheet formed during decarburization and primary recrystallization annealing and the carbon content of the steel sheet. The formation of the forsterite coating is suppressed by using the annealing separator, and can be easily realized by depositing the tension coating on the smoothed surface.

When the composition of the annealing separator was changed and the forsterite film formation was suppressed, the surface layer of the steel plate base metal was investigated in detail.
Dispersion of oxide particles containing O ₂ as the main component was observed, and since this is an extremely small amount, it does not affect the magnetic properties of the steel sheet in the smoothed state, but a tension coating was applied to this. In some cases, it was found that the tension effect causes deterioration of magnetism.

On the other hand, if the oxygen basis weight of the decarburized / primary recrystallization annealed sheet is reduced to 0.3 g / m ² or less per side, the oxide particles are dispersed only in the surface layer of the steel sheet after the final finish annealing. This layer is sufficiently removed by the usual smoothing treatment. However, when the oxygen basis weight is restricted to 0.3 g / m ² or less per side, if an annealing separator with Al ₂ O ₃ as the main component is used, the purification of the steel sheet during the final annealing is not sufficient, and this is not preferable. , It is necessary to use an annealing separating agent containing MgO as a main component, and even in this case, the forsterite coating is not formed.

The oxygen basis weight of the decarburized / primary recrystallization annealed sheet is 0.3
If it is regulated to g / m ² or less, significant iron loss often occurs, that is, the oxygen basis weight is 0.3 g / side per side.
When reducing to m ² or less, carbon remaining in high concentration in the steel sheet finally deteriorates the magnetic properties of the product, so decarburization.
It is necessary to regulate the carbon content of the steel sheet after the secondary recrystallization annealing to 0.003% or less. Then, in order to reduce the oxygen basis weight to 0.3 g / m ² or less per side by decarburization / primary recrystallization annealing, the carbon content in the steel sheet after cold rolling before decarburization / primary recrystallization annealing is It is desirable to adjust it to 0.50% or less.

Next, a detailed description will be given of an advantageous method for controlling the oxygen basis weight and the carbon content in the present invention.

Generally, the decarburization reaction and the oxidation reaction on the surface of the steel sheet simultaneously proceed due to the action of water vapor in the annealing atmosphere, so the annealing conditions for promoting the decarburization and suppressing the oxidation have a narrow range and poor reproducibility. .

Further, the method of removing the surface oxides of the steel sheet after decarburization and primary recrystallization annealing by grinding and polishing is effective when the oxygen weight is low, but the cost is increased when the oxygen weight is high. Not preferable.

In order to perform sufficient decarburization despite the low oxygen basis weight,
It is preferable to control the amount of carbon before decarburizing and annealing, and it is desirable to keep the amount of carbon before decarburizing and annealing to be 0.050% or less. This includes a method of reducing the carbon content of the slab, a method of reducing carbon during hot rolling, a method of reducing carbon during normalizing a hot rolled sheet, and an intermediate annealing between two cold rollings. There is a method to reduce carbon.

In the rolling before decarburization and primary recrystallization annealing, the surface roughness of the steel sheet was Ra: 0.
It can also be realized by setting the thickness to 2 μm or less.

Also, if the Si content in the slab is restricted to 2% or less, α-γ transformation will occur even with a low C content of 0.010% or less during hot rolling, so decarburization during decarburization and primary recrystallization annealing Is advantageous to At this time, a slab using AlN as an inhibitor is advantageous, and MnS or MnSe may be added as an inhibitor besides this. At this time, the effective Al range is acid-soluble Al 0.010 to 0.060%, and the total N is 0.003 to 0.01.
0% is the proper range.

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

The starting material is a conventionally known unidirectional silicon steel material component, for example, C: 0.01 to 0.060%, Si: 2.50 to 4.5%, Mn: 0.
01 to 0.2%, Mo: 0.003 to 0.1%, Sb: 0.005 to 0.
2%, 1 or 2 total of S or Se, 0.00
Composition containing 5 to 0.05% C: 0.01 to 0.08%, Si: 2.0 to 4.0%, Sol AL: 0.
005 to 0.06%, S: 0.005 to 0.05%, N: 0.001 to 0.01
%, Sn: 0.01 to 0.5%, Cu: 0.01 to 0.3%, Mn: 0.
Composition containing 01 to 0.2% C: 0.01 to 0.06%, Si: 2.0 to 4.0%, S: 0.005
~ 0.05%, B: 0.0003-0.0040%, N: 0.001-0.01
%, Mn: 0.01-0.2%, and the like. Then, the hot-rolled sheet is homogenized at 800-1100 ° C and then cold-rolled once to obtain the final sheet thickness. Rolling method or usually 850 ℃
In the latter case, the initial rolling reduction is about 50% to 80% and the final rolling reduction is about 50% to 85%. mm to 0.35
The final cold-rolled sheet thickness is mm.

