JP4888124B2 - Steel cooling device and cooling method - Google Patents

Description

  The present invention relates to a steel material cooling apparatus and a steel material cooling method using the same.

  In the process of manufacturing a steel sheet by hot rolling, it is common to supply cooling water or air cooling to control the rolling temperature, but in recent years, the cooling water is injected at a high speed and is high. Development of technology to increase the strength of the steel sheet by obtaining a cooling rate to refine the structure is active.

  For example, in order to cool the upper surface of the steel sheet, a plurality of laminar cooling waters are poured linearly across the width direction from a circular laminar cooling nozzle directly above the roller table for conveying the steel sheet. On the other hand, as a method for cooling the lower surface of the steel sheet, a spray nozzle is provided between the roller tables, and a method of injecting cooling water therefrom is generally used.

  For example, there is a technique described in Patent Document 1 as a technique for cooling a steel sheet by supplying cooling water. This is to raise and lower a slit nozzle unit that sprays cooling water in the direction of steel sheet conveyance, and it is said that a wide range of cooling rates can be secured by using it together with a separately provided laminar nozzle and spray nozzle. Yes.

Moreover, there exists a technique described in patent document 2 as another technique which cools a steel plate by supplying cooling water. This is because the header having slit-like nozzles is inclined to face each other and the film-like cooling water is sprayed, and the partition plate is provided to fill the cooling water between the steel plate and the partition plate to obtain a high cooling rate. Yes.
JP-A-62-260022 JP 59-144513 A

  However, the techniques described in Patent Documents 1 and 2 have major problems in ensuring cooling uniformity and equipment costs.

  That is, in the technique described in Patent Document 1, when the distance between the nozzle and the steel plate is increased, the cooling water sprayed from the nozzle spreads, and a cooling water collision occurs with respect to the steel plate conveyance speed (for example, 60 to 600 mpm). The flow velocity at that time cannot be ensured, resulting in uneven cooling. Moreover, even if the injection speed from the nozzle is reduced to suppress the spread of the cooling water, the flow rate at the time of the cooling water collision cannot be ensured with respect to the conveying speed of the steel sheet, resulting in uneven cooling. That is, unless the nozzle is brought close to the steel plate, the flow rate at the time of cooling water collision cannot be ensured with respect to the conveying speed of the steel plate, resulting in uneven cooling.

  Therefore, in the technique described in Patent Document 1, the slit nozzle unit must be brought close to the steel plate, and when cooling the steel plate with the tip or tail end warped, the steel plate collides with the slit nozzle unit, and the slit nozzle unit May be damaged, or the steel plate may not be able to move, causing the production line to stop or the yield to decrease. Therefore, it is conceivable that when the tip and tail ends pass, the lifting mechanism is operated to retract the slit nozzle unit upward. In this case, the leading and trailing ends are not sufficiently cooled, and the desired material is obtained. It becomes impossible. Furthermore, there is a problem that the equipment cost for providing the lifting mechanism is increased.

  In the technique described in Patent Document 2, the cooling water is not filled between the steel plate and the partition plate unless the nozzle is brought close to the steel plate. When the nozzle is brought close to the steel plate, similarly to the technique described in Patent Document 1, inconvenience occurs when cooling the steel plate with the tip and tail ends warped.

  The present invention has been made in view of the above circumstances, and when supplying a cooling medium (for example, cooling water) to a steel material, the steel material can be uniformly and stably cooled at a high cooling rate. It aims at providing the cooling device and cooling method of steel materials.

  In order to solve the above problems, the present invention has the following features.

[1] In a steel material cooling device including a header having a nozzle for injecting a cooling medium,
In the nozzle, the length of the flow path formed therein is 15 times or more of the diameter, the vertical distance from the nozzle tip to the pass line is 500 mm or more, and the cooling medium injection speed is The relationship between the inner diameter D of the tip of the nozzle and the diameter Dk of the cooling medium at the position where the cooling medium collides with the steel material is Dk <2D. Cooling system.

[ 2 ] The steel cooling device according to [1], wherein the nozzles are arranged in a grid pattern or a staggered pattern on the header.
[3] The steel material cooling device according to [1] or [2], wherein the cooling medium is water and a water density is 4 m ³ / m ² mim or more.

