JPH093542A - Production of grain oriented silicon steel sheet having extremely low iron loss and extremely high magnetic flux density - Google Patents

Abstract

PURPOSE: To stably obtain a grain oriented silicon steel sheet having extremely high magnetic flux density by using a steel slab having a Bi-added specific composition as a starting material and specifying the flow rate of atmospheric gas at finish annealing. CONSTITUTION: A slab, having a composition consisting of, by weight, 0.03-0.15% C, 2.5-4.0% Si, 0.02-0.30% Mn, 0.005-0.040% S and/or Se, 0.015-0.040% acid soluble Al, 0.0030-0.0150% N, 0.0005-0.05% Bi, and the balance Fe, is heated and hot-rolled. The resulting hot rolled plate is finished to product sheet thickness by being subjected to hot rolled plate annealing and to finish cold rolling, or by being cold-rolled plural times while process-annealed between cold rolling stages, or by being subjected to hot rolled plate annealing and then cold-rolled plural times while process-annealed between cold rolling stages. Then, decarburizing annealing is performed. After the application of a separation agent at annealing, finish annealing is done. In this manufacturing method, the flow rate of atmospheric gas at finish annealing is regulated to a value in the range satisfying (flow rate of atmospheric gas)/(furnace volume) >=0.5Nm<3> /(h.m<3> ). By this method, the grain oriented silicon steel sheet with extremely high magnetic flux density, having >=1.92T magnetic flux density B8 , can be stably obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an ultra-high magnetic flux density unidirectional electrical steel sheet having a highly developed {110} <001> orientation integration used as an iron core of a transformer or the like.

[0002]

2. Description of the Related Art Unidirectional electrical steel sheets are mainly used as iron core materials for transformers and other electric equipment, and are required to have excellent magnetic characteristics such as excitation characteristics and iron loss characteristics. The value that shows the excitation characteristics is usually 800 A /
Magnetic flux density B in a magnetic field of m (this is shown below as B ₈ )
Is used. Also, as a representative numerical value showing the iron loss characteristic,
W _17/50 (iron loss per unit of 1 kg when magnetized to 1.7 _{T at a} frequency of 50 Hz) is used.

[0003] The magnetic flux density is an important controlling factor of the iron loss characteristics. Generally speaking, the higher the magnetic flux density, the better the iron loss. However, when the magnetic flux density is too high, abnormal eddy current loss is increased due to an increase in secondary recrystallized grains, and iron loss may be deteriorated. On the other hand, iron loss can be improved by controlling the magnetic domains regardless of the secondary recrystallized grains.

[0004] In the finish annealing in the manufacturing process, the grain-oriented electrical steel sheet causes secondary recrystallization to cause {110} on the steel sheet surface.
It is obtained by developing a so-called Goss structure having <001> in the rolling direction. Among them, B ₈ ≧
Those having excellent excitation characteristics of 1.88T are called high magnetic flux density unidirectional magnetic steel sheets.

As a typical method for producing a high magnetic flux density unidirectional electrical steel sheet, there are JP-B-40-15644 and JP-B-51-13469. Goss
MnS and AlN are used in the former, and MnS, MnSe, Sb, etc. are used in the latter as main inhibitors that cause secondary recrystallization of the tissue. Products produced by these manufacturing methods are currently produced worldwide. According to Japanese Examined Patent Publication No. 40-15644, the manufacturing method is characterized in that after the hot-rolled sheet is annealed, the cold-rolling rate is 80-95% once.

Further, it is required that a coating having an electrically insulating property is formed on the surface of the unidirectional electrical steel sheet. In addition to maintaining insulating properties, this coating also has a role of applying tension to the steel sheet to reduce iron loss. Therefore, it is extremely important to form them uniformly.

