JP2014188543A - Manufacturing method for thick steel plate and manufacturing facility - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a thick steel plate and a manufacturing facility, capable of assuring a thick steel plate of high quality, with less variation in material quality.SOLUTION: In a method of manufacturing a thick steel plate by a hot rolling step, a shape correction step, and an acceleration cooling step in this order, between the shape correction step and the acceleration cooling step, there are provided a temperature control step in which a surface of the thick steel plate is modified by air-cooling a surface temperature of the thick steel plate to less than Armodification point, otherwise, by water-cooling by supplying cooling water to upper and lower surfaces of the thick steel plate at a water amount density of 0.3-2.2 m/mmin, and a descaling step in which a high pressure water of energy density 0.05 J/mmor higher is jetted to the surface of the thick steel plate, after the temperature control step but before the acceleration cooling step.

Description

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

  In the process of manufacturing thick steel plates by hot rolling, the application of cooling control is expanding. For example, as shown in FIG. 1, after the thick steel plate (not shown) is reheated in the heating furnace 1, the thick steel plate is descaled in the descaling device 2. 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. In addition, the arrow in a figure is the advancing direction of a thick steel plate.

  When water-cooling a thick steel plate with an accelerated cooling device, it is known that the cooling rate increases as the scale on the surface of the thick steel plate becomes thicker as shown in FIG. However, if the scale thickness varies, the cooling rate becomes non-uniform, and there is a problem that materials such as strength and hardness vary.

  Further, when the scale thickness is non-uniform, the cooling rate is non-uniform as described above. In such a case, it is known that the distribution of the steel plate surface temperature (hereinafter referred to as “cooling stop temperature”) at the time of accelerated cooling stop in the thick steel plate width direction varies as shown in FIG. Thus, since the cooling stop temperature of the thick steel plate varies, there is a problem that a uniform material cannot be obtained. When a specific example is shown, when the place where scale thickness is 40 micrometers and 20 micrometers coexists in the thickness direction of a thick steel plate, the cooling stop temperature when cooling a thick steel plate with a thickness of 25 mm from 800 ° C. to a target temperature of 500 ° C. is 40 μm. It becomes 460 degreeC in a location, and 500 degreeC in a location of 20 micrometers. At the 40 μm portion, the cooling stop temperature falls below 40 ° C. from the target temperature, and as a result, a uniform material cannot be obtained.

  Therefore, Patent Document 1 discloses a method for achieving uniform cooling stop temperature by controlling the thickness of the scale to equalize the cooling rate. In Patent Document 1, using a descaling device provided before and after the rolling mill during rolling, when the cooling stop temperature of the tail end of the thick steel plate is lower than that of the tip, the descaling injection on the tail end side is performed. By controlling the amount of water to be greater than the amount of water sprayed on the tip side, and controlling the scale removal rate and remaining thickness in the longitudinal direction of the thick steel plate, the heat transfer coefficient of the steel plate surface during controlled cooling can be changed, and the thick steel plate The cooling stop temperature in the longitudinal direction is made uniform.

JP-A-6-330155

  In the conventional technology, the cooling stop temperature has been made uniform by adjusting the amount of cooling water and the conveyance speed. However, in this method, since the cooling rate varies due to the variation in scale thickness, it is difficult not only to make the cooling rate uniform, but also to make the cooling stop temperature uniform.

  In addition, in the method of Patent Document 1, since the heat transfer coefficient cannot be controlled unless the scale removal rate and the remaining thickness can be controlled online, it is not possible to realize a uniform cooling rate with high accuracy. Further, when the scale removal rate is changed, the cooling stop temperature is different between the remaining scale portion and the peeled portion, so that the material varies.

  An object of the present invention is to solve the above-mentioned problems and to provide a method and equipment for manufacturing a thick steel plate that can secure a high-quality thick steel plate with less material variation.

