JPH0617132A - Ultra-low iron loss grain oriented electrical steel sheet with extremely high magnetic flux density and method of manufacturing the same - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to an ultra-low iron loss grain-oriented electrical steel sheet having no glass coating and having an extremely high magnetic flux density and good workability, and a method for producing the same. [Structure] When finish annealing a steel sheet after primary recrystallization annealing, Li, K, Na, B is added to 100 parts by weight of MgO.
a, Ca, Mg, Zn, Fe, Zr, Sr, Sn, Al
, Etc., using an annealing separator containing 2 to 30 parts by weight of one or more selected from chlorides, carbonates, nitrates, sulfates, sulfides, etc., and the temperature rising rate during finish annealing is 10 ° C. / Hr
Hereinafter, the atmosphere is set to N ₂ + H ₂ of 30% or more of N ₂ , and then linear or dotted scratches are imparted in a direction of 45 to 90 ° with respect to the rolling direction by laser, tooth profile roll, press, scribing, local etching, etc. To do. At this time, of the primary recrystallized grains of the steel sheet after the primary recrystallization annealing, the primary recrystallized grains that exceed twice the average grain size are less than 10%.

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 no glass coating (forsterite coating), especially a high magnetic flux density ultra-low iron loss grain-oriented electromagnetic material which is remarkably excellent in workability such as cutting property and punching property. The present invention relates to a steel plate and a manufacturing method thereof.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are generally used as a soft magnetic material, mainly as an iron core of transformers and other electric equipment, and are required to have good magnetic excitation characteristics and iron loss characteristics. It In order to obtain good magnetic properties, it is important to highly align the <001> axis, which is the easy magnetization axis, with the rolling direction. Further, the plate thickness, the grain size, the specific resistance, the coating, etc. have a great influence on the magnetic properties, and are important.

Regarding the crystal orientation, AlN, MnS
It has been significantly improved by a method characterized by final cold rolling under high pressure using as an inhibitor, and now the magnetic flux density is close to the theoretical value. on the other hand,
When used in the consumer of grain-oriented electrical steel sheets, what is important along with magnetic properties is workability due to the coating. Usually, the grain-oriented electrical steel sheet is treated on its surface with a two-layer coating consisting of a glass coating and an insulating coating formed during final finishing annealing. The glass film is a reaction product of MgO which is an annealing separator and SiO ₂ which is formed during decarburization annealing and is forsterite (Mg ₂
SiO ₄ ) is the main film. This ceramic coating is hard and has strong wear resistance, and has a significant adverse effect on the durability of tools such as slits, cutting and punching when processing electromagnetic steel sheets. For example, in the case of punching a grain-oriented electrical steel sheet having a glass coating, the die wears, and the punch returns a large number of times when punched, resulting in problems during use. A certain degree of return will occur. Therefore, it is necessary to re-polish the mold and replace it with a new one. This results in a reduction in the work efficiency of the customer when processing the iron core and an increase in cost. Also,
Although the magnetic properties of the electromagnetic steel sheet itself have an effect of improving iron loss due to the film tension, there is a problem that the magnetic flux density decreases due to the non-magnetic material due to an increase in the film thickness depending on the formation state. For this reason, in the case where the iron loss improvement effect due to the film tension cannot be expected, such as a thick steel plate material, or in the case where the magnetic loss can be improved by subdividing the magnetic domain by other means, etc. A grain-oriented electrical steel sheet without a glass coating is desired.

In particular, in recent years, as a magnetic domain subdivision technique, a technique developed by optical, mechanical and chemical means has been developed so that iron loss can be improved without the tension of the glass coating. It has also been found that the grain-oriented electrical steel sheet that does not have the advantage is advantageous because it does not have an adverse effect such as the internal oxide layer of the glass coating that causes the pinning phenomenon of wall movement during magnetization. Therefore, the development of a high magnetic flux density grain-oriented electrical steel sheet without a glass coating is important when considering various usage conditions in the consumer, and needs are increasing.

At present, amorphous alloys are currently being used as a soft magnetic material to replace grain-oriented electrical steel sheets. However, in practical applications, such as low magnetic flux density, low space factor, and poor workability. We are facing various difficulties. Therefore, in order to develop a grain-oriented electrical steel sheet that can counter an amorphous alloy in iron loss characteristics, it has become important to develop a material having no glass coating.

