TWI432269B - Cooling system, cooling method, manufacturing apparatus, and manufacturing method of hot-rolled steel sheet - Google Patents

Description

Cooling device and cooling method for hot-rolled steel sheet, and manufacturing device and manufacturing method for hot-rolled steel sheet

The present invention relates to a cooling device and a cooling method for a hot-rolled steel sheet, and a manufacturing apparatus and a manufacturing method. The present invention relates, in particular, to a cooling apparatus, a cooling method, a manufacturing apparatus, and a method of producing a hot-rolled steel sheet having ultrafine crystal grains suitable for use in a hot-rolled steel sheet for producing a hot-rolled steel sheet having ultrafine crystal grains.

Steels used for automobiles and structural materials are required to have excellent mechanical properties such as strength, workability, and toughness, and in order to comprehensively improve these mechanical properties, it is effective to refine the crystal grains of the hot-rolled steel sheet. Therefore, everyone is experiencing a manufacturing method for obtaining a hot-rolled steel sheet having fine crystal grains. Further, if the crystal grains can be made fine, even if the amount of the alloying elements is reduced, a high-strength hot-rolled steel sheet having excellent mechanical properties can be produced.

The method for refining the crystal grains of the hot-rolled steel sheet is subjected to high-pressure rolling in the hot rolling, especially in the latter stage, so that the Worstian iron particles are refined and the rolling deformation is accumulated in the grains, and after cooling (or after the metamorphosis) The method of obtaining the fineness of the ferrite iron particles is well known. Next, from the viewpoint of suppressing the recrystallization and recovery of the Worthfield iron particles and promoting the deformation of the ferrite and iron, the steel sheet is cooled to a specific temperature or lower (for example, 720 ° C or lower) for a short time after the rolling, and is effective. Methods. That is, in order to produce a hot-rolled steel sheet having fine crystal grains, it is an effective method to provide a steel sheet which is cooled after being subjected to hot rolling and is cooled by a conventional cooling apparatus.

A technique of producing a hot-rolled steel sheet having fine crystal grains, or a technique suitable for producing a hot-rolled steel sheet having fine crystal grains, as shown above. For example, Patent Document 1 is a method for producing a hot-rolled steel sheet by multi-path hot rolling of a steel sheet or a sheet steel comprising C: 0.01 to 0.3% by mass of carbon steel or low alloy steel, and finally rolling. The method of producing a superfine crystal grain hot-rolled steel sheet in which the path is completed at a temperature of not less than ₃ points of Ar and thereafter cooled to 720° C. or less within 0.4 seconds. Further, in the technique described in Patent Document 2, the final rolling table, the first cooling device, the second cooling device, and the winding device in the hot rolling mill row are sequentially disposed in the steel sheet conveying direction, and the first cooling device and the second cooling are disposed in the second cooling device. A device for manufacturing a hot-rolled steel sheet in a non-cooling region is disposed between the devices, and the first cooling device includes a nozzle that forms a strip-shaped or oblong-shaped jet impact region on the cooled surface of the steel sheet, and a nozzle for stopping from the nozzle The squeezing roller of the cooling water is sprayed, and the sump of the cooling water is formed in the region between the roller of the rolling table and the roller, and the steel plate conveyed into the first cooling device is immersed in the cooling water of the puddle. Set the stop roller. Further, in the hot-rolling rolling apparatus for a steel sheet of Patent Document 3, the steel sheet is supplied with cooling water on the upper surface of the steel sheet while passing the position of the rolling mill on the inlet side or/and the exit side of the rolling mill which is close to the hot rolling. a cooling device which has a nozzle for spraying a rod-shaped cooling water with a magnetic inclination angle of 30° to 60° on the side of the steel sheet to the position of the cooling water supplied to the steel sheet by the work roll of the rolling mill The header. Next, Patent Document 3 describes that the distance between the front end of the upper nozzle and the pass line should be 500 mm to 1800 mm in order to prevent the cooling water from being dispersed and to be non-stick-shaped and to prevent the cooling water from acting.

[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2005-213595

[Patent Document 2] Japanese Patent No. 4029865

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2007-61838

According to the technique disclosed in Patent Document 1, since the steel sheet having a temperature of Ar ₃ or more is cooled to 720 ° C within 0.4 seconds after the end of the final rolling path, ultrafine crystal grains (for example, average particle diameter) can be produced. The hot-rolled steel sheet is a crystal grain of 2 μm or less and the same as the following. However, Patent Document 1 does not disclose a detailed configuration of a cooling device that cools the steel sheet to 720 ° C within 0.4 seconds after the end of the final rolling path. Further, according to the technique disclosed in Patent Document 2, since the steel sheet is immersed in the cooling water puddle in the region between the roller of the final rolling table and the rolling roller formed in the hot rolling mill row, the cooling energy rate of the hot rolled steel sheet should be improved. . Here, the rapid cooling required for producing a hot-rolled steel sheet having ultrafine crystal grains is a cooling rate of at least 400 ° C / s as shown in Patent Document 1. Therefore, it is required to rapidly cool the steel sheet by nuclear boiling cooling. However, as shown in Patent Document 2, the puddle of the cooling water is actively formed to cool the steel sheet, and it is difficult to increase the impact pressure of the cooling water on the surface of the impact steel sheet to such an extent that nuclear boiling cooling can be performed, in order to manufacture ultrafine crystals. The hot-rolled steel sheet of the grain has a problem of further technical improvement. In addition, in the case of rapid cooling necessary for producing a hot-rolled steel sheet having ultrafine crystal grains, it is necessary to set the impact pressure of the cooling water on the surface of the impact steel sheet to a specific value or more. In contrast, in the technique disclosed in Patent Document 3, only The injection angle of the rod-shaped cooling water supplied to the steel sheet is specified. Further, in Patent Document 3, since the cooling water sprayed on the steel sheet flows to the portion where the steel sheet contacts the work roll, the portion can be immediately cooled. However, the cooling water flowing on the steel sheet after the impact cannot be sufficiently filled. Quenching, the cooling of this portion hardly expects the formation of ultrafine crystal grains. Therefore, the use of this technique alone makes it difficult to produce a hot-rolled steel sheet having ultrafine crystal grains.

Therefore, the object of the present invention is to provide a cooling device for a hot-rolled steel sheet capable of producing a hot-rolled steel sheet having ultrafine crystal grains and improving the use efficiency of cooling water, a method for cooling a hot-rolled steel sheet, and a manufacturing apparatus for a hot-rolled steel sheet. And a method of manufacturing a hot rolled steel sheet.

The inventors of the present invention conducted a survey on the production of a hot-rolled steel sheet having ultrafine crystal grains (hereinafter also referred to as "ultrafine grain steel"), and obtained the following findings.

(1) As shown in Fig. 11, after the rolling is performed in the temperature range of Ar ₃ or more and the cooling is completed to 720 ° C in 0.2 seconds, the crystal grains can be made finer.

(2) In order to reduce the cooling of 100 ° C, for example, 820 ° C to 720 ° C at an Ar ₃ point or higher, it is completed within 0.2 seconds after the rolling, for example, it is necessary to quench at an average cooling rate of 500 ° C / s or more. It is good to carry out quenching at a cooling rate of 600 ° C / s or more. Here, the pressure point below the final rolling table in the hot rolling mill row refers to the bottom dead center of the work roll on the steel plate contacting the rolled steel, and the top dead center of the work roll under the steel plate contacting the rolled roll, the same as the following The length of the steel sheet conveyance direction in the area up to the exit side of the arch of the final rolling mill (hereinafter also referred to as the "inner rolling area") is L1, and the length of the steel sheet conveying direction in the rapid cooling section of the inner portion of the rolling table is L2, the cooling rate in this section is Z1, the length of the steel sheet conveyance direction in the hard-to-quick cooling zone in the rolling table is L3, and the cooling rate in this section is Z2, which is represented by {L2×Z1+L3×Z2}/L1 The cooling rate is the average cooling rate. When the steel sheet was cooled at a cooling rate of 600 ° C / s, the time required to lower the temperature of the steel sheet by 100 ° C was 0.167 seconds. Therefore, in order to end the cooling within 0.2 seconds, it is necessary to start cooling within 0.033 seconds after the rolling. For example, when the steel sheet is moved at a speed of 10 m/s, the distance moved by 0.033 seconds is 0.33 m. Therefore, the quenching after rolling is started within the radius of the final rolling table of the hot rolling mill corresponding to the working roll, and quenching is performed substantially continuously in at least the final rolling stand of the hot rolling mill.

(3) For example, when the rolling speed of the steel sheet is 10 m/s, the distance that the steel sheet moves between 0.2 seconds is 2 m. In addition, the distance from the pressure point below the final rolling stand of the hot rolling mill to the exit side of the arch of the final rolling stand is also about 2 m. Therefore, the necessary rapid cooling must be carried out roughly in the final rolling stand. However, there is also a portion where it is difficult to perform rapid cooling between the pressure point of the position close to the pressing point and the exit side of the arch of the final rolling stand. Therefore, if it is considered that there is a portion where it is difficult to perform rapid cooling, it is necessary to increase the cooling rate of the rapid cooling range (the portion from the pressing point to the exit side of the rolling stand, which is difficult to perform rapid cooling, the same below). The necessary average cooling rate for the area up to the exit side of the arch of the final rolling mill is ensured.

