JP5515440B2 - Thick steel plate cooling equipment and cooling method thereof - Google Patents

Description

  The present invention relates to a thick steel plate cooling facility and a cooling method therefor.

  In the process of manufacturing a thick steel plate by hot rolling, for example, in an equipment as shown in FIG. 5, after hot rough rolling and finish rolling, the structure is controlled by water cooling or air cooling. When cooled to a relatively low temperature, for example, about 450 to 650 ° C. by water cooling, a fine ferrite and bainite structure can be obtained and the strength can be secured. Therefore, a technique for cooling a thick steel plate by spray cooling water, laminar cooling water, etc. is generally used. Is. In recent years, the development of techniques for obtaining a high cooling rate, making the structure finer, and increasing the strength of the thick steel plate has been actively developed.

  For example, there is a technique disclosed in Patent Document 1 as a technique for supplying a large amount of rod-shaped cooling water to cool the lower surface of a steel plate. It is possible to obtain a high cooling rate by injecting rod-shaped cooling water into the circular pipe in the water tank and entraining the water in the circular pipe to increase the apparent amount of cooling water, and excellent in material properties. It is said that the product can be manufactured.

  Moreover, there exists a technique of patent document 2 as another technique which cools a hot-steel plate by supplying cooling water. This is a structure in which a large number of small holes are made on the upper surface of the cooling header that also serves as an apron, and cooling water is injected to cool the lower surface of the steel plate, so that cooling efficiency is high and uniform cooling can be achieved. ing.

JP 2001-1027 A Japanese Patent Publication No. 05-86298

    However, the conventional technique has a problem in securing the cooling capacity and the cooling uniformity.

  In the technique of Patent Document 1, an embodiment is shown in which the pitch in the width direction of the nozzles is constant in the nozzle rows arranged in the longitudinal direction.

  However, in order to efficiently cool the entire bottom surface of the thick steel plate, the nozzle arrangement is not optimal for the following reasons. FIG. 6 is a top view and a side view schematically showing the arrangement of the conventional lower surface cooling water injection nozzle and the flow of the lower surface cooling water. The surface temperature of the lower surface of the thick steel plate gradually increases as the cooling of the thick steel plate proceeds. Since it decreases, the wettability of the surface of the thick steel plate is improved, and the circular area (peripheral cooling section shown in FIG. 6) in which the cooling water sprayed in the form of a fountain spreads along the bottom surface of the thick steel plate becomes wider toward the downstream side of the thick steel plate. . In particular, when transporting thick steel plates at low speed, the difference is obvious. Therefore, when the width direction pitch of the nozzle is constant, the area of the portion where the cooling water spreading along the bottom surface of the thick steel plate does not reach is wider on the upstream side where the temperature is lower than the downstream side where the surface temperature of the bottom surface of the thick steel plate is low. Therefore, the lower surface of the thick steel plate cannot be efficiently cooled.

  Further, the nozzle arrangement was not optimal for ensuring cooling uniformity for the following reasons. For example, in the case where the nozzles are arranged in a staggered manner and the steel plate is conveyed and cooled at a low speed (about 0.1 m / s), when passing through the nozzle position in the first row, the portion that passes immediately above the nozzle (see FIG. 6). The surface at the position A) has a high cooling rate, but the portion passing through the middle immediately above the nozzle (position B in FIG. 6) is also the portion cooled at the high cooling speed (position A in FIG. 6). It is cooled to some extent by thermal diffusion.

  Accordingly, the temperature has already dropped when the portion passing through the middle immediately above the nozzles in the first row (the position of B in FIG. 6) passes immediately above the nozzles in the second row (A in FIG. 6). A high cooling rate is not obtained as when the first position passes through the first row. In such a case, since the initial cooling rate changes, hardness unevenness occurs in the width direction. Therefore, it has been difficult to produce a thick steel plate that requires high hardness on the entire upper and lower surfaces of the thick steel plate, such as wear-resistant steel.

  Since the technology of Patent Document 2 has a structure in which a large number of holes are formed on the upper surface of the cooling header that also serves as an apron, when the rod-shaped cooling water supplied to the lower surface of the steel sheet falls, it becomes stagnant water on the apron and is subsequently injected. It becomes an obstacle to the cooling water to be.