[0006] As a method for producing a grain-oriented electrical steel sheet having no glass coating, for example, there is one disclosed in JP-A-53-22113. This is because the decarburization annealing has a thickness of an oxide film of 3 μm or less, and fine particles of alumina containing 5 to 40% of hydrous silicate mineral powder are used as an annealing separator, which is applied to a steel sheet and finish annealed. Become.
According to this method, it is said that an oxide film is thinned and a glass coating film that is easily peeled off is formed by adding a hydrous silicate mineral, and a glass film having a metallic luster is obtained. As a method for suppressing the formation of a glass film by using an annealing separator, as disclosed in JP-A-56-65983,
There is a method in which an annealing separator containing 20 parts by weight of an additive for removing impurities of aluminum hydroxide and 10 parts by weight of an inhibitor is applied to a steel sheet to form a thin glass film of 0.5 μm or less. Further, in Japanese Patent Laid-Open No. 59-96278, Al _{2 which} has a weak reaction with SiO ₂ in an oxide layer formed by decarburization annealing.
An annealing separator composed of O ₃ and MgO whose activity has been reduced by firing at a high temperature of 1300 ° C. or higher has been proposed. According to this annealing separator, the formation of forsterite is suppressed.

All of these prior arts are conventional orientations.
The magnetic flux density called the ent core is B ₈Value of 1.88T or less
A low-grade grain-oriented electrical steel sheet with a low bottom and therefore a high iron loss value
It is a technology based on the ultra low iron loss as in the present invention.
Stable grain oriented electrical steel sheets that meet the requirements for realization
The technology to gain is not yet developed.

[0008]

DISCLOSURE OF THE INVENTION The present invention provides a high magnetic flux density ultra-low iron loss grain-oriented electrical steel sheet which is excellent in punching property, slitting property, cutting property, etc. and has a substantially uniform glass coating, and an industrial steel sheet. It is an object of the present invention to provide a method of economically manufacturing.

[0009]

The subject matter of the present invention is as follows. (1) By weight, the amount of the internal oxide layer containing Si: 1.0 to 7.0% and distributed within 15 μm from the metal surface of the steel sheet is 1% or less in terms of the oxygen content in the thickness region. , B
Ultra low iron loss grain-oriented electrical steel sheet with extremely high magnetic flux density of ₈ ≧ 1.93T.

(2) An ultra-low iron loss having an extremely high magnetic flux density according to claim 1, wherein linear or dot-like scratches are provided on the surface in the direction of 45 to 90 degrees from the rolling direction at intervals of 2 to 15 mm. Grain-oriented electrical steel sheet. (3) Si: 1.0 to 7.0% by weight, acid-soluble A
After the hot rolling, cold rolling, primary recrystallization annealing, and application of the annealing separator, a steel ingot or slab containing 1: 0. 10 to 0.070% and the balance Fe and unavoidable impurities , In a method of producing a grain-oriented electrical steel sheet by performing high temperature finish annealing and heat flattening,
Of the primary recrystallized grains of the steel sheet after the primary recrystallization annealing, those having a grain size of more than twice the average grain size were adjusted to be less than 10%, and the same steel sheet was treated with 100 parts by weight of MgO as an annealing separator. In contrast, Li, K, Na, Ba, Ca, Mg, Z
n, Fe, Zr, Sn, Sr, Al chlorides, carbonates,
2 to 30 parts by weight of one or more selected from nitrates, sulfates and sulfides is applied, and the temperature rising rate at the time of high temperature finish annealing is 10 to 90 ° C. at 950 to 1150 ° C.
C./hr or less and the annealing atmosphere is at least N ₂ 3
A method for producing an ultra-low iron loss grain-oriented electrical steel sheet having an extremely high magnetic flux density, which is characterized in that N ₂ + H ₂ is 0% or more.

(4) Si: 1.0 to 7.0 by weight
%, Acid-soluble Al: 0.010 to 0.070%, C:
0.021 to 0.075%, N: 0.003 to 0.01
30%, S ≦ 0.030%, Mn: 0.05 to 0.45
%, With the balance being Fe and unavoidable impurities, the slab being heated before hot rolling at a temperature below 1280 ° C.,
The method for producing an ultra-low iron loss grain-oriented electrical steel sheet with extremely high magnetic flux density according to the above item 3, wherein nitriding is performed after the completion of primary recrystallization and before the start of secondary recrystallization of high temperature finish annealing.

