JP3397277B2 - Manufacturing method of ultra-low iron loss ultra-high magnetic flux density unidirectional electromagnetic steel strip - Google Patents

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 magnetic steel strip 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 electromagnetic steel strips are mainly used as iron core materials for transformers and other electrical equipment, and are required to have excellent magnetic properties such as excitation properties and iron loss properties. The value that shows the excitation characteristics is usually 800 A /
Magnetic flux density B in a magnetic field of m (hereinafter referred to as B ₈ )
Is used. W _17/50 (iron loss per unit Kg when magnetized to 1.7 T at a frequency of 50 Hz) is used as a representative numerical value showing the iron loss characteristics.

The magnetic flux density is an important controlling factor of the iron loss characteristics, and generally speaking, the higher the magnetic flux density, the better the iron loss. However, if the magnetic flux density becomes too high, the abnormal eddy current loss may increase due to the increase in the size of the secondary recrystallized grains, which may deteriorate the iron loss. On the other hand, iron loss can be improved by controlling the magnetic domains regardless of the secondary recrystallized grains.

The unidirectional electrical steel strip undergoes secondary recrystallization during finish annealing in the manufacturing process to cause {110},
It is obtained by developing a so-called Goss structure having <001> in the rolling direction. Among them, B ₈ ≧ 1.
Those with excellent excitation characteristics of 88T are called high magnetic flux density unidirectional electromagnetic steel strip.

Typical methods for producing a high magnetic flux density unidirectional magnetic steel strip include Japanese Patent Publication No. 40-15644 and Japanese Patent Publication No. 51-13469 by Taguchi et al. MnS and AlN are used in the former and MnS, MnSe, Sb, etc. are used in the latter as the main inhibitors that cause secondary recrystallization of the Goss structure. Products based on the above patents are currently produced on a global scale.
According to Japanese Examined Patent Publication No. 40-15644, the manufacturing method is characterized by performing hot-rolled sheet annealing and then performing cold rolling once at a cold rolling rate of 80 to 95%.

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

The coating of the high magnetic flux density unidirectional magnetic steel strip 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 surface of the steel strip during decarburization annealing in the manufacturing process with the annealing separating agent applied thereafter. 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, by Takashima et al., B ₈ ≧
An ultrahigh magnetic flux density unidirectional electrical steel strip having an extremely excellent excitation characteristic of 1.94T has been reported. As a typical example thereof, there is JP-A-6-88174. Further, as a typical example of the manufacturing method thereof, JP-A-6-8817
No. 1 publication is mentioned. All of them are characterized by containing Bi in the slab, but the others are not different from the manufacturing method described in Japanese Patent Publication No. 40-15644 by Taguchi et al.

[0009]

However, when the magnetic flux density is 1.
Despite the fact that 94T or more has been obtained, it is often the case that deterioration of the adhesion of the primary coating and the difficulty of forming the primary coating, which is considered to be due to the inclusion of Bi in the steel. Therefore, there is a problem that the ultimate iron loss level is not good even though the magnetic flux density is 1.94 T or more. This is because the applied tension is insufficient due to the small amount of the primary coating formed, and the contribution of reducing the iron loss is reduced.

Therefore, in order to stably form the primary coating of the super high magnetic flux density unidirectional electromagnetic steel strip, it is considered necessary to provide extremely strict conditions for each condition of each process. It is the current situation that it is not clear which conditions should be set for which process.

The present invention solves such a problem, enables stable production of a primary coating of a unidirectional magnetic steel strip having an extremely high magnetic flux density, and is provided for deterioration of adhesion of the primary coating and formation of the primary coating. The purpose is to improve iron loss failure due to insufficient tension.

[0012]