The coating of the high magnetic flux density unidirectional magnetic steel sheet has a two-stage structure of a primary coating and a secondary coating. Among them, the primary coating is obtained by reacting SiO ₂ formed on the steel sheet surface in the decarburizing annealing in the manufacturing process with the subsequently applied annealing separator. In general, an annealing separator containing MgO as a main component is used, and it reacts with SiO ₂ at the time of finish annealing to react with M.
It becomes g ₂ SiO ₄ , which becomes the primary coating.

By the way, recently, an ultrahigh magnetic flux density unidirectional electrical steel sheet having an extremely excellent excitation characteristic of B ₈ ≧ 1.92T has been reported. As a typical example thereof, Japanese Patent Laid-Open No. 6-88
No. 174 publication is cited. Further, as a typical example of the manufacturing method thereof, there is JP-A-6-88171.
All of them are characterized by containing Bi in the slab, but the others are the same as the manufacturing method described in Japanese Patent Publication No. 40-15644 and there are no major restrictions.

[0009]

However, even if the magnetic flux density of 1.92 T or more is obtained, if Bi is contained in the steel,
It is often the case that the adhesion of the primary coating is considered to be deteriorated and the primary coating is difficult to form. for that reason,
Even if a magnetic flux density of 1.92 T or more is obtained, the effect of reducing iron loss cannot be obtained because the formation of the primary coating is insufficient, and the achieved iron loss level may not be good. The present invention avoids such a problem, enables stable production of a grain-oriented electrical steel sheet having an extremely high magnetic flux density, deteriorates adhesion of the primary coating, and causes iron loss due to insufficient applied tension because the primary coating is not formed. Aim to improve.

[0010]

The features of the present invention are as follows. 1) wt%, C: 0.03 to 0.15%, Si: 2.
5 to 4.0%, Mn: 0.02 to 0.30%, S and or Se: 0.005 to 0.040%, acid-soluble Al: 0.015 to 0.040%, N: 0. 0030 ~
0.0150%, Bi: 0.0005 to 0.05%, balance: Fe and slab consisting of unavoidable impurities are heated as a starting material, then hot rolled, hot rolled sheet annealed, then finish cold rolled, or intermediate annealed. After finishing the product sheet thickness by multiple cold rolling including multiple cold rolling including hot-rolled sheet annealing or intermediate annealing after annealing, decarburization annealing, after applying an annealing separator, finish annealing is performed. In the method for producing a grain-oriented electrical steel sheet, the atmospheric gas flow rate in finish annealing is set in the range shown below, and a method for producing a grain-oriented electrical steel sheet with ultra-low iron loss and ultra-high magnetic flux density of B ₈ ≧ 1.92T. . Atmospheric gas flow rate / (furnace volume-steel plate volume) ≧ 0.5 Nm ³
/ (H ・ m ³ )

2) C: 0.03 to 0.15 by weight%
%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.3%
0%, S and / or Se: 0.005-0.040
%, Acid-soluble Al: 0.015 to 0.040%, N:
0.0030 to 0.0150%, Sn: 0.05 to 0.
50%, Bi: 0.0005 to 0.05%, balance: Fe
And the method for producing an ultra-low iron loss ultra-high magnetic flux density grain-oriented electrical steel sheet as described in 1) above, wherein a slab consisting of inevitable impurities is used as a starting material.

3) C: 0.03 to 0.15 by weight%
%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.3%
0%, S and / or Se: 0.005-0.040
%, Acid-soluble Al: 0.015 to 0.040%, N:
0.0030 to 0.0150%, Sn: 0.05 to 0.
50%, Cu: 0.01 to 0.10%, Bi: 0.00
The method for producing an ultra-low iron loss ultra-high magnetic flux density grain-oriented electrical steel sheet as described in 1) above, wherein a slab consisting of 05 to 0.05% and the balance: Fe and inevitable impurities is used as a starting material.