The present invention has been made to solve the above-mentioned conventional problems, and the gist thereof is as follows.
[1] In the method for producing a thick steel plate in the order of the hot rolling step, the shape correction step, and the accelerated cooling step, the surface temperature of the thick steel plate is less than the Ar ₃ transformation point between the shape correction step and the accelerated cooling step. A temperature adjusting step for transforming the surface of the thick steel plate by cooling with air 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 and cooling with water. And a thick steel plate having a descaling step of injecting high pressure water having an energy density of 0.05 J / mm ² or more onto the surface of the thick steel plate after the temperature adjustment step and before the accelerated cooling step. Manufacturing method.
[2] The method for producing a thick steel plate according to [1], wherein, in the descaling step, an injection pressure of the high-pressure water is set to 10 MPa or more.
[3] A hot rolling device, a shape correcting device, a temperature adjusting device, a descaling device, and an accelerated cooling device are arranged in this order from the upstream side in the conveying direction, and in the temperature adjusting device, the surface temperature of the thick steel plate is changed to the Ar ₃ transformation point. Air cooling to less than that, or cooling water 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 to transform the thick steel plate surface, and the descaling device Then, high-pressure water having an energy density of 0.05 J / mm ² or more is sprayed onto the surface of the thick steel plate.
[4] The equipment for manufacturing a thick steel plate according to [3], wherein in the descaling apparatus, an injection pressure of the high-pressure water is set to 10 MPa or more.

According to the present invention, between the shape correction step and the accelerated cooling step, the temperature adjusting step for transforming the steel plate surface by lowering the steel plate surface temperature below the Ar ₃ transformation point, and the steel plate after the temperature adjusting step. By having a descaling step of injecting high pressure water having an energy density of 0.05 J / mm ² or more onto the surface of the film, the cooling rate and the cooling stop temperature can be made uniform. As a result, it is possible to manufacture a high-quality thick steel plate with little material variation.

It is the schematic which shows the manufacturing equipment of the conventional thick steel plate. It is a figure which shows the relationship between scale thickness at the time of accelerated cooling, cooling time, and a steel plate surface temperature. It is a figure which shows the relationship between the width direction position of a thick steel plate and cooling stop temperature after accelerated cooling. It is the schematic which shows the manufacturing equipment of the thick steel plate which is one Embodiment of this invention. It is a figure which shows the relationship between the presence or absence of the transformation of the surface of a thick steel plate, the energy density of high pressure water, and a scale peeling rate. It is a figure which shows the relationship between the temperature of the steel plate surface after completion | finish of rolling, and the injection pressure required in order for a scale to be destroyed. It is a figure which defines the temperature difference of the steel plate surface before a descaling process start from a temperature adjustment process. It is a figure which shows the relationship between the amount of temperature drop on the surface of a thick steel plate, and the dispersion | variation in cooling stop temperature. It is a side view of the cooling device concerning one embodiment of the present invention. It is a side view of the other cooling device which concerns on one Embodiment of this invention. It is a figure explaining the example of nozzle arrangement of the partition concerning one embodiment of the present invention. It is a figure explaining the flow of the cooling waste water on a partition. It is a figure explaining other flows of cooling drainage on a partition. It is a figure explaining the thick steel plate width direction temperature distribution of a prior art example. It is a figure explaining the flow of the cooling water in an acceleration cooling device. It is a figure explaining non-interference with the cooling drainage on the partition in an acceleration cooling device.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 4 is a schematic view showing a thick steel plate manufacturing facility according to an embodiment of the present invention. In FIG. 4, an arrow is a conveyance direction of a thick steel plate. From the upstream side in the conveying direction of the thick steel plate, the heating furnace 1, the descaling device 2, the rolling mill 3, the shape correcting device 4, the temperature adjusting device 6, the descaling device 7, and the accelerated cooling device 5 are arranged in this order. In FIG. 4, after the thick steel plate (not shown) is reheated in the heating furnace 1, the thick steel plate is descaled in the descaling device 2 to remove the primary scale. The thick steel plate is hot-rolled by the rolling mill 3 and corrected by the shape correcting device 4. After the temperature adjusting device 6 lowers the surface temperature of the thick steel plate, the descaling device 7 completely removes the scale. Scaling is performed. Then, controlled cooling by water cooling or air cooling is performed in the acceleration cooling device 5.

In the present invention, a temperature adjustment device 6 and a descaling device 7 are arranged between the shape correction device 4 and the acceleration cooling device 5. Then, the temperature adjustment device 6, to transform the steel plate surface by reducing the steel plate surface temperature Ar less than ₃ transformation point. Thereafter, the descaling device 7 performs descaling by injecting high-pressure water having an energy density of 0.05 J / mm ² or more onto the thick steel plate.

The temperature adjustment device 6 is disposed between the shape correction device 4 and the descaling device 7. In temperature control process in a temperature adjustment device 6, by transformation of the steel plate surface by reducing the steel plate surface temperature Ar less than ₃ transformation point, in a subsequent descaling step, to facilitate removal of the scale.

