KR20150016435A

KR20150016435A - Non-oriented electrical steel sheet and method for manufacturing the same

Info

Publication number: KR20150016435A
Application number: KR1020130091563A
Authority: KR
Inventors: 이세일; 배병근; 박준수
Original assignee: 주식회사 포스코
Priority date: 2013-08-01
Filing date: 2013-08-01
Publication date: 2015-02-12

Abstract

In the present invention, disclosed are a non-oriented electrical steel sheet having significantly improved magnetic properties compared to a previous steel sheet by using a relationship of Al with Sn, Sb, and P contained in the electrical steel sheet and efficiently arranging texture favorable to the magnetic properties, and a manufacturing method thereof. The non-oriented electrical steel sheet of the present invention is composed of 1.0-3.5 weight% of Si, 0.0005-0.02 weight% of Al, 0.01-0.50 weight% of Mn, 0.004 weight% or less of C, 0.004 weight% or less of N, 0.004 weight% or less of Ti, and the remainder consisting of Fe and inevitable impurities, and additionally includes at least one of Sn, Sb, and P. The content of each of Sn, Sb, and P is higher than that of Al, and the each content is 0.01-0.1 weight%.

Description

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

The present invention relates to a non-oriented electrical steel sheet, and more particularly, to a non-oriented electrical steel sheet having improved magnetic properties by effectively controlling the addition amount of Al, Sn, Sb and P to improve magnetic properties will be.

The nonoriented electric steel sheet has an important influence on the energy efficiency of the electric equipment because the nonoriented electric steel sheet is used as an iron core material in rotating devices such as motors and generators and stationary devices such as small transformers, To mechanical energy.

The magnetic properties of the electric steel sheet include iron loss and magnetic flux density. The iron loss is energy loss, so the lower the better. On the other hand, in the case where the magnetic flux density characteristic showing the property of easy magnetization is high, since the same magnetic flux density can be obtained even when a smaller current is applied, the magnetic flux density generated in the coiled copper wire can be reduced, .

In order to improve the iron loss among the magnetic properties of the non-oriented electrical steel sheet, a method of adding Si, Al, Mn or the like, which is an alloy element having a large resistivity, is generally used for increasing the electrical resistance. However, addition of an alloying element reduces the iron loss, but also decreases the magnetic flux density due to the decrease of the saturation magnetic flux density. In addition, if the addition amount of Si and Al is increased, the workability is lowered, which makes it difficult to perform cold rolling, resulting in a decrease in productivity and an increase in hardness, resulting in poor workability.

The method that is effectively used for the improvement of the aggregate structure is known as a method of adding a trace alloy element. By using this, it is possible to manufacture a clean steel by reducing the fraction of crystal grains parallel to the <111> axis in the direction perpendicular to the sheet, which is a harmful texture, or by reducing the amount of impurities extremely. However, all of these technologies cause a rise in manufacturing cost and difficulties in mass production, and therefore, there is a need for a technique that is excellent in magnetic improvement effect without significantly increasing manufacturing cost.

In order to solve such problems, there have been continuous efforts in Japanese Patent Application No. 2012-112015, Japanese Patent Application Laid-Open No. 2011-179027 and Korean Patent Laid-Open No. 1998-026183, but there have been problems such as deterioration of magnetism, increase in cost or decrease in productivity.

In addition, Al, together with Si and Mn, is a main element for increasing electrical resistivity, and it plays a role of reducing eddy loss by lowering vortex loss. However, Al forms a fine inclusion by binding with N in steel, But also serves as a factor to deteriorate the magnetic properties. However, there are few techniques to improve the magnetic flux density by controlling the addition amount of Al in the steel. Japanese Patent Application Laid-Open No. 2004-292829 discloses a method for improving the magnetic properties at 0.0005% or less of Al and 0.7-1.5% of Si. However, the difficulty in manufacturing and refining a small amount of Al less than 0.0005% Accordingly, it has been difficult to apply it to high-grade electrical steel sheets.

Disclosure of the Invention The present invention has been devised to solve the problems as described above, and it is an object of the present invention to provide a method of manufacturing a magnetic steel sheet by efficiently arranging an aggregate structure favorable to magnetism utilizing the relationship between Al, Sn, Sb, And a method of manufacturing the same.

