WO2019132315A1 - Non-oriented electrical steel sheet having excellent shape property, and manufacturing method therefor - Google Patents

Abstract

The present invention relates to a non-oriented electrical steel sheet having an excellent shape property, and a manufacturing method therefor. One embodiment of the present invention provides a non-oriented electrical steel sheet having an excellent shape property, and a manufacturing method therefor, the non-oriented electrical steel sheet comprising Si: 2.8 to 4.0 wt％, Al: 0.1 to 1.5 wt%, Mn: 0.05 to 1.5 wt%, Sn: 0.005 to 0.20 wt%, P: 0.002 to 0.15 wt%, and the balance being Fe and other unavoidable impurities, wherein said Si, Al, Mn, Sn, and P satisfy relational expression 1 below, and a widthwise thickness variation (△t_CR) of a strip satisfies relational expression 2 below. [Relational expression 1] 3.8 ≤ Si+Al+0.5Mn+0.8Sn+5P ≤ 5.4 [Relational expression 2] △t_CR ≤ 36*(S/t)^-0.48 (in relational expression 1 above, Si, Al, Mn, Sn, and P represent the respective amounts (wt%) thereof, and in relational expression 2, △t_CR is a widthwise thickness variation (㎛) of a strip, S is a thickness measurement position (mm) of a point which is separated from a strip widthwise edge by a certain distance, and t is the thickness (mm) of the strip.)

Description

Non-oriented electrical steel sheet excellent in shape quality and manufacturing method thereof

The present invention relates to a non-oriented electrical steel sheet excellent in shape quality and a manufacturing method thereof.

In recent years, due to global warming, environmental regulations around the world have further strengthened, and demand for non-oriented electric steel sheets used for automobile driving motors and generator motors is rapidly increasing due to increase in supply of hybrid cars and electric vehicles. The driving motor and the generator motor are required to be installed in a limited space in the vehicle, and in order to reduce the weight of the vehicle, the downsizing is strongly demanded. In particular, unlike ordinary motors, drive motors among automotive motors have to have excellent electrical characteristics in all areas from low speed to high speed. Therefore, it is necessary to make a large torque at low speed or acceleration, and to reduce loss at constant speed and high speed driving. Suitable properties in the area are needed.

In order to satisfy such a characteristic, it is required to have a large magnetic flux density characteristic at low speed rotation, a high frequency iron loss must be small in high speed rotation region, and a centrifugal force generated at high speed rotation must be endured. . In manufacturing the motor, since the material is slitted and laminated after punching to produce the final part, the thickness deviation in the width direction, that is, the quality of the appearance shape, is considerably important. Therefore, the thickness in the width / length direction must be uniform.

On the other hand, Patent Document 1, for example, discloses a technique relating to a non-oriented electrical steel sheet that improves magnetic properties. Patent Document 1 discloses a non-oriented electrical steel sheet in which 0.1 to 5% of Co is added to steel having Si of 4% or less. In Patent Document 2, the hot-rolled sheet annealing is performed by box annealing with a slow cooling rate by setting the content of P to 0.07 to 0.20% and the content of Si to 0.17 to 3.0%. In the annealing process, There has been proposed a technique for achieving a high density of data. Also, in Patent Document 3, a method of reducing the content of Al by 0.017% or less to achieve high magnetic flux density has been proposed. Patent Document 4 proposes a technique of adding Sb or Sn as an element other than those described above to give a high magnetic flux density. Patent Document 5 proposes a technique of improving magnetic characteristics by controlling Ti, Nb, V and B. In the case of the nonoriented electric steel sheet, most of the technologies for improving the magnetic properties by controlling the alloy components are very small.

[Prior Art Literature]

(Patent Document 1) Japanese Laid-Open Patent Publication No. 2000-129410

(Patent Document 2) Japanese Patent Publication No. 3870893

(Patent Document 3) Japanese Patent Publication No. 4126479

(Patent Document 4) Japanese Patent Publication No. 2500033

(Patent Document 5) Korean Patent Laid-Open No. 10-2016-0078183

One aspect of the present invention is to provide a non-oriented electrical steel sheet excellent in shape quality and a manufacturing method thereof.

The object of the present invention is not limited to the above description. It will be apparent to those skilled in the art that there is no difficulty in understanding the present invention from the broader context of the present invention.

An embodiment of the present invention is a steel sheet comprising, by weight%, 2.8 to 4.0% of Si, 0.1 to 1.5% of Al, 0.05 to 1.5% of Mn, 0.005 to 0.20% of Sn, 0.002 to 0.15% of P, Wherein the Si, Al, Mn, Sn and P satisfy the following relational expression 1 and the thickness variation Δt _{CR in} the width direction of the strip satisfies the following relational expression 2: .

[Relation 1] 3.8? Si + Al + 0.5Mn + 0.8Sn + 5P? 5.4

[Relation 2]? T _CR ? 36 * (S / t) ^-0.48

(In the above relational expression 1, Si, Al, Mn, Sn and P represent the respective contents (% by weight), and? T _CR in the above relational expression 2 is the thicknesswise deviation (Mm), and t is the thickness (mm) of the strip.

Another embodiment of the present invention is a steel sheet comprising, by weight%, 2.8 to 4.0% of Si, 0.1 to 1.5% of Al, 0.05 to 1.5% of Mn, 0.005 to 0.20% of Sn, 0.002 to 0.15% of P, Continuously casting molten steel containing unavoidable impurities and Si, Al, Mn, Sn and P satisfying the following relational expression 1 to obtain a thin slab; Subjecting the thin slab to rough rolling to obtain a bar; Heating the bar; Hot rolling the heated bar to obtain a hot rolled steel sheet; And winding the hot-rolled steel sheet, wherein each of the steps is carried out continuously, cold-rolling the rolled hot-rolled steel sheet to obtain a cold-rolled steel sheet; And recrystallizing and annealing the cold-rolled steel sheet. The method of manufacturing a non-oriented steel sheet excellent in shape quality by applying lubricating oil to the surface of the bar at 5 to 40 L / min per 1 m 2 in the first rolling mill during hot rolling to provide.

[Relation 1] 3.8? Si + Al + 0.5Mn + 0.8Sn + 5P? 5.4

According to an aspect of the present invention, it is possible to provide an electrical steel sheet excellent in shape quality and a method of manufacturing the same using a high speed casting and continuous continuous rolling mode in a performance-to-rolling direct connection process.