In the temperature adjustment process, the steel plate surface is transformed by lowering the surface temperature of the steel plate to below the Ar ₃ transformation point, causing transformation of the base iron and causing a shift at the interface between the scale and the base iron. descend. This is considered to be due to the following mechanism. When the surface of the thick steel plate is cooled below the Ar ₃ transformation point, the ground iron transforms from austenite to ferrite. At this time, since the ground iron expands, a force is applied to the interface between the scale and the ground iron, and a crack occurs at the interface. As a result, it is considered that the adhesion of the scale is reduced. Accordingly, by removing the surface of the thick steel plate by lowering the surface temperature of the thick steel plate to less than the Ar ₃ transformation point, scale removal can be facilitated during the descaling process in the descaling apparatus 7. The Ar ₃ transformation point can be calculated by the following formula (*).
Ar ₃ = 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo (*)
However, an element symbol shows content (mass%) in steel of each element.

Next, the descaling device 7 performs descaling for the thick steel plate whose surface is transformed by lowering the surface temperature of the thick steel plate to less than the Ar ₃ transformation point. At this time, the scale can be completely removed by spraying high-pressure water having an energy density of 0.05 J / mm ² or more (in the present invention, 5 MPa or more is high-pressure water) onto the thick steel plate. By completely removing the scale in this descaling process, cooling control can be performed in the subsequent accelerated cooling process in the heating and cooling device 5. As a result, uniform cooling rate and uniform cooling stop temperature can be achieved. The high pressure water may be sprayed over the entire length of the thick steel plate.

About the influence of the presence or absence of the transformation of the steel plate surface before a descaling process about the certain steel grade, the present inventors are the energy density of high-pressure water and the scale peeling rate (the ratio of the area where the scale peeled and the steel plate area). When the relationship was examined, the knowledge shown in FIG. 5 was obtained. From FIG. 5, it was found that when the energy density is large, the scale peeling rate is increased, and by changing the surface of the thick steel plate, the scale peeling is possible even when the energy density is small. Also, from FIG. 5, when descaling is performed after transformation, when the energy density is less than 0.05 J / mm ² , the scale peeling rate is low, so the scale remains in a part of the thick steel plate, and the cooling stop temperature is It can be said that the material is uneven and the material becomes uneven. Therefore, the energy density of the high pressure water is set to 0.05 J / mm ² or more. Preferably, it is 0.10 J / mm ² or more. In addition, from the viewpoint of energy consumption of a pump that supplies high-pressure water, the energy density of high-pressure water is preferably 0.60 J / mm ² or less.

  In the present invention, it is preferable to inject high-pressure water having an injection pressure of 10 MPa or more in the descaling step. By making the injection pressure 10 MPa or more, the scale can be completely removed. Therefore, the cooling rate and the cooling stop temperature in the accelerated cooling process can be made uniform. In order to destroy the scale, the pressure when the high-pressure water droplet collides with the thick steel plate needs to exceed the hardness of the scale. When the present inventors investigated the relationship between the temperature of the surface of the thick steel plate after the end of rolling and the injection pressure of high-pressure water necessary for breaking the scale, the knowledge of FIG. 6 was obtained. When manufacturing a thick steel plate that requires controlled cooling as in the present invention, the temperature of the surface of the thick steel plate after the end of rolling is generally around 900 ° C. at the highest. Therefore, in the present invention, in order to destroy the scale, it is preferable 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 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 / m ² min) is a value calculated by “cooling water injection flow rate ÷ 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 by “cooling water collision thickness ÷ thick steel plate conveyance speed”. Note that the relationship between the energy density of the high-pressure water of the present invention and the scale peeling rate calculated by this simple definition is the same as in FIG.

In the temperature adjusting step, the surface temperature of the thick steel plate is lowered below the Ar ₃ transformation point by air cooling or water cooling. In the case of air cooling, on the table rollers for conveying the steel plate may be air cooled as appropriate Ar less than ₃ transformation point.

In the present invention, when water cooling is performed in the temperature adjustment step, cooling water is supplied 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. If the water density is less than 0.3 m ³ / m ² min, the thick steel plate surface temperature cannot be lowered below the Ar ₃ transformation point, and the thick steel plate surface cannot be transformed. As a result, scale remains on the thick steel plate, and even if cooling control is performed in the subsequent accelerated cooling process, the cooling stop temperature varies and the material becomes non-uniform. On the other hand, if the water density is larger than 2.2 m ³ / m ² min, the temperature drop ΔT in the temperature adjustment step described later exceeds 200 ° C., the cooling stop temperature varies, and the material becomes uneven.