In order to achieve the above object, the non-oriented electrical steel sheet according to an embodiment of the present invention comprises 1.0 to 3.5% of Si, 0.0005 to 0.02% of Al, 0.01 to 0.50% of Mn, 0.004% or less of C, N: not more than 0.004%, Ti: not more than 0.004%, and the balance of Fe and other inevitably added impurities, and further contains at least one selected from Sn, Sb and P, And the content thereof is 0.01 to 0.1%.

When a plurality of components are selected from Sn, Sb and P, the sum of the contents of these components may be equal to or more than the content of Al.

The non-oriented electrical steel sheet may further contain 0.05 wt% or less of Cu, Ni, or Cr, respectively, and may further contain Zr, Mo, or V in an amount of 0.01 wt% or less.

The non-oriented electrical steel sheet may have an average grain size of the steel sheet after annealing of the cold rolled steel sheet of 30 탆 or more and 1,000 탆 or less.

According to another preferred embodiment of the present invention, there is provided a method of manufacturing a non-oriented electrical steel sheet, comprising: 1.0 to 3.5% Si, 0.005 to 0.02% Al, 0.01 to 0.50% Mn, 0.004% 0.004% or less, Ti: 0.004% or less, and the remainder includes Fe and other inevitably added impurities, and further includes at least one selected from Sn, Sb and P, Reheating the steel slab having a content of 0.01 to 0.1% to 1,200 ° C or less, hot-rolling the reheated steel slab, hot-rolling the hot-rolled steel sheet at a temperature of 900 ° C to 1,200 ° C within 5 minutes And cold-rolling the hot-rolled sheet and annealing the cold-rolled sheet at a temperature of 800 to 1,200 ° C within 5 minutes, wherein the annealing temperature of the hot-rolled sheet is higher than the annealing temperature of the cold-rolled sheet.

The steel slab further contains Cu, Ni and Cr in an amount of 0.05% or less, and Zr, Mo and V in an amount of 0.01% or less, respectively.

The cold rolling may be two or more cold rolling with primary cold rolling or intermediate annealing in between.

The non-oriented electrical steel sheet according to the present invention strictly limits the addition amount of Al and controls the addition amount of Sn, Sb and P added in a very small amount to control the generation of fine inclusions or promote the growth of the aggregate structure preferable for magnetism, Directional electric steel sheet can be manufactured with improved strength.

Fig. 1 shows the B ₅₀ magnetic flux density according to Example 2 of the present invention, which is an annealing temperature after hot-rolled sheet annealing of a hot-rolled sheet and an annealing temperature after cold rolling.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described in detail below. However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims. Like reference numerals refer to like elements throughout the specification.

In the non-oriented electrical steel sheet according to an embodiment of the present invention, the addition amount of Al is strictly controlled in the component system to which Si, Mn and Sn, Sb and P are added so that the addition amount is 0.0005 to 0.02% by weight, more preferably 0.001 To 0.005% by weight, Sn, Sb and P alone may be contained in an amount of 0.01 to 0.10% by weight, or each of the elements may be contained in an amount of 0.01 to 0.10% by weight and the weight of Al inducing generation of inclusions in the grain boundaries may be limited It is possible to maximize the effect of improving the texture during annealing by Sn, Sb, P or the like as a grain boundary material.

For this purpose, a method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes: 1.0 to 3.5% of Si, 0.005 to 0.02% of Al, 0.01 to 0.50% of Mn, 0.004% : 0.004% or less, Ti: 0.004% or less, the balance including Fe and other inevitably added impurities, and further comprising at least one selected from Sn, Sb and P, Reheating a steel slab having a content of 0.01 to 0.1% to 1,200 ° C or less, hot-rolling the reheated steel slab, hot-rolling the hot-rolled steel sheet at a temperature of 900 ° C to 1,200 ° C within 5 minutes, Annealing; And cold-rolling the hot-rolled sheet and annealing the cold-rolled sheet at a temperature of 800 to 1,200 ° C within 5 minutes, wherein the annealing temperature of the hot-rolled sheet is higher than the annealing temperature of the cold-rolled sheet.

