JP2010247227A - Equipment and method for manufacturing thick steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide equipment for manufacturing thick steel plates excellent in the shape of a steel plate and a mechanical property, by performing uniform cooling in the cooling stage while suppressing the defective surface properties of a product caused by rolled-in scale when straightening the shape. <P>SOLUTION: The equipment for manufacturing thick steel plates is constituted so that a slab extracted from a heating furnace 2 is rolled into the thick steel plate of a predetermined thickness by passing through a hot-rolling mill 3 several times; the hot-rolling mill 3, a descaler device 4, a shape leveling device 5 and a cooling system 6 are arranged in this order from the upstream side in the conveying direction; wherein the impact pressure P [MPa] of cooling water which the descaler 4 jets toward the surface of the thick steel plate 1 is set to ≥1.8. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

In recent years, the application of cooling control is expanding as a manufacturing process for thick steel plates. In general, however, hot thick steel plates are not necessarily uniform in shape, surface properties, etc., so temperature unevenness is likely to occur in the thick steel plates during cooling, and deformation, residual stress, material non-uniformity, etc. occur in the thick steel plates after cooling. This leads to poor quality and operational problems.
Therefore, Patent Document 1 discloses a method in which descaling is performed at least immediately before and immediately after the final pass of finish rolling, followed by hot correction, and then descaling and starting forced cooling. Yes.
Further, Patent Document 2 discloses a method in which finish rolling and hot straightening are performed, descaling is performed immediately before control cooling, and control cooling is performed.

JP-A-9-57327 Patent No. 3796133

  However, when a thick steel plate is actually manufactured by the methods of Patent Documents 1 and 2, the scale does not completely peel off during descaling, but rather scale unevenness occurs due to descaling, resulting in poor surface properties. There is a case. That is, Patent Documents 1 and 2 do not describe the collision pressure of the cooling water on the thick steel plate surface in descaling, but the injection pressure and injection distance from the nozzles described in Patent Documents 1 and 2, and in general In the collision pressure derived from the types of typical nozzles, it is estimated that the pressure is 0.08 to 1.00 MPa in Patent Document 1 and about 0.06 to 0.08 MPa in Patent Document 2, and the collision pressure of cooling water is low and uniform. There is not enough ability to descal. As a result, there is a problem in that uniform cooling cannot be performed at the time of controlled cooling because the surface properties are different depending on whether or not the scale is peeled off.

In particular, in recent years, the level of material uniformity required for thick steel plates has become stricter, and the uneven cooling rate during controlled cooling caused by the unevenness of scale as described above has an effect on the material uniformity especially in the width direction of thick steel plates. The negative effects can no longer be ignored.
Further, according to the methods of Patent Documents 1 and 2, a secondary scale is generated in a considerable amount until hot correction, and scale is generated by pressing the scale by hot correction, resulting in poor surface properties. In addition, since the surface properties of the portion where the scale wrinkles are generated are different from those of other portions, there is a problem in that uniform cooling cannot be performed during controlled cooling.

  Therefore, the present invention has been made paying attention to the above-mentioned unsolved problems of the conventional example, and performs uniform descaling in the descaling process, and surface characteristics of the product due to scale biting during shape correction. It is an object of the present invention to provide a manufacturing apparatus and a manufacturing method for a thick steel plate that can suppress defects and that is excellent in steel plate shape and mechanical properties by achieving uniform cooling in the cooling process.

In order to achieve the above object, a steel plate manufacturing facility according to the present invention includes a hot rolling mill, a descaling device, a shape correcting device, and a cooling device arranged in this order from the upstream side in the transport direction, and the descaling device. Impingement pressure P [MPa] of the cooling water sprayed toward the surface of the thick steel plate was set to 1.8 or more.
The inventors of the present application have made extensive studies on the force that causes scale peeling with high-pressure water. As shown in FIG. 5, the collision pressure P [MPa] of cooling water injected from the descaling device onto the thick steel plate is 1.8 or more. If so, it was clarified that the scale thickness of the product decreased and became uniform. This is because the scale was once peeled uniformly and completely due to high impact pressure descaling, and then the scale was thinly and uniformly regenerated. Therefore, according to the present invention, the scale thickness of the thick steel plate before passing through the cooling device becomes thin and uniform, so there is almost no variation in the surface temperature at the position in the width direction of the thick steel plate when passing through the cooling device. It can be cooled and becomes a thick steel plate excellent in steel plate shape and mechanical properties.

