KR101565510B1 - Non-oriented electrical steel steet and manufacturing method for the same - Google Patents

Abstract

A method for producing a non-oriented electrical steel sheet is presented. A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes: 2.5 to 3.5% of Si, 0.2 to 1.5% of Al, 0.05 to 0.8% of Mn, 0.1% or less of P, 0.003 %, S: not more than 0.004%, N: not more than 0.002%, and the balance Fe and other inevitably added impurities; Charging the slab into a heating furnace and reheating the slab; Reheating the slab and then hot rolling the slab; Pre-cold-rolling the hot-rolled hot-rolled sheet in a range of 20 to 40%; Annealing the preliminarily cold-rolled steel sheet, and cold-rolling the final annealed steel sheet and finally annealing.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-oriented electrical steel sheet,

The present invention relates to a non-oriented electrical steel sheet and a manufacturing method thereof, and more particularly to a finest non-oriented electrical steel sheet having a low iron loss and a high magnetic flux density and widely used as an important component of a rotating machine, and a manufacturing method thereof.

In general, the nonoriented electric steel sheet is an important iron core material necessary for converting electric energy into mechanical energy in a rotating machine. Therefore, it is important to have magnetic properties such as low iron loss and high magnetic flux density in order to save energy. Here, iron loss is the energy that turns into heat in the energy conversion process, so the lower the energy is, the more efficient the magnetic flux density becomes.

Recently, technologies for converting existing internal combustion engine vehicles into HEV (hybrid vehicle) / EV (electric vehicle) have been rapidly developed as measures to reduce fossil fuel shortage and greenhouse gas reduction. These HEV / EVs are cars that can convert some or all of the drive system into electric motors to reduce the consumption of gasoline or diesel fuel, which is a fuel for existing internal combustion engines, while achieving better fuel economy.

The motors used in such automobiles must produce a large torque at low speeds or accelerations, and at high speeds at constant speeds and at high speeds. Therefore, the nonoriented electric steel sheet, which is a motor iron core material, should have a large magnetic flux density characteristic at low speed rotation and a low iron loss at high speed. In general, high-frequency iron loss refers to iron loss at a frequency of 200 Hz or more, but the value of W10 / 400 is generally used for automotive non-oriented electrical steel sheets.

In order to improve the high-frequency iron loss, the alloy elements such as Si, Al, and Mn, which are the resistivity elements of the electric steel sheet, should be moved upward, and impurities should be reduced to facilitate the movement of the magnetic domains. However, when the non-magnetic alloy element such as Si, Al, and Mn is highly contained, the magnetic flux density becomes low. In particular, it is essential to use a material having a high magnetic flux density for a material such as an environmentally friendly electric automobile drive motor which is continuously required to be lightweight.

Japanese Patent JP1999-222653 uses a method of improving the properties of the hot-rolled steel sheet by making it less than 2.0 mm. Japanese Patent JP1996-088114 discloses a method of improving magnetic properties by including high-Al and annealing twice twice . JP2002-206114 also proposes a method for hot smelting through a thin slab manufacturing method.

However, the method of lowering the hot-rolled steel sheet thickness as in JP1999-222653 or JP2002-206114 has a limitation in roll force in the general hot-rolling process, making it difficult to mass-apply the steel sheet, and the two annealing twice rolling process as proposed in JP1996-088114, Some improvement is observed, but the cost increase factor is large and the characteristics of the circumference tends to deteriorate due to excessive gusset texture development.

An embodiment of the present invention is to provide a non-oriented electrical steel sheet excellent in magnetic properties without deteriorating the circumferential property by performing appropriate cold rolling after hot rolling.

According to one aspect of the present invention, there is provided a steel sheet comprising, by weight percent, 2.5 to 3.5% of Si, 0.2 to 1.5% of Al, 0.05 to 0.8% of Mn, 0.1% (Excluding O%), S: 0.004% or less (excluding O%), N: 0.002% or less (excluding O%), and the balance Fe and other inevitably added impurities. Charging the slab into a heating furnace and reheating the slab; Reheating the slab and then hot rolling the slab; Pre-cold-rolling the hot-rolled hot-rolled sheet in a range of 20 to 40%; A step of annealing the preliminarily cold-rolled steel sheet, and a step of final annealing after cold-rolling the annealed steel sheet is provided

At this time, the thickness of the hot-rolled steel sheet may be 1.6 mm to 2.0 mm.