The hot-rolled electrical steel sheet produced through the continuous rolling process is much superior in the widthwise thickness deviation of the conventional hot-rolled steel produced through the batch process. Therefore, it is excellent in dimension / shape in the production of the final part, and it is possible to uniformly laminate the material, thereby making it easy to manufacture the part.

 In addition, it is possible to use steel in which scrap of scrap iron or the like is dissolved in an electric furnace through a thin slab-making method, thereby enhancing the recyclability of resources.

1 is a schematic view of a facility for a performance-rolling direct process that can be applied to the present invention.

2 is another schematic diagram of a facility for a performance-rolling direct process that can be applied to the present invention.

3 is a schematic view showing a thickness measurement position and a widthwise thickness deviation at a position a certain distance from the edge in the strip width direction.

4 is a schematic view for explaining the thickness variation in the width direction of the strip.

5 is a widthwise thickness deviation of S / t and a thermal laminate (HR material) of Inventive Steel (Inventive Examples 1 to 19), Comparative Steel (Comparative Examples 1 to 8) and Conventional Steel (Conventional Example 1).

6 is a widthwise thickness deviation of S / t and the final product (CR material) of Inventive Steel (Inventive Examples 1 to 19), Comparative Steel (Comparative Examples 1 to 8) and Conventional Steel (Conventional Example 1).

7 is a widthwise thickness deviation of S / t and a thermal laminate (HR material) of inventive steels (inventive examples 20 to 25) and comparative steels (comparative examples 9 and 10).

8 is a widthwise thickness deviation of the S / t and the final product (CR material) of the inventive steel (Inventive Examples 20 to 25) and the comparative steel (Comparative Examples 9 to 12).

[Description of Symbols]

a: Slab b: Bar

c: Hot-rolled steel sheet

100: continuous casting machine 200, 200 ': heater

300: RSB (Roughing Mill Scale Breaker, rough rolling scale breaker)

400: rough rolling mill

500: FSB (Fishing Mill Scale Breaker, Finishing Rolled Scale Breaker)

502: Cooling water injection nozzle

504: Cooling water

600: finishing mill 700: run-out table

800: High speed shear machine 900: Winder

Conventionally, in the conventional hot melt mill process, slabs having a thickness of 200 mm or more are produced through low speed casting, and the slabs thus produced are reheated in a heating furnace and are reduced in thickness by hot rolling in a batch form. In the case of this type of batch rolling, since the top portion is drawn into the rolling mill for each slab and the tail portion must escape from the rolling mill, a frequent accident occurs in the operation, so that an electric steel sheet having excellent hot- There are a lot of limitations.

The inventors of the present invention have pointed out that the problem of manufacturing such an electric steel sheet can be solved when a manufacturing process (mini-mill process) using a so-called thin slab, particularly a continuous casting (performance) Leading to the present invention.

In other words, the process of direct rolling of the steel to the rolling process is excellent in the material deviation because the width of the strip and the temperature deviation in the longitudinal direction are small due to the process characteristic of constant velocity isotherm. In addition, unlike conventional processes in which the slabs or bars are finely rolled in batches, only the first slab or the top portion of the bar is drawn between rolls and rolls of the rolling mill, It is possible to drastically reduce the possibility of a problem of accident involving the introduction of a slab or a bar. In addition, since it produces products through constant velocity isothermal rolling, it is considered to be a suitable process for manufacturing hot-rolled steel sheets because it has the advantages of excellent dimensional accuracy of thickness and width compared with existing batch materials and low crown crowns .

In addition, the electric steel sheet produced by the direct rolling process from the performance to the rolling has excellent performance in terms of the inner material as compared with the electric steel sheet produced by the conventional batch rolling method.

Hereinafter, the electric steel sheet of the present invention and its manufacturing method will be described in detail.

 First, the alloy composition of the electric steel sheet of the present invention will be described. The alloy composition described below is based on weight percent unless otherwise specified.

Si: 2.8 to 4.0%

Silicon (Si) is generally added as a deoxidizing agent in steel, but it is an important element in an electric steel sheet because it has an effect of reducing an iron loss at a high frequency by increasing an electric resistance. In order to obtain such effect, addition of 2.8% or more is required. However, if it exceeds 4.0%, the rolling load during cold rolling may increase, resulting in a defective shape. Therefore, the Si content is preferably 2.8 to 4.0%, more preferably 3.0 to 3.8%, and even more preferably 3.1 to 3.7%.

Al: 0.1 to 1.5%

Aluminum (Al) is generally used as a deoxidizing agent for steel, like Si, and is an element having a large effect of decreasing iron loss by increasing electrical resistance. However, if it exceeds 1.5%, casting may be interrupted due to lack of lubrication and physical properties of the mold flux may be picked up in the mold flux during continuous casting, and the rolling load during cold rolling may increase, Lt; / RTI > Therefore, the Al content is preferably 0.1 to 1.5%, more preferably 0.2 to 1.3%, and even more preferably 0.3 to 1.0%.

Mn: 0.05 to 1.5%

Since manganese (Mn) is an element capable of raising the resistivity in the steel and lowering iron loss, it is preferable to add Mn of 0.05% or more. However, when it exceeds 1.5%, there is a disadvantage that it forms a coarse MnS precipitate in combination with the steel S to form an austenite phase in the annealing temperature range of the present invention, and makes it difficult to coarsen crystal grains for iron loss reduction . Therefore, the Mn is preferably in the range of 0.05 to 1.5%, more preferably 0.1 to 1.3%, still more preferably 0.2 to 1.0%.

Sn: 0.005 to 0.20%

Tin (Sn) suppresses the diffusion of nitrogen through the grain boundaries as a grain boundary element and inhibits formation of {111}, {112} texture which is harmful to magnetism and increases {100} and {110} It is preferably added in an amount of 0.005% or more in order to improve the magnetic properties and to increase the effect of addition. However, when it is added in an amount exceeding 0.20%, crystal growth is inhibited and the magnetic property is lowered and the rolling property is weakened. Therefore, the Sn content is preferably 0.005 to 0.20%, more preferably 0.01 to 0.15%, still more preferably 0.02 to 0.10%.