The steel plate manufacturing facility according to the present invention is configured such that the transport speed from the descaling device to the cooling device is V [m / s] and the steel plate temperature before cooling is T [K]. The distance L [m] from the apparatus to the cooling apparatus preferably satisfies the expression L ≦ V × 5 × 10 ⁻⁹ × exp (25000 / T). According to this invention, it becomes possible to stabilize the cooling of the thick steel plate by the cooling device.
Moreover, it is preferable that the manufacturing equipment of the thick steel plate which concerns on this invention arrange | positions each apparatus so that the distance L from the said descaling apparatus to the said cooling device may be 12 m or less. According to this invention, the cooling of the thick steel plate by the cooling device is very stable.

Moreover, the manufacturing equipment of the thick steel plate according to the present invention includes a header for supplying cooling water to the upper surface of the thick steel plate, a cooling water injection nozzle for injecting rod-shaped cooling water suspended from the header, A partition wall disposed between the thick steel plate and the header, the partition wall having a water supply port for inserting a lower end portion of the cooling water injection nozzle, and a cooling water supplied to the upper surface of the thick steel plate It is preferable that a large number of drain outlets for draining water on the partition walls are provided.
According to this invention, the cooling water supplied from the cooling water injection nozzle through the water supply port cools the upper surface of the thick steel plate and becomes high-temperature drainage and flows from the drain port to the upper side of the partition wall. Since the drainage is quickly removed from the thick steel plate, a sufficient cooling capability in the width direction and uniform in the width direction of the cooling device can be obtained.

Moreover, the manufacturing method of the thick steel plate which concerns on this invention is the method of manufacturing a thick steel plate in order of a hot rolling process, a hot straightening process, and a cooling process, Between the said hot rolling process and the said hot straightening process. The descaling step of injecting cooling water having a collision pressure of 1.8 MPa or more onto the surface of the thick steel plate was performed.
According to the present invention, since the scale thickness of the thick steel plate before the cooling step is thin and uniform, when performing the cooling step, there is almost no variation in the surface temperature at the position in the width direction of the thick steel plate and the steel plate can be uniformly cooled. It is possible to produce a thick steel plate excellent in steel plate shape and mechanical properties.
Furthermore, in the method for manufacturing a thick steel plate according to the present invention, when the temperature of the thick steel plate before cooling is T [K], the time t [s] from the completion of the descaling step to the start of the cooling step is t ≦ preferably satisfy the equation of ^{5 × 10 -9 × exp (25000} / T). According to this invention, it becomes possible to stabilize the cooling of the thick steel plate by the cooling process.

  According to the manufacturing equipment and the manufacturing method of the thick steel plate according to the present invention, while performing uniform descaling in the descaling step, it is possible to suppress the surface property defect of the product due to scale biting during hot correction, Moreover, the thick steel plate excellent in the steel plate shape and the mechanical characteristic can be manufactured by aiming at uniform cooling at a cooling process.

It is a figure which shows the outline | summary of the hot rolling equipment which concerns on this invention. It is a figure which shows an example of the cooling device which comprises the hot rolling equipment which concerns on this invention. It is a figure which shows the partition which comprises a cooling device. It is a figure which shows the flow of the cooling water and drainage of a cooling device. It is a graph which shows the relationship between the collision pressure of the cooling water of a descaling apparatus, and the scale thickness which generate | occur | produces on the product surface of a thick steel plate. It is a graph which shows the relationship between the width direction position and temperature of the thick steel plate at the time of the cooling process in this invention. It is a graph which shows the relationship between the width direction position and temperature of the thick steel plate at the time of the cooling process in the conventional installation which is not equipped with the descaling process before the cooling process.

DESCRIPTION OF EMBODIMENTS Hereinafter, modes for carrying out the present invention (hereinafter referred to as embodiments) will be described in detail with reference to the drawings.
As shown in FIG. 1, the hot rolling facility according to the present embodiment, in order from the upstream side in the conveying direction of the thick steel plate 1, is a heating furnace 2, a hot rolling mill 3, a descaling device 4, and a first shape correction device. 5, a cooling device 6 and a second shape correction device 7 are installed.
The slab extracted from the heating furnace 2 is rolled into a thick steel plate 1 having a predetermined thickness by passing a hot rolling mill 3 a plurality of times, and the hot rolled steel plate 1 is a table roller (not shown). It is transported from the upstream side to the downstream side, and surface-treated by the descaling device 4. Although only one hot rolling mill 3 is illustrated, it may be constituted by a rough rolling mill and a finish rolling mill.