The features of the present invention are as follows. 1) By weight%, C: 0.03 to 0.15%, Si: 2.5 to 4.
0%, Mn: 0.02 to 0.30%, at least one of S and Se: 0.005 to 0.040
%, Sol.Al: 0.015 to 0.040%, N: 0.0030 to 0.0150%, Bi: 0.00
A step of heating a slab containing 0.05 to 0.02 % of the balance Fe and unavoidable impurities as a starting material, followed by hot rolling, and further hot-rolled sheet annealing followed by finish cold-rolling, or a plurality of cold-treatments including intermediate annealing. After finishing the product sheet thickness by one of the steps of performing rolling or a plurality of steps of performing cold rolling including intermediate annealing after hot-rolled sheet annealing, decarburization annealing, after applying an annealing separator, finish annealing In the method for producing an ultra-high magnetic flux density unidirectional electrical steel strip, the atmosphere gas flow rate in finish annealing is set to a range shown in the following formula: ultra-low iron loss ultra-high magnetic flux of B ₈ ≧ 1.94T Method for producing density unidirectional electrical steel strip. Atmospheric gas flow rate / total surface area of steel strip ≧ 0.002 (Nm ³ / h · m ² ) Here, the total surface area of the steel strip refers to the sum of the surface areas of the 6 surfaces of the steel strip. 2) C: 0.03 to 0.15% by weight, Si: 2.5 to 4.
0%, Mn: 0.02 to 0.30%, at least one of S and Se: 0.005 to 0.040
%, Sol.Al: 0.015 to 0.040%, N: 0.0030 to 0.0150%, Sn: 0.0
5 to 0.50%, Bi: 0.0005 to 0.02 %, and a slab composed of the balance Fe and inevitable impurities is used as a starting material. Manufacturing method of high magnetic flux density unidirectional electromagnetic steel strip. 3) By weight, C: 0.03 to 0.15%, Si: 2.5 to 4.0
%, Mn: 0.02 to 0.30%, at least one of S and Se: 0.005 to 0.040
%, Sol.Al: 0.015 to 0.040%, N: 0.0030 to 0.0150%, Sn: 0.0
5 to 0.50%, Cu: 0.01 to 0.10%, Bi: 0.0005 to
The method for producing an ultra-low iron loss ultra-high magnetic flux density unidirectional electromagnetic steel strip as described in 1) above, wherein a slab containing 0.02 % and the balance Fe and unavoidable impurities is used 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%, at least one of S and Se: 0.005 to 0.040
%, Sol.Al: 0.015 to 0.040%, N: 0.0030 to 0.0150%, Sb and Mo: 0.0030 to 0.3%, Bi: 0.0005 to 0.02 %. The method for producing an ultra-low iron loss ultra-high magnetic flux density unidirectional electromagnetic steel strip as described in 1) above, wherein a slab containing the balance Fe and unavoidable impurities is used as a starting material.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention will be described below. The present inventor has conducted various studies to stably obtain a so-called ultra-high magnetic flux density unidirectional electromagnetic steel strip, and as a result, B
A slab for unidirectional electrical steel strip containing MnS and AlN containing i as a main inhibitor is heated as a starting material and then hot-rolled, followed by hot-rolled sheet annealing, finish cold-rolling, or a plurality of cold-rolling including intermediate annealing, Alternatively, after finishing the product sheet thickness by one of the steps of multiple cold rolling including intermediate annealing after hot-rolled sheet annealing, decarburization annealing, after applying an annealing separator, finish annealing, super high magnetic flux density one direction In the manufacturing method for high-strength electromagnetic steel strip, stable production of ultra-high magnetic flux density unidirectional electromagnetic steel strip with extremely high magnetic flux density and low iron loss by setting the atmospheric gas flow rate during finish annealing to the range shown in the following formula succeeded in. Atmospheric gas flow rate / total steel strip surface area ≥ 0.002 (Nm ³ / h ・
m ² ) Here, the total surface area of the steel strip indicates the sum of the surface areas of the 6 surfaces of the steel strip.

The upper limit of the atmospheric gas flow rate / total surface area of the steel strip is not particularly limited, but is preferably 0.4 (Nm ³ / h · m ² ) or less from the viewpoint of cost. The atmosphere gas is preferably a mixed gas of nitrogen and hydrogen, but the mixing ratio thereof is not particularly limited.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Conditions for the components of the present invention will be described. C is O. If it is less than 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 magnetic aging called magnetic aging in products. 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 Se contain one or two of these and are important elements forming Mn and MnS and / or MnSe described above. If it deviates from the above range, a sufficient inhibitory effect cannot be obtained, so 0.005 to 0.
It is necessary to limit it to 040%.

Sol. (Acid-soluble) Al is a main inhibitor constituent element for high magnetic flux density unidirectional electrical steel strip, and if less than 0.015%, it is insufficient in quantity and the inhibitor strength is insufficient, which is preferable. Absent. On the other hand, if it exceeds 0.040%, AlN precipitated as an inhibitor becomes coarse,
As a result, the inhibitor strength is lowered, which is not preferable.