  In view of the above, the present invention efficiently uses cooling water when supplying cooling water to the lower surface of a thick steel plate, particularly a steel plate that is conveyed at a low conveying speed of 0.5 m / s or less. An object is to provide a technique for uniformly cooling a thick steel plate at a speed.

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

  A first invention is a steel plate cooling facility installed in a hot rolling line for steel plates, a header installed between table rolls for supplying cooling water to the bottom surface of the steel plate, and protruding from the header A cooling water injection nozzle group that is provided and injects rod-shaped cooling water toward the lower surface of the thick steel plate, and the cooling water injection nozzle group forms a plurality of nozzle rows in the conveying direction of the thick steel plate, and the plurality of nozzles The nozzle pitch in the width direction of the thick steel plate in each nozzle row constituting the upstream nozzle row group including one or more nozzle rows including the most upstream row among the rows, the downstream side consisting of a plurality of downstream nozzle rows A thick steel plate cooling facility characterized in that it is shorter than the nozzle pitch in the width direction in each nozzle row constituting the nozzle row group.

  2nd invention sets the nozzle pitch of the thick steel plate width direction in each nozzle row contained in the said upstream nozzle row group to 30-90 mm, The cooling equipment of the thick steel plate as described in 1st invention characterized by the above-mentioned It is.

  According to a third aspect of the invention, the upstream nozzle row group is composed of two or more nozzle rows in a range of 50 mm in the conveying direction of the thick steel plate, and all the nozzles included in the upstream nozzle row group are 15 in the width direction. It is the cooling equipment of the thick steel plate as described in the 1st or 2nd invention characterized by arranging in the same pitch of -30 mm.

According to a fourth aspect of the present invention, the cooling water spray nozzle group has an inner diameter of 5 to 12 mm, a flow rate of cooling water sprayed from the cooling water spray nozzle of 2 to 20 m / s, and cooling water sprayed from the cooling water spray nozzle group. The cooling equipment for thick steel plates according to any one of the first to third inventions, wherein an average water density between the table rolls of water is 1.5 to 4.0 m ³ / m ² · min. is there.

  5th invention is cooling the thick steel plate in the hot rolling line of a thick steel plate which injects rod-shaped cooling water toward the lower surface of a thick steel plate from the cooling water injection nozzle group provided in the header installed between table rolls. In this method, the landing portion where the rod-shaped cooling water collides with the lower surface of the thick steel plate forms a plurality of landing portion rows in the conveying direction of the thick steel plate, and the most upstream row among the plurality of landing portion rows The landing portion spacing in the steel plate width direction in each landing portion row constituting the upstream landing portion row group composed of one or more landing portion rows including a plurality of downstream landing portion rows. In the method for cooling a thick steel plate, the rod-shaped cooling water is injected so as to be shorter than the interval between the landing portions in the width direction in each landing portion row constituting the downstream landing portion row group. is there.

  6th invention is set to 30-90 mm in the water landing part space | interval of the thick steel plate width direction in each water landing part row | line | column contained in the said upstream water landing part row | line group, It is described to 5th invention characterized by the above-mentioned. This is a cooling method for thick steel plates.

  7th invention is comprised by the 2 or more landing part row | line | column which the said upstream side landing part row | line group exists in the range of the conveyance direction 50mm of a thick steel plate, and is contained in the said upstream side landing part row | line group It is the cooling method of the thick steel plate according to the fifth or sixth invention, wherein the landing portions are arranged at equal intervals of 15 to 30 mm in the width direction.

8th invention sets the inside diameter of the cooling water injection nozzle which injects the said rod-shaped cooling water to 5-12 mm, the flow rate of the said rod-shaped cooling water is 2-20 m / s, and the average amount of water between the said table rolls of the said rod-shaped cooling water It is a cooling method of the thick steel plate in any one of the 5th thru | or 7th invention characterized by setting a density to 1.5-4.0m < ³ > / m < ² > * min.

  By using the steel plate cooling equipment of the present invention, cooling water can be used efficiently, a high cooling rate can be obtained, and the steel plate can be quickly cooled to the target temperature, which can contribute to productivity improvement. In addition, since the cooling of the bottom surface of the thick steel plate can be performed uniformly without temperature unevenness in the width direction of the thick steel plate, a high quality thick steel plate having a particularly uniform hardness distribution in the width direction can be manufactured.