  The first shape straightening device 5 corrects the shape of distortion generated in the thick steel plate 1 during hot rolling, and a roller leveler that clamps the thick steel plate 1 with straightening rolls arranged in a staggered pattern on the top and bottom. Although a type of shape correction apparatus is illustrated, the present invention is not limited to this, and a skin pass type or press type shape correction apparatus may be used. Further, when the hot rolling mill 3 is constituted by a rough rolling mill and a finishing rolling mill, skin pass correction may be performed by the finishing rolling mill. And if finish rolling is complete | finished by the heating furnace 2 side, skin pass correction can be implemented, without inhibiting rolling efficiency significantly.

The second shape correction device 7 corrects the shape of distortion generated in the thick steel plate 1 during cooling by the cooling device 6, but this shape correction device may not be used in the present invention. The second shape correction device 7 uses a roller leveler method, but is not limited thereto, and a skin pass method or press method shape correction device may be used.
The cooling device 6 is a device for controlling the structure of the thick steel plate 1 to obtain a desired material by controlling and cooling the hot thick steel plate 1 after hot rolling under a predetermined temperature condition. Any cooling device may be used as long as desired cooling conditions can be obtained, but a cooling device capable of performing uniform cooling in the upper and lower surfaces, the longitudinal direction, and the width direction of the thick steel plate 1 is preferable. Therefore, in the present embodiment, the cooling device 6 shown in FIG. 2 having a high cooling capacity and particularly excellent cooling uniformity in the width direction is used.

  As shown in FIG. 2, the cooling device 6 of the present embodiment includes an upper header 10 that supplies cooling water to the upper surface of the thick steel plate 1, and an upper portion that extends downward from the upper header 10 toward the thick steel plate 1. Cooling water is supplied to the cooling water injection nozzle 11, the partition wall 12 having a large number of through holes installed horizontally across the steel plate width direction between the upper header 10 and the thick steel plate 1, and the lower surface of the thick steel plate 1. A lower header 13, a lower cooling water injection nozzle 15 extending upward from the lower header 13 toward the thick steel plate 1, and draining rolls 16 and 17 disposed upstream and downstream in the conveying direction of the thick steel plate 1. I have.

  As shown in FIG. 3, the partition wall 12 has a large number of through holes 18 formed in a grid pattern, and the upper cooling water spray nozzles 11 are inserted into the predetermined through holes 18 in a staggered manner. A lower end opening of the through hole 18 through which the water injection nozzle 11 is inserted is a water supply port 19. The lower end opening of the through hole 18 through which the upper cooling water injection nozzle 11 is not inserted is a drain port 20. The tip of the upper cooling water injection nozzle 11 is installed so as to be inserted into the through-hole 18 (water supply port 19) and above the lower end of the partition wall 12, but this tip is temporarily warped upward. This is to prevent the upper cooling water spray nozzle 11 from being damaged by the partition wall 12 even when the steel sheet has entered.

Then, as shown in FIG. 4, the cooling water supplied from the upper cooling water injection nozzle 11 through the water supply port 19 cools the upper surface of the thick steel plate 1 to become high temperature drainage, and the partition wall through the drain port 20. 12 flows upward. Further, the cooling water supplied from the lower cooling water injection nozzle 15 cools the lower surface of the thick steel plate 1 and flows downward.
Here, if there is no partition wall 12, the cooling water supplied to the upper surface of the thick steel plate 1 flows and drains in the width direction on the upper surface of the thick steel plate 1, particularly in the vicinity of the plate width end, The flow of this drainage prevents the cooling water from the upper cooling water injection nozzle 11 from reaching the upper surface of the thick steel plate 1, the cooling capacity near the end of the plate width is reduced, and uniform cooling is performed in the width direction. I can't. Therefore, the temperature distribution in the width direction of the thick steel plate 1 is a concave shape having a low central portion and a high plate end. On the other hand, in the cooling device 6 of the present embodiment, the drained water after cooling is quickly removed from the upper surface of the thick steel plate 1 to above the partition wall 12 and is thus ejected from the upper cooling water injection nozzle 11. Sufficient cooling capacity is obtained when the cooling water sequentially contacts the thick steel plate 1.