The steel sheet that has been finished cold-rolled and finished to the product thickness is subjected to decarburization and primary recrystallization annealing treatment in wet hydrogen at 750 ° C to 850 ° C after surface degreasing.

Here, the oxygen basis weight of the steel sheet after decarburization / primary recrystallization annealing is 0.3 g / m ² or less per side, and the carbon content of the steel sheet is 0.003% or less. If the oxygen areal weight of the steel sheet exceeds 0.3 g / m ² per side, a forsterite film is formed after the final finish annealing, and it becomes difficult to smooth the surface. If the carbon content exceeds 0.003%, the magnetic properties of the product deteriorate. After that, an annealing separator having MgO as a main component is applied to the surface of the steel sheet and wound. If MgO is not more than 50% as the separating agent component, the purification of the inhibitor will be insufficient in the purification annealing in the next step, and good characteristics cannot be obtained.

Then, a final annealing including a secondary recrystallization annealing and a subsequent purification annealing is performed.

This secondary recrystallization annealing process is performed to sufficiently develop the secondary recrystallized grains in the {110} <001> orientation, and is usually heated to 1000 ° C or higher by box annealing or maintained at that temperature. It is done by doing things, but in the {110} <001> direction,
82 to develop highly uniform secondary recrystallized grain structure
In some cases, it may be advantageous to carry out the holding annealing at a low temperature of 0 ° C. to 900 ° C. In addition, the annealing may be performed at a heating rate of 0.5 to 15 ° C./h.

The purification annealing after the secondary recrystallization annealing requires annealing in dry hydrogen at 1100 ° C. or higher for 1 to 20 hours to achieve purification of the steel sheet.

Then, after this annealing, the non-metal substance on the surface is removed by a known chemical removal method such as pickling, a mechanical removal method such as cutting or grinding, or a combination thereof.

After this removal treatment, the steel plate surface is made smooth by the conventional method such as chemical polishing such as chemical polishing and electrolytic polishing, mechanical polishing such as buffing, or a combination thereof, that is, the center line average roughness is 0.4 μm or less. It can be finished easily.

Further, it is possible to finish it to 0.4 μm or less by further rolling. In this case, since the recrystallization annealing is performed after applying the tension film in the next step, the crystal grain size of the steel sheet is small, and it is suitable as a high-frequency silicon steel sheet. Therefore, the plate thickness in this rolling is preferably 0.020 to 0.150 mm. Ie 0.020 mm
If it is less than 0.1 mm, rolling becomes difficult, and if it exceeds 0.150 mm, it is disadvantageous in terms of high-frequency magnetic properties.

Further, if the surface state is rougher than the average roughness Ra: 0.4 μm, the effect of the tension coating cannot be obtained.

After that, it is necessary to form a tension film on the surface of the steel sheet in a smooth surface state by CVD, ion plating or ion implantation.

At this time, as a device used for CVD, ion plating or ion implantation, a conventionally known device may be used.

Examples of the ultrathin tension film formed by these methods include T
iN, TiC, VN, VC, NbN, NbC, Si ₃ N ₄ , Si
C, Cr ₂ N, Cr ₃ C ₇ , AlN, Al ₄ C, BN, Ni
C, CoC, CoN, Mo ₂ C, WC, W ₂ N, ZrC, Hf
C, Mn ₂ C, TaC, TaN, Al ₂ O ₃ , SiO ₂ , ZnO, Ti
O ₂ , ZrO ₂ , SnO ₂ , Fe ₂ O ₃ , NiO, CuO, MgO and the like are suitable.

Furthermore, after forming an ultrathin tension film by CVD or ion plating with ion plating, an insulating film mainly composed of phosphate and colloidal silica is applied and baked on top of this. Ten thousand
Needless to say, it is necessary in the use of a large-capacity transformer as high as KVA, and a conventionally known method may be used for forming the insulating coating baking layer.

In addition, after finishing to a smooth surface state, a magnetic domain refining treatment is applied to apply a tension coating, and after a tension coating is applied, a magnetic domain refining treatment is applied, whereby the magnetic characteristics are additively added. improves. As the magnetic domain subdivision processing, known methods such as laser irradiation and ion implantation can be applied.

(Example) (a) Example 1 Applicable Example 1 C: 0.047%, Si: 3.4%, Mn: 0.062%, Mo:
A hot-rolled sheet containing 0.025%, Se: 0.022%, Sb: 0.020% was homogenized and annealed at 900 ℃ for 3 minutes, and then cold-rolled twice with an intermediate anneal at 950 ℃ to 0.23. The final cold-rolled sheet with a thickness of mm was used.

