KR20150003595A - Apparatus and method for manufacturing wire rod - Google Patents

Abstract

The present invention relates to an apparatus and a method for manufacturing a wire rod. The apparatus comprises: a reheating furnace heating a metal material; a rough rolling part rolling the metal material discharged from the reheating furnace in a certain thickness as a pre-treating process for final rolling; a finishing rolling part rolling the metal material discharged from the rough rolling part in a final thickness; a laying head coiling the metal material discharged from the finishing rolling part; and an air cooling part cooling the metal material coiling-processed in the laying head. The finishing rolling part is composed of first and second finishing rollers, and a water cooling loop is arranged between the first and second finishing rollers. According to the present invention, provided is an effect of improving the quality of the wire rod by optimally decreasing deviation of materials per part of the wire rod, as rolling the wire rod is mostly processed in a rough rolling step by changing a rolling rate in the rough rolling step, a finishing rolling step, or the like, the wire rod is cooled more by adding a water cooling loop or the like, and the wire rod is uniformly cooled by slowly cooling the wire rod on an air cooling platform.

Description

[0001] Apparatus and method for manufacturing wire rod [0002]

The present invention relates to an apparatus and a method for manufacturing a wire rod, and more particularly, to a wire rod manufacturing apparatus and method that can uniformly cool wire rods by site change by changing a rolling rate at each step, cooling through a water- The present invention relates to an apparatus and a method for manufacturing a wire rod.

1, a billet is heated to approximately 1000 to 1100 占 폚, and then the rough mill, the intermediate rough rolling mill 30, the intermediate cold rolling mill 40, The intermediate winding machine and the finishing rolling machine 50 are cooled in the final cold machine 60 and the wire coil is produced through a winding process in the laying head 70, And then put in the correction line.

At this time, according to the rolling step, the coil of the wire rod will produce a small diameter wire having a diameter of 5.5 to 15 mm and a wire having a diameter of 15 to 42 mm.

On the other hand, in the case of a small diameter wire rod, if it is formed in the form of a non-concentric circular coil through the laying head 70, heat treatment is performed in parallel with the conveyance of the conveying device (conveying conveyor) And then injected into the inspection line.

2A and 2B, the wire coil M thus wound is continuously dropped and conveyed on the roller 83 of the conveying conveyor 81, and the wound wire coil M is conveyed to the conveying conveyor 81 That is, the cooling air blown from the air blowing unit 50 installed at the lower portion while passing through the cooling unit 81. [

Then, the wound wire coil M is dropped on the collector 60 associated with the conveying conveyor 81 and integrated into the final product.

As shown in FIGS. 2A and 2B, the wire coil continuously wound in the form of a coil in the laying head 70, which is a winding machine, is continuously wound on the conveying conveyor 81, The air is blown from the air blowing unit 50 provided with several units along the conveying conveyor 81 under the conveying conveyor 81 to the conveying conveyor 81 during the falling and conveying on the conveying roller 83 of the conveying conveyor 81, The blown air is brought into contact with the wire rod coil M to be conveyed so that the wire rod coil M in a high temperature state is cooled to a low temperature before the accumulation is performed so that the wire rod coil M is subjected to a heat treatment process.

At this time, the temperature of the wire coil M wound up and dropped by the feed roller is approximately 800 to 900 DEG C, and the wire coil M that has been cooled is approximately 300 to 400 DEG C.

On the other hand, the blowing unit 50 includes a duct 54 provided at a lower portion of the blower 52, and an opening portion 85 disposed between the conveying rollers 83, that is, (56) are disposed.

At this time, as shown in FIG. 2A, the wire coil M can be divided into three parts, that is, the center part CN, the middle part MI, and the edge part ED, have.

On the other hand, although such an air blowing unit 50 is also called a stellmor, it provides an advantage that various cooling rates can be obtained according to the cooling conditions such as the strength of the wind power or the feeding speed of the wire coil M , There is a problem in implementing the same blowing in the width direction of the wire coil M.

3A, when the wire rod coil M is extracted from the laying head and is transported in a full length on the transporting roller 83 of the transporting conveyor 81, the edge portion M of the wire rod coil M As shown in Fig. 3 (b), at the time when the transformation of the material cooled under the same blowing environment occurs, the maximum density Lt; 0 > C.