  Further, if the water supply port 19 and the drain port 20 are the same through hole 18, the cooling water supplied to the upper surface of the thick steel plate 1 is difficult to escape above the partition wall 12, and the upper surface of the thick steel plate 1 and the partition wall 12. The flow of the drainage hinders the cooling water from the upper cooling water jet nozzle 11 from reaching the upper surface of the thick steel plate 1, and cools the vicinity of the plate width end. The capacity is reduced, and uniform cooling cannot be performed in the width direction. On the other hand, in the cooling device 6 of the present embodiment shown in FIG. 2, the through holes 18 are provided to share the function between the water supply port 19 and the drainage port 20, so that the flow of cooling water and cooling drainage is smooth. is there. Furthermore, since the tip of the upper cooling water spray nozzle 11 is inserted into the through hole 18 of the partition wall 12, the waste water flowing in the width direction above the partition wall 12 interferes with the cooling water ejected from the upper cooling water spray nozzle 11. Therefore, uniform cooling in the width direction can be performed, and a uniform temperature distribution in the width direction can be obtained as shown in FIG.

  Incidentally, if the total cross-sectional area of the drain port 20 is 1.5 times or more the total cross-sectional area of the inner diameter of the upper cooling water injection nozzle 11, it is desirable that the cooling water is discharged from the drain port 20 quickly. . If this value is smaller than 1.5 times, the flow resistance of the drainage port becomes large, and the stagnant water is not easily drained onto the partition wall, so that it flows between the upper surface of the thick steel plate and the partition wall toward the plate width end. In particular, the cooling capacity in the vicinity of the end portion of the plate width decreases. 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 12 will be reduced and it will be easily damaged when the steel plates collide. Therefore, the ratio of the total cross-sectional area of the drain outlet 20 and the total cross-sectional area of the inner diameter of the upper cooling water injection nozzle 11 is preferably in the range of 1.5 to 20.

Further, in order to allow the cooling water to penetrate the staying water film and reach the steel plate and perform uniform cooling in the width direction, the inner diameter and length of the upper cooling water injection nozzle 11, the cooling water injection speed, It is desirable to optimize 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 upper cooling water injection nozzle 11 is preferably 120 to 240 mm. If the upper cooling water injection nozzle 11 is shorter than 120 mm, the distance between the lower surface of the upper header 10 and the upper surface of the partition wall 12 becomes too short, so that the drainage space above the partition wall 12 becomes small and cooling drainage cannot be discharged smoothly. On the other hand, if it is longer than 240 mm, the pressure loss of the upper cooling water spray nozzle 11 becomes large, and the force penetrating the staying water film becomes weak.

  The jetting speed of the cooling water from the nozzle is preferably 6 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 upper cooling water injection nozzle 11 to the surface of the steel plate 1 is preferably 30 to 120 mm. If it is less than 30 mm, the frequency with which the steel plate 1 collides with the partition wall 12 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.

The range of the water density where the cooling device 6 of the present embodiment is most effective 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 the known technology of 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 There is also. 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 cooling device 6 of this embodiment, but there are problems in practical use such as an increase in equipment cost. Therefore, 1.5 to 4.0 m ³ / m ² · min is the most practical water density.

  In the cooling device 6 shown in FIG. 2, an example of the lower header 13 including the lower cooling water injection nozzle 12 similar to the cooling device on the upper surface side is shown, but the cooling water injected in the cooling on the lower surface side of the steel plate is Since it falls spontaneously after colliding with the steel plate, the temperature unevenness in the width direction does not become a big problem like the upper surface side of the steel plate. Therefore, the cooling device on the lower surface side of the steel plate is not particularly limited.

On the other hand, the descaling device 4 is a device that removes the scale generated on the surface of the thick steel plate 1 by directing a plurality of injection nozzles to the surface of the thick steel plate 1 after hot rolling and injecting high-pressure water from these nozzles. It is.
Here, in the present embodiment, the collision pressure P [MPa] of high-pressure water sprayed from the spray nozzle of the descaling device 4 to the surface of the thick steel plate 1 is set to 1.8 or more. The scale generated on the surface of the steel plate 1 is removed, the shape of the strain generated in the thick steel plate 1 is corrected by the first correcting device 5, and then the thick steel plate 1 is cooled by the cooling device 6. The steel plate shape and mechanical properties of the steel plate 1 can be improved.