[4] In a method for cooling a steel material using a header having a nozzle for injecting a cooling medium,
The length of the flow path formed in the nozzle is 15 times or more of the diameter, the vertical distance from the tip of the nozzle to the pass line is 500 mm or more, and the jetting speed of the cooling medium is set. The method of cooling steel material, wherein the relationship between the inner diameter D of the tip of the nozzle and the diameter Dk of the cooling medium at the position where the cooling medium collides with the steel material is Dk <2D. .

[ 5 ] The steel cooling method according to [4], wherein the nozzles are arranged in a grid pattern or a staggered pattern on the header.
[6] The method for cooling a steel material according to [4] or [5], wherein the cooling medium is water and a water density is 4 m ³ / m ² mim or more.

  By using the present invention, the steel material can be cooled to the target temperature uniformly and stably at a high cooling rate. As a result, a high quality steel material can be manufactured.

  First, the basic concept of the present invention will be described. The present invention can be applied to all steel materials such as thick plates, shaped steels, and steel pipes, but will be described below by taking steel plates as an example.

  When cooling a steel sheet with a cooling medium (for example, cooling water), in order to reliably perform the cooling, it is necessary to reliably make the cooling water reach the steel sheet and make it collide. For that purpose, it is necessary to break the water film on the surface of the steel plate to allow the fresh cooling water to reach the steel plate, not a cooling water flow with weak penetrating force like droplets ejected from the spray nozzle, It is not a plate-shaped laminar water, but a columnar laminar flow (bar-shaped cooling water) similar to that flowing continuously from a tap. Note that the laminar flow using a circular tube laminar nozzle that has been used in the past is a free-falling flow. Therefore, if there is a stagnant water film, it is difficult for cooling water to reach the steel plate, and cooling is performed with or without stagnant water. There is a difference in ability.

  Therefore, the diameter Dk of the cooling water at the position where the cooling water jetted from the nozzle collides with the steel sheet (collision point) needs to be smaller than twice the inner diameter D of the tip of the nozzle (that is, Dk <2D). ). This is because if the diameter Dk of the cooling water at the collision point is larger than that, the cooling water when reaching the steel plate becomes only a cooling water flow having a weak penetrating force such as a droplet group ejected from the spray nozzle.

  Here, the cooling water diameter Dk at the position where the cooling water sprayed from the nozzle collides with the steel sheet (collision point) is the diameter of the collision point at which the cooling water is sprayed perpendicularly to the steel sheet. The diameter of the collision point can be obtained using a transparent plate instead of the steel plate, or the diameter of the collision point can be obtained from the pressure distribution using a pressure sensor. Further, Dk when cooling water is injected obliquely with respect to the steel sheet refers to the diameter of the collision point on the plane perpendicular to the injection direction immediately before the cooling water collides with the steel sheet, and steel materials such as steel pipes other than the steel sheet Similarly, Dk is the diameter immediately before the cooling water collides with the steel plate.

Further, when the cooling water is jetted at a speed of 10 m / s or more, the cooling water film on the steel plate surface is broken (especially on the upper surface of the steel plate), and fresh cooling water can reach the steel plate. That is, in a cooling device that cools a hot-rolled steel sheet, when the water density is 4 m ³ / m ² mim or more, the cooling water to be sprayed breaks through the water film staying on the steel sheet and uniformly cools it. Requires a cooling water speed of 10 m / s or more.

  In addition, in order to prevent the upper nozzle from being damaged by warpage of the steel plate, the vertical distance Hp from the tip of the upper nozzle to the pass line is set to 500 mm or more.

  FIG. 5 shows a nozzle flow path for a nozzle having a flow path length L and a flow path inner diameter D, using the nozzle injection distance (that is, the cooling water injection distance from the nozzle tip to the steel plate) H as a parameter. An example of the relationship between the ratio L / D and the amount of heat removal will be shown. Here, the nozzle channel inner diameter (nozzle tip inner diameter) D was fixed at 6 mm, the channel length L was changed variously, the 800 ° C. steel plate was cooled, and the heat removal amount was calculated from the temperature drop. . FIG. 6 shows an example of the relationship between the nozzle flow path shape ratio L / D and the cooling water spread (cooling water diameter at the collision point) Dk when reaching the steel plate, using the nozzle injection distance H as a parameter. The spread Dk of the cooling water when reaching the steel plate was determined from the pressure distribution read from the pressure sensitive paper placed on the steel plate. Here, the speed of the cooling water in FIGS. 5 and 6 is V = 14 m / s.