4) C: 0.03 to 0.15 by weight%
%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.3%
0%, S and / or Se: 0.005-0.040
%, Acid-soluble Al: 0.015 to 0.040%, N:
0.0030 to 0.0150%, Sb and / or M
o: 0.0030 to 0.3%, Bi: 0.0005 to
The method for producing an ultra-low iron loss ultra-high magnetic flux density grain-oriented electrical steel sheet as described in 1) above, wherein a slab consisting of 0.05% and the balance: Fe and inevitable impurities is used as a starting material.

The present invention will be described in detail below. First, the component conditions of the present invention will be described. If C is less than 0.03%, crystal grains grow abnormally during slab heating prior to hot rolling, and secondary recrystallization defects called linear fine grains occur in the product, which is not preferable. On the other hand, when the content exceeds 0.15%, decarburization annealing after cold rolling requires a long time for decarburization, which is not economical, and the decarburization is likely to be incomplete, resulting in a magnetic aging called magnetic aging in the product. It is not preferable because it causes defects.

Si is an extremely effective element for increasing the electrical resistance of steel and reducing the eddy current loss that constitutes a part of iron loss, but if it is less than 2.5%, the eddy current loss of the product cannot be suppressed. . Further, if it exceeds 4.0%, the workability is remarkably deteriorated and cold rolling at room temperature becomes difficult, which is not preferable.

Mn is an important element that forms MnS and / or MnSe called an inhibitor that influences secondary recrystallization. If it is less than 0.02%, the absolute amount of MnS necessary for causing secondary recrystallization is insufficient, which is not preferable. On the other hand, if it exceeds 0.30%, not only is it difficult to form a solid solution during heating of the slab, but also the precipitation size during hot rolling tends to become coarse, and the optimum size distribution as an inhibitor is impaired, which is not preferable.

S and / or Se are Mn and M listed above.
It is an important element that forms nS and / or MnSe. If it deviates from the above range, a sufficient inhibitory effect cannot be obtained, so it is necessary to limit the content to 0.005 to 0.040%.

Acid-soluble Al is a main inhibitor constituent element for high magnetic flux density grain-oriented electrical steel sheet, and is 0.0
If it is less than 15%, it is not preferable because the amount is insufficient and the inhibitor strength is insufficient. On the other hand, if it exceeds 0.040%, AlN precipitated as an inhibitor becomes coarse, and as a result, the inhibitor strength is lowered, which is not preferable.

N is an important element that forms AlN with the acid-soluble Al mentioned above. If it deviates from the above range, a sufficient inhibitory effect cannot be obtained, so 0.0030 to 0.0
It must be limited to 150%.

Further, Sn is effective as an element for stably obtaining secondary recrystallization of thin products, and also has an effect of reducing secondary recrystallization grains. To get this effect,
It is necessary to add 0.05% or more, and if it exceeds 0.50%, the action is saturated, so from the viewpoint of cost increase, it is limited to 0.50% or less.

Cu is effective as an element for improving the primary coating of Sn-added steel. If it is less than 0.01%, the effect is small, and if it exceeds 0.10%, the magnetic flux density of the product is undesirably reduced.

Sb and / or Mo are effective as elements for stably obtaining secondary recrystallization of thin products.
In order to obtain this effect, it is necessary to add 0.0030% or more. If it exceeds 0.30%, the effect is saturated, so that the content is limited to 0.30% or less from the viewpoint of cost increase.

Bi is an essential element in the slab in the production of the superhigh magnetic flux density grain-oriented electrical steel sheet of B ≧ ₈ ≧ 1.92T according to the present invention. That is, if the magnetic flux density improving effect is less than 0.0005%, the effect is not sufficiently obtained, and if it exceeds 0.05%, not only the magnetic flux density improving effect is saturated, but also at the end of the hot rolled coil. It is not preferable because cracks occur.

Next, the manufacturing process of the present invention will be described.
The molten steel for producing an ultra-high magnetic flux density unidirectional electrical steel sheet having the components adjusted as described above is cast by a usual method. There is no particular limitation on the casting method. Then, it is rolled into a hot rolled coil by ordinary hot rolling.