P: 0.002 to 0.15%

Phosphorus (P) is an element capable of increasing iron specific resistance and lowering iron loss, and is an element capable of improving magnetic flux density when added as a magnetic material. It is preferable to add 0.002% or more for the above effect. However, if it exceeds 0.15%, there is a disadvantage that it is present as a segregation element which induces the fracture of the rolled plate in the ferrite grain boundary at the room temperature rolling, and weakens the bonding force between grain boundaries to a great extent. Therefore, the P content is preferably in the range of 0.002 to 0.15%, more preferably 0.004 to 0.10%, still more preferably 0.006 to 0.05%.

In the non-oriented electrical steel sheet of the present invention, it is preferable that Si, Al, Mn, Sn and P satisfy the following relational expression (1). If the value of Si + Al + 0.5Mn + 0.8Sn + 5P is more than 5.4 in the above relational expression 1, the yield strength of the thermal laminate becomes too high, so that the appearance quality of the final product It can fall. On the other hand, if it is less than 3.8, the component content is low and the desired resistivity and yield strength of the final product may not be satisfied.

[Relation 1] 3.8? Si + Al + 0.5Mn + 0.8Sn + 5P? 5.4

(Si, Al, Mn, Sn and P in the above relational expression 1 represent the content (% by weight), respectively).

The remainder of the present invention is iron (Fe). However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of manufacturing.

On the other hand, the electrical steel sheet of the present invention contains at least one of C, S, and N as impurities in a total amount of 0.05 wt% or less in addition to the above alloy composition, and Nb, V, Ti, Mo, Cu , And at least one selected from the group consisting of Cr, Ni, Zn, Se, Sb, Zr, W, Ga, Ge and Mg in a total amount of not more than 0.2%. When the total of at least one of C, S and N is less than 0.05% by weight, carbonitrides, sulfides and the like may be formed and the iron loss may be large. The tramp element is an impurity element derived from scrap used as a raw material in the steelmaking process, ladle, tundish refractory or the like. When the total amount exceeds 0.2%, the tramp element is liquefied at a high temperature to deteriorate performance , Precipitates, sulfides and inclusions may be formed to deteriorate iron loss.

In the non-oriented electrical steel sheet of the present invention, it is preferable that the thickness variation Δt _{CR in} the width direction of the strip satisfies the following relational expression (2). When satisfying the following expression (2), it is possible to secure a superior appearance shape quality. On the other hand, the smaller the value of the relational expression 2 is, the more excellent the appearance quality can be secured.

[Relation 2]? T _CR ? 36 * (S / t) ^-0.48

(In the above-mentioned relational expression 2, Δt _CR is the thickness deviation (μm) in the width direction of the strip, S is the thickness measurement position (mm) at a distance from the edge in the strip width direction, and t is the thickness box.)

The thickness of the non-oriented electrical steel sheet provided by the present invention is preferably 0.15 to 0.35 mm. When the thickness is less than 0.15 mm, the productivity decreases. When the thickness exceeds 0.35 mm, the iron loss reduction effect may be small, and the widthwise thickness deviation may be increased.

In addition, the electrical steel sheet may have a resistivity of 50 to 65 占 cm and a yield strength in the rolling horizontal direction (L direction) of 415 MPa or more.

Hereinafter, a method for manufacturing a non-oriented electrical steel sheet of the present invention will be described.

1 is a schematic view of a facility for a performance-to-rolling direct process that can be applied to the present invention, and is a schematic diagram of a performance-to-rolling direct process facility applicable to the manufacture of hot rolled steel sheets for obtaining a final electrical steel sheet. The steel slabs of excellent shape quality according to one embodiment of the present invention can be manufactured from the hot-rolled steel sheets produced by applying the direct rolling-to-rolling direct connection equipment as shown in Fig. The performance-to-rolling direct connection facility consists largely of a continuous casting machine 100, a roughing mill 400, and a finishing mill 600. The performance-to-rolling direct connection plant comprises a high-speed continuous casting machine (100) producing a thin slab (a) of a first thickness and a rolling bar (b) of a second thickness thinner than the first thickness A rough rolling mill 600 for rolling the bars of the second thickness to a hot rolled steel sheet c of a third thickness, and a winder 900 for winding the hot rolled steel sheet. A roughing scale breaker 300 and a finishing mill scale breaker 500 are placed in front of the roughing mill 400 and before the finishing mill 600, FSB '), and it is possible to produce an electrical steel sheet having excellent surface quality in the post-process because of easy removal of the surface scale. In addition, it is possible to perform isothermal constant speed rolling through the process of rolling to rolling, so that the steel plate width and longitudinal temperature deviation are remarkably low, so precise cooling control is possible in ROT [Run Out Table (700)] It is possible to produce a hot rolled steel sheet having excellent isotropic properties. The hot-rolled steel sheet thus rolled and cooled can be cut by a high-speed shear machine 800 and wound by a winder 900 to be produced as a product. Meanwhile, the finishing rolling scale breaker 500 may be provided with a heater 200 for further heating the bar.

2 is another schematic diagram of a facility for a performance-rolling direct process that can be applied to the present invention. The apparatus for direct rolling-to-rolling process disclosed in FIG. 2 is substantially identical in construction to the apparatus disclosed in FIG. 1, but includes a heater 200 'for further heating a slab in front of the rough rolling mill 400, It is possible to lower the occurrence of edge defects and is advantageous in securing the surface quality. In addition, a space of at least one slab length is secured before the roughing mill, and batch rolling is possible.

The hot rolled steel sheet having excellent magnetic properties and shapes of the present invention can be produced in all of the performance-rolling direct connection facilities disclosed in Figs. 1 and 2.

First, molten steel having the above-described alloy composition is continuously cast to obtain a thin slab. At this time, the continuous casting is preferably performed at a casting speed of 3.5 to 8.0 mpm (m / min). The reason why the casting speed is set to 3.5 mpm or more is that a high speed casting and a rolling process are connected and a casting speed higher than a certain level is required to secure the target rolling temperature. If the casting speed is less than 3.5 mpm, Al may increase the amount of pick-up in the mold flux, thereby changing the physical properties of the mold flux, resulting in reduced lubricity and casting failure. If it exceeds 8.0 mpm, the operation success rate may be reduced due to instability of the molten steel bath surface. Therefore, the casting speed is preferably in the range of 3.5 to 8.0 mpm, more preferably 4.0 to 7.5 mpm , And more preferably in the range of 4.5 to 6.5 mpm.