It is a side view which shows arrangement | positioning of the upper-lower surface cooling equipment which concerns on one embodiment of this invention. It is a schematic diagram which shows the flow of lower surface cooling water. It is the upper surface and side view which show arrangement | positioning of a lower cooling water injection nozzle. It is a figure which shows the temperature history of the steel plate conveyance direction of a lower surface temperature and plate | board thickness average temperature. It is a figure explaining the outline of the thick plate rolling line in which this invention is used. It is the upper surface and side view which show arrangement | positioning of the lower cooling water injection nozzle of a prior art.

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

FIG. 5 is a schematic diagram showing an example of a thick plate rolling line in which the present invention is used.
The slab extracted from the heating furnace is subjected to rough rolling and finish rolling by a rolling mill to a predetermined finishing temperature and finishing plate thickness, and then conveyed to an accelerated cooling facility online. It is suitable for obtaining a uniform material to perform accelerated cooling after adjusting the shape of the thick steel plate through a pre-leveler before cooling. In the accelerated cooling facility, the thick steel plate is cooled to a predetermined temperature by the cooling water sprayed from the upper surface cooling facility and the lower surface cooling facility.

FIG. 1 is a side view showing the arrangement of the upper and lower surface cooling facilities according to the embodiment of the present invention. The upper surface cooling equipment includes an upper header 1 for supplying cooling water to the upper surface of the thick steel plate 12, and an upper cooling water injection nozzle 3 suspended from the upper header 1. The upper cooling water injection nozzle 3 is a rod-shaped cooling water. It consists of the circular tube nozzle 3 which injects. The upper surface cooling is performed by supplying cooling water at a high speed perpendicularly to the upper surface of the thick steel plate from the circular tube nozzle 3 provided in the upper header 1. The cooling water breaks the staying water film and reaches the upper surface of the thick steel plate, so that a high cooling capacity can be obtained.
On the other hand, the lower surface cooling equipment is installed between the table rolls 11 and is provided to protrude from the lower header 2 for supplying the cooling water to the lower surface of the thick steel plate 12, and jets the cooling water upward in the vertical direction. The lower cooling water injection nozzle 4 includes a circular pipe nozzle 4 for injecting rod-shaped cooling water. The lower cooling water injection nozzles 4 form a plurality of nozzle rows in the direction of transporting the thick steel plate, and an upstream nozzle row group 41 including one or more nozzle rows including the most upstream row, and the downstream side thereof. A downstream nozzle row group 42 including a plurality of nozzle rows is configured. The lower surface cooling is performed by supplying cooling water perpendicularly to the lower surface of the thick steel plate from the lower cooling water injection nozzle 4 provided on the lower surface header. In the cooling on the lower surface side of the thick steel plate, the injected cooling water naturally falls after colliding with the thick steel plate.

  Here, the rod-shaped cooling water in the present invention is cooling water injected in a state of being pressurized to some extent from a circular (including elliptical or polygonal) nozzle outlet, and is cooled from the nozzle outlet. The water jet velocity is 2 m / s or more, and it refers to cooling water of continuous and straight water flow in which the cross section of the water flow injected from the nozzle outlet is maintained in a substantially circular shape. That is, it is different from a free fall flow from a circular tube laminar nozzle or a liquid ejected in a droplet state such as a spray.

Next, the flow of the cooling water on the lower surface side of the thick steel plate will be examined in detail.
FIG. 2 is a schematic diagram showing the flow of the lower surface cooling water 6, and FIG. 3 is a top view and a side view schematically showing the arrangement of the lower cooling water injection nozzle 4 and the flow of the lower surface cooling water. The cooling water sprayed in a rod shape from the lower cooling water spray nozzle 4 collides with the thick steel plate 12 (the portion called the landing portion 21 in the figure) and then flows in the horizontal direction along the bottom surface of the thick steel plate, and the peripheral cooling portion The part called 22 is cooled and detached from the bottom surface of the thick steel plate and dropped. The water landing part 21 and the peripheral cooling part 22 are parts where the cooling water is in direct contact with the lower surface of the thick steel plate. In order for the cooling equipment to have a high cooling capacity, the area occupied by these two parts should be made as wide as possible. It is important to have a nozzle layout.

  By the way, the lower the surface temperature, the better the wettability on the surface of the thick steel plate, so that the cooling water easily spreads along the bottom surface of the thick steel plate. Therefore, the nozzle row A2 and the nozzle row are more than the circular cooling portion (the portion in which the landing portion 21 and the peripheral cooling portion 22 are combined) in the nozzle row A1 and the nozzle row B1 (upstream nozzle row group 41) in FIG. The cooling part (the part combining the landing part 21 and the peripheral cooling part 22) in B2 (downstream nozzle array group 42) becomes wider.