At this time, in the reheating step, the slab may be reheated at 1,100 ° C to 1,150 ° C.

At this time, the cold-rolled steel sheet can be annealed at a temperature of 850 to 1,150 ° C.

At this time, the annealed hot rolled sheet can be cold-rolled at a reduction ratio of 70 to 85%.

At this time, the cold-rolled steel sheet may be cold-rolled to have a thickness of 0.15 mm to 0.30 mm.

At this time, the final annealing may be performed at a temperature of 900 to 1,050 DEG C for 1 minute or more so that the crystal grain diameter becomes 50 to 150 mu m.

In this case, the non-oriented electrical steel sheet produced by the method of producing the non-oriented electrical steel sheet has a core loss (W10 / 400) of 12.5 W / Kg or less, a magnetic flux density of 1.68 T or more, The density may be 1.66 T or more.

At this time, the non-oriented electrical steel sheet produced by the method of producing the non-oriented electrical steel sheet is manufactured such that the fraction of (001) fibers is not less than 30% and the fraction of Goss is not more than 2% based on a thickness of 0.27 mm . According to another aspect of the present invention, there is provided a ferritic stainless steel comprising, by weight, 2.5 to 3.5% of Si, 0.2 to 1.5% of Al, 0.05 to 0.8% of Mn, 0.1% (Excluding 0%), S: not more than 0.004% (excluding 0%), N: not more than 0.002% (excluding 0%), and the balance Fe and other inevitably added The slab composed of the impurities is reheated, hot rolled, preliminarily cold rolled at a reduction ratio of 20 to 40%, and subsequently subjected to hot-rolled sheet annealing, final cold-rolling and final annealing, (W10 / 400) of 12.5 W / Kg or less, a magnetic flux density of 1.68 T or more, and a circumferential magnetic flux density of 1.66 T or more.

At this time, the thickness of the steel sheet may be 1.6 mm to 2.0 mm by the hot rolling.

At this time, the thickness of the steel sheet may be 0.15 mm to 0.30 mm by the present cold rolling.

At this time, the steel sheet may have a grain diameter of 50 to 150 mu m by the final annealing.

At this time, the steel sheet may have a (001) fiber fraction of 30% or more and a Goss fraction of 2% or less based on a thickness of 0.27 mm.

According to an embodiment of the present invention, a high-grade non-oriented electrical steel sheet having a magnetic property, particularly, a circumferential property is remarkably improved through a cold rolling process after hot rolling, thereby finally providing excellent magnetic characteristics.

The non-oriented electrical steel sheet according to an embodiment of the present invention can contribute to the improvement of the efficiency of the automotive drive motor.

FIG. 1 is a graph showing changes in RC average and circumferential average according to a cold rolling rate after hot rolling in a non-oriented electrical steel sheet manufacturing method according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification.

A method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes: 2.5 to 3.5% of Si, 0.2 to 1.5% of Al, 0.05 to 0.8% of Mn, 0.1% or less of P (Excluding 0%), S: not more than 0.004% (excluding 0%), N: not more than 0.002% (excluding 0%), C: not more than 0.003% After reheating at 1100 to 1150 ° C using a slab made of other unavoidable impurities, the steel sheet is hot rolled to 2.0 to 1.6 mm, pre-cold-rolled at a reduction ratio of 20 to 40%, annealed at 1000 ° C or higher And then cold-rolled to a final product thickness, and then annealed at a temperature of 900 to 1000 ° C. for 1 minute. Thus, the magnetic flux density is 1.68 T or more and the iron loss (W 10/400) is 12.5 W / Kg Or less, and particularly, an electric steel sheet excellent in magnetic property having a circumferential average magnetic flux density of 1.66 T or more can be provided since the fraction of (001) fiber is 30% or more and the fraction of Goss texture is 2% or less.

 First, the reason for limiting the range of the constituent elements constituting the embodiment of the present invention and the addition ratio between the constituent elements will be described.

Unless otherwise stated, the unit of content is weight percent (wt%).