The thickness of the thin slab is preferably 80 to 120 mm. When the thickness of the thin slab is more than 120 mm, high-speed casting is difficult, and the rolling load during rough rolling is increased. When the thickness is less than 80 mm, the temperature of the cast steel is rapidly decreased and uniform structure is hardly formed. In order to solve this problem, it is possible to additionally provide a heating apparatus, but this is a factor for improving the production cost, so it is preferable to exclude it. Therefore, the thickness of the thin slab is preferably controlled to 80 to 120 mm, more preferably 80 to 115 mm, and even more preferably 90 to 110 mm.

Thereafter, the continuously cast thin slab is rough-rolled to obtain bars. At this time, the thickness of the bar is preferably 10 to 30 mm. If the thickness of the bar exceeds 30 mm, the rolling load due to the increase in the reduction rate during the finish rolling may increase sharply and the thickness variation in the width direction in the strip may be worsened. If the thickness is less than 10 mm, the resistance to rolling deformation becomes large, And it is difficult to secure the temperature during finish rolling. The thickness of the bar is preferably in the range of 10 to 30 mm, more preferably in the range of 12 to 28 mm, and even more preferably in the range of 14 to 26 mm.

On the other hand, the inlet temperature during the rough rolling may be 1000 to 1200 ° C. If the rough rolling inlet temperature is less than 1000 캜, an increase in the rough rolling load and cracks may occur in the edges of the bars. On the other hand, if it is higher than 1200 ° C, the hot-rolled scale remains and the quality of the hot-rolled surface may deteriorate. The temperature at the time of rough rolling is preferably in the range of 1000 to 1200 ° C, more preferably in the range of 1020 to 1180 ° C, and even more preferably in the range of 1040 to 1160 ° C.

The temperature at the time of rough rolling may be 900 ° C or higher. If it is less than 900 ° C, it is difficult to secure the finishing rolling temperature.

The bar is then heated. The heating temperature of the bar is preferably 1000 to 1200 ° C. The reason for controlling the heating temperature of the bar is to stably produce the hot rolled steel sheet and to secure the surface quality. If the temperature is less than 1000 ° C, the finish rolling rolling temperature is lowered and the rolling load is rapidly increased, Plate breakage may occur. If the temperature exceeds 1200 ° C, the scale may be excessively generated and the surface quality may be deteriorated. The heating temperature of the bar is preferably in the range of 1000 to 1200 ° C, more preferably in the range of 1020 to 1180 ° C, and even more preferably in the range of 1040 to 1160 ° C.

Thereafter, the heated bar is hot-finished and rolled to obtain a hot-rolled steel sheet. The finish rolling can be performed in a finishing mill having 3 to 6 stands. The finish rolling is preferably performed at 650 to 900 ° C. If the finish rolling temperature exceeds 900 ° C, the scale may be excessively generated and the surface quality may be deteriorated. Since the high temperature ductility is too high, plate breakage may occur due to excessive tension control. On the other hand, when the temperature is less than 650 ° C, the strength rapidly increases, so that plate rupture may occur due to poor ductility due to an increase in the rolling load. The finishing rolling preferably has a range of 650 to 900 ° C, more preferably a range of 670 to 880 ° C, and still more preferably a range of 690 to 860 ° C.

It is preferable that the average passing speed during the final rolling at the time of the hot rolling is 250 to 750 mpm. In the finish rolling, the passing speed in the last rolling mill can be directly connected to the casting speed and the thickness of the hot rolled product. If the rolling speed in the last rolling mill is more than 750 mPm, it is possible to cause an accident such as a plate rupture, and since a uniform temperature is not secured due to difficulty in isothermal constant rolling, a material and thickness variation may occur . On the other hand, in the case of less than 250 mpm, the final rolling speed is too slow, which may cause problems in mass balance and heat balance, and it may be difficult to carry out continuous continuous rolling. The average passing speed during the final rolling in the hot rolling is preferably in the range of 250 to 750 mpm, more preferably 270 to 730 mpm, and even more preferably 290 to 710 mpm.

In addition, it is preferable to control the speed deviation to 50 mpm or less during the production of one strip in the final rolling in the hot rolling. If the difference in speed of the last rolling mill exceeds 50 mpm, the temperature and rolling load become uneven, resulting in material and thickness variations of the hot rolled steel sheet, and uneven rolling during cold rolling can increase the thickness variation of the final product. The speed deviation is preferably 50 mpm or less, more preferably 45 mpm or less, and even more preferably 40 mpm or less.

On the other hand, during the hot finish rolling, lubricating oil is applied to the surface of the bar to decrease the friction coefficient between the bar and the rolling roll, thereby reducing the rolling load, thereby reducing the thickness deviation. Preferably, the lubricating oil is applied in the first rolling mill having a very high rolling load during the hot finishing rolling. It is preferable that the lubricating oil is applied to the surface of the bar at a rate of 5 to 40 L / min per 1 m2. When the application of the lubricating oil is less than 5 L / min, the effect described above is insignificant. If the lubricating oil is more than 40 L / min, the manufacturing cost may be increased due to excessive use of the lubricant. During the hot rolling, the lubricating oil is preferably applied to the surface of the bar at a rate of 5 to 40 L / min per 1 m2 of the surface of the bar, more preferably at 7 to 38 L / min per 1 m2 of the surface of the bar , And more preferably 9 to 36 L / min per 1 m < 2 > on the surface of the bar.

Thereafter, the hot-rolled steel sheet is wound. The coiling temperature is preferably 480 to 700 ° C. When the coiling temperature is less than 480 캜, the yield strength is too high, so that the rolling load during cold rolling may increase, leading to a large thickness deviation in the width direction due to poor ductility. When the coiling temperature exceeds 700 캜, It is advantageous for the control, but the secondary scale may be generated and the quality such as the illuminance and the surface whiteness may be deteriorated. The coiling temperature is preferably 480 to 700 占 폚, more preferably 490 to 690 占 폚, and still more preferably 500 to 680 占 폚.

The hot-rolled steel sheet preferably has a thickness of 1.8 mm or less. As the thickness of the steel sheet is reduced, the recrystallized texture increases, uniform structure after annealing can be secured, the crystal orientation of the? -Fiber can be reduced by decreasing the cold rolling reduction and the magnetic property can be improved, Can also be reduced. However, if it exceeds 1.8 mm, the above effect may not be sufficient. Therefore, the thickness of the hot-rolled steel sheet is preferably 1.8 mm or less, more preferably 1.6 mm or less.