In addition, the steel slab may further contain Sn, Sb and P in addition to the above composition, and Sn, Sb and P may be contained in an amount of 0.01 to 0.10% by weight alone or in a plurality of 0.01 to 0.10% .

The Al added as a resistivity element causes fine nitrides to be formed which cause the magnetism to become dull. If the size of the article is small in the non-oriented electrical steel sheet, it will interfere with the movement of the magnetic wall and deteriorate the magnetism. Therefore, it is necessary to increase the frequency of formation of coarse inclusions.

In addition, AlN plays a role of suppressing the growth of crystal grains by fixing the grain boundaries during annealing. As a result, it is impossible to maximize the effect of improving the texture during annealing by Sn, Sb and P, which are the grain boundary elements. In the present invention, the addition amount of Al is limited to 0.005 to 0.02% by weight so that the effect of improving the texture of the segregated elements is maximized Respectively.

Hereinafter, the reason for limiting the numerical value of the component according to the embodiment of the present invention will be described.

Si: 1.0 to 3.5 wt%

Since Si is a component which increases the resistivity of steel and lowers vortex loss during iron loss, it is difficult to obtain low iron loss property when it is less than 1.0% and it is difficult to obtain low iron loss property when it is added. When it is added in excess of 3.5% In one embodiment of the invention, Si is limited to 1.0 to 3.5 wt%.

Mn: 0.01 to 0.50 wt%

Since the Mn has the effect of increasing the specific resistance and lowering the iron loss in addition to Si and Al, the conventional unoriented electric steel sheet was attempted to improve the iron loss by adding at least 0.05% of Mn. However, as the Mn addition amount increased, the saturation magnetic flux density decreased Therefore, the magnetic flux density when a constant current is applied decreases. Therefore, in order to improve the magnetic flux density and prevent the increase of iron loss due to inclusions, the amount of Mn is preferably limited to 0.05 to 0.50%, more preferably 0.05 to 0.30% in one embodiment of the present invention, so as to minimize the Mn content.

Al: 0.0005 to 0.02 wt%

Al is an element which is inevitably added for deoxidizing steel in the steelmaking process. In general steel making process, 0.01% or more of Al is present in the steel. However, when added in a large amount, the saturation magnetic flux density is reduced and fine AlN is formed to suppress the grain growth, thereby lowering the magnetic property. Therefore, it is limited to 0.0005 to 0.02%.

P: 0.01 to 0.10 wt%

The P decreases the iron loss by lowering the specific resistance and segregates in the grain boundaries to inhibit the formation of {111} texture which is harmful to the magnetism and forms {100} which is an advantageous aggregate structure. However, 0.15% by weight. P is an element that lowers the surface energy of the {100} surface in the steel sheet surface, and the amount of P segregated on the surface is increased by further containing the P content, thereby further lowering the surface energy of the {100} It is possible to improve the growth rate of crystal grains having a {100} plane. As a result, the addition amount of P is defined as described above so that the sum of the {100} plane fraction and the {110} plane fraction is 35%, which is advantageous for magnetism.

Sn or Sb: 0.01 to 0.10 wt%

The Sn and Sb are segregated elements in the grain boundaries to suppress the diffusion of nitrogen through the grain boundaries and suppress the {111} texture detrimental to the magnetism and increase the advantageous {100} texture to enhance the magnetic properties. Sn and Sb Add 0.1% or more of each element individually or in combination to reduce grain growth and deteriorate the magnetic properties and deteriorate the rolling property. Therefore, Sn and Sb are added singly or in combination at 0.01 to 0.1% for each element.

C: not more than 0.004% by weight

When C is added heavily, it enlarges the austenite region and increases the phase transformation period. It suppresses the grain growth of ferrite during annealing and increases the iron loss. It combines with Ti and forms carbide to dislocate magnetism. The iron loss is increased by magnetic aging at the time of use after use. Therefore, the content of C is limited to 0.004% or less in one embodiment of the present invention.

S: 0.001 to 0.005% by weight or less

S is an element which forms sulfides such as MnS, CuS and (Cu, Mn) S which are harmful to the magnetic properties, and therefore it is known that it is preferable to add S low. However, when S is segregated on the surface of the steel, it has the effect of lowering the surface energy of {100} plane. Therefore, by adding S, a texture having strong {100} plane can be obtained. If the addition amount is less than 0.001%, the formation of aggregate structure is disadvantageously deteriorated and the magnetic property is deteriorated. Therefore, it is required to contain 0.001% or more, and when it is added in excess of 0.005%, the addition amount is limited because there is deterioration of iron loss due to sulfide.