[Si: 2.5 to 3.5% by weight]

When Si is added in an amount of less than 2.5%, the effect of improving the high-frequency iron loss is insufficient. When the Si content exceeds 3.5%, the hardness of the material increases, It is undesirable to heat.

[Al: 0.2 to 1.5% by weight]

Al increases the resistivity of the material and lowers the iron loss and forms nitride. When Al is added in an amount of less than 0.2%, there is no effect on reduction of high-frequency iron loss, and nitride is formed finely to deteriorate magnetism. When added in an amount exceeding 1.5%, problems occur in all processes such as steelmaking and continuous casting, .

 [Mn: 0.05 to 0.8% by weight]

Mn enhances the resistivity of the material to improve the iron loss and form sulphide. When the Mn content is less than 0.05%, MnS is precipitated finely and deteriorates the magnetism. If Mn is added in excess of 0.8%, the magnetic flux density is reduced by promoting the formation of [111] texture unfavorable to magnetism, so that the addition amount of Mn is preferably limited to 0.05 to 0.8%.

[P: 0.1 wt% or less] (excluding O%)

P is mostly used in the steel and has an effect of improving iron loss, but if it exceeds 0.1%, it is segregated in the grain boundaries to deteriorate the toughness of the material, which lowers the productivity and saturation, which is not preferable.

[S: 0.004% or less] (excluding O%)

Since S forms fine precipitates MnS and CuS to deteriorate magnetic properties, it is preferable to control it at a low level. It is preferable to remove the refining process as much as possible as an element indispensably present in steel. However, , The S content is limited to 0.004% or less in one embodiment of the present invention.

[N: 0.002% or less] (excluding O%)

N is preferably as small as possible because it forms fine and long AlN precipitates inside the base material to suppress grain growth and thereby lower the iron loss. In the present invention, the N content is limited to 0.002% or less.

[Other unavoidable impurity element]

In addition to the above impurity elements, inevitably incorporated impurities such as C and Ti may be included. C causes self aging, so it is preferable to limit it to 0.004% or less, preferably 0.003% or less (excluding O%). Ti and Nb promote the growth of the [111] texture, which is an undesirable crystal orientation in the non-oriented electrical steel sheet, so that it is preferable to limit it to 0.004% or less, more preferably 0.002% or less (excluding 0%).

 Hereinafter, a method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention will be described.

In the steelmaking step of the method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention, it is preferable to use a material having a high purity of an alloy element in order to minimize the pickup of impurities.

The molten steel thus controlled is solidified in a continuous casting process to produce a slab.

The slab is charged into a furnace and reheated at 1,100 ° C to 1,150 ° C. It is preferable to reheat at a low temperature as low as possible in order to prevent redeposition of the precipitate during reheating, so it is necessary to heat at 1150 DEG C or less. When the temperature is less than 1100 DEG C, the deformation resistance during hot rolling is too large. Reheat at 1100 ° C or higher.

When hot rolling after reheating, it is advantageous to perform hot rolling as low as possible. This is to minimize the disadvantageous (111) recrystallization texture when the cold reduction rate is high.

In one embodiment of the present invention, the hot rolled steel sheet should be hot rolled to 2.0 mmt or less in order to obtain a RC average of 1.68 T or more and a circumferential average of 1.66 T by improving the texture, and when the steel sheet is rolled in excess of 2.0 mmt, Even when rolled, the RC characteristic can be improved to 1.68 T or more in the Goss texture, but the circumferential average characteristic is less than the target characteristic.

However, hot rolling at a temperature of less than 1.6 mmt is difficult in general hot rolling equipment when considering the ducting and workability, so that the thickness of the lower limit is limited.

 The hot-rolled hot-rolled sheet is subjected to preliminary cold-rolling at a reduction ratio of 20 to 40%, followed by annealing of the hot-rolled sheet.

When the hot-rolled sheet is subjected to the preliminary cold-rolling, a strong plastic deformation particularly occurs from the surface layer, and when the hot-rolled sheet annealing, the final cold rolling and the final plate annealing are performed, the (111) ), And (101) texture occurs. Such an effect is maximized at a ratio of 20% or more, but when the ratio exceeds 40%, the magnetization-favorable aggregate structure at the center of the hot-rolled sheet is converted into a Goss aggregate structure to improve the RC average characteristic, but the circumferential property is deteriorated. Therefore, preliminary cold rolling of the hot rolled sheet is preferably carried out within a range of 20 to 40% reduction.