  As shown in FIGS. 5 and 6, when the ratio L / D of the length L and the inner diameter D of the flow path formed inside the nozzle is 15 or more, the straightness of the cooling water is improved and the nozzle injection distance H is 500 mm. It can be seen that the steel sheet can be uniformly cooled without decreasing the heat removal amount and without causing a difference in cooling capacity even if it is separated from ˜1200 mm.

  Also, from FIG. 6, as described above, the diameter Dk of the cooling water at the position where the cooling water sprayed from the nozzle collides with the steel plate (collision point) is made smaller than twice the inner diameter D of the tip of the nozzle. I understand that it is necessary.

  FIG. 4 shows an example of a fluid nozzle based on the above concept. The fluid nozzle 42 is a straight tube nozzle composed of a nozzle main body 43 and an attachment screw portion 44 whose outer periphery is threaded to attach the nozzle 42 to a fluid supply pipe (header) 41. A cooling water flow path 45 is provided inside the nozzle body 43 and the mounting screw portion 44.

  The length L and the inner diameter D of the flow path (straight pipe portion) 45 are set so as to satisfy the relationship of L / D ≧ 15 based on FIGS. However, if the L / D is too large, the pipe friction loss becomes large and the processing of the nozzle becomes difficult, so it is preferable to satisfy L / D ≦ 70.

  In addition, although the shape of the flow path 45 is not ask | required, in order to suppress a pressure loss, a cylindrical shape is more preferable.

  Further, the mounting screw portion 44 may be provided at any position in the nozzle length direction as long as the header 41 and the nozzle 42 can be connected. Even if the nozzle 42 protrudes outside the header 41, it protrudes inside the header 41. However, in many cases, foreign matter such as scales peeled off due to the decrease in the fluid velocity is collected near the wall surface of the header 41, so that the nozzle 42 protrudes 5 mm or more into the header 41. Preferably it is. Moreover, you may attach an inflow port to the side in the part which protrudes.

  Next, a steel sheet cooling device according to an embodiment of the present invention will be described.

  1 and 2 are explanatory views of a steel sheet cooling device according to an embodiment of the present invention.

  The cooling device according to this embodiment is a passage-type cooling device installed on a hot rolling line for steel plates, and includes one or a plurality of cooling units 20 shown in FIG. 1 or cooling units 30 shown in FIG. ing.

  And the cooling unit 20 shown in FIG. 1 has the upper header 21 installed in the upper surface side of the steel plate 10, and the upper nozzle attached to the upper header 21 in order to inject the rod-shaped cooling water 23 toward the steel plate 10 upper surface. 22 and a draining roll 25 for draining the stagnant water 24 on the upper surface of the steel plate 10, and rod-shaped cooling water from between the table rollers (not shown) for conveying the steel plate 10 toward the lower surface of the steel plate 10. In order to inject 28, a lower header 26 installed on the lower surface side of the steel plate 10 and a lower nozzle 28 attached to the lower header 26 are provided.

  Here, the upper nozzle 22 is a circular tube nozzle 42 that satisfies the above-described flow channel shape ratio L / D ≧ 15, and is arranged in a row at predetermined intervals in the steel plate width direction so that cooling water can be supplied to the full width of the steel plate. A plurality of nozzle rows (here, six rows) are arranged in the steel plate conveyance direction.

  FIG. 3 shows a specific example of the arrangement of the upper nozzle 22.

  FIG. 3A shows a grid-like nozzle arrangement, in which nozzles are arranged at virtual grid-like intersections. That is, nozzle rows arranged at a predetermined interval (for example, 40 mm) in the steel plate width direction are arranged in a plurality of rows (here, 6 rows) at a predetermined interval (for example, 35 mm) in the steel plate conveyance direction.

  FIG. 3B shows a staggered nozzle arrangement, in which the nozzles are arranged in a zigzag manner (in a staggered manner) in the steel plate conveyance direction. That is, compared with the nozzle arrangement of FIG. 3A, the nozzles in adjacent rows are arranged so as to be displaced by half the nozzle interval in the steel plate width direction (for example, if the nozzle interval is 40 mm, the half of the nozzle is 20 mm). ing.

  And the rod-shaped cooling water 23 injected from each upper nozzle 22 has an injection speed V of 10 m / s or more, an injection angle θ in the steel plate conveyance direction of 90 °, and a diameter Dk at the collision point on the upper surface of the steel plate 10. , Smaller than twice the inner diameter D of the nozzle tip (that is, Dk <2D).

  Although the inner diameter D of the upper nozzle 22 is not particularly defined, the inner diameter D of the upper nozzle 22 is preferably in the range of 3 to 8 mm in order to prevent the nozzle from clogging and to ensure the cooling water injection speed. .