N: not more than 0.004% by weight

N is an element which is detrimental to magnetism such as forming a nitride by binding with Al, Ti or the like to inhibit crystal growth, and therefore it is preferable to contain N in a small amount. In one embodiment of the present invention, N is limited to 0.004 wt% or less.

Ti: 0.004% by weight or less

Ti forms fine carbides and nitrides to inhibit crystal growth. As the amount of Ti is increased, the magnetization is deteriorated due to the increase of carbides and nitrides, resulting in deterioration of magnetism. Therefore, the Ti content is limited to 0.004% or less in one embodiment of the present invention.

In addition to the above elements, Cu, Ni, and Cr, which are inevitably added in the steelmaking process, react with impurity elements to form fine sulfides, carbides, and nitrides, thereby detrimentally affecting the magnetic properties. Limit. 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 at 0.01% by weight or less.

In addition to the above composition, the remainder is composed of Fe and other unavoidable impurities.

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

The non-oriented steel sheet steel slab prepared as described above is reheated to a temperature of 1200 DEG C or less and then hot rolled. When the reheating temperature is 1200 ° C or higher, precipitates such as AlN and MnS present in the slab are refined and precipitated during hot rolling to suppress crystal growth and lower magnetic properties, so that the reheating temperature is limited to below 1200 ° C. Finishing rolling in hot rolling is finished in ferrite phase and final rolling reduction is 20% or less for plate shape calibrating.

According to one embodiment of the present invention, rolling in the ferrite phase can add a large amount of ferrite-like expansion elements such as Si, Al, P, or less Mn and C, which are elements that suppress ferrite phase, The temperature of the finish rolling may be rolled to a ferrite phase temperature. In particular, when the Si content is 2 wt% or more, hot rolling on ferrite is possible without any control. As described above, when rolled on ferrite, a large number of {100} planes are formed in the texture, thereby improving the magnetic properties.

The hot-rolled sheet prepared as described above is rolled up at 750 ° C or lower and cooled in air. The rolled hot-rolled sheet, if necessary, is subjected to hot-rolled sheet annealing, pickling, cold-rolling, and finally cold-rolled sheet annealing.

The hot-rolled sheet annealing is to anneal the hot-rolled sheet when necessary for improving the magnetic properties, and the hot-rolled sheet annealing temperature is set to 800 to 1200 ° C. If the annealing temperature of the hot-rolled sheet is lower than 800 ° C, the grain growth is insufficient. If the annealing temperature exceeds 1200 ° C, the crystal grains excessively grow and the surface defects of the plate become excessive, Is set at 800 to 1200 ° C.

The hot rolled sheet picked up by a conventional method or the annealed hot rolled sheet is cold rolled.

The cold rolling is final rolled to a thickness of 0.10 mm to 0.70 mm, and if necessary, can be subjected to primary cold rolling and secondary cold rolling after intermediate annealing, and the final rolling reduction is in the range of 50 to 95%.

The final cold-rolled steel sheet is cold-rolled sheet annealed. In the step of annealing the cold rolled sheet, the temperature of the annealing of the cold rolled sheet during the annealing is set to 800 to 1200 占 폚. If the annealing temperature of the cold-rolled sheet is lower than 800 ° C, the growth of the crystal grains is insufficient and the time required for recrystallization is long, which is difficult to realize in the process. When the temperature is higher than 1200 ° C, the crystal grains grow excessively, The cold-rolled sheet has a cracking temperature of 800 to 1200 ° C in an embodiment of the present invention.

The annealed sheet is shipped to the customer after the insulating coating treatment. The insulating coating may be treated with an organic, inorganic and organic composite coating, or may be treated with other insulating coatings. The customer can use the steel sheet after processing.

Hereinafter, a method of manufacturing a non-oriented electrical steel sheet according to the present invention will be described in detail with reference to examples. The following examples are illustrative of the present invention only and are not intended to limit the scope of the present invention.