(5) Before or after the heat flattening, a linear or dot-like flaw is imparted to the surface of the steel sheet by local processing such as laser, tooth profile roll, press, scribe, local etching, or the like. 4. The method for manufacturing an ultra-low iron loss grain-oriented electrical steel sheet according to 4, which has an extremely high magnetic flux density. Hereinafter, the present invention will be described in detail.

In the process for producing the high magnetic flux density ultra-low iron loss grain oriented electrical steel sheet of the present invention, the inhibitor elements such as Al, N, Mn and S are not completely dissolved in the steel during the slab heating step, After decarburization annealing, the material is subjected to a nitriding treatment in a strong reducing atmosphere to form an inhibitor containing (Al, Si) N as a main component, and good secondary recrystallization is developed in the finish annealing process. The basic process is to subdivide the magnetic domains.

Books based on the starting materials and processes of the above-mentioned composition
High magnetic flux density grain-oriented electrical steel sheet without glass coating of the invention
In the method of obtaining the
There is a characteristic in the method of processing. Material cold rolled to final plate thickness
Is decarburized and annealed in a continuous line. This decarburization annealing
Removes C in the steel and performs primary recrystallization.
SiO on the plate surface ₂The oxide film mainly composed of
It The decarburization annealing is performed at a temperature of 800 to 875 ° C., and the atmosphere is
N₂+ H₂It is performed by controlling the dew point inside. Next
In the latter half or after the decarburization annealing, or both
Nitriding on the same line or on a separate line at the stage
Processing is performed. The nitride generated at this time is
As a result, secondary recrystallization is developed during final finish annealing.

After that, an annealing separator is applied, dried, wound, and finally finish annealed. The composition of the annealing separator at this time plays an important role in controlling the formation of the glass film and in the decomposition reaction. The annealing separator used in the present invention contains MgO as a main component, and Li, K, Na, Ba, C as additives.
2 to 30 parts by weight of one or more of chlorides, carbonates, nitrates, sulfates, sulfides such as a, Mg, Zn, Fe, Zr, Sn, Sr, and Al are used.

What is important in the present invention together with the annealing separator is the condition of the final finish annealing which is the third elemental technique. The present inventors have found that as an inhibitor (A
In the case of adopting the steps of controlling the formation of the glass film and causing the decomposition reaction by using the annealing separator and the final finishing annealing condition, the annealing atmosphere condition is the stabilization of the secondary recrystallization and the high magnetic flux density. As a result of enormous experiments and research, we have determined that it will be an important factor for the realization.

That is, as in the present invention, (Al, Si) N
In the process of utilizing the system inhibitor, it is necessary to control the glass film formation and carry out the decomposition reaction up to the temperature range of the secondary recrystallization initiation temperature to maintain the inhibitor strength at a constant level. This is because the process of initiating the decomposition of the glass film by the annealing separator once initiating the decomposition reaction,
This is because the decomposition of the inhibitor in the steel rapidly progresses from the time when the decomposition reaction of the glass film starts. For this reason,
As in the present invention, unless finish annealing is performed under specific conditions,
Good secondary recrystallization and high magnetic flux density cannot be obtained. As the finish annealing condition, the atmosphere when the secondary recrystallization starts / progresses at the time of temperature rise at which the decomposition reaction of the glass coating starts, and N ₂
It is performed as 30% or more. This suppresses the decomposition rate of (Al, Si) N during the progress of secondary recrystallization,
The grain growth rate is optimized.

This effect is more remarkable when the temperature rising rate is slow, and when the N ₂ partial pressure of 30% or more and the gradual heating are combined, an extremely high B ₈ value is obtained, but the N ₂ partial pressure is increased. On the contrary, if it is low, secondary recrystallization failure occurs. The finish annealed steel sheet is 80 in a continuous annealing line for shape correction and strain relief annealing.
The insulating coating agent is baked and heat flattened at 0 to 900 ° C. Before or after this heat flattening, the depth is 5 to 50 μm and the distance is 2 to 15 mm by laser, tooth profile roll, press, scribing, local etching, etc.
Thus, linear scratches or dot scratches are introduced in the direction of 45 to 90 degrees with respect to the rolling direction. After that, various insulating coating agents are applied and baked according to the purpose of use in the consumer.