It is preferable that the thickness deviation in the width direction of the strip of the hot-rolled steel sheet satisfies the following relational expression (3). The lower the value of? T _HR is, the better the appearance quality of the finished product can be given to the final product after cold rolling.

[Relation 3]? T _HR ? 230 * (S / t) ^-0.50

(Where, △ t _HR is a width direction thickness of a hot rolled steel sheet deviation (㎛), S is a predetermined distance position (mm) the thickness measurement of the position apart from the hot-rolled steel plate width direction edge, t is the thickness (mm) of the hot rolled steel sheet Meaning.)

The hot-rolled steel sheet preferably has a yield strength average value of 750 MPa or less in the rolling horizontal direction (L direction) and the vertical direction (C direction), and preferably satisfies the following relational expression (4). When the value of Si + Al + Mn / 2-t / 5 is more than 5.0 in the following relational expression 4, the yield strength of the hot-rolled steel sheet exceeds 750 MPa and the rolling load during cold rolling increases sharply, , And when the value of Si + Al + Mn / 2-t / 5 is less than 3.0, it may be difficult to secure the yield strength of the target final product.

[Relation 4] 3.0? Si + Al + Mn / 2? T / 5? 5.0

(Si, Al and Mn represent the respective contents (% by weight) and t represents the thickness (mm) of the hot-rolled steel sheet in the relational expression 4)

On the other hand, the above-described method for producing a hot-rolled steel sheet is characterized in that the above-described respective steps are performed continuously by using the continuous rolling mode in the performance-to-rolling direct connection process.

Thereafter, the rolled hot-rolled steel sheet is cold-rolled to obtain a cold-rolled steel sheet. On the other hand, before the cold rolling, a step of pickling the hot-rolled steel sheet to remove the oxide layer may be further included. The pickling can be carried out under ordinary conditions, and the pickling treatment that can be used in the present invention is not particularly limited as long as it is applicable to any treatment method used in the process of pickling an electrical steel sheet.

Thereafter, the cold-rolled steel sheet is recrystallized and annealed. The above-mentioned recrystallization annealing can also be carried out under the conditions conventionally used in the related art.

Hereinafter, the present invention will be described in more detail with reference to Examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

(Example 1)

The molten steel having the alloy composition shown in the following Table 1 was prepared, and then the molten steel was continuously cast at a casting speed of 5.8 mpm by applying a direct rolling process to obtain a thin slab having a thickness of 90 mm. The thin slab was rough- Thereafter, the above bars were subjected to finish rolling under the manufacturing conditions shown in Table 2 to obtain Hot Rolled (HR) having a thickness of 1.2 to 1.8 mm, followed by cold rolling at a reduction ratio of 79 to 85% to obtain 0.25 / Cold rolled steel sheet having a thickness of 5 mm was manufactured and then subjected to annealing to produce a final product. Annealing conditions at the time of annealing were a line speed (Line Speed) of 170 mpm, a heating zone temperature of 780 캜, and a cracking zone temperature of 850 캜. On the other hand, in the case of Conventional Example 1, a hot-rolled steel sheet having a thickness of 1.6 mm was produced in a conventional batch process under the manufacturing conditions shown in Table 2, after casting a slab having a thickness of 200 mm in a conventional hot- Rolled and annealed to produce a 0.27 mm thick final product.

For example, edge-to-25 mm, edge-to-100 mm, etc., at a point spaced a certain distance from the edges of the strip widthwise direction of the resistivity, thermal laminate and final product with respect to the inventive example, comparative example, The thickness deviation in the width direction and the yield strength were measured, and the results are shown in Table 3 below. 3 is a schematic view showing a thickness measurement position and a widthwise thickness deviation at a position a certain distance from the edge in the strip width direction.

As shown in Fig. 4, the widthwise thickness deviation is calculated by dividing the thickness of the center portion (C _t ) in the width direction of the strip and the thickness average [E 1 _{x t} + E2x _t ) / 2]. The smaller the value, the better the appearance quality of the strip. In addition, the widthwise thickness deviation of the thermal extension and the final product means the average value of the top, middle and tail. 4 is a schematic view for explaining the thickness variation in the width direction of the strip.

JIS 5 specimens were used for the yield strength and specimens were taken from the vertical direction (C direction) and horizontal direction (L direction) of the rolled steel sheet, and the results were averaged. The final product was measured in the horizontal direction The results are shown in Table 3 below. ≪ tb > < TABLE >

division	Steel grade	Alloy composition (% by weight)					Relationship 1
		Si	Al	Mn	Sn	P
Inventive Steel 1	A	3.42	0.72	0.36	0.057	0.008	4.41
Invention river 2	B	3.25	0.35	0.52	0.032	0.011	3.94
Invention steel 3	C	3.7	0.56	0.36	0.06	0.007	4.52
Inventive Steel 4	D	3.1	One	0.36	0.05	0.01	4.37
Invention steel 5	E	3.62	0.75	0.32	0.052	0.015	4.65
Invention steel 6	F	3.15	0.95	0.62	0.045	0.01	4.5
Invention steel 7	H	3.35	0.79	0.75	0.059	0.009	4.61
Inventive Steel 8	I	3.65	1.01	0.62	0.051	0.011	5.07
Invention river 9	J	3.65	0.55	0.56	0.045	0.012	4.58
Invented Steel 10	K	3.8	0.56	0.35	0.039	0.016	4.65
Invention steel 11	L	3.23	0.98	0.46	0.061	0.011	4.54
Invention steel 12	M	3.9	0.36	0.35	0.052	0.011	4.53
Invention steel 13	N	3.15	0.89	0.69	0.049	0.012	4.48
Comparative River 1	O	4.1	1.25	0.52	0.032	0.011	5.69
Comparative River 2	P	4.02	1.2	0.62	0.052	0.012	5.61
Comparative Steel 3	Q	4.12	0.95	0.52	0.052	0.011	5.43
Comparative Steel 4	R	4.53	0.68	0.32	0.039	0.015	5.48
Comparative Steel 5	S	2.55	0.35	0.52	0.052	0.012	3.51
Comparative Steel 6	T	2.65	0.25	0.36	0.045	0.011	3.42
Comparative Steel 7	U	2.42	0.55	0.5	0.049	0.015	3.61
Invented Steel 14	V	3.41	0.7	0.41	0.053	0.007	4.39
[Relation 1] Si + Al + 0.5Mn + 0.8Sn + 5P