  The reason is as follows. If the conventional hot rolling equipment is passed through a straightening device without a surface treatment by a descaling device, the scale may be partially peeled off, and the scale thickness distribution varies about 10 to 50 μm depending on whether or not the scale is peeled off. In that case, it is difficult to uniformly cool the thick steel plate during cooling by the cooling device. That is, when cooling a thick steel plate having a variation in scale thickness distribution in a conventional hot rolling facility, as shown in FIG. 7, the surface temperature variation in the width direction position is large, and cannot be cooled uniformly. The steel plate shape and mechanical properties are affected.

On the other hand, the inventors of the present application have found that scale peeling is not sufficiently performed depending on descaling conditions, and rather, unevenness of scale is promoted. And when earnestly examining about the force which causes scale peeling enough, as shown in FIG. 5, the collision pressure P [MPa] injected from the injection nozzle of the descaling device 4 onto the surface of the thick steel plate 1 is 1.8 or more. It was also clarified that the scale peels uniformly and completely after that, and the scale thickness to be regenerated thereafter becomes uniform at 5 μm or less. In particular, when the collision pressure P [MPa] is set to 2.0 or more, uniform thinning can be realized.
The collision pressure P is, for example, the following equation (1) obtained experimentally, and is a value obtained by converting the collision pressure Pc calculated by the equation (1) into the SI unit MPa. .
Pc = 0.05757 × (Q / A) ^1.08 × Ps ^0.473 (1)
However, Pc: collision pressure [kgf / cm ² ], Q: injection flow rate [L / min], A: injection area [cm ² ], Ps: injection pressure [kgf / cm ² ].

Here, the injection area A is obtained by the following equation (2) by an injection experiment.
A = B × T = (2Htan (θ / 2)) × (0.051 H ^0.78 × Q ^0.09 × Ps− ^0.045 ) (2)
Where B: spray spray width [cm], T: spray spray thickness [cm], H: spray distance (distance between spray nozzle of descaling device 4 and thick steel plate 1 surface) [cm], θ: nozzle The spray angle (the spread angle of descaling water sprayed from the nozzle) [°].
Substituting equation (2) into equation (1) gives an approximate expression:
Pc = 0.6775 × Q × H ⁻² (tan (θ / 2)) ^−1.08 × Ps ^0.5 (3)
Is obtained.
Note that the form of the equation for obtaining the collision pressure P is not limited to this, and an equation obtained by actually performing an injection experiment and regressing the pressure value at the landing position measured by the pressure sensor may be used.

The injection distance H [cm] for obtaining a predetermined collision pressure is obtained by the following equation (4) by modifying the equation (3).
H = ((0.6775 × Q × (tan (θ / 2)) − ^1.08 × Ps ^0.5 ) / Pc) ^0.5 (4)
However, Pc: collision pressure [kgf / cm ² ], Q: injection flow rate [L / min], Ps: injection pressure [kgf / cm ² ], θ: nozzle injection angle [°].
Thereby, in order to make the collision pressure P [MPa] injected to the surface of the thick steel plate 1 1.8 or more, the injection distance H is set to Pc = 1.8 / 9.8 × 100 = (4) What is necessary is just to be below the value of H calculated | required by substituting 18.4 [kgf / cm < ² >].

  According to this embodiment, the descaling device 4 in which the collision pressure P [MPa] of the high-pressure water is set to 1.8 or more removes the scale generated on the surface of the thick steel plate 1, thereby eliminating variations in the scale thickness distribution. When the thick steel plate 1 is cooled by the cooling device 6, as shown in FIG. 6, there is almost no variation in the surface temperature at the position in the width direction, and the thick steel plate can be uniformly cooled and has excellent steel plate shape and mechanical properties. 1 can be manufactured.

  In addition, although the temperature unevenness in the width direction of the thick steel plate that has passed through the cooling device without surface treatment by the descaling device is about 40 ° C., the cooling by a general cooling device is performed after the descaling of the present invention described above. The uneven temperature in the width direction of the thick steel plate is reduced to about 10 ° C. Furthermore, after passing through the descaling device 4 and performing descaling of the present invention, temperature unevenness in the width direction of the thick steel plate 1 subjected to uniform cooling in the width direction by the cooling device 6 of the present embodiment shown in FIG. It decreases to about 4 ° C.

