KR101919529B1 - Non-oriented electrical steel sheet and method for manufacturing the same - Google Patents

Abstract

The non-oriented electrical steel sheet according to an embodiment of the present invention may contain 1.0 to 4.0% of Si, 0.7 to 1.5% of Mn, 0.4 to 1.0% of Al, 0.001 to 0.01% of P, and Fe and unavoidable impurities And satisfies the following equations (1) to (3).
[Formula 1]
1? [Mn] / [Al]? [Si] / [Al]
[Formula 2]
4.1? ([Si] + [Mn] + [Al])
[Formula 3]
0.4? ([Mn] + [Al]) / [Si]? 0.55
(In the formulas 1 to 3, [Si], [Mn] and [Al] indicate the content (% by weight) of Si, Mn and Al, respectively.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a non-oriented electrical steel sheet,

A non-oriented electrical steel sheet and a manufacturing method thereof. And more particularly, to a non-oriented electrical steel sheet having excellent productivity and iron loss, and a method of manufacturing the same.

The nonoriented electrical steel sheet is used as an iron core material in rotating equipment such as motors, generators, and stationary equipment such as small transformers, and it transforms electrical energy into mechanical energy. Therefore, it is essential to improve the characteristics of the non-oriented electrical steel sheet in the situation where energy saving is a very important material for determining the energy efficiency of the electric device and the social issue is emerging.

The typical magnetic properties of the nonoriented electrical steel sheet are iron loss and magnetic flux density. The lower the iron loss, the less energy is lost because the energy loss is smaller. In order to achieve the high efficiency characteristics required for the motor and generator, low iron loss characteristics are very important . The most efficient method for lowering the iron loss is to increase the amount of Si, which is an essential alloy element added to the non-oriented electrical steel sheet, and an element having a high resistivity. However, since the increase of the amount of Si is disadvantageous in that it lowers the productivity by lowering the rolling property, a method of simultaneously improving the rolling property and iron loss by replacing the amount of Si added by Al is used. The rolling property still needs further improvement, and development of a product capable of satisfying both iron loss and rolling property is still a difficult part.

In order to improve the magnetic properties with high productivity, a technique of introducing additional manufacturing processes such as improving the magnetic properties by improving the texture by using special additive elements such as REM or annealing twice twice is used. However, all of these technologies cause a rise in manufacturing cost and a difficulty in mass production.

In order to solve this problem, the composition weight ratio (MnO / SiO ₂ ) of MnO and SiO ₂ in the oxide inclusions in the steel is adjusted to improve the magnetic properties through the improvement of the texture, and during the hot rolling, the finish rolling is performed by friction between steel and roll A method of annealing a hot-rolled sheet, cold-rolling and cold-rolled sheet annealing in a ferrite single-phase region having a coefficient of 0.2 or less and a finish rolling temperature of 700 ° C or more. However, at this time, since the thickness of the hot-rolled sheet must be controlled to 1.0 mm or less, productivity is low and commercial production is difficult.

In addition, in order to manufacture a non-oriented electrical steel sheet having excellent magnetic properties in the rolling direction, skin pass rolling is further performed at a reduction rate of 3 to 10% in addition to the steps of hot rolling, hot rolling annealing, cold rolling and cold rolling annealing, The process was presented. This also has the problem of cost increase due to the additional process.

In order to improve the magnetic properties, there is proposed a method of annealing twice twice, including intermediate annealing, as a hot-rolled sheet, and a method of twice rolling including intermediate annealing in cold rolling is proposed. There is a problem that the manufacturing cost is increased due to the addition of the process.

One embodiment of the present invention provides a non-oriented electrical steel sheet and a method of manufacturing the same. Specifically, a non-oriented electrical steel sheet excellent in productivity and iron loss and a method of manufacturing the same are provided.

The non-oriented electrical steel sheet according to an embodiment of the present invention may contain 1.0 to 4.0% of Si, 0.7 to 1.5% of Mn, 0.4 to 1.0% of Al in weight percent. P: 0.001 to 0.01% and the remainder contains Fe and unavoidable impurities, and satisfies the following formulas 1 to 3.