At this time, the rolling roll having a surface roughness of # 120 finish was used, and the surface roughness of the steel plate was Ra of 0.25 μm. Decarburization of this steel sheet under wet hydrogen atmosphere under the conditions shown in Table 1
Next recrystallization annealing was performed. After that, an annealing separating agent containing MgO as a main component was applied, followed by secondary recrystallization annealing at 850 ° C. for 50 hours, and subsequent purification annealing in dry hydrogen at 1200 ° C. for 8 hours. After that, brushing and H ₂ SO ₄ pickling are performed to remove the non-metallic substance layer on the surface layer, and then 3% HF and H ₂ S ₂ are added.
The surface was smoothed by chemical polishing in a liquid containing The melting amount of the steel sheet at this time was 3 μm. After this, 10KV
A TiN tension insulating film having a thickness of 0.5 μm was formed by ion plating for 3 minutes with the ionization voltage of.

Next, an insulating coating baking layer containing phosphate and colloidal silica as main components was formed, and then strain relief annealing was performed at 800 ° C. for 2 hours.

Comparative Example 1 As shown in Table 3 for the same steel sheet as in the conforming example 1, only the conditions of decarburization and primary recrystallization were changed to 2 conditions, and all the treatments were performed under the same conditions as in the conforming example 1.

Application Example 2 When the same hot-rolled sheet as in Application Example 1 was cold-rolled twice in the same process to obtain the final product thickness, it was rolled using a rolling roll having a surface roughness of # 600 finish, The surface roughness Ra was 0.16 μm. This steel sheet was subjected to decarburization / primary recrystallization annealing under the same conditions as in Comparative Example 1 (b), and was otherwise treated under the same conditions as in Comparative Example 1.

Application Example 3 The same steel sheet as in Application Example 1 that has finished rolling to the final plate thickness is shown in Table 3 with the steel sheet as a cathode in a plating bath mainly containing sulfate prior to decarburization and primary recrystallization annealing. Fe and C in basis weight
O, Ni, Mn and Cd were plated. After that, decarburization
Primary recrystallization annealing was carried out under the same conditions as in Comparative Example 1 (b), and subsequently, under the same conditions as in Compatible Example 1.

Comparative Example 2 Fe and Ni were used as the plating prior to decarburization / primary recrystallization annealing, and the basis weights were set as shown in Table 3, and the same treatment as in Comparative Example 3 was performed.

Application Example 4 The same steel plate as in Application Example 1 was processed in the same process as in Application Example 1, and after the smoothing, the acceleration voltage was 150 KV in vacuum.
Magnetic domain refinement processing was performed by linearly irradiating an electron beam with a diameter of 0.5 mm at intervals of 5 mm perpendicular to the rolling direction. This magnetic domain subdivision processing is (a) TiN after smoothing.
Before applying the tension coating of (1) or (b) smoothing and then applying the tension coating in two different stages. Only in this case, the magnetism was measured before the strain relief annealing.

Conformance example 5 Decarburization of the same steel sheet as in conformity example 1 under the same conditions as in comparison example 1 (b).
After the subsequent recrystallization annealing, the surface was ground with an abrasive grain-containing cloth roll (Scotchbright) to reduce the oxygen basis weight of the surface layer to 0.7 g / m ² . Then, it processed on the same conditions as the example 1 of adaptation.

Regarding the above-mentioned conformity examples 1-5 and comparative examples 1 and 2, decarburization.
Table 3 shows the measurement results of the C content of the steel sheet after the subsequent recrystallization annealing, the oxygen basis weight of the surface layer, and the magnetic properties after the strain relief annealing.

(B) Example 2 C: 0.043%, Si: 3.46%, Mn: 0.060%, Mo:
A hot-rolled sheet containing 0.026%, Se: 0.023%, Sb: 0.025% was homogenized and annealed at 900 ° C for 3 minutes, and then cold-rolled twice with intermediate annealing at 950 ° C for 0.20. The final cold-rolled sheet with a thickness of mm was used.

Then, after decarburization annealing in wet hydrogen at 800 ° C., the surface of the steel sheet was ground to give an oxygen basis weight of 0.25 g / m ² per side. At this time, the carbon content was 0.002%. Then coil 2
Divide and apply an annealing separator consisting of MgO (80%) and Al ₂ O ₃ (20%) on one side (Example), and on the other side Al ₂ O ₃ (70%)
And an annealing separator composed of MgO (30%) were applied (comparative example). These coils were subjected to a secondary recrystallization annealing at 850 ° C. for 50 hours and a purification annealing at 1180 ° C. for 10 hours in dry hydrogen.

As a result, neither of the forsterite coatings was formed.

After that, it was lightly pickled and then chemically polished in a 3% HF and H ₂ O ₂ solution to obtain a smooth surface having a center line average roughness Ra of 0.05 μm.