Thereafter, the plate subjected to hot rolling and preliminary cold rolling is subjected to hot-rolled sheet annealing at a temperature of 850 to 1,150 DEG C to increase the crystal orientation favorable to magnetism. If the annealing temperature of the hot-rolled sheet is less than 850 캜, the structure does not grow or grows finely and the synergistic effect of the magnetic flux density is small. If the annealing temperature exceeds 1,150 캜, the magnetic properties are rather deteriorated. The temperature range is limited to 850 to 1,150 ° C. More preferably, the annealing temperature of the hot-rolled sheet is 950 to 1,150 ° C.

Next, the hot-rolled sheet is pickled and then cold-rolled at a reduction ratio of 70 to 85% to form a predetermined thickness. The electric steel sheet used for HEV / EV has a thickness of 0.30 mm 0.15 mm t.

The present cold-rolled cold-rolled sheet is subjected to final annealing. If the final annealing temperature is less than 750 캜, recrystallization does not sufficiently occur. If the final annealing temperature exceeds 1,050 캜, the crystal grain diameter becomes too large and the high-frequency iron loss tends to heat. Therefore, final annealing is performed at a temperature of 900 to 1,050 캜 For at least one minute.

Hereinafter, the present invention will be described in more detail by way of examples.

The slabs composed of 3.4% Si, 0.6% Al, 0.4% Mn, 0.002%, 0.003%, 0.05%, 0.002%, 0.0015% and other unavoidable impurities were reheated and the results are shown in Table 1 The hot-rolled steel sheet was pre-cold-rolled, hot-rolled at 1100 ° C.

Hot rolled annealed sheet was subjected to cold rolling at 0.27 mm t after pickling and final annealing was performed at 950 ° C in 20% hydrogen and 80% nitrogen for 1 minute.

The RC average magnetic measurement was averaged in the rolling direction and in the direction perpendicular to the rolling direction using a 60 × 60 mm ² single-piece measuring instrument. The circumferential average magnetic properties were measured by using a 10 mm diameter ring sample with an outer diameter of 60 mm and an inner diameter of 50 mm The magnetic properties were measured by laminating copper wires and winding.

The fraction of the texture is obtained by taking an XRD pole figure for each of 0.05 mm ground and 0.15 mm ground from the surface of the product plate, then calculating the ODF and integrating the fraction within the 15 degree offset range for each texture orientation Respectively.

* Hot-rolled plate Rolling rate  ; (Initial thickness - Later Thickness ) / Initial thickness * 100 Psalter
number Hot rolling
thickness
(mm) Cold rolled pre-cold rolled thickness
(mm) Hot-rolled plate
Rolling rate *
(%) However,
W10 / 400
W / Kg Magnetic flux density
RC average,
B50 (T) Magnetic flux density,
Circumference average,
B50 (T) (001)
Fiber
ratio
(%) Goss
ratio
(%) Remarks One 2.3 2.3 0 13.1 1.65 1.63 14 0.3 Comparison 1 2 2.3 2 13 13.1 1.652 1.632 17 0.6 Comparative material 2 3 2.3 1.8 22 13 1.655 1.631 18 1.2 Comparative material 3 4 2.3 1.6 30 12.9 1.662 1.637 26 1.3 Comparison 4 5 2.3 1.4 39 12.8 1.668 1.645 24 1.8 Comparative material 5 6 2.3 1.2 48 12.4 1.685 1.655 20 2.8 Comparative material 6 7 2 2 0 13 1.662 1.641 16 0.5 Comparison 7 8 2 1.8 10 12.8 1.671 1.649 19 0.7 COMPARISON 8 9 2 1.6 20 12.4 1.682 1.665 32 1.2 Inventory 1 10 2 1.4 30 12.2 1.691 1.668 34 1.3 Inventory 2 11 2 1.2 40 12.1 1.695 1.664 34 1.7 Inventory 3 12 2 One 50 12 1.701 1.656 24 2.9 Comparative material 9 13 1.8 1.8 0 13 1.665 1.641 18 0.4 Comparative material 10 14 1.8 1.6 11 12.9 1.672 1.65 22 0.9 Comparative material 11 15 1.8 1.4 22 12.2 1.691 1.67 31 1.1 Invention 4 16 1.8 1.2 33 12 1.698 1.672 34 1.4 Invention Article 5 17 1.8 One 44 11.8 1.705 1.653 23 3.1 Comparative material 12 18 1.8 0.8 56 11.6 1.712 1.651 22 4.5 Comparative material 13 19 1.6 1.6 0 12.9 1.672 1.648 20 0.6 Comparative material 14 20 1.6 1.4 13 12.8 1.675 1.652 22 0.8 Comparative material 15 21 1.6 1.2 25 12.1 1.685 1.668 35 1.4 Inventions 6 22 1.6 One 38 11.8 1.696 1.669 36 1.7 Invention 7 23 1.6 0.8 50 1.711 1.645 23 3.1 Comparative material 16 24 1.4 Non-hot rolling due to hot rolling roll force problem Comparative material 17