division	Steel grade	Thermal Thickness (mm)	Finishing rolling (finishing rolling)				Coiling temperature (캜)	Cold rolling reduction (%)	Final product thickness (mm)
			The amount of lubricating oil at the first rolling mill inlet (l / min per 1 m 2)	Coefficient of Friction (μ)	Last mill average speed (mpm)	Final mill speed deviation (mpm)
Inventory 1	A	1.2	25	0.36	450	25	592	79	0.25
Inventory 2		1.3	25	0.35	415	26	582	79	0.27
Inventory 3		1.4	25	0.36	385	25	591	81	0.27
Honorable 4		1.6	25	0.36	335	23	600	83	0.27
Inventory 5	B	1.4	30	0.34	385	23	601	81	0.27
Inventory 6		1.6	30	0.34	335	25	589	83	0.27
Honorable 7		1.8	25	0.35	300	31	595	85	0.27
Honors 8	C	1.4	15	0.37	385	26	589	81	0.27
Proposition 9		1.8	10	0.37	300	25	592	85	0.27
Inventory 10	D	1.4	20	0.36	385	22	589	81	0.27
Exhibit 11	E	1.4	20	0.36	385	23	595	81	0.27
Inventory 12	F	1.4	20	0.36	385	22	599	81	0.27
Inventory 13	H	1.4	20	0.36	385	22	601	81	0.27
Inventory 14	I	1.4	20	0.36	385	22	596	81	0.27
Honorable Mention 15	J	1.4	20	0.36	385	23	589	81	0.27
Inventory 16	K	1.4	30	0.36	385	21	591	81	0.27
Inventory 17	L	1.4	30	0.36	385	25	598	81	0.27
Inventory 18	M	1.4	30	0.36	385	22	585	81	0.27
Evidence 19	N	1.4	10	0.37	385	25	590	81	0.27
Comparative Example 1		1.4	3	0.41	385	25	860	81	0.27
Comparative Example 2	O	1.4	20	0.36	385	25	592	81	0.27
Comparative Example 3	P	1.4	15	0.37	385	24	588	81	0.27
Comparative Example 4	Q	1.4	25	0.36	385	23	594	81	0.27
Comparative Example 5	R	1.4	20	0.34	385	25	597	81	0.27
Comparative Example 6	S	1.4	24	0.33	385	22	608	81	0.27
Comparative Example 7	T	1.4	20	0.34	385	25	605	81	0.27
Comparative Example 8	U	1.4	15	0.32	385	26	601	81	0.27
Conventional Example 1	V	1.6	-	-	750	200	600	83	0.27

division	Resistivity (μΩ · cm)	Rolling load reduction rate (%)	Rolling load deviation (ton)	Heat series						Final product
				Thickness deviation in the width direction (占 퐉)				Rolling vertical and horizontal average yield strength (MPa)	Relation 4	Thickness deviation in the width direction (占 퐉)				Rolling horizontal yield strength (MPa)
				25mm	100mm	200mm	300mm			25mm	50mm	100mm	200mm
Inventory 1	56	15	49	28	9	4	3	669	4.1	1.50	1.25	1.05	0.50	444
Inventory 2	56	15	51	29	10	5	4	667	4.1	1.60	1.50	1.06	0.71	442
Inventory 3	56	15	50	31	11	7	4	666	4.0	1.80	1.62	1.55	1.15	439
Honorable 4	56	15	48	35	14	9	4	663	4.0	2.10	1.95	1.71	1.21	438
Inventory 5	53	18	48	32	12	8	3	627	3.6	1.70	1.59	1.51	1.02	431
Inventory 6	53	19	45	35	15	9	5	624	3.5	2.20	2.01	1.82	1.35	435
Honorable 7	53	15	56	41	21	14	8	621	3.5	3.00	2.86	2.13	1.68	429
Honors 8	59	12	49	31	11	5	3	680	4.2	2.10	1.85	1.75	1.26	452
Proposition 9	59	9	47	45	23	13	6	674	4.1	2.90	2.55	2.25	1.68	447
Inventory 10	55	13	48	30	11	6	4	656	4.0	1.70	1.45	1.32	0.82	445
Exhibit 11	60	13	49	32	12	7	3	685	4.3	1.80	1.62	1.52	1.09	451
Inventory 12	58	13	48	32	13	8	3	666	4.1	1.70	1.45	1.32	0.75	446
Inventory 13	56	13	48	33	12	6	3	678	4.2	1.80	1.52	145	0.85	449
Inventory 14	64	13	48	38	18	10	7	718	4.7	1.80	1.67	1.32	0.79	464
Honorable Mention 15	57	13	49	31	11	7	4	682	4.2	1.90	1.75	1.53	0.95	449
Inventory 16	60	19	46	32	12	6	4	689	4.3	2.00	1.91	1.78	1.32	452
Inventory 17	61	19	47	30	11	5	3	670	4.2	1.90	1.85	1.66	1.16	452
Inventory 18	58	19	43	29	10	6	4	684	4.2	1.80	1.68	1.52	1.02	447
Evidence 19	57	10	47	31	12	7	5	664	4.1	1.80	1.61	1.43	0.95	443
Comparative Example 1	57	3	51	63	38	32	15	669	4.1	4.31	3.51	2.69	1.89	446
Comparative Example 2	69	13	47	51	32	25	14	775	5.3	4.55	3.58	2.70	2.05	482
Comparative Example 3	70	12	47	60	39	31	14	768	5.3	4.40	3.45	2.61	1.95	492
Comparative Example 4	68	15	46	53	32	25	15	755	5.1	4.20	3.41	2.52	2.09	473
Comparative Example 5	67	13	47	58	38	31	14	767	5.1	4.25	3.42	2.56	1.94	475
Comparative Example 6	45	14	42	29	10	6	4	561	2.9	1.80	1.62	1.51	1.01	401
Comparative Example 7	44	13	45	31	11	5	4	557	2.8	1.70	1.53	1.34	0.85	395
Comparative Example 8	46	12	47	30	13	7	4	563	2.9	1.70	1.52	1.35	0.75	405
Conventional Example 1	56	-	1600	59	39	29	15	642	4.0	5.90	3.82	2.61	2.01	425
[Relation 4] Si + Al + Mn / 2-t / 5

As can be seen from Tables 1 to 3, Inventive Examples 1 to 19, which satisfy both the alloy composition, the component relation and the manufacturing conditions proposed in the present invention, satisfy both the thickness variation in the width direction and the yield strength , And the thickness deviation and the yield strength in the width direction of the final product are all satisfied. In the case of Inventive Examples 1 to 19, the widthwise thickness variation (crown) of the thermal expansion material is significantly lower than that of Conventional Example 1, and the thickness variation in the width direction of the final product is also very small. Therefore, in the case of Inventive Examples 1 to 19, it can be seen that the quality of the appearance quality of the conventional example 1 is very excellent.