By the way, about the scale of the surface of the thick steel plate 1 which affects the stability at the time of cooling of the thick steel plate 1 by the cooling device 6, the growth of the scale of the thick steel plate 1 can generally be arranged by diffusion rate control. 5) It is known that it is represented by the formula.
ξ ² = a × exp (−Q / RT) × t (5)
Where ξ: scale thickness, a: constant, Q: activation energy, R: constant, t: time.

  Therefore, in consideration of the scale growth after the scale removal by the descaling device 4, a simulation experiment of scale growth was performed at various temperatures and times, and the constants of the above equation were derived experimentally. Furthermore, as a result of intensive studies on scale thickness and cooling stability, it was found that cooling is stable when the scale thickness is 15 μm or less, more stable when the scale thickness is 10 μm or less, and very stable when the scale thickness is 5 μm or less.

That is, when the time t [s] from the end of removal of the scale of the thick steel plate 1 by the descaling device 4 to the start of cooling of the thick steel plate 1 by the cooling device 6 satisfies the following equation (6): It became clear that the cooling by the cooling device 6 was stable.
t ≦ 5 × 10 ⁻⁹ × exp (25000 / T) (6)
However, T: Thick steel plate temperature [K] before cooling.

Further, when the time t [s] from the end of removing the scale of the thick steel plate 1 by the descaling device 4 until the cooling of the thick steel plate 1 is started by the cooling device 6 satisfies the following equation (7): It became clear that the cooling by the cooling device 6 was more stable.
^{t ≦ 2.2 × 10 -9 × exp} (25000 / T) ...... (7)
Furthermore, when the time t [s] from the end of removal of the scale of the thick steel plate 1 by the descaling device 4 until the cooling of the thick steel plate 1 by the cooling device 6 satisfies the following equation (8): It became clear that the cooling by the cooling device 6 was very stable.
t ≦ 5.6 × 10 ⁻¹⁰ × exp (25000 / T) (8)

On the other hand, the distance L from the descaling device 4 to the cooling device 6 is based on the conveying speed V of the thick steel plate 1 and the time t (time from the end of the process of the descaling device 4 to the start of the process of the cooling device 6). To satisfy the following equation (9).
L ≦ V × t (9)
And it is preferable that the said (9) Formula satisfies the following (10) Formula from the said (6) Formula.
L ≦ V × 5 × 10 ⁻⁹ × exp (25000 / T) (10)

Moreover, it is more preferable that the formula (9) satisfies the following formula (11) from the formula (7).
L ≦ V × 2.2 × 10 ⁻⁹ × exp (25000 / T) (11)
Furthermore, it is more preferable that the above expression (9) satisfies the following expression (12) from the above expression (8).
L ≦ V × 5.6 × 10 ⁻¹⁰ × exp (25000 / T) (12)

From the above formulas (10) to (12), for example, when the temperature of the thick steel plate 1 before cooling by the cooling device 6 is 820 ° C. and the conveying speed of the thick steel plate 1 is 0.28 to 2.50 m / s, The distance L from the scaling device 4 to the cooling device 6 is stable at 12 to 107 m or less, the cooling is more stable at 5 to 47 m or less, and the cooling is very stable at 1.3 to 12 m or less.
Accordingly, when the distance L from the descaling device 4 to the cooling device 6 is 12 m or less, the cooling is stable even when the transport speed V of the thick steel plate 1 is slow (for example, V = 0.28 m / s). When the conveying speed V of the thick steel plate 1 is fast (for example, V = 2.50 m / s), the cooling is very stable, which is preferable. More preferably, the distance L from the descaling device 4 to the cooling device 6 is 5 m or less.

As described above, the hot rolling facility of the present embodiment is generated on the surface of the thick steel plate 1 by the descaling device 4 before the shape correction of the distortion generated in the thick steel plate 1 is performed by the first shape correcting device 5. By removing the scale, the biting of the scale and the scale peeling during the correction by the first shape correction device 5 can be suppressed.
Further, by setting the collision pressure P [MPa] sprayed from the spray nozzle of the descaling device 4 to the surface of the thick steel plate 1 to 1.8 or more, the scale generated in the thick steel plate 1 is made uniform and cooled. By achieving uniform cooling with the device 6, the thick steel plate 1 having excellent shape and mechanical properties can be produced.