Subsequently, the product sheet thickness is finished by hot-rolled sheet annealing followed by finish cold-rolling, a plurality of cold-rolled sheets including intermediate annealing, or a plurality of cold-rolled sheets including hot-rolled sheet annealing and intermediate annealing. In the annealing before finish cold rolling, the crystal structure is homogenized and AlN precipitation is controlled.

After cold rolling, continuous decarburization annealing is performed, and an annealing separator containing MgO as a main component is applied, followed by finish annealing. At this time, the atmospheric gas flow rate should be within the range shown below. The present invention is characterized. Atmosphere gas flow rate / furnace internal volume ≧ 0.5 Nm ³ / (h · m ³ ) In the final annealing, continuous strain relief annealing, secondary coating application and baking are performed. Further, laser irradiation and magnetic domain subdivision processing such as grooves are performed if necessary.

The present inventors pay attention to the atmospheric gas flow rate during finish annealing in order to stably manufacture an ultra-low iron loss ultra-high magnetic flux density grain-oriented electrical steel sheet with a sufficient iron loss reduction effect by the primary coating. Then, the following experiment was conducted.

[Experiment 1] C: 0.077%, Si: 3.25%, Mn: 0.08
%, S: 0.024%, acid-soluble Al: 0.025%,
A slab containing N: 0.0086% and Bi: 0 to 0.0200% or more was subjected to an annealing separation material coating containing MgO as a main component in a normal process. After that, finish annealing is performed and the furnace is inserted into a finish annealing furnace having a volume of 1 m ³ and the flow rate of the atmosphere gas composed of nitrogen: hydrogen = 1: 1 is 0.1-1.
0Nm ³ finish annealing, further post-process treatment,
Magnetic flux density B ₈ value of the obtained steel sheet and iron loss W after magnetic domain control
_The value of _17/50 was measured and the adhesion of the primary coating was evaluated. FIG.
_{Shows the} Bi content, the value of the atmosphere gas flow rate / the furnace internal volume, the iron loss W _17/50 value after the magnetic domain control, and the primary coating adhesion rating. A is the best score, followed by B and C.

As is clear from the figure, the Bi content is 5
When it is less than ppm, the flow rate of the atmosphere gas / internal volume <0.
Even with 5 Nm ³ / (h · m ³ ), the primary film adhesion rating is 0.
No difference is observed when it is set to 5 Nm ³ / (h · m ³ ) or more. However, if the Bi content is 5 ppm or more,
Atmospheric gas flow rate / furnace internal volume <0.5 Nm ³ / (h · m ³ )
In the case of, the primary coating adhesion rating is A or B.
It has become. Along with that, extremely low iron loss is obtained.

[Experiment 2] C: 0.078%, Si: 3.22%, Mn: 0.08
%, S: 0.025%, acid-soluble Al: 0.025%,
N: 0.0088%, Sn: 0.10%, Bi: 0
A slab containing 0.0050% or more is produced in a normal process with a product thickness of 0.220
After finishing to mm, the annealing separation material containing MgO as a main component was applied. After that, finish annealing is performed and the furnace volume is 1 m.
^It was inserted into the finishing annealing furnace of No. ³ and annealed with the flow rate of the atmosphere gas composed of nitrogen: hydrogen = 1: 2 being 0.1 to 20 Nm ³ , and the secondary film coating and the post-process treatment of the magnetic domain control were performed to obtain the Magnetic flux density B ₈ value of the obtained steel sheet, primary coating amount, iron loss W
_17/50 was measured. The result of Experiment 2 is shown in FIG.