Comparative Example 1 does not satisfy the amount of lubricating oil applied in the first rolling mill at the finish rolling proposed in the present invention, so that the rolling load is high and it can be understood that the target thickness deviation in the width direction is not satisfied.

In Comparative Examples 2 to 5, the value of Si + Al + 0.5Mn + 0.8Sn + 5P in Relation 11 exceeded 5.4, and in the case of not satisfying Relational Expression 4, the thickness deviation in the width direction was large, High level.

In Comparative Examples 6 to 8, the value of Si + Al + 0.5Mn + 0.8Sn + 5P in Relation 1 was less than 3.8, and the relation 4 was not satisfied, and the target specific resistance and the yield strength of the final product were not satisfied I can not see that.

On the other hand, FIG. 5 is a graph examining the correlation between the S / t and the thermal gradient widthwise thickness deviation for Inventive Examples 1 to 19, Comparative Examples 1 to 8, and Conventional Example 1. FIG. As can be seen from FIG. 5, the S / t and thickness-direction thickness deviations of inventive steels (Inventive Examples 1 to 19) have the relationship as shown in Equation 1, and the comparative steels (Comparative Examples 2 to 5) And Conventional Example 1 has the same relationship as Equation 3.

[Derivation 1] Thickness variation in thickness in the width direction (? T _HR ) = 373 * (S / t) ^-0.82

[Derived expression 2] Comparative example Thickness deviation in the width direction (? T _HR ) = 231 * (S / t) ^-0.47

[Equation 3] Conventional example Thickness deviation in the width direction (? T _HR ) = 241 * (S / t) ^-0.49

(Where S is the thickness measurement position (mm) at a position a certain distance from the edge in the width direction of the hot-rolled steel sheet and t is the thickness (mm) of the hot-rolled steel sheet).

From the relationship between Table 3 and FIG. 5 and Derived Equations 1 to 3, it can be seen that the strip prepared according to the present invention is much superior to the comparative example and the conventional example 1 in appearance quality. Therefore, in the case of the invention example, it is preferable to satisfy the following relational expression 3 in order to improve the appearance quality of the conventional example 1.

Fig. 6 is a graph examining the correlation between the S / t and the thickness deviation in the width direction of the final product for Inventive Examples 1 to 19, Comparative Examples 1 to 8 and Conventional Example 1. Fig. From these results, it can be understood that the S / t and the lateral thickness deviation of the inventive steel (Inventive Examples 1 to 19) have the relationship as shown in Equation 4, the comparative steels (Comparative Examples 2 to 5) It can be seen that Conventional Example 1 has the same relationship as Equation 6.

[Equation 4] Thickness deviation in the width direction of the invention (Δt _CR ) = 7.5 * (S / t) ^-0.29

[Equation 5] Thickness deviation (Δt _CR ) in the comparative steel width direction = 36 * (S / t) ^-0.46

[Equation 6] Conventional thickness direction thickness deviation? T _CR = 60 * (S / t) ^-0.49

(Where S is the thickness measurement position (mm) at a position a certain distance from the edge in the strip width direction and t is the thickness (mm) of the strip).

(Example 2)

The relationship between the thickness deviation in the transverse direction of the thermal laminate, the yield strength and the thickness deviation in the width direction of the final product according to the first rolling mill speed deviation and the coiling temperature at the finish rolling of the steel 1 (steel piece A) The results are shown in Tables 4 and 5 below.

division	Steel grade	Thermal Thickness (mm)	Finishing rolling (finishing rolling)			Coiling temperature (캜)	Final product thickness (mm)
			The amount of lubricating oil at the first rolling mill inlet (l / min per 1 m 2)	Coefficient of Friction (μ)	The final rolling speed difference (mpm)
Inventory 20	A	1.4	20	0.36	26	601	0.27
Inventory 21		1.4	20	0.36	30	595	0.27
Inventory 22		1.4	15	0.37	35	605	0.27
Comparative Example 9		1.4	25	0.36	62	592	0.27
Comparative Example 10		1.4	20	0.36	85	600	0.27
Invented steel 23		1.4	20	0.36	27	552	0.27
Invented Steel 24		1.4	25	0.36	26	515	0.27
Comparative Example 11		1.4	15	0.37	27	440	0.27
Comparative Example 12		1.4	20	0.36	28	462	0.27
Honors 25		1.4	20	0.36	27	486	0.27

division	Pressure drop rate (%)	Rolling load deviation (ton)	Heat series					Final product
			Thickness deviation in the width direction (占 퐉)				Average yield strength in the vertical and horizontal directions (MPa)	Thickness deviation in the width direction (占 퐉)
			25mm	100mm	200mm	300mm		25mm	50mm	100mm	200mm
Inventory 20	13	47	30	11	6	5	665	1.91	1.62	1.55	1.15
Inventory 21	13	55	32	12	7	4	664	2.02	1.62	1.55	1.14
Inventory 22	12	61	35	14	8	6	665	2.05	1.75	1.62	1.26
Comparative Example 9	15	87	59	35	26	18	669	4.31	3.30	2.79	1.90
Comparative Example 10	13	105	68	59	37	16	672	4.72	3.35	2.88	2.08
Invented steel 23	13	49	31	12	6	4	692	2.21	1.62	1.55	1.15
Invented Steel 24	15	48	32	11	7	4	705	2.51	2.55	2.15	1.78
Comparative Example 11	12	48	31	12	6	5	761	4.23	3.39	2.79	1.94
Comparative Example 12	12	49	32	13	9	6	752	4.45	3.39	2.92	1.85
Honors 25	13	48	32	14	11	6	730	3.35	2.75	1.97	1.35

As can be seen from Tables 4 and 5, Inventive Samples 20 to 25, which satisfy both the alloy composition, the component relation and the manufacturing conditions proposed in the present invention, satisfy both the thickness variation in the width direction and the yield strength , And the thickness deviation and the yield strength in the width direction of the final product are all satisfied.