Moreover, even if the distance L from the descaling device 4 to the cooling device 6 satisfies L ≦ V × 5 × 10 ⁻⁹ × exp (25000 / T), the cooling of the thick steel plate 1 by the cooling device 6 is stabilized. Can be made.
Further, the time t [s] from the end of removal of the scale of the thick steel plate 1 by the descaling device 4 to the start of cooling of the thick steel plate 1 by the cooling device 6 is expressed as t ≦ 5 × 10 ⁻⁹ × exp (25000 / When T) is satisfied, the cooling of the thick steel plate 1 by the cooling device 6 can be stabilized.

  Further, as shown in FIG. 4, the cooling device 6 according to the present embodiment cools the upper surface of the thick steel plate 1 by the cooling water supplied from the upper cooling water injection nozzle 11 through the water supply port 19 and has a high temperature. Since it becomes drainage and flows in the width direction of the thick steel plate 1 from above the partition wall 12 through the drain port 20, the drainage after cooling is quickly removed from the thick steel plate 1. The cooling water flowing from the nozzle 11 through the water supply port 19 sequentially comes into contact with the thick steel plate 1 so that sufficient and uniform cooling capability can be obtained in the width direction.

  In addition, like this embodiment, the surface treatment of the thick steel plate 1 is performed by the descaling device 4, the distortion generated during rolling is corrected by the first shape correction device 5, and the controllability of cooling is stabilized. Therefore, the thick steel plate 1 processed by the second shape straightening device 7 originally has high flatness and the temperature of the thick steel plate 1 is uniform, so that the straightening reaction force of the second shape straightening device 7 does not need to be so high. . In addition, the distance between the cooling device 6 and the second shape correcting device 7 may be longer than the maximum length of the thick steel plate 1 manufactured by the line. This is often the case where the second shape correction device 7 performs reverse correction or the like, and therefore the effect of preventing troubles such as the reversely fed thick steel plate 1 jumping on the transport roll and colliding with the cooling device 7, or cooling. It can be expected that the slight temperature deviation generated inside is made uniform, and the effect of avoiding the warp caused by the temperature deviation after correction is expected.

  After the thick steel plate 1 having a thickness of 30 mm and a width of 3500 mm rolled by the hot rolling mill 3 passes through the descaling device 4 and the first shape correction device 5, cooling control from 820 ° C. to 420 ° C. is performed. . Here, the conditions under which the cooling calculated from the above-described equations (6), (7), and (8) is stable are as follows. After removing the scale of the thick steel plate 1 by the descaling device 4, the thick steel plate 1 is removed by the cooling device 6. The time t until the start of cooling is 42 s or less, preferably 19 s or less, more preferably 5 s or less.

The descaling device 4 has a nozzle injection pressure of 17.7 MPa, an injection flow rate per nozzle of 64 L / min / unit, a distance between the steel plate 1 and the nozzle of 120 mm, a nozzle injection angle of 32 °, and a nozzle attack angle. The angle is set to 15 °, and one row is arranged in the width direction so that the injection regions of adjacent nozzles are wrapped to some extent, and the collision pressure is 1.8 MPa at all positions in the width direction.
The cooling facility 6 is a facility provided with a flow path that allows the cooling water supplied to the upper surface of the steel plate to flow above the partition wall as shown in FIG. 2 and further drains from the side of the steel plate width direction as shown in FIG. . In the partition wall, holes with a diameter of 12 mm are drilled like a grid, and as shown in FIG. 3, the upper cooling water injection nozzles are inserted into the water supply ports arranged in a staggered pattern, and the remaining holes are used as drainage ports. Using. The distance between the lower surface of the upper header and the upper surface of the partition wall was 100 mm.

The upper cooling water injection nozzle had an inner diameter of 5 mm, an outer diameter of 9 mm, and a length of 170 mm, and its upper end protruded into the header. Moreover, the injection speed of the rod-shaped cooling water was 8.9 m / s. The nozzle pitch in the steel plate width direction was 50 mm, and 10 rows of nozzles were arranged in the longitudinal direction in a zone with a distance between table rollers of 1 m. The water density on the upper surface was 2.1 m ³ / m ² · min. The lower end of the nozzle for cooling the upper surface was installed so as to be at an intermediate position between the upper and lower surfaces of the partition wall having a thickness of 25 mm, and the distance to the steel plate surface was 80 mm.
As for the lower surface cooling facility, as shown in FIG. 2, a cooling facility similar to the upper surface cooling facility is used except that the partition wall is not provided, and the jet speed and water density of the rod-shaped cooling water are 1.5 times the upper surface. did.