  When the surface of the thick steel plate is transformed in the temperature adjusting device 6, the thick steel plate surface is cooled in a state where the scale is attached to the thick steel plate. When the temperature drop amount by cooling in the temperature adjusting device 6 is large, the present inventors affect the uniformization of the cooling stop temperature and the variation in the cooling stop temperature (the target after the accelerated cooling step). The inventors have found that the difference between the steel sheet surface temperature and the actual steel sheet surface temperature after accelerated cooling is increased. Here, the temperature drop amount ΔT on 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 at the start of cooling and the lowest temperature reached on the surface of the thick steel plate, as shown in FIG.

The present inventors manufactured a steel plate in the order of a temperature adjustment step, a descaling step and an accelerated cooling step using a thick steel plate having a surface temperature of 800 ° C. and a plate thickness of 25 mm after the rolling in the rolling mill. Here, the energy density at the time of descaling was set to 0.2 J / mm ² as a condition that the surface of the steel plate at the time of descaling can be completely removed before and after the transformation. In the accelerated cooling process, cooling was performed so that the surface temperature of the thick steel plate was 500 ° C. As a result, it has been found that the relationship between the temperature drop amount ΔT in the temperature adjustment step and the variation in the cooling stop temperature is as shown in FIG. From FIG. 8, in order to obtain a uniform material, it is preferable that the variation in the cooling stop temperature is 25 ° C. or less and the temperature drop ΔT in the temperature adjustment step is 200 ° C. or less.

  With respect to the accelerated cooling device 5 of the present invention, as shown in FIG. 9, an upper header 11 that supplies cooling water to the upper surface of the thick steel plate 10, and a cooling water injection nozzle that injects rod-like cooling water suspended from the upper header 11. 13, and a partition wall 15 installed between the thick steel plate 10 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 the thick steel plate 10. It is preferable that a large number of drain ports 17 for draining the cooling water supplied to the upper surface 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 10, a cooling water injection nozzle 13 suspended from the upper header 11, and the upper header 11 and the thick steel plate 10. 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 substantially circular cross-section and is a continuous and straight water flow cooling water. 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. 16, there is no interference 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. 11, 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. 9, 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, led to the upper side of the partition wall 15 through the drain port 17, and quickly discharged. The FIG. 12 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. The cooling drainage drained upward is turned to the outside in the width direction of the thick steel plate and flows through the drainage channel between the upper header 11 and the partition wall 15 and drained.

  On the other hand, in the example shown in FIG. 13, 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, as shown in FIG. 14, when the drainage port and the water supply port are installed in the same through hole, the cooling water does not easily escape above the partition wall 15 after colliding with the steel plate, and the steel plate 10. 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 10 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, in the case of a thick plate having a plate width of 3 m or more, the influence cannot be ignored. 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 device 5 of the present invention, as shown in FIG. 15, the water supply port 16 and the water discharge port 17 are provided separately and share the roles of water supply and water discharge. 15 flows smoothly through the drainage port 17 and 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, but in consideration of work accuracy and mounting error, a gap of up to 3 mm that is substantially less affected. Is acceptable. 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, if 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 increases, 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 10 is preferably 30 to 120 mm. If it is less than 30 mm, the frequency with which the thick steel plate 10 collides with the partition wall 15 becomes extremely high, and equipment maintenance becomes difficult. This is because if the thickness 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 to the outside in the width direction of the thick steel plate, but the cooling water tends to stay in the vicinity of the draining roll 20.

  Therefore, as shown in FIG. 10, among the rows of the circular tube nozzles 13 aligned in the thick steel plate width direction, the cooling water jet nozzles in the uppermost stream side row in the thick steel plate transport direction are 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. If 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 is because it cannot discharge in the steel plate width direction.

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, but there are problems in practical use such as an increase in equipment cost. The most practical water density is 1.5 to 4.0 m ³ / m ² · min.

  The cooling technique of the present invention is particularly effective when draining rolls are arranged before and after the cooling header, but can also be applied 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. 9 and 10, 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, but in the cooling on the lower surface side of the thick steel plate, the injected cooling water is Since it falls spontaneously after colliding with a thick steel plate, there is no need for the partition wall 15 for discharging cooling drainage such as cooling on the upper surface side 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.

  In addition, about the heating furnace 1 and the descaling apparatus 2 of this invention, it does not restrict | limit in particular, A conventional apparatus can be used. The descaling device 2 need not have the same configuration as the descaling device 7 of the present invention.

