JPWO2014156086A1 - Manufacturing equipment and manufacturing method for thick steel plate - Google Patents

Abstract

The purpose is to provide uniform manufacturing equipment and a manufacturing method for thick steel sheets that are uniformly cooled in the cooling process by making the scale generated on the surface of the thick steel sheets uniform in the descaling process, and in the cooling process. To do. A hot rolling mill, a shape correction device, a descaling device, and an accelerated cooling device are arranged in this order from the upstream side in the conveying direction, and the energy density E of the cooling water that the descaling device injects toward the surface of the thick steel plate. Equipment for manufacturing thick steel plates with 0.10 J / mm2 or more.

Description

  The present invention relates to a thick steel plate manufacturing facility and a manufacturing method for performing hot rolling, shape correction, and controlled cooling of a thick steel plate.

  In recent years, the application of controlled cooling has expanded as a manufacturing process for thick steel plates. However, in general, hot thick steel plates are not necessarily uniform in shape, surface properties, and the like. For this reason, temperature unevenness is likely to occur in the thick steel plate during cooling, and deformation, residual stress, material non-uniformity, etc. occur in the thick steel plate after cooling, leading to quality defects and operational troubles.

  Therefore, Patent Document 1 discloses a method in which descaling is performed at least immediately before and immediately after the final pass of finish rolling, followed by hot correction, and then descaling and forced cooling. . Patent Document 2 discloses a method of performing control cooling after performing descaling after performing finish rolling and hot straightening. Patent Document 3 discloses a method of performing descaling while controlling the collision pressure of cooling water immediately before the controlled cooling.

JP-A-9-57327 Patent No. 3796133 JP 2010-247228 A

  However, when a thick steel plate is actually manufactured by the methods of Patent Documents 1 and 2 above, the scale does not completely peel off during descaling, but rather scale unevenness occurs due to descaling, and uniform cooling is performed during control cooling. There is a problem that it cannot be done. In addition, a high collision pressure is required in order to prevent scale unevenness by the method of Patent Document 3. For this reason, scale unevenness occurs at a low collision pressure, and as a result, there is a problem that uniform cooling cannot be performed during control cooling.

  In particular, in recent years, the level of material uniformity required for thick steel plates has become stricter, and the uneven cooling rate during controlled cooling caused by the unevenness of scale as described above has an effect on the material uniformity especially in the width direction of thick steel plates. The negative effects can no longer be ignored.

  Therefore, the present invention has been made paying attention to the unsolved problems of the above-described conventional example, and by uniformizing the scale generated on the surface of the thick steel plate in the descaling process, it is uniform in the cooling process. It aims at providing the manufacturing equipment and manufacturing method of a thick steel plate which cools and was excellent in the thick steel plate shape.

The present inventors diligently studied the force that causes scale peeling by cooling water. When descaling is performed after hot shape correction, the energy density of cooling water injected from the descaling device to the thick steel plate is 0.10 J / It was found that the thickness of the scale generated on the surface after the product is uniform when the thickness is ² mm or more. As a result, it has been found that when passing through the accelerated cooling apparatus, the steel plate can be uniformly cooled with almost no variation in the surface temperature at the position in the width direction of the thick steel plate, resulting in a thick steel plate having an excellent thick steel plate shape.

The gist of the present invention is as follows.
[1] Hot rolling mill, shape correction device, descaling device, and accelerated cooling device are arranged in this order from the upstream side in the conveying direction, and the energy of the cooling water sprayed by the descaling device toward the surface of the thick steel plate A thick steel plate manufacturing facility, wherein the density E is 0.10 J / mm ² or more.
[2] The distance from the descaling device to the accelerated cooling device when the transport speed from the descaling device to the accelerated cooling device is V [m / s] and the steel plate temperature before cooling is T [K]. L [m] satisfies the formula of L ≦ V × 5 × 10 ⁻⁹ × exp (25000 / T), the thick steel plate manufacturing facility according to [1].
[3] The equipment for manufacturing a thick steel plate according to [2], wherein each device is arranged such that a distance L from the descaling device to the accelerated cooling device is 12 m or less.
[4] The spray distance H from the spray nozzle of the descaling device to the surface of the thick steel plate is 40 mm or more and 200 mm or less, according to any one of [1] to [3] Equipment for manufacturing thick steel plates.
[5] The accelerated cooling device includes a header that supplies cooling water to the upper surface of the thick steel plate, a cooling water injection nozzle that injects rod-shaped cooling water suspended from the header, and the thick steel plate and the header. A partition wall to be installed, and a water supply port for interpolating a lower end portion of the cooling water injection nozzle, and a drain port for draining the cooling water supplied to the upper surface of the thick steel plate to the partition wall. And a plurality of the thick steel plate manufacturing equipment according to any one of [1] to [4].
[6] In the method of manufacturing a thick steel plate in the order of the hot rolling step, the hot straightening step, and the accelerated cooling step, the energy density E is 0. 0 on the surface of the thick steel plate during the hot straightening step and the cooling step. A method for producing a thick steel sheet, comprising a descaling step of injecting cooling water of 10 J / mm ² or more.
[7] The time t [s] from the completion of the descaling process to the start of the accelerated cooling process satisfies an expression of t ≦ 5 × 10 ⁻⁹ × exp (25000 / T). The manufacturing method of the thick steel plate as described in [6]. However, T: Thick steel plate temperature (K) before cooling.

  According to the present invention, by uniforming the scale generated on the surface of the thick steel plate in the descaling step, uniform cooling can be performed in the accelerated cooling step, and a thick steel plate having an excellent thick steel plate shape is manufactured. be able to.