As is apparent from the figure, the atmospheric gas flow rate /
When the internal volume of the furnace is <0.5 Nm ³ / (h · m ³ ), the amount of primary coating is less than 2 g / m ^2, so iron loss is considered to be excessive due to insufficient applied tension. However, when the atmospheric gas flow rate / furnace internal volume ≧ 0.5 Nm ³ / (h · m ³ ),
It can be seen that since the amount of primary coating is 2 g / m or more, the applied tension is sufficient and excellent iron loss is obtained.

The reason for this is as follows. That is, finish annealing is generally performed on the coil, but the atmosphere gas flow rate / furnace internal volume ≧ 0.5 Nm ³ / (h ·
m ³ ) makes it possible to diffuse Bi in the base metal during finish annealing, and Bi in the base iron escapes without staying at the interface with the base layer or the oxide layer for a long time. Therefore, it is considered that stable formation was achieved without destruction after the formation of the primary coating.

From the results of the above experiments, it is necessary to set the atmospheric gas flow rate during finish annealing within the range shown below to obtain an ultra-low iron loss ultra-high magnetic flux density unidirectional electrical steel sheet with a sufficient iron loss reduction effect by the primary coating. Was found to be extremely important in the manufacture of. Atmospheric gas flow rate / furnace internal volume ≧ 0.5 Nm ³ / (h · m ³ ) The upper limit value of atmospheric gas flow rate / furnace internal volume is not particularly limited, but from the viewpoint of cost, it is 20 Nm ³ / (h
・ It is desirable to be less than m ³ ). The atmosphere gas is preferably a mixed gas of nitrogen and hydrogen, but the mixing ratio thereof is not particularly limited.

Controlling the gas flow rate during finish annealing in the manufacture of high magnetic flux density grain-oriented electrical steel sheets has been previously described. For example, Japanese Patent Laid-Open No. 12581/1991
No. 5 publication is mentioned. This is because when the gas flow rate during finish annealing is set to 2 cc / min · kg or more, the purification of S, Se, and N in the ground iron and forsterite is significantly improved, and the magnetic flux density and iron loss characteristics are improved. I am trying.

On the other hand, the present invention considers that the behavior of Bi in the base metal during finish annealing has a great influence on the primary coating, and the behavior is controlled by the gas flow rate during finish annealing. It is completely different from the conventional technology.

[0036]

【Example】

[Example 1] C: 0.078%, Si: 3.22%, M
n: 0.08%, S: 0.025%, acid-soluble Al:
0.025%, N: 0.0084%, Bi: 0.007
The slab containing 0% was heated at 1350 ° C. and immediately hot-rolled into a hot-rolled coil having a thickness of 2.4 mm.

The hot rolled coil was annealed at 1100 ° C., once cold rolled to a thickness of 0.220 mm, and then decarburized and annealed at 860 ° C.

Next, after applying an annealing separation material containing MgO as a main component, it was inserted into a finish annealing furnace having a furnace internal volume of 1 m ³ .
Annealing was performed with the flow rate of the atmosphere gas composed of nitrogen: hydrogen = 3: 1 being 0.2 Nm ³ / h and 2.0 Nm ³ / h.

After that, the secondary coating was applied and the magnetic domains were controlled by laser irradiation. In order to evaluate the adhesion of the primary coating, 5 sheets each having a width of 60 mm and a length of 300 mm were cut out as samples.

Atmosphere gas flow rate / furnace internal volume and magnetic flux density B ₈
Table 1 shows the primary coating adhesion rating and the iron loss W _17/50 after controlling the magnetic domains. A is the best score, followed by B and C.

[0041]

[Table 1]

As is clear from Table 1, by setting the atmospheric gas flow rate / furnace internal volume to 2.0 Nm ³ / (h · m ³ ), an extremely excellent primary coating adhesion rating was obtained. And it shows an extremely excellent iron loss characteristic of 0.75 W / kg or less.

[Example 2] C: 0.076%, Si:
3.25%, Mn: 0.08%, S: 0.025%, acid-soluble Al: 0.028%, N: 0.0080%, S
A slab containing n: 0.12% and Bi: 0.00120% was heated at 1330 ° C. and immediately hot rolled to give a hot rolled coil having a thickness of 2.3 mm.