(4) The pressure (surface pressure) of the steel plate sprayed against the steel plate is related to the cooling rate of the steel sheet (see Fig. 6). By increasing the pressure of the cooling water against the steel sheet, the cooling rate of the steel sheet can be increased. In order to manufacture ultrafine grained steel, high-pressure spray water must be sprayed on the steel plate to perform nuclear boiling cooling on the steel plate.

Further, from the metallurgical point of view, cooling should be started as early as 0.2 seconds after the rolling, and cooling should be started at a position closer to the pressure point below the final rolling table. Similarly, a stronger cooling should be achieved near the pressure point below the final rolling table. The inventors investigated the influence of the refinement of crystal grains on the portion close to the pressure point below the final rolling stand, that is, particularly in the radial position corresponding to the work roll. Specifically, the rolling and cooling tests are performed under the cooling conditions between the radius of the work roll and the exit side of the arch of the arch, and the crystal grain size of the ferrite structure of the obtained steel plate is performed. survey. In this investigation, the distance from the pressing point to the exit side of the arch column is 1.8 m, the work roll radius is 0.35 m, and the jetted cooling water directly hits the most upstream side of the steel plate (hereinafter referred to as the "cooling start point". ”) is 0.15m from the pressing point, the plate speed is 10m/s, and the plate thickness of the steel plate is 3mm. Further, the water supply pressure of the cooling water was 1.5 MPa in the cooling header portion. Only the conditions of 2 μm or less which can reach the target of crystal grain size were extracted, and the results are shown in Table 1.

In Table 1, the area corresponding to the area corresponding to the radius of the work roll (hereinafter referred to as "area 1") is "1", and is used to indicate the area to the side of the arch stand below (below Also referred to as "Zone 2", the standard is "2". The cooling rate of each zone is V1, V2, the impact pressure of the cooling water on the steel plate is P1, P2, and the flow density of the cooling water is W1, W2. In addition, the area from the cooling start point (0.15 m) to the exit side of the arch (1.8 m) (hereinafter referred to as "full cooling zone") is marked with "m" and the full cooling zone is attached. The average value (Vm, Pm, Wm). As shown in Fig. 6, the cooling rate V is related to the impact pressure P, and in order to obtain a high cooling rate, it is necessary to have a high impact pressure. In addition, under the condition that the cooling water pressure (1.5 MPa) in the header is constant, in order to obtain a high impact pressure, a high cooling water injection speed is required. The value used to replace the jet velocity is the flow rate per unit surface, that is, the flow density W. If the length of the sprayed cooling water in the width direction of the steel sheet is constant, since the cooling area is also constant, the flow density W is an index of the amount of cooling water used, and is a comparative indicator of the necessary energy for the pump for supplying the cooling water.

As shown in Table 1, with respect to Test No. 1 in which cooling was performed by V1 = V2, the average cooling rate Vm of the entire cooling zone was maintained at the same 615 ° C/s as in Test No. 1, and V1 was greater than V2. In Test Nos. 2 and No. 3, the effect of refining the crystal grains was increased, and the grain size of the ferrite particles which was finer than Test No. 1 was obtained. Further, with respect to Test No. 3, in Test No. 4 and Test No. 5, V1 was kept at a constant 1600 ° C / s and V 2 was lowered, and the crystal grain refining effect was lowered, but the average cooling rate was 404 ° C. Under the condition of Test No. 5 of /s, it was confirmed that a target particle diameter of 2 μm or less was obtained. Comparing Test No. 1, Test No. 4, and Test No. 5, substantially the same degree of crystal grain refinement effect was obtained, and Wm of Test No. 4 and Test No. 5 was smaller than Wm of Test No. 1. Overall, fine granulation can be achieved with good efficiency with less cooling water (it can improve the efficiency of cooling water use). Further increasing V1 can increase the effect of refining the crystal grains and increase the efficiency of use of the cooling water. However, when the local flow density of the region 1 is too high, the cooling water in the rolling mill is discharged, and the retained water reduces the cooling water. The impact force on the steel sheet is sprayed, and as a result, V1 may not be increased. Therefore, considering the drainage in the rolling mill, etc., the upper limit of the flow density W1 should be about 20 m ³ /m ² ‧ min, and the upper limit of the cooling rate V1 corresponding to the thickness of 3 mm should be 1600 ° C / s .

The present invention has been completed based on the above findings, and the gist thereof is as follows.

Hereinafter, the present invention will be described. In addition, in order to facilitate the understanding of the present invention, the reference numerals of the attached drawings are attached to the parentheses, however, the present invention is not limited to the illustrated form.

The cooling device for a hot-rolled steel sheet according to the first aspect of the present invention is disposed on the downstream side of the final rolling table (11g) of the hot rolling mill row (11), and has a steel plate that can be conveyed toward the rolling line (1) a cooling device (20) for hot-rolled steel sheets of the headers (21, 22) of the plurality of nozzles (21a, 21a, ..., 22a, 22a, ...) disposed on the surface of the high-pressure jet water, The utility model is characterized in that the average cooling rate of the surface of the steel plate which is cooled by impinging high-pressure spray water on the surface of the steel plate which is within the radius position of the work roll of the final rolling table is V1, and is equivalent to the work roll existing in the final rolling table. The radius of the steel plate surface between the radius of the final rolling table and the exit side of the arch of the final rolling stand impacts the high-pressure spray water to cool the surface of the steel plate at an average cooling rate of V2, V1 ≧ V2, and, for the cooling start point existing in the final rolling stand The average surface cooling rate Vm of the steel sheet surface which is impacted by the high-pressure spray water on the steel sheet surface between the exit side of the arch of the final rolling mill is 400 ° C / s or more.

Here, the "downstream side" means the downstream side of the conveyance direction of the steel plate (1). Further, "high-pressure jet water" means a jet water having a pressure at which the steel sheet (1) can be subjected to nuclear boiling cooling. In addition, "the final rolling table corresponds to the radial position of the work roll" as shown in Fig. 4, from the portion where the rolled steel sheet (1) is in contact with the final rolling table (11gw, 11gw) (more specific) In other words, it is in contact with the bottom dead point of the work roll (11gwu) above the steel plate (1) and the top dead center of the work roll (11gwd) under the contact steel plate (1). Point") is located at a position on the downstream side of the conveyance direction of the steel sheet (1) from the radius of the work rolls (11 gw, 11 gw) of the final rolling table. In addition, "the surface of the steel sheet which is present in the final rolling table corresponding to the radius of the work roll" means that it exists between the radial position of the final rolling table corresponding to the work roll and the lower pressing point (present in the ratio The surface of the steel plate (1) (above and below) of the final rolling table corresponding to the radius of the work roll closer to the side of the lower pressing point. In addition, the "average cooling rate of the surface of the steel sheet" is a cooling calculated by a plurality of parallelogram regions considered for the vertical component of the average value of the steel sheet conveying direction of the high-pressure jet water, for example, which will be described later. The average of the speed. In addition, "V1" means that the upper (or lower) surface of the steel sheet which is present in the final rolling table corresponding to the radius of the work roll is divided into the plural area by the parallelogram area, and the cooling rate calculated for each parallelogram area is calculated. average value. At this time, the upstream boundary of the region closest to the work roll is the most upstream side of the portion where the high-pressure spray water directly hits the steel sheet, that is, the point closest to the depression point (cooling start point). When the high-pressure spray is disposed closest to the roller, it corresponds to the point at which the tangent of the nozzle injection hole to the circumference of the roller reaches the steel plate. In addition, the “final side of the arch of the final rolling mill” refers to the outside of the arch of the final rolling mill (11gh) (outside the downstream side of the steel sheet conveying direction). In addition, "V2" means that the upper (or lower) portion of the steel sheet which exists between the radial position of the final rolling table corresponding to the work roll and the exit side of the final rolling stand is divided into plural areas by the parallelogram area, and is The average of the resulting cooling rates is calculated for each parallelogram area. In addition, "Vm" means that the upper (or lower) portion of the steel sheet existing between the cooling start point in the final rolling stand and the exit side of the final rolling stand is divided into plural areas by the parallelogram area, and for each parallelogram The average of the cooling rates obtained from the area calculation.

According to a second aspect of the present invention, the steel sheet surface of the high-pressure spray water which is present on the surface of the steel sheet which is within the radius of the work roll of the final rolling table The vertical component of the average value of the steel sheet conveyance direction of the impact pressure is P1, the steel surface of the high-pressure spray water which is present on the surface of the steel sheet which is present between the radius of the work roll and the exit side of the arch of the final rolling stand. When the vertical component of the average value of the steel sheet conveyance direction of the impact pressure is P2, P1≧P2, and the high-pressure injection of the steel plate surface impact between the cooling start point existing in the final rolling table and the exit side of the final rolling stand The vertical component force Pm of the average value of the steel sheet conveyance direction of the steel sheet surface impact pressure should be 2.7 kPa or more.