FIG. 1 is a schematic view showing an example of a thick plate rolling line. FIG. 2 is a graph showing the relationship between the energy density of the cooling water to be jetted and the scale thickness generated on the product surface of the thick steel plate in the descaling apparatus. FIG. 3 is a diagram illustrating the relationship between the spray distance of the spray nozzle and the fluid velocity in the descaling apparatus. FIG. 4 is a side view of a cooling device according to an embodiment of the present invention. FIG. 5 is a side view of another cooling device according to an embodiment of the present invention. FIG. 6 is a diagram illustrating an example of the nozzle arrangement of the partition wall according to the embodiment of the present invention. FIG. 7 is a diagram for explaining the flow of the cooling drainage on the partition wall. FIG. 8 is a diagram for explaining another flow of the cooling drainage on the partition wall. FIG. 9 is a view for explaining a temperature distribution in the width direction of a thick steel plate of a conventional example. FIG. 10 is a diagram illustrating the flow of cooling water in the acceleration cooling device. FIG. 11 is a diagram for explaining non-interference with cooling drainage on the partition wall in the acceleration cooling device.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. Here, a case where the present invention is used for cooling a thick steel plate in a thick plate rolling process will be described as an example.

  FIG. 1 is a schematic view showing an example of a thick plate rolling line used for carrying out the present invention. The slab extracted from the heating furnace 2 is subjected to rough rolling and finish rolling by a rolling mill 3 and rolled into a thick steel plate 1 having a predetermined plate thickness. After the scale generated on the surface of the thick steel plate 1 is removed by the descaling device 4, the thick steel plate 1 is conveyed to the accelerated cooling device 6 online. Here, it is suitable for the shape of the thick steel plate after cooling to perform the accelerated cooling after adjusting the shape of the thick steel plate through the first shape correction device 5. In the accelerated cooling device 6, 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. Thereafter, the shape of the thick steel plate is corrected by the second shape correction device 7 as necessary.

  The descaling device 4 is a device that removes the scale generated on the surface of the thick steel plate 1. In the descaling device 4, after rolling, a plurality of injection nozzles are directed to the surface of the thick steel plate 1 after the shape correction of the strain generated in the thick steel plate 1 by the first shape straightening device 5, and cooling water is supplied from these nozzles. Spray.

The present inventors have obtained the knowledge that the scale peeling is not sufficiently performed by the descaling condition, and rather the scale unevenness is promoted. And when earnestly examining the conditions under which scale peeling is sufficiently performed, when descaling is performed after shape correction, as shown in FIG. 2, it is sprayed from the spray nozzle of the descaling device 4 onto the surface of the thick steel plate 1. It has been clarified that when the energy density E of the cooling water is set to 0.10 J / mm ² or more, the scale thickness to be regenerated thereafter becomes uniform at 5 μm or less. This is considered to be because the scale was once completely peeled off uniformly by descaling, and then the scale was thinly and uniformly regenerated.

In the present invention, the scale generated on the surface of the thick steel plate 1 is removed by performing descaling with the energy density E of the cooling water set to 0.10 J / mm ² or more. Thereafter, the accelerated cooling device 6 performs accelerated cooling of the thick steel plate 1. In the present invention, since the scale thickness of the thick steel plate becomes thin and uniform by descaling, it can be cooled uniformly with almost no surface temperature variation in the position in the width direction of the thick steel plate when passing through the accelerated cooling device. It becomes a thick steel plate excellent in steel plate shape.

  The reason is as follows. In conventional rolling equipment, when scale removal is performed in a descaling apparatus after shape correction, the scale may be partially peeled off. Then, since the scale is not peeled off uniformly, a variation in the scale thickness distribution of about 10 to 50 μm occurs. In this case, it is difficult to uniformly cool the thick steel plate in the subsequent accelerated cooling device. That is, if a thick steel plate having a variation in scale thickness distribution in a conventional rolling facility is accelerated and cooled, the variation in the surface temperature at the position in the width direction is large and cannot be uniformly cooled. As a result, the thick steel plate shape is affected.

Accordingly, by performing descaling with the descaling device 4 by setting the energy density E of the cooling water to 0.10 J / mm ² or more, there is no variation in the scale thickness distribution, so the thick steel plate 1 is cooled by the accelerated cooling device 6. At this time, there is almost no variation in the surface temperature at the position in the width direction, and cooling can be performed uniformly. As a result, the thick steel plate 1 having an excellent thick steel plate shape can be manufactured. In the case of the present invention, even when the collision pressure is low, the same descaling as in the case of using a high collision pressure can be achieved by adjusting the conveyance speed.

Here, the energy density E (J / mm ² ) of the cooling water sprayed onto the thick steel plate is an index of the ability to remove the scale by descaling and is defined as the following equation (1).
E = Q / (d × W ) × ρv 2/2 × t ... (1)
However, Q: Descaling water injection flow rate [m ³ / s], d: Flat nozzle spray injection thickness [mm], W: Flat nozzle spray injection width [mm], Fluid density ρ [kg / m ³ ] , Fluid velocity v [m / s] at the time of collision of thick steel plate, collision time t [s] (t = d / 1000 / V, transport speed V [m / s]).

  However, since it is not always easy to measure the fluid velocity v at the time of collision with a thick steel plate, a great deal of labor is required to obtain the energy density E defined by the equation (1) strictly.