After pickling, pre-cold rolled to 1.75 mm,
After annealing at 0 ° C, the thickness was 0.200 mm. Next, after applying an annealing separator containing MgO as a main component, the furnace was inserted into a finishing annealing furnace having an internal volume of 1 m ³ , and the flow rate of an atmosphere gas composed of nitrogen and hydrogen was 0.1 Nm ³ / h and 10%. Annealed at 0.0 Nm ³ / h. Then, the same treatment as in Example 1 was performed.

Atmosphere gas flow rate / furnace internal volume and magnetic flux density B ₈
Table 1 shows the primary coating amount.

[0046]

[Table 2]

As is clear from Table 2, it can be seen that the primary coating amount is secured and formed by setting the atmospheric gas flow rate / furnace internal volume to 10.0 Nm ³ / (h · m ³ ).

Table 3 shows Comparative Example 1 shown in Table 2 and the magnetic flux densities B ₈ and W 17/50 after magnetic domain control in Example 1 of the present invention.

[0049]

[Table 3]

As is clear from Table 3, the iron loss after the magnetic domain refining treatment is also extremely excellent, and can be said to be industrially very valuable and useful.

[Example 3] C: 0.078%, Si:
3.30%, Mn: 0.08%, S: 0.025%, acid-soluble Al: 0.022%, N: 0.0084%, S
A slab containing Bi: 0.0178% added to molten steel containing n: 0.16% and Cu: 0.060% at 1350 ° C.
Immediately after it was heated in, a hot rolled coil having a thickness of 2.5 mm was obtained.

The hot rolled coil was annealed at 1050 ° C.
After twice cold rolling sandwiching an intermediate annealing of 80 ° C to a thickness of 0.220 mm, decarburization annealing was performed at 840 ° C.

Next, after applying an annealing separation material containing MgO as a main component, it was inserted into a finishing annealing furnace having a furnace internal volume of 1 m ³ .
The flow rate of the atmosphere gas composed of nitrogen and hydrogen is 0.4 Nm ³
/ H and 0.5 Nm ³ / h. Then, the same treatment as in Example 1 was performed.

Atmosphere gas flow rate / furnace volume and magnetic flux density B ₈
Table 4 shows the primary coating adhesion rating and the iron loss W _17/50 after controlling the magnetic domains. A is the best score, followed by B and C.

[0055]

[Table 4]

As is clear from Table 4, by setting the atmospheric gas flow rate / furnace internal volume to 0.5 Nm ³ / (h · m ³ ), an extremely excellent primary coating adhesion rating was obtained and the magnetic domain The iron loss after control is also extremely excellent.

[Example 4] C: 0.078%, Si:
3.30%, Mn: 0.08%, Se: 0.025%,
Acid-soluble Al: 0.026%, N: 0.0084%, S
b: 0.020%, Mo: 0.014%, Bi: 0.0
The slab containing 024% was heated at 1350 ° C. and immediately hot-rolled into a hot-rolled coil having a thickness of 2.3 mm.

After being twice cold-rolled with an intermediate anneal at 1000 ° C. to obtain a thickness of 0.220 mm, decarburization anneal was performed at 860 ° C.

Next, after applying an annealing separation material containing MgO as a main component, it was inserted into a finishing annealing furnace having a furnace internal volume of 1.0 m ³ , and the flow rate of an atmosphere gas composed of nitrogen and hydrogen was 0.3.
And annealed as Nm ³ / h and 3.0Nm ³ / h. Then, the same treatment as in Example 1 was performed.

Atmosphere gas flow rate / furnace internal volume and magnetic flux density B ₈
Table 5 shows the primary coating amount.