  Further, in order to prevent the upper nozzle 22 from being damaged by warpage of the steel plate 10, the vertical distance Hp from the tip of the upper nozzle 22 to the pass line is set to 500 mm or more. However, if the position of the tip of the upper nozzle 22 is too far away from the pass line, the cooling water will be dispersed and will not be rod-like and the cooling capacity will be reduced. Therefore, the nozzle injection distance H of the cooling water from the tip of the upper nozzle 22 to the steel plate is 1800 mm. The following is preferable.

  And the lower nozzle 27 is also the circular tube nozzle 42 which satisfy | filled the flow-path shape ratio L / D> = 15 similarly to the upper nozzle 22, and it is a steel plate width direction so that cooling water can be supplied to the full width of a steel plate. The nozzle rows are attached in a row at a predetermined interval, and the nozzle rows are arranged in a plurality of rows (here, 6 rows) in the steel plate conveyance direction. A specific nozzle arrangement is shown in FIG.

  And the rod-shaped cooling water 28 injected from each lower nozzle 27 has an injection speed of 10 m / s or more, an injection angle in the steel plate conveyance direction of 90 °, and the diameter at the collision point of the lower surface of the steel plate 10 is the tip of the nozzle. It is smaller than twice the inner diameter.

  Although the inner diameter of the lower nozzle 27 is not particularly defined, the inner diameter of the lower nozzle 27 is preferably in the range of 3 to 8 mm in order to prevent the nozzle from being clogged and to ensure the cooling water injection speed.

  By the way, if the upper and lower sides of the steel sheet are not cooled in the same way, the steel sheet may bend and warp and the product directivity may decrease, so the cooling capacity for the upper and lower sides of the steel sheet is the same. However, if the cooling capacity is the same, the upper header 21 and the lower header 26 may be the same or different. The upper nozzle 22 and the lower nozzle 27 may also have different nozzle inner diameters and flow path lengths.

  On the other hand, the cooling unit 30 shown in FIG. 2 has a pair of upper headers 31 installed so as to face each other in the steel plate conveyance direction on the upper surface side of the steel plate 10 in order to inject the rod-shaped cooling water 33 toward the upper surface of the steel plate 10. And a lower header 36 installed on the lower surface side of the steel plate 10 in order to inject the rod-shaped cooling water 38 toward the lower surface of the steel plate 10, and an upper nozzle 32 attached to each upper header 31. A lower nozzle 38 attached to the lower header 36 is provided.

  Here, the injection angle θ of the upper nozzle 32 is not particularly defined, but is preferably 30 ° to 90 °. This is because if the injection angle is smaller than 30 °, the vertical velocity component of the rod-shaped cooling water 33 becomes small, the collision with the steel plate 10 becomes weak, and uneven cooling occurs.

  Further, an intermediate header may be provided between the opposing upper headers to increase the cooling capacity between the opposing headers, and the number thereof may be any number.

  Other points are the same as those of the cooling unit 20 described above.

  And by installing the cooling device provided with the cooling unit 20 or the cooling unit 30 as described above in the hot rolling line for thick steel plate or thin steel rice, the steel plate is uniformly and stably at a high cooling rate to the target temperature. As a result, a high-quality steel sheet can be manufactured.

  It goes without saying that the cooling device of the present invention can be used for cooling steel materials such as shaped steel and steel pipes.

  Examples of the present invention are described below.

  FIG. 7 is a diagram showing a hot rolling line for steel plates used in the examples of the present invention and a conveyance pattern there.

  The steel sheet hot rolling line includes a heating furnace 11, a reversible rolling mill 12, a hot leveler 13, and a cooling device 14, and performs accelerated cooling after finish rolling. Here, the slab extracted from the heating furnace 11 is subjected to rough rolling and finish rolling by a reversible rolling machine 12 to a plate thickness of 25 mm, and then passed through a hot leveler 13 and a cooling device 14 has a temperature drop of 150 ° C. Accelerated cooling was performed.

  And as invention example 1, based on said embodiment, 6 units of the cooling unit 20 shown in FIG. 1 were installed in the cooling device 14, and the steel plate was cooled. At that time, for the upper nozzle 22, the height position of the nozzle tip is set to 500 mm in the vertical distance from the pass line, the nozzle inner diameter D is 6 mm, the flow channel shape ratio L is the grid-like arrangement shown in FIG. / D was 17 and the injection speed V was 10 m / s.