Therefore, as a result of further investigation, the present inventors adopted water density × injection pressure × collision time as a simple definition of the energy density E (J / mm ² ) of cooling water injected into the thick steel plate. I found out that I should do it. Here, the water density (m ³ / mm ² · min) is a value calculated by “cooling water injection flow rate ÷ cooling water collision area”. The injection pressure (N / m ² (= MPa)) is defined by the discharge pressure of the cooling water. The collision time (s) is a value calculated by “cooling water collision thickness ÷ thick steel plate conveyance speed”. The relationship between the energy density of the cooling water calculated by this simple definition and the scale thickness generated on the product surface is the same as in FIG. 2, and the scale thickness decreases as the energy density of the cooling water increases. That is, when the energy density E is smaller than 0.10 J / mm ² , the thickness variation of the thick steel plate becomes large, and it is not possible to cool uniformly, and it is not possible to manufacture a thick steel plate having an excellent thick steel plate shape. There is. On the other hand, if the energy density E is 0.10 J / mm ² or more, such a failure is avoided. Therefore, in the present invention, the energy density E of the cooling water is 0.10 J / mm ² or more, and more preferably 0.15 J / mm ² or more.

  Next, the present inventors examined the fluid velocity v of the cooling water ejected from the ejection nozzle of the descaling device 4. As a result, it was found that the relationship between the fluid velocity v and the ejection distance is as shown in FIG. The fluid velocity on the vertical axis was obtained by solving an equation of motion considering buoyancy and air resistance. Until the cooling water reaches the thick steel plate, the fluid velocity v of the cooling water is decelerated as compared with the time of jetting. For this reason, the smaller the injection distance, the larger the fluid velocity v at the time of the collision with the thick steel plate, and a larger energy density can be obtained. From FIG. 3, since the attenuation increases particularly when the injection distance H exceeds 200 mm, the injection distance H is preferably 200 mm or less.

  And, as the injection distance is shorter, the injection pressure and the injection flow rate for obtaining a predetermined energy density can be reduced, so that the pumping capacity of the descaling device 4 can be reduced. In the embodiment of the present invention as shown in FIG. 1, the thick steel plate 1 that has been straightened by the first straightening device 5 moves into the descaling device 4. Can be brought closer to the surface of the thick steel plate 1. However, considering the contact between the injection nozzle and the thick steel plate 1, the lower limit value of the injection distance is preferably 40 mm or more. As mentioned above, in this invention, it is preferable that the injection distance H is 40 mm or more and 200 mm or less.

Moreover, in the descaling apparatus 4, the injection pressure of the cooling water is preferably 10 MPa or more, more preferably 15 MPa or more. This is effective because the energy density of the cooling water can be set to 0.10 J / mm ² or more without excessively reducing the conveyance speed. The upper limit value of the injection pressure is not particularly limited. However, when the injection pressure is increased, the energy consumed by the pump for supplying high-pressure water becomes enormous, and therefore the injection pressure is preferably 50 MPa or less.

By the way, regarding the scale of the surface of the thick steel plate 1 that affects the stability of the thick steel plate 1 when it is cooled by the accelerated cooling device 6, the growth of the scale of the thick steel plate 1 can be generally organized by diffusion rate control. It is known that it is represented by the equation (2).
ξ ² = a × exp (−Q / RT) × t (2)
Where ξ: scale thickness, a: constant, Q: activation energy, R: constant, T: thick steel plate temperature [K] before cooling, t: time.

  Therefore, considering the scale growth after descaling by the descaling device 4, simulation experiments of scale growth are performed at various temperatures and times, the constant of the above equation (2) is experimentally derived, The cooling stability was studied earnestly. As a result, it was found that cooling was stable when the scale thickness was 15 μm or less, more stable when the scale thickness was 10 μm or less, and very stable when the scale thickness was 5 μm or less.

When the scale thickness is 15 μm or less, the following formula (3) can be derived based on the above formula (2). That is, when the time t [s] from the end of descaling of the thick steel plate 1 by the descaling device 4 to the start of cooling the thick steel plate 1 by the accelerated cooling device 6 satisfies the following equation (3): Cooling by the acceleration cooling device 6 is stabilized.
t ≦ 5 × 10 ⁻⁹ × exp (25000 / T) (3)
However, T: Thick steel plate temperature [K] before cooling.

When the scale thickness is 10 μm or less, the following formula (4) can be derived based on the above formula (2). That is, when the time t [s] from the end of removal of the scale of the thick steel plate 1 by the descaling device 4 to the start of the cooling of the thick steel plate 1 by the accelerated cooling device 6 satisfies the following equation (4): The cooling by the acceleration cooling device 6 becomes more stable.
t ≦ 2.2 × 10 ⁻⁹ × exp (25000 / T) (4)
Furthermore, when the scale thickness is 5 μm or less, the following formula (5) can be derived based on the above formula (2). That is, when the time t [s] from the end of descaling of the thick steel plate 1 by the descaling device 4 to the start of cooling of the thick steel plate 1 by the accelerated cooling device 6 satisfies the following equation (5): Cooling by the acceleration cooling device 6 is very stable.
t ≦ 5.6 × 10 ⁻¹⁰ × exp (25000 / T) (5)
On the other hand, the distance L from the exit side of the descaling device 4 to the entrance side of the acceleration cooling device 6 is the transport speed V of the thick steel plate 1 and time t (from the end of the descaling device 4 process start of the acceleration cooling device 6 process). Until the following equation (6) is satisfied.
L ≦ V × t (6)
However, L: Distance (m) from descaling device 4 to acceleration cooling device 6, V: Conveying speed (m / s) of thick steel plate 1, t: Time (s)
Then, the following equation (7) can be derived from the above equation (6) and the above equation (3). In the present invention, it is more preferable to satisfy the expression (7).
L ≦ V × 5 × 10 ⁻⁹ × exp (25000 / T) (7)
Further, the following equation (8) can be derived from the above equation (6) and the above equation (4). In the present invention, it is more preferable to satisfy the formula (8).
L ≦ V × 2.2 × 10 ⁻⁹ × exp (25000 / T) (8)
Furthermore, the following equation (9) can be derived from the above equation (6) and the above equation (5). In the present invention, it is preferable that the expression (9) is satisfied.
L ≦ V × 5.6 × 10 ⁻¹⁰ × exp (25000 / T) (9)
From the above formulas (7) to (9), for example, when the temperature of the thick steel plate 1 before cooling by the accelerated cooling device 6 is 820 ° C. and the transport speed of the thick steel plate 1 is 0.28 to 2.50 m / s, The distance L from the descaling device 4 to the accelerated cooling device 6 is 12 to 107 m, cooling is stable, 5 to 47 m is more stable, and 1.3 to 12 m is very stable.