  Examples of the present invention will be described below. In the following description, the steel plate temperature is the temperature of the steel plate surface.

The thick steel plate of the present invention was manufactured using a thick steel plate manufacturing facility as shown in FIG. After the slab was reheated in the heating furnace 1, the primary scale was removed in the descaling device 2, hot rolled by the rolling mill 3, and the shape was corrected by the shape correcting device 4. After the shape correction, the temperature adjustment device 6 adjusted the temperature of the surface of the thick steel plate, and then the descaling device 7 performed descaling. In the descaling device 7, the spray distance (the surface distance between the spray nozzle of the descaling device 7 and the thick steel plate) was 130 mm, the nozzle spray angle was 32 °, and the nozzle attack angle was 15 °. After descaling by the descaling device 7, it was cooled to 500 ° C. by the acceleration cooling device 5. Here, the temperature adjustment step and the descaling step after temperature adjustment were performed under the conditions shown in Table 1. The cooling length of the temperature adjusting device 5 was 1 m. The Ar ₃ transformation point of the thick steel plate used was 780 ° C. The plate thickness after rolling in the rolling mill 3 was 25 mm, and the thick steel plate temperature was 830 ° C. The temperature drop ΔT in the temperature adjustment process was measured only when water cooling was employed in the temperature adjustment process. This is because when temperature adjustment is performed by air cooling, problems due to excessive temperature drop do not occur.

  In order to obtain a thick steel plate with less material variation with respect to the obtained thick steel plate, a steel plate having a cooling stop temperature variation of 25 ° C. or less was accepted based on the relationship of FIG.

  Production conditions and results are shown in Table 1.

In Invention Example 1, the thick steel plate surface temperature was lowered to 770 ° C. by air cooling in the temperature adjusting device 6 after the end of rolling. Thereafter, in the descaling device 7, the energy density is 0.08 J / mm ² , the injection pressure is 15 MPa, the injection flow rate per nozzle is 40 L / min (= 6.7 × 10 ⁻⁴ m ³ / s), and the high-pressure water Was sprayed over the entire length of the thick steel plate, and then cooled with the accelerated cooling device 5 to produce. Since the descaling was performed after the thick steel plate surface was transformed from austenite to ferrite, the scale could be completely removed, and the temperature unevenness was 10 ° C.

In Invention Example 2, after the completion of rolling, the temperature adjusting device 6 supplied cooling water to the upper and lower surfaces 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 descaling device 7, 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. Since the water density for water cooling in the temperature adjusting device 6 was 1.0 m ³ / m ² min, the steel plate temperature during descaling was 750 ° C., and the descaling was performed after the steel plate surface was transformed from austenite to ferrite. Could be done. Since the temperature drop ΔT in the temperature adjustment step was also 80 ° C., the temperature unevenness was 19 ° C.

In Invention Example 3, the surface temperature of the thick steel plate was lowered to 770 ° C. by air cooling after the end of rolling. Thereafter, in the descaling device 7, the injection pressure is 15 MPa, the injection flow rate per nozzle is 40 L / min (= 6.7 × 10 ⁻⁴ m ³ / s), the energy density is 0.13 J / mm ² , and the high-pressure water Was sprayed over the entire length of the thick steel plate, and then cooled with the accelerated cooling device 5 to produce. Descaling was performed after the surface of the thick steel plate transformed from austenite to ferrite. For this reason, the scale could be removed completely and the temperature unevenness was 10 ° C.

In Invention Example 4, the thick steel plate surface temperature was lowered to 770 ° C. in the temperature adjusting device 6 after the end of rolling. Thereafter, in the descaling device 7, high-pressure water was injected 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 cooled by an acceleration cooling device. Since the injection pressure was 8 MPa, which was outside the range preferred in the present invention, it was considered that the scale could not be destroyed and remained slightly, and the temperature unevenness was 23 ° C. Although the injection pressure of Invention Example 4 was larger than that of Invention Example 3 which is within the preferred range of the present invention, the other requirements were satisfied by the present invention, so the target 25 Within ° C was achieved.

In Comparative Example 1, the surface temperature of the thick steel plate was lowered to 770 ° C. by air cooling in the temperature adjusting device 6 after the end of rolling. Thereafter, in the descaling device 7, high-pressure water was injected 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 cooled by the acceleration cooling device 5. Since the energy density was 0.04 J / mm ² , it was considered that the scale remained in a part of the thick steel plate, and the temperature unevenness was 36 ° C. Further, when the surface of the thick steel plate of Comparative Example 1 cooled to room temperature was visually observed, unevenness was confirmed in the surface color tone, and the cause of the temperature unevenness was that the scale remained in a part of the thick steel plate. It is presumed to be caused by being.

