TWI569898B - Manufacture method and manufacturing equipment of thick steel plate - Google Patents

Description

Manufacturing method and manufacturing equipment for thick steel plate

The present invention relates to a method and apparatus for manufacturing a thick steel plate.

In the process of manufacturing thick steel sheets by hot rolling, the application of cooling control has been expanded. For example, as shown in FIG. 1, after the thick steel plate (not shown) is reheated by the heating furnace 1, the thick steel plate is rust-removed in the descaling apparatus 2. Then, the thick steel plate is rolled by the rolling mill 3, and then corrected by the shape correcting device 4, and then controlled cooling by water cooling or air cooling is performed in the accelerated cooling device 5. Furthermore, the arrow in the figure is the traveling direction of the thick steel plate.

It is known that when the thick steel plate is water-cooled by the accelerated cooling device, as shown in FIG. 2, the thicker the surface of the thick steel plate is, the shorter the cooling time is. Therefore, it is understood that the cooling rate is increased. However, if there is a variation in the thickness of the scale, the cooling rate becomes uneven, and therefore there is a problem that the materials such as strength and hardness are deviated.

Further, when the thickness of the scale is not uniform, as described above, the cooling rate becomes uneven. In this case, it is known that the distribution of the surface temperature of the thick steel sheet (hereinafter referred to as "cooling stop temperature") when the accelerated cooling in the width direction of the thick steel plate is stopped is varied as shown in FIG. Since the cooling stop temperature of such a thick steel plate varies, there is a problem that a uniform material cannot be obtained. In the case of exemplifying a specific example, when a portion having a thickness of 40 μm and 20 μm is mixed in the width direction of the thick steel plate, the cooling stop temperature when the steel plate having a thickness of 25 mm is cooled from 800 ° C to a target temperature of 500 ° C is 40μm The portion became 460 ° C and became 500 ° C at a portion of 20 μm. At a portion of 40 μm, the cooling stop temperature was lowered by 40 ° C from the target temperature, and as a result, a uniform material could not be obtained.

Therefore, Patent Document 1 discloses a method of controlling the thickness of the scale to uniformize the cooling rate, thereby achieving uniformization of the cooling stop temperature. In Patent Document 1, a rust removing device provided before and after the rolling press is used in the rolling process, so that the end side side is rust-proofed when the end of the thick steel plate is lower than the front end. The amount of water is more than the amount of water sprayed on the front end side, and the scale removal rate and residual thickness are controlled in the longitudinal direction of the thick steel plate, thereby controlling the heat transfer coefficient of the steel sheet surface during cooling to control the length of the thick steel plate. The cooling of the direction stops the homogenization of the temperature.

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open No. Hei 6-330155

In the conventional technique, it is desirable to achieve uniformization of the cooling stop temperature by adjusting the amount of cooling water or the conveying speed. However, in this method, since the cooling rate varies depending on the variation in the thickness of the scale, not only the uniformization of the cooling rate is difficult, but also the uniformity of the cooling stop temperature is difficult.

Further, in the method of Patent Document 1, if the scale removal rate or the residual thickness cannot be controlled on the line, the heat transfer coefficient cannot be controlled, and therefore, the uniformization of the high-precision cooling rate cannot be achieved. Further, when the scale removal rate is changed, the cooling stop temperature of the remaining portion of the scale and the peeling portion is different, and thus the material varies.

An object of the present invention is to solve the above problems and to provide a method and a manufacturing apparatus for a thick steel plate having a high-quality thick steel plate which can ensure a small variation in material.

The present invention has been made to solve the above-mentioned problems, and the gist thereof is as follows.

[1] A method for producing a thick steel plate, which is a method for producing a thick steel plate in the order of a hot rolling step, a shape correcting step, and an accelerated cooling step, characterized in that between the shape correcting step and the accelerated cooling step a temperature adjustment step and a descaling step, wherein the temperature adjustment step is performed by air cooling the surface temperature of the thick steel plate to a point of less than Ar ₃ metamorphism, or by a water density of 0.3 to 2.2 m ³ /(m ² ‧ min) The upper and lower surfaces are supplied with cooling water to be water-cooled, thereby causing the surface of the thick steel plate to be metamorphosed; and the descaling step is performed after the temperature adjustment step and before the accelerated cooling step, the surface of the thick steel plate is sprayed with an energy density of 0.05 J. High pressure water of /mm ² or more.

[2] The method for producing a thick steel plate according to [1], wherein in the rust removing step, the injection pressure of the high pressure water is 10 MPa or more.

[3] A manufacturing apparatus for a thick steel plate, wherein the hot rolling device, the shape correcting device, the temperature adjusting device, the rust removing device, and the accelerated cooling device are disposed on the upstream side in the self-transporting direction, and the temperature adjusting device is disposed In the middle, the surface temperature of the thick steel plate is air-cooled to less than the Ar ₃ metamorphic point, or the cooling water is supplied to the upper surface of the thick steel plate at a water density of 0.3 to 2.2 m ³ /(m ² ‧ min), thereby causing water cooling. The surface of the thick steel plate is metamorphosed, and in the above-described descaling device, the surface of the thick steel plate is sprayed with high-pressure water having an energy density of 0.05 J/mm ² or more.