[Example 1]

The slabs formed as shown in Table 1 below were heated at 1150 占 폚, hot-rolled to a thickness of 2.5 mm, and wound at 650 占 폚. The hot-rolled steel sheet cooled in air was annealed at 1080 ° C for 3 minutes, pickled, and then cold-rolled to a thickness of 0.35 mm. The specimens of the above compositions were subjected to annealing for 1 to 5 minutes under the annealing temperature after hot rolling and the annealing temperature after cold rolling as shown in Table 2. [ The iron loss and magnetic flux density of the specimens were measured using a magnetometer, and the results are shown in Table 2 below.

Steel grade C Si Mn P S Al N Ti Sn Sb A1 15 1.2 0.13 0.05 35 0.002 15 31 0.05 0.01 A2 25 1.5 0.04 0 25 0.003 18 18 0.08 0 A3 22 1.6 0.16 0.09 25 0.012 16 13 0.08 0 A4 51 2.1 0.05 0.05 12 0.002 15 18 0.04 0 A5 21 2.1 0.65 0.09 35 0.003 13 16 0.09 0.1 A6 35 2.2 0.2 0.1 26 0.002 13 12 0.03 0.02 A7 36 2.4 0.05 0.03 48 0.009 28 7 0.05 0.03 A8 21 2.45 0.5 0.15 8 0.015 25 16 0.01 0 A9 26 2.5 0.2 0.003 32 0.01 23 12 0 0 A10 25 2.4 0.25 0.01 65 0.002 19 14 0.01 0.03 A11 30 2.45 0.2 0.05 24 0.05 12 18 0.02 0.01 A12 26 2.4 0.35 0.09 15 0.003 13 14 0.03 0.02 A13 23 2.6 0.4 0.08 16 0.004 25 13 0.06 0.01 A14 15 2.9 0.15 0.02 21 0.001 36 12 0.05 0.01 A15 18 3.3 0.05 0.01 25 0.001 26 11 0.05 0.03

In Table 1, the unit of the component content is% by weight. However, the content of C, S, N, and Ti is in ppm.

Steel grade After hot rolling
The annealing temperature (Th) After cold rolling
The annealing temperature (Tc) Th? Tc Iron loss W15 / 50 Magnetic flux density
B50 Remarks A1 1050 900 O 4.05 1.79 Honor A2 1050 950 O 3.54 1.77 Honor A3 1050 1050 O 3.15 1.77 Honor A4 850 950 X 3.75 1.62 Comparative Example A5 950 1000 X 3.67 1.65 Comparative Example A6 1150 1050 O 2.83 1.76 Honor A7 1150 1100 O 2.71 1.76 Honor A8 950 950 O 3.89 1.65 Comparative Example A9 950 1000 X 3.32 1.63 Comparative Example A10 1050 1000 O 3.18 1.69 Comparative Example A11 1050 1050 O 3.12 1.68 Comparative Example A12 950 1000 X 3.51 1.66 Comparative Example A13 900 900 O 3.01 1.71 Honor A14 950 900 O 1.98 1.72 Honor A15 950 950 O 1.91 1.71 Honor

1) _Iron loss (W _15/50 ) is the average loss (W / kg) in the rolling direction and the rolling direction perpendicular to the magnetic flux density of 1.5 Tesla at 50 Hz frequency.

2) The magnetic flux density (B ₅₀ ) is the magnitude of the flux density (Tesla) induced when a magnetic field of 5000 A / m is added.

As shown in Table 2, the specimens A1, A2, A3, A6, A7, A8, and A8 satisfying the condition that the annealing temperature after hot rolling is higher than the annealing temperature after cold rolling during the manufacturing process of the electric steel sheet according to the embodiment of the present invention, A10, A11, A13, A14, A15.

Of these, Sn, Sb and P are added in an amount of 0.01% to 0.10% by weight or 0.01% to 0.10% by weight, respectively, A3, A6, A7, A13, A14, and A15, which have excellent magnetic flux densities, were investigated.

On the other hand, among the specimens satisfying the range of the above invention, A4 and A12 were found to have low magnetic flux density and magnetic properties because they did not satisfy the condition of Th? Tc.

In addition, A5 satisfies the condition of T _h ? T _c , but the magnetic density and the iron loss are inferior because the condition [Mn] of <0.50% by weight is not satisfied.