  Accordingly, when the distance L from the descaling device 4 to the acceleration cooling device 6 is 12 m or less, the cooling is stable even when the transport speed V of the thick steel plate 1 is slow (for example, V = 0.28 m / s), and conversely When the conveying speed V of the thick steel plate 1 is fast (for example, V = 2.50 m / s), the cooling is very stable, which is preferable. More preferably, the distance L from the descaling device 4 to the acceleration cooling device 6 is 5 m or less.

  Furthermore, in general, most of the thick steel plates 1 that require controlled cooling are conditions in which cooling is very stable at the transport speed V, considering that the transport speed V is 0.5 m / s or more. More preferably, the distance L is 2.5 m or less.

  Here, the case where the temperature of the thick steel plate 1 before cooling by the accelerated cooling device 6 is set to 820 ° C. has been described. Similarly, when the temperature of the thick steel plate 1 before cooling by the accelerated cooling device 6 is other than 820 ° C., the distance L from the descaling device 4 to the accelerated cooling device 6 is preferably 12 m or less, more preferably 5 m or less, Preferably, cooling can be stabilized by setting it to 2.5 m or less. When the temperature of the thick steel plate 1 before cooling by the accelerated cooling device 6 is lower than 820 ° C., the values on the right side of the above formula (7), the above formula (8), and the above formula (9) are respectively T Therefore, if the distance L from the descaling device 4 to the accelerated cooling device 6 is set appropriately for the case of T = 820 ° C., the equation (7) and the equation (8) are satisfied. This is because the formula (9) is necessarily satisfied. On the contrary, when the temperature of the thick steel plate 1 before cooling by the accelerated cooling device 6 is higher than 820 ° C., by adjusting the transport speed V of the thick steel plate 1 appropriately lower, The above formula (8) and the above formula (9) can be satisfied.

  Next, as shown in FIG. 4, the accelerated cooling device 6 of the present invention includes an upper header 11 that supplies cooling water to the upper surface of the thick steel plate 1, and cooling water that injects rod-shaped cooling water suspended from the upper header 11. The injection nozzle 13 includes a partition wall 15 installed between the thick steel plate 1 and the upper header 11, and the partition wall 15 includes a water supply port 16 for inserting a lower end portion of the cooling water injection nozzle 13, and a thick steel plate. It is preferable that a large number of drain ports 17 for draining the cooling water supplied to the upper surface of 1 onto the partition wall 15 are provided.

  Specifically, the upper surface cooling facility includes an upper header 11 for supplying cooling water to the upper surface of the thick steel plate 1, a cooling water injection nozzle 13 suspended from the upper header 11, and the upper header 11 and the thick steel plate 1. And a partition wall 15 having a large number of through-holes (water supply port 16 and drain port 17) installed horizontally in the width direction of the thick steel plate. The cooling water injection nozzle 13 is composed of a circular tube nozzle 13 for injecting rod-shaped cooling water, and its tip is inserted into a through-hole (water supply port 16) provided in the partition wall 15, from the lower end of the partition wall 15. It is installed to be on the top. The cooling water injection nozzle 13 may be inserted into the upper header 11 so that the upper end of the cooling water injection nozzle 13 protrudes into the upper header 11 in order to prevent the foreign matter at the bottom in the upper header 11 from being sucked and clogged. preferable.

  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 injection speed is 6 m / s or more, preferably 8 m / s or more, and the water flow jetted from the nozzle outlet has a continuous circular shape, and the water flow has a continuous and straight flow. Say. 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.

  The reason why the tip of the cooling water spray nozzle 13 is inserted into the through hole and is located above the lower end of the partition wall 15 is that the partition wall 15 is inserted even when a thick steel plate whose tip is warped upward enters. This is to prevent the cooling water injection nozzle 13 from being damaged. As a result, the cooling water injection nozzle 13 can be cooled for a long period of time in a good state, so that it is possible to prevent the occurrence of uneven temperature in the thick steel plate without repairing the equipment.

  Further, since the tip of the circular tube nozzle 13 is inserted into the through hole, as shown in FIG. 11, it does not interfere with the flow in the width direction of the drained water 19 indicated by the dotted arrow flowing through the upper surface of the partition wall 15. Therefore, the cooling water jetted from the cooling water jet nozzle 13 can reach the upper surface of the thick steel plate equally regardless of the position in the width direction, and uniform cooling in the width direction can be performed.

  As an example of the partition wall 15, as shown in FIG. 6, a large number of through-holes having a diameter of 10 mm are opened in a grid pattern at a pitch of 80 mm in the thick steel plate width direction and 80 mm in the transport direction. A cooling water injection nozzle 13 having an outer diameter of 8 mm, an inner diameter of 3 mm, and a length of 140 mm is inserted into the water supply port 16. The cooling water injection nozzles 13 are arranged in a staggered pattern, and the through holes through which the cooling water injection nozzles 13 do not pass serve as cooling water drains 17. As described above, the large number of through holes provided in the partition wall 15 of the accelerated cooling device of the present invention are composed of the substantially same number of water supply ports 16 and drain ports 17, and each share a role and function.