N is an important element forming AlN and sol.Al described above. If it deviates from the above range, a sufficient inhibitory effect cannot be obtained, so 0.0030 to 0.01
It should be limited to 50%.

Further, Sn is effective as an element for stably obtaining secondary recrystallization of thin products, and also has an effect of reducing the secondary recrystallization grain size. In order to obtain this effect, it is necessary to add 0.05% or more, and when 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 decreases, which is not preferable.

[0023] Sb and Mo are those containing these both, is effective secondary recrystallization of thin products as stable obtained element. To obtain this effect, 0.003
It is necessary to add 0% or more, and when it exceeds 0.30%, the action is saturated, so from the viewpoint of cost increase, it is limited to 0.30% or less.

Bi is an essential element in the slab in the production of the superhigh magnetic flux density unidirectional electrical steel strip of B ₈ ≧ 1.94T according to the present invention. That is, there is an effect of improving the magnetic flux density. If it is less than 0.0005%, the effect is not sufficiently obtained, and if it exceeds 0.02 %, not only the effect of improving the magnetic flux density is saturated, but also cracks occur at the end of the hot rolled coil, which is not preferable. .

Next, the method for producing the primary coating of the ultrahigh magnetic flux density unidirectional electromagnetic steel strip of the present invention will be described. The super-high magnetic flux density unidirectional electromagnetic steel strip for producing molten steel 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, either one of the step of performing finish annealing after hot-rolled sheet annealing, the step of performing a plurality of cold rolling including intermediate annealing, or the step of performing a plurality of cold rolling including intermediate annealing after hot-rolled sheet annealing. Depending on the process, the product sheet thickness is finished, but in the annealing before finish cold rolling, homogenization of the crystal structure and Al
The precipitation of N is controlled.

After cold rolling, continuous decarburization annealing is applied, and after applying an annealing separator containing MgO as a main component, finish annealing is carried out.
It is a feature of the present invention that the flow rate of the atmospheric gas at this time is within the range of the formula shown below. Atmospheric gas flow rate / total steel strip surface area ≥ 0.002 (Nm ³ / h ・
m ² ) After finish annealing, continuous strain relief annealing / secondary film coating and baking are performed. Further, magnetic domain subdivision processing such as laser irradiation and groove formation is performed if necessary.

So far, no particular reference has been made to the formation of a primary coating in the production of ultra high magnetic flux density unidirectional electrical steel strip. In JP-A-6-88171, nothing is mentioned. Nevertheless, the primary coating may be defective in some cases, and the current situation is that stable production has not been achieved.

However, setting the atmospheric gas flow rate during finish annealing within the range shown below is extremely important for the stable formation of the primary coating of the unidirectional electromagnetic steel strip having a very high degree of {110} <001> orientation integration. As a result, it was found that the product had extremely excellent iron loss. Atmospheric gas flow rate / total steel strip surface area ≥ 0.002 (Nm ³ / h ・
m ² ) Here, the total surface area of the steel strip indicates the sum of the surface areas of the 6 surfaces of the steel strip.

In FIG. 1, C: 0.079%, Si: 3.2
0%, Mn: 0.08%, S: 0.024%, sol.A
1: 0.025%, N: 0.0086%, Bi: 0
A 0.965 m wide 3 ton slab containing 0.0200% was finished to a plate thickness of 0.220 mm in a normal process (steel strip total surface area = 3565.5236 m ³ ), and an annealing separator containing MgO as a main component was applied. . After that, it was charged into a finishing annealing furnace having a volume of 8 m ³ , annealed with a flow rate of an atmosphere gas composed of nitrogen: hydrogen = 1: 1 at 1 to 40 Nm ³ / h, and a Bi content when subjected to a post-process. And magnetic flux density B ₈ , primary coating adhesion rating and iron loss W _17/50 after magnetic domain control. A is the best score, followed by B, C, D and E.