4A and 4B are photographs showing the temperature distribution in the width direction of the wire coil (ring) measured by an infrared thermal image thermometer at the actual operation site. The cooling imbalance due to the difference in the overlap density of the wire coils Besides, since the ring is one-dimensionally stacked on the conveyor and cooled, the inter-ring overlap is severely generated.

5A and FIG. 5B, a difference in the overlapping density of the wire rod coils results in a hot-spot portion where the wire rod coil does not cool well. The hot-spot portion overlapping with the wire coil is not easily cooled by the air blowing method, and even if the air blowing amount is increased, the material deviation is caused by the cooling deviation.

On the basis of the photographs of the temperature measurement shown in Figs. 4A and 4B, as shown in Fig. 6, in the case of a wire coil having 0.8% of carbon and a diameter of 5.5 mm, It can be seen that the difference in temperature history between the center portion CN and the edge portion ED of the wire rod coil M is significant.

That is, the temperature variation due to the difference in the cooling density between the center portion and the edge portion of the wire coil due to the difference in the rack density and the occurrence of the hot-spot portion (overlapping portion) And eventually leads to product failure.

On the other hand, a known conventional wire coil cooling apparatus for reducing the temperature variation in the width direction of the wire coil is disclosed in Japanese Patent Application No. 2011-0062993, one example of which is shown in Fig. 2C.

2C, a partition wall 58 is provided in the longitudinal direction inside the duct 54 of the air blowing unit 50 in the conventional case so that the damper 58a and the deflector 58b, which are upper and lower, The air blowing is concentrated more intensively on the edge portion ED of the wire-wound coil 1 which has a high overlapping density due to the high overlapping density, so that the widthwise velocity distribution is provided in the wire- .

However, the conventional method of achieving uniform cooling in consideration of the overlap density of the wire coil is that the cooling speed between the lower ring and the upper ring of the overlapped wire coil is different and virtually cooling is achieved at the hot spot portion Therefore, unevenness in cooling in the width direction of the wire rod coil is generated even if the air flow concentrates by the wire rod coil portion.

That is, when cooling is performed by blowing while being extracted from the laying head and conveyed, only when the unit rings of the wire coil do not change the shape of the overlapped ring, for example, by controlling the blowing direction or the concentration of the blowing air for each part of the wire coil, 5A and 5B), the uniform cooling of the wire coil ring by each part was limited. In addition, because air cooling is performed, there is a limit to the cooling ability that can be obtained with air, and thus, the cooling ability is inevitably lacking. Because of the continuous cooling by air, a fine pearlite structure can not be obtained in the case of high carbon steel.

The present invention has been proposed in order to overcome the above-mentioned problems of the prior art, and it is an object of the present invention to change the rolling rate in the rough rolling step and the finishing rolling step so that most of the rolling of the wire rod proceeds in the rough rolling step, And to provide a device and a method for improving the quality of a wire rod by cooling the wire rod uniformly by cooling the wire rod in the air cooling zone and ultimately reducing the material deviation of each wire rod.

In order to achieve the above object, an embodiment of the present invention provides an apparatus and method for manufacturing a wire rod as described below.

According to an embodiment of the present invention, there is provided an apparatus for manufacturing a wire rod, comprising: a reheating furnace for heating a metal material; and a rough rolling section disposed behind the reheating furnace and rolling the metal material discharged from the reheating furnace to a predetermined thickness as a pre- A rough rolling section disposed at the rear of the rough rolling section for rolling the metal material discharged from the rough rolling section to a final thickness and a coil disposed at the rear of the finishing rolling section for coiling the metal material discharged from the finishing rolling mill And an aircooling unit disposed behind the laying head and cooling the metal material coiled in the laying head, wherein the finishing rolling unit is composed of a first and a second finishing mill, A water-cooled loop can be disposed between the two.

According to an embodiment of the present invention, there is provided a method of manufacturing a wire rod using the wire rod manufacturing apparatus, wherein the rough rolling unit comprises a first and second rough rolling mills arranged successively, The thickness may be in the range of 59.4% to 65.6% of the thickness of the initial metal material.

In one embodiment, in the second rough rolling mill, the metal material discharged from the first rough rolling mill may be rolled to a range of 12.5% to 18.8% of the initial thickness of the metal material.

In one embodiment, the finishing rolling section may be configured to roll the metal material discharged from the rough rolling section to a range of 3.4% to 12.5% of the initial thickness of the metal material.

In one embodiment, the temperature at which the metal material is heated in the reheating furnace may be in the range of 950 to 1050 ° C.