  At this time, the total cross-sectional area of the drain port 17 is sufficiently larger than the total cross-sectional area of the inner diameter of the circular pipe nozzle 13 of the cooling water injection nozzle 13, and about 11 times the total cross-sectional area of the inner diameter of the circular pipe nozzle 13 is ensured. As shown in FIG. 4, the cooling water supplied to the upper surface of the thick steel plate is filled between the thick steel plate surface and the partition wall 15, guided to the upper side of the partition wall 15 through the drain port 17, and quickly discharged. The FIG. 7 is a front view for explaining the flow of cooling drainage near the end in the width direction of the thick steel plate on the partition wall. The drainage direction of the drainage port 17 is upward opposite to the cooling water injection direction, and the cooling drainage drained upward from the partition wall 15 changes the direction outward in the thick steel plate width direction, between the upper header 11 and the partition wall 15. It drains through the drainage channel.

  On the other hand, in the example shown in FIG. 8, the drain port 17 is inclined in the thick steel plate width direction, and is inclined in the width direction outward so that the drain direction is directed outward in the thick steel plate width direction. By doing in this way, the flow of the discharged water 19 on the partition wall 15 in the thickness direction of the steel plate becomes smooth and drainage is promoted, which is preferable.

  Here, when the drain port and the water supply port are installed in the same through hole as shown in FIG. 9, after the cooling water collides with the thick steel plate, it becomes difficult to escape above the partition wall 15. And the partition wall 15 flow toward the end in the width direction of the thick steel plate. Then, since the flow rate of the cooling drainage between the thick steel plate 1 and the partition wall 15 increases as it approaches the end in the plate width direction, the force that the jet cooling water 18 penetrates the staying water film and reaches the thick steel plate is the plate width. The direction end portion is inhibited.

  In the case of a thin plate, since the plate width is about 2 m at most, the influence is limited. However, the influence cannot be ignored especially in the case of a thick plate having a plate width of 3 m or more. Accordingly, the cooling at the end in the width direction of the thick steel plate is weakened, and the temperature distribution in the width direction of the thick steel plate in this case becomes a non-uniform temperature distribution.

  On the other hand, in the accelerated cooling apparatus of the present invention, as shown in FIG. 10, the water supply port 16 and the water discharge port 17 are provided separately and share the roles of water supply and water discharge. And smoothly flows above the partition wall 15. Accordingly, since the drainage after cooling is quickly removed from the upper surface of the thick steel plate, the cooling water supplied subsequently can easily penetrate the staying water film, and a sufficient cooling capacity can be obtained. In this case, the temperature distribution in the width direction of the thick steel plate is a uniform temperature distribution, and a uniform temperature distribution in the width direction can be obtained.

  Incidentally, if the total cross-sectional area of the drain port 17 is 1.5 times or more the total cross-sectional area of the inner diameter of the circular tube nozzle 13, the cooling water is quickly discharged. This can be realized, for example, by making holes larger than the outer diameter of the circular tube nozzle 13 in the partition wall 15 and making the number of drain ports equal to or greater than the number of water supply ports.

  If the total cross-sectional area of the drain port 17 is smaller than 1.5 times the total cross-sectional area of the inner diameter of the circular tube nozzle 13, the flow resistance of the drain port increases, and the stagnant water becomes difficult to drain, resulting in penetration of the stagnant water film. Then, the amount of cooling water that can reach the surface of the thick steel plate is greatly reduced, and the cooling ability is lowered, which is not preferable. More preferably, it is 4 times or more. On the other hand, if there are too many outlets or the sectional diameter of the outlet becomes too large, the rigidity of the partition wall 15 will be reduced and it will be easily damaged when the steel plate collides. Therefore, the ratio of the total cross-sectional area of the drain outlet and the total cross-sectional area of the inner diameter of the circular tube nozzle 13 is preferably in the range of 1.5 to 20.

  The gap between the outer peripheral surface of the circular tube nozzle 13 inserted in the water supply port 16 of the partition wall 15 and the inner surface of the water supply port 16 is preferably 3 mm or less. If this gap is large, the cooling drainage discharged to the upper surface of the partition wall 15 is drawn into the gap between the outer peripheral surface of the circular pipe nozzle 13 of the water supply port 16 due to the influence of the accompanying flow of the cooling water injected from the circular pipe nozzle 13. As a result, the steel sheet is again supplied onto the thick steel plate, resulting in poor cooling efficiency. In order to prevent this, it is more preferable that the outer diameter of the circular tube nozzle 13 is substantially the same as the size of the water supply port 16. However, in consideration of machining accuracy and mounting errors, a gap of up to 3 mm that has substantially little influence is allowed. More preferably, it is 2 mm or less.

  Furthermore, in order to allow the cooling water to penetrate the staying water film and reach the thick steel plate, it is necessary to optimize the inner diameter and length of the circular tube nozzle 13, the cooling water injection speed and the nozzle distance.

  That is, the nozzle inner diameter is preferably 3 to 8 mm. If it is smaller than 3 mm, the bundle of water sprayed from the nozzle becomes thin and the momentum becomes weak. On the other hand, when the nozzle diameter exceeds 8 mm, the flow rate becomes slow, and the force penetrating the staying water film becomes weak.

  The length of the circular tube nozzle 13 is preferably 120 to 240 mm. The length of the circular tube nozzle 13 here means the length from the inlet at the upper end of the nozzle that penetrates into the header to some extent to the lower end of the nozzle inserted into the water supply port of the partition wall. When the circular tube nozzle 13 is shorter than 120 mm, the distance between the lower surface of the header and the upper surface of the partition wall becomes too short (for example, the header thickness is 20 mm, the protrusion amount of the nozzle upper end into the header is 20 mm, and the insertion amount of the nozzle lower end into the partition wall is 10 mm. Therefore, the drainage space above the partition wall becomes small, and the cooling drainage cannot be discharged smoothly. On the other hand, if it is longer than 240 mm, the pressure loss of the circular tube nozzle 13 becomes large, and the force penetrating the staying water film becomes weak.