When the Bi content is less than 5 ppm, the atmospheric gas flow rate / total steel strip surface area <0.002 (Nm ³ / h · m ² ).
However, the primary coating adhesion score was 0.002 (Nm ³ / h ・ m
² ) There is no difference from the above. However, when the Bi content is 5 ppm or more, when the gas flow rate during finish annealing / total steel strip surface area <0.002 (Nm ³ / h · m ² ) or more, the primary coating adhesion score is almost C. On the other hand, when it is 0.002 (Nm ³ / h · m ² ) or more, the primary coating adhesion score is A or B. Accordingly, extremely low iron loss is obtained.

FIG. 2 shows C: 0.076% and Si: 3.2.
2%, Mn: 0.08%, S: 0.025%, sol.A
1: 0.027%, N: 0.0088%, Sn: 0.0
A 9 ton slab with a width of 0.965 m containing 9% and Bi: 0.0078% is finished to a product plate thickness of 0.220 mm in a normal process (steel strip total surface area = 3565.5236 m ³ ), and MgO
The process was performed up to the application of the annealing separator containing as a main component. Then, it was charged into a finishing annealing furnace having a furnace volume of 8 m ³ , and nitrogen: hydrogen =
The flow rate of the atmospheric gas composed of 1: 2 is 1 to 40 Nm ³ / h
The following shows the amount of primary coating, magnetic flux density B ₈ and iron loss W _17/50 after annealing, coating of secondary coating, and post-treatment of magnetic domain control.

Atmospheric gas flow rate / total steel strip surface area <0.00
At 2 (Nm ³ / h · m ² ), the amount of primary coating is less than 2 g / m ^2, so iron loss is considered excessive due to insufficient applied tension. However, when the atmospheric gas flow rate / total surface area of steel strip ≧ 0.002 (Nm ³ / h · m ² ), the primary coating amount was 2 g / m ² or more, so the applied tension was sufficient and excellent iron loss was achieved. It can be seen that is obtained.

The reason for this is as follows. That is, finish annealing is generally performed in the form of a coil, but the flow rate of atmospheric gas / total surface area of steel strip ≧ 0.002 (Nm
³ / h · m ² ) allows Bi in the base metal to diffuse during finish annealing, and Bi in the base iron stays at the interface between the base iron and the oxide layer or in the oxide layer for a long time. Since it can be removed without any damage, it is considered that stable formation was achieved without destruction after the formation of the primary coating.

The control of the gas flow rate of the finish annealing in the production of high magnetic flux density unidirectional electrical steel strip has been previously described. For example, JP-A-2-125815
The gazette is mentioned. This is because, by setting the gas flow rate during finish annealing to 2 cc / min · kg or more, the purification of S, Se, N in the base steel and forsterite is significantly improved, and the magnetic flux density and iron loss characteristics are improved. I'm supposed to.

On the other hand, the present invention is based on the idea that the behavior of Bi in the base metal during finish annealing has a great influence on the behavior of forming the primary coating. That is, Bi is 0.
0005 to 0.0200 % content and control of gas flow rate: atmosphere gas flow rate / total steel strip surface area ≧ 0.002
By setting (Nm ³ / h · m ² ), B ₈ ≧ 1.94T and an extremely excellent primary coating can be obtained, which is completely different from the prior art.

[0037]

【Example】

(Example 1) C: 0.077%, Si: 3.22%, M
n: 0.08%, S: 0.026%, sol.Al:0.0
A 3 ton slab with a width of 0.965 m containing 26%, N: 0.0084%, and Bi: 0.0070% at 1350 ° C.
Immediately after it was heated in, a hot rolled coil having a thickness of 2.4 mm was obtained. After the hot rolled coil is annealed at 1100 ° C and cold rolled once to a thickness of 0.220 mm (total steel strip surface area = 3565.5236m
³ ), decarburization annealing was performed at 860 ° C.

Next, after applying an annealing separating agent containing MgO as a main component, it was charged into a finishing annealing furnace having a furnace internal volume of 1 m ³ and a flow rate of an atmosphere gas composed of nitrogen: hydrogen = 3: 1. 5 Nm
Annealed at ³ / h and 10 Nm ³ / h. After that, the secondary coating was applied and the magnetic domain was 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. Table 1 shows the atmospheric gas flow rate / total steel strip surface area, magnetic flux density B ₈ , primary coating adhesion rating, and iron loss W _17/50 after magnetic domain control. A is the best score, followed by B, C, D and E.