[4] The apparatus for manufacturing a thick steel plate according to [3], wherein in the rust removing device, the injection pressure of the high pressure water is 10 MPa or more.

According to the invention, between the shape correcting step has a step of accelerated cooling the steel plate surface temperature dropped to less than the Ar ₃ transformation point of the steel plate surface temperature of the abnormal adjusting step, the surface of a steel plate, and after the temperature adjusting step The rust removal step of the high-pressure water having an ejection energy density of 0.05 J/mm ² or more, whereby the cooling rate and the cooling stop temperature can be uniformized. As a result, it is possible to manufacture a high-quality thick steel plate having a small material variation.

1‧‧‧heating furnace

2‧‧‧Descaling device

3‧‧‧ rolling press

4‧‧‧Shaping correction device

5‧‧‧Accelerated cooling device

6‧‧‧Temperature adjustment device

7‧‧‧Descaling device

10‧‧‧ thick steel plate

11‧‧‧Upper tube

12‧‧‧ Lower header

13‧‧‧Upper cooling water jet nozzle (round nozzle)

14‧‧‧Under cooling water jet nozzle (round nozzle)

15‧‧‧ partition wall

16‧‧‧Water supply

17‧‧‧Drainage

18‧‧‧Spray cooling water

19‧‧‧ discharged water

20‧‧‧Dewatering roller

21‧‧‧Dewatering roller

△T‧‧‧ Temperature drop

Fig. 1 is a schematic view showing a manufacturing apparatus of a conventional thick steel plate.

Fig. 2 is a graph showing the relationship between the thickness of the scale during the accelerated cooling, the cooling time, and the surface temperature of the thick steel plate.

Fig. 3 is a view showing the relationship between the position in the width direction of the thick steel plate after the accelerated cooling and the cooling stop temperature.

Fig. 4 is a schematic view showing a manufacturing apparatus of a thick steel plate according to an embodiment of the present invention.

Fig. 5 is a graph showing the relationship between the metamorphosis of the surface of the thick steel plate, the energy density of the high-pressure water, and the peeling rate of the scale.

Fig. 6 is a graph showing the relationship between the temperature of the surface of the thick steel sheet after the end of the rolling and the injection pressure required to break the scale.

Figure 7 is a graph defining the temperature difference from the temperature adjustment step to the surface of the thick steel plate before the start of the descaling step.

Fig. 8 is a graph showing the relationship between the amount of temperature drop on the surface of the thick steel plate and the deviation from the cooling stop temperature.

Fig. 9 is a side view of a cooling device according to an embodiment of the present invention.

Figure 10 is a side elevational view of another cooling device in accordance with an embodiment of the present invention.

Fig. 11 is a view for explaining an example of arrangement of nozzles of a partition wall according to an embodiment of the present invention.

Fig. 12 is a view for explaining the flow of the cooling drain on the partition wall.

Fig. 13 is a view for explaining another flow of the cooling drain on the partition wall.

Fig. 14 is a view for explaining a temperature distribution in the width direction of a thick steel plate according to a conventional example.

Fig. 15 is a view for explaining the flow of cooling water in the accelerated cooling device.

Fig. 16 is a view for explaining the non-interference with the cooling drain on the partition wall in the accelerated cooling device.

Hereinafter, the mode for carrying out the invention will be described with reference to the drawings.

Fig. 4 is a schematic view showing a manufacturing apparatus of a thick steel plate according to an embodiment of the present invention. In Fig. 4, the arrow is the conveying direction of the thick steel plate. The heating furnace 1, the rust removing device 2, the rolling press 3, the shape correcting device 4, the temperature adjusting device 6, the rust removing device 7, and the accelerated cooling device 5 are disposed in this order from the upstream side in the conveying direction of the thick steel plate. In Fig. 4, after the thick steel plate (not shown) is reheated by the heating furnace 1, the thick steel plate is first derusted in the descaling device 2 to remove the scale. Then, the thick steel plate is hot-rolled by the rolling mill 3, and after being corrected by the shape correcting device 4, the surface temperature of the thick steel plate is lowered by the temperature adjusting device 6, and then the scale is completely removed in the rust removing device 7. Rust removal. Then, controlled cooling by water cooling or air cooling is performed in the accelerating cooling device 5.

In the present invention, the temperature adjustment device 6 and the descaling device 7 are disposed between the shape correcting device 4 and the accelerated cooling device 5. Further, in the temperature adjusting device 6, the surface temperature of the thick steel plate is lowered to a point where the Ar ₃ transformation is not completed, and the surface of the thick steel plate is deformed. The present invention is characterized in that, in the rust removing device 7, rust removal of high-pressure water having an energy density of 0.05 J/mm ² or more is applied to a thick steel plate.

The temperature adjustment device 6 is disposed between the shape correction device 4 and the rust removal device 7. The surface of the thick steel plate is deformed by lowering the surface temperature of the thick steel plate to a point other than the Ar ₃ metamorphic point in the temperature adjustment step of the temperature adjusting device 6, and the scale is easily removed in the subsequent rust removing step.