In one embodiment, the water cooling loop may be configured to cool the metal material to within the range of 650 to 700 < 0 > C.

In one embodiment, the air cooling unit may be configured to cool the metal material to a range of 0.5 to 0.7 DEG C / s.

In one embodiment, the moving speed of the metal material in the air-cooled part may be in the range of 0.2 to 0.3 m / s.

One embodiment of the apparatus and method for manufacturing a wire rod according to the present invention is characterized in that in the rough rolling step, the rolling rate is increased so that most of the wire rod is rolled, and in the finish rolling stage, a reduction force of about dummy or skin passes is applied, The temperature rise is reduced and a water cooling loop is additionally provided to lower the entry temperature of the wire rod in the air cooling zone, thereby achieving uniform cooling of the wire rod in each part between the air cooling.

Further, in the air-cooling zone, the wire material is slowly cooled to alleviate the cooling deviation between the center portion and the edge portion of the wire material, and ultimately, the quality of the wire material can be improved.

Fig. 1 is a configuration diagram showing a conventional wire manufacturing apparatus.
FIGS. 2A and 2B are views showing a cooling process and an accumulation process of the coiled coil in the air-cooled zone.
2C is a structural view showing a blowing structure for uniform cooling in a conventional air cooling zone.
FIG. 3A is a view showing a state in which the coiled wire shown in FIG.
FIG. 3B is a graph showing the temperature variation in the width direction of the wire according to the state of the wire rod shown in FIG. 3A.
FIGS. 4A and 4B are diagrams showing temperature deviations as the edge portions of the coil are stacked and stacked. FIG.
5A and 5B are diagrams showing the temperature distribution state of the edge lapped portion of the wire.
6 is a graph showing the degree of cooling of the wire rod by the distance when the air cooling band enters the laying head.
FIG. 7 is a block diagram showing a wire manufacturing apparatus according to an embodiment of the present invention.
FIG. 8 is a graph showing a cooling deviation between a center portion and an edge of the wire rod with respect to time by the conventional wire rod manufacturing apparatus shown in FIG. 2 and the wire rod producing apparatus shown in FIG.
Fig. 9 is a comparative diagram of tensile strength and elongation between the wire rod produced by the invention shown in Fig. 7 and the wire rod produced by the invention shown in Fig.

Hereinafter, an apparatus and method for manufacturing a wire rod according to an embodiment of the present invention will be described in detail in order to facilitate understanding of the features of the present invention.

In order to facilitate understanding of the embodiments described below, in the reference numerals shown in the accompanying drawings, the related components among the components that perform the same function in the respective embodiments are denoted by the same or an extension line number.

Embodiments related to the present invention are basically based on improving the quality of the wire rod by reducing the material deviation of each wire rod.

Hereinafter, a specific embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 7 is a block diagram showing a wire manufacturing apparatus according to an embodiment of the present invention.

7, a wire material manufacturing apparatus 100 according to an embodiment of the present invention includes a reheating furnace 110 for heating a metal material and a metal material discharged from the reheating furnace 110 as a pre- A rough rolling section 130 for rolling the metal material discharged from the rough rolling section 120 to a final thickness and a laying head for coiling the metal material discharged from the finishing mill And an air cooling unit 170 for cooling the coiled metal material in the laying head 160. The finishing rolling unit 130 is composed of first and second finishing mills 131 and 133, The water-cooling loop 150 may be disposed between the 1,2 and 3 flame mills 131 and 133.

The metal material may be a billet or a billet produced in a steelmaking process. In the following description, the metal material is limited to a billet or a wire material according to each process.

The reheating furnace 110 may be provided to heat the billet to facilitate rolling. In an embodiment of the present invention, the reheating furnace 110 may heat the billet to 950 to 1050 ° C.

Conventionally, the billet is heated to 1000 to 1100 ° C, and the temperature range in which rolling to the billet is progressed as a whole is high between the respective processes. As a result, the entry temperature of the wire rod finally entering the air cooling portion 170 is high, The temperature deviation due to cooling was severely generated between the center portion and the edge portion of the laminated wire rod.

Accordingly, the initial temperature at which the billet enters the respective processes from the reheating furnace 110 is lowered, thereby lowering the entry temperature of the wire rod entering the air-cooling unit 170 by performing the entire process in a relatively lower temperature range. This leads to a reduction in the amount of cooling for the wire rod in the air cooling unit 170, thereby relieving the cooling deviation between the center of the wire rod and the edge of the wire rod between air cooling. A detailed explanation will be given later.