[Formula 1]

1? [Mn] / [Al]? [Si] / [Al]

[Formula 2]

4.1? ([Si] + [Mn] + [Al])

[Formula 3]

0.4? ([Mn] + [Al]) / [Si]? 0.55

(In the formulas 1 to 3, [Si], [Mn] and [Al] indicate the content (% by weight) of Si, Mn and Al, respectively.

0.005 wt% or less of C, 0.001 to 0.005 wt% of S, 0.005 wt% or less of N, and 0.005 wt% or less of Ti.

Sn and Sb alone or in a total amount of 0.02 to 0.08% by weight.

At least one of Cu: 0.05 wt% or less, Ni: 0.05 wt% or less, Cr: 0.05 wt% or less, Zr: 0.01 wt% or less, Mo: 0.01 wt% or less and V: 0.01 wt% .

And the average grain size may be 50 to 150 mu m.

The iron loss (W _15/50 ) may be 2.0 W / kg or less, and the iron loss (W _10/400 ) may be 15.5 W / kg or less.

A method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention comprises: 1.0 to 4.0% of Si, 0.7 to 1.5% of Mn, 0.4 to 1.0% of Al, 0.001 to 0.01% of P, And unavoidable impurities, and heating the slab satisfying the following equations (1) to (3); Hot rolling the slab to produce a hot rolled sheet; A step of cold-rolling the hot-rolled sheet to produce a cold-rolled sheet, and a step of finally annealing the cold-rolled sheet.

[Formula 1]

1? [Mn] / [Al]? [Si] / [Al]

[Formula 2]

4.1? ([Si] + [Mn] + [Al])

[Formula 3]

0.4? ([Mn] + [Al]) / [Si]? 0.55

(In the formulas 1 to 3, [Si], [Mn] and [Al] indicate the content (% by weight) of Si, Mn and Al, respectively.

The slab may further contain 0.005 wt% or less of C, 0.001 to 0.005 wt% of S, 0.005 wt% or less of N, and 0.005 wt% or less of Ti.

The slab may further include at least one of Sn and Sb alone or in an amount of 0.02 to 0.08% by weight.

The slab may contain at least one of Cu: at most 0.05 wt%, Ni: at most 0.05 wt%, Cr: at most 0.05 wt%, Zr: at most 0.01 wt%, Mo: at most 0.01 wt% .

After the step of producing the hot-rolled steel sheet, the step of annealing the hot-rolled steel sheet may further include the step of annealing the hot-rolled steel sheet.

After the hot-rolled sheet annealing step, the hot-rolled sheet may have an average grain size of 120 to 180 탆.

The non-oriented electrical steel sheet and the manufacturing method according to an embodiment of the present invention are excellent in productivity and iron loss.

The terms first, second and third, etc. are used to describe various portions, components, regions, layers and / or sections, but are not limited thereto. These terms are only used to distinguish any moiety, element, region, layer or section from another moiety, moiety, region, layer or section. Thus, a first portion, component, region, layer or section described below may be referred to as a second portion, component, region, layer or section without departing from the scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms as used herein include plural forms as long as the phrases do not expressly express the opposite meaning thereto. Means that a particular feature, region, integer, step, operation, element and / or component is specified and that the presence or absence of other features, regions, integers, steps, operations, elements, and / It does not exclude addition.

When referring to a portion as being "on" or "on" another portion, it may be directly on or over another portion, or may involve another portion therebetween. In contrast, when referring to a part being "directly above" another part, no other part is interposed therebetween.

Unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Commonly used predefined terms are further interpreted as having a meaning consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or very formal meanings unless defined otherwise.

Unless otherwise stated,% means% by weight, and 1 ppm is 0.0001% by weight.

In an embodiment of the present invention, the term further includes an additional element, which means that an additional amount of the additional element is substituted for the remaining iron (Fe).

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

In one embodiment of the present invention, the composition in the non-oriented electrical steel sheet, particularly the range of Si, Al, and Mn, which is a main additive component, can be optimized to provide a non-oriented electrical steel sheet having excellent productivity as well as excellent iron loss.

The non-oriented electrical steel sheet according to an embodiment of the present invention is characterized in that the non-oriented electrical steel sheet according to an embodiment of the present invention contains 1.0 to 4.0% Si, 0.7 to 1.5% Mn, 0.4 to 1.0% Al, The remainder includes Fe and unavoidable impurities.