By changing the surface temperature of the thick steel plate to less than the Ar ₃ metamorphic point in the temperature adjustment step, the surface of the thick steel plate is metamorphosed, causing the deformation of the substrate iron, and the interface between the scale and the substrate iron is offset and the scale is closely adhered. The force is reduced. The reason can be considered as the following mechanism. If the surface of the thick steel plate is cooled to less than the Ar ₃ metamorphic point, the base iron is metamorphosed from austenite to ferrite. At this time, since the substrate iron expands, the interface between the scale and the substrate iron is applied, and cracks are generated at the interface. It is considered that as a result, the adhesion of the scale is lowered. Therefore, the surface of the thick steel plate is deformed by lowering the surface temperature of the thick steel plate to less than the Ar ₃ transformation point, and the scale removal is facilitated by the rust removal step by the rust removing device 7. Further, the Ar ₃ metamorphic point can be calculated according to the following formula (*).

Ar ₃ =910-310C-80Mn-20Cu-15Cr-55Ni-80Mo...(*)

Here, the element symbol indicates the content (% by mass) of the steel of each element.

Next, the thick steel plate in which the surface temperature of the thick steel plate is lowered to the point where the Ar ₃ transformation point is not formed and the surface of the thick steel plate is deformed is attached to the rust removing device 7 to remove the rust. At this time, by spraying high-pressure water having an energy density of 0.05 J/mm ² or more on the thick steel plate (in the present invention, the case where the injection pressure is 5 MPa or more is referred to as high-pressure water), the scale can be completely removed. Since the scale is completely removed in the descaling step, the cooling control can be performed in the subsequent accelerated cooling step using the heating and cooling device 5. As a result, uniformization of the cooling rate with high precision and uniformity of the cooling stop temperature can be achieved. Further, the high-pressure water may be sprayed over the entire length of the thick steel plate.

The inventors of the present invention investigated the energy density of the high-pressure water and the peeling rate of the scale (the ratio of the area of the peeled surface of the scale to the area of the thick steel plate) using the influence of the presence or absence of the deformation of the surface of the thick steel plate before the rust removal step. Relationship. As a result, the insight as shown in FIG. 5 is obtained. As can be seen from Fig. 5, when the energy density is large, the scale peeling rate is increased, and by deforming the surface of the thick steel sheet, even if the energy density is small, the scale can be peeled off. Further, according to Fig. 5, when the rust is removed after the metamorphosis, when the energy density is less than 0.05 J/mm ² , the peeling rate of the scale is low, and therefore, the scale remains in one part of the thick steel plate, and the cooling is performed. The temperature is stopped and the material becomes uneven. Therefore, the energy density of the high pressure water is set to 0.05 J/mm ² or more. It is preferably 0.10 J/mm ² or more. Further, from the viewpoint of energy consumption of the pump for supplying high-pressure water, the energy density of the high-pressure water is preferably 0.60 J/mm ² or less.

In the present invention, it is preferred to spray high-pressure water having an injection pressure of 10 MPa or more in the rust removing step. The scale can be completely removed by setting the injection pressure to 10 MPa or more. Therefore, the uniformization of the cooling rate and the cooling stop temperature in the accelerated cooling step can be achieved. In order to destroy the scale, the pressure of the droplets of high-pressure water against the thick steel plate must exceed the hardness of the scale. The inventors of the present invention investigated the relationship between the temperature of the surface of the thick steel plate after the completion of the rolling and the injection pressure of the high-pressure water required for the destruction of the scale, and as a result, the findings of Fig. 6 were obtained. In general, in the case of manufacturing a thick steel plate which requires controlled cooling as in the present invention, the temperature of the surface of the thick steel plate after the completion of the rolling is only about 900 ° C even higher. Therefore, in the present invention, in order to destroy the scale, it is preferred to set the injection pressure of the high-pressure water to 10 MPa or more.

Here, the energy density E (J/mm ² ) of the cooling water sprayed on the thick steel plate refers to an index of the ability to remove the scale by rust removal, and is defined as in the following formula (1).

E=Q/(d×W)×ρv ² /2×t...(1)

Where Q: jet flow rate of rust-removing water [m ³ /s], d: spray spray thickness [mm] of flat nozzle, W: spray jet width [mm] of flat nozzle, fluid density ρ [kg/m ³ ] The fluid velocity v[m/s] and the collision time t[s] (t=d/1000/V, transport speed V[m/s]) when the thick steel plate collides.

However, since the measurement of the fluid velocity v at the time of collision of a thick steel plate is not necessarily easy, if the energy density E defined by the formula (1) is to be strictly obtained, it is extremely labor intensive.

Therefore, the present inventors have further studied and found that the water density x the injection pressure x the collision time can be used as a simple definition of the energy density E (J/mm ² ) of the cooling water sprayed on the thick steel plate. Here, the water amount density (m ³ /(m ² ‧ min)) is a value calculated from "injection flow rate of cooling water ÷ cooling water collision area". The injection pressure (MPa) is defined by the discharge pressure of the cooling water. The collision time (s) is a value calculated from "the cooling water impact thickness and the conveying speed of the thick steel plate". Further, the relationship between the energy density of the high-pressure water of the present invention and the scale peeling rate calculated by the simple definition is also the same as that of Fig. 5.

In the temperature adjustment step, the surface temperature of the thick steel plate is lowered to below the Ar ₃ metamorphic point by air cooling or water cooling. Further, in the case of performing air cooling, it is only necessary to appropriately cool the conveying roller of the thick steel plate to a point where the Ar ₃ transformation state is not completed.