The rough rolling unit 120 may be composed of first and second rough rolling mills 121 and 123. In the first rough rolling mill 121, the ratio of the thickness of the rolled billet to the thickness of the first billet is 59.4% To 65.6%, and more specifically from 59.38% to 65.63%, and the ratio of the thickness of the rolled billet to the thickness of the first billet in the second rough rolling mill 123 is 12.5% to 18.8%, more specifically 12.50% to 18.75% It can be in range.

For example, assuming that the billet discharged from the reheating furnace 110 has a thickness of 160 mm x 160 mm, the first rough rolling machine 121 rolls the billet to a range of 95 to 105 mm. In the second rough rolling mill 123, the billet discharged from the first rough rolling mill 121 is further rolled to a range of 20 to 30 mm. As a result, the billet having the first size of 160 mm x 160 mm is rolled to a range of 20 to 30 mm in the rough rolling section 120.

Conventionally, a billet having a thickness of 160 mm × 160 mm was rolled in a range of 30 to 40 mm in the rough rolling step. In an embodiment of the present invention, the billet is rolled in a larger amount in the rough rolling section 120 than in the conventional rough rolling step, thereby reducing the rolling amount of the billet relatively in the finish rolling section 130.

That is, by preliminarily rolling a large amount in advance in the rough rolling section 120, the amount of rolling the billet to the final thickness of the wire rod in the finishing rolling section 130 is reduced, and ultimately, Which is lower than the previous one. This can lower the entry temperature of the billet entering the air cooling unit 170.

Next, the finishing rolling section 130 may roll the billets discharged from the rough rolling section 120 to a range of 3.4% to 12.5%, specifically 3.44% to 12.50% of the thickness of the first billet.

For example, assuming that the thickness of the first billet discharged from the reheating furnace 110 is 160 mm x 160 mm, the diameter of the wire rod is finally rolled to a range of 5.5 to 20 mm in the finishing rolling section 130.

Since the billet having a thickness of 160 mm x 160 mm is already rolled in the rough rolling section 120 to a range of 20 to 30 mm and then rolled to a range of 5.5 to 20 mm in the finish rolling section 130, Is reduced.

In the conventional case, since the rolling is performed in the rough rolling step to a range of 30 to 40 mm and the remainder is rolled to a range of 5.5 to 20 mm in the finishing rolling step, a larger amount is rolled than the finishing rolling part 130 of the present invention , So that the temperature of the wire rod is relatively increased.

If the diameter of the wire rod to be finally produced is 20 mmØ, the wire rod may be passed through the dummy pass in the finishing rolling section 130. If the diameter of the wire rod is about 15 to 18 mm, So that the temperature rise is reduced. This is possible because most of the rolled amount has already been advanced in the rough rolling section 120.

That is, in the case of the present invention, the range of rolling in the finishing rolling section 130 is reduced, and the temperature rise of the finally rolled wire rod is reduced accordingly. As a result, the entering temperature of the wire rod entering the air- do. As a result, the amount of cooling of the wire rod in the air cooling unit 170 is reduced, so that the cooling deviation at the center portion of the wire rod and the edge portion of the piled wire rod can be mitigated.

For example, if the initial entry temperature of the wire rod entering the air cooling part 170 in the finishing rolling part 130 is 800 ° C and the temperature of the wire rod to be finally cooled in the air cooling part 170 is 300 ° C, The cooling range will be approximately 500 ° C. Otherwise, if the initial entry temperature of the wire rod is 600 캜, the cooling range of the wire rod to be executed in the air cooling part 170 will be 300 캜.

If the cooling range of the wire is large, such as 500 ℃, the cooling deviation between the center of the wire and the edge of the laminated wire becomes large. In other words, the center of the wire will be cooled rapidly, but the edge of the wire will be cooled more slowly as it is stacked in multiple layers. The temperature range to be cooled according to time will show a larger difference as in the case of Fig. 8, which may cause a quality deviation in each part of the wire rod.

On the contrary, when the cooling range of the wire rod is small, such as 300 DEG C, the absolute amount of cooling actually required is reduced as in the development material of Fig. 8, so that the cooling variation between the center portion of the wire rod and the edge portion of the wire rod is relatively reduced.