[0061]

[Table 5]

As is clear from Table 5, it can be seen that the amount of the primary coating is secured and formed by setting the atmospheric gas flow rate / furnace internal volume to 3.0 Nm ³ / (h · m ³ ).

Table 6 shows Comparative Example 5 shown in Table 5 and the magnetic flux densities B ₈ and W _17/50 after magnetic domain control in Example 4 of the present invention.

[0064]

[Table 6]

As is clear from Table 6, the iron loss after the magnetic domain refining treatment is also extremely excellent, and can be said to be industrially very valuable and useful.

[0066]

As described above, according to the present invention, in the method for producing a grain-oriented electrical steel sheet containing Bi, by adjusting the atmospheric gas flow rate in finish annealing,
It is possible to obtain an ultra-high magnetic flux density grain-oriented electrical steel sheet having a primary coating with excellent adhesion, and also have extremely excellent iron loss properties after magnetic domain refinement treatment, which is very valuable industrially. I can say.

[Brief description of drawings]

FIG. 1 Bi content, atmosphere gas flow rate / furnace volume, magnetic flux density B ₈ , primary coating adhesion rating, and iron loss W after magnetic domain control
It is a chart showing the correlation of _17/50 .

FIG. 2 shows the amount of primary coating, magnetic flux density B ₈ and iron loss W _17/50 .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Eiichi Namba 1 Fujimachi, Hirohata-ku, Himeji-shi, Hyogo Shin Nippon Steel Corp. Hirohata Works

Claims (4)

[Claims] 1. By weight%, C: 0.03 to 0.15%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.30%, S and or Se: 0. 005 to 0.040%, acid-soluble Al: 0.015 to 0.040%, N: 0.0030 to 0.0150%, Bi: 0.0005 to 0.05%, balance: Fe and unavoidable impurities After heating with a slab as a starting material, hot rolling, hot-rolled sheet annealing and finish cold rolling,
Alternatively, after finishing the product sheet thickness by a plurality of cold rolling including intermediate annealing or a plurality of cold rolling including hot rolled sheet annealing and intermediate annealing, decarburization annealing, after applying an annealing separation material, finish annealing is performed. In a method for producing a high magnetic flux density unidirectional electrical steel sheet, an atmosphere gas flow rate in finish annealing is set to a range shown below, ultra low iron loss of B ₈ ≧ 1.92 T, ultrahigh magnetic flux density unidirectional electromagnetic field. Steel plate manufacturing method. Atmosphere gas flow rate / Internal furnace volume ≧ 0.5 Nm ³ / (h · m ³ ) 2. By weight%, C: 0.03 to 0.15%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.30%, S and or Se: 0. 005-0.040%, acid-soluble Al: 0.015-0.040%, N: 0.0030-0.0150%, Sn: 0.05-0.50%, Bi: 0.0005-0. 05% balance: The method for producing an ultra-low iron loss ultra-high magnetic flux density grain-oriented electrical steel sheet according to claim 1, wherein a slab composed of Fe and inevitable impurities is used as a starting material. 3. By weight%, C: 0.03 to 0.15%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.30%, S and or Se: 0. 005-0.040%, acid-soluble Al: 0.015-0.040%, N: 0.0030-0.0150%, Sn: 0.05-0.50%, Cu: 0.01-0. 10%, Bi: 0.0005-0.05% The balance: The manufacturing method of the super-low iron loss super-high magnetic flux density grain-oriented electrical steel sheet of Claim 1 which used the slab which consists of Fe and inevitable impurities as a starting material. 4. By weight%, C: 0.03 to 0.15%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.30%, S and or Se: 0. 005-0.040%, acid-soluble Al: 0.015-0.040%, N: 0.0030-0.0150%, Sb and / or Mo: 0.0030-0.3%, Bi: 0. The method for producing an ultra-low iron loss ultra-high magnetic flux density grain-oriented electrical steel sheet according to claim 1, wherein a slab composed of the balance: Fe and inevitable impurities is used as a starting material.