In order to form a tension coating film for achieving ultra-low iron loss, a phosphate-colloidal silica coating agent as disclosed in, for example, Japanese Patent Publication No. 53-28375 is used as an insulating coating agent. Is applied and baked. Further, when good workability is required in the subsequent consumer use process, an organic coating agent or a semi-organic coating agent may be applied and baked on the steel plate after heat flattening and used. Then, the inorganic coating agent may be applied and baked, and then the organic coating agent may be applied and baked to form a two-layer coating. The organic coating agent is (1) one or two or more kinds of all organic coating agents of resins such as acrylic, polyvinyl, vinyl acetate, epoxy, styrene and / or polymers and cross-linked products thereof. (2) The above A semi-organic coating agent comprising the resin in (1) and one or a mixture of two or more of chromate, phosphoric acid, phosphate, boric acid, borate and the like is used.
Use by applying and baking at a temperature of ~ 450 ° C.

By applying and baking these organic coating agents, the punching property, slitting property and cutting property are remarkably improved. According to the present invention, the punchability of a conventional product having a glass coating is about 5,000 times when a steel die is used, whereas the product having no glass coating is coated with an inorganic insulating coating agent.・ When baked
When the semi-organic coating agent is applied and baked about 100,000 times, the punchability is improved up to about 2 million times.

Next, the reasons for limiting the constituents of the present invention will be described. First, the reasons for limiting the component composition of the electromagnetic steel slab used as a starting material are as follows. When the content of C is less than 0.021%, the secondary recrystallization becomes unstable, and the magnetic flux density of the product becomes as low as about 1.80 T at B ₈ even when the secondary recrystallization is performed. On the other hand, 0.075%
If it exceeds this value, it takes a long time for the decarburization annealing process, which hinders the productivity.

The specific resistance of Si changes depending on its content, and the larger the content, the better the iron loss characteristics. When it is less than 1.0%, an oxide layer of SiO ₂ is difficult to be formed on the surface of the steel sheet during decarburization annealing, and the surface sealing effect at the time of secondary recrystallization according to the present invention is difficult to be obtained. When the Si content exceeds 7.0%, the toughness of the final product is extremely deteriorated and it cannot be put to practical use. In addition,
From the viewpoint of easy realization of ultra-low iron loss, it is desirable to secure the specific resistance of the product by setting the Si content to 2.5% or more, and from the viewpoint of productivity, Si4.5% or less,
It is desirable to reduce cracking and breakage prevention during cold rolling.

If S is too much, the amount of S during the secondary recrystallization is decreased.
Bitter strength out of balance and high B ₈value Can't get
As in the present invention, when performing glassless secondary recrystallization,
If the lab heating temperature is less than 1280 ° C, 0.030% or less
High enough even if added in B₈value Is obtained. Mn is small
If it is too large, hot-rolling cracks due to S segregation will be induced, and if too much, secondary
Debalance the inhibitor during recrystallization and decarburize
Poor glasslessness by increasing the [O] adhesion amount during annealing
Make a sound. From this viewpoint, the Mn content is 0.05 to
It is limited to 0.45%.

In the present invention, (Al, Si) N is used as a precipitate necessary for secondary recrystallization. Therefore, the minimum required A
To secure 1N, 0.010% or more of acid-soluble Al and 0.0030% or more of N are required. However, when the acid-soluble Al exceeds 0.070%, a large amount of oxide containing Al is generated on the surface of the steel sheet in the purification step, and the iron loss characteristics are impaired, so the content was made 0.07% or less. On the other hand, if the content of N exceeds 0.0130%, cracks on the surface of the steel sheet called blister occur, and the grain size of primary recrystallization cannot be adjusted, so it is limited to 0.0030 to 0.0130%.

The conditions for the final finish annealing are very important in the step of properly forming and decomposing the glass film in the final annealing process as in the present invention. Usually, N ₂ or H ₂ or a mixed gas of these is used as the atmosphere gas in the final finish annealing of the grain-oriented electrical steel sheet, but N ₂ + H ₂ is advantageous from the viewpoints of surface oxidation control and cost. For the present invention, for controlling the strength of the inhibitor in the course of a glass-free reaction, consisting of at least N ₂ 30% or more N _2, H ₂ and other inert gas as the atmosphere gas in NoboriAtsushichu atmosphere Is used. When the N ₂ partial pressure is less than 30%, there is no effect of suppressing weakening of (Al, Si) N generated in the glassless reaction process, and a high magnetic flux density material cannot be obtained stably. If such a N ₂ 100% on the contrary, depending on the physical properties of MgO, by increasing the degree of oxidation of between steel plates, to cause oxidation, tend to irregularities on the surface of the steel sheet occurs, preferably N ₂ 30 ˜90% range.