However, in FIG. 7, it is shown that the quenching process is applied to the quenching in the air-cooling portion 170 and the slow cooling process is applied to the developing material, but this portion will be described later.

In summary, one embodiment of the present invention allows a relatively large number of rolling operations on the wire rod in the rough rolling section 120, compared with the conventional method, and the rolling is performed in the finishing rolling section 130 in a relatively small amount. Thus, the temperature of the wire rod is raised in advance in the rough rolling section 120, and then cooled to an appropriate range. In the finishing rolling section 130, the temperature rise of the wire rod is reduced relatively to the air cooling section 170, The temperature of the incoming wire is lowered.

This ultimately reduces the cooling range of the wire rod in the air cooling unit 170, so that the temperature deviation of each wire rod portion can be relaxed and the quality can be maintained uniformly.

In one embodiment of the present invention, a first cold rolling mill 181 disposed between the rough rolling unit 120 and the finishing rolling unit 130, a first finishing mill 131 and a water cooling loop 150 And a third hydraulic hoist 185 disposed between the second finishing mill 133 and the laying head 160. The second water mill 183 is disposed between the second finishing mill 133 and the laying head 160,

First, the first water jacket 181 is provided to cool the billet discharged from the rough rolling unit 120, and the billet is cooled to a temperature in the range of 850 to 900 ° C. The billet discharged from the reheating furnace 110 is further raised in temperature in the rolling process in the rough rolling section 120 and is lowered to a proper temperature range in the first hydro-cooling table 181, 130).

 The second water jacket 183 is provided to cool the billets rolled and discharged in the first fin-rolling mill 131, and the billets are cooled to a temperature in the range of 850 to 900 ° C. This reduces the temperature of the billet raised during the rolling in the first finishing mill 131 and supplies it to the second finishing mill 133.

At this time, the water-cooling loop 150 may be disposed between the second water mill 183 and the second mill 190. In the water-cooled loop 150, the billet discharged from the second water-cooled table 183 is cooled to a temperature in the range of 650 to 700 ° C. and supplied to the second finishing mill 133.

The lowering of the temperature of the wire rod in the water-cooled loop 150 becomes possible when most of the rolling of the wire rod with respect to the diameter of the wire rod proceeds in the rough rolling section 120. That is, since the rolling amount of the wire rod in the finishing rolling unit 130 is relatively reduced, the temperature rise of the wire rod is reduced.

Depending on the circumstance, since the wire rod is rolled only by the dummy pass or the skin pass down force as described above in the finishing rolling unit 130, the finishing rolling step proceeds at a relatively low temperature compared to the conventional one, It is possible to lower the rolling temperature of the wire rod in the water cooling loop 150 and to result in a decrease in the entry temperature of the wire rod into the air cooling portion 170.

In the conventional case, since the amount of rolling is large in the finishing rolling step, the temperature of the wire rod should be maintained at about 850 to 900 ° C so that rolling can be easily performed.

Next, in the third hydraulic jack 185, the wire material discharged from the second finishing mill 133 is cooled again to a temperature in the range of 600 to 700 ° C., and the wire material is supplied to the laying head 160.

Conventionally, if the entry temperature of the wire rod entering the laying head 160 is in the range of 800 to 900 占 폚, it can be reduced to 600 to 700 占 폚 in one embodiment of the present invention.

As described above, the reheating temperature of the billet is initially lowered in the reheating furnace 110 and most of the billet is progressed in the rough rolling section 120, so that in the finish rolling section 130, Pass rolling or skin pass, so that the temperature rise of the wire rod can be suppressed as compared with the conventional method as it goes to the rear side of the rolling step.

The decrease in the rolling amount in the finishing rolling section 130 allows the rolling of the water-cooling loop 150 to be sufficiently performed even if the temperature of the wire rod is further lowered. As a result, the entry temperature of the wire rod entering the air cooling portion 170 is lowered.

On the other hand, the cooling capacity of the wire rod in the air cooling unit 170 may be in the range of 0.5 to 0.7 DEG C / s, and the moving speed of the wire rod may be in the range of 0.2 to 0.3 m / s.

Conventionally, as shown in the cooling graph of Fig. 8, the cooling capacity of the wire rod in the air-cooled zone is rapidly cooled to approximately 10 DEG C / s. At this time, the moving speed of the wire was moved at a speed as high as about 0.7 m / s. If the wire rod is quenched while moving at a practically high speed, the temperature deviation due to cooling between the center portion of the wire rod and the edge portion of the laminated wire rod becomes more severe. As a result, the quality deviation of the wire rod is generated.