The comparative examples 9 and 10 do not satisfy the velocity deviation in the final rolling mill proposed in the present invention, and it can be seen that the widthwise thickness deviation of the thermal laminate and the final product is severe.

In Comparative Examples 11 and 12, since the coiling temperature proposed in the present invention is not satisfied, it can be seen that the yield strength average value in the horizontal direction (L direction) and the vertical direction (direction C) It can be seen that the thickness deviation in the width direction of the final product is severe.

Figs. 7 and 8 are graphs for examining the correlation between S / t of Inventive Samples 20 to 25 and Comparative Examples 9 to 12 and the widthwise thickness deviation of the thermal laminate and the final product, respectively. As can be seen from the results, in the case of the inventive example in which the velocity deviation and the coiling temperature in the last mill proposed in the present invention satisfy the relational expressions 2 and 3, the comparative examples 9 to 12 do not satisfy the relational expressions 2 and 3, It can be seen that the thickness variation in the width direction is severely generated.

Claims (19)

1. And a balance of Fe and other unavoidable impurities, wherein the content of Si is from 2.8 to 4.0%, Al is from 0.1 to 1.5%, Mn is from 0.05 to 1.5%, Sn is from 0.005 to 0.20%, P is from 0.002 to 0.15%

   Wherein Si, Al, Mn, Sn and P satisfy the following relational expression 1,

   The non-oriented electrical steel sheet according to any one of claims 1 to 3, wherein the thickness deviation (Δt _CR ) in the width direction of the strip satisfies the following formula (2).

   [Relation 1] 3.8? Si + Al + 0.5Mn + 0.8Sn + 5P? 5.4

   [Relation 2]? T _CR ? 36 * (S / t) ^-0.48

   (In the above relational expression 1, Si, Al, Mn, Sn and P represent the respective contents (% by weight), and? T _CR in the above relational expression 2 is the thicknesswise deviation (Mm), and t is the thickness (mm) of the strip.
2. The method according to claim 1,

   V, Ti, Mo, Cu, Cr, Ni, Zn, Se, or the like as a tramp element in a total amount of 0.05 wt% or less, Sb, Zr, W, Ga, Ge and Mg in a total amount of not more than 0.2%.
3. The method according to claim 1,

   Wherein the electrical steel sheet has a thickness of 0.15 to 0.35 mm and is excellent in shape quality.
4. The method according to claim 1,

   Wherein the electrical steel sheet has an excellent shape quality with a resistivity of 50 to 65 占 占 ㎝.
5. The method according to claim 1,

   Wherein the electrical steel sheet has excellent shape quality with a yield strength in the rolling horizontal direction (L direction) of 415 MPa or more.
6. And the balance Fe and other unavoidable impurities, wherein the content of Si is from 2.8 to 4.0%, Al is from 0.1 to 1.5%, Mn is from 0.05 to 1.5%, Sn is from 0.005 to 0.20%, P is from 0.002 to 0.15% Si, Al, Mn, Sn and P are obtained by continuously casting molten steel satisfying the following relational expression 1 to obtain a thin slab;

   Subjecting the thin slab to rough rolling to obtain a bar;

   Heating the bar;

   Hot rolling the heated bar to obtain a hot rolled steel sheet; And

   And winding the hot-rolled steel sheet,

   Each of the above steps is performed continuously,

   A step of cold-rolling the wound hot-rolled steel sheet to obtain a cold-rolled steel sheet; And

   And recrystallizing and annealing the cold-rolled steel sheet,

   A method for producing a non-oriented electrical steel sheet excellent in shape quality by applying lubricating oil to the surface of the bar at a rate of 5 to 40 L / min per 1 m 2 in the first rolling mill during hot rolling.

   [Relation 1] 3.8? Si + Al + 0.5Mn + 0.8Sn + 5P? 5.4
7. The method of claim 6,

   The molten steel contains at least one of C, S and N as impurities in a total amount of 0.05 wt% or less, and the molten steel contains Nb, V, Ti, Mo, Cu, Cr, Ni, Zn, , Zr, W, Ga, Ge and Mg in a total amount of not more than 0.2%.
8. The method of claim 6,

   Wherein the continuous casting is performed at a casting speed of 3.5 to 8.5 mpm.
9. The method of claim 6,

   Wherein the thin slab has a thickness of 80 to 120 mm and is excellent in shape quality.
10. The method of claim 6,

    The method of manufacturing a non-oriented electrical steel sheet having excellent shape quality with an inlet side temperature of 900 to 1200 DEG C during the rough rolling.
11. The method of claim 6,

    Wherein the raw steel sheet has an excellent appearance quality at an output temperature of 900 DEG C or more during the rough rolling.
12. The method of claim 6,

    Wherein the heating temperature of the bar is 900 to 1200 DEG C.
13. The method of claim 6,

    Wherein the finish rolling is performed at 650 to 900 占 폚.
14. The method of claim 6,

    Wherein the average passing speed during final rolling at the finish rolling is 250 to 750 mpm.
15. The method of claim 6,

    Wherein the speed deviation in the final rolling mill during finish rolling is 50 mpm or less.
16. The method of claim 6,

    Wherein the coiling is performed at 480 to 700 占 폚.
17. The method of claim 6,

    Wherein the hot-rolled steel sheet has an excellent shape quality with a thickness of 1.8 mm or less.
18. The method of claim 6,

    Wherein the hot-rolled steel sheet has an excellent shape quality in which the thickness-wise deviation of the strip satisfies the following relational expression (3).

    [Relation 3]? T _HR ? 230 * (S / t) ^-0.50

    (Where, △ t _HR is a width direction thickness of a hot rolled steel sheet deviation (㎛), S is a predetermined distance position (mm) the thickness measurement of the position apart from the hot-rolled steel plate width direction edge, t is the thickness (mm) of the hot rolled steel sheet Meaning.)
19. The method of claim 6,

    Wherein the hot rolled steel sheet has an average yield strength in a horizontal direction of rolling (L direction) and a vertical direction (C direction) of 750 MPa or less, and satisfies the following formula (4).

    [Relation 4] 3.0? Si + Al + Mn / 2? T / 5? 5.0

    (Si, Al and Mn represent the respective contents (% by weight) and t represents the thickness (mm) of the hot-rolled steel sheet in the relational expression 4)

Images