0.001 to 0.01 wt% of P, 0.005 wt% or less of P, 0.001 to 0.005 wt% of S, 0.005 wt% or less of N, and 0.005 wt% or less of Ti.

Sn and Sb alone or in a total amount of 0.02 to 0.08% by weight.

At least one of Cu: 0.05 wt% or less, Ni: 0.05 wt% or less, Cr: 0.05 wt% or less, Zr: 0.01 wt% or less, Mo: 0.01 wt% or less and V: 0.01 wt% .

First, the reason for limiting the components of the non-oriented electrical steel sheet will be described.

Si: 1.0 to 4.0 wt%

Silicon (Si) is a major element added to increase the resistivity of the steel and to reduce vortex loss during iron loss. If too little is added, the iron loss improving effect may be insufficient. On the other hand, if too much is added, the magnetic flux density can be decreased and the rolling property can be disadvantageously reduced. Therefore, Si can be added in the above-mentioned range.

Mn: 0.7 to 1.5 wt%

Manganese (Mn) is an element that decreases the iron loss by increasing the resistivity in addition to Si and Al. It is an element which does not significantly inhibit the rolling property, though its effect is less than that of Si and Al. If the addition amount is too small, the effect on the magnetism is insignificant, and if the addition amount is too large, the magnetic flux density can be greatly lowered. Therefore, Mn can be added in the above-mentioned range.

Al: 0.4 to 1.0 wt%

Aluminum (Al) plays the role of reducing the iron loss by increasing the resistivity like Si. If added too little, the magnetic flux density can be greatly reduced and the rolling properties can be also reduced. Therefore, Al can be added in the above-mentioned range.

The above-mentioned Si, Mn and Al can satisfy the following formulas 1 to 3.

[Formula 1]

1? [Mn] / [Al]? [Si] / [Al]

[Formula 2]

4.1? ([Si] + [Mn] + [Al])

[Formula 3]

0.4? ([Mn] + [Al]) / [Si]? 0.55

(In the formulas 1 to 3, [Si], [Mn] and [Al] indicate the content (% by weight) of Si, Mn and Al, respectively.

The most effective way to reduce iron loss in non-oriented electrical steel sheets is the reduction of eddy currents by increasing the resistivity, and Si, Mn, and Al are the most effective elements for increasing the resistivity. Therefore, the addition amount of Si, Mn and Al as the non-resistive elements is increasing in products having lower iron loss characteristics. Of these, Si and Al are the most effective elements, and thus the amounts of Si and Al are increasingly being increased . Mn is an element that increases the resistivity, but its effect is smaller than that of Si and Al, and thus it is added to assist Si and Al. However, since the increase of the addition amount of Si and Al leads to the damping of the rolling property, it is necessary to actively utilize the effect of Mn by increasing the addition amount of Mn in order to improve the rolling property and iron loss. Therefore, both rolling and iron loss can be improved by controlling the addition amount of Si, Al and Mn so as to satisfy the above-mentioned formulas 1 to 3 by increasing the amounts of Si, Al and Mn to maintain low iron loss characteristics of the high alloy system.

P: 0.001 to 0.01 wt%

Phosphorus (P) plays a role of lowering the iron loss by increasing the resistivity and segregating at grain boundaries and improving the texture. However, it is an element which lowers the rolling property in the high alloy steel, so that if P is further added, it may be added in the range of 0.001 to 0.01% by weight.

C: 0.005 wt% or less

Carbon (C) is combined with Ti to form carbide to dislocate magnetism. It is preferable that the carbon (C) contains iron because it increases iron loss by magnetic aging when it is used as an electrical product in the final product. When C is further added, C can be added in the above-mentioned range.

S: 0.001 to 0.005 wt%

Sulfur (S) is an element which forms sulfides such as MnS, CuS and (Cu, Mn) S harmful to the magnetic properties, and therefore it is preferable to add as low as possible. However, if it is added too little, the magnetization may deteriorate due to disadvantage of formation of aggregate structure. If too much is added, the magnetism may become dull due to the increase of fine sulfides. Therefore, when S is further added, S can be added in the above-mentioned range.

N: 0.005 wt% or less

Nitrogen (N) is an element which is harmful to magnetism, such as nitrides being formed by binding with Al, Ti or the like to inhibit crystal growth, and therefore, it is preferable that nitrogen is contained less. When N is further added, N can be added in the above-mentioned range.