  Further, as Invention Example 2, based on the above embodiment, 6 units of the cooling unit 20 shown in FIG. 1 were installed in the cooling device 14 to cool the steel plate. At that time, with respect to the upper nozzle 22, the height position of the nozzle tip is set to 1200 mm in the vertical distance from the pass line, the nozzle inner diameter D is 6 mm, the flow path shape ratio L / D was 17 and the injection speed V was 10 m / s.

  As Invention Example 3, based on the above embodiment, 6 units of the cooling unit 20 shown in FIG. 1 were installed in the cooling device 14 to cool the steel plate. At that time, with respect to the upper nozzle 22, the height position of the nozzle tip is set to 1200 mm as a vertical distance from the pass line, the nozzle inner diameter D is 6 mm, the flow channel shape ratio L is the grid-like arrangement shown in FIG. / D was 23 and the injection speed V was 10 m / s.

  As Invention Example 4, based on the above embodiment, 6 units of the cooling unit 30 shown in FIG. 2 were installed in the cooling device 14 to cool the steel sheet. At that time, with respect to the upper nozzle 22, the height position of the nozzle tip is set to 1200 mm as a vertical distance from the pass line, the nozzle inner diameter D is set to 5 mm, the flow channel shape ratio L is set in a grid-like arrangement shown in FIG. / D was 15, the injection angle θ was 90 °, and the injection speed V was 10 m / s.

  On the other hand, as Comparative Example 1, the cooling device 14 was changed to a conventional general tube laminar cooling device, and the steel sheet was cooled. At that time, the height position of the nozzle tip was set to 1200 mm as a vertical distance from the pass line, the flow path shape ratio L / D was set to 13, and the injection speed V was set to 7 m / s.

  Moreover, as Comparative Example 2, the cooling device 14 was changed to a conventional general tube laminar cooling device, and the steel sheet was cooled. At that time, the height position of the nozzle tip was 1200 mm in vertical distance from the pass line, the flow path shape ratio L / D was 13, and the injection speed V was 10 m / s.

  Further, as Comparative Example 3, the steel plate was cooled by using the cooling device 14 as a conventional general tube laminar cooling device. At that time, the height position of the nozzle tip was 1200 mm in vertical distance from the pass line, the flow path shape ratio L / D was 15, and the injection speed V was 7 m / s.

  Further, as Comparative Example 4, the basic configuration is the same as that of the cooling unit 20 in FIG. 1, but 6 units of cooling units having a vertical distance of 100 mm from the pass line are installed in the cooling device 14 at the top nozzle tip height position. Then, the steel sheet was cooled. At that time, the upper nozzle was arranged in a grid pattern shown in FIG. 3A, the nozzle inner diameter D was 6 mm, the flow path shape ratio L / D was 10, and the injection speed V was 10 m / s.

  Further, as Comparative Example 5, the basic configuration is the same as that of the cooling unit 20 in FIG. 1, but 6 units of cooling units having a vertical distance of 100 mm from the pass line are installed in the cooling device 14 at the top nozzle tip height position. Then, the steel sheet was cooled. At that time, the upper nozzle was arranged in a grid pattern shown in FIG. 3A, the nozzle inner diameter D was 6 mm, the flow path shape ratio L / D was 17, and the injection speed V was 10 m / s.

  Further, as Comparative Example 6, the basic configuration is the same as that of the cooling unit 20 in FIG. 1, but 6 units of cooling units having an upper nozzle channel shape ratio L / D of 10 are installed in the cooling device 14, The steel sheet was cooled. At that time, for the upper nozzle, the height position of the nozzle tip is set to 500 mm as a vertical distance from the pass line, the nozzle inner diameter D is set to 6 mm, and the injection speed V is set to 10 m / m in the grid-like arrangement shown in FIG. s.

  In addition, as Comparative Example 7, the basic configuration is the same as that of the cooling unit 20 in FIG. 1, but 6 units of cooling units having an upper nozzle channel shape ratio L / D of 10 are installed in the cooling device 14, The steel sheet was cooled. At that time, with respect to the upper nozzle, the height position of the nozzle tip is set to 1200 mm in the vertical distance from the pass line, the nozzle inner diameter D is set to 6 mm, and the injection speed V is set to 10 m / m in the grid-like arrangement shown in FIG. s.