  And as shown in Table 1, the distance L from the descaling device 4 to the cooling device 6, the conveyance speed V of the steel plate, and the time from the descaling device 4 to the cooling device 6 were variously changed. The descaling in Table 1 is a scale removing process of the thick steel plate 1 by the descaling device 4, and the controlled cooling is a cooling process of the thick steel plate 1 by the cooling device 6.

Inventive Examples 1 to 4 (thick steel plate 1) in Table 1 are flatly cooled with almost no variation in the surface temperature in the width direction when cooled by the cooling device 6, as shown in FIG. The degree of re-correction due to poor shape was low, and the surface properties were good.
In particular, Examples 1 to 3 of the present invention in which the distance from the descaling device 4 to the cooling device 6 is 11 m are used to cool the thick steel plate 1 with the cooling device 6 after the descaling device 4 removes the scale of the thick steel plate 1. The time t until the start of the steel sheet is 42 S or less, which is a condition for stabilizing the cooling by the cooling device 6 from the above-described equation (6), regardless of the steel sheet conveying speed V, and the re-correction rate is good at 10% or less. Met.

On the other hand, in Comparative Example 1 in which the descaling device 4 did not remove the scale and the cooling device 6 cooled, the flatness considered to be caused by the temperature distribution of the steel sheet deteriorated, and the recorrection rate was 40%. became.
Further, the setting conditions by the descaling device 4 are as follows: the water pressure is 10 MPa, the injection flow rate per nozzle is 10 L / min / line, the distance between the steel plate 1 and the nozzle is 180 mm, the nozzle injection angle is 37 °, and the nozzle attack angle is 15 In Comparative Example 2 in which the collision pressure was 0.09 MPa, the temperature distribution in the width direction of the steel sheet deteriorated due to partial peeling of the scale, and the re-correction rate became 70%.

  DESCRIPTION OF SYMBOLS 1 ... Thick steel plate, 2 ... Heating furnace, 3 ... Hot rolling mill, 4 ... Descaling device, 5 ... 1st shape correction device (shape correction device), 6 ... Cooling device, 7 ... 2nd shape correction device DESCRIPTION OF SYMBOLS 10 ... Upper header (header), 11 ... Upper cooling water injection nozzle (cooling water injection nozzle), 12 ... Partition, 13 ... Lower header, 15 ... Lower cooling water nozzle, 15 ... Through-hole, 16, 17 ... Water draining roll , 18 ... through hole, 19 ... water supply port, 20 ... drain port

Claims (6)

  A hot rolling mill, a descaling device, a shape correcting device, and a cooling device are arranged in this order from the upstream side in the conveying direction, and the collision pressure P [MPa] of cooling water sprayed by the descaling device toward the surface of the thick steel plate A thick steel plate manufacturing facility characterized by having a thickness of 1.8 or more. When the transport speed from the descaling device to the cooling device is V [m / s] and the steel plate temperature before cooling is T [K], the distance L [m] from the descaling device to the cooling device is L <V * 5 * 10 < ^-9 > * exp (25000 / T) is satisfy | filled, The manufacturing equipment of the thick steel plate of Claim 1 characterized by the above-mentioned.   The equipment for manufacturing a thick steel plate according to claim 1, wherein each device is arranged such that a distance L from the descaling device to the cooling device is 12 m or less. The cooling device has a header for supplying cooling water to the upper surface of the thick steel plate, a cooling water injection nozzle for injecting rod-shaped cooling water suspended from the header, and a partition wall installed between the thick steel plate and the header. And a plurality of water supply ports for interpolating the lower end portion of the cooling water injection nozzle and drainage ports for draining the cooling water supplied to the upper surface of the thick steel plate onto the partition wall. The equipment for manufacturing a thick steel plate according to any one of claims 1 to 3, wherein the equipment is provided.   In the method of manufacturing a thick steel plate in the order of the hot rolling step, the hot straightening step, and the cooling step, a collision pressure of 1.8 MPa or more is applied to the surface of the thick steel plate during the hot rolling step and the hot straightening step. A method for producing a thick steel plate, comprising performing a descaling step of injecting cooling water. Assuming that the steel plate temperature before cooling is T [K], the time t [s] from the completion of the descaling step to the start of the cooling step is t ≦ 5 × 10 ⁻⁹ × exp (25000 / T). The method for producing a thick steel plate according to claim 5, wherein the formula is satisfied.

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