After that, an extremely thin tension film of TiC was formed with a film thickness of 0.4 μm by the CVD method.

The magnetic characteristics of the product at that time were B ₁₀ = 1.92T in the example,
W _17/50 = 0.69 W / kg, comparative example is B ₁₀ = 1.90T, W
_{It was 17/50} = 0.95 W / kg.

(C) Example 3 C: 0.061%, Si: 3.38%, Mn: 0.080%, Al:
A hot-rolled sheet containing 0.025%, S: 0.029% and N: 0.0068% was uniformly annealed at 1150 ° C for 3 minutes, then quenched, and then warm-rolled at 300 ° C to give a final cooling of 0.23mm. It was a rolled sheet. At that time, a smooth roll was used as a rolling roll, and the surface roughness of the steel sheet was Ra: 0.15 μm. Then, after decarburizing annealing in wet hydrogen at 850 ° C, MgO (90%) and ZrO ₂ were applied to the surface.
After applying the annealing separator consisting of (10%), 850 to 11
After re-crystallizing by heating up to 50 ℃ at 8 ℃ / hr, 1200
Purification annealing was performed in dry hydrogen at 8 ° C. for 8 hours.

After that, it was lightly pickled to remove non-metallic substances on the surface, and then this coil was divided into two, one of which was rolled to a thickness of 0.100 mm. The average surface roughness Ra at this time was 0.3 μm. A TiN film was deposited on the surface of the steel sheet by a vapor deposition method, and then recrystallization annealing was performed at 900 ° C. for 5 minutes. The high frequency magnetic characteristics of the product at this time are B ₁₀ : 1.85T, W _5/1000 :
4.3 W / kg, W _10/1000 : 20.1 W / kg, W _10/400 : 5.1
W / kg and W _15/400 : 10.3 W / kg. The remaining one was chemically polished in a 3% HF and H ₂ O ₂ solution to have a smooth surface finish with a center line average roughness of Ra 0.3 μm.

Then, by ion implantation, B was linearly injected in a direction perpendicular to the longitudinal direction of the coil of the steel sheet at a distance of 5 mm, and then a TiN tension coating was applied to the entire surface by ion plating. Next, after forming an insulating coating baking layer containing phosphate and colloidal silica as main components, strain relief annealing was performed at 800 ° C. for 2 hours.

The magnetic properties of the product at that time were B ₁₀ = 1.94T, W _17/50
= 0.63 W / kg.

(Effects of the Invention) According to the present invention, it is possible to establish an appropriate manufacturing method for suppressing the formation of forsterite film without impairing the magnetic properties of the product.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between magnetic characteristics and polishing thickness.

Claims (7)

[Claims] 1. A hot-rolled sheet obtained by hot-rolling a silicon steel slab is cold-rolled once or twice with intermediate annealing to obtain a final sheet thickness, and then decarburized. After performing the secondary recrystallization annealing, after applying the annealing separation agent and subsequent final finishing annealing including secondary recrystallization annealing and purification annealing, after removing the non-metallic substance layer on the steel sheet surface, the average roughness To a smooth surface of 0.4 μm or less with Ra, and a metal or ceramic tension coating is formed on this surface by the CVD method, ion plating method or ion implantation method.・ Oxygen basis weight of the surface layer of the steel sheet after the primary recrystallization annealing is 0.3 g / m ² or less per side and the carbon content of the steel sheet is 0.003 wt% or less, and MgO is used as an annealing separator. Characterized by using a separating agent as the main component Method for producing an extremely low-oriented electrical steel sheet the iron loss to be. 2. A silicon steel slab containing C: 0.010 wt% or less, Si: 2.0 wt% or less, acid-soluble Al: 0.010 to 0.060.
The manufacturing method according to claim 1, which contains wt% and Total N: 0.003 to 0.010 wt%. 3. The rolling before decarburization / primary recrystallization annealing is performed by using a smooth roll to reduce the average roughness of the steel sheet surface to Ra of 0.2 μm or less. Production method. 4. The manufacturing method according to claim 1, wherein the smooth surface finish is a rolling treatment. 5. The manufacturing method according to claim 4, wherein the rolling treatment is performed so that the plate thickness is 0.02 to 0.15 mm. 6. A reduction of the oxygen basis weight is achieved by 0.5 g / m ² or more and 20 g or more of one or more selected from Fe, Co, Ni, Mn and Cd prior to decarburization / primary recrystallization annealing. /
The manufacturing method according to claim 1, which is performed by plating with an adhesion amount of less than m ² . 7. The manufacturing method according to claim 1, wherein the oxygen basis weight is reduced by grinding the surface layer of the steel sheet after decarburization and primary recrystallization annealing.