Inventive materials 1 to 7 of Table 1 are all those with a hot rolled steel sheet thickness of 2.0 mm t or less, a cold rolled steel sheet pre-cold rolling reduction of 20 to 40%, an iron loss (W10 / 400) of 12.5 W / Kg or less, A density of 1.68 T or more, and a circumferential average magnetic flux density of 1.66 T or more. In particular, the (001) fiber ratio of the inventive material was more than 30%, and the Goss ratio was less than 3%, both of the RC characteristic and the circumferential average magnetic flux density were high.

The comparative materials 1 to 6 had a hot-rolled sheet thickness of 2.3 mmt. However, when the pre-cold-rolling was carried out after hot rolling, some properties were improved, but the degree of improvement was not 1.68 T. To improve the properties to 1.68 T or more, When the preliminary cold rolling reduction ratio is increased by 50%, the goss fraction is increased and the circumferential characteristic is decreased.

In the case of comparative materials 7 to 16, the RC average characteristic is less than 1.68 T when the pre-cold rolling reduction is 20% or less, and the circumferential average characteristic is decreased to 1.66 T or less when the pre-cold rolling reduction is 40% or more.

FIG. 1 clearly shows the change of the RC average (a) and the circumferential mean (b) according to the preliminary cold rolling rate after hot rolling at 1.8 mmt. When the preliminary cold rolling reduction is 20 to 40%, the circumference characteristic is the highest, and it can show the best characteristics when applied to an actual motor.

Comparative material 17 was not able to be hot-rolled due to the hot rolling force and the ducting problem in the conventional hot rolling equipment, the hot temperature and the width.

In order to investigate the influence of the content of other alloying elements, a steel ingot as shown in Table 2 was prepared. Each material was reheated at 1,130 ° C, hot rolled at 1.8 mmt, preliminary cold rolled to 1.4 mmt, and annealed at 1100 ° C. The hot - rolled and annealed sheets were subjected to cold rolling at 0.27 mm after pickling, and final annealing was performed at 950 ° C in 20% hydrogen and 80% nitrogen for 1 minute. The magnetic measurement was the same as in the previous method.

Psalter
number Si
(wt%) Al
(wt%) Mn
(wt%) P
(wt%) S
(wt%) N
(wt%) However,
W10 / 400
(W / Kg) Magnetic flux density,
B50
(T) Remarks One 3.4 0.7 0.5 0.05 0.002 0.0015 12 1.684 Inventory 1 2 2.7 0.7 0.5 0.05 0.002 0.0015 12.4 1.72 Inventory 2 3 2.3 0.7 0.5 0.05 0.002 0.0015 13.3 1.73 Comparison 1 4 3.7 0.7 0.5 0.05 0.002 0.0015 Inoperable Comparative material 2 5 3.4 0.1 0.5 0.05 0.002 0.0015 12.7 1.7 Comparative material 3 6 3.4 0.3 0.5 0.05 0.002 0.0015 12.4 1.687 Inventory 3 7 3.4 2 0.5 0.05 0.002 0.0015 11.3 1.64 Comparison 4 8 3.4 0.7 One 0.05 0.002 0.0015 11.5 1.66 Comparative material 5 9 3.4 0.7 0.5 0.12 0.002 0.0015 Inoperable Comparative material 6 10 3.4 0.7 0.5 0.05 0.005 0.0015 13 1.65 Comparison 7 11 3.4 0.7 0.5 0.05 0.002 0.004 13.1 1.64 COMPARISON 8