Here, the "vertical component of the average value of the steel sheet conveyance direction of the high-pressure water jet impact pressure" means any position in the width direction of the steel sheet, for example, the center portion in the width direction, and is measured or calculated along the line segment of the steel sheet conveyance direction. The impact pressure of the high-pressure jet water subjected to the surface of the steel sheet, and the vertical component of the average area (hereinafter, also referred to as "average impact pressure" or "average impact pressure"). In order to uniformly cool the steel sheet in the width direction of the sheet, the vertical component of the average value of the sheet conveyance direction in the entire width direction of the sheet is made equal. At least in consideration of the surface having a width corresponding to the nozzle pitch, the vertical component of the steel sheet surface impact pressure obtained by the line segment should be equal. Therefore, when the vertical component of the average value of the steel sheet conveyance direction is obtained, the average impact pressure of the steel sheet surface from which one nozzle is taken is determined for each nozzle row juxtaposed in the steel sheet conveyance direction, and the average direction of the steel sheet conveyance direction may be averaged. (see Figures 4 and 9). When the nozzle is a flat spray nozzle, as shown in Fig. 7, the nozzle pitch in the width direction of the steel sheet is A, and the nozzle pitch in the conveyance direction of the steel sheet, that is, when the header interval is B, the steel sheet surface of one nozzle is received. The average impact pressure can be used to The hit area is calculated by dividing the force of the cooling water (impact force) of the parallelogram area indicated by A × B by the area A × B of the parallelogram. On the other hand, when the nozzle is a columnar nozzle, the nozzle pitch in the width direction of the steel sheet is A, and the nozzle pitch in the conveying direction of the steel sheet is B, and the average impact pressure of the steel sheet surface of one nozzle is received. The force (impact force) of the high-pressure jet water in the parallelogram region indicated by A × B is divided by the area A × B of the parallelogram region. In addition, "Pm" means that the upper (or lower) portion of the steel sheet existing between the cooling start point in the final rolling stand and the exit side of the final rolling stand is divided into plural areas by the parallelogram area, and for each parallelogram The average of the average impact pressure calculated from the area.

Further, in the first aspect of the present invention and the second aspect of the present invention, the amount of water per unit area of the high-pressure water sprayed on the surface of the steel sheet which is within the radial position of the work roll which is present in the final rolling table is W1, When the amount of water per unit area of the high-pressure jet water sprayed on the surface of the steel sheet between the radial position of the final rolling table and the exit side of the arch of the final rolling stand is W2, it should be W1≧W2.

Here, the "unit area" is not particularly limited as long as the area when the water amount W1 is derived is the same as the area when the water amount W2 is derived. For the "unit area", for example, a parallelogram area used for deriving the vertical component of the average value of the steel sheet conveyance direction of the high-pressure jet water can be used.

Further, in the first aspect of the present invention, the high-pressure water jet nozzle and the steel plate are disposed at the nozzle closest to the position of the work roll of the final rolling table. When the distance between the high-pressure jet water injection port of the nozzle which is D1 and disposed at the position closest to the exit side of the arch of the final rolling stand is D2, it should be D1≦D2.

Further, in the above-described configuration of the first aspect of the present invention, the nozzle is directed from the nozzle toward the upper surface and the lower surface of the steel sheet from the radial position corresponding to the work roll of the final rolling table to the exit side of the final rolling stand. The high-pressure jet water is continuously sprayed in the direction in which the steel sheet is conveyed.

Here, "from the position of the final rolling table corresponding to the radius of the work roll" means the radius between the radial position corresponding to the work roll existing in the final rolling table and the lower pressing point (the radius of the final rolling table corresponding to the work roll) High-pressure spray water sprayed from the nozzles (21a, 21a, ..., 22a, 22a, ...) is supplied above and below the steel plate (1) which is located closer to the pressing point side. The strict starting point of the section in which the high-pressure jet water is continuously injected is the most upstream side of the portion where the high-pressure jet water directly hits the steel sheet at a position corresponding to the radius of the work roll, that is, a point close to the press-down point. When the nozzle for injecting high-pressure jet water is placed on the work roll closest to the final rolling table, the point from the center of the injection hole of the nozzle to the tangent to the surface of the work roll reaches the surface of the steel plate, which is equivalent to the strict start of the interval of continuous injection of high-pressure jet water. point. In addition, the “final side of the arch of the final rolling mill” refers to the outside of the arch of the final rolling mill (11gh) (outside the downstream side of the steel sheet conveying direction). In addition, "the configuration in which the high-pressure spray water is continuously ejected from the nozzle toward the steel sheet conveyance direction" means a plurality of nozzles (21a, 21a, ..., 22a, 22a, ... arranged at a predetermined interval in the conveyance direction of the steel sheet (1). The composition of the high-pressure jet water can be continuously sprayed toward the upper and lower sides of the steel sheet (1).

Further, in the first aspect of the present invention, the vertical component of the average value of the steel sheet conveyance direction of the steel sheet surface impact pressure of the high-pressure jet water in the section is 3.5 kPa or more on the upper surface and the lower surface.

Further, in the first aspect of the invention described above, the nozzles (21a, 21a, ..., 22a, 22a, ...) should be flat spray nozzles.

Further, in the first aspect of the present invention, the space between the both end faces of the cooling device (20) in the width direction of the steel sheet and the end faces of the final rolling table (11g) in the width direction of the steel sheet should be ensured.

Here, "the both end faces of the cooling device (20) in the width direction of the steel plate" mean the outer surfaces of the cooling device (20) on the both ends of the steel plate (1) in the width direction. In addition, "the end surface of both ends of the steel plate width direction of the final rolling table (11g)" means the inner surface of the arch column (11gh) of the final rolling stand on both ends of the width direction of the steel plate (1).

Further, in the first aspect of the present invention, the header (21) and the nozzles (21a, 21a, ...) disposed on the upper surface side of the steel sheet (1) are disposed between the nozzle and the rolling line. The upper guiding portion (23) should be constructed in one piece.

Here, the "upper guide portion (23)" refers to a nozzle for preventing the steel sheet (1) which is rolled by the final rolling table (11g) from hitting the final rolling table (11gwu) and the cooling device (20) ( For the purpose of 21a, 21a, ...), etc., the member of the cooling device (20) provided on the upper side of the steel plate (1).

Further, in the first aspect of the present invention, the header (22) and the nozzles (22a, 22a, ...) disposed on the lower surface side of the steel sheet (1) are disposed between the nozzle and the rolling line. The lower guiding portion (24) should be constructed in one piece.

Here, the "lower guide portion (24)" refers to a nozzle (11gwd) and a nozzle of the cooling device (20) which are used to prevent the steel sheet (1) which is rolled in the final rolling table (11g) from impacting the final rolling table ( For the purpose of 22a, 22a, ...), etc., the member of the cooling device (20) provided on the lower side of the steel plate (1).

Further, in the first aspect of the present invention, the plurality of headers (21, 31, 22, 32) are provided, and at least a part of the headers should be disposed in the direction in which the steel sheets (1) are transported, and The nozzles (31a, 31a, ..., 32a, 32a, ...) of the plurality of rows in the width direction of the steel sheet (1) are uniformly supplied with cooling water.

In addition, at least a part of the header is a first embodiment of the present invention in which cooling water is uniformly supplied to each of a plurality of nozzles arranged in a plurality of rows in the steel sheet conveying direction and the steel sheet width direction, and a plurality of sets are disposed on the upper surface side of the steel sheet. The flow tubes (21, 31) are disposed in the headers on the upper side of the steel sheet, and are disposed at least on the upstream side of the steel sheet conveying direction (31), and should be disposed in the steel sheet conveying direction and the steel sheet width. Each of the nozzles (31a, 31a, ...) of the plurality of directions is uniformly supplied with a header composed of cooling water.

In addition, at least a part of the header is a first embodiment of the present invention in which cooling water is uniformly supplied to each of a plurality of nozzles arranged in a plurality of rows in the steel sheet conveying direction and the steel sheet width direction, and a plurality of sets are disposed on the lower surface side of the steel sheet. The flow tubes (22, 32) are disposed in the headers on the lower side of the steel sheet, and are disposed at least on the upstream side of the steel sheet conveying direction (32), and are disposed in the steel sheet conveying direction and the steel sheet width. Multiple of direction Each of the nozzles (32a, 32a, ...) uniformly supplies a header composed of cooling water.

According to a third aspect of the present invention, there is provided a method of cooling a hot-rolled steel sheet by using a cooling device for a hot-rolled steel sheet according to the first aspect of the present invention or the second aspect of the present invention.

According to a fourth aspect of the present invention, the final rolling table (11g) of the hot rolling mill row (11) is provided in the conveying direction of the steel sheet (1), and the first aspect of the invention or the above-described invention is A cooling device (20, 20') for a hot-rolled steel sheet according to a second aspect; a manufacturing apparatus (10) for a hot-rolled steel sheet.

According to a fifth aspect of the present invention, the final rolling station (11g) processed in the hot rolling mill row (11) is subjected to rolling by using the apparatus (10) for manufacturing the hot-rolled steel sheet according to the fourth aspect of the present invention. The step of the steel sheet (1); the method for producing the hot-rolled steel sheet.