  Explaining the above based on the specific test results, when cooling water is injected from the lower cooling water injection nozzle 4 having an inner diameter of 5 mm when the steel plate temperature is 800 ° C. and the steel plate conveyance speed is 0.2 m / s. The diameter of the cooling portion of nozzle row A1 and nozzle row B1 (the portion where water landing portion 21 and peripheral cooling portion 22 are combined) is about 20 mm, and the cooling portion of nozzle row A2 and nozzle row B2 (water landing portion 21 and its surroundings) The diameter of the portion combined with the cooling part 22) was about 40 mm.

FIG. 4 shows the temperature history in the steel plate conveyance direction of the lower surface side surface temperature and the plate thickness average temperature of the thick steel plate 12 at this time. The surface temperature on the lower surface side of the thick steel plate at the position A in FIG. 3 is As and the average thickness temperature is Am. Similarly, the surface temperature on the lower surface side of the thick steel plate at the position B in FIG. . As shown in FIG. 4, these temperature histories are almost equal at the position A and the position B, and hardness unevenness does not occur in the thick steel plate width direction. However, when the conveyance time from the nozzle row A1 to the nozzle row B1 is long, the surface temperature on the lower surface side of the thick steel plate starts to decrease before reaching the position of the nozzle row B1 at the position B due to the influence of thermal diffusion from the nozzle row A1. , A temperature history like Bs ′ in FIG. 4 is obtained. In this case, since the cooling rate from the Ar ₃ transformation start temperature becomes low, high strength cannot be obtained in this portion.

  In order not to cause such non-uniform cooling, the passage time difference between the nozzle row A1 and the nozzle row B1 needs to be within 0.5 sec. Since the conveying speed of the thick steel plate is the slowest and is about 0.1 m / s, the distance L1 between the nozzle row A1 and the nozzle row B1 is preferably within 50 mm.

  In addition, the diameter of the cooling portion (the portion where the landing portion 21 and the peripheral cooling portion 22 are combined) of the nozzle row A1 and the nozzle row B1 (upstream nozzle row group 41) is the nozzle inner diameter, injection speed, thick steel plate surface Although it changes with temperature etc., it is 15-30 mm in general conditions. Therefore, for example, under the condition that the diameter of the cooling portion is 20 mm, the nozzle pitch S1 in the thickness direction of the steel plate in the nozzle rows of the nozzle row A1 and the nozzle row B1 may be twice that of 40 mm. Further, as the upstream nozzle row group 41, three nozzle rows (A1, B1, C1) may be arranged at intervals of 25 mm in the conveyance direction within a range of 50 mm in the conveyance direction. The nozzle pitch S1 in the thick steel plate width direction may be set to 60 mm, which is three times that nozzle pitch S1.

  That is, the upstream nozzle row group 41 is preferably composed of two or more nozzle rows within a range of 50 mm from the most upstream nozzle row A1, and nozzles in the thick steel plate width direction in the nozzle row. The pitch S1 may be appropriately set according to the size of the cooling portion (the portion where the landing portion 21 and the peripheral cooling portion 22 are combined), the number of nozzle rows in the upstream nozzle row group, and the like. A range of 15 mm (in the case of two rows) to 90 mm (in the case of three rows with a cooling part diameter of 30 mm) is preferred. Since the nozzle must be attached with a tool, it is difficult to make the pitch in the width direction of the thick steel plate less than 30 mm. If the pitch in the width direction exceeds 90 mm, it is necessary to provide four or more nozzle rows. However, it is better to shorten the pitch in the width direction and to reduce the time difference of the water cooling start by reducing the nozzle rows.