In the present invention, when water cooling is performed in the temperature adjustment step, cooling water is supplied to the upper surface of the upper and lower portions of the thick steel plate at a water density of 0.3 to 2.2 m ³ /(m ² ‧ min). If the water density is less than 0.3 m ³ /(m ² ‧ min), the surface temperature of the thick steel plate cannot be lowered to the point where the Ar ₃ transformation is not completed, and the surface of the thick steel plate cannot be deformed. As a result, the scale remains on the thick steel plate, and even if the cooling control is performed in the subsequent accelerated cooling step, the cooling stop temperature varies and the material becomes uneven. In addition, when the water amount density is more than 2.2 m ³ /(m ² ‧ min), the temperature drop amount ΔT in the following temperature adjustment step exceeds 200 ° C, and the cooling stop temperature varies, and the material becomes uneven.

When the surface of the thick steel plate is deformed in the temperature adjusting device 6, the surface of the thick steel plate is cooled while the scale is attached to the thick steel plate. The present inventors have found that when the temperature drop amount during cooling in the temperature adjusting device 6 is large, the adhesion state of the scale affects the uniformity of the cooling stop temperature, and the deviation of the cooling stop temperature (accelerated cooling step) The difference between the surface temperature of the target steel sheet and the actual steel sheet surface temperature after the accelerated cooling is increased. Here, the temperature drop amount ΔT of the surface of the thick steel plate in the temperature adjusting device 6 is defined as the difference between the surface temperature of the thick steel plate and the lowest temperature of the surface of the thick steel plate at the start of cooling, as shown in Fig. 7 .

The inventors of the present invention used a thick steel plate having a surface temperature of 800 ° C and a thickness of 25 mm after the completion of the rolling press of the rolling mill, and manufactured a thick steel plate in the order of the temperature adjustment step, the rust removal step, and the accelerated cooling step. Here, as the condition that all the scales can be removed before or after the surface of the steel sheet in the case of rust removal, the energy density at the time of rust removal is set to 0.2 J/mm ² . Further, in the accelerated cooling step, the surface temperature of the thick steel plate was cooled to 500 °C. As a result, it is understood that the relationship between the temperature drop amount ΔT and the cooling stop temperature in the temperature adjustment step is as shown in FIG. According to Fig. 8, in order to obtain a uniform material, it is preferable that the variation in the cooling stop temperature is 25 ° C or lower and the temperature decrease amount ΔT in the temperature adjustment step is 200 ° C or lower.

As shown in FIG. 9, the accelerated cooling device 5 of the present invention preferably includes a header 11 for supplying cooling water to the upper surface of the thick steel plate 10, and a spray rod shape suspended from the upper header 11. a cooling water spray nozzle 13 for cooling water, a partition wall 15 provided between the thick steel plate 10 and the upper header 11, and a plurality of water supply ports 16 for interposing the lower end portions of the cooling water spray nozzles 13 at the partition wall 15. And will be supplied to the thick steel plate 10 The cooling water of the surface is discharged to the partition wall 15 by the drain port 17.

Specifically, the upper surface cooling device includes: an upper header 11 that supplies cooling water to the upper surface of the thick steel plate 10; a cooling water spray nozzle 13 that hangs from the upper header 11; and a partition wall 15 that is thick The width direction of the steel sheet is horizontally disposed between the upper header 11 and the thick steel plate 10, and has a plurality of through holes (the water supply port 16 and the water discharge port 17). Further, the cooling water spray nozzle 13 includes a circular tube nozzle 13 that sprays a rod-shaped cooling water, and has a tip end interposed in a through hole (water supply port 16) provided in the partition wall 15 and a lower end portion of the partition wall 15 Set it up more. Further, the cooling water spray nozzle 13 preferably penetrates into the upper header 11 so that the upper end thereof protrudes into the inside of the upper header 11 to prevent the foreign matter at the bottom of the upper header 11 from being sucked.

Here, the rod-shaped cooling water in the present invention refers to cooling water sprayed from a nozzle discharge port having a circular shape (including an elliptical or polygonal shape) in a state of being pressurized to some extent, and is sprayed from a nozzle. The jetting speed of the outlet cooling water is 6 m/s or more, preferably 8 m/s or more, and the cross section of the water jet jetted from the nozzle discharge port is maintained as a substantially circular cooling water having a continuous and straight flow of water. That is, it is different from the free fall flow from the laminar flow nozzle of the circular tube or the spray in the state of the droplet as in the case of a spray.

The reason why the front end of the cooling water spray nozzle 13 is inserted into the through hole and is located above the lower end portion of the partition wall 15 is that even when the thick steel plate which is warped upward at the front end enters the case, The partition wall 15 prevents the cooling water spray nozzle 13 from being damaged. Thereby, the cooling water spray nozzle 13 can be cooled for a long period of time in a good state. Therefore, it is not necessary to perform equipment maintenance or the like, and it is possible to prevent temperature unevenness of the thick steel plate.