In the present invention, the average cooling rate V1 at which the high-pressure spray water is sprayed on the surface of the steel sheet which is closer to the lower pressing point side of the final rolling table, which is located closer to the lower pressing point side, is cooled, which is equivalent to the existence of the final rolling table. The average cooling rate V2 of cooling is performed by the high-pressure spray water sprayed on the surface of the steel sheet between the work roll radius position and the exit side of the arch of the final rolling stand, and Vm ≧ 400 ° C / s. Further, in the present invention, the vertical component of the average value of the steel sheet conveyance direction of the high-pressure spray water of the high-pressure spray water which is present on the surface of the steel sheet which is closer to the lower pressure point side of the final rolling table. P1, for the surface of the steel plate which exists between the radial position of the work roll which is present in the final rolling table and the exit side of the arch of the final rolling table The vertical component force P2 of the average value of the steel sheet conveyance direction of the steel sheet surface impact pressure of the high-pressure spray water is not less than P2 and 2.7 kPa. Therefore, according to the present invention, immediately after the completion of the rolling of the final rolling mill, the steel sheet can be quenched immediately, and the use efficiency of the cooling water used in the production of the ultrafine grain steel can be improved. Immediately after the completion of the rolling, the steel sheet is quenched to suppress the restoration of the Worthite iron structure. Therefore, according to the present invention, it is possible to provide a cooling device for a hot-rolled steel sheet, a method for cooling a hot-rolled steel sheet, a manufacturing device for a hot-rolled steel sheet, and a cooling device for improving the production efficiency of the hot-rolled steel sheet of the ultrafine crystal grain and the use efficiency of the cooling water. A method of manufacturing a hot rolled steel sheet.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Fig. 1 is a partial schematic view showing a cooling device 20 for a hot-rolled steel sheet according to the present invention and a manufacturing apparatus 10 for a hot-rolled steel sheet according to the present invention including the cooling device 20. In the first drawing, the steel sheet 1 is conveyed from the left side (upstream side) to the right side (downstream side), and the upper and lower sides of the drawing are in the vertical direction. Hereinafter, the upstream side and the downstream side direction may be described as the conveyance direction, and the plate width direction of the steel sheet to be conveyed may be described as the steel plate width direction in the direction perpendicular thereto. In addition, for the sake of brevity of the drawing, the description of the repeated symbols is omitted in the drawings.

As shown in Fig. 1, the apparatus for manufacturing a hot-rolled steel sheet according to the present invention (hereinafter also referred to simply as "the manufacturing apparatus 10") includes a hot rolling mill train 11 and a cooling device 20 of the hot-rolled steel sheet according to the present invention (below Also referred to simply as "cooling device 20"), transport roller 12, and pinch roller 13. In addition, the illustration and the description are omitted. However, on the upstream side of the hot rolling mill row 11, a heating furnace, a rough rolling mill train, and the like are disposed to adjust the conditions of the steel sheet rolled by the hot rolling mill row 11. . On the other hand, on the downstream side of the nip roller 13, another cooling device, a coiler, and the like are disposed, and various devices for the purpose of shipping the steel sheet by the coil are disposed.

The hot rolled steel sheet is roughly produced in the following manner. That is, a thick rod which is taken out from the heating furnace and rolled into a specific thickness by a rough rolling mill is continuously rolled into a specific thickness by the hot rolling mill train 11 while controlling the temperature. Thereafter, rapid cooling is performed by the cooling device 20. Here, the cooling device 20 is a working roll 11gw, 11gw which is very close to the final rolling table from the inside of the arching column 11gh of the final rolling stand of the hot rolling mill train 11 (hereinafter, the working roll 11gw which is also in contact with the upper steel plate 1 is also called The "work roll 11gwu" and the work roll 11gw which contact the lower surface of the steel plate 1 are called "work roll 11gwd" are provided. Next, the steel sheet by the pinch roller 13 is cooled by a cooling device to a specific coiling temperature, and is wound into a coil shape by a winder.

As described above, the manufacturing apparatus 10 is provided with the hot rolling mill train 11 . In the present embodiment, seven rolling mills (11a, 11b, 11c, ..., 11g) are arranged in parallel in the conveying direction. Each of the rolling mills 11a, 11b, ..., 11g is a so-called rolling mill for each rolling stand, and the lowering ratio and the like are set in accordance with conditions such as the thickness, mechanical properties, and surface quality required for the final product.

2 and 3 are enlarged views of a portion in which the cooling device 20 is disposed. Fig. 2 is a diagram showing the state of the cooling device 20 which is quenched above and below the steel sheet by the pressure point below the final rolling table 11g, and the broken line of Fig. 2 Indicates high pressure jet water. On the other hand, Fig. 3 shows the state of the cooling device 20 when the work rolls 11gw and 11gw of the final rolling table 11g are exchanged. In addition, Fig. 4 is the vertical component of the average position of the steel sheet conveyance direction of the final rolling table corresponding to the radius position of the work roll, the exit side of the arch of the final rolling stand 11gh, and the steel plate surface impact pressure of the high-pressure spray water ( Hereinafter, it is also referred to as an explanatory diagram of "average impact pressure of cooling water". On the left side of the drawing, the left side of the drawing is the upstream side of the steel sheet conveying direction, and the right side of the drawing of the fourth drawing is the downstream side of the steel sheet conveying direction. Fig. 5 is a conceptual diagram of pressure distribution of high-pressure jet water sprayed on the steel sheet 1. The vertical axis of Fig. 5 is the vertical component force [kPa" of the average value of the steel sheet surface direction of the high-pressure jet water sprayed on the steel sheet 1, and the horizontal axis of Fig. 5 is the pressure point from the final rolling table. the distance. In addition, in Fig. 5, X1 is the position of the final rolling table corresponding to the radius of the work roll, and X2 is the position of the exit side of the arch of the final rolling stand. Hereinafter, the cooling device 20 will be specifically described with reference to FIGS. 2 to 5 .

As shown in FIGS. 2 and 3, the cooling device 20 is disposed on the downstream side of the final rolling stand 11g of the hot rolling mill train 11. The cooling device 20 includes a headers 21, 21, and a connection that connect the plurality of flat spray nozzles 21a, 21a, ... (hereinafter, simply referred to as "nozzles 21a") that spray high-pressure spray water onto the upper surface of the steel sheet 1. In the plural, the headers 22, 22 of the flat spray nozzles 22a, 22a, ... (hereinafter also simply referred to as "nozzles 22a", etc.) of the high-pressure jet water are sprayed below the steel sheet 1. The manifolds 21 are connected to a plurality of nozzles 21a, 21a, ... arranged at a specific pitch in the width direction of the steel sheet, and the plurality of headers 21, 21, ... are arranged at a specific pitch in the steel sheet conveyance direction. Similarly, in the header 22, the specific direction is in the width direction of the steel sheet. The plurality of nozzles 22a, 22a, ..., the plurality of headers 22, 22, ... are arranged at a specific pitch in the steel sheet conveyance direction. The headers 21, 21, ... can uniformly supply the cooling water to the plurality of nozzles 21a, 21a, ... arranged at a specific pitch in the width direction of the steel sheet 1, and the headers 22, 22, ... can be The configuration in which the cooling water is supplied to the plurality of nozzles 22a, 22a, ... which are arranged at a specific pitch in the width direction of the steel sheet 1 is unified. Two rows of nozzles 21a and 21a disposed on the upper surface side of the steel sheet 1 on the most upstream side in the conveyance direction of the steel sheet 1 and two rows of nozzles 22a and 22a on the lower surface side of the steel sheet 1 are disposed so as to be capable of jetting high-pressure jet water obliquely toward the upstream side in the conveyance direction of the steel sheet 1. It is arranged such that its axial direction intersects with the vertical plane. The cooling device 20 is disposed at an angle formed by the axial direction of the nozzles 21a and 22a on the most upstream side in the conveyance direction of the steel sheet 1 with respect to the vertical plane (hereinafter, also referred to as "vertical in-plane inclination angle"), and is the nozzles 21a and 22a. The vertical plane inward angle formed by the nozzles 21a and 22a on the downstream side in the conveyance direction of the steel sheet 1 is equal to or greater than the vertical plane. The nozzles 21a, 21a, ... and the nozzles 22a, 22a, ... disposed near the work rolls 11gw and 11gw are arranged so as to be as close as possible to the distance between the work rolls 11gw and 11gw as close as possible to the steel sheet 1. Further, the nozzles 21a, 21a, ... close to the work rolls 11gwu are disposed as close as possible to the work rolls 11gwu so that the angle (injection angle) of the jetted high-pressure spray water with respect to the upper surface of the steel sheet 1 is smaller. Similarly, the nozzles 22a, 22a, ... disposed in the vicinity of the work rolls 11gwd are disposed as close as possible to the work rolls 11gwd so that the angle (injection angle) of the injected high-pressure spray water with respect to the lower surface of the steel sheet 1 is smaller.

The cooling device 20 is provided with upper guide portions 23 and 23 for preventing the nozzles 21a, 21a, ... from colliding with the steel sheet 1 between the nozzles 21a, 21a, ... and the upper surface of the steel sheet 1, for the nozzles 22a, 22a, ... and the lower surface of the steel plate 1 are provided with the lower side guide parts 24 and 24 for preventing the nozzles 22a, 22a, ... from impacting with the steel plate 1. The cooling device 20, the header 21 of the work roll 11gwu close to the final rolling table 11g and the upper guide portion 23 are integrally formed, and the header 22 and the lower guide portion 24 of the work roll 11gwd close to the final rolling table 11g are One body. Therefore, for example, when the work rolls 11gw and 11gw of the final rolling stand are exchanged, as shown in Fig. 3, the upper guide portion 23 of the work roll 11gwu close to the final rolling stand moves simultaneously with the header 21, and is closer to the final rolling. The lower guide portion 24 of the table work roll 11gwd moves simultaneously with the header tube 22, whereby the wheel block (not shown) on the drive side (the far side of the drawing surface of Fig. 3) can be vacated to the operation side. Space, but the work of scrolling the wheel.