The slower the temperature rising rate during finish annealing, the higher the magnetic flux density is likely to be obtained, and the effect is particularly exhibited at a rate of 10 ° C./hr or less. The primary recrystallized grains gradually grow until the secondary recrystallization is started while the BAF temperature is rising. Therefore, when the temperature rising rate is slow, the amount of growth also becomes large, and it is necessary to control the primary recrystallized grain size to be small. At this time, the grain size distribution and texture of the crystal grains grown for a long time during finish annealing are optimized for secondary recrystallization, so even if the average grain size is the same, high magnetic flux density Can be obtained.

That is, in the secondary recrystallization, the highest B₈
There is an optimum average particle size for which a value is obtained. This average particle size is
If it is too large, it may cause secondary recrystallization failure, that is, the generation of fine grains.
If it is too small, the orientation integration is insufficient and good magnetic properties are obtained.
Can't get However, by increasing the decarburization annealing temperature,
Aiming at an appropriate average particle size will result in a gradual particle size distribution.
Many grains are generated. This coarse grain prevents stable secondary recrystallization.
Hurt. On the other hand, the grain size after decarburization annealing was slightly reduced.
The primary annealing by gradually heating the finish annealing.
Optimizing the average crystal grain size immediately after crystallization results in a sharp grain size distribution.
And the generation of coarse particles is suppressed. As a result, high B₈Value
And stable secondary recrystallization is obtained. Actually books
Experiments conducted by the inventors show that the examples are also shown.
Is the area ratio of crystal grains with a size more than twice the average grain size.
If the average particle size is more than 10%,
Secondary recrystallization failure occurred (see FIG. 2). In fact, the inventors
Fig. 1 shows the experimental results of trials using 0.15mm thick material.
You When the heating rate is fast, the decarburization annealing temperature is relatively high.
Even at (840 ℃) secondary recrystallization occurs, but the obtained magnetic flux density
Is low. On the other hand, when heating slowly,
Nitrogen partial pressure of (N ₂50%) decarburization annealing temperature
B is low but high₈value Has been obtained.

By the way, in the process in which the secondary recrystallization and the film disappearance are parallel to each other as in the present invention, if the nitrogen partial pressure in BAF is low, the decomposition of (Al, Si) N proceeds rapidly, so that the temperature rising rate is increased. When it is late, the primary recrystallized grains grow too much and the secondary recrystallization becomes unstable. Therefore, if the N ₂ partial pressure is increased to suppress the decomposition of the inhibitor, the growth of the primary recrystallized grains is optimized, and an extremely high magnetic flux density is obtained. Particularly when the plate thickness is as thin as 0.17 mm or less, it is desirable that the N ₂ partial pressure be 50% or more. Further, these finish annealing conditions need to be satisfied at least from 950 ° C., which is just before the start of secondary recrystallization, to 1150 ° C., which is complete. Furthermore, it is desirable to carry out at 700 ° C. or higher, which is effective in stabilizing (Al, Si) N.

As described above, according to the present invention, a high magnetic flux density can be obtained by decreasing the temperature rising rate of finish annealing, increasing the N ₂ partial pressure, and decreasing the grain size immediately after primary recrystallization. I knew I could do it.

[0030]

EXAMPLES Si: 3.50%, C: 0.054%, M
n: 0.14%, S: 0.008%, Al: 0.029
Steel containing 5% and N: 0.073% and the balance Fe and unavoidable impurities was cast into a slab by continuous casting, hot-rolled by heating the slab at 1200 ° C., annealing, pickling, The sheet was cold rolled to a thickness of 0.22 mm and decarburized and annealed for 110 seconds. At this time, the temperature of decarburization annealing is 830
C. and 840.degree. C. were applied at two levels. At this time, the average grain size of the primary recrystallized grains and the ratio of grains exceeding twice the average grain size are shown in FIG.
Shown in. This decarburized annealed sheet was subjected to nitriding treatment [N] = 2.
After adjusting to 26 ppm, an annealing separator containing chloride, carbonate, nitrate, sulfate, etc. was applied to finish annealing. The high temperature finish annealing cycle was performed under the three conditions shown in FIG. The secondary recrystallized plate thus obtained was subjected to a light pickling treatment with a 2.5% sulfuric acid solution at 80 ° C. for 10 seconds in a continuous line to obtain 50% Al (H ₂ PO ₄ ) ₃ 50 kg + 30% colloidal silica 70 kg + CrO. _An insulation coating agent consisting of 35 kg was applied, followed by baking at 850 ° C. for 30 seconds and heat flattening treatment. Then, using a laser, the interval was 5 mm and the irradiation width was 0.
Straining was performed under the conditions of 15 mm and the depth of the irradiation mark was 2.0 μm to obtain a final product.