[0039]

[Table 1]

As is clear from Table 1, by setting the atmospheric gas flow rate / total surface area of steel strip ≧ 0.002 (Nm ³ / h · m ² ), 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: 0.075%, Si:
3.20%, Mn: 0.08%, S: 0.025%, so
l.Al: 0.028%, N: 0.0080%, Sn:
0.9 containing 0.12%, Bi: 0.00114%
A 3-ton slab having a width of 65 m was heated at 1330 ° C. and immediately hot-rolled into a hot-rolled coil having a thickness of 2.3 mm. After pickling 1.6
It was pre-cold rolled to mm and annealed at 1000 ° C. to 0.220 mm (total surface area of steel strip = 3565.5236 m ³ ). Next, after applying an annealing separator containing MgO as a main component, the furnace internal volume was 8 m ³
It was charged into the finishing annealing furnace of and was annealed with the flow rate of the atmosphere gas composed of nitrogen and hydrogen being 2 Nm ³ / h and 20 Nm ³ / h. After that, the same treatment as in Example 1 was performed. Atmosphere gas flow rate /
Table 2 shows the total surface area of the steel strip, the magnetic flux density B ₈ and the amount of primary coating.

[0042]

[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 / total steel strip surface area ≧ 0.002 (Nm ³ / h · m ² ). . 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.

[0044]

[Table 3] As is clear from Table 3, the iron loss characteristics after the magnetic domain refinement treatment are 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%, so
l.Al: 0.022%, N: 0.0084%, Sn:
In molten steel containing 0.16%, Cu: 0.060%, B
3 with a width of 0.965 m containing i added 0.00178%
1. Heat the tongue slab immediately after heating at 1350 ° C.
A hot rolled coil having a thickness of 5 mm was used. The hot-rolled coil is annealed at 1000 ° C., and an intermediate anneal at 980 ° C. is sandwiched between two cold-rollings to reach 0.
After making 220mm thick (steel strip total surface area = 3565.5236
m ³ ), decarburization annealing was performed at 850 ° C.

Next, after applying an annealing separating agent containing MgO as a main component, it was charged into a finishing annealing furnace having a furnace internal volume of 8 m ³ , and the flow rate of an atmosphere gas composed of nitrogen and hydrogen was 7 Nm ³ / h. And 1
Annealed at 0 Nm ³ / h. After that, the same treatment as in Example 1 was performed. Atmospheric gas flow rate / total steel strip surface area and magnetic flux density B
₈ and the primary coating adhesion rating and the iron loss W _17/50 after controlling the magnetic domains are shown in Table 4. A is the best score, followed by B, C,
Followed by D and E.

[0047]

[Table 4]

As is clear from Table 4, by setting the atmospheric gas flow rate / total steel strip surface area ≧ 0.002 (Nm ³ / h · m ² ), 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 4) C: 0.078%, Si:
3.28%, Mn: 0.08%, S: 0.024%, so
l.Al: 0.026%, N: 0.0084%, Sb:
0.020%, Mo: 0.014%, Bi: 0.003
3 ton slab 0.965 m wide containing 5%
Immediately after heating at 50 ° C., hot rolling was performed to obtain a hot rolled coil having a thickness of 2.3 mm. 0.2 in cold-rolled twice with 1000 ℃ intermediate annealing
After making it 20 mm thick (steel strip total surface area = 3565.5236 m ³ ),
Decarburization annealing was performed at 860 ° C.

Next, after applying an annealing separator containing MgO as a main component, the furnace was charged into a finishing annealing furnace having an internal volume of 8 m ³ , and the flow rate of an atmosphere gas composed of nitrogen and hydrogen was 1 Nm ³ / h. And 4
Annealed at 0 Nm ³ / h. After that, the same treatment as in Example 1 was performed. Atmospheric gas flow rate / total steel strip surface area and magnetic flux density B
₈ and the primary coating amount are shown in Table 5.

[0051]

[Table 5]

As is clear from Table 5, by setting the atmospheric gas flow rate / total steel strip surface area ≧ 0.002 (Nm ³ / h · m ² ), an extremely excellent primary coating amount was secured and formed. I understand. Table 6 shows Comparative Example 2 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.