Further, as described above, the diameter of the cooling portion of the upstream nozzle row group 41 (the portion where the landing portion 21 and the peripheral cooling portion 22 are combined) varies depending on the inner diameter of the nozzle, the injection speed, the steel plate surface temperature, and the like. However, it is 15-30 mm under general conditions. Therefore, the upstream nozzle row group 41 so that all the portions in the thick steel plate width direction pass through the cooling portion of the upstream nozzle row group 41 (the portion in which the landing portion 21 and the peripheral cooling portion 22 are combined). It is preferable that the intervals in the width direction (S2) of all the nozzles included in are arranged at an equal pitch of 15 to 30 mm.
For example, when there are two nozzle rows in the upstream nozzle row group 41, as shown in FIG. 3, the nozzle positions in the width direction of the nozzle rows A1 and B1 are set to be 1/2 of the width direction nozzle pitch. It is preferable to install them by shifting. Similarly, when the number of nozzle rows in the upstream nozzle row group 41 is 3, the nozzle positions in the width direction may be shifted between the nozzle rows by 1/3 of the nozzle pitch in the nozzle row.

  Further, in order to efficiently cool the thick steel plate, it is necessary to optimize the inner diameter of the lower cooling water injection nozzle 4, the cooling water injection speed, and the nozzle distance.

  That is, the inner diameter of the lower cooling water injection nozzle 4 is preferably 5 to 12 mm. This is because if the thickness is less than 5 mm, the bundle of water sprayed from the nozzle becomes thin and the expansion of the cooling water after colliding with the lower surface of the thick steel plate is small. On the other hand, when the nozzle diameter of the lower cooling water injection nozzle 4 exceeds 12 mm, the flow velocity becomes slow, and the expansion of the cooling water after colliding with the lower surface of the thick steel plate is reduced. In addition, if the number of points where the cooling water directly hits the bottom surface of the steel plate is reduced, the cooling capacity is lowered. Therefore, increasing the nozzle installation density by setting the nozzle diameter to 12 mm or less can efficiently cool the bottom surface of the steel plate. it can.

  The injection speed of the lower cooling water injection nozzle 4 is preferably 2 m / s or more. If it is less than 2 m / s, the height of the fountain becomes 200 mm or less, and the way in which the cooling water strikes the lower surface of the thick steel plate varies, and temperature unevenness in the width direction tends to occur. Moreover, 20 m / s or less is preferable. If the flow rate is too high, the pumping water pressure must be increased, resulting in high equipment costs. In addition, the nozzle installation density for achieving the required water density becomes low, and the lower surface of the thick steel plate cannot be efficiently cooled.

The average water density between the table rolls is preferably 1.5 to 4.0 m ³ / m ² · min. If it is less than 1.5 m ³ / m ² · min, a sufficient cooling rate cannot be obtained at the initial stage of cooling, and a thick steel plate having a hard surface such as wear-resistant steel cannot be produced. Even if it exceeds 4.0 m ³ / m ² · min, it is effective to use the technique of the present invention, but it is not preferable from the viewpoint of cooling by efficiently using the amount of water and increasing the equipment cost.

  The present invention aims to obtain a high cooling efficiency while preventing the timing of the first cooling from greatly deviating depending on the position in the width direction. Therefore, in FIG. 1, the direction of the lower cooling water injection nozzle 4 is set to the vertical direction, but the nozzle direction may not be vertical as long as the nozzle landing portion 21 satisfies the above-described nozzle arrangement relationship. For example, the nozzle may be sprayed while being inclined toward the table roll.

  That is, the landing section in the width direction of the thick steel plate in each landing section row constituting the upstream landing section row group including one or more landing section rows including the most upstream row among the plurality of landing section rows. The rod-shaped cooling water is used so that the interval is shorter than the interval between the landing portions in the width direction in each of the landing portion rows constituting the downstream landing portion row group composed of the plurality of downstream landing portion rows. By injecting, the same effect as the embodiment shown in FIG. 1 having the above-described nozzle arrangement can be obtained.

  In the above description, the flow of the lower surface cooling equipment and the lower surface cooling water is mainly described in detail, but the upper surface cooling is not particularly defined in the present invention. That is, in FIG. 1, the upper surface cooling facility is depicted as the same cooling facility as the lower surface cooling facility, but is not limited thereto. Even if the bottom surface cooling technique of the present invention is used, it is preferable to perform uniform cooling at the top and bottom, but the top surface cooling is the bottom surface cooling. It is sufficient to have a cooling capacity that balances with the other, and a known technique may be used.

  Hereinafter, as an embodiment of the present invention, a case of cooling a steel plate in a thick plate rolling process will be described with reference to the drawings.

  In the thick plate hot rolling facility schematically shown in FIG. 5, the slab extracted from the heating furnace was subjected to forming and tentering rolling by a rolling mill, followed by rough rolling and finish rolling. The steel plate surface temperature measured immediately after finish rolling, that is, the finish temperature was 820 ° C. Thereafter, accelerated cooling was performed in an accelerated cooling facility through a hot leveler.