Ti: 0.005 wt% or less

Titanium (Ti) forms fine carbides and nitrides to inhibit grain growth. As the amount of titanium (Ti) increases, carbides and nitrides increase. When Ti is further added, Ti can be added in the above-mentioned range.

Sn and Sb: 0.02 to 0.08 wt%

Tin (Sn) and antimony (Sb) are crystal grain segregated elements that inhibit the diffusion of nitrogen through grain boundaries and inhibit the formation of {111}, {112} It is added to improve the magnetic properties by increasing the texture, but it is not effective when the addition amount is small, and when the amount is large, the magnetic growth is suppressed by suppressing the grain growth. When Sn or Sb is added, it may be added alone or in an amount of 0.02 to 0.08% by weight. That is, when Sn is contained singly, it contains 0.02 to 0.08% by weight of Sn or Sb alone, 0.02 to 0.08% by weight of Sb, or Sn and Sb, 0.02 to 0.08% by weight in total.

Impurity element

In addition to the above elements, inevitably incorporated impurities such as Cu, Ni, Cr, Zr, Mo, and V may be included. In the case of Cu, Ni and Cr, they react with impurity elements to form fine sulfides, carbides and nitrides, which have harmful effects on magnetism. Therefore, these contents are limited to 0.05 wt% or less. Since Zr, Mo, V and the like are also strong carbonitride-forming elements, they are preferably not added as much as possible and are each contained in an amount of 0.01 wt% or less.

As described above, by precisely controlling the components, a non-oriented electrical steel sheet excellent in productivity and iron loss can be obtained. Specifically, the non-oriented electrical steel sheet according to an embodiment of the present invention may have an iron loss (W _15/50 ) of 2.0 W / kg or less and an iron loss (W _10/400 ) of 15.5 W / kg or less. In addition, the non-oriented electrical steel sheet according to an embodiment of the present invention may have an average crystal grain diameter of 50 to 150 mu m.

A method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes 1.0 to 4.0% of Si, 0.7 to 1.5% of Mn, 0.4 to 1.0% of Al, and the balance of Fe and unavoidable impurities, Heating the slab satisfying equations 1 to 3; Hot rolling the slab to produce a hot rolled sheet; A step of cold-rolling the hot-rolled sheet to produce a cold-rolled sheet, and a step of finally annealing the cold-rolled sheet. Hereinafter, each step will be described in detail.

First heat the slab. The reason why the addition ratio of each composition in the slab is limited is the same as the reason for limiting the composition of the non-oriented electrical steel sheet described above, so repeated description is omitted. The composition of the slab is substantially the same as that of the non-oriented electrical steel sheet because the composition of the slab does not substantially change during the manufacturing process such as hot rolling, hot rolling annealing, cold rolling and final annealing, which will be described later.

The slab is charged into a heating furnace and heated to 1100 to 1200 캜. Precipitates such as AlN and MnS existing in the slab when heated at a temperature exceeding 1200 deg. C are reused and then precipitated by hot rolling to suppress grain growth and decrease magnetism.

The heated slab is hot-rolled to 2 to 2.3 mm to produce a hot-rolled sheet. Finishing rolling in hot rolling can be carried out at a final rolling reduction of 20% or less for plate shape calibrating. The hot rolled sheet is rolled up at 700 ° C or less and cooled in air.

After the step of producing the hot-rolled steel sheet, the step of annealing the hot-rolled steel sheet may further include the step of annealing the hot-rolled steel sheet. At this time, the hot-rolled sheet annealing temperature may be 950 to 1150 ° C. If the annealing temperature of the hot-rolled sheet is less than 950 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 1150 캜, the magnetic properties are rather deteriorated. Can be bad. At this time, the average grain diameter after annealing of the hot-rolled steel sheet can be controlled to 120 to 180 占 퐉. If the average grain size of the hot-rolled steel sheet after annealing the hot-rolled steel sheet is smaller than the above range, the grain growth is insufficient and the magnetism is disadvantageous. If the grain size is large, the cold rolling property may be deteriorated.

Next, the hot rolled sheet is pickled and cold rolled to a predetermined thickness. The cold-rolled steel sheet may be cold-rolled by applying a reduction ratio of 50 to 95% to a final thickness of 0.10 to 0.70 mm. If necessary, it may include a plurality of cold rolling processes including intermediate annealing.