In addition, A11 satisfying the condition as above, T _c _h ≥T is [Al] of the conditions of <0.02% by weight of the invention, the magnetic flux density and the iron loss was inferior dissatisfied.

In addition, as described above, A8 which satisfies the condition of T _h ≥T _c was found to have high iron loss due to the content of P exceeding the scope of the present invention and to satisfy the requirement of high iron loss.

In addition, the A10 satisfying the condition of T _h > _Tc is not satisfactory because the content of added S exceeds the range of the invention, so that the iron loss is high even though the precipitate is excessively fished and the magnetic flux density is relatively good .

It was also found that the content of P, Sn, and Sb added in A9 did not satisfy the range of the invention and at the same time, the magnetic flux density was low and the magnetism was heated because T _h ? T _c was not satisfied.

[Example 2]

0.001% of C, 0.002% of N, 0.002% of S, 0.001% of Ti, 0.001% of Ti, and the balance of Fe and 0.003% And other inevitably added impurities was heated at 1150 占 폚, hot-rolled to a thickness of 2.5 mm, and wound at 650 占 폚. The B ₅₀ magnetic flux density according to the annealing temperature after hot rolling and annealing temperature after cold rolling of the hot-rolled sheet is shown in Fig. The hot-rolled steel sheet was annealed for 3 minutes, cold-rolled to 0.35 mm thickness after pickling. Annealing after cold rolling was carried out for 2 minutes.

As shown in FIG. 1, when the annealing temperature (T _h ) after hot rolling is 900 ° C. or more and the annealing temperature (T _h ) after hot rolling is higher than the annealing temperature after cold rolling (T _c ) A non-oriented electrical steel sheet superior in magnetic flux density can be produced.

In FIG. 1, the numbers between the horizontal axis (annealing temperature after cold rolling) and the vertical axis (annealing temperature after hot rolling) are the values representing the magnetic flux density of the final product, and the unit is Tesla.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, You will understand.

It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 1.0 to 3.5% of Si, 0.0005 to 0.02% of Al, 0.01 to 0.50% of Mn, 0.004% or less of C, 0.004% or less of N and 0.004% or less of Ti, Containing impurities,
Sn, Sb, and P, wherein the content of each of the non-oriented electrical steel sheets is higher than the content of Al, and the content thereof is 0.01 to 0.1%.

The method according to claim 1,
Wherein when a plurality of components are selected from Sn, Sb and P, the sum of the contents of the components is not less than the content of Al.

3. The method according to claim 1 or 2,
Further comprising 0.05 wt% or less of Cu, Ni and Cr, respectively, and further containing 0.01 wt% or less of Zr, Mo and V, respectively.

The method of claim 3,
Wherein an average grain size of the steel sheet after annealing the cold-rolled sheet is 30 占 퐉 or more and 1,000 占 퐉 or less.

0.004% or less of N, 0.004% or less of N, or 0.004% or less of Ti, the balance being Fe and other inevitable impurities, in terms of% by weight, Si: 1.0 to 3.5%, Al: 0.005 to 0.02%, Mn: 0.01 to 0.50% And at least one selected from the group consisting of Sn, Sb and P, wherein the content of each selected is higher than the content of Al, and the steel slab having the content of 0.01 to 0.1% is reheated to 1,200 캜 or lower step;
Hot-rolling the reheated steel slab;
Annealing the hot-rolled hot-rolled sheet at a temperature of 900 ° C to 1,200 ° C within 5 minutes; And
Subjecting the hot rolled sheet to cold rolling and annealing the cold rolled sheet at a temperature of 800 to 1,200 ° C within 5 minutes,
Wherein the annealing temperature of the hot-rolled sheet is higher than the annealing temperature of the cold-rolled sheet.

6. The method of claim 5,
Wherein when a plurality of components are selected from Sn, Sb and P, the sum of the contents of the components is equal to or more than the content of Al.

The method according to claim 5 or 6,
Wherein the steel slab further contains 0.05% or less of Cu, Ni and Cr, and further contains 0.01% or less of Zr, Mo and V, respectively.

6. The method of claim 5,
Wherein the cold rolling is cold rolling at least two times with primary cold rolling or intermediate annealing being interposed therebetween.