In the case of inventive materials 1 to 3 falling within the alloying element range of the present invention, excellent iron loss and magnetic flux density were simultaneously achieved. In the case of comparative materials 1 and 3, where the amount of the alloy was too small, iron loss was insufficient, and excessive comparative materials 2, 4, 5 and 6 were not rolled. In the case of the comparative materials 7 and 8 including the impurities which are outside the scope of the present invention, both the iron loss and the magnetic flux density were not satisfied.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (15)

(Excluding 0%), C: not more than 0.003% (provided that 0% is not more than 0%), Si: 2.5 to 3.5%, Al: 0.2 to 1.5% ), S: not more than 0.004% (excluding 0%), N: not more than 0.002% (excluding 0%), and the balance Fe and other inevitably added impurities step;
Charging the slab into a heating furnace and reheating the slab;
Hot rolling the slab to a thickness of 1.6 mm to 2.0 mm after reheating the slab;
Pre-cold-rolling the hot-rolled hot-rolled sheet in a rolling reduction range of 20 to 40%;
Annealing the pre-cold-rolled steel sheet by hot-rolling; and
And finally annealing the annealed steel sheet after cold-rolling the steel sheet. delete The method according to claim 1,
Wherein the slab is reheated at 1,100 ° C to 1,150 ° C in the step of reheating the slab. The method of claim 3,
Wherein the cold-rolled steel sheet is annealed at a temperature of 850 to 1,150 占 폚. 5. The method of claim 4,
Wherein the annealed hot-rolled sheet is cold-rolled at a reduction ratio of 70 to 85%. 6. The method of claim 5,
Wherein the cold rolling is carried out by cold rolling so as to have a thickness of 0.15 mm to 0.30 mm during the main cold rolling. The method according to claim 6,
Wherein the final annealing is performed at a temperature of 900 to 1,050 占 폚 for one minute or longer so that the grain diameter becomes 50 to 150 占 퐉. 8. The method according to any one of claims 1 to 7,
(W10 / 400) of 12.5 W / Kg or less, a magnetic flux density of 1.68 T or more, and a circumferential magnetic flux density Is 1.66 T or more. 8. The method according to any one of claims 1 to 7,
The non-oriented electrical steel sheet produced by the method of producing the non-oriented electrical steel sheet is characterized in that the non-oriented electrical steel sheet is produced such that the fraction of (001) fiber is not less than 30% and the fraction of goss is not more than 2% A method of manufacturing a steel sheet. 9. The method of claim 8,
The non-oriented electrical steel sheet produced by the method of producing the non-oriented electrical steel sheet is characterized in that the non-oriented electrical steel sheet is produced such that the fraction of (001) fiber is not less than 30% and the fraction of goss is not more than 2% A method of manufacturing a steel sheet. (Excluding 0%), C: not more than 0.003% (provided that 0% is not more than 0%), Si: 2.5 to 3.5%, Al: 0.2 to 1.5% (Excluding 0%), S: not more than 0.004% (excluding 0%) and N: not more than 0.002% (excluding 0%), and the remainder Fe and other inevitably added impurities are reheated , Hot-rolled to a thickness of 1.6 mm to 2.0 mm, pre-cold-rolled at a reduction rate of 20 to 40%, subsequently subjected to hot-rolled sheet annealing, final cold-
(W10 / 400) of not more than 12.5 W / Kg, a magnetic flux density of not less than 1.68 T, and a circumferential magnetic flux density of not less than 1.66 T based on a thickness of 0.27 mm. delete 12. The method of claim 11,
Wherein the steel sheet has a thickness of from 0.15 mm to 0.30 mmt by the primary cold rolling. 14. The method of claim 13,
Wherein the steel sheet has a grain diameter of 50 to 150 占 퐉 by the final annealing. The method according to any one of claims 11, 13 and 14,
Wherein the steel sheet has a (001) fiber fraction of 30% or more and a Goss fraction of 2% or less based on a thickness of 0.27 mm.

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