Further, since the front end of the round nozzle 13 is inserted into the through hole, as shown in Fig. 16, the interference does not flow in the width direction of the discharge water 19 which is a broken line arrow flowing along the upper surface of the partition wall 15. Therefore, the cooling water sprayed from the cooling water spray nozzle 13 It can reach the upper surface of the thick steel plate equally regardless of the position in the width direction, so that uniform cooling can be performed in the width direction.

As an example of the partition wall 15, as shown in Fig. 11, a plurality of through holes having a diameter of 10 mm are formed in the partition wall 15 in a grid shape of 80 mm in the width direction of the thick steel plate and 80 mm in the transport direction. Further, a cooling water spray nozzle 13 having an outer diameter of 8 mm, an inner diameter of 3 mm, and a length of 140 mm was inserted into the water supply port 16. The cooling water spray nozzles 13 are arranged in a staggered lattice shape, and the through holes through which the cooling water spray nozzles 13 do not pass are the drain ports 17 for the cooling water. As described above, the plurality of through holes provided in the partition wall 15 of the accelerated cooling device of the present invention include the water supply port 16 and the water discharge port 17 having substantially the same number, and share functions and functions, respectively.

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 round pipe nozzle 13 of the cooling water spray nozzle 13, and 11 times the total cross-sectional area of the inner diameter of the round pipe nozzle 13 is ensured. Left and right, as shown in Fig. 9, the cooling water supplied to the upper surface of the thick steel plate is filled between the surface of the thick steel plate and the partition wall 15, and is guided to the upper side of the partition wall 15 through the drain port 17, and is quickly discharged. Fig. 12 is a front view for explaining the flow of the cooling water discharge in the vicinity of the end portion in the width direction of the thick steel plate on the partition wall. The drainage direction of the drain port 17 is an upward direction opposite to the direction in which the cooling water is sprayed, and the cooling water flowing through the partition wall 15 changes toward the outer side in the width direction of the thick steel plate, along the upper header 11 and the partition wall 15. The drainage flow path flows and is discharged.

On the other hand, in the example shown in FIG. 13, the drain hole 17 is inclined in the width direction of the thick steel plate, and the drainage direction is inclined toward the outer side in the width direction so as to face the outer side in the width direction of the thick steel plate. Thereby, the flow of the thick steel sheet in the partition wall 15 on the partition wall 15 becomes smoother in the width direction, and drainage is promoted, which is preferable.

Here, if the drain port and the water supply port are provided in the same manner as shown in FIG. In the through hole, the cooling water collides with the thick steel plate, and it is difficult to flow over the partition wall 15, and the thick steel plate 10 and the partition wall 15 flow toward the end portion in the width direction of the thick steel plate. As a result, the flow rate of the cooling water between the thick steel plate 10 and the partition wall 15 is closer to the end portion in the width direction of the plate. Therefore, the force that the jet cooling water 18 passes through the retained water film and reaches the thick steel plate is more The more the end portion near the width direction of the plate is hindered.

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

On the other hand, the accelerating cooling device 5 of the present invention is provided with the water supply port 16 and the water discharge port 17 separately as shown in Fig. 15, and shares the functions of the water supply and the drainage. Therefore, the cooling water is smoothly flowed through the water discharge port 17 of the partition wall 15. Above the partition wall 15. Therefore, the cooled drain is quickly removed from the upper surface of the thick steel plate, so that the subsequently supplied cooling water can easily pass through the retained water film, and sufficient cooling capacity can be obtained. In this case, the temperature distribution in the width direction of the thick steel plate becomes a uniform temperature distribution, so that a uniform temperature distribution can be obtained in the width direction.

Further, as long as the total cross-sectional area of the drain port 17 is 1.5 times or more of the total cross-sectional area of the inner diameter of the round pipe nozzle 13, the discharge of the cooling water can be quickly performed. In this case, for example, it is sufficient that the partition wall 15 has a hole larger than the outer diameter of the nozzle 13 and the number of the drain ports is equal to or exceeds the number of the water supply ports.

If the total cross-sectional area of the drain port 17 is less than 1.5 times the total cross-sectional area of the inner diameter of the round pipe nozzle 13, the flow resistance of the drain port becomes large, and the retained water is difficult to be discharged. As a result, the water film can be retained to reach the thickness. The amount of cooling water on the surface of the steel sheet is greatly reduced, so that the cooling capacity is lowered, which is not preferable. More preferably 4 times or more. On the other hand, if there are too many drains or When the cross-sectional diameter of the drain port becomes too large, the rigidity of the partition wall 15 becomes small, and it is easily damaged when the thick steel plate collides. Therefore, the comparison of the total cross-sectional area of the drain port with the total cross-sectional area of the inner diameter of the round pipe nozzle 13 is preferably in the range of 1.5 to 20.

Further, the gap between the outer circumferential surface of the circular tube nozzle 13 and the inner surface of the water supply port 16 which is inserted into the water supply port 16 of the partition wall 15 is desirably set to 3 mm or less. If the gap is large, the cooling water discharged to the upper surface of the partition wall 15 is introduced to the outer peripheral surface of the water supply port 16 and the round pipe nozzle 13 due to the influence of the accompanying flow of the cooling water sprayed from the round pipe nozzle 13. The gap is again supplied to the thick steel plate, so that the cooling efficiency is deteriorated. In order to prevent this, it is more preferable to set the outer diameter of the circular nozzle 13 to be substantially the same as the size of the water supply port 16. However, in consideration of work accuracy or installation error, a gap of up to 3 mm is allowed to be substantially affected. More preferably, it is set to 2 mm or less.