In order to solve this problem, in the embodiment of the present invention, at first, the entry temperature of the wire rod entering the air cooling portion 170 is lowered compared with the conventional one, and at the same time, The slow cooling step is performed.

As the cooling range for the wire rod in the air cooling unit 170 is reduced, the absolute amount of cooling of the wire rod is reduced as described above, so that the cooling deviation between the center of the wire rod and the edge of the wire rod will be relaxed. In this case, when the wire material is slowly cooled, the exposure time of the edge portion of the wire material is increased by that much as compared with the quenching, and the shape gradually decreases as in the cooling graph of the developed material shown in FIG. 8, The cooling deviation between the edge portions of the wire rod is relaxed. This results in the effect of maintaining a relatively uniform quality of each part in the final produced wire.

As shown in FIG. 9, it can be seen that the developed material manufactured according to one embodiment of the present invention has an improved elongation and tensile strength as compared with the presence of a base material as the wire material uniformly cools the parts.

The development material is a high carbon 0.8 carbon vacancy steel. After the vacant steel is reheated to about 980 ° C in the reheating furnace 110, rolling is carried out in the rough rolling section 120, and in the finishing rolling section 130, And proceeded to the skin pass to produce a wire having a diameter of about 13 mm.

At this time, the winding temperature of the laying head 160 was about 670 캜, and the cooling ability and the moving speed of the air-cooling unit 170 were about 0.5 캜 / s and 0.25 m / s, respectively. In the air-cooling unit 170, all of the slow cooling covers were closed and subjected to constant-temperature cooling.

In the present invention, the rolling rate is changed in the rough rolling step, the finishing rolling step and the like so that the rolling of the wire rod proceeds substantially in the rough rolling step, and the wire rod is further cooled by adding a water- , And in the air-cooling zone, the wire material is slowly cooled to uniformly cool the wire material, thereby ultimately reducing the material deviation of the wire material, thereby improving the quality of the wire material.

The above matters are only specific examples of the wire manufacturing apparatus and method.

Therefore, it should be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. do.

100 ... preheating apparatus 110 ... reheat furnace
120 ... rough rolling section 121, 123 ... first and second mills
130 ... Finishing rolling sections 131, 133 ... First and second finish rolling sections
150 ... water-cooled loop 160 ... leing head
170 air-cooled parts 181, 183, 185 ... first, second,

Claims (8)

A reheating furnace for heating a metal material;
A rough rolling section disposed behind the reheating furnace and rolling the metal material discharged from the reheating furnace to a predetermined thickness as a preliminary step for final rolling;
A finish rolling section disposed behind the rough rolling section and rolling the metal material discharged from the rough rolling section to a final thickness;
A laying head disposed behind the finishing rolling section and coiling the metal material discharged from the finishing mill; And
And an air cooling unit disposed at the rear of the laying head for cooling the coiled metal material in the laying head,
Wherein the finishing rolling section comprises a first and a second finishing mill, and a water cooling loop is disposed between the first finishing mill and the second finishing mill.
A method for manufacturing a wire rod using the wire rod manufacturing apparatus according to claim 1,
Wherein the rough rolling section is composed of first and second rough rolling mills arranged one after the other, wherein the thickness of the rolled metal material in the first rough rolling mill is in the range of 59.4% to 65.6% Way.
3. The method of claim 2,
Wherein in the second rough rolling mill, the metal material discharged from the first rough rolling mill is rolled to a range of 12.5% to 18.8% of the thickness of the first metal material.
The method of claim 3,
And the metal material discharged from the rough rolling section is rolled in a range of 3.4% to 12.5% of the thickness of the first metal material in the finishing rolling section.
5. The method according to any one of claims 2 to 4,
Wherein a temperature at which the metal material is heated in the reheating furnace is in the range of 950 to 1050 ° C.
6. The method of claim 5,
Wherein the water cooling loop cools the metal material to within a range of 650 to 700 占 폚.
The method according to claim 6,
Wherein the metal material is cooled in the range of 0.5 to 0.7 占 폚 / s in the air-cooled portion.
8. The method of claim 7,
Wherein the moving speed of the metal material in the air-cooled part is in the range of 0.2 to 0.3 m / s.

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