  And in each case, after cooling (after fully ripening), the steel plate width direction temperature was continuously measured using the radiation thermometer, and the temperature distribution of the steel plate upper surface was investigated. The temperature variation (difference between the highest temperature and the lowest temperature) in the stationary part excluding the cutting edge, the tail edge, and the width direction plate edge was defined as temperature unevenness and compared. The magnitude of the temperature unevenness almost corresponded to the variation in mechanical properties of the product such as tensile strength.

  The results are shown in Table 1.

  First, in Comparative Examples 1 and 3, the cooling capacity was small, and the temperature unevenness was 80 ° C. in the accelerated cooling after finish rolling, and the strength variation of the products was large.

  In Comparative Example 2, the cooling capacity increased compared to Comparative Example 1, but because Dk ≧ 2D and the cooling water spread Dk were large, the temperature unevenness was 150 ° C. in the accelerated cooling after finish rolling, and the strength of the product varied. Was also big.

  In Comparative Examples 4 and 5, since the upper nozzle had to be brought close to the steel plate, the equipment might be damaged when the warpage of the steel plate occurred. Since the steel plate that collided with the equipment did not become a product, the yield of the product decreased compared to Comparative Example 1. In addition, since it took a considerable amount of time to repair the damaged equipment, the production efficiency also declined.

  Further, in Comparative Examples 6 and 7, the cooling water sprayed from the upper nozzle was widened as Dk ≧ 2D, the cooling capacity was low, and temperature unevenness occurred in the width direction depending on the spreading method.

  On the other hand, Examples 1 to 4 of the present invention have a small spread of cooling water, can perform substantially the same cooling over the entire length, and the temperature unevenness can be suppressed to an extremely low value of 8 to 15 ° C. It was possible to produce a high quality steel plate with little material variation.

  From the above results, the effectiveness of the present invention was confirmed.

It is explanatory drawing of the cooling device which concerns on one Embodiment of this invention. It is explanatory drawing of the other cooling device which concerns on one Embodiment of this invention. It is a figure which shows the example of arrangement | positioning of the nozzle in one Embodiment of this invention. It is a figure for demonstrating the nozzle shape in one Embodiment of this invention. It is the figure which showed the influence which the ratio of the flow path length of a nozzle and the nozzle internal diameter has on cooling capacity. It is the figure which showed the influence which the ratio of the flow path length of a nozzle and the nozzle internal diameter has on the spreading of cooling water. It is explanatory drawing of the hot rolling line and conveyance pattern of the steel plate in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Heating furnace 12 Rolling machine 13 Hot leveler 14 Cooling device 20 Cooling unit 21 Upper header 22 Circular pipe nozzle 23 Bar-shaped cooling water 24 Stagnating water 25 Draining roll 26 Lower header 27 Circular pipe nozzle 28 Bar-shaped cooling water 30 Cooling unit 31 Upper header 32 yen Pipe nozzle 33 Bar-shaped cooling water 34 Stagnant water 36 Lower header 37 Circular pipe nozzle 38 Bar-shaped cooling water 41 Header 42 Nozzle 43 Nozzle body 44 Mounting screw section 45 Nozzle flow path

Claims (6)

In a steel cooling apparatus including a header having a nozzle for injecting a cooling medium,
In the nozzle, the length of the flow path formed therein is 15 times or more of the diameter, the vertical distance from the nozzle tip to the pass line is 500 mm or more, and the cooling medium injection speed is The relationship between the inner diameter D of the tip of the nozzle and the diameter Dk of the cooling medium at the position where the cooling medium collides with the steel material is Dk <2D. Cooling system. The steel nozzle cooling device according to claim 1, wherein the nozzles are arranged in a grid pattern or a staggered pattern on the header. The cooling medium is water and the water density is 4 m. ³ / M ² The steel material cooling device according to claim 1, wherein the steel material cooling device is mim or more. In a method for cooling a steel material using a header having a nozzle for injecting a cooling medium,
The length of the flow path formed in the nozzle is 15 times or more of the diameter, the vertical distance from the tip of the nozzle to the pass line is 500 mm or more, and the jetting speed of the cooling medium is set. The method of cooling steel material, wherein the relationship between the inner diameter D of the tip of the nozzle and the diameter Dk of the cooling medium at the position where the cooling medium collides with the steel material is Dk <2D. . The method of cooling a steel material according to claim 4, wherein the nozzles are arranged on the header in a grid pattern or a staggered pattern. The cooling medium is water and the water density is 4 m. ³ / M ² 6. The method for cooling a steel material according to claim 4, wherein the cooling method is not less than mim.

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