In Comparative Example 2, after the end of rolling, the temperature adjusting device 6 does not lower the temperature of the thick steel plate surface, and a thick steel plate having a steel plate surface temperature of 800 ° C. is injected into the descaling device 7 with an energy density of 0.08 J / mm ² . After the high pressure water was sprayed over the entire length of the thick steel plate at a pressure of 15 MPa, it was cooled by the accelerated cooling device 5 and manufactured. Although the energy density was within the range of the present invention, since the descaling was performed in a state where the surface of the thick steel plate was not transformed, it is considered that the scale remained in a part of the thick steel plate, and the temperature unevenness became 40 ° C. It was. Further, when the surface of the thick steel plate of Comparative Example 2 cooled to room temperature was visually observed, unevenness was confirmed in the surface color tone, and the cause of the temperature unevenness was that the scale remained in a part of the thick steel plate. It is presumed to be caused by being.

In Comparative Example 3, the cooling water was supplied to the upper and lower surfaces of the thick steel plate at a water density of 0.2 m ³ / m ² min in the temperature adjusting device 6 after the end of rolling. Thereafter, in the descaling device 7, 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. Since the water density was as small as 0.2 m ³ / m ² min, the steel plate temperature was reduced only to 785 ° C., and descaling was performed in a state where the steel plate surface was not transformed. For this reason, it was thought that the scale remained in a part of the thick steel plate, and the temperature unevenness was 41 ° C. When the surface of the thick steel plate of Comparative Example 3 cooled to room temperature was visually observed, unevenness was confirmed in the color tone of the surface, and the cause of the temperature unevenness was that the scale remained in a part of the thick steel plate. It is presumed to be caused by this.

In Comparative Example 4, the cooling water was supplied to the upper and lower surfaces of the thick steel plate at a water density of 2.4 m ³ / m ² min in the temperature adjusting device 6 after the end of rolling. Thereafter, in the descaling device 7, 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. Since the water density was as large as 2.4 m ³ / m ² min, ΔT during cooling before descaling was 220 ° C., and the temperature unevenness was 27 ° C. When the surface of the thick steel plate of Comparative Example 4 cooled to room temperature was visually observed, unevenness was confirmed in the surface color tone, and the cause of the temperature unevenness was that the scale remained in a part of the thick steel plate. It is presumed to be caused by this.

DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Descaling apparatus 3 Rolling mill 4 Shape correction apparatus 5 Acceleration cooling apparatus 6 Temperature adjustment apparatus 7 Descaling apparatus 10 Thick steel plate 11 Upper header 12 Lower header 13 Upper cooling water injection nozzle (circular pipe 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 (4)

In the method of manufacturing a thick steel plate in the order of the hot rolling step, the shape correction step, and the accelerated cooling step, between the shape correction step and the accelerated cooling step, the steel plate surface temperature is air-cooled to less than the Ar ₃ transformation point. Or a temperature adjusting step for transforming the surface of the thick steel plate 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 and cooling with water, and A method for producing a thick steel plate comprising a descaling step of injecting high-pressure water having an energy density of 0.05 J / mm ² or more onto the surface of the thick steel plate after the temperature adjustment step and before the accelerated cooling step .   2. The method for producing a thick steel plate according to claim 1, wherein in the descaling step, an injection pressure of the high-pressure water is set to 10 MPa or more. A hot rolling device, a shape correcting device, a temperature adjusting device, a descaling device, and an accelerated cooling device are arranged in this order from the upstream side in the conveying direction. In the temperature adjusting device, the steel plate surface temperature is air-cooled to less than the Ar ₃ transformation point. Alternatively, the cooling water is supplied to the upper and lower surfaces of the thick steel plate by water cooling at a water density of 0.3 to 2.2 m ³ / m ² min to transform the surface of the thick steel plate. An apparatus for producing a thick steel plate, wherein high-pressure water having an energy density of 0.05 J / mm ² or more is sprayed onto the surface of the steel plate.   In the said descaling apparatus, the injection pressure of the said high pressure water shall be 10 Mpa or more, The manufacturing apparatus of the thick steel plate of Claim 3 characterized by the above-mentioned.

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