Further, in order to allow the cooling water to pass through the retained water film and reach the thick steel plate, it is necessary to optimize the inner diameter and length of the round nozzle 13 and the jetting speed of the cooling water or the nozzle distance.

That is, the inner diameter of the nozzle is preferably 3 to 8 mm. If it is less than 3 mm, the water jet that is ejected from the nozzle becomes thinner and the strength becomes weak. On the other hand, if the nozzle diameter exceeds 8 mm, the flow velocity becomes slow, and the force for penetrating the water film is weakened.

The length of the round nozzle 13 is preferably 120 to 240 mm. The length of the round pipe nozzle 13 as used herein means the length from the flow inlet of the upper end of the nozzle inside the header to some extent until the lower end of the nozzle of the water supply port of the partition wall. If the round 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, if the thickness of the header is set to 20 mm, the amount of protrusion of the upper end of the nozzle toward the header is set to 20 mm. When the insertion amount of the lower end of the nozzle toward the partition wall is 10 mm, it is less than 70 mm), so that the drainage space on the upper side of the partition wall becomes smaller, thereby cooling the drainage water. Can not be discharged smoothly. On the other hand, when it is longer than 240 mm, the pressure loss of the round pipe nozzle 13 becomes large, and the force which penetrates the water film is weakened.

The jetting speed of the cooling water from the nozzle must be 6 m/s or more, preferably 8 m/s or more. The reason for this is that if it is less than 6 m/s, the force of the cooling water flowing through the water film is extremely weak. If it is 8 m/s or more, it is preferable to ensure a larger cooling capacity. Further, the distance from the lower end of the cooling water spray nozzle 13 cooled from the upper surface to the surface of the thick steel plate 10 is preferably set to 30 to 120 mm. If it is less than 30 mm, the frequency at which the thick steel plate 10 collides with the partition wall 15 is extremely high, and it is difficult to secure the equipment. When it exceeds 120 mm, the force of the cooling water flowing through the water film is extremely weak.

It is preferable to provide the dewatering roll 20 before and after the upper header 11 so that the cooling water does not diffuse in the longitudinal direction of the thick steel plate when the upper surface of the thick steel plate is cooled. Thereby, the length of the cooling zone becomes fixed, and temperature control becomes easy. Here, since the flow of the cooling water in the direction in which the thick steel sheet is conveyed is blocked by the dewatering roller 20, the cooling water discharge flows outward in the width direction of the thick steel plate. However, it is easy to retain cooling water in the vicinity of the dewatering roller 20.

Therefore, as shown in FIG. 10, in the row of the circular tube nozzles 13 arranged in the width direction of the thick steel plate, the cooling water spray nozzles on the most upstream side in the thick steel sheet conveying direction are inclined toward the upstream direction of the thick steel plate conveying direction. 15 to 60 degrees, the cooling water injection nozzle of the most downstream side of the thick steel plate conveying direction is inclined by 15 to 60 degrees toward the downstream direction of the thick steel plate conveying direction. Thereby, the cooling water can be supplied to the position close to the dewatering roller 20, and the cooling water does not stay in the vicinity of the dewatering roller 20, and the cooling efficiency is improved, which is preferable.

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 of the flow path 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 becomes the total cross-sectional area of the inner diameter of the cooling water spray nozzle. It is set to be 1.5 times or more, for example, about 100 mm or more. The cross-sectional area of the flow path in the width direction of the thick steel plate is not in the cooling water spray nozzle When the total cross-sectional area of the diameter is 1.5 times or more, the cooling water discharged from the drain port 17 provided in the partition wall to the upper surface of the partition wall 15 cannot be smoothly discharged in the width direction of the thick steel plate.

In the accelerated cooling device of the present invention, the range of the water density which is most effective is 1.5 m ³ /(m ² ‧ min) or more. When the water density is lower than this, the retained water film is not so thick, and there are cases where the temperature in the width direction is not uniform even if a known technique of cooling the thick steel plate by freely dropping the rod-shaped cooling water is applied. So big. On the other hand, even when the water amount density is higher than 4.0 m ³ /(m ² ‧ min), the technique of the present invention is effective, but there are problems in practical use such as high equipment cost, and therefore, 1.5 to 4.0. m ³ /(m ² ‧min) is the most practical water density.

The use of the cooling technique of the present invention is particularly effective in the case where the dewatering roll is disposed after cooling the header. However, it can also be applied to the case without a dewatering roll. For example, it can also be applied to a cooling device which is relatively long in the longitudinal direction (about 2 to 4 m), and sprays a water spray for flushing before the header to prevent orientation. Water leakage in the water-cooled area.

Further, 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. 9 and 10, an example of the cooling lower header 12 having the same circular nozzle 14 as the cooling device on the upper surface side is shown. However, when the cooling water on the lower surface side of the thick steel plate is cooled, the injected cooling water collides with the thick steel plate and naturally falls. Therefore, the partition wall 15 which discharges the cooling water in the width direction of the thick steel plate as in the case of cooling on the front side may not be provided. Further, a known technique of supplying film-like cooling water or spray-like spray cooling water can be used.