The final cold-rolled cold-rolled sheet is subjected to final annealing. The final annealing temperature may be 750 to 1050 占 폚. If the final annealing temperature is too low, recrystallization may not occur sufficiently, and if the final annealing temperature is too high, rapid growth of crystal grains may occur and magnetic flux density and high frequency iron loss may be caused to heat. More specifically, final annealing can be performed at a temperature of 900 to 1000 ° C. In the final annealing process, all the processed structures formed in the previous cold rolling stage can be recrystallized (i.e., 99% or more). The average grain size of the crystal grains of the final annealed steel sheet may be 50 to 150 占 퐉.

The thus produced non-oriented electrical steel sheet can be subjected to an insulating coating treatment. The insulating coating may be treated with an organic, inorganic or organic composite coating, or may be treated with other insulating coatings.

Hereinafter, the present invention will be described in more detail with reference to examples. However, these embodiments are only for illustrating the present invention, and the present invention is not limited thereto.

Example

A slab containing the remainder Fe and unavoidable impurities was prepared as shown in Tables 1 and 2 below. The slab was heated to 1140 占 폚 and hot-rolled at a finishing temperature of 880 占 폚 to obtain a hot-rolled sheet having a thickness of 2.2 mm, rolled in air and cooled. The hot-rolled sheet was subjected to hot-rolled sheet annealing at the temperatures listed in Table 3, followed by pickling and cold rolling to a thickness of 0.35 mm and final annealing at 1000 ° C for 120 seconds.

The iron loss (W _15/50) for each specimen, the iron loss (W _10/400), after the end of hot-rolled sheet annealing to the average grain diameter of the hot-rolled sheets shown in Table 3 below. W _15/50 means that the average loss (W / kg) in the rolling direction and the direction perpendicular to the rolling direction when the magnetic flux density of 1.5T in the organic frequency of 50Hz, and W _10/400 are of 1.0T at a frequency of 40Hz (W / kg) in the rolling direction and the direction perpendicular to the rolling direction when the magnetic flux density is induced.

Steel grade
(weight%) Si Mn Al Si / Al Mn / Al Si + Mn + Al (Mn + Al) / Si A1 2.9 0.7 0.6 4.83 1.17 4.2 0.45 A2 3 0.5 0.5 6 One 4 0.33 A3 3.3 1.2 1.1 3 1.09 5.6 0.7 A4 3 1.1 0.5 6 2.2 4.6 0.53 A5 3.2 One 0.5 6.4 2 4.7 0.47 A6 2.3 0.5 0.7 3.29 0.71 3.5 0.52 A7 2.5 1.2 0.3 8.33 4 4 0.6 A8 3.4 1.1 0.7 4.86 1.57 5.2 0.53 A9 3 0.7 One 3 0.7 4.7 0.57 A10 3.4 0.8 0.6 5.67 1.33 4.8 0.41 A11 3.5 0.8 0.7 5 1.14 5 0.43 A12 2.8 1.2 0.6 4.67 2 4.6 0.64

Steel grade
(weight%) P C S N Ti Sn Sb A1 0.007 0.0026 0.0026 0.0031 0.0009 0.02 0.05 A2 0.003 0.0021 0.0022 0.0033 0.0011 0.05 0 A3 0.004 0.0022 0.0013 0.0025 0.0024 0 0.05 A4 0.002 0.0019 0.0034 0.0012 0.001 0.05 0 A5 0.003 0.0013 0.0024 0.003 0.0013 0 0.03 A6 0.006 0.0019 0.0031 0.0027 0.0007 0.02 0 A7 0.007 0.001 0.0041 0.0013 0.0034 0 0.04 A8 0.008 0.0031 0.0013 0.0023 0.0024 0.06 0 A9 0.006 0.0037 0.003 0.0037 0.0019 0.03 0.03 A10 0.005 0.0029 0.0021 0.0028 0.0016 0.01 0.03 A11 0.003 0.0033 0.0038 0.0011 0.0011 0 0.06 A12 0.002 0.0026 0.0025 0.0022 0.0026 0.07 0