Table 1 shows a list of conditions for additives to the annealing separator, and Table 2 shows the obtained results.

[0032]

[Table 1]

[0033]

[Table 2]

All of the examples according to the present invention did not have an oxide film on the surface of the steel sheet and were excellent in glasslessness.
Also, when the temperature rising rate during finish annealing is slowed, if the N ₂ partial pressure is increased and the decarburization annealing temperature is lowered, the B
_Eight values were obtained.

[0035]

EFFECTS OF THE INVENTION According to the present invention, an ultra-low iron loss grain oriented electrical steel sheet having no glass coating and having an extremely high magnetic flux density, especially a high magnetic flux density low which is remarkably excellent in workability such as cutting property and punching property. Iron loss direction electrical steel sheet can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a diagram showing a change in magnetic flux density when a decarburization annealing temperature and a finishing annealing cycle are changed for a plate having a thickness of 0.15 mm. The annealing separator is CaCl ₂ for 100 g of MgO.
5g is added.

FIG. 2 is a diagram showing a relationship between a primary recrystallized grain size and a decarburization annealing temperature.

FIG. 3 is a diagram showing finish annealing conditions.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroaki Masui 1-1 No. 1 Tobita-cho, Tobata-ku, Kitakyushu, Fukuoka Prefecture New Nippon Steel Corporation Yawata Works

Claims (5)

[Claims] 1. The amount of the internal oxide layer containing Si: 1.0 to 7.0% by weight and distributed within 15 μm from the metal surface of the steel sheet is 1% or less in terms of oxygen content in the thickness region. And an ultra-low iron loss grain-oriented electrical steel sheet with an extremely high magnetic flux density, in which B ₈ ≧ 1.93T. 2. The ultra-low iron loss direction with extremely high magnetic flux density according to claim 1, wherein linear or dot-like scratches are provided on the surface in the direction of 45 to 90 degrees from the rolling direction at intervals of 2 to 15 mm. Magnetic electrical steel sheet. 3. A steel ingot or slab containing Si: 1.0 to 7.0% by weight, acid-soluble Al: 0.010 to 0.070% by weight, and the balance being Fe and inevitable impurities, Hot rolling, cold rolling, primary recrystallization annealing, after applying an annealing separator, high temperature finish annealing, in the method of producing a grain-oriented electrical steel sheet by performing heat flattening, the primary recrystallization annealing Of the primary recrystallized grains of the subsequent steel sheet, those having a grain size exceeding twice the average grain size were adjusted to less than 10%, and MgO was used as an annealing separator on the same steel sheet.
Li, K, Na, Ba, Ca, M for 100 parts by weight
2 to 30 parts by weight of one or more selected from chlorides, carbonates, nitrates, sulfates, and sulfides of g, Zn, Fe, Zr, Sn, Sr, and Al is added, and applied. The magnetic flux density is characterized in that the temperature rising rate during high-temperature finish annealing is 10 ° C./hr or less between 950 and 1150 ° C., and the annealing atmosphere is N ₂ + H ₂ of at least N ₂ 30% or more. Of extremely low iron loss grain oriented electrical steel sheet with extremely high 4. By weight, Si: 1.0 to 7.0%, acid-soluble Al: 0.010 to 0.070%, C: 0.021.
~ 0.075%, N: 0.003-0.0130%, S
≦ 0.030%, Mn: 0.05 to 0.45% is contained, and the rest is heated before hot rolling of a slab consisting of Fe and unavoidable impurities at a temperature of less than 1280 ° C. to complete primary recrystallization. The method for producing an ultra-low core loss grain-oriented electrical steel sheet having an extremely high magnetic flux density according to claim 3, wherein the nitriding is performed after that and before the start of secondary recrystallization in high temperature finish annealing. 5. A linear or point-like scratch is imparted to the surface of the steel sheet by local processing such as laser, tooth roll, press, scribe, local etching, etc., before or after heat flattening. 4. The method for manufacturing an ultra-low iron loss grain-oriented electrical steel sheet according to 4, which has an extremely high magnetic flux density.