  The jetting speed of the cooling water from the nozzle needs to be 6 m / s or more, preferably 8 m / s or more. This is because if it is less than 6 m / s, the force of the cooling water penetrating through the staying water film becomes extremely weak. If it is 8 m / s or more, a larger cooling capacity can be secured, which is preferable. Moreover, the distance from the lower end of the cooling water jet nozzle 13 for upper surface cooling to the surface of the thick steel plate 1 is preferably 30 to 120 mm. If it is less than 30 mm, the frequency with which the thick steel plate 1 collides with the partition wall 15 becomes extremely high, and equipment maintenance becomes difficult. If it exceeds 120 mm, the force through which the cooling water penetrates the staying water film becomes extremely weak.

  In cooling the upper surface of the thick steel plate, it is preferable to install draining rolls 20 before and after the upper header 11 so that the cooling water does not spread in the longitudinal direction of the thick steel plate. Thereby, the cooling zone length becomes constant and the temperature control becomes easy. Here, since the flow of the cooling water in the direction of transporting the thick steel plate is blocked by the draining roll 20, the cooling drainage flows outward in the width direction of the thick steel plate. However, the cooling water tends to stay in the vicinity of the draining roll 20.

  Therefore, as shown in FIG. 5, among the rows of the circular tube nozzles 13 aligned in the thick steel plate width direction, the cooling water jet nozzle in the uppermost stream side row in the thick steel plate transport direction is 15 to the upstream in the thick steel plate transport direction. It is preferable that the cooling water jet nozzles at the most downstream side in the thick steel plate conveyance direction are inclined 15 to 60 degrees in the downstream direction in the thick steel plate conveyance direction. By carrying out like this, a cooling water can be supplied also to the position near the draining roll 20, a cooling water does not stay in the draining roll 20 vicinity, and it is suitable for a cooling efficiency to rise.

  The distance between the lower surface of the upper header 11 and the upper surface of the partition wall 15 is such that the cross-sectional area in the width direction of the thick steel plate in the space surrounded by the lower surface of the header and the upper surface of the partition wall is 1.5 times the total cross-sectional area of the cooling water spray nozzle inner diameter. For example, it is about 100 mm or more. When the cross-sectional area of the thick steel plate in the width direction is not 1.5 times or more than the total cross-sectional area of the cooling water jet nozzle inner diameter, the cooling drainage discharged from the drain port 17 provided on the partition wall to the top surface of the partition wall 15 is smoothly thick. It cannot be discharged in the width direction of the steel sheet.

In the accelerated cooling device of the present invention, the range of the water density that exhibits the most effect is 1.5 m ³ / m ² · min or more. When the water density is lower than this, the staying water film does not become so thick, and even if a known technique for cooling the steel plate by free-falling the rod-shaped cooling water is applied, the temperature unevenness in the width direction does not become so large. In some cases. On the other hand, even when the water density is higher than 4.0 m ³ / m ² · min, it is effective to use the technique of the present invention. However, since there are problems in practical use such as an increase in equipment cost, 1.5 to 4.0 m ³ / m ² · min is the most practical water density.

  The cooling technique of the present invention is particularly effective when draining rolls are arranged before and after the cooling header. However, it is possible to apply even when there is no draining roll. For example, the header is relatively long in the longitudinal direction (when it is about 2 to 4 m), and is applied to a cooling facility that sprays a water spray for purging before and after the header to prevent water leakage to the non-water cooling zone. Is also possible.

  In the present invention, the cooling device on the lower surface side of the thick steel plate is not particularly limited. In the embodiment shown in FIGS. 4 and 5, an example of the cooled header 12 including the circular tube nozzle 14 similar to the cooling device on the upper surface side is shown. 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. Therefore, there is no need for the partition wall 15 for discharging cooling drainage like the upper surface side cooling in the width direction of the thick steel plate. Moreover, you may use the well-known technique which supplies film-form cooling water, spray-like spray cooling water, etc.

As mentioned above, the manufacturing equipment of the thick steel plate of the present invention sets the energy density E sprayed on the surface of the thick steel plate 1 from the spray nozzle of the descaling device 4 to 0.10 J / mm ² or more. 1 can be made uniform, and the accelerated cooling device 6 can achieve uniform cooling. As a result, the thick steel plate 1 having an excellent thick steel plate shape can be manufactured.

  In addition, by performing the shape correction of the thick steel plate 1 with the first shape correction device 5, the spray nozzle of the descaling device 4 can be brought close to the surface of the thick steel plate 1.

  Further, when the spray distance H (the surface distance between the spray nozzle of the descaling device 4 and the thick steel plate 1) is 40 mm or more and 200 mm or less, the descaling capability is improved. In addition, since the injection pressure and the injection flow rate for obtaining the predetermined energy density E may be small, the pumping capacity of the descaling device 4 can be reduced.

Further, the distance L from the descaling device 4 to the acceleration cooling device 6 satisfies L ≦ V × 5 × 10 ⁻⁹ × exp (25000 / T), thereby stabilizing the cooling of the thick steel plate 1 by the acceleration cooling device 6. Can be made.