Steel grade Hot-rolled sheet annealing temperature (캜) Grain size (㎛) _Iron loss (W _15/50 , W / kg) _Iron loss (W _10/400 , W / kg) Remarks A1 1000 138 1.95 15.1 Honor A2 1020 185 2.35 16.9 Comparative Example A3 1010 137 2.28 16.8 Comparative Example A4 1050 168 1.91 14.9 Honor A5 1070 176 1.86 14.8 Honor A6 1040 164 2.84 18.7 Comparative Example A7 1040 153 2.49 18.2 Comparative Example A8 980 133 1.88 15.2 Honor A9 1040 169 2.42 17.6 Comparative Example A10 1050 156 1.83 14.5 Honor A11 1000 173 1.85 14.7 Honor A12 1000 128 2.47 17.9 Comparative Example

As shown in Tables 1 to 3, A1, A4, A5, A8, A10 and A11 corresponding to the range of the present invention were excellent in iron loss W _15/50 and W _10/400 in the final product.

It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims and their equivalents. It will be understood that the invention may be practiced. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (12)

The balance comprising Fe and unavoidable impurities, and satisfying the following formulas (1) to (3), wherein the content of Si is 1.0 to 4.0%, the content of Mn is 0.7 to 1.5%, the content of Al is 0.4 to 1.0% Non - oriented electric steel sheet.
[Formula 1]
1? [Mn] / [Al]? [Si] / [Al]
[Formula 2]
4.1? ([Si] + [Mn] + [Al])
[Formula 3]
0.4? ([Mn] + [Al]) / [Si]? 0.55
(In the formulas 1 to 3, [Si], [Mn] and [Al] indicate the content (% by weight) of Si, Mn and Al, respectively. The method according to claim 1,
0.005 wt% or less of C, 0.001 to 0.005 wt% of S, 0.005 wt% or less of N, and 0.005 wt% or less of Ti. The method according to claim 1,
Sn and Sb alone or in an amount of 0.02 to 0.08% by weight, based on the total weight of the non-oriented electrical steel sheet. The method according to claim 1,
At least one of Cu, at most 0.05% by weight, at most 0.05% by weight of Ni, at most 0.05% by weight of Cr, at most 0.01% by weight of Zr, at most 0.01% by weight of Mo and at most 0.01% Non - oriented electric steel sheet. The method according to claim 1,
The non-oriented electrical steel sheet having an average grain size of 50 to 150 占 퐉. The method according to claim 1,
An _unoriented electric steel sheet having an iron loss (W _15/50 ) of 2.0 W / kg or less and an iron loss (W _10/400 ) of 15.5 W / Kg or less. The balance comprising Fe and unavoidable impurities, and satisfying the following formulas (1) to (3), wherein the content of Si is 1.0 to 4.0%, the content of Mn is 0.7 to 1.5%, the content of Al is 0.4 to 1.0% Heating the slab;
Hot rolling the slab to produce a hot rolled sheet;
Cold rolling the hot rolled sheet to produce a cold rolled sheet; and
And finally annealing the cold rolled steel sheet.
[Formula 1]
1? [Mn] / [Al]? [Si] / [Al]
[Formula 2]
4.1? ([Si] + [Mn] + [Al])
[Formula 3]
0.4? ([Mn] + [Al]) / [Si]? 0.55
(In the formulas 1 to 3, [Si], [Mn] and [Al] indicate the content (% by weight) of Si, Mn and Al, respectively. 8. The method of claim 7,
Wherein the slab further contains 0.005 wt% or less of C, 0.001 to 0.005 wt% of S, 0.005 wt% or less of N, and 0.005 wt% or less of Ti. 8. The method of claim 7,
Wherein the slab further comprises 0.02 to 0.08% by weight of at least one of Sn and Sb, alone or in combination. 8. The method of claim 7,
The slab may contain at least one of Cu, at most 0.05 wt%, at most 0.05 wt% of Ni, at most 0.05 wt% of Cr, at most 0.01 wt% of Zr, at most 0.01 wt% of Mo, Further comprising the steps of: 8. The method of claim 7,
After the step of producing the hot rolled sheet,
Further comprising the step of annealing the hot-rolled sheet by hot-rolling. 12. The method of claim 11,
Wherein the hot-rolled sheet has an average grain size of 120 to 180 占 퐉 after the hot-rolled sheet annealing step.