Further, the heating furnace 1 and the rust removing device 2 of the present invention are not particularly limited, and a conventional device can be used. Regarding the rust removing device 2, it is not necessary to have the same configuration as the rust removing device 7 of the present invention.

[Example 1]

Hereinafter, embodiments of the invention will be described. In the following description, the steel sheet temperature is the temperature of the surface of the steel sheet.

The thick steel plate of the present invention was produced using a manufacturing apparatus of a thick steel plate as shown in FIG. After the slab is reheated by the heating furnace 1, the scale is first removed in the rust removing device 2, hot rolled by the rolling mill 3, and the shape is corrected by the shape correcting device 4. After the shape correction, the temperature of the surface of the thick steel plate is adjusted by the temperature adjusting device 6, and then the rust removing device 7 performs derusting. The rust removing device 7 is a spray distance (the surface distance between the spray nozzle of the rust removing device 7 and the thick steel plate) is set to 130 mm, the nozzle spray angle is set to 32°, and the nozzle angle of attack is set to 15°. After derusting by the descaling device 7, it is cooled to 500 ° C by the accelerated cooling device 5. Here, the temperature adjustment step and the rust removal step after the temperature adjustment were carried out under the conditions shown in Table 1. Further, the cooling length of the temperature adjusting device 6 was set to 1 m. Further, the Ar ₃ metamorphic point of the thick steel plate used was 780 °C. The sheet thickness after the end of the rolling press of the rolling mill 3 was 25 mm, and the temperature of the thick steel plate was 830 °C. The temperature drop amount ΔT in the temperature adjustment step is measured only in the case where water cooling is employed in the temperature adjustment step. The reason for this is that when the temperature adjustment is performed by air cooling, there is no problem caused by excessive temperature drop.

In order to obtain a thick steel plate having a small material deviation, the thick steel plate having a variation in the cooling stop temperature of 25 ° C or less was qualified according to the relationship of FIG. 8 .

The manufacturing conditions and results are shown in Table 1.

In Inventive Example 1, after the completion of the rolling, the surface temperature of the thick steel plate was lowered to 770 ° C by air cooling in the temperature adjusting device 6. Thereafter, in the descaling device 7, the energy density is 0.08 J/mm ² , the injection pressure is 15 MPa, and the injection flow rate per nozzle is 40 L/min (= 6.7 × 10 ^-4 m ³ /s) over the entire length of the thick steel plate. The high-pressure water is then produced by cooling with the accelerated cooling device 5. Since the surface of the thick steel plate is derusted after being transformed from austenite to ferrite iron, the scale can be completely removed, and the deviation of the cooling stop temperature (hereinafter, simply referred to as temperature unevenness) becomes 10 °C.

In the second invention, after the completion of the rolling, the temperature adjustment device 6 supplies cooling water to the upper surface of the upper and lower portions of the thick steel plate at a water density of 1.0 m ³ /(m ² ‧ min) to lower the surface temperature of the thick steel plate to 750 ° C. . Thereafter, in the rust removing device 7, high-pressure water is sprayed over the entire length of the thick steel plate at an energy density of 0.08 J/mm ² , and then cooled by the accelerated cooling device 5 to be produced. In the temperature adjusting device 6, the water density for water cooling is 1.0 m ³ /(m ² ‧ min), so the temperature of the thick steel plate at the time of rust removal is 750 ° C, and the surface of the thick steel plate can be changed from austenite. Derusting after the ferrite is iron. Since the temperature drop amount ΔT of the temperature adjustment step is also 120 ° C, the temperature unevenness becomes 19 ° C.

In Inventive Example 3, after the end of the rolling, the surface temperature of the thick steel plate was lowered to 770 ° C by air cooling. Thereafter, in the rust removing apparatus 7, the injection pressure is 15 MPa, the injection flow rate per one nozzle 1 is 40 L/min (= 6.7 × 10 ^-4 m ³ /s), and the energy density is 0.13 J/mm ² throughout the entire length of the thick steel plate. The high-pressure water is sprayed and then produced by cooling with the accelerated cooling device 5. The surface of the thick steel plate is derusted after being transformed from austenite to ferrite. Therefore, the scale can be completely removed, and the temperature unevenness becomes 10 °C.

In Inventive Example 4, after the end of the rolling, the surface temperature of the thick steel plate was lowered to 770 ° C in the temperature adjusting device 6. Then, in the rust removing device 7, high-pressure water is sprayed over the entire length of the thick steel plate at an energy density of 0.13 J/mm ² and an injection pressure of 8 MPa, and then it is produced by cooling with an accelerated cooling device. Since the injection pressure was 8 MPa, which is outside the range of the preferred range of the present invention, it was considered that the scale was not damaged and remained slightly, and the temperature unevenness was 23 °C. Although the injection pressure of Inventive Example 4 is larger than that of Invention Example 3 within the preferable range of the present invention, other aspects satisfy the conditions necessary for the present invention, and therefore, the target is set to within 25 °C.