  The conveyance speed is set to 0.2 m / s, and cooling is performed from a cooling start temperature of 800 ° C. to a cooling end temperature (a value obtained by measuring the temperature after reheating on the exit side of the accelerated cooling equipment) to 200 ° C., and the surface hardness (Brinell hardness; load) (3000 kgf, 10 mm steel ball) A wear-resistant steel plate having a 400 HB class, a plate thickness of 60 mm, and a plate width of 3.0 m was manufactured.

  As an example of the present invention, the cooling equipment shown in the above-described embodiment was used. The cooling water injection nozzle had an inner diameter of 5 mm and an outer diameter of 9 mm, and the cooling water injection speed was 11.5 m / s for the upper surface cooling and 16.8 to 18.3 m / s for the lower surface cooling. The nozzle pitch in the width direction of the thick steel plate for upper surface cooling was 60 mm, and the layout of the lower surface nozzle was changed to compare the cooling efficiency.

  The nozzle rows arranged in the conveying direction of the thick steel plate in the zone having a distance between table rolls of 0.9 m were 6 rows in Invention Example 1 and Comparative Example, and 9 rows in Invention Example 2.

  The diameter of the circular water-cooled portion shown in FIG. 3 is about 20 mm in the upstream nozzle row group 41 (nozzle row A1, nozzle row B1, nozzle row C1) that performs the first cooling, and the downstream nozzle that performs the second cooling. In the row group 42 (nozzle row A2, nozzle row B2, nozzle row C2), it was assumed that the length was about 40 mm, and the following nozzle arrangement was determined.

  In Invention Example 1, two rows of nozzle row A1 and nozzle row B1 are arranged within 50 mm of the most upstream in the transport direction, and the nozzle pitch (S1) in the thick steel plate width direction in the row is 40 mm. In the row B1, the nozzle position deviation in the width direction (S2) was set to 20 mm. The nozzle pitches in the nozzle row A2 and the nozzle row B2 downstream of the nozzle row A1 and the nozzle row B1 were 80 mm in the thick steel plate conveyance direction and 80 mm in the thick steel plate width direction in the row. As a result of the optimal dispersion of the circular cooling portion (the combined portion of the landing portion 21 and the peripheral cooling portion 22) where the cooling water comes into contact with the lower surface of the thick steel plate, a high cooling capacity was obtained.

The water density on the lower surface where the water capacity density of the upper surface cooling is 1.5 m ³ / m ² · min and the cooling capacity is balanced is 2.2 m ³ / m ² · min. The uniformity in the width direction of the cooled thick steel plate was good, and the surface layer hardness in the width direction of the wear-resistant steel plate was within the range of HB390-400.

  In Invention Example 2, three rows of nozzle row A1, nozzle row B1, and nozzle row C1 are arranged in the uppermost 50 mm in the transport direction, and the nozzle pitch (S1) in the thick steel plate width direction in the row is set to 60 mm. In the row A1, the nozzle row B1, and the nozzle row C1, the nozzle position deviation (S2) in the width direction was set to 20 mm. The nozzle pitch in nozzle row A2, nozzle row B2, and nozzle row C2 downstream from nozzle row A1, nozzle row B1, and nozzle row C1 is 50 mm in the conveying direction of the thick steel plate, and in the width direction of the thick steel plate in the row. 120 mm. As a result of the optimal dispersion of the circular cooling portion (the combined portion of the landing portion 21 and the peripheral cooling portion 22) where the cooling water comes into contact with the lower surface of the steel plate, a high cooling capacity was obtained.

The water density on the lower surface where the water capacity density of the upper surface cooling is 1.5 m ³ / m ² · min and the cooling capacity is balanced is 2.2 m ³ / m ² · min. The uniformity in the width direction of the cooled thick steel plate was good, and the surface layer hardness in the width direction of the wear-resistant steel plate was within the range of HB390-420.