[0053]

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

[0054]

EFFECT OF THE INVENTION A step of hot-rolling a hot-rolled coil obtained from a slab for unidirectional electromagnetic steel strips containing Bi, followed by finish cold-rolling, or a step of performing a plurality of cold-rolling including intermediate annealing, Alternatively, ultra-high magnetic flux that performs finish annealing after decarburizing annealing after applying a sheet thickness by one of the steps of multiple cold rolling including intermediate annealing after hot-rolled sheet annealing, and applying an annealing separator. In the method for producing a primary coating of a density unidirectional electrical steel strip, by setting the atmospheric gas flow rate during finish annealing within the range shown in the following formula, an ultrahigh magnetic flux density unidirectional electrical steel strip having a primary coating with excellent adhesion is obtained. As well as
The iron loss property after the magnetic domain refinement treatment is also extremely excellent, and a useful product having a very high industrial value can be obtained. Atmospheric gas flow rate / total steel strip surface area ≥ 0.002 (Nm ³ / h ・
m ² ) Here, the total surface area of the steel strip indicates the sum of the surface areas of the 6 surfaces of the steel strip.

[Brief description of drawings]

FIG. 1 is a chart showing Bi content, atmospheric gas flow rate in finish annealing / total steel strip surface area, magnetic flux density B ₈ , primary coating adhesion rating, and iron loss W _17/50 after magnetic domain control.

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

Continued front page    (72) Inventor Chitaro Chikuma               1 Fuji-machi, Hirohata-ku, Himeji-shi, Hyogo               Inside the Hirohata Works (72) Inventor Eiichi Namba               1 Fuji-machi, Hirohata-ku, Himeji-shi, Hyogo               Inside the Hirohata Works                (56) Reference JP-A-6-88174 (JP, A)                 JP-A-6-184640 (JP, A)                 JP-A-2-125815 (JP, A)                 JP-A-5-171284 (JP, A)                 JP-A-5-117752 (JP, A)                 Kimio Maeyama et al., Rotary annealing furnace for silicon steel, Kawa               Saki Steel Works, Japan, Kawasaki Steel Co., Ltd.,               December 1983, Vol. 15, No. 4, p. 56-60

Claims (4)

(57) [Claims] 1. By weight%, C: 0.03 to 0.15%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.30%, at least one of S and Se: 0.005-0.040
%, Acid-soluble Al: 0.015 to 0.040%, N: 0.0030 to 0.0150%, Bi: 0.0005 to 0.02 %, and a slab containing the balance Fe and inevitable impurities. After heating as a starting material, hot-rolling, further hot-rolled sheet annealing and finish cold-rolling step, or multiple cold-rolling step including intermediate annealing, or multiple cold-rolling including hot-rolled sheet annealing after intermediate annealing After finishing the product sheet thickness by any of the steps to be performed, decarburization annealing, after applying the annealing separator, in the method of manufacturing an ultra-high magnetic flux density unidirectional electrical steel strip to perform finish annealing, in finish annealing A method for producing an ultra-low iron loss ultra-high magnetic flux density unidirectional electromagnetic steel strip having B ₈ ≧ 1.94 T, characterized in that an atmospheric gas flow rate is set to a range shown in the following formula. Atmospheric gas flow rate / total surface area of steel strip ≧ 0.002 (Nm ³ / h · m ² ) Here, the total surface area of the steel strip refers to the sum of the surface areas of the 6 surfaces of the steel strip. 2. By weight%, C: 0.03 to 0.15%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.30%, at least one of S and 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 0.02 % The method for producing an ultra-low iron loss ultra-high magnetic flux density unidirectional electromagnetic steel strip according to claim 1, wherein a slab consisting of the balance Fe and unavoidable impurities is used as a starting material. 3. In weight%, C: 0.03 to 0.15%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.30%, at least one of S and 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: The ultra-low iron loss ultra-high magnetic flux density unidirectional electromagnetic steel strip according to claim 1, wherein a slab containing 0.0005 to 0.02 % and the balance Fe and unavoidable impurities is used as a starting material. Manufacturing method. 4. By weight%, C: 0.03 to 0.15%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.30%, at least one of S and Se: 0.005-0.040
%, Acid soluble Al: 0.015 to 0.040%, N: 0.0030 to 0.0150%, Sb and Mo: 0.0030 to 0.3%, Bi: 0.0005 to 0.02 %. The method for producing an ultra-low iron loss ultra-high magnetic flux density unidirectional electrical steel strip according to claim 1, characterized in that a slab containing the balance Fe and unavoidable impurities is used as a starting material.