As shown in FIGS. 2 and 4, when the steel sheet 1 is rapidly cooled by the cooling device 20, the high-pressure injection shock field injected from the nozzle 21a reaches a depression point corresponding to the radius of the work roll exceeding the final rolling table 11g. In the side region, the high-pressure jet impact region injected from the nozzle 22a reaches a region on the lower pressing point side of the final rolling table 11g corresponding to the radius of the work roll. Further, as shown in FIGS. 2 and 3, the headers 21, 21 connected to the plurality of nozzles 21a, 21a, ... connected to the cooling device 20 at a predetermined pitch in the width direction of the steel sheet are connected to each other. The headers 22 and 22 of the plurality of nozzles 22a, 22a, ... arranged at a predetermined pitch in the width direction of the steel sheet are arranged at a specific pitch in the steel sheet conveyance direction. Therefore, by using the cooling device 20, high-pressure jet water can be continuously sprayed on the upper and lower surfaces of the steel sheet 1 in the section from the radial position of the final rolling table 11g to the side of the arch of the final rolling mill 11lg. Further, in the cooling device 20 shown in Figs. 2 and 4, the average cooling rate V1a on the upper side of the steel plate 1 at the position closer to the lower pressing point than the position of the final rolling table 11g is the final rolling table. 11g is equivalent to the average cooling rate V2a of the steel sheet 1 at the position of the work roll radius and the position between the exit side 11lg of the final rolling table 11g, and the final rolling table 11g is equivalent to the work roll radius position closer to the lower The average cooling rate V1b under the steel sheet 1 at the pressure point side is the average cooling rate below the steel sheet 1 at the position corresponding to the work roll radius position of the final rolling table 11g and the exit side of the arch of the final rolling table 11g. In a manner in which V2b is equal, high-pressure jet water is sprayed toward the steel sheet 1.

On the other hand, as shown in Fig. 5, the average value of the impact pressure P1 of the cooling water sprayed from the nozzle 21a toward the lower rolling point side region corresponding to the work roll radius position X1 of the final rolling table 11g should be the same from the nozzle 21a. The impact pressure average value P2 of the cooling water sprayed between the work roll radius position X1 of the final rolling table 11g and the final roll end 11g of the final rolling stand 112 is equal. As will be described later, the average value of the impact pressure of the cooling water is related to the average cooling rate of the steel sheet, and by increasing the average value of the impact pressure of the cooling water, the average cooling rate of the steel sheet can be increased. Therefore, the cooling device 20 is present not only on the upper and lower sides of the steel sheet between the surface of the final rolling table 11g corresponding to the work roll radius and the final rolling stand 11g, and is present at the final roll table 11g corresponding to the work roll radius position. The upper and lower sides of the steel plate 1 may be quenched by high-pressure water spray. Further, as described above, when the apparatus 20 is cooled, the nozzles 21a, 21a near the work rolls 11gwu are closer to the work rolls 11gwu, and the high-pressure spray water to be sprayed should be smaller (the spray angle) from the upper surface of the steel sheet 1 (i.e., vertical). The larger the in-plane inclination angle is, the closer the nozzles 22a, 22a near the work rolls 11gwd are to the work rolls 11gwd, the higher the jet water to be injected (the injection angle) is smaller (i.e., the vertical plane). The way the inward angle is larger). Therefore, the impact is present in the high-pressure spray water above and below the steel sheet 1 corresponding to the final rolling table 11g, which is equivalent to the radius of the work roll, and then proceeds toward the work rolls 11gwu, 11gwd side, by impacting the work rolls 11gwu, 11gwd, A jet flow is generated in the vicinity of the work rolls 11gwu and 11gwd (within the final roll table corresponding to the radius of the work roll). Here, when a jet flow is generated on the upper and lower surfaces of the steel sheet 1, the pressure of the jet water above and below the impact steel sheet 1 may increase. Therefore, according to the cooling device 20, the jet flow is generated by spraying the high-pressure spray water on the upper and lower surfaces of the steel sheet 1 which is located within the radius of the work roll in the final rolling table 11g, and the high-pressure spray water above and below the impact steel plate 1. The steel sheet 1 after passing through the pressing point can be immediately quenched. Of course, it is also possible to increase the impact of the water supply pressure corresponding to the high pressure spray within the radius of the work roll or to change the nozzle type to increase the P1. That is, by the relevant form of the cooling device 20, it is possible to continuously and continuously cool the upper and lower surfaces of the steel sheet 1 passing through the pressing point earlier. Therefore, the present invention can provide a cooling device 20 which can manufacture ultrafine grain steel. Further, even if the retained water is present on the surface of the steel sheet 1, the high-pressure spray water can penetrate the boiling film on the surface of the steel sheet. Therefore, the steel sheet 1 can be subjected to nucleate boiling cooling (quenching) by spraying the high-pressure spray water on the steel sheet 1.

Figure 6 is the steel plate carrier of the high-pressure jet water surface impact pressure A graph showing the relationship between the average value and the average cooling rate of the steel sheet. Fig. 6 shows the average cooling rate [°C/s] when the temperature of the steel plate with a thickness of 3 mm from the surface of the longitudinal axis of the cooling water is reduced from 750 ° C to 600 ° C from both sides (upper and lower), Fig. 6 The horizontal axis is the average value of the steel sheet conveyance direction [kPa] of the steel sheet surface impact pressure of the high-pressure jet water. As shown in Fig. 6, the average value of the steel sheet conveyance direction of the high-pressure jet water is related to the average cooling rate of the steel sheet, and the average value of the steel sheet conveyance direction of the high-pressure spray water is increased. The average cooling rate will increase. In addition, the average value of the steel sheet conveyance direction of the steel sheet surface impact pressure of the high-pressure spray water is as shown in Fig. 7, when the nozzle pitch in the width direction of the steel sheet reaching the surface of the steel sheet is A, and the nozzle pitch in the steel sheet conveyance direction is B, The force (the impact force) of the cooling water in the quadrilateral region represented by A×B can be divided by the area A×B of the quadrilateral region, and the average impact pressure per nozzle is the interval in the conveying direction. To average.

In the present invention, the vertical component of the average value of the steel sheet conveyance direction of the high-pressure spray water jetted from the cooling device 20 to the steel sheet 1 is 2.7 kPa or more. It should be 3.5 kPa or more from the viewpoint of easily quenching the steel sheet 1 while suppressing the restoration of the Worth grain. Further, in the present invention, it is preferable to quench the steel sheet 1 at an average cooling rate of 1000 ° C/s or more from the viewpoint that the crystal grains can be made finer. In the case of the form in which the steel sheet 1 is rapidly cooled at an average cooling rate of 1000 ° C / s or more, in the present invention, the average impact pressure of the cooling water is preferably 8 kPa or more. The cooling rate will vary due to the thickness of the plate and is roughly inversely proportional to the thickness of the plate. When the cooling device for hot-rolled steel sheets according to the present invention has the ability to rapidly cool a steel sheet having a thickness of 3 mm at an average cooling rate of 1000 ° C/s, the steel sheet having a thickness of 5 mm can be rapidly cooled at an average cooling rate of 600 ° C / s.

As described above, the average impact pressure per nozzle should be equal to the impact force of the high-pressure jet water ejected from the nozzle divided by the cooling area of the nozzle. Therefore, even if the measured pressure is used instead of the measured pressure, the average value of the impact pressure of the cooling water can be calculated. In addition, the impact force of the high-pressure jet water can be obtained by the flow rate and the flow rate, because the flow rate and the flow rate are the water supply pressure to the nozzle. As determined, as long as the specific pressure loss is estimated, the average value of the steel plate impact pressure can be estimated from the water supply pressure to the nozzle. An example of a method of calculating the average value of the impact pressure of the steel sheet is as follows.

Average value of steel plate impact pressure Ps=F/(A‧B) [Pa]

Here, the A-type steel plate width direction nozzle pitch [m], the B-system conveyance direction nozzle pitch [m], and the F-type high-pressure jet water impact force on the steel sheet surface [N]. The impact force F can be obtained by the following formula.

Impact force F=44.7‧C‧q‧P ⁰⁵ [N]

Here, 44.7 is the constant of the 0.5th power density [N ⁰⁵ s/m ² ], the C-system loss coefficient (0.8-1.0 degree), the q-system flat spray nozzle flow rate [m ³ /s], and the P-series water supply. Pressure [Pa]. Further, the flow rate of the flat spray nozzle is determined in accordance with the nozzle form (characteristic) in relation to the water supply pressure.

Further, in the present invention, when the retained water is present on the surface of the steel sheet, the pressure of the high-pressure spray water sprayed from the nozzle 21a is lowered by the retained water, and the impact pressure of the high-pressure spray water when reaching the surface of the steel sheet 1 is liable to lower. Therefore, from the viewpoint of facilitating the form in which the steel sheet 1 is rapidly cooled, the retained water on the surface of the steel sheet 1 should be reduced. From this point of view, in the present invention, a space for discharging the cooling water is secured between the both end faces of the cooling device 20 in the width direction of the steel sheet and the end faces of the final rolling table 11g in the width direction of the steel sheet.

In the above description of the cooling device 20 of the present invention, the nozzles 21a, 21a, ... and the nozzles 22a, 22a disposed near the work rolls 11gw and 11gw are brought closer to the steel plate 1 by the distances of the work rolls 11gw and 11gw. (That is, the form of D1 < D2) is taken as an example. According to the above aspect, even when the apparatus 20 is cooled, the angles of the high-pressure spray water sprayed on the upper surface of the steel sheet 1 by the nozzles 21a, 21a, ... which are closer to the work rolls 11g, the smaller, and closer to the nozzles 22a of the work rolls 11gwd. 22a, ... the smaller the angle of the high-pressure spray water sprayed under the steel sheet 1, still V1 = V2 and P1 = P2, however, the cooling device of the hot-rolled steel sheet of the present invention is not limited to this form. The cooling device for the hot-rolled steel sheet of the present invention may also be D1=D2 or V1>V2 and P1>P2. In the cooling device of the hot-rolled steel sheet of the present invention, the closer to the work roll of the final rolling table, the smaller the angle (injection angle) to the surface of the steel sheet, when the high-pressure spray water is sprayed from the nozzle near the work roll, for example, in the presence of The amount of water per unit area of the high-pressure jet water sprayed on the surface of the steel sheet corresponding to the radius of the work roll of the final rolling table, and the column position of the final rolling table corresponding to the radius of the work roll and the final rolling stand The high-pressure jet water may be injected into the high-pressure jet water by the water amount W2 per unit area of the high-pressure jet water sprayed on the surface of the steel sheet between the sides, and may be V1≧V2 and P1≧P2.