On the other hand, in the comparative example, the pitch of the cooling water injection nozzles was fixed at 70 mm in the conveying direction of the thick steel plate and 60 mm in the width direction of the thick steel plate in the row. The area of the circular cooling part where the cooling water comes into contact with the bottom surface of the thick steel plate is narrow at the upstream in the conveying direction and widened at the downstream, and the cooling capacity at the same water density is slightly lower than those of Examples 1 and 2. It was. The water density on the upper surface was 1.5 m ³ / m ² · min, and the water density on the lower surface where the cooling capacity was balanced was 2.4 m ³ / m ² · min, resulting in an extra running cost. Since there was strength in the width direction in the initial cooling, the uniformity in the width direction of the thick steel plate for cooling was inferior to that of Invention Examples 1 and 2, and the surface layer hardness in the width direction of the wear-resistant steel plate varied in the range of HB340 to 420. .

DESCRIPTION OF SYMBOLS 1 Upper header 2 Lower header 3 Upper cooling water injection nozzle 4 Lower cooling water injection nozzle 41 Upstream nozzle row group 42 Downstream nozzle row group 5 Upper surface cooling water 6 Lower surface cooling water 7 Falling water 8 Stagnating water film 10 Draining roll 11 Table Roll 12 Thick steel plate 21 Water landing part 22 Peripheral cooling part 23 Direct irradiation area

Claims (8)

  A steel plate cooling facility installed in a hot rolling line for steel plates, a header installed between table rolls for supplying cooling water to the bottom surface of the steel plate, and a bottom surface of the steel plate provided protruding from the header A cooling water injection nozzle group for injecting rod-shaped cooling water toward the surface, the cooling water injection nozzle group forming a plurality of nozzle rows in the conveying direction of the thick steel plate, and the most upstream of the plurality of nozzle rows A nozzle pitch in the width direction of the thick steel plate in each nozzle row that constitutes an upstream nozzle row group that includes one or more nozzle rows including the row is configured as a downstream nozzle row group that includes a plurality of downstream nozzle rows. A thick steel plate cooling facility characterized by being shorter than the nozzle pitch in the width direction in each nozzle row.   The thick steel plate cooling equipment according to claim 1, wherein a nozzle pitch in a width direction of the thick steel plate in each nozzle row included in the upstream nozzle row group is set to 30 to 90 mm.   The upstream nozzle row group is composed of two or more nozzle rows in the range of 50 mm in the conveying direction of the thick steel plate, and all the nozzles included in the upstream nozzle row group are at a constant pitch of 15 to 30 mm in the width direction. The cooling equipment for thick steel plates according to claim 1 or 2, characterized in that they are arranged side by side. The inner diameter of the cooling water injection nozzle is 5 to 12 mm, the flow rate of cooling water injected from the cooling water injection nozzle is 2 to 20 m / s, and the table water between the table rolls of cooling water injected from the cooling water injection nozzle group The cooling equipment for thick steel plates according to any one of claims 1 to ³ , wherein the average water density of the steel sheet is 1.5 to 4.0 m ³ / m ² · min.   A method of cooling a thick steel plate in a hot rolling line of a thick steel plate, injecting rod-shaped cooling water from a cooling water injection nozzle group provided in a header installed between table rolls toward the lower surface of the thick steel plate, The landing portion where the rod-shaped cooling water collides with the lower surface of the thick steel plate forms a plurality of landing portion rows in the conveying direction of the thick steel plate, and one or more landing portions including the most upstream row among the plurality of landing portion rows The downstream landing portion consisting of a plurality of downstream landing portions in which the interval between the landing portions in the steel plate width direction in each landing portion row constituting the upstream landing portion row group consisting of the water portion rows is A method for cooling a thick steel plate, characterized in that the rod-shaped cooling water is sprayed so as to be shorter than the interval between landing portions in the width direction in each landing portion row constituting the row group.   6. The method for cooling a thick steel plate according to claim 5, wherein an interval between landing portions in the width direction of the thick steel plate in each landing portion row included in the upstream landing portion row group is 30 to 90 mm.   The upstream landing section row group is constituted by two or more landing section rows within a range of 50 mm in the conveying direction of the thick steel plate, and all the landing portions included in the upstream landing section row group are in the width direction. The thick steel plate cooling method according to claim 5 or 6, wherein the steel plate is arranged at regular intervals of 15 to 30 mm. An inner diameter of the cooling water injection nozzle for injecting the rod-shaped cooling water is 5 to 12 mm, a flow rate of the rod-shaped cooling water is 2 to 20 m / s, and an average water density between the table rolls of the rod-shaped cooling water is 1.5 to The method for cooling a thick steel plate according to any one of claims 5 to 7, wherein 4.0 m ³ / m ² · min is set.