In Comparative Example 1, after the completion of the rolling, the surface temperature of the thick steel plate was lowered to 770 ° C by air cooling in the temperature adjusting device 6. Then, in the rust removing apparatus 7, high-pressure water is sprayed over the entire length of the thick steel plate at an energy density of 0.04 J/mm ² and an injection pressure of 12 MPa, and then it is produced by cooling by the accelerated cooling device 5. Since the energy density is 0.04 J/mm ² , it is considered that there is a scale remaining in one part of the thick steel plate, and the temperature unevenness is 36 ° C. Further, when the surface of the thick steel plate of Comparative Example 1 cooled to room temperature was visually observed, the color tone of the surface was unevenly observed. Therefore, the reason why the temperature unevenness was estimated was that the scale remained in one of the thick steel plates.

In Comparative Example 2, after the end of the rolling, the temperature of the surface of the thick steel plate was not lowered in the temperature adjusting device 6, and in the descaling device 7, the high-pressure water pair having an energy density of 0.08 J/mm ² and an injection pressure of 15 MPa was used. A thick steel plate having a thick steel plate surface temperature of 800 ° C is sprayed over the entire length of the thick steel plate, and then cooled by the accelerated cooling device 5 to be produced. The energy density is within the scope of the invention. However, since the rust removal is performed in a state where the surface of the thick steel plate is not deformed, it is considered that there is a scale remaining in one part of the thick steel plate, and the temperature unevenness is 40 °C. Further, when the surface of the thick steel plate of Comparative Example 2 cooled to room temperature was visually observed, unevenness in the color tone of the surface was observed. Therefore, the reason why the temperature unevenness was estimated was that the scale remained in one part of the thick steel plate.

In Comparative Example 3, after the completion of the rolling, the cooling water was supplied to the upper surface of the thick steel plate at a water density of 0.2 m ³ /(m ² ‧ min) in the temperature adjusting device 6. Thereafter, in the rust removing device 7, high-pressure water is sprayed over the entire length of the thick steel plate at an energy density of 0.08 J/mm ² , and then cooled by the accelerated cooling device 5 to be produced. Since the water density is small at 0.2 m ³ /(m ² ‧ min), the temperature of the thick steel plate is only lowered to 785 ° C, and the rust is removed in a state where the surface of the thick steel plate is not metamorphosed. Therefore, it is considered that there is a scale remaining in one part of the thick steel plate, and the temperature unevenness is 41 °C. When the surface of the thick steel plate of Comparative Example 3 cooled to room temperature was visually observed, unevenness in the color tone of the surface was observed. Therefore, the reason why the temperature unevenness was estimated was that the scale remained in one part of the thick steel plate.

In Comparative Example 4, after the completion of the rolling, the cooling water was supplied to the upper surface of the thick steel plate at a water density of 2.4 m ³ /(m ² ‧ min) in the temperature adjusting device 6, and thereafter, in the rust removing device 7 The high-pressure water was sprayed over the entire length of the thick steel plate at an energy density of 0.08 J/mm ² , and then cooled by the accelerated cooling device 5 to be produced. Since the water density is 2.4 m ³ /(m ² ‧ min), the ΔT at the time of cooling before rusting is 220 ° C, and the temperature unevenness is 27 ° C. When the surface of the thick steel plate of Comparative Example 4 cooled to room temperature was visually observed, unevenness in the color tone of the surface was observed. Therefore, the reason why the temperature unevenness was estimated was that the scale remained in one part of the thick steel plate.

1‧‧‧heating furnace

2‧‧‧Descaling device

3‧‧‧ rolling press

4‧‧‧Shaping correction device

5‧‧‧Accelerated cooling device

Claims (4)

A method for manufacturing a thick steel plate, which is a method for manufacturing a thick steel plate in the order of a hot rolling step, a shape correcting step, and an accelerated cooling step, characterized in that a temperature adjusting step is provided between the shape correcting step and the accelerated cooling step And a descaling step, wherein the temperature adjustment step is performed by air cooling the surface temperature of the thick steel plate to less than the Ar ₃ metamorphic point, or supplying the upper surface of the thick steel plate with a water density of 0.3 to 2.2 m ³ /(m ² ‧ min) Cooling water is water-cooled to thereby deform the surface of the thick steel plate; and the rust removing step is performed after the temperature adjusting step and before the accelerated cooling step, the surface of the thick steel plate is sprayed with an energy density of 0.05 J/mm ² In the above high pressure water, the energy density is the water density x the injection pressure x the collision time. The method for producing a thick steel plate according to the first aspect of the invention, wherein in the rust removing step, the injection pressure of the high-pressure water is 10 MPa or more. A manufacturing apparatus for a thick steel plate, characterized in that a hot rolling device, a shape correcting device, a temperature adjusting device, a rust removing device, and an accelerated cooling device are disposed in the upstream direction of the self-transporting direction, and the temperature adjusting device is borrowed The surface of the thick steel plate is cooled by air-cooling the surface temperature of the thick steel plate to less than the Ar ₃ metamorphic point, or by supplying cooling water to the upper and lower surfaces of the thick steel plate at a water density of 0.3 to 2.2 m ³ /(m ² ‧ min). In the above-described descaling apparatus, the surface of the thick steel plate is subjected to high-pressure water having an ejection energy density of 0.05 J/mm ² or more, and the energy density is water density density × injection pressure × collision time. The apparatus for manufacturing a thick steel plate according to the third aspect of the invention, wherein the high pressure water injection pressure is 10 MPa or more in the rust removing device.