  Further, as shown in FIG. 4, the accelerated cooling device 6 of the present invention cools the upper surface of the thick steel plate 1 by the cooling water supplied from the upper cooling water injection nozzle 13 through the water supply port 16 and has a high temperature. It becomes drainage and flows in the width direction of the steel plate 1 from above the partition 15 using the drain port 17 through which the upper cooling water injection nozzle 13 is not inserted as a drainage channel, and the drainage after cooling is quickly removed from the steel plate 1. Therefore, the cooling water flowing from the upper cooling water injection nozzle 13 through the water supply port 16 sequentially comes into contact with the thick steel plate 1 to obtain sufficient cooling capacity in the width direction. Can do.

As a result of investigations by the present inventors, it was found that the temperature unevenness in the width direction of the thick steel plate subjected to accelerated cooling without performing descaling as in the present invention was about 40 ° C. On the other hand, using the descaling device 4 of the present invention, after performing descaling at an energy density of cooling water of 0.10 J / mm ² or more, temperature unevenness in the width direction of the thick steel plate subjected to accelerated cooling. It was found that the temperature decreased to about 10 ° C. Furthermore, after performing descaling with the descaling device 4, it is found that the temperature unevenness in the width direction of the thick steel plate subjected to acceleration cooling using the acceleration cooling device 6 shown in FIG. 4 is reduced to about 4 ° C. It was. The temperature unevenness of the thick steel plate was measured by measuring the steel plate surface temperature distribution after accelerated cooling with a scanning thermometer, and the temperature unevenness in the width direction was calculated from the measurement result.

  Further, as in the present invention, the distortion generated during rolling is corrected by the first shape correction device 5, the descaling device 4 performs the descaling of the thick steel plate 1, and the cooling controllability is stabilized. The thick steel plate 1 that is corrected by the second shape correcting device 7 originally has high flatness and the temperature of the thick steel plate 1 is also uniform. Therefore, it is not necessary to make the correction reaction force of the second shape correcting device 7 so high. Moreover, the distance between the acceleration cooling device 6 and the second shape correction device 7 is preferably longer than the maximum length of the thick steel plate 1 manufactured on the rolling production line. As a result, reverse correction or the like is often performed by the second shape correction device 7, so that the effect of preventing troubles such as the reversely fed thick steel plate 1 jumping on the transport roll and colliding with the acceleration cooling device 6, The slight temperature deviation generated during cooling in the acceleration cooling device 6 can be made uniform, and the effect of avoiding the occurrence of warpage due to the temperature deviation after correction can be expected.

  The thick steel plate 1 having a thickness of 30 mm and a width of 3500 mm rolled by the rolling mill 3 was subjected to controlled cooling from 820 ° C. to 420 ° C. after passing through the first shape correction device 5 and the descaling device 4. Here, the conditions under which the cooling is stabilized are calculated from the above-described equations (3), (4), and (5). After the removal of the scale of the thick steel plate 1 by the descaling device 4, the accelerated cooling device 6 uses the thick steel plate. The time t until the cooling of 1 is started is preferably 42 s or less, more preferably 19 s or less, and even more preferably 5 s or less.

The descaling device 4 has a nozzle injection pressure of 17.7 MPa, an injection flow rate per nozzle of 50 L / min (= 8.3 × 10 ⁻⁴ m ³ / s), an injection distance (injection of the descaling device 4 The surface distance between the nozzle and the thick steel plate 1 is 130 mm, the nozzle injection angle is 32 °, the nozzle attack angle is 15 °, and one row is arranged in the width direction so that the injection regions of adjacent nozzles are wrapped to some extent. The spray spray thickness is 3 mm and the spray spray width is 77 mm. Here, the energy density of the cooling water is a value defined by the above-mentioned water amount density × injection pressure × collision time. The collision time (s) is the time during which descaling water is sprayed on the surface of the thick steel plate, and is obtained by dividing the spray spray thickness by the transport speed.

  The accelerated cooling device 6 is provided with a flow path that allows the cooling water supplied to the upper surface of the thick steel plate to flow above the partition as shown in FIG. 4 and further drains from the side of the thick steel plate in the width direction as shown in FIG. The equipment. In the partition wall, holes with a diameter of 12 mm are drilled like a grid, and as shown in FIG. 6, the upper cooling water injection nozzles are inserted into the water supply ports arranged in a staggered pattern, and the remaining holes are used as drainage ports. Using. The distance between the lower surface of the upper header and the upper surface of the partition wall was 100 mm.

The upper cooling water spray nozzle of the accelerated cooling device 6 had an inner diameter of 5 mm, an outer diameter of 9 mm, and a length of 170 mm, and its upper end protruded into the header. Moreover, the injection speed of the rod-shaped cooling water was 8.9 m / s. The nozzle pitch in the thick steel plate width direction was 50 mm, and 10 rows of nozzles were arranged in the longitudinal direction in a zone having a distance between table rollers of 1 m. The water density on the upper surface was 2.1 m ³ / m ² · min. The lower end of the nozzle for cooling the upper surface was set so as to be in the middle position between the upper and lower surfaces of the partition wall having a thickness of 25 mm, and the distance to the surface of the thick steel plate was 80 mm.

  For the bottom surface cooling facility, the cooling facility similar to the top surface cooling facility is used except that no partition wall is provided as shown in FIG. did.

  As shown in Table 1, the distance L from the descaling device 4 to the acceleration cooling device 6, the conveying speed V of the thick steel plate, and the time t from the descaling device 4 to the acceleration cooling device 6 were variously changed.

  The thick steel plate shape was evaluated by the additional correction rate (%). Specifically, if the warpage of the total length of the steel sheet and / or the warpage of the full width of the steel sheet is within the standard value defined in the product standard corresponding to the steel sheet, it passes, and if it exceeds the standard value, additional correction is performed. The material was judged as an implementation material, and the additional correction rate was calculated as (number of additional correction implementation materials) / (total number of target materials) × 100.