Further, the above description relating to the cooling device 20 of the present invention is based on the angle of the high-pressure spray water sprayed from the nozzles 21a, 21a, ... near the work rolls 11gwu of the work rolls 11gwu with respect to the upper surface of the steel plate 1 (jetting The smaller the angle, the closer the angle (injection angle) of the high-pressure spray water sprayed from the nozzles 22a, 22a, ... near the work rolls 11gwd of the work rolls 11gwd to the lower surface of the steel sheet 1 is to inject high-pressure jet water. The form is taken as an example, however, the cooling device of the hot-rolled steel sheet of the present invention is not limited to this form. However, the high-pressure spray water sprayed in the radial position corresponding to the work roll toward the final rolling table is actively impacted on the work roll, and a jet flow is generated in the vicinity of the lower press point, so as to easily correspond to the work roll existing in the final rolling stand. From the viewpoint of the form in which the surface of the steel sheet within the radius position is rapidly cooled, the injection jet of the high-pressure spray water which is closer to the work roll is injected, and the high-pressure spray water is injected.

The above description of the cooling device 20 of the present invention is exemplified by the form of the flat spray nozzles 21a, 21a, ..., 22a, 22a, ..., however, the cooling device of the hot rolled steel sheet of the present invention is It is not limited to this form, and it may be in the form of a so-called columnar nozzle. However, from the viewpoint of providing a cooling device that reduces the clogging of the nozzle and increases the vertical component of the average value of the steel sheet conveyance direction of the steel sheet surface impact pressure of the high-pressure spray water even when there is water remaining on the surface, The shape of the flat spray nozzle. this In addition, the flat spray nozzle can make the directivity of the cooling water drainage existing on the surface of the steel sheet by the work of the arrangement form, so that the drainage performance can be improved.

Fig. 8 is a view showing an example of the shape of a quadrangular region considered in the case where the shape of the portion of the high-pressure water sprayed from the nozzle hits the surface of the steel sheet and the vertical component of the average value of the steel sheet conveyance direction of the high-pressure spray water. In the eighth (a) diagram, when the nozzle is a flat spray nozzle, the eighth (b) nozzle is a cylindrical nozzle. In Fig. 8, the far/near direction of the drawing is the thickness direction of the steel plate. Further, the colored portion in Fig. 8 indicates the portion where the high-pressure jet water hits the surface of the steel sheet.

As shown in Fig. 8(a), when the nozzle is a flat spray nozzle, the portion of the high-pressure spray water striking the surface of the steel sheet has an elliptical shape or an oblong shape. At this time, the area of the quadrilateral region (parallelogram region) considered in the vertical component of the average value of the steel sheet conveyance direction of the high-pressure jet water is derived, and the nozzle pitch A in the width direction of the steel sheet and the steel sheet conveyance direction can be utilized. The nozzle pitch B is multiplied to calculate. Further, as shown in Fig. 8(b), when the nozzle is a columnar nozzle, the portion where the high-pressure jet water hits the surface of the steel sheet has a circular shape. At this time, the area of the quadrilateral region (rectangular region) considered in the vertical component of the average value of the steel sheet conveyance direction of the high-pressure jet water is derived, and the nozzle pitch A in the width direction of the steel sheet and the conveyance direction of the steel sheet can be utilized. The nozzle pitch B is multiplied to calculate.

Further, the above description relating to the cooling device 20 of the present invention is not limited to the section from the side of the arch of the final rolling stand of the hot rolling mill, but is also disposed in the region further downstream than the section. It Morphology, however, the invention is not limited to this form. However, it can be known that the steel sheet should be quenched to a temperature lower than 720 ° C in a short time after the end of the rolling. Therefore, from the viewpoint of providing a cooling device capable of quenching the steel sheet to a temperature lower than 720 ° C, the interval up to the exit side of the arching column of the final rolling mill in the hot rolling mill, and more than the interval A flat spray nozzle should be continuously arranged in the area on the downstream side.

Further, in the above description of the cooling device 20 of the present invention, the header 21 disposed on the upper surface side of the steel sheet 1 and the upper guide portion 23 are integrally formed, and the header 22 disposed on the lower surface side of the steel sheet 1 is provided. The configuration in which the lower guide portion 24 is integrally formed is taken as an example. However, the cooling device for the hot-rolled steel sheet of the present invention is not limited to this configuration. The cooling device for the hot-rolled steel sheet according to the present invention may be configured such that the header and the lower guide portion disposed on the lower surface side of the steel sheet are not integrally formed, or the header and the upper guide portion are disposed on the upper surface side of the steel sheet. It is a form that is not integrated. In order to exchange the rollers provided in the final rolling stand of the hot rolling mill, the collecting pipe 21 disposed near the work roll 11gwu, the upper guiding portion 23, the collecting pipe 22 disposed close to the work roll 11gwd, and the lower guiding portion 24, It should be a movable structure, and the above can be moved by a well-known means such as a hydraulic cylinder. However, from the viewpoint of easily improving the efficiency of the roller exchange operation, it is preferable that the header and the upper guide portion disposed on the upper surface of the steel sheet can simultaneously perform the retracting or restoring operation, and therefore, it should be integrally formed. Similarly, the header and the lower guide portion disposed on the lower surface side of the steel sheet should be integrally formed.

Further, in the above description of the cooling device 20 of the present invention, the plurality of nozzles 21a arranged at a specific pitch in the width direction of the steel sheet 1 are connected, The plurality of headers 21, 21, ... of 21a, ... are arranged at a specific pitch in the conveyance direction of the steel sheet 1, and are connected to the plurality of nozzles 22a, 22a, which are arranged at a specific pitch in the width direction of the steel sheet 1. The plural collecting headers 22, 22, ... are arranged at a specific pitch in the conveying direction of the steel sheet 1. However, the cooling device for the hot-rolled steel sheet of the present invention is not limited to this configuration. The cooling device of the present invention may be a header (hereinafter also referred to as a "collective header") which is configured by uniformly supplying cooling water to a plurality of nozzles which are disposed at a specific pitch in the width direction of the steel sheet and the direction in which the steel sheet is conveyed. It is disposed on the upper side and/or the lower side of the steel plate. The form of the cooling device of the hot-rolled steel sheet according to the present invention having a collecting type header is shown in Fig. 9, for example. Fig. 9 is an explanatory view showing a form of a cooling device for a hot-rolled steel sheet having a collecting header, and Fig. 9 is a view showing a radius of the final rolling table corresponding to the working roll and a final rolling mill. A conceptual diagram of the vertical component of the average value of the steel sheet conveyance direction of the column exit side and the high-pressure jet water. In the ninth embodiment, the same components as those of the manufacturing device 10 and the cooling device 20 are denoted by the same reference numerals as those used in the fourth embodiment, and the description thereof will be appropriately omitted.

As shown in Fig. 9, the cooling device 30 (hereinafter also referred to simply as "cooling device 30") of the hot-rolled steel sheet according to the present invention has a uniform pair on the upper side of the steel sheet 1 to form the most upstream side of the steel sheet conveying direction. The collective headers 31 of the three spray nozzle rows 31a, 31a, ... (hereinafter, simply referred to as "nozzles 31a") for supplying cooling water are provided on the lower side of the steel sheet 1 A collective type header in which cooling water is supplied to each of the flat spray nozzles 32a, 32a, ... (hereinafter, also simply referred to as "nozzle 32a") of the three rows of flat spray nozzle rows on the most upstream side of the steel sheet conveyance direction 32, the rest is the same configuration as the cooling device 20. The two rows of nozzles 31a and 31a connected to the collective header 31 are connected so as to be obliquely sprayed with high-pressure water from the upstream side of the steel sheet 1 in the direction of the upper direction of the steel sheet 1 in the conveyance direction, and are connected to the collective header. The nozzles 32a and 32a of the two rows of 32 are connected so as to obliquely eject high-pressure jet water from the most upstream side in the conveyance direction of the steel sheet 1 toward the upstream side in the conveyance direction of the steel sheet 1. In the cooling device 30, the vertical in-plane inclination angle of the nozzles 31a and 32a disposed on the most upstream side in the conveyance direction of the steel sheet 1 is a vertical plane formed by the nozzles 31a and 32a and the nozzles 31a and 32a adjacent to the downstream side in the conveyance direction of the steel sheet 1. Above the internal inclination angle. Further, the high-pressure spray water sprayed by the nozzles 31a and 32a disposed on the most upstream side in the conveyance direction of the steel sheet 1 reaches a region closer to the lower pressure point side than the radial position corresponding to the work roll of the final rolling table. Therefore, such a cooling device 30 and the cooling device 20 can manufacture ultrafine grain steel.

As described above, the ultrafine grain steel can be produced by the cooling devices 20, 30 of the present invention. Therefore, ultrafine grain steel can be manufactured by the manufacturing apparatus 10 which has the cooling device 20, and the manufacturing apparatus of the hot-rolled steel plate which has the cooling device 30. Further, in the form of a step of processing the steel sheet which is rolled in the final rolling stand of the hot rolling mill by the manufacturing apparatus and the manufacturing apparatus 10 of the hot-rolled steel sheet provided with the cooling device 30, it is possible to provide heat for manufacturing ultrafine grain steel. A method of manufacturing a rolled steel sheet.

In the present invention, the distance between the nozzle disposed on the upper surface side of the steel sheet and the upper surface of the steel sheet is not particularly limited. However, when the nozzle is brought close to the surface of the steel sheet, the average value of the impact pressure of the cooling water is easily increased, and the steel sheet is easily quenched. Therefore, in view of the form in which the steel sheet is easily quenched, the distance from the nozzle surface of the steel sheet surface (the jet surface of the high-pressure spray water) to the surface of the steel sheet should be 500 mm or less. It is preferably 350mm or less.

In the above description, a configuration in which a vertical surface inward angle is applied to a nozzle disposed on the upstream side in the steel sheet conveyance direction is taken as an example. However, the present invention is not limited to this embodiment. However, it is easy to make a high pressure in a nozzle row including one or two or more nozzle rows arranged in the upstream direction of the steel sheet conveying direction, in particular, the nozzle row disposed at the position closest to the work rolls of the final rolling table. The spray water impact is more rapid than the upper and lower sides of the steel sheet which is closer to the roll gap position than the final roll position corresponding to the radius of the work roll, and the steel sheet after the roll is easily quenched. Therefore, in the viewpoint of the form of the rapid cooling of the steel sheet, the nozzle array including one or two or more nozzle rows arranged in the position of the work rolls closest to the final rolling stand (the most upstream side in the steel sheet conveyance direction) is required ( The nozzle rows arranged on the upper side and the lower side of the steel sheet are respectively provided with a vertical in-plane inclination angle, and the more the nozzle is disposed on the upstream side in the steel sheet conveying direction, the larger the vertical in-plane inclination angle is to be imparted. In addition, it is preferable to provide a vertical surface inward angle to the nozzle row disposed on the most upstream side in the steel sheet conveyance direction, and to arrange the nozzle list surface on the most upstream side in the steel sheet conveyance direction from the viewpoint of facilitating the rapid cooling of the steel sheet. The spray surface of the spray water is the shortest distance from the surface of the steel sheet.

Further, in the above description, the steel sheet is continuously impacted on the high-pressure water jet by at least the region corresponding to the radial position of the final rolling table of the hot rolling mill to the exit side of the arch of the final rolling mill. The present invention is described in the form in which the steel sheet is quenched immediately after passing the pressing point. However, the present invention is not limited to this form. In the present invention, as long as the steel sheet can be cooled to 720 ° C or less within 0.2 seconds after passing through the pressing point, there is a section in which the high-pressure spray water is not continuously applied to the steel sheet in the inner portion of the rolling table. When there is a portion in the rolling table where rapid cooling is difficult (the high-pressure jet water cannot continuously strike the steel plate), the necessary cooling of the inner region of the rolling table is ensured by increasing the cooling rate of the inner portion of the rolling table other than the portion. The speed may be such that the steel sheet is cooled to 720 ° C or less within 0.2 seconds after passing through the pressing point. The portion which is present in the inner portion of the rolling table where rapid cooling is difficult, for example, may be exemplified by a section between the roll gap position shown in Fig. 4 and the upstream end of the steel sheet conveying direction in the range of continuous cooling. Further, in the cooling device 20' of the hot-rolled steel sheet shown in Fig. 10, when the conveying roller 12 is disposed on the lower surface side of the steel plate between the pressing point and the exit side of the arching stand of the final rolling stand, the carrying roller 12 hinders The portion on the lower side of the steel plate which is impacted by the high-pressure water jet is also a portion which is difficult to perform rapid cooling. Even if the cooling device 20' is used, ultrafine particles can be formed by cooling the steel sheet to 720 ° C or lower within 0.2 seconds after the pressing point. Therefore, the ultrafine grain steel can be produced by the manufacturing apparatus of the hot rolled steel sheet provided with the cooling device 20', and by the cooling step by the cooling device 20'. Further, in the form of a step of treating a steel sheet which has been subjected to rolling in a final rolling stand of a hot rolling mill by a manufacturing apparatus having a cooling device 20' hot-rolled steel sheet, it is possible to provide a hot-rolled steel sheet capable of producing ultrafine grain steel. method.

[Examples]

A roll mill having a diameter of 700 mm (radius: 350 mm) and a distance from the press point to the exit side of the arch of the arch is 1800 mm, and a steel sheet containing 0.1% by mass of C and 1% by mass of Mn is rolled at a side speed of 600 mpm. The plate thickness of the lower pressing point side was 3 mm, and thereafter, the quenching test was performed. The rolling end temperature was 820 ° C, and the downstream side of the following 100 mm pressure point was used as the quenching start position. The average impact pressure P1 of the cooling spray up to 350 mm of the radius of the roller and the average impact pressure P2 from the place to the exit side of the arch of the arch of the arch of the arch is changed, and the final obtained particle size of the ferrite is compared. . In addition, when the section up to the side of the arch of the arch was not cooled to 720 ° C, the subsequent cooling device on the exit side of the arch was used for cooling. Further, the water supply pressure of the cooling water was 1.5 MPa at the cooling header portion. The results are shown in Table 2. Conditions No. 1 to 6 are examples (invention examples), a cooling rate V1 ≧ V2, an average impact pressure P1 ≧ P2, and a flow rate W1 ≧ W2 per unit area. Conditions No. 7 to 8 are comparison sides, and V1 < V2, P1 < P2, and W1 < W2. In addition, in Table 2, the average value of the impact pressure of the cooling water is described as "impact pressure", and the particle size of the ferrite iron is described as "particle diameter". In addition, in Table 2, the "height D1" is the distance between the high-pressure jet water injection port of the nozzle which is disposed closest to the roll gap and the steel plate, and the "height D2" is disposed at the nozzle closest to the exit side of the arch of the arch. The distance between the high pressure jet water jet and the steel plate. In addition, in Table 1, "X~Ymm section" means the section from the pressing point of the distance of Xmm~Ymm.

As shown in Table 2, when conditions No. 1 to 6, V1 ≧ V2, and the average value of the total cooling range from the pressing point of 100 mm to 1800 mm, the cooling rate was 400 ° C / s or more. Therefore, in the case of No. 1 to 6, an ultrafine grain structure having a ferrite iron particle diameter of 2 μm or less was obtained. Further, in the case of the conditions No. 1 to 6, P1 ≧ P2, and the impact pressure (average impact pressure) is 2.7 kPa or more in the average value of the total cooling range from the pressing point of 100 mm to 1800 mm. Further, in the case of Nos. 1 to 6, W1 ≧ W2 has a flow density of 2.8 m ³ /(m ² ‧ min) or more in an average value of the entire cooling range from the pressing point of 100 mm to 1800 mm. On the other hand, in the condition No. 7, V1 < V2, and since P1 < P2 and W1 < W2, the grain size of the ferrite iron is larger than 2 μm. In addition, in condition No. 8, V1 ≧ V2, and also because P1 ≧ P2 and W1 ≧ W2, the average value (Vm) of the entire cooling range of the cooling rate fails to satisfy the lower limit value (400 ° C / s), and The average value (Pm) of the full cooling zone of the pressure also failed to meet the lower limit value (2.7 kPa), and the particle size of the ferrite iron was greater than 2 μm. Further, in the case of Condition No. 1 and Condition No. 4 within the range of the present invention, the same ferrite particle diameter can be obtained, however, the difference between V1 and V2 is large, and the difference between P1 and P2 is large. On the 4th, the average value of the flow density is small and the amount of cooling water is small. That is, Condition No. 4 is higher in the use efficiency of the cooling water than Condition No. 1. Similarly, Condition No. 3 and Condition No. 6 can also obtain the same ferrite particle size. However, the difference between V1 and V2 is large, and the difference between P1 and P2 is large. The average is small and the amount of cooling water is small. That is, Condition No. 6 is higher in the use efficiency of the cooling water than Condition No. 3. From the above, it was confirmed that V1≧V2 and P1≧P2 can promote the refinement of crystal grains, and the difference between V1 and V2 and P1 and P2 has an effect of improving the use efficiency of cooling water.

The above is a description of the present invention in a practical manner, but the present invention is not limited to the embodiment shown in the specification of the present patent application, and does not violate the scope of the patent application and the overall specification. The scope of the invention or the scope of the invention to be read may be changed as appropriate, and the cooling device of the hot-rolled steel sheet and the cooling method of the hot-rolled steel sheet, and the manufacturing apparatus of the hot-rolled steel sheet and the manufacture of the hot-rolled steel sheet, which are produced by the change The method is also included in the technical scope of the present invention.

The cooling device for hot-rolled steel sheets and the method for cooling hot-rolled steel sheets according to the present invention, and a method for producing a hot-rolled steel sheet and a method for producing a hot-rolled steel sheet can be used to produce a hot-rolled steel sheet having ultrafine crystal grains. In addition, the hot-rolled steel sheet having ultrafine crystal grains can be used for materials used for automobiles, home appliances, mechanical structures, and construction.

1‧‧‧ steel plate

10‧‧‧Manufacturing device for hot rolled steel sheets

11‧‧‧Hot Rolling Mill

11g‧‧‧ final rolling table

11gh‧‧‧The final column of the rolling platform

11gw‧‧‧ final roll work roll

11gwu‧‧‧ final roll work roll

11gwd‧‧‧ final roll work roll

12‧‧‧Handling roller

13‧‧‧ pinch roller

20, 20'‧‧‧Coiled steel plate cooling device

21‧‧‧ collecting tube

21a‧‧‧Nozzles

22‧‧‧ collecting tube

22a‧‧‧Nozzles

23‧‧‧Top guide

24‧‧‧ below the guide

30‧‧‧Cooling device for hot rolled steel sheet

31‧‧‧Collection manifold

31a‧‧‧Nozzles

32‧‧‧Collection manifold

32a‧‧‧Nozzles

Fig. 1 is a partial schematic view showing a manufacturing apparatus of a hot-rolled steel sheet according to the present invention.

Fig. 2 is an enlarged view of a portion of the cooling device of the hot-rolled steel sheet according to the first embodiment of the present invention.

Fig. 3 is a view showing an example of a configuration of a cooling device for a hot-rolled steel sheet according to the present invention.

Fig. 4 is a conceptual explanatory diagram of the vertical component of the average value of the steel sheet conveyance direction of the final rolling table corresponding to the radial position of the work roll, the exit side of the final rolling stand, and the steel plate surface impact pressure of the high pressure spray water.

Fig. 5 is a conceptual diagram of the pressure distribution of the high-pressure jet water sprayed on the steel sheet.

Fig. 6 is a graph showing the relationship between the average value of the steel sheet conveyance direction of the high-pressure spray water and the average cooling rate of the steel sheet.

Fig. 7 is an explanatory diagram showing the average value of one nozzle of the steel sheet surface impact pressure of the high-pressure jet water.

Fig. 8 is a diagram showing a parallelogram area considered in consideration of the shape of the portion of the high-pressure jet water sprayed by the nozzle against the surface of the steel sheet and the vertical component of the average value of the steel sheet conveyance direction of the high-pressure spray water. In the eighth (a) diagram, when the nozzle is a flat spray nozzle, the eighth (b) nozzle is a cylindrical nozzle.

Figure 9 is a steel plate corresponding to the radius position of the work roll of the final rolling table of the cooling device of the hot-rolled steel sheet according to the present invention of the other embodiment, the exit side of the arch of the final rolling stand, and the steel plate surface impact pressure of the high-pressure spray water. A conceptual illustration of the vertical component of the average direction of the transport direction.

Figure 10 is a cold form of the hot rolled steel sheet of the present invention. A magnified view of the part of the device.

Fig. 11 is a graph showing the relationship between the cooling time up to 720 ° C and the particle size of the obtained ferrite.

1. . . Steel plate

11g. . . Final rolling table

11gh. . . The final column of the rolling platform

11gw. . . Final roll work roll

12. . . Carrying roller

13. . . Clamping roller

20. . . Hot rolling steel plate cooling device

twenty one. . . Collector

21a. . . nozzle

twenty two. . . Collector

22a. . . nozzle

twenty three. . . Upper guide

twenty four. . . Lower guide

Claims (16)

A cooling device for a hot-rolled steel sheet, comprising: a header that is disposed on a downstream side of a final rolling mill in a hot rolling mill row, and that is capable of injecting a plurality of nozzles of high-pressure jet water toward a surface of a steel sheet that is conveyed by a rolling line; In the cooling device of the hot-rolled steel sheet, the nozzle is disposed at least on the upstream side in the conveyance direction of the steel sheet, and the high-pressure jet water is sprayed obliquely toward the upstream side in the conveyance direction of the steel sheet. The direction is disposed so as to intersect with the vertical surface of the steel sheet, and the surface of the steel sheet which is cooled by the high-pressure spray water present on the surface of the steel sheet corresponding to the radial position of the work roll of the final rolling table is used. The average cooling rate is V1, and the steel sheet is cooled by high-pressure spray water which is stored on the surface of the steel sheet between the radial position of the work roll corresponding to the final rolling table and the exit side of the arch of the final rolling stand. When the average cooling rate of the surface is V2, V1 ≧ V2, and the impact is present at the cooling start point in the aforementioned final rolling stand and the foregoing The average cooling speed Vm of the high voltage between the surface of the finishing station of a side plate of the housing posts spraying water to cool the surface of the steel sheet was produced by the 400 ℃ / s or more. A cooling device for a hot-rolled steel sheet, comprising: a header that is disposed on a downstream side of a final rolling mill in a hot rolling mill row, and that is capable of injecting a plurality of nozzles of high-pressure jet water toward a surface of a steel sheet that is conveyed by a rolling line; A cooling device for a hot-rolled steel sheet, characterized in that the nozzle is disposed at least on the most upstream side in the conveyance direction of the steel sheet The high-pressure jet water is sprayed obliquely toward the upstream side in the conveyance direction of the steel sheet, and the axial direction thereof is intersected with respect to the vertical surface of the steel sheet, and the impact is present in the final rolling station corresponding to the work roll. The vertical component of the average value of the steel sheet conveyance direction of the high-pressure jet water of the surface of the steel sheet within the radius position is P1, the impact is present at a radial position of the work roll corresponding to the final rolling station, and the final rolling is performed. When the vertical component of the average value of the steel sheet conveyance direction of the steel sheet surface impact pressure generated by the high-pressure spray water on the surface of the steel sheet between the exit side of the pillar of the Taipai arch is P2, P1≧P2, and the impact exists in the aforementioned final The vertical component force Pm of the average value of the steel sheet conveyance direction of the steel sheet surface impact pressure generated by the high-pressure water sprayed on the surface of the steel sheet between the cooling start point in the rolling stand and the exit side of the final rolling stand is 2.7 kPa. the above. A cooling device for a hot-rolled steel sheet according to the first or second aspect of the invention, wherein the unit area of the high-pressure water sprayed to the surface of the steel sheet which is present in a radial position corresponding to the work roll of the final rolling table is When the amount of water is W1, the amount of water per unit area of the high-pressure jet water sprayed onto the surface of the steel sheet between the radial position of the work roll corresponding to the final rolling table and the exit side of the arch of the final rolling stand is W2, W1≧W2. A cooling device for a hot-rolled steel sheet according to claim 1 or 2, wherein the spray is disposed at a position closest to a work roll of the final rolling stand The distance between the high-pressure jet water jet opening of the nozzle and the steel plate is D1, and the distance between the high-pressure jet water jet port of the nozzle disposed at the position closest to the exit side of the arch of the final rolling mill is D2, and D1≦ D2. The cooling device for a hot-rolled steel sheet according to the first or second aspect of the invention, wherein the distance from the radial position corresponding to the work roll of the final rolling table to the exit side of the arch of the final rolling stand is The high-pressure spray water is continuously sprayed from the nozzle toward the upper surface and the lower surface of the steel sheet in the conveyance direction of the steel sheet. The cooling device for a hot-rolled steel sheet according to the first or second aspect of the invention, wherein the vertical component of the average value of the steel sheet conveyance direction of the high-pressure jet water in the interval is the upper surface and the lower surface 3.5kPa or more. A cooling device for a hot-rolled steel sheet according to the first or second aspect of the invention, wherein the nozzle is a flat spray nozzle. The cooling device for a hot-rolled steel sheet according to the first or second aspect of the invention, wherein both end faces of the cooling device in the width direction of the steel sheet and the end faces of the final rolling table in the width direction of the steel sheet ensure that the cooling water can be discharged. space. The cold of the hot rolled steel sheet as described in the first or second patent application scope. In the device, the header and the nozzle disposed on the upper surface side of the steel sheet and the upper guide portion disposed between the nozzle and the rolling line are integrally formed. The cooling device for a hot-rolled steel sheet according to the first or second aspect of the invention, wherein the header and the nozzle disposed on a lower surface side of the steel sheet are disposed between the nozzle and the rolling line The lower guiding portion is integrally formed. The cooling device for a hot-rolled steel sheet according to the first or second aspect of the invention, wherein the plurality of the headers are provided, and at least a part of the headers are configured to face the conveyance direction of the steel sheet and the foregoing Cooling water is supplied to the nozzles arranged in a plurality of rows in the width direction of the steel sheet. The cooling device for a hot-rolled steel sheet according to claim 11, wherein the plurality of headers are disposed on the upper surface side of the steel sheet, and are disposed in the header of the upper surface of the steel sheet, at least The header of the upstream side of the steel sheet conveyance direction is configured to supply cooling water to the nozzles arranged in a plurality of rows in the conveyance direction of the steel sheet and the width direction of the steel sheet. The cooling device for hot-rolled steel sheets according to claim 11, wherein the plurality of headers are disposed on a lower surface side of the steel sheet. Among the headers disposed on the lower surface side of the steel sheet, at least the headers disposed on the most upstream side in the conveyance direction of the steel sheet are configured to face the conveyance direction of the steel sheet and the width direction of the steel sheet. The aforementioned nozzles arranged in the plurality of columns are supplied with cooling water. A method of cooling a hot-rolled steel sheet, which is characterized in that the steel sheet is cooled by a cooling device for a hot-rolled steel sheet according to any one of claims 1 to 13. A manufacturing apparatus for a hot-rolled steel sheet, comprising: a final rolling stage of a hot rolling mill, and a hot-rolled steel sheet according to any one of claims 1 to 13 of the present invention. Cooling device. A method for producing a hot-rolled steel sheet, comprising the steps of: processing a rolled steel sheet in a final rolling stage of a hot rolling mill by using a manufacturing apparatus of a hot-rolled steel sheet according to claim 15 of the patent application.