表１の本発明例１〜５は、エネルギー密度がいずれも０．１０Ｊ／ｍｍ^２以上であることから、形状不良による追加矯正率が低く、良好な結果を得られた。これは、加速冷却装置６で冷却した際に、幅方向位置の表面温度のバラツキが殆ど無く均一に冷却され、厚鋼板の温度分布に起因すると考えられる平坦度が優れ、その結果、形状不良による追加矯正率が低くなったと考えられる。また、本発明例１〜５はいずれもスケール除去されており、表面性状も良好であった。なお、表面性状の評価は、室温まで冷却された厚鋼板表面の画像を用いて、スケール残存部と剥離部との色調差を利用した画像処理からスケール有無を判断し、評価した。

In Invention Examples 1 to 5 in Table 1, since the energy density was 0.10 J / mm ² or more, the additional correction rate due to shape defects was low, and good results were obtained. This is because, when cooled by the accelerating cooling device 6, it is uniformly cooled with almost no variation in the surface temperature at the position in the width direction, and the flatness considered to be caused by the temperature distribution of the thick steel plate is excellent. It is considered that the additional correction rate has decreased. In addition, the inventive examples 1 to 5 were all scale-removed and the surface properties were good. The surface property was evaluated by determining the presence or absence of scale from image processing using the color tone difference between the remaining scale part and the peeled part using an image of the surface of the thick steel plate cooled to room temperature.

  In particular, Examples 1 to 3 of the present invention in which the distance from the descaling device 4 to the acceleration cooling device 6 is 5 m are as follows. Regardless of the transport speed V of the thick steel plate, the time t until the start of the cooling was 19 s or less, which is a condition for the cooling by the accelerated cooling device 6 to be more stable. Therefore, the additional correction rate was good at 5% or less.

  In addition, Example 5 of the present invention gave good results by setting the energy density within the range of the present invention without requiring high collision pressure (1.0 MPa) as in Patent Document 1 and Patent Document 2. .

  On the other hand, in Comparative Example 1 in which the descaling device 4 did not remove the scale and the cooling by the accelerated cooling device 6 was performed, the flatness considered to be caused by the temperature distribution of the thick steel plate deteriorated, and the additional correction rate was 40%. It became.

Further, the setting conditions by the descaling device 4 are a water pressure of 9 MPa, an injection flow rate per nozzle of 25 L / min (= 4.2 × 10 ⁻⁴ m ³ / s), and other conditions are Example 2 of the present invention. In Comparative Example 2 in which the energy density was 0.08 J / mm ² , the temperature distribution in the width direction of the thick steel plate deteriorated due to partial peeling of the scale, and the flatness of the thick steel plate also deteriorated accordingly. The additional correction rate was 70%.

  In Comparative Example 3, since the energy density was outside the range of the present invention even though it was within the range of high collision pressure as in Patent Document 1 and Patent Document 2, the scale was partially peeled off. Since the temperature distribution in the width direction of the steel plate deteriorated and the flatness of the thick steel plate also deteriorated along with it, the additional correction rate became 65%.

DESCRIPTION OF SYMBOLS 1 Thick steel plate 2 Heating furnace 3 Rolling mill 4 Descaling device 5 1st shape correction device 6 Accelerated cooling device 7 2nd shape correction device 11 Upper header 12 Lower header 13 Upper cooling water injection nozzle (circular tube nozzle)
14 Lower cooling water injection nozzle (circular tube nozzle)
15 Bulkhead 16 Water supply port 17 Drainage port 18 Injection cooling water 19 Drained water 20 Draining roll 21 Draining roll

Claims (7)

A hot rolling mill, a shape correction device, a descaling device, and an accelerated cooling device are arranged in this order from the upstream side in the conveying direction, and the energy density E of the cooling water that the descaling device injects toward the surface of the thick steel plate. A thick steel plate manufacturing facility characterized by 0.10 J / mm ² or more. When the transport speed from the descaling device to the accelerated cooling device is V [m / s] and the steel plate temperature before cooling is T [K], the distance L [m from the descaling device to the accelerated cooling device ] Satisfies the formula of L ≦ V × 5 × 10 ⁻⁹ × exp (25000 / T). The equipment for manufacturing a thick steel plate according to claim 1.   The apparatus for manufacturing a thick steel plate according to claim 2, wherein each apparatus is arranged such that a distance L from the descaling apparatus to the accelerated cooling apparatus is 12 m or less.   4. The thick steel plate manufacturing equipment according to claim 1, wherein a spray distance H from a spray nozzle of the descaling device to a surface of the thick steel plate is 40 mm or more and 200 mm or less. 5.   The accelerated cooling device is installed between a header for supplying cooling water to the upper surface of the thick steel plate, a cooling water injection nozzle for injecting rod-shaped cooling water suspended from the header, and the thick steel plate and the header. A partition wall, and the partition wall includes a water supply port for interpolating a lower end portion of the cooling water injection nozzle, and a drain port for draining the cooling water supplied to the upper surface of the thick steel plate to the partition wall. The manufacturing equipment for thick steel plates according to any one of claims 1 to 4, wherein a large number are provided. In the method of manufacturing a thick steel plate in the order of the hot rolling step, the hot straightening step and the accelerated cooling step, the energy density E is 0.10 J / mm on the surface of the thick steel plate during the hot straightening step and the cooling step. ^A method for producing a thick steel plate, comprising a descaling step of injecting ^two or more cooling waters. The time t [s] from the completion of the descaling process to the start of the accelerated cooling process satisfies an expression of t ≦ 5 × 10 ⁻⁹ × exp (25000 / T). The manufacturing method of the thick steel plate as described in 1 .. However, T: Thick steel